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+*** START OF THE PROJECT GUTENBERG EBOOK 78430 ***
+
+
+
+
+  TRANSCRIBER’S NOTE
+
+  - Some minor changes to the text are noted at the end of the book.
+  - Italic text is denoted by _underscores_.
+  - Bold text is denoted by =equal signs=.
+  - Small-cap text has been changed to ALL-CAP text.
+  - Footnote anchors are denoted by [number], and the footnotes have
+      been placed at the end of the book.
+
+
+
+
+                        A PRACTICAL COURSE IN
+                                BOTANY
+
+              WITH ESPECIAL REFERENCE TO ITS BEARINGS ON
+
+                AGRICULTURE, ECONOMICS, AND SANITATION
+
+
+                                  BY
+
+                            E. F. ANDREWS
+                AUTHOR OF “BOTANY ALL THE YEAR ROUND”
+
+
+                      WITH EDITORIAL REVISION BY
+
+                           FRANCIS E. LLOYD
+
+          MACDONALD PROFESSOR OF BOTANY, McGILL UNIVERSITY,
+              FORMERLY OF ALABAMA POLYTECHNIC INSTITUTE
+
+                            [Illustration]
+
+
+                 NEW YORK ·:· CINCINNATI ·:· CHICAGO
+                        AMERICAN BOOK COMPANY
+
+
+
+
+                         COPYRIGHT, 1911, BY
+                            E. F. ANDREWS.
+
+                 ENTERED AT STATIONERS’ HALL, LONDON.
+
+
+                         ANDREW’S PR. BOTANY.
+
+                               W. P. 7
+
+
+
+
+PREFACE
+
+
+In preparing the present volume, the aim of the writer has been to
+meet all the college entrance requirements and at the same time
+to bring the study of botany into closer touch with the practical
+business of life by stressing its relations with agriculture,
+economics, and, in certain of its aspects, with sanitation. While
+technical language has been avoided so far as the requirements of
+scientific accuracy will permit, the student is not encouraged
+to shirk the use of necessary botanical terms, out of a mere
+superstitious fear of words because they happen to be a little new or
+unfamiliar. Such a practice not only leads to careless and inaccurate
+modes of expression, but tends to foster a slovenly habit of mind,
+and in the long run causes the waste of more time and labor in the
+search after roundabout, and often misleading, substitutes, than it
+would require to master the proper use of a few new words and phrases.
+
+In the choice of materials for experiment and illustration, the
+endeavor has been to call for such only as are familiar and easily
+obtained. The specimens for flower dissection have been selected
+mainly from common cultivated kinds, because their wide distribution
+makes them easy to obtain everywhere, while in cities and large
+towns they are practically the only specimens available. Another
+important consideration has been the desire to spare our native
+wild flowers, or at least not to hasten the extinction with which
+they are threatened by the ravages of Sunday excursionists and
+summer tourists, to whose unthinking, but none the less destructive,
+incursions, the automobile has laid open the most secret haunts
+of nature. The influence of the public school teacher, and more
+especially the teacher of botany, is the most potent factor from
+which we can hope for aid in putting a stop to the relentless
+persecution that has practically exterminated many of our choicest
+wild plants and is fast reducing the civilized world to a depressing
+monotony of weediness and artificiality. Except for purely systematic
+and anatomical work, flowers can be studied to better purpose in
+their living, active state than as dead subjects for dissection;
+and the best way to show our interest in them, or to get the most
+rational enjoyment out of them, is not, as a general thing, to
+cut their heads off and throw them away to wither and die by the
+roadside. The teacher, by instilling into the minds of the rising
+generation a reverence for plant life, may do a great deal to aid
+in the conservation of one of our chief national assets for the
+gratification of the higher esthetic instincts. The fruits and
+flowers of cultivation do not stand in the same need of protection,
+since they are produced solely with a view to the use and pleasure of
+man, and their propagation is provided for to meet all his demands.
+
+To avoid too frequent interruptions of the subject matter, the
+experiments are grouped together at the beginning or end of the
+sections to which they belong, according as they are intended to
+explain what is coming, or to illustrate what has gone before. A few
+exceptions are made in cases where the experiment is such an integral
+part of the subject that it would be meaningless if separated from
+the context. Under no circumstances should those capable of being
+performed in the schoolroom be omitted, as much of the information
+which the book is intended to give is conveyed by their means. For
+this reason, and also because the aim of the book is to present the
+science from a practical rather than from an academic point of view,
+the experiments outlined are for the most part of a simple, practical
+nature, such as can be performed by the pupils themselves with a
+moderate expenditure of ingenuity and money. The experience of the
+writer has been that for the average boy or girl who wishes to get
+a good general knowledge of the subject, but does not propose to
+become a specialist in botany, the best results are often obtained
+by the use of the simplest and most familiar appliances, as in
+this way attention is not distracted from the experiment itself to
+the unfamiliar apparatus for making it. In saying this, it is not
+meant to underrate the value of a complete laboratory equipment,
+but merely to emphasize the fact that the lack of it, while a
+disadvantage, need not be an insuperable bar to the successful
+teaching of botany. It is, of course, taken for granted that in
+schools provided with a suitable laboratory outfit, teachers will be
+prepared to supplement or to replace the exercises here outlined with
+such others as in their judgment the subject may demand. There are as
+many ideals in teaching as there are teachers, and the most that a
+textbook can do is to present a working model which every teacher is
+free to modify in accordance with his or her own method.
+
+The writer takes pleasure in acknowledging here the many obligations
+due to Professor Francis E. Lloyd, of the Botanical Department of the
+Alabama Polytechnic Institute, at Auburn, Ala., for his valuable aid
+in the revision of the manuscript, for the highly interesting series
+of illustrations relating to phototropic movements, and for advice
+and information on points demanding expert knowledge which have
+contributed very materially to whatever merit this volume may possess.
+
+Other members of the Auburn faculty to whom the author feels
+especially indebted are Mr. C. S. Ridgeway, assistant in the
+Botanical Department, Professor J. E. Duggar, of the Agricultural
+Department, and Dr. B. B. Ross and Professor C. W. Williamson of the
+Department of Chemistry. Acknowledgments are due also to Professor
+George Wood of the Boys’ High School, Brooklyn, for suggestions
+which have been of great assistance in the preparation of this work;
+to Professor W. R. Dodson, of the University of Louisiana, for
+illustrative material furnished, and to Professor William Trelease
+for the loan of original material used in reproducing the beautiful
+cuts from the Reports of the Missouri Botanical Garden, credit for
+which is given in the proper place.
+
+For original photographs and drawings by the author, and familiar
+selections from well-known works, which can be generally recognized,
+it has not been thought necessary to give special credit.
+
+                                                        E. F. ANDREWS.
+
+  AUBURN, ALABAMA.
+
+
+
+
+                    FULL-PAGE ILLUSTRATIONS
+
+
+  PLATE                                                           PAGE
+
+  1. A GROVE OF LIVE OAKS NEAR SAVANNAH, GEORGIA         _Frontispiece_
+
+  2. CARRYING WATER OVER THE MISSISSIPPI LEVEE BY SIPHON TO
+  IRRIGATE RICE FIELDS                                               8
+
+  3. AËRIAL ROOTS OF A MEXICAN STRANGLING FIG                       73
+
+  4. A FOREST OF BAMBOO                                             99
+
+  5. A GROUP OF CONIFERS                                           108
+
+  6. A WHITE OAK, SHOWING THE GREAT SPREAD OF BRANCHES             117
+
+  7. A TIMBER TREE SPOILED BY STANDING TOO MUCH ALONE              125
+
+  8. AN AMERICAN ELM, ILLUSTRATING DELIQUESCENT GROWTH             130
+
+  9. VEGETATION OF A MOIST, SHADY RAVINE                           151
+
+  10. A MOSAIC OF MOONSEED LEAVES                                  179
+
+  11. HYBRID BETWEEN A RED AND A WHITE CARNATION                   227
+
+  12. GOOSEBERRIES, SHOWING IMPROVEMENT BY SELECTION               251
+
+  13. THE EFFECTS OF IRRIGATION                                    272
+
+  14. A XEROPHYTE FORMATION OF YUCCAS AND SWITCH PLANTS            282
+
+  15. A GIANT TULIP TREE OF THE SOUTH ATLANTIC FOREST REGION       293
+
+
+
+
+                    CONTENTS
+
+
+          CHAPTER I. THE SEED                                     PAGE
+
+  I. THE STORAGE OF FOOD IN SEEDS                                    1
+
+  II. SOME PHYSIOLOGICAL PROPERTIES OF SEEDS                        10
+
+  III. TYPES OF SEEDS                                               12
+
+  IV. SEED DISPERSAL                                                21
+
+  FIELD WORK                                                        28
+
+
+          CHAPTER II. GERMINATION AND GROWTH
+
+  I. PROCESSES ACCOMPANYING GERMINATION                             29
+
+  II. CONDITIONS OF GERMINATION                                     33
+
+  III. DEVELOPMENT OF THE SEEDLING                                  40
+
+  IV. GROWTH                                                        47
+
+  FIELD WORK                                                        52
+
+
+          CHAPTER III. THE ROOT
+
+  I. OSMOSIS AND THE ACTION OF THE CELL                             53
+
+  II. MINERAL NUTRIMENTS ABSORBED BY PLANTS                         58
+
+  III. STRUCTURE OF THE ROOT                                        61
+
+  IV. THE WORK OF ROOTS                                             65
+
+  V. DIFFERENT FORMS OF ROOTS                                       72
+
+  FIELD WORK                                                        80
+
+
+          CHAPTER IV. THE STEM
+
+  I. FORMS AND GROWTH OF STEMS                                      81
+
+  II. MODIFICATIONS OF THE STEM                                     88
+
+  III. STEM STRUCTURE
+
+  A. MONOCOTYLS                                                     96
+
+  B. HERBACEOUS DICOTYLS                                           102
+
+  C. WOODY STEMMED DICOTYLS                                        107
+
+  IV. THE WORK OF STEMS                                            112
+
+  V. WOOD STRUCTURE IN ITS RELATION TO INDUSTRIAL USES             118
+
+  VI. FORESTRY                                                     124
+
+  FIELD WORK                                                       128
+
+
+          CHAPTER V. BUDS AND BRANCHES
+
+  I. MODES OF BRANCHING                                            131
+
+  II. BUDS                                                         138
+
+  III. THE BRANCHING OF FLOWER STEMS                               141
+
+  FIELD WORK                                                       145
+
+
+          CHAPTER VI. THE LEAF
+
+  I. THE TYPICAL LEAF AND ITS PARTS                                147
+
+  II. THE VEINING AND LOBING OF LEAVES                             154
+
+  III. TRANSPIRATION                                               160
+
+  IV. ANATOMY OF THE LEAF                                          164
+
+  V. FOOD MAKING                                                   168
+
+  VI. THE LEAF AN ORGAN OF RESPIRATION                             174
+
+  VII. THE ADJUSTMENT OF LEAVES TO EXTERNAL RELATIONS              177
+
+  VIII. MODIFIED LEAVES                                            189
+
+  FIELD WORK                                                       194
+
+
+          CHAPTER VII. THE FLOWER
+
+  I. DISSECTION OF TYPES WITH SUPERIOR OVARY                       196
+
+  II. DISSECTION OF TYPES WITH INFERIOR OVARY                      204
+
+  III. STUDY OF A COMPOSITE FLOWER                                 210
+
+  IV. SPECIALIZED FLOWERS                                          214
+
+  V. FUNCTION AND WORK OF THE FLOWER                               219
+
+  VI. HYBRIDIZATION                                                223
+
+  VII. PLANT BREEDING                                              230
+
+  VIII. ECOLOGY OF THE FLOWER
+
+  A. THE PREVENTION OF SELF-POLLINATION                            235
+
+  B. WIND POLLINATION                                              239
+
+  C. INSECT POLLINATION                                            241
+
+  D. PROTECTIVE ADAPTATION                                         245
+
+  FIELD WORK                                                       249
+
+
+          CHAPTER VIII. FRUITS
+
+  I. HORTICULTURAL AND BOTANICAL FRUITS                            250
+
+  II. FLESHY FRUITS                                                255
+
+  III. DRY FRUITS                                                  260
+
+  IV. ACCESSORY, AGGREGATE, AND MULTIPLE FRUITS                    265
+
+  FIELD WORK                                                       269
+
+
+          CHAPTER IX. THE RESPONSE OF THE PLANT TO
+                      ITS SURROUNDINGS
+
+  I. ECOLOGICAL FACTORS                                            271
+
+  II. PLANT ASSOCIATIONS                                           277
+
+  III. ZONES OF VEGETATION                                         288
+
+  FIELD WORK                                                       294
+
+
+          CHAPTER X. CRYPTOGAMS
+
+  I. THEIR PLACE IN NATURE                                         296
+
+  II. ALGÆ                                                         299
+
+  III. FUNGI                                                       303
+
+    A. BACTERIA                                                    306
+
+    B. YEASTS                                                      314
+
+    C. RUSTS                                                       317
+
+    D. MUSHROOMS                                                   323
+
+  IV. LICHENS                                                      329
+
+  V. LIVERWORTS                                                    334
+
+  VI. MOSSES                                                       341
+
+  VII. FERN PLANTS                                                 344
+
+  VIII. THE RELATION BETWEEN CRYPTOGAMS AND SEED PLANTS            354
+
+  IX. THE COURSE OF PLANT EVOLUTION                                359
+
+  FIELD WORK                                                       362
+
+
+          APPENDIX
+
+  1. SYSTEMATIC BOTANY                                             364
+
+  2. WEIGHTS, MEASURES, AND TEMPERATURES                           367
+
+
+[Illustration: PLATE 1.—Live oaks covered with Spanish moss
+(_Tillandsia_).]
+
+
+
+
+CHAPTER I. THE SEED
+
+
+          I. THE STORAGE OF FOOD IN SEEDS
+
+  MATERIAL.—In addition to the four food tests described in Exps.
+  1-6, there should be provided some raw starch, a solution of grape
+  sugar, the white of a hard-boiled egg, and any fatty substance,
+  such as lard or oil. For Exps. 8 and 9, a little diastase solution
+  will be necessary. “Taka” diastase, made from rice acted upon by a
+  fungus, can be obtained for a trifle at almost any drug store.
+
+  LIVING MATERIAL.—Grains of corn and wheat, and seeds of some kind
+  of bean, the larger the better. The “horse bean” (_Vicia faba_),
+  if it can be obtained, makes an excellent object for study, as the
+  cells are so large that they can be seen with the naked eye. For
+  showing the presence of proteins (aleurone grains) and oily matter,
+  use thin cross sections through the kernel of a castor bean or a
+  Brazil nut. Specimens for the study of the individual cell will be
+  found in the hairs growing on squash seedlings, in the epidermis of
+  one of the inner coats of an onion, in the roots of oat or radish
+  seedlings, or in the section of a young corn root.
+
+  A compound microscope will be required for this study.
+
+=1. The economic importance of seeds.=—As a source of food to both
+man and the lower animals, the importance of seeds can hardly be
+overrated. All the flour, meal, rice, hominy, and other breadstuffs
+sold in the market come from them, to say nothing of the fleece from
+the cotton seed that clothes the greater part of the world, besides
+furnishing a substitute for lard and an important food for cattle.
+The oils and fats stored in nuts are also to be taken into account,
+the peanut alone yielding the greater part of the so-called olive
+oil of commerce. Since the value of our farm crops depends largely
+upon the kind and quantity of these substances furnished by them, it
+is worth our while, as a matter of economic as well as scientific
+interest, to learn something about the nature of the different foods
+contained in plants.
+
+[Illustration: FIGS. 1-3.—The world’s three most important food
+grains (magnified): 1, section of a rice grain; _a_, cuticle; _b_,
+aleurone, or protein layer; _c_, starch cells; _d_, germ; 2, section
+of a wheat grain; _k_, germ; _s_, starch; _a_, gluten; _t_, _t_,
+_t_, layers of the seed coat; 3, section of a grain of corn; _c_,
+husk; _e_, aleurone layer containing proteins; _eg_, yellowish,
+horny endosperm, containing proteins and starch; _ew_, lighter
+starchy endosperm: the darker part below is rich in oil and proteins,
+and contains the _embryo_, consisting of the absorbing organ, or
+_cotyledon_, _sc_; the rudimentary bud, _s_; and the root, _w_. (1,
+from Circular 77, La. Exp. Station; 2, from Francé; 3, from Sachs.)]
+
+=2. Why food is stored in seeds.=—The one purpose for which plants
+produce their seed is to give rise to a new generation and so carry
+on the life of the species. The seed is the nursery, so to speak, in
+which the germ destined to produce a new plant is sheltered until
+it is ready to begin an independent existence. But the young plant,
+like the young animal, is incapable of providing for itself at first,
+and would die unless it received nourishment from the mother plant
+until it has formed roots and leaves so that it can manufacture food
+for itself. Plants in general require very much the same food that
+animals do, and they have the power, which animals have not, of
+manufacturing it out of the crude materials contained in the soil
+water and in the air. Such of these foods as are not needed for
+immediate consumption, they store up to serve as a provision for the
+young shoot when the seed begins to germinate.
+
+[Illustration: FIGS. 4-7.—Sections of corn grains showing different
+qualities of food contents: 4, 5, small germ and large proportion
+of horny part, showing high protein; 6, 7, large germ and smaller
+proportion of horny part, showing high oil content.]
+
+=3. Food substances contained in seeds.=—There are four principal
+classes of food stored in seeds: _sugars_, _starches_, _oils_, and
+_proteins_. The first are held in solution and can be detected, if
+in sufficient quantity, by the taste. The most important varieties
+of this group are cane and grape sugar, the latter occurring most
+abundantly in fruits, the former in roots and stems. Oil usually
+occurs in the form of globules. It is very abundant in some seeds,
+_e.g._ flax, castor bean, and Brazil nut. In the corn grain it is
+found in the part constituting the germ, or embryo (Figs. 6, 7).
+Starches and proteins occur in the form of small granules, which have
+specific shapes in different plants (Figs. 8, 9). Those containing
+proteins are called _aleurone_ grains, and are, as a rule, smaller
+than the starch grains with which they are intermixed in the bean
+and some other seeds. In wheat, corn, rice, and most grains they
+form a layer just inside the husk, as shown in Fig. 10. This is the
+reason why polished rice and finely bolted flour are less nutritious
+than the darker kinds, from which this valuable food substance has
+not been removed. The two most familiar kinds of proteins are the
+_albumins_, of which the white of an egg is a well-known example, and
+the _glutins_, which give to the dough of wheat flour and oatmeal
+their peculiar gummy or “glutinous” structure.
+
+[Illustration: FIGS. 8-9.—Different forms of starch grains: 8, rice;
+9, wheat.]
+
+=4. Organic foods.=—These four substances, starch, sugar, fats, and
+proteins, with some others of less frequent occurrence, are called
+_organic foods_, because they are produced, in a state of nature,
+only through the action of organized living bodies, or, more strictly
+speaking, of living vegetable bodies.
+
+[Illustration: FIG. 10.—Transverse section near the outside of a
+wheat grain: _e_, the husk; _a_, cells containing protein granules;
+_s_, starch cells (_after_ Tschirch).]
+
+=5. Our dependence upon plants.=—While the animal organism can digest
+and assimilate these substances after they have been formed by
+plants, it has no power to manufacture them for itself, and, so far
+as we know at present, is wholly dependent upon the vegetable world
+for these necessaries of life. In one sense the whole animal kingdom
+may be said to be parasitic on plants. The wolf that eats a lamb is
+getting his food indirectly from the grains and grasses consumed by
+its victim, and the lion that devours the wolf that ate the lamb is
+only one step further removed from a vegetable diet.
+
+=6. The vegetable cell.=—If you will break open a well-soaked horse
+bean and examine the contents with a lens, you will see that they
+are composed of small oval or roundish granules packed together
+like stones in a piece of masonry. These little bodies, called
+_cells_, are the ultimate units out of which all animal and vegetable
+structures are built up, as a wall is built of bricks and stones.
+They differ very much from bricks and stones, however, in that they
+are, or have been, living structures with their periods of growth,
+activity, decline, and death, just like other living matter, as
+will be seen by and by, when we come to look more particularly into
+their life history. They consist usually of an inclosing membrane
+which contains a living substance called _protoplasm_. This is the
+essential part of the cell, and, so far as we know at present, the
+physical basis of all life. Cells are commonly more or less rounded
+in shape, though they take different forms according to the purpose
+they serve. Sometimes, as in the fibers of cotton and the down of
+young leaves, they are long and hairlike; when closely packed, they
+often become angular by pressure, like those shown in Figs. 10, 11.
+The cells composing the thick body of the bean are for the most
+part starch and other substances stored up for food, which render
+observation difficult. It will, therefore, be better to choose for a
+study of the individual cell some kind that will show the essential
+parts more distinctly.
+
+[Illustration: FIG. 11—Typical cells: _n_, nucleus; _p_, protoplasm;
+_w_, cell wall; _s_, sap.]
+
+=7. Microscopic examination of a cell.=—Place under a high power
+of the microscope a portion of fresh skin from one of the inside
+scales of an onion, or a piece of the root tip of a very young corn
+or oat seedling, and fix your attention on one of the individual
+cells. Notice (1) the cell wall or inclosing membrane, _w_ (Fig. 11);
+(2) the protoplasm, _p_, which may be recognized by its granular
+appearance; (3) the _nucleus_, _n_; and (4) the cell sap, _s_. In
+very young cells the protoplasm will be seen to fill most of the
+interior; but in mature ones, like the large one on the right of the
+figure, it forms a thin lining around the wall, with the nucleus
+on one side, while the cell sap, composed of various substances in
+solution, occupies the central portion. Though there is generally
+an inclosing wall, this is not essential, its office being to give
+strength and mechanical support by holding the contents together, as
+an India-rubber bag holds water. It is the turgidity of the cell,
+when distended with liquid, that gives firmness to herbaceous plants
+and the tender parts of woody ones. This may be illustrated by
+observing the difference between a rubber bag when quite full and
+when only half full of water, or a football when partially and when
+fully inflated. In its simplest form, however, the cell is a mere
+particle of protoplasm, which has one part, constituting the nucleus,
+a little more dense in appearance than the rest, but this kind is not
+common in vegetable structures.
+
+=8. How food substances get into the cells.=—As there are no openings
+in the cell walls, the only way substances can get into a cell or
+out of it is by soaking through the inclosing membrane, as will be
+explained in a later chapter. Since starch, oil, and proteins, the
+most important foods stored in seeds, are none of them soluble in the
+cell sap, it is clear that they could not have got into the cells in
+their present state, but must have undergone some change by which
+they were rendered capable of passing through the cell wall.
+
+=9. Digestion.=—The process by which this change is brought about
+is known as _digestion_, from its similarity to the same function
+in animals. Not only are foods, in the state in which we find them
+stored in the seed, incapable of passing through the cell wall,
+but the protoplasm, the living part of the cell, has no power to
+assimilate and to utilize these substances as food until they have
+been reduced to a soluble form in which they can be diffused freely
+from cell to cell through any part of the plant. By _diffusion_ is
+meant the gradual spread of soluble substances through the containing
+medium, as when a lump of sugar or salt, dropped into a glass of
+water, dissolves and slowly diffuses through the contents, imparting
+a sweet or salty taste to the whole.
+
+[Illustration: FIG. 12.—Starch grains of wheat in different stages of
+disintegration under the action of a ferment (diastase), accompanying
+germination: _a_, slightly corroded; _b_, _c_, and _d_, more advanced
+stages of decomposition.]
+
+During the process of digestion the different kinds of food are
+acted upon and made soluble by certain chemical ferments, which are
+secreted in plants for the purpose. The digestion of starch, the most
+abundant of plant foods, is effected by diastase, a common ferment
+obtained from germinating grains of barley, wheat, corn, rice, etc.
+By the presence of diastase starch is converted into grape sugar,
+a substance which is readily soluble in water, and which can be
+diffused easily through the tissues of the plant to any part where it
+is needed. In this way food travels from the leaf, where it is made,
+to the seed, where the sugar is generally reconverted into starch and
+stored up for future use, though sometimes, as in the sugar corn and
+sugar pea, it remains in part unchanged. The kernels of this kind of
+corn can be distinguished readily from those of the ordinary starch
+corn, after maturity, by their wrinkled appearance, owing to their
+greater loss of water in drying.
+
+=10. Food tests.=—In order to tell whether any of the food substances
+named occur in the seeds that we are going to examine, it will be
+necessary to understand a few simple tests by which their presence
+may be recognized. The chemicals required can be ordered ready for
+use from a druggist or may be prepared in the laboratory as needed,
+according to the directions given. Write in your notebook a brief
+account of each experiment made, with the conclusions drawn from it.
+
+  EXPERIMENT 1. TO DETECT THE PRESENCE OF FATS.—Rub a small lump of
+  butter or a drop of oil on a piece of thin white paper. What is the
+  effect?
+
+  EXPERIMENT 2. ANOTHER TEST FOR FATS.—Place some macerated alcanna
+  root in a vessel with alcohol enough to cover it, and leave for
+  an hour. Add an equal bulk of water and filter. The solution will
+  stain fats, oils, and resins deep red.
+
+[Illustration: PLATE 2.—Carrying water over the Mississippi levee
+by siphon to irrigate rice fields. (_From_ Circular of La. Exp.
+Station.)]
+
+  EXPERIMENT 3. TO SHOW THE PRESENCE OF STARCH.—Put a drop of iodine
+  solution on some starch. What change of color takes place? To
+  make iodine solution, add to one part of iodine crystals 4 parts
+  potassium iodide and 95 parts water. It should be kept in the
+  dark, as light decomposes it. Iodine colors starch blue, protein
+  substances light brown. In testing for starch, the solution should
+  be diluted till it is of a pale color, otherwise the stain will be
+  so deep as to appear black.
+
+  EXPERIMENT 4. A TEST FOR PROTEINS.—Place a small quantity of the
+  white of an egg, diluted with water, in a clean glass and add a few
+  drops of nitric acid; or drop some of the acid on the white of a
+  hard-boiled egg. What is the effect?
+
+  Nitric acid turns proteins yellow; if the color is indistinct, add
+  a drop of ammonia, when an orange color will ensue.
+
+  EXPERIMENT 5. ANOTHER TEST FOR PROTEINS.—Place on the substance to
+  be examined a drop of a saturated solution of cane sugar and water;
+  add a drop of pure sulphuric acid; if proteins are present, they
+  will be colored red. See also Exp. 3.
+
+  EXPERIMENT 6. A TEST FOR GRAPE SUGAR.—Heat a teaspoonful of
+  Fehling’s Solution to the boiling point in a test tube (a common
+  glass vial can be used by heating gradually in water) and pour in a
+  few drops of grape sugar solution. Heat again and observe the color
+  of the precipitate that forms.
+
+  Fehling’s Solution may be obtained of the druggist, or, if
+  preferred, it may be prepared in the laboratory as follows: (_a_)
+  Dissolve 173 grams of crystallized Rochelle salts and 125 grams
+  of caustic potash in 500 cc. of water; (_b_) dissolve 34.64 grams
+  crystallized copper sulphate in 500 cc. of water, and mix equal
+  parts as needed. (For English equivalents, see Appendix, Weights
+  and Measures.) The two mixtures must be kept separate till wanted
+  for use, or prepared fresh as needed.
+
+  Grape Sugar causes Fehling’s Solution to form a red precipitate.
+
+  EXPERIMENT 7. TO SHOW THE DIFFERENCE BETWEEN SUGAR AND STARCH IN
+  REGARD TO SOLUBILITY.—Mix some sugar with water and notice how
+  readily it dissolves. Try the same experiment with starch and
+  observe its different behavior.
+
+  EXPERIMENT 8. TO SHOW HOW STARCH IS DISINTEGRATED IN THE ACT OF
+  DIGESTION.—Place a few grains of starch on a slide, add a drop or
+  two of diastase solution, and observe under the microscope; the
+  starch granules will be seen to disintegrate and melt away. Even
+  with a hand lens it can be seen, from the greater clearness of the
+  liquid in comparison with a mixture of untreated starch and water,
+  that the grains have been dissolved.
+
+  EXPERIMENT 9. TO SHOW THAT DIASTASE CONVERTS STARCH INTO
+  SUGAR.—Make a paste of boiled starch so thin that it looks like
+  water. Pour a small quantity of it into each of two tubes, adding a
+  little diastase to one and leaving the other untreated. Keep in a
+  warm place for twenty-four hours, then test both tubes for starch,
+  as directed in Exp. 3, and note the result. If the diastase has not
+  acted, add a little more and watch.
+
+
+          Practical Questions
+
+  1. Name all the food and other economic products you can think of
+  that are derived from the seed of maize; from wheat; from flaxseed;
+  from cotton.
+
+  2. Mention some seeds from which medicines are procured.
+
+  3. Name all the seeds you can think of from which oil is obtained;
+  starch; some that are rich in proteins. (Exps. 1-5.)
+
+  4. Describe some of the ways in which these products are frequently
+  adulterated.
+
+  5. If you were raising corn to sell to a starch factory, what part
+  of the seed would you seek to develop? If to feed stock, what part?
+  Why, in each case? (3; Figs. 4-7.)
+
+  6. What grain feeds more human beings than does any other?
+
+  7. Name all the seeds you can think of that contain sugar in
+  sufficient quantity to be detected without chemical tests; that is,
+  by tasting alone.
+
+  8. Is “coal oil” a mineral or an organic substance? Explain, by
+  giving an account of its origin.
+
+  9. What is gluten? (3.) Name some grains that are especially rich
+  in it.
+
+  10. Which of our three chief food grains is a water plant? (See
+  Plate 2.) Which grows farthest south? Which farthest north? Which
+  one is of American origin?
+
+
+          II. SOME PHYSIOLOGICAL PROPERTIES OF SEEDS
+
+  MATERIAL.—Seeds of squash, pumpkin, or other melon; castor bean;
+  any kind of common kidney bean; grains of Indian corn.
+
+  APPLIANCES.—In the absence of gas, an alcohol or kerosene lamp may
+  be used for heating. A double boiler can easily be made by using
+  two tin vessels of different sizes. Partly fill the larger one with
+  water, set in it the smaller one with the substance to be heated,
+  and place over a burner. A pair of scales, a strong six-ounce
+  bottle, wire-netting, cord, and wax or paraffin should be provided.
+
+  EXPERIMENT 10. DO SEEDS IN THEIR ORDINARY QUIESCENT STATE CONTAIN
+  ANY WATER?—Place a number of beans, or grains of corn or wheat in
+  a glass bottle, making a small perforation in the cork to allow
+  the air to escape, and heat gently. Does any moisture form on the
+  glass?
+
+  A better test is to weigh two or three ounces of seeds, and heat
+  them in a double boiler or in oil to prevent scorching. Weigh at
+  intervals. If there is any loss of weight, to what is it due?
+
+  EXPERIMENT 11. DO SEEDS ABSORB WATER?—Soak a number of beans or
+  grains of corn in water for 12 to 24 hours and compare with dry
+  ones. What difference do you notice? To what cause is it due?
+
+  EXPERIMENT 12. HOW DID WATER GET INTO THE SOAKED SEEDS?—Dry gently
+  with a soft cloth some of the seeds used in the last experiment and
+  press them lightly to see if water comes out, and where. Place a
+  number of dry seeds of different kinds—squash, bean, castor bean,
+  quince, etc.—in warm water and notice whether any bubbles of air
+  form on them and at what point. Examine with a lens and see if this
+  point differs in any way from the rest of the seed cover. Does it
+  correspond with the point from which water exuded in the soaked
+  seeds? Could hard seeds like the squash, castor bean, buckeye, and
+  Brazil nut get water readily without an opening somewhere in the
+  coat?
+
+  EXPERIMENT 13. TO FIND OUT WHETHER WATER IS ABSORBED THROUGH THE
+  SEED COATS.—Place in moist sand or sawdust two rows of beans as
+  nearly as possible of the same size and weight, with the eye
+  pressed down to the substratum in one row and turned up in the
+  other, so that no moisture can enter through it. In the same way
+  arrange two rows of castor beans with the little end down in one
+  row and uppermost in the other. In the last set carefully break
+  away the spongy mass near the tip, without injuring the parts about
+  it. Watch and see in which rows water is absorbed most readily.
+  What change takes place in the spongy masses at the tips of those
+  castor beans on which they were left?
+
+[Illustration: FIG. 13.—Effect of the expansion of seeds due to
+absorption of water.]
+
+  EXPERIMENT 14. IS THE RATE OF GERMINATION AFFECTED BY THE PRESENCE
+  OR ABSENCE OF OPENINGS?—Seal up with wax or paraffin all the
+  openings of a number of air-dry peas or beans, and leave an equal
+  number of the same size and weight untreated. Be careful that the
+  sealing is absolutely water-tight, since otherwise the experiment
+  will be worthless. Plant both sets and keep under like conditions
+  of soil, temperature, and moisture. Do you see any difference in
+  the rate of germination of the two sets?
+
+  EXPERIMENT 15. DO SEEDS EXERT FORCE IN ABSORBING WATER?—Fill a
+  common six-ounce bottle as full as it will hold with dry peas,
+  beans, or grains of corn; then pour in water till the bottle is
+  full. Tie a piece of wire-netting or stout sackcloth over the top
+  to keep the seeds from being forced out. Bind both the neck and the
+  body of the bottle tightly with strong cords encircling it in both
+  a horizontal and vertical direction, and place under water in a
+  moderately warm temperature. Watch for results.
+
+  EXPERIMENT 16. IS THE FORCE EXERTED IN THE LAST EXPERIMENT A
+  MERELY MECHANICAL ONE, LIKE THE BURSTING OF A WATER PIPE, OR IS IT
+  PHYSIOLOGICAL AND THUS DEPENDENT ON THE FACT THAT THE SEEDS ARE
+  ALIVE?—To answer this question try Exp. 15 with seeds that have
+  been killed by heat or by soaking in formalin.
+
+
+          Practical Questions
+
+  1. Will a pound of pop corn weigh as much after being popped as
+  before? (Exp. 10.)
+
+  2. What causes the difference, if there is any? (Exp. 10.)
+
+  3. Does the tuft of downy hairs at the tip of wheat and oat grains
+  influence their water supply? The spongy covering of black walnuts
+  and almonds? The pithy inside layers of pecans and English walnuts?
+  (Exps. 12, 13.)
+
+  4. Why will seeds, as a general thing, germinate more readily after
+  being soaked? (Exps. 11, 14, 16.)
+
+
+          III. TYPES OF SEEDS
+
+  MATERIAL.—Dry and soaked grains of corn, wheat, or oats; bean,
+  squash, castor bean, and pine seed, or any equivalent specimens
+  showing the differences as to number of cotyledons and the
+  presence or absence of endosperm. Each student should be provided
+  with several specimens, both soaked and dry, of the kind under
+  consideration. Corn, beans, and wheat need to be soaked from 12
+  to 24 hours; squash and pumpkin from 2 to 5 days, and very hard
+  seeds, like the castor bean and morning-glory, from 5 to 10. If
+  such seeds are _clipped_, before soaking, that is, if a small piece
+  of the coat is chipped away from the end opposite the scar, or eye,
+  they will soften more quickly. Keep them in a warm place with an
+  even temperature till just before they begin to sprout, when the
+  contents become softened. Very brittle cotyledons may be softened
+  quickly by boiling for a few minutes.
+
+  No appliances are needed beyond the pupil’s individual outfit and
+  some of the food tests given in Section I of this chapter.
+
+=11. Dissection of a grain of corn.=—Examine a dry grain of corn
+on both faces. What differences do you notice? Sketch the grooved
+side, labeling the hard, yellowish outer portion, _endosperm_, the
+depression near the center, _embryo_, or _germ_.
+
+Next take a grain that has been soaked for twenty-four hours. What
+changes do you see? How do you account for the swelling of the
+embryo? Remove the skin and observe its texture. Make an enlarged
+sketch of a grain on the grooved side with the coat removed, labeling
+the flat oval body embedded in the endosperm, _cotyledon_; the upper
+end of the little budlike body embedded in the cotyledon, _plumule_,
+the lower part, _hypocotyl_—words meaning, respectively, “seed leaf,”
+“little bud,” and “the part under the cotyledon.” As this part has
+not yet differentiated into root and stem, we cannot call it by
+either of these names. The cotyledon, hypocotyl, and plumule together
+compose the embryo. Pick out the embryo and sketch as it appears
+under the lens. Crush it on a piece of white paper; what does it
+contain?
+
+[Illustration: FIGS. 14-16.—Dissection of a grain of corn: 14, soaked
+grain, seen flatwise, cut away a little and slightly enlarged, so as
+to show the embryo lying in the endosperm; 15, in profile section,
+dividing the grain through the embryo and cotyledon; 16, the embryo
+taken out whole. The thick mass is the cotyledon; the narrow body
+projecting upwards, the plumule; the short projection at the base,
+the hypocotyl (_after_ GRAY).]
+
+Make a vertical section of another soaked grain at right angles to
+its broader face, and sketch, labeling the parts as they appear in
+profile. Make a cross section through the middle of another grain and
+sketch, labeling the parts as before. What proportion of the grain is
+endosperm and what embryo? Put a drop of iodine and of nitric acid
+separately on pieces of the endosperm, and note the effects. Test the
+seed coats and the cotyledon to see if they contain any starch.
+
+Notice that the corn grain has but one cotyledon, hence such seeds
+are said to be _monocotyledonous_, or one-cotyledoned. The grains are
+not typical seeds, but are selected for examination because they are
+large and easy to handle, can be obtained everywhere, and germinate
+readily.
+
+=12. Dissection of a bean.=—Sketch a dry bean as it lies in the pod,
+showing its point of attachment and any markings that may appear on
+its surface. Then take it from the pod and examine the narrow edge
+by which it was attached. Notice the rather large scar (commonly
+called the eye of the bean) where it broke away from the point of
+attachment. This is the _hilum_. Near the hilum, look for a minute
+round pore like a pinhole. This is called the _micropyle_, from a
+Greek word meaning “a little gate,” because it is the entrance to
+the interior of the seed coat. There was no micropyle observed in
+the corn grain, because it is not a true seed but a fruit inclosing
+a single seed. The inclosing membrane is the fruit skin, which has
+become incorporated with the seed coat and taken its place as a
+protective covering. Compare a soaked bean with a dry one; what
+difference do you perceive? How do you account for the change in size
+and hardness? Find the hilum and the micropyle in the soaked bean.
+Lay it on one side and sketch, with the micropyle on top; then turn
+toward you the narrow edge that was attached to the pod and sketch,
+labeling all the parts. Make a section through the long diameter at
+right angles to the flat sides, press it slightly open, and sketch
+it. Notice the line or slit that seems to cut the section in half
+longitudinally, and the small round object between the halves at one
+end; can you tell what it is?
+
+[Illustration: FIGS. 17, 18.—A kidney bean: 17, side view; 18, front
+view, showing _h_, hilum, _m_, micropyle.]
+
+[Illustration: FIG. 19.—Cotyledon of a bean, showing plumule.]
+
+Slip off the coat from a whole bean and notice its texture. Hold it
+up to the light and see if it shows any signs of veining. See whether
+the scar at the hilum extends through the kernel, or marks only the
+seed coat. Lay open the two flat bodies into which the kernel divides
+when stripped of its coats, keeping them side by side, with the part
+above the micropyle toward the top. Sketch their inner face and
+label them _cotyledons_. Be careful not to break or displace the
+tiny bud packed away between the cotyledons, just above the hilum.
+Label the round portion of this bud, _hypocotyl_, and the upper, more
+expanded part, _plumule_. Which way does the base of the hypocotyl
+point; toward the micropyle, or away from it? Pick out this budlike
+body entire and sketch as it appears under the lens. Open the plumule
+with a pin and examine it with a lens; of what does it appear to
+consist? Do you find any endosperm around the cotyledons, as in the
+corn and oats? Break one of the soaked cotyledons, apply the proper
+tests (Exps. 2, 3, 5), and report what substances it contains. Where
+is the nourishment for the young plant stored? What part of the bean
+gives it its value as food?
+
+Notice that in the bean the embryo consists of three parts, the
+hypocotyl, plumule, and the two cotyledons, which completely fill
+the seed coats, leaving no place for endosperm. Seeds like the bean,
+squash, and castor bean, which have two cotyledons, are said to be
+_dicotyledonous_.
+
+=13. The castor bean.=—Lay a castor bean on a sheet of paper before
+you with its flat side down; what does it look like? The resemblance
+may be increased by soaking the seed a few minutes, in order to swell
+the two little protuberances at the small end. Can you think of any
+benefit a plant might derive from this curious resemblance of its
+seed to an insect?
+
+Sketch the seed as it lies before you, labeling the protuberance
+at the apex, _caruncle_. The caruncle is an appendage of the
+seed-covering developed by various plants; its use is not always
+clear. What appears to be its object in the castor bean? Refer to
+Exp. 13 and see if there is any other purpose it might serve.
+
+Turn the seed over and sketch the other side. Notice the colored
+line or stripe that runs from the large end to the caruncle. This
+is the _rhaphe_, and shows the position that would be occupied by
+the seed stalk if it were present. Its starting point near the large
+end, which is marked in fresh seeds by a slight roughness, is the
+_chalaza_, or organic base of the seed, where the parts all come
+together like the parts of a flower at their insertion on the stem.
+Where was it situated in the common bean? How does this differ from
+its position in the castor bean? Where the rhaphe ends, just at the
+beak of the caruncle, you will find the hilum. The micropyle is
+covered by the caruncle, which is an outgrowth around it.
+
+[Illustration: FIGS. 20-22.—Castor bean (slightly magnified);
+20, back view; 21, front view; _ch_, chalaza; _r_, rhaphe; _ca_,
+caruncle; 22, vertical section; _en_, endosperm; _cc_, cotyledons;
+_hy_, hypocotyl; _hi_, hilum; _m_, micropyle.]
+
+Now cut a vertical section through a seed that has been soaked
+for several days, at right angles to the broad sides, and sketch
+it. Label the white, pasty mass within the seed coats, endosperm.
+Can you make out what the narrow white line running through the
+center of the endosperm, dividing it into two halves, represents?
+Make a similar sketch of a cross section. Notice the same white
+line running horizontally across the endosperm, dividing it into
+two equal parts. To find out what these lines are, take another
+seed (always use soaked seeds for dissection) and remove the coats
+without injuring the kernel. Split the kernel carefully round the
+edges, remove half the endosperm, and sketch the other half with the
+delicate embryo lying on its inner face. You will have no difficulty
+now in recognizing the lines in your drawings as sections of the
+thin cotyledons. Where is the hypocotyl, and which way does its base
+point? Remove the embryo from the endosperm, separate the cotyledons
+with a pin, hold them up to the light, and observe their beautiful
+texture. Sketch them under the lens, showing the delicate venation.
+Is there any plumule?
+
+Test the endosperm with a little iodine. Does it give a blue or a
+brown reaction? Crush another bit of it on a piece of white paper and
+see if it leaves a grease spot. What does this show that it contains?
+Test the embryo in the same way, and see whether it contains any oil.
+
+  NOTE.—It should be borne in mind that the castor bean bears no
+  relation whatever to the true beans. It belongs to the spurge
+  family, which is botanically very remote from that of the peas and
+  beans.
+
+[Illustration: FIGS. 23-25.—Seed of a squash; 23, seed from the
+outside; 24, vertical section perpendicular to the broad side;
+25, section parallel to the broad side, showing inner side of a
+cotyledon; _a_, seed coat; _c_, cotyledons; _h_, hypocotyl; _p_,
+plumule.]
+
+=14. Study of a squash or gourd seed.=—How does the coat of a squash
+seed differ from that of the bean? At the small end, look for two
+dots, or pinholes, close together. Refer to your drawing of the bean
+and see if you can make out, with the help of a lens, what they are.
+The bean is a curved seed, which is bent so as to bring the hilum
+close to the micropyle on one side. But by far the greater number
+of seeds are _inverted_, or turned over on their stalks, as you
+sometimes see huckleberry blossoms and bell flowers on their stems,
+so that when the stalk breaks away from its attachment, the scar and
+the micropyle come close together at one end, as in the squash seed.
+
+[Illustration: FIG. 26.—Diagram of an inverted or anatropous seed,
+showing the parts in section: _a_, outer coat; _b_, inner coat;
+_c_, kernel; _d_, rhaphe; _ch_, chalaza; _h_, hilum; _m_, micropyle
+(_After_ GRAY).]
+
+Make a drawing of the outside of a seed, labeling all the parts you
+have observed; then gently remove the hard coat, or _testa_, as it
+is called. The thin, greenish covering that lines it on the inside
+is the endosperm. How does it compare in quantity with that in the
+corn and castor bean? How do the cotyledons compare in thickness
+with those of the bean? Carefully separate them and draw, labeling
+the parts as you make them out. The tiny pointed object between the
+cotyledons at their point of union is the plumule; is it as well
+developed as in the bean? Can you see any reason why seeds like the
+pea and bean, which have cotyledons too thick and clumsy to do well
+the work of true leaves, should have a well-developed plumule, while
+those with thin cotyledons, like the squash and pumpkin, do not,
+as a general thing, form a large plumule in the embryo? The little
+projection in which the cotyledons end is the hypocotyl; which way
+does it point? Where did you find the micropyle to be? Test the
+cotyledons and some of the endosperm for food substances; what do you
+find in them?
+
+=15. Study of a pine seed.=—Remove one of the scales from a pine cone
+and sketch the seed as it lies in place on the cone scale. Notice
+its point of attachment to the scale, and look near this point for a
+small opening, which you can easily recognize as the micropyle. The
+seed with its wing looks very much like a fruit of the maple, but
+differs from it in being a naked seed borne on the inner side of a
+cone scale, without a pod or husk or outer covering of any kind, such
+as beans and nuts and grains are provided with. Plants like the pine,
+which bear their seed in this way, are called _Gymnosperms_, a word
+that means “naked seeds,” in contradistinction to the _Angiosperms_,
+which bear their seeds in pods or other closed envelopes.
+
+[Illustration: FIGS. 27, 28.—Pitch pine seeds: 27, scale, or open
+carpel, with one seed in place; 28, winged seed, removed. (_After_
+GRAY.)]
+
+[Illustration: FIG. 29.—Section of pine seed, showing the
+polycotyledonous embryo (GRAY).]
+
+Remove the coat from a seed that has been soaked for twenty-four
+hours, and examine it with a lens. Does it consist of one or more
+layers? Is there any difference in color between the inner and outer
+layers? Look at the base of the hypocotyl for some loose, cobwebby
+appendages. These are the remains of other embryos with certain
+appendages belonging to them that were formed in the endosperm, but
+failed to develop. Did you find remains of this kind in any of the
+other seeds examined? Pick out the embryo from the endosperm and
+test both for food substances. Which of these do you find? Which
+are absent? How does the embryo differ from those already examined?
+How many cotyledons are there? Make an enlarged sketch of a seed in
+longitudinal section, labeling correctly all the parts observed.
+
+=16. Comparison as to food value of seeds.=—Make in your notebook a
+tabular statement after the model here given, of the food contents
+found in the different seeds you have examined. Indicate the relative
+quantity of each by writing under it, in the appropriate column, the
+words, “much,” “little,” or “none,” as the case may be.
+
+
+                 MODEL FOR RECORD OF SEEDS EXAMINED
+
+  +================+===========================================+
+  |                |               FOODS TESTED                |
+  | SEEDS EXAMINED +----------+----------+----------+----------+
+  |                |  Starch  |   Sugar  |   Oil    | Proteins |
+  +----------------+----------+----------+----------+----------+
+  | Corn           |          |          |          |          |
+  +----------------+----------+----------+----------+----------+
+  | Wheat          |          |          |          |          |
+  +----------------+----------+----------+----------+----------+
+  | Bean           |          |          |          |          |
+  +----------------+----------+----------+----------+----------+
+  | Squash         |          |          |          |          |
+  +----------------+----------+----------+----------+----------+
+  | Castor bean    |          |          |          |          |
+  +----------------+----------+----------+----------+----------+
+  | Pine           |          |          |          |          |
+  +----------------+----------+----------+----------+----------+
+
+By far the greater number of seeds contain endosperm; that is, they
+consist of an embryo with more or less nourishing matter stored
+about it. Even in seeds which appear to have none, the endosperm is
+present at some period during development, but is absorbed by the
+cotyledons before germination.
+
+=17. Manner of storing nourishment.=—In the various seeds examined,
+we have seen that the nourishment for the young plant is either
+stored in the embryo itself, as in the cotyledons of the bean, acorn,
+squash, etc., or packed about them in the form of endosperm, as in
+the corn, wheat, and castor bean.
+
+=18. The number of cotyledons.=—Seeds are also classed according
+to the number of their cotyledons, as having one, two, or many
+cotyledons. The first two kinds make up the great class of
+Angiosperms, which includes all the true flowering plants and forms
+the most important part of the vegetation of the globe. The last
+is characteristic of the great natural division of Gymnosperms, or
+naked-seeded plants, of which we have had an example in the pine.
+They are the most primitive type of living seed-bearing plants.
+Though they are not so abundant now as in past ages, numbering only
+about four hundred known species, they present many diversities of
+form, which seem to ally them on the one hand with the lower, or
+spore-bearing plants (ferns, mosses, etc.), and on the other hand
+with the Angiosperms.
+
+
+          Practical Questions
+
+  1. Make a list of all the seeds you can find that have very thick
+  cotyledons, and underline those that are used as food by man or
+  beast.
+
+  2. Make a similar list of all the kinds with thin cotyledons and
+  more or less endosperm, that are used for food or other purposes.
+
+  3. Do you find a greater number of foodstuffs among the one kind
+  than the other?
+
+  4. How do the two kinds compare, as a general thing, in size and
+  weight?
+
+  5. From what part of the castor bean do we get oil? of the peanut?
+  of cotton seed? (Exps. 1-6.)
+
+  6. Is there any valid objection to the wholesomeness of peanut oil,
+  and of cottonseed lard as compared with hog’s lard? (1, 3.)
+
+  7. What is bran? Does it contain any nourishment? (11, 12; Exps.
+  1-6.)
+
+  8. What gives to Indian corn its value as food? to oats? wheat?
+  rice? (3; Exps. 1-6.)
+
+  9. Which of these grains has the larger proportion of endosperm to
+  embryo? (Figs. 1-3.)
+
+  10. Which contains the larger amount of starch in proportion to its
+  bulk, rice or Indian corn?
+
+  11. If you wished to produce a variety of corn rich in oil, you
+  would select seed for planting with what part well developed? (3;
+  Figs. 4-7.)
+
+
+          IV. SEED DISPERSAL
+
+  MATERIAL.—Fruits and seeds of any kind that show adaptations for
+  dispersal. Some common examples are: (1) Wind: ash, elm, maple,
+  ailanthus, milkweed, clematis, sycamore, linden, dandelion,
+  thistle, hawkweed. (2) Water: pecan, filbert, cranberry, lotus,
+  hickory nut, coconut—obtain one with the husk on, if possible. (3)
+  Animal agency (involuntary): cocklebur, tickseed, beggar-ticks,
+  burdock; (voluntary) almost all kinds of edible fruits, especially
+  the bright-colored ones—wild plums, cherries, haws, dogwood,
+  persimmons, etc. (4) Explosive and self-planting: witch-hazel,
+  wood sorrel, violet, crane’s-bill, wild vetch, peanut, medick,
+  stork’s-bill (Erodium).
+
+  EXPERIMENT 17. TO SHOW HOW SEEDS ARE DISPERSED BY WIND.—Take a
+  number of winged and plumed fruits and seeds, such as those of the
+  maple, ash, ailanthus, dandelion, clematis, milkweed, and trumpet
+  creeper; stand on a chair or table in a place where there is a
+  draft of air and let them all go. Which travel the farther, the
+  winged or the plumed kinds? Which sort is better fitted to aërial
+  transportation?
+
+  EXPERIMENT 18. DISPERSAL BY WATER.—Place in a bucket of water a
+  hazelnut, an acorn, an orange, a cranberry, a pecan, a hickory nut,
+  a fresh apple, and a coconut with the husk on. Which are the best
+  floaters? Cut open or break open the good swimmers, compare with
+  the non-floaters, and see to what peculiarity of structure their
+  floating qualities are due. In what situations do the cranberry and
+  the coconut grow? Can you see any advantage to a plant so situated
+  in producing fruits that float easily?
+
+  EXPERIMENT 19. DISPERSAL BY EXPLOSIVE CAPSULES.—Moisten slightly
+  some mature but unopened capsules of witch hazel, wood sorrel,
+  rabbit pea, or violet, and leave in a warm, dry place for fifteen
+  to forty-five minutes. What happens when the pods begin to dry?
+  Measure the distance to which the different kinds of seeds have
+  been ejected. Which were thrown farthest? What was the object of
+  the movement? What caused the explosion?
+
+  EXPERIMENT 20. THE USE OF ADHESIVE FRUITS.—Scatter broadcast
+  a handful of hooked or prickly seeds or fruits—cocklebur,
+  tickseed, beggar-ticks, bur grass, etc. Are they suited for wind
+  transportation? Drop one of them on your sleeve, or on the coat
+  of a fellow student; will it stay there? What would be the effect
+  if it became attached to the fur of a roaming animal? Is this a
+  successful mode of dissemination?
+
+[Illustration: FIGS. 30-32.—30, A pod of wild vetch, with mature
+valves twisting spirally to discharge the seed; 31, pod of
+crane’s-bill discharging its seed; 32, capsules of witch-hazel
+exploding.]
+
+[Illustration: FIGS. 33-36.—Fruits adapted to wind dispersal: 33,
+winged pod of pennycress; 34, spikelet of broom sedge; 35, akene of
+Canada thistle; 36, head of rolling spinifex grass.]
+
+=19. Agencies of dispersal.=—The means at nature’s disposal for this
+purpose, as shown by the experiments just made, are four; namely,
+wind, water, the explosion of capsules due to the withdrawal of
+water, and the agency of animals, including man. The first three
+are purely mechanical. The last, animal agency, is either voluntary
+or involuntary, according as it is conscious and intentional, or
+accidental merely. Man, of course, is the only consciously voluntary
+agent. Of the four agencies named, animals and wind are the most
+effective, and the greater number of adaptations observed will be
+found to have reference to these.
+
+[Illustration: FIG. 37.—Good quality of clover seed.]
+
+[Illustration: FIG. 38.—Inferior quality of clover seed mixed with
+“screenings.”]
+
+[Illustration: FIG. 39.—Dodder on red clover, showing how the seeds
+get mixed.]
+
+=20. Involuntary dispersal.=—The lower animals may be voluntary
+agents in a way, though not designedly so, as when a squirrel buries
+nuts for his own use and then forgets the location of his hoard and
+leaves them to germinate; or when a jaybird flies off with a pecan
+in his bill, intending to crack and eat it, but accidentally lets
+it fall where it will sprout and take root. Both man and the lower
+animals are not only involuntary, but often unwilling agents of
+dispersal. Some of the most troublesome weeds of civilization have
+been unwittingly distributed by man as he journeyed from place to
+place, carrying, along with the seed for planting his crops, the
+various weed seeds, or “screenings,” as these mixtures are called
+by dealers, with which they have been adulterated either through
+carelessness and ignorance, or from unavoidable causes. The neglected
+animals, also, that are allowed by short-sighted farmers to wander
+about with their hair full of cockleburs and other adhesive weed
+pests, are no doubt very unwilling carriers of those disagreeable
+burdens.
+
+=21. Tempting the appetite.=—This is the most important adaptation
+to dispersal by animals. Have you ever asked yourself how it could
+profit a plant to tempt birds and beasts to devour its fruit, as so
+many of the bright berries we find in the autumn woods seem to do? To
+answer this question, examine the edible fruits of your neighborhood
+and you will find that almost without exception the seeds are hard
+and bony, and either too small to be destroyed by chewing, and
+thus capable of passing uninjured through the digestive system of
+an animal; or, if too large to be swallowed whole, compelling the
+animal, by their hardness or disagreeable flavor, to reject them.
+In cases where the seeds themselves are edible and attractive, the
+fruits are usually armed during the growing season with protective
+coverings, like the bur of the chestnut and the astringent hulls
+of the hickory nut and walnut. The acidity or other disagreeable
+qualities of most unripe fruits serves a similar purpose, while their
+green color, by making them inconspicuous among the foliage leaves,
+tends still further to insure them against molestation.
+
+[Illustration: FIGS. 40-42.—Adhesive fruits: 40, fruit of
+hound’s-tongue; 41, akene of bur marigold; 42, fruit of bur grass
+(cenchrus).]
+
+=22. Voluntary agency.=—The cultivated fruits and grains owe their
+distribution and survival almost entirely to the voluntary agency
+of man. Dispersal by this means, whether intentional or accidental,
+is purely artificial, and except in the case of a few annuals like
+horseweed, bitterweed, ragweed, goosefoot, and other field pests that
+have adjusted their season of growth and flowering to the conditions
+of cultivation, is not correlated with any special modification of
+the plants for self-propagation. On the contrary, many of the most
+widely distributed weeds of cultivation, such as the oxeye daisy, the
+rib grass, mayweed and bitterweed, possess very imperfect natural
+means of dispersal, and are largely dependent for their propagation
+on the involuntary agency of man.
+
+=23. Use of the fruit in dispersal.=—It will be seen from the
+foregoing observations that the fruit plays a very important part in
+the work of dispersal, most of the adaptations for this purpose being
+connected with it. In cases where a number of seeds are contained in
+a large pod that could not conveniently be blown about by the breeze,
+adaptations for wind dispersal are attached to the individual seeds,
+as in the willow, milkweed, trumpet creeper, and paulonia; but as a
+general thing, adaptations of the seed are for protection, the work
+of dispersal being provided for by the fruit. In the case of the
+large class of plants known as “tumbleweeds,” the whole plant body is
+fitted to assist in the work of transportation. Such plants generally
+grow in light soils and either have very light root systems, or are
+easily broken from their anchorage and left to drift about on the
+ground. The spreading, bushy tops become very light after fruiting,
+so as to be easily blown about by the wind, dropping their seeds
+as they go, until they finally get stranded in ditches and fence
+corners, where they often accumulate in great numbers during the
+autumn and winter.
+
+[Illustration: FIG. 43.—A fruiting plant of winged pigweed
+(_Cycloloma_), showing the bunchy top and weak anchorage of a typical
+tumbleweed.]
+
+[Illustration: FIG. 44.—Panicle of “old witch grass,” a common
+tumbleweed.]
+
+=24. The advantages of dispersal.=—Seed cannot germinate unless
+they are placed in a suitable location as to soil, moisture, and
+temperature. In order to increase the chances of securing these
+conditions, it is clearly to the advantage of a species that its
+seeds should be dispersed as widely as possible, both that the
+seedlings may have plenty of room, and that they may not have to draw
+their nourishment from soil already exhausted by their parents. The
+farmer recognizes this principle in the rotation of crops, because
+he knows that successive growths of the same plant will soon exhaust
+the soil of the substances required for its nutrition, while they may
+leave it richer in nourishment for a different crop.
+
+[Illustration: FIG. 45.—Self-planting pod of peanut.]
+
+=25. Self-planting seeds.=—Dispersal is not the only problem the
+seed has to meet. The majority of seeds cannot germinate well on
+top of the ground, and must depend on various agencies for getting
+under the soil. Some of them do this for themselves. The seeds of the
+stork’s-bill, popularly known as “filarees,” have a sharp-pointed
+base and an auger-shaped appendage at the apex, ending in a
+projecting arm (the “clock” of the filaree) by which it is blown
+about by the wind with a whirling motion till it strikes a soft
+spot, when it begins at once to bore its way into the ground. The
+common peanut is another example. The blossoms are borne under the
+leaves, near the base of the stem, and as soon as the seeds begin to
+form, the flower stalks lengthen several inches, carrying the young
+pods down to the ground, where they bore into the soil and ripen
+their seeds.
+
+
+          Practical Questions
+
+  1. Name the ten most troublesome weeds of your neighborhood.
+
+  2. What natural means of dispersal have they?
+
+  3. Which of them owe their propagation to man?
+
+  4. Are there any tumbleweeds in your neighborhood?
+
+  5. Would you expect to find such weeds in a hilly or a well-wooded
+  region? (19, 23; Exp. 17.)
+
+  6. What situations are best fitted for their propagation? (19, 23;
+  Exp. 17.)
+
+  7. Make a list of all the fruits and seeds you can think of that
+  are adapted to dispersal by wind; by water; by animals.
+
+  8. By what means of dissemination, or protection, or both, is each
+  of the following distinguished: the squash; apple; fig; pecan;
+  poppy; bean; beggar-tick; linden; grape; rice; pepper; olive;
+  cranberry; jimson weed; thistle; corn; wheat; oats?
+
+  9. What is the agent of dispersion, or what the danger to be
+  provided against, in each case?
+
+  10. Could our cultivated fruits and grains survive in their present
+  state without the agency of man? (22.)
+
+  11. Name all the plants you can think of that bear winged seeds and
+  fruits; are they, as a general thing, tall trees and shrubs, or low
+  herbs?
+
+  12. Name all you can think of that bear adhesive seeds and fruits;
+  are they tall trees or low herbs?
+
+  13. Give a reason for the difference. (Exps. 17, 20.)
+
+  14. Why is the dandelion one of the most widely distributed weeds
+  in the world? (19; Exp. 17.)
+
+  15. Is the wool that covers cotton seed for dispersal or protection?
+
+  16. What advantage to the Indian shot (canna) is the excessive
+  hardness of its seeds? (21.)
+
+  17. What is the use to the species, of the bitter taste of lemon
+  and orange seed? (21.)
+
+  18. Why are the seeds of dates and persimmons and haws so hard?
+  (21.)
+
+  19. Do you find any edible seeds without protection? If so, account
+  for the want of it. (21, 22.)
+
+  20. Name some of the agencies that may assist in covering seeds
+  with earth.
+
+  21. Do you know of any seeds that bury themselves?
+
+  22. The seeds of weeds and other refuse found mixed with grain
+  sold on the market are known, commercially, as “screenings.” Wheat
+  brought to mills in Detroit showed screenings that contained, among
+  other things, seeds of black bindweed, green foxtail grass, yellow
+  foxtail, chess, oats, ragweed, wild mustard, corn cockle, and
+  pigweed. Can you mention some of the ways in which these foreign
+  substances may have gotten into the crop and suggest means for
+  keeping them out?
+
+
+          Field Work
+
+  The subjects treated in the foregoing chapter are, in general,
+  better suited to laboratory than to field work. There are some
+  details, however, which can be observed to advantage out of doors.
+  Many of the seeds found in your walks will show peculiarities of
+  shape and external markings and color that will invite observation.
+  Examine also the contents of different kinds you may meet with, as
+  to the presence or absence of endosperm and the arrangement and
+  development of the embryo. Note: (1) whether, as a general thing,
+  there is any difference in size and weight and amount of nourishing
+  matter in the two kinds; (2) the greater variety in the shape and
+  arrangement of the cotyledons in the albuminous kind, and in the
+  arrangement of the embryo; (3) the differences in the development
+  of the plumule in the two kinds,—and give a reason for the facts
+  observed.
+
+  Among the different seeds you may find, look for adaptations for
+  dispersal, and decide to what particular method each is suited.
+  Study the agencies by which various kinds may get covered with
+  soil. If the common stork’s-bill (_Erodium cicutarium_) grows in
+  your neighborhood, its seeds will well repay a little study, and if
+  there is a field of peanuts within reach, do not fail to pay it a
+  visit.
+
+
+
+
+CHAPTER II. GERMINATION AND GROWTH
+
+
+          I. PROCESSES ACCOMPANYING GERMINATION
+
+  MATERIAL.—A pint or two of corn, peas, beans, or any quickly
+  germinating seed.
+
+  APPLIANCES.—Matches; wood splinters; gas jet or alcohol lamp; test
+  tubes; a small quantity of mercuric oxide; a thermometer; a couple
+  of two-quart preserve jars, and a smaller wide-mouthed bottle that
+  can be put into one of them; some limewater; a glass tube (the
+  straws used by druggists for soft drinks will answer).
+
+=26. Preliminary exercises.=—Before taking up the study of
+germinating seeds, it is important to learn from what sources the
+organic substances used by the growing plant are derived, and some of
+the processes that accompany growth and development.
+
+  EXPERIMENT 21. TO SHOW THE CHANGES THAT ACCOMPANY OXIDATION.—Strike
+  a match and let it burn out. Examine the burnt portion remaining
+  in your hand; what changes do you notice? These changes have been
+  caused by the union of some substance in the match with something
+  outside of it, in the act of burning; let us see if we can find out
+  what this outside substance is.
+
+  EXPERIMENT 22. TO SHOW THE ACTIVE AGENT IN OXIDATION.—Heat some
+  mercuric oxide in a test tube over the flame of a burner. The
+  heat will cause the oxygen to separate from the mercury, and in a
+  short time the tube will be filled with the gas. Extinguish the
+  flame from a lighted splinter and thrust the glowing end into the
+  tube; what happens? The oxygen unites with something in the wood
+  and causes it to burn just as the match did. Compare your burnt
+  splinter with the burnt end of the match; what resemblance do you
+  notice between them?
+
+  EXPERIMENT 23. TO SHOW THAT CARBON DIOXIDE IS A PRODUCT OF
+  OXIDATION.—Your experiment with the match showed that ignition
+  is accompanied by heat, and if active enough, by light, and also
+  that it left behind a solid substance in the form of charcoal. But
+  how about the part that united with the oxygen to produce these
+  results? Let us see what became of it. Hold a lighted candle
+  under the open end of a test tube, or under the mouth of a small
+  glass jar. Does any vapor collect on the inside? After two or
+  three minutes quickly invert the jar or the tube, and thrust in a
+  lighted match: what happens? Can the substance now in the jar be
+  ordinary air? Why not? (Exps. 21, 22.) Pour in a small quantity of
+  limewater, holding your hand over the mouth of the tube to prevent
+  the air from getting in; the gas inside, being heavier than air,
+  will not escape immediately unless agitated. What change do you
+  notice in the limewater?
+
+  It has been proved by experiment that the kind of gas formed by
+  the burning candle has the property of turning limewater milky;
+  hence, whenever you see this effect produced in limewater, you may
+  conclude that this gas, known as _carbon dioxide_, is present;
+  and conversely, the presence of carbon dioxide, especially if
+  accompanied by some of the other effects observed, as the giving
+  out of heat and moisture, may be taken as evidence that some
+  process similar to that going on in the burning candle is, or has
+  been, at work.
+
+  EXPERIMENT 24. DO THESE EFFECTS ACCOMPANY ANY OF THE LIFE PROCESSES
+  OF ANIMALS?—Blow your breath against the palm of your hand; what
+  sensation do you feel? Blow it against a mirror, or a piece of
+  common glass; what do you see? Blow through a tube into the bottom
+  of a glass containing limewater; how is the water affected? How do
+  these facts correspond with the results of Exp. 23?
+
+  EXPERIMENT 25. IS THERE ANY EVIDENCE THAT A SIMILAR PROCESS GOES ON
+  IN PLANTS?—(1) Half fill a small, wide-mouthed jar with limewater,
+  place it inside a larger one (Fig. 46), and fill the space between
+  them, up to the neck of the smaller vessel, with well-soaked
+  peas, beans, or barleycorns, on a bed of moist cotton or blotting
+  paper. Cover with a piece of glass and keep at a moderately warm
+  temperature. (2) As a control experiment, place beside this another
+  jar arranged in precisely the same way, except that seeds must
+  be used whose vitality has been destroyed by heat. To prevent
+  the entrance of germs among the dead seeds, which might cause
+  fermentation and thus interfere with the experiment, set the jar
+  containing them in a vessel of water and boil an hour or two before
+  the experiment begins. Otherwise, treat precisely as in (1).
+
+[Illustration: FIG. 46.—Diagrammatic section, showing arrangement
+of jars for Exp. 25.]
+
+  After germination has taken place in (1), what change do you notice
+  in the limewater? If the effect is not apparent, gently stir with a
+  straw or a glass rod to mix it with the gas in the larger jar. Has
+  the limewater in the control experiment undergone the same change?
+  (It may show a slight milkiness due to the carbon dioxide in the
+  air.) Insert a thermometer among the seeds in both of the larger
+  jars, and compare their temperature with that of the outside air;
+  which shows the greater rise? From this experiment and the last
+  one, what process, common to animals, would you conclude has been
+  going on in the germinating seeds?
+
+  NOTE.—Heat in germinating seeds is not always due to this cause
+  alone, but is sometimes increased by the presence of minute
+  organisms called bacteria. Germinating barley and rye in breweries
+  sometimes show an increase in temperature of 40 to 70 degrees, due
+  to these organisms, and spontaneous combustion in seed cotton has
+  been reported from the same cause.
+
+=27. Oxidation.=—The process that brought about the results observed
+in the foregoing experiments, and popularly known as _combustion_, is
+more accurately defined by chemists as _oxidation._ It takes place
+whenever substances enter into new combinations with oxygen. The most
+familiar examples of it are when oxygen enters into combination with
+substances containing carbon. It was the union of a portion of the
+oxygen of the air in Exp. 21, and of that in the tube in Exp. 22,
+with some of the carbon in the wood, that caused the burning. The
+effect was more marked in the second case because the oxygen in the
+tube was pure, while in the air it is mixed with other substances.
+
+=28. Carbon.=—The black substance left in your hand after oxidation
+of the wood in Exps. 21 and 22 is _carbon_. It composes the greater
+part of most plant bodies, and, in fact, is the most important
+element in the realm of organic nature. There is not a living thing
+known, from the smallest microscopic germ to the most gigantic tree
+in existence, that does not contain carbon as one of its essential
+constituents.
+
+=29. Carbon dioxide.=—The gas produced by the burning candle in Exp.
+23, by the germinating seeds in Exp. 25, and expelled from your own
+lungs in Exp. 24, is carbon dioxide. Chemists designate it by the
+symbol CO₂, which means that it consists of one part carbon to two
+parts oxygen. It is an invariable product wherever the oxidation of
+substances containing carbon goes on. Heat and moisture are evolved
+at the same time, and if oxidation is very active, as in Exps. 21 and
+22, light also. When the process takes place very slowly, no light is
+evolved, and so little heat as to be imperceptible without special
+observation. Hence, oxidation may go on around us and even in our own
+bodies without our being conscious of the fact.
+
+Carbon dioxide is of prime importance to the well-being of plants. It
+furnishes the material from which the greater part of their organic
+food is derived, as will be seen when we take up the study of the
+leaf and its work. To animals, on the contrary, its presence is so
+injurious that if the proportion of it in the air we breathe ever
+rises much above 1 part to 1000, the ill effects become painfully
+sensible. It is not, however, as was formerly supposed, a poison,
+the harm it does being to decrease the proportion of oxygen in the
+atmosphere so that animals cannot get enough of it to breathe, and
+die of suffocation.
+
+=30. Respiration in plants and in animals.=—It was shown in Exp.
+24 that respiration in animals is accompanied by the products of
+oxidation; hence we conclude that respiration is a form of oxidation.
+And since these same products are given off by plants (Exp. 25), the
+inference is clear that the same process goes on in them. But in
+plants the life functions are so much more sluggish than in animals
+that it is only in their most active state, during germination and
+flowering, that evidence of it is to be looked for.
+
+=31. Respiration and energy.=—In plants, as in animals, respiration
+is the expression or measure of energy. Sleeping animals breathe
+more slowly than waking ones, snakes and tortoises more slowly than
+hares and hawks. The more we exert ourselves and the more vital
+force we expend, the harder we breathe; hence, respiration is more
+active in children than in older persons and in working people than
+in those at rest. It is the same with plants; respiration is most
+perceptible in germinating seeds and young leaves, in buds and
+flowers, where active work is going on. Hence, in this condition
+they consume proportionately larger quantities of oxygen and
+liberate correspondingly larger quantities of carbon dioxide, with
+a proportionate increase of heat. In some of the arums,—calla lily,
+Jack-in-the-pulpit, colocasia, etc.,—and in large heads of compositæ,
+like the sunflower, where a great number of small flowers are brought
+together within the same protecting envelope, the rise of temperature
+is sometimes so marked that it may be perceived by placing a flower
+cluster against the cheek.
+
+
+          Practical Questions
+
+  1. What is charcoal? (28.)
+
+  2. Is any of this substance contained in the seed? in the flour and
+  meal made from seed? (28; Exp. 25.)
+
+  3. What combination takes place when the cook lets the stove get
+  too hot and burns the biscuits? (27, 28.)
+
+  4. Of what does the burned part consist? (28.) What was it before
+  it was burned? (27, 28).
+
+  5. Which burns the more readily, an oily seed or a starchy one?
+  Which leaves the more solid matter behind? (Suggestion: test by
+  putting a bean, or a large grain of corn, and an equal quantity
+  of the kernel of a Brazil nut on the end of a piece of wire and
+  thrusting into a flame.)
+
+  6. Is there any rational ground for the statement that the wooden
+  buildings formerly used on Southern plantations as cotton ginneries
+  were sometimes destroyed through spontaneous combustion due to the
+  heat generated by piles of decaying cotton seed? (Exp. 25, Note.)
+
+
+          II. CONDITIONS OF GERMINATION
+
+  MATERIAL.—Several ounces each of various kinds of seed. For the
+  softer kinds, pea, bean, corn, oats, wheat are recommended; for
+  those with harder coverings, squash, castor bean, apple, pear, or,
+  where obtainable, cotton; for still harder kinds, persimmon and
+  date seeds, or the stones of plum and cherry.
+
+  APPLIANCES.—1 dozen common earthenware plates for germinators; 1
+  dozen two-ounce wide-mouthed bottles; 2 common glass tumblers;
+  clean sand, sawdust, or cotton batting, for bedding; a double
+  boiler; a gas burner, or a lamp stove.
+
+=32. Recording observations.=—For this purpose a page should be ruled
+off in the notebook of each student, after the model here given,
+and the facts brought out by the different experiments set down as
+observed.
+
+
+                 NUMBER OF SEEDS GERMINATED
+
+  ==============+=+==+==+==+====+====+====+====+====+=====+====
+   No. of hours | |24|48|72|4 d.|5 d.|6 d.|7 d.|8 d.|10 d.|2 w.
+                +-+--+--+--+----+----+----+----+----+-----+----
+   No. of vessel|1|  |  |  |    |    |    |    |    |     |
+                +-+--+--+--+----+----+----+----+----+-----+----
+   No. of vessel|2|  |  |  |    |    |    |    |    |     |
+                +-+--+--+--+----+----+----+----+----+-----+----
+   No. of vessel|3|  |  |  |    |    |    |    |    |     |
+                +-+--+--+--+----+----+----+----+----+-----+----
+   No. of vessel|4|  |  |  |    |    |    |    |    |     |
+                +-+--+--+--+----+----+----+----+----+-----+----
+   No. of vessel|5|  |  |  |    |    |    |    |    |     |
+                +-+--+--+--+----+----+----+----+----+-----+----
+   No. of vessel|6|  |  |  |    |    |    |    |    |     |
+  ==============+=+==+==+==+====+====+====+====+====+=====+====
+
+  EXPERIMENT 26. CAN SEEDS HAVE TOO MUCH MOISTURE?—Drop a number
+  of dry beans or grains of corn, oats, or other convenient seed,
+  into a vessel with a bedding of cotton or paper that is barely
+  moistened, and an equal number of soaked seeds of the same kind
+  into another vessel with a saturated bedding of the same material.
+  In a third vessel place the same number of soaked seed, covering
+  them partially with water, and in a fourth cover the same number
+  entirely. Label them 1, 2, 3, and 4; keep all together in a warm,
+  even temperature, and observe at intervals of twenty-four hours for
+  a week. What condition as to moisture do you find most favorable
+  to germination? Would seeds germinate in the entire absence of
+  moisture? How do you know?
+
+  EXPERIMENT 27. WAS IT THE PRESENCE OF TOO MUCH WATER, OR THE LACK
+  OF AIR CAUSED BY IT, THAT INTERFERED WITH GERMINATION IN THE LAST
+  EXPERIMENT?—To answer this question experimentally is not easy,
+  since it is difficult to obtain a complete vacuum without special
+  appliances. The simplest way is to fill with mercury a glass tube
+  30 inches long, closed at one end, and invert it over a small
+  vessel—a teacup, or an egg cup will answer—containing mercury
+  enough to cover the bottom to a depth of two or three centimeters
+  (see Appendix, Weights and Measures, for English equivalents.)
+  The tube must be supported in such a way that its lower end will
+  dip into the mercury without touching the bottom of the vessel.
+  With a pair of forceps insert under the mouth of the tube two or
+  three seeds that have been well soaked in water deprived of air
+  by previous boiling. Being lighter than mercury, they will float
+  to the top, where there is a complete absence of air while other
+  conditions favorable to germination are present. Before releasing,
+  they should be well shaken under the mercury to free them from air
+  bubbles, and if the coats are loose fitting so that they can be
+  removed without injury to the parts inclosed in them, they should
+  be slipped off in order to get rid of any imprisoned air they
+  may contain. Additional moisture may be supplied, if necessary,
+  by injecting, by means of a medicine dropper inserted under the
+  mouth of the tube, a drop or two of water that has been previously
+  boiled. Keep in a warm, even temperature, under conditions
+  favorable to germination, and compare the behavior of the seeds
+  with those placed in the different vessels in Exp. 26.
+
+  If appliances for this experiment are lacking, a rough
+  approximation can be made by using the seeds of aquatic plants,
+  such as the lotus, water lily, and the so-called Chinese sacred
+  bean, sold in the variety stores, which we know are capable of
+  germinating in the limited amount of air contained in ordinary
+  soil water. Place an equal number of such seeds, of about the same
+  size and weight, on a bedding of common garden soil in two glass
+  tumblers. Fill one vessel a little over half full of ordinary soil
+  water and the other to the same height with water from which the
+  air has been expelled by boiling. Pour over the liquid a film of
+  sweet oil or castor oil, to prevent the access of air, leaving the
+  surface of the water in the other vessel exposed. In which do the
+  seeds come up most freely?
+
+[Illustration: FIG. 47.—To find out the proper depth at which to
+plant seeds.]
+
+  Some seeds, especially those rich in proteins, as peas and beans,
+  will germinate in a vacuum, because oxygen is supplied for a time
+  by the chemical decomposition of substances in their tissues which
+  contain it, but when these are exhausted, respiration ceases and
+  death ensues.
+
+  EXPERIMENT 28. DOES THE DEPTH AT WHICH SEEDS ARE PLANTED AFFECT
+  THEIR GERMINATION?—Plant a number of peas or grains of corn at
+  different depths in a wide-mouthed glass jar filled with moist
+  sand, as shown in Fig. 47, the lowest ones at the bottom, the top
+  ones barely covered. Try different kinds of seed and grain,—radish,
+  squash, cotton, or wheat,—and watch them make their way to the
+  surface. Do you notice any difference in this respect between large
+  seed and small ones? Between those with thick cotyledons and thin
+  ones? At what depth do you find, from your recorded observations,
+  that seed germinate best?
+
+  EXPERIMENT 29. WHAT TEMPERATURE IS MOST FAVORABLE TO
+  GERMINATION?—Put half a dozen soaked beans on moist cotton or
+  sawdust in three wide-mouthed bottles of the same size or in
+  germinators arranged as in Figs. 48, 49, the seed also being
+  selected with a view to similarity of size and weight. Keep one at
+  a freezing temperature; the second in a temperature of 15° to 20°
+  C. (see Appendix for Fahrenheit equivalents); and the third, at
+  30° C. If a place can be found near a stove or a register, where
+  an even temperature of about 125° F. is maintained, place a fourth
+  receptacle there. Observe at intervals of twenty-four hours for a
+  week or ten days, keeping the temperature as even as possible, and
+  maintaining an equal quantity of moisture in each vessel. Make a
+  daily record of your observations. What temperature do you find
+  most favorable to germination?
+
+[Illustration: FIGS. 48, 49.—Home-made germinators: 48, closed; 49,
+showing interior arrangement.]
+
+  EXPERIMENT 30. AT WHAT TEMPERATURE DO SEEDS LOSE THEIR
+  VITALITY?—Place about two dozen each of grains of corn, beans,
+  squash seed, and castor beans, with an equal number of plum or
+  cherry stones, in water, and heat to a temperature of 150° F. After
+  an exposure of ten minutes, take out six of each kind and place
+  in germinators made of two plates with moist sand or damp cloth
+  between them, as shown in Figs. 48, 49. Raise the temperature to
+  175° F., and after ten minutes take out six more of each kind of
+  seed and place in another germinator. Raise the water in the vessel
+  to 200°, take out another batch of seeds; raise to the boiling
+  point for ten minutes more, and plant the remaining six of each
+  lot. Number the four germinators, and observe at intervals of
+  twenty-four hours for two weeks. The harder kinds should be kept
+  under observation for three or four weeks, as they germinate slowly.
+
+  Try the same experiments with the same kinds of seeds at a dry
+  heat, using a double boiler to prevent scorching, and record
+  observations as before.
+
+  EXPERIMENT 31. TIME REQUIRED FOR GERMINATION.—Arrange in
+  germinators seeds of various kinds, such as corn, wheat, peas,
+  turnip, apple, orange, grape, castor bean, etc. “Clip” some of the
+  harder ones and keep all the kinds experimented with under similar
+  conditions as to moisture, temperature, etc., and record the time
+  required for each to sprout. What is the effect of clipping, and
+  why?
+
+  EXPERIMENT 32. ARE VERY YOUNG OR IMMATURE SEEDS CAPABLE OF
+  GERMINATING?—Plant some seeds from half-grown tomatoes, and grains
+  of wheat, oats, or barley before they are ready for harvesting. Try
+  as many kinds as you like, and see how many will come up. Notice
+  whether there is any difference in the health and vigor of plants
+  raised from seeds in different stages of maturity.
+
+  EXPERIMENT 33. THE RELATIVE VALUE OF PERFECT AND INFERIOR
+  SEED.—From a number of seeds of the same species select half a
+  dozen of the largest, heaviest, and most perfect, and an equal
+  number of small, inferior ones. If a pair of scales is at hand, the
+  different sets should be weighed and a record kept for comparison
+  with the seedlings at the end of the experiment. Plant the two sets
+  in pots containing exactly the same kind of soil, and keep under
+  identical conditions as to light, temperature, and moisture. Keep
+  the seedlings under observation for two or three weeks, making
+  daily notes and occasional drawings of the height and size of the
+  stems, and the number of leaves produced by each.
+
+[Illustration: FIGS. 50, 51.—Stem development of seedlings: 50,
+raised from healthy grains of barley; weight, 39.5 grams (about 500
+grs.); 51, raised under exactly similar conditions from the same
+number of inferior grains; weight, 23 grams (about 350 grs.).]
+
+[Illustration: FIGS. 52, 53.—Improvement of corn by selection: 52,
+original type; 53, improved type developed from it.]
+
+=33. Resistance to heat and cold.=—In making experiments with regard
+to temperature, notice how the extremes tolerated are influenced,
+first, by the length of time the seeds are exposed; second, by the
+amount of water contained in them; and third, by the nature of the
+seed coats. Every farmer knows that the effect of freezing is much
+more injurious to plants or parts of plants when full of sap (water)
+than when dry. This, in the opinion of the most recent investigators,
+is because the water in the spaces outside the cells freezes first
+and as moisture is gradually withdrawn from the inside to take its
+place, the soluble salts which may be present in the cell sap become
+more concentrated, and by their chemical action on the contained
+proteins cause them to be precipitated, or “salted out,” as we see
+sugar or salt precipitated from solutions of those substances when
+water is withdrawn by evaporation. In this way, it is believed, the
+fundamental protoplasm of the cell may be so disorganized that death
+ensues if the freezing is continued long enough, since the protein
+precipitates become “denatured” and cannot be reabsorbed if kept
+in a solid state too long. The length of time necessary to produce
+death from this cause is, of course, different in different plants,
+according to the kind of salts dissolved in the sap and the nature of
+the proteins acted on by them. The proteins in the sap of Begonia,
+or Pelargonium, plants which are very sensitive to cold, yield a
+denatured precipitate at, or a little below the freezing point of
+water, while those of winter rye withstand a temperature of -15° C.,
+and of pine needles, -40° C.
+
+Mechanical injury through rupture of parts by freezing is not apt
+to cause serious damage except in cases of sudden and violent cold
+at a time when the tissues are gorged with sap, as not infrequently
+happens during the abrupt changes of temperature which sometimes
+occur in spring after the trees have put forth their leaves. In an
+extreme case of this kind, the writer has seen the trunk of an oak
+a foot or more in diameter split in deep seams from the effects of
+freezing.
+
+=34. The length of time during which seeds may retain their
+vitality.=—No direct experiment can be made to test this point,
+since it would require months, or even years, covering in some
+instances more than the lifetime of a generation. It has been stated
+on good authority that seeds of the water chinquapin (Nelumbo) have
+germinated after more than a hundred years, and moss spores preserved
+in herbariums, after fifty. But the records in such cases are not
+always trustworthy, and there is absolutely no foundation for the
+statements sometimes made about the germination of wheat grains found
+preserved with mummies over two thousand years old. If kept perfectly
+dry, however, seed may sometimes be preserved for months, or even
+years. Peas have been known to sprout after ten years, red clover
+after twelve, and tobacco after twenty. Ordinarily, however, the
+vitality of seeds diminishes with age, and in making experiments it
+is best to select fresh ones. Those used for comparison should also,
+as far as possible, be of the same size and weight.
+
+=35. Effect of precocious germination.=—It has been found by
+experiment that plants raised from immature seed, when they will
+germinate at all (Exp. 32), yield earlier and larger crops than the
+same kinds from mature seed. Early tomatoes and some other vegetables
+are produced in this way. The majority of seeds, however, require
+a period of rest before beginning their life work. Those that are
+forced to take up the burden of “child labor” show the effect of such
+abnormal condition by yielding fruits that are smaller and less firm
+than those raised from mature seed, so that they do not keep well and
+have to be marketed quickly. Under what circumstances does it pay to
+cultivate such fruits?
+
+
+          Practical Questions
+
+  1. What are the principal external conditions that affect
+  germination? (Exps. 26-29.)
+
+  2. What effect has cold? want of air? too much water?
+
+  3. Is light necessary to germination?
+
+  4. What is the use of clipping seeds? (Exps. 12, 13, 14, and
+  Material, p. 12.)
+
+  5. In what cases should it be resorted to? (Exp. 31.)
+
+  6. Why will seed not germinate in hard, sunbaked land without
+  abundant tillage? Why not on undrained or badly drained land?
+  (Exps. 26, 27.)
+
+  7. Will seeds that have lost their vitality swell when soaked?
+  (Exp. 16.)
+
+  8. Are there any grounds for the statement that the seeds of plums
+  boiled into jam have sometimes been known to germinate?[1] (33;
+  Exp. 30.)
+
+  9. Could such a thing happen in the case of apple or sunflower
+  seed, and why or why not? (33.)
+
+  10. Does it make any difference in the health and vigor of a plant
+  whether it is grown from a large and well-developed seed or from a
+  weak and puny one? (Exp. 33.)
+
+  11. Would a farmer be wise who should market all his best grain and
+  keep only the inferior for seed?
+
+  12. What would be the result of repeated plantings from the worst
+  seed?
+
+  13. Of constantly replanting the best and most vigorous?
+
+  14. Suppose seed would germinate without moisture; would this be an
+  advantage, or a disadvantage to agriculturists?
+
+  15. Why is a cool, dry place best for keeping seeds? (Exps. 26, 29.)
+
+  16. Why are the earliest tomatoes found in the market usually
+  smaller than those offered later? (35.)
+
+  17. Why is continued rain so injurious to wheat, oats, and other
+  grains before they are mature enough to be harvested? (35; Exp. 32.)
+
+  18. Would the same effect be likely to occur in the case of very
+  oily seeds, such as flax and castor beans? Why? (Suggestion: try
+  the effect of putting water on a piece of oiled paper.)
+
+  19. Explain why many seeds cannot germinate successfully without
+  air. (30, 31; Exp. 25.)
+
+  20. Mention some of the practical advantages that a farmer, a
+  gardener, or a careful housewife might gain from experiments like
+  those made in this section.
+
+  21. Explain why seeds can endure so much greater extremes of
+  temperature than growing plants. (23, 33.)
+
+
+          III. DEVELOPMENT OF THE SEEDLING
+
+  MATERIAL.—Seedlings of various kinds in different stages of growth.
+  It is recommended that the same species be used that were studied
+  in Section III, Chapter I, or such equivalents as may have been
+  substituted for them. Enough should be provided to give each pupil
+  three or four specimens in different stages of development. Seeds,
+  even of the same kind, develop at such different rates that it
+  will probably not be necessary to make more than two plantings of
+  each sort, from 2 to 5 days apart. Soaked seeds of corn and wheat
+  will germinate in from 3 to 7 days, according to the temperature;
+  oats in 1 to 4; beans in 4 to 6; squash and castor beans in from
+  8 to 10. Very obdurate ones may be hastened by clipping. Keep the
+  germinators in an even temperature, at about 70° to 80° F.
+
+  Pine is a very difficult seed to germinate, requiring usually
+  from 18 to 21 days. By soaking the mast for twenty-four hours and
+  planting in damp sand or sawdust kept at an even temperature of 23°
+  C. or about 75° F., specimens may be obtained.
+
+[Illustration: FIGS. 54, 55.—Seedling of corn (_after_ GRAY): 54,
+early stage of germination; 55, later stage.]
+
+=36. Seedlings of monocotyls.=—Examine a seedling of corn that has
+just begun to sprout; from which side does the seedling spring, the
+plain or the grooved one? Refer to your sketch of the dry grain and
+see if this agrees with the position of the embryo as observed in the
+seed. Make sketches of four or five seedlings in different stages of
+advancement, until you reach one with a well-developed blade. From
+what part of the embryo has each part of the seedling developed?
+Which part first appeared above ground? Is it straight, or bent in
+any way? In what direction does the plumule grow? The hypocotyl? Does
+the cotyledon appear above ground at all? Slip off the husk and see
+if there is any difference in the size and appearance of the contents
+as you proceed from the younger to the older plants. How would you
+account for the difference?
+
+=37. The root.=—Examine the lower end of the hypocotyl and find where
+the roots originate; would you say that they are an outgrowth from
+the stem, or the stem from the root? Observe that the root of the
+corn does not continue to grow in a single main axis like that of
+the castor bean, but that numerous adventitious and secondary roots
+spring from various points near the base of the hypocotyl and spread
+out in every direction, thus giving rise to the fibrous roots of
+grains and grasses.
+
+=38. Root hairs.=—Notice the grains of sand or sawdust that cling to
+the rootlets of plants grown in a bedding of that kind. Examine with
+a lens and see if you can account for their presence. Lay the root
+in water on a bit of glass, hold up to the light and look for root
+hairs; on what part are they most abundant?
+
+[Illustration: FIG. 56.—Seedling of wheat, with root hairs.]
+
+The hairs are the chief agents in absorbing moisture from the
+soil. They do not last very long, but are constantly dying and
+being renewed in the younger and tenderer parts of the root. These
+are usually broken away in tearing the roots from the soil, so
+that it is not easy to detect the hairs except in seedlings, even
+with a microscope. In oat, maple, and radish seedlings they are
+very abundant and clearly visible to the naked eye. The amount of
+absorbing surface on a root is greatly increased by their presence.
+
+[Illustration: FIG. 57.—Diagrammatic section of a root tip: _a_,
+cortex; _b_, central cylinder in which the conducting vessels are
+situated; _c_, root cap; _g_, growing point.]
+
+=39. The root cap.=—Look at the tip of the root through your lens
+and notice the soft, transparent crescent or horseshoe-shaped mass
+in which it terminates. This is the root cap and serves to protect
+the tender parts behind it as the roots burrow their way through the
+soil. Being soft and yielding, it is not so likely to be injured by
+the hard substances with which it comes in contact as would be the
+more compact tissue of the roots. It is composed of loose cells out
+of which the solid root substance is being formed; the growing point
+of the root, _g_, is at the extremity of the tip just behind the
+cap, _c_ (Fig. 57). The cap is very apparent in a seedling of corn,
+and can easily be seen with the naked eye, especially if a thin
+longitudinal section is made. It is also well seen in the water roots
+of the common duckweed (_Lemna_), and on those developed by a cutting
+of the wandering Jew, when placed in water. Are there any hairs on
+the root cap? Can you account for their absence?
+
+  NOTE.—For a minute study of the structure of roots, see =67=.
+
+=40. Organs of vegetation.=—The three parts, root, stem, and leaf,
+are called organs of vegetation in contradistinction to the flower
+and fruit, which constitute the organs of reproduction. The former
+serve to maintain the plant’s individual existence, the latter to
+produce seed for the propagation of the species, so we find that the
+seed is both the beginning and the end of vegetable life.
+
+[Illustration: FIG. 58.—Seedlings of bean in different stages
+of growth: _cc_, cotyledons, showing the plumule and hypocotyl
+before germination; _a_, _b_, _d_, and _e_, successive stages of
+advancement. At _d_ the arch of the hypocotyl is beginning to
+straighten; at _e_ it has entirely erected itself.]
+
+=41. Definitions.=—Organ is a general name for any part of a living
+thing, whether animal or vegetable, set apart to do a certain work,
+as the heart for pumping blood, or the stem and leaves of a plant for
+conveying and digesting sap. By “function” is meant the particular
+work or office that an organ has to perform.
+
+=42. Seedlings of dicotyls. The bean.=—Sketch, without removing it, a
+bean seedling that has just begun to show itself above ground; what
+part is it that protrudes first? Sketch in succession four or five
+others in different stages of advancement. Notice how the hypocotyl
+is arched where it breaks through the soil. Does this occur in the
+monocotyls examined? Do the cotyledons of the bean appear above
+ground? How do they get out? Can you perceive any advantage in their
+being dragged out of the ground backwards in this way rather than
+pushed up tip foremost? What changes have the cotyledons undergone
+in the successive seedlings? Remove from the earth a seedling just
+beginning to sprout and sketch it. From what point does the hypocotyl
+protrude through the coats? Does this agree with its position as
+sketched in your study of the seed? In which part of the embryo does
+the first growth take place?
+
+Remove in succession the several seedlings you have sketched and
+note their changes. How does the root differ from that of the corn
+and oats? The first root formed by the extension of the hypocotyl is
+the _primary_ root and should be so labeled in your drawings; the
+branches that spring from it are _secondary_ roots. Look for root
+hairs; if there are any, where do they occur?
+
+[Illustration: FIG. 59.—Stages in the germination of a typical
+seedling of the squash family: _a_, a seed before germination; _b_,
+_c_, _e_, the same in different stages of growth; _d_, the empty
+testa, with kernel removed; _hi_, hilum; _m_, micropyle; _p_, _p_,
+the peg in the heel; _h_, _h_, _h_, the hypocotyl; _ar_, arch of the
+hypocotyl; _co_, cotyledons; _pl_, plumule; _pr_, primary root; _sc_,
+secondary roots.]
+
+=43. Germination of the squash.=—How does the manner of breaking
+through the soil compare with that of the bean? With the corn?
+From which end of the seed, the large or the small one, does the
+hypocotyl spring? Do the cotyledons come above ground? How do they
+get out of the seed coat? Notice the thick protuberance developed
+by the hypocotyl and pressing against the lower half of the coat at
+the point where the hypocotyl breaks through. This is called the
+“peg”; can you tell its use? Could the cotyledons get out of their
+hard covering without it? Slip the peg below the coat in one of your
+growing specimens, leave it in the soil, and see what will happen.
+How do the cotyledons of the squash differ from those of the bean
+as they come out of the seed cover? Do they act as foliage leaves?
+Do you see any difference in the development of the plumule in the
+two seeds (Figs. 19, 25) to account for the different behavior of
+the cotyledons? Sketch three seedlings in different stages, labeling
+correctly the parts observed. Make a similar study of the castor
+bean, or other seedling selected by your teacher, and illustrate by
+drawings.
+
+=44. Arched and straight hypocotyls.=—This difference in the manner
+of getting above ground is an important one. That by means of the
+arched hypocotyl is, in general, characteristic of the process of
+germination in which the cotyledons come above ground, while the
+straight kind, which was illustrated in the corn and wheat, is the
+prevailing method when the cotyledons remain below ground. Can you
+give a reason for the difference?
+
+[Illustration: FIG. 60.—Pine seedling (_After_ GRAY).]
+
+=45. Polycotyledons; germination of the pine.=—Examine a pine
+seedling just beginning to sprout. What part emerges first from
+the seed coat? Where does it break through? Where did you find the
+micropyle in the pine seed? (15.) Can you give a reason why the
+hypocotyl in seeds should break through the coats at this point? How
+do the cotyledons get out of the testa? Is the hypocotyl arched or
+straight in germination? How does it compare with the bean and squash
+in this respect? With the corn? Is any endosperm left in the testa
+after the cotyledons have come out? What has become of it? Do the
+cotyledons function as leaves? How many of them have the specimen
+you are studying? Notice the little knob or button at the upper
+end of the hypocotyl, just above the point where the cotyledons are
+attached; this is the _epicotyl_, or part above the cotyledons, here
+identical with the plumule; does it develop as rapidly as in the
+other seedlings you have examined?
+
+=46. Relation of parts in the seedling.=—Before leaving this subject,
+it is important to fix clearly in mind the different parts of the
+germinating seedling and their relation to both the embryo from
+which they originated and the plant into which they are to develop.
+The part labeled “hypocotyl” in your sketches is all that portion
+of the embryo below the point of attachment of the cotyledons. In
+germination its upper part will become the stem, and in the embryo
+constitutes the _caulicle_, or stemlet, while its lower part, from
+which the root will develop, is the _radicle_, or rootlet; hence
+the term “hypocotyl” includes both the future root and stem. The
+plumule is that part of the embryo between the cotyledons and _above_
+their point of attachment to the caulicle. It is the upward growing
+point of the young plant, and hence the place of attachment of the
+cotyledon is the first _node_, or point of leaf origin, on the stem.
+
+The epicotyl, in contradistinction to the hypocotyl, is all that
+part of the plant _above_ the insertion of the cotyledons. Before
+germination it is identical with the plumule. As the seedling grows,
+the epicotyl advances its growing point by adding new nodes and
+_internodes_, as the spaces between the successive points of leaf
+insertion are called.
+
+=47. Botanical terms.=—As the prefixes _hypo_ and _epi_ are of
+frequent occurrence in botanical works, it will aid in understanding
+their various compounds if you will remember that _hypo_ always
+refers to something below or beneath, and _epi_, to something over
+or above. With this idea in mind you will see that botanical terms
+are a labor-saving device, since it is much easier, in making notes,
+to use a single descriptive word than to write out the long English
+equivalent, such as “the part under (or over) the cotyledons.”
+
+
+          Practical Questions
+
+  1. Do the cotyledons, as a general thing, resemble the mature
+  leaves of the same plants?
+
+  2. Name some plants in which you have observed differences, and
+  account for them; could convenience of packing in the seed coats,
+  for instance, or of getting out of them, have any bearing on the
+  matter?
+
+  3. Does the position in which seeds are planted in the ground have
+  anything to do with the position of the seedlings as they appear
+  above the surface?
+
+  4. Is this fact of any importance to the farmer?
+
+  5. Will grain that has begun to germinate make good meal or flour?
+  Why? (27, 36; Exp. 25.)
+
+
+          IV. GROWTH
+
+  MATERIAL.—Two young potted plants; some lily or hyacinth
+  bulbs; seedlings of different kinds,—some with well-developed
+  taproots,—apple, cotton, and maple are good examples.
+
+  APPLIANCES.—A small flat dish, some mercury, and a piece of cork.
+
+[Illustration: FIGS. 61, 62.—Seedling of corn, marked to show
+region of growth: 61, early stage of germination; 62, later stage.]
+
+  EXPERIMENT 34. HOW DOES THE ROOT INCREASE IN LENGTH?—Mark off the
+  root of a very young corn seedling into sections by moistening
+  a piece of sewing thread with indelible ink and applying it to
+  the surface of the root at intervals of about two millimeters (⅒
+  of an inch), or by tying a thread lightly around it at the same
+  intervals. Lay the seedling on a moist bedding between two panes
+  of glass kept apart by a sliver of wood to prevent their injuring
+  the root by pressure. Watch for a day or two, and you will see that
+  growth takes place from a point just back of the tip (Figs. 61, 62).
+
+  Mark off a seedling of the bean in the same way and watch to see
+  whether it increases in the same manner as the corn.
+
+  EXPERIMENT 35. HOW DOES THE STEM INCREASE IN LENGTH?—Mark off a
+  portion of the stem of a bean seedling as explained in the last
+  experiment, and find out how it grows. Allow a seedling to develop
+  until it has put forth several leaves and measure daily the spaces
+  between them. Label these spaces in your drawings, “internodes,”
+  and the points where the leaves are attached, “nodes.” Does an
+  internode stop growing when the one next above it has formed? When
+  is growth most rapid? Reverse the position of a number of seedlings
+  that have just begun to sprout and watch what will happen. After a
+  few days reverse again and note the effect.
+
+[Illustration: FIGS. 63, 64.—Root of bean seedling, measured to show
+region of growth: 63, early stage of germination; 64, later stage.
+FIGS. 65, 66.—Stem of bean seedling, measured to show region of
+growth: 65, early stage of growth; 66, later stage.]
+
+  EXPERIMENT 36. CAN PLANTS GROW AND LOSE WEIGHT AT THE SAME
+  TIME?—Remove the scales from a white lily bulb, weigh them, and
+  lay in a warm, but not too damp place, away from the light. After
+  a time bulblets will form at the bases of the scales. Weigh
+  them again, and if there has been any loss, account for it. The
+  experiment may be tried by allowing a potato tuber or a hyacinth
+  bulb to germinate without absorbing moisture enough to affect its
+  weight.
+
+[Illustration: FIGS. 67, 68.—Experiment showing the direction of
+growth in stems: 67, young potato planted in an inverted position;
+68, the same after an interval of eight days.]
+
+  EXPERIMENT 37. IS THE DIRECTION OF GROWTH A MATTER OF ANY
+  IMPORTANCE?—Plant in a pot suspended as shown in Fig. 67, a healthy
+  seedling of some kind, two or three inches high, so that the
+  plumule shall point downward through the drain hole and the root
+  upward into the soil. Watch the action of the stem for six or
+  eight days, and sketch it at successive intervals. After the stem
+  has directed itself well upward, invert the pot again, and watch
+  the growth. After a week remove the plant and notice the direction
+  of the root. Sketch it entire, showing the changes in direction of
+  growth.
+
+  At the same time that this experiment is arranged, lay another pot
+  with a rapidly growing plant on one side, and every forty-eight
+  hours reverse the position of the pot, laying it on the opposite
+  side. At the end of ten or twelve days remove the plant and
+  examine. How has the growth of root and stem been affected?
+
+  What do we learn from these experiments and from Exp. 35 as to the
+  normal direction of growth in these two organs respectively? Can
+  you think of any natural force that might influence this direction?
+
+[Illustration: FIG. 69.—Experiment showing the root of a seedling
+forcing its way downward through mercury.]
+
+  EXPERIMENT 38. TO SHOW THAT PLANTS WILL EXERT FORCE RATHER THAN
+  CHANGE THEIR DIRECTION OF GROWTH.—Pin a sprouted bean to a cork and
+  fasten the cork to the side of a flat dish, as shown in Fig. 69.
+  Cover the bottom of the dish with mercury at least half an inch
+  deep, and over the mercury pour a layer of water. Cover the whole
+  with a pane of glass to keep the moisture in, and leave for several
+  days. The root will force its way downward into the mercury,
+  although the latter is fourteen times heavier than an equal bulk
+  of the bean root substance, and the root must thus overcome a
+  resistance equal to at least fourteen times its own weight.
+
+=48. What growth is.=—With the seedling begins the growth of the
+plant. Most people understand by this word mere increase in size; but
+growth is something more than this. It involves a change of form,
+usually, but not necessarily, accompanied by increase in bulk. Mere
+mechanical change is not growth, as when we bend or stretch an organ
+by force, though if it can be kept in the altered position till such
+position becomes permanent, or as we say in common speech, “till it
+grows that way,” the change may become growth. To constitute true
+growth, the change of form must be permanent, and brought about, or
+maintained, by forces within the plant itself.
+
+=49. Conditions of growth.=—The internal conditions depend upon
+the organization of the plant. The essential external conditions
+are the same as those required for germination: food material,
+water, oxygen, and a sufficient degree of warmth. It may be greatly
+influenced by other circumstances, such as light, gravitation,
+pressure, and (probably) electricity; but the four first named are
+the essential conditions without which no growth is possible.
+
+=50. Cycle of growth.=—When an organ becomes rigid and its
+form fixed, there is no further growth, but only nutrition and
+repair,—processes which must not be confounded with it. Every plant
+and part of a plant has its period of beginning, maximum, decline,
+and cessation of growth. The cycle may extend over a few hours, as in
+some of the fungi, or, in the case of large trees, over thousands of
+years.
+
+=51. Geotropism.=—The general tendency of the growing axes of
+plants to take an upward and downward course as shown in Exp.
+37—in other words, to point to and from the center of the earth—is
+called _geotropism_. It is _positive_ when the growing organs point
+downward, as most primary roots do; _negative_ when they point
+upward, as in most primary stems; and _transverse_, or _lateral_,
+when they extend horizontally, as is the case with most secondary
+roots and branches.
+
+=52. Gravity and growth.=—It cannot be proved directly that
+geotropism is due to gravity, because it is not possible to remove
+plants from its influence so as to see how they would behave in
+its absence. The effect of gravity may be neutralized, however, by
+arranging a number of sprouting seeds on the vertical disk of a
+clinostat, an instrument fitted with a clockwork movement by means of
+which they may be kept revolving steadily for several days. By this
+constant change of position gravity is made to act on them in all
+directions alike, which is the same in some respects as if it did not
+act at all. If the disk is made to revolve rapidly, the growing root
+tips turn toward the axis of motion, without showing a tendency to
+grow downward. We may then conclude that geotropism is a reaction to
+gravity.
+
+=53. Geotropism an active force.=—It must be noted, however, that the
+force here alluded to is not the mere mechanical effect of gravity,
+due to weight of parts, as when the bough of a fruit tree is bent
+under the load of its crop, but a certain stimulus to which the plant
+reacts by a spontaneous adjustment of its growing parts. In other
+words, geotropism is an active, not a passive function, and the plant
+will overcome considerable resistance in response to it. (Exp. 38).
+
+=54. Other factors.=—The direction of growth is influenced by many
+other factors, such as light, heat, moisture, contact with other
+bodies, and perhaps by electricity. The result of all these forces is
+an endless variety in the forms and growth of organs that seems to
+defy all law.
+
+[Illustration: FIG. 70.—A piece of a haulm of millet that has been
+laid horizontally, righting itself through the influence of negative
+geotropism.]
+
+Heat, unless excessive, generally stimulates growth; contact
+sometimes stimulates it, causing the stem to curve away from the
+disturbing object, and sometimes retards it, causing the stem to
+curve toward the object of contact by growing more rapidly on the
+opposite side, as in the stems of twining vines. Light stimulates
+nutrition, but generally retards growth. The movements of plants
+toward the light are effected in this way; growth being checked on
+that side, the plant bends toward the light.
+
+
+          Practical Questions
+
+  1. Why do stems of corn, wheat, rye, etc., straighten themselves
+  after being prostrated by the wind? (51, 54.)
+
+  2. Do plants grow more rapidly in the daytime, or at night? (54.)
+
+  3. Reconcile this with the fact that green plants will die if
+  deprived of light.
+
+  4. Which grows more rapidly, a young shoot or an old one? (31, 50.)
+
+  5. Which, as a general thing, are the more rapid growers, annuals
+  or perennials? Herbaceous or woody-stemmed plants?
+
+  6. Name some of the most rapid growers you know.
+
+  7. Of what advantage is this habit to them?
+
+  8. Why do roots form only on the under side of subterraneous stems?
+  (51.)
+
+  9. Why do new twigs develop most freely on the upper side of
+  horizontal branches? (51.)
+
+
+          Field Work
+
+  (1) Notice the various seedlings met with in your walks and see how
+  many you can recognize by their resemblance to the mature plants.
+  Account for any differences you may observe between seedlings
+  and older plants of the same species. Observe the cotyledons as
+  they come up and their manner of getting out of the ground, and
+  notice the ways in which this is influenced by moisture, light,
+  and the nature of the soil. Where the cotyledons do not appear,
+  dig into the ground and find out the reason. Notice which method
+  of emergence occurs in each case, the arched, or straight, and
+  account for it. Observe particularly the behavior of seedlings in
+  hard, sunbaked soil. If you see any of them lifting cakes of earth,
+  compare the size and weight of the cake with that of the seed; if
+  there is any disparity, what does this imply? What is the force
+  called which the plant exercises in lifting the weight? (51.)
+
+  (2) Notice if there are any seeds germinating successfully on top
+  of the ground, and find out by what means their roots get into the
+  soil. Observe what effect sun and shade, moisture and drought, and
+  the nature of the soil have on the process. Find out whether roots
+  exercise force in penetrating the soil; what kinds they penetrate
+  most readily, and what kinds, if any, they fail to penetrate at
+  all. Notice whether seedlings with taproots, like the turnip and
+  castor bean, or those with fibrous roots, like corn and wheat, are
+  more successful in working their way downward.
+
+  (3) Look for tree seedlings. Explain why seedlings of fruit trees
+  are so much more widely distributed in cultivated districts, and so
+  much easier to find than those of forest trees. Where do the latter
+  occur, as a general thing? Account for the fact that seedling
+  trees are so much more rare than germinating herbs, and why trees
+  like the oak and chestnut and black walnut propagate so much more
+  slowly, in a state of nature, than the pine, cedar, ash, and maple.
+
+  (4) Observe the direction of growth in plants on the sides of
+  gullies and ravines, and tell how it is influenced by geotropism.
+  Notice whether there are other influences at work; for instance,
+  light, or in the case of roots, the attraction of moisture.
+
+
+
+
+CHAPTER III. THE ROOT
+
+
+          I. OSMOSIS AND THE ACTION OF THE CELL
+
+  MATERIAL.—For experiments in osmosis provide fresh and boiled
+  slices of red beet, a fresh egg, a piece of ox bladder or some
+  parchment paper; glass tubing, thread, twine, elastic bands, salt
+  and sugar solutions. A common medicine dropper with the small end
+  cut off will answer instead of tubing for making an artificial
+  cell; or an eggshell may be used, by blowing out the contents
+  through a puncture in the small end, and carefully chipping away a
+  portion of the shell at the big end, leaving the lining membrane
+  intact. The different liquids can be put into the shell and the
+  exposed membrane placed in contact with the liquid in the glass,
+  by fitting over the latter a piece of cardboard with a hole in
+  the center large enough for the exposed surface to protrude
+  sufficiently to touch the water.
+
+[Illustration: FIG. 71.—Artificial cell.]
+
+=55. Object of the experiments.=—In order to understand clearly the
+action of roots in absorbing nutrients from the soil, it will be
+necessary to learn something about the movement of liquids through
+the cells, upon which the physiological processes of the plant
+depend. For this purpose make an artificial cell by tying a piece of
+ox bladder or parchment paper tightly over one end of a small glass
+tube, as shown in Fig. 71.
+
+  EXPERIMENT 39. HOW DOES ABSORPTION TAKE PLACE IN THE CELL?—(_a_)
+  Put some salt water in a wineglass, partly fill the tube of the
+  artificial cell with fresh water, and mark on the outside of both
+  vessels the height at which the contained liquid stands. Set the
+  tube in the glass of salt water and wait for results, having first
+  tested carefully to make sure that there are no leaks in the
+  membrane. After half an hour, notice whether there is any increase
+  of water in the glass, as indicated by the mark. If so, where did
+  it come from? Is there any loss of water in the tube? What has
+  become of it? How did it get out? Taste it to see if any of the
+  salt water has got in. Which is the heavier, salt water, or fresh?
+  (If you do not know, weigh an equal quantity of each.) In which
+  direction did the principal flow take place; from the heavier to
+  the lighter, or from the lighter to the heavier liquid?
+
+  (_b_) Put a sugar or salt solution in the tube, and clear, fresh
+  water in the glass, marking the height in each as before. Does the
+  liquid rise or fall in the tube? Does any of it escape into the
+  water of the glass, and if so, is it more or less than before?
+  Which now contains the denser fluid, the tube or the glass? What
+  principle governs the course of the liquid? Try the same experiment
+  with (_c_), the same liquid in both vessels, and notice whether
+  there is a greater flow in one direction than the other, as
+  indicated by a comparison with the marks on the outside. (_d_) Put
+  in the tube some of the white of a raw egg, insert in a glass of
+  pure water, and note the effect. (_e_) Reverse, with water in the
+  tube and white of egg in the glass. Does the water rise in the tube
+  as before? Test the contents for proteins; has any of the albumin
+  passed through the membrane into the tube?
+
+  EXPERIMENT 40. TO TEST THE BEHAVIOR OF LIVING AND DEAD CELLS.—Slice
+  a fresh piece of red beet into a vessel of water and of a boiled
+  one into another vessel of the same liquid at the same temperature.
+  What difference do you notice? Can you think of any reason why the
+  boiled one gives up its juices and the other one does not?
+
+=56. Osmosis.=—The passage of liquids or of solids in solution
+through membranes is known as _osmosis_. Our experiments have
+shown that the principles governing the osmotic movement are: (1)
+the passage of water from the thinner liquid toward the denser
+takes place more rapidly than in the opposite direction; (2) the
+rapidity of the transfer depends on the difference in density; (3)
+crystallizable substances in solution, like sugar and salt, osmose
+readily; (4) albuminous or gelatinous substances, such as the white
+of an egg, osmose so slowly that the cell wall may be regarded as
+practically impermeable to them.
+
+=57. Osmosis a form of diffusion.=—Osmosis is related to diffusion
+as a part to the whole. In other words, it is a name given to the
+process when it takes place through a membrane, whether solid, as the
+outer wall of the cell, or semi-fluid, as the inner wall of living
+protoplasm. Diffusion may therefore take place without osmosis,
+that is, in the absence of a membrane, as, for example, when we
+sweeten our tea or coffee by allowing sugar to diffuse through it.
+Many membranes offer little resistance to the osmotic movement of
+crystallizable substances. Such membranes are said to be _permeable_.
+Membranes which are not permeable to the dissolved solids, are called
+_semi-permeable_, since they allow the diffusion of water but not of
+the substances in solution. Living protoplasm is of this class. It is
+only very slightly permeable to many substances toward which, when
+dead, it acts as a permeable membrane.
+
+=58. Absorption in living and dead cells.=—There is one great
+difference between the action of the artificial cell used in the
+foregoing experiments and that of the cells of which a living body
+is built up. The living cell always has at least two membranes. One
+of these, the cell wall, is readily permeable, while the other, the
+protoplasm, is semi-permeable—that is, substances in solution usually
+diffuse more or less slowly, while water diffuses rapidly. Hence
+in the living cell the protoplasm exercises a power of absorption
+independent of the cell wall, sometimes rejecting substances admitted
+by the latter, sometimes retaining others to which it is permeable,
+as shown in Exp. 40. In the boiled beet the protoplasm had been
+killed and the red coloring matter passed through it unhindered,
+while in the living one it was held back by the protoplasmic lining,
+which is thus seen to control the absorptive properties of the cell.
+
+=59. Plasmolysis.=—Cells can be killed or injured in other ways
+than by heat; for example, by cold, by poisons, by starvation, and
+by overfeeding through the use of too much fertilizer or too rich
+a one. In this last case, the soil water becomes impregnated with
+soluble matter from the manure, which may render it denser than the
+sap in the roots. When this happens, it will cause the osmotic flow
+to set outward and thus deplete the cell of its water; whence we have
+the paradox that a cell, or even a whole plant, may be starved by
+overfeeding. This action of osmosis in withdrawing the contents from
+a cell is termed _plasmolysis_, and you can easily understand how
+very important a knowledge of the principles governing it is to the
+farmer in determining the application of fertilizers to his crops.
+
+Dead cells, although powerless to carry on the life processes of a
+plant, have nevertheless important uses in serving the purposes of
+mechanical support and also to some extent in assisting in the work
+of absorption, though their function here is a purely mechanical one.
+
+[Illustration: FIG. 72.—Root of a tree enveloping a rock. The large
+sycamore, whose base is partly concealed by the trumpet creeper on
+the left of the picture, is growing in very hard, stony soil, and
+one of its main roots has molded itself so completely to the ledge
+of rock protruding on the right, that when a portion of it was torn
+away, as shown where the light streak ends at _a_, the impress of its
+fibers was so strongly marked on the rock as to give the latter the
+appearance of a petrified root.]
+
+=60. Selective absorption.=—Different plants through their roots
+absorb different substances from the soil water, or the same
+substance in varying degrees. Hence, one kind of crop will exhaust
+the soil of certain minerals while leaving other kinds intact, or
+very little diminished; and _vice versa_, another kind will take
+up abundantly what its predecessor has rejected. In this sense,
+plants are said to exercise a selective power in the absorption
+of nutrients. The expression must not be understood, however, as
+implying any kind of volitional discrimination. It is merely a short
+and convenient way of saying that the cells of different plants
+possess different degrees of permeability to certain substances, some
+being more permeable to one thing, some to another. But beyond this
+rejection of untransmissible substances there is no active power of
+discrimination, any substance that can pass through the cell wall and
+its protoplasmic lining being taken in, whether useful, unnecessary,
+or even harmful. These may, however, be got rid of by excretion, as
+the superfluous water taken in with dissolved minerals is exhaled
+from the leaves; or if incapable of passing out by osmosis, rendered
+harmless and retained in the form of the curious “crystalloids”
+found in various parts of plants. But while the kind of selection
+exercised by vegetable cells implies no power of choice, as a matter
+of fact those substances most used by the plant in carrying on its
+life processes are absorbed in much greater quantities than others,
+being transferred to parts where growth or other changes in the plant
+tissues are going on, and there used up in the work of nutrition, or
+excreted in part as waste products. In either case their passage from
+cell to cell will give rise to a continuous osmotic current in that
+direction, and the absorption of new matter will go on in proportion
+to the amounts used up.
+
+[Illustration: FIG. 73.—Roots of elm and sycamore contending for
+possession of the soil on a rocky bluff on the Potomac.]
+
+=61. Definition.=—Tissue is a word used to denote any animal or
+vegetable substance having a uniform structure organized to perform
+a particular office or function. Thus, for instance, we have bony
+tissue and muscular tissue in animals; that is, tissue made of bone
+substance and muscle substance and doing the work of bone and muscle
+respectively. Likewise in plants, we have strengthening tissue
+made up of hard, thick-walled cells, serving mainly for purposes
+of mechanical support, and vascular tissue, made up of conducting
+vessels for conveying sap—and so on, for every separate function.
+
+
+          Practical Questions
+
+  1. Why do raspberries and strawberries have a flabby, wilted look
+  if sugar has been put on them too long before they are served? (7,
+  56.)
+
+  2. Where has the juice gone? What caused it to go out of the
+  berries? (56, 59.)
+
+  3. Is a knowledge of the principles governing osmosis of any
+  practical use to the housekeeper?
+
+  4. Why cannot roots absorb water as freely in winter as in summer?
+  (Suggestion: which is the heavier, cold or warm water?)
+
+  5. Why does fertilizing too heavily sometimes injure a crop? (59.)
+
+  6. Do you see any apparent contradiction between the action
+  of plasmolysis and the selective power of protoplasm? Can you
+  reconcile it?
+
+  7. If a piece of beet that has been frozen is placed in water
+  it will behave just as the slice of boiled beet did in Exp. 40;
+  explain. (58, 59.)
+
+
+          II. MINERAL NUTRIMENTS ABSORBED BY PLANTS
+
+  MATERIAL.—A dozen or two each of different kinds of seeds and
+  grains. A small portion from a growing shoot of a woody and a
+  herbaceous land plant, and of some kind of succulent water or marsh
+  plant, such as arrow grass (_Sagittaria_), water plantain, etc.
+
+  APPLIANCES.—A pair of scales; a lamp, stove, or other means of
+  burning away the perishable parts of the specimens to be studied.
+
+  EXPERIMENT 41.—DO THE TISSUES OF PLANTS CONTAIN MINERAL
+  MATTER?—Take about a dozen each of grains and seeds of different
+  kinds, weigh each kind separately, and then dry them at a high
+  temperature, but not high enough to scorch or burn them. After they
+  have become perfectly dry, weigh them again. What proportion of the
+  different seeds was water, as indicated by their loss of weight in
+  drying?
+
+  Burn all the solid part that remains, and then weigh the ash. What
+  proportion of each kind of seed was of incombustible material? What
+  proportion of the solid material was destroyed by combustion?
+
+  EXPERIMENT 42.—DO THEY CONTAIN DIFFERENT KINDS AND QUANTITIES OF
+  MINERALS?—Test in the same way the fresh, active parts of any kind
+  of ordinary land plant (sunflower, hollyhock, pea vines, etc.), and
+  of some kind of succulent water or marsh plant (Sagittaria, water
+  lily, fern). Do you notice any difference in the amount of water
+  given off and of solid matter left behind? In the character of the
+  ashes left? Have you observed in general any difference between the
+  ashes of different woods; as, for instance, hickory, pine, oak?
+  Compare with the residue left in Exp. 21; would you judge that the
+  residual substances are of the same composition?
+
+[Illustration: FIG. 74.—Water cultures of buckwheat, showing effect
+of the lack of the different food elements: 1, with all the elements;
+2, without potassium; 3, with soda instead of potash; 4, without
+calcium; 5, without nitrates or ammonia salts.]
+
+=62. Essential constituents.=—The composition of the ash of any
+particular plant will depend upon two things: the absorbent capacity
+of the plant itself and the nature of the substances contained in the
+soil in which it grows. But chemical analysis has shown that however
+the ashes may vary, they always contain some proportion of the
+following substances: potassium (potash), calcium (lime), magnesium,
+phosphorus, and (in green plants) iron. These elements occur in all
+plants, and if any one of them is absent, growth becomes abnormal if
+not impossible.
+
+The part of the dried substances that was burned away after expelling
+the water consists, in all plants, mainly of carbon, hydrogen,
+oxygen, nitrogen, and sulphur, in varying proportions. These five
+rank first in importance among the essential elements of vegetable
+life, and without them the plant cell itself, the physiological unit
+of vegetable structure, could not exist. They compose the greater
+part of the substance of every plant, carbon alone usually forming
+about one half the dry weight. Other substances may be present in
+varying proportions, but the two groups named above are found in all
+plants without exception, and so we may conclude that (with the
+possible addition of chlorine) they form the indispensable elements
+of plant food. Carbon, hydrogen, oxygen, nitrogen, sulphur, and
+phosphorus compose the structure of which the plant is built. The
+other four ingredients do not enter into the substance as component
+parts, but aid in the chemical processes by which the life functions
+of the plant are carried on, and are none the less essential elements
+of its food. Figure 74 shows the difference between a plant grown in
+a solution where all the food elements are present, and others in
+which some of them are lacking.
+
+[Illustration: FIG. 75.—Roots of soy bean bearing tubercle-forming
+bacteria.]
+
+=63. How plants obtain their food material.=—Plants obtain their
+supply of the various mineral salts from solutions in the soil
+water which they absorb through their roots. With a few doubtful
+exceptions, they cannot assimilate their food unless it is in a
+liquid or gaseous form. Of the gases, carbon dioxide, oxygen, and
+hydrogen can be freely absorbed from the air, or from water with
+various substances in solution, but most plants are so constituted
+that they cannot absorb free nitrogen from the air; they can take it
+only in the form of compounds from nitrates dissolved in the soil,
+and hence the importance of ammonia and other nitrogenous compounds
+in artificial fertilizers. Some of the pea family, however, bear
+on their roots little tubers formed by minute organisms called
+bacteria, which have the power of extracting nitrogen directly from
+the free air mingled with the soil; and hence the soil in which these
+tuber-bearing legumes decay is enriched with nitrogen in a form ready
+for use.
+
+
+          Practical Questions
+
+  1. Could any normal plant grow in a soil from which nitrogen was
+  lacking? Potash? Lime? Phosphorus? (62.)
+
+  2. Could it live in an atmosphere devoid of oxygen? Nitrogen?
+  Carbon dioxide? (62.)
+
+  3. Why are cow peas or other legumes planted on worn-out soil to
+  renew it? (63.)
+
+  4. Is the same kind of fertilizer equally good for all kinds of
+  soil? For all kinds of plants? (60, 62.)
+
+  5. Why does too much watering interfere with the nourishment of
+  plants? (Exps. 26, 27.)
+
+  6. Are ashes fit for fertilizers after being leached for lye? (62.)
+
+  7. Why will plants die, or make very slow growth, in pots, unless
+  the soil is renewed occasionally? (60, 62.)
+
+
+          III. STRUCTURE OF THE ROOT
+
+  MATERIAL.—Taproot of a young woody plant not over one or two years
+  old; apple and cherry shoots make good specimens. For showing root
+  hairs, seedlings of radish, turnip, or oat are good, also roots of
+  wandering Jew grown in water; for the rootcap, corn, sunflower,
+  squash.
+
+[Illustration: FIG. 76.—Cross section of a young taproot; _a_, _a_,
+root hairs; _b_, epidermis; _c_, cortical layer; _d_, fibrovascular
+cylinder. Note the absence of medullary rays during the first year of
+growth.]
+
+=64. Gross anatomy of the root.=—Cut a cross section of any woody
+taproot, about halfway between the tip and the ground level,
+examine it with a lens, and sketch. Label the dark outer covering,
+_epidermis_, the soft layer just within that, _cortex_, the hard,
+woody axis that you find in the center, _vascular cylinder_, and
+the fine silvery lines that radiate from the center to the cortex,
+_medullary rays_ (in a very young root these will not appear). Cut
+a section through a root that has stood in coloring fluid for about
+three hours and note the parts colored by the fluid. What portion of
+the root, would you judge from this, acts as a conductor of the water
+absorbed from the ground?
+
+Make a longitudinal section passing through the central portion of
+the root and extending an inch or two into the lower part of the
+stem. Do you find any sharp line of division between them? Notice the
+hard, woody axis that runs through the center. This is the vascular
+cylinder and contains the conducting vessels, the cut ends of which
+were shown in cross section in Fig. 76.
+
+[Illustration: FIG. 77.—Verti-section of branching root, showing the
+branches, _n_, _n_, originating in the central axis, _f_, and passing
+through the cortex, _r_, _r_.]
+
+=65. Distinctions between root and stem.=—Pull off a branch from
+the stem and one from the root; which comes off the more easily?
+Examine the points of attachment of the two and see why this is so.
+This mode of branching from the central axis instead of from the
+external layers, as in the stem, is one marked distinction between
+the structure of the two organs. In stems, moreover, branches occur
+normally above the points of leaf insertion at the nodes (46), while
+in the root they tend to arrange themselves in straight vertical
+rows. The shoots and cions that often originate from them are not
+normal root branches, but outgrowths from irregular or _adventitious_
+buds, that may occur on any part of a plant. The root is not divided
+into nodes like the stem, and never bears leaves.
+
+[Illustration: FIG. 78.—Root of a tree on the side of a gulley,
+acting as stem.]
+
+=66. The active part of the root.=—It is only the newest and most
+delicate parts of the root that produce hairs and are engaged in the
+active work of absorption, the older parts acting mainly as carriers.
+Hence, old roots lose much of their characteristic structure and
+take on more and more of the office of the stem, until there is
+practically no difference between them. On the sides of gullies,
+where the earth has been washed from around the trees, we often
+see the upper portion of the root covered with a thick bark and
+fulfilling every office of a true stem.
+
+=67. Minute structure of the root.=—(_a_) Mount in water and place
+under the microscope a portion of the root of an oat or radish
+seedling containing a number of hairs. In studying the thin,
+transparent roots of very young seedlings a section will not be
+necessary. Observe whether the hairs originate from the epidermis or
+from the interior. Are they true roots, or mere outgrowths from the
+cells of the epidermis? Do they consist of a single cell or a number
+of cells each? Notice what very thin cell walls the hairs have; is
+there any advantage in this? The interior, transparent portion of
+the hair contains the sap, and the protoplasm forms a thin lining on
+the inner surface of the wall; why not the sap next the wall and the
+protoplasm in the interior? (58, 60.)
+
+[Illustration: FIG. 79.—Longitudinal section through the tip of
+a young root, somewhat diagrammatic: _h_, _h_, root hairs; _ep_,
+epidermis; _a_, cortex; _b_, central cylinder; _e_, sheath of the
+cylinder (endodermis); _g_, growing point; _c_, root cap; _d_, dead
+and dying cells loosened from the extremity of the cap.]
+
+(_b_) Next examine a portion of the body of the root and try to
+make out the parts as shown in Fig. 79, and compare them with your
+observations in 64. The light line running through the middle is
+the _central cylinder_, up which the water passes, as was shown by
+the colored liquid in 64. Outside this is a darker portion (_a_,
+Fig. 79), corresponding to the cortex (_rr_, Fig. 77). Besides other
+uses, the cortex serves to prevent the loss of water as it passes up
+to the stem, and also, in fleshy roots like the carrot and turnip,
+for the storage of nourishment. Its innermost row of cells is
+thickened into the sheath, or _endodermis_ (_e_), which serves as an
+additional protection to the conducting tissues. The extreme outer
+layer, from the cells of which the root hairs are developed, is, as
+already stated, the epidermis, and in the older and more exposed
+parts of perennial roots is displaced by the bark, which becomes
+indistinguishable from that of the stem. (66.)
+
+(_c_) Look at the tip of the root for a loose structure (_c_) fitting
+over it like a thimble. This is the rootcap. Do you see any loose
+cells that seem to have broken away from it? These are old cells that
+have been pushed to the front by the formation of new growth back of
+them, and, being of no further use, are rubbed off by friction as the
+root bores its way through the soil. Draw a longitudinal section of
+the root as it appears under the microscope, labeling all the parts.
+If they cannot be made out distinctly in the specimen examined, use
+sections of young corn or bean roots, which are larger and show the
+parts more distinctly.
+
+[Illustration: FIG. 80.—Cross section of a young root, magnified:
+_h_, hairs; _a_, cortex; _b_, central cylinder; _e_, sheath or
+endodermis; _ep_, epidermis; _sp_, cut ends of the ducts.]
+
+(_d_) Place under the microscope a thin cross section through the
+hairy portion of a primary root of a bean or pea seedling, and try
+to make out the parts noted above and shown in cross section in
+Fig. 80. Make a sketch of what you see, labeling all the parts you
+can recognize. Show in your drawing the differences in the size
+and shape of the cells composing the different tissues. Notice in
+the central cylinder (Fig. 80) several groups of what look in the
+section like little round pits, or holes, _sp_. These are the cut
+ends of large-sized tubes or _ducts_ that convey the water absorbed
+by the roots to the stem. Each set of these tubes, together with a
+number of smaller ones belonging to the same group, constitutes a
+_fibrovascular bundle_—a very important element in the structure of
+all roots and stems, as these bundles make up the conducting system
+of the plant body.
+
+
+          IV. THE WORK OF ROOTS
+
+  MATERIAL.—Germinating seedlings of radish, bean, corn, etc.;
+  a potted plant of calla, fuchsia, tropæolum, touch-me-not
+  (_Impatiens_), or corn; a plant that has been growing for some time
+  in a porous earthen jar.
+
+  APPLIANCES.—Glass tumblers; coloring fluid; wax; some coarse
+  netting; dark wrapping paper, or a long cardboard box; a sheet of
+  oiled paper; some half-inch glass tubing; a few inches of rubber
+  tubing; an ounce of mercury; some blue litmus paper; a flower pot
+  full of earth; a few handfuls of sand, clay, and vegetable mold; a
+  pair of scales; a half dozen straight lamp chimneys, or long-necked
+  bottles from which the bottoms have been removed as directed in
+  Exp. 53.
+
+  EXPERIMENT 43. USE OF THE EPIDERMIS.—Cut away the lower end
+  of a taproot; seal the cut surface with wax so as to make it
+  perfectly water-tight, and insert it in red ink for at least half
+  the remaining length, taking care that there is no break in the
+  epidermis. Cut an inch or two from the tip of the lower piece, or
+  if material is abundant, from another root of the same kind, and
+  without sealing the cut surface, insert it in red ink, beside the
+  other. At the end of three or four hours, examine longitudinal
+  sections of both pieces. Has the liquid been absorbed equally by
+  both? If not, in which has it been absorbed the more freely? What
+  conclusion would you draw from this, as to the passage of liquids
+  through the epidermis?
+
+  From this experiment we see that the epidermis, besides protecting
+  the more delicate parts within from mechanical injury by hard
+  substances contained in the soil, serves by its comparative
+  imperviousness to prevent evaporation, or the escape of the sap by
+  osmosis as it flows from the root hairs up to the stem and leaves.
+
+  EXPERIMENT 44. TO SHOW THAT ROOTS ABSORB MOISTURE.—Fill two pots
+  with damp earth, put a healthy plant in one, and set them side by
+  side in the shade. After a few days examine by digging into the
+  soil with a fork and see in which pot it is drier. Where has the
+  moisture gone? How did it get out?
+
+  EXPERIMENT 45. TO SHOW THAT ROOTS SHUN THE LIGHT.—Cover the top
+  of a glass of water with thin netting, and lay on it sprouting
+  mustard or other convenient seed. Allow the roots to pass through
+  the netting into the water, noting the position of root and stem.
+  Envelop the sides of the glass in heavy wrapping paper, admitting
+  a little ray of light through a slit in one side, and after a few
+  days again observe the relative position of the two organs. How is
+  each affected by the light?
+
+  EXPERIMENT 46. TO FIND OUT WHETHER ROOTS NEED AIR.—Remove a plant
+  from a porous earthenware pot in which it has been growing for some
+  time; the roots will be found spread out in contact with the walls
+  of the pot instead of embedded in the soil at the center. Why is
+  this?
+
+  EXPERIMENT 47. TO SHOW THAT ROOTS SEEK WATER.—Stretch some coarse
+  netting covered with moist batting over the top of an empty
+  tumbler. Lay on it some seedlings, as in Exp. 45, allowing the
+  roots to pass through the meshes of the netting. Keep the batting
+  moist, but take care not to let any of the water run into the
+  vessel. Observe the position of the roots at intervals, for twelve
+  to twenty-four hours, then fill the glass with water to within
+  10 millimeters (a half inch, nearly) or less of the netting, let
+  the batting dry, and after eight or ten hours again observe the
+  position of the roots. What would you infer from this experiment as
+  to the affinity of roots for water?
+
+  EXPERIMENT 48. WHAT BECOMES OF THE WATER ABSORBED BY ROOTS.—Cover
+  a calla lily, young cornstalk, sunflower, tropæolum, or other
+  succulent herb with a cap of oiled paper to prevent evaporation
+  from the leaves, set the pot containing it in a pan of tepid water,
+  and keep the temperature unchanged. After a few hours look for
+  water drops on the leaves. Where did this water come from? How did
+  it get up into the leaves?
+
+  EXPERIMENT 49. TO SHOW THE FORCE OF ROOT PRESSURE.—Cut off the stem
+  of the plant 6 or 8 centimeters (3 or 4 inches) from the base. Slip
+  over the part remaining in the soil a bit of rubber tubing of about
+  the same diameter as the stem, and tie tightly just below the cut.
+  Pour in a little water to keep the stem moist, and slip in above,
+  a short piece of tightly fitting glass tubing. Watch the tube for
+  several days and note the rise of water in it. The same phenomenon
+  may be observed in the “bleeding” of rapidly growing, absorbent
+  young shoots, such as grape, sunflower, gourd, tobacco, etc., if
+  cut off near the ground in spring when the earth is warm and moist.
+  By means of an arrangement like that shown in Fig. 81, the force
+  of the pressure exerted can be measured by the displacement of the
+  mercury. This flow cannot be due to the giving off of moisture
+  by the leaves, since they have been removed. Their action, when
+  present, by causing a deficiency of moisture in certain places may
+  influence the direction and rapidity of the current, but does not
+  furnish the motive power, which evidently comes, in part at least,
+  from the roots, and is the expression of their absorbent activity.
+
+[Illustration: FIG. 81.—Arrangement for estimating the force of root
+pressure: _s_, stub of the cut stem; _g_, glass tubing joined by
+means of the rubber tubing, _t_, to the stem; _m_, mercury forced up
+the glass tube by water, _w_, pumped from the soil by the roots.]
+
+  EXPERIMENT 50. TO SHOW THAT ROOTS CAUSE THE OCCURRENCE OF
+  ACIDS.—Lay a piece of blue litmus paper on a board or on a piece
+  of glass slightly tilted at one end to secure drainage. Cover the
+  surface with an inch of moist sand and plant in it a number of
+  healthy seedlings. Acids have the property of changing blue litmus
+  to red; hence, if you find any red stains on the paper where the
+  roots have penetrated, what are you to conclude?
+
+  Carbon dioxide has a slight acid reaction and is caused to form in
+  varying quantities by all roots. Probably other substances, and
+  these not a few, are actually excreted.
+
+  EXPERIMENT 51. CAN THE ABSORBENT POWER OF ROOTS BE INTERFERED
+  WITH?—Place the roots of a number of seedlings with well-developed
+  hairs in a weak solution of saltpeter—10 grams (about ⅓ of an
+  ounce) to a pint of water, and others in a stronger solution—say 30
+  grams, or 1 ounce, to a pint. Try the same experiment with weak and
+  strong solutions of any conveniently obtainable liquid fertilizer.
+  After 45 minutes or an hour examine the roots under a lens and note
+  the change that has taken place. What has gone out of them? What
+  caused the loss of the contained sap?
+
+  EXPERIMENT 52. TO TEST THE WEIGHT OF SOILS.—Thoroughly dry and
+  powder a pint each of sand and clay, measure accurately, and
+  balance against each other in a pair of scales. Which weighs more,
+  bulk for bulk, a “light” soil, or a “heavy” one? (77.)
+
+  EXPERIMENT 53. TO TEST THE CAPACITY OF SOILS FOR ABSORBING AND
+  RETAINING MOISTURE.—Arrange, as shown in Fig. 82, a number of
+  long-necked bottles from which the bottom has been removed. This
+  can be done by making a small indentation with a file at the point
+  desired and leading the break round the circumference with the end
+  of a glowing wire or a red-hot poker. The crack will follow the
+  heated object with sufficient regularity to answer the purpose.
+  Tie a piece of thin cloth over the mouth of each bottle and invert
+  with the necks extending an inch or two into empty tumblers placed
+  beneath. Fill all to the same height with soils of different
+  kinds—sand, clay, gravel, loam, vegetable mold, etc.—and pour over
+  each the same quantity of water from above. Watch the rate at which
+  the liquid filters through into the tumblers. Which loses its
+  moisture soonest? Which retains it longest?
+
+[Illustration: FIG. 82.—Apparatus for testing the capacity of soils
+to take in and retain moisture.]
+
+  Next leave the soils in the bottles dry, fill the tumblers up to
+  the necks of the bottles, and watch the rate at which the water
+  rises in the different ones. The power of soils to absorb moisture
+  is called _capillarity_. Which of your samples shows the highest
+  capillarity? Which the lowest? Do you observe any relation between
+  the capillarity of a soil and its power of retention?
+
+=68. Roots as holdfasts.=—One use of ordinary roots is to serve as
+props and stays for anchoring plants to the soil. Tall herbs and
+shrubs, and vegetation generally that is exposed to much stress of
+weather, are apt to have large, strong roots. Even plants of the same
+species will develop systems of very different strength according as
+they grow in sheltered or exposed places.
+
+[Illustration: FIG. 83.—Dandelion: _a_, common form, grown in plains
+region at low altitude; _b_, alpine form.]
+
+=69. Root pull.=—Roots are not mere passive holdfasts, but exert
+an active downward pull upon the stem. Notice the rooting end of a
+strawberry or raspberry shoot and observe how the stem appears to
+be drawn into the ground at the rooting point. In the leaf rosettes
+of herbs growing flat on the ground or in the crevices of walls and
+pavements, the strong depression observable at the center is due to
+root pull. (Fig. 84.)
+
+[Illustration: FIG. 84.—Raspberry stolon showing root pull.]
+
+=70. Storage of food.=—Another office of roots is to store up food
+for the use of the plant. This is done chiefly in the tissues of
+fleshy roots and tubers, and gives to them their great economic
+value. Next to grains and cereals, roots probably furnish a larger
+portion of food to the human race than any other crop. In addition to
+this they are also the source of valuable drugs, condiments, and dyes.
+
+=71. Absorption and conveyance of sap.=—But the most important
+function of roots is that of absorption. By their action the soil
+water and the minerals contained in it are drawn up into the plant
+body and made available for conversion by the leaves into organic
+foods, as will be explained in another chapter. From the nature
+of their function, most roots have naturally a strong affinity
+for water, and its presence or absence has a marked influence on
+their direction of growth, being often sufficient to overcome that
+of geotropism (Exp. 47). There are many trees and shrubs, notably
+willow, sweet bay, red birch, and the like, that grow best on the
+banks of streams and ponds, where their roots can have direct access
+to water. Excess of moisture, however, is injurious to most land
+plants by preventing the roots from getting sufficient air for
+respiration.
+
+=72. The conditions of absorption.=—The sap in the root cells is
+normally denser than the water in the soil, so there is a continuous
+flow from the latter to the former. But if, for any reason, the
+density of the liquids should be reversed, the flow would set in the
+opposite direction, and if continued long enough, the strength of the
+plant would be literally “sapped” by the exhaustion of its tissues,
+so that it would die. What is this process of cell exhaustion called?
+
+=73. The use of acid secretions to the root.=—It was shown in Exp.
+50 that carbon dioxide and probably other substances occur in the
+immediate vicinity of roots. Carbon dioxide is an active agent in
+dissolving the various mineral matters contained in the soil, and as
+these last can be absorbed only in a liquid or a gaseous state (63),
+the advantage to the root as an absorbent organ, of being able to
+secrete such active solvents, is obvious.
+
+[Illustration: FIG. 85.—A natural root etching, found on a piece of
+slate.]
+
+=74. Relation of roots to the soil.=—In order to perform their work
+of absorption, roots must have access to a suitable soil. To produce
+the best results a soil must contain (1) all the essential mineral
+constituents (62); (2) moisture for dissolving these materials; and
+(3) air enough to supply the oxygen which is necessary to the life
+processes of all green plants.
+
+=75. Composition of soils.=—Sand, clay, and humus, or vegetable
+mold, with the various substances dissolved in them, constitute the
+basis of cultivated soils. A mixture of sand, clay, and humus is
+called loam. When the proportion of humus is very large and well
+decomposed, the mixture is called _muck_. Pure sand contains but
+little nourishing matter and is too porous to retain water well. Pure
+clay is too compact to be easily permeable to either air or water.
+Most soils are composed of a mixture of the two with vegetable mold
+in varying proportions, giving a sandy loam, or a clay loam, as the
+case may be.
+
+=76. Tillage.=—The advantages of tillage are: (_a_) that by breaking
+up the hard lumps it renders the soil more permeable to air and water
+and more easily penetrable by the roots in their search for food;
+(_b_) the covering of loose, friable earth left by the plow and the
+harrow acts as a mulch, and by shading the soil below, prevents
+too rapid a loss of water by evaporation. Where the essential food
+ingredients are present, good tillage counts for more in making a
+crop than the original quality of the soil.
+
+=77. Light and heavy soils.=—These terms are used by farmers not
+in relation to the weight of soils, but in reference to the ease
+or difficulty with which they are worked. Light soils contain a
+preponderance of sand; heavy ones, of clay.
+
+
+          Practical Questions
+
+  1. Will plants grow better in an earthen pot or a wooden box than
+  in a vessel of glass or metal? Why? (Exp. 46.)
+
+  2. Which absorb more from the soil, plants with light roots and
+  abundant foliage, or those with heavy roots and scant foliage?
+  (Suggestion: roots absorb from the soil; leaves, mainly from the
+  air.)
+
+  3. Why are willows so generally selected for planting along the
+  borders of streams in order to protect the banks from washing? (71.)
+
+  4. Why are the conducting tissues of roots at the center instead of
+  near the surface as in stems? (67, _b_.)
+
+  5. Why does corn never grow well in swampy ground? (74; Exp. 46.)
+
+  6. Why are fleshy roots so much larger in cultivated plants than in
+  wild ones of the same species? (74, 76.)
+
+  7. When the use of a particular kind of fertilizer causes the
+  leaves of the plants to which it has been applied to turn brown, so
+  that the farmer says they have been “burned” by it, to what cause
+  is the trouble due? (59, 72.)
+
+  8. Why do farmers speak of turnips and other root crops as “heavy
+  feeders”? (70, 71.)
+
+  9. Which is more exhausting to the soil, a crop of beets, or one of
+  oats? Onions, or green peas? (See 2, suggestion.)
+
+  10. Why will inserting the end of a wilted twig in warm water
+  sometimes cause it to revive? (Exps. 48, 49.)
+
+
+          V. DIFFERENT FORMS OF ROOTS
+
+  MATERIAL.—Examples of taproots: bean, pea, cotton, maple seedlings,
+  or any kind of very young woody root. Fibrous: any kind of grass
+  or grain. Fleshy: parsnip, turnip, carrot, dahlia, sweet potato.
+  Water: duckweed, pondweed, or a cutting of wandering Jew grown
+  in water. Parasitic: mistletoe, dodder, beech drops. Aërial and
+  adventitious: the aërial roots of old scuppernong vines, climbing
+  roots of ivy and trumpet vine, prop roots from the lower nodes of
+  cornstalks and sugar cane.
+
+=78. Basis of distinction.=—Roots vary in form and external structure
+according to their origin, function, and surroundings. In reference
+to the first, they are classed as primary or secondary; in regard to
+the second, as dry or fleshy; while as to surroundings, they may be
+adapted to either the soil, water, air, or the parasitic habit. Soil
+roots are the normal form. According to their mode of growth they are
+either fibrous or axial.
+
+[Illustration: PLATE 3.—Aërial roots of a Mexican “strangling” fig,
+enveloping the trunk of a palm (_From_ “Rep’t. Mo. Bot. Garden”).]
+
+=79. Taproots.=—These are the common form of the axial type. Compare
+the root of any young hardwood cion a year or two old with one
+of a mature stalk of corn or other grain, and with the roots of
+seedlings of the same species. Notice the difference in their mode
+of growth. In the first kind a single stout prolongation called a
+taproot proceeds from the lower end of the hypocotyl and continues
+the axis of growth straight downward, unless turned aside by some
+external influence. A taproot may be either simple, as in the turnip,
+radish, and dandelion, or branched, as in most shrubs and trees. In
+the latter case the main axis is called the primary root, and the
+branches are secondary ones.
+
+[Illustration: FIG. 86.—Branched taproot of maple.]
+
+=80. Fibrous and fascicled roots.=—Where the main axis fails
+to develop, as in the corn and grasses generally, a number of
+independent branches take its place, forming what are known as
+fibrous roots. Both fibrous and taproots may be either hard or
+fleshy. The turnip and carrot are examples of fleshy taproots, the
+dahlia and rhubarb of fascicled roots. The function of both is the
+storage of nourishment. The sweet potato is an example of a tuberous
+root.
+
+=81. Practical importance of this distinction.=—The difference
+between axial and fibrous roots has important bearings in
+agriculture. The first kind, which are characteristic of most
+dicotyls, strike deep and draw their nourishment from the lower
+strata of the soil, while the fibrous and fascicled, or radial kinds,
+as we may call them for want of a better name, spread out near the
+surface and are more dependent on external conditions.
+
+[Illustration: FIG. 87.—Fibrous root.]
+
+=82. Roots that grow above ground.=—The kinds of roots that have
+just been considered are all subterranean, and bring the plant
+into relation with the earth, whether for the purpose of absorbing
+nourishment, or of mechanical support, or, as in the majority of
+cases, for both. Many plants, however, do not get their mineral
+nutrients directly from the soil, and these give rise to various
+forms suited to other conditions of alimentation.
+
+=83. Adventitious roots.=—This name applies to any kinds of roots
+that occur on stems, or in other unusual positions. They may be
+considered as intermediate between the two classes named in 81; for
+while their starting point is above ground, they generally end by
+fixing themselves in the soil, where they often function as normal
+roots. Familiar examples are the roots that put out from the lower
+nodes of corn and sugar cane stalks, and serve both to supply
+additional moisture and to anchor the plant more firmly to the soil.
+Most plants will develop adventitious roots if covered with earth, or
+even if merely kept in contact with the ground. The gardener takes
+advantage of this capacity when he propagates by cuttings and layers.
+
+=84. Water roots.=—These are generally white and threadlike and more
+tender and succulent than ordinary soil roots, because they have less
+work to do. Floating and immersed plants, such as bladderwort and
+hornwort (_Ceratophyllum_) have no need of absorbent roots, since the
+greater part of their surface is in contact with water and can absorb
+directly what is needed.
+
+Land plants will often develop water roots and thrive for a time if
+the liquid holds in solution a sufficient quantity of air and mineral
+nutrients. Place a cutting of wandering Jew in a glass of clear
+water, and in from four to six days it will develop beautiful water
+roots in which both hairs and cap are clearly visible to the naked
+eye.
+
+=85. Haustoria=, from a Latin word meaning to drain, or exhaust,
+is a name given to the roots of parasitic plants, or such as live
+by attaching themselves to some other living organism, from which
+they draw their nourishment ready made. Their roots are adapted
+to penetrating the substance of the _host_, as their victim is
+called, and absorbing the sap from it. Dodder and mistletoe are the
+best-known examples of plant parasites, though the latter is only
+partially parasitic, as it merely takes up the sap from the host and
+manufactures its own food by means of its green leaves.
+
+[Illustration: FIG. 88.—Beech root: _A_, grown in unsterilized wood
+humus: _p_, strands of fungal hyphæ, associated at _a_, with humus;
+_B_, grown in wood humus freed from fungus by sterilization—it is not
+provided with fungal hyphæ, and has root hairs, _h_. (_A_ and _B_
+both several times magnified.)]
+
+=86. Saprophytes.=—Akin to parasites are saprophytes, which live
+on dead and decaying vegetable matter. They are only partially
+parasitic and do not bear the haustoria of true parasites. Many of
+them, of which the Indian pipe (_Monotropa_) and coral root are
+familiar examples, obtain their nourishment in part, at least, by
+association with certain saprophytic fungi, which enmesh their roots
+in a growth of threadlike fibers that take the place of root hairs
+and absorb organic food from the rich humus in which these plants
+grow. Such growths are called _mycorrhiza_, meaning “fungal roots.”
+Similar associations are formed by some of the higher plants also.
+The rootlets of the common beech and of certain of the pine family,
+for instance, are often enveloped in a network of fungus fibers,
+and in this case root hairs are developed very poorly, or not at
+all. Besides greatly increasing the absorbent surface by their
+ramification through the soil, the mycorrhizal threads may possibly
+benefit the plant in other ways also, as, for instance, by bringing
+about chemical changes that might aid in the work of nutrition.
+
+[Illustration: FIG. 89.—An air plant (_Tillandsia_), growing on the
+underside of a bough.]
+
+[Illustration: FIG. 90.—A single strand of _Tillandsia usneoides_, a
+rootless epiphyte belonging to the pineapple family; better known as
+the “Spanish moss” that drapes the boughs of trees so conspicuously
+in the warm parts of America. Two-thirds natural size. (Photographed
+by C. F. O’Keefe.)]
+
+=87. Epiphytes, or air plants.=—In the proper meaning of the word
+these are not parasitic, but use their host merely as a mechanical
+support to bring them into better light relations. The name, however,
+is loosely applied to all plants that find a lodgment on the trunks
+and branches of trees, whether parasites or true epiphytes that draw
+no nourishment from the host. Not infrequently the latter is killed
+by them through suffocation, overweighting, or the constriction of
+the stems by close clinging twiners.
+
+=88. Aërial roots= are such as have no connection at all with the
+soil or with any host plant, except as they may lodge upon the trunks
+and branches of trees for a support. In other than purely epiphytic
+plants, which get all their nourishment from the air, they are
+generally subsidiary to soil roots, like the long dangling cords that
+hang from some species of old grapevines; or they subserve other
+purposes altogether than absorbing nourishment, as the climbing roots
+of the trumpet vine and poison ivy. A very remarkable development
+of aërial roots takes place in the “strangling fig” of Mexico and
+Florida, which begins life as a small epiphyte, from seeds dropped by
+birds on the boughs or trunks of trees. When it gets well started,
+the young plant sends down enormous aërial roots, which find their
+way to the ground, and in time so completely envelop the host that it
+is literally strangled to death (Plate 3, p. 73). When this support
+is removed, the sheathing roots take its place and become to all
+intents and purposes the stem of the fig tree, which now leads an
+independent life.
+
+[Illustration: FIG. 91.—Root system of a tobacco plant.]
+
+=89. The root system.=—The entire mass of roots belonging to a
+plant, with all its ramifications and subdivisions, composes a root
+system. The extent of root expansion is in general about equal to
+that of the crown, thus bringing the new and active parts under the
+drip of the boughs where the moisture is most abundant. Some plants
+have root systems out of all seeming proportion to their size. A
+catalpa seedling six months old showed, by actual measurement,
+250 feet of root growth, and it is estimated that the roots of a
+thrifty cornstalk, if laid end to end, would extend a mile. In the
+development of the root system, a great deal depends upon external
+conditions. In a poor, dry soil, the roots have to travel farther in
+search of a livelihood, and so a larger system has to be developed
+than in a more favorable location.
+
+
+          Practical Questions
+
+  1. Which is better to succeed a crop of turnips on the same land,
+  hay or carrots? (81.)
+
+  2. Write out what you think would be a good rotation for four or
+  five successive crops based on the forms of the roots.
+
+  3. Study the following rotations and give your opinion about them,
+  on the same principle. Suggest any improvements that may occur
+  to you, and give a reason for the change. Beets, barley, clover,
+  wheat; cotton, oats, peas, corn; oats, melons, turnips; cotton,
+  oats, corn and peas mixed, melons; cotton, hay, corn, peas.
+
+  4. Give three good reasons in favor of a rotation over a
+  single-crop system. (24, 60, 62, 81.)
+
+  5. Which will require deeper tillage, a bed of carrots or one of
+  strawberries? (81.)
+
+  6. Explain why some plants keep green and fresh when the surface of
+  the soil is dry, while others wilt or die. (81, 89.)
+
+  7. Which will better withstand drought, a crop of alfalfa or one of
+  Indian corn? Why? (81.)
+
+  8. Which will interfere less with the trees if planted in an
+  orchard, beets or onions? (81.)
+
+  9. Ought a crop of hemp and tobacco to succeed each other on the
+  same land? (81, 89.)
+
+  10. Why does a gardener manure a grass plot by scattering the
+  fertilizer on the surface, while he digs around the roses and
+  lilacs and deposits it under ground? (81.)
+
+  11. Do the adventitious roots of such climbers as ivy and trumpet
+  vine draw any nourishment from the objects to which they cling?
+  (83-88.)
+
+  12. How can you tell?
+
+  13. Do partial dependents of this kind injure trees by climbing
+  upon them; and if so, how? (87, 88.)
+
+  14. What is the use of the aërial roots of the scuppernong grape?
+  (88.)
+
+  15. Is the resurrection fern (_Polypodium incanum_), that grows on
+  tree trunks in our Southern States, a parasite or an air plant?
+  (87.)
+
+  16. On what plants in your neighborhood does mistletoe grow most
+  abundantly? Dodder?
+
+  17. Is mistletoe injurious to the host? (85.)
+
+  18. Name some plants that are propagated mainly, or solely, by
+  roots and cuttings.
+
+  19. Where do aërial roots get their nourishment? (88.)
+
+  20. Would they be of any use to a plant in a very cold or dry
+  climate?
+
+  21. Where should manure be placed to benefit a tree or shrub with
+  wide-spreading roots? (66, 89.)
+
+  22. Is it a wise practice to mulch a tree by raking up dead leaves
+  and piling them around the base of the trunk, as is often done?
+  Why, or why not? (66, 89.)
+
+
+          Field Work
+
+  (1) Examine the underground parts of hardy winter herbs in your
+  neighborhood, also of any weeds or grasses that are particularly
+  troublesome, and see if there is anything about the structure of
+  these parts to account for their persistence. Note the difference
+  between roots of the same species in low, moist places and in
+  dry ones; between those of the same kind of plants in different
+  soils; in sheltered and in exposed situations. Study the direction
+  and position of the roots of trees and shrubs with reference to
+  any stream or body of water in the neighborhood. (The elm, fig,
+  mulberry, and willow are good subjects for such observations.)
+  Notice also whether there is any relation between the underground
+  parts and the leaf systems of plants in reference to drainage and
+  transpiration.
+
+  (2) Observe the effect of root pull upon low herbs. Look along
+  washes and gullies for roots doing the office of stems, and note
+  any changes of structure consequent thereon. Study the relative
+  length and strength of the root systems of different plants, with
+  reference to their value as soil binders, or their hurtfulness in
+  damaging the walls of cellars, wells, sewers, etc. Dig your trowel
+  a few inches into the soil of any grove or copse you happen to
+  visit, note the inextricable tangle of roots, and consider the
+  fierce competition for living room in the vegetable world that it
+  implies.
+
+  (3) Tests might be made of the different soils in the neighborhood
+  of the schoolhouse by planting seeds of various kinds and noting
+  the rate of germination; first, without fertilizers, then by adding
+  the different elements in succession to see what is lacking. The
+  field for study suggested by this subject is almost inexhaustible.
+
+
+
+
+CHAPTER IV. THE STEM
+
+
+          I. FORMS AND GROWTH OF STEMS
+
+  MATERIAL.—Vigorous young hop or beau seedlings grown in pots; a
+  fresh dandelion stalk; a stem of pea, squash, cucumber, grape, or
+  passion flower vine, with tendrils.
+
+  APPLIANCES.—A bowl of fresh water; rods of different sizes and
+  smoothness for testing the hold of climbers.
+
+  EXPERIMENT 54. TO SHOW THE MOVEMENTS OF TWINING STEMS.—Raise a
+  young hop or bean seedling in the schoolroom and allow it to grow
+  about two decimeters—8 to 10 inches—in length before providing
+  it with a support. Does the stem form any coils? Bring it in
+  contact with a suitable upright support and watch for a day or
+  two. What happens? Notice whether it starts to coil from right to
+  left or from left to right and see if you can coax it to turn in
+  the opposite direction. When it has reached the end of its stake,
+  allow it to grow about five centimeters (two inches, approximately)
+  beyond, and watch the revolution of the tip. Cut a hole through the
+  center of a piece of cardboard about 14 centimeters (five to six
+  inches) in diameter, slip it over the loose end of the stem, and
+  fasten it to the stake in a horizontal position, with a pin. Note
+  the position of the stem tip at regular intervals and mark on the
+  cardboard; how long does it take to complete a revolution? Does it
+  continue to coil, or to coil as readily, after leaving its stake as
+  before? What would you infer from this as to the effect of contact
+  in stimulating it to coil?
+
+  Find out by experiment if it can climb well by means of a glass or
+  other smooth rod; by a fine wire; a broomstick; a large, smooth
+  post. See whether it does better on a horizontal or an upright
+  support.
+
+  EXPERIMENT 55. TO ILLUSTRATE THE COILING OF STEMS.—Run a gathering
+  thread in one side of a narrow strip of muslin and notice how the
+  ruffle thus drawn will curl into a spiral when allowed to dangle
+  from the needle. Can you think of any cause that might act on a
+  stem in the same way? Suppose, for instance, that one side should
+  grow faster than the other; what would be the effect? (54.)
+
+  Split the stem of a fresh dandelion, or other herbaceous scape,
+  longitudinally, and immerse it in a pan of fresh water for a few
+  minutes. Notice how the two halves curve outward, or even coil up
+  like the strip of muslin. This is due to the tension caused by the
+  more rapid absorption of the thinner walled cells of the internal
+  tissues. These, when relieved of the resistance of the thicker
+  walled outer tissues, swell on their free side, but are held back
+  on the other by the non-absorbent outer parts, as one side of the
+  muslin ruffle was held by the gathering thread.
+
+  EXPERIMENT 56. TO FIND OUT WHETHER THE DIRECTION OF STEM GROWTH IS
+  INFLUENCED BY LIGHT.—Place two rapidly growing young pea, bean,
+  sunflower, or squash plants, each with several well-developed
+  leaves, in a room or box with a light exposure on one side only.
+  After two or three days, notice the position of the stems in regard
+  to the light. Does either one show a more decided inclination
+  toward it than the other?
+
+  EXPERIMENT 57. IS THE LIGHT RELATION OF THE STEM INFLUENCED BY THE
+  LEAVES?—Cut the leaves from one of the plants used in Exp. 56,
+  covering the cut surfaces with vaseline to prevent “bleeding”;
+  reverse the positions of both with regard to the light, and watch
+  for two or three days. In which is the response to light the more
+  rapid? What does this indicate as one object of the stem in seeking
+  light? What is the best position of a stem, ordinarily, for getting
+  its leaves into the light?
+
+[Illustration: FIG. 92.—Stems of red oak and hickory that have
+grafted themselves.]
+
+=90. Classification.=—Stems are classed according to (1) duration, as
+annuals, biennials, and perennials; (2) with reference to hardness
+or softness of structure, as herbaceous and woody; (3) in regard to
+position and direction of growth, as erect, prostrate, climbing,
+inclined, declined, underground, etc.
+
+=91. Annuals= complete their life cycle in a single season and then
+die down as soon as they have perfected their seed. Many of our most
+troublesome weeds belong to this class and might be exterminated
+by the simple expedient of mowing them down before their time of
+flowering.
+
+=92. Biennials=, as the name implies, live for two years. Their
+energy during the first season is spent chiefly in laying by a store
+of nourishment, usually in the tissues of fleshy roots (70). By this
+means they get a good start in the second season and mature their
+seeds early. Many of our common garden vegetables, such as turnips,
+carrots, parsnips, and cabbage, belong to this class. Where is the
+nourishment stored in the cabbage?
+
+[Illustration: FIG. 93.—A biennial plant, mullein, in winter
+condition with stem reduced to little more than a disk supporting
+a rosette of leaves. Notice how close they cling to the earth, and
+compare them with their fruiting condition a few months later as
+shown in Fig. 237.]
+
+=93. Perennials= are plants that live on indefinitely, like most of
+our forest trees and woody-stemmed shrubs. Woody stems are usually
+perennial and may live for hundreds and even thousands of years, as
+those of the giant sequoias of California, and the famous chestnut of
+Mt. Etna.
+
+=94. Herbaceous stems= are more or less succulent and die down after
+fruiting. They are usually annuals, though some kinds, like the
+garden geraniums and the common St.-John’s-wort, show a tendency
+to become woody, especially at the base, and live on from year to
+year. Others, such as the hawkweed and dahlia, die down above ground
+in winter, but are enabled to keep their underground parts alive
+indefinitely, through the nourishment stored in them, and are thus
+perennial below ground and annual above. Woody-stemmed annuals, such
+as the cotton and castor oil plant, are not, properly speaking,
+herbs. In the tropical countries to which they belong they are
+perennial shrubs, or even small trees, but on being transplanted to
+colder regions have been compelled to take on the annual habit as an
+adaptation to climate.
+
+[Illustration: FIG. 94.—Orange hawkweed with runners.]
+
+[Illustration: FIG. 95.—Prostrate stem of Lycopodium with assurgent
+branches.]
+
+[Illustration: FIG. 96.—Diagram of stem growth: _ps_, surface of the
+ground; _e_, erect position; _d_, declined; _a_, assurgent; _p_,
+prostrate; _u_, vertical direction underground.]
+
+=95. Direction and habit of growth.=—As to manner of growth, there
+are many forms, from the upright boles of the beech and pine to the
+trailing, prostrate, and creeping stems of which we have examples
+in the running periwinkle, the prostrate spurge and the creeping
+partridge berry (_Mitchella repens_), respectively. Trailing and
+prostrate stems are very apt to become creepers by the development of
+adventitious roots at their nodes wherever they come in contact with
+the soil. The rooting stems of dewberries, the runners and stolons of
+strawberries and currants, are familiar examples.
+
+Between the extremes of prostrate and upright, stems may be inclined
+or bent in various degrees. As shown in Fig. 96, there are two modes
+of inclination: _assurgent_, _a_, from the prostrate, _p_, toward
+the upright, _e_; and _declined_, _d_, from the upright toward the
+prostrate. Below the surface, _ps_, occur only underground stems. Is
+the prostrate habit an advantageous one for light exposure? Can you
+think of any compensating advantages a plant might derive from it;
+for example, in regard to warmth and moisture?
+
+[Illustration: FIG. 97.—Twining stems: _A_, hop twining with the sun;
+_B_, convolvulus twining against the sun.]
+
+=96. Climbing stems.=—These are such as lift themselves from the
+ground and attain the advantages of the upright position by clinging
+to supports of various kinds—usually, in a state of nature, the
+stems and boughs of other plants. The means of climbing may be:
+(1) by merely leaning upon or propping themselves up by the aid of
+the supporting object—examples, the rose, wistaria, star jessamine
+(_Jasminum officinalis_); (2) by coiling their main axes spirally
+around the support—hop, bean, morning-glory; (3) by means of
+adventitious roots—poison ivy, common English ivy, trumpet vine
+(_Tecoma radicans_); (4) by organs specially developed for the
+purpose, called tendrils—gourd, cucumber, grape, passion flower.
+
+[Illustration: FIG. 98.—Leaf of common pea, showing upper leaflets
+reduced to tendrils.]
+
+=97. Tendrils.=—The part assigned to do the work of climbing may be
+a secondary branch, a flower stem, a leafstalk, a leaf, a leaflet,
+or a group of leaflets (Fig. 98). Tendrils behave in general very
+much like twining stems, except that they are more sensitive and
+respond more quickly to any cause that may influence their movement.
+While young, their tips revolve just as do the tips of twining stems,
+until they meet with an object round which they can coil. When this
+happens, not only the part in contact with the object coils, but
+the free part between it and the main axis will usually respond by
+twisting itself into a helix (Fig. 99). As the distance between the
+base and tip of the tendril is shortened by coiling, the body of
+the plant is drawn upward proportionally. It will be observed that
+the helix is interrupted at one or more points, above and below
+which the coils turn in opposite directions. This is because the
+tendril is attached at both ends and cannot adjust itself to the
+opposite strains of torsion. Twist with your fingers a piece of tape
+so attached, and you will see that on one side of your hand it turns
+from right to left and on the other from left to right.
+
+=98. The cause of twining.=—Botanists are not fully agreed on this
+point. The explanation most generally accepted at present is that
+the twining of stems is due to the combined action of lateral and
+negative geotropism (51). The first causes one side to grow more
+rapidly than the other, thus forming a succession of coils, while
+the second, by stimulating the upward growth of the axis, stretches
+it into a spiral, and in this way draws it more tightly round the
+support. For this reason twining stems do best on an upright support.
+
+[Illustration: FIG. 99.—Stems of a passion flower transformed into
+tendrils. (_After_ GRAY.)]
+
+In tendrils, the twining is thought to be due not to gravity, but to
+contact with a solid body, which, by inducing unequal development
+on opposite sides of the tendril, causes it to turn about an
+available object. The coiling of the free part of the twining
+organ is in response to the stimulus transmitted from the part in
+contact—_stimulus_, in this sense, denoting the influence of any
+external agent that calls forth a responsive adjustment on the part
+of the plant.
+
+[Illustration: FIG. 100.—Showing the economy of labor and building
+material effected by the climbing habit. Notice how the grapevine
+coils like an anaconda around the tree boles, and overtops their
+tallest branches. Compare the diameter of the vine with that of the
+trees.]
+
+=99. The object of the various habits of stem growth.=—To bring
+the growing parts of the plant into the best possible relations
+with light and air is one of the special functions of the stem, and
+the various habits of growth described in this section have been
+developed with reference to this function. In the case of prostrate
+and underground stems other factors may intervene; can you name some
+of the causes that might influence the position of the stem in such
+cases?
+
+
+          Practical Questions
+
+  1. Why is the normal direction of most stems upright? (Exp. 56.)
+
+  2. Name a dozen woody-stemmed plants; a dozen with herbaceous stems.
+
+  3. Name all the plants you can think of that have prostrate stems,
+  or leaf rosettes that hug the earth, like mullein and dandelion.
+  Which of these are wintergreen plants? Which are hot-weather
+  growers?
+
+  4. Can you explain in what ways both hot-weather and cold-weather
+  plants may be advantaged by the habit of clinging close to the
+  earth? (94, 95.)
+
+  5. Is there any difference in the height of the stem of a dandelion
+  flower and a dandelion ball?
+
+  6. Of what advantage is this to the plant? (Exp. 17.)
+
+  7. Name all the means you can think of by which a stem may climb,
+  and give an example of each.
+
+  8. Why do we support peas with brush, and hops or beans with poles?
+  (98; Exp. 54.)
+
+  9. Are the vines of gourds, watermelons, squashes, and pumpkins
+  normally climbing or prostrate? How can you tell? (96, 97.)
+
+  10. Why does not the gardener provide them with poles or trellises
+  to climb on?
+
+  11. Do twining plants grow equally well on horizontal and upright
+  supports? (98; Exp. 54.)
+
+  12. If there is any difference, which do they seem to prefer?
+
+  13. Can you give any reasons for thinking that the climbing habit
+  might lead to parasitism? (83, 85, 87.)
+
+  14. What method of climbing would be most favorable to the
+  development of such a habit? (Suggestion: What mode of climbing
+  brings the stem into closest contact with its support?)
+
+  15. Name some plants the stems of which are used as food.
+
+  16. Name some from which gums and medicines are obtained.
+
+  17. Explain how it can benefit a plant to have its leaves, or some
+  of them, modified into tendrils. (99.)
+
+  18. In what way is the loss of the normal function of the leaves so
+  modified, compensated for? (Exp. 57.)
+
+  19. Suppose the vine shown in Fig. 100 had to lift itself without
+  the aid of a support; could it reach the same height and carry the
+  same weight of foliage and flowers with the same expenditure of
+  labor and building material?
+
+
+          II. MODIFICATIONS OF THE STEM
+
+  MATERIAL.—A shoot of asparagus; thorny branches of locust, plum, or
+  haw; a cactus plant; bulbs of lily and hyacinth or onion; tubers of
+  potato; rootstocks of iris, fern, or violet. If fresh specimens are
+  not accessible, dried rootstocks of the sweet flag and Florentine
+  iris may be obtained at the drug stores under the names of calamus
+  and “orris” root.
+
+=100. How to recognize modified parts.=—Stems, like roots, are often
+modified to serve other than their normal purpose, and in adapting
+themselves to these new functions they sometimes undergo such changes
+of form and structure that it would be impossible to recognize their
+true nature from appearances alone. The safest tests in such cases
+are: (1) by a comparison of the parts of the modified structure with
+those of known organs of the same kind; and (2) by observing its
+position in reference to other parts. For instance, we know that
+the stem is the part of the plant which normally bears leaves and
+flowers, and if either of these, or if the small scales which often
+take the place of leaves, are found growing on any plant structure,
+we may usually take for granted that it is a stem. Then, again, as
+will be shown in the next chapter, buds and branches naturally appear
+only at the nodes, in or near the _axil_, or inner angle made by a
+leaf with the stem. Hence, if you see any growth springing from such
+a position, you may generally conclude it to be a stem.
+
+[Illustration: FIG. 101.—Stem-leaves (cladophylls) of a ruscus,
+bearing flowers.]
+
+=101. Stems as foliage.=—The connection between stem and leaf is so
+intimate that we need not be surprised to find a frequent interchange
+of function between them, the leaf, or some part of it, doing the
+work of the stem (Fig. 98), the stem more often taking upon itself
+the office of the leaf. A common example is the garden asparagus.
+Examine one of the young shoots sold in the market, and notice that
+it bears a number of small scales in place of leaves. On an older
+shoot that has gone to seed, the green, threadlike appendages, which
+are usually taken for foliage, will be found to spring each from the
+axil of one of these scales. What, therefore, are we to conclude that
+it is?
+
+In the butcher’s-broom of Europe, the transformation has gone so far
+that the branches of the stem have assumed the flattened appearance
+of leaves (Fig. 101), but their real nature is evident both from
+their position in the axils of leaf scales, and from the fact that
+they bear flower clusters in the axil of a scale on their upper face.
+Another example of this sort of modification is seen in the pretty
+little _myrsiphyllum_ of the greenhouses (wrongly called smilax),
+which is so much used for decoration. The delicate green blades are
+merely altered stems, shortened and flattened to simulate leaves.
+
+[Illustration: FIG. 102.—Thorn branches of _Holocantha Emoryi_, a
+plant growing in arid regions.]
+
+=102. Weapons of defense.=—Conspicuous examples of these are the
+bristling thorns of the honey locust. Is their frequent branching
+any indication of their real nature? Does it _prove_ anything, or
+must you look for other evidence? What further indications might
+you expect to find, if they are true branching stems? (100.) On old
+haw, plum, crab, and pear trees, stems can be found in all stages
+of transition, from stubby, ill-developed branches, to well-defined
+thorns.
+
+[Illustration: FIG. 103.—Melon cactus, showing greatly condensed stem
+for the storage and preservation of moisture.]
+
+=103. Storage of nourishment.=—This is one of the most frequent
+causes of modification in both roots and stems. Of stems that grow
+above ground, the sugar cane probably comes first in economic
+importance on this account. In hot, arid regions, where the moisture
+drawn from the earth would, during prolonged drought, be too rapidly
+dissipated by an expanded surface of leaves, the whole plant, as
+in the case of the cactus, is sometimes compacted into a greatly
+thickened stem, which fills the triple office of leaf, stalk, and
+water reservoir.
+
+[Illustration: FIG. 104.—Rootstock of creeping panic grass.]
+
+=104. The uses of underground stems.=—It is in these that the storage
+of nourishment most frequently takes place, and the modifications
+that stems undergo for this purpose are in some cases so great that
+their real nature becomes apparent only after a careful examination.
+But while the chief function of underground stems is the storage of
+nourishment, they serve other purposes also. In plants requiring a
+great deal of moisture, like the ferns, and in others growing in dry
+places and needing to husband moisture carefully, like the blackberry
+lily, underground stems may be useful in preventing the too rapid
+evaporation that would take place through aërial stems. Defense
+against frost, cold, heat, and other dangers, as well as quickness of
+propagation, are also attained or assisted by this means.
+
+=105. Rootstocks and rhizomes.=—From a prostrate stem like that
+shown in Fig. 95 to a creeping rootstock like the one in Fig. 104,
+the transition is so easy that we find no difficulty in accounting
+for it. From the prostrate rootstock to the thickened storage
+rhizome (Fig. 105) of such plants as the iris, puccoon, bulrush, and
+Solomon’s-seal, is a longer step, but the bud with its leaf scales
+at the growing tip, _a_, the remains of the flower stem at the node,
+_b_, and the roots from the under surface sufficiently indicate its
+nature. The peculiar scars from which the Solomon’s-seal takes its
+name are caused by the falling away each year of the flowering stem
+of the season after its work is done, leaving behind the node of the
+underground stem from which it originated. In this way the rhizome
+lives on indefinitely, growing and increasing at one end as fast as
+it dies at the other. Test a little of the substance of the rhizome
+with iodine. Of what does it consist? Of what use is it to the plant?
+
+[Illustration: FIG. 105.—Rhizome of Solomon’s-seal: _a_, growing bud
+at the tip; _b_, remains of the past season’s flower stem; _c_, _c_,
+_c_, scars of old stems. (_After_ GRAY.)]
+
+[Illustration: FIG. 106.—Potato tuber showing lenticels, _A_, _A_, or
+pores for air on the surface; _S_, leaf scale, or scar.]
+
+=106. The tuber.=—A still further thickening and shortening of
+the rhizome gives rise to the tuber, of which the potato and the
+Jerusalem artichoke are familiar examples. Can you give any evidence
+to show that the potato is a modified stem? Find the point of
+attachment of the tuber to its stem and stand it on this end, which
+is its natural base. Notice that the eye sits in the axil of the
+little scale that forms the eyelid. What does the scale represent?
+What is the eye? (100.) Do the scales occur in any regular order—that
+is, opposite, or alternating with, each other, like the leaves on
+a stem? Look on the surface for a number of small, lens-shaped
+dots (_A_, _A_, Fig. 106) scattered irregularly over it. These are
+aërating pores called _lenticels_, and are found in most dicotyl
+stems. Does their presence help to throw light on the real nature
+of the tuber? If any sprouts occur on your specimen, where do they
+originate? Where do buds and sprouts originate on plants above
+ground? Make a sketch of the outside of a potato, showing the
+lenticels, eyes, and scales, or the scars left by the scales in case
+they have fallen away, as has probably happened, if your specimen is
+an old one.
+
+[Illustration: FIGS. 107, 108.—Transverse and longitudinal sections
+of the potato: _A_, skin; _B_, cortical layer; _C_, outer pith layer;
+_D_, inner pith layer.]
+
+Cut a small slice from the stem end of two potatoes, stand them in
+coloring fluid for four or five hours, then divide into cross and
+vertical sections, as shown in Figs. 107, 108, and draw, labeling the
+parts that you can make out. Through which has the liquid ascended
+most rapidly? Test with iodine and find out in which part nourishment
+is most abundant. It is this abundant store of food that makes
+the potato such a valuable crop in cold countries like Norway and
+Iceland, where the seasons are too short to admit of the slow process
+of developing the plant from the seed.
+
+[Illustration: FIG. 109.—Scaly bud of oak, enlarged.]
+
+[Illustration: FIG. 110.—Scaly bulb of lily (GRAY).]
+
+Compare a common potato with a sweet potato. Are there any eyes or
+buds on the latter? Is there a scale below them? Do they occur in any
+regular order? Do you see any lenticels? The common potato and the
+sweet potato are both tubers; can you give some of the reasons why
+the one is regarded as a modified branch, and the other as a root?
+(100.) Compare their food contents; which contains most starch? Which
+most sugar? How can you judge about the sugar without a chemical test?
+
+=107. The bulb= is a form of underground stem reduced to a single
+bud. Get the scaly bulb of a lily, and sketch it from the outside
+and in cross and vertical section. Compare it with the scaly winter
+buds of the oak and hickory, or other common deciduous tree. Make an
+enlarged sketch of the latter on the same scale as the lily bulb, and
+the resemblance will at once become apparent. The scales of the bulb
+are, in fact, only thick, fleshy leaves closely packed around a short
+axis that has become dilated into a flat disk. From the center of
+the disk, which is the terminal node of this transformed stem, rises
+the flower stalk, or _scape_, as it is called, of the season. After
+blossoming, the scape perishes with its bulb, and their place is
+taken by new ones which are developed from the axils of the scales,
+thus revealing their leaflike nature.
+
+[Illustration: FIG. 111.—Leaf of an onion divided lengthwise showing
+the base enlarged into the coat of a bulb.]
+
+That bulbs are only modified buds is further shown by the bulblets
+that sometimes appear among the flowers of the onion, and in the leaf
+axils of certain lilies. They never develop into branches, but drop
+off and grow into new plants just as the subterranean bulbs do.
+
+The bulbs of the onion and hyacinth are still further modifications,
+in which the scales consist of the thickened bases of leafstalks that
+are dilated until each one completely envelops the growing parts
+within.
+
+=108. Morphology= is the part of botany that treats of the origin,
+form, and uses of the different organs of plants, and of the
+modifications they undergo in adapting themselves to changes of
+condition or function. Organs or parts that have the same origin
+but have become adapted to different functions, like the flattened
+stems of the butcher’s-broom or the bulb scales of the lily, are
+said to be _homologous_; those that are different in origin but
+adapted to the same function, as the sweet and common potatoes, are
+_analogous_. In other words, homologous organs are morphologically
+alike, but may be physiologically different; analogous organs are
+alike physiologically, but differ morphologically.
+
+=109. Economic value of stems.=—We probably get a greater variety
+of economic products from the stem than from any other part of the
+plant. Consider the vast amount of food stored in underground stems
+like the potato; the resins, gums, and sugar found in the sap of
+plants like the sugar cane, the pine, and India-rubber trees; the
+medicines, dyes, and extracts obtained from the tissues; the valuable
+fibers, such as flax, jute, and hemp, furnished by the bast; the wood
+pulp for making paper; and the timber for building and furnishing
+our houses that we get from the woody trunks of trees. When we think
+of all these things, it seems hardly possible to overestimate the
+importance of this part of the vegetable kingdom to man, or to exert
+ourselves too strenuously to regulate and prevent the destruction of
+these invaluable natural resources.
+
+
+          Practical Questions
+
+  1. Would you judge from the observations made in the foregoing
+  section, that the work of an organ determines its form, or that the
+  form determines its work? (99, 100, 108.)
+
+  2. Which is the more important, form or function?
+
+  3. Name some plants that are propagated by rootstocks; by runners
+  or stolons; by rhizomes; by tubers; by bulbs.
+
+  4. What is the advantage of propagating in this way over planting
+  the seed? (104, 106.)
+
+  5. Mention any other advantages that the various plants named may
+  gain from the development of their underground parts. (104.)
+
+  6. What makes the nut grass so troublesome to farmers in some parts
+  of the country?
+
+  7. Is its “nut” a root or a tuber? How can you tell? (106.)
+
+  8. Suggest some ways for destroying weeds that are propagated in
+  this way.
+
+  9. Could you get rid of wild onions in a pasture by mowing them
+  down? By digging them up? (107.)
+
+  10. Is it wise for farmers to neglect the appearance of such a weed
+  in their neighborhood, even though it does not infest their own
+  land?
+
+  11. Name any plants of your neighborhood, either wild or
+  cultivated, that are valued for their rhizomes; for their tubers.
+
+  12. What part of the plants named below do we use for food or other
+  purposes? Ginger, angelica, ginseng, cassava, arrowroot, garlic,
+  onion, sweet flag, iris, sweet potato, Cuba yam, artichoke.
+
+  13. Why are the true roots of bulbous and rhizome-bearing plants
+  generally so much smaller in proportion to the other parts than
+  those of ordinary plants? (89, 104.)
+
+  14. If the Canada thistle grows in your vicinity, examine the roots
+  and see if there is anything about them that will help to account
+  for its hardihood and persistency.
+
+  15. If you live in the region of the horse nettle (_Solanum
+  Carolinense_), explain how it is helped by its root system. (89.)
+
+
+          III. STEM STRUCTURE
+
+
+     A. MONOCOTYLS
+
+  MATERIAL.—Fresh cornstalks with several well-developed nodes, some
+  of which should have stood in coloring fluid from 1 to 3 hours. If
+  fresh specimens cannot be obtained from the fields, a number of
+  seedlings may be grown in boxes of rich earth and cared for by the
+  pupils either at home or in the schoolroom; they should be planted
+  4 or 5 weeks before needed. Asparagus and smilax sprouts may be
+  used, or the stem of any large grass, or of wheat and other grains,
+  but stalks of corn or sugar cane make the best subjects for study
+  where they can be obtained.
+
+  APPLIANCES.—A compound microscope will be needed for detailed
+  study. Prepared slides can be used, but it is better for students
+  to make their own sections where practicable.
+
+[Illustration: FIG. 112.—Cross section of a cornstalk (reduced): _v_,
+fibrovascular bundles; _c_, cortex; _p_, pith.]
+
+=110. Gross anatomy of a monocotyl stem.=—Obtain a fresh
+cornstalk,—preferably one that has begun to tassel,—and observe its
+external characters. How are the internodes divided from one another?
+What is the use of the very firm, smooth epidermis? Notice a hollow,
+grooved channel running down one side between the _joints_, or nodes;
+does it occur in all of them? Is it on the same side or on the
+opposite sides of alternate internodes? Follow one of these grooves
+to the node from which it originates; what do you find there? After
+studying the internal structure of the stalk, you will understand why
+this groove should occur on the side of an internode bearing a bud or
+fruit.
+
+Cut a cross section midway between two nodes, and observe the
+composition of the interior; of what does the bulk of it appear to
+consist? Notice the arrangement of the little dots, like the ends of
+cut-off threads, that are scattered through the pith; where are they
+most abundant, toward the center or the circumference?
+
+[Illustration: FIG. 113.—Vertical section of cornstalk (reduced):
+_g_, groove; _c_, cortex; _v_, fibrovascular bundles mingled with
+parenchyma; _b_, bud; _n_, node.]
+
+Make a vertical section through one of the nodes. Cut a thin slice
+of the pith, hold it up to the light, and examine with a hand lens.
+Observe that it is composed of a number of oblong cells packed
+together like bricks in a wall. These are filled with protoplasm
+and cell sap, and constitute what is known to botanists as the
+_parenchyma_ or fundamental tissue from which all the other tissues
+are derived. Apply the iodine test; in what parts does starch occur
+most abundantly?
+
+Draw out one of the woody threads running through the pith. Break
+away a bit of the epidermis, and see how very closely they are packed
+on its inner surface. Trace the course of the veins in the bases
+of the leaves; find their point of union with the stem; with what
+part of it do they appear to be continuous? Has this anything to do
+with the greater abundance of fibers near the epidermis? Can you
+follow the fibers through the nodes, or do they become confused and
+intermixed with other threads there? (If a stalk of sugar cane can be
+obtained, the ring of scars left by the vascular bundles as they pass
+from the leaves into the stem will be seen beautifully marked just
+above the nodes.)
+
+If there is an eye or bud at the node, see if any of the threads go
+into it. Can you account now for the depression that occurs in the
+internode above the eye?
+
+Make drawings of both cross and vertical sections, showing the points
+brought out in your examination of the cornstalk.
+
+=111. The vascular system.=—To find out the use of the threads that
+you have been tracing, examine a piece of a living stem that has
+stood in red ink for three to twenty-four hours. Notice the course
+the coloring fluid has taken; what would you infer from this as to
+the use of the woody fibers?
+
+These threads constitute what is called the _vascular system_ of the
+stem, because they are made up of _vessels_ or _ducts_, along which
+the sap is conveyed from the roots to the leaves and back from the
+leaves to the parts where it is needed after it has contributed to
+the elaboration of food.
+
+On account of this double line of communication which they have to
+maintain, the vascular threads, or _bundles_, as they are technically
+called, are double; one part composed of larger vessels, carrying
+water up, the other consisting of smaller ones, bringing back the
+food. Can you give a reason for their difference in size?
+
+[Illustration: FIG. 114.—Longitudinal section through the stem of a
+palm, showing the curved course of the fibrovascular bundles (GRAY,
+_after_ FALKENBERG).]
+
+=112. Woody monocotyls.=—Examine sections of yucca, smilax, or
+of palmetto from the handle of a fan, and compare them with your
+sketches of the cornstalk. In which are the vascular fibers most
+abundant? Which is the toughest and strongest? Why? Trace the course
+of the leaf fibers from the point of insertion to the interior. How
+does it differ from that of the fibers in a cornstalk?
+
+=113. Growth of monocotyl stems.=—After tracing the course of the
+leaf veins at the nodes of the cornstalk, you will have no difficulty
+in identifying these veins as part of the vascular system. In jointed
+stems like those of the corn and sugar cane and other grasses, their
+intercalation between the vascular bundles of the stem takes place,
+as we have seen, at the nodes, forming the hard rings known as
+joints; but in other monocotyls the fibers entering the stem from the
+leaves usually tend first downward, toward the interior (Fig. 114),
+then bend outward, toward the surface, where they become entwined
+with others and form the tough, inseparable cortex that gives to
+palmetto and bamboo stems their great strength. Generally, monocotyl
+stems do not increase in diameter after a certain point, and as
+they can contain only a limited number of vascular fibers, they are
+incapable of supporting an extended system of leaves and branches.
+Hence plants of this class, with a few exceptions, like smilax and
+asparagus, are characterized by simple, columnar stems and a limited
+spread of leaves. Such plant forms are admirably adapted by their
+structure to the purposes of mechanical support. It is a well-known
+law of mechanics that a hollow cylinder is a great deal stronger than
+the same mass would be in solid form, as may easily be tested by the
+simple experiment of breaking in your fingers a cedar pencil and a
+joint of cane or a stem of smilax of the same weight. In stems that
+may be technically classed as solid in structure, like the corn and
+palmetto, the interior is so light compared with the hard epidermis
+that the result is practically a hollow cylinder.
+
+[Illustration: PLATE 4.—Forest of bamboo, showing the tall, straight,
+branchless habit of monocotyl stems.]
+
+=114. Minute study of a monocotyl stem.=—Place under the microscope
+a very thin transverse section of a cornstalk. The little dots that
+looked like the cut ends of threads to the naked eye will now appear
+as the complex group of cells shown in Fig. 115. The same parts are
+shown longitudinally in Fig. 116. As seen in cross section, their
+arrangement suggests a grotesque resemblance to the face of an old
+woman wearing a pair of enormous spectacles and surrounded by a cap
+frill of netting with very wide meshes. These are parenchyma cells,
+_f_, _f_, Fig. 115, and constitute the greater portion of the living
+tissues.
+
+[Illustration: FIG. 115.—Transverse section through the fibrovascular
+bundle of a cornstalk: _a_, annular tracheid; _sp_, spiral tracheid;
+_m_ and _m′_, ducts; _l_, air space; _v_, sieve tubes; _s_, companion
+cells; _vg_, strengthening fibers; _cp_, bast; _f_, _f_, parenchyma.]
+
+[Illustration: FIG. 116.—Vertical section of the same; _a_ and _a′_,
+rings of a decomposed annular tracheid; _v_, sieve tubes; _s_,
+companion cells; _cp_, bast; _l_, air space; _vg_, strengthening
+tissue; _sp_, spiral duct.]
+
+The two large openings, _m_, _m′_, that represent the spectacles, are
+ducts for carrying water _up_ the stem. They are called pitted ducts
+on account of the bordered pits which cover their outer surface. The
+two smaller openings between and slightly below the pitted ducts are
+also vessels for carrying liquids up the stem. The lower one, _a_,
+is called the annular _tracheid_ because its tube is strengthened
+by rings on the inside. The upper, smaller one, _sp_, is known as
+the spiral tracheid, because its walls are reinforced by spiral
+thickenings. Can you think what is the use of these strengthening
+contrivances in the walls of conducting cells? (Suggestion: What is
+the use of the spiral wire on a garden hose?) The large, irregular
+opening below the ducts is an air space. What is its object? Why has
+it no surrounding wall?
+
+Next look above the ducts for a group of rhomboidal or hexagonal
+cells, _v_, _v_, with smaller ones, _s_, between them. The larger of
+these are _sieve tubes_, the smaller ones, _companion cells_. The
+sieve tubes carry sap _down_ the stem after it has been made into
+food by the leaves. They get their name from the sievelike openings
+between the connecting walls of the cells which form them—as if a row
+of pepper boxes with perforations at both top and bottom were placed
+end to end, so as to form a long tube divided into compartments
+by perforated walls. Can you give a reason why the cells of ducts
+that carry elaborated nutriment should have a more open line of
+communication than those carrying crude sap? [56 (2).] Which one of
+the organic food substances was shown by Exp. 39 to be unable, or
+nearly so, to pass through the cell wall by osmosis? [56 (4).] The
+conducting cells are surrounded by a mass of strengthening fibers
+separating them from the parenchyma, _f_, and constituting with
+them a _fibrovascular bundle_. The larger vessels, _m_, _m′_, _a_,
+and _sp_, compose the _xylem_, the harder, more woody part of the
+bundle, and the smaller ones, _v_, _s_, the _phloëm_, or softer part.
+Notice also that there is no parenchyma in contact with the xylem
+and phloëm in the fibrovascular bundles of a monocotyl, to supply
+material for new growth, but they are entirely surrounded by a sheath
+of strengthening tissue, whence such bundles are said to be _closed_,
+and are incapable of further growth by the addition of new cells.
+
+[Illustration: FIG. 117.—Horizontal view of the sieve tube of a gourd
+stem, showing perforations.]
+
+[Illustration: FIG. 118.—Side view of the sieve tube of a gourd
+stem: _pr_, protoplasm layer; _u_, albuminous contents, forming
+mucilaginous strand.]
+
+
+     B. HERBACEOUS DICOTYLS
+
+  MATERIAL.—Young stems of sunflower, hollyhock, burdock, ragweed,
+  cocklebur, castor bean, or any large herbaceous plant. In schools
+  unprovided with compound microscopes, the minute anatomy can be
+  studied with some degree of profit by the aid of pictures.
+
+=115. Gross anatomy.=—Examine the outside of a young stem of
+sunflower, burdock, or other herbaceous dicotyl. Notice whether it
+is smooth, or roughened with hairs, scales, ridges, or grooves. If
+hairy, observe the nature of the hairs, whether bristly, downy,
+sticky, etc. Notice the color of the epidermis, whether uniform, or
+splotched or striped with other colors, as, for example, jimson weed,
+and pigweed (amarantus). If there are any buds, branches, or flower
+stems, notice where they originate; what is the angle between the
+leaf and stem called? (100.)
+
+Make a transverse cut through a portion of the stem that has stood
+for a time in coloring fluid and examine with a lens. Four regions
+can easily be distinguished: (1) the epidermis, _e_, Fig. 119; (2)
+the primary cortex, _c_; (3) a ring of fibrovascular bundles, _f_;
+and (4) a central cylinder of parenchyma, _p_. In some specimens
+there will be a fifth region, the pith, which will appear in the
+section as a white circular spot in the center of the parenchyma.
+
+[Illustration: FIG. 119.—Transverse section of a very young stem
+of burdock, showing fibrovascular bundles not completely united
+into a ring: _e_, epidermis; _c_, primary cortex; _f_, a ring of
+fibrovascular bundles; _p_, central cylinder of parenchyma.]
+
+In specimens a little older than the one shown in Fig. 119, a narrow
+circular line will be seen running through the ring of bundles nearly
+midway between their inner and outer extremities, connecting them
+into an unbroken circle around the central cylinder. This is the
+_cambium_ layer, which supplies the vascular region with materials
+for new growth, and thus enables dicotyl stems to increase in
+diameter by the successive addition of fresh vascular rings from year
+to year.
+
+Examine in the same way a vertical section, and find the parts
+corresponding to those shown in Fig. 119. Make enlarged sketches of
+both sections, labeling the various parts observed.
+
+=116. Minute structure of a dicotyl stem.=—Place successively under
+a high power of the microscope thin transverse and longitudinal
+sections of the stem just examined, or such other specimen as the
+teacher may provide. Bring one of the fibrovascular bundles into the
+field, and try to make out the parts shown in Figs. 120 and 121.
+The corresponding parts in the two sections are indicated by the
+same letters. Notice the cortex, _R_, on the outside and the pith,
+_M_, on the inside; between these, the cambium, _C_, the _xylem_,
+or woody tissue, included between the radiating lines _X_, and the
+newer tissues composing the _phloëm_ between the lines _P_. The
+cambium and pith, which includes the medullary rays so conspicuous
+in perennial stems, are composed of live parenchyma cells, from
+which alone growth can take place; they are the active part of the
+stem. The xylem contains the large vessels, _t_ and _s_, that convey
+water _up_ the stem, together with the wood fibers, _h_. These are
+the permanent tissues. After completing their growth the cells of
+the xylem gradually lose their protoplasm, and all vitality ceases.
+Even the cell sap disappears, and sometimes the walls of the ducts
+are disintegrated, leaving a mere air space like that shown at _l_
+in Figs. 115 and 116. The dead cells and tissues, however, are by
+no means useless. They constitute the heartwood that is so valuable
+for timber, and serve an important purpose as a mechanical support
+for the stem. The phloëm contains on its outer face a mass of hard
+fibers, _b_, called bast, and toward the interior, the sieve tubes,
+_sb_, with a number of smaller vessels that convey _down_ the stem
+the sap containing the food made in the leaves. It is separated from
+the cortex by the bundle sheath, _e_, and on its other side, from
+the exterior face of the xylem by the cambium, _C_. In this position
+the growing cambium adds new cells to the inner side of the phloëm,
+and to the outer side of the xylem, so that the former grows on its
+inner face and the latter on its outer. In perennial plants, as new
+rings are added to the xylem from season to season, the older ones
+die and are changed into heartwood, which thus gradually increases in
+thickness till in some of the giant redwoods and eucalypti, it may
+attain a diameter of thirty-five or forty feet. In the phloëm, on
+the other hand, as new cells are added from within, the older ones
+are gradually changed into hard bast, _b_, then into bark, and are
+finally sloughed off and fall to the ground. It is this free line of
+communication with the active cambium that enables dicotyl stems to
+grow on indefinitely, the sheath, _e_, being formed on the exterior
+face of the bundles only, leaving the other free, whence they are
+said to be _open_.
+
+[Illustration: FIGS. 120-121.—Transverse and longitudinal sections of
+a fibrovascular bundle in the stem of a sunflower. The two sections
+are lettered to correspond: _M_, pith (parenchyma); _X_, xylem
+region; _P_, phloëm; _R_, cortex; _s_, spiral ducts; _s′_, annular
+ducts; _t_, _t_, pitted ducts; _C_, cambium between the phloëm and
+xylem regions; _sb_, sieve tubes; _b_, bast; _e_, bundle sheath;
+_ic_, cambium (parenchyma) cells; _h_, wood fibers.]
+
+Make drawings of cross and vertical sections of a dicotyl stem as
+it appears under the microscope, labeling correctly all the parts
+observed. Show the shape and relative size of the different cells.
+Compare your drawings with those made in your study of monocotyl
+stems, and write in your notebook the essential points of difference
+between the two.
+
+[Illustration: FIG. 122.—Internal structure of a pine stem, showing
+longitudinal section of a fibrovascular bundle through a medullary
+ray, _sm_, _sm′_; _s_, tracheids; _t_, bordered pits, surface view;
+_c_, cambium; _v_, sieve tubes; _vt_, sieve pits, analogous to the
+sieve plates in dicotyl stems.]
+
+[Illustration: FIG. 123.—Internal structure of a pine stem, showing
+transverse section of a tracheid: _i_, cell walls; _m_, intermediate
+layer between walls of adjoining cells; _m′_, intercellular space
+here occupied by substance of intermediate layer; _b_, bordered pit
+in section at right angles to the surface; _t_, membrane for closing
+the pit canal.]
+
+=117. The stems of conifers=, the group of Gymnosperms to which the
+pine belongs, do not differ greatly from those of dicotyls, the
+chief difference being that the vascular bundles contain tracheids
+only, corresponding to the smaller vessels of the phloëm, _s_ and
+_s′_, shown in Fig. 121. These tracheids have large sunken places in
+their walls, called bordered pits (Fig. 123), closed by a very thin
+membrane through which water and dissolved food materials can more
+readily percolate. In all other essentials, the internal structure of
+pine stems is like that of dicotyls. (See Plate 5.)
+
+
+     C. WOODY STEMMED DICOTYL
+
+  MATERIAL.—Elm, basswood, mulberry, leatherwood, and pawpaw show the
+  bast well; sassafras, slippery elm, and (in spring) hickory and
+  willow show the cambium; grape and trumpet vine, the ducts. Some
+  of the specimens used should be placed in coloring fluid from 3 to
+  8 hours before the lesson begins. The rate at which the liquid is
+  absorbed varies with the kind of stem and the season. It is more
+  rapid in spring and slower in winter. If a cutting stands too long
+  in the fluid, the dye will gradually percolate through all parts of
+  it; care should be taken to guard against this.
+
+[Illustration: FIG. 124.—Part of a young China tree shoot, showing,
+_A_, lenticels; _B_, leaf scar; _C_, _C_, traces left by the broken
+ends of fibrovascular bundles that passed from the stem into the
+leaf. Natural size.]
+
+=118. The external layer.=—While the primary structures, as shown
+in the last section, are essentially the same in all dicotyl stems,
+the continued yearly growth of perennials causes them to develop
+a number of secondary structures and variations of detail that
+differentiate them in a marked degree from soft-stemmed annuals. Take
+a piece of a three-year-old shoot of cherry, horse chestnut, or any
+convenient hardwood tree, and notice that the soft, green epidermis
+has given place to a thicker, harder, and usually darker colored
+bark. Notice the presence of lenticels (106) and their porous, corky
+texture for the admission of air to the interior. They are slightly
+raised above the surface of the bark, and are usually round, or more
+or less elongated in different directions, according as they are
+stretched vertically or horizontally by the growth of the axis. The
+characteristic markings of birch bark, which make it so ornamental,
+are due to the lenticels. In most trees they disappear on the older
+parts, where the bark is constantly breaking away and sloughing off.
+
+[Illustration: PLATE 5.—Stem of a conifer, _Sequoia gigantea_,
+Mariposa Grove, California. The first branch, 6 feet in diameter,
+leaves the parent trunk 125 feet above the ground. The photographer
+sitting on one of the exposed roots affords a good standard for
+comparison. The tree is noted for its massive limbs. The smaller
+trees in the background show the characteristic mode of branching in
+trees of this class.]
+
+=119. Internal structures.=—Cut a transverse section through your
+specimen, and notice under the epidermis a greenish layer of young
+bark; beneath this a layer of rather tough, stringy bast fibers, and
+beyond these a harder woody substance that constitutes the bulk of
+the interior; within this, at the very center of the axis, we find
+a cylinder of lighter texture, the pith, or medulla, occupying the
+place of the soft parenchyma which fills this space in very young
+stems.
+
+Between the woody axis and the bark notice a more or less soft and
+juicy ring.
+
+=120. The cambium layer.=—This is not always easily distinguishable
+with a hand lens, but is conspicuous in the stems of sassafras,
+slippery elm, and aristolochia. If some of these cannot be obtained,
+the presence of the cambium can be recognized by observing the
+tendency of most stems to “bleed,” when cut, between the wood and
+bark. The reason for this is because the cambium is the active part
+of the stem, in which growth is taking place, and consequently it is
+most abundantly supplied with sap. In spring, especially, it becomes
+so full of sap that if a rod of hickory or elder is pounded, the
+pulpy cambium is broken up and the bark may be slipped off whole from
+the wood.
+
+=121. Medullary rays.=—Observe the whitish, silvery lines that
+radiate in every direction from the center, like the spokes of a
+wheel from the hub. These are the medullary rays, and consist of
+threads of pith that serve as lines of communication between the
+“central cylinder” and the growing cambium layer. In old stems the
+central pith frequently disappears and its office is filled by the
+medullary rays, which become quite conspicuous.
+
+[Illustration: FIGS. 125, 126.—Cross sections of twigs: 125, section
+across a young twig of box elder, showing the four stem regions: _e_,
+epidermis, represented by the heavy bounding line; _c_, cortex; _w_,
+vascular cylinder; _p_, pith; 126, section across a twig of box elder
+three years old, showing three annual growth rings, in the vascular
+cylinder. The radiating lines (_m_), which cross the vascular region
+(_w_), represent the pith rays, the principal ones extending from the
+pith to the cortex (_c_). (_From_ COULTER’S “Plant Relations.”)]
+
+=122. Structural regions of a woody stem.=—Sketch cross and vertical
+sections of your specimen, as seen under the lens, labeling the
+different parts. Refer to Figs. 125, 126, if you have any difficulty
+in distinguishing the parts. In a year-old shoot (Fig. 125), the
+structural regions correspond closely to those shown in Fig. 119,
+except that the ring of fibrovascular bundles is here compact and
+woody, and crossed by the radiating lines of the medullary rays. In
+a three-year-old shoot (Fig. 126), the main divisions are the same,
+but the soft parenchyma of the central cylinder is replaced by the
+pith, and the vascular ring is composed of three layers corresponding
+to the three years of growth. In general, mature dicotyl stems may be
+said to include four well-defined regions: (1) the epidermis, or the
+bark; (2) the cortex, made up of bast and certain other tissues; (3)
+the cambium; (4) the woody vascular cylinder, made up of concentric
+rings, each representing a year’s growth. The pith, or medulla,
+constitutes a fifth region, but is obvious only in young stems.
+Notice the little pores or cavities that dot the woody part in the
+cross section; where are they largest and most abundant? How are the
+rings marked off from one another? These pores are the sections of
+ducts. They are very large in the grapevine, and a cutting two or
+three years old will show them distinctly. Examine sections of a twig
+that has stood in red ink from three to twelve hours, and observe
+the course the fluid has taken. How does this accord with the facts
+observed in your study of the conducting tissues in monocotyl and
+herbaceous stems? (111, 115, 116.)
+
+[Illustration: FIG. 127.—Diagram illustrating the annual growth of
+dicotyledons.]
+
+=123. The rings= into which the woody cylinder is divided mark the
+yearly additions to the growth of the stem, which increases by the
+constant accession of new material to the outside of the permanent
+tissues (116). The cambium constantly advances outward, beginning
+every spring a new season’s growth, and leaving behind the ring of
+ducts and woody fibers made the year before. As the work of the plant
+is most active and its growth most vigorous in spring, the largest
+ducts are formed then, the tissue becoming closer and finer as the
+season advances, thus causing the division into annual rings that is
+so characteristic of woody dicotyl stems. Each new stratum of growth
+is made up of the fibrovascular bundles that supply the leaves and
+buds and branches of the season. In this way we see that the increase
+of dicotyl trunks and branches is approximately in an elongated cone
+(Fig. 127), the number of rings gradually diminishing toward the top
+till at the terminal bud of each bough it is reduced to a single one,
+as in the stems of annuals.
+
+Sometimes a late autumn, succeeding a very dry summer, will cause
+trees to take on a second growth, and thus form two layers of wood
+in a single season. On this account we cannot always rely absolutely
+upon the number of rings in estimating the age of a tree, though the
+method is sufficiently exact for all practical purposes.
+
+
+          Practical Questions
+
+  1. Old Fort Moultrie near Charleston was built originally of
+  palmetto logs; was this good engineering or not? Why? (113.)
+
+  2. Explain the advantages of structure in a culm of wheat; a stalk
+  of corn; a reed. (113.)
+
+  3. Would the same quality be of advantage to an oak? Why, or why
+  not?
+
+  4. Is it of any advantage to the farmer that grain straw is so
+  light?
+
+  5. Explain why boys can slip the bark from certain kinds of wood in
+  spring to make whistles. (120.)
+
+  6. Why cannot they do this in autumn or winter? (123.)
+
+  7. Name some of the plants commonly used for this purpose.
+
+  8. Is the spring, after the buds begin to swell, a good time to
+  prune fruit trees and hedges? (120.)
+
+  9. What is the best time, and why?
+
+  10. Why are grapevines liable to bleed to death if pruned too late
+  in spring? (120, 123.)
+
+  11. Why are nurserymen, in grafting, so careful to make the cambium
+  layer of the graft hit that of the stock? (120.)
+
+  12. In calculating the age of a tree or bough from the rings of
+  annual growth, should we take a section from near the tip, or from
+  the base? Why? (123.)
+
+
+          IV. THE WORK OF STEMS
+
+  MATERIAL.—Leafy shoots of grape, balsam, peach, or other active
+  young stems; a cutting of willow, currant, or any kind of easily
+  rooting stem. Two bottles of water and some linseed or cottonseed
+  oil.
+
+[Illustration: FIG. 128.—Experiment showing that moisture is thrown
+off by the leaves of plants.]
+
+  EXPERIMENT 58. DO THE LEAVES HAVE ANY ACTIVE PART IN EFFECTING THE
+  MOVEMENT OF SAP IN THE STEM?—Take two healthy young shoots of the
+  same kind—grape, peach, corn, tropæolum, calla lily absorb rapidly.
+  Trim the leaves from one shoot and close the cut surfaces with
+  a little vaseline or gardener’s wax to prevent loss of water by
+  evaporation. Place the lower end of each in a glass jar or tumbler
+  filled to the same height with water. Cut off _under water_ a
+  half inch from the bottom of each shoot, to get a fresh absorbing
+  surface. This is necessary because exposure to air for even a
+  second greatly hinders absorption by permitting the entrance of air
+  into the severed ends of the ducts. Pour a little oil on the water
+  in both jars to prevent evaporation. (Do not use kerosene; it is
+  injurious to plants.) At the end of twenty-four hours, which vessel
+  has lost the more water? How do you account for the difference?
+
+  EXPERIMENT 59. WHAT BECOMES OF THE WATER THAT GOES INTO THE
+  LEAVES?—Cover the top of the vessel containing the leafy twig used
+  in the last experiment with a piece of cardboard, having first
+  cut a slit in one side, as shown in Fig. 128, so that it can be
+  slid into place without injuring the stem. Invert over the twig a
+  tumbler that has first been thoroughly dried, and leave in a warm,
+  dry place. After an hour or two, what do you see on the _inside_ of
+  the tumbler? Where did the moisture come from?
+
+[Illustration: FIG. 129.—A twig which had been kept standing in water
+after the removal of a ring of cortical tissue: _a_, level of the
+water; _b_, swelling formed at the upper denudation; _c_, roots.]
+
+  EXPERIMENT 60. THROUGH WHAT PART OF THE STEM DOES THE SAP FLOW
+  UPWARD?—Remove a ring of the cortical layer from a twig of any
+  readily rooting dicotyl, such as willow, being careful to leave the
+  woody part, with the cambium, intact. Place the end _below_ the cut
+  ring in water, as shown in Fig. 129. The leaves above the girdle
+  will remain fresh. How is the water carried to them? How does this
+  agree with the movement of red ink observed in 115 and 122?
+
+  EXPERIMENT 61. THROUGH WHAT PART DOES THE SAP COME DOWN?—Next prune
+  away the leaves and protect the girdled surface with tin foil, or
+  insert it below the neck of a deep bottle to prevent evaporation,
+  and wait until roots develop. Do they come more abundantly from
+  above or below the decorticated ring?
+
+=124. The three principal functions of the stem= are:—(1) to serve
+as a mechanical support and framework for binding the other organs
+together and bringing them into the best attainable relations with
+light and air; (2) as a water carrier, or pipe line, for conveying
+the sap from the roots to the parts where it is needed; and (3) as a
+receptacle for the storage of foods.
+
+=125. Movement of water.=—It has already been shown (71, 111) that
+a constant interchange of liquid is taking place through the stem,
+between the roots, where it is absorbed from the ground, and the
+leaves, where it is used partly in the manufacture of food. Just
+what causes the rise of sap in the stem is one of the problems of
+vegetable physiology that botanists have not yet been able to solve.
+There are, however, certain forces at work in the plant, which,
+though they may not account for all the phenomena of the movement,
+undoubtedly influence them to a great extent. From experiments 58-61,
+we can obtain an idea of what some of these forces may be.
+
+[Illustration: FIG. 130.—The stump of a large oak that was injured by
+lightning many years ago. The interior is completely decayed, leaving
+only a hollow shell of living tissue, from which branches continue to
+put forth leaves year after year.]
+
+=126. Direction of the current.=—These experiments show that the
+upward movement of crude sap toward the leaves is mainly through the
+ducts in the woody portion of the stem, while the downward flow of
+elaborated sap from the leaves takes place chiefly through the soft
+bast and certain other vessels of the cortical layer. The action of
+the leaves in giving off part of the water absorbed, as shown in Exp.
+59, probably has also an important influence on the course of sap
+movement. If loss of water takes place in any organ through growth or
+other cause, the osmotic flow of the thinner sap from the roots will
+set in that direction.
+
+=127. Ringing fruit trees.=—The course of the sap explains why
+farmers sometimes hasten the ripening of fruit by the practice of
+_ringing_. As the food material cannot pass below the denuded ring,
+the parts above become gorged, and a process of forcing takes place.
+The practice, however, is not to be commended, except in rare cases,
+as it generally leads to the death of the ringed stem. The portion
+below the ring can receive no nourishment from above, and will
+gradually be so starved that it cannot even act as a carrier of crude
+sap to the leaves, and so the whole bough will perish.
+
+[Illustration: FIG. 131.—Diagram showing general movement of sap.]
+
+=128. Sap movement not circulation.=—It must not be supposed that
+this flow of sap in plants is analogous to the circulation of the
+blood in animals, though frequently spoken of in popular language
+as the “circulation of the sap.” There is no central organ like the
+heart to regulate its flow, and the water taken up by the roots does
+not make a continual circuit of the plant body as the blood does of
+ours, but is dispersed by a process of general diffusion, partly into
+the air through the leaves and partly through the plant body as food,
+wherever it is needed. Figure 131 gives a good general idea of the
+movement of sap in trees, the arrows indicating the direction of the
+movement of the different substances.
+
+=129. Unexplained phenomena.=—Though the forces named above
+undoubtedly exert a powerful influence over sap movement, their
+combined action has not been proved capable of lifting the current
+to a height of more than 200 feet, while in the giant redwoods of
+California and the towering blue gums of Australia, it is known to
+reach a height of more than 400 feet. The active force exerted by the
+cell protoplasm has been suggested as an efficient cause, but as the
+upward flow takes place through the cells of the xylem, which contain
+no protoplasm (116), this explanation is inadequate, and we must be
+content, in the present state of our knowledge, to accept the fact as
+one which science has yet to account for.
+
+
+          Practical Questions
+
+  1. Why will a leafy shoot heal more quickly than a bare one? (125,
+  126; Exp. 58.)
+
+  2. Why does a transverse cut heal more slowly than a vertical one?
+  (126, 127.)
+
+  3. Why does a ragged cut heal less rapidly than a smooth one?
+
+  4. Why does the formation of wood proceed more rapidly as the
+  amount of water given off by the leaves is increased? (126; Exp.
+  59.)
+
+  5. Why do nurserymen sometimes split the cortex of young trees in
+  summer to promote the formation of wood? (116, 118.)
+
+  6. What is the advantage of scraping the stems of trees?
+
+  7. Explain the frothy exudation that often appears at the cut ends
+  of firewood, and the singing noise that accompanies it. [120, 124
+  (2).]
+
+  8. Of what advantage is it to high climbing plants, like grape and
+  trumpet vine (_Tecoma_), to have such large ducts? (111, 116, 122.)
+
+  9. Why is the process of layering more apt to be successful if the
+  shoot is bent or twisted at the point where it is desired to make
+  it root? (127; Exps. 60, 61.)
+
+  10. Why do oranges become dry and spongy if allowed to hang on the
+  tree too long? (72, 126; Exps. 60, 61.)
+
+  11. Why will corn and fodder be richer in nourishment if, at
+  harvest, the whole stalk is cut down and both fodder and grain are
+  allowed to mature upon it? (126, 127; Exps. 60, 61.)
+
+  12. Is the injury done to plants by freezing due, as a general
+  thing, to mechanical, or to chemical action? (33.)
+
+  13. Why in pruning a branch is it best to make the cut just above a
+  bud? (Exps. 60, 61.)
+
+  14. Why is the rim of new bark, or callus, that forms on the upper
+  side of a horizontal wound, thicker than that on the lower side?
+  (126, 127; Exps. 60, 61.)
+
+  15. Why is it that the medicinal or other special properties of
+  plants are found mostly in the leaves and bark, or in the parts
+  immediately under the bark? (120, 126.)
+
+  16. Why does twisting the footstalk of a bunch of grapes, just
+  before ripening, make them sweeter? (127.)
+
+[Illustration: PLATE 6.—A white oak, one of the monarchs of the
+dicotyl type. The owner of the ground on which this noble tree stands
+left a clause in his will bequeathing it in perpetuity a territory
+of 8 feet in every direction from its base. Refer to 89 and decide
+whether such an amount of standing room is sufficient to secure the
+preservation of this beautiful object.]
+
+  17. Is it a mere superstition to drive nails into the stems of plum
+  and peach trees to make them bear larger or more abundant fruit?
+  (126, 127.)
+
+  18. Why is a living corn stalk heavier than a dry one? (124.)
+
+  19. Why is a stalk of sugar cane heavier than one of corn?
+  Suggestion: Which is the heavier, pure water, or water holding
+  solids in solution?
+
+
+          V. WOOD STRUCTURE IN ITS RELATION TO INDUSTRIAL USES
+
+  MATERIAL.—Select from the billets of wood cut for the fire, sticks
+  of various kinds; hickory, ash, oak, chestnut, maple, walnut,
+  cherry, pine, cedar, tulip tree, all make good specimens. Red
+  oak shows the medullary rays well. Get sticks of green wood, if
+  possible, and have them planed smooth at the ends. Collect also,
+  where they can be obtained, waste bits of dressed lumber from a
+  carpenter or joiner. If nothing better is available, any pieces of
+  unpainted woodwork about the schoolroom will furnish subjects for
+  study.
+
+=130. Detailed structure of a woody stem.=—Select a good-sized billet
+of hard wood, and count the rings of annual growth. How old was the
+tree or the bough from which it was taken? Was its growth uniform
+from year to year? How do you know? Are the rings broader, as a
+general thing, toward the center or the circumference? How do you
+account for this? Is each separate ring of uniform thickness all the
+way round? Mention some of the circumstances that might cause a tree
+to grow less on one side than on the other. Are the rings of the same
+thickness in all kinds of wood? Which are the more rapid growers,
+those with broad or with narrow rings? Do you notice any difference
+in the texture of the wood in rapid and in slow growing trees? Which
+makes the better timber as a general thing, and why?
+
+=131. Heartwood and sapwood.=—Notice that in some of your older
+specimens (cedar, black walnut, barberry, black locust, chestnut,
+oak, Osage orange, show the difference distinctly) the central part
+is different in color and texture from the rest. This is because
+the sap gradually abandons the center (116, 123) to feed the outer
+layers, where growth in dicotyls takes place; hence, the outer
+part of the stem usually consists of sapwood, which is soft and
+worthless as timber, while the dead interior forms the durable
+heartwood so prized by lumbermen. The heartwood is useful to the
+plant principally in giving strength and firmness to the axis. It
+will now be seen why girdling a stem,—that is, chipping off a ring of
+the softer parts all round, will kill it, while vigorous and healthy
+trees are often seen with the center of the trunk entirely hollow.
+
+[Illustration: FIG. 132.—Cross section through a black oak, showing
+heartwood and sapwood. (_From_ PINCHOT, U. S. Dept. of Agr.)]
+
+[Illustration: FIG. 133.—Vertical section through a black oak.
+(_From_ PINCHOT, U. S. Dept. of Agr.)]
+
+[Illustration: FIGS. 134-136.—Diagrams of sections of timber: 134,
+cross section; 135, radial; 136, tangential. (_From_ PINCHOT, U. S.
+Dept. of Agr.)]
+
+=132. Different ways of cutting.=—In studying the vertical
+arrangement of stems, two sections are necessary, a radial and a
+tangential one. The former passes along the axis, splitting the stem
+into halves (Fig. 135); the latter cuts between the axis and the
+perimeter, splitting off a segment from one side (Fig. 136). The
+appearance of the wood used in carpentry and joiner’s work is due
+largely to the manner in which the planks are cut.
+
+=133. The cross cut.=—The section seen at the end of a log (Figs.
+132, 134) is called by carpenters a cross cut. It passes at
+right angles to the grain of the wood, and severs what important
+structures? (116, 119, 122.) Examine a cross cut at the end of a
+rough plank, or the top of a stump or an old fence post, and tell why
+this kind of cut is seldom used in carpentry.
+
+[Illustration: FIG. 137.—Tangential section of mountain ash, showing
+ends of the medullary rays.]
+
+=134. The tangent cut= is so called because it is made at right
+angles to the radius of a log. Repeat the geometrical principle upon
+which such a cut is described as “tangential.” It passes through
+the medullary rays and the annual rings diagonally (Fig. 136), and
+is the cheapest way of cutting timber, since the entire log is made
+into planks and there is no waste except the “slabs” and “edgings,”
+as shown in Fig. 138. The cut ends of the medullary rays appear on
+the surface as small lines or slits (Fig. 137), and give to this kind
+of plank its peculiar graining. The wavy or “watered” appearance of
+the annual rings (Figs. 133, 136, 140, 141), so often seen in cheap
+furniture and in the woodwork of cheaply constructed houses, is
+caused by the tangential cut, which strikes them at various angles.
+
+[Illustration: FIG. 138.—Diagram to show the common method of sawing
+a log. The circles represent rings of annual growth: _R_, _R_,
+diameter of the log; _r_, _r_, _r_ and _t_, _t_, _t_, boards cut
+perpendicular to it, giving for the two or three central ones radial,
+for the others, tangential, cuts. The waste portions are the “slabs”
+and “edgings,” shown in the dark segments at _R_, _R_, and the small
+triangular blocks, _e_, _e_, _e_.]
+
+[Illustration: FIG. 139.—Diagram illustrating the “quartered” cut:
+_d_, _d_ and _d′_, _d′_, radial cuts (diameters) by which the log is
+“quartered”; _c_, center of the log; _r_, _r_, radii passing through
+the middle of each quarter, parallel to which the planks _t_, _t_,
+_t_ are cut. The circles represent rings of annual growth.]
+
+=135. The radial, or quartered cut=, familiar to most of us in the
+“quartered oak” of commerce, passes through the center of the log
+and cuts the rings of annual growth perpendicularly, giving it the
+“striped” appearance (Fig. 135) seen in the best woodwork. It gets
+its name from the practice of dealers in first sawing a log into
+quarters and then cutting parallel to the radius passing through the
+middle of each quarter, as shown in Fig. 139. In this way each cut
+strikes the rings perpendicularly, but except in the case of very
+large logs, only narrow planks can be obtained in this manner. A
+better way of treating small logs is shown in Fig. 138, where the
+three central planks, _r_, _r_, _r_, on and near the diameter, will
+give the “quartered” effect, while the rest can be used for the
+cheaper tangential cuttings. Examine a piece of quartered board, or a
+log of wood that has been split down the center, and notice that the
+medullary rays appear as silvery bands or plates (Figs. 140, 141).
+This is because the cut runs parallel to them. It is the medullary
+rays chiefly that give to commercial woods their characteristic
+graining. Knots, buds, and other adventitious causes also influence
+it in various degrees.
+
+[Illustration: FIG. 140.—Sections of sycamore wood: _a_, tangential;
+_b_, radial; _c_, cross. (_From_ PINCHOT, U. S. Dept. of Agr.)]
+
+[Illustration: FIG. 141.—Section of white pine wood. (_From_ PINCHOT,
+U. S. Dept. of Agr.)]
+
+[Illustration: FIG. 142.—Section of tree trunk showing knot.]
+
+=136. The swelling and shrinking of timber.=—The capacity possessed
+by certain substances of bringing about an increase of volume by
+the absorption of liquids is termed _imbibition_. Care must be
+taken not to confound imbibition with capillarity. (Exp. 53.) When
+liquids are carried into a body by capillary attraction, they merely
+fill up vacant spaces already existing between small particles of
+the substance, and therefore do not cause any swelling or increase
+in size. When imbibition takes place, the _molecules_, or chemical
+units of the liquid, force their way between those of the imbibing
+substance, and thus, in making room for themselves, bring about an
+increase in volume of the imbibing body. To this cause is due the
+alternate swelling and shrinking of timber in wet and dry weather.
+
+[Illustration: FIGS. 143-144.—Diagrams of tree trunks, showing knots
+of different ages: 143, from tree grown in the open; 144, from tree
+grown in a dense forest.]
+
+=137. Knots.=—Look for a billet with a knot in it. Notice how the
+rings of growth are disturbed and displaced in its neighborhood.
+If the knot is a large one, it will itself have rings of growth.
+Count them, and tell what its age was when it ceased to grow. Notice
+where it originates. Count the rings from its point of origin to the
+center of the stem. How old was the tree when the knot began to form?
+Count the rings from the origin of the knot to the circumference
+of the stem; how many years has the tree lived since the knot was
+formed? Does this agree with the age of the knot as deduced from its
+own rings? As the tree may continue to live and grow indefinitely
+after the bough which formed the knot died or was cut away, there
+will probably be no correspondence between the two sets of rings,
+especially in the case of old knots that have been covered up and
+embedded in the wood. The longer a dead branch remains on a tree the
+more rings of growth will form around it before covering it up, and
+the greater will be the disturbance caused by it. Hence, timber trees
+should be pruned while very young, and the parts removed should be
+cut as close as possible to the main branch or trunk. Sometimes knots
+injure lumber very much by falling out and leaving the holes that are
+often seen in pine boards. In other cases, however, when the knots
+are very small, the irregular markings caused by them add greatly to
+the beauty of the wood. The peculiar marking of bird’s-eye maple is
+caused by abortive buds buried in the wood.
+
+
+          Practical Questions
+
+  1. Is the swelling of wood a physical or a physiological process?
+
+  2. Does wood swell equally with the grain and across it?
+  (Suggestion: test by keeping a block under water for 10 to 20 days,
+  measuring its dimensions before and after immersion.)
+
+  3. In building a fence, what is the use of “capping” the posts?
+  (133.)
+
+  4. In laying shingles, why are they made to touch, if the work is
+  done in wet weather, and placed somewhat apart, if in dry weather?
+  (136.)
+
+  5. What is the difference between timber and lumber? Between a
+  plank and a board? Between a log, stick, block, and billet?
+
+  6. Why does sapwood decay more quickly than heartwood? (131.)
+
+  7. Explain the difference between osmosis, diffusion, capillarity,
+  and imbibition. (9, 56, 57, 136; Exp. 53.)
+
+
+          VI. FORESTRY
+
+=138. Practical bearings.=—This part of our subject is closely
+related to lumbering and forestry. The business of the lumberman is
+to manufacture growing trees into merchantable timber, and to do this
+successfully he must understand enough about the structure of wood
+to cut his boards to the best advantage, both for economy and for
+bringing out the grain so as to produce the most desirable effects
+for ornamental purposes.
+
+[Illustration: PLATE 7.—Timber tree spoiled by standing too much
+alone in early youth. Notice how the crowded young timber in the
+background is righting itself, the lower branches dying off early
+from overshading, leaving tall, straight, clean boles. (_From_
+PINCHOT, U. S. Dept. of Agr.)]
+
+[Illustration: FIG. 145.—After the forest fire.]
+
+=139. Forestry has for its object=: (1) the preservation and
+cultivation of existing forests; (2) the planting of new ones, or
+the reforestation of tracts from which the timber has been destroyed.
+Forests may be either _pure_, that is, composed mainly of one kind of
+tree, as a pine or a fir wood; or _mixed_, being made up of a variety
+of different growths, as are most of our common hardwood forests.
+
+[Illustration: FIG. 146.—Oyster fungus on linden.]
+
+=140. Enemies of the forest.=-The first step in the preservation of
+our forests is to know the dangers to be guarded against. The chief
+of these are: (1) fires; (2) the ignorance or recklessness of man in
+cutting for commercial purposes; (3) fungi; (4) injurious insects;
+(5) sheep, hogs, and other animals that eat the seeds and the young,
+tender growth.
+
+=141. How to protect the forests.=—The annual destruction of forests
+by fires probably exceeds that from all other causes combined. The
+only effectual safeguard against this danger is watchfulness on the
+part of _everybody_. We can each one of us help in this work by at
+least being careful ourselves never to kindle a fire in the woods
+without taking every precaution against its spreading. A single
+match, or the glowing stump of a cigar, carelessly thrown among dry
+leaves or grass, may start a conflagration that will destroy millions
+of dollars’ worth of standing timber.
+
+To prevent the spread of fungi, dead trees should be removed, and
+broken or decayed branches trimmed off and the cut surfaces painted.
+Birds which destroy insects should be protected; sheep and hogs
+should be kept out, and dead leaves left on the ground to cover the
+roots and fertilize the soil with the humus created by their decay.
+Finally, none but mature trees should be cut for industrial purposes,
+and the cutting ought to be done in such a way that the young
+surrounding growth will not be injured by the falling trunks.
+
+=142. The usefulness of forests.=—Aside from the value of their
+products, forests are useful in many other ways. They influence
+climate beneficially by acting as windbreaks, by giving off moisture
+(Exp. 58), by shading the soil, and thus preventing too rapid
+evaporation. Their roots also help to retain the water in the soil,
+and by this means tend to prevent the washing of the land by heavy
+rains and to restrain the violence of freshets.
+
+=143. Forests and water supply.=—It is especially important that
+the watershed of any region should be well protected by forests,
+to prevent contamination of the streams and to insure an unfailing
+supply of water by checking the escape of the rainfall from the soil.
+
+
+          Practical Questions
+
+  1. Explain the difference between a forest, grove, copse, wood,
+  woodland.
+
+  2. In pruning a tree why ought the branch to be cut as close to the
+  stock as possible? (137.)
+
+  3. Name the principal timber trees of your neighborhood. What gives
+  to each its special value?
+
+  4. Name six trees that produce timber valuable for ornament; for
+  toughness and strength.
+
+  5. Which is the better for timber, a tree grown in the open, or one
+  grown in a forest, and why? (Plate 7.)
+
+  6. What are the objects to be attained in pruning timber trees?
+  Orchard and ornamental trees?
+
+  7. Is the outer bark of any use to a tree, and if so, what?
+
+  8. Why should pruning not be done in wet weather? [140 (3), 141.]
+
+  9. Why should vertical shoots be cut off obliquely? [133, 140 (3),
+  141.]
+
+
+          Field Work
+
+  (1) Make a study of the various climbing plants of your
+  neighborhood with reference to their modes of ascent, and the
+  effect, injurious, or other, upon the plants to which they attach
+  themselves. Note the origin and position of tendrils, and try to
+  make out what modification has taken place in each case. Consider
+  the twining habit in reference to parasitism, especially in the
+  case of soft-stemmed twiners when brought into contact with
+  soft-stemmed annuals. Observe the various habits of stem growth:
+  prostrate, declined, ascending, etc., and decide what adaptation to
+  circumstances may have influenced each case.
+
+  (2) Notice the shape of the different stems met with, and learn
+  to recognize the forms peculiar to certain of the great families.
+  Observe the various appliances for defense and protection with
+  which they are provided, and try to find out the meaning of the
+  numerous grooves, ridges, hairs, prickles, and secretions that are
+  found on stems. Always be on the alert for modifications, and learn
+  to recognize a stem under any disguise, whether thorn, tendril,
+  foliage, water holder, rootstock, or tuber.
+
+  (3) Note the color and texture of the bark of the different trees
+  you see and learn to distinguish the most important kinds:
+
+    (_a_) scaly—peeling off annually in large plates, as sycamore,
+    shagbark-hickory;
+
+    (_b_) fibrous—detached in stiff threads and fibers, as grape;
+
+    (_c_) fissured—split into large, irregular cracks by the growth
+    of the stem in thickness, as oak, chestnut, and most of our large
+    forest trees;
+
+    (_d_) membranous—separating in dry films and ribbons, as common
+    birch (_Betula alba_).
+
+  Observe the difference in texture and appearance of the bark on
+  old and young boughs of the same species. Try to account for the
+  varying thickness of the bark on different trees and on different
+  parts of the same tree. Notice the difference in the timber of
+  the same species when grown in different soils, at different ages
+  of the tree, and in healthy and weakly specimens. Find examples
+  of self-pruning trees (Plate 7), and explain how the pruning was
+  brought about.
+
+  (4) Select a small plot, about a fourth of an acre, of any wooded
+  tract in your neighborhood, and make a study of all the trees and
+  shrubs it contains. Make a list of the different kinds, with the
+  number of each. Take note of those that show themselves, by vigor
+  and abundance of growth, best adapted to the situation. These are
+  the “climax” or dominant vegetation of the plot. Find out, if you
+  can, to what cause their superiority is due.
+
+[Illustration: PLATE 8.—The American elm—a perfect type of
+deliquescent branching.]
+
+
+
+
+CHAPTER V. BUDS AND BRANCHES
+
+
+          I. MODES OF BRANCHING
+
+  MATERIAL.—For determinate growth, have twigs of an alternate and
+  an opposite-leaved plant showing well-developed terminal buds:
+  hickory, sweet gum, cottonwood, poplar, chestnut, are good examples
+  of the first; maple, ash, horse-chestnut, viburnum, of the second;
+  for the two-forked kind, mistletoe, buckeye, horse-chestnut, jimson
+  weed, lilac. For showing indefinite growth: rose, willow, sumach,
+  and ailanthus are good examples. Gummy buds, like horse-chestnut
+  and poplar, should be soaked in warm water before dissecting, to
+  soften the gum; the same treatment may be applied when the scales
+  are too brittle to be handled without breaking. Buds with heavy fur
+  on the scales cannot very well be studied in section; the parts
+  must be taken out and examined separately.
+
+[Illustration: FIG. 147.—Diagram of excurrent growth.]
+
+[Illustration: FIG. 148.—Diagram of deliquescent growth.]
+
+=144. Modes of branching.=—Compare the arrangement of the boughs
+on a pine, cedar, magnolia, etc., with those of the elm, maple,
+apple, or any of our common deciduous trees. Draw a diagram of each,
+showing the two modes of growth. The first represents the _excurrent_
+kind, from the Latin _excurrere_, to run out; the second, in which
+the trunk seems to divide at a certain point and flow away, losing
+itself in the branches, is called _deliquescent_, from the Latin
+_deliquescere_, to melt or flow away. The great majority of stems,
+as a little observation will show, present a combination of the two
+modes.
+
+[Illustration: FIG. 149.—Winter twig of sugar maple: _t_, terminal
+bud; _ax_, axillary buds; _ls_, leaf scars; _tr_, leaf traces; _l_,
+lenticels; _rs_, ring of scars left by bud scales of preceding
+season.]
+
+=145. Terminal and axillary buds.=—Notice the large bud at the end of
+a twig of hickory, sweet gum, beech, cottonwood, etc. This is called
+the _terminal_ bud because it terminates its branch. Notice the
+scars left by the leaves of the season as they fell away, and look
+for small buds just above them. These are _lateral_, or _axillary_,
+buds, so called because they spring from the axils of the leaves. How
+many leaves did your twig bear? What difference in size do you notice
+between the terminal and lateral buds?
+
+=146. The leaf scars.=—Examine the leaf scars with a hand lens,
+and observe the number and position of the little dots in them.
+Ailanthus, varnish tree, sumach, and China tree show these very
+distinctly. They are called _leaf traces_, and mark the points where
+the fibrovascular bundles from the leaf veins passed into the stem.
+Look on the bark, or epidermis, for lenticels.
+
+=147. Bud scales and scars.=—Notice the stout, hard scales by which
+the winter buds are covered in most of our hardy trees and shrubs.
+Remove these from the terminal one of your specimen, and notice the
+ring of scars left around the base. Look lower down on your twig
+for a ring of similar scars left from last year’s bud. Is there any
+difference in the appearance of the bark above and below this ring?
+If so, what is it, and how do you account for it? Is there more than
+one of these rings of scars on your twig, and if so, how many? How
+old is the twig and how much did it grow each year? Has its growth
+been uniform, or did it grow more in some years than in others?
+
+[Illustration: FIG. 150.—Diagram of opposite bud scales.]
+
+=148. Arrangement and use of the scales.=—Notice the manner in
+which the scales overlap so as to “break joints,” like shingles
+on the roof of a house. Where the leaves are opposite, the manner
+of superposition is very simple. Remove the scales one by one,
+representing the number and position of the pairs by a diagram
+after the model given in Fig. 150. In the bud of an alternately
+branched twig the order will be different, and the diagram must be
+varied accordingly. Do you observe any difference as to size and
+texture between the outer and inner scales? Notice how the former
+inclose the tenderer parts within like a protecting wall. In cold
+climates the outer scales are frequently coated with gum, as in the
+horse-chestnut, for greater security against the weather. The hickory
+and various other trees have the inner scales covered with fur or
+down that envelops the tender bud like a warm blanket.
+
+=149. Nature of the scales.=—The position of the scales shows
+that they occupy the place of leaves or of some part of a leaf.
+In expanding buds of the lilac and many other plants, they can be
+found in all stages of transition, from scales to true leaves. In
+the buckeye and horse-chestnut, they will easily be recognized as
+modified leaf stalks (Fig. 151). In the tulip tree, magnolia, India
+rubber tree, fig, elm, and many others, they represent appendages
+called _stipules_, often found at the bases of leaves. (See 165,
+166.) In this case a pair of scales is attached with each separate
+leaflet, and as the growing axis lengthens in spring, they are
+carried apart by the elongation of the internodes so that the scars
+are separated, a pair at each node, making rings all along the stem,
+as shown in Fig. 152, instead of having them compacted into bands at
+the base of the bud. These scars are sometimes very persistent, and
+in the common fig and magnolia may often be traced on stems six to
+eight years old. Do they furnish any indication as to the relative
+age of the different parts of the stem, like the bands of scars on
+twigs of horse-chestnut and hickory? Give a reason for your answer.
+(Fig. 152.)
+
+[Illustration: FIG. 151.—Development of the parts of the bud in the
+buckeye. (_After_ GRAY.)]
+
+[Illustration: FIG. 152.—Stem of tulip tree: _s_, _s_, scars left by
+stipular scales; _l_, _l_, leaf scars.]
+
+=150. Different rates of growth.=—Notice the very great difference
+between branches in this respect. Sometimes the main stem will have
+lengthened from twenty to fifty centimeters or more in a single
+season, while some of the lateral ones will have grown but an inch
+or two in four or five seasons. One reason for this is because the
+terminal bud, being on the great trunk line of sap movement, gets
+a larger share of nourishment than the others, and being stronger
+and better developed to begin with, starts out in life with better
+chances of success.
+
+Make a drawing of your specimen, showing all the points brought out
+in the examination just made. Cut sections above and below a set of
+bud scars and count the rings of annual growth in each section. What
+is the age of each? How does this agree with your calculation from
+the number of scar clusters left by the bud scales?
+
+=151. Irregularities.=—Take a larger bough of the same kind that you
+have been studying, and observe whether the arrangement of branches
+on it corresponds with the arrangement of buds on the twig. Did
+all the buds develop into branches? Do those that did develop all
+correspond in size and vigor? If all the buds developed, how many
+branches would a tree produce every year?
+
+In the elm, linden, beech, hornbeam, hazelnut, willow, and various
+other plants, the terminal bud always dies and the one next in order
+takes its place, giving rise to the more or less zigzag axis that
+generally characterizes trees of these species. (Fig. 153.)
+
+[Illustration: FIG. 153.—Bud development of beech: _a_, as it is,
+many buds failing to develop; _b_, as it would be if all the buds
+were to live.]
+
+=152. Forked stems.=—Take a twig of buckeye, horse-chestnut, or
+lilac, and make a careful sketch of it, showing all the points that
+were brought out in the examination of your previous specimen. Which
+is the larger, the lateral or the terminal bud? Is their arrangement
+alternate or opposite? What was the leaf arrangement? Count the leaf
+traces in the scars; are they the same in all? If all the buds had
+developed into branches, how many would spring from a node? Look for
+the rings of scars left by the last season’s bud scales. Do you find
+any twig of more than one year’s growth, as measured by the scar
+rings?
+
+[Illustration: FIG. 154.—Two-forked twig of horse-chestnut.]
+
+Look down between the forks of a branched stem for a round scar.
+This is not a leaf scar, as we can see by its shape, but one left by
+the last season’s flower cluster. The flower, as we know, dies after
+perfecting its fruit, and so a flower bud cannot continue the growth
+of its axis as other buds do, but has just the opposite effect and
+stops all further growth in that direction. Hence, stems and branches
+that end in a flower bud cannot continue to develop their main axis,
+but their growth is usually carried on, in alternate-leaved stems, by
+the nearest lateral bud, or in opposite-leaved ones, by the nearest
+pair of buds. In the first case there results the zigzag spray
+characteristic of such trees as the beech and elm (Fig. 155, _B_); in
+the second, the two-forked, or _dichotomous_ branching, exemplified
+by the buckeye, horse-chestnut, jimson weed, mistletoe, and dogwood
+(Fig. 155, _A_).
+
+Draw a diagram of the buckeye, or other dichotomous stem, as it would
+be if all the buds developed into branches, and compare it with
+your diagrams of excurrent and deliquescent growth. Draw diagrams
+to illustrate the branching of the elm, beech, lilac, linden, rose,
+maple, or their equivalents.
+
+[Illustration: FIG. 155.—Diagrams of two-forked branching. The
+pointed bodies in the forks shows where terminal flower buds or
+flower clusters have changed the direction of growth.]
+
+=153. Definite and indefinite annual growth.=—The presence or absence
+of terminal buds gives rise to another important distinction in
+plant development—that of _definite_ and _indefinite_ annual growth.
+Compare with any of the twigs just examined, a branch of rose, honey
+locust, sumac, mulberry, etc., and note the difference in their
+modes of termination. The first kind, where the bough completes its
+season’s increase in a definite time and then devotes its energies to
+developing a strong terminal bud to begin the next year’s work with,
+are said to make a _definite or determinate annual growth_. Those
+plants, on the other hand, which make no provision for the future,
+but continue to grow till the cold comes and literally nips them in
+the bud, are _indefinite_, or _indeterminate_ annual growers. Notice
+the effect of this habit upon their mode of branching. The buds
+toward the end of each shoot, being the youngest and tenderest, are
+most readily killed off by frost or other accident, and hence new
+branches spring mostly from the older and stronger buds near the base
+of the stem. It is their mode of branching that gives to plants of
+this class their peculiar bushy aspect. Such shrubs generally make
+good hedges on account of their thick undergrowth. The same effect
+can be produced artificially by pruning.
+
+[Illustration: FIG. 156.—A mixed wood in winter, showing the trend of
+the branches.]
+
+=154. Differences in the branching of trees.=—We are now prepared
+to understand something about the causes of that endless variety in
+the spread of bough and sweep of woody spray that makes the winter
+woods so beautiful. Where the terminal bud is undisputed monarch
+of the bough, as in the pine and fir, or where it is so strong and
+vigorous as to overpower its weaker brethren and keep the lead, as
+in the magnolia, tulip tree, and holly, we have excurrent growth. In
+plants like the oak and apple, where all the buds have a more nearly
+equal chance, the lateral branches show more vigor, and the result is
+either deliquescent growth, or a mixture of the two kinds. In the elm
+and beech, where the usurping pseudo-terminal bud keeps the mastery,
+but does not completely overpower its fellows, we find the long,
+sweeping, delicate spray characteristic of those species. Examine a
+sprig of elm, and notice further that the flower buds are all down
+near the base of the stem, while the leaf buds are near the tip. The
+chief development of the season’s growth is thus thrown toward the
+end of the branch, giving rise to that fine, feathery spray which
+makes the elm an even more beautiful object in winter than in summer
+(Fig. 158).
+
+An examination of the twigs of other trees will bring out the various
+peculiarities that affect their mode of branching. The angle, for
+instance, which a twig makes with its bough has a great effect in
+shaping the contour of the tree. Compare in this respect the elm and
+hackberry; the tulip tree and willow; ash and hickory. As a general
+thing, acute angles produce slender, flowing effects; right or obtuse
+angles, more bold and rugged outlines.
+
+[Illustration: FIG. 157.—Winter spray of ash, an opposite-leaved
+tree.]
+
+[Illustration: FIG. 158.—Winter spray of elm.]
+
+
+          Practical Questions
+
+  1. Has the arrangement of leaves on a twig anything to do with the
+  way a tree is branched? (145, 151, 152.)
+
+  2. Why do most large trees tend to assume the excurrent, or axial,
+  mode of growth if let alone? (150, 154.)
+
+  3. If you wished to alter the mode of growth, or to produce what
+  nurserymen call a low-headed tree, how would you prune it? (152,
+  153.)
+
+  4. Would you top a timber tree? (152, 153.)
+
+  5. Are low-headed or tall trees best for an orchard? Why?
+
+  6. Why is the growth of annuals generally indefinite?
+
+  7. Name some trees of your neighborhood that are conspicuous for
+  their graceful winter spray.
+
+  8. Name some that are characterized by sharpness and boldness of
+  outline.
+
+  9. Account for the peculiarities in each case.
+
+
+          II. BUDS
+
+  MATERIAL.—Expanding leaf and flower buds in different stages of
+  development; large ones show the parts best and should be used
+  where attainable. Some good examples for the opposite arrangement
+  are horse-chestnut, maple, lilac, ash; for the alternate: hickory,
+  sweet gum, balsam poplar, beech, elm. Where material is scarce, the
+  twigs used in the last section may be placed in water and kept till
+  the buds begin to expand.
+
+=155. Folding of the leaves.=—Remove the scales from a bud of
+horse-chestnut nearly ready to open, and notice the manner in
+which the young leaves are folded. This is called _vernation_, or
+_prefoliation_, words meaning respectively “spring condition” and
+“condition preceding the leaf.” Leaves are packed in the bud so as to
+occupy the least space possible, and in different plants they will be
+found folded in a great many different ways, according to the shape
+and texture of the leaf and the space available for it in the bud.
+When doubled back and forth like a fan, or crumpled and folded as in
+the buckeye, horse-chestnut, and maple, the vernation is _plicate_
+(Figs. 160, 162).
+
+[Illustration: FIG. 159.—Expanding bud of English walnut, showing
+twice conduplicate vernation.]
+
+[Illustration: FIG. 160.—A partly expanded leaf of beech, showing
+plicate-conduplicate vernation.]
+
+=156. Position of the flower cluster.=—What do you find within the
+circle of leaves? Examine one of the smaller axillary buds, and
+see if you find the same object within it. If you are in any doubt
+as to what this object is, examine a bud that is more expanded,
+and you will have no difficulty in recognizing it as a rudimentary
+flower cluster. Notice its position with reference to the scales and
+leaves. If at the center of the bud, it will, of course, terminate
+its axis when the bud expands, and the growth of the branch will
+culminate in the flower. The branching of any kind of stem that
+bears a central flower cluster must, then, be of what order? Compare
+your drawings with the section of a hyacinth bulb or jonquil, and
+note the similarity in position of the flower clusters. In a bud
+of the hickory, walnut, oak, etc., the position of the flower
+clusters is different from that of flowers in the buds of lilac
+and horse-chestnut. Look for a bud containing them, and find out
+where they occur. Can the axis continue to grow after flowering,
+in this kind of stem? Give a reason for your answer. Make sketches
+in transverse and longitudinal section (see Figs. 162, 163) of two
+different kinds of buds, illustrating the terminal and axillary
+position of the flower cluster.
+
+[Illustration: FIGS. 161, 162.—Buds of maple: 161, vertical section
+of a twig; 162, cross section through bud, showing folded leaves in
+center and scales surrounding them.]
+
+[Illustration: FIG. 163.—Vertical section of hickory bud: _a_, furry
+inner scales; _b_, outer scales; _l_, folded leaf; _r_, receptacle.]
+
+=157. Dormant buds.=—A bud may often lie dormant for months or even
+years, and then, through the injury or destruction of its stronger
+rivals, or some other favoring cause, develop into a branch. Such
+buds are said to be _latent_ or _dormant_. The sprouts that often put
+up from the stumps of felled trees originate from this source.
+
+[Illustration: FIG. 164.—Twig of red maple, showing supernumerary
+bud, _b_; _rs_, ring of scars left by last year’s bud scales.
+(_After_ GRAY.)]
+
+=158. Supernumerary buds.=—Where more than one bud develops at a
+node, as is so often the case in the oak, maple, honey locust,
+etc., all except the normal one in the axil are _supernumerary_
+or _accessory_. These must not be confounded with _adventitious_
+buds—those that occur elsewhere than at a node.
+
+
+          Practical Questions
+
+  1. Would protected buds be of any use to annuals? Why, or why not?
+
+  2. Of what use is the gummy coating found on the buds of the
+  horse-chestnut and balm of Gilead? (148.)
+
+  3. Can you name any plants the buds of which serve as food for man?
+
+  4. How do flower buds differ in shape from leaf buds?
+
+  5. At what season can the leaf bud and the flower bud first be
+  distinguished? Is it the same for all flowering plants?
+
+  6. Watch the different trees about your home, and see when the buds
+  that are to develop into leaves and flowers the next season are
+  formed in each species.
+
+
+          III. THE BRANCHING OF FLOWER STEMS
+
+  MATERIAL.—Typical flower clusters illustrating the definite and
+  indefinite modes of inflorescence. Some of those mentioned in the
+  text are:—
+
+  Indefinite: hyacinth, shepherd’s purse, wallflower, carrot, lilac,
+  blue grass, smartweed (_Polygonum_), wheat, oak, willow, clover.
+
+  Definite: chickweed, spurge (_Euphorbia_), comfrey, dead nettle,
+  etc. Any examples illustrating the principal kinds of cluster will
+  answer.
+
+=159. Inflorescence= is a term used to denote the position and
+arrangement of flowers on the stem. It is merely a mode of branching,
+and follows the same laws that govern the branching of ordinary stems.
+
+The stalk that bears a flower is called the _peduncle_. In a cluster
+the main axis is the common peduncle, and the separate flower stalks
+are _pedicels_. A simple leafless flower stalk that rises directly
+from the ground, like those of the dandelion and daffodil, is called
+a _scape_ (Fig. 165).
+
+[Illustration: FIG. 165.—Solitary terminal flower of a lily.]
+
+[Illustration: FIG. 166.—Indeterminate inflorescence of moneywort.
+(_After_ GRAY.)]
+
+=160. Two kinds of inflorescence.=—The growth of flower stems,
+like that of leaf stems, is of two principal kinds, definite and
+indefinite, or, as it is frequently expressed, determinate and
+indeterminate. The simplest kind of each is the solitary, a single
+flower either terminating the main axis, as the tulip, daffodil,
+trillium, magnolia, etc., or springing singly from the axils, as the
+running periwinkle, moneywort, and cotton.
+
+[Illustration: FIG. 167.—Raceme of milk vetch (_Astragalus_).]
+
+[Illustration: FIG, 168.—Catkins of aspen.]
+
+=161. Indeterminate inflorescence= is always axillary, since the
+production of a terminal flower would stop further growth in that
+direction and thus terminate the development of the axis. The
+_raceme_ is the typical flower cluster of the indefinite sort. In
+such an arrangement the oldest flowers are at the lower nodes,
+new ones appearing only as the axis lengthens and produces new
+internodes. The little scale or _bract_ usually found at the base of
+the pedicel in flower clusters of this sort is a reduced leaf, and
+the fact that the flower stalk springs from the axil shows it to be
+of the essential nature of a branch. When the flowers are sessile
+and crowded on the axis in various degrees, the cluster produced may
+be a _spike_, as seen in the plantain, knotweed, etc., or a _head_,
+like that of the clover, buttonwood, and sycamore. The _catkins_ that
+form the characteristic inflorescence of most of our forest trees
+are merely pendant spikes. The _corymb_ is a modification of the
+raceme in which the lower pedicels are elongated so as to place their
+flowers on a level with those of the upper nodes, making a convex, or
+more or less flat-topped cluster, as in the wallflower and hawthorn.
+The _umbel_ differs from the corymb in having the pedicels with their
+bracts all gathered at the top of the peduncle, from which they
+spread in every direction like the rays of an umbrella, as the name
+implies. This is the prevalent type of flower cluster in the parsley
+family, which takes its botanical name, _Umbelliferæ_, from its
+characteristic form of inflorescence. The pedicels of an umbel are
+called _rays_, and the circle of bracts at the base of the cluster is
+an _involucre_.
+
+[Illustration: FIG. 169.—Corymb of plum blossoms.]
+
+[Illustration: FIG. 170.—Umbel of milkweed.]
+
+[Illustration: FIG. 171.—Panicle of grass, a compound cluster of the
+racemose type.]
+
+[Illustration: FIG. 172.—Flat-topped cyme of sneezeweed.]
+
+=162. Determinate, or cymose, inflorescence.=—In the _cyme_, the
+typical cluster of the determinate kind, the older blossoms in the
+center, being terminal, stop the axis of growth in that direction and
+force the stem, in continuing its growth, to send out side branches
+from the axils of the topmost leaves, in a manner precisely similar
+to the two-forked branching of stems like the horse-chestnut and
+jimson weed. When the older peduncles are lengthened as described
+in 161, a flat-topped cyme is produced, which is distinguished
+from the corymb by its order of flowering, the oldest blossoms
+being at the center, while in the corymb they appear in the reverse
+order. A peculiar form of cyme is found in the scorpioid or coiled
+inflorescence of the pink-root (_Spigelia_), heliotrope, comfrey,
+etc. Its structure will be made clear by an inspection of Figs.
+174-176.
+
+[Illustration: FIG. 173.—Scorpioid cyme.]
+
+=163. The nature of flower stems.=—A comparison of the types of
+inflorescence with the modes of branching in ordinary stems (144,
+152, 153) will show a strict correspondence between them. Both bear
+leaves and buds, and the individual flowers of a cluster usually
+spring from the axils of leaves or from bracts, which are merely
+reduced leaves. What, then, is the essential nature of flower stems?
+
+[Illustration: FIGS. 174-176.—Diagrams of cymose inflorescence, with
+flowers numbered in the order of their development: 174, cyme half
+developed (scorpioid); 175, a flat-topped or corymbose cyme; 176,
+development of a typical cyme.]
+
+=164. Significance of the clustered arrangement.=—As a general thing
+the clustered arrangement marks a higher stage of development than
+the solitary, just as in human life the rudest social state is a
+distinct advance upon the isolated condition of the savage. In plant
+life it is the beginning of a system of coöperation and division of
+labor among the associated members of the flower cluster, as will be
+seen later when we take up the study of the flower.
+
+
+          Practical Questions
+
+  1. Name as many solitary flowers as you can think of.
+
+  2. Do you, as a rule, find very small flowers solitary, or in
+  clusters?
+
+  3. Would the separate flowers of the clover, parsley, or grape be
+  readily distinguished by the eye among a mass of foliage?
+
+  4. Should you judge from these facts that it is, in general,
+  advantageous to plants for their flowers to be conspicuous?
+
+
+          Field Work
+
+  (1) In connection with 144-154, the characteristic modes of
+  branching among the common trees and shrubs of each neighborhood
+  should be observed and accounted for. The naked branches of the
+  winter woods afford exceptional opportunities for studies of this
+  kind, which cannot well be carried on except out of doors. Note
+  the effect of the mode of branching upon the general outline of
+  the tree; compare the direction and mode of growth of the larger
+  boughs with that of small twigs in the same species, and see if
+  there is any general correspondence between them; note the absence
+  of fine spray on the boughs of large-leaved trees, and account
+  for it. Account for the flat sprays of trees like the elm, beech,
+  hackberry, etc.; the irregular stumpy branches of the oak and
+  walnut; the stiff straight twigs of the ash; the zigzag switches of
+  the black locust, Osage orange, elm, and linden. Measure the twigs
+  on various species, and see if there is any relation between the
+  length and thickness of branches. Notice the different trend of
+  the upper, middle, and lower boughs in most trees, and account for
+  it. Observe the mode of branching of as many different species as
+  possible of some of the great botanical groups of trees; the oaks,
+  hickories, hawthorns, and pines, for instance, and notice whether
+  it is, as a general thing, uniform among the species of the same
+  group, and how it differs from that of other groups.
+
+  (2) In connection with 155-158, buds of as many different kinds
+  as possible should be examined with reference to their means of
+  protection, their vernation and leaf arrangement, and the resulting
+  modes of growth. Compare the folding of the cotyledons in the seed
+  with the vernation of the same plants, and observe whether the
+  folding is the same throughout a whole group of related plants,
+  or only for the same species. Notice which modes seem to be most
+  prevalent. Select a twig on some tree near your home or your
+  schoolhouse, and keep a record of its daily growth from the first
+  sign of the unfolding of its principal bud to the full development
+  of its leaves. Any study of buds should include an observation of
+  them in all stages of development.
+
+  (3) With 160-165, study the inflorescence of the common plants and
+  weeds that happen to be in season, until you have no difficulty
+  in distinguishing between the definite and indefinite sorts, and
+  can refer any ordinary cluster to its proper form. Notice whether
+  there is any tendency to uniformity in the mode of inflorescence
+  among flowers of the same family. Consider how each kind is adapted
+  to the shape and habit of the flowers composing it, and what
+  particular advantage each of the specimens examined derives from
+  the way its flowers are clustered. In cases of mixed inflorescence,
+  see if you can discover any reason for the change from one form to
+  the other.
+
+
+
+
+CHAPTER VI. THE LEAF
+
+
+          I. THE TYPICAL LEAF AND ITS PARTS
+
+  MATERIAL.—Leaves of different kinds showing the various modes of
+  attachment, shapes, texture, etc. For stipules, leaves on very
+  young twigs should be selected, as these bodies often fall away
+  soon after the leaves expand. The rose, Japan quince, willow,
+  strawberry, pea, pansy, and young leaves of beech, apple, elm,
+  tulip tree, India rubber tree, magnolia, knotweed, furnish good
+  examples of stipules. For the different orders of leaf arrangement,
+  lilac, maple, spurge, trillium, cleavers (Galium) show the opposite
+  and whorled kinds. Elm, basswood, grasses; alder, birch, sedges;
+  peach, apple, cherry, show respectively for each group the three
+  principal orders of alternate arrangement.
+
+=165. Parts of the leaf.=—Examine a young, healthy leaf of apple,
+quince, or elm, as it stands upon the stem, and notice that it
+consists of three parts: a broad expansion called the _blade_; a
+leaf stalk or _petiole_ that attaches it to the stem; and two little
+leaflike or bristle-like bodies at the base, known as _stipules_.
+Make a sketch of any leaf provided with all these parts, and label
+them, respectively, blade, petiole, and stipules. These three parts
+make up a perfect or typical leaf, but as a matter of fact, one or
+more of them is usually wanting.
+
+[Illustration: FIG. 177.—A typical leaf and its parts: _b_, blade;
+_p_, petiole; _s_, _s_, stipules.]
+
+[Illustration: FIG. 178.—Spiny stipules of clotbur.]
+
+=166. Stipules.=—The office of stipules, when present, is generally
+to subserve in some way the purposes of protection. In many cases,
+as in the fig, elm, beech, oak, magnolia, etc., they appear only as
+protective scales that cover the bud during winter, and fall away as
+soon as the leaf expands. When _persistent_, that is, enduring, they
+take various forms according to the purposes they serve. But under
+whatever guise they occur, their true nature may be recognized by
+their position on each side of the base of the petiole, and not in
+the _axil_, or angle formed by the leaf with the stem. (149.)
+
+[Illustration: FIG. 179.—Adnate stipules of clover. FIG. 180.—Leaves
+of smilax, showing stipular tendrils. FIG. 181.—Leafy stipules of
+Japan quince.]
+
+=167. Leaf attachment.=—The normal use of the petiole is to secure a
+better light exposure for the leaves, but, like other parts, it is
+subject to modifications, and is often wanting altogether. In this
+case the leaf is said to be _sessile_, that is, _seated_, on the
+stem, and the leaf bases are designated by various terms descriptive
+of their mode of attachment. The meaning of these terms, when not
+self-explanatory, can best be learned by a comparison of living
+specimens with Figs. 184-187.
+
+=168. Arrangement of leaves on the stem.=—The mode of attachment is
+something quite distinct from the mode of leaf arrangement on the
+stem, or _phyllotaxy_, as it is termed by botanists. It was seen in
+148 that this takes place in two different ways, the alternate and
+opposite. These two kinds of arrangement represent the principal
+forms of leaf disposition on the stem, the different varieties of
+each depending on the manner in which the leaves are distributed.
+
+[Illustration: FIGS. 182-187.—Petioles, and leaf attachment: 182,
+petioles of jasmine nightshade (_Solanum jasminoides_) acting as
+tendrils; 183, acacia, showing petiole transformed to leaf blade;
+184, sessile leaves of epilobium; 185, clasping leaf of lactuca; 186,
+perfoliate leaves of uvularia; 187, peltate leaf of tropæolum. (182
+and 186 _after_ GRAY.)]
+
+Where three or more occur at a node, as in the trillium and cleavers
+(_Galium_), they constitute a whorl, which is only a variant of the
+opposite arrangement. There is no limit to the number of leaves that
+may be in a whorl except the space around the stem to accommodate
+them.
+
+The phyllotaxy of alternate leaves is more complicated. The
+different forms are characterized by the angular distance between the
+points of leaf insertion around the stem. In the elm, basswood, and
+most grasses, they are distributed in two rows or ranks on opposite
+sides of the stem, each just half way round the circumference from
+the one next in succession (Fig. 189), the third in vertical order
+standing directly over the first. In most of our common trees and
+shrubs five leaves are passed in making two turns round the stem, the
+sixth leaf in vertical order standing over the first. This is called
+the five-ranked arrangement, and is the most common order among
+dicotyls.
+
+[Illustration: FIG. 188.—Whorled leaves of Indian cucumber.]
+
+[Illustration: FIG. 189.—Twig of a hackberry (_Celtis cinerea_),
+showing the two-ranked arrangement. Notice how the position of the
+stems and branches of the main axis corresponds to that of the
+leaves.]
+
+=169. Relation between the shape and arrangement of
+leaves.=—Phyllotaxy is of importance chiefly on account of its
+influence on the light relation of leaves. A compact, close-ranked
+arrangement tends to shut off the light from the lower nodes, and
+hence, in plants where it prevails, the leaves are apt to be long
+and narrow in proportion to the frequency of the vertical rows.
+The yucca, oleander, Canada fleabane and bitterweed (_Helenium
+tenuifolium_), illustrate this relation.
+
+[Illustration: PLATE 9.—Vegetation of a moist, shady ravine. Notice
+the expanded surface of the leaf blades and the long internodes that
+separate the individual leaves. (From Rep’t. Mo. Botanical Garden.)]
+
+[Illustration: FIG. 190.—Narrow leaves in crowded vertical rows.]
+
+On the other hand, when the leaves are large and rounded in outline,
+as those of the sunflower, hollyhock, and catalpa, they are usually
+separated by longer internodes, or their blades are cut and incised
+so that the sunlight easily strikes through to the lower ones.
+
+=170. Other external characteristics= to be observed in leaves are:—
+
+(1) General Outline: whether round, oval, heart-shaped, etc. (Figs.
+191-197).
+
+(2) Margins: whether unbroken (_entire_), or variously toothed and
+indented. (Figs. 198-202.)
+
+(3) Texture: whether thick, thin, soft, hard, fleshy, leathery,
+brittle.
+
+(4) Surface: smooth, shining, dull, wrinkled, hairy, or otherwise
+roughened.
+
+[Illustration: FIGS. 191-197.—Shapes of leaves: 191, lanceolate; 192,
+spatulate; 193, oval; 194, obovate; 195, kidney-shaped; 196, deltoid;
+197, lyrate. (191-195 _after_ GRAY.)]
+
+Not only do leaves of different kinds exhibit these characteristics
+in varying degrees, but young and old leaves, or those on young and
+old plants of the same kind, often differ from each other in color,
+size, shape, texture, mode of attachment, and the like, to such a
+degree (Figs. 203, 204) that one not familiar with them in both
+stages would hardly recognize them as belonging to the same species.
+The young leaves of eucalyptus, mulberry, and some oaks afford
+conspicuous examples of such differences, and they exist between the
+cotyledons and mature leaves of most plants.
+
+Can you see any benefit, in the case of the plant whose leaves you
+are studying, that could be derived from such of the characteristics
+named above as they may exhibit?
+
+[Illustration: FIGS. 198-202.—Margins of leaves: 198, serrate; 199,
+dentate; 200, crenate; 201, undulate; 202, sinuate. (_After_ GRAY.)]
+
+[Illustration: FIGS. 203, 204.—Leaves of paper mulberry tree: 203,
+leaf from an old tree; 204, leaf from a two-year-old sprout.]
+
+
+          Practical Questions
+
+  1. Tell the nature and use of the stipules in such of the following
+  plants as you can find: tulip tree; fig; beech; apple; willow;
+  pansy; garden pea; Japan quince (_Pyrus Japonica_); sycamore; rose;
+  paper mulberry (_Broussonetia_).
+
+  2. How would you distinguish between a chinquapin, a chestnut, a
+  chestnut oak, and a horse-chestnut tree by their leaves alone? By
+  their bark and branches? Between a hickory, ash, common elder, box
+  elder, ailanthus, sumach? Between beech, birch, elm, hackberry,
+  alder?
+
+  (Any other sets of leaves may be substituted for those named, the
+  object being merely to form the habit of distinguishing readily the
+  differences and resemblances among those that bear some general
+  likeness to one another.)
+
+  3. From the study of these or similar specimens, would you conclude
+  that resemblances in leaves are confined to those of closely
+  related kinds?
+
+  4. Name some causes independent of botanical relationship that
+  might influence them. (169, 170; Exps. 48, 57.)
+
+  5. Do you find, as a general thing, more leaves with stipules or
+  without?
+
+  6. Is their absence from a mature leaf always a sign that it is
+  really exstipulate? (166.)
+
+  7. Can you trace any line of development through intervening
+  forms from a merely sessile leaf, like that of the pimpernel or
+  specularia, to a peltate one? (Figs. 184-187, and observation of
+  living specimens.)
+
+  8. Does the leaf determine the position of the node, or the node
+  the position of the leaf?
+
+  9. Strip the leaves from a twig of one order of arrangement and
+  replace them with foliage from a twig of a different order; for
+  instance, place basswood upon white oak, birch upon lilac, elm upon
+  pear, honeysuckle upon barberry, etc. Is the same amount of surface
+  exposed as in the natural order?
+
+  10. What disadvantage would it be to a plant if the leaves were
+  arranged so that they stood directly over one another? (169.)
+
+  11. Why are the internodes of vigorous young shoots, or scions,
+  generally so long? (150.)
+
+  12. If the upward growth of a stem or branch is stopped by pruning,
+  what effect is produced upon the parts below, and why? (152, 153.)
+
+  13. Give some of the reasons why corn grows so small and stunted
+  when sown broadcast for forage? (60, 63, 169.)
+
+  14. What is the use of “chopping” (_i.e._ thinning out) cotton?
+
+
+          II. THE VEINING AND LOBING OF LEAVES
+
+  MATERIAL.—Leaves of any monocotyl and dicotyl will show the
+  difference between parallel and net-veining. To illustrate the
+  palmate and pinnate kinds, the leaves of grasses and arums may be
+  used for monocotyls, and for dicotyls, those of ivy, maple, grape,
+  elm, peach, cherry, etc.; for division, examine lobed and compound
+  leaves of as many kinds as are attainable. A specimen showing each
+  kind of veining should be placed in coloring fluid a short time
+  before the lesson begins. The leafstalks of celery and plantain
+  are excellent for showing the relation between the leaf veins and
+  vascular system of the plant.
+
+=171. Parallel and net veining.=—Compare a leaf of the wandering
+Jew, lily, or any kind of grass, with one of grape, ivy, or willow.
+Hold each up to the light, and note the veins or little threads of
+woody substance that run through it. Make a drawing of each so as to
+show plainly the direction and manner of veining. Write under the
+first, _parallel-veined_, and under the second, _net-veined_. This
+distinction of leaves into parallel and net-veined corresponds with
+the two great classes into which seed-bearing plants are divided,
+monocotyls, as a general thing, being characterized by the first
+kind, and dicotyls by the second.
+
+[Illustration: FIG. 205.—Parallel-veined leaf of lily of the valley
+(_After_ GRAY).]
+
+[Illustration: FIG. 206.—Net-veined leaf of a willow.]
+
+[Illustration: FIG. 207.—Pinnately parallel-veined leaf of calla lily
+(_After_ GRAY).]
+
+[Illustration: FIG. 208.—Palmately net-veined leaf of wild ginger.]
+
+=172. Pinnate and palmate veining.=—Next, compare a leaf of the
+canna, calla lily, or any kind of arum, with one of the elm, peach,
+cherry, etc. What resemblances do you notice between the two? What
+differences? Which is parallel-veined and which is net-veined? Make
+a drawing of each, and compare with the first two. Notice that in
+leaves of this kind, the petiole is continued in a large central
+vein, called the _midrib_, from which the secondary veins branch off
+on either side like the pinnæ of a feather; whence such leaves are
+said to be _pinnately_, or _feather_ veined, as in Figs. 206, 207. In
+the cotton, maple, ivy, etc., on the other hand, the petiole breaks
+up at the base of the leaf (Fig. 208) into a number of primary
+veins or ribs, which radiate in all directions like the fingers from
+the palm of the hand; hence, such a leaf is said to be _palmately_
+veined. Net-veined leaves—the plantain (Fig. 209), wild smilax,
+beech, dogwood—are sometimes ribbed in a way that might lead an
+inexperienced observer to confound them with parallel-veined ones,
+but the reticulations between the ribs show that they belong to the
+net-veined class.
+
+[Illustration: FIG. 209.—Ribbed leaf of plantain.]
+
+=173. Veins as a mechanical support.=—Hold up a stiff, firm leaf
+of any kind, like the magnolia, holly, or India rubber, to the
+light, having first scraped away a little of the under surface, and
+examine it with a lens. Compare it with one of softer texture, like
+the peach, maple, or clover. In which are the veins the closer and
+stronger? Which is the more easily torn and wilted? Tear a blade of
+grass longitudinally and then cross-wise; in which direction does it
+give way the more readily? Tear apart gently a leaf of maple, or ivy,
+and one of elm or other pinnately veined plant; in which direction
+does each give way with least resistance? What would you judge from
+these facts as to the mechanical use of the veins?
+
+=174. Effect upon shape.=—By comparing a number of leaves of each
+kind it will be seen that the feather-veined ones tend to assume
+elongated outlines (Figs. 197, 207); the palmate-veined ones, broad
+and rounded forms (Figs. 195, 208). Notice also that the straight,
+unbroken venation of parallel-veined leaves is generally accompanied
+by smooth, unbroken margins, while the irregular, open meshes of
+net-veined leaves are favorable to breaks and indentations.
+
+=175. Veins as water carriers.=—Examine a leaf from a stem that has
+stood in red ink for an hour or two. Do you see evidence that it has
+absorbed any of the liquid? Cut across the blade and examine with a
+lens. What course has the absorbed liquid followed? What use does
+this indicate for the veins, besides the one already noted? Observe
+the point of insertion on the stem, and examine the scar with a lens:
+do you see any evidence of a connection between the leaf veins and
+the fibrovascular bundles of the stem? (111, 125, 126.) Notice where
+and how the veins end. Are they of the same size all the way, or do
+they grow smaller toward the tip? Are they separate and distinct, or
+are they connected throughout their ramifications, like the veins and
+arteries of the human body? How do you know? Do you see any of the
+coloring fluid in the small reticulations between the veins? How did
+it get there?
+
+=176. The nature and office of veins.=—We learn from 173 and 175 that
+the veining serves two important purposes in the economy of the leaf:
+first, as a skeleton or framework, to support the expanded blade;
+and second, as a system of water pipes, for conveying the sap out
+of which its food is manufactured. In other words the veins are a
+continuation of the fibrovascular bundles into the leaves, by means
+of which the latter are put in communication with the body of the
+plant.
+
+=177. The relation between veining and lobing.=—Compare the outline
+of a leaf of maple or ivy with one of oak or chrysanthemum. Do
+you perceive any correspondence between the manner of lobing or
+indentation of their margins, and the direction of the veins? (Figs.
+210, 211.) To what class would you refer each one?
+
+The lobes themselves may be variously cut, as in the fennel and rose
+geranium, thus giving rise to twice-cleft, thrice-cleft (Fig. 212),
+four-cleft, or even still more intricately divided blades.
+
+=178. Compound leaves.=—Compare with the specimens just examined
+a leaf of horse-chestnut, clover, or Virginia creeper, and one
+of rose, black locust, or vetch. Notice that each of these last is
+made up of entirely separate divisions or leaflets, thus forming a
+_compound leaf_. Notice also that the two kinds of compound leaves
+correspond to the two kinds of veining and lobing, so that we
+have palmately and pinnately compound ones. In pinnate leaves the
+continuation of the common petiole along which the leaflets are
+ranged is called the _rhachis_.
+
+[Illustration: FIG. 210.—Pinnately lobed leaf of horse nettle. FIG.
+211.—Palmately lobed leaf of grape.]
+
+[Illustration: FIG. 212.—Palmately parted leaf of a buttercup. FIG.
+213.—Pinnately compound leaf of black locust.]
+
+[Illustration: FIG. 214.—Palmately compound leaf of horse-chestnut.
+FIG. 215.—Pinnately trifoliolate leaf of a desmodium. FIG.
+216.—Palmately trifoliolate leaf of wood sorrel.]
+
+
+          Practical Questions
+
+  1. In selecting leaves for decorations that are to remain several
+  hours without water, which of the following would you prefer, and
+  why: smilax or Madeira vine (_Boussingaultia_); ivy or Virginia
+  creeper; magnolia or maple; maidenhair or shield fern (_Aspidium_)?
+  (173.)
+
+  2. Would you select very young leaves, or more mature ones, and why?
+
+  3. Can you name any parallel-veined leaves that have their margins
+  lobed, or indented in any way?
+
+  4. Which are the more common, parallel-veined or net-veined leaves?
+
+  5. Why do the leaves of corn and other grains not shrivel
+  lengthwise in withering, but roll inward from side to side? (173.)
+
+  6. Can you name any palmately veined leaves in which the secondary
+  veins are pinnate? Any pinnately veined ones in which the secondary
+  veins are palmate?
+
+  7. Lay one of each kind before you; try to draw a pinnate leaf with
+  palmate divisions. Do you see any reason now why these so seldom
+  occur in nature?
+
+  8. Name some advantages to a plant in having its leaves cut-lobed
+  or compound. (169.)
+
+  9. Mention some circumstances under which it might be advantageous
+  for a plant to have large, entire leaves. (169; Plate 9.)
+
+  10. How would the floating qualities of the leaves of the pond lily
+  be affected if their blades were cut-lobed or compound?
+
+  11. Do the leaves of the red cedar and arbor vitæ contribute to
+  their value as shade trees?
+
+  12. Name some of the favorite shade trees of your neighborhood; do
+  they, as a general thing, have their leaves entire, or lobed and
+  compound?
+
+  13. Which of the following are the best shade trees, and why: pine,
+  white oak, mimosa (_Albizzia_), sycamore, locust, horse-chestnut,
+  fir, maple, linden, China tree, cedar, ash?
+
+  14. Which would shade your porch best, and why: cypress vine,
+  grape, gourd, morning-glory, wistaria, clematis, smilax, kidney
+  bean, Madeira vine, rose, yellow jasmine, passion flower?
+
+
+          III. TRANSPIRATION
+
+  MATERIAL.—Leafy twigs of actively growing young plants. Sunflower,
+  corn, peach, grape, calla, and arums in general transpire rapidly;
+  thick-leaved evergreens and hairy or rough species, like mullein
+  and horehound more slowly. For Exp. 63, small-leaved, large-leaved,
+  and thick-leaved kinds will be needed.
+
+  APPLIANCES.—Glass jars and bottles with air-tight stoppers; a
+  little vaseline, oil, gardener’s wax, thread, cardboard, and a pair
+  of scales.
+
+  EXPERIMENT 62. TO SHOW WHY LEAVES WITHER.—Dry two self-sealing jars
+  thoroughly, by holding them over a stove or a lighted lamp for a
+  short time to prevent “sweating.” Place in one a freshly cut leafy
+  sprig of any kind, leaving the other empty. Seal both jars and set
+  them in the shade. Place beside them, but without covering of any
+  kind, a twig similar to the one in the jar. Both twigs should have
+  been cut at the same time, and their cut ends covered with wax or
+  vaseline, to prevent access of air. Look at intervals to see if
+  there is any moisture deposited on the inside of either jar. If
+  there is none, set them both in a refrigerator or cover with a wet
+  cloth and allow to cool for half an hour, and then examine again.
+  In which jar is there a greater deposit of dew? How do you account
+  for it? Take the twig out of the jar and compare its leaves with
+  those of the one left outside; which have withered the more, and
+  why?
+
+  EXPERIMENT 63. TO MEASURE THE RATE AT WHICH WATER IS GIVEN OFF BY
+  LEAVES OF DIFFERENT KINDS.—Fill three glass vessels of the same
+  size with water and cover with oil to prevent evaporation. Insert
+  into one the end of a healthy twig of peach or cherry; into the
+  second a twig of catalpa, grape, or any large-leaved plant, and
+  into the third, one of magnolia, holly, or other thick-leaved
+  evergreen, letting the stems of all reach well down into the water.
+  Care must be taken to select twigs of approximately the same size
+  and age, since the absorbent properties of very young stems are
+  more injured by cutting and exposure than those of older ones. All
+  specimens should be cut under water as directed in Exp. 58. Weigh
+  all three vessels, and at the end of twenty-four hours, weigh
+  again, taking note of the quantity of liquid that has disappeared
+  from each glass. This will represent approximately the amount
+  absorbed by the leaves from the twigs to replace that given off.
+  Which twig has lost most? Which least? Note the condition of the
+  leaves on the different twigs; have they all absorbed water about
+  as rapidly as they have lost it? How do you know this? Pluck the
+  leaves from each twig, one by one, lay them on a flat surface
+  that has been previously measured off, into square inches or
+  centimeters, and thus form a rough estimate of the area covered by
+  each specimen. Make the best estimate you can of the number of
+  leaves on each tree, and calculate the number of kilograms of water
+  it would give off at that rate in a day.
+
+  EXPERIMENT 64. THROUGH WHAT PART OF THE LEAF DOES THE WATER GET
+  OUT?—Take some healthy leaves of tulip tree, grape, tropæolum,
+  or any large, soft kind attainable. Cover with vaseline the
+  _leafstalk_ and _upper_ surface of one; the stalk and _under_
+  surface of a second; the stalk and _both_ surfaces of a third, and
+  leave a fourth one untreated. Suspend all four in a dry place by
+  means of a thread attached to the petioles so that both surfaces
+  may be equally exposed. The leaves must be all of the same species,
+  and as nearly as possible of the same age, size, and vigor, and
+  care must be taken that none of the vaseline is rubbed off in
+  handling. Examine at intervals of a few hours. Which of the leaves
+  withers soonest? Which keeps fresh longest? From what part would
+  you conclude, judging by this experiment, that the water escapes
+  most rapidly?
+
+=179. Transpiration, nutrition, and growth.=—We learn from the
+foregoing, and from Exps. 58 and 59, that plants give off moisture
+very much as animals do by perspiration. The two processes must not
+be classed together, however, for they are physiologically different.
+The action, in plants, is called _transpiration_. It is usually
+assumed that a large amount of water must pass through the plant
+in order to bring to it the necessary supply of food material; but
+since the entrance of mineral salts is brought about by osmosis,
+conditioned by the living cells of the root; and since osmosis
+of salts may take place in a direction opposite to that of the
+greater movement of water, it follows that the entrance of salts is
+independent of transpiration.
+
+Inasmuch, however, as a certain amount of water is necessary to bring
+the living cells into a condition of turgor (7) so that they may
+grow, it follows that there is a relation between transpiration and
+growth. If transpiration exceeds absorption for any length of time,
+the tissues will be depleted of their moisture, as is shown by the
+wilting of crops in dry, hot weather; and if the unequal movement
+continues long enough, the plant will die. Hence, a knowledge of the
+laws governing this important function is necessary to all who are
+interested in cultivating agricultural products.
+
+[Illustration: FIG. 217.—A “weeping tree,” showing the effect where
+absorption exceeds transpiration. Notice the position of the tree
+near the water where the roots have unlimited moisture. (_After_
+FRANCÉ.)]
+
+=180. Magnitude of the work of transpiration.=—Few people have any
+idea of the enormous quantities of water given off by leaves. It
+has been calculated that a healthy oak may have as many as 700,000
+leaves, and that 111,225 kilograms of water—equal to about 244,700
+pounds—may pass from its surface in the five active months from June
+to October. At this rate 226 times its own weight may pass through it
+in a year, and it would transpire water enough during that time to
+cover the ground shaded by it to a depth of 20 feet![2] Lawn grass
+gives off water at such a rate that a vacant lot of 150 × 50 feet,
+if well turfed, would be capable of transpiring over a ton of water
+a day. Compare these figures with the average yearly rainfall in our
+Gulf States—53 inches, approximately—and you can form some estimate
+of the injury done to a growing crop from this cause alone. The
+moisture is drawn from the surface by shallow rooted weeds (81) and
+dissipated through the leaves. In the case of forest trees the effect
+is different. Their roots, striking deep into the soil, draw up water
+from the lower strata and distribute it to the thirsty air in summer.
+
+As the water given off by transpiration is in the form of vapor,
+it must draw from the plant the amount of heat necessary for its
+vaporization, and thus has the effect of making the leaves and the
+air in contact with them cooler than the surrounding medium. At the
+same time the coolness and moisture of the air tend to check the
+loss by evaporation from the surface soil. It is partly to this
+cause, and not alone to their shade, that the coolness of forests is
+due. Measurements at various weather bureau stations in the United
+States show that in summer the temperature of oak woods is 4° C.
+lower during the day than in the open, and as much higher at night.
+In a beech wood in Germany the difference between the forest and the
+general temperature amounted to as much as 7° C.
+
+
+          Practical Questions
+
+  1. Is there any foundation in fact for the accounts of “weeping
+  trees” and “rain trees” that we sometimes read about in the papers?
+  (180; Exp. 48.)
+
+  2. Can you explain the fact, sometimes noticed by farmers, that in
+  wooded districts, springs which have failed or run low during a dry
+  spell sometimes begin to flow again in autumn when the trees drop
+  their leaves, even though there has been no rain? (180; Exp. 63.)
+
+  3. Other things being equal, which would have the cooler,
+  pleasanter atmosphere in summer, a well-wooded region or a treeless
+  one? (180.)
+
+  4. Could you keep a bouquet fresh by giving it plenty of fresh air?
+  (Exp. 62.)
+
+  5. Why does a withered leaf become soft and flabby, and a dried one
+  hard and brittle? (7; Exp. 62.)
+
+  6. Why do large-leaved plants, as a general thing, wither more
+  quickly than those with small leaves? (Exp. 63.)
+
+  7. Is the amount of water absorbed always a correct indication of
+  the amount transpired? Explain. (179.)
+
+  8. Explain the difference between the withering caused by excessive
+  transpiration and the shrinkage of cells due to plasmolysis. Are
+  both of these physiological processes?
+
+  9. Why is it best to trim a tree close when it is transplanted?
+  (179, 180.)
+
+  10. Why should transplanting be done in winter or very early
+  spring, before the leaves appear? (180.)
+
+
+          IV. ANATOMY OF THE LEAF
+
+  MATERIAL.—For study of the epidermis, leaves of the white garden
+  lily (_Lilium album_) are best, as the stomata can be seen on
+  their lower surface with the naked eye. Wandering Jew, Spanish
+  bayonet (_Yucca aloifolia_), anemone, narcissus, iris, canna, show
+  them under a hand lens, but less distinctly. For sections, beet,
+  mustard, and beech leaves may be used, or ready-mounted specimens
+  obtained of a dealer.
+
+  A compound microscope is needed for a minute study of the leaf
+  structure.
+
+[Illustration: FIGS. 218, 219.—Stomata of white lily leaf: 218,
+closed; 219, open. (_After_ GRAY.)]
+
+=181. Stomata.=—It was shown in Exp. 64 that the water of
+transpiration escapes most rapidly, as a general thing, from the
+under surface of leaves. To find out why this is so, a careful study
+of the epidermis will be necessary. For this purpose procure, if
+possible, the leaf of a white garden lily (_Lilium album_), wandering
+Jew, Spanish bayonet (_Yucca aloifolia_), anemone, narcissus, iris,
+or canna. The first-named is preferable, as the transpiration pores
+can be seen on it with the naked eye. Examine the under surface
+with a hand lens, and you will see that it is covered with small
+eye-shaped dots like those shown in Figs. 218 and 219. Strip off
+a portion of the epidermis, hold it up to the light on a piece of
+moistened glass, and they can be seen quite clearly with a lens.
+These dots are the pores through which the water vapor escapes in
+transpiration, and through which air finds its way into the tissues
+of the leaf. They are called _stomata_ (sing., _stoma_), from a Greek
+word meaning “a mouth.” Look for stomata on the upper epidermis; do
+you find any, and if so, are there as many as on the under surface?
+Do you see any relation between this fact and the results obtained
+from Exp. 64? Can you see any good reasons why the stomata should be
+placed on the under side in preference to the upper? Are they as much
+exposed to excessive light and heat, or as liable to be choked by
+dust, rain, and dew here as on the upper side?
+
+=182. Distribution of stomata.=—While stomata are generally more
+abundant on the under side of leaves, this is not always the case.
+In vertical leaves, like those of the iris, which have both sides
+equally exposed to the sun, they are distributed equally on both
+sides. In plants like the water lily, where the under surface lies
+upon the water, they occur only on the upper side. Succulent leaves,
+as a general thing, have very few, because they need to conserve all
+their moisture. Submerged leaves have none at all; why?
+
+[Illustration: FIG. 220.—A small piece of the under epidermis of
+an oak leaf, highly magnified to show the stomata, _g_, and minute
+hairs, _h_.]
+
+[Illustration: FIG. 221.—Under epidermis of an oat leaf, showing
+stomata.]
+
+=183. Minute study of a leaf epidermis.=—Place a bit of the lower
+epidermis of a leaf under the microscope, and examine with a high
+power. It will appear, if a monocotyl, to be composed of long, flat,
+rectangular spaces (Fig. 221); if the leaf of a dicotyl is used,
+they will be more or less irregular (Fig. 220), with the outlines
+fitting into each other like the tiling of a floor or the blocks of a
+Chinese puzzle. These spaces are the cells of the epidermis, and the
+lines are the cell walls. Can you find any of the cell contents? The
+cell sap is not often visible; do you see the nuclei? Can you give
+a reason why the epidermal cells are so thin and flat? Between some
+of the cells you will see two kidney-shaped bodies placed with their
+concave sides together so as to leave a lenticular opening between
+them. This is a _stoma_, and the kidney-shaped bodies (Figs. 218,
+219) are _guard cells_. They are given this name because they open
+or close the mouth of the stoma. If you will imagine a toy balloon
+made in the form of a hollow ring, like the tire of a bicycle, you
+can easily see, from Figs. 218, 219, that when the ring is strongly
+inflated, it will expand, and in enlarging its own circumference,
+will at the same time increase the diameter of the opening in the
+center. When the expansive force is removed, it collapses, thus
+closing, or greatly reducing, the aperture.
+
+[Illustration: FIG. 222.—Outline of a stoma of hellebore in vertical
+section. The darker lines show the shape assumed by the guard cells
+when the stoma is open; the lighter lines, when the stoma is closed.
+The cavities of the guard cells with the stoma closed are shaded, and
+are distinctly smaller than when the stoma is open.]
+
+In the same way the guard cells, when there is abundance of water in
+them, expand, thus opening the stoma so that the water vapor passes
+out more readily. But when there is a dearth of moisture, or when,
+by reason of chemical action in the soil, the roots fail to supply
+it, the leaves wilt, the guard cells, losing their water, collapse,
+closing the pore, and transpiration is thus prevented or greatly
+retarded. (Fig. 222.)
+
+Sketch a portion of the epidermis as it appears under the microscope,
+labeling the parts. If stomata can be found in both conditions, make
+sketches showing them both open and closed.
+
+=184. Internal structure of a leaf.=—Roll a leaf blade, or fold it
+tightly to facilitate cutting, and with a scalpel, or a very sharp
+razor, cut the thinnest possible slice through the roll. This will
+give a section at right angles to the epidermis. It should be so
+thin as to appear almost transparent. Put a small bit of a section
+in a drop of water on a slide, place under the microscope, using a
+high power, and look for the parts shown in Fig. 223. Notice the
+horizontally flattened cells of the upper epidermis, _e_, and of the
+lower epidermis, _e′_; also the vertically elongated palisade cells,
+_p_, filled with particles of green coloring matter. These particles
+are the chlorophyll bodies, to which the green color of the leaf is
+due. They are the active agents in the manufacture of plant food,
+and in a leaf removed from the plant during the day time and viewed
+under a high power, the chlorophyll bodies, on treatment with iodine,
+will be seen to contain granules of starch which they are in the act
+of elaborating. The collecting cells, _t_, receive the assimilated
+product from the palisade cells and pass it on through the spongy
+parenchyma, _sch_, to the fibrovascular bundles. Notice how much
+more abundant the green matter is in the upper part of the leaf than
+in the lower; has this anything to do with the deeper color of the
+upper surfaces of leaves? Notice the opening, _st_, lower epidermis;
+do you recognize it? (See Fig. 222.) It is a stoma, seen in vertical
+section. Notice the intercellular air spaces, _i_, _i_, in the spongy
+parenchyma, and the much larger one, _a_, just behind the stoma. Why
+is this last so much larger?
+
+[Illustration: FIG. 223.—Transverse section through a leaf of beet:
+_e_, upper epidermis; _e′_, lower epidermis; _st_, stoma; _a_, air
+space; _p_, palisade cells; _t_, collecting cells; _sch_, spongy
+parenchyma; _i_, _i_, intercellular air spaces; _Fbv_, section of a
+vein (fibrovascular bundle).]
+
+[Illustration: FIG. 224.—Chlorophyll bodies containing starch grains
+in the course of formation. Magnified 250 times.]
+
+Sketch the section of your specimen as it appears under the
+microscope. It will perhaps differ in some details from the one shown
+in the figure, but you can recognize and label the corresponding
+parts. Be sure that your drawing represents accurately the relative
+size and shapes of the different kinds of cells.
+
+It is in the upper surface, where the chlorophyll particles abound,
+that the manufacture of food goes on most actively, and from the
+under surface, where the stomata are situated, that transpiration
+takes place and air and other gases pass to and from the interior.
+These facts have important bearings on the growth and external
+characters of leaves.
+
+
+          Practical Questions
+
+  1. Explain why a plant cannot thrive if its stomata are clogged
+  with foreign matter. (179; Exp. 64; 184.)
+
+  2. Mention some of the ways in which this might happen. (181.)
+
+  3. Why must the leaves of house plants be washed occasionally to
+  keep them healthy? (179, 181.)
+
+  4. Why is it so hard for trees and hedges to remain healthy in a
+  large manufacturing town?
+
+
+          V. FOOD MAKING
+
+  MATERIAL.—A sprig of pondweed, mare’s-tail (_Hippuris_), hornwort
+  (_Ceratophyllum_), marsh St.-John’s-wort (_Elodea_), or other green
+  aquatic plant; bean or tropæolum, or other green leaves gathered
+  from plants growing in the sunshine; a healthy potted plant; a
+  small, fresh cutting.
+
+  APPLIANCES.—A shallow dish of water and two glass tumblers or
+  wide-mouthed jars; a bent glass or rubber tube; a piece of black
+  cloth or paper; a half pint of alcohol; iodine solution; a glass
+  funnel or a long-necked bottle from which the bottom has been
+  removed.
+
+  EXPERIMENT 65. IS THERE ANY RELATION BETWEEN SUNLIGHT AND THE GREEN
+  COLOR OF LEAVES?—Place a seedling of oats, or other rapidly growing
+  shoot, in the dark for a few days, and note its loss of color.
+  Leave it in the dark indefinitely, and it will lose all color and
+  die. Hence we may conclude that there is some intimate connection
+  between the action of light and the green coloring matter of leaves.
+
+  EXPERIMENT 66. DO LEAVES GIVE OFF ANYTHING ELSE BESIDES
+  WATER?—Submerge a green water plant, with the cut end uppermost,
+  in a glass vessel full of water, and invert over it a glass
+  funnel, or a long-necked bottle from which the bottom has been
+  removed as directed in Exp. 53. Expel the air from the neck of the
+  funnel—or bottle—by submerging and corking under water so as to
+  make it air-tight. Place in the sunlight and notice the bubbles
+  that begin to rise from the cut end of the plant. When they have
+  partly filled the neck of the funnel, remove the stopper and thrust
+  in a glowing splinter. If it bursts into flame, or glows more
+  brightly, what is the gas that was given off? (Exp. 22.)
+
+  As oxygen is not a product of respiration, some other process must
+  be at work here, during which oxygen is set free, and some other
+  substance used up. (Exps. 24 and 25.)
+
+[Illustration: FIG. 225.—Experiment showing that green plants give
+off oxygen in sunlight.]
+
+[Illustration: FIG. 226.—Experiment for showing that leaves absorb
+carbon dioxide from the atmosphere.]
+
+  EXPERIMENT 67. WHAT IS THE SUBSTANCE TAKEN IN WHEN OXYGEN IS GIVEN
+  OFF?—Fill two glass jars, or two tumblers, with water, to expel the
+  air, and invert in a shallow dish of water, having first introduced
+  a freshly cut sprig of some healthy green plant into one of them.
+  Then, by means of a bent tube, blow into the mouth of each tumbler
+  till all the water is expelled by the impure air from the lungs.
+  Set the dish in the sunshine and leave it, taking care that the
+  end of the cutting is in the water of the dish. After forty-eight
+  hours remove the tumblers by running under the mouth of each,
+  before lifting from the dish, a piece of glass well coated with
+  vaseline (lard will answer), and pressing it down tight so that no
+  air can enter. Place the tumblers in an upright position, keeping
+  them securely covered. Fasten a lighted taper or match to the end
+  of a wire, plunge it quickly first into one tumbler, then into the
+  other, and note the result. What was the gas blown from your lungs
+  into the jars? (Exps. 23, 24.) Why did the taper not go out in the
+  second jar? What had become of the carbon dioxide?
+
+  EXPERIMENT 68. TO SHOW THAT LIGHT IS NECESSARY FOR A PLANT TO
+  ABSORB CARBON DIOXIDE AND GIVE OFF OXYGEN.—Repeat Exp. 66, keeping
+  the plant in a dark or shady place; do you see any bubbles? Test
+  with a glowing match; is any oxygen formed in the tube of the
+  funnel? Move back into the sunlight and leave for a few hours; what
+  happens when you thrust a glowing splinter into the tube?
+
+  EXPERIMENT 69. IS ANY FOOD PRODUCT FOUND IN LEAVES?—Crush a few
+  leaves of bean, sunflower, or tropæolum, and soak in alcohol until
+  all the chlorophyll is dissolved out. Rinse them in water, and soak
+  the leaves thus treated in a weak solution of iodine for a few
+  minutes, then wash them and hold them up to the light. If there
+  are any blue spots on the leaves, what are you to conclude? If a
+  test for sugar is to be made, use sap pressed from fresh leaves;
+  for oils and fats, leaves should be dried without being placed in
+  alcohol.
+
+[Illustration: FIG. 227.—Leaf arranged with a piece of tin foil to
+exclude light from a portion of the surface.]
+
+  EXPERIMENT 70. HAS THE PRESENCE OR ABSENCE OF LIGHT ANYTHING TO DO
+  WITH THE OCCURRENCE OF STARCH IN LEAVES?—Exclude the light from
+  parts of healthy leaves on a growing plant of tropæolum, bean,
+  etc., by placing patches of black cloth or paper over them. Leave
+  in a bright window, or preferably out of doors, for several hours,
+  and then test for starch as in the last experiment; do you find any
+  in the shaded spots?
+
+  EXPERIMENT 71. IS THE PRESENCE OF AIR NECESSARY FOR THE PRODUCTION
+  OF STARCH?—Cover the blades and the petioles of several leaves with
+  vaseline or other oily substance so as to exclude the air, and
+  after a day or two test as before.
+
+=185. Influence of plants on the atmosphere.=—These experiments
+show that leaves cannot do their work without light and air. The
+particular element of the atmosphere used by them in the process of
+food making is carbon dioxide. Their action in absorbing this gas
+and giving off oxygen tends to counterbalance the opposite action of
+respiration, decomposition, and combustion of all kinds, by which the
+proportion of it in the atmosphere tends to be constantly increased.
+In this way they help to regulate the quantity of it present and have
+a beneficial effect in ridding the air of one source of impurity.
+
+=186. Photosynthesis.=—In our examination of the internal structure
+of the leaf, the chlorophyll bodies (184) were found to contain small
+granules of starch which the chlorophyll, under the stimulus of
+light, had elaborated as a nutriment for the plant tissues. Hence,
+the leaf may be regarded as a factory in which vegetable food,
+mainly starch, is manufactured out of the water brought up from the
+soil, and the carbon dioxide derived through the stomata from the
+atmosphere. In this process carbon dioxide (CO_{2}) is combined
+with water (H_{2}O) in such proportions that part of the oxygen is
+returned to the surrounding air. This is a fundamental food-forming
+process characteristic of green plants, and can take place only in
+the light. For this reason it has been named _Photosynthesis_, a word
+which means “building up by means of light,” just as _photography_
+means “drawing or engraving by means of light.”
+
+In carrying on the operation of photosynthesis, sunshine is the
+power, the chlorophyll bodies the working machinery, carbon dioxide
+and water the raw materials, and starch or oil the finished product,
+while oxygen and the water of transpiration represent the waste or
+by-products.
+
+=187. How the new combination is effected.=—It may seem strange that
+a gas and a liquid should combine to make something so different
+from either as starch, but their chemical constituents are the same
+in different proportions. Water is made up of 2 parts hydrogen and
+1 part oxygen; carbon dioxide, of 1 part carbon and 2 parts oxygen,
+while starch contains carbon, hydrogen, and oxygen, in the ratios of
+6, 10, and 5, respectively. Hence, by taking sufficient quantities
+of water and carbon dioxide and combining them in the proper
+proportions, the leaf factory can turn them into starch. If we use
+the letters C, H, and O, to represent Carbon, Hydrogen, and Oxygen,
+respectively, the new combination of materials can be expressed by an
+equation; thus:—
+
+  _water_    _carbon dioxide_      _starch_            _by-products_
+  5(H_{2}O)  + 6(CO_{2})       = (C_{6}H_{10}O_{5}) +  6(O_{2}) = 12(O).
+
+The water not used up in the process is given off as a waste product
+in transpiration, while the oxygen is returned to the air, as shown
+by Exp. 66. This equation is not to be understood as representing the
+chemical changes that actually take place in the leaf. These are too
+complicated, and at present too imperfectly known, to be considered
+here. It will serve, however, to give a fair idea of the final result
+from the process of photosynthesis, however brought about.
+
+Simple as the operation appears, the chemist has not, as yet,
+been able to imitate it. He can analyze starch into its original
+constituents, but while he has the ingredients at hand in abundance,
+and knows the exact proportions of their combination, it is beyond
+his power, in the present state of our knowledge, to put them
+together. Hence, both man and the lower animals are dependent on
+plants for this most important food element. The so-called factories
+that supply the starch of commerce do not _make_ starch any more than
+the miller makes wheat, but merely separate and render available for
+use that already elaborated by plants.
+
+=188. Proteins.=—Foods of this class are mainly instrumental in
+furnishing material for the growth and repair of the tissues out
+of which the bodies of both plants and animals are built up. They
+embrace a great variety of substances, but their chemical nature
+is very complex and very imperfectly understood. Nitrogen is an
+important element in their composition, whence they are commonly
+distinguished as “nitrogenous foods.” Besides nitrogen, there are
+present carbon, hydrogen, oxygen, and sulphur, and traces of the
+mineral salts absorbed from the soil are found in varying quantities
+in the ash of different proteins. The percentages in which these
+ingredients are combined and the processes concerned in their
+formation are at present a matter of pure hypothesis. Botanists
+are not agreed even as to whether they are made in the leaf or in
+some other part or parts of the plant, though the weight of opinion
+inclines to the view that their construction takes place in the leaf.
+
+=189. The activities of leaves.=—As there are only 4 parts of CO_{2}
+to every 10,000 parts of ordinary free air, it has been estimated
+that in order to supply the leaf factory with the raw material it
+needs, an active leaf surface of one square meter—a little over
+one square yard—uses up, during every hour of sunshine, the CO_{2}
+contained in 1000 liters (1000 quarts, approximately) of air. Suppose
+an oak tree to bear 500,000 leaves, each having a surface of 16 sq.
+cm., or 4 sq. in., and working 12 hours a day for 6 months in the
+year; you will then have some idea of the enormous quantity of air
+that passes each season through its leaf system. Add to this the
+almost incredible volume of water transpired in the same time (180),
+and we may well stand amazed at the tremendous activities of these
+silent workers that we are in the habit of regarding as mere passive
+elements in the general landscape.
+
+=190. The economic value of leaves.=—Besides their importance as
+sanitary and food-making agencies, leaves have a direct commercial
+value as food products in the hay and fodder they supply for our
+domestic animals, the tea and salads with which they provide our
+tables, the aromatic flavors and seasonings contained in them, and
+the drugs, medicines, and dyes of various kinds for which they
+furnish the ingredients.
+
+
+          Practical Questions
+
+  1. Why do gardeners “bank” celery? (Exp. 65.)
+
+  2. Why are the buds that sprout on potatoes in the cellar, white?
+  (Exp. 65.)
+
+  3. Why does young cotton look pale and sickly in long-continued wet
+  or cloudy weather? (Exp. 65.)
+
+  4. Why do parasitic plants generally have either no leaves or very
+  small, scalelike ones? (85, 186, 187.)
+
+  5. The mistletoe is an exception to this; explain why, in the light
+  of your answer to question 4.
+
+  6. Could an ordinary nonparasitic plant live without green leaves?
+  (186, 187.)
+
+  7. Are abundance and color of foliage any indication of the health
+  of a plant? (186, 187; Exp. 65.)
+
+  8. Is the practice of lopping and pruning very closely, as in the
+  process called “pollarding,” beneficial to a tree under ordinary
+  conditions? (186, 189; Exp. 63.)
+
+  9. Name some plants of your neighborhood that grow well in the
+  shade.
+
+  10. Compare in this respect Bermuda grass and Kentucky blue
+  grass; cotton and maize; horse nettle (_Solanun Carolinense_) and
+  dandelion; beech, oak, red maple, dogwood, pine, cedar, holly,
+  magnolia, etc.
+
+  11. Name all the aromatic leaves you can think of; all that are
+  used as food, beverages, drugs, and dyes.
+
+  12. What is the use of aromatic and medicinal leaves to the plant
+  itself? (Suggestion: Why does the housewife put lavender or tobacco
+  leaves in her woolen chest?)
+
+  13. Which would be richer in nourishment, hay cut in the evening or
+  in the morning, and why? (54, 186; Exp. 70.)
+
+  14. Mention three important sanitary services that are rendered by
+  a tree like that shown in plate 6 or 8. (180, 185, 189.)
+
+  15. Name some of the plants employed in the manufacture of starch.
+
+
+          VI. THE LEAF AN ORGAN OF RESPIRATION
+
+  MATERIAL.—A number of vigorous, freshly cut green leaves; a liter
+  or two (one or two quarts) of expanding flower or leaf buds.
+
+  APPLIANCES.—Some wide-mouthed jars of one or two liters’ capacity;
+  two small open vials of limewater.
+
+  EXPERIMENT 72. DO LEAVES GIVE OFF CARBON DIOXIDE?—Cover the
+  bottoms of two wide-mouthed jars with water about two centimeters
+  (1 inch) deep. Place in one a number of healthy green leaves with
+  their stalks in the water, and insert among them a small open
+  vial containing limewater. In the other jar place only a vial of
+  limewater in the clear water at the bottom, this last being merely
+  to make the conditions in both vessels the same. Seal both tight
+  and keep together in the dark for about 48 hours, and then examine.
+  In which jar does the limewater indicate the greater accumulation
+  of CO_{2}? (It may show a slight milkiness in the other vessel
+  due to gas derived from the inclosed air and water.) From this
+  experiment, what process would you conclude has been going on among
+  the leaves in jar No. 1? (Exp. 25.)
+
+[Illustration: FIG. 228.—Arrangement of apparatus to show that heat
+and carbon dioxide are given off by leaf buds.]
+
+  EXPERIMENT 73. IS THE EXHALATION OF CARBON DIOXIDE ACCOMPANIED
+  BY ANY OTHER CONCOMITANT OF RESPIRATION?—In Exps. 24, 25, it was
+  shown that respiration is accompanied by heat; hence, if the
+  production of carbon dioxide by the leaf is due to this cause, it
+  should be attended by the evolution of heat. To find out whether
+  this is the case, partly fill a glass jar of two liters’ capacity
+  with unfolding leaf buds arranged in layers alternating with damp
+  cotton batting or blotting paper (Fig. 228); close the jar tightly
+  and leave from 12 to 24 hours in the dark to prevent the action
+  of photosynthesis. Then insert a thermometer and note the rise in
+  temperature. If a lighted taper is plunged in, it will quickly be
+  extinguished, showing that respiration has been going on.
+
+=191. Respiration in leaves.=—We see from experiments like the
+foregoing that the leaf, besides carrying on the functions of
+digestion, photosynthesis, and transpiration, is also an active agent
+in the work of respiration. In this function oxygen is used up and
+carbon dioxide given off, just as in the respiration of animals; but
+the process is so slow in plants that it is much more difficult to
+detect than the contrary action in photosynthesis, and is, in fact,
+not perceptible at all while the latter is going on, though it does
+not cease even then.
+
+But while the leaf is the principal organ of respiration, the process
+is carried on in other parts of the plant as well, else it could not
+survive during the leafless months of winter. It _appears_ to be most
+active at night, but this is only because it is not obscured then,
+as during the day, by the more active function of photosynthesis.
+Indeed, it was for a long time supposed that plants “breathed” only
+at night, and it was thought to be unwholesome to keep them in a
+bedroom. It is now known, however, that respiration goes on at all
+times and in all living parts of the plant, but the quantity of
+oxygen taken in is so small from a hygienic point of view that it may
+be disregarded.
+
+=192. Distinctions between respiration and photosynthesis.=—While
+these two functions are contrasting and antipodal, so to speak, in
+their action, they are mutually complementary and interdependent, the
+one manufacturing food and the other using it up, or rather marking
+the activity of those life processes by which it is used up. The
+difference between them will be made clear by a comparison of the two
+processes as summarized in the following statement:
+
+           PHOTOSYNTHESIS                        RESPIRATION
+
+  Goes on only in sunlight and in      Goes on at all times and in all
+  the green parts of plants.           parts of the plant.
+
+  Produces starch and sugar.           Releases energy (heat and working
+                                       power).
+
+  Gives off, as by-product, oxygen.    Gives off, as by-products, CO₂
+                                       and water.
+
+  A constructive process, in which     A destructive, or consumptive
+  energy is used up to make food.      process, in which food is used up
+                                       in expending energy.
+
+=193. Metabolism.=—The total of all the life processes of plants,
+including growth, waste, repair, etc., is summed up under the general
+term _metabolism_. It is a _constructive_ or building-up process when
+it results in the making of new tissues out of food material absorbed
+from the earth and air, and the consequent increase of the plant in
+size or numbers. But, as in the case of animals, so with plants, not
+all the food provided is converted into new tissue, part being used
+as a source of energy, and part decomposed and excreted as waste.
+In this sense, metabolism is said to be _destructive_. The waste in
+healthy growing plants is always, of course, less than the gain,
+and a portion of the food material is laid by as a reserve store.
+For this reason, photosynthesis, being a constructive process, is
+usually more energetic than respiration, which is the measure of the
+destructive change of materials that attends all life processes.
+
+It is evident also, from what has been said, that growth and repair
+of tissues can take place only so long as the plant has sufficient
+oxygen for respiration, since the energy liberated by it is necessary
+for the assimilation of nourishment by the tissues.
+
+Thus we see that plants are dependent on air not only for
+respiration, but for nutrition, and none of their life processes can
+be carried on without it.
+
+
+          Practical Questions
+
+  1. Can a plant be suffocated, and if so, in what ways? (87, 193;
+  Exps. 26, 27.)
+
+  2. The roots on the palm shown in plate 3 are not drawing any sap
+  from it as parasites; why does their continued growth bring about
+  the death of the tree? (87, 193.)
+
+  3. Is it unwholesome to keep flowering plants in a bedroom? Leafy
+  ones? Why, in each case? (191.)
+
+  4. Would there be any more reason for objecting to the presence of
+  flowers by night than by day? Explain. (191.)
+
+  5. Why is respiration much less marked in plants than in animals?
+  (30, 31.)
+
+
+          VII. THE ADJUSTMENT OF LEAVES TO EXTERNAL RELATIONS
+
+  MATERIAL.—A potted plant of oxalis, spotted medick, white clover,
+  or other sensitive species. The subject is better suited for
+  outdoor observation than for laboratory work.
+
+  EXPERIMENT 74. TO SHOW THAT LEAVES ADJUST THEMSELVES TO CHANGES IN
+  INTENSITY OF LIGHT.—Keep a healthy potted plant of oxalis, white
+  clover, or spotted medick in your room for observation. Note the
+  daily changes of position the leaves undergo. Sketch one as it
+  appears at night and in the morning.
+
+[Illustration: FIGS. 229, 230.—Leaves of a peanut plant: 229, in day
+position; 230, in night position.]
+
+  In order to determine whether these changes are due to want of
+  light or of warmth, put your plant in a dark closet in the middle
+  of the day, without change of temperature. After several hours note
+  results. Transfer to a refrigerator, or in winter place outside a
+  window where it will be exposed to a temperature of about 5° C.
+  (40° F.) for several hours, and see if any change takes place. Next
+  put it at night in a well-lighted room and note the effect. If
+  practicable, keep a specimen for several weeks in some place where
+  electric lights are burning continuously all night, and watch the
+  results.
+
+  EXPERIMENT 75. TO SHOW THAT THE FALL OF THE LEAF MAY RESULT FROM
+  OTHER CAUSES THAN COLD OR FROST.—Wrap some leaves of ailanthus,
+  Kentucky coffee tree, ash, walnut, or hickory in a damp towel and
+  keep them in the dark for several days; the leaflets will fall
+  away, leaving a clear scar like those on winter twigs.
+
+  EXPERIMENT 76. TO SHOW THAT ADJUSTMENTS TO TEMPERATURE MAY BE MADE
+  BY CHEMICAL MEANS.—Place a small twig of oleander, laurestinus,
+  or other broad-leaved evergreen in a 5 to 10 per cent solution of
+  sugar, and transfer it at the end of a few days to a temperature of
+  6° to 8° below freezing. On comparison with a similar twig that has
+  stood for the same length of time in pure water, it will be found
+  to possess a greater power of resistance to cold.
+
+[Illustration: FIG. 231.—A plant that has been growing near an open
+window, showing the leaves all turned toward the light.]
+
+=194. The light relation.=—The principal external conditions to which
+leaves have to adjust themselves are light, air, moisture, gravity,
+temperature, and the attacks of animals. From the knowledge of their
+work and function gained in the preceding sections, it will be clear
+that the primary relation of the leaf is a light relation, and to
+this, first of all, it must adjust itself.
+
+It was shown in Exps. 56 and 57 how promptly leaves respond to
+changes in the direction of light, and a little observation (Exp.
+74) will convince us that they are equally sensitive to changes in
+intensity and periodicity of illumination.
+
+=195. Phototropism.=—The movement of plants in response to light is
+called _phototropism_—a word that means “turning toward or away from
+light.” It includes all kinds of light adjustments, and examples of
+it are to be met with everywhere in the disposition of leaves with
+reference to their light exposure.
+
+=196. Horizontal and vertical adjustment.=—Take two sprigs, one
+upright, the other horizontal, from any convenient shrub or tree—and
+notice the difference in the position of the leaves. Examine their
+points of attachment and see how this is brought about, whether by a
+twist of the petiole or of the base of the leaf blades, or by a half
+twist of the stem between two consecutive leaves, or by some other
+means.
+
+[Illustration: PLATE 10.—A mosaic of moonseed leaves, showing
+adjustment for light exposure.
+
+(_From_ Mo. Botanical Garden Rep’t.)]
+
+Observe both branches in their natural position; what part of the
+leaf is turned upward, the edge or the surface of the blade? Change
+the position of the two sprigs, placing the vertically growing one
+horizontal, and the horizontal one vertical. What part of the leaves
+is turned upward in each?
+
+[Illustration: FIGS. 232, 233.—Adjustment of leaves to different
+positions: 232, upright; 233, procumbent.]
+
+[Illustration: FIG. 234.—Leaf mosaic of elm.]
+
+=197. Leaf mosaics.=—Trees with horizontal or drooping branches,
+like the elm and beech, and vines growing along walls or trailing
+on the ground, generally display their foliage in flat, spreading
+layers, each leaf fitting in between the interstices of the others
+like the stones in a mosaic, whence this has been called the _mosaic_
+arrangement. (Plate 10.) In plants of more upright or bunchy habit,
+the leaves are placed at all angles, giving the appearance of a
+rosette when viewed from above, whence this is called the _rosette_
+arrangement.
+
+A variety of the same disposition is seen in the pyramidal shape
+assumed by plants with large, undivided leaves like the mullein and
+burdock (Fig. 237), in which access of light is secured by a mutual
+adjustment between the size and position of leaves, the upper ones
+becoming successively smaller.
+
+=198. Heliotropism=—“turning with the sun”—is the name given to the
+daily movement of plants like the cotton and sunflower in turning
+their leaves or their blossoms to face the sun. If you live where
+cotton is grown, notice the leaves in a field about ten o’clock on
+a bright sunny morning, and again from the same point of view at
+about four or five in the afternoon. Do you perceive any difference
+in their general disposition? Watch on a cloudy day and see if any
+change takes place. Find out by observation whether the “heliotrope”
+of the hothouses is really heliotropic.
+
+[Illustration: FIGS. 235, 236.—Horse-chestnut leaves: 235, leaf
+rosette seen from above; 236, the same seen sidewise, showing the
+formation of rosettes by the lengthening of the lower petioles.]
+
+[Illustration: FIG. 237.—Leaf pyramid of mullein.]
+
+[Illustration: FIGS. 238, 239.—A compass plant, rosinweed (_Silphium
+laciniatum_): 238, seen from the east; 239, seen from the south.]
+
+=199. Adjustment against too great intensity of light.=—Plants
+frequently have to protect themselves against excess of light and
+heat. An interesting example of this kind of adjustment is furnished
+by the rosinweed, or compass plant (_Silphium laciniatum_, Figs. 238,
+239), which grows in the prairies of Alabama and westward, where it
+is exposed to intense sunlight. The leaves not only stand vertical,
+but have a tendency to turn their edges north and south so that the
+blades are exposed only to the gentler morning and evening rays. The
+prickly lettuce manifests the same habit in a less marked degree.
+
+[Illustration: FIGS. 240, 241.—A plant of the guayule (_Parthenium
+argentatum_), to the leaves of which indexes have been affixed to
+show their day and night position: 240, day position; 241, night
+position. (_From_ photographs by Prof. F. E. Lloyd.)]
+
+=200. Night and day adjustments.=—These are movements in response to
+changes in the degree of illumination and temperature, as evidenced
+by the fact that they become feeble and soon cease altogether if
+the plant is kept a sufficient time under uniform conditions as
+to these two factors. (Exp. 74.) They are called “nyctitropic” or
+sleep movements, because they are most obvious in certain plants
+that undergo periodic adjustments to the alternations of day and
+night suggestive of an imaginary likeness to the sleep of animals.
+Examples are most frequently met with among members of the pea
+family (_Leguminosæ_), the spurges (_Euphorbiaceæ_), and the sorrel
+(_Oxalis_) family. They are found among other species also, and
+indeed are much more general than is usually supposed, most plants
+showing signs of them if carefully tested. A simple way of doing
+this is by attaching bristles about two inches long to the tips of
+two leaves on opposite sides of the stem, as in Figs. 240, 241,
+and comparing the divergence of the bristles during the day and at
+nightfall. In this way a change of position in the leaves, too
+slight to attract attention otherwise, will be made apparent. The
+positions assumed vary in different plants, and even in the parts of
+the same compound leaf; in the kidney bean, for instance, the common
+petiole turns up at night, while the individual leaflets turn down.
+One of the common pigweeds (_Amaranthus Palmeri_, Figs. 242-244) is
+heliotropic in the day time and nyctitropic at night.
+
+[Illustration: FIGS. 242-244.—Showing the movements of _Amaranthus
+Palmeri_: 242, 243, position at sunrise and sunset (heliotropic);
+244, night position (nyctitropic) half an hour after sunset. (_From_
+photographs by Prof. F. E. Lloyd.)]
+
+The very striking nyctitropic adjustments of the wild senna (_Cassia
+tora_) photographed by Professor Francis E. Lloyd of the Alabama
+Polytechnic Institute (Figs. 245-250), though obviously influenced by
+the sun, are not directed toward it as in those of truly heliotropic
+plants.
+
+[Illustration: FIGS. 245-250.—Wild senna (_Cassia tora_), showing the
+nyctitropic adjustments of its leaves. The upper figures show their
+horizontal arrangement; those below, the vertical: 245, 248, position
+of the leaves at 9 A.M.; 246, 249, at 3 P.M.; 247, 250, at 6.30 P.M.
+(_From_ photographs by Prof. F. E. Lloyd.)]
+
+These movements are common also among flowers, many of them having
+regular hours for opening and closing, as indicated by such names as
+“morning-glory” and “four-o’clock.” In these cases, however, other
+causes (277, 280) than the light relation must be taken into account.
+
+=201. Irritability= is a general term applied to the power in plants
+of receiving and responding by spontaneous movements to impressions
+from without. In its widest acceptation, irritability includes,
+besides the various forms of adjustment described in this section and
+the next, all movements due to geotropism, those of roots seeking
+air and moisture, the revolution of twining stems and tendrils,
+the circulation of protoplasm in the cell—any movement, in short,
+that is made in response to an impression from the environment is a
+manifestation of irritability. It may be of various degrees, but is
+possessed to some extent by every living vegetable organism.
+
+The term is usually applied, however, more especially to those
+obvious and pronounced responses made by plants to their
+surroundings, as exemplified in the cases just given. Still more
+marked instances are to be found in the movements of the tentacles
+of insectivorous plants, and the sensitive leaflets of the mimosa
+that close at the slightest touch. The tendrils of the passion flower
+are said to appreciate and respond to a pressure that cannot be
+distinguished even by the human tongue, and many plants will detect
+and respond to the ultra-violet rays of light, which are entirely
+invisible to man.
+
+This faculty of irritability among plants corresponds, in an
+imperfect, rudimentary way, to what we recognize in animals as
+nervous excitability. By this it is not meant to imply that the two
+things are identical in their ultimate manifestations, though we
+may regard them as fundamentally the same in that they are both to
+be referred to the property inherent in protoplasm of responding to
+stimuli. There is no indication, however, that irritability in the
+vegetable kingdom is accompanied by anything like consciousness or
+volition, or that plants possess any power of initiative. While the
+movements in response to stimuli are in many cases eminently adapted
+to a purpose, we have no evidence of a controlling power behind them.
+The movement comes automatically in response to the stimulus, whether
+the effect at the moment be advantageous or the reverse.
+
+=202. Adjustments in relation to moisture.=—These adjustments may
+be—(1) To guard against excess of moisture; _e.g._ glands for
+excreting water and salts; scales, wax, down, etc., on the surface of
+leaves. These may serve also for protection against cold, insects,
+excess of light and heat. (2) For the conservation of moisture;
+_e.g._ the revolute leaf margins of grasses and sand plants growing
+along the seashore; the fleshy leaves of stonecrops and purselanes;
+the hard epidermis of yuccas and aloes; the scales, scurf, and down,
+by which the moisture absorbed from the soil by plants growing in
+dry and barren places is prevented from escaping too rapidly through
+the stomata; the leaf cups and holders sometimes formed by winged
+petioles and clasping leaf bases for retaining dew or rain water.
+(3) For leaf drainage, or the conduction of moisture, by means of
+grooves, channels, and taper-pointed leaves, which act as natural
+gutters and drain pipes.
+
+[Illustration: FIG. 251.—Cross sections of the leaf of sand grass:
+_a_, unrolled in its ordinary position; _b_ and _c_, rolled up to
+prevent too rapid transpiration.]
+
+[Illustration: FIG. 252.—Winged petiole of _Polymnia_. FIG.
+253.—Water cups of _Silphium perfoliatum_.]
+
+[Illustration: FIG. 254.—Fallen leaves. Notice how they cover the
+ground with a warm mulch, protecting the soil from denudation, and
+the roots and seeds from frost.]
+
+=203. The fall of the leaf.=—This is, in effect, an adjustment to
+change of temperature, but that it is not directly due to cold is
+shown by Exp. 75, and also by the fact that leaves in the tropics
+and those of evergreens, while they do not fall at stated periods
+like the bulk of the foliage in the temperate zones, are cut off just
+the same and replaced by new ones, whenever, for any reason, they
+are unable to perform their function. In cold climates they fall
+at the approach of winter, not because the frost loosens them, but
+because the roots are not able to absorb enough moisture to supply
+them with material for making food. The needles and the scale-leaves
+characteristic of evergreens in cold regions are enabled to persist
+indefinitely by reason of their contracted surface. This prevents the
+dissipation of moisture and affords no lodging for the accumulations
+of sleet and snow that would otherwise cumber and perhaps break the
+boughs with their weight. Trees and shrubs that shed their leaves
+in winter are said to be _deciduous_, from a Latin word meaning “to
+fall.” Can you mention some advantages of the deciduous habit to a
+plant with broad, expanded leaves, growing in a cold climate?
+
+The mechanical means by which the leaf fall is accomplished is
+through the growth of a corky layer of loose cells that forms at
+the base of the petiole and cuts it away from the stem, leaving a
+smooth, clean scar. Tear some fresh young leaves from a growing
+twig and compare the scars with those on a winter bough. Do you see
+any difference? This corky layer can be made to form in some plants
+artificially, by depriving them of working material. (Exp. 75.)
+
+=204. The protection of wintergreen leaves.=—A great many, perhaps
+the majority of broad-leaved evergreens, bear no obvious protection
+against cold, while a large proportion, such as chickweed, violet,
+fumitory, groundsel (_Senecio_), and dead nettle (_Lamium_), would
+seem peculiarly unfitted, by their delicate structure, to withstand
+it. But recent investigations by the Swedish botanist, Lidforss,
+have shown that all wintergreen leaves, with the exception of those
+on submerged water plants, which are sufficiently protected by the
+medium in which they live, lose their starch in winter and contain
+instead an increased percentage of sugar. The same is true of other
+vegetable structures also, where starch is present, such as roots,
+stems, tubers, and winter fruits—nuts, haws, persimmons, and the
+like, which, as every schoolboy knows, become perceptibly sweeter
+after frost.
+
+The presence of certain substances, of which sugar is the most
+frequent, enables plants to withstand a greater degree of cold
+than they could otherwise endure (Exp. 76). This effect, as shown
+by Lidforss’s experiments, is due to the action of sugar in
+counteracting, or retarding, the “salting out” of proteins by cold,
+as explained in 33.
+
+As sugar is readily reconverted into starch by exposure to a
+moderately high temperature for even a few days, we may find here
+an explanation of the fact that plants which have survived the
+prolonged cold of winter are often killed by a single sharp night
+frost following a few warm days in early spring, before the tender
+new growth has appeared. The plant suffers, not from the direct
+effects of cold, but from the warmth preceding it, which stimulated
+the transformation into starch of the sugar that would have prevented
+the loss of proteins. On the same principle we may account for the
+puzzling fact that the sunny southern side of trees and shrubs
+usually suffers more from the effects of sudden frost than the shaded
+and colder northern face.
+
+In apparent conflict with this reasoning is the fact that sugar
+cane and the sugar beet are peculiarly susceptible to cold. This,
+however, does not invalidate the premises established by Lidforss’s
+researches, but merely emphasizes the need of further investigation,
+which may either reconcile all the facts, or modify their
+interpretation.
+
+=205. The colors of autumn leaves.=—These are due to the breaking
+up and disappearance of the chlorophyll when the leaf factory has
+to “shut down” for want of raw material to work with (203). It is
+closely connected with the appearance of frost, since the same
+changes of temperature which produce frost cause the cessation of sap
+flow that brings about the disorganization of the chlorophyll and the
+formation of various pigments derived from it. Besides these, leaves
+may contain other coloring matters that are perceptible only when the
+chlorophyll disappears; and in the sap there is a reddish pigment
+which becomes either a very bright red, or a dark purplish maroon,
+from the effect of chemicals that combine with it in the leaves. With
+these coloring materials at command it is easy to see how the autumn
+woods can assume such splendid hues.
+
+
+          Practical Questions
+
+  1. How would you explain the fact that the outer twigs of trees
+  generally are the most leafy? (99, 194; Exps. 57, 74.)
+
+  2. Is the common sunflower a compass plant? Is cotton?
+
+  3. Are there any such plants in your neighborhood?
+
+  4. Compare the leaves of half a dozen shade-loving plants of your
+  neighborhood with those of as many sun-loving ones; which, as a
+  general thing, are the larger and less incised?
+
+  5. Give a reason for the difference. (169.)
+
+  6. Why do most leaves—notably grasses—curl their edges backward in
+  withering? (182.)
+
+  7. What advantage is gained by doing this? (202.)
+
+  8. Observe such of the following plants as are found in your
+  neighborhood, and report any changes of position that may take
+  place in their leaves and the causes to which such changes should
+  be ascribed: wood sorrel, mimosa, honey locust, wild senna,
+  partridge pea, wild sensitive plant, redbud, bush clover, Japan
+  clover, Kentucky coffee tree, sensitive brier (_Schrankia_),
+  peanut, kidney bean.
+
+  9. Which of the trees named below shed their leaves from base to
+  tip of the bough (centripetally), and which in the reverse order:
+  ash, beech, hazel, hornbeam, lime, willow, poplar, pear, peach,
+  sweet gum, elm, sycamore, mulberry, China tree, sumac, chinquapin?
+
+  10. Account for the fact that evergreen trees and shrubs have
+  generally thick, hard, and shiny leaves, like those of the holly
+  and magnolia, or scales and needles, as the cedar and pine. (203.)
+
+  11. Why do many plants which are deciduous at the North tend to
+  become evergreen at the South? (203.)
+
+  12. Why are evergreens more abundant in cold than in warm climates?
+  (203.)
+
+  13. There is an apparent inconsistency between questions 11 and 12;
+  can you reconcile it? (203.)
+
+  14. Why is it more important to protect the south side of trees
+  against exposure to frost than the northern side? (33, 204.)
+
+  15. Explain why peach orchards on the tops and northern slopes of
+  elevated areas are less liable to have their fruit destroyed by
+  late frost than those in the valleys and on the southern slopes.
+  (33, 204.)
+
+
+          VIII. MODIFIED LEAVES
+
+  MATERIAL.—Get from a florist a potted plant of sundew,
+  Venus’s-flytrap, sarracenia, or, if possible, one of all three, and
+  keep in the schoolroom for observation. The subject can be studied
+  best in a well-stocked greenhouse, if one is accessible.
+
+[Illustration: FIG. 255.—Spearlike leaves of Spanish bayonet.]
+
+=206. Modification and adaptation.=—Modification is structural
+adjustment, or adaptation, carried so far as to obscure the original
+form of an organ. Its true nature, however, can generally be
+determined by some of the tests mentioned in 100.
+
+Examples of the modification of leaves to do the work of other
+organs have already been noticed, as also their entire disappearance
+in certain cases (97, 101, 149) and replacement by other parts; it is
+unnecessary, therefore, to revert to this branch of the subject here.
+
+=207. Protective modifications.=—The most general protective
+modifications that leaves undergo are (1) for the conservation
+of moisture, as explained in 202, and (2) for protection against
+animals. Many of the adaptations for the former purpose serve
+incidentally for defense against animals also. Spines, hairs, scales,
+sticky exudations, water holders, clasping and perfoliate leaves bar
+the way to crawling insects; horny cuticles, as well as offensive
+odors, bitter secretions, and poisonous juices warn leaf-eating
+cattle and bugs away. These devices are merely protective, however,
+and adapted to a passive attitude of self-defense.
+
+[Illustration: FIGS. 256-258.—Protective hairs magnified: 256,
+mullein; 257, cinque-foil 258, Shepherdia.]
+
+=208. Insectivorous leaves.=—But sometimes a plant becomes the
+aggressor, and instead of standing on the defensive or suffering
+itself to be quietly devoured, proceeds to capture and devour small
+game on its own account, and in this case, the leaf sometimes becomes
+a deadly weapon of destruction.
+
+=209. Pitcher plants.=—The sarracenia, or trumpet leaf, is a
+familiar example of this class. The lower part of the leaf blade is
+transformed into a hollow vessel for holding water, and the top is
+rounded into a broad flap called the _lamina_. Sometimes the lamina
+stands erect, as in the common yellow trumpets of our coast regions,
+and when this is the case, it is brilliantly colored and attracts
+insects (Fig. 259). Sometimes, as in the parrot-beaked and the
+spotted trumpet leaf, it is bent over the top of the water vessel
+like a lid, and the back of the leaf, near the foot of the lamina, is
+dotted with transparent specks that serve to decoy foolish flies away
+from the true opening and tempt them to wear themselves out in futile
+efforts to escape, as we often see them do against a window pane.
+
+[Illustration: FIG. 259.—Yellow trumpets (_Sarracenia flava_).
+(_From_ the Mo. Botanical Garden Rep’t.)]
+
+[Illustration: FIG. 260.—Plant of sundew.]
+
+If the contents of one of these leaves are examined with a lens,
+there will generally be found mixed with the water at the bottom the
+remains of the bodies of a large number of insects. The hairs on the
+outside all point up, toward the rim of the pitcher, while those on
+the inside turn down, thus smoothing the way to destruction, but
+making return impossible to a small insect when once it is ensnared.
+When we remember that these plants are generally found in poor,
+barren soil, we can appreciate the value to them of the animal diet
+thus obtained.
+
+[Illustration: FIGS. 261-263.—Leaves of sundew magnified: 261, leaf
+expanded; 262, leaf closing over captured insect; 263, leaf digesting
+a meal.]
+
+=210. Flytraps.=—The most remarkable examples of insect-catching
+leaves are the Venus’s-flytrap, found in the seacoast region of
+North Carolina, and the sundew (_Drosera rotundifolia_), common
+on the margins of sandy bogs and ponds. The latter is a delicate,
+innocent-looking little plant, and owes its poetic name to the
+dewlike appearance of a shining, sticky fluid exuded from glands on
+its leaves, which glitter in the sun like dewdrops. It is, however,
+a most voracious carnivorous plant, the sticky leaves acting as so
+many bits of fly paper by means of which it catches its prey. When a
+fly has been trapped, the tentacles close upon it, the edges of the
+leaf curve inward, making a sort of stomach, from the glands of which
+an acid juice exudes and digests the meal. After a number of days,
+varying according to the digestibility of the diet, the blades slowly
+unfold again and are ready for another capture.
+
+[Illustration: FIG. 264.—Bladderwort, showing finely dissected
+submerged leaves bearing bladders for capturing animalculæ.]
+
+The bladderwort, common in pools and still waters nearly everywhere,
+has its petioles transformed into floats, while the finely dissected,
+rootlike blades bear little bladders which, when examined under the
+microscope, are found to contain the decomposed remains of captured
+animalculæ.
+
+
+          Practical Questions
+
+  1. Can you find any kind of leaf that is not preyed upon by
+  something? If so, how do you account for its immunity?
+
+  2. Make a list of some of the most striking of the protected leaves
+  of your neighborhood.
+
+  3. What is the nature of the protective organ in each case?
+
+  4. For protection against what does it seem to be specially adapted?
+
+  5. Are the plants in your list for the most part useful ones, or
+  troublesome weeds?
+
+  6. Examine the leaves of the worst weeds that you know of and see
+  if these will help in any way to account for their persistency.
+
+
+          Field Work
+
+  (1) In connection with Sections I and II, observe the effect of the
+  lobing and branching of leaves in letting the sunlight through.
+  Notice any general differences that may appear as to shape, margin,
+  and texture in the leaves of sun plants, shade plants, and water
+  plants, and account for them. Study the arrangement of leaves on
+  stems of various kinds, with reference to the size and shapes of
+  leaves and their light relations. Consider the value of the various
+  kinds of foliage for shade; for ornament; as producers of moisture;
+  as food; as insect destroyers, etc.
+
+  Make a special study of the twelve principal deciduous trees of
+  your neighborhood. Compare the leaves, bark, and branches of the
+  same trees so that you will be able to recognize them by any one of
+  these means alone.
+
+  (2) In connection with Sections III and V, consider the effects
+  upon soil moisture of transpiration from the leaves of forest
+  trees and from those of shallow-rooted herbs and weeds that draw
+  their water supply from the surface. Consider the value of forests
+  in protecting crops from excessive evaporation by acting as wind
+  breaks. Study the effect of the fall of leaves upon the formation
+  of soil. In any undisturbed forest tract turn up a few inches of
+  soil with a garden trowel and see what it is composed of. Notice
+  what kind of plants grow in it. Note the absence of weeds and
+  account for it. Compare the appearance of trees scattered along
+  windy hillsides, where the fallen leaves are constantly blown away,
+  or in any position where the soil is unrenewed, with those in an
+  undisturbed forest, and then give an opinion as to the wisdom of
+  hauling away the leaves every year from a timber lot.
+
+  (3) In Section VII, observe, in different kinds of leaf mosaics,
+  the means by which the adjustment has been brought about and the
+  purpose it subserves. Make a list of plants illustrating the two
+  habits. Notice the form and position of petioles of different
+  leaves, and their effect upon light exposure, drainage, etc., and
+  the behavior of the different kinds in the wind. Look for compass
+  plants in your neighborhood, and for other examples of adjustment
+  to heat and light. Study the position of leaves at different times
+  of day and in different kinds of weather and note what changes
+  occur and to what they are due.
+
+  Make a list of ten plants that seem to you to have best worked out
+  the problem of leaf adjustment, giving the reasons for your opinion.
+
+  Study the drainage system of different plants and observe whether
+  there is any general correspondence between the leaf drainage and
+  the root systems. This will lead to interesting questions in
+  regard to irrigation and manuring. Where plants are crowded, the
+  growth of both roots and leaves is complicated with so many other
+  factors that it is best to select for observations of this sort
+  specimens growing in more or less isolated situations.
+
+  Notice the time of the expansion and shedding of the leaves of
+  different plants, and whether the early leafers, as a general
+  thing, shed early or late; in other words, whether there seems to
+  be any general time relation between the two acts of leaf expansion
+  and leaf fall.
+
+  (4) Under Section VIII, look for instances of modified leaves;
+  study the nature of the different modifications you find, and try
+  to understand their meaning and object. Make a collection (_a_)
+  of all the leaves you can find modified to serve other than their
+  normal purposes; (_b_) of all the organs of other kinds that
+  have been modified to serve as leaves; (_c_) of all the modified
+  parts of leaves—stipules and petioles—that you can find. Keep the
+  collections separate, labeling each specimen with the name of the
+  plant it belongs to, what part it is, what use it serves, when and
+  where found. These collections need not be made individually, but
+  by the class as a whole and kept for the use of the school.
+
+  Observe also (_d_) the differences between young and old leaves of
+  the same kind, and the leaves of young and old plants or parts of
+  plants of the same kind; (_e_) resemblances between young leaves
+  belonging to plants of different species; (_f_) between young
+  leaves of one species and mature ones of one or more different
+  species. Make a collection of all the specimens you can find
+  illustrating the three points mentioned, referring each to its
+  proper head, and giving the name and relative age—old or young—of
+  all specimens collected.
+
+
+
+
+CHAPTER VII. THE FLOWER
+
+
+          I. DISSECTION OF TYPES WITH SUPERIOR OVARY
+
+  MATERIAL.—For monocotyls, any flower of the lily family,
+  such as tulip, dogtooth violet (_Erythronium_), trillium,
+  star-of-Bethlehem, yucca, bear’s grass, and the like. The large
+  garden lilies make particularly good examples, but they are for the
+  most part spring bloomers. For autumn, spiderwort (_Tradescantia_),
+  arrow grass (_Sagittaria_), or late specimens of colchicum and
+  tiger lily may be used. Any of these will meet the essential
+  conditions of the analysis given in the text, but care should be
+  taken not to select for this exercise lily-like flowers of the iris
+  and amaryllis families, which have the _ovary inferior_.
+
+  For examples of hypogynous dicotyls, flax, linden, pinks,
+  corn cockle, wood sorrel, poppies, tomato blossoms, and other
+  common flowers can usually be obtained without difficulty. In
+  autumn, the geraniums so largely cultivated for ornament will
+  meet all the conditions of the analysis. Specimens of the cress
+  family—wallflower, cabbage, mustard, turnip—can generally be found
+  everywhere and at all seasons, and they possess the advantage of
+  having their flowers throughout the order put up on so nearly the
+  same pattern that a description of one species will answer, even in
+  details, for the rest.
+
+  For sympetalous specimens of the hypogynous type, hyacinth, lily of
+  the valley, bearberry, huckleberry, or other equivalent forms may
+  be used.
+
+  APPLIANCES.—A compound microscope may be needed for examining
+  minute objects, such as pollen grains and ovules; but for all other
+  purposes, a good hand lens, with the pupil’s ordinary laboratory
+  equipment of drawing-materials, notebook, and dissecting needles,
+  will be sufficient for the studies outlined in this and the four
+  succeeding sections.
+
+[Illustration: FIGS. 265-267.—Flower of a monocotyl
+(star-of-Bethlehem), with superior ovary dissected: 265, entire
+flower, showing the different sets of organs: _pet_, petals; _sep_,
+sepals; _sta_, stamens; _pist_, pistil; _ped_, peduncle; 266, side
+view with all the petals and sepals but two removed to show order
+of the parts: _r_, receptacle; _o_, ovary; _sty_, style; _stig_,
+stigma—parts composing the pistil; _f_, filament; _a_, anther—parts
+composing the stamen; 267, cross section of the ovary: _c_, _c_,
+carpels; _ov_, ovules; _pl_, placenta.]
+
+=211. The floral envelopes.=—Make a sketch of your specimen flower
+from the outside. Is it solitary, or one of a cluster? If the latter,
+refer to 160-162 and tell the nature of the cluster. Notice the
+color; is it conspicuous enough to attract attention or not? Can this
+have anything to do with its clustered or solitary position? Label
+the head of the peduncle that supports the flower, _receptacle_;
+the outer greenish leaves, _sepals_; the inner, lighter-colored
+ones, _petals_. The sepals taken together form the _calyx_, and the
+petals, the _corolla_. Where the petals and sepals are all separate
+and distinct, as in the tulip and the star-of-Bethlehem, the corolla
+is said to be _polypetalous_ and the calyx _polysepalous_, words
+meaning, respectively, many-petaled and many-sepaled. _Monopetalous_
+and _monosepalous_, or _sympetalous_ and _synsepalous_, are terms
+used to describe a condition in which the petals or sepals are all
+united into one, as in the morning-glory and lily of the valley. In
+many flowers, there is little or no difference between the two sets
+of organs. In such cases the calyx and corolla together are called
+the _perianth_, but the distinction of parts is always observed, the
+outer divisions being regarded as sepals, the inner ones as petals.
+These two sets of organs constitute the _floral envelopes_, and are
+not essential parts of the flower, as it can fulfill its office
+of producing fruit and seed without them. Note their number, mode
+of attachment to the receptacle, and how they alternate with each
+other. Remove one of the sepals and one of the petals, and notice
+any differences between them as to size, shape, or color. Which is
+most like a foliage leaf? Hold each up to the light and try to make
+out the veining. Is it the same as that of the foliage leaves? If a
+light-colored flower is used, examine a specimen that has stood in
+coloring fluid. How many of each set are there?
+
+[Illustration: FIGS. 268-269.—Yucca blossom: 268, external view:
+_br_, bract; _pd_, peduncle; _r_, receptacle; _s_, sepal; _pet_,
+petal; 269, vertical section: _ped_, peduncle; _br_, bract; _r_,
+receptacle; _per_, perianth; _sta_, stamen; _o_, ovary; _sty_, style;
+_stg_, stigma. The last three parts named compose the pistil.]
+
+[Illustration: FIGS. 270-274.—Stamens: 270, a typical stamen with the
+terminal anther, _b_, surmounting the filament, _a_, and opening in
+the normal manner down the outer side of each cell; 271, stamen of
+tulip tree, with adnate extrorse anther; 272, stamen of an evening
+primrose (_Œnothera_) with versatile anther; 273, stamen of pyrola,
+the anther cells opening by chinks or pores at the top; 274, stamen
+of a cranberry, with the anther cells prolonged into a tube and
+opening by a pore at the apex. (_After_ GRAY.)]
+
+=212. The essential organs.=—Next sketch the flower on its inner
+face, labeling the appendages just within the petals, _stamens_,
+and the central organ within the ring of stamens, _pistil_. These
+are called essential _organs_ because they are necessary to the
+production of fruit and seed. Note their mode of insertion, three of
+the stamens in a flower like the star-of-Bethlehem alternating with
+the petals, and the other three with these and with the lobes of the
+base of the pistil.
+
+=213. The stamens.=—Notice whether the stamens are all alike, or
+whether there are differences as to size, height, shape, color, etc.
+Do these differences, if there are any, occur indiscriminately and
+without order, or in regular succession between the alternating
+stamens? Examine one of the little powdery yellow bodies at the tip
+of the stamens, and see whether they face toward the pistil or away
+from it.
+
+Remove one of the stamens and sketch as it appears under the lens,
+labeling the powdery yellow body at the top, _anther_, and the
+stalklike body supporting it, _filament_. Usually the filaments
+are threadlike, whence their name, but sometimes, as in the
+star-of-Bethlehem, they are flattened and look like altered petals.
+See if you can find such a one. What would you infer from this fact
+as to the possible origin of the stamens? (100.)
+
+[Illustration: FIGS. 275-278.—Forms of pollen: 275, from _mimulus_;
+276, star cucumber; 277 wild balsam apple; 278, _hibiscus_. (_After_
+GRAY.)]
+
+Notice the two little sacs or pouches that compose the anther, as to
+their shape and manner of opening, or dehiscing, to discharge the
+powder contained in them. This powder is called _pollen_, and will
+be seen under the lens to consist of little yellow grains. These are
+of different shapes, colors, and sizes, in different plants, and
+their surface often appears beautifully grooved and striate when
+sufficiently magnified. Place some of the pollen under the microscope
+and draw two of the grains, with their markings. In the hibiscus and
+others of the mallow family, they are large enough to be seen with a
+hand lens.
+
+=214. The pistil.=—Remove the stamens and sketch the pistil as it
+stands on the receptacle. Label the round or oval enlargement at
+the base, _ovary_, the threadlike appendage rising from its center,
+_style_, and the tip end of the style, _stigma_. In some specimens
+the style may be very short, or wanting. In this case the stigma is
+_sessile_, and the pistil consists of stigma and ovary alone. If the
+stigma is lobed or parted, count the divisions and see if there is
+any correspondence between them and the number of petals and sepals,
+or of the lobes of the ovary. Examine the tip with a lens and notice
+the sticky, mucilaginous exudation that moistens it. Can you think of
+any use for this? If not, touch one of the powdery anthers to it, and
+examine it again with a lens. What do you see? Can you blow or dust
+the pollen from the stigma?
+
+=215. Pollination=, or the transfer of pollen from the anther to
+the stigma, is a matter of great importance, as the pistil cannot
+develop seed without it, except in the case of a few plants like the
+Alpine everlasting, some species of meadow rue (_Thalictrum_), and
+_Alchemilla_, which have the unusual faculty of perfecting seeds in
+the absence of pollen. Note the relative position of pistils and
+stamens and see if it is such that the pollen can reach the stigma
+without external agency.
+
+=216. The ovary.=—Observe the shape of the ovary, and the number of
+ridges, or grooves, that divide the surface. Select a flower which
+has begun to wither, so that the ovary is well developed, cut a cross
+section near the middle, and try to make out the number of _locules_,
+or internal divisions. Do you perceive any correspondence in number
+between these and the ridges or lobes outside (Fig. 280)? Between
+them and the lobes of the stigma? The walls that inclose the cavities
+of the ovary are called _carpels_, and the ridges or depressions that
+mark their point of union on the outside are the _sutures_, or seams.
+The little round bodies in the locules, as the compartments of the
+ovary are called, are the _ovules_, which will later be developed
+into seeds. Their place of attachment is the _placenta_. If they are
+attached to the walls of the carpels (Fig. 281), the placenta is
+_parietal_; if to a central axis formed by the edges of the carpels
+projecting inwards (Fig. 282), it is central and axial; if instead of
+being attached to the carpels, the ovules are borne on a projection
+from the receptacle, the placenta is a _free central_ one (Fig. 283).
+If your cross section shows a central placenta, make a vertical cut
+down to the receptacle and find out whether it is free, or axial.
+What appears to be the primary office of the ovary? Make an enlarged
+sketch of your specimen in both vertical and horizontal section,
+labeling correctly all the parts observed.
+
+[Illustration: FIGS. 279, 280.—Ovary of yucca, a hypogynous
+monocotyl, dissected: 279, vertical section; _ov_, ovules; 280,
+diagram of a horizontal section of the same, enlarged, showing the
+three carpels and six locules; _ds_, dorsal sutures; _vs_, ventral
+sutures; _ov_, ovules; _pl_, placenta.]
+
+[Illustration: FIGS. 281-283.—Different kinds of placenta: 281,
+parietal; 282, central and axial; 283, free central. 281 and 282 are
+horizontal sections; 283, vertical.]
+
+[Illustration: FIG. 284.—Horizontal diagram of a flower of the lily
+kind. The dot represents the growing axis of the plant.]
+
+=217. Numerical plan.=—Make a horizontal diagram of the plan of the
+whole flower, after the model given in Fig. 284, showing the order
+of attachment of the different cycles,—sepals, petals, stamens,
+and pistils,—the number of organs in each set, and their mode of
+alternation with the organs of the other cycles. Notice that the
+parts of each set are in threes, or multiples of three. This is
+called the numerical plan of the flower, and is the prevailing number
+among monocotyls. It is expressed in botanical language by saying
+that the flower is _trimerous_, a word meaning measured, or divided
+off, into parts for three.
+
+=218. Vertical order.=—Next make a vertical diagram of your specimen
+after the manner shown in Fig. 269, and note carefully that the
+ovary stands _above_ the other organs (this is true of all the lily
+family), and is entirely separate and distinct from them. In such
+cases the ovary is said to be _free_, or _superior_, and the other
+organs _inferior_, or _hypogynous_, a word meaning “inserted under
+the pistil.” These terms should be remembered, as the distinction is
+an important one in plant evolution.
+
+=219. Summary of observations.=—In the flower just examined, we
+found that there were four sets of floral organs present—sepals,
+petals, stamens, and pistil; that the individual organs in each set
+were alike in size and shape; that there were the same number, or
+multiples of the same number of parts in each set, and that all the
+parts of each set were entirely separate and disconnected, the one
+from the other, and from those of the other cycles. Such a flower is
+said to be:—
+
+_Perfect_, that is, provided with both kinds of organs essential to
+the production of seed—stamens and pistil.
+
+_Complete_, having all the kinds of organs that a flower can have:
+viz. two sets of essential organs, and two sets of floral envelopes.
+
+_Symmetrical_, having the same number of organs, or multiples of the
+same number, in each set.
+
+_Regular_, having all the parts of each set of the same size and
+shape, as in the wild rose and bellflower, or if different, arranged
+in regular order or pairs, so that there will be a correspondence
+between the two sides of the flower, as in the violet, sweet
+pea, sage, and larkspur. For convenience, the two kinds may be
+distinguished as _complete_ and _bilateral regularity_, respectively.
+
+The opposites of these terms are: _imperfect_, _incomplete_,
+_asymmetrical_ or _unsymmetrical_, and _irregular_.
+
+Note that regularity refers to form, symmetry to number of parts, and
+that a flower may be perfect without being complete.
+
+[Illustration: FIGS. 285-288.—A flower of the cress family: 285,
+side view; 286, view from above; 287, diagram of parts: _p_, petals;
+_s_, sepals; _st_, stamens; _pi_, pistil; _cl_, claw of petal; +, +,
+position of the missing stamens; 288, pistil and stamens, enlarged.
+(_After_ GRAY.)]
+
+[Illustration: FIG. 289.—Section of a tomato flower, showing the
+hypogynous arrangement: _cx_, calyx; _c_, corolla; _s_, stamens; _p_,
+pistil; _o_, ovary; _st_, stigma. (Twice natural size.)]
+
+=220. Dissection of a typical dicotyl flower.=—(Poppy, flax, pink,
+tomato, linden, etc., can be substituted for the specimen used in
+the text.) Gently remove the sepals and petals from a wallflower,
+stock, mustard, or other cress flower, lay them on the table before
+you in exactly the order in which they grew on the stem, and sketch
+them. How many of each are there, and how do they alternate with
+one another? Sketch the pistil and stamens as they stand on the
+receptacle; how many of the latter are there? Notice that two of the
+six are outside and a little below the others, alternate with the
+petals, while the other four stand opposite them, as is natural,
+if they were alternating with another ring of stamens between
+themselves and the corolla. Put a dot before two of the sepals in
+your first drawing to indicate the position of the two outer stamens,
+and a cross before the other two to show where stamens are wanting
+to complete the symmetry of this set, as in Fig. 287. When parts
+necessary to complete the plan of a flower are wanting, as in this
+case, they are said to be _obsolete_, _suppressed_, or _aborted_.
+Place dots before the petals to represent the other four stamens.
+Sketch one of the anthers as it appears under a lens, showing the
+arrow-shaped base, and the mode of attachment to the filament. Is it
+such that the pollen can reach the stigma without external agency? In
+what manner do the anthers open to discharge their pollen? Are the
+anthers and stigma mature at the same time? Remove all the stamens
+from a flower and sketch the pistil, showing the long, slender
+ovary, the very short style, and the _capitate_ (that is, round
+and knoblike) stigma. Make cross and vertical sections of one of
+the older pistils lower down on the stem. How many ovules does it
+contain? How are they attached? Represent the position of the pistil
+by a small circle in the center of your sketch of the separate parts.
+You have now a complete ground plan of the flower. Diagram a vertical
+section, as in Fig. 289, showing the position of the ovary with
+reference to the other parts, and report in your notebook as to the
+following points:—
+
+   Numerical plan                       Presence or absence of parts
+   Symmetry                             Union of parts
+   Regularity (complete or bilateral)   Position of ovary
+
+
+
+
+          II. DISSECTION OF TYPES WITH INFERIOR OVARY
+
+  MATERIAL.—For monocotyls: in spring and early summer, iris,
+  snowflake, freesia, crocus, narcissus, daffodil, can be used;
+  in autumn, gladiolus, blackberry lily, fall crocus, star grass
+  (_Hypoxys_). For dicotyls: in spring, flowers of apple, pear,
+  quince, gooseberry, squash, gourd, melon (with both male and female
+  flowers); in late summer and autumn, fuchsia, evening primrose
+  (_Œnothera_), willow-herb (_Epilobium_).
+
+=221. Study of a monocotyl flower.=—Compare with the specimens
+examined in the last section, a narcissus, snowflake, or iris flower.
+What difference do you notice in the position of the ovary? Would
+you call it _inferior_ (below the other parts) or _superior_ (above
+them)? How was it in the lily and the hyacinth? If your specimen
+is an iris, notice that it is sessile in the axil of a large bract
+called a _spathe_, which conceals the lower part of the flower.
+Remove the spathe and observe that the lower part of the perianth is
+united into a long, narrow tube, from the top of which the sepals and
+petals extend as long, curving lobes.
+
+[Illustration: FIG. 290.—Iris flower: _sp_, spathes; _s_, sepals +
+_p_, petals = perianth.]
+
+[Illustration: FIG. 291.—Vertical section of iris flower: _ov_,
+ovules; _pl_, placenta; _tu_, tube of the perianth inclosing the
+style; _sta_, stamen; _sti_, stigma: _o_, ovary. (_After_ GRAY.)]
+
+[Illustration: FIG. 292.—Vertical section of iris flower, with
+perianth removed, showing a stamen and three stigmas: _su_, stigmatic
+surface.]
+
+[Illustration: FIG. 293.—Cross section of ovary of iris flower: _c_,
+_c_, carpels; _l_, _l_, locules; _ov_, ovules; _pl_, placenta.]
+
+=222. Arrangement of parts.=—Sketch the outside of the flower,
+labeling the oblong, three-lobed enlargement at the base, _ovary_;
+the prolongation above it, _tube of the perianth_; the three outer
+lobes with the broad sessile bases, _sepals_; the others, with
+their bases narrowed and bent inward, _petals_. Now turn the flower
+over and sketch the inside, labeling the three large, petal-like
+expansions in the center, _stigmas_. Do you see any stamens? Remove
+one of the sepals and look under the stigma; what do you find there?
+Notice the little honey pockets at the foot of the stamen. Run the
+head of your pencil into them and see what would happen to the head
+of an insect probing for honey.
+
+Remove the perianth and sketch the remaining organs in profile,
+showing the position of the stamens. Do you see any advantage in
+their position? Can you determine the use of the crest of hairlike
+filaments on the upper side of the sepals? Remove a stamen and sketch
+it.
+
+=223. The pistil.=—Remove as much of the upper part of the perianth
+tube as you can without injuring the pistil, and with a sharp knife
+cut a vertical section down through the ovary so as to show the long
+style and its connection with the placenta. Make a sketch of this
+longitudinal section (see Fig. 291), labeling the parts observed.
+Notice whether the placenta is central or parietal. Draw a cross
+section of the ovary; how many locules has it? How many ovules in
+each? Where are they attached? Is the placenta free central or axial
+(Fig. 293)? Examine with a lens the little flap at the base of the
+two-cleft apex of one of the stigmas, and look for a moist spot to
+which the pollen will adhere. Label this in your sketch, _stigmatic
+surface_. No seeds can be matured unless some of the pollen reaches
+this surface; can you think by what agency it is carried there? What
+insects have you seen hovering about the iris? Notice that in drawing
+his head _out_ of the flower, an insect would not touch the stigmatic
+surface, since it is on the _upper_ side of the flap and he would be
+probing _under_ it. But in entering the next flower that he visits,
+he is likely to strike his head against the flap and turn it under,
+thus dusting it with pollen brought from another flower.
+
+[Illustration: FIG. 294.—Horizontal diagram of iris flower.]
+
+=224. Diagrams.=—Draw diagrams showing the horizontal and vertical
+arrangement of parts in the iris or other specimen examined, and
+compare with those made of the monocotyl studied in the preceding
+section. In what respect does it differ from them? How do you account
+for the difference in the number of stamens, if there is any? (220.)
+
+=225. The vertical order.=—The difference in vertical arrangement is
+an important one. Bear in mind that flowers of this type have the
+ovary _inferior_, that is, inserted _under_ the other organs (Figs.
+296, 304), which are then said to be superior, or _epigynous_, a word
+which, as you know from the prefix _epi_ (47), means over or above
+the pistil. To make the matter clear, the two sets of terms employed
+for describing the position of the ovary are given below in parallel
+columns:
+
+       Hypogynous                     Epigynous
+       Ovary superior                 Ovary inferior
+       Calyx or perianth inferior     Calyx or perianth superior
+
+The epigynous arrangement is considered as marking a higher stage of
+floral development than the hypogynous, which is characteristic of a
+more simple and primitive structure.
+
+[Illustration: FIGS. 295-296.—Evening primrose, dicotyl flower with
+inferior ovary: 295, exterior view; 296, longitudinal section,
+showing vertical arrangement of parts.]
+
+=226. Dissection of a dicotyl flower.=—Sketch a blossom of quince
+or apple, fuchsia, evening primrose, etc., first from the outside,
+then from the inside, and then in vertical section, labeling the
+parts as in your other sketches. Notice in the pear or apple how the
+ovary is sunk in the hollowed-out receptacle. Where are the other
+parts attached? Are they inferior or superior? Hold up a petal to the
+light and examine its venation through a lens. (Use for this purpose
+a petal from a flower that has stood in red ink for two or three
+hours.) Is it parallel-veined or net-veined? If the flowers are
+clustered, what is the order of inflorescence? Does the position of
+the flowers on their branch correspond to that of the leaf axils on
+the same kind of plant?
+
+[Illustration: FIGS. 297-300.—Flower and sections of pear: 297,
+cluster of blossoms, showing inflorescence; 298, vertical section
+of a flower; 299, ground plan of a flower; 300, vertical section of
+fruit.]
+
+[Illustration: FIG. 301.—Vertical section of an almond blossom with
+petals removed, showing the perigynous arrangement.]
+
+=227. The stamens.=—Remove the petals from a flower and examine
+the stamens with a lens. Notice the attachment and shape of the
+anthers. Are they all of the same color? How do you account for
+the difference, if there is any? Is the position of the pistil and
+stamens such that the pollen from the anthers can readily reach
+the stigmas without external aid? Examine the pistil in flowers of
+different ages, and see if the stigma is mature (that is, moist and
+sticky) at the same time that the anthers are discharging their
+pollen. Make an enlarged sketch of a stamen showing the shape of the
+anther and the method of opening to discharge pollen.
+
+=228. The pistils.=—How many pistils do you find in the apple blossom
+(or other flower under examination)? Are they distinct, or united?
+Find where the styles originate; what do you see there? Make a cross
+section of the ovary and count the locules; how does their number
+compare with that of the styles? Can you make out the number of
+ovules in each? If not, use a young fruit; as it is only an enlarged
+ovary, it will show the parts correctly. Compare it with a ripe fruit
+and see if all the ovules matured. Can you think of any reasons why
+some of them might fail? Do you see any signs of nourishment stored
+in the ovary? Name all the ways you can think of in which the ovary
+can benefit the ovules and seeds. Draw the ovary in cross and
+vertical sections, labeling correctly all the parts.
+
+[Illustration: FIGS. 302-304.—Diagrams showing arrangement of parts
+with reference to the ovary: _bd_, receptacle; _k_, calyx; _kr_,
+corolla; _st_, stamens; _fr_, ovary; _g_, style; _n_, stigma; 302,
+perigynous; 303, hypogynous; 304, epigynous.]
+
+=229. The numerical plan of dicotyls.=—Diagram the plan of the flower
+in cross and vertical section. How many parts are there in each set?
+Can you tell readily the number of stamens? When the individuals of
+any set or cycle of organs are too numerous to be easily counted,
+like the stamens of the apple, pear, and peach, or the petals of the
+water lily, they are said to be _indefinite_. It is very seldom that
+perfect symmetry is found in all parts of the flower. The stamens and
+pistil, in particular, show a great tendency to variation, so that
+the numerical plan is generally determined by the calyx and corolla.
+Where the parts are in fives, as in the pear, quince, and wild rose,
+the flower is said to be _pentamerous_, or in sets of five. This is
+the prevailing number among dicotyls, though other orders are not
+uncommon. In the mustard family (220) and other well-known species,
+the fourfold order prevails, while some of the saxifrages have their
+parts in twos, and the magnolia and the pawpaw have a threefold
+arrangement.
+
+=230. Intermediate types.=—Flowers like the peach and rose represent
+an intermediate type in which the calyx, petals, and stamens are
+attached to a prolongation of the receptacle that extends above the
+ovary, but is not united with it (Fig. 301). In general, a flower is
+not considered as belonging to the epigynous kind unless the ovary is
+more or less consolidated with the parts around it (Fig. 304).
+
+
+          III. STUDY OF A COMPOSITE FLOWER
+
+  MATERIAL.—The largest heads attainable should be selected, as the
+  florets are small at best, and difficult to handle. The large
+  cultivated sunflower (_Helianthus annuus_) makes an ideal specimen,
+  if accessible. Oxeye daisy and dandelion can be obtained throughout
+  the season almost everywhere, but the former has no pappus, and
+  the latter does not show the tubular disk flowers. Other common
+  specimens are: for spring, mayweed, Jerusalem artichoke, coreopsis,
+  arnica; for late summer and autumn, China aster, golden aster
+  (_Chrysopsis_), sneezeweed, elecampane—and, in fact, the great
+  majority of flowers to be found at this season are of the composite
+  family. Oxeye daisy is used as a model in the text on account of
+  its general accessibility, but almost any specimen of the radiate
+  kind will meet all essential conditions of the analysis.
+
+[Illustration: FIGS. 305-308.—An oxeye daisy: 305, a flower head;
+306, vertical section of a head; 307, disk flower; 308, ray flower,
+enlarged.]
+
+=231. The ray flowers.=—Examine the upper side of an oxeye daisy
+through a lens. Of what is the yellow button in the center composed?
+Count the narrow, petal-like rays disposed around the center. To
+decide what they are, look for a small two-cleft body at the base of
+the ray; this is the pistil. Do you see any stamens in the ray? An
+examination will show that all rays contain pistils, but no stamens;
+they are, therefore, not petals, but the corollas of imperfect
+flowers. Look at the upper edge of a ray of sneezeweed, coreopsis,
+arnica, chicory, etc., for small teeth or notches; these represent
+the lobes of a sympetalous corolla. Split one of the tubular corollas
+of the disk down one side and open it out flat; does it throw any
+light on the morphology of the ray? In many composite plants, as the
+sunflower, coneflower, coreopsis, the rays are all _neutral_; that
+is, they have neither pistil nor stamens. Are they of any use in such
+cases? If you are in doubt, remove all the rays from a head; would
+the disk be noticeable enough to attract attention without them? What
+is the principal office of the rays?
+
+=232. The involucre.=—Look at the cluster of green, leafy scales on
+the under side of the head. It is not a calyx, but a collection of
+bracts, called an _involucre_. Have you ever noticed the bracts under
+the separate flowers on a raceme? (161.) What would be the position
+of the bracts if all the flowers of the raceme were compacted into a
+head like the daisy or sunflower? Is the involucre of any use? Cut
+it away gently so as not to disturb the other organs and see what
+happens to the rays.
+
+=233. The disk flowers.=—Cut a vertical section through the head of a
+flower and notice the broad, flat receptacle (in some cases round or
+columnar) on which the tiny florets are seated. Observe whether it is
+naked, or whether it bears chaffy scales inclosing the florets. Make
+an enlarged drawing of this section, showing the insertion of the
+different parts and labeling them all correctly. What differences do
+you observe between the disk and the ray flowers?
+
+=234. The pappus.=—Open one of the disk flowers with a dissecting
+needle and observe the small striate (in some specimens, hairy)
+body to which the base of the style is attached. This is the
+ovary, inclosed in the lower part of the calyx, which has become
+incorporated with it. When mature, it will form a small, one-seeded
+fruit called an _akene_. Can you see the ovule? Where is it
+attached? (Use a mature akene for this purpose.) In most plants of
+this family, the akene is surmounted by delicate hairy bristles,
+as in the dandelion, wild lettuce, and groundsel; or by small
+chaffy scales, as in the sneezeweed and sunflower, and sometimes by
+hooks and barbed hairs, like those of the tickseed, bur marigold,
+and cocklebur. These appendages constitute the _pappus_. They are
+modifications of the sepals, and serve an important purpose in aiding
+the distribution of the seed. Can you suggest some of the ways in
+which they may aid in accomplishing this object?
+
+[Illustration: FIGS. 309-314.—Akenes of the composite family:
+309, mayweed (no pappus); 310, chicory (pappus a shallow cup);
+311, sunflower (pappus of two deciduous scales); 312, sneezeweed
+(_Helenium_, pappus of five scales); 313, sow thistle (pappus of
+delicate downy hairs); 314, dandelion, tapering below the pappus into
+a long beak. (_After_ GRAY.)]
+
+[Illustration: FIGS. 315-317.—Flowers of _Arnica montana_, showing
+successive stages in pollination: 315, pistil just extruding from
+anther tube, covered with pollen, but with stigmatic surfaces closed;
+316, stigma opened and mature; 317, stigma recurved to receive pollen
+from its own or neighboring anthers if foreign pollen has not reached
+it.]
+
+=235. The stamens and pistil.=—Remove the corolla of a disk flower
+carefully so as not to disturb the inclosed organs, and notice how
+the stamens are united into a tube by their anthers. Flatten out the
+tube and make an enlarged sketch of it, showing the long, narrow
+shape of the anthers and their mode of attachment. Can you make out
+how they open to discharge their pollen? Examine one of the younger
+florets near the center of the disk, and observe that the tip of the
+style is inclosed in the anther tube with the lobes of the stigma
+pressed tightly together by their inner faces (Fig. 315), so that it
+is impossible for any of the pollen to reach the stigmatic surface.
+It remains in this position till the anthers have shed their pollen,
+then, as may be seen by examining an older flower, the style begins
+to elongate, pushing up the pollen that has fallen on the hairy
+outside of the closed stigma, and forcing it out of the corolla tube,
+where it can be scattered by insects among the other flowers of the
+cluster. When the pollen of its own floret has been thus disposed of,
+the stigma lobes open and curl outward, ready to receive the pollen
+from other flowers. This arrangement is practically universal among
+plants of the composite family; can you divine its object? It will be
+shown later, that much larger and stronger seeds are produced when
+the pistil is pollinated from a different flower, or, better still,
+from a different plant of the same species; hence, you see what a
+useful adaptation this is.
+
+=236. Nature of a composite flower.=—It will be evident, from the
+examination just made, that the daisy, dandelion, sunflower, etc.,
+are not single flowers, but compact heads of small blossoms so
+closely united as to appear like a single individual; hence they
+are said to be _composite_, or compound. They are the most numerous
+and widely disseminated of all plants, comprising one seventh of
+the entire flowering vegetation of the globe, and are regarded
+by botanists as representing the most advanced stage of floral
+evolution. Can you point out some of the adaptations to which their
+success in solving the problems of plant life is due? (164.)
+
+
+          IV. SPECIALIZED FLOWERS
+
+  MATERIAL.—For spring and early summer: sweet pea, black locust,
+  wistaria, lupine, or any of the characteristic butterfly-shaped
+  flowers of the pea family. For autumn or late summer: tropæolum,
+  monkshood, or a bilabiate flower—snapdragon, digitalis, dead
+  nettle, salvia, catalpa, etc.—of the mint or figwort family.
+
+=237. Irregularity and specialization.=—Irregularity and bilateral
+regularity are, as a rule, indicative of specialization, or
+adaptation to a particular purpose, such as the ready distribution
+of pollen, or its protection against injury. These adaptations
+are more noticeable in the corolla than in other parts, and hence
+flowers of this kind are usually classed according to the shape of
+their corollas. The most highly specialized flowers in this respect
+are the orchids, but they are too rare and difficult of access
+to be available objects for study. The most familiar and widely
+distributed kinds of specialized corollas are the _bilabiate_, or
+two-lipped, and the _papilionaceous_, or butterfly, forms. The
+first is characteristic of the mint and figwort families, of which
+the toadflax, sage, and catalpa are familiar examples. The second
+comprises the well-known papilionaceous flowers of the pea family,
+named from the Latin word _papilio_, a butterfly, on account of their
+general resemblance to that insect.
+
+=238. Dissection of a papilionaceous flower.=—Sketch a blossom of any
+kind of pea or vetch as it appears on the outside. Are the sepals
+all of the same length and shape? If not, which are the shorter, the
+upper or the lower ones?
+
+Turn the flower over and examine its inner face. Notice the large,
+round, and usually upright petal at the back, the two smaller ones
+on each side, and the boat-shaped body between them, formed of
+two small petals more or less united at the apex. Press the side
+petals gently down with the thumb and forefinger and notice how
+the essential organs are forced out from the little boat in which
+they are concealed. Observe how the end of the style is bent over
+so as to bring the stigma uppermost when the petals are depressed.
+Imagine the legs of a bee or a butterfly resting there as he probed
+for honey; with what organ would his body first come in contact when
+he alighted? If his thorax and abdomen had previously become dusted
+with pollen when visiting another flower, where would the pollen be
+deposited? Do you notice anything in the color, shape, or odor of
+this flower that would be likely to attract insects? Have you ever
+observed insects hovering around flowers of this kind; for example,
+in clover and pea fields, and about locust trees and wistaria vines?
+What kind of insects, chiefly, have you seen about them?
+
+[Illustration: FIGS. 318-322.—Dissection of a papilionaceous flower:
+318, front view of a corolla; 319, the petals displayed: _v_,
+vexillum, or standard; _w_, wings; _k_, keel; 320, side view with
+all except one of the lower petals removed, showing the essential
+organs protected in the keel: _l_, loose stamen; _st_, stamen tube;
+321, side view, showing how the anthers protrude when the keel is
+depressed; 322, ground plan. (_After_ GRAY.)]
+
+Remove the sepals and petals from one side, and sketch the flower in
+longitudinal section, showing the position of the pistil and stamens.
+Then remove all the petals, and spread in their natural order on the
+table before you, and sketch as they lie (Fig. 319). Label the large,
+round upper one, _standard_ or _vexillum_; the smaller pair on each
+side, _wings_, and the two more or less coherent ones in which the
+pistil and stamens are contained, _keel_.
+
+=239. The stamens.=—Count the stamens, and notice how they are united
+into two sets of nine and one. Stamens united in this way, no matter
+what the number in each set, are said to be _diadelphous_, that is,
+in two brotherhoods. Notice the position of the lone brother, whether
+below the pistil—next to the keel—or above, facing the _vexillum_.
+Would the projection of the pistil, when the wings are depressed, be
+facilitated to the same extent if the opening in the stamen tube were
+on the other side, or if the filaments were _monadelphous_—all united
+into one set? Flatten out the stamen tube, or sheath, formed by the
+united filaments, and sketch it.
+
+=240. The pistil.=—Remove all the parts from around the pistil, and
+sketch it as it stands upon the receptacle. Look through your lens
+for the stigmatic surface (223). See if there are any hairs on the
+style, and if so, whether they are on the front, the back, or all
+around. Can you think of a use for these hairs? Notice how the long,
+narrow ovary is attached to the receptacle; is it sessile, or raised
+on a short footstalk? If the latter, label the footstalk, _stipe_.
+Select a well-developed pistil from one of the lower flowers, open
+the ovary parallel with its flattened sides, and sketch the two
+halves as they appear under the lens. Notice to which side the ovules
+are attached, the upper (toward the vexillum) or the lower, and label
+it, placenta. How many locules has the ovary? How many carpels? How
+can you tell (216)?
+
+=241. Plan of the flower.=—Diagram the flower in horizontal and
+vertical section, and decide upon the following points:—
+
+    Numerical plan
+    Symmetry
+    Regularity
+    Union of parts
+    Position of the ovary
+
+[Illustration: FIGS. 323, 324.—Salvia: 323, a newly opened flower,
+showing the pollen-covered anther striking the back of a visiting
+bee; 324, an older flower, with the protruding pistil rubbing against
+the back of a bee covered with pollen from a younger flower.]
+
+=242. Significance of these distinctions.=—These distinctions are
+important to remember, not only because they are very useful in
+grouping and classifying plants, but because they mark successive
+stages in the evolution of the flower. In general, flowers of a
+primitive type and less advanced organization are characterized
+by having their organs free and hypogynous, while the more highly
+developed forms show a tendency to consolidation and union of parts,
+and the epigynous mode of insertion. Irregularity also, since it
+indicates specialization and adaptation to a particular purpose, may
+be regarded as a mark of advanced evolution.
+
+[Illustration: FIGS. 325, 326.—Salvia: 325, longitudinal section
+through a flower, showing the rocking connective which is struck at
+_a_ by a visiting insect; 326, section of the same flower after being
+visited, showing the lower arm of the connective pushed back and
+lowering the anther.]
+
+=243. Dissection of a bilabiate flower.=—Make a similar study of the
+flower of a salvia, dead nettle, catalpa, or other specimen of the
+bilabiate kind. Make diagrams and report as to (1) numerical plan;
+(2) presence or absence of parts; (3) regularity; (4) union of parts;
+(5) position of ovary. Observe especially the relative position of
+stigma and anthers; is it such that the pollen can reach the stigma
+without external aid? Does the peculiar shape of the corolla serve
+any other purpose than to attract the attention of insect visitors
+by its conspicuous appearance? What is the use of the projecting
+underlip? Is it any convenience to a bee, for instance, to have a
+platform to rest on while gathering pollen or honey? What is the use
+of the arched upper lip? Cut it away and notice the exposed condition
+of the stamens and pistil. Turn a flower upside down; what would be
+the effect on a visiting bee or butterfly? (Exps. 83, 84.)
+
+[Illustration: FIG. 327.—Staminodia, transformed stamens of canna
+simulating petals: _pet_, petals; _st_, staminodia.]
+
+[Illustration: FIG. 328.—Flower of a cactus (_cereus greggii_),
+showing transition from scales to petals.]
+
+=244. Morphology of the flower.=—We have seen that the venation of
+petals and sepals corresponds in a general way with that of foliage
+leaves of the class to which they belong, and that their arrangement
+around their axis is analogous to the arrangement of foliage leaves
+on the branch. In our study of inflorescence, it was observed that
+flowers and flower buds occur in the same positions where leaf buds
+occur, and that they are subject to the same laws of arrangement
+and growth. We learned, also, in our study of leaves, something
+about the wonderful modifications that these organs are capable of
+undergoing; and finally, an examination of a number of different
+flowers has shown them capable of undergoing modifications to an
+equal or even greater extent, and examples of the transition of
+almost any floral organ into another may be observed by one who will
+take the trouble to look for it. Stamens and petals are found in all
+stages of transformation, from the slightly flattened filament of
+the star-of-Bethlehem, or the yellow pollen speck on the petal of
+a rose, to the brilliant staminodia, or transformed stamens of the
+canna (Fig. 327), which simulate petals so perfectly that their real
+nature is never suspected by the ordinary observer. The transition
+from spines and bracts to the brilliant corolla of the cactus (Fig.
+328) is so gradual that we are hardly aware of it till we examine a
+specimen and see it actually going on before our eyes.
+
+It must not be supposed, however, that an organ is ever developed as
+one thing and then deliberately changed into something else. When we
+speak loosely of one organ being modified into another, the meaning
+is merely that it has developed into one thing instead of into
+something else that it was equally capable of developing into.
+
+=245. The course of floral evolution.=—For the reasons mentioned,
+the flower is regarded as merely a branch with modified leaves and
+the internodes indefinitely shortened so as to bring the successive
+cycles into close contact, the whole being greatly altered and
+specialized to serve a particular purpose. With this conception
+of the nature of the flower, we can readily see that the less
+specialized its organs are and the more nearly they approach in
+structure and arrangement to the condition of an undifferentiated
+branch, the more primitive and undeveloped is the type to which it
+belongs. On the other hand, if the parts are highly specialized and
+widely differentiated from the crude branch, a proportionately high
+stage of floral evolution is indicated.
+
+
+          V. FUNCTION AND WORK OF THE FLOWER
+
+  MATERIAL.—For this exercise, flowers of the mallow
+  family—hollyhock, abutilon, mallow, hibiscus, cotton, okra,
+  etc.—are particularly recommended because they have pollen grains
+  so large that they can be studied fairly well with a hand lens.
+  Lily, tulip, iris, etc., will also meet all essential conditions of
+  the study outlined in the text. A strand of silk from a pollinated
+  ear of corn is an excellent example for showing the growth of the
+  pollen tube, under the microscope.
+
+  APPLIANCES.—A compound microscope; a watch crystal; sugar solution
+  of 5 to 15 per cent.
+
+  EXPERIMENT 77. TO SHOW THE GERMINATION OF POLLEN GRAINS.—Put a drop
+  of 5 per cent sugar solution into a watch crystal or a concave
+  slide, seal by smearing the edges with vaseline, and cover with a
+  glass to keep out the dust. Examine at intervals of five minutes
+  under the microscope (a hand lens will show the result with the
+  specimens recommended, though not so well), and the pollen grains
+  will be observed to send out long filaments or tubes into the
+  sirup, as a germinating seedling sends its radicle into the soil.
+
+=246. Office of the flower.=—The one object of the flower is the
+production of fruit and seed, and all its wonderful specializations
+and variations of form and color tend either directly or indirectly
+to this end.
+
+=247. Pollination and fertilization.=—It was stated in 215 that only
+in very exceptional cases can seed be developed unless some of the
+pollen reaches the stigma. This act, called _pollination_, is an
+essential step in seed production, but is not sufficient to secure
+that end unless it leads to the process known as _fertilization_.
+Successful pollination is a necessary preliminary to fertilization,
+and the one begins where the other ends.
+
+=248. The next step toward fertilization.=—Examine with a lens the
+pollinated pistil of a mallow, lily, or other large flower, and
+notice the flabby, withered appearance of grains that have stood for
+some time on the stigma, as compared with those of a newly opened
+anther. Can you account for the difference? Touch the tip of your
+tongue to the stigma, or apply the proper chemical test, and it will
+be seen that the sticky fluid which it exudes, contains sugar. Refer
+to Exp. 77 and say what effect this substance has on the pollen.
+
+[Illustration: FIG. 329.—A pollen grain emitting a tube (magnified).]
+
+=249. The pollen tube.=—The same thing happens when a pollen grain
+falls on the moist surface of the stigma. It begins to germinate by
+sending a little tube down into the substance of the pistil, and the
+withered appearance of the grains on the stigma results from the
+nourishment in them having been exhausted, just as the endosperm of
+the seed is exhausted when the embryo begins to germinate. Here,
+however, the analogy ends, for the pollen tube is not adapted, like
+the radicle of the seedling, to absorb and convey nourishment up to
+the other parts, but to feed and carry down to the ovary two small
+bodies called _generative cells_, which it discharges there, and
+then its work is done and it disappears. So it must be borne in mind
+that when we speak of the germination of the pollen grains, we mean
+something really very different from the germination of a seed.
+
+=250. The course of the pollen tube.=—Cut the thinnest possible
+section through a freshly pollinated pistil and place under the
+microscope. Watch the pollen tubes from the grains on the stigma as
+they descend through the style toward the ovary. A pollinated strand
+of corn silk—which is only a very much elongated style—is excellent
+for this purpose. It is so thin and transparent that no section need
+be made, and the tube can be traced as it works its way down through
+the entire length of the threadlike style to the young grain, or
+ovary, on the cob. The time required for the tube to penetrate to the
+ovary varies in different flowers according to the distance traversed
+and the rate of growth. In the crocus it takes from one to three
+days; in the spotted calla, about five days; and in orchids, from ten
+to thirty days. As a rule, it occupies only a few hours. Sometimes
+the pistil is hollow, affording a free passage to the pollen tube;
+in other cases, it is solid, and the growing tube eats its way down,
+as it were, feeding on the substance of the pistil as it grows. How
+is it in the flower you are examining? It takes a grain of pollen
+to fertilize each ovule, and where more than one seed is produced
+to a carpel, as is commonly the case, at least as many pollen
+tubes must find their way to each locule of the ovary as there are
+ovules—provided all are fertilized.
+
+[Illustration: FIG. 330.—Diagram of a simple flower, showing course
+of the pollen tube: _a_, transverse section of an anther before its
+dehiscence; _b_, an anther dehiscing longitudinally, with pollen;
+_c_, filament; _d_, base of floral leaves; _e_, nectaries; _f_, wall
+of carpels; _g_, style; _h_, stigma; _i_, germinating pollen grains;
+_m_, a pollen tube which has reached and entered the micropyle of the
+ovule; _n_, stalk of ovule; _o_, base of the inverted ovule; _p_,
+outer integument or testa; _q_, inner integument; _t_, cavity of the
+embryo sac; _u_, its basal portion; _z_, oösphere.]
+
+=251. Fertilization.=—When a pollen tube has penetrated to the ovary,
+it next enters one of the ovules, usually through the micropyle
+(Fig. 330, _m_). There it penetrates the wall of a baglike inclosure
+called the _embryo sac_ (Fig. 330, _u_, _t_, _z_), where one of the
+generative cells emitted by the pollen tube fuses with a large cell
+contained in the embryo sac, known as the _germ cell_, or _egg cell_
+(Fig. 330, _z_). The fusion of these two bodies is what constitutes
+fertilization. The cell formed by their union finally develops into
+the embryo, and the other contents of the sac into the endosperm, and
+the ripened ovules become seeds.
+
+=252. Stability of the process of fertilization.=—The phenomena
+that characterize the functions of fertilization and reproduction
+are the most uniform and stable of all the life processes, varying
+little not only in different species and orders, but throughout the
+whole vegetable kingdom. And since these functions furnish a more
+reliable standard for judging of the real affinities of the different
+groups than do mere external resemblances, which are more liable
+to variation and may often be accidental, they have been chosen by
+botanists as the ultimate basis for the classification of plants.
+
+=253. Embryology.=—The study of the developing plantlet, known as
+_embryology_, is a comparatively recent branch of science, and has
+greatly enlarged our knowledge of the life history of both plants and
+animals, by bringing to light resemblances that exist between the
+most widely divergent species in their earlier stages of development
+and thus showing traces of a common origin. It has shown further,
+that every individual plant or animal, in its development from the
+embryo to the mature state, passes briefly through stages apparently
+similar to those which the species has traversed in the course of
+its evolution. This summary repetition, by the individual, of the
+evolutionary progress of its kind is known as the _biogenetic law_,
+and through its intelligent application some of the most intricate
+problems in both physiology and psychology have been solved.
+
+
+          Practical Questions
+
+  1. Does the biogenetic law throw any light on the resemblances
+  sometimes observed between leaves of different ages in unlike
+  species; for example, the fig and the mulberry? (170; Field Work,
+  p. 195.)
+
+  2. Can you name any other examples of plants or parts of plants
+  which show mutual resemblances in their early stages that do not
+  exist at maturity?
+
+  3. Are there other causes than those acting under the biogenetic
+  law to which some of these resemblances may be referred; for
+  instance, the down and waxy coating on young leaves and bud scales?
+  (148, 207.)
+
+
+          VI. HYBRIDIZATION
+
+  MATERIAL.—Several potted plants of tulip, lily, or any attainable
+  large flowered kind; or preferably a small plot in a garden or
+  nursery.
+
+  APPLIANCES.—A pair of dissecting scissors, a camel’s-hair brush,
+  and some paper bags.
+
+  EXPERIMENT 78. DOES IT MAKE ANY DIFFERENCE WHETHER A FLOWER HAS
+  ITS OVULES FERTILIZED WITH ITS OWN POLLEN OR WITH THAT OF ANOTHER
+  FLOWER OF THE SAME KIND?—Carefully remove the _unopened_ anthers
+  from a bud of a tulip, or other large flower just ready to unfold
+  (Fig. 331), inclose the mutilated bud in a small paper bag until
+  the stigma is mature, as shown by stickiness, then transfer to it
+  with a camel’s-hair brush some pollen from another flower. On the
+  stigma of a second flower of the same kind place some of its own
+  pollen, and cover with a paper bag until the stigma withers, to
+  keep foreign pollen from reaching it by means of wind or insects.
+  Watch until seeds are matured. Which flower produces the more
+  seeds or the better ones? Plant the seeds; which produce the more
+  vigorous progeny?
+
+[Illustration: FIGS. 331-333.—Flower of Lorillard tomato: 331, newly
+opened bud, showing stage in which the stamens should be removed;
+332, mature flower: _cx_, calyx; _c_, corolla; _s_, stamens; _st_,
+stigma; 333, flower with stamens removed for pollination. (Natural
+size.)]
+
+  EXPERIMENT 79. CAN A FLOWER BE FERTILIZED WITH POLLEN OF A
+  DIFFERENT KIND?—Dust the stigma of a tulip or a lily, from which
+  the stamens have been removed, with pollen from a narcissus, iris,
+  or amaryllis. Cover to protect from wind and insects. Are any seeds
+  produced?
+
+  Experiments of this kind, to be conclusive, ought to be performed
+  on a sufficient number of plants and through at least three
+  generations. This is hardly practicable for class work, but
+  students who are specially interested in the subject may carry
+  on experiments at home, or supply their place, to some extent,
+  by observations out of doors, if there are any farms or gardens
+  accessible.
+
+[Illustration: FIGS. 334-335.—Seeds of Bartlett pear, showing the
+advantage of cross-fertilization: 334, cross-fertilized; 335,
+self-fertilized.]
+
+=254. Self-fertilization= takes place when a stigma is pollinated
+from the same flower. Horticulturists have long known that continued
+self-fertilization, or “in-breeding” as it is called by nurserymen,
+tends to deteriorate a stock; but Charles Darwin was the first to
+explain, by a series of pains-taking experiments, the meaning of
+those careful adjustments which the more highly organized plants, as
+a rule, have developed to guard against it.
+
+[Illustration: FIG. 336.—Showing the effect of in-breeding on corn in
+one generation. The two left-hand rows are from self-fertilized seed.]
+
+=255. Cross-fertilization= is effected by the pollination of a
+stigma from another flower of the same variety or species. As
+used by practical horticulturists, the expression means that the
+two factors, pollen and ovule, belong to different plants. Since
+pollination is the necessary antecedent to fertilization, and the
+only means by which we can control it, the breeder’s part in crossing
+is concerned with this act only and nature does the rest. Darwin’s
+experiments—and they are confirmed by the experience of plant growers
+everywhere—prove that the offspring from crossing different plants
+of the same kind is usually stronger and more productive than that
+from self-fertilized ones; and if the parent stocks are grown in
+different places and under different conditions, the offspring
+is more vigorous than that from the same kind of plants grown
+under like conditions. For instance, plants from crossed seeds of
+morning-glory vines growing near each other exceeded in height those
+from self-fertilized seeds as 100:76; while the offspring of plants
+growing under different conditions exceeded those of the other cross,
+in height, as 100:78; in number of pods, as 100:57, and in weight
+of pods, as 100:51. Knowledge of this kind, when applied to the
+raising of fruits and grains for market, is of incalculable value to
+gardeners and farmers, and also to the amateur who raises fruits or
+flowers for pleasure.
+
+=256. Hybridization= is the crossing of two plants of different
+species or of widely separated varieties of the same species. The
+resulting offspring is a _hybrid_. Hybridization can take place only
+within certain limits. If the species are too unlike, the pollen will
+either not take effect at all, or the resulting offspring will be too
+weak and spindling to live; or if they survive, will not be able to
+set seed (Exp. 79).
+
+[Illustration: PLATE 11.—Hybrid between a red and a white carnation,
+showing characters intermediate between the two parents.]
+
+=257. Effects of hybridization.=—The most important practical uses of
+hybridizing are: (1) it “breaks the type” by causing plants to vary,
+and thus gives the breeder a fresh starting point for a new strain;
+and (2) when the parent species are not too unlike, it accentuates
+the good effects of crossing, and sometimes gives rise to offspring
+greatly surpassing either parent in size and vigor. In regard to
+variability it may act in three ways: (1) the hybrid may wholly
+resemble one parent or the other, in which case there is, of course,
+no variation; (2) it may resemble one parent more than the other; or
+(3) it may show a blending of the characters of the two, as when a
+cross between a red poppy and a white gives rise to a light pink, or
+a mixed red and white variety. In the first two cases, the characters
+of the parent that manifest themselves are said to be _dominant_;
+those which do not, _recessive_.
+
+[Illustration: FIG. 337.—Effect of hybridization between related
+species in imparting superior vigor to offspring: _M_, Californian
+black walnut (_Juglans californica_), male parent; _F_, Eastern black
+walnut (_J. nigra_), female parent; _H_, hybrid.]
+
+=258. Mendel’s Law.=—So long ago as the middle of the last century
+it was discovered by Gregor Mendel, an Austrian investigator, that
+hybrids vary in certain cases according to a fixed law, by means
+of which the proportionate share of the characteristics of the two
+parent forms inherited by the offspring can be foretold with almost
+mathematical precision. The controversy over Darwin’s “Origin of
+Species,” which was raging at the time, caused Mendel’s discoveries
+to be overlooked for a generation, and it is only within the last
+few years that their importance has been realized. The principle
+of variation demonstrated by him in a series of experiments,
+and confirmed by later investigators is, briefly, this: If two
+parents differing in some fixed characteristic be crossed, the
+entire offspring, in the first generation, will be like the parent
+possessing the dominant quality. If all the seed of this generation
+is planted and carefully protected from foreign pollen, its offspring
+composing the second generation from the parents will vary in the
+proportion of ¾ dominants (_D_, _D′_, line 2 of the diagram) to ¼
+recessives (_R_). Planting _all_ the seeds of the second generation
+and carefully shielding their progeny from foreign pollen, we
+get from _D_, line 2, all pure dominants (_D_, line 3)—that is,
+plants producing only their own type, and from _R_, line 2, all
+pure recessives (_R_, line 3). But from each of the two sets of
+dominants, _D′D′_, line 2, marked “impure” in the diagram, and so
+called because their seeds may produce both dominants and recessives,
+we get the same result as in the second generation, namely: pure
+dominants (_D′D′_, line 3), pure recessives (_R′R′_, line 3), and
+impure dominants (_D″D″_, _D″D″_, line 3). If it were possible to
+distinguish the seeds of these impure dominants before germination
+and plant them only, for no matter how many generations, the result
+would always be approximately the same,—¼ pure dominants, ¼ pure
+recessives, and ²⁄₄ impure dominants capable of producing both
+dominants and recessives in the proportion of 3:1.
+
+[Illustration: Diagram illustrating Mendel’s Law.]
+
+=259. Practical applications.=—Four principles of great importance
+to plant breeders follow from this law in cases to which it applies:
+(1) the absence of variation in the first generation of hybrids is
+no sign that it may not occur later; (2) pure recessives always
+breed true; hence, if they show the desired character, no further
+selection is necessary for that character; (3) pure dominants always
+breed true, but the distinction between pure and impure is usually
+not apparent in one generation; (4) the descendants of “impure”
+parents cannot be depended upon to come true to either type, but
+impure dominants may breed recessives, and _vice versa_, with the
+presumption, however, of 3:1 in favor of dominants.
+
+
+          Practical Questions
+
+  1. Would hybridization account for some of the diversities
+  mentioned in 170? (See 257.)
+
+  2. To what cases would it not apply? (256; Exp. 79.)
+
+  3. Would it be worth while to try to hybridize the potato and
+  squash? The squash and pumpkin? The lily and rose? Sweetbrier and
+  wild rose? Apple and peach? Wild crab and sweet apple? Blackberry
+  and strawberry? Blackberry and raspberry? Lemon and watermelon?
+  Lemon and orange? Why, or why not, in each case? (256; Exps. 78,
+  79.)
+
+
+          VII. PLANT BREEDING
+
+  MATERIAL.—If practicable, visit a market garden, a florist’s
+  establishment, or, lacking these, the fruit and vegetable stalls of
+  a city market.
+
+=260. Fixing the type.=—It is the tendency of plants to vary under
+the influence of climate, soil, food supply, crossing, and other
+causes perhaps unknown to us, that makes the plant breeder’s art
+possible. When a horticulturist sets out to produce a new fruit
+or vegetable, he first forms in his mind a clear idea of what he
+wants—whether increase of yield or size, resistance to cold, drought,
+or disease, improvement in flavor, color, shape, etc., or change
+in the time of maturing or flowering (early and late varieties).
+Suppose, for instance, he wishes to produce an oxeye daisy with
+all the disk florets changed to white ones like the rays. He will
+begin by selecting plants with the greatest number of rays and the
+most conspicuous ones that he can find, and sowing the seeds of
+the flowers which show the greatest tendency to the development of
+these qualities. He will continue this process from generation to
+generation, rigorously destroying all specimens that do not approach
+nearer the ideal sought, until all disposition to “rogue,” as the
+tendency to revert is called, has been eliminated. When variations
+cease to occur and the seed of the new variety always “come true,”
+the type is said to be _fixed_; though some care will always be
+necessary to keep it so, as the influence of changed surroundings and
+the danger of mixture with foreign pollen must always be provided
+against.
+
+[Illustration: FIG. 338.—A field of pumpkins grown from selected
+seed.]
+
+=261. Survival of the fittest.=—In the fierce struggle continually
+going on among both plants and animals for food, shelter, and elbow
+room in the world, any individual that happens to vary in a way which
+adapts it to its surroundings a little better than its rivals, has an
+advantage that will enable it to survive when less favored members of
+the species will perish. Its offspring, or some of them, may inherit
+this quality and transmit it, with the attendant advantage, to their
+posterity, and so on, till that particular breed outstrips all
+competitors, and in time, as the less favored intervening forms die
+out, becomes differentiated as a new species. This is, in brief, the
+doctrine of natural selection and the survival of the fittest.
+
+=262. Artificial selection.=—Artificial selection enables the breeder
+to accomplish more quickly what nature appears to do by the slow
+process of natural selection. It is by this means that our choicest
+fruits and vegetables have been developed from greatly inferior, and
+sometimes inedible, wild forms. Plants respond so readily to the
+influence of selection, and the changes brought about by it are so
+rapid, that new styles of fruits and flowers succeed each other in
+the market with almost as great frequency and in as ready response
+to demand as the new styles of women’s bonnets and gowns in the shop
+windows.
+
+[Illustration: FIG. 339.—Variation in blackberry leaves due to
+hybridization.]
+
+=263. Causes of variation.=—While man cannot directly force plants
+to vary in any given direction, he can hasten the process of
+variation by crossing, or by changing the conditions under which
+they are growing. This is called “breaking the type.” Hybridization
+furnishes the readiest means to this end. Change of food supply,
+especially if accompanied by excess of nourishment, is probably the
+expedient that ranks next in effectiveness. Light, temperature,
+moisture, character of the soil, exposure to wind, and the like,
+also have their influence; and in adapting themselves to changes
+in these various conditions, plants are apt to exhibit an unusual
+number of variations, when removed from one locality to another,
+especially if the difference in soil and climate is very marked.
+Now comes the breeder’s opportunity. By taking advantage of such
+variations as may occur either spontaneously, or as the result of
+his efforts to break the type, he will generally find some that will
+meet his requirements; and knowing the effect produced by different
+conditions, he can, to a certain extent, influence the course of
+variation in the direction desired, by subjecting his specimens to
+the conditions that tend to produce it. If he wishes to develop a
+dwarf variety, for instance, he will take notice that overcrowding,
+lack of nourishment, and cold tend to produce that result in
+nature, and by acting on this hint he can direct his efforts more
+intelligently. He will learn, too, not to waste time in trying to
+breed a plant contrary to its nature. He must not expect to gather
+figs from thistles by any art of selection or skill in culture. By
+attention to Mendel’s law, a still further saving of time and labor
+may be effected.
+
+It is obvious, from what has been said, that a breeder’s chance of
+finding what he wants will be greater in proportion to the number
+of individual plants he has to choose from. For this reason, a
+horticulturist sometimes uses thousands and hundreds of thousands of
+specimens of a single kind in conducting his experiments. In this way
+he compresses into a short space of time the advantage that nature
+can gain only by spreading her random experiments over a long series
+of years, or even centuries.
+
+[Illustration: FIG. 340.—Mutation in twin ears of corn, showing the
+sudden variations that sometimes occur, by which a new type may be
+provided without the labor of selection.]
+
+=264. Mutation and variation.=—There are at least two ways in which
+changes in vegetable and animal forms are thought to occur: (1)
+by the preservation and fixation through selection and heredity,
+of slight differences that may appear from time to time, such
+divergences being called “fluctuating variations”; (2) by the
+appearance now and then, due to causes as yet unknown, of definite
+and sudden changes creating a new form at a single, though perhaps
+small, leap. When such a change is temporary and passes away with
+the individual in which it first appeared, it is called a “sport,”
+and leads to no important results; but when it is inherited by the
+offspring, so that it is capable of giving rise to a new species,
+it constitutes a “mutation.” The value of a mutation to breeders
+in saving time and trouble is obvious. Professor Hugo de Vries, a
+Dutch botanist, was the first to call attention to the importance of
+mutation and its bearing upon the production of new species.
+
+=265. Factors in the evolution of species.=—Variation, heredity, and
+selection are the three principal agents underlying all changes,
+whether for the improvement or deterioration of living organisms.
+The influence of external surroundings in keeping up a variation
+once begun, or in starting new ones, is also a factor that cannot
+be disregarded. It is for this reason that natural species are so
+much more stable than those brought about by man. The former, being
+evolved in response to natural conditions, are liable to change
+only as alterations in their surroundings are brought about by the
+slow operation of natural causes. But the types resulting from the
+breeder’s art, produced as they often are in response to human
+demands and in direct opposition to the requirements of natural
+conditions, are in a sense purely artificial, and can be preserved
+only by keeping up the artificial surroundings by which they were
+developed. Hence, the importance of diligent cultivation and constant
+care and tillage, without which the most carefully selected stocks
+may quickly “run out” and degenerate into worthless forms.
+
+
+          Practical Questions
+
+  1. Which are the more pliable to the breeder’s art, annuals or
+  perennials? Why? (91, 93, 262, 263.)
+
+  2. What advantage is gained by using buds and grafts instead of
+  seedlings in making new varieties of fruit trees? (257, 259, 260.)
+
+  3. Would it be practicable to breed new varieties of slow-growing
+  forest trees, like oak, cypress, redwood, from seeds? Why or why
+  not? (93, 262, 263.)
+
+  4. Can you account for the existence of the numerous intermediate
+  forms between the different species of oaks found in nature? (255,
+  257.)
+
+  5. If a breeder wished to produce a sweet-scented daisy or pansy,
+  how would he make his selections? (260.)
+
+  6. Which would be the more useful for his purpose, a plant that
+  showed a general tendency to variability, or one that remained
+  steadily fixed to its type? (260.)
+
+  7. What could he do to break the type? (263.)
+
+  8. Would an intelligent breeder set out to produce edible roots and
+  tubers from wheat or barley? (263.)
+
+  9. Would he think it worth while to try to develop a fleshy fruit
+  from a filbert or a walnut tree? From a haw? From sheepberry and
+  black haw? From tupelo (ogeechee lime)? (263.)
+
+  10. Suppose a florist should wish to change the color of a rose
+  from pink to deep red; how could he hasten the process? (257, 263.)
+
+  11. Explain why it is so much easier to produce new varieties of
+  plants when there are already many kinds in existence, as, for
+  example, the rose, peach, and chrysanthemum. (255, 256; Exps. 78,
+  79.)
+
+
+          VIII. ECOLOGY OF THE FLOWER
+
+
+          A. THE PREVENTION OF SELF-POLLINATION
+
+  MATERIAL.—Any kind of unisexual flowers obtainable. Some good
+  examples for illustrating points mentioned in the text are: for
+  spring and early summer, catkins of almost any of our common forest
+  trees,—oak, hickory, willow, poplar, etc.; tassels and young ears
+  of early corn; for summer and early fall, flowers of late corn, and
+  of melon, squash, pumpkin, or others of the gourd family. Examples
+  of _dichogamy_ are: evening primrose, showy primrose (_Œnothera
+  speciosa_), willow herb (_Epilobium_), dandelion, artichoke,
+  sunflower, or any of the composite family; of _dimorphism_:
+  English primrose (_Primula_), loosestrife (_Pulmonaria_), bluets
+  (_Houstonia_), partridge berry; _cleistogamic_: fringed polygala,
+  violets. Peanuts, while not technically classed as cleistogamic,
+  are strictly close-fertilized, and approach the type so nearly that
+  they may be used as an illustration.
+
+=266. Ecology= is the study of plants and animals in relation to
+their surroundings. The principal modifications that flowers undergo
+in this respect are in adapting themselves for (1) pollination, and
+(2) protection.
+
+[Illustration: FIGS. 341, 342.—Unisexual flowers of willow: 341,
+staminate; 342, pistillate.]
+
+[Illustration: FIG. 343.—Twig of oak with both kinds of flowers:
+_f_, fertile flowers; _s_, _s_, staminate; _a_, pistillate flower,
+enlarged; _b_, vertical section of pistillate flower, enlarged; _c_,
+portion of one of the sterile aments, enlarged, showing the clusters
+of stamens.]
+
+=267. Unisexual flowers.=—The advantages of cross fertilization were
+shown in the last two sections. It was also shown that the first
+step taken by the breeder to secure this result is to render the
+flower incapable of self-fertilization, by removing the stamens.
+Nature accomplishes the same purpose by the more effectual expedient
+of providing imperfect, or _unisexual_ flowers, in which stamens
+only, or pistils only, occur in the same flower. When the stamens
+alone are present, the flower is said to be staminate, or _sterile_,
+because it is incapable of producing seeds of its own, though its
+pollen is a necessary factor in seed production. If, on the other
+hand, the ovary is present and the stamens absent, the flower is
+pistillate and _fertile_; that is, capable of producing fruit when
+impregnated with pollen. Sometimes both stamens and pistils are
+wanting, as in the showy corollas of the garden “snowball,” the
+hydrangea, and the rays of the sunflower. Such blossoms are said to
+be _neutral_, from the Latin word _neuter_, meaning neither, because
+they have neither pistils nor stamens. They can, of course, have no
+direct part in the production of fruit, but are for show merely.
+(231.)
+
+=268. Monœcious and diœcious plants.=—When both kinds of flowers,
+staminate and pistillate, are borne on the same plant, as in the oak,
+pine, hickory, and most of our common forest trees, they are said
+to be _monœcious_, a word which means “belonging to one household”;
+when borne on separate plants, as in the willow, sassafras, and black
+gum, they are _diœcious_, or “of two households.” Draw a flowering
+twig of oak, pine, or willow. Where are the fertile flowers situated?
+Notice how very much more numerous the staminate flowers are than the
+fertile ones. Why is this necessary? (275.)
+
+[Illustration: FIGS. 344, 345.—Flower of fireweed (_Epilobium
+angustifolium_): 344, with mature stamens and immature pistil; 345,
+the same a few days older, with expanded pistil after the anthers
+have shed their pollen. (_After_ GRAY.)]
+
+=269. Dichogamy= is the name applied to a condition where the stamens
+and pistils mature at different times, as in the evening primrose,
+oxeye daisy, and most of the composite family. It is a very common
+method in nature for preventing self-pollination, and quite as
+effective as the monœcious arrangement, since it renders the flowers
+practically unisexual.
+
+[Illustration: FIGS. 346-347.—Flower of pulmonaria: 346, long styled;
+347, short styled.]
+
+=270. Dimorphism= denotes a condition in which the stamens and
+pistils are of different relative lengths in different flowers of
+the same species, the stamens being long and the pistils short in
+some, the pistils long and the stamens short in others. Flowers
+of this sort are said to be _dimorphous_, or _dimorphic_, that
+is, of two forms; and some species are even _trimorphic_, having
+the two sets of organs long, short, and medium, respectively, in
+different individuals. Examples of dimorphic flowers are the pretty
+little bluets (_Houstonia cœrulea_), the partridge berry, the swamp
+loosestrife, and the English cowslip. Of trimorphic flowers we have
+examples in the wood sorrel and the spiked loosestrife (_Lythrum
+salicaria_) of the gardens. These flowers were a great puzzle to
+botanists until the celebrated naturalist, Charles Darwin, proved
+by experiment that the seeds produced by pollinating a dimorphous
+flower with its own pollen, or with pollen from a flower of similar
+form, are of very inferior quality to those produced by impregnating
+a long-styled flower with pollen from a short-styled one, and _vice
+versa_.
+
+[Illustration: FIGS. 348-350.—Three forms of loosestrife (_Lythrum
+salicaria_).]
+
+=271. “Nature abhors self-fertilization.”=—These are the
+three principal methods by which nature provides against
+self-fertilization. Other cases occur in which the relative position
+of the two organs is such that self-pollination is difficult, or
+impossible, as in the iris and bear’s grass; or the pollen may be
+incapable of acting on the stigma of the flower that produced it.
+This aversion to self-fertilization is so great that many flowers,
+even when capable of it, will give preference to the pollen of
+another plant of the same kind, if dusted with both. From his
+observations on the behavior of plants in reference to this function,
+Charles Darwin drew the conclusion that “Nature abhors perpetual
+self-fertilization.”
+
+=272. Cleistogamic flowers.=—Apparent exceptions to this rule are
+the hidden flowers found on certain plants which seem to have been
+constructed with a special view to self-fertilization. They are
+called _cleistogamic_, or closed, because they never open, but are
+fertilized in the bud; and those of the fringed polygala do not
+even rise above ground at all. Flowers of this kind can be found on
+several species of violet, concealed under the leaves, close to the
+ground; and the flowers of the peanut, found in the same situation,
+while they open slightly, are close-fertilized and practically
+cleistogamic. They are much more prolific than ordinary flowers,
+but are not common, and seem to be a provision against accident, for
+the plants producing them are generally provided with other flowers
+of the usual kind,—some, as the violet, having elaborate special
+adaptations for cross fertilization.
+
+
+          Practical Questions
+
+  1. Why does a strawberry bed sometimes fail to fruit well, although
+  it may flower abundantly? (267, 268.)
+
+  2. Are berries found on all sassafras trees? On all buckthorns?
+  Hollies?
+
+  3. Would a solitary hop-vine produce fruit? A solitary ash tree?
+  (267.)
+
+  4. Why is a mistletoe bough with berries on it so much harder to
+  find than one with foliage merely? (267, 268.)
+
+
+          B. WIND POLLINATION
+
+  MATERIAL.—In spring, catkins of forest trees, staminate and
+  pistillate flowers of pine. At nearly all seasons, heads of grain
+  and panicles of various kinds of grass can be obtained. For
+  experiment, a potted plant of any kind, just about to bloom, may be
+  used.
+
+  EXPERIMENT 80. TO TEST THE EFFECT OF SHUTTING OUT EXTERNAL
+  AGENCIES.—Tie paper bags over flower buds of different kinds when
+  nearly ready to open and leave until the flowers have withered.
+  On removing the bags, mark with colored threads the flowers that
+  had been covered, and watch until seed time. Do you notice any
+  difference in the number, size, or weight of the seed produced by
+  them and by those of the same kind left exposed? How do you account
+  for the difference, if there is any? By what agencies could foreign
+  pollen have been carried to the stigmas of the exposed flowers? If
+  any of the covered specimens wither and drop their seed vessels
+  without any attempt to fruit, examine a fresh flower, and see if it
+  is capable of self-pollination.
+
+  As already explained, experiments of this kind, to be conclusive,
+  should be tried on as many specimens as possible. The greater the
+  number of species and individuals included, the better. Where it is
+  not practicable to carry on experiments by the class, pupils who
+  are interested can make them at home.
+
+=273. The problem of pollination.=—When a plant has provided against
+self-pollination, its problem is only half solved, as it must now
+depend upon the conveyance of pollen to the stigma by extraneous
+means.
+
+[Illustration: FIG. 351.—Feathery stigmas of a grass adapted to wind
+pollination.]
+
+=274. Adaptations to wind pollination.=—A very large number of
+plants, among which are included nearly all our principal forest
+trees, grains, and grasses of every kind, depend exclusively upon
+the wind for the distribution of their pollen. This being the case,
+it is, of course, an advantage to them to get rid of all unnecessary
+appendages that might hinder a free play of the wind among their
+flowers, and so they consist, as a rule, of essential organs only
+(Figs. 341, 342). Such flowers are often distinguished, however,
+especially among grasses and low herbs, by large, feathery stigmas
+that are well adapted to catch and hold any stray pollen grains which
+may be floating in the air. Place a stigma of oat or other grass
+under the microscope and you will probably see a number of pollen
+grains clinging to its branches.
+
+=275. The disadvantages of wind pollination.=—This is a very clumsy
+and wasteful method, however, for so much pollen is lost by the
+haphazard mode of distribution that the plant is forced to spend its
+energies in producing a vast amount more than is actually needed,
+and great masses of it are frequently seen in spring floating like
+patches of sulphur on ponds and streams in the neighborhood of pine
+thickets. Like those that are self-pollinated, wind-pollinated
+flowers are generally very inconspicuous, devoid of odor, and of all
+attractions of form or color, because they have no need of these
+allurements to attract the visits of insects. Besides being wasteful,
+wind pollination is very uncertain. The pollen cannot be blown about
+very well unless it is dry, and in rainy weather it may all be rotted
+or washed away before it can reach the stigmas that are ready to
+receive it.
+
+
+          Practical Questions
+
+  1. Why do the flowers of oak, willow, and other wind-fertilized
+  plants generally appear before the leaves? (274.)
+
+  2. Can you account for the showers of “sulphur” sometimes reported
+  in the newspapers? (275.)
+
+  3. Do you see any connection between the feathery stigmas of most
+  grasses and their mode of pollination? (274.)
+
+  4. Why are house plants not apt to seed so well as those left in
+  the open? (Exp. 80.)
+
+  5. Why are the tassels of corn placed at the tip of the stalk?
+  (274.)
+
+  6. Can you trace any connection between the winds and the corn
+  crop? (274.)
+
+  7. If March winds should cease to blow, would vegetation be
+  affected in any way? (274.)
+
+  8. Why are wind-fertilized plants generally trees or tall herbs?
+  (274.)
+
+  9. Is it good husbandry to plant different varieties of corn or
+  other grain in the same field, if it is desired to keep the strain
+  pure? (255, 274.)
+
+  10. Is water a good pollen carrier? (275.)
+
+  11. What is the only class of plants it is likely to reach?
+
+  12. What is the only other agency, besides wind and water, by which
+  this office can be performed?
+
+
+          C. INSECT POLLINATION
+
+  MATERIAL.—Half a dozen panes of glass, about 6 × 9; squares of
+  bright-colored cloth or paper; a few spoonfuls of honey or sirup;
+  perfumes of various kinds, preferably flower extracts; fetid and
+  disagreeable smelling substances, such as a bit of decaying animal
+  or vegetable matter. Observations on living plants can best be made
+  out of doors or in a greenhouse, as opportunity offers.
+
+  EXPERIMENT 81. HAS THE COLOR OF FLOWERS ANY ATTRACTION FOR
+  INSECTS?—Place half a dozen panes of ordinary window glass out of
+  doors or in an open window to which insects can have free access.
+  Lay under the first pane a piece of black paper or cloth, and under
+  the others bright-colored pieces of red, blue, white, yellow, and
+  purple. Drop on the center of each pane a little honey or sirup,
+  and watch. Do insects show any color preferences? Which color
+  attracts fewest visitors? Which most?
+
+  EXPERIMENT 82. DOES ODOR INFLUENCE INSECTS?—Try the same experiment
+  with different odors, removing the bright colors and sprinkling
+  some kind of perfume on each pane. Try also the effect of decaying
+  meat and other malodorous substances. Are any insects attracted
+  by these? What kinds? Does this account for the noisome smells
+  of the “carrion-flower” and skunk cabbage? What kinds of insects
+  are attracted by sweet-smelling substances? Do the greater number
+  appear to be attracted by these, or by foul odors? Are flowers of
+  the sweet-smelling or the foul-smelling kind more common in nature?
+  Do insects seem to be more strongly influenced by colors or by
+  odors?
+
+=276. The color of flowers=, being an adaptation to changing external
+conditions, is a very unstable quality, and varies greatly within
+the limits of the same species. Even on the same stem, flowers of
+different colors are often found, due, probably, to hybridization.
+Yet, notwithstanding all this apparently random intermingling of
+hues, the range of color for each species is confined, approximately,
+within certain limits. Nobody has ever seen a blue rose or a yellow
+aster; and though the florist’s art is constantly narrowing the
+application of this law, it still remains true that in a state of
+nature, certain colors seem to be associated together in the floral
+art gamut. Yellow is considered the simplest and most primitive color
+in flowers, and blue the latest and most highly evolved. Yellow,
+white, and purple, in the order named, are the commonest flower
+colors in nature; blue, the rarest. Do you see any relation between
+these facts and the color preferences of insects?
+
+=277. Advantages of insect pollination.=—It is evident that this is
+a much more certain as well as a more economical method of securing
+pollination than through the haphazard agency of wind or water.
+In probing around for the nectar or the pollen upon which they
+feed, these busy little creatures get themselves dusted with the
+fertilizing powder, which they unconsciously convey from the stamen
+of one flower to the pistil of another. Insects usually confine
+themselves, as far as possible, to the same species during their
+day’s work, and since less pollen is wasted in this way than would
+be done by the wind, it is clearly to the advantage of a plant to
+attract such visitors, even at the expense of a little honey, or of a
+liberal toll out of the pollen they distribute.
+
+=278. Special partnerships.=—Some plants have adapted themselves
+to the visits of one particular kind of insect so completely that
+they would die out if that species were to become extinct. The
+well-known alliance between red clover and the bumblebee was brought
+to light when the plant was first introduced into Australia. It grew
+luxuriantly and blossomed profusely, but would never set seed till
+the bumblebee was introduced to keep it company.
+
+[Illustration: FIG. 352.—Pod of _yucca_ pierced by the _Pronuba
+yuccasella_.]
+
+[Illustration: FIG. 353.—Pronuba pollinating pistil of yucca.]
+
+[Illustration: FIG. 354.—Moth resting on yucca blossom.]
+
+A remarkable partnership of this kind exists between the _pronuba_,
+or yucca moth, and the flowering yuccas, of which the bear’s grass
+and Spanish bayonet are familiar examples. The pods of these plants
+are never perfect, but all show a constriction at or near the middle,
+such as is sometimes seen in the sides of wormy plums and pears. This
+is caused by the larvæ of the moth, which feed upon the unripe seeds.
+A glance under the nodding perianth of a yucca blossom (Fig. 354)
+will show that the short stamens are curved back from the pistil in
+such a manner that, under ordinary circumstances, the pollen cannot
+reach the stigma except by the rarest accident. But the yucca moth,
+as soon as she has deposited her eggs in the seed vessel, takes care
+to provide a crop of food for her offspring by gathering a ball of
+pollen in her antennæ and deliberately plastering it over the stigma
+(Fig. 353). In this way fertilization of the ovules and maturing of
+the fruit is secured. The larvæ feed on the unripe seeds for a time,
+but so few are destroyed in proportion to the number matured that the
+plant can well afford to pay the small toll charged in return for the
+service rendered.
+
+[Illustration: FIG. 355.—Upper boughs of a caprifig tree, showing an
+abundant crop of spring fruit.]
+
+[Illustration: FIG. 356.—Female wasps issuing from the galls of
+caprifigs, in which the eggs are laid.]
+
+=279. Caprification of the fig.=—A more complicated case of
+specialization is that of the Smyrna fig of commerce—the only one
+of the species that is capable of perfecting seeds. The staminate
+flowers are borne on a separate tree, the caprifig, which grows wild
+in the countries bordering on the Mediterranean. The caprifigs,
+as the fruit of this tree is called, are worthless except as the
+breeding and nesting places of a small insect, the fig wasp. This
+insect is the necessary agent in conveying pollen from the stamens of
+the caprifig to the pistils of the Smyrna fig, which it penetrates at
+certain seasons of the year in the effort to lay its eggs. In order
+to insure _caprification_, as this process is called, the caprifigs
+are strung by hand on fillets of cord or raffia and hung about on the
+trees which are to be fertilized. In this case we have an example
+of a threefold partnership between man, the fig tree, and the wasp,
+which is necessary to the existence of two of the parties.
+
+
+          D. PROTECTIVE ADAPTATION
+
+  EXPERIMENT 83. ARE THE FLORAL ENVELOPES OF ANY USE?—Carefully
+  remove the calyx and corolla from a young flower bud on a growing
+  plant and see what will happen. Remove them from a flower just
+  unfolding. Mark each by tying a colored thread lightly around the
+  petiole and see if it sets as many seeds, or as good ones, as the
+  unmutilated flowers on the same plant.
+
+  EXPERIMENT 84. IS THE POSITION OF A FLOWER ON THE STEM OF ANY
+  IMPORTANCE?—Invert a blossom of pea or sage, and see what parts
+  would come in contact with the body of a visiting insect. How would
+  its chances for pollination be affected? Try to make a flower grow
+  in an inverted position by tying or weighting it down, and watch
+  the effect on seed production.
+
+  EXPERIMENT 85. IS THE POSITION OF FLOWERS ON THE STEM INFLUENCED
+  BY LIGHT?—Place a potted plant with expanding flower buds near a
+  window so that the light will reach it from one side only, and
+  notice the position of the buds. After a day or two reverse the
+  position with regard to light, and watch whether any change of
+  position takes place.
+
+[Illustration: FIGS. 357-359.—Flower of monkshood, showing the
+changes by which it returns to its original position under the
+influence of geotropism after the axis of inflorescence, s, has
+been inverted: 357, inverted position; 358, change due to negative
+geotropism; 359, change due to lateral geotropism.]
+
+  EXPERIMENT 86. IS THE POSITION OF FLOWERS ON THE STEM INFLUENCED
+  BY GEOTROPISM?—Lay a potted plant of lily of the valley, larkspur,
+  gladiolus, or digitalis in a horizontal position, tie the main stem
+  to keep it from changing its direction of growth, and leave for two
+  or three days in a place where it is lighted equally on all sides.
+  How do the individual flowers behave? What part bends to turn them
+  up? Vary the experiment by turning the pot bottom upwards so
+  that the flowering axis will point downwards. This can be done by
+  inclosing the pot in a bag of strong cheesecloth, with the string
+  tied loosely but firmly around the foot of the stem to prevent the
+  contents from falling out, and suspending the whole bottom upwards.
+  In making these experiments, use flowers that grow in a long
+  cluster, or raceme, and hold the main axis in a vertical position
+  by tying or weighting it down. Watch the behavior of the individual
+  flowers. Arrange another pot containing the same kind of plant, in
+  the same way, and suspend one in a dark place, keeping the other
+  in the light. Does the same movement take place in both? Is it in
+  response to light, or to gravity?
+
+[Illustration: FIGS. 360, 361.—Protection of pollen in the thistle:
+360, position at night, or during wet weather; 361, position in
+sunshine.]
+
+[Illustration: FIGS. 362, 363.—A bell flower: 362, position in
+daylight; 363, position at night, or during wet weather.]
+
+=280. Means of protection.=—Where plants have adapted themselves to
+insect pollination, it is, of course, important to shut out intruders
+that would not make good carriers. In general, small, creeping
+things, like ants and plant lice, are not such efficient pollen
+bearers as winged insects, and hence the various devices, such as
+hairs, scales, and constrictions, at the throat of the corolla, by
+means of which their access to the pollen is prohibited. To this
+class of adaptations belong the hairy filaments of the spiderwort,
+the sticky ring about the peduncles of the catchfly, the swollen
+lips of the snapdragon, the scales or hairs in the throat of the
+hound’s-tongue, the velvet petals of the partridge berry, and the
+recurved edges of corollas like those of the morning-glory and
+tobacco, over which small crawling insects cannot easily climb.
+
+Of flowers that are pollinated by night moths, some close during
+the day, as the four-o’clock and the evening primrose; and _vice
+versa_, the morning-glory, dandelion, and dayflower (_Commelyna_)
+unfold their beauties only in the sunlight. For similar reasons,
+night-blooming flowers are generally white or very light-colored, and
+shed their fragrance only after sunset. A nodding position is assumed
+by many flowers at night, or during a shower, to keep the pollen from
+being injured by dew or rain.
+
+[Illustration: FIG. 364.—A flower of the trumpet vine (_Tecoma
+radicans_) adapted to pollination by humming birds and humming bird
+moths, which has been pierced by a bee or bird for honey.]
+
+[Illustration: FIG. 365.—Head of the swordbill, a bird adapted to
+feeding on nectar from long, tubular corollas.]
+
+=281. Insect depredators.=—The secretion of honey is a common
+means of attracting insects, and various adaptations, such as
+spurs, sacs, and pockets, are provided for protecting it against
+unwelcome intruders. In general, plants that have long, tubular
+flowers, like the trumpet honeysuckle (_Lonicera sempervirens_) and
+the trumpet vine, are reserving their sweets for humming birds, or
+long-tongued moths and butterflies. This protective device is not
+always successful, however, against insect depredators, for it is not
+uncommon to find such corollas with a puncture near the base, made by
+wasps or bees, and sometimes by humming birds themselves, in their
+impatience to get at the feast before the flower is open. Through the
+breach thus made, a rabble of petty thieves can then find entrance.
+
+
+          Practical Questions
+
+  1. Of what use is the brilliant coloring of the camellia? The large
+  flowers of the magnolia? The perfume of the rose and the violet?
+  The fetid odor of the ailanthus? (277; Exps. 81, 82.)
+
+  2. Are the tastes of insects in regard to odors always the same as
+  ours? (Exp. 82.)
+
+  3. Have flowers any economic value except for decorative purposes?
+
+  4. Can you name any that are used as food or beverages? Any that
+  furnish spices and flavorings? Drugs, medicines, or dyes?
+
+  5. What commercial food product is obtained almost entirely from
+  flowers?
+
+  6. Name some of the flowers that are most valued by the beekeeper.
+
+  7. Mention another important industry that is entirely dependent on
+  flowers.
+
+  8. Name some of the flowers that are most important to the perfumer.
+
+  9. Why do the seeds of fruit trees so seldom produce offspring true
+  to the stock? (256, 257, 271, 277.)
+
+  10. Would you place a beehive near a field of buckwheat? Of clover?
+  Near a strawberry bed? In a peach orchard? Near a fig tree? Under a
+  grape arbor?
+
+  11. Why are very conspicuous flowers, like the camellia, hollyhock,
+  and pelargoniums, so frequently without odor?
+
+  12. Why is the wallflower “sweetest by night”? (280.)
+
+  13. What advantage can flowers like the morning-glory gain by their
+  early closing? (280.)
+
+  14. Of what use to the cotton plant, Japan honeysuckle, and
+  hibiscus is the change of color their blossoms undergo a few hours
+  after opening? (277, 278, 280.)
+
+  15. Why does the Japan honeysuckle, which has run wild so
+  abundantly in many parts of our country, produce so few berries?
+  (278, 280.)
+
+  16. If the trumpet vine grows in your neighborhood, examine a
+  number of corollas and account for the dead ants found in them.
+  Account also for the large hole (sometimes three quarters of an
+  inch in diameter) often found near the base of the tube. (281.)
+
+  17. Do you see any connection between the greater freshness and
+  beauty of flowers early in the morning, and the activity of bees,
+  birds, and butterflies at that time?
+
+  18. The flowers most frequented by humming birds are the trumpet
+  honeysuckle, cardinal flower, trumpet vine, horsemint (_Monarda_),
+  wild columbine, canna, fuchsia, etc.; what inference would you draw
+  from this as to their color preferences?
+
+
+          Field Work
+
+  1. The ecology of the flower is so suggestive a subject and so
+  peculiarly appropriate to outdoor work that it seems hardly
+  necessary to point out the many attractive fields of inquiry it
+  opens to the student of nature. In this way alone can experiments
+  in insect pollination be carried on to the best advantage. Try
+  the effect of enveloping buds of various kinds in gauze so as
+  to exclude the visits of insects, and note the result as to the
+  production of fruit and seed. Envelop a cluster of milkweed
+  blossoms in this way and notice how much longer the flowers so
+  protected continue in bloom than do the others; why is this? Try
+  the same experiment upon the blooms of cotton and hibiscus, if you
+  live where they grow, and see whether the characteristic change in
+  color occurs in flowers from which insects have been excluded, and
+  whether good seed pods are produced by them. Try the effect upon
+  fruit production of excluding insects from clusters of apple, pear,
+  and peach blossoms.
+
+  2. Make a list of all the outdoor plants, both wild and cultivated,
+  that are found blooming in your neighborhood, keeping a record of
+  the earliest specimens of each as you find them. The best way is to
+  keep a sort of daily calendar, and at the end of each month give a
+  summary of the species found in bloom during that period. In this
+  way a fairly complete annual record of the flowering time of the
+  different plants for that vicinity will be obtained. The record
+  should be kept up the whole year round. Don’t stop in winter,
+  but go straight on through the coldest as well as the hottest
+  season, and you will make some surprising discoveries, especially
+  if the record is continued year after year. Give the common name
+  of each plant, adding the botanical one if you know it. Any facts
+  that you may know or may discover in regard to particular plants,
+  such as their medicinal or other uses, their poisonous or edible
+  properties, the insects that visit them, and in the case of weeds,
+  their origin and introduction, will greatly enhance the interest
+  and value of the record.
+
+
+
+
+CHAPTER VIII. FRUITS
+
+
+          I. HORTICULTURAL AND BOTANICAL FRUITS
+
+  MATERIAL.—Green ears of corn or wheat, fresh pods of beans, young
+  fruits of apple, grape, tomato, melon, buckeye, chestnut, or pecan.
+  A young fruiting stem of squash, gourd, or tomato.
+
+  APPLIANCES.—Coloring fluid, glasses of water, a piece of cardboard,
+  tin-foil, vaseline.
+
+  EXPERIMENT 87. WHERE DO THE FOOD SUBSTANCES CONTAINED IN FRUITS
+  COME FROM?—Apply your food tests to the pulp of a young apple,
+  squash, bean pod, chestnut, buckeye, or a “green” ear of corn or
+  wheat, and see what it contains. Test the stem and roots of a plant
+  of the same kind in the same way. Do you find the same foods in
+  them? Where is the food stored?
+
+  EXPERIMENT 88. THROUGH WHAT PARTS OF THE STEM AND FRUIT DO WATER
+  AND NOURISHMENT TRAVEL TO THE SEED?—Cut a young squash or cucumber
+  from the vine, leaving stem enough to insert by its cut end in a
+  glass of eosin solution. Leave for two or three days, then make a
+  vertical section through the stem and fruit. What course has the
+  liquid followed? Can you trace some of it into each seed? Do you
+  see now a use for the seed stalk and the rhaphe?
+
+  EXPERIMENT 89. DOES THE SURFACE OF FRUITS GIVE OFF WATER BY
+  TRANSPIRATION?—Try Exp. 59, using in place of leaves a young
+  squash, eggplant, or a bunch of grapes, and after a day or two
+  notice whether any moisture has been given off. If the fruit skin
+  gives off moisture, it is natural to expect that it would be
+  provided with stomata, like other transpiring organs. To find out
+  whether this is so, place a thin piece of the outer epidermis of
+  a grape, tomato, plum, or apple under the microscope. Do you find
+  stomata on any of them? Do you see anything else? Try the skin of
+  an apple, and compare the corky dots you find there with those on
+  the bark of a young dicotyl stem (118) and decide what they are.
+
+  EXPERIMENT 90. WILL FRUITS RIPEN WELL IN THE ABSENCE OF LIGHT AND
+  AIR?—Envelop a number of immature fruits in bags of dark cloth or
+  paper so that no light can reach them. Keep a number of others well
+  coated with oil or vaseline, and watch. Do the fruits so treated
+  mature as quickly or develop as fully as those of the same kind
+  left untreated?
+
+[Illustration: PLATE 12.—The improvement of fruits by cultivation and
+selection: 1, the common wild gooseberry; 2, Houghton gooseberry,
+seedling of the wild form; 3, Downing gooseberry, seedling of the
+Houghton. (All natural size, adapted from Bailey.)]
+
+  EXPERIMENT 91. WHAT IS THE USE OF THE RIND TO THE FRUIT?—Select
+  two apples of equal size, peel one, and weigh both. After 12 to 24
+  hours, weigh them again. Which shows the greater loss in weight?
+  Leave peeled and unpeeled fruits in an exposed place and see which
+  is the more readily attacked by insects. Which decays the sooner?
+  What are some of the uses of the rind?
+
+=282. What is a fruit?=—Horticulturally and commercially the
+distinction between a fruit and a vegetable depends very much upon
+the use we make of it—whether as food, or as a mere gratification of
+the palate. Broadly speaking, those fruits that are lacking in sugar,
+as the tomato and cucumber, are classed as vegetables. Botanically, a
+fruit is any ripened seed vessel, or ovary, with such connected parts
+as may have become incorporated with it; and hence, to the botanist,
+a boll of cotton, a tickseed, or a cocklebur is just as much a fruit
+as a peach or a watermelon.
+
+=283. Classification of fruits.=—For convenience of description,
+fruits are classed as:
+
+(_a_) Dry or fleshy, according as they have a more or less hard and
+bony, or soft and fleshy, texture.
+
+(_b_) Dehiscent, or indehiscent, according as they open at maturity
+in a regular way to discharge their seed, or remain closed until the
+covering wears away or is burst by the germinating embryo.
+
+Fleshy fruits are very seldom dehiscent, though some few, as the
+balsam apple and the chayote, or one-seeded squash, discharge their
+seed when mature. The banana and some other fleshy fruits, when
+peeled, separate along regular lines, and in this respect behave very
+much as if they were fleshy pods.
+
+=284. When is a fruit ripe?=—A fruit is ripe horticulturally, when
+it is good to eat; it is ripe botanically, when it has set its seed.
+Many of our choicest table fruits, such as the pineapple, banana, and
+most varieties of fig, seldom are botanically ripe, since they rarely
+produce perfect seeds.
+
+It is the constant effort of the horticulturist to develop those
+parts of a plant that are useful to man, while in a state of nature
+the plant seeks to develop such parts as best serve its own purpose
+in the struggle for existence. The plants most useful to man have,
+as a general thing, been subjected to a long course of artificial
+breeding and selection. They are forced developments, often
+monstrosities, from the plant’s point of view, if we could conceive
+of it as capable of having an opinion. Nature is continually striving
+to reclaim them; and if left to themselves, they must either obey
+“the call of the wild,” or die out.
+
+[Illustration: FIG. 366.—A seedless citrange, hybrid between the
+orange and the lemon.]
+
+=285. Seedless fruits and vegetables.=—As the seed is the most
+important thing to the plant, the edible parts in wild fruits are, as
+a rule, subsidiary to its development. In a state of nature, fruits
+will generally wither and drop from the stem, if for any reason they
+have become incapable of perfecting their seed. It is only in a few
+kinds, limited to those which can successfully propagate themselves
+by other means, that the production of seed does not take place.
+Among cultivated species, however, where propagation is carefully
+provided for by man, the seed is of less importance, and sterile
+varieties that might soon die out under natural conditions, continue
+their existence indefinitely under his fostering hand. The seeds
+of edible fruits are, as a general thing, both indigestible and
+unpalatable (21), and hence the efforts of the horticulturist are
+directed largely to getting rid of them, or to very greatly reducing
+their size and number in proportion to the edible parts.
+
+=286. How seedless fruits arise.=—The perfecting of seed requires a
+great consumption of food and energy on the part of the plant, and
+when it is led, for any reason, to expend an unusual amount of force
+in some other function,—as for instance, in producing tubers or in
+growing bulbs,—it is apt to bear few seeds and to depend more or less
+completely upon other methods of reproduction.
+
+Among cultivated plants, selection on the part of man, whether
+conscious or unconscious, has perhaps contributed more than any
+other cause to bring about the same result. To this agency is
+probably due the development of our common domestic fig, of which
+over four hundred varieties that mature fruits without fertilization
+are cultivated in the United States alone. The fig was one of the
+earliest fruits known to cultivation; and the early navigators,
+ignorant of the processes of fertilization, would naturally, in
+choosing specimens to carry home with them, select only fruit-bearing
+trees. Such of these as matured fruits would be preserved and
+propagated, until, by repeated selection, hundreds of edible
+varieties have been developed that ripen fruits without caprification
+(279).
+
+=287. The use of the fruit to the plant.=—The object of the fruit is
+to furnish protection to the seeds during their period of development
+and inactivity, and to aid in various ways the work of dispersal.
+It probably takes part also in digesting and diffusing nourishment
+for the use of the developing seeds. It has been shown in previous
+chapters that plants, almost without exception, are in the habit of
+storing up food in various ways as a provision for fruiting. That a
+large portion of the stored nourishment is used up in the performance
+of this function is proved by its disappearance from those parts—for
+example, from fleshy roots, such as beets and turnips, after they
+have “gone to seed.”
+
+
+          Practical Questions
+
+  1. What is the use of the down on the peach? The bloom of the plum
+  and grape? [202, (1); Exp. 91.]
+
+  2. Why are apples, pears, plums, and other fleshy fruits nearly
+  always rosier on one side than on the other? (Exp. 90.)
+
+  3. Can annuals be improved in any other way than by seed selection?
+
+  4. Would a seedless annual be perpetuated under natural conditions?
+
+  5. Why is decrease of moisture and increase of light desirable as
+  the fruiting season approaches? (126, 127; Exp. 90.)
+
+  6. Why are turnips, carrots, and other fleshy roots unfit to eat if
+  left over till the plants have seeded? (92, 287.)
+
+
+          II. FLESHY FRUITS
+
+  MATERIAL.—A specimen of each of the four principal kinds of fleshy
+  fruits. Examples of the pome are: apple, pear, quince, rose hip,
+  haw; of the berry: grape, tomato, cranberry, currant, gooseberry,
+  lemon; of the pepo: melon, squash, pumpkin; of the drupe: peach,
+  plum, cherry, dogwood. Specimens of the commoner kinds can nearly
+  always be found in the market; if nothing better is available,
+  pickled and dried ones may be used—figs, prunes, dates, raisins,
+  etc.
+
+[Illustration: FIG. 367.—Outside of an apple, showing lenticels on
+the skin.]
+
+=288. Dissection of a pome fruit.=—Examine with a lens the outside of
+an apple or a pear. Can you make out the lenticels? What difference
+in color do you notice between the ripe and unripe fruit? What
+difference in taste? What substance would you judge from this, do
+ripe fruits contain which green ones do not? Test both kinds for
+sugar and starch; which contains the more of each? Strictly speaking,
+sugar and starch are merely different forms of the same chemical
+compound. In ripe fruits the starch has been cooked by the sun and
+converted into sugar.
+
+With the point of a pencil separate the little dry scales that cover
+the depression in the center of the fruit at the end opposite the
+stem. How many of them are there? How does this accord with the
+plan of the flower as outlined in 229? They are the remains of the
+sepals, as will be more apparent on comparing them with the larger
+and more leaflike ones on a hip, which is clearly only the end of the
+footstalk enlarged and hollowed out with the calyx sepals at the
+top. Cut a cross section midway between the stem and the blossom end,
+and make an enlarged sketch of it. Label the thin, papery walls that
+inclose the seed, _carpels_. How many of them are there, and how many
+seeds does each contain? The carpels, together with all that portion
+of the fruit which surrounds and adheres to the ovary, constitute
+the _pericarp_, or wall of the seed vessel. The fleshy part of the
+apple is no part of the ovary proper, but consists merely of the
+receptacle, or end of the footstalk, which becomes greatly enlarged
+and thickened in fruit. Look for a ring of dots outside the carpels,
+connected (usually) by a faint scalloped line. How many of these dots
+are there? How do they compare in number with the carpels? With the
+remnants of the sepals adhering to the blossom end of the fruit?
+
+[Illustration: FIG. 368.—Cross section of a pome: _pl_, placenta;
+_c_, carpels; _f_, fibrovascular bundles.]
+
+[Illustration: FIG. 369.—Vertical section of a pome: _p_, peduncle;
+_f_, fibrovascular bundles; _s_, seeds; _pl_, placenta; _c_, carpel.]
+
+Next make a vertical section through a fruit, and sketch, enlarging
+it sufficiently to show all the parts distinctly. Observe the line of
+woody fibers outside the carpels, inclosing the core of the apple.
+Compare this with your cross section; to what does it correspond?
+Where do these threads originate? Where do they end? Can you make
+out what they are? (176.) Notice how and where the stem is attached
+to the fruit. Label the external portion of the stem, _peduncle_;
+the upper part, from which the fibrovascular bundles branch, the
+_receptacle_. It is the enlargement of this which forms the fleshy
+part of the fruit. Try to find out, with the aid of your lens and
+dissecting pins, the exact spot at which the seeds are attached to
+the carpels, and label this point, _placenta_. Notice whether it is
+in the axis where the carpels all meet at their inner edges, or on
+the outer side. Observe, also, whether the seed is attached to the
+placenta by its big or its little end. If you can find a tiny thread
+that attaches the seed to the carpel; label it, seed stalk. Fruits
+of this kind are classed, botanically, as _pomes_. Write, from your
+analysis, a definition of the pome.
+
+[Illustration: FIGS. 370, 371.—Enlarged receptacle of Carolina
+allspice (_Calycanthus_), containing fruits attached to its inner
+surface: 370, exterior; 371, vertical section.]
+
+=289. Modifications of the receptacle.=—Compare with the drawings
+you have made, a haw and a hip. What points of agreement do you see?
+What differences? Which of the two more closely resembles the typical
+pome? The receptacle is subject to a variety of modifications,
+and forms a part of many fruits, for example, the fig, lotus, and
+calycanthus (Figs. 370, 371); but a fruit is not a pome unless the
+containing receptacle becomes more or less soft and edible.
+
+=290. The pepo, or melon.=—Next examine a gourd, cucumber, squash, or
+any kind of melon, and compare its blossom end with that of the apple
+or pear. Do you find any remains of a calyx, or other part of the
+flower? Examine the peduncle and observe how the fruit is attached
+to it. Can you tell what made the outer epidermis of the rind? Put
+a small piece under the microscope; do you see any stomata, or
+lenticels? Cut cross and vertical sections, and sketch them, labeling
+each part. There may be some difficulty in making out the carpels,
+for they are not separate and distinct as in the pome, but confluent
+with the enlarged receptacle, which in these fruits forms the outer
+portion of the rind, and also with each other at their edges, so
+as to form one unbroken circle, as if they had all grown together.
+And this is precisely what has happened. The placentas are greatly
+enlarged and modified, and it may be necessary to refer to the
+diagram, Fig. 372, _c_, in order to make them out. How many locules,
+or chambers, are there in your specimen? How many placentas? Notice
+that these are central and double, but extend to the pericarp before
+dividing so that they appear to be parietal, and twice their real
+number, which is only three. Are the seeds vertical, as in the apple,
+or horizontal? Look for the little stalk, or thread, that attaches
+them to the placenta.
+
+_Pepo_ is the name given by botanists to this kind of fruit. Write in
+your notebook a proper definition of it, from the specimens examined.
+
+[Illustration: FIG. 372.—Cross section of gourd: _c_, one of the
+carpels in diagram. (_After_ GRAY.)]
+
+[Illustration: FIGS. 373, 374.—A potato berry: 373, exterior; 374,
+cross section.]
+
+=291. The berry.=—Examine a tomato, an eggplant, a grape, cranberry,
+lemon, or orange, in both cross and vertical section, and compare
+it with the melon and the apple. What differences and resemblances
+do you find? Cut a cross section, and draw, showing the attachment
+of the seeds. How many locules are there? Normally the tomato is a
+two-celled fruit, like the potato berry (Fig. 374), but it has been
+so modified by cultivation that the original plan is not always easy
+to distinguish. See if you can make it out. Do the seeds in your
+specimen appear to be healthy and well developed, or are some of them
+small and aborted? How do you account for this? (285, 286.) What
+difference do you notice in color between the ripe and unripe fruit?
+Write a definition of the berry from the study you have made of it.
+
+Berries are the commonest of all fleshy fruits, and the most variable
+and difficult to define. In general, any soft, pulpy, or juicy mass,
+like the grape and tomato, whether one or many seeded, inclosed in
+a containing envelope, whether skin or rind, is a berry. Its typical
+forms are such fruits as the grape, mistletoe, pokeberry, etc.,
+though such diverse forms as the eggplant, persimmon, red pepper,
+orange, banana, and pomegranate have been classed as berries; and, in
+fact, the melon and the pumpkin are only greatly modified kinds of
+the same fruit. In popular language, any small, round, edible fruit
+is called a berry. This is a good commercial classification, though
+not botanically correct.
+
+[Illustration: FIG. 375.—Vertical section of a drupe. (_After_ GRAY.)]
+
+=292. The drupe, or stone fruit.=—Examine a section of a green plum,
+peach, or cherry, before the stone has hardened, and tell from what
+part it is formed. This stony covering, composed of the inner layer
+of the pericarp, and enveloping the seed like an outer coat, is the
+main distinction between the drupe and the berry, but it is not
+always possible to make out its real nature except by an examination
+of the young ovary. In a green drupe, before the stone has hardened,
+its connection with the fleshy part is very evident, and the ripe
+fruit will answer inquiries if we know how to put them. Open the
+stone, and the seed will be exposed with its own coverings inside.
+When a stone has more than one kernel,—for instance, an almond or
+peach stone, —the stone is not a seed coat, but the hardened inner
+wall of a seed vessel or ovary; for a seed coat can never contain
+more than one seed, any more than the same skin can contain more than
+one animal.
+
+All the fruits considered in this section belong to the fleshy class.
+These form the bulk of the fruits sold in the market, and are of
+special importance to the horticulturist.
+
+
+          Practical Questions
+
+  1. Is the tomato horticulturally a fruit or a vegetable? the
+  squash? eggplant? cranberry? olive? elderberry? pepper? date?
+  maypop? crab apple? black haw? To what class does each belong?
+  (283, 288-292.)
+
+  2. Of what use to the plant is the hard stone of the drupe? (21.)
+
+  3. Is the pulp of fleshy fruits agreeable to the taste before they
+  are ripe? After? What advantage is this to the plant? (21.)
+
+  4. Are the seeds of edible fruits, as a general thing, digestible
+  or agreeable to the palate?
+
+  5. Is this an advantage to man? To the plant? (21, 284, 285.)
+
+  6. What are the most common fleshy fruits in autumn?
+
+  7. With what vegetative parts of the plant does the skin of many
+  fruits present correspondences? Are these such as to indicate
+  homology, or analogy only, between them? (100, 118, 288, 289; Exp.
+  89.)
+
+  8. Name six of the most watery fruits that grow in your
+  neighborhood.
+
+  9. Under what conditions as to soil, heat, moisture, etc., does
+  each thrive best?
+
+  10. Would a gardener act wisely to infer that because a fruit
+  contains a great deal of water it should be planted in a very wet
+  place?
+
+  11. Which contains more water, the fruit or the leaves of the apple?
+
+  12. Why does not the fruit, when separated from the tree, wither as
+  quickly as do the leaves? (Exp. 91.)
+
+
+          III. DRY FRUITS
+
+  MATERIAL.—Some easily attainable specimens of dry fruits are (1)
+  nuts: acorn, hickory nut, walnut, chestnut, pecan, filbert; (2)
+  pods: pea and bean pods, capsules of larkspur, milkweed, jimson
+  weed, cotton; (3) grains: corn, wheat, oats, rice; (4) akene:
+  sunflower, thistle, dandelion, buckwheat, clematis.
+
+=293. Importance of dry fruits.=—Dry fruits are not in general so
+conspicuous or so attractive as fleshy ones, but on account of their
+great number and variety they offer a wide field for study. They are
+also of great interest from an economic point of view: (1) because
+they include the cereal grains that furnish so large a portion of our
+food, and (2) because the greater part of the troublesome weeds that
+infest our crops are scattered by fruits of this class.
+
+=294. Indehiscent fruits.=—These kinds are so simple that it will not
+be necessary to give much time to them. Compare an acorn, a chestnut,
+or a filbert with a ripe bean pod or with a capsule of morning-glory.
+Try to open each with your fingers; which _dehisces_, or opens, the
+more readily? Which is indehiscent, having no regular way of opening?
+How many seeds or kernels do you find in the dehiscent pod? How many
+in the indehiscent one? Would it be of any advantage for a one-seeded
+pod to open? Remove the kernel from the indehiscent fruit; has it any
+covering besides the shell? Which is the pericarp, and which the seed
+coat?
+
+[Illustration: FIGS. 376, 377.—Nut of the pecan tree: 376, exterior;
+377, cross section.]
+
+[Illustration: FIGS. 378, 379.—Nutlike seeds: 378, horse-chestnut;
+379, seed of the fetid sterculia.]
+
+=295. The nut= is easily recognized by its hard, bony covering,
+containing usually, when mature, a single large seed that fills
+the interior. Care should be taken not to confound with true nuts,
+large bony seeds, like those of the buckeye, horse-chestnut, date,
+and the Brazil nut sold in the markets. In the true nut, the hard
+covering is the seed vessel, or pericarp, and not a part of the seed
+itself, though it often adheres to it so closely as to seem so. In
+bony seeds, like those of the horse-chestnut and persimmon, the hard
+covering is the outer seed coat. The distinction is not always easy
+to make out unless the seed can be examined while still attached to
+the placenta of the fruit.
+
+[Illustration: FIGS. 380, 381.—Akenes (magnified): 380, of buckwheat;
+381, of cinque-foil.]
+
+[Illustration: FIGS. 382-384.—Cremocarps, fruits of the parsley
+family.]
+
+=296. The akene=, of which we have examples in the tailed fruit of
+the clematis, the tiny pits on the strawberry, and the so-called
+seeds of the thistle, dandelion, and sunflower, is a small, dry,
+one-seeded, indehiscent fruit, so like a naked seed that it is
+generally taken for one by persons not acquainted with botany. It
+is the commonest of all fruits, and there are so many kinds that
+special names have been applied to some of the most marked varieties.
+The akene of the composite family may generally be known by the
+various appendages in the form of scales, hooks, hairs, or chaff,
+that crown it (Figs. 309-314). The fruits of the parsley family are
+merely a sort of double akene attached by the inner face to a slender
+stalk from which it separates at maturity.
+
+The _samara_, or key fruit, is an akene provided with a wing to
+aid in its dispersion by the wind. The maple, ash, and elm furnish
+familiar examples.
+
+[Illustration: FIGS. 385, 386.—Samaras: 385, ailanthus; 386, maple.]
+
+[Illustration: FIGS. 387, 388.—Grain of wheat with husks on: 387,
+front view; 388, back view.]
+
+=297. The grain=, so familiar to us in all kinds of grasses, is
+economically the most important of all fruits. It is popularly
+classed as a seed, and for practical purposes may be treated as such,
+but it is really a modification of the akene in which the seed coats
+have so completely fused with the pericarp that they can no longer be
+distinguished as separate organs. Peel the husk from a grain of corn
+that has been soaked for twenty-four hours, and you will find the
+contents exposed without any covering; remove the shell of an acorn
+or a hickory nut, and the seed will still be enveloped by its own
+coats. Would it be of any advantage for the seed of an indehiscent
+fruit, like a grain of corn or oats, to have a separate special
+covering of its own?
+
+[Illustration: FIG. 389.—Follicle of milkweed.]
+
+[Illustration: FIG. 390.—Leaflike follicle of Japan varnish tree:
+_S_, outer (dorsal) suture; _S′_, inner (ventral) suture.]
+
+=298. Dehiscent fruits.=—_Pod_, or _capsule_, is the general name
+applied to all dehiscent fruits. The simplest possible kind of pod
+is the _follicle_, composed of a single carpel, like those of the
+larkspur, milkweed, and marsh marigold, and may be regarded as a
+modified leaf. Examine one of these pods and you will find that
+it splits down one side, which corresponds to the edges of the
+leaf brought together and turned inward to form a placenta for the
+attachment of the seed. This line of union is called a “suture,” from
+a Latin word meaning a “seam.”
+
+=299. The legume.=—Get a pod of any kind of bean or pea, and observe
+that it differs from the follicle in having two sutures or lines
+of dehiscence. One of these runs along the back of the carpel and
+corresponds to the midrib of the leaf; the other, corresponding to
+the united edges of the carpellary leaf, always turns inward, toward
+the axis of the flower, and forms the placenta.
+
+[Illustration: FIGS. 391-393.—Legumes: 391, legume of bean: _v_,
+ventral suture; _d_, dorsal suture; 392, constricted legume of senna
+(_Cassia Nelsonia_); 393, legume of a pea, with partially constricted
+pod.]
+
+[Illustration: FIG. 394.—Loment of beggar-ticks.]
+
+The beggar-ticks, so unpleasantly familiar to most of us, are merely
+a kind of legume constricted between the seeds and breaking up into
+separate joints at maturity. What kind of indehiscent fruits do the
+joints become when separated? (296.)
+
+[Illustration: FIG. 395.—Cross section of one-celled syncarpous
+capsule of frostweed, with parietal placentæ. (_After_ GRAY.) FIG.
+396.—Follicles of larkspur borne on the same torus, but distinct.]
+
+=300. Compound or syncarpous pods.=—The carpellary leaves may unite
+either by their open edges, as if a whorl like that represented in
+Fig. 188 were to grow together by the margins (Fig. 395); or each
+may first roll itself into a simple follicle like the larkspur
+and columbine (Fig. 396), and then a number of these may unite by
+their ventral sutures into a single syncarpous capsule, with as
+many locules as there are carpels (Fig. 398). The seed-bearing
+sutures being all brought together in the center, the placenta
+becomes _central_ and _axial_. In the first case (Fig. 395) the open
+carpels form a one-chambered capsule, though the placentas sometimes
+project, as in the cotton, so far as to produce the effect of true
+partitions with a central axial placenta. In capsules with only one
+compartment, the number of carpels can generally be determined by the
+number of sutures or of placentas.
+
+[Illustration: FIG. 397.—Pods of Echeveria, contiguous, but distinct.]
+
+[Illustration: FIG. 398.—Capsule of Colchicum, with carpels united into
+a syncarpous pod.]
+
+[Illustration: FIG. 399.—Capsule of corn cockle, with free central
+placenta.]
+
+
+          Practical Questions
+
+  1. To what class of fruits does each of the following belong—rice;
+  beggar-ticks; poppy; peanut; jimson weed; chinquapin; caraway?
+
+  2. Is the coconut, as usually sold in the market, a fruit or a seed?
+
+  Suggestion: carefully examine the “eyes,” from without and from
+  within; if you can get a specimen with the husk on, it will help to
+  a decision.
+
+  3. Can you name any syncarpous, or compound capsule, that is
+  single-seeded?
+
+  4. Can you name any indehiscent fruit that has normally more than
+  one seed?
+
+  5. Give a reason for the difference. (23.)
+
+  6. Name the weeds of your neighborhood that are most troublesome on
+  account of their adhesive fruits.
+
+  7. Do these fruits belong, as a rule, to the dehiscent or to the
+  indehiscent class?
+
+  8. Give a reason for the difference, if any is noted. (23.)
+
+
+          IV. ACCESSORY, AGGREGATE, AND MULTIPLE FRUITS
+
+  MATERIAL.—For autumn and winter, examples of accessory fruits are:
+  pineapple, common apple, pear, rose hip; aggregate: magnolia,
+  tulip tree, wild cucumber, sweet flag (_Calamus_); multiple: osage
+  orange, sweet gum balls, pine cones, figs, fresh or dried.
+
+  For spring and summer, examples of accessory fruits are: raspberry,
+  strawberry, squash, cucumber; aggregate: strawberry, blackberry,
+  Jack-in-the-pulpit; multiple: fig, mulberry. Most of those named
+  will be found to belong to more than one class; the strawberry, for
+  instance, is both accessory and aggregate; the fig and pineapple,
+  accessory and multiple.
+
+=301.= Besides the varieties already named, all fruits, whether
+fleshy or dry, may be simple, accessory, aggregate, or collective.
+Fruits of the first kind need no explanation; they consist merely
+of a single ripened ovary, whether of one or more carpels, as the
+peach, cherry, bean, and lemon.
+
+[Illustration: FIGS. 400, 401.—Vertical sections showing the relation
+between a strawberry flower and fruit: 400, the flower; 401, the
+fruit developed from it. The corresponding parts are indicated by
+connecting lines; _r_, receptacle; _a_, sepal; _b_, petal; _s_,
+stamens; _c_, carpel (akene in fruit); _p_, style of the pistil;
+_pl_, pulp of the fruit.]
+
+=302. Accessory fruits= are so called because some other part than
+the seed vessel, or ovary proper, is coherent with, or accessory to
+it, in forming the fruit, as in the apple and the hip. The accessory
+part may consist of any organ, but is more frequently the calyx or
+the receptacle. In the strawberry, the little hard bodies, usually
+called seeds, that dot the surface are the true fruits (akenes). A
+vertical section through the center will show the edible part to
+consist wholly of the enlarged receptacle. In the pineapple, the
+edible stalk may be traced through a mass of flowers whose seed
+vessels have become enlarged and ripened into fruits.
+
+=303. Aggregate fruits.=—Some accessory fruits, the strawberry and
+blackberry for example, are, at the same time, aggregate; that is,
+they are composed of a number of separate individual fruits produced
+from a single flower. The cone of the magnolia and of the tulip tree
+are aggregate fruits; can you name any others?
+
+[Illustration: FIGS. 402-404.—Multiple fruit of the pineapple: 402,
+external view of a ripe fruit, showing the prolonged receptacle
+growing into a new plant above, and the scaly bracted covering below;
+403, vertical section through the axis of a fruit, showing _a_, the
+receptacle, with _b_, _b_, the fleshy ovaries cohering around it
+and forming the edible part of fruit; 404, a single “eye” or scale,
+somewhat reduced, showing the scaly bract from the axil of which the
+(generally) abortive flower originates.]
+
+=304. Collective, or multiple, fruits.=—The pineapple is an example
+of both an accessory and a multiple fruit, being composed of the
+ripened ovaries of a number of separate flowers that have become
+more or less coherent. The osage orange, sweet gum balls, fig, and
+mulberry are other examples of this class.
+
+=305. Dissection of a multiple fruit.=—Get one of the dried figs sold
+by the grocers. Look at the small end where the skin originates; of
+what part is it a modification? (289.) Can think of a reason for this
+curious, urnlike enlargement of the receptacle? Is there anything
+about the fig, for instance, that renders it peculiarly liable to be
+preyed upon by birds and insects? Could any but a very small insect
+get through the eye without injuring the fruit? Could it free itself
+from the sticky mass inside and get out again without difficulty?
+Would you judge from this that the caprification of the fig is easily
+effected (279), even when the fig wasp is present? Can you now
+account for the fact that over four hundred varieties of cultivated
+figs ripen their fruit without fertilization?
+
+[Illustration: FIG. 405.—Vertical section of a fig, showing the
+minute flowers inside the closed receptacle.]
+
+Open your specimen and examine the contents; what do you find? From a
+dried specimen it will hardly be practicable to make out clearly that
+the pulp of the fig consists of hundreds of tiny pistillate blossoms
+that line the inner face of the receptacle. The little grains
+usually taken for seeds are really small akenes—the ripened ovaries
+of flowers that have been pollinated from the caprifig (279, 286).
+Crush one gently and examine with a lens, or under a low power of the
+microscope. It is these “botanically” ripe fruits (284) that give to
+the dried figs of commerce their plumpness and their pleasant, nutty
+flavor. Why are our native American figs lacking in these qualities
+(279)? Could this defect be remedied? Do you know of any efforts
+being made in that direction by American cultivators?
+
+[Illustration: FIGS. 406-409.—Non caprificated and caprificated
+figs: 406, outside appearance of non caprificated fig; 407, outside
+appearance of caprificated fig; 408, interior of caprificated fig;
+409, interior of non caprificated fig.]
+
+=306. Fruit clusters.=—Be careful not to confound aggregate and
+collective fruits with mere clusters, like a bunch of grapes or of
+sumac berries. The distinction is not always easy to make out. The
+clump of akenes that make up a dandelion ball, for instance, though
+held on a common receptacle, like the mulberry and other collective
+fruits, have so little connection with each other, and separate
+so completely at maturity, as to partake more of the nature of a
+cluster than of a collective fruit. The same is true of the clump
+of tailed akenes that make up the fruit of the clematis. Though the
+product of a single flower and thus technically an aggregate fruit,
+they are really only a compact head or cluster. Some degree of
+cohesion is necessary to constitute a cluster of matured ovaries into
+an aggregate or a multiple fruit.
+
+=307. The individual fruits= that make up the various kinds just
+described may belong to any of the classes mentioned in the two
+preceding sections: those of the blackberry, for instance, are
+drupes; of the strawberry, akenes; of the sweet gum, capsules.
+
+
+          Practical Questions
+
+  1. To what class of fruits would you refer the following: a banana;
+  a tickseed; a dewberry; a cocklebur; a string bean; a watermelon;
+  a cantaloupe; a pomegranate; a black haw; a dogwood berry; a red
+  pepper?
+
+  2. Tell which of the following are aggregate or multiple fruits,
+  and which are fruit clusters: an ear of corn; of wheat; a
+  buttonwood or a sycamore ball; a hop; a dewberry; a pine cone; a
+  prickly pear. (303, 304, 306.)
+
+  3. Tell the nature of the individual fruits composing the different
+  combinations mentioned in the last question.
+
+  4. Can you suggest any advantage that might accrue to a species
+  from having its fruits clustered or compound? (21, 23, 24, 287.)
+
+
+          Field Work
+
+  1. Study the various edible fruits of your neighborhood with regard
+  to their means of dissemination and protection. Consider the object
+  of the protective adaptations in each case, whether against heat,
+  cold, moisture, animals, etc. Notice the color of the different
+  kinds, and trace its significance; for example, the bright red of
+  the holly, the dull color of muscadine, black haw, and wild smilax.
+  Account for the prevalence of red among autumn fruits. Notice the
+  position of the fruit on the bough and explain its object; as, for
+  instance, the clustering of dogwood at the end of the twig, the
+  pendent position of grapes and honey locusts. Observe the relation
+  between the color and size of fruits and their grouping. What
+  advantage is it for sumac and bird haws to be gathered in large
+  clusters?
+
+  2. Compare wild with cultivated fruits and notice in what respects
+  man has altered the latter for his own benefit. Note, for instance,
+  the difference between cultivated apples and the wild crab, between
+  the cultivated grains and wild grasses. Observe the great number of
+  varieties of each kind in cultivation and try to account for it.
+
+  3. Notice the situations in which different kinds of fruits
+  grow, whether hot, dry, moist, windy, or sheltered, and how they
+  are affected by their surroundings. For example, account for
+  the difference between blackberries growing on a dry hillside,
+  and those in moist land along the borders of a stream. Give the
+  conclusions drawn from your observations in each case.
+
+  4. Notice what animals feed upon the different kinds, and whether
+  their visits are harmful or beneficial. Consider in what respects
+  the interests of the plant itself, the interests of man, and the
+  interests of other animals may clash or coincide. Examine the
+  vegetation along the hedgerows and borders of fields and old
+  fences. Notice the kind of plants that compose it—sumac, sassafras,
+  cedars, cat brier, etc. The list will be slightly different
+  for different localities, but this will not alter the general
+  conclusion. What kinds of fruits and seeds do these shrubs produce?
+  What kinds of living creatures frequent hedgerows and feed upon the
+  seeds of such plants? Do you see any relation between these facts
+  and one of the modes of seed dispersal?
+
+  5. Classify all the fruits you have collected during your
+  walk, under their proper heads, as fleshy or dry, dehiscent or
+  indehiscent, simple, accessory, aggregate, collective. Be careful
+  to distinguish between compact clusters, like the heads of clematis
+  or buttonwood, and truly compound fruits.
+
+
+
+
+CHAPTER IX. THE RESPONSE OF THE PLANT TO ITS SURROUNDINGS
+
+
+          I. ECOLOGICAL FACTORS
+
+  MATERIAL.—A number of small flowerpots filled with soils of as many
+  different kinds as can be found in the neighborhood.
+
+=308. Definition.=—By _ecology_ is meant the relation of plants to
+their surroundings, which may be considered under three general
+heads: their relations to inanimate nature, to other plants, and
+to animals. The subject has been touched upon repeatedly in the
+foregoing pages, and, in fact, it is impossible to treat of any
+branch of botany without some reference to it. All that was said
+about the adjustment of leaves for light and moisture, and their
+adaptations for protection and food storage, about the devices for
+pollination, and for fruit and seed dispersal, really belong to
+ecology.
+
+=309. Symbiosis.=—The relations of plants to animate nature are
+_biological factors_, and may act in two ways: (1) through the
+destruction of vegetation by hungry animals and by parasitic and
+disease-producing organisms; and (2) by associations for mutual
+benefit, such as are described in section viii of chapter VII.
+Associations of this kind are included under the general term
+_symbiosis_, a word which means “living together.” In its broadest
+sense symbiosis refers to any sort of dependence or intimate organic
+relation between different kinds of individuals, and so may include
+the climbing and parasitic habits; but it is usually restricted to
+cases where the relation is one of mutual benefit. It may exist
+either between plants of one kind with those of another, between
+animals with animals, or between plants and animals, as in the case
+of the clover and bumblebee, and the yucca and pronuba.
+
+[Illustration: PLATE 13.—Showing the quick response of vegetation to
+surroundings. The upper cut shows the appearance of an irrigation
+canal in the arid plains region, when first completed; the lower cut,
+ten years after completion.]
+
+The occurrence of root tubercles on certain of the leguminosæ (63) is
+a clear case of symbiosis, the microscopic organisms in the tubercles
+getting their food from the plant and at the same time enabling it to
+get food for itself from the air in a way that it could not otherwise
+do.
+
+=310. Relations with inanimate nature.=—But it is to the relations of
+plants with inanimate nature, and their grouping into societies under
+the influence of such conditions, that the term “ecology” is more
+strictly applied. The external conditions that lead to the grouping
+are called _ecological factors_. The most important of these are
+temperature, moisture, soil, light, and air, including the direction
+and character of the prevailing winds. Each of these factors is
+complicated with the others and with conditions of its own in a way
+that often makes it difficult to determine just what effect any one
+of them may have in the formation of a given plant society.
+
+=311. Temperature= may be even and steady, like that of most oceanic
+regions, or it may be subject to sudden caprices and variations,
+like the “heated terms” and “cold snaps” that afflict our Eastern
+coast region every few years. It is not the average temperature of
+a climate, but its extremes, especially of cold, that limit the
+character of vegetation.
+
+Temperature probably has more influence than any other factor upon
+the distribution of plants over the globe; but it can have little
+or no effect in evolving local differences in vegetation, because
+the temperature of any given locality, except on the sides of high
+mountains, will ordinarily be the same within a circuit of many miles.
+
+=312. Moisture=, again, may be of all degrees, from the
+superabundance of lakes and rivers and standing swamps, to the arid
+dryness of the desert, and the water may be still and sluggish,
+or in rapid motion. It may exist more or less permanently in the
+atmosphere, as in moist climates like those of England and Ireland,
+where vegetation is characterized by great verdure; or it may come
+irregularly in the form of sudden floods, or at fixed intervals,
+causing an alternation of wet and dry seasons. Moreover, the moisture
+of the soil or the atmosphere may be impregnated with minerals or
+gases, which may affect the vegetation independently of the actual
+amount of water absorbed.
+
+[Illustration: FIG. 410.—The effect of cold—a Mt. Katahdin bog.
+(_From_ Mo. Botanical Garden Rep’t.)]
+
+Snow is a form of water which may act in two entirely opposite ways:
+(1) by keeping the atmospheric precipitation locked up in a solid
+state and thus bringing about a condition analogous to drought—for
+example, in arctic deserts and Alpine snow fields; (2) by causing
+annual floods and overflows when it melts in the spring, as in the
+Nile and Mississippi valleys.
+
+In cold temperate regions it also influences vegetation to a
+considerable extent by covering the warm earth like a blanket during
+winter, and thus protecting tender seeds and shoots that otherwise
+would not be able to survive.
+
+[Illustration: FIG. 411.—Dogwood, a tree tolerant of shade, growing
+and blooming in a deeply wooded glen.]
+
+=313. Light= may be of all degrees of intensity, from the blazing
+sun of the treeless plain to the darkness of caves and cellars where
+no green thing can exist. Between these extremes are numberless
+intermediate stages: the dark ravines on the northern side of
+mountains, the dense shade of beech and hemlock forests, and the
+light, lacy shadows of the pines,—each characterized by its peculiar
+form of vegetation. Absence of light, too, is usually accompanied by
+a lowering of temperature and a reduction of transpiration, factors
+which tend to accentuate the difference between sun plants and shade
+plants, giving to the latter some of the characteristics of aquatic
+vegetation. Generally, the tissues of these are thin and delicate,
+and having no need to guard against excessive transpiration, they
+wither rapidly when cut or exposed to too great intensity of heat and
+light.
+
+[Illustration: FIG. 412.—A red cedar grown in a barren, wind-beaten
+situation.]
+
+[Illustration: FIG. 413.—A red cedar grown under normal conditions.]
+
+=314. Winds= affect vegetation, not only as to the manner of
+seed distribution and the conveyance of pollen, but directly by
+increasing transpiration, and necessitating the development of strong
+holdfasts in plants growing upon mountain sides and in other exposed
+situations. The nature of the region from which they blow—whether
+moist, dry, hot, cold, etc.—is also an important factor. In a
+district open to sea breezes, live oaks, which require a salt
+atmosphere, may sometimes be found as far as a hundred miles from the
+coast.
+
+=315. Soil.=—While water is the most important, soil is perhaps the
+most interesting of these factors to the farmer, because it is the
+one that he has it most largely in his power to modify. It is to be
+viewed under two aspects: first, as to its mechanical properties,
+whether soft, hard, compact, porous, light, heavy, etc.; secondly, as
+to its chemical composition and the amount of plant food-materials
+contained in it. The first can be regulated by tillage and drainage,
+the second by a proper use of fertilizers.
+
+  EXPERIMENT 92. TO SHOW THE INFLUENCE OF SOIL AS AN ECOLOGICAL
+  FACTOR.—Fill a number of small earthen pots with all the different
+  kinds of soil that are to be found in your neighborhood. Keep well
+  moistened and make a list of the plants that appear spontaneously
+  in each. Is there any difference in the kinds produced by different
+  soils? In vigor or abundance of the same or different kinds? Do
+  more seedlings appear in any of the pots than could live if left
+  alone? What becomes of a majority of the seedlings that come up in
+  a state of nature?
+
+  After a time, stop watering until all the plants are dead and new
+  ones cease to appear. Notice the rate at which vegetation dies out
+  in each and the kind of plants that can live longest without water.
+  Which of the different soils is capable of sustaining vegetation
+  longest without a fresh supply of moisture? To what quality of the
+  soil is this due? (Exp. 53.)
+
+
+          Practical Questions
+
+  1. Is the relation between man and the plants cultivated by him a
+  symbiosis? (309.)
+
+  2. Why is it that plants of the same, or closely related species
+  are found in such different localities as the shores of Lake
+  Superior, the top of Mt. Washington, and the Black Mountains in
+  North Carolina? (311, 330.)
+
+  3. Which of the five ecological factors mentioned in paragraphs
+  311-315 has probably most largely influenced their distribution?
+
+  4. What is the prevailing character of the soil in your
+  neighborhood?
+
+  5. Is your climate moist or dry? Warm or cold?
+
+  6. Can you trace any connection between these factors and the
+  prevailing types of vegetation?
+
+
+          II. PLANT ASSOCIATIONS
+
+  MATERIAL.—The subject is not well suited to laboratory work,
+  though, if time permits, it is recommended that a detailed study
+  be made of at least one typical hydrophyte, halophyte, and
+  xerophyte plant. Some good examples are: (1) Hydrophyte: pond
+  weed, waterlily, pipewort (_Eriocaulon_), bladderwort, arrowhead
+  (_Sagittaria_); (2) Halophyte: sea lavender, sea rocket, sea
+  lettuce, water hyacinth; (3) Xerophyte: cactus, century plant,
+  pineapple, stonecrop, purslane, lichen.
+
+=316. Modes of grouping.=—Plants group themselves in their favorite
+habitats, not according to their botanical relationships, but with
+regard to the predominance of one or more of the ecological factors
+that influence their growth. Sometimes one or two species will
+take practical possession of large areas, like the coarse grasses
+that spread over certain salt marshes, or the pines that formerly
+constituted the sole forest growth over extensive regions in North
+Carolina and Maine. Exclusive growths of this kind over limited
+areas are sometimes called plant _colonies_, and the individuals
+composing them belong, as a general thing, to the hardy, pushing sort
+known as “pioneers,” which are among the first to take possession
+of new soil and force their way into unoccupied territory. But more
+usually we find a great diversity of forms brought together by their
+common requirements as to shade, soil, moisture, and other external
+conditions.
+
+Any well-defined assemblage of plants, whether of one kind or many,
+originating in such a common response to the same influences, is
+called a _formation_. These associations are variously classed,
+according to the nature of their habitat, as salt water, fresh water,
+sand hill, swamp, bog, river bottom, or such other kinds as their
+ecological character may indicate. Local conditions in limited
+areas may lead to the segregation of smaller and more compact groups
+called _societies_. This term, however, is used rather loosely, being
+treated in some works as synonymous with formations, in others as
+analogous with what have here been defined as colonies.
+
+[Illustration: FIG. 414.—A colony of Alabama primroses (_Œnothera
+speciosa_).]
+
+=317. Principles of subdivision.=—The mixed associations described in
+the last paragraph are quite independent of botanical relationships,
+and any of the factors named in 310, or others of a different kind,
+could be made the basis of their classification. They might be
+grouped, for instance, according to their economic uses, or according
+to origin, whether native or introduced, as best suited the purpose
+of the classification in each case. The moisture factor, however, has
+been generally agreed upon as the one most convenient for ordinary
+purposes. Upon this principle plants are divided into three great
+groups:—
+
+=Hydrophytes=, or water plants, those that require abundant moisture.
+
+=Xerophytes=, or drought plants, those that have adapted themselves
+to desert or arid conditions.
+
+[Illustration: FIG. 415.—A water plant (_Limnophila_), with water
+leaves and air leaves and transitional forms.]
+
+=Mesophytes=, plants that live in conditions intermediate between
+excessive drought and excessive moisture. To this class belong
+most of our ordinary cultivated plants and the greater part of the
+vegetation of the globe.
+
+=Halophytes=, “salt plants,” is a term used to designate a fourth
+class, based not directly upon the water factor, but upon the
+presence of a particular mineral in the water or the soil which
+they can tolerate. They seem to bear a sort of double relation to
+hydrophytes on the one hand and to zerophytes on the other.
+
+=318. Hydrophyte societies.=—These embrace a number of forms, from
+those inhabiting swamps and wet moors, to the submerged vegetation of
+lakes and rivers. An examination of almost any kind of water plant
+will show some of the physiological effects of unlimited moisture.
+Take a piece of pondweed, or other immersed plant, out of the water
+and notice how completely it collapses. This is because, being buoyed
+up by the water, it has no need to spend its energies in developing
+woody tissue. Floating and swimming plants will generally be found
+to have no root system or very small ones, because they absorb their
+nourishment through all parts of the epidermis directly from the
+medium in which they live. That they may absorb readily, the tissues
+are apt to be soft and succulent and the walls of the cells composing
+them very thin. In some of the pipeworts (_Eriocaulon_), the ells
+are so large as to be easily seen with the unaided eye. If you can
+obtain one of these, examine it with a lens and notice how very thin
+the walls are. Water plants also contain numerous air cavities, and
+often develop bladders and floats, as in the common bladderwort and
+many seaweeds. The leaves of submerged plants are usually either
+greatly reduced in size or very much cut and divided, while the ones
+that rise above water, like those of the water lily, are apt to be
+large and entire, to facilitate floating, and have stomata on their
+upper surface. Floating plants sometimes form such large colonies as
+to be a serious menace to navigation. Well-known instances of this
+are the water hyacinths in the St. John’s River, Florida, and the
+vast formations of swimming gulfweed from which the Sargasso Sea
+takes its name.
+
+[Illustration: FIG. 416.—Seaweed (_sargassum_) with bladderlike
+floats.]
+
+[Illustration: FIG. 417.—A pioneer swamp colony of cattails. (_From_
+a photograph by Harry B. Shaw, U.S. Dept. Agr.)]
+
+=319. Swamp societies.=—These include what may be regarded as the
+amphibious portion of the hydrophyte group. They compose the sedge
+and cattail bogs, reed jungles, moss and fern thickets, forests of
+cypress, magnolia, black gum, pine, tamarack, balsam, and the like.
+The sedges and cattails are the pioneers of these societies, which
+tend constantly to encroach upon the water and so prepare the way
+for the advance of other colonists. Drawing their nourishment from
+the loose soil in which they are anchored, and lacking the support
+of a liquid medium, they develop roots and vascular stems. The roots
+of plants growing in swamps have difficulty in obtaining proper
+aëration on account of the water, which shuts off the air from them;
+hence they are furnished with large air cavities, and the bases
+of the stems are often greatly enlarged, as in the Ogeechee lime
+(_Nyssa capitata_) and cypress, to give room for the formation of air
+passages. The peculiar hollow projections known as “cypress knees”
+are arrangements for aërating the roots of these trees.
+
+[Illustration: FIG. 418.—A Southern cypress swamp, showing on the
+left the peculiar enlargements for aëration, known as “cypress
+knees.” (_From_ Mo. Botanical Garden Rep’t.)]
+
+=320. Xerophyte societies= are adapted to conditions the reverse of
+those affected by hydrophytes. The extreme of these conditions is
+presented by regions of perennial drought, like our Western arid
+plains and the great deserts of the interior of Asia and Africa.
+Under these conditions plants have two problems to solve,—to collect
+all the moisture they can and to keep it as long as they can. Hence,
+plants of such regions have a diminished evaporating surface, owing
+to the absence of foliage and the compacting of their tissues into
+the stem, after the manner of the cactus and prickly euphorbia; or
+their leaves may become thick and fleshy so as to resist evaporation
+and retain large amounts of moisture, as in the case of the yucca and
+century plant. They also frequently develop a thick, hard epidermis,
+or cover themselves with protective hairs and scales.
+
+The principal types of xerophyte plants are: (1) the lichens, mosses,
+and saxifrages found on bald rocks and mountain cliffs; (2) sand
+plants, such as cockspur grass, sand spurry, wiregrass, and the
+like, inhabiting sea beaches and pine barrens; (3) the sage brush,
+greasewood, and switch plants of our Western alkali plains; (4) the
+cactus and yuccas of southern California, Arizona, and Mexico; (5)
+the acacias, agaves, and hardy “chapparal” thickets of southern
+Texas and Mexico. The first class are of importance as the pioneers
+and pathfinders of the xerophyte community. In tropical and polar
+deserts alike they are the first settlers, and by aiding in the
+disintegration of rocks and their gradual conversion into soil, they
+pave the way for the coming of the higher plants, and it may be of
+man himself.
+
+[Illustration: PLATE 14.—A xerophyte formation of yuccas, cacti,
+and switch plants, near Zacatecas, Mexico. (_From_ a photograph by
+Professor F. E. Lloyd.)]
+
+=321. Partial xerophytes.=—Plants exposed to periodic and occasional
+droughts frequently provide against hard times by laying up stores
+of nourishment in bulbs and rootstocks and retiring underground
+until the stress is over. This is known as the _geophilous_, or
+earth-loving, habit. Others, as some of the lichens, and the little
+resurrection fern (_Polypodium incanum_, Figs. 419, 420), so common
+on the trunks of oaks and elms in the Southern States, make no
+resistance, but wither away completely during dry weather, only to
+waken again to vigorous life with the first shower.
+
+[Illustration: FIGS. 419, 420.—A resurrection fern: 419, in dry
+weather; 420, after a shower.]
+
+=322. Physiological xerophytes.=—Plants growing in thin or poor
+soil, such as that on denuded hillsides, fresh railroad cuts, and
+newly graded streets, are apt to take on a more or less xerophytic
+character, even though there may be no lack of moisture. Such soils
+are called “new” because the mineral elements in them have not
+been exposed long enough to have become decomposed and mixed with
+humus, and the vegetation that first populates them has to do the
+pioneer work of disintegrating and impregnating the substratum with
+humus. For similar reasons the vegetation of sandy bogs and sea
+beaches, owing to the poverty of the soil in nitrogenous matter,
+usually develops xerophyte adaptations, even though there may be a
+superabundance of moisture. Plants growing on high mountain tops and
+in cold arctic bogs take on the same characteristics (Fig. 410).
+Such situations are said to be “physiologically dry,” because the
+moisture they have is not in a condition to be readily absorbed. The
+vegetation of arctic regions suffers more from physiological drought
+than from cold.
+
+[Illustration: FIG. 421.—A halophyte swamp of mangroves. Notice the
+tangle of adventitious prop roots assisting in the work of absorption
+from the brackish marsh soil. (_From_ Mo. Botanical Garden Rep’t.)]
+
+=323. Halophytes= include plants growing by the seashore and
+the vegetation around salt springs and lakes and that of alkali
+deserts. Seaweeds are in a sense halophytes, since they live in salt
+water, but as they are true aquatic plants and exhibit many of the
+peculiarities of hydrophytes in their mechanical structure, they are
+classed with them. The name _halophyte_ applies more particularly to
+land plants that have adapted themselves to the presence in the soil
+or in the atmospheric vapor, of certain minerals, popularly known as
+salts, which cause them to take on many xerophyte characteristics.
+The reason for this, as was shown in Exp. 39, is because the mixture
+of salt in the water of the soil increases its density so that it
+is difficult for the plant to absorb as much as it needs, and thus
+halophytes are living under “physiologically” xerophyte conditions.
+If you have ever spent any time at the seashore, you cannot fail
+to have observed the thick and fleshy habit exhibited by many
+of the plants growing there, such as the samphire, sea purslane
+(_Sesuvium_), and sea rocket (_Cakile_). A form of goldenrod found by
+the seashore has thick, fleshy leaves, and is as hard to dry as some
+of the fleshy xerophytes.
+
+Another characteristic of desert plants that is common also to
+seaside vegetation is the frequent occurrence of a thick, hard
+epidermis, as in the sea lavender and saw grass. The live oaks, trees
+that love the salt air and never flourish well beyond reach of the
+sea breezes, have small, thick, hard leaves, very like those of the
+stunted oaks that grow on the dry hills of California. The presence
+of spines and hairs, it will be observed, is also very common;
+_e.g._ the salsola, the sea oxeye, and the low primrose (_Œnothera
+humifusa_). In other cases the leaf blades are so strongly involute
+or revolute (202) as to make them appear cylindrical. All these, it
+will be observed, are xerophyte adaptations, and the object in both
+cases is the same—the conservation of moisture.
+
+=324. Mesophytes.=—These embrace the great body of plants growing
+under the ordinary conditions of temperate regions, which may vary
+from the liberal water supply of low meadows and shady forests to
+the almost desert barrenness of dusty lanes and gullied, treeless
+hillsides. The forms and conditions they present are so varied that
+it would be impracticable to consider them all in a work like this,
+but they may be summed up under the two general heads of (1) _open
+ground_ and (2) _woodland_. Under the first are included: (_a_) all
+cultivated grounds—fields, meadows, lawns, pastures, and roadsides,
+with their characteristic shrubs, flowers, and grasses; (_b_) heaths
+and plains of northern or alpine regions, with their low, stunted
+perennials and bright, but fugacious, flowers. Under the second are
+classed all woods, thickets, and copses, with the shrubs and herbs
+that form their undergrowth. These may be grouped in three main
+divisions: (_c_) mixed forests of maple, ash, oak, hickory, birch,
+sweet gum, etc.; (_d_) pure forests of pine, balsam, fir, cypress,
+and the like; and finally (_e_), the perennial splendors of the
+tropical forest, where the vegetation of the globe reaches its climax
+in luxuriance and variety of growth.
+
+
+          Practical Questions
+
+  1. Why do florists cultivate cactus plants in poor soil? (320.)
+
+  2. What would be the effect on such a plant of copious watering and
+  fertilizing?
+
+  3. Why must an asparagus bed be sprinkled occasionally with salt?
+  (323.)
+
+  4. If a gardener wished to develop or increase a fleshy habit in a
+  plant, to what conditions of soil and moisture would he subject it?
+  (320, 323.)
+
+  5. What difference do you notice between blackberries and
+  dewberries grown by the water and on a dry hillside?
+
+  6. Are there corresponding differences in the root, stem, and
+  leaves of plants growing in the two situations, and if so account
+  for them?
+
+  7. When a tract of dry land is permanently overflowed by the
+  building of a dam or levee, why does all the original vegetation
+  die, or take on a sickly appearance? (319.)
+
+  8. Should plants with densely hairy leaves be given much water, as
+  a general thing? (202, 320.)
+
+  9. A farmer planted a grove of pecan trees on a high, dry hilltop;
+  had he paid much attention to ecology? Give a reason for your
+  answer.
+
+  10. Why do the branches of trees often die, or fail to develop, on
+  the windward side? (314.)
+
+  11. Why do trees grown in dry soil have harder wood than the same
+  kind grown in wet soil? (123, 318.)
+
+
+          III. ZONES OF VEGETATION
+
+[Illustration: FIG. 422.—A pioneer colony of sumac growing on a
+railroad cutting. (_From_ a photograph by J. M. Coulter.)]
+
+=325. The origin of vegetable zones.=—The terms “zone” and “zonation”
+are used to express a general tendency of plant societies and
+formations to distribute themselves in more or less regular belts
+or strata, relatively to the varying intensity of the prevalent
+ecological factor of their habitat. In almost every locality there
+exists some special feature—a pond, a brook, a small ravine, an
+isolated hilltop, a deserted quarry, a gravel pit, or a railroad
+cut,—sufficiently distinct from the general surroundings to exercise
+a perceptible control over the vegetation in its immediate vicinity,
+and thus to become the starting point of a series of plant zones
+that mark the decreasing influence of the factor concerned, by
+their change of character as they recede from its point of greatest
+intensity. Starting from a barren, exposed hilltop, for example,
+with a covering of dry broom sedge (_Andropogon_) and fleabane, we
+encounter next an almost desert zone of washed and gullied slopes
+in whose hard, sunbaked soil nothing but a few scrub pines and
+brambles can gain a foothold. This will, perhaps, be succeeded, by a
+straggling belt of sassafras, sumac, and buckthorn, mixed with cat
+brier and blackberry canes, beyond which, at the foot of the hill,
+begins a stretch of meadow, or a bit of woodland crossed by a brook,
+or hollowed into a boggy depression. From this new factor originates
+a second series of zonations, passing through all the stages of bog,
+swamp, shade, and sun plants, back to the prevailing type of the
+region. Moisture is really the controlling factor in both cases, its
+influence in the first being negative,—that is, inversely,—and in the
+other, positive, or directly proportioned to the quantity present.
+
+=326. Direction of zonation.=—When the direction in which the
+controlling factor changes is horizontal, as with soil and water,
+the zonation will be _horizontal_; when, as in the case of light,
+it is vertical, the zonation or stratification will be _vertical_.
+Examples of this can be observed in the growth of almost any forest
+area, the natural order of succession being: (1) a ground layer of
+mosses and fungi; (2) low, creeping vines,—partridge berry, trailing
+arbutus, twinflower (_Linnæa_); (3) small ferns and low flowering
+herbs—pyrola, clintonia, trillium; (4) a zone of tall herbs and low
+bushes—royal fern, cohosh (_Actæa_), blueberries; (5) tall herbs and
+shrubs, small trees, and climbing vines—kalmia, dogwood, farkleberry,
+smilax, Virginia creeper; (6) tall treetops towering up into full
+sunlight.
+
+When the physical cause of intensity is a central area, such as a
+pond or a hilltop, the zonation will be _concentric_; that is, the
+different belts will succeed each other in widening circles more
+or less complete. Where the controlling cause extends in a line,
+as a river, or a chain of mountains, the zones run in parallel
+belts on each side of it, and the zonation is _bilateral_. In any
+case, however, it is seldom regular, being frequently broken and
+interrupted through the intervention of other factors. Nor must
+precisely the same kind of plants be always looked for in similar
+situations, though their place is usually occupied by kindred species
+and genera. The common pitch pine, for instance, of the Northern sand
+barrens is represented in sandy districts farther south by the tall,
+long-leaved pine, a kindred species.
+
+=327. Succession.=—Zonation is a regular succession of different
+kinds of plants in space; there is also an analogous succession in
+time, as, when the vegetation of a locality is killed off by fire or
+other cause, plants of an entirely different character will nearly
+always spring up to occupy its place. A forest of pine, for instance,
+is rarely followed by conifers, but by a growth of hardwood trees,
+and _vice versa_—nature thus giving an impressive example as to the
+effectiveness of a rotation of crops.
+
+[Illustration: FIG. 423.—A thicket of pines that has succeeded a
+mixed growth of hard wood trees.]
+
+Succession may be influenced by a variety of causes. Two of the most
+efficient are: (1) the exhaustion of the soil by the long-continued
+growth of one formation (60), thus causing a deficiency of mineral
+material suited for the support of plants of that kind; (2) the
+migration of new species into the denuded territory where those which
+have different requirements as to mineral nutrients from the former
+inhabitants will, other things being equal, have the best chance to
+succeed.
+
+[Illustration: FIG. 424.—A successful invasion—Japanese honeysuckle
+covering the banks of a ravine and climbing over shrubs and tree
+tops.]
+
+=328. Invasion.=—A rapid and widespread occupation of any territory
+by a new species is called an _invasion_. Notable examples of
+invaders are those of the Russian thistle in the northwestern states
+of the Union, and the “bitterweed” (_Helenium tenuifolium_) that
+has almost driven out the hardy dog fennel (_Anthemis cotula_)
+which formerly held undisputed possession of arid places throughout
+the South Atlantic states. A still more remarkable instance is
+the invasion of the Japanese honeysuckle (_Lonicera Japonica_),
+originally introduced for ornament, but which has naturalized itself
+within the last thirty years and overrun waste places everywhere,
+from the Gulf to the Potomac, with a vigor and luxuriance equaled by
+few of our native species. As its beauty and fragrance are even more
+conspicuous in a state of nature than under cultivation, and as it
+can, moreover, be made very useful in stopping gullies and washes,
+its phenomenally rapid occupation of so large a territory has caused
+no alarm and consequently attracted little attention.
+
+=329. Climatic zones.=—These are more general groupings than those
+we have been considering. They follow in a rough way the parallels
+of latitude, and are classed accordingly as: (1) tropical; (2)
+subtropical; (3) temperate; (4) boreal or (on mountains) subalpine;
+(5) arctic or (on high mountains) alpine. Taking the cultivated
+plants of our own country by way of illustration, we have the
+subtropical zone, embracing Florida and the southern portion of the
+Gulf states, where sugar cane, rice, and tropical fruits are the
+staple crops. Then comes the temperate zone, with three agricultural
+subdivisions: (_a_) the great cotton belt, with Indian corn, sweet
+potatoes, and the peach, melon, and fig as secondary products.
+Farther north, in the Central and Middle Atlantic states, we find
+(_b_) the region of maize, hemp, and tobacco, with grapes, apples,
+pears, cherries, and a great variety of garden vegetables as side
+crops. Finally comes (_c_) the great wheat-growing region of the
+North, with buckwheat, hay, and Irish potatoes as subsidiary crops.
+
+Technically, the distribution of the natural zones of vegetation from
+south to north is classed under the three general heads of Forest,
+Grass Land, and Arctic Desert, with numerous subdivisions in each.
+
+=330. Boundaries of the zones.=—While the broad continental zones
+of vegetation follow, in a general way, the climatic zones outlined
+above, they are not sharply defined, but run into each other and
+overlap in various degrees, so that a map depicting the range of
+vegetation in any wide area would show a marked deviation from those
+of latitude. Various other geographical factors, such as mountain
+ranges and bodies of water, influence the direction and character of
+the prevailing winds and rains, and through them the moisture and
+temperature, to so great an extent that they become the controlling
+factors over wide areas. In countries bordering on the sea, the coast
+line always marks a belt of its own, and on the sides of a mountain
+range, all the climatic zones from the equator to the pole may be
+repeated during an ascent of a few miles.
+
+In our own country, where the mountain chains and coast lines run
+approximately north and south, the great continental zones have been
+superseded, for all practical purposes, by four regional divisions
+running almost at right angles to them. These are, disregarding minor
+subdivisions:—
+
+(1) The Forest region, occupying the eastern and south central
+portion of the Union. In classifying this territory as forest, it is
+not meant to imply that it is now, or ever was, one unbroken jungle,
+like parts of central Africa, but that it combines the conditions
+most favorable to a vigorous and varied forest growth.
+
+(2) The Plains region, extending from the very irregular western
+boundary of the forest region to the Rocky Mountains.
+
+(3) The Rocky Mountain region, including the Rockies and the Sierra
+Nevadas with the desert area between them.
+
+(4) The Pacific Slope, a narrow strip between the Sierras and the
+Pacific Ocean.
+
+[Illustration: PLATE 15.—This giant tulip tree is a relic of the
+primitive forest. It is twenty-seven feet in circumference, at a
+distance of four feet from the ground. Notice the sharp elbows of
+the large boughs, a mode of branching characteristic of this kind of
+tree.]
+
+The boundaries of these regions, like those of the great continental
+zones, overlap in various ways, the plants of one region often
+appearing in another, like an arm of the sea projecting into the
+land. But the district where any class of plants reaches its highest
+development is its proper habitat, and as a general thing the one
+where its cultivation pays best. It would be a waste of time and
+money to try to raise cotton in Maine, or cranberries in Georgia.
+
+
+          Practical Questions
+
+  1. Does the native wild growth of a region furnish any indication
+  of the kind of crops which could be successfully grown there? (325,
+  326.)
+
+  2. Can you give a reason why the zones of cultivation may, in some
+  cases, be more extensive than the natural range of wild plants in
+  the same region? (262, 265.)
+
+  3. Can you give reasons why the reverse may sometimes be true?
+  (261, 284.)
+
+  4. What crops are raised in different parts of your own state?
+
+  5. Name some of the native plants characteristic of different parts
+  of your state. What are its principal plant formations?
+
+
+          Field Work
+
+  1. Ecology offers the most attractive subject for field work of all
+  the departments of botany. It can be studied anywhere that a blade
+  of vegetation is to be found. In riding along the railroad, there
+  is an endless fascination in watching the different plant societies
+  succeed one another and noting the variations they undergo with
+  every change of soil or climate.
+
+  2. Students in cities can find interesting subjects for study in
+  the vegetation that springs up on vacant lots, around doorsteps
+  and area railings, and even between the paving stones of the more
+  retired streets. On a vacant lot near the public library in Boston,
+  over thirty different kinds of weeds and herbs were found, and in
+  the heart of Washington, D.C., on a vacant space of about twelve by
+  twenty feet, nineteen different species were counted. Just where
+  such things come from, how they get into such positions, and why
+  they stay there, will be interesting questions for city students to
+  solve.
+
+  3. But the country always has been and always will be the happy
+  hunting ground of the botanist. All the factors considered in the
+  two preceding sections can hardly be found in any one locality, but
+  by selecting areas traversed by brooks, or by gullies and ravines,
+  very marked changes in the character of vegetation may often be
+  observed. Barren, sandy, or rocky soils, the sunbaked clay of naked
+  hillsides, and the borders of treeless, dusty roads will offer
+  close approximations to xerophyte conditions.
+
+  4. If there are any bodies of water in your neighborhood, examine
+  their vegetation and see of what it consists. Notice the difference
+  in the shape and size of floating and immersed leaves and account
+  for it. Note the general absence of free-swimming plants in
+  running water, and account for it. Note the difference between
+  the swamp and border plants and those growing in the water, and
+  what trees or shrubs grow in or near it. Compare the vegetation of
+  different bogs and pools in your neighborhood, and account for any
+  differences you may observe. Compare the water plants with those
+  growing in the dryest and barrenest places in your vicinity, note
+  their differences of structure, and try to find out what special
+  adaptations have taken place in each case. Make a list of those in
+  each location examined that you would class as pioneers.
+
+  5. Draw a map of the vegetation of some locality in your
+  neighborhood that presents a variety of conditions, such as a
+  steep hillside, a field or meadow traversed by a brook, the slopes
+  and borders of a ravine, or the change from cultivated ground to
+  uncultivated moor or woodland. Represent the different zones and
+  formations by different colored inks or crayons, or by different
+  degrees of shading with the pencil.
+
+  6. Draw a map of your state showing the different agricultural
+  regions, as indicated by the character of the cultivated plants in
+  each; use different colors, or light and dark shading, to define
+  the boundaries. Notice any irregularities of outline and account
+  for them—whether due to soil, moisture, geological formation,
+  winds, or temperature. What is the controlling factor of each
+  region?
+
+
+
+
+CHAPTER X. CRYPTOGAMS
+
+
+          I. THEIR PLACE IN NATURE
+
+=331. Order of development.=—All the forms that have hitherto claimed
+our attention belong to the great division of Spermatophytes, or
+seed-bearing plants, designated also as _Phanerogams_, or flowering
+plants. They comprise the higher forms of vegetable life, and because
+they are more conspicuous and better known than the other groups,
+they have been taken up first, since it is more convenient, for
+ordinary purposes, to work our way backward from the familiar to the
+less known, rather than in the reverse order.
+
+But it must be understood that this is not the order of nature. The
+geological record shows that the simplest forms of life were the
+first to appear, and from these all the higher forms were gradually
+evolved. There is no sharp line of division between any of the orders
+and groups of plants, but the line of development can be traced
+through a succession of almost imperceptible changes from the lowest
+forms to the highest, and it is only by a study of the former that
+botanists have come to understand the true nature and structure of
+the latter.
+
+=332. Basis of distinction.=—_Cryptogams_, or seedless plants as
+a whole, are distinguished from the phanerogams by their simpler
+structure and by their mode of propagation, which in the former
+is by means of spores, while in the phanerogams it is by seeds. A
+spore is a simple organic body, consisting usually of a single cell
+which separates from the parent plant at maturity and gives rise to
+a new individual. A seed is a complicated, many-celled structure,
+containing within itself the rudimentary structure of a new plant
+already organized.
+
+Beginning with the simplest forms, cryptogams are grouped in three
+great orders:—
+
+=333. I. Thallophytes=, or thallus plants.—This group takes its name
+from the _thallus_ structure that characterizes its vegetation. In
+its typical form, a thallus is a more or less flat, expanded body, of
+which the lichens and liverworts offer familiar examples among land
+plants, and the kelps and laminarias among seaweeds. It may be of any
+size and shape, however, and sometimes consists of a mere filament,
+as in the common brook silk, or even of a single cell (Fig. 429).
+The term is applied in general to the simplest kinds of vegetable
+structure, in which there is no differentiation of tissues, and no
+true distinction of root, stem, and leaves. While it is not peculiar
+to the thallophytes, it has attained its most typical development
+among them, and the name is therefore retained as distinctive of
+that group. It embraces two great divisions, the Algæ and Fungi. The
+first includes seaweeds and the common freshwater brook silks and
+pond scums, besides numerous microscopic forms whose presence escapes
+the eye altogether, or is made known only by the discolorations and
+other changes caused by them in the water. To the fungi belong the
+mushrooms and puffballs, the molds, rusts, mildews, and the vast
+tribe of microscopic organisms called _bacteria_, which are so active
+in the production of fermentation, putrefaction, and disease.
+
+[Illustration: FIG. 425.—A seaweed with broad, expanded thallus.]
+
+[Illustration: FIG. 426.—Anthoceros, a liverwort with flat, spreading
+thallus.]
+
+=334. II. Bryophytes=, or moss plants.—This group likewise contains
+two main divisions, Mosses and Liverworts. Familiar examples of the
+latter are the flat, spreading green plants, bearing somewhat the
+aspect of lichens, met with everywhere on wet rocks and banks around
+shady watercourses. The name is a reminiscence of their former use in
+medicine as a specific for diseases of the liver, and not, as in the
+case of the liver leaf, of a fancied resemblance to that organ.
+
+Mosses are one of the best defined of botanical orders, and are
+easily recognized by their slender, leafy fruiting stalks, growing
+usually in dense, spreading mats, and presenting every appearance of
+a highly organized structure, well differentiated into root, stem,
+and leaves.
+
+The liverworts represent the more primitive division of the group,
+and in some of their forms approach so near the thallophytes that it
+is not difficult to recognize them as connecting links in the same
+chain of life. Their relationship to the next higher group is not
+clear, but while they represent a more primitive stage of evolution
+than the mosses, the development of the latter has followed a course
+divergent from the main line of evolutionary progress.
+
+[Illustration: FIG. 427.—A shoot of peat moss with ripe spore fruits,
+_f_, _f_.]
+
+[Illustration: FIG. 428.—A common fern (_Polypodium vulgare_).]
+
+=335. III. Pteridophytes=, or fern plants, are classed roughly in
+the three divisions of ferns, horsetails, and club mosses. They
+differ greatly in structure, but all possess a vascular system, and
+a well-organized structure of root, stem, and leaves. They rank next
+to the spermatophytes in the order of development, and the group is
+of especial interest on account of its relationship to the higher
+plants. One of its divisions, the club mosses, has probably given
+rise to at least one section of the gymnosperms, while the ferns are
+regarded as the ancestors of the true flowering plants, which make
+up the great class of angiosperms, and represent the highest type of
+evolution yet attained in the vegetable kingdom.
+
+
+          II. THE ALGÆ
+
+  MATERIAL.—Simple forms of green algæ can be found on the shady side
+  of tree trunks, damp walls, old fence palings, and the outside of
+  flowerpots. _Pleurococcus_, one of the commonest kinds, occurs as a
+  green, powdery mat or felt in damp places, and is often accompanied
+  by _protococcus_, another good specimen for study. _Spirogyra_ and
+  other filamentous algæ can be found in stagnant pools and ditches
+  and in old rain barrels.
+
+  APPLIANCES.—Eosin solution, nitric acid, alcohol, iodine solution;
+  a white china plate; a hand lens; a compound microscope, and slides.
+
+=336. Variety of forms.=—This group embraces plants of the greatest
+diversity of form and structure, from the minute volvox and desmids
+that hover near the uncertain boundaries dividing the vegetable from
+the animal world, to the giant kelps of the ocean, which sometimes
+attain a length of from six hundred to one thousand feet. They are
+usually classed according to their color, as green, brown, and red
+algæ, including various subdivisions of each group. They all contain
+chlorophyll, by means of which they manufacture their own food,
+though in the red and brown divisions it is masked by the presence of
+other pigments—an adaptation to the modified light that reaches them
+at various depths under water. With few exceptions they can live only
+in the water, and unlike any other form of plant life, attain their
+highest development in the salty depths of the ocean. The freshwater
+forms are small and inconspicuous, and generally of a more simple
+type than the seaweeds. The great majority of them belong to the two
+classes of green and blue-green algæ. The former is believed to have
+furnished the type from which the higher plants have been evolved.
+
+[Illustration: FIG. 429.—Three stages in the division of a one-celled
+alga (_Glœocaspa polydermatica_): _A_, division of a cell just
+beginning; _B_, division further advanced; _C_, four cells after
+division, remaining in contact.]
+
+=337. Study of a one-celled alga.=—Put a little of the green algæ
+in water on a glass slide. Hold up to the light, or over a sheet
+of white paper, and examine with a hand lens; then place under
+the microscope. It will probably be found to contain a number of
+minute organisms, but the pleurococci can be recognized as small
+round bodies of a bright green color, some of them separate, others
+adhering together in groups of two, four, or more, with the sides
+that are in contact slightly flattened. Each of these bodies is an
+individual plant consisting of a single cell, whence they are said
+to be _unicellular_. Draw one of the single cells and one of the
+groups, or colonies, as they appear under the microscope. Try to
+make out the cell wall and the nucleus, and label all the parts (see
+7). If you have any difficulty in distinguishing the cell wall, drop
+a little glycerine or salt water on the slide. This will cause the
+cell contents to shrink by osmosis (56, 59). Can you make out the
+structure of the cell colonies? They have resulted from the peculiar
+mode of multiplication that prevails among this class of plants. A
+cell elongates, contracts in the middle, and divides into two parts,
+each of which becomes an independent plant like the mother cell. See
+if you can find one in the process of division. The daughter cells
+repeat the process, each one giving rise to two new individuals, and
+so on indefinitely. The new cells do not always separate immediately
+on their formation, but frequently adhere together for a time, in
+colonies, before falling away and beginning an independent existence.
+
+=338. Reproduction by fission.=—This kind of reproduction is called
+_fission_, or cell division, and marks a very primitive stage of
+development. Under stress of adverse conditions the cells formed
+by division may remain inactive for a time. They are then called
+_resting spores_, and when more favorable circumstances arise, they
+begin again their work of reproduction and growth as actively as ever.
+
+=339. Meaning of the name.=—The suffix _coccus_ is a Latin noun
+(plural _cocci_) meaning a grain or berry, and is a general term
+applied to any small, round organism consisting of a single cell;
+hence, _micrococcus_, a minute round body; _protococcus_, a primitive
+form, or prototype of one-celled bodies; and _pleurococcus_, which
+may be freely translated “a one-sided little round body,” from the
+flattening of the adjacent sides during fission—_pleuro_ meaning
+lateral, or pertaining to the side.
+
+It is important to remember this definition, as the term _coccus_
+is of very frequent occurrence in works of biology, as a suffix for
+designating small round bodies of various kinds.
+
+=340. Examination of a filamentous alga.=—Place on a white dish a
+few drops of water containing some of the green pond scum common in
+stagnant pools and ditches. Examine with a hand lens; of what does
+it appear to consist? Are the filaments all alike, or are they of
+different lengths and thickness? Soak a number of them in alcohol for
+half an hour and examine again; where has the green matter gone? Do
+these algæ contain chlorophyll? (336; Exp. 65.) This class are called
+filamentous algæ on account of their slender, threadlike thalli,
+which look like bits of fine floss floating about in the water. The
+bubbles of oxygen which they sometimes give off in great abundance
+cause the frothy appearance that has given rise to their popular
+name, “frog spit.”
+
+[Illustration: FIGS. 430, 431.—_Spirogyra_ (magnified): 430, two
+filaments beginning to conjugate; 431, formation of spores.]
+
+=341. Spirogyra.=—The filamentous algæ are very numerous, and a
+drop of pond scum will probably contain several kinds. At least
+one of these, it is likely, will be a _Spirogyra_, as this is one
+of the commonest and most widely distributed of them all. Place a
+filament under the microscope and notice the spiral bands in which
+the chlorophyll is disposed within the cells. It is from this spiral
+arrangement that the species takes its name. Do you notice any
+roundish particles inclosed in the chlorophyll bands? Test with a
+little iodine solution and see what they contain. Each filament will
+be seen, when sufficiently magnified, to consist of a number of more
+or less cylindrical cells joined together in a vertical row, and thus
+forming the simple threadlike thallus which characterizes this class
+of algæ. Physiologically, each cell is an independent individual, and
+often exists as such. Can you see the cell nucleus? If not, place a
+few filaments in a solution of eosin and add a drop of acetic acid to
+give the solution a pale rose color. After twenty to thirty minutes,
+examine again; the nucleus will be stained a deep red. If you can
+find an unbroken filament, examine both ends to see whether there is
+any differentiation of base and apex.
+
+=342. Conjugation.=—See if you can find two filaments sending out
+lateral protuberances toward each other. Watch and notice that after
+a time these projections come together and unite by breaking down
+the cell walls dividing them, the protoplasm in each contracts, the
+contents of one pass over into the other, and the two coalesce,
+forming a new cell but little, if any, larger than the original
+conjugating bodies. This cell germinates under favorable conditions
+and produces a new individual. This method of reproduction is known
+as _conjugation_. The cells thus produced by the union of the
+contents of two separate cells may either germinate at once, and give
+rise to new individuals, or remain quiescent for a time, as resting
+spores.
+
+
+          Practical Questions
+
+  1. Are any of the green algæ parasitic? How do you know? (186, 336.)
+
+  2. Why is their presence in water regarded as denoting unhygienic
+  conditions?
+
+  3. Mention some of the ways in which their presence may contribute
+  to the contamination of drinking water.
+
+  4. Refer to Exp. 66, and account for the bubbles and froth that
+  usually accompany these plants in the water.
+
+  5. Can you suggest any other causes than the evolution of oxygen
+  that might produce the same effect?
+
+  6. Is the presence of these gas bubbles of any use to floating
+  plants?
+
+
+          III. FUNGI
+
+[Illustration: FIG. 432.—A common form of mold, magnified, showing
+thallus modified into a fibrous mycelium: _a_, _a_, spore cases; _b_,
+mycelium. (_After_ KOPF, in part.)]
+
+=343. Classification.=—In the fungi the thallus structure is greatly
+modified, appearing usually as a network of fine threads called the
+_mycelium_ (pl., _mycelia_), from a Greek word meaning “fungus”
+(369). These plants are all, with a few doubtful exceptions,
+parasites or saprophytes which contain no chlorophyll and are
+incapable of supporting an independent existence. Biologists are
+divided as to their position in the genealogical tree of life.
+The weight of authority at present inclines to the view that they
+are degenerate forms derived from the algæ, but they have been so
+modified by their parasitic habits as to render their position in the
+general scheme of life a doubtful one. They represent an offshoot,
+or side branch, as it were, of the great evolutionary line, and so
+may be considered for the present as standing apart in a class by
+themselves.
+
+=344. Numbers and variety.=—Fungi exceed every other class of
+living organisms both in the number of species and of individuals
+composing them. They include such diverse forms as bacteria, molds,
+rusts, mildews, mushrooms, and the like, ranging in size all the way
+from the giant puffball, a foot or more in diameter, to the almost
+inconceivably minute influenza bacillus, of which nearly two thousand
+million can inhabit a single drop of water without inconvenient
+crowding!
+
+[Illustration: FIG. 433.—Cephalothecium, a fungus parasitic on
+rosehips—greatly magnified. (_From_ Mo. Botanical Garden Rep’t.
+Photographed by Hedgcock.)]
+
+=345. The parasitic habit.=—But while their life history is obscure
+and hard to trace, the fungi are, as a class, well differentiated by
+their parasitic habit. They contain no chlorophyll, can manufacture
+no food, and consequently have to obtain it ready-made from the
+tissues of living or dead animals and plants. On this account they
+are active agents in the production of disease and decay, especially
+certain of those manifold forms that have been grouped together
+under the general head of bacteria. While not responsible for all
+the disease known to be caused by living organisms,—some very
+serious ones, such as malaria and cattle fever, being due to animal
+parasites,—the majority of those that have been most carefully
+investigated are traced to the bacteria, or other fungi. After any
+of these parasites have found a lodgment in the body of an organism
+whose tissues furnish them a congenial habitat, they multiply with
+enormous rapidity, and through the action of certain poisons called
+_toxins_, which they excrete, give rise to the most destructive
+diseases in both animals and plants; and no rational sanitary science
+is possible without a knowledge of their habits and life history. Add
+to the vast amount of human suffering that is to be laid at their
+door the economic damage done by rust and smut fungi, by molds and
+blights and mildews, and we shall be tempted to conclude that the
+“battle of life” is largely a struggle against these invisible foes.
+
+[Illustration: FIGS. 434-437.—Disease-producing bacteria: 434,
+bacteria of consumption (_Bacillus tuberculosis_); 435, cholera
+bacillus; 436, bacilli of anthrax, showing spores; 437, typhoid
+bacillus.]
+
+=346. Useful fungi.=—Not all fungi, however, are injurious. On the
+contrary, the great majority of them are harmless, and very many
+kinds are positively beneficial to man. Without the yeasts and
+bacteria of fermentation we could not have our bread and cheese.
+Other forms are active agents in the fertilization of soils, it
+having been estimated that there are 100,000 or more of these
+infinitesimal laborers at work in every cubic centimeter (about ¹⁄₁₆
+of a cubic inch) of virgin soil! Even the bacteria of putrefaction,
+which we are accustomed to regard as the embodiment of all that is
+foul and loathesome, are engaged in an unceasing work as scavengers,
+without which life would no longer be possible on our globe, as will
+be shown in the following section.
+
+
+          A. BACTERIA
+
+  MATERIAL.—A vessel of water in which hay has been left to soak for
+  several hours; a freshly boiled potato.
+
+  APPLIANCES.—A double boiler for sterilizing; a number of clean
+  glass jars and bottles; cotton wool for stoppers; a compound
+  microscope.
+
+  CULTURE MEDIUMS.—A freshly boiled potato answers very well for
+  ordinary purposes. “Bread mash” can be made by drying some bread
+  crumbs in an oven, then mashing and mixing them to a paste with
+  boiling water; sterilize by three successive heatings in a double
+  boiler. A sterilized preparation of gelatine solution is the medium
+  most commonly used.
+
+=347. How to obtain specimens for observation.=—While bacteria are
+plentiful almost everywhere, it is not always easy to capture them
+just when and where you want them. For this purpose, put some hay
+in water and leave in a warm place away from the light until the
+liquid becomes cloudy or a film forms on the surface. This will show
+that bacteria are present. If it is desired to study any particular
+kind of bacterium, inoculate one of the culture mediums described
+under “material,” or a few drops of sterilized extract of beef, with
+a small quantity of the substance to be examined, or with dust or
+scrapings from the locality under consideration.
+
+  EXPERIMENT 93. BY WHAT MEANS ARE BACTERIA COMMONLY DISTRIBUTED?—Put
+  a slice of freshly boiled potato into each of three glass tumblers
+  and cover with a filter of cotton wool held in place by tying
+  tightly with a cord, or by an elastic band. Set them all in a
+  vessel of water, bring it to a boil, and keep at that temperature
+  for half an hour, to sterilize the air in the tumblers. When they
+  have cooled, lift the cotton from (1) for a minute or two and then
+  replace. Carefully pass the tip of a medicine dropper through the
+  filter of (2) so as to prevent the entrance of unsterilized air,
+  and put on the slice of potato a small quantity of the bacterial
+  liquid prepared as directed in the last paragraph. Leave (3)
+  unopened. Keep all together in a warm, dark place and observe at
+  intervals of from 12 to 24 hours. Do any bacteria appear in (3)?
+  Do any appear on the potato in (2), where the liquid was dropped?
+  Are they more, or less abundant than in (1)? Since cotton wool is
+  entirely impervious to the smallest microörganisms known, would you
+  judge from this experiment that bacteria can get into any place
+  unless carried there by the air, or by some other means?
+
+  EXPERIMENT 94. CAN BACTERIA BE CARRIED BY PURE AIR?—On a warm (and
+  preferably cloudy) day, put a slice of potato on a plate, and leave
+  uncovered in an unused room or closet, free from dust, and kept
+  carefully closed. Put another slice arranged in exactly the same
+  way in an open window on a dusty street, or in a room that is used
+  and daily swept and dusted. Do bacteria appear in the first plate?
+  In the second? Is air free from dust a good conveyor of bacteria?
+
+  EXPERIMENT 95. WHAT CONDITIONS ARE FAVORABLE TO BACTERIAL
+  GROWTH?—Strain some of your culture liquid into half a dozen small
+  bottles of the same size, filling each about half full. Put (1) in
+  a dark, cool place—on ice, if the weather is warm; (2) in a dark,
+  warm place; (3) in a warm, well-lighted place; into (4) put a drop
+  of carbolic acid, formalin, corrosive sublimate, or boracic acid,
+  and keep in a dark, warm place. Keep (5) in boiling water for half
+  an hour or more, and then place beside (2). Keep (6) in a freezing
+  mixture of salt and ice for several hours, then place with (2) and
+  (5). Examine all at intervals of from 12 to 24 hours. In which
+  bottles is the presence of bacteria indicated by cloudiness of the
+  contained liquid, or the formation of a surface film? In which do
+  they appear first? In which most abundantly? In which last, or not
+  at all? What is the effect of light and darkness on their growth?
+  Of heat and cold? Of disinfectants? Name the circumstances that
+  tend to hinder their growth, in the order of their efficacy.
+
+=348. Microscopic study of bacteria.=—Put a drop of hay infusion on a
+slide and examine with the highest power of the microscope. You will
+see a multitude of very small glistening bodies including different
+kinds of bacteria, a majority of which are probably the hay bacillus,
+_B. subtilis_, shown in Figs. 443, 444. Notice that some forms move
+about freely, while others are non-motile. Which kind are the more
+numerous? The motion may be either mechanical, resembling that of
+the small dust particles we see dancing about in the sunshine, or
+apparently voluntary, and caused by the vibration of little whiplike
+cilia. Can you distinguish the two kinds? Try to make out clearly
+the different shapes you see. Some appear as slender chains or
+filaments, but this is due to the individual cells’ adhering together
+for a time before breaking up and beginning an independent existence.
+The small, rounded bodies, like a period (Fig. 438), are _cocci_; the
+slender, rod-shaped ones—sometimes slightly curved (Fig. 440)—are
+_bacilli_ (sing., _bacillus_); the comma-shaped ones, and those
+generally showing a slight spiral curvature, are _vibrios_ (Fig.
+441); the spirally twisted ones, like a corkscrew (Fig. 442), are
+_spirilli_ (sing., _spirillum_). These are the principal forms which
+it is important to distinguish and remember. The names are applied
+very loosely, however, in practice, bacillus being often used as a
+general term applicable to almost any kind,—the spirillum of cholera,
+for instance, being commonly known as the cholera bacillus, while by
+some authors vibrios are ranked as a variety of spirillum.
+
+[Illustration: FIGS. 438-442.—Typical forms of bacteria: 438, coccus
+type; 439, the same, hanging together in chains; 440, rod-shaped
+bacteria (bacillus type), the clear areas in some of these are
+spores; 441, forms of vibrio; 442, forms of spirillum.]
+
+=349. Life history of a typical bacterium.=—A pure culture of the
+_Bacillus subtilis_ can easily be obtained by boiling some of the
+hay infusion for half an hour and then leaving in a warm place till
+the usual indications of the presence of bacteria appear (347).
+The spores of this micro-organism are so resistant that they can
+withstand the temperature of boiling water for several hours, while
+those of most other forms of bacteria are killed by a few minutes’
+exposure to it; hence, the crop that develops after boiling will
+consist of a pure culture of the hay bacillus.
+
+[Illustration: FIGS. 443, 444.—Hay bacillus (_B. subtilis_): 443, a
+portion of the film from the culture liquid, the black lines, _e_,
+being bacteria in the vegetative state; 444, spore formation; _a_,
+_d_, motile cells and chain of cells: _b_, non-motile cells; _c_,
+spores and chain of spores from the film _e_.]
+
+In their active state these organisms will be seen to consist of
+single-celled, rod-shaped bodies, about three or four times as long
+as broad, and generally cohering in bands or filaments, as shown in
+Fig. 444, _c_. The black dots within the cells are the spores. Each
+individual bacterium produces but a single spore, or rather becomes
+a spore itself, by the contraction of its contents and the formation
+around them of a strong inclosing membrane. On germinating, the
+spores give rise to little ciliated, one-celled organisms called
+“swarm spores,” that swim about freely in the containing medium and
+multiply rapidly for a time by cell division. After this they pass
+again into the quiescent state, ready, whenever favorable conditions
+arise, to begin anew the repetition of their life cycle, which is an
+irregular alternation of cell division and spore formation.
+
+=350. Resistance of spores.=—Bacteriologists are not fully agreed as
+to the cause of spore formation, some holding that it takes place
+only when conditions are most favorable for bacterial growth, others
+claiming the reverse. The consensus of opinion at present is toward
+the view that the spores are a provision for tiding over periods of
+stress and difficulty. They are capable of retaining their vitality
+for a long time, and are much harder to kill than the bacterial
+cells in their ordinary vegetative state, as was seen in the case of
+the hay bacillus. The spores of one species of potato bacillus have
+retained their vitality after four hours of boiling, and those of the
+typhoid bacillus after continuous exposure to a freezing temperature
+for more than three months. The majority of bacteria, in their
+vegetative state, are, however, either killed or rendered inert by
+temperatures ranging below 10° or above 50° centigrade—equivalent to
+about 50° and 122° Fahrenheit, respectively. It is easy to see what
+important bearing these facts have on the process of disinfection.
+
+=351. Reproduction and multiplication.=—The ordinary mode of
+reproduction in bacteria, as in other unicellular organisms, is by
+fission (337, 338). As each individual forms but a single spore, no
+increase in numbers could take place by this means alone. Hence,
+while the spores are an important factor in the preservation of
+the species by continuing its existence under conditions which the
+active organisms could not survive, their successful propagation
+depends on their power of rapid multiplication by division. If
+this process were to go on unchecked, every hour, in an unbroken
+geometrical progression, the progeny of a single bacterium would,
+in 24 hours, number nearly 17 million; in 25 hours, 34 million; in
+26 hours, 68 million, and in five days they would cover the entire
+surface of the globe, land and sea, to a depth of 3 feet! In ordinary
+standard milk sold by dairymen, and containing, when examined, less
+than 10,000 microbes to the cubic centimeter,—about 20 drops,—the
+number was found to have increased after 24 hours to 600 million.
+It is comforting to know, however, that the majority of these are
+of the harmless kinds which are the active agents in the making of
+buttermilk and cheese.
+
+The effects of their rapid multiplication will be better appreciated
+when we consider that bacteria are the smallest of known living
+creatures. If 1000 of the influenza bacilli were spread out in
+a single layer with their sides touching, but not overlapping,
+they would not take up more room than one of the periods used in
+punctuating this book; and a coccus concerned in a tubercular disease
+prevalent among cattle in South America has recently been discovered,
+of which double that number could be accommodated in the same space.
+
+[Illustration: FIGS. 445, 446.—Milk (highly magnified): 445, pure,
+fresh milk, showing fat globules; 446, milk that has stood for hours
+in a warm room in a dirty dish, showing fat globules and many forms
+of bacteria.]
+
+=352. Distribution of bacteria.=—Ordinary air, when free from
+dust, contains, on the average, not more than five germs to the
+liter—equal to about 1 for every 12 cubic inches. Pathogenic, or
+disease-producing, germs seldom occur in ordinary fresh air, and
+even when present are, under ordinary circumstances, harmful only to
+people whose bodies, by reason of physical weakness or unhygienic
+habits, offer a congenial soil for their multiplication. Numerous
+instances are known in which perfectly healthy persons have carried
+about infectious disease germs in their bodies and even transmitted
+them to others without experiencing any inconvenience, or even being
+aware of their presence. Among others, the germs of pneumonia,
+diphtheria, and tuberculosis are often found in the mouth, nose,
+and sputum of perfectly healthy persons. There are also a number
+of bacteria that are regular inhabitants of the mouth, some of
+which are the cause of decayed teeth and foul breath. One form of
+bacterium, concerned in the production of inflammation and abscesses
+(_Staphylococcus_) is so constantly present on the human epidermis
+that one authority has declared it impossible to sterilize the
+skin so thoroughly as to free it entirely of this microbe. It is
+ordinarily not harmful unless it comes in contact with open wounds
+and abrasions.
+
+=353. The economic importance of bacteria.=—It is hard to say
+whether these organisms concern us most on account of the damages
+attributable to them on the one hand, or the benefits we owe them
+on the other. If they were all as harmful as the pathogenic kinds,
+life would hardly be possible on the globe, while without their
+presence life as we know it would have ceased to be possible long
+ago. They are nature’s great army of scavengers, the sole agents of
+decomposition, without which dead organic matter would be subject
+only to the slow changes by which the rocks and mineral matter of the
+earth’s crust are disintegrated, and the undecomposed bodies of the
+vast procession of plants and animals that have existed since life
+first began on our globe would long ago have cumbered its surface to
+such an extent as to render impossible the continued development of
+life such as we know.
+
+=354. Sterilization= is the process of ridding a substance of living
+microörganisms. To do this effectively, the process must be repeated
+several times at intervals, so as to give any spores that may have
+survived previous applications time to pass into the vegetative
+state, when their power of resistance is diminished and they are more
+easily destroyed. The incubation period, as the time required for
+the germination of the spores is called, is different for different
+kinds of bacteria; hence the importance, from a sanitary point of
+view, of a thorough knowledge of their life history.
+
+=355. Disinfection= is sterilization on a large scale, and the same
+principles apply to both. Heat is the safest disinfectant for objects
+that will bear it, if continued long enough and repeated often enough
+at a sufficiently high temperature. Freezing will destroy some kinds
+of germs and check or retard the development of nearly all, but
+is not to be relied on as a permanent germicide, since even among
+flowering plants there are many kinds, not only of seeds, but of
+perennial vegetative forms that are capable of enduring an arctic
+temperature of many degrees below freezing for long continued periods.
+
+Chemical disinfectants act usually as microbe poisons, and are
+unsuitable as sterilizers for food, though valuable in the
+purification of houses, clothing, and utensils—especially the
+instruments employed in surgical operations.
+
+The prevention of the growth of bacteria, especially in wounds
+and surgical incisions, whether by means of chemical or physical
+agencies, is known as _antisepsis_.
+
+
+          Practical Questions
+
+  1. Why should a person recovering from an ague continue for some
+  time after to take quinine every third or every seventh day? (350,
+  354.)
+
+  2. Name some of the principal diseases produced by bacteria.
+
+  3. What is the principle to be acted on in the avoidance of such
+  diseases? (Exps. 94, 95.)
+
+  4. Are the same means equally effective for prevention and for
+  cure? (354, 355; Exps. 93-95.)
+
+  5. Why is “fresh air” beneficial in a sick room? (352; Exp. 94.)
+
+  6. Does it act as a disinfectant, or as a mere diluent of the
+  infected air of the room? (352.)
+
+  7. Why ought preserved fruits and vegetables to be scalding hot
+  when put into the can? (355.)
+
+  8. Why is it necessary to exclude the air from them? (Exps. 93, 94.)
+
+  9. Reconcile question 8 with question 5.
+
+  10. Why does the use, for drinking purposes, of water that has been
+  boiled render a person less liable to infectious diseases? (355.)
+
+  11. Was the old-fashioned practice of handing the baby round to be
+  promiscuously kissed by friends and neighbors a good one for the
+  baby? (352.)
+
+  12. Why is the spitting habit to be condemned? The use of common
+  drinking cups in schoolrooms and other public places? (352.)
+
+  13. Is it proper from a sanitary point of view that roommates at
+  a boarding school, or even members of the same family, should use
+  soap, towels, and other articles of the toilet in common? (352.)
+
+
+          B. YEASTS
+
+  MATERIAL.—A piece of fresh baker’s yeast, some warm water, and a
+  little honey or sugar solution; a pipette, or a medicine dropper;
+  three or four clean pint bottles or preserve jars.
+
+  To raise a crop of yeast fungi for observation, rub one fourth of a
+  fresh yeast cake in water enough to make a paste; add one pint of
+  water, with a tablespoonful of honey or sugar, and stir well.
+
+  EXPERIMENT 96. WHAT CONDITIONS FAVOR THE GROWTH OF YEAST?—Pour
+  equal parts of the liquid made as directed (see Material) into each
+  of three pint bottles, stopper lightly, and label. Put (1) in a
+  warm, dark place; (2) in a cool, dark place; and (3) in a bright
+  light in a warm place. Observe at intervals of a few hours the
+  changes that occur in each. Notice the bubbles that rise from the
+  liquid. In which bottle do they form most rapidly? Lower a lighted
+  match into it, or transfer some of the gas with a pipette into a
+  vessel containing limewater, and tell what it is. Taste some of the
+  fermenting liquid. Is it sweet? What has become of the sugar that
+  was put into it?
+
+=356. Yeasts and ferments.=—Yeasts belong to a very different order
+of fungi from the bacteria, but on account of their simplicity of
+structure and the similarity of their action to that of some of the
+latter, it is usual to consider them together. They are the active
+agents of fermentation, and include a large number of species. The
+kind used for household purposes is the same as that employed in
+making beer. Of this species there are many varieties, each one of
+which gives a characteristic taste to the beer made from it; and
+brewers, by paying attention to the cultivation of yeasts, give their
+product the special flavors peculiar to the different brands. This
+kind of yeast is not known to exist except in a state of cultivation,
+and probably owes its survival and present condition of development
+to a symbiosis with man, on account of its usefulness in bread
+making, and still more, perhaps, to its part in the gratification of
+his bibulous propensities, for among savage tribes the manufacture of
+fermented liquors is practiced long before the wholesome art of bread
+making.
+
+[Illustration: FIGS. 447-449.—Forms of common yeast (_Saccharomyces
+cerevisiæ_): 447, brewers’ yeast; 448, household yeast (the large
+grains are starch); 449, yeast from beer sediment, showing budding.
+(Figs. 447, 448 × 250; Fig. 449 × 1270.)]
+
+There are other yeasts existing in a state of nature, such as those
+on the surface of fruits, which cause the latter, under certain
+circumstances, to ferment and decay. For this reason artificial
+ferments are not needed in making wine and other alcoholic liquors
+from fruits. Fermentation is also caused by certain forms of
+bacteria, as in the formation of vinegar and the souring of milk.
+Such bacteria often contaminate the yeast ferments.
+
+=357. Microscopic examination.=—Place a drop of the cultural
+liquid on a slide and examine under the highest power of the
+microscope. What do you see? These egg-shaped bodies are yeast
+plants, unicellular organisms like the pleurococcus. Do you see any
+chlorophyll? Are the yeasts parasitic? How do you know? What do they
+live on? (Suggestion: What food substance that has disappeared was
+put into the culture liquid?) In getting their nourishment from the
+sugar, these fungi disintegrate it into alcohol and carbon dioxide,
+which is a process of fermentation. It is the bubbles of gas that
+were seen rising in the liquid which cause beer to effervesce and
+bread to rise. They permeate the dough and by their expansion produce
+the sponginess peculiar to leavened bread. Look for a cell with a
+bud forming on it; from what part does it appear to grow? Where a
+number of buds remain for some time attached to the mother cell (Fig.
+449), they form a _colony_. Make a sketch of a single cell and of a
+colony of two or more adherent ones, labeling all the parts. If the
+cell wall cannot be made out clearly, run a little glycerine, or salt
+water, under the cover glass with a medicine dropper. What causes the
+contents of the cell to contract and leave the wall? (56, 59.)
+
+=358. Reproduction.=—From time to time buds break away from the
+mother cell and form new individuals or colonies of their own. This
+process is called multiplication by budding, and is only another form
+of cell division.
+
+Whenever reproduction takes place by other means than seeds or
+spores, it is said to be _vegetative_. This sort of reproduction
+is not confined to unicellular plants, but exists also among the
+phanerogams, the propagation of species by means of buds, tubers,
+rootstocks, runners, grafting, and the like being variations of
+the same process. On the other hand, yeasts and bacteria and the
+unicellular algæ have the power, under extreme conditions, to form
+resting spores, which sometimes lie dormant for years and resume
+their activity when favorable conditions return.
+
+
+          Practical Questions
+
+  1. When is fermentation useful to man?
+
+  2. What is the effect on canned fruits and vegetables if yeast
+  cells get into them?
+
+  3. Why does milk turn sour in warm weather? (350, 351; Exp. 96.)
+
+  4. Why do buttermilk and clabber spoil if left standing too long?
+  (345, 356.)
+
+  5. What causes bread to be “heavy”? (356, 357.)
+
+  6. Why will dough not rise unless kept in a warm place? (Exp. 96.)
+
+  7. Why is beer kept cold during fermentation? (350, 356.)
+
+
+          C. RUSTS
+
+  MATERIAL.—A leaf of wheat affected with red rust; a leaf or a stalk
+  with black rust. Some barberry leaves with yellowish pustules on
+  the under side, which under the lens look like clusters of minute
+  white corollas. These are popularly known as “cluster cups.” As the
+  spots on barberry occur in spring, the red rust in summer, and the
+  black rust in autumn, gather the specimens as they can be found,
+  and preserve for use.
+
+[Illustration: FIGS. 450, 451.—Leaf of wheat affected with orange
+leaf-rust (_Puccinia rubigo-vera_), uredo stage: 450, upper side of
+leaf; 451, under side.]
+
+  The orange leaf, or brown, rust (_Puccinia rubigo-vera_) is more
+  common in some parts of the country than the ordinary wheat rust
+  (_Puccinia graminis_), but the two are so much alike that the
+  directions given will do for either. If the orange leaf-rust (so
+  named from its color, and not from any connection with orange
+  leaves, the logical relation of the words being orange leaf-rust,
+  and not orange-leaf rust) is used, the cups and pustules should be
+  looked for on plants of the borage family—comfrey, hound’s-tongue,
+  etc. The orange leaf-rust of apple is caused by a fungus which will
+  serve to illustrate the same class of parasites. The “teleuto”
+  stage of this will be found on cedar trees, in the excrescences
+  commonly known as “cedar apples”; the “cluster cups” on the leaves
+  of apple and haw trees affected with the disease.
+
+=359. Red rust.=—Uredo stage. Examine a leaf of “red rusted” wheat
+under the lens, and notice the little oblong brown dots that cover
+it. These are clusters of spore cases, and are the only part that
+appears above the surface. Viewed under the microscope, the red rust
+will be seen to consist of a mycelium (see Fig. 452), which ramifies
+through the tissues of the leaf and bears clusters of single-celled
+reddish spores that break through the epidermis and form the reddish
+brown spots and streaks from which the disease takes its name. These
+spores, falling upon other leaves, germinate in a few hours and form
+new mycelia, from which, in six to ten days, fresh spores arise.
+Formerly this was thought to complete the life history of the fungus,
+to which the name of _Uredo_ was given. It is now known, however,
+that the red rust is merely a stage in the life cycle of the plant,
+and to this stage the old name uredo is applied, the spores being
+called _uredospores_.
+
+=360. Black rust.=—Teleuto stage. Next examine with a lens a part
+of the plant attacked by black rust. Do you observe any difference
+except in the color? Do the two kinds of rust attack all parts
+of the plant equally? If not, what part does each seem to affect
+more particularly? At what season does the black rust appear most
+abundantly? Place a section of the diseased part under the microscope
+and notice that the difference in color is due to a preponderance
+of long, two-celled bodies with very thick, black walls (Fig. 453).
+These are called _teleutospores_, a word meaning “final spores,”
+because they are formed only toward the end of the season. They are
+developed from the same mycelium with the uredospores, and are not
+a product of the latter, but collateral with them and belong to the
+same stage in the life history of the fungus. After they appear,
+the uredospores cease to be developed at all, and only the dark
+teleutospores are produced. These remain on the culms in the stubble
+fields over winter, ready to begin the work of reproduction in
+spring. For this reason the teleutos are popularly known as “winter
+spores” in contradistinction to the uredos, or “summer spores,” whose
+activity is confined to the warm months.
+
+[Illustration: FIG. 452.—Uredo spores of wheat rust (_Puccinia
+graminis_), magnified. (_From_ COULTER’S “Plant Structures.”)]
+
+[Illustration: FIG. 453.—Teleutospores of wheat rust, magnified.
+(_From_ COULTER’S “Plant Structures.”)]
+
+[Illustration: FIG. 454.—Teleutospore germinating and forming
+sporidia, _s_, _s_. (_From_ COULTER’S “Plant Structures.”)]
+
+It was formerly supposed that black rust was caused by a different
+fungus from that producing red rust, and to it the name _Puccinia_
+was given. This has been retained as a general designation for all
+fungi undergoing these two phases, and the particular form of fungus
+that we are now considering is known in all its stages as _Puccinia
+graminis_.
+
+=361. The nonparasitic stage.=—The formation of teleutospores
+completes that portion of the life history of the fungus during which
+it is parasitic on wheat and grasses of different kinds. In spring
+they begin to germinate on the ground, each cell producing a small
+filament, from which arise in turn several small branches. Upon the
+tip of each of these branches is developed a tiny sporelike body
+called a _sporidium_ (Fig. 454), which continues the generation of
+the rust fungus through the next stage of its existence. The filament
+which bears these sporidia is not parasitic, but when the sporidia
+ripen and the spores contained in them are scattered by the wind,
+there begins a second parasitic phase, which forms the most curious
+part of this strange life history.
+
+=362. The æcidium.=—Examine next the under side of some barberry
+leaves (or comfrey, etc., if orange leaf-rust is used) for clusters
+of small whitish bodies that appear under the lens like little white
+corollas with yellow anthers in the center. Examine a section of one
+of these under the microscope and notice that the yellow substance
+is composed of regular layers of colored spores. The corolla-like
+receptacles containing them, popularly known as “cluster cups,”
+are borne on a mycelium produced from the spores described in the
+last paragraph. This mycelium is parasitic on barberry or other
+leaves, according to the kind of fungus, and was long believed to be
+a distinct plant, to which the name _Æcidium_ (pl., _Æcidia_) was
+given. This term is now applied to the cluster cups, and those fungi
+which at any period of their life history produce them are called
+æcidium fungi.
+
+[Illustration: FIG. 455.—Section through a barberry leaf, showing on
+the upper side two spermogonia, _s_, _s_; and on the under side, an
+æcidium, _æ_.]
+
+=363. Spermogonia.=—On the upper surface of the leaves that bear
+the æcidia, notice some small black dots hardly larger than pin
+points, but which, when sufficiently magnified, appear as little
+flask-shaped bodies (Fig. 455) under the epidermis. These are known
+as _spermogonia_, or _pycnidia_. When mature, they break through
+the epidermis so that the necks protrude, and discharge a quantity
+of minute cells or spores, very like some that, later on, we shall
+find playing an important part in the reproductive processes of
+certain other fungi, and of mosses and liverworts. In the rust fungi,
+however, their function is not understood. They may possibly be
+survivals of organs which were once active in the life processes of
+the plant, but have become useless under changed conditions. Do such
+organs throw any light on the evolutionary history of plants?
+
+[Illustration: FIG. 456.—A species of “cedar apple”
+(_Gymnosporangum_), showing the uredo-teleuto stage of the apple rust
+fungus. (_From_ a photograph by Prof. F. E. Lloyd.)]
+
+=364. Connection between barberry and wheat rust.=—With the discharge
+of the æcidium spores, the part of the life cycle of the fungus
+spent on the barberry comes to an end, and it is ready to begin the
+uredo-teleuto stage over again as soon as it finds a suitable host.
+Where there are no barberries, it is capable of propagating without
+them, either by adapting itself to some other host plant, or by
+omitting the æcidium stage altogether. The parasitic habit being an
+acquired one, the fungus, like some animal organisms that we know of,
+can often be “educated” by force of circumstances into tolerating,
+and even thriving upon, foods which under other circumstances it
+would reject. The wheat rust is known to be capable of propagating
+year after year in the uredo stage, the spores surviving through
+the winter on volunteer grains and grasses; and in no other country
+in the world does rust do greater damage to the wheat crop than in
+Australia, where the barberry is practically unknown. This power of
+accommodation possessed by many parasites is one of the difficulties
+the agriculturist has to contend with in the development of rustproof
+varieties.
+
+=365. Polymorphism.=—Plants that pass through different stages in
+their life history are said to be _polymorphic_, that is, of many
+forms. The habit is very common among the lower forms of vegetation.
+The fact that one or more of the phases are sometimes omitted, as
+the æcidium phase of wheat rust in warm climates, suggests the idea
+that it may be of use in helping the plant to tide over difficult
+conditions. Besides giving better chances of obtaining nourishment,
+it probably has the same effect as cross fertilization among
+flowering plants, in imparting increased strength and vitality to the
+succeeding generation. Wheat rust produced from barberry æcidia is
+said to be much more vigorous—and consequently more destructive—than
+when derived from a uredo that has reproduced itself for several
+generations.
+
+=366. The damage done by rust= to the host is through the destruction
+of its tissues by the mycelium. The chlorophyll is destroyed so that
+the plant can no longer manufacture food, and is too starved to
+produce good grain. There are many varieties of wheat rust, which
+have been found on twenty-seven different kinds of grain. Most
+of them are specialized to a particular host plant and will not,
+ordinarily (364), infest any other. Has this fact any bearing upon
+the production of rustproof varieties?
+
+
+          Practical Questions
+
+  1. Is a farmer wise to leave scabby and mildewed weeds and bushes
+  in the neighborhood of his grain fields? (364, 365.)
+
+  2. Are there any objections to the presence of volunteer grain
+  stalks along roadsides and in fence corners during winter? (364.)
+
+  3. Should cedar trees be allowed to grow near an apple orchard?
+  Give a reason for your answer. (p. 317, Material.)
+
+  4. Should diseased plants be plowed under? (361.)
+
+  5. What disposition should be made of them?
+
+  6. Ought diseased fruits to be left hanging on the tree?
+
+  7. Why is it necessary to pick over and discard from a crate or bin
+  all decaying fruits and vegetables?
+
+  8. Does a rotation of crops tend to prevent the spread of disease
+  in plants? Give reasons for your answer.
+
+  9. Are rustproof varieties to be relied on indefinitely? (364.)
+
+
+          D. MUSHROOMS
+
+  MATERIAL.—Any kind of gilled mushroom in different stages of
+  development, with a portion of the substratum on which it grows,
+  containing some of the so-called spawn. The common mushroom sold in
+  the markets (_Agaricus campestris_) can usually be obtained without
+  difficulty. Full directions for cultivating this fungus are given
+  in Bulletin 53 of the U. S. Department of Agriculture. From 6 to 12
+  hours before the lesson is to begin, cut the stem from the cap of a
+  mature specimen, close up to the gills, lay it, gills downward, on
+  a piece of clean paper, cover with a bowl or pan to keep the spores
+  from being blown about by the wind, and leave until a print (Fig.
+  466) has been formed.
+
+=367. Mushrooms and toadstools.=—The popular distinction which limits
+the term “mushroom” to a single species, the _Agaricus campestris_,
+and classes all others as toadstools, has no sanction in botany. All
+mushrooms are toadstools and all toadstools are mushrooms, whether
+poisonous or edible. The real distinction is between mushrooms and
+puffballs, the former term being more properly applied to fungi which
+have the spore-bearing surface exposed.
+
+=368. Examination of a typical specimen.=—The most highly specialized
+of the fungi, and the easiest to observe on account of their size and
+abundance, are the mushrooms that are such familiar objects after
+every summer shower. The _gilled_ kind—those with the rayed laminæ
+under the cap—are usually the most easily obtained. Specimens should
+be examined as soon after gathering as possible, since they decay
+very quickly.
+
+=369. The mycelium.=—Examine some of the white fibrous substance
+usually called spawn through a lens. Notice that it is made up of
+fine white threads interlacing with each other, and often forming
+webby mats that ramify to a considerable distance through the
+substratum of rotten wood or other material upon which the fungus
+grows. This webby structure, often mistaken for root fibers, is
+the thallus or true vegetative body of the plant, the part rising
+above ground, and usually regarded as the mushroom, being only the
+fruit, or reproductive organ. Place some of the mycelium under the
+microscope and notice that it is composed of delicate filaments made
+up of single cells placed end to end, as in Spirogyra (341). These
+filaments are called _hyphæ_.
+
+=370. The button.=—Look on the mycelium for one of the small round
+bodies called buttons (Fig. 457). These are the beginning of the
+fruiting body popularly known as the mushroom, and are of various
+sizes, some of the youngest being barely visible to the naked eye.
+After a time they begin to elongate and make their way out of the
+substratum.
+
+[Illustration: FIG. 457.—Mycelium of a mushroom (_Agaricus
+campestris_), with young buttons (fruiting organs) in different
+stages: 1, 2, 3, 4, 5, sections of fructification at successive
+periods of development; _m_, mycelium; _st_, stipe; _p_, pileus; _l_,
+gill, or lamina; _v_, veil.]
+
+[Illustration: FIG. 458.—Diagram of unexpanded _Amanita_, showing
+parts: _a_, volva; _b_, pileus; _c_, gills; _d_, veil; _e_, stipe;
+_m_, mycelium.]
+
+=371. The veil and the volva.=—Make a vertical section through the
+center of one of the larger buttons after it is well above ground,
+and sketch. Notice whether it is entirely enveloped from root to cap
+in a covering membrane—the _volva_ (Fig. 458, _a_)—or whether the
+enveloping membrane extends only from the upper part of the stem to
+the margin of the cap—the _veil_ (Fig. 458, _d_); whether it has both
+veil and volva, or finally, whether it is naked, that is, devoid of
+both.
+
+=372. The stipe, or stalk.=—Notice this as to length, thickness,
+color, and position; that is, whether it is inserted in the center
+of the cap or to one side (excentric), or on one edge (lateral).
+Observe the base, whether bulbous, tapering, or straight, and whether
+surrounded by a cup, or merely by concentric rings or ragged bits
+of membrane (the remains of the volva). Look for the _annulus_ or
+ring (remains of the veil) near the insertion of the stipe into the
+cap, and if there is one, notice whether it adheres to the stipe, or
+moves freely up and down (Fig. 459, _a_); whether it is thick and
+firm, or broad and membranous so that it hangs like a sort of curtain
+round the upper part of the stipe (Fig. 467, _a_). Break the stem
+and notice whether it is hollow or solid; observe also the texture,
+whether brittle, cartilaginous, fibrous, or fleshy.
+
+[Illustration: FIG. 459.—Parasol mushroom (_Lepiota procera_),
+showing movable annulus: _st_, stipe; _a_, annulus, or ring; _u_,
+umbo; _p_, _p_, floccose patches left by volva.]
+
+[Illustration: FIG. 460.—Chanterelle (_Cantharellus cibarius_), with
+infundibuliform pileus and decurrent gills.]
+
+=373. The pileus, or cap.=—Observe this as to color and surface,
+whether dry, or moist and sticky; smooth, or covered with scurf or
+scales left by the remains of the volva, as it was stretched and
+broken up by the expanding cap (Fig. 459, _p_, _p_). Note also the
+size and shape, whether conical, expanded, funnel-shaped (Fig. 460),
+or _umbonate_—having a protuberance at the apex (Fig. 459)—or whether
+the margin is turned up at the edge (revolute, Fig. 467), or under
+(involute, Fig. 459).
+
+=374. The gills, or laminæ.=—Look at the under surface and notice
+whether the gills are broad or narrow, whether they extend straight
+from stem to margin, or are rounded at the ends, or curved, toothed,
+or lobed in any way. Notice their attachment to the stipe, whether
+_free_, not touching it at all; _adnate_, attached squarely to the
+stem at their anterior ends; or _decurrent_, running down on the stem
+for a greater or less distance (Fig. 460).
+
+[Illustration: FIGS. 461-463.—Section of a gilled mushroom: 461,
+through one side, showing sections of the pendent gills, _g_, _g_
+(slightly magnified); 462, one of the gills more enlarged, showing
+the central tissue of the trama, _tr_, and the broad border formed by
+the hymenium, _h_; 463, a small section of one side of a gill very
+much enlarged, showing the club-shaped basidia, _b_, _b_, standing
+at right angles to the surface, bearing each two small branches with
+a spore, _s_, _s_, at the end. The sterile paraphyses, _p_, are seen
+mixed with the basidia.]
+
+[Illustration: FIGS. 464, 465.—A tube fungus (_Boletus edulis_): 464,
+entire; 465, section, showing position of the tubes.]
+
+=375. The hymenium.=—Cut a tangential section through one side of
+the pileus and sketch the section of the gills as they appear under
+a lens, or a low power of the microscope. Notice that the blade
+consists of a central portion called the _trama_ (_tr_, Fig. 462)
+and a somewhat thickened portion, _h_, constituting the _hymenium_,
+or spore-bearing surface. Now examine, under a high power, a small
+section from the edge of a gill, including a bit of the trama.
+Notice that this last consists of a tissue of mycelial cells (Fig.
+463) covered by the hymenium, or spore-bearing membrane, which is
+thickly clothed with a layer of elongated, club-shaped cells (_b_,
+_b_ and _p_, _p_, Fig. 463) set upon it at right angles to the
+surface. Some of these put out from two to four, or in some species
+as many as eight, little prongs, each bearing a spore (_s_, _s_,
+Fig. 463), while others remain sterile. The spore-bearing cells
+are called _basidia_; the sterile ones, _paraphyses_; and the
+whole spore-bearing surface together, the _hymenium_, from a Greek
+word meaning a membrane. It is from the presence of this expanded
+fruiting membrane that the class of mushrooms we are considering gets
+its botanical name, _Hymenomycetes_, membrane fungi. The hymenium
+is not always borne on gills, but is arranged in various ways which
+serve as a convenient basis for distinguishing the different orders.
+In the tube fungi, to which the edible boletus belongs (Figs. 464,
+465), the basidia are placed along the inside of little tubes that
+line the under side of the pileus, giving it the appearance of a
+honeycomb. In another order, the porcupine fungi, they are arranged
+on the outside of projecting spines or teeth, while in the morelles
+they are held in little cups or basins.
+
+[Illustration: FIG. 466.—Spore print of a gilled mushroom.]
+
+[Illustration: FIG. 467.—Deadly agaric (_Amanita phalloides_),
+showing the broad pendent annulus, _a_, formed by the ruptured veil;
+the cup at the base, _c_, and floccose patches on the pileus, left by
+the breaking up of the volva.]
+
+=376. Spore prints.=—When the gills are ripe, they shed their spores
+in great abundance. Take up the pileus that was laid on paper,
+as directed under Material, on page 323, and examine the print
+made by the discharged spores; it will be found to give an exact
+representation of the under side of the pileus.
+
+=377. The spores.=—Notice the color of the spores as shown in the
+print. This is a matter of importance in distinguishing gill-bearing
+fungi, which are divided into five sections according to the color of
+the spores. One source of danger, at least, to mushroom eaters would
+be avoided if this difference was always attended to, for the deadly
+amanita (_Amanita phalloides_) and the almost equally dangerous fly
+mushroom (_A. muscaria_) both have white spores, while the favorite
+edible kind (_Agaricus campestris_), though white-gilled when young,
+produces dark, purple-brown spores that cannot fail to distinguish it
+clearly for any one who will take the trouble to make a print.
+
+=378. Economic properties.=—Most of the wood-destroying fungi belong
+to this and allied orders. They are among the worst enemies the
+forester has to deal with (140), and millions of feet of lumber are
+destroyed every year by them.
+
+[Illustration: FIG. 468.—Portion of the root of a maple affected with
+rot caused by the mycelium of a fungus that has penetrated to its
+interior.]
+
+Over seven hundred kinds of fungi growing in the United States have
+been described as edible, but the evil repute into which the whole
+class has been brought by the poisonous qualities of a few species,
+and the difficulty, to any but an expert, of distinguishing between
+these and the harmless kinds, has caused them to be generally
+neglected as articles of diet. While they are pleasant relishes and
+furnish an agreeable variety to our daily fare, their food value has
+been greatly exaggerated. They contain a large proportion of water,
+often over 90 per cent, and the most valued of them, the _Agaricus
+campestris_, is about equivalent to cabbage in nutrient properties.
+
+
+          Practical Questions
+
+  1. Why are mushrooms generally grown in cellars? (186, 343.)
+
+  2. Name any fungi you know of that are good for food or medicine or
+  any other purpose.
+
+  3. Name the most dangerous ones you know of.
+
+  4. Do you find fungi most abundant on young and healthy trees, or
+  on old, decrepit ones? Account for the difference. (141, 343, 378.)
+
+  5. Do you ever find them growing on perfectly sound wood anywhere?
+
+  6. Are they ever beneficial to a tree? (86.)
+
+  7. Is it wise to leave old, unhealthy trees and decaying trunks in
+  a timber lot?
+
+
+          IV. LICHENS
+
+  MATERIAL.—Specimens can be found almost everywhere, growing on
+  rocks, walls, logs, stumps, and trees. Some of the more common
+  kind are: _Parmelia_, recognizable by the shallow spore cups borne
+  on the upper surface of the thallus; _Cladonia_, by the little
+  stalked receptacles, like goblets, in which its spores are held;
+  _Physcia_, by its bright orange color. Where practicable, it is
+  well to have several different kinds for comparison. Iceland moss
+  (_Cetraria islandica_) can generally be obtained from the grocers,
+  and is a good example of an intermediate form between foliaceous
+  and fruticose lichens.
+
+  If the specimens are very dry, they will be too brittle to handle
+  conveniently, and should be moistened by soaking a short time in
+  water. This will render them quite flexible and also bring out the
+  green color more clearly.
+
+[Illustration: FIG. 469.—Foliaceous lichens: _A_, _Xanthoria
+(Physcia) parietina_; _B_, _Parmelia conspersa_; _a_, spore cups.]
+
+=379. Examination of a typical specimen.=—The commonest kind of
+lichens, and generally the most easily obtained, are those that
+grow on rocks and tree trunks in flat, spreading patches. Their
+margins are much dented and curled, giving them a somewhat leaflike
+appearance, whence they are called “foliaceous” lichens. This broad,
+expanded body is the thallus, or vegetative part, as distinguished
+from its reproductive part. Examine carefully the thallus of your
+specimen. Note the size and shape of the indentations. Is there any
+order or regularity about them, such as was observed in the lobing of
+leaves? Is there any difference in color between the upper and under
+sides? What other differences do you notice? Do you see anything
+like hairs, or rootlets, on the under side? Mount one of them in
+water and place under the microscope. What does it look like? Compare
+with one of the hairs from a leaf of mullein, gromwell, blueweed, or
+other hairy plant, with the hypha of a fungus mycelium, and with your
+study of the root hair in 67 (_a_). Is it a hair or a root? These
+rootlike hairs are called _rhizoids_, and serve to anchor the lichen
+to its substratum. Look on the upper side for little cup-shaped or
+saucer-shaped receptacles. On what part of the thallus are they
+situated? Examine with a lens and see if you can make out what they
+contain. These cups are the spore cases. The lichen fungus belongs to
+the division of sac fungi, which produce their spores in closed sacs,
+or cups.
+
+[Illustration: FIG. 470.—Portion of the thallus of a lichen,
+magnified, showing imprisoned algæ.]
+
+=380. Structure of the thallus.=—Make a thin section through a
+thallus and place under the microscope. Notice the small green bodies
+enveloped in the hyphæ of the fungus. Are they most abundant near the
+upper or the lower epidermis? Has their green color anything to do
+with this, and with the difference in color between the two surfaces
+of the thallus? (184.) Do they look like chlorophyll granules? Can
+you tell what they are? Compare with your study of the unicellular
+algæ (337) and with Fig. 429. Does this throw any light on their real
+nature?
+
+[Illustration: FIG. 471.—Artificial lichen mycelium, _m_, made by
+sowing spores of a fungus, _sp_, among alga cells, _a_.]
+
+=381. The lichen thallus a composite body.=—You will probably have no
+difficulty in making out that these small round bodies are green algæ
+of some kind, but of what species will depend upon the kind of lichen
+with which it is associated. In Cladonia and the bearded lichen
+(Fig. 473), it is a protococcus; in other forms, a pleurococcus or a
+nostoc—and so on, each species of lichen fungus being specialized to
+a certain form of alga. The great botanist, De Bary, showed that it
+is even possible to produce a lichen thallus artificially by sowing
+the spores of a fungus among the cells of the particular alga with
+which it is able to unite. The spores will germinate without the
+alga, but soon perish unless they come in contact with the right
+one. It is thus made clear that the lichen plant as a whole is a
+combination of elements belonging to two distinct orders, the algæ
+and fungi, but so closely associated as to constitute practically a
+single individual.
+
+=382. Slavery, or partnership?=—Now, what can be the object of this
+peculiar association? Is it a symbiosis, or a case of enslavement?
+The fungi, as we know, are all parasites, unable to manufacture
+their own food or to exist at all except at the expense of other
+organisms, living or dead. But the lichens have refined upon the
+gross rapacity of their order, and instead of indiscriminately
+destroying the hosts that furnish their nourishment, have used their
+victims to better purpose by converting them into contented, well-fed
+slaves! The imprisoned algæ perform for them the same service that
+the chlorophyll bodies do for the higher plants, and so the lichen
+fungi have the advantage of other parasites in getting their food
+manufactured at home, so to speak. And while the algæ have to do
+double work in order to feed both themselves and their masters,
+the fungus, in return, shelters them against cold and drought, and
+prolongs their growing period by giving them a more continuous supply
+of moisture and food materials, which it draws from the substratum by
+means of its rhizoids. In this way both plants are enabled to live in
+situations that neither could occupy without the other.
+
+[Illustration: FIG. 472.—A crustaceous lichen (_Graphis elegans_)
+growing on holly: _A_, natural size; _B_, slightly magnified.]
+
+=383. Reproduction.=—The multiplication of the lichen algæ is
+exclusively vegetative. The fungus, on the other hand, reproduces
+normally by spores, and the fruiting bodies found on the thallus
+originate from the fungus mycelium.
+
+=384. Classification.=—To be strictly accurate, the two kinds of
+vegetable bodies that make up the lichen thallus would probably have
+to be classified separately, as algæ or fungi, respectively, but as
+fructification is the generally accepted basis of classification,
+and the plant body is too intimately permeated with both kinds of
+tissue to be divided, each lichen body as a whole is classed with
+its particular kind of fungus. The entire group, on account of the
+distinctive characters that mark it, is placed in a separate order
+of its own. This includes three principal divisions, distributed
+according to the shape of the thallus, and its habit of growth:
+(1) _Crustaceous_, those that adhere closely to the substratum, as
+if glued or inscribed on it; (2) _Foliaceous_, with a broad, more
+or less lobed and leaflike thallus that adheres loosely to the
+substratum by means of rhizoids springing from its under surface; (3)
+_Fruticose_, with branching, stemlike thallus attached at the base
+like a regularly rooting plant (Figs. 473, 474). Among these are the
+Iceland moss, used as an article of food by man, and the reindeer
+moss (_Cladonia rangiferina_), which is the chief sustenance of the
+reindeer.
+
+[Illustration: FIGS. 473, 474.—Fruticose lichens: 473, _Usnea
+barbata_, bearded lichen; 474, _Cladonia rangiferina_, reindeer moss:
+_A_, sterile; _B_, fruiting portion.]
+
+
+          Practical Questions
+
+  1. Have lichens any economic value? (384.)
+
+  2. In what way are they most useful? (320.)
+
+  3. Do you find them, as a general thing, on healthy young trees and
+  boughs, or on old ones, and those showing signs of decay?
+
+  4. Do you ever find them growing on trees or other objects in
+  densely inhabited areas,—cities, large towns, and manufacturing
+  centers?
+
+  5. Do they grow more thickly on the shady (northern) side of
+  rocks, walls, and trees growing in the open, than on the sunny and
+  (presumably) warmer sides?
+
+  6. Mention some ways in which a growth of lichens might be
+  beneficial to a tree.
+
+  7. In what ways could it be harmful?
+
+
+          V. LIVERWORTS
+
+  MATERIAL.—Liverworts can generally be found growing with mosses
+  in damp, shady places, and are easily recognized by their flat,
+  spreading habit, which gives them the appearance of green lichens.
+  _Marchantia polymorpha_ (Fig. 475), one of the largest and best
+  specimens for study, is common in shady, damp ground throughout
+  the states. It is diœcious, and specimens bearing both male and
+  female organs should be provided. _Lunularia_, a smaller species
+  that can be recognized by the little crescent-shaped receptacles on
+  some of the divisions of the thallus, is abundant in greenhouses on
+  the floor, or on the sides of pots and boxes kept in damp places;
+  but the spore-bearing receptacles are seldom or never present, the
+  species being an introduced one and possibly rendered sterile by
+  changed conditions. _Anthoceros_ (Fig. 426) and leafy liverworts,
+  such as that shown in Fig. 484, also make good examples for study.
+
+  EXPERIMENT 97. WHY ARE THE UPPER AND UNDER SIDES OF A LIVERWORT
+  DIFFERENT?—Plant a growing branch of marchantia, or of any flat,
+  spreading liverwort, in moist earth so that the upper side will lie
+  next the soil, and watch for a week or two, noting the changes that
+  take place. What would you infer from these as to the cause of any
+  differences that may have been observed between the two surfaces?
+
+=385. Examination of a typical liverwort=—The thallus.—The broad,
+flat, branching organ that forms the body of the plant is the
+thallus. Examine the end of each branch; what do you find there? Are
+the two forks into which the apex of the branches divides equal or
+unequal? Compare the growing end with the distal one; does it proceed
+from a true root? Notice that as the lower end dies, the growing
+branches go on increasing and reproducing the thallus.
+
+[Illustration: FIGS. 475, 476.—Umbrella liverwort (_Marchantia
+polymorpha_): 475, portion of a female thallus about natural size,
+showing dichotomous branching; _f_, _f_, archegonial or female
+receptacles; _r_, rhizoids; 476, portion of a male thallus bearing an
+antheridial disk or receptacle, _d_, and gemmæ, _g_, _g_.]
+
+[Illustration: FIG. 477.—A portion of the upper epidermis of
+marchantia, magnified, showing rhomboidal plates with a stoma in
+each.]
+
+Do you find anything like a midrib? If so, trace it through the
+branches and body of the thallus; where does it end? Does it seem
+to be formed like the midrib of a leaf? Hold a piece of the thallus
+up to the light and see if you can detect any veins. Is it of the
+same color in all parts, and if there is a difference, can you give
+a reason for it? Examine the upper surface with a lens. Peel off a
+piece of the epidermis, place it under a low power of the microscope,
+or between two moistened bits of glass, and hold up to the light,
+keeping the upper surface toward you; what is its appearance?
+Observe a tiny dot near the center of the rhomboidal areas into which
+the epidermis is divided and compare it with your drawings of stomata
+(181, 183). What would you judge that these dots are for? While
+differing in structure from the stomata of leaves, they serve the
+same purposes and may be regarded a more rudimentary form of the same
+organ.
+
+=386. Rhizoids.=—Wash the dirt from the under side of a thallus and
+examine with a lens; how does it differ from the upper surface? Do
+you see anything like roots? Place one in a drop of water under the
+microscope. Compare with similar organs found on the lichen (379).
+What are they? Would rhizoids be of any use on the upper side?
+stomata on the under side?
+
+=387. Gemmæ.=—Look along the upper surface for little saucer-shaped
+(in lunularia, crescent-shaped) cupules (_g_, _g_, Fig. 476). Notice
+their shape and position, whether on a midrib or near the margin.
+Examine the contents with a lens and see if you can tell what they
+are. These little bodies, called _gemmæ_, are of the nature of
+buds, by which the plant propagates itself vegetatively somewhat
+as the onion and the tiger lily do by means of bulblets. Sow some
+of the gemmæ on moist sand, cover them with a tumbler to prevent
+evaporation, and watch them develop the thalloid structure.
+
+=388. The fruiting receptacles.=—Procure, if possible, thalli with
+upright pedicels bearing flattened enlargements at the top (Figs.
+475, 476). These are thallus branches modified into receptacles
+containing the reproductive organs, which, in marchantia, are
+diœcious, the two kinds growing on separate thalli. Notice their
+difference in shape, one kind being slightly lobed or scalloped, the
+other rayed like the spokes of a wheel. The first kind are known as
+_antheridial_, or male, receptacles; the second as _archegonial_, or
+female.
+
+=389. The antheridia.=—Examine one of the male receptacles on
+both surfaces and in vertical section. Notice the tiny egg-shaped
+bodies sunk in little cavities between the lobes just under the
+upper epidermis (Fig. 478). These are antheridia. When mature, they
+rupture at the apex, and multitudes of extremely small bodies, called
+_antherozoids_, or _spermatozoids_, are discharged from them.
+
+[Illustration: FIG. 478.—Longitudinal section of a male receptacle of
+marchantia polymorpha, magnified: _a_, antheridia; _t_, thallus; _s_,
+ventral scales; _r_, rhizoids.]
+
+[Illustration: FIG. 479.—Under side of an archegonial receptacle
+enlarged. The archegonia are borne among the hairs on the under
+surface, which is presented to view in the figure; _f_, a spore case.]
+
+=390. Archegonia.=—Next examine one of the female receptacles. Look
+on the under surface, between the narrow divisions of the receptacle,
+for radiating rows of flask-shaped bodies with their necks turned
+downward, and all surrounded by a toothed sheath or involucre
+(Fig. 479). These bodies are the archegonia, or female organs, and
+correspond, loosely speaking, to the ovaries of flowering plants. If
+the receptacle is a mature one, the archegonia will be replaced by
+the ripe spore cases (_sporangia_), as at _f_, Fig. 479.
+
+Make enlarged drawings of the upper surface of a male and a female
+receptacle, and of a vertical section of each, passing through
+an antheridium in the male, and an archegonial row in the female
+receptacle. Label the parts observed in each.
+
+=391. Minute study of an archegonium.=—Place under the microscope
+a very thin, longitudinal section through a ray of a receptacle
+containing a young archegonium, and observe that the latter consists
+of a lower portion, the _venter_, _v_, Fig. 480, and an upper part,
+the neck, which is perforated by the _neck canal_, _ca_. The venter
+contains the _egg cell_, _o_, and the ventral canal cell, _vc_. The
+neck canal is filled with small cells which, at maturity, dissolve
+into a mucilaginous substance that swells on being wet and discharges
+itself through the top of the neck, leaving an open passage to the
+venter, where the egg cell is ready to be fertilized.
+
+[Illustration: FIGS. 480, 481.—480, young archegonium of M.
+polymorpha; _v_, ventral portion; _o_, egg cell; _vc_, ventral canal
+and cells; _ca_, neck canal with cells; 481, the same ready for
+fertilization after discharge of the mucilaginous fluid.]
+
+Make a drawing of the section as seen under the microscope, labeling
+all the parts.
+
+=392. Fertilization.=—In the liverworts, and in cryptogams generally,
+this process has to take place under water, as the antherozoids are
+motile only in a liquid, but the amount required is so small that a
+few drops of rain or dew will enable them to make their journey to
+the archegonium. The mucilaginous substances discharged from the neck
+canal attract them to the mouth of the opening, one or more of them
+penetrates to the egg cell, and fertilization is accomplished. Do you
+see any analogies between this and the same function among flowering
+plants? (250, 251.)
+
+=393. The spore case.=—After fertilization the egg becomes an
+_oöspore_, capable of producing a new plant. Instead, however, of
+separating from the mother plant and giving rise to an independent
+growth, it germinates within the archegonium and produces there a
+small, stalked body, called a _sporogonium_, or _sporophyte_, which
+at length ripens into a spore case, as shown at _f_, Fig. 479. At
+maturity this capsule-like sporophyte ruptures at the apex, and
+discharges a mass of spores, mingled with elongated filaments
+called _elators_, which, by their elastic movements, assist in
+disseminating the spores. These latter, on germinating, produce,
+not a simple sporophyte like that which bore them, but the thallus
+of the liverwort with all its complicated arrangement of antheridia
+and archegonia and vegetative organs that seem to foreshadow, by the
+analogies they suggest, the coming of the higher plants.
+
+=394. Sexual and asexual reproduction.=—We find here a very marked
+change from the simple reproductive processes observed in the algæ
+and fungi. In the forms thus far considered, this function was
+carried on mainly by simple vegetative fission or budding, with a
+more or less irregular intervention of resting spores. If only one
+kind of spore is concerned, reproduction is said to be _asexual_.
+When two different kinds of cells, the egg and sperm cell, unite to
+form an oöspore, as in the liverworts, reproduction is said to be
+_sexual_. While sexual reproduction takes place to some extent among
+both algæ and fungi, the prevailing method among thallophytes is
+asexual, and may be carried on in three different ways: by fission
+(and budding), by resting spores, and by conjugation.
+
+Representing the plant body by _A_ and the resting spores by _a_,
+the primitive asexual processes may be expressed to the eye by the
+accompanying formulas:—
+
+    (1) Fission and budding: _A_ → _A_ → _A_ → _A_ →
+    (2) Resting spores: _A a_ → _A a_ → _A a_ →
+    (3) Conjugation: _A_ + _A_ → _a_ → _A_ + _A_ → _a_ →
+
+In (3), as was seen in the conjugating cells of the spirogyra (342),
+the method is a little more complicated, showing an approach toward
+the sexual process. In each of these cases, however, there is only
+one kind of cell concerned, while in the liverworts there are not
+only different kinds, technically known as _gametes_, but specialized
+organs, archegonia and antheridia, for producing them. The thallus
+body bearing these organs is termed the _gametophyte_, because it
+bears the gametes, or sexual organs,—the suffix _phyte_ meaning a
+plant; for example, _epiphyte_, on or upon plants; _spermophyte_,
+or _spermatophyte_, seed plant; _sporophyte_, spore plant. The
+_sporophyte_, produced within the archegonium, bears simple nonsexual
+spores that are capable of germinating independently. Structurally it
+is a separate, individual organism, though it does not appear as such
+in this class, but lives inclosed in the archegonium, as a parasite
+on the mother plant.
+
+=395. Alternation of generations.=—If we represent the sporophyte
+by _S_, the thallus, or gametophyte, by _G_, the female gamete, or
+egg cell, by _fg_, the antherozoids (male gametes) by _mg_, the
+fertilized egg cell, or oöspore, resulting from their union by _oös_,
+and the asexual spores discharged from the sporophyte by _o_, this
+complicated mode of reproduction may be expressed diagrammatically as
+follows:—
+
+       _fg_                     _fg_
+      ╱    ╲                   ╱    ╲
+  _G_        _oös_→_s_→_o_→_G_        _oös_→_s_→_o_→_G_→etc.
+      ╲    ╱                   ╲    ╱
+       _mg_                     _mg_
+
+A glance at the diagram will show a continual interchange of the
+sexual and asexual modes of reproduction, in which each generation
+gives rise to its _opposite_, the asexual sporophyte producing
+the sexual gametophyte, and this in turn, through its gametes,
+giving rise to the asexual sporophyte. This regular recurrence
+in genealogical succession of two differing forms is what is
+meant by the expression “alternation of generations.” Analogous
+processes occur also among some of the thallophytes, but as there
+is no well-defined differentiation of sporophyte and gametophyte,
+alternation proper may be regarded as beginning with the bryophytes.
+The subject is a complicated one and somewhat difficult to grasp,
+but it is important to form a correct idea of it and to fix clearly
+in mind the different modes of reproduction as we proceed from the
+lower to the higher forms of vegetation, since in this way alone can
+their biological relationships and their order of succession in the
+evolutionary scale be made intelligible.
+
+
+          VI. MOSSES
+
+  MATERIAL.—One of the most widely distributed of mosses is the
+  Sphagnum, or peat moss, so generally used by florists in packing
+  plants for shipment, and it can be obtained from them at almost all
+  times. It is rather difficult, however, to find specimens with the
+  fruiting organs, since they are rarely to be met with except in
+  late autumn or early spring. Other common forms are _Polytrichum_,
+  _Funaria_, and _Mnium_, any of which will meet all essential
+  conditions of the study outlined in the text.
+
+[Illustration: FIGS. 482, 483.—Protonema of a moss: 482, germinating
+spore; 483, protonema; _kn_, buds; _r_, rhizoids; _s_, spore.]
+
+=396. The protonema or thallus stage.=—In mosses the sexual, or
+gametophyte generation differs from that of liverworts in undergoing
+two phases. The germinating cells of the sporophyte do not develop
+immediately into the leafy stem, which is the typical gametophyte
+of true mosses, but produce first a filamentous, creeping structure
+called the _protonema_ (Fig. 483), that spreads over the ground
+and forms the tangled green felt usually observed where mosses are
+growing. Place a few of these filaments on a slide in water, and
+examine under the microscope. Do they remind you of any of the
+forms of algæ? Look near the base of the branches for knots or
+enlargements, like those seen at _kn_, Fig. 483. These are buds
+from which the leafy moss stems will develop. Do they correspond
+to anything observed among the thallophytes? Notice the rootlike
+filaments that extend under ground; how do they differ from the ones
+above ground? Why are they colorless? How do you know that they are
+not true roots? [67 (_a_), 379.] Sketch one of each kind of filament
+sufficiently enlarged to show the cells composing it.
+
+A protonema that arises directly from the spore is said to be
+_primary_, while those which sometimes spring from rhizoids above
+ground, or from stems or leaves, are _secondary_. The fact that a
+protonema can bud from parts of the fruiting stems shows that the two
+do not belong to different generations, but are merely successive
+stages of a single generation, and both together compose the
+gametophyte.
+
+=397. The leafy stage.=—In their fully developed state the true
+mosses show a marked advance in organization over the liverworts.
+There is a distinct differentiation of the growing axis into stem
+and leaves, though no true roots are formed. The leaves are arranged
+spirally, on upright stems, while in the liverworts the vegetative
+body is either a flat, spreading thallus, or the leaves are arranged
+horizontally on opposite sides of a prostrate, or more or less
+inclined, axis. Sometimes a second set occurs, on the upper side of
+the axis, but in this case the leaves are usually much smaller and
+inclined to the horizontal arrangement, as shown in Fig. 484.
+
+[Illustration: FIG. 484.—Scapania, a liverwort with leafy thallus,
+approaching the form of mosses and lycopodiums. (_From_ COULTER’S
+“Plant Structures.”)]
+
+[Illustration: FIG. 485.—Fruiting receptacle of a moss (_Phascum
+cuspidatum_), bearing both antheridia, _an_, and archegonia, _ar_, at
+the bifurcated apex; _b_, leaves; _p_, paraphyses.]
+
+[Illustration: FIG. 486.—Fruiting stem of a moss (_Polytrichum
+commune_) with ripe capsules: _s_, seta, or footstalk; _c_, capsule
+with calyptra; _f_, capsule after the calyptra has fallen away; _d_,
+operculum, or lid.]
+
+=398. The reproductive organs.=—The antheridia and archegonia are
+borne in groups at the end either of the main axes, or of lateral
+branches (Figs. 485, 486), but as a rule only one archegonium is
+fertilized, so the mature sporogonia are solitary. The plants may be
+either diœcious or monœcious, as in Fig. 485; and in the latter case,
+the reproductive organs may be borne on the same, or on different,
+receptacles. The antheridia and the archegonia are both mixed with
+club-shaped hairs called paraphyses (Fig. 485).
+
+=399. The sporophyte.=—An examination of the fruiting capsule of any
+of the true mosses will show that it consists of a long footstalk,
+the _seta_, _s_, Fig. 486, bearing a capsule, or ripened sporogonium,
+_f_, which is at first surmounted by a cap or hood, known as the
+_calyptra_, _c_. The hood represents the excessively developed and
+often highly specialized wall of the archegonium. It falls away at
+maturity, and the spores are discharged through an opening made by
+the removal of the _operculum_, or lid, _d_. The spores and the
+capsule are both developed from the fertilized egg (oöspore), within
+the archegonium, in much the same manner as in the liverworts, and
+together constitute the sporophyte, or asexual generation. It never
+leads a completely independent existence, but remains a partial
+parasite on the mother plant, though the lower part of the young
+sporogonium is usually provided with stomata and chlorophyll so
+that it is capable of manufacturing food. In this respect it shows
+a distinct advance on the corresponding phase of the liverworts—if
+we except the single genus _Anthoceros_, which alone among the
+liverworts has the cells of the sporogonium provided with chlorophyll.
+
+=400. Alternation of generations.=—The process of reproduction
+in mosses is so closely similar to that of liverworts that it is
+unnecessary to repeat the details. There are some minor variations,
+but in all essentials the processes are the same and may be
+represented to the eye by the same formula.
+
+=401. Relative position of mosses and liverworts in the line of
+evolution.=—Though mosses, as a rule, show a higher degree of
+organization than liverworts, in both generations, their development
+has been _away_ from the general course of evolution followed by
+the higher plants. This, as will be seen later, tends towards a
+decreasing complexity of the gametophyte with increasing complexity
+of the sporophyte, while the mosses show increasing complexity of
+_both_. Like the order of birds in the animal kingdom, they form a
+highly specialized and somewhat isolated group. While they may be
+regarded as descendants from a common ancestral stock with the ferns
+and club mosses, they have been switched off, so to speak, on a
+side track of the great evolutionary trunk line, and their advance
+on this side track has carried them to a point more remote from the
+course along which the higher forms of plant life have traveled than
+the distant junction at which they branched off from their less
+progressive kindred, the humble liverworts.
+
+
+          VII. FERN PLANTS
+
+  MATERIAL.—Any kind of fern in the fruiting stage. Several different
+  varieties should be cultivated in the schoolroom for observation.
+  While gathering specimens, look along the ground under the fronds,
+  or in greenhouses where ferns are cultivated, among the pots and
+  on the floor, for a small, heart-shaped body like that represented
+  in Figs. 501, 502, called a _prothallium_. It is found only in
+  moist and shady places, and care should be taken in collecting
+  specimens, as in their early stages the prothallia bear a strong
+  resemblance to certain liverworts found in the same situations. The
+  best way is for each class to raise its own specimens by scattering
+  the spores of a fern in a glass jar, on the bottom of which is a
+  bed of moist sand or blotting paper. Cover the jar loosely with a
+  sheet of glass and keep it moist and warm, and not in too bright a
+  light. Spores of the sensitive ferns (_Onoclea_) will germinate in
+  from two to ten days, according to the temperature. Those of the
+  royal fern (_Osmunda_) germinate promptly if sown as soon as ripe,
+  but if kept even for a few weeks are apt to lose their vitality.
+  The spores of sensitive fern can be kept for six months or longer,
+  while those of the bracken (_Pteris_) and various other species
+  require a rest before germinating, so that in these cases it is
+  better to use spores of the previous season.
+
+[Illustration: FIGS. 487-491.—A fern plant: 487, fronds and
+rootstock; 488, fertile pinna: _s_, _s_, sori; 489, cross section of
+a stipe, showing ends of the fibrovascular bundles; 490, a cluster of
+sporangia, magnified; 491, a single sporangium still more magnified,
+shedding its spores.]
+
+=402. Study of a typical fern.=—Observe the size and general outline
+of the fronds, and note whether those of the same plant are all
+alike, or if they differ in any way, and how. Observe the shape
+and texture of the divisions or pinnæ composing the frond, their
+mode of attachment to the rachis, and whether they are simple, or
+notched, or branched in any way. Hold a pinna up to the light and
+notice the veining. Is it like any of the kinds described in 171,
+172? In what respect is it different? This forked venation is a very
+general characteristic of ferns. When the forks do not reticulate
+or intercross, the veins are said to be free; are they free in your
+specimen, or reticulated? Make a sketch, labeling the primary
+branches of the frond, _pinnæ_ (sing., _pinna_), the secondary ones,
+if any, _pinnules_, and the common stalk that supports them, _stipe_.
+Note the color, texture, and surface of the stipe. If any appendages
+are present, such as hairs, chaff, or scales (in Pteris, nectar
+glands), notice whether they are equally distributed. If not, where
+are they most abundant?
+
+Examine the mode of attachment of the stipes to their underground
+axis. Break one away and examine the scar. Compare with your drawings
+of leaf scars and with Fig. 105. Do the stipes grow from a root or a
+rhizome? How do you know? Do you find any remains of leafstalks of
+previous years? How does the rootstock increase in length? Measure
+some of the internodes; how much did it increase each year? Cut a
+cross section and look for the ends of the fibrovascular bundles.
+Trace their course through several internodes. Do they run straight,
+or do they turn or bend in any way at the nodes? If so, where do they
+go? Do you see anything like roots? Where do they originate? Put one
+of them under the microscope and find out whether they are roots or
+hairs.
+
+True roots are first developed in the pteridophytes. Since those of
+the fern spring from an underground stem, to what class of roots do
+they belong? (83.)
+
+=403. Minute study of a fern stem.=—Place a very thin section of
+a fern rhizoma, or of the stipe of a frond, under the microscope.
+Except in very young stems the vascular bundles are arranged in a
+ring, or sometimes in two or more rings (Fig. 492), with plates of
+strengthening tissue, _l_, _l_, between the inner and outer rings.
+Notice the inner epidermal layer of hard brown tissue, and within
+that, the soft parenchyma, which fills the rest of the interior. Test
+it with iodine and observe how rich in starch it is. If the section
+of a petiole is under observation, the details will be somewhat
+different; would you expect to find as much starch in the stipe as in
+the rootstock? Why, or why not?
+
+Make a longitudinal section of a rhizome through the point where
+a leafstalk is attached and trace the course of the bundles. This
+will be facilitated if the specimen has stood in eosin solution a
+few hours. Make enlarged drawings of both sections, labeling all the
+parts.
+
+[Illustration: FIG. 492.—Diagram of a cross section through the
+stem of a fern (_Pteris_): _s_, _s_, _s_, rings of fibrovascular
+bundles; _l_, _l_, plates of strengthening tissue, with a ring of
+fibrovascular bundles between them; _lp_, zone of strengthening
+fibers; _r_, cortex; _e_, epidermis.]
+
+[Illustration: FIGS. 493-494.—Parts of fertile pinnæ: 493, of
+_polypodium_, enlarged, showing the sori without indusium; 494, of
+_pellea_, showing indusium formed by the revolute margin.]
+
+Clearly differentiated conducting bundles occur in the mosses,
+but they are of much simpler structure than in the pteridophytes,
+consisting usually of a single central strand, and are found
+more frequently in the leaves than in the stems. A true vascular
+structure appears first in the pteridophytes, whence these plants are
+distinguished as _vascular cryptogams_.
+
+=404. Fructification.=—Examine the back of a fruiting frond; what
+do you find there? These dots are the _sori_ (sing., _sorus_), or
+spore clusters, and the fronds or pinnæ bearing them are said to be
+_fertile_. Are there any differences of size, shape, etc., between
+the fertile and the sterile fronds of your specimen? between the
+fertile and the sterile pinnæ? On what part of the frond are the
+fertile pinnæ borne? Notice the shape and position of the sori,
+and their relation to the veins, whether borne at the tips, in the
+forks, on the upper side (toward the margin), or the lower (toward
+the midrib). Look for a delicate membrane (_indusium_) covering the
+sori, and observe its shape and mode of attachment. If the specimen
+under examination is a polypodium, there will be no indusium; if a
+maidenhair, or a bracken, it will be formed of the revolute margin
+of the pinna. In lady fern and Christmas fern (_Aspidium_), the sori
+frequently become confluent, that is, so close together as to appear
+like a solid mass. Sketch a fertile pinna as it appears under the
+lens, bringing out all the points noted.
+
+[Illustration: FIGS. 495-496.—Christmas fern (_Aspidium_): 495, part
+of a fertile frond, natural size; 496, a pinna enlarged, showing the
+sori confluent under the peltate indusia.]
+
+[Illustration: FIGS. 497-500.—Spores of pteridophytes, magnified:
+497, a fern spore; 498, 499, two views of a spore of a club moss;
+500, spore of a common horsetail (_Equisetum arveuse_).]
+
+=405. The spore cases.=—Look under the indusium at the cluster
+of little stalked circular appendages (Fig. 490). These are the
+_sporangia_, or spore cases, in which the reproductive bodies are
+borne. Place one of them under the microscope, and it will be found
+to consist of a little stalked circular body like a tennis racket
+(Fig. 491), surrounded by a jointed ring called the _annulus_. Watch
+a few moments and see if you can find out the use of the annulus. If
+not, warm the slide and you will probably see the ring straighten
+itself with a sudden jerk, rupturing the wall of the sporangium and
+discharging the spores with considerable force. If this does not
+happen, add a drop of strong glycerine to a specimen mounted in
+water; the rupture will be apt to follow quickly. What causes it, in
+either case? [56, (1); Exp. 19.]
+
+=406. The sporophyte.=—The spores found in such abundance on the
+fertile pinnæ; are all alike, and each one is capable of germinating
+and continuing the work of reproduction as effectually as the sexual
+spores of the bryophytes. The fertile frond, or part of a frond, on
+which they are borne is called a _sporophyll_ (spore-bearing leaf),
+and the entire plant is the _sporophyte_, which, with its crop of
+spores, makes up one generation.
+
+It is important to observe that in the ferns and in all pteridophytes
+the sporophyte is the conspicuous and highly organized body that
+is commonly recognized as the normal growing plant; while with the
+bryophytes just the reverse holds true,—the sexual generation,
+or gametophyte, represents the normal plant structure, while the
+sporophyte is an insignificant appendage which never attains an
+independent existence. Broadly speaking, in bryophytes, it is a spore
+fruit; in the pteridophytes and spermatophytes a highly developed
+plant.
+
+[Illustration: FIGS. 501, 502.—Prothallium of a common fern
+(_Aspidium_): 501, under surface, showing rhizoids, _rh_, antheridia,
+_an_, and archegonia, _ar_; 502, under surface of an older
+gametophyte, showing rhizoids, _rh_, young sporophyte, with root,
+_w_, and leaf, _b_.]
+
+=407. The gametophyte.=—When one of these asexual spores germinates,
+it produces, not a fern plant like the one that bore it, but a small,
+heart-shaped body like that shown in Fig. 501. Examine one of these
+bodies carefully with a lens. Observe that there are no veins nor
+fibrovascular bundles, and the whole body of the plant seems to
+consist of one uniform tissue. Compare it with the forked apex of
+a branching thallus of a liverwort. Do you perceive any points of
+similarity? The two are, in fact, morphologically the same. This
+heart-shaped body is called a _prothallium_, and is the gametophyte
+of the fern. It may be of different shapes, and in some species is
+branching and filamentous, like the protonema of a moss. Generally,
+however, it is flat and more or less two-lobed, as shown in Fig.
+501. It is small and inconspicuous and very short-lived, being of
+importance only in connection with the work of reproduction.
+
+Look with your lens for a cluster of small, bottle-shaped bodies
+just below the deep cleft in the heart. If you cannot make out what
+they are, put a thin section through a part of the prothallium
+containing one under the microscope, and you will see that they are
+the archegonia. Lower down among the rhizoids, near the pointed base,
+will be found the antheridia. In some species the prothalli are
+diœcious, one kind bearing antheridia, the other archegonia, but this
+is rare among the true ferns.
+
+[Illustration: FIG. 503.—Young archegonium of a fern, magnified: _K_,
+neck canal cell; _K′_, ventral canal cell: _O_, egg cell.]
+
+=408. Fertilization.=—This process is the same in all essentials as
+in the bryophytes. As in other cryptogams, it can take place only
+under water,—a circumstance which points to an aquatic origin for
+this sub-kingdom, and through them to the entire flora of the globe.
+The archegonia differ somewhat in shape from those of the liverworts
+and mosses, but a section under the microscope will show that they
+consist of essentially the same parts. On account of the similarity
+of these organs, the pteridophytes and bryophytes are often classed
+together as _Archegoniates_.
+
+=409. Alternation of generations.=—Among the section of ferns that
+we have been considering, the order of alternation corresponds in
+all essentials to that prevailing among the bryophytes, and may
+be represented by the same formula. The chief difference is in the
+relatively much greater importance of the sporophyte, which may be
+expressed by putting it first:—
+
+               _fg_                     _fg_
+              ╱    ╲                   ╱    ╲
+  _S_→_o_→_G_        _oös_→_S_→_o_→_G_        _oös_→_S_→_o_→_G_ etc.
+              ╲    ╱                   ╲    ╱
+               _mg_                     _mg_
+
+But some of the pteridophytes—of which the Selaginella offers a
+conspicuous example—have differentiated their asexual spores (_o_
+of the formula) into two kinds, large and small, known respectively
+as _megaspores_ and _microspores_. The prothallia developed by the
+former bear archegonia containing female gametes only; those by the
+latter, antheridia containing male gametes—while in the diœcious
+bryophytes, the archegonial and antheridial thalli are produced by
+spores of the same kind.
+
+[Illustration: FIGS. 504.-508.—A kind of pteridophyte (_Selaginella
+martensii_) with its organs of fructification: 504, a fruiting
+branch; 505, a microsporophyll with a microsporangium, showing
+microspores through a rupture in the wall; 506, a megasporophyll
+with a megasporangium; 507, megaspores; 508, microspores. (_From_
+COULTER’S “Plant Structures.”)]
+
+The differentiation of the asexual spores in the higher pteridophytes
+gives rise to corresponding changes in the sporangia that bear
+them, and even in the sporophylls themselves, one kind bearing
+microsporangia only, the other megasporangia. In this way the
+differentiation of sex is pushed back, step by step, until it
+virtually begins with the sporophyte, or asexual generation.
+
+Using the same terms as before, and representing the microspores
+by the abbreviation _mo_, the megaspores by _Mo_, the archegonial
+gametophyte by _arG_, the antheridial by _anG_, the formula may be
+modified to express this more complicated process of alternation, as
+follows:—
+
+       _Mo_→_arG_→_fg_             _Mo_→_arG_→_fg_
+      ╱               ╲           ╱               ╲
+  _s_                   _oös_→_S_                   _oös_→_S_ etc.
+      ╲               ╱           ╲               ╱
+       _mo_→_anG_→_mg_             _mo_→_anG_→_mg_
+
+
+Comparing this formula with the preceding, it will be seen that the
+increased complexity affects the sporophyte at the expense of the
+gametophyte, which has now become a mere dependent on the former.
+
+=410. Advantages of alternation.=—This roundabout mode of
+reproduction would hardly have been developed unless it had been of
+some benefit to the plants in which it occurs. The chief advantage
+seems to be in more rapid multiplication and consequently better
+chance to propagate the species, as compared with the slow process
+of sexual reproduction were the plant confined to that method alone.
+Only one plant is produced by each oöspore, and if this were a
+gametophyte with its limited number of archegonia, multiplication
+would be slow; but the sporophyte with its millions of spores,
+each capable of producing a new individual, enables the species
+to multiply indefinitely. At the same time the interposition of a
+gametophyte, or sexual generation, secures the introduction of a new
+strain with effects analogous to those of cross fertilization.
+
+[Illustration: FIG. 509.—Part of the fruiting stem of a scouring
+rush, _Equisetum limosum_, showing the cone-like spore cluster.
+(_After_ GRAY.)]
+
+=411. Classification of pteridophytes.=—In our study of this group,
+the ferns have been taken as the type because they are the most
+familiar and most widely distributed of all the vascular cryptogams.
+But while they exceed in numbers, both of individuals and species,
+all the other orders combined, they form only one division of three
+great groups that make up the class Pteridophyta. These groups are:
+(1) ferns, under which are included, besides the true ferns, two
+widely differing orders, with the grape ferns and adder’s-tongue in
+one, and the water ferns in the other; (2) the club mosses, embracing
+the two subdivisions of _Lycopodium_ and _Selaginella_; (3) the
+horsetail family, including horsetails and scouring rushes. Orders
+(2) and (3) are grouped together as cone-bearing (strobilaceous)
+pteridophytes, because their sporangia are clustered in oblong heads,
+or _strobiles_ (Fig. 509), somewhat like the cones of the pine. The
+orders of pteridophytes differ greatly among themselves, but agree
+in possessing certain characteristics that point to their derivation
+from a common ancestry.
+
+=412. Distinction between pteridophytes and bryophytes.=—In passing
+from the Thallophytes and Bryophytes to the vascular cryptogams, we
+cross the widest chasm in the vegetable kingdom—a gap relatively as
+great as that between vertebrates and invertebrates among animals.
+The most important modifications that discriminate the two groups
+are: (1) the presence in Pteridophytes of a highly organized vascular
+system accompanied by a well-marked differentiation of the plant body
+into root and stem; (2) increased importance and complexity of the
+sporophyte with proportionate diminution of the gametophyte.
+
+While vessels for conducting water occur in some of the bryophytes
+(403), a well-defined vascular system and true roots are met with
+first in the Pteridophytes. The change in the relative importance
+of sporophyte and gametophyte is so marked that in Selaginella, the
+genus which approaches nearest in structure to the seed-bearing
+plants, the suppression of the gametophyte has proceeded so far that
+it never leads an independent existence at all and is difficult even
+to recognize as a distinct individual.
+
+
+          Practical Questions
+
+  1. Have ferns any economic use—that is, are they good for food,
+  medicines, etc.?
+
+  2. What is their chief value?
+
+  3. Under what ecological conditions do they grow?
+
+  4. Are they often attacked by insects, or by blights and disease of
+  any kind?
+
+  5. Of what advantage is it to ferns to have their stems
+  underground, in the form of rootstocks? (321.)
+
+  6. What causes the young frond of ferns to unroll? (54, 98.)
+
+  7. Name the ferns indigenous to your neighborhood.
+
+  8. Which of these are most ornamental, and to what peculiarities of
+  structure do they owe that quality?
+
+  9. Are cultivated ferns usually raised from the spores or in some
+  other way? Why?
+
+  10. After the great eruption of Krakatoa in 1883, by which the
+  vegetation of the island was completely destroyed, ferns were the
+  first plants to reappear. Explain why. (19; Exp. 17.)
+
+
+          VIII. THE RELATION BETWEEN CRYPTOGAMS AND SEED PLANTS
+
+=413. No break in the chain of life.=—The great gap that was once
+supposed to exist between the cryptogams and phanerogams has been
+bridged over by the discovery of analogies in the reproductive
+processes of the two groups that connect them together as successive
+links in one continuous chain of vegetable life. It is therefore very
+important to have a clear understanding of the nature and meaning of
+these processes, for the chief turning points in the life history of
+the different groups of plants are connected with them, their natural
+relationships to each other, and their distribution according to
+their respective places in the evolutionary scale, being determined
+largely by a comparison of their modes of continuing the life of the
+group.
+
+=414. Alternation of generations in seed plants.=—This process, so
+conspicuous among Bryophytes and Pteridophytes, and not unknown
+among Thallophytes, is universal among seed plants (Spermatophytes)
+also, though in so masked a form that it is not easy to recognize
+without a more detailed study than would be practicable within the
+limits of a book like this. Briefly, we may say that the stamens of
+spermatophytes, and the pistils, or rather the carpels, which we
+have seen to be transformed leaves (298), represent the sporophylls
+(406) of the higher pteridophytes. The pollen sacs and ovules are
+sporangia, bearing microspores and megaspores (409), represented
+respectively by the pollen grains in the anther and the embryo sac
+in the ovule. These go through a series of microscopic changes in
+the body of the ovule analogous to the production of the oöspore
+in the archegonia of ferns and liverworts, but the process is so
+obscure that to an ordinary observer the pollen grains and the ovule
+appear to be the real gametes, and were long supposed to be such.
+The fertilized germ cell in the embryo sac (251) corresponds to
+an oöspore; the embryo sac with the endosperm found in all seeds
+(previous to its absorption by the cotyledons) is a rudimentary
+gametophyte; and the embryo in the matured seed is the undeveloped
+sporophyte, destined, after germination and further growth, to
+produce a new generation with its recurrent cycle of alternating
+phases.
+
+[Illustration: FIG. 510.—Diagrammatic section through the ovule of a
+gymnosperm belonging to the spruce family: _i_, integument covering
+the ovule; _e_, endosperm (corresponding to female gametophyte),
+which fills the embryo sac, containing two archegonia, _a_; _o_, egg
+cell; _p_, pollen grains; _t_, pollen tubes entering the neck, _c_,
+of the archegonia.]
+
+In the gymnosperms,—pines, yews, cycads, etc.,—which represent the
+most ancient and primitive type of existing seed-bearing plants,
+the similarity of these processes to those of certain of the
+pteridophytes is very striking, and it was through the study of
+these that the sequences of the process were traced in the much
+more obscure form in which they occur among the angiosperms. From
+the endosperm in the seeds of gymnosperms archegonia were found to
+be developed (Fig. 510) in much the same way as in Selaginella,
+from the prothallium, thus showing the endosperm to be a modified
+and greatly reduced gametophyte. In some cases, it has even been
+found to protrude a little way out of the embryo sac and to take
+on a slightly greenish tinge—another reminiscence of its origin.
+Fertilization, too, takes place in precisely the same manner as in
+the pteridophytes, except that in all but the ginkgo and the cycads,
+the fertilizing cells in the pollen grains are non-motile, and find
+their way to the ovule by growing down into the embryo sac with the
+pollen tube, instead of swimming to it—an adaptation probably brought
+about in response to changed condition during the course of evolution
+from aquatic to terrestrial life.
+
+The analogies between the sequence of alternations in the two classes
+will be made clearer by a comparison of the accompanying diagrams.
+The corresponding terms applied to the various organs stand in
+the same vertical row. Diagram (1) shows the process as it takes
+place in the more highly developed Pteridophytes; diagram (2) the
+corresponding phases in angiosperms.
+
+
+                             PTERIDOPHYTES
+
+                  _mospl_→_mic_→_mo_→_anG_→_ant_→_mg_→
+                 ╱                                    ╲
+         (1) _S_                                        _öos_→_S_
+                 ╲                                    ╱
+                  _Mospl_→_Mgc_→_Mo_→_arG_→_arc_→_fg_→
+
+_mospl_, microsporophyll; _mic_, microsporangium; _mo_, microspores;
+_anG_, male gametophyte; _ant_, antheridia; _mg_, antherozoids. The
+letters in the lower line stand for the corresponding female organs.
+
+
+                             SPERMATOPHYTES
+
+                 _st_→_an_→_pol_→_fc_→   _not_   →_gc_→
+               ╱                      _developed_       ╲
+       (2) _S_                                            _öos_→_S_
+               ╲                      _developed_       ╱
+                 _p_ →_ov_→_em_→_end_→ _only in_ →_ec_→
+                                     _gymnosperms_
+
+_st_, stamen; _an_, anther; _pol_, pollen; _fc_, food cells in pollen
+grain; _gc_, generative cell; _p_, pistil; _ov_, ovules; _em_, embryo
+sac; _end_, endosperm; _ec_, egg cell.
+
+
+=415. Disappearance of the gametophyte.=—The seed is a comparatively
+recent development in plant evolution. It has no counterpart anywhere
+among the cryptogams, but is strictly characteristic of the three
+great orders of Spermophytes: Monocotyl, Dicotyl, and Gymnosperms,
+which compose the greater part of the vegetation of the globe.
+Structurally, it is a matured sporangium containing a rudimentary
+sporophyte (the embryo), and a reduced gametophyte (the embryo sac),
+which, under the form of endosperm, has dwindled to an insignificance
+that makes it difficult to recognize it as a phase in an alternation
+of generations.
+
+=416. Significance of the sporophyte.=—The gametophyte is obviously a
+more ancient and primitive structure than the sporophyte, which first
+becomes prominent in the ferns and their allies. The sudden and
+violent break in the succession of vegetable life that accompanies
+the appearance of the pteridophytes (412) is probably to be explained
+by the development of a land flora and the necessity of adaptation to
+life in a new medium. The fact that no living cell, whether vegetable
+or animal, can absorb nourishment except in a liquid form, seems to
+point to an aquatic origin more or less remote for all life. This
+inference is further strengthened, in the case of plants, by the
+fact that even in so highly organized a group as the pteridophytes,
+fertilization cannot take place except in water. Such a requirement
+would manifestly be a great disadvantage to land plants, and one of
+the first steps in response to the demands of a new habitat would be
+to get rid, as far as possible, of the primitive gametophyte with
+its outgrown adaptations to a liquid medium, and to transfer the
+greater part of the work of reproduction to the asexual generation,
+in which the problem of fertilization did not have to be directly
+met, the asexual spores germinating without it. The greater the
+number of these produced, the better the chance that at least some of
+the gametes developed from them would meet the difficult conditions
+of fertilization, and the survival of the species be assured. At the
+same time, in order to meet the requirements of terrestrial life
+successfully, and to provide for continuing the sexual generation,
+correlative changes would have to take place in the gametophyte by
+which the increasing uncertainty of fertilization due to structural
+changes in the sporophyte, and the absence of a liquid medium for
+the conveyance of free swimming antherozoids would be avoided. This
+necessity has been met by the development of the pollen tube, which
+bores its way to the egg cell, carrying with it the generative cells,
+which in seed plants have taken the place of the more primitive
+antherozoids. With the concomitant reduction of the gametophyte and
+development of the seed habit, the adaptation to land conditions has
+been made complete.
+
+Roughly speaking, it may be said: (1) that Thallophytes are
+predominantly aquatic; (2) Archegoniates (Bryophytes and
+Pteridophytes), amphibious; (3) Spermophytes, terrestrial; (4) that
+the seed habit is a response to terrestrial conditions; and (5)
+that the increased development of the sporophyte was a necessary
+adaptation to meet those conditions.
+
+
+          IX. THE COURSE OF PLANT EVOLUTION
+
+=417. Plant genealogy.=—It has been shown by a study of existing
+forms of plant life that there is no hard and fast line of division
+anywhere between the different groups, but that they are all
+connected by ties of kinship more or less defined, according to their
+distance from a common ancestral stock. The geological record points
+to the same conclusion, and our classification of them into families,
+orders, and species is merely a very imperfect genealogical table
+of their supposed pedigrees. This does not mean, however, that we
+can assert positively that such and such a species is derived from
+such or such another, but that both are descended from some common
+intermediate form more or less remote. While we have reason to
+believe that the flowering plants are derived through pteridophyte
+and bryophyte types from some of the green algæ, no direct connection
+has ever been traced between any particular kind of flowering
+plant and any particular kind of alga,—or between a liverwort and
+an alga, for that matter,—and probably never will be, because the
+intermediate forms die out, or pass on by variation into other lines
+of development. But while this is true, all the evidence we possess
+does go to show that, since the beginning of life on the globe, there
+has been a general progressive evolution from lower and simpler to
+higher and more complex forms.
+
+=418. Retrogressive evolution.=—While the general course of evolution
+has been upward and onward, the movement has not always followed
+a straight line, but, like a mountain road, shows many windings
+and deviations from the direct route. The monocotyls furnish a
+conspicuous example of this departure from the general law of
+progression. It was formerly supposed, on account of their greater
+simplicity of structure, that they were a more ancient type than
+dicotyls, but recent investigations point to the conclusion that
+they are a later offshoot, derived from some primitive form of
+aquatic dicotyl, and represent, not an ancient and primitive stock,
+but a case of retrogressive evolution from a higher type. Strong
+presumptions in favor of this view are: (1) that various species of
+dicotyls show an unequal development of the seed leaves, amounting,
+in the bryony, to complete abortion of one of them, while some
+monocotyl seeds show morphological characters that can best be
+explained as survivals, or inheritances, from a dicotyl ancestor;
+(2) the structural resemblances between gymnosperms and dicotyls are
+closer than between gymnosperms and monocotyls, which could hardly
+be the case if the latter were the more ancient; (3) the geological
+record does not show them to have appeared before dicotyls; (4) the
+number of cotyledons furnishes no criterion as to the relative age
+of any plant group, since all three types are represented among the
+pteridophytes, where plants are found bearing one, two, or more
+cotyledons.
+
+The theory of their comparatively recent origin from an aquatic
+ancestor is further borne out by the many points of similarity
+between their internal structure and that of hydrophytes (318), and
+also by the great proportion of aquatic plants among them, amounting
+to thirty-three per cent, while in dicotyls the proportion is only
+four per cent. Can you give any reasons, from your examination of
+their internal structure (113, 114), for believing that the line of
+development which they have followed is a less effective one for
+meeting conditions now existing on the globe than that attained by
+dicotyls?
+
+We should remember, too, that while progressive evolution implies
+successful adjustment to surroundings, it is possible to conceive of
+a state, as our planet approaches the period of cosmic debility and
+decay, when the conditions of existence may become progressively more
+and more unfavorable. In this case the course of evolution would be
+reversed, the higher types gradually dying out as the struggle for
+life became more severe, and the tendency would be constantly toward
+lower and simpler forms, until finally all life would become extinct
+on our planet. We have no right, however, to assume that during such
+a course of retrogressive evolution the same forms would be repeated
+in reverse order as have already appeared, because there is no reason
+to believe that the conditions brought about by planetary decline and
+“old age” would be the same as those attending planetary birth and
+adolescence.
+
+[Illustration: FIG. 511.—Diagram showing the supposed course of plant
+evolution.]
+
+=419. Explanation of the diagram.=—An attempt to show the general
+course of plant evolution up to the present time is made in the
+accompanying diagram. The four great divisions, Thallophytes,
+Bryophytes, Pteridophytes, and Spermatophytes, are represented by
+spaces between four horizontal lines arranged one above the other in
+the order of their succession in time and complexity of organization.
+It should be borne in mind that these dividing lines are not sharply
+defined in nature, but overlap or indent the territory between them
+with varying degrees of irregularity, like the coast line on a
+map. The relative positions of the different orders we have been
+considering are represented by upright and diagonal lines, the
+general course of which, as indicated by the arrows, is intended to
+give an idea of the trend of evolutionary progress in the particular
+group represented by each line. No one of these lines is made to
+originate directly in any other, because, with the possible exception
+of the monocotyls, we have no authority for asserting that any such
+direct connection exists between plants as we know them, but only
+that certain types give evidence of descent from a common ancestry.
+This lack of certainty is expressed by placing the point of origin
+for any given line in more or less close proximity to the one which
+is supposed to be the nearest living representative of the common
+ancestor. The line of ferns, for instance, is depicted as originating
+in the region of the bryophytes, somewhere in the neighborhood of
+the liverworts, but the two lines nowhere come in contact, because
+there is no evidence that any fern, living or fossil, is directly
+descended from any particular kind of liverwort known to us. With
+these explanations, the diagram shows, in a rough way, the generally
+accepted view of plant relationships as based on the evidence at
+present before us. But in questions of this sort it is wise to keep
+in mind the blunt remark of a famous old American statesman, that
+“only fools and dead people never change their opinions.”
+
+
+          Field Work
+
+  1. If you live in the country, study the appearance of plants
+  affected with blights, smuts, rusts, and mildews, and learn to
+  recognize the different kinds of disease by their signs. Notice
+  which kinds are most prevalent in your neighborhood, and what
+  plants are most affected by them.
+
+  2. Notice the different kinds of mushrooms you find growing wild.
+  Observe the difference between those that grow on the ground and
+  those that grow on logs, stumps, and trees; between those found
+  in the woods and those in open ground. Find out how those on the
+  ground get their nourishment. Uncover the mycelium, and notice
+  the extent of its surface. Examine the soil and find out if it
+  contains anything upon which they could feed. Note the prevalence
+  of shelf fungi on trees. Examine the condition of the wood where
+  they grow, and decide in what ways they injure their hosts. Notice
+  whether they abound most on healthy or on decaying trunks and
+  boughs, and decide whether this is because the fungus prefers that
+  kind of host, or whether the injury it does causes the decay, or
+  whether both causes operate together. Notice what fungi grow on
+  different trees, and study their preferences in this respect.
+
+  3. Observe the different kinds of lichens found in your walks
+  and try to distinguish the three classes. Which kind are most
+  abundant in your neighborhood? Which least so? Note the situations
+  in which you find each kind growing, whether on stumps, trees,
+  rocks, or the ground. Consider how the algæ and fungi aid each
+  other in the different positions; could either, for instance, exist
+  independently on bald rocks? Notice on what kind of trees the
+  different lichens seem to thrive best and on which poorly or not at
+  all, and whether the character of the bark—rough, smooth, scaly—has
+  anything to do with their choice of a habitat.
+
+
+
+
+APPENDIX
+
+
+
+
+          SYSTEMATIC BOTANY
+
+
+=Taxonomy, or systematic botany=, deals with the family relationships
+of plants in the order of their nearness or remoteness with regard
+to a common line of descent. Its chief value is the insight it
+gives into the course of plant evolution and into the nature of
+the modifications that differentiate each group from the ancestral
+type. While it is not advisable to spend too much time in the mere
+identification of species, a sufficient number should be examined
+and described to familiarize the student with the distinctive
+characteristics of the principal botanical orders.
+
+=Principles of classification.=—All the known plants in the world,
+numbering not less than one hundred and twenty thousand species
+of the seed-bearing kind alone, are ranged according to certain
+resemblances of structure, into a number of great groups known as
+families or orders. The names of these families are distinguished by
+the ending _aceæ_; the rose family, for instance, are the _Rosaceæ_;
+the pink family, _Caryophyllaceæ_; the walnut family, _Juglandaceæ_,
+etc. Each of these families is divided into lesser groups called
+_genera_ (singular, _genus_), characterized by similarities showing
+a still greater degree of affinity than that which marks the larger
+groups or orders; and finally, when the differences between the
+individual plants of a kind are so small as to be disregarded, they
+are considered to form one species; all the common morning-glories,
+for instance, of whatever shade or color, belong to the species
+_Ipomea purpurea_. The small differences that arise within a species
+as to the color and size of flowers, and other minor points,
+constitute mere varieties, and have no special names applied to them.
+The line between varieties and species is not clearly defined, and
+in the nature of things can never be, since progressive development,
+through unceasing change, is the law of all life.
+
+In botanical descriptions, the name both of the species and the genus
+is given, just as in designating a person, like Mary Jones or John
+Robinson, we give both the surname and the Christian name. The genus,
+or generic name, answers to the surname, and that of the species to
+the Christian name—except that in botanical nomenclature the order
+is reversed, the generic, or surname, coming first, and the specific
+or individual name last; for example, _Ipomea_ is the generic, or
+surname, of the morning-glories, and _purpurea_ the specific one.
+
+=How to use the key.=—Any good manual will answer the purpose. Gray’s
+“School and Field Book” is, perhaps, the best available at present
+for the states east of the Mississippi. Reference to the floral
+analyses in sections =I-IV= of Chapter VII will make its use clear.
+Suppose, for instance, we want to find out to what botanical species
+the morning-glory or the sweet potato belongs. Turning to the key,
+we find the sub-kingdom of Phænerogams—flowering or seed-bearing
+plants—divided into two great classes, Angiosperms and Gymnosperms,
+as explained in 18. A glance will show that our specimen belongs
+to the former class. Angiosperms, again, are divided into the two
+subclasses of Dicotyledons and Monocotyledons (18, 171). We at
+once recognize our plant, by its net-veined leaves and pentamerous
+flowers, as a dicotyledon (171, 229), and turning again to the key,
+we find this subclass divided into three great groups: Sympetalous
+(211), called also Monopetalous and Gamopetalous; Apopetalous, or
+Polypetalous (211), and Apetalous—having no petals or corolla. A
+glance will refer our blossom to the sympetalous or monopetalous
+group, which we find divided into two sections, characterized by
+the superior or inferior ovary (218, 225). Further examination will
+show that the morning-glory belongs to the former class, which is
+in turn divided into two sections, according as the corolla is
+_regular_, or _more or less irregular_. We see at once that we must
+look for our specimen in the group having regular corollas. This we
+find again subdivided into four sections, according to the number and
+position of the stamens, and we find that the morning-glory falls
+under the last of these,—“Stamens as many as the lobes or parts of
+the corolla and alternate with them.” A very little further search
+brings us to the family _Convolvulaceæ_, and turning to that title
+in the descriptive analysis, we find under the genus, _Ipomea_, a
+full description of the common morning-glory, in the species _Ipomea
+purpurea_, and of the sweet potato in the species _Ipomea batatas_.
+
+=Making collections.=—Mere labeled aggregations of species are not
+recommended, but the collection of examples illustrating special
+points in morphology and plant variation may be made with profit;
+such, for instance, as the adaptations observed in tendrils and
+stipular appendages, the various modifications of leaves and stems
+to serve other than their normal purposes, or the different forms
+of leaves and flowers on the same stem, or on different plants of
+the same species. A collection made with some specific object in
+view would also be instructive, and might prove of great value; for
+instance, to get together examples of all the troublesome weeds of
+a locality for the purpose of studying their habits and devising
+means for their eradication; or of all the native useful plants, with
+detailed analyses of their economic properties, and observations on
+their habits and the practicability of further developing them. In
+short, wherever collecting is carried on, it should be done with some
+object other than the mere identification of species, which often
+results in greater detriment to the wild plants of a neighborhood
+than profit to the collector.
+
+
+
+
+                    WEIGHTS, MEASURES, AND TEMPERATURES
+
+
+As the metric system of weights and measures and the Centigrade
+appraisement of temperatures are universally employed in scientific
+works, the following tables showing the equivalents in our common
+English standards of those in most frequent use, are given for the
+convenience of students who have not already familiarized themselves
+with the subject. The values given are approximate only, but will
+answer for all practical purposes, except in cases where very
+great exactitude is required. The micron, or micrometer, is used
+principally by scientific investigators for measuring extremely
+minute objects seen under the microscope.
+
+
+                    MEASURES OF LENGTH
+
+  ================================+=====================================
+              METRIC              |          ENGLISH EQUIVALENTS
+  -----------------+--------------+-------------------------------------
+  Kilometer        | km.          | ⅔ of a mile.
+  -----------------+--------------+-------------------------------------
+  Meter            | m.           | 39 inches.
+  -----------------+--------------+-------------------------------------
+  Decimeter        | dm.          | 4 inches.
+  -----------------+--------------+-------------------------------------
+  Centimeter       | cm.          | ⅖ of an inch.
+  -----------------+--------------+-------------------------------------
+  Millimeter       | mm.          | ¹⁄₂₅ of an inch.
+  -----------------+--------------+-------------------------------------
+  Micron           | µ            | ¹⁄₂₅₀₀₀ of an inch.
+  -----------------+--------------+-------------------------------------
+
+
+                    CAPACITY
+
+  -----------------+---------+------------------------------------------
+  Liter            | l.      | 61 cubic inches, or 1 quart, U.S. measure
+  -----------------+---------+------------------------------------------
+  Cubic centimeter | cc.     | ¹⁄₁₆ of a cubic inch.
+  -----------------+---------+------------------------------------------
+
+
+                    WEIGHT
+
+  -----------------+---------------+------------------------------------
+  Kilogram         | kg., or kilo. | 2⅕ pounds.
+  -----------------+---------------+------------------------------------
+  Gram             | gm.           | 15½ grains avoirdupois.
+                   |               | ¹⁄₂₈ of an ounce avoirdupois.
+  =================+===============+====================================
+
+
+                    METRIC AND ENGLISH SCALES
+
+[Illustration: 10 CENTIMETERS = 1 DECIMETER
+
+100 MILLIMETERS
+
+4 INCHES]
+
+
+                    TEMPERATURE EQUIVALENTS
+
+The next table gives the Fahrenheit equivalent, in round numbers, for
+every tenth degree Centigrade from absolute zero to the boiling point
+of water. To find the corresponding F. for any degree C., multiply
+the given C. temperature by nine, divide by five, and add thirty-two.
+Conversely, to change F. to C. equivalent, subtract thirty-two,
+multiply by five, and divide by nine.
+
+    Cent.   Fahr.
+  ----------------
+     100     212
+      90     194
+      80     176
+      70     158
+      60     140
+      50     122
+      40     104
+      30      86
+      20      68
+      10      50
+       0      32
+     −10      14
+     −20      −4
+     −30     −22
+     −40     −40
+     −50     −58
+    −100    −148
+  ————————————————
+   Absolute zero.
+    -273    -459
+
+
+
+
+FOOTNOTES:
+
+[1] Vines, “Lectures on the Physiology of Plants,” p. 282. See also
+Sachs, “Physiology of Plants.”
+
+[2] Marshall Ward, “The Oak.”
+
+
+
+
+INDEX
+
+(The numbers, unless otherwise designated, refer to paragraphs.)
+
+
+  Aborted, 220, 291.
+
+  Absorption, 58, 71, 72; Exp. 39.
+    selective, 60.
+
+  Accessory buds, 158.
+
+  Accessory fruits, 302.
+
+  Adaptation, 206, 237.
+
+  Adhesive fruits, 20; Exp. 20.
+
+  Adjustment of leaves, 196-202.
+
+  Adnate, 374.
+
+  Adventitious buds, 65, 158.
+
+  Adventitious roots, 37, 83.
+
+  Æcidium, 362.
+
+  Aëration, 319.
+
+  Aërial roots, 88.
+
+  Aggregate fruits, 301, 303.
+
+  Air space, 114, 116, 184.
+
+  Akene, 234, 296, 302, 305.
+
+  Albumin, 3.
+
+  Albuminous, 56.
+
+  Albuminous seed, _i.e._, containing endosperm;
+    Field work, p. 28.
+
+  Aleurone, 3.
+
+  Algæ, 333, 336-342.
+
+  Alternate leaves, 168.
+
+  Alternation of generations, 395, 400, 409, 414.
+
+  Analogous, 108.
+
+  Anatropous, Fig. 26.
+
+  Angiosperms, 15, 18; Fig. 511.
+
+  Annuals, 91.
+
+  Annulus, 372, 405.
+
+  Anther, 213, 235; Figs. 270-274.
+
+  Antheridia, 389, 394, 398, 407.
+
+  Antheridial, 388.
+
+  Antherozoids, 389, 392, 395, 416.
+
+  Antisepsis, 355.
+
+  Arch of the hypocotyl, 42, 44.
+
+  Archegonia, 390, 394, 407, 408.
+
+  Archegonial, 388.
+
+  Archegoniates, 408, 416.
+
+  Archegonium, 391, 394, 398.
+
+  Asexual generation, 395, 399, 409, 416.
+
+  Asexual reproduction, 394, 395.
+
+  Asexual spore, 395, 407, 409, 410, 416.
+
+  Assurgent, 95.
+
+  Axial placenta, 216, 300.
+
+  Axil, 100, 166.
+
+  Axillary buds, 145.
+
+  Axis, 64, 65, 79, 152, 156, 159, 161.
+
+
+  Bacillus, 348, 349.
+
+  Bacteria, 333, 345, 347-353.
+
+  Bark, 118, 119, 122, p. 128, (3).
+
+  Basidia, 375.
+
+  Bast, 116, 119, 122.
+
+  Berry, 291.
+
+  Biennial, 92.
+
+  Bilabiate, 237, 243.
+
+  Bilateral regularity, 219.
+
+  Bilateral zonation, 326.
+
+  Black rust, 360.
+
+  Blade of leaf, 165.
+
+  Biogenetic law, 253.
+
+  Biological factors, 309.
+
+  Bordered pits, 114, 117; Fig. 123.
+
+  Boreal, 329.
+
+  Bract, 161.
+
+  Bryophytes, 334, 385-401.
+
+  Bud scales, 147-149.
+
+  Buds, 145, 155-158.
+
+  Bulb, 107.
+
+  Button (of mushroom), 370.
+
+
+  Calyptra, 399.
+
+  Calyx, 211.
+
+  Cambium, 115, 116, 120, 123.
+
+  Cap, 372, 373.
+
+  Capillarity, 136; Exp. 53.
+
+  Capitate, 220.
+
+  Caprification, 279, 305.
+
+  Caprifig, 279.
+
+  Capsule, 298.
+
+  Carbon, 27, 28, 62.
+
+  Carbon dioxide, 29, 63, 185, 186, 187, 189; Exps. 23, 25.
+
+  Carpels, 216, 288.
+
+  Caruncle, 13.
+
+  Catkin, 161.
+
+  Caulicle, 46.
+
+  Cedar apples, Fig. 456.
+
+  Cell, 6, 7.
+    collecting, 184.
+    companion, 114.
+
+  Cell sap, 7, 110.
+
+  Cell wall, 7, 183.
+
+  Central cylinder, 67.
+
+  Central placenta, 216, 300.
+
+  Chalaza, 13.
+
+  Chlorophyll, 186, 341, 366.
+
+  Chlorophyll bodies, 184, 186, 382.
+
+  Cion, 65.
+
+  Classification, 90, 252, 283, 343, 384, 411, 417.
+
+  Cleistogamic flowers, 272.
+
+  Climatic zones, 329.
+
+  Climbing stems, 96-98.
+
+  Clipped seed, p. 12 (material).
+
+  Closed bundle, 114.
+
+  Close-fertilized, 272.
+
+  Cluster cups, 362.
+
+  Coccus (pl. cocci), 339, 348.
+
+  Coiled inflorescence, 162.
+
+  Collective fruits, 304.
+
+  Colony, 316, 337, 357.
+
+  Color of flowers, 276.
+
+  Compass plants, 199.
+
+  Complete flower, 219.
+
+  Composite, 235, 381.
+
+  Composite flower, 236.
+
+  Compound leaf, 178.
+
+  Conduplicate, Figs. 159, 160.
+
+  Confluent, 404.
+
+  Conifers, 117, 327.
+
+  Conjugation, 342, 394.
+
+  Corolla, 211.
+
+  Cortex, 64, 115, 122.
+
+  Corymb, 161.
+
+  Cotyledon, 11, 12, 18.
+
+  Cross cut, 133.
+
+  Cross fertilization, 255.
+
+  Cross pollination, 255.
+
+  Crustaceous lichen, 384.
+
+  Cryptogam, 332.
+
+  Crystalloids, 60.
+
+  Culture medium, 347; p. 306 (material).
+
+  Cycle, 217, 219, 229.
+
+  Cycle of growth, 50.
+
+  Cyme, 162.
+
+  Cymose inflorescence, 162.
+
+  Cypress knees, 319.
+
+
+  Deciduous, 203.
+
+  Declined, 95.
+
+  Decurrent, 374.
+
+  Definite annual growth, 153.
+
+  Definite inflorescence, 160, 162.
+
+  Dehiscent fruits, 283, 298.
+
+  Deliquescent, 144.
+
+  Determinate growth, 153.
+
+  Determinate inflorescence, 160, 162.
+
+  Diadelphous, 239.
+
+  Diastase, 9.
+
+  Dichogamy, 269.
+
+  Dichotomous, 152; Fig. 155.
+
+  Dicotyl, 42, 115, 116, 171, 220.
+
+  Dicotyledonous, 12.
+
+  Differentiate, 245, 345, 409.
+
+  Diffusion, 9, 57.
+
+  Digestion, 9.
+
+  Dimorphic, 270.
+
+  Dimorphism, 270.
+
+  Dimorphous, 270.
+
+  Diœcious, 268.
+
+  Disinfection, 355.
+
+  Disk flower, 233.
+
+  Dispersal of seed, 19-25.
+
+  Dominant, 257, 258.
+
+  Dormant buds, 157.
+
+  Dorsal; Figs. 390, 391.
+
+  Drupe, 292.
+
+  Dry fruits, 283, 293-300.
+
+  Duct, 67, 111, 114.
+
+
+  Ecological factors, 310.
+
+  Ecology, 266, 308, 310.
+
+  Edgings, 134.
+
+  Egg cell, 251, 391.
+
+  Elators, 393.
+
+  Embryo, 11.
+
+  Embryology, 253.
+
+  Embryo sac, 251.
+
+  Endodermis, 67 (b).
+
+  Endosperm, 11, 13, 14, 16, 17, 414.
+
+  Epicotyl, 45, 46, 47.
+
+  Epidermis, 64, 115, 122, 183.
+
+  Epigynous, 225, 230.
+
+  Epiphyte, 87, 394.
+
+  Essential constituents, 62.
+
+  Essential organs, 212.
+
+  Evolution, 242, 245, 265, 334, 335, 401, 414, 415, 417, 418, 419.
+
+  Evolutionary, 253, 413.
+
+  Excentric attachment, 372.
+
+  Excurrent, 144, 154.
+
+
+  Factors, 54, 265, 310.
+
+  Fall of the leaf, 203.
+
+  Fascicled roots, 80, 81.
+
+  Fats, 1, 3, 4.
+
+  Feather-veined, 172.
+
+  Ferments, 9, 356.
+
+  Fertile, 404.
+
+  Fertile flower, 267.
+
+  Fertilization, 247, 251, 252, 392, 408, 416.
+
+  Fibrous roots, 37, 78, 80, 81.
+
+  Fibrovascular bundle, 67, 114, 116, 176, 288.
+
+  Fig wasp, 279.
+
+  Filament of the stamen, 213;
+    a hairlike appendage, 341, 361, 369, 393, 396.
+
+  Filamentous algæ, 340, 341.
+
+  Fission, 338, 394.
+
+  Fleshy fruits, 283, 288-292.
+
+  Floral envelopes, 211.
+
+  Foliaceous lichen, 379, 384.
+
+  Follicle, 298.
+
+  Forestry, 139-142.
+
+  Forked stems, 152.
+
+  Formation, 316.
+
+  Free, 218, 374.
+
+  Free central placenta, 216.
+
+  Free gills, 374.
+
+  Free ovary, 218.
+
+  Free veining, 402.
+
+  Freezing, 33.
+
+  Frog’s spit, 340.
+
+  Frond, 402.
+
+  Fruit, 282.
+
+  Fruticose lichen, 384.
+
+  Function, 41.
+
+  Fungi, 333, 343, 344, 345, 346, 378.
+
+  Fungus, 86, 364.
+
+
+  Gametes, 394.
+
+  Gametophyte, 394, 395, 396, 406, 407, 410, 412, 414, 415, 416.
+
+  Gemmæ, 387.
+
+  Generative cell, 249, 416.
+
+  Geophilous, 321.
+
+  Geotropism, 51, 52, 53.
+
+  Germ, 2, 11.
+
+  Germ cell, 251, 414.
+
+  Germination, 32, 35; Exps. 25, 26-29.
+
+  Germs, 352, 355.
+
+  Gills (of mushroom), 374.
+
+  Girdling, 131.
+
+  Glutin, 3.
+
+  Gourd, 14, 290.
+
+  Grain, 11, 297.
+
+  Grain of timber, 133, 134, 135.
+
+  Gravity, 52.
+
+  Growth, 48-52, 179.
+
+  Guard cell, 183.
+
+  Gymnosperms, 15, 18, 117, 414.
+
+  Gymnosporangium, Fig. 456.
+
+
+  Halophyte, 317, 323.
+
+  Haustoria, 85.
+
+  Hay bacillus, 348, 349.
+
+  Head, 161.
+
+  Heartwood, 131.
+
+  Heliotropic, 200.
+
+  Heliotropism, 198.
+
+  Herbaceous, 90, 94, 115, 116.
+
+  Heredity, 264, 265.
+
+  Hilum, 12, 13, 14.
+
+  Homologous, 108.
+
+  Host plant, 85.
+
+  Humus, 75, 86.
+
+  Hybrid, 256.
+
+  Hybridization, 256, 257, 263.
+
+  Hydrophytes, 317, 318, 319.
+
+  Hymenium, 375.
+
+  Hymenomycetes, 375.
+
+  Hyphæ (sing. hypha), 369, 380.
+
+  Hypocotyl, 11, 12, 14, 46.
+    arched, 42, 44.
+    straight, 44.
+
+  Hypogynous, 218, 225.
+
+
+  Imbibition, 136.
+
+  Imperfect flower, 219, 231, 267.
+
+  Impure hybrid, 258, 259.
+
+  In-breeding, 254.
+
+  Incomplete flower, 219.
+
+  Incubation, 354.
+
+  Indefinite annual growth, 153.
+
+  Indefinite inflorescence, 160, 161.
+
+  Indefinite number of parts, 229.
+
+  Indehiscent fruit, 283, 294.
+
+  Indeterminate growth, 153.
+
+  Indeterminate inflorescence, 160, 161.
+
+  Indusium, 404.
+
+  Inferior ovary, 221, 225.
+
+  Inflorescence, 159.
+
+  Insectivorous plants, 208-210.
+
+  Internode, 46, 110; Exp. 35.
+
+  Invasion, 328.
+
+  Inverted seed, 14.
+
+  Involucre, 161, 232.
+
+  Involute, 373; Fig. 251.
+
+  Iodine solution, Exp. 3.
+
+  Irregular flower, 219, 237.
+
+  Irritability, 201.
+
+
+  Joint, 110, 113.
+
+
+  Keel, 238.
+
+  Knots, 137.
+
+
+  Lamina, 209.
+
+  Laminæ, 368, 374.
+
+  Lateral, 372, 398.
+
+  Lateral buds, 145.
+
+  Leaf attachment, 167.
+
+  Leaf cups, 202.
+
+  Leaf scars, 146.
+
+  Leaf traces, 146.
+
+  Legume, 299.
+
+  Lenticels, 106, 118, 288.
+
+  Lichen, 379.
+
+  Life cycle, 359, 364.
+
+  Loam, 75.
+
+  Lobing, 177; Figs. 210-212.
+
+  Locule, 216.
+
+  Loment, Fig. 394.
+
+  Lyrate, Fig. 197.
+
+
+  Medulla, 119, 122.
+
+  Medullary rays, 64, 116, 121, 122, 134, 135.
+
+  Megasporangia, 409.
+
+  Megaspore, 409, 414.
+
+  Mendel’s law, 258.
+
+  Mesophyte, 317, 324.
+
+  Metabolism, 193.
+
+  Microbe, 351, 355.
+
+  Micrococcus, 339.
+
+  Micropyle, 12, 13, 14, 15, 45.
+
+  Microsporangia, 409.
+
+  Microspore, 409, 414.
+
+  Midrib, 172.
+
+  Mixed forest, 139, 324.
+
+  Modification, 100-108, 206, 207, 289.
+
+  Molecule, 136.
+
+  Monadelphous, 239.
+
+  Monocotyl, 110, 112, 171, 217, 221, 418.
+
+  Monocotyledonous, 11.
+
+  Monœcious, 268.
+
+  Monopetalous, 211.
+
+  Monosepalous, 211.
+
+  Morphology, 108.
+    of the flower, 244.
+
+  Mosaic (leaf), 197.
+
+  Mosses, 334, 396-401.
+
+  Muck, 75.
+
+  Multiple fruit, 304, 305.
+
+  Mushroom, 333, 367.
+
+  Mutation, 264.
+
+  Mycelium, 343, 359, 369.
+
+  Mychorrhiza, 86.
+
+
+  Neck canal, 391.
+
+  Net-veined, 171.
+
+  Neuter, 267.
+
+  Neutral flower, 231, 267.
+
+  Nitrogen, 62, 63, 188.
+
+  Nitrogenous food, 188.
+
+  Node, 46, 65, 110, 113.
+
+  Nucleus, 7, 341.
+
+  Numerical plan, 217, 229.
+
+  Nut, 295.
+
+  Nutriment, 3, 186.
+
+  Nutrition, 50, 54, 179, 193.
+
+  Nyctitropic, 200.
+
+
+  Obsolete, 220.
+
+  Oil, 1, 3, 8.
+
+  Oöspore, 393, 394, 395.
+
+  Open bundle, 116.
+
+  Operculum, 399.
+
+  Opposite leaves, 168.
+
+  Organ, 41.
+
+  Organic foods, 4.
+
+  Organs of reproduction, 40.
+    of vegetation, 40.
+
+  Osmosis, 56, 57.
+
+  Ovary, 214, 216, 223.
+
+  Ovule, 216.
+
+  Oxidation, 27; Exps. 21, 22.
+
+  Oxygen, 62, 63, 186, 187; Exps. 22, 66.
+
+
+  Palisade cells, 184.
+
+  Palmate veining, 172.
+
+  Panicle, Fig. 171.
+
+  Papilionaceous, 237, 238.
+
+  Pappus, 234.
+
+  Parallel veining, 171.
+
+  Paraphyses, 375, 398.
+
+  Parasitic, 5, 345, 364.
+
+  Parasitic plants, 85, 343, 382.
+
+  Parenchyma, 110, 114, 115.
+
+  Parietal, 216.
+
+  Pathogenic, 352, 353.
+
+  Pedicel, 159.
+
+  Peduncle, 159, 288.
+
+  Pentamerous, 229.
+
+  Pepo, 290.
+
+  Perennial, 93.
+
+  Perfect flower, 219.
+
+  Perianth, 211.
+
+  Pericarp, 288.
+
+  Perigynous, Figs. 301, 302.
+
+  Persistent, 166.
+
+  Petals, 211.
+
+  Petiole, 165.
+
+  Phanerogams, 331, 332.
+
+  Phloem, 114, 116.
+
+  Photosynthesis, 186, 192, 193.
+
+  Phototropism, 195.
+
+  Phyllotaxy, 168, 169.
+
+  Pileus, 373.
+
+  Pinna, 402.
+
+  Pinnate veining, 172.
+
+  Pinnule, 402.
+
+  Pioneer plant, 316, 319, 320.
+
+  Pistil, 212, 214, 223, 228, 240.
+
+  Pistillate, 267.
+
+  Pitcher plant, 209.
+
+  Pith, 110, 115, 116, 119, 121, 122.
+
+  Pitted ducts, 114.
+
+  Placenta, 216, 288, 298, 300.
+
+  Plant society, 316.
+
+  Plasmolysis, 59.
+
+  Pleurococcus, 337.
+
+  Plicate, 155.
+
+  Plumule, 11, 12, 14, 45, 46.
+
+  Pod, 298.
+
+  Pollen, 213.
+
+  Pollen grains, 213.
+
+  Pollen sac, 213.
+
+  Pollen tubes, 249, 250.
+
+  Pollination, 215, 247.
+
+  Polycotyledons, 15, 45.
+
+  Polymorphic, 365.
+
+  Polymorphism, 365.
+
+  Polypetalous, 211.
+
+  Polysepalous, 211.
+
+  Pome, 288.
+
+  Prefoliation, 155.
+
+  Primary, 396.
+
+  Primary root, 42, 79.
+
+  Pronuba, 278.
+
+  Prostate, 95.
+
+  Protection, 199, 204, 207, 280, 287.
+
+  Proteins, 3, 8, 33, 188, 204.
+
+  Prothallium, 407.
+
+  Protonema, 396.
+
+  Protoplasm, 6, 7, 57, 58, 67, 110, 116.
+
+  Pteridophytes, 335, 411, 412.
+
+  Puccinia, 360.
+
+  Pure dominant, 258, 259.
+
+  Pure forest, 139, 324.
+
+  Pure recessive, 258, 259.
+
+  Pycnidia, 363.
+
+
+  Quartered cut, 135.
+
+
+  Raceme, 161.
+
+  Rhachis, 178.
+
+  Radial section, 132, 135.
+
+  Radicle, 46.
+
+  Rhaphe, 13.
+
+  Ray, 161, 391.
+
+  Ray flowers, 231.
+
+  Receptacle, 211, 288, 289, 388, 390, 398.
+
+  Recessive, 257, 258.
+
+  Red rust, 359.
+
+  Regular flower, 219.
+
+  Reproduction, 338, 351, 358, 383.
+
+  Respiration, 30, 31, 191, 192.
+
+  Resting spore, 338, 342, 358, 394.
+
+  Reticulation, 172, 402.
+
+  Retrogressive evolution, 418.
+
+  Revolute, 373, 404.
+
+  Rhizoids, 379, 386.
+
+  Rhizome, 105.
+
+  Ringing, 127.
+
+  Rings of growth, 122, 123, 134, 135.
+
+  Rogue, 260.
+
+  Root cap, 39.
+
+  Root hairs, 38, 67.
+
+  Root pressure, Exp. 49.
+
+  Root pull, 69.
+
+  Rootstock, 105.
+
+  Root system, 89.
+
+  Root tubercles, 63, 300.
+
+  Rosette, 197.
+
+  Rotation of crops, 24, 327.
+
+  Runner, 95.
+
+
+  Samara, 296.
+
+  Sap movement, 125, 126, 128, 129.
+
+  Saprophyte, 86.
+
+  Sapwood, 131.
+
+  Scale leaves, 101, 106, 107, 147-149, 207.
+
+  Scape, 107, 159.
+
+  Scorpioid inflorescence, 162; Figs. 173-176.
+
+  Screenings, 20; p. 28, Qn. 22.
+
+  Secondary roots, 37, 42, 79.
+
+  Seed, 11-18, 332, 415.
+
+  Seed coat, 12, 14, 15, 43.
+
+  Seedless fruits, 285, 286.
+
+  Seedlings, 36, 42, 43, 45.
+
+  Seed plants, 331, 414.
+
+  Seed vessel, 282.
+
+  Selection, 260, 265, 286.
+    artificial, 262.
+    natural, 261.
+
+  Self-fertilization, 254, 271.
+
+  Sepals, 211.
+
+  Sessile, 167, 214.
+
+  Seta, 399.
+
+  Sexual generation, 395, 396, 406, 410, 416.
+
+  Sexual reproduction, 394, 395, 410.
+
+  Sheath, 67, 116.
+
+  Shrinking of timber, 136.
+
+  Sieve tube, 114.
+
+  Slabs, 134.
+
+  Sleep movements, 200.
+
+  Soils, 75, 77.
+
+  Sori, 404.
+
+  Spathe, 221.
+
+  Specialization, 237.
+
+  Spermatophytes, 331, 335, 394, 414.
+
+  Spermatozoid, 389.
+
+  Spermogonia, 363.
+
+  Spike, 161.
+
+  Spirillum, 348.
+
+  Spirogyra, 341.
+
+  Sporangia, 390, 405.
+
+  Spore, 332, 349, 350, 377, 406, 410.
+
+  Spore case, 390, 393, 405.
+
+  Spore print, 376.
+
+  Sporidium, 361.
+
+  Sporogonium, 393, 399.
+
+  Sporophyll, 406, 414.
+
+  Sporophyte, 393-395, 399, 406, 410, 412, 414, 416.
+
+  Sport, 264.
+
+  Stamen, 212, 213.
+
+  Staminate, 267, 268.
+
+  Staminodia, 244.
+
+  Standard, 238.
+
+  Starch, 3, 4, 187, 204, 288; Exps. 69, 70.
+
+  Stems, 90-99.
+
+  Sterile flower, 267.
+
+  Sterilization, 354.
+
+  Stigma, 214.
+
+  Stigmatic surface, 223.
+
+  Stimulus, 98, 186, 201.
+
+  Stipe, 240, 372, 402.
+
+  Stipule, 149, 165, 166.
+
+  Stolon, 95.
+
+  Stoma, 181, 182, 183.
+
+  Stomata, 181, 182.
+
+  Stone fruit, 292.
+
+  Storage of food, 2, 3, 4, 17, 70, 103, 104-107, 287.
+
+  Strangling fig, 88.
+
+  Strobile, 411.
+
+  Strobiliaceous, 411.
+
+  Style, 214.
+
+  Succession, 327.
+
+  Sugars, 3, 4, 204, 288.
+
+  Summer spores, 360.
+
+  Sundew, 210.
+
+  Superior ovary, 218, 221, 225.
+
+  Supernumerary buds, 158.
+
+  Suppressed, 220.
+
+  Survival of the fittest, 261.
+
+  Suture, 216, 298, 299.
+
+  Swarm spore, 349.
+
+  Swelling of timber, 136.
+
+  Symbiosis, 309, 382.
+
+  Symmetrical flower, 219.
+
+  Sympetalous, 211.
+
+  Syncarpous, 300.
+
+  Synsepalous, 211.
+
+  Systematic botany, _see_ Appendix.
+
+
+  Tangential cut, 132, 134.
+
+  Tap root, 79.
+
+  Teleutospore, 360.
+
+  Tendril, 96, 97.
+
+  Terminal bud, 145, 154.
+
+  Testa, 14.
+
+  Thallophytes, 333.
+
+  Thallus, 333, 341, 343, 379, 380, 381, 385.
+
+  Tillage, 76.
+
+  Tissue, 60, 61.
+
+  Toadstools, 367.
+
+  Toxins, 345.
+
+  Tracheids, 114, 117.
+
+  Trailing, 95.
+
+  Trama, 375.
+
+  Transpiration, 179, 180.
+
+  Trifoliolate, Figs. 215, 216.
+
+  Trimerous, 217.
+
+  Trimorphic, 270.
+
+  Tuber, 106.
+
+  Tumbleweeds, 23.
+
+  Turgidity, 7.
+
+  Turgor, 179.
+
+  Twining, cause of, 98; Exp. 55.
+
+  Twining stems, 96; Exp. 54.
+
+  Type, 18, 260, 263, 265, 336, 411.
+
+
+  Umbel, 161.
+
+  Umbonate, 373.
+
+  Underground stems, 104-107.
+
+  Unicellular, 337.
+
+  Unisexual, 267.
+
+  Uredo, 359.
+
+  Uredospore, 359, 360.
+
+
+  Variation, 263, 264, 265.
+
+  Vascular bundles, 111.
+
+  Vascular cryptogams, 403, 411, 412.
+
+  Vascular cylinder, 64.
+
+  Vascular system, 111, 113, 335.
+
+  Vegetative reproduction, 358.
+
+  Veil, 371.
+
+  Veins, 173-176.
+
+  Venter, 391.
+
+  Ventral, Figs. 390, 391.
+
+  Vernation, 155.
+
+  Vessels, 111.
+
+  Vexillum, 238, 239.
+
+  Vibrio, 348.
+
+  Vitality of seeds, 34; Exp. 30.
+
+  Volva, 371.
+
+
+  Water roots, 39, 84.
+
+  Whorled leaves, 168.
+
+  Wind pollination, 274, 275.
+
+  Wings, 238.
+
+  Winter spores, 360.
+
+
+  Xerophyte, 317.
+
+  Xerophyte societies, 317, 320-322.
+
+  Xylem, 114, 116.
+
+
+  Yeast, 356.
+
+  Yeast colony, 357.
+
+  Yellow trumpets, 209.
+
+  Yucca, 278.
+
+  Yucca moth, 278.
+
+
+  Zonation, 325, 327.
+    bilateral, 326.
+    concentric, 326.
+    horizontal, 326.
+    vertical, 326.
+
+  Zones of vegetation, 325.
+
+
+
+
+TRANSCRIBER’S NOTE
+
+
+  Obvious typographical errors and punctuation errors have been
+  corrected after careful comparison with other occurrences within
+  the text and consultation of external sources.
+
+  Some hyphens in words have been silently removed, some added,
+  when a predominant preference was found in the original book.
+
+  Except for those changes noted below, all misspellings in the text,
+  and inconsistent or archaic usage, have been retained.
+
+  p.  45: ‘many of them has’        amended to ‘many of them have’
+  p. 281: ‘are adpated’             amended to ‘are adapted’
+  p. 291: ‘and as it can, moveover’ amended to ‘and as it can, moreover’
+  p. 354: ‘eruption of Krakatao’    amended to ‘eruption of Krakatoa’
+
+
+
+
+*** END OF THE PROJECT GUTENBERG EBOOK 78430 ***
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+<body>
+<div style='text-align:center'>*** START OF THE PROJECT GUTENBERG EBOOK 78430 ***</div>
+
+<div class="transnote">
+<p>TRANSCRIBER’S NOTE</p>
+
+<p>Some minor changes to the text are noted at the end of the book.</p>
+</div>
+
+<figure class="figcenter illowp60" id="cover" style="max-width: 112.5em;">
+  <img class="w100" src="images/cover.jpg" alt="Book Cover">
+</figure>
+
+<hr class="chap x-ebookmaker-drop">
+<div class="chapter"></div>
+
+<h1>
+<span class="fs120">A PRACTICAL COURSE IN<br>
+BOTANY</span></h1>
+<br>
+
+<p class="center">
+<span class="fs80">WITH ESPECIAL REFERENCE TO ITS BEARINGS ON</span><br>
+<br>
+<span class="fs120">AGRICULTURE, ECONOMICS, AND SANITATION</span><br>
+<br>
+<br>
+<span class="fs80">BY</span><br>
+<br>
+<span class="fs120">E. F. ANDREWS</span><br>
+<span class="fs60">AUTHOR OF “BOTANY ALL THE YEAR ROUND”</span><br>
+<br>
+<br>
+<span class="fs80">WITH EDITORIAL REVISION BY</span><br>
+<br>
+<span class="fs100">FRANCIS E. LLOYD</span><br>
+<br>
+<span class="fs80">MACDONALD PROFESSOR OF BOTANY, McGILL UNIVERSITY,<br>
+FORMERLY OF ALABAMA POLYTECHNIC INSTITUTE</span><br>
+</p>
+
+<figure class="figcenter illowp75" id="i_001colophon" style="max-width: 6.1875em;">
+  <img class="w100" src="images/i_001colophon.jpg" alt="">
+</figure><br>
+
+
+<p class="center">
+<span class="fs80">NEW YORK&emsp;⁘&emsp;CINCINNATI&emsp;⁘&emsp;CHICAGO</span><br>
+<span class="fs120 gesperrt ws1">AMERICAN BOOK COMPANY</span><br>
+</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+
+<div class="chapter">
+<p class="center">
+<span class="smcap fs80">Copyright, 1911, by<br>
+E. F. ANDREWS.</span><br>
+<br>
+<span class="smcap">Entered at Stationers’ Hall, London.</span></p>
+<hr class="r5">
+<p class="center">
+<span class="smcap fs60">ANDREW’S PR. BOTANY.<br>
+W. P. 7</span><br>
+</p>
+</div>
+
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_iii">[Pg iii]</span></p>
+
+<h2 class="nobreak" id="PREFACE">PREFACE</h2>
+</div>
+
+
+<p>In preparing the present volume, the aim of the writer has
+been to meet all the college entrance requirements and at the
+same time to bring the study of botany into closer touch with
+the practical business of life by stressing its relations with
+agriculture, economics, and, in certain of its aspects, with sanitation.
+While technical language has been avoided so far
+as the requirements of scientific accuracy will permit, the
+student is not encouraged to shirk the use of necessary botanical
+terms, out of a mere superstitious fear of words because
+they happen to be a little new or unfamiliar. Such a practice
+not only leads to careless and inaccurate modes of expression,
+but tends to foster a slovenly habit of mind, and in the long run
+causes the waste of more time and labor in the search after
+roundabout, and often misleading, substitutes, than it would
+require to master the proper use of a few new words and
+phrases.</p>
+
+<p>In the choice of materials for experiment and illustration,
+the endeavor has been to call for such only as are familiar and
+easily obtained. The specimens for flower dissection have been
+selected mainly from common cultivated kinds, because their
+wide distribution makes them easy to obtain everywhere, while
+in cities and large towns they are practically the only specimens
+available. Another important consideration has been the desire
+to spare our native wild flowers, or at least not to hasten the
+extinction with which they are threatened by the ravages of Sunday
+excursionists and summer tourists, to whose unthinking,
+but none the less destructive, incursions, the automobile has laid
+open the most secret haunts of nature. The influence of the
+public school teacher, and more especially the teacher of botany,
+is the most potent factor from which we can hope for aid in
+putting a stop to the relentless persecution that has practically
+exterminated many of our choicest wild plants and is fast<span class="pagenum" id="Page_iv">[Pg iv]</span>
+reducing the civilized world to a depressing monotony of
+weediness and artificiality. Except for purely systematic and
+anatomical work, flowers can be studied to better purpose in
+their living, active state than as dead subjects for dissection;
+and the best way to show our interest in them, or to get the
+most rational enjoyment out of them, is not, as a general thing,
+to cut their heads off and throw them away to wither and die
+by the roadside. The teacher, by instilling into the minds of
+the rising generation a reverence for plant life, may do a great
+deal to aid in the conservation of one of our chief national assets
+for the gratification of the higher esthetic instincts. The fruits
+and flowers of cultivation do not stand in the same need of protection,
+since they are produced solely with a view to the use
+and pleasure of man, and their propagation is provided for to
+meet all his demands.</p>
+
+<p>To avoid too frequent interruptions of the subject matter,
+the experiments are grouped together at the beginning or end
+of the sections to which they belong, according as they are
+intended to explain what is coming, or to illustrate what has
+gone before. A few exceptions are made in cases where the
+experiment is such an integral part of the subject that it would
+be meaningless if separated from the context. Under no
+circumstances should those capable of being performed in the
+schoolroom be omitted, as much of the information which the
+book is intended to give is conveyed by their means. For this
+reason, and also because the aim of the book is to present the
+science from a practical rather than from an academic point of
+view, the experiments outlined are for the most part of a simple,
+practical nature, such as can be performed by the pupils themselves
+with a moderate expenditure of ingenuity and money.
+The experience of the writer has been that for the average boy
+or girl who wishes to get a good general knowledge of the
+subject, but does not propose to become a specialist in botany,
+the best results are often obtained by the use of the simplest
+and most familiar appliances, as in this way attention is not
+distracted from the experiment itself to the unfamiliar apparatus
+for making it. In saying this, it is not meant to underrate<span class="pagenum" id="Page_v">[Pg v]</span>
+the value of a complete laboratory equipment, but merely
+to emphasize the fact that the lack of it, while a disadvantage,
+need not be an insuperable bar to the successful teaching of
+botany. It is, of course, taken for granted that in schools provided
+with a suitable laboratory outfit, teachers will be prepared
+to supplement or to replace the exercises here outlined
+with such others as in their judgment the subject may demand.
+There are as many ideals in teaching as there are teachers, and
+the most that a textbook can do is to present a working model
+which every teacher is free to modify in accordance with his
+or her own method.</p>
+
+<p>The writer takes pleasure in acknowledging here the many
+obligations due to Professor Francis E. Lloyd, of the Botanical
+Department of the Alabama Polytechnic Institute, at Auburn,
+Ala., for his valuable aid in the revision of the manuscript, for
+the highly interesting series of illustrations relating to phototropic
+movements, and for advice and information on points
+demanding expert knowledge which have contributed very materially
+to whatever merit this volume may possess.</p>
+
+<p>Other members of the Auburn faculty to whom the author
+feels especially indebted are Mr. C. S. Ridgeway, assistant in the
+Botanical Department, Professor J. E. Duggar, of the Agricultural
+Department, and Dr. B. B. Ross and Professor C. W.
+Williamson of the Department of Chemistry. Acknowledgments
+are due also to Professor George Wood of the Boys’ High
+School, Brooklyn, for suggestions which have been of great
+assistance in the preparation of this work; to Professor W. R.
+Dodson, of the University of Louisiana, for illustrative material
+furnished, and to Professor William Trelease for the loan of
+original material used in reproducing the beautiful cuts from
+the Reports of the Missouri Botanical Garden, credit for which
+is given in the proper place.</p>
+
+<p>For original photographs and drawings by the author, and
+familiar selections from well-known works, which can be generally
+recognized, it has not been thought necessary to give
+special credit.</p>
+
+<p class="right">
+E. F. ANDREWS.<br>
+</p>
+
+<div class="blockquot">
+
+<p><span class="smcap">Auburn, Alabama.</span></p>
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_vi">[Pg vi]</span></p>
+
+<h2 class="nobreak" id="FULL-PAGE_ILLUSTRATIONS">FULL-PAGE ILLUSTRATIONS</h2>
+</div>
+
+
+<table class="autotable fs90 wd70">
+<tr>
+<td class="tdl fs80">PLATE</td>
+<td class="tdr fs80">PAGE</td>
+</tr>
+<tr>
+<td class="tdl smcap">&nbsp; 1. A grove of live oaks near Savannah, Georgia</td>
+<td class="tdr"><i><a href="#i_010">Frontispiece</a></i></td>
+</tr>
+</table>
+
+<table class="autotable fs90 wd70 smcap">
+<tr>
+<td class="tdl">&nbsp; 2. Carrying water over the Mississippi levee by siphon to irrigate rice fields</td>
+<td class="tdr"><a href="#Page_8">8</a></td>
+</tr>
+<tr>
+<td class="tdl">&nbsp; 3. Aërial roots of a Mexican strangling fig</td>
+<td class="tdr"><a href="#Page_73">73</a></td>
+</tr>
+<tr>
+<td class="tdl">&nbsp; 4. A forest of bamboo</td>
+<td class="tdr"><a href="#Page_99">99</a></td>
+</tr>
+<tr>
+<td class="tdl">&nbsp; 5. A group of conifers</td>
+<td class="tdr"><a href="#Page_108">108</a></td>
+</tr>
+<tr>
+<td class="tdl">&nbsp; 6. A white oak, showing the great spread of branches</td>
+<td class="tdr"><a href="#Page_117">117</a></td>
+</tr>
+<tr>
+<td class="tdl">&nbsp; 7. A timber tree spoiled by standing too much alone</td>
+<td class="tdr"><a href="#Page_125">125</a></td>
+</tr>
+<tr>
+<td class="tdl">&nbsp; 8. An American elm, illustrating deliquescent growth</td>
+<td class="tdr"><a href="#Page_130">130</a></td>
+</tr>
+<tr>
+<td class="tdl">&nbsp; 9. Vegetation of a moist, shady ravine</td>
+<td class="tdr"><a href="#Page_151">151</a></td>
+</tr>
+<tr>
+<td class="tdl">10. A mosaic of moonseed leaves</td>
+<td class="tdr"><a href="#Page_179">179</a></td>
+</tr>
+<tr>
+<td class="tdl">11. Hybrid between a red and a white carnation</td>
+<td class="tdr"><a href="#Page_227">227</a></td>
+</tr>
+<tr>
+<td class="tdl">12. Gooseberries, showing improvement by selection</td>
+<td class="tdr"><a href="#Page_251">251</a></td>
+</tr>
+<tr>
+<td class="tdl">13. The effects of irrigation</td>
+<td class="tdr"><a href="#Page_272">272</a></td>
+</tr>
+<tr>
+<td class="tdl">14. A xerophyte formation of yuccas and switch plants</td>
+<td class="tdr"><a href="#Page_282">282</a></td>
+</tr>
+<tr>
+<td class="tdl">15. A giant tulip tree of the South Atlantic forest region</td>
+<td class="tdr"><a href="#Page_293">293</a></td>
+</tr>
+</table>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_vii">[Pg vii]</span></p>
+
+<h2 class="nobreak" id="CONTENTS">CONTENTS</h2>
+</div>
+
+<table class="autotable fs90 smcap">
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#CH_I">CHAPTER I</a>. THE SEED</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdr fs80" colspan="2">PAGE</td>
+</tr>
+<tr>
+<td class="tdr">I.</td>
+<td class="tdl"><a href="#CH_I_I">The Storage of Food in Seeds</a></td>
+<td class="tdr">1</td>
+</tr>
+<tr>
+<td class="tdr">II.</td>
+<td class="tdl"><a href="#CH_I_II">Some Physiological Properties of Seeds</a></td>
+<td class="tdr">10</td>
+</tr>
+<tr>
+<td class="tdr">III.</td>
+<td class="tdl"><a href="#CH_I_III">Types of Seeds</a></td>
+<td class="tdr">12</td>
+</tr>
+<tr>
+<td class="tdr">IV.</td>
+<td class="tdl"><a href="#CH_I_IV">Seed Dispersal</a></td>
+<td class="tdr">21</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl"><a href="#CH_I_FIELD">Field Work</a></td>
+<td class="tdr">28</td>
+</tr>
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#CH_II">CHAPTER II</a>. GERMINATION AND GROWTH</td>
+</tr>
+<tr>
+<td class="tdr">I.</td>
+<td class="tdl"><a href="#CH_II_I">Processes accompanying Germination</a></td>
+<td class="tdr">29</td>
+</tr>
+<tr>
+<td class="tdr">II.</td>
+<td class="tdl"><a href="#CH_II_II">Conditions of Germination</a></td>
+<td class="tdr">33</td>
+</tr>
+<tr>
+<td class="tdr">III.</td>
+<td class="tdl"><a href="#CH_II_III">Development of the Seedling</a></td>
+<td class="tdr">40</td>
+</tr>
+<tr>
+<td class="tdr">IV.</td>
+<td class="tdl"><a href="#CH_II_IV">Growth</a></td>
+<td class="tdr">47</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl"><a href="#CH_II_FIELD">Field Work</a></td>
+<td class="tdr">52</td>
+</tr>
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#CH_III">CHAPTER III</a>. THE ROOT</td>
+</tr>
+<tr>
+<td class="tdr">I.</td>
+<td class="tdl"><a href="#CH_III_I">Osmosis and the Action of the Cell</a></td>
+<td class="tdr">53</td>
+</tr>
+<tr>
+<td class="tdr">II.</td>
+<td class="tdl"><a href="#CH_III_II">Mineral Nutriments absorbed by Plants</a></td>
+<td class="tdr">58</td>
+</tr>
+<tr>
+<td class="tdr">III.</td>
+<td class="tdl"><a href="#CH_III_III">Structure of the Root</a></td>
+<td class="tdr">61</td>
+</tr>
+<tr>
+<td class="tdr">IV.</td>
+<td class="tdl"><a href="#CH_III_IV">The Work of Roots</a></td>
+<td class="tdr">65</td>
+</tr>
+<tr>
+<td class="tdr">V.</td>
+<td class="tdl"><a href="#CH_III_V">Different Forms of Roots</a></td>
+<td class="tdr">72</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl"><a href="#CH_III_FIELD">Field Work</a></td>
+<td class="tdr">80</td>
+</tr>
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#CH_IV">CHAPTER IV</a>. THE STEM</td>
+</tr>
+<tr>
+<td class="tdr">I.</td>
+<td class="tdl"><a href="#CH_IV_I">Forms and Growth of Stems</a></td>
+<td class="tdr">81</td>
+</tr>
+<tr>
+<td class="tdr">II.</td>
+<td class="tdl"><a href="#CH_IV_II">Modifications of the Stem</a></td>
+<td class="tdr">88</td>
+</tr>
+<tr>
+<td class="tdr">III.</td>
+<td class="tdl"><a href="#CH_IV_III">Stem Structure</a></td>
+<td class="tdr"></td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_IV_III_A">A. Monocotyls</a></td>
+<td class="tdr">96</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_IV_III_B">B. Herbaceous Dicotyls</a></td>
+<td class="tdr">102</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_IV_III_C">C. Woody Stemmed Dicotyls</a></td>
+<td class="tdr">107<span class="pagenum" id="Page_viii">[Pg viii]</span></td>
+</tr>
+<tr>
+<td class="tdr">IV.</td>
+<td class="tdl"><a href="#CH_IV_IV">The Work of Stems</a></td>
+<td class="tdr">112</td>
+</tr>
+<tr>
+<td class="tdr">V.</td>
+<td class="tdl"><a href="#CH_IV_V">Wood Structure in its Relation to Industrial Uses</a></td>
+<td class="tdr">118</td>
+</tr>
+<tr>
+<td class="tdr">VI.</td>
+<td class="tdl"><a href="#CH_IV_VI">Forestry</a></td>
+<td class="tdr">124</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl"><a href="#CH_IV_FIELD">Field Work</a></td>
+<td class="tdr">128</td>
+</tr>
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#CH_V">CHAPTER V</a>. BUDS AND BRANCHES</td>
+</tr>
+<tr>
+<td class="tdr">I.</td>
+<td class="tdl"><a href="#CH_V_I">Modes of Branching</a></td>
+<td class="tdr">131</td>
+</tr>
+<tr>
+<td class="tdr">II.</td>
+<td class="tdl"><a href="#CH_V_II">Buds</a></td>
+<td class="tdr">138</td>
+</tr>
+<tr>
+<td class="tdr">III.</td>
+<td class="tdl"><a href="#CH_V_III">The Branching of Flower Stems</a></td>
+<td class="tdr">141</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl"><a href="#CH_V_FIELD">Field Work</a></td>
+<td class="tdr">145</td>
+</tr>
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#CH_VI">CHAPTER VI</a>. THE LEAF</td>
+</tr>
+<tr>
+<td class="tdr">I.</td>
+<td class="tdl"><a href="#CH_VI_I">The Typical Leaf and its Parts</a></td>
+<td class="tdr">147</td>
+</tr>
+<tr>
+<td class="tdr">II.</td>
+<td class="tdl"><a href="#CH_VI_II">The Veining and Lobing of Leaves</a></td>
+<td class="tdr">154</td>
+</tr>
+<tr>
+<td class="tdr">III.</td>
+<td class="tdl"><a href="#CH_VI_III">Transpiration</a></td>
+<td class="tdr">160</td>
+</tr>
+<tr>
+<td class="tdr">IV.</td>
+<td class="tdl"><a href="#CH_VI_IV">Anatomy of the Leaf</a></td>
+<td class="tdr">164</td>
+</tr>
+<tr>
+<td class="tdr">V.</td>
+<td class="tdl"><a href="#CH_VI_V">Food Making</a></td>
+<td class="tdr">168</td>
+</tr>
+<tr>
+<td class="tdr">VI.</td>
+<td class="tdl"><a href="#CH_VI_VI">The Leaf an Organ of Respiration</a></td>
+<td class="tdr">174</td>
+</tr>
+<tr>
+<td class="tdr">VII.</td>
+<td class="tdl"><a href="#CH_VI_VII">The Adjustment of Leaves to External Relations</a></td>
+<td class="tdr">177</td>
+</tr>
+<tr>
+<td class="tdr">VIII.</td>
+<td class="tdl"><a href="#CH_VI_VIII">Modified Leaves</a></td>
+<td class="tdr">189</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl"><a href="#CH_VI_FIELD">Field Work</a></td>
+<td class="tdr">194</td>
+</tr>
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#CH_VII">CHAPTER VII</a>. THE FLOWER</td>
+</tr>
+<tr>
+<td class="tdr">I.</td>
+<td class="tdl"><a href="#CH_VII_I">Dissection of Types with Superior Ovary</a></td>
+<td class="tdr">196</td>
+</tr>
+<tr>
+<td class="tdr">II.</td>
+<td class="tdl"><a href="#CH_VII_II">Dissection of Types with Inferior Ovary</a></td>
+<td class="tdr">204</td>
+</tr>
+<tr>
+<td class="tdr">III.</td>
+<td class="tdl"><a href="#CH_VII_III">Study of a Composite Flower</a></td>
+<td class="tdr">210</td>
+</tr>
+<tr>
+<td class="tdr">IV.</td>
+<td class="tdl"><a href="#CH_VII_IV">Specialized Flowers</a></td>
+<td class="tdr">214</td>
+</tr>
+<tr>
+<td class="tdr">V.</td>
+<td class="tdl"><a href="#CH_VII_V">Function and Work of the Flower</a></td>
+<td class="tdr">219</td>
+</tr>
+<tr>
+<td class="tdr">VI.</td>
+<td class="tdl"><a href="#CH_VII_VI">Hybridization</a></td>
+<td class="tdr">223</td>
+</tr>
+<tr>
+<td class="tdr">VII.</td>
+<td class="tdl"><a href="#CH_VII_VII">Plant Breeding</a></td>
+<td class="tdr">230</td>
+</tr>
+<tr>
+<td class="tdr">VIII.</td>
+<td class="tdl"><a href="#CH_VII_VIII">Ecology of the Flower</a></td>
+<td class="tdr"></td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_VII_VIII_A">A. The Prevention of Self-pollination</a></td>
+<td class="tdr">235</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_VII_VIII_B">B. Wind Pollination</a></td>
+<td class="tdr">239</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_VII_VIII_C">C. Insect Pollination</a></td>
+<td class="tdr">241</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_VII_VIII_D">D. Protective Adaptation</a></td>
+<td class="tdr">245</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl"><a href="#CH_VII_FIELD">Field Work</a></td>
+<td class="tdr">249<span class="pagenum" id="Page_ix">[Pg ix]</span></td>
+</tr>
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#CH_VIII">CHAPTER VIII</a>. FRUITS</td>
+</tr>
+<tr>
+<td class="tdr">I.</td>
+<td class="tdl"><a href="#CH_VIII_I">Horticultural and Botanical Fruits</a></td>
+<td class="tdr">250</td>
+</tr>
+<tr>
+<td class="tdr">II.</td>
+<td class="tdl"><a href="#CH_VIII_II">Fleshy Fruits</a></td>
+<td class="tdr">255</td>
+</tr>
+<tr>
+<td class="tdr">III.</td>
+<td class="tdl"><a href="#CH_VIII_III">Dry Fruits</a></td>
+<td class="tdr">260</td>
+</tr>
+<tr>
+<td class="tdr">IV.</td>
+<td class="tdl"><a href="#CH_VIII_IV">Accessory, Aggregate, and Multiple Fruits</a></td>
+<td class="tdr">265</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl"><a href="#CH_VIII_FIELD">Field Work</a></td>
+<td class="tdr">269</td>
+</tr>
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#CH_IX">CHAPTER IX</a>. THE RESPONSE OF THE PLANT TO ITS SURROUNDINGS</td>
+</tr>
+<tr>
+<td class="tdr">I.</td>
+<td class="tdl"><a href="#CH_IX_I">Ecological Factors</a></td>
+<td class="tdr">271</td>
+</tr>
+<tr>
+<td class="tdr">II.</td>
+<td class="tdl"><a href="#CH_IX_II">Plant Associations</a></td>
+<td class="tdr">277</td>
+</tr>
+<tr>
+<td class="tdr">III.</td>
+<td class="tdl"><a href="#CH_IX_III">Zones of Vegetation</a></td>
+<td class="tdr">288</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl"><a href="#CH_IX_FIELD">Field Work</a></td>
+<td class="tdr">294</td>
+</tr>
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#CH_X">CHAPTER X</a>. CRYPTOGAMS</td>
+</tr>
+<tr>
+<td class="tdr">I.</td>
+<td class="tdl"><a href="#CH_X_I">Their Place in Nature</a></td>
+<td class="tdr">296</td>
+</tr>
+<tr>
+<td class="tdr">II.</td>
+<td class="tdl"><a href="#CH_X_II">Algæ</a></td>
+<td class="tdr">299</td>
+</tr>
+<tr>
+<td class="tdr">III.</td>
+<td class="tdl"><a href="#CH_X_III">Fungi</a></td>
+<td class="tdr">303</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_X_III_A">A. Bacteria</a></td>
+<td class="tdr">306</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_X_III_B">B. Yeasts</a></td>
+<td class="tdr">314</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_X_III_C">C. Rusts</a></td>
+<td class="tdr">317</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl pad2"><a href="#CH_X_III_D">D. Mushrooms</a></td>
+<td class="tdr">323</td>
+</tr>
+<tr>
+<td class="tdr">IV.</td>
+<td class="tdl"><a href="#CH_X_IV">Lichens</a></td>
+<td class="tdr">329</td>
+</tr>
+<tr>
+<td class="tdr">V.</td>
+<td class="tdl"><a href="#CH_X_V">Liverworts</a></td>
+<td class="tdr">334</td>
+</tr>
+<tr>
+<td class="tdr">VI.</td>
+<td class="tdl"><a href="#CH_X_VI">Mosses</a></td>
+<td class="tdr">341</td>
+</tr>
+<tr>
+<td class="tdr">VII.</td>
+<td class="tdl"><a href="#CH_X_VII">Fern Plants</a></td>
+<td class="tdr">344</td>
+</tr>
+<tr>
+<td class="tdr">VIII.</td>
+<td class="tdl"><a href="#CH_X_VIII">The Relation between Cryptogams and Seed Plants</a></td>
+<td class="tdr">354</td>
+</tr>
+<tr>
+<td class="tdr">IX.</td>
+<td class="tdl"><a href="#CH_X_IX">The Course of Plant Evolution</a></td>
+<td class="tdr">359</td>
+</tr>
+<tr>
+<td class="tdr"></td>
+<td class="tdl"><a href="#CH_X_FIELD">Field Work</a></td>
+<td class="tdr">362</td>
+</tr>
+<tr>
+<td class="tdc pad-chap" colspan="3"><a href="#APPENDIX">APPENDIX</a></td>
+</tr>
+<tr>
+<td class="tdr">1.</td>
+<td class="tdl"><a href="#APP_1">Systematic Botany</a></td>
+<td class="tdr">364</td>
+</tr>
+<tr>
+<td class="tdr">2.</td>
+<td class="tdl"><a href="#APP_2">Weights, Measures, and Temperatures</a></td>
+<td class="tdr">367</td>
+</tr>
+</table>
+
+<p><span class="pagenum" id="Page_x">[Pg x]</span></p>
+
+<figure class="figcenter illowp100" id="i_010" style="max-width: 100.25em;">
+  <img class="w100" src="images/i_010.jpg" alt="">
+  <figcaption><p class='center'><span class="smcap">Plate 1.</span>—Live oaks covered with Spanish moss (<i>Tillandsia</i>).</p></figcaption>
+</figure>
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_1">[Pg 1]</span></p>
+
+<h2 class="nobreak" id="CH_I">CHAPTER I. THE SEED</h2>
+</div>
+
+
+<h3 id="CH_I_I">I. THE STORAGE OF FOOD IN SEEDS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—In addition to the four food tests described in <a href="#exp-1">Exps.
+1-6</a>, there should be provided some raw starch, a solution of grape
+sugar, the white of a hard-boiled egg, and any fatty substance, such
+as lard or oil. For Exps. 8 and 9, a little diastase solution will be necessary.
+“Taka” diastase, made from rice acted upon by a fungus, can
+be obtained for a trifle at almost any drug store.</p>
+
+<p><span class="smcap">Living material.</span>—Grains of corn and wheat, and seeds of some
+kind of bean, the larger the better. The “horse bean” (<i>Vicia faba</i>), if
+it can be obtained, makes an excellent object for study, as the cells are
+so large that they can be seen with the naked eye. For showing the
+presence of proteins (aleurone grains) and oily matter, use thin cross sections
+through the kernel of a castor bean or a Brazil nut. Specimens
+for the study of the individual cell will be found in the hairs growing on
+squash seedlings, in the epidermis of one of the inner coats of an onion, in
+the roots of oat or radish seedlings, or in the section of a young corn root.</p>
+
+<p>A compound microscope will be required for this study.</p>
+</div>
+
+<p id="p-1"><b>1. The economic importance of seeds.</b>—As a source of
+food to both man and the lower animals, the importance of
+seeds can hardly be overrated. All the flour, meal, rice,
+hominy, and other breadstuffs sold in the market come from
+them, to say nothing of the fleece from the cotton seed that
+clothes the greater part of the world, besides furnishing a
+substitute for lard and an important food for cattle. The
+oils and fats stored in nuts are also to be taken into account,
+the peanut alone yielding the greater part of the so-called
+olive oil of commerce. Since the value of our farm crops
+depends largely upon the kind and quantity of these substances
+furnished by them, it is worth our while, as a matter
+of economic as well as scientific interest, to learn something
+about the nature of the different foods contained in plants.</p>
+
+<p><span class="pagenum" id="Page_2">[Pg 2]</span></p>
+
+<figure class="figcenter illowp100" id="i_012" style="max-width: 50em;">
+  <img class="w100" src="images/i_012.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 1-3.</span>—The world’s three most important food grains (magnified): 1, section
+of a rice grain; <i>a</i>, cuticle; <i>b</i>, aleurone, or protein layer; <i>c</i>, starch cells; <i>d</i>, germ;
+2, section of a wheat grain; <i>k</i>, germ; <i>s</i>, starch; <i>a</i>, gluten; <i>t</i>, <i>t</i>, <i>t</i>, layers of the seed
+coat; 3, section of a grain of corn; <i>c</i>, husk; <i>e</i>, aleurone layer containing proteins;
+<i>eg</i>, yellowish, horny endosperm, containing proteins and starch; <i>ew</i>, lighter starchy
+endosperm: the darker part below is rich in oil and proteins, and contains the <i>embryo</i>,
+consisting of the absorbing organ, or <i>cotyledon</i>, <i>sc</i>; the rudimentary bud, <i>s</i>; and
+the root, <i>w</i>. (1, from Circular 77, La. Exp. Station; 2, from Francé; 3, from Sachs.)</p></figcaption>
+</figure>
+
+<p id="p-2"><b>2. Why food is stored in seeds.</b>—The one purpose
+for which plants produce their seed is to give rise to a new
+generation and so carry on the life of the species. The
+seed is the nursery, so to speak, in which the germ destined
+to produce a new plant
+is sheltered until it is
+ready to begin an independent
+existence. But
+the young plant, like
+the young animal, is
+incapable of providing
+for itself at first, and
+would die unless it received
+nourishment from
+the mother plant until
+it has formed roots and
+leaves so that it can
+manufacture food for<span class="pagenum" id="Page_3">[Pg 3]</span>
+itself. Plants in general require very much the same food
+that animals do, and they have the power, which animals
+have not, of manufacturing it out of the crude materials contained
+in the soil water and in the air. Such of these foods
+as are not needed for immediate consumption, they store up
+to serve as a provision for the young shoot when the seed
+begins to germinate.</p>
+
+<figure class="figcenter illowp60" id="i_012a" style="max-width: 25em;">
+  <img class="w100" src="images/i_012a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 4-7.</span>—Sections of corn grains showing
+different qualities of food contents: 4, 5, small
+germ and large proportion of horny part, showing
+high protein; 6, 7, large germ and smaller proportion
+of horny part, showing high oil content.</p></figcaption>
+</figure>
+
+<p id="p-3"><b>3. Food substances contained in seeds.</b>—There are four
+principal classes of food stored in seeds: <em>sugars</em>, <em>starches</em>, <em>oils</em>,
+and <em>proteins</em>. The first are held in solution and can be
+detected, if in sufficient quantity, by the taste. The most
+important varieties of this group are cane and grape sugar,
+the latter occurring most abundantly in fruits, the former in
+roots and stems. Oil usually occurs in the form of globules.
+It is very abundant in some seeds, <i>e.g.</i> flax, castor bean, and
+Brazil nut. In the corn grain it is found in the part constituting
+the germ, or embryo (<a href="#i_012a">Figs. 6, 7</a>). Starches and proteins
+occur in the form of small granules, which have specific
+shapes in different plants (<a href="#i_013">Figs. 8, 9</a>). Those containing proteins
+are called <em>aleurone</em> grains, and are, as a rule, smaller
+than the starch grains with which they are intermixed in the
+bean and some other seeds. In wheat, corn, rice, and most
+grains they form a layer just inside the husk, as shown in
+<a href="#i_014">Fig. 10</a>. This is the reason why polished rice and finely
+bolted flour are less nutritious
+than the darker
+kinds, from which this
+valuable food substance
+has not been removed.
+The two most familiar
+kinds of proteins are the
+<em>albumins</em>, of which the
+white of an egg is
+a well-known example,
+and the <em>glutins</em>, which give to the dough of wheat flour and
+oatmeal their peculiar gummy or “glutinous” structure.</p>
+
+<figure class="figcenter illowp60" id="i_013" style="max-width: 25em;">
+  <img class="w100" src="images/i_013.jpg" alt="">
+  <figcaption><p id="fig-8"><span class="smcap">Figs. 8-9.</span>—Different forms of starch grains:
+8, rice; 9, wheat.</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_4">[Pg 4]</span></p>
+
+<p id="p-4"><b>4. Organic foods.</b>—These four substances, starch, sugar,
+fats, and proteins, with some others of less frequent occurrence,
+are called <em>organic
+foods</em>, because they are produced,
+in a state of nature,
+only through the action of
+organized living bodies, or,
+more strictly speaking, of
+living vegetable bodies.</p>
+
+<figure class="figcenter illowp50" id="i_014" style="max-width: 25em;">
+  <img class="w100" src="images/i_014.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 10.</span>—Transverse section near the
+outside of a wheat grain: <i>e</i>, the husk; <i>a</i>, cells
+containing protein granules; <i>s</i>, starch cells
+(<i>after</i> Tschirch).</p></figcaption>
+</figure>
+
+<p id="p-5"><b>5. Our dependence upon
+plants.</b>—While the animal
+organism can digest and
+assimilate these substances
+after they have been formed
+by plants, it has no power
+to manufacture them for
+itself, and, so far as we know at present, is wholly dependent
+upon the vegetable world for these necessaries of life.
+In one sense the whole animal kingdom may be said to be
+parasitic on plants. The wolf that eats a lamb is getting
+his food indirectly from the grains and grasses consumed
+by its victim, and the lion that devours the wolf that ate
+the lamb is only one step further removed from a vegetable
+diet.</p>
+
+<p id="p-6"><b>6. The vegetable cell.</b>—If you will break open a well-soaked
+horse bean and examine the contents with a lens, you
+will see that they are composed of small oval or roundish
+granules packed together like stones in a piece of masonry.
+These little bodies, called <em>cells</em>, are the ultimate units out
+of which all animal and vegetable structures are built up, as
+a wall is built of bricks and stones. They differ very much
+from bricks and stones, however, in that they are, or have
+been, living structures with their periods of growth, activity,
+decline, and death, just like other living matter, as will be
+seen by and by, when we come to look more particularly
+into their life history. They consist usually of an inclosing<span class="pagenum" id="Page_5">[Pg 5]</span>
+membrane which contains a living substance called
+<em>protoplasm</em>. This is the essential part of the cell, and, so
+far as we know at present, the physical basis of all life.
+Cells are commonly more or less rounded in shape, though
+they take different forms according to the purpose they
+serve. Sometimes, as in the fibers of cotton and the down
+of young leaves, they are long and hairlike; when closely
+packed, they often become angular by pressure, like those
+shown in <a href="#i_014">Figs. 10</a>, <a href="#i_015">11</a>. The cells composing the thick body of
+the bean are for the most part starch and other substances
+stored up for food, which render observation difficult. It
+will, therefore, be better to choose for a study of the individual
+cell some kind that will show the essential parts more
+distinctly.</p>
+
+<figure class="figright illowp30" id="i_015" style="max-width: 25em;">
+  <img class="w100" src="images/i_015.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 11</span>—Typical cells:
+<i>n</i>, nucleus; <i>p</i>, protoplasm;
+<i>w</i>, cell wall; <i>s</i>, sap.</p></figcaption>
+</figure>
+
+<p id="p-7"><b>7. Microscopic examination of a cell.</b>—Place under a high
+power of the microscope a portion of fresh skin from one of
+the inside scales of an onion, or a piece
+of the root tip of a very young corn or oat
+seedling, and fix your attention on one of
+the individual cells. Notice (1) the cell
+wall or inclosing membrane, <i>w</i> (<a href="#i_015">Fig. 11</a>);
+(2) the protoplasm, <i>p</i>, which may be
+recognized by its granular appearance;
+(3) the <em>nucleus</em>, <i>n</i>; and (4) the cell sap, <i>s</i>.
+In very young cells the protoplasm will
+be seen to fill most of the interior; but
+in mature ones, like the large one on the
+right of the figure, it forms a thin lining
+around the wall, with the nucleus on one side, while the cell
+sap, composed of various substances in solution, occupies the
+central portion. Though there is generally an inclosing wall,
+this is not essential, its office being to give strength and mechanical
+support by holding the contents together, as an
+India-rubber bag holds water. It is the turgidity of the cell,
+when distended with liquid, that gives firmness to herbaceous
+plants and the tender parts of woody ones. This<span class="pagenum" id="Page_6">[Pg 6]</span>
+may be illustrated by observing the difference between a
+rubber bag when quite full and when only half full of water,
+or a football when partially and when fully inflated. In
+its simplest form, however, the cell is a mere particle of
+protoplasm, which has one part, constituting the nucleus,
+a little more dense in appearance than the rest, but this
+kind is not common in vegetable structures.</p>
+
+<p id="p-8"><b>8. How food substances get into the cells.</b>—As there
+are no openings in the cell walls, the only way substances
+can get into a cell or out of it is by soaking through the
+inclosing membrane, as will be explained in a later chapter.
+Since starch, oil, and proteins, the most important foods
+stored in seeds, are none of them soluble in the cell sap, it is
+clear that they could not have got into the cells in their
+present state, but must have undergone some change by
+which they were rendered capable of passing through the
+cell wall.</p>
+
+<p id="p-9"><b>9. Digestion.</b>—The process by which this change is
+brought about is known as <em>digestion</em>, from its similarity to
+the same function in animals. Not only are foods, in the
+state in which we find them stored in the seed, incapable
+of passing through the cell wall, but the protoplasm, the
+living part of the cell, has no power to assimilate and to
+utilize these substances as food until they have been reduced
+to a soluble form in which they can be diffused freely
+from cell to cell through any part of the plant. By <em>diffusion</em>
+is meant the gradual spread of soluble substances through
+the containing medium, as when a lump of sugar or salt,
+dropped into a glass of water, dissolves and slowly diffuses
+through the contents, imparting a sweet or salty taste to the
+whole.</p>
+
+<figure class="figright illowp50" id="i_017" style="max-width: 25em;">
+  <img class="w100" src="images/i_017.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 12.</span>—Starch grains of wheat in
+different stages of disintegration under the
+action of a ferment (diastase), accompanying
+germination: <i>a</i>, slightly corroded; <i>b</i>, <i>c</i>,
+and <i>d</i>, more advanced stages of decomposition.</p></figcaption>
+</figure>
+
+<p>During the process of digestion the different kinds of
+food are acted upon and made soluble by certain chemical
+ferments, which are secreted in plants for the purpose. The
+digestion of starch, the most abundant of plant foods, is
+effected by diastase, a common ferment obtained from germinating<span class="pagenum" id="Page_7">[Pg 7]</span>
+grains of barley, wheat, corn, rice, etc. By the
+presence of diastase starch is converted into grape sugar, a
+substance which is readily soluble in water, and which can
+be diffused easily through the tissues of the plant to any
+part where it is needed. In this way food travels from the
+leaf, where it is made, to
+the seed, where the sugar is
+generally reconverted into
+starch and stored up for
+future use, though sometimes,
+as in the sugar corn
+and sugar pea, it remains
+in part unchanged. The
+kernels of this kind of corn
+can be distinguished readily
+from those of the ordinary
+starch corn, after maturity,
+by their wrinkled appearance,
+owing to their greater
+loss of water in drying.</p>
+
+<p id="p-10"><b>10. Food tests.</b>—In order
+to tell whether any of
+the food substances named
+occur in the seeds that we are going to examine, it will be
+necessary to understand a few simple tests by which their
+presence may be recognized. The chemicals required can
+be ordered ready for use from a druggist or may be prepared
+in the laboratory as needed, according to the directions
+given. Write in your notebook a brief account of each experiment
+made, with the conclusions drawn from it.</p>
+
+<div class="blockquot">
+
+<p id="exp-1"><span class="smcap">Experiment 1. To detect the presence of fats.</span>—Rub a small lump
+of butter or a drop of oil on a piece of thin white paper. What is the effect?</p>
+
+<p id="exp-2"><span class="smcap">Experiment 2. Another test for fats.</span>—Place some macerated
+alcanna root in a vessel with alcohol enough to cover it, and leave for an
+hour. Add an equal bulk of water and filter. The solution will stain
+fats, oils, and resins deep red.</p>
+</div>
+
+<p><span class="pagenum" id="Page_8">[Pg 8]</span></p>
+
+<figure class="figcenter illowp100" id="i_018" style="max-width: 99.5625em;">
+  <img class="w100" src="images/i_018.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 2.</span>—Carrying water over the Mississippi levee by siphon to irrigate rice fields. (<i>From</i> Circular of La. Exp. Station.)</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_9">[Pg 9]</span></p>
+
+<div class="blockquot">
+
+<p id="exp-3"><span class="smcap">Experiment 3. To show the presence of starch.</span>—Put a drop of
+iodine solution on some starch. What change of color takes place? To
+make iodine solution, add to one part of iodine crystals 4 parts potassium
+iodide and 95 parts water. It should be kept in the dark, as light
+decomposes it. Iodine colors starch blue, protein substances light brown.
+In testing for starch, the solution should be diluted till it is of a pale color,
+otherwise the stain will be so deep as to appear black.</p>
+
+<p id="exp-4"><span class="smcap">Experiment 4. A test for proteins.</span>—Place a small quantity of
+the white of an egg, diluted with water, in a clean glass and add a few
+drops of nitric acid; or drop some of the acid on the white of a hard-boiled
+egg. What is the effect?</p>
+
+<p>Nitric acid turns proteins yellow; if the color is indistinct, add a drop
+of ammonia, when an orange color will ensue.</p>
+
+<p id="exp-5"><span class="smcap">Experiment 5. Another test for proteins.</span>—Place on the substance
+to be examined a drop of a saturated solution of cane sugar and
+water; add a drop of pure sulphuric acid; if proteins are present, they
+will be colored red. See also <a href="#exp-3">Exp. 3</a>.</p>
+
+<p id="exp-6"><span class="smcap">Experiment 6. A test for grape sugar.</span>—Heat a teaspoonful of
+Fehling’s Solution to the boiling point in a test tube (a common glass vial
+can be used by heating gradually in water) and pour in a few drops of
+grape sugar solution. Heat again and observe the color of the precipitate
+that forms.</p>
+
+<p>Fehling’s Solution may be obtained of the druggist, or, if preferred,
+it may be prepared in the laboratory as follows: (<i>a</i>) Dissolve 173 grams
+of crystallized Rochelle salts and 125 grams of caustic potash in 500 cc. of
+water; (<i>b</i>) dissolve 34.64 grams crystallized copper sulphate in 500 cc.
+of water, and mix equal parts as needed. (For English equivalents, see
+Appendix, Weights and Measures.) The two mixtures must be kept separate
+till wanted for use, or prepared fresh as needed.</p>
+
+<p>Grape Sugar causes Fehling’s Solution to form a red precipitate.</p>
+
+<p id="exp-7"><span class="smcap">Experiment 7. To show the difference between sugar and
+starch in regard to solubility.</span>—Mix some sugar with water and
+notice how readily it dissolves. Try the same experiment with starch
+and observe its different behavior.</p>
+
+<p id="exp-8"><span class="smcap">Experiment 8. To show how starch is disintegrated in the act
+of digestion.</span>—Place a few grains of starch on a slide, add a drop or
+two of diastase solution, and observe under the microscope; the starch
+granules will be seen to disintegrate and melt away. Even with a hand
+lens it can be seen, from the greater clearness of the liquid in comparison
+with a mixture of untreated starch and water, that the grains have been
+dissolved.</p>
+
+<p><span class="pagenum" id="Page_10">[Pg 10]</span></p>
+
+<p id="exp-9"><span class="smcap">Experiment 9. To show that diastase converts starch into
+sugar.</span>—Make a paste of boiled starch so thin that it looks like water.
+Pour a small quantity of it into each of two tubes, adding a little diastase
+to one and leaving the other untreated. Keep in a warm place for twenty-four
+hours, then test both tubes for starch, as directed in <a href="#exp-3">Exp. 3</a>, and note
+the result. If the diastase has not acted, add a little more and watch.</p>
+</div>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Name all the food and other economic products you can think of
+that are derived from the seed of maize; from wheat; from flaxseed;
+from cotton.</p>
+
+<p>2. Mention some seeds from which medicines are procured.</p>
+
+<p>3. Name all the seeds you can think of from which oil is obtained;
+starch; some that are rich in proteins. (<a href="#exp-1">Exps. 1-5</a>.)</p>
+
+<p>4. Describe some of the ways in which these products are frequently
+adulterated.</p>
+
+<p>5. If you were raising corn to sell to a starch factory, what part of
+the seed would you seek to develop? If to feed stock, what part? Why,
+in each case? (<a href="#p-3">3</a>; <a href="#i_012a">Figs. 4-7</a>.)</p>
+
+<p>6. What grain feeds more human beings than does any other?</p>
+
+<p>7. Name all the seeds you can think of that contain sugar in sufficient
+quantity to be detected without chemical tests; that is, by tasting alone.</p>
+
+<p>8. Is “coal oil” a mineral or an organic substance? Explain, by
+giving an account of its origin.</p>
+
+<p>9. What is gluten? (<a href="#p-3">3</a>.) Name some grains that are especially rich in it.</p>
+
+<p>10. Which of our three chief food grains is a water plant? (See <a href="#i_018">Plate
+2</a>.) Which grows farthest south? Which farthest north? Which one is
+of American origin?</p>
+</div>
+
+
+<h3 id="CH_I_II">II. SOME PHYSIOLOGICAL PROPERTIES OF SEEDS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Seeds of squash, pumpkin, or other melon; castor bean;
+any kind of common kidney bean; grains of Indian corn.</p>
+
+<p><span class="smcap">Appliances.</span>—In the absence of gas, an alcohol or kerosene lamp may
+be used for heating. A double boiler can easily be made by using two tin
+vessels of different sizes. Partly fill the larger one with water, set in it
+the smaller one with the substance to be heated, and place over a burner.
+A pair of scales, a strong six-ounce bottle, wire-netting, cord, and wax
+or paraffin should be provided.</p>
+
+<p id="exp-10"><span class="smcap">Experiment 10. Do seeds in their ordinary quiescent state
+contain any water?</span>—Place a number of beans, or grains of corn or
+wheat in a glass bottle, making a small perforation in the cork to allow
+the air to escape, and heat gently. Does any moisture form on the glass?</p>
+
+<p><span class="pagenum" id="Page_11">[Pg 11]</span></p>
+
+<p>A better test is to weigh two or three ounces of seeds, and heat them
+in a double boiler or in oil to prevent scorching. Weigh at intervals. If
+there is any loss of weight, to what is it due?</p>
+
+<p id="exp-11"><span class="smcap">Experiment 11. Do seeds absorb water?</span>—Soak a number of
+beans or grains of corn in water for 12 to 24 hours and compare with
+dry ones. What difference do you notice? To what cause is it due?</p>
+
+<p id="exp-12"><span class="smcap">Experiment 12. How did water get into the soaked seeds?</span>—Dry
+gently with a soft cloth some of the seeds used in the last experiment
+and press them lightly to see if water comes out, and where. Place a number
+of dry seeds of different kinds—squash, bean, castor bean, quince,
+etc.—in warm water and notice whether any bubbles of air form on them
+and at what point. Examine with a lens and see if this point differs in any
+way from the rest of the seed cover. Does it correspond with the point
+from which water exuded in the soaked seeds? Could hard seeds like
+the squash, castor bean, buckeye, and Brazil nut get water readily without
+an opening somewhere in the coat?</p>
+
+<p id="exp-13"><span class="smcap">Experiment 13. To find out whether water is absorbed
+through the seed coats.</span>—Place in moist sand or sawdust two rows
+of beans as nearly as possible of the same size and weight, with the eye
+pressed down to the substratum in one row and turned up in the other, so
+that no moisture can enter through it. In the same way arrange two
+rows of castor beans with the little end down in one row and uppermost
+in the other. In the last set carefully break away the spongy mass near
+the tip, without injuring the parts about it. Watch and see in which
+rows water is absorbed most readily. What change takes place in the
+spongy masses at the tips of those castor beans on
+which they were left?</p>
+
+<figure class="figright illowp20" id="i_021" style="max-width: 25em;">
+  <img class="w100" src="images/i_021.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 13.</span>—Effect
+of the expansion of
+seeds due to absorption
+of water.</p></figcaption>
+</figure>
+
+<p id="exp-14"><span class="smcap">Experiment 14. Is the rate of germination
+affected by the presence or absence of
+openings?</span>—Seal up with wax or paraffin all the
+openings of a number of air-dry peas or beans, and
+leave an equal number of the same size and weight
+untreated. Be careful that the sealing is absolutely
+water-tight, since otherwise the experiment will
+be worthless. Plant both sets and keep under like
+conditions of soil, temperature, and moisture. Do
+you see any difference in the rate of germination of
+the two sets?</p>
+
+<p id="exp-15"><span class="smcap">Experiment 15. Do seeds exert force in
+absorbing water?</span>—Fill a common six-ounce bottle
+as full as it will hold with dry peas, beans, or<span class="pagenum" id="Page_12">[Pg 12]</span>
+grains of corn; then pour in water till the bottle is full. Tie a piece of
+wire-netting or stout sackcloth over the top to keep the seeds from being
+forced out. Bind both the neck and the body of the bottle tightly with
+strong cords encircling it in both a horizontal and vertical direction, and
+place under water in a moderately warm temperature. Watch for results.</p>
+
+<p id="exp-16"><span class="smcap">Experiment 16. Is the force exerted in the last experiment
+a merely mechanical one, like the bursting of a water pipe, or
+is it physiological and thus dependent on the fact that the
+seeds are alive?</span>—To answer this question try <a href="#exp-15">Exp. 15</a> with seeds
+that have been killed by heat or by soaking in formalin.</p>
+</div>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Will a pound of pop corn weigh as much after being popped as before?
+(<a href="#exp-10">Exp. 10</a>.)</p>
+
+<p>2. What causes the difference, if there is any? (<a href="#exp-10">Exp. 10</a>.)</p>
+
+<p>3. Does the tuft of downy hairs at the tip of wheat and oat grains
+influence their water supply? The spongy covering of black walnuts and
+almonds? The pithy inside layers of pecans and English walnuts?
+(<a href="#exp-12">Exps. 12</a>, <a href="#exp-13">13</a>.)</p>
+
+<p>4. Why will seeds, as a general thing, germinate more readily after
+being soaked? (<a href="#exp-11">Exps. 11</a>, <a href="#exp-14">14</a>, <a href="#exp-16">16</a>.)</p>
+</div>
+
+
+<h3 id="CH_I_III">III. TYPES OF SEEDS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Dry and soaked grains of corn, wheat, or oats; bean,
+squash, castor bean, and pine seed, or any equivalent specimens showing
+the differences as to number of cotyledons and the presence or absence of
+endosperm. Each student should be provided with several specimens,
+both soaked and dry, of the kind under consideration. Corn, beans, and
+wheat need to be soaked from 12 to 24 hours; squash and pumpkin from
+2 to 5 days, and very hard seeds, like the castor bean and morning-glory,
+from 5 to 10. If such seeds are <em>clipped</em>, before soaking, that is, if a small
+piece of the coat is chipped away from the end opposite the scar, or eye,
+they will soften more quickly. Keep them in a warm place with an even
+temperature till just before they begin to sprout, when the contents become
+softened. Very brittle cotyledons may be softened quickly by boiling
+for a few minutes.</p>
+
+<p>No appliances are needed beyond the pupil’s individual outfit and some
+of the food tests given in Section I of this chapter.</p>
+</div>
+
+
+<p id="p-11"><b>11. Dissection of a grain of corn.</b>—Examine a dry grain
+of corn on both faces. What differences do you notice?
+Sketch the grooved side, labeling the hard, yellowish outer<span class="pagenum" id="Page_13">[Pg 13]</span>
+portion, <em>endosperm</em>, the depression near the center, <em>embryo</em>, or
+<em>germ</em>.</p>
+
+<p>Next take a grain that has been soaked for twenty-four
+hours. What changes do you see? How do you account for
+the swelling of the embryo? Remove the skin and observe
+its texture. Make an enlarged sketch of a grain on the
+grooved side with the coat removed, labeling the flat oval body
+embedded in the endosperm, <em>cotyledon</em>; the upper end of the
+little budlike body embedded in the cotyledon, <em>plumule</em>, the
+lower part, <em>hypocotyl</em>—words
+meaning, respectively, “seed
+leaf,” “little bud,” and
+“the part under the cotyledon.”
+As this part has not
+yet differentiated into root
+and stem, we cannot call it
+by either of these names.
+The cotyledon, hypocotyl,
+and plumule together compose
+the embryo. Pick out
+the embryo and sketch as
+it appears under the lens.
+Crush it on a piece of white paper; what does it contain?</p>
+
+<figure class="figright illowp50" id="i_023" style="max-width: 31.25em;">
+  <img class="w100" src="images/i_023.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 14-16.</span>—Dissection of a grain of
+corn: 14, soaked grain, seen flatwise, cut
+away a little and slightly enlarged, so as to
+show the embryo lying in the endosperm;
+15, in profile section, dividing the grain
+through the embryo and cotyledon; 16, the
+embryo taken out whole. The thick mass is
+the cotyledon; the narrow body projecting
+upwards, the plumule; the short projection
+at the base, the hypocotyl (<i>after</i> <span class="smcap">Gray</span>).</p></figcaption>
+</figure>
+
+<p>Make a vertical section of another soaked grain at right
+angles to its broader face, and sketch, labeling the parts as
+they appear in profile. Make a cross section through the
+middle of another grain and sketch, labeling the parts as before.
+What proportion of the grain is endosperm and what
+embryo? Put a drop of iodine and of nitric acid separately
+on pieces of the endosperm, and note the effects. Test the
+seed coats and the cotyledon to see if they contain any starch.</p>
+
+<p>Notice that the corn grain has but one cotyledon, hence
+such seeds are said to be <em>monocotyledonous</em>, or one-cotyledoned.
+The grains are not typical seeds, but are selected for examination
+because they are large and easy to handle, can be obtained
+everywhere, and germinate readily.</p>
+
+<p><span class="pagenum" id="Page_14">[Pg 14]</span></p>
+
+<p id="p-12"><b>12. Dissection of a bean.</b>—Sketch a dry bean as it lies in
+the pod, showing its point of attachment and any markings
+that may appear on its surface. Then take it from the pod and
+examine the narrow edge by which it was attached. Notice
+the rather large scar (commonly called the eye of the bean)
+where it broke away from the point of
+attachment. This is the <em>hilum</em>. Near the
+hilum, look for a minute round pore like
+a pinhole. This is called the <em>micropyle</em>,
+from a Greek word meaning “a little
+gate,” because it is the entrance to the
+interior of the seed coat. There was no
+micropyle observed in the corn grain,
+because it is not a true seed but a fruit
+inclosing a single seed. The inclosing
+membrane is the fruit skin, which has become incorporated
+with the seed coat and taken its place as a protective covering.
+Compare a soaked bean with a dry one; what difference do
+you perceive? How do you account for the change in size and
+hardness? Find the hilum and the micropyle in the soaked
+bean. Lay it on one side and sketch, with the micropyle on
+top; then turn toward you the narrow edge that
+was attached to the pod and sketch, labeling all
+the parts. Make a section through the long diameter
+at right angles to the flat sides, press it
+slightly open, and sketch it. Notice the line or
+slit that seems to cut the section in half longitudinally,
+and the small round object between the
+halves at one end; can you tell what it is?</p>
+
+<figure class="figleft illowp30" id="i_024" style="max-width: 28.125em;">
+  <img class="w100" src="images/i_024.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 17, 18.</span>—A kidney
+bean: 17, side view;
+18, front view, showing <i>h</i>,
+hilum, <i>m</i>, micropyle.</p></figcaption>
+</figure>
+
+<figure class="figright illowp20" id="i_024a" style="max-width: 25em;">
+  <img class="w100" src="images/i_024a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 19 .</span>—Cotyledon of
+a bean, showing
+plumule.</p></figcaption>
+</figure>
+
+<p>Slip off the coat from a whole bean and notice its
+texture. Hold it up to the light and see if it shows
+any signs of veining. See whether the scar at the hilum extends
+through the kernel, or marks only the seed coat. Lay open the
+two flat bodies into which the kernel divides when stripped of
+its coats, keeping them side by side, with the part above the
+micropyle toward the top. Sketch their inner face and label<span class="pagenum" id="Page_15">[Pg 15]</span>
+them <em>cotyledons</em>. Be careful not to break or displace the tiny
+bud packed away between the cotyledons, just above the
+hilum. Label the round portion of this bud, <em>hypocotyl</em>, and
+the upper, more expanded part, <em>plumule</em>. Which way does the
+base of the hypocotyl point; toward the micropyle, or away
+from it? Pick out this budlike body entire and sketch as it appears
+under the lens. Open the plumule with a pin and examine
+it with a lens; of what does it appear to consist? Do you
+find any endosperm around the cotyledons, as in the corn and
+oats? Break one of the soaked cotyledons, apply the proper
+tests (Exps. 2, 3, 5), and report what substances it contains.
+Where is the nourishment for the young plant stored? What
+part of the bean gives it its value as food?</p>
+
+<p>Notice that in the bean the embryo consists of three parts,
+the hypocotyl, plumule, and the two cotyledons, which completely
+fill the seed coats, leaving no place for endosperm.
+Seeds like the bean, squash, and castor bean, which have
+two cotyledons, are said to be <em>dicotyledonous</em>.</p>
+
+<p id="p-13"><b>13. The castor bean.</b>—Lay a castor bean on a sheet
+of paper before you with its flat side down; what does it
+look like? The resemblance may be increased by soaking
+the seed a few minutes, in order to swell the two little protuberances
+at the small end. Can you think of any benefit
+a plant might derive from this curious resemblance of its seed
+to an insect?</p>
+
+<p>Sketch the seed as it lies before you, labeling the protuberance
+at the apex, <em>caruncle</em>. The caruncle is an appendage
+of the seed-covering developed by various plants; its use
+is not always clear. What appears to be its object in the
+castor bean? Refer to <a href="#exp-13">Exp. 13</a> and see if there is any other
+purpose it might serve.</p>
+
+<p>Turn the seed over and sketch the other side. Notice the
+colored line or stripe that runs from the large end to the caruncle.
+This is the <em>rhaphe</em>, and shows the position that
+would be occupied by the seed stalk if it were present. Its
+starting point near the large end, which is marked in fresh<span class="pagenum" id="Page_16">[Pg 16]</span>
+seeds by a slight roughness, is the <em>chalaza</em>, or organic base of
+the seed, where the parts all come together like the parts of a
+flower at their insertion on the stem. Where was it situated
+in the common bean? How does this differ from its
+position in the castor bean? Where the rhaphe ends,
+just at the beak of the caruncle, you will find the hilum.
+The micropyle is covered by the caruncle, which is an
+outgrowth around it.</p>
+
+<figure class="figleft illowp50" id="i_026" style="max-width: 31.25em;">
+  <img class="w100" src="images/i_026.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 20-22.</span>—Castor bean (slightly magnified); 20,
+back view; 21, front view; <i>ch</i>, chalaza; <i>r</i>, rhaphe; <i>ca</i>,
+caruncle; 22, vertical section; <i>en</i>, endosperm; <i>cc</i>, cotyledons;
+<i>hy</i>, hypocotyl; <i>hi</i>, hilum; <i>m</i>, micropyle.</p></figcaption>
+</figure>
+
+<p>Now cut a vertical section through a seed that has been
+soaked for several days, at right angles to the broad sides,
+and sketch it. Label the white, pasty mass within the
+seed coats, endosperm. Can you make out what the narrow
+white line running through the center of the endosperm, dividing
+it into two halves, represents? Make a similar sketch
+of a cross section.
+Notice the same
+white line running
+horizontally across
+the endosperm, dividing
+it into two
+equal parts. To
+find out what these
+lines are, take another
+seed (always
+use soaked seeds for
+dissection) and remove the coats without injuring the kernel.
+Split the kernel carefully round the edges, remove half the
+endosperm, and sketch the other half with the delicate embryo
+lying on its inner face. You will have no difficulty
+now in recognizing the lines in your drawings as sections of
+the thin cotyledons. Where is the hypocotyl, and which way
+does its base point? Remove the embryo from the endosperm,
+separate the cotyledons with a pin, hold them up to the light,
+and observe their beautiful texture. Sketch them under the
+lens, showing the delicate venation. Is there any plumule?</p>
+
+<p>Test the endosperm with a little iodine. Does it give a<span class="pagenum" id="Page_17">[Pg 17]</span>
+blue or a brown reaction? Crush another bit of it on a piece
+of white paper and see if it leaves a grease spot. What does
+this show that it contains? Test the embryo in the same way,
+and see whether it contains any oil.</p>
+
+<div class="blockquot">
+
+<p><span class="smcap">Note.</span>—It should be borne in mind that the castor bean bears no relation
+whatever to the true beans. It belongs to the spurge family, which
+is botanically very remote from that of the peas and beans.</p>
+</div>
+
+<figure class="figcenter illowp100" id="i_027" style="max-width: 50em;">
+  <img class="w100" src="images/i_027.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 23-25.</span>—Seed of a squash; 23, seed from the outside; 24, vertical section
+perpendicular to the broad side; 25, section parallel to the broad side, showing inner
+side of a cotyledon; <i>a</i>, seed coat; <i>c</i>, cotyledons; <i>h</i>, hypocotyl; <i>p</i>, plumule.</p></figcaption>
+</figure>
+
+<p id="p-14"><b>14. Study of a squash or gourd seed.</b>—How does the coat
+of a squash seed differ from that of the bean? At the small
+end, look for two dots, or pinholes, close
+together. Refer to your drawing of the
+bean and see if you can make out, with
+the help of a lens, what they are. The
+bean is a curved seed, which is bent so as
+to bring the hilum close to the micropyle
+on one side. But by far the greater
+number of seeds are <em>inverted</em>, or turned
+over on their stalks, as you sometimes
+see huckleberry blossoms and bell flowers
+on their stems, so that when the stalk
+breaks away from its attachment, the
+scar and the micropyle come close together
+at one end, as in the squash seed.</p>
+
+<figure class="figright illowp30" id="i_027a" style="max-width: 18.75em;">
+  <img class="w100" src="images/i_027a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 26.</span>—Diagram of
+an inverted or anatropous
+seed, showing the
+parts in section: <i>a</i>, outer
+coat; <i>b</i>, inner coat; <i>c</i>,
+kernel; <i>d</i>, rhaphe; <i>ch</i>,
+chalaza; <i>h</i>, hilum; <i>m</i>,
+micropyle (<i>After</i> <span class="smcap">Gray</span>).</p></figcaption>
+</figure>
+
+<p>Make a drawing of the outside of a
+seed, labeling all the parts you have observed; then gently<span class="pagenum" id="Page_18">[Pg 18]</span>
+remove the hard coat, or <em>testa</em>, as it is called. The thin, greenish
+covering that lines it on the inside is the endosperm. How
+does it compare in quantity with that in the corn and castor
+bean? How do the cotyledons compare in thickness with
+those of the bean? Carefully separate them and draw, labeling
+the parts as you make them out. The tiny pointed
+object between the cotyledons at their point of union is the
+plumule; is it as well developed as in the bean? Can you see
+any reason why seeds like the pea and bean, which have cotyledons
+too thick and clumsy to do well the work of true leaves,
+should have a well-developed plumule, while those with thin
+cotyledons, like the squash and pumpkin, do not, as a general
+thing, form a large plumule in the embryo? The little projection
+in which the cotyledons end is the hypocotyl; which
+way does it point? Where did you find the micropyle to be?
+Test the cotyledons and some of the endosperm for food substances;
+what do you find in them?</p>
+
+<p id="p-15"><b>15. Study of a pine seed.</b>—Remove one of the scales from
+a pine cone and sketch the seed as it lies in place on the cone
+scale. Notice its point of attachment to
+the scale, and look near this point for a
+small opening, which you can easily recognize
+as the micropyle. The seed with its
+wing looks very much like a fruit of the
+maple, but differs from it in being a naked
+seed borne on the inner side of a cone scale,
+without a pod or husk or outer covering of
+any kind, such as beans and nuts and grains
+are provided with. Plants like the pine,
+which bear their seed in this way, are called
+<em>Gymnosperms</em>, a word that means “naked
+seeds,” in contradistinction to the <em>Angiosperms</em>, which bear
+their seeds in pods or other closed envelopes.</p>
+
+<table>
+<tr>
+<td class='tdc wd50'>
+<figure class="figcenter illowp80" id="i_028" style="max-width: 15.5em;">
+  <img class="w100" src="images/i_028.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 27, 28.</span>—Pitch
+pine seeds:
+27, scale, or open
+carpel, with one seed
+in place; 28, winged
+seed, removed. (<i>After</i>
+<span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+</td>
+<td class='tdc wd50'>
+<figure class="figcenter illowp80" id="i_029" style="max-width: 10.5em;">
+  <img class="w100" src="images/i_029.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 29.</span>—Section
+of pine seed,
+showing the
+polycotyledonous
+embryo
+(<span class="smcap">Gray</span>).</p></figcaption>
+</figure>
+</td></tr></table>
+
+<p class='cb'>Remove the coat from a seed that has been soaked for
+twenty-four hours, and examine it with a lens. Does it consist
+of one or more layers? Is there any difference in color<span class="pagenum" id="Page_19">[Pg 19]</span>
+between the inner and outer layers? Look at the base of the
+hypocotyl for some loose, cobwebby appendages. These are
+the remains of other embryos with certain appendages
+belonging to them that were formed in the
+endosperm, but failed to develop. Did you find
+remains of this kind in any of the other seeds examined?
+Pick out the embryo from the endosperm
+and test both for food substances. Which
+of these do you find? Which are absent? How
+does the embryo differ from those already examined?
+How many cotyledons are there? Make
+an enlarged sketch of a seed in longitudinal
+section, labeling correctly all the parts observed.</p>
+
+<p id="p-16"><b>16. Comparison as to food value of seeds.</b>—Make in your
+notebook a tabular statement after the model here given, of
+the food contents found in the different seeds you have examined.
+Indicate the relative quantity of each by writing
+under it, in the appropriate column, the words, “much,”
+“little,” or “none,” as the case may be.</p>
+
+
+<p class="p2 center fs90 smcap">Model for Record of Seeds Examined</p>
+
+<table class="autotable fs80 wd80">
+<tr>
+<td class="bt" colspan="5"></td>
+</tr>
+<tr>
+<td class="tdc bt wd20 smcap" rowspan="2">Seeds Examined</td>
+<td class="tdc bl bt" colspan="4"><span class='smcap'>Foods Tested</span></td>
+</tr>
+<tr>
+<td class="tdc bl bt">Starch</td>
+<td class="tdc bl bt">Sugar</td>
+<td class="tdc bl bt">Oil</td>
+<td class="tdc bl bt">Proteins</td>
+</tr>
+<tr>
+<td class="tdl bt">Corn</td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+</tr>
+<tr>
+<td class="tdl bt">Wheat</td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+</tr>
+<tr>
+<td class="tdl bt">Bean</td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+</tr>
+<tr>
+<td class="tdl bt">Squash</td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+</tr>
+<tr>
+<td class="tdl bt">Castor bean</td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+</tr>
+<tr>
+<td class="tdl bt">Pine</td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+<td class="bl bt"></td>
+</tr>
+<tr>
+<td class="bt" colspan="5"></td>
+</tr>
+<tr>
+<td class="bt" colspan="5"></td>
+</tr>
+</table>
+
+<p>By far the greater number of seeds contain endosperm;
+that is, they consist of an embryo with more or less nourishing<span class="pagenum" id="Page_20">[Pg 20]</span>
+matter stored about it. Even in seeds which appear to
+have none, the endosperm is present at some period during
+development, but is absorbed by the cotyledons before germination.</p>
+
+<p id="p-17"><b>17. Manner of storing nourishment.</b>—In the various seeds
+examined, we have seen that the nourishment for the young
+plant is either stored in the embryo itself, as in the cotyledons
+of the bean, acorn, squash, etc., or packed about them
+in the form of endosperm, as in the corn, wheat, and castor
+bean.</p>
+
+<p id="p-18"><b>18. The number of cotyledons.</b>—Seeds are also classed
+according to the number of their cotyledons, as having one,
+two, or many cotyledons. The first two kinds make up the
+great class of Angiosperms, which includes all the true flowering
+plants and forms the most important part of the vegetation
+of the globe. The last is characteristic of the great
+natural division of Gymnosperms, or naked-seeded plants,
+of which we have had an example in the pine. They are the
+most primitive type of living seed-bearing plants. Though
+they are not so abundant now as in past ages, numbering
+only about four hundred known species, they present many
+diversities of form, which seem to ally them on the one hand
+with the lower, or spore-bearing plants (ferns, mosses, etc.),
+and on the other hand with the Angiosperms.</p>
+
+
+<div class="blockquot">
+
+<h4>Practical Questions</h4>
+
+<p>1. Make a list of all the seeds you can find that have very thick cotyledons,
+and underline those that are used as food by man or beast.</p>
+
+<p>2. Make a similar list of all the kinds with thin cotyledons and more or
+less endosperm, that are used for food or other purposes.</p>
+
+<p>3. Do you find a greater number of foodstuffs among the one kind
+than the other?</p>
+
+<p>4. How do the two kinds compare, as a general thing, in size and
+weight?</p>
+
+<p>5. From what part of the castor bean do we get oil? of the peanut?
+of cotton seed? (<a href="#exp-1">Exps. 1-6</a>.)</p>
+
+<p>6. Is there any valid objection to the wholesomeness of peanut oil, and
+of cottonseed lard as compared with hog’s lard? (<a href="#p-1">1</a>, <a href="#p-3">3</a>.)</p>
+
+<p><span class="pagenum" id="Page_21">[Pg 21]</span></p>
+
+<p>7. What is bran? Does it contain any nourishment? (<a href="#p-11">11</a>, <a href="#p-12">12</a>; <a href="#exp-1">Exps. 1-6</a>.)</p>
+
+<p>8. What gives to Indian corn its value as food? to oats? wheat?
+rice? (<a href="#p-3">3</a>; <a href="#exp-1">Exps. 1-6</a>.)</p>
+
+<p>9. Which of these grains has the larger proportion of endosperm to
+embryo? (<a href="#i_012">Figs. 1-3</a>.)</p>
+
+<p>10. Which contains the larger amount of starch in proportion to
+its bulk, rice or Indian corn?</p>
+
+<p>11. If you wished to produce a variety of corn rich in oil, you would
+select seed for planting with what part well developed? (<a href="#p-3">3</a>; <a href="#i_012a">Figs. 4-7</a>.)</p>
+</div>
+
+
+<h3 id="CH_I_IV">IV. SEED DISPERSAL</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Fruits and seeds of any kind that show adaptations for
+dispersal. Some common examples are: (1) Wind: ash, elm, maple,
+ailanthus, milkweed, clematis, sycamore, linden, dandelion, thistle,
+hawkweed. (2) Water: pecan, filbert, cranberry, lotus, hickory nut,
+coconut—obtain one with the husk on, if possible. (3) Animal agency
+(involuntary): cocklebur, tickseed, beggar-ticks, burdock; (voluntary)
+almost all kinds of edible fruits, especially the bright-colored ones—wild
+plums, cherries, haws, dogwood, persimmons, etc. (4) Explosive and
+self-planting: witch-hazel, wood sorrel, violet, crane’s-bill, wild vetch,
+peanut, medick, stork’s-bill (Erodium).</p>
+
+<p id="exp-17"><span class="smcap">Experiment 17. To show how seeds are dispersed by wind.</span>—Take
+a number of winged and plumed fruits and seeds, such as those of the
+maple, ash, ailanthus, dandelion, clematis, milkweed, and trumpet creeper;
+stand on a chair or table in a place where there is a draft of air and let
+them all go. Which travel the farther, the winged or the plumed kinds?
+Which sort is better fitted to aërial transportation?</p>
+
+<p id="exp-18"><span class="smcap">Experiment 18. Dispersal by water.</span>—Place in a bucket of water
+a hazelnut, an acorn, an orange, a cranberry, a pecan, a hickory nut, a fresh
+apple, and a coconut with the husk on. Which are the best floaters? Cut
+open or break open the good swimmers, compare with the non-floaters, and
+see to what peculiarity of structure their floating qualities are due. In
+what situations do the cranberry and the coconut grow? Can you see
+any advantage to a plant so situated in producing fruits that float easily?</p>
+
+<p id="exp-19"><span class="smcap">Experiment 19. Dispersal by explosive capsules.</span>—Moisten
+slightly some mature but unopened capsules of witch hazel, wood sorrel,
+rabbit pea, or violet, and leave in a warm, dry place for fifteen to forty-five
+minutes. What happens when the pods begin to dry? Measure the
+distance to which the different kinds of seeds have been ejected. Which
+were thrown farthest? What was the object of the movement? What
+caused the explosion?</p>
+
+<p><span class="pagenum" id="Page_22">[Pg 22]</span></p>
+
+<p id="exp-20"><span class="smcap">Experiment 20. The use of adhesive fruits.</span>—Scatter broadcast
+a handful of hooked or prickly seeds or fruits—cocklebur, tickseed, beggar-ticks,
+bur grass, etc. Are they suited for wind transportation? Drop one
+of them on your sleeve, or on the coat of a fellow student; will it stay
+there? What would be the effect if it became attached to the fur of a
+roaming animal? Is this a successful mode of dissemination?</p>
+</div>
+
+<figure class="figcenter illowp100" id="i_032" style="max-width: 50em;">
+  <img class="w100" src="images/i_032.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 30-32.</span>—30, A pod of wild vetch, with mature valves twisting spirally to
+discharge the seed; 31, pod of crane’s-bill discharging its seed; 32, capsules of witch-hazel
+exploding.</p></figcaption>
+</figure>
+
+<figure class="figcenter illowp100" id="i_032a" style="max-width: 50em;">
+  <img class="w100" src="images/i_032a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 33-36.</span>—Fruits adapted to wind dispersal: 33, winged pod of pennycress;
+34, spikelet of broom sedge; 35, akene of Canada thistle; 36, head of rolling spinifex
+grass.</p></figcaption>
+</figure>
+
+<p id="p-19"><b>19. Agencies of dispersal.</b>—The means at nature’s disposal
+for this purpose, as shown by the experiments just made,
+are four; namely, wind, water, the explosion of capsules due
+to the withdrawal of water, and the agency of animals, including
+man. The first three are purely mechanical. The
+last, animal agency, is either voluntary or involuntary, according
+as it is conscious and intentional, or accidental merely.
+Man, of course, is the only consciously voluntary agent. Of<span class="pagenum" id="Page_23">[Pg 23]</span>
+the four agencies named, animals and wind are the most effective,
+and the greater number of adaptations observed will be
+found to have reference to these.</p>
+
+<table class='autotable'>
+<tr><td class='vat'>
+<figure class="figcenter illowp90" id="i_033xl" style="max-width: 23.0em;">
+  <img class="w100" src="images/i_033xl.jpg" alt="">
+  <figcaption>
+    <p><span class="smcap">Fig. 37.</span>—Good quality of clover seed.</p>
+  </figcaption>
+</figure>
+</td><td class='vat'>
+<figure class="figcenter illowp90" id="i_033xr" style="max-width: 23.0em;">
+  <img class="w100" src="images/i_033xr.jpg" alt="">
+  <figcaption>
+    <p><span class="smcap">Fig. 38.</span>—Inferior quality of clover seed mixed with “screenings.”</p>
+  </figcaption>
+</figure></td></tr></table>
+
+<figure class="figright illowp40" id="i_033b" style="max-width: 25em;">
+  <img class="w100" src="images/i_033b.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 39.</span>—Dodder on red clover,
+showing how the seeds get mixed.</p></figcaption>
+</figure>
+
+<p id="p-20"><b>20. Involuntary dispersal.</b>—The lower animals may be
+voluntary agents in a way, though not designedly so, as when
+a squirrel buries nuts for his own use and then forgets the location
+of his hoard and leaves them to germinate; or when
+a jaybird flies off with a pecan in his bill, intending to crack
+and eat it, but accidentally lets
+it fall where it will sprout and
+take root. Both man and the
+lower animals are not only involuntary,
+but often unwilling
+agents of dispersal. Some of the
+most troublesome weeds of civilization
+have been unwittingly distributed
+by man as he journeyed
+from place to place, carrying,
+along with the seed for planting
+his crops, the various weed seeds,
+or “screenings,” as these mixtures
+are called by dealers, with which
+they have been adulterated either through carelessness and
+ignorance, or from unavoidable causes. The neglected
+animals, also, that are allowed by short-sighted farmers to
+wander about with their hair full of cockleburs and other<span class="pagenum" id="Page_24">[Pg 24]</span>
+adhesive weed pests, are no doubt very unwilling carriers of
+those disagreeable burdens.</p>
+
+<p id="p-21"><b>21. Tempting the appetite.</b>—This is the most important
+adaptation to dispersal by animals. Have you ever asked
+yourself how it could profit a plant to tempt birds and beasts
+to devour its fruit, as so many of the bright berries we find in
+the autumn woods seem to do? To answer this question,
+examine the edible fruits of your neighborhood and you will
+find that almost without exception the seeds are hard and
+bony, and either too
+small to be destroyed
+by chewing, and thus
+capable of passing
+uninjured through
+the digestive system
+of an animal; or, if
+too large to be swallowed
+whole, compelling
+the animal,
+by their hardness or
+disagreeable flavor,
+to reject them. In
+cases where the seeds
+themselves are edible
+and attractive,
+the fruits are usually
+armed during the
+growing season with
+protective coverings,
+like the bur of the chestnut and the astringent hulls of the hickory
+nut and walnut. The acidity or other disagreeable qualities
+of most unripe fruits serves a similar purpose, while their
+green color, by making them inconspicuous among the foliage
+leaves, tends still further to insure them against molestation.</p>
+
+<figure class="figcenter illowp50" id="i_034" style="max-width: 25em;">
+  <img class="w100" src="images/i_034.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 40-42.</span>—Adhesive fruits: 40, fruit of hound’s-tongue;
+41, akene of bur marigold; 42, fruit of bur
+grass (cenchrus).</p></figcaption>
+</figure>
+
+<p id="p-22"><b>22. Voluntary agency.</b>—The cultivated fruits and grains
+owe their distribution and survival almost entirely to the<span class="pagenum" id="Page_25">[Pg 25]</span>
+voluntary agency of man. Dispersal by this means, whether
+intentional or accidental, is purely artificial, and except in the
+case of a few annuals like horseweed, bitterweed, ragweed,
+goosefoot, and other field pests that have adjusted their season
+of growth and flowering to the conditions of cultivation,
+is not correlated with any special modification of the plants
+for self-propagation. On the contrary, many of the most
+widely distributed weeds of cultivation, such as the oxeye
+daisy, the rib grass, mayweed and bitterweed, possess very
+imperfect natural means of dispersal, and are largely dependent
+for their propagation on the involuntary agency of man.</p>
+
+<p id="p-23"><b>23. Use of the fruit in dispersal.</b>—It will be seen from the
+foregoing observations that the fruit plays a very important
+part in the work
+of dispersal, most
+of the adaptations
+for this purpose
+being connected
+with it.
+In cases where a
+number of seeds
+are contained
+in a large pod
+that could not
+conveniently be
+blown about by
+the breeze,
+adaptations for
+wind dispersal are attached to the individual seeds, as in the
+willow, milkweed, trumpet creeper, and paulonia; but as a
+general thing, adaptations of the seed are for protection, the
+work of dispersal being provided for by the fruit. In the case
+of the large class of plants known as “tumbleweeds,” the
+whole plant body is fitted to assist in the work of transportation.
+Such plants generally grow in light soils and either
+have very light root systems, or are easily broken from their<span class="pagenum" id="Page_26">[Pg 26]</span>
+anchorage and left to drift about on the ground. The spreading,
+bushy tops become very light after fruiting, so as to be
+easily blown about by the wind, dropping their seeds as they
+go, until they finally get stranded in ditches and fence corners,
+where they often accumulate in great numbers during the
+autumn and winter.</p>
+
+<table class='autotable'>
+<tr><td class='vab'>
+<figure class="figcenter illowp80" id="i_035_43" style="max-width: 38.25em;">
+  <img class="w100" src="images/i_035_43.jpg" alt="">
+  <figcaption>
+    <p><span class="smcap">Fig.</span> 43.—A fruiting plant of winged pigweed (<i>Cycloloma</i>), showing the bunchy top and weak anchorage of a typical tumbleweed.</p>
+  </figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp80" id="i_035_44" style="max-width: 31.125em;">
+  <img class="w100" src="images/i_035_44.jpg" alt="">
+  <figcaption>
+    <p><span class="smcap">Fig.</span> 44.—Panicle of “old witch grass,” a common tumbleweed.</p>
+  </figcaption>
+</figure></td></tr></table>
+
+<p id="p-24"><b>24. The advantages of dispersal.</b>—Seed cannot germinate
+unless they are placed in a suitable location as to soil, moisture,
+and temperature. In order to increase the chances of securing
+these conditions, it is clearly to the advantage of a species
+that its seeds should be dispersed as widely as possible, both
+that the seedlings may have plenty of room, and that they
+may not have to draw their nourishment from soil already
+exhausted by their parents. The farmer recognizes this
+principle in the rotation of
+crops, because he knows that
+successive growths of the
+same plant will soon exhaust
+the soil of the substances required
+for its nutrition, while
+they may leave it richer in
+nourishment for a different
+crop.</p>
+
+<figure class="figcenter illowp40" id="i_036" style="max-width: 25em;">
+  <img class="w100" src="images/i_036.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 45.</span>—Self-planting pod of peanut.</p></figcaption>
+</figure>
+
+<p id="p-25"><b>25. Self-planting seeds.</b>—Dispersal
+is not the only
+problem the seed has to meet.
+The majority of seeds cannot
+germinate well on top of the
+ground, and must depend on
+various agencies for getting
+under the soil. Some of them
+do this for themselves. The
+seeds of the stork’s-bill, popularly known as “filarees,” have
+a sharp-pointed base and an auger-shaped appendage at the
+apex, ending in a projecting arm (the “clock” of the filaree)
+by which it is blown about by the wind with a whirling motion<span class="pagenum" id="Page_27">[Pg 27]</span>
+till it strikes a soft spot, when it begins at once to bore its
+way into the ground. The common peanut is another example.
+The blossoms are borne under the leaves, near the base
+of the stem, and as soon as the seeds begin to form, the
+flower stalks lengthen several inches, carrying the young pods
+down to the ground, where they bore into the soil and ripen
+their seeds.</p>
+
+
+<div class="blockquot">
+
+<h4>Practical Questions</h4>
+
+<p>1. Name the ten most troublesome weeds of your neighborhood.</p>
+
+<p>2. What natural means of dispersal have they?</p>
+
+<p>3. Which of them owe their propagation to man?</p>
+
+<p>4. Are there any tumbleweeds in your neighborhood?</p>
+
+<p>5. Would you expect to find such weeds in a hilly or a well-wooded
+region? (<a href="#p-19">19</a>, <a href="#p-23">23</a>; <a href="#exp-17">Exp. 17</a>.)</p>
+
+<p>6. What situations are best fitted for their propagation? (<a href="#p-19">19</a>, <a href="#p-23">23</a>;
+<a href="#exp-17">Exp. 17</a>.)</p>
+
+<p>7. Make a list of all the fruits and seeds you can think of that are
+adapted to dispersal by wind; by water; by animals.</p>
+
+<p>8. By what means of dissemination, or protection, or both, is each of
+the following distinguished: the squash; apple; fig; pecan; poppy;
+bean; beggar-tick; linden; grape; rice; pepper; olive; cranberry;
+jimson weed; thistle; corn; wheat; oats?</p>
+
+<p>9. What is the agent of dispersion, or what the danger to be provided
+against, in each case?</p>
+
+<p>10. Could our cultivated fruits and grains survive in their present state
+without the agency of man? (<a href="#p-22">22</a>.)</p>
+
+<p>11. Name all the plants you can think of that bear winged seeds and
+fruits; are they, as a general thing, tall trees and shrubs, or low herbs?</p>
+
+<p>12. Name all you can think of that bear adhesive seeds and fruits; are
+they tall trees or low herbs?</p>
+
+<p>13. Give a reason for the difference. (<a href="#exp-17">Exps. 17</a>, <a href="#exp-20">20</a>.)</p>
+
+<p>14. Why is the dandelion one of the most widely distributed weeds in
+the world? (<a href="#p-19">19</a>; <a href="#exp-17">Exp. 17</a>.)</p>
+
+<p>15. Is the wool that covers cotton seed for dispersal or protection?</p>
+
+<p>16. What advantage to the Indian shot (canna) is the excessive hardness
+of its seeds? (<a href="#p-21">21</a>.)</p>
+
+<p>17. What is the use to the species, of the bitter taste of lemon and
+orange seed? (<a href="#p-21">21</a>.)</p>
+
+<p>18. Why are the seeds of dates and persimmons and haws so hard?
+(<a href="#p-21">21</a>.)</p>
+
+<p><span class="pagenum" id="Page_28">[Pg 28]</span></p>
+
+<p>19. Do you find any edible seeds without protection? If so, account
+for the want of it. (<a href="#p-21">21</a>, <a href="#p-22">22</a>.)</p>
+
+<p>20. Name some of the agencies that may assist in covering seeds with
+earth.</p>
+
+<p>21. Do you know of any seeds that bury themselves?</p>
+
+<p>22. The seeds of weeds and other refuse found mixed with grain sold
+on the market are known, commercially, as “screenings.” Wheat brought
+to mills in Detroit showed screenings that contained, among other things,
+seeds of black bindweed, green foxtail grass, yellow foxtail, chess, oats,
+ragweed, wild mustard, corn cockle, and pigweed. Can you mention some
+of the ways in which these foreign substances may have gotten into the
+crop and suggest means for keeping them out?</p>
+
+
+<h4 id="CH_I_FIELD">Field Work</h4>
+
+<p>The subjects treated in the foregoing chapter are, in general, better
+suited to laboratory than to field work. There are some details, however,
+which can be observed to advantage out of doors. Many of the seeds
+found in your walks will show peculiarities of shape and external markings
+and color that will invite observation. Examine also the contents of different
+kinds you may meet with, as to the presence or absence of endosperm
+and the arrangement and development of the embryo. Note: (1) whether,
+as a general thing, there is any difference in size and weight and amount of
+nourishing matter in the two kinds; (2) the greater variety in the shape
+and arrangement of the cotyledons in the albuminous kind, and in the arrangement
+of the embryo; (3) the differences in the development of
+the plumule in the two kinds,—and give a reason for the facts observed.</p>
+
+<p>Among the different seeds you may find, look for adaptations for dispersal,
+and decide to what particular method each is suited. Study the agencies
+by which various kinds may get covered with soil. If the common stork’s-bill
+(<i>Erodium cicutarium</i>) grows in your neighborhood, its seeds will well
+repay a little study, and if there is a field of peanuts within reach, do not
+fail to pay it a visit.</p>
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_29">[Pg 29]</span></p>
+
+<h2 class="nobreak" id="CH_II">CHAPTER II. GERMINATION AND GROWTH</h2>
+</div>
+
+
+<h3 id="CH_II_I">I. PROCESSES ACCOMPANYING GERMINATION</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A pint or two of corn, peas, beans, or any quickly germinating
+seed.</p>
+
+<p><span class="smcap">Appliances.</span>—Matches; wood splinters; gas jet or alcohol lamp;
+test tubes; a small quantity of mercuric oxide; a thermometer; a couple
+of two-quart preserve jars, and a smaller wide-mouthed bottle that can
+be put into one of them; some limewater; a glass tube (the straws used
+by druggists for soft drinks will answer).</p>
+</div>
+
+<p id="p-26"><b>26. Preliminary exercises.</b>—Before taking up the study
+of germinating seeds, it is important to learn from what
+sources the organic substances used by the growing plant
+are derived, and some of the processes that accompany
+growth and development.</p>
+
+<div class="blockquot">
+
+<p id="exp-21"><span class="smcap">Experiment 21. To show the changes that accompany oxidation.</span>—Strike
+a match and let it burn out. Examine the burnt portion
+remaining in your hand; what changes do you notice? These changes
+have been caused by the union of some substance in the match with
+something outside of it, in the act of burning; let us see if we can find
+out what this outside substance is.</p>
+
+<p id="exp-22"><span class="smcap">Experiment 22. To show the active agent in oxidation.</span>—Heat
+some mercuric oxide in a test tube over the flame of a burner.
+The heat will cause the oxygen to separate from the mercury, and in a
+short time the tube will be filled with the gas. Extinguish the flame
+from a lighted splinter and thrust the glowing end into the tube; what
+happens? The oxygen unites with something in the wood and causes it to
+burn just as the match did. Compare your burnt splinter with the burnt
+end of the match; what resemblance do you notice between them?</p>
+
+<p id="exp-23"><span class="smcap">Experiment 23. To show that carbon dioxide is a product of
+oxidation.</span>—Your experiment with the match showed that ignition
+is accompanied by heat, and if active enough, by light, and also that
+it left behind a solid substance in the form of charcoal. But how
+about the part that united with the oxygen to produce these results?<span class="pagenum" id="Page_30">[Pg 30]</span>
+Let us see what became of it. Hold a lighted candle under the open end
+of a test tube, or under the mouth of a small glass jar. Does any vapor
+collect on the inside? After two or three minutes quickly invert the jar
+or the tube, and thrust in a lighted match: what happens? Can the
+substance now in the jar be ordinary air? Why not? (Exps. 21, 22.)
+Pour in a small quantity of limewater, holding your hand over the mouth
+of the tube to prevent the air from getting in; the gas inside, being heavier
+than air, will not escape immediately unless agitated. What change do
+you notice in the limewater?</p>
+
+<p>It has been proved by experiment that the kind of gas formed by the
+burning candle has the property of turning limewater milky; hence,
+whenever you see this effect produced in limewater, you may conclude
+that this gas, known as <em>carbon dioxide</em>, is present; and conversely, the
+presence of carbon dioxide, especially if accompanied by some of the other
+effects observed, as the giving out of heat and moisture, may be taken as
+evidence that some process similar to that going on in the burning candle
+is, or has been, at work.</p>
+
+<p id="exp-24"><span class="smcap">Experiment 24. Do these effects accompany any of the life
+processes of animals?</span>—Blow your breath against the palm of your
+hand; what sensation do you feel? Blow it against a mirror, or a piece
+of common glass; what do you see? Blow through a
+tube into the bottom of a glass containing limewater;
+how is the water affected? How do these facts correspond
+with the results of <a href="#exp-23">Exp. 23</a>?</p>
+
+<p id="exp-25"><span class="smcap">Experiment 25. Is there any evidence that
+a similar process goes on in plants?</span>—(1) Half fill
+a small, wide-mouthed jar with limewater, place it inside
+a larger one (<a href="#i_040">Fig. 46</a>), and fill the space between
+them, up to the neck of the smaller vessel, with well-soaked
+peas, beans, or barleycorns, on a bed of moist
+cotton or blotting paper. Cover with a piece of glass
+and keep at a moderately warm temperature. (2) As
+a control experiment, place beside this another jar arranged
+in precisely the same way, except that seeds
+must be used whose vitality has been destroyed by
+heat. To prevent the entrance of germs among the
+dead seeds, which might cause fermentation and thus
+interfere with the experiment, set the jar containing them in a vessel of
+water and boil an hour or two before the experiment begins. Otherwise,
+treat precisely as in (1).</p>
+
+<figure class="figleft illowp20" id="i_040" style="max-width: 18.75em;">
+  <img class="w100" src="images/i_040.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 46.</span>—Diagrammatic
+section,
+showing arrangement
+of jars for
+Exp. 25.</p></figcaption>
+</figure>
+
+<p>After germination has taken place in (1), what change do you notice in
+the limewater? If the effect is not apparent, gently stir with a straw or
+<span class="pagenum" id="Page_31">[Pg 31]</span>
+a glass rod to mix it with the gas in the larger jar. Has the limewater in
+the control experiment undergone the same change? (It may show a
+slight milkiness due to the carbon dioxide in the air.) Insert a thermometer
+among the seeds in both of the larger jars, and compare their temperature
+with that of the outside air; which shows the greater rise?
+From this experiment and the last one, what process, common to animals,
+would you conclude has been going on in the germinating seeds?</p>
+
+<p><span class="smcap">Note.</span>—Heat in germinating seeds is not always due to this cause
+alone, but is sometimes increased by the presence of minute organisms
+called bacteria. Germinating barley and rye in breweries sometimes
+show an increase in temperature of 40 to 70 degrees, due to these organisms,
+and spontaneous combustion in seed cotton has been reported from the
+same cause.</p>
+</div>
+
+<p id="p-27"><b>27. Oxidation.</b>—The process that brought about the
+results observed in the foregoing experiments, and popularly
+known as <em>combustion</em>, is more accurately defined by chemists
+as <em>oxidation.</em> It takes place whenever substances enter into
+new combinations with oxygen. The most familiar examples
+of it are when oxygen enters into combination with substances
+containing carbon. It was the union of a portion of the
+oxygen of the air in <a href="#exp-21">Exp. 21</a>, and of that in the tube in <a href="#exp-22">Exp.
+22</a>, with some of the carbon in the wood, that caused the
+burning. The effect was more marked in the second case
+because the oxygen in the tube was pure, while in the air it
+is mixed with other substances.</p>
+
+<p id="p-28"><b>28. Carbon.</b>—The black substance left in your hand
+after oxidation of the wood in Exps. 21 and 22 is <em>carbon</em>.
+It composes the greater part of most plant bodies, and, in
+fact, is the most important element in the realm of organic
+nature. There is not a living thing known, from the smallest
+microscopic germ to the most gigantic tree in existence, that
+does not contain carbon as one of its essential constituents.</p>
+
+<p id="p-29"><b>29. Carbon dioxide.</b>—The gas produced by the burning
+candle in <a href="#exp-23">Exp. 23</a>, by the germinating seeds in <a href="#exp-25">Exp. 25</a>, and
+expelled from your own lungs in <a href="#exp-24">Exp. 24</a>, is carbon dioxide.
+Chemists designate it by the symbol CO<sub>2</sub>, which means that
+it consists of one part carbon to two parts oxygen. It is an<span class="pagenum" id="Page_32">[Pg 32]</span>
+invariable product wherever the oxidation of substances
+containing carbon goes on. Heat and moisture are evolved
+at the same time, and if oxidation is very active, as in <a href="#exp-21">Exps.
+21</a> and <a href="#exp-22">22</a>, light also. When the process takes place very
+slowly, no light is evolved, and so little heat as to be imperceptible
+without special observation. Hence, oxidation may
+go on around us and even in our own bodies without our
+being conscious of the fact.</p>
+
+<p>Carbon dioxide is of prime importance to the well-being of
+plants. It furnishes the material from which the greater
+part of their organic food is derived, as will be seen when
+we take up the study of the leaf and its work. To animals,
+on the contrary, its presence is so injurious that if the proportion
+of it in the air we breathe ever rises much above 1
+part to 1000, the ill effects become painfully sensible. It
+is not, however, as was formerly supposed, a poison, the
+harm it does being to decrease the proportion of oxygen
+in the atmosphere so that animals cannot get enough of it
+to breathe, and die of suffocation.</p>
+
+<p id="p-30"><b>30. Respiration in plants and in animals.</b>—It was shown
+in <a href="#exp-24">Exp. 24</a> that respiration in animals is accompanied by the
+products of oxidation; hence we conclude that respiration
+is a form of oxidation. And since these same products are
+given off by plants (<a href="#exp-25">Exp. 25</a>), the inference is clear that the
+same process goes on in them. But in plants the life functions
+are so much more sluggish than in animals that it is
+only in their most active state, during germination and
+flowering, that evidence of it is to be looked for.</p>
+
+<p id="p-31"><b>31. Respiration and energy.</b>—In plants, as in animals,
+respiration is the expression or measure of energy. Sleeping
+animals breathe more slowly than waking ones, snakes and
+tortoises more slowly than hares and hawks. The more
+we exert ourselves and the more vital force we expend, the
+harder we breathe; hence, respiration is more active in
+children than in older persons and in working people than in
+those at rest. It is the same with plants; respiration is most<span class="pagenum" id="Page_33">[Pg 33]</span>
+perceptible in germinating seeds and young leaves, in buds
+and flowers, where active work is going on. Hence, in this
+condition they consume proportionately larger quantities
+of oxygen and liberate correspondingly larger quantities of
+carbon dioxide, with a proportionate increase of heat. In
+some of the arums,—calla lily, Jack-in-the-pulpit, colocasia,
+etc.,—and in large heads of compositæ, like the sunflower,
+where a great number of small flowers are brought
+together within the same protecting envelope, the rise of
+temperature is sometimes so marked that it may be perceived
+by placing a flower cluster against the cheek.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. What is charcoal? (<a href="#p-28">28</a>.)</p>
+
+<p>2. Is any of this substance contained in the seed? in the flour and
+meal made from seed? (<a href="#p-28">28</a>; <a href="#exp-25">Exp. 25</a>.)</p>
+
+<p>3. What combination takes place when the cook lets the stove get too
+hot and burns the biscuits? (<a href="#p-27">27</a>, <a href="#p-28">28</a>.)</p>
+
+<p>4. Of what does the burned part consist? (<a href="#p-28">28</a>.) What was it before
+it was burned? (<a href="#p-27">27</a>, <a href="#p-28">28</a>).</p>
+
+<p>5. Which burns the more readily, an oily seed or a starchy one?
+Which leaves the more solid matter behind? (Suggestion: test by putting
+a bean, or a large grain of corn, and an equal quantity of the kernel
+of a Brazil nut on the end of a piece of wire and thrusting into a flame.)</p>
+
+<p>6. Is there any rational ground for the statement that the wooden
+buildings formerly used on Southern plantations as cotton ginneries were
+sometimes destroyed through spontaneous combustion due to the heat
+generated by piles of decaying cotton seed? (<a href="#exp-25">Exp. 25</a>, Note.)</p>
+</div>
+
+
+<h3 id="CH_II_II">II. CONDITIONS OF GERMINATION</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Several ounces each of various kinds of seed. For the
+softer kinds, pea, bean, corn, oats, wheat are recommended; for those
+with harder coverings, squash, castor bean, apple, pear, or, where obtainable,
+cotton; for still harder kinds, persimmon and date seeds, or the
+stones of plum and cherry.</p>
+
+<p><span class="smcap">Appliances.</span>—1 dozen common earthenware plates for germinators;
+1 dozen two-ounce wide-mouthed bottles; 2 common glass tumblers;
+clean sand, sawdust, or cotton batting, for bedding; a double boiler; a
+gas burner, or a lamp stove.</p>
+</div>
+
+<p><span class="pagenum" id="Page_34">[Pg 34]</span></p>
+
+<p id="p-32"><b>32. Recording observations.</b>—For this purpose a page
+should be ruled off in the notebook of each student, after
+the model here given, and the facts brought out by the different
+experiments set down as observed.</p>
+
+
+<p class="p2 center fs80 smcap">Number of Seeds Germinated</p>
+
+<table class="autotable fs80 wd80">
+<tr>
+<td class="bt" colspan="12"></td>
+</tr>
+<tr>
+<td class="tdl bt">No. of hours</td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt">24</td>
+<td class="tdc bl bt">48</td>
+<td class="tdc bl bt">72</td>
+<td class="tdc bl bt">4 d.</td>
+<td class="tdc bl bt">5 d.</td>
+<td class="tdc bl bt">6 d.</td>
+<td class="tdc bl bt">7 d.</td>
+<td class="tdc bl bt">8 d.</td>
+<td class="tdc bl bt">10 d.</td>
+<td class="tdc bl bt">2 w.</td>
+</tr>
+<tr>
+<td class="tdl">No. of vessel</td>
+<td class="tdc bl bt">1</td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+</tr>
+<tr>
+<td class="tdl">No. of vessel</td>
+<td class="tdc bl bt">2</td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+</tr>
+<tr>
+<td class="tdl">No. of vessel</td>
+<td class="tdc bl bt">3</td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+</tr>
+<tr>
+<td class="tdl">No. of vessel</td>
+<td class="tdc bl bt">4</td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+</tr>
+<tr>
+<td class="tdl">No. of vessel</td>
+<td class="tdc bl bt">5</td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+</tr>
+<tr>
+<td class="tdl">No. of vessel</td>
+<td class="tdc bl bt">6</td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+<td class="tdc bl bt"></td>
+</tr>
+<tr>
+<td class="bt" colspan="12"></td>
+</tr>
+<tr>
+<td class="bt" colspan="12"></td>
+</tr>
+</table>
+
+<div class="blockquot">
+
+<p id="exp-26"><span class="smcap">Experiment 26. Can seeds have too much moisture?</span>—Drop a
+number of dry beans or grains of corn, oats, or other convenient seed,
+into a vessel with a bedding of cotton or paper that is barely moistened,
+and an equal number of soaked seeds of the same kind into another vessel
+with a saturated bedding of the same material. In a third vessel place
+the same number of soaked seed, covering them partially with water, and
+in a fourth cover the same number entirely. Label them 1, 2, 3, and 4;
+keep all together in a warm, even temperature, and observe at intervals
+of twenty-four hours for a week. What condition as to moisture do
+you find most favorable to germination? Would seeds germinate in the
+entire absence of moisture? How do you know?</p>
+
+<p id="exp-27"><span class="smcap">Experiment 27. Was it the presence of too much water, or
+the lack of air caused by it, that interfered with germination
+in the last experiment?</span>—To answer this question experimentally is
+not easy, since it is difficult to obtain a complete vacuum without special
+appliances. The simplest way is to fill with mercury a glass tube 30
+inches long, closed at one end, and invert it over a small vessel—a teacup,
+or an egg cup will answer—containing mercury enough to cover
+the bottom to a depth of two or three centimeters (see Appendix, Weights
+and Measures, for English equivalents.) The tube must be supported in
+such a way that its lower end will dip into the mercury without touching
+the bottom of the vessel. With a pair of forceps insert under the mouth of
+the tube two or three seeds that have been well soaked in water deprived
+of air by previous boiling. Being lighter than mercury, they will float to
+the top, where there is a complete absence of air while other conditions<span class="pagenum" id="Page_35">[Pg 35]</span>
+favorable to germination are present. Before releasing, they should be
+well shaken under the mercury to free them from air bubbles, and if the
+coats are loose fitting so that they can be removed without injury to the
+parts inclosed in them, they should be slipped off in order to get rid of any
+imprisoned air they may contain. Additional moisture may be supplied,
+if necessary, by injecting, by means of a medicine dropper inserted under
+the mouth of the tube, a drop or two of water that has been previously
+boiled. Keep in a warm, even temperature, under conditions favorable
+to germination, and compare the behavior of the seeds with those placed
+in the different vessels in <a href="#exp-26">Exp. 26</a>.</p>
+
+<p>If appliances for this experiment are lacking, a rough approximation
+can be made by using the seeds of aquatic plants, such as the lotus, water
+lily, and the so-called Chinese sacred bean, sold in the variety stores,
+which we know are capable of germinating in the limited amount of air
+contained in ordinary soil water. Place an equal number of such seeds,
+of about the same size and weight, on a bedding of common garden soil
+in two glass tumblers. Fill one vessel a little over half full of ordinary
+soil water and the other to the same height with
+water from which the air has been expelled by boiling.
+Pour over the liquid a film of sweet oil or castor
+oil, to prevent the access of air, leaving the surface of
+the water in the other vessel exposed. In which do
+the seeds come up most freely?</p>
+
+<figure class="figright illowp20" id="i_045" style="max-width: 12.5em;">
+  <img class="w100" src="images/i_045.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 47.</span>—To find
+out the proper depth
+at which to plant
+seeds.</p></figcaption>
+</figure>
+
+<p>Some seeds, especially those rich in proteins, as
+peas and beans, will germinate in a vacuum, because
+oxygen is supplied for a time by the chemical decomposition
+of substances in their tissues which contain it,
+but when these are exhausted, respiration ceases and
+death ensues.</p>
+
+<p id="exp-28"><span class="smcap">Experiment 28. Does the depth at which seeds
+are planted affect their germination?</span>—Plant a
+number of peas or grains of corn at different depths
+in a wide-mouthed glass jar filled with moist sand, as
+shown in <a href="#i_045">Fig. 47</a>, the lowest ones at the bottom, the
+top ones barely covered. Try different kinds of seed
+and grain,—radish, squash, cotton, or wheat,—and
+watch them make their way to the surface. Do you
+notice any difference in this respect between large
+seed and small ones? Between those with thick cotyledons
+and thin ones? At what depth do you find,
+from your recorded observations, that seed germinate
+best?</p>
+
+<p><span class="pagenum" id="Page_36">[Pg 36]</span></p>
+
+<p id="exp-29"><span class="smcap">Experiment 29. What temperature is most favorable to germination?</span>—Put
+half a dozen soaked beans on moist cotton or sawdust in
+three wide-mouthed bottles of the same size or in germinators arranged as
+in <a href="#i_046x">Figs. 48, 49</a>, the seed also being selected
+with a view to similarity of size and weight.
+Keep one at a freezing temperature; the
+second in a temperature of 15° to 20° C.
+(see Appendix for Fahrenheit equivalents);
+and the third, at 30° C. If a place can
+be found near a stove or a register, where
+an even temperature of about 125° F.
+is maintained, place a fourth receptacle
+there. Observe at intervals of twenty-four
+hours for a week or ten days, keeping
+the temperature as even as possible, and
+maintaining an equal quantity of moisture
+in each vessel. Make a daily record of
+your observations. What temperature do
+you find most favorable to germination?</p>
+
+<figure class="figcenter illowp30" id="i_046x" style="max-width: 25em;">
+  <img class="w100" src="images/i_046x.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 48, 49.</span>—Home-made germinators:
+48, closed; 49, showing interior arrangement.</p></figcaption>
+</figure>
+
+<p id="exp-30"><span class="smcap">Experiment 30. At what temperature do seeds lose their vitality?</span>—Place
+about two dozen each of grains of corn, beans, squash
+seed, and castor beans, with an equal number of plum or cherry stones,
+in water, and heat to a temperature of 150° F. After an exposure of
+ten minutes, take out six of each kind and place in germinators made
+of two plates with moist sand or damp cloth between them, as shown
+in <a href="#i_046x">Figs. 48, 49</a>. Raise the temperature to 175° F., and after ten minutes
+take out six more of each kind of seed and place in another germinator.
+Raise the water in the vessel to 200°, take out another batch of seeds;
+raise to the boiling point for ten minutes more, and plant the remaining
+six of each lot. Number the four germinators, and observe at intervals
+of twenty-four hours for two weeks. The harder kinds should be
+kept under observation for three or four weeks, as they germinate slowly.</p>
+
+<p>Try the same experiments with the same kinds of seeds at a dry heat,
+using a double boiler to prevent scorching, and record observations as before.</p>
+
+<p id="exp-31"><span class="smcap">Experiment 31. Time required for germination.</span>—Arrange in
+germinators seeds of various kinds, such as corn, wheat, peas, turnip, apple,
+orange, grape, castor bean, etc. “Clip” some of the harder ones and keep
+all the kinds experimented with under similar conditions as to moisture,
+temperature, etc., and record the time required for each to sprout. What
+is the effect of clipping, and why?</p>
+
+<p id="exp-32"><span class="smcap">Experiment 32. Are very young or immature seeds capable of
+germinating?</span>—Plant some seeds from half-grown tomatoes, and grains<span class="pagenum" id="Page_37">[Pg 37]</span>
+of wheat, oats, or barley before they are ready for harvesting. Try as
+many kinds as you like, and see how many will come up. Notice whether
+there is any difference in the health and vigor of plants raised from seeds
+in different stages of maturity.</p>
+
+<p id="exp-33"><span class="smcap">Experiment 33. The relative value of perfect and inferior
+seed.</span>—From a number of seeds of the same species select half a dozen of
+the largest, heaviest,
+and most perfect, and
+an equal number of
+small, inferior ones. If
+a pair of scales is at
+hand, the different sets
+should be weighed and
+a record kept for comparison
+with the seedlings
+at the end of the
+experiment. Plant the
+two sets in pots containing
+exactly the
+same kind of soil, and
+keep under identical
+conditions as to light,
+temperature, and
+moisture. Keep the
+seedlings under observation
+for two or three
+weeks, making daily
+notes and occasional
+drawings of the height
+and size of the stems,
+and the number of
+leaves produced by
+each.</p>
+</div>
+
+<figure class="figright illowp60" id="i_047" style="max-width: 25em;">
+  <img class="w100" src="images/i_047.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 50, 51.</span>—Stem development of seedlings: 50,
+raised from healthy grains of barley; weight, 39.5
+grams (about 500 grs.); 51, raised under exactly similar
+conditions from the same number of inferior grains;
+weight, 23 grams (about 350 grs.).</p></figcaption>
+</figure>
+
+<figure class="figright illowp60" id="i_047x" style="max-width: 25em;">
+  <img class="w100" src="images/i_047x.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 52, 53.</span>—Improvement of corn by selection:
+52, original type; 53, improved type developed from it.</p></figcaption>
+</figure>
+
+<p id="p-33"><b>33. Resistance
+to heat and cold.</b>—In
+making experiments
+with regard to temperature, notice how the extremes
+tolerated are influenced, first, by the length of time the
+seeds are exposed; second, by the amount of water contained
+in them; and third, by the nature of the seed coats. Every
+farmer knows that the effect of freezing is much more injurious<span class="pagenum" id="Page_38">[Pg 38]</span>
+to plants or parts of plants when full of sap (water)
+than when dry. This, in the opinion of the most recent
+investigators, is because the water in the spaces outside the
+cells freezes first and as moisture is gradually withdrawn
+from the inside to take its place, the soluble salts which may
+be present in the cell sap become more concentrated, and by
+their chemical action on the contained proteins cause them
+to be precipitated, or “salted out,” as we see sugar or salt
+precipitated from solutions of those substances when water
+is withdrawn by evaporation. In this way, it is believed,
+the fundamental protoplasm of the cell may be so disorganized
+that death ensues if the freezing is continued long enough,
+since the protein precipitates become “denatured” and cannot
+be reabsorbed if kept in a solid state too long. The length of
+time necessary to produce death from this cause is, of course,
+different in different plants, according to the kind of salts
+dissolved in the sap and the nature of the proteins acted on
+by them. The proteins in the sap of Begonia, or Pelargonium,
+plants which are very sensitive to cold, yield a denatured
+precipitate at, or a little below the freezing point of
+water, while those of winter rye withstand a temperature of
+-15° C., and of pine needles, -40° C.</p>
+
+<p>Mechanical injury through rupture of parts by freezing
+is not apt to cause serious damage except in cases of sudden
+and violent cold at a time when the tissues are gorged with
+sap, as not infrequently happens during the abrupt changes
+of temperature which sometimes occur in spring after the
+trees have put forth their leaves. In an extreme case of
+this kind, the writer has seen the trunk of an oak a foot
+or more in diameter split in deep seams from the effects
+of freezing.</p>
+
+<p id="p-34"><b>34. The length of time during which seeds may retain
+their vitality.</b>—No direct experiment can be made to test
+this point, since it would require months, or even years,
+covering in some instances more than the lifetime of a generation.
+It has been stated on good authority that seeds of the<span class="pagenum" id="Page_39">[Pg 39]</span>
+water chinquapin (Nelumbo) have germinated after more
+than a hundred years, and moss spores preserved in herbariums,
+after fifty. But the records in such cases are not
+always trustworthy, and there is absolutely no foundation
+for the statements sometimes made about the germination
+of wheat grains found preserved with mummies over two
+thousand years old. If kept perfectly dry, however, seed
+may sometimes be preserved for months, or even years.
+Peas have been known to sprout after ten years, red clover
+after twelve, and tobacco after twenty. Ordinarily, however,
+the vitality of seeds diminishes with age, and in making experiments
+it is best to select fresh ones. Those used for
+comparison should also, as far as possible, be of the same size
+and weight.</p>
+
+<p id="p-35"><b>35. Effect of precocious germination.</b>—It has been found
+by experiment that plants raised from immature seed, when
+they will germinate at all (<a href="#exp-32">Exp. 32</a>), yield earlier and larger
+crops than the same kinds from mature seed. Early tomatoes
+and some other vegetables are produced in this way.
+The majority of seeds, however, require a period of rest
+before beginning their life work. Those that are forced to
+take up the burden of “child labor” show the effect of
+such abnormal condition by yielding fruits that are smaller
+and less firm than those raised from mature seed, so that
+they do not keep well and have to be marketed quickly.
+Under what circumstances does it pay to cultivate such
+fruits?</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. What are the principal external conditions that affect germination?
+(<a href="#exp-26">Exps. 26-29</a>.)</p>
+
+<p>2. What effect has cold? want of air? too much water?</p>
+
+<p>3. Is light necessary to germination?</p>
+
+<p>4. What is the use of clipping seeds? (<a href="#exp-12">Exps. 12</a>, <a href="#exp-13">13</a>, <a href="#exp-14">14</a>, and Material,
+<a href="#Page_12">p. 12</a>.)</p>
+
+<p>5. In what cases should it be resorted to? (<a href="#exp-31">Exp. 31</a>.)</p>
+
+<p>6. Why will seed not germinate in hard, sunbaked land without<span class="pagenum" id="Page_40">[Pg 40]</span>
+abundant tillage? Why not on undrained or badly drained land? (<a href="#exp-26">Exps.
+26</a>, <a href="#exp-27">27</a>.)</p>
+
+<p>7. Will seeds that have lost their vitality swell when soaked? (<a href="#exp-16">Exp. 16</a>.)</p>
+
+<p>8. Are there any grounds for the statement that the seeds of plums
+boiled into jam have sometimes been known to germinate?<a id="FNanchor_1" href="#Footnote_1" class="fnanchor">[1]</a> (<a href="#p-33">33</a>; <a href="#exp-30">Exp. 30</a>.)</p>
+
+<p>9. Could such a thing happen in the case of apple or sunflower seed,
+and why or why not? (<a href="#p-33">33</a>.)</p>
+
+<p>10. Does it make any difference in the health and vigor of a plant
+whether it is grown from a large and well-developed seed or from a weak
+and puny one? (<a href="#exp-33">Exp. 33</a>.)</p>
+
+<p>11. Would a farmer be wise who should market all his best grain and
+keep only the inferior for seed?</p>
+
+<p>12. What would be the result of repeated plantings from the worst
+seed?</p>
+
+<p>13. Of constantly replanting the best and most vigorous?</p>
+
+<p>14. Suppose seed would germinate without moisture; would this be
+an advantage, or a disadvantage to agriculturists?</p>
+
+<p>15. Why is a cool, dry place best for keeping seeds? (<a href="#exp-26">Exps. 26</a>, <a href="#exp-29">29</a>.)</p>
+
+<p>16. Why are the earliest tomatoes found in the market usually smaller
+than those offered later? (<a href="#p-35">35</a>.)</p>
+
+<p>17. Why is continued rain so injurious to wheat, oats, and other grains
+before they are mature enough to be harvested? (<a href="#p-35">35</a>; <a href="#exp-32">Exp. 32</a>.)</p>
+
+<p>18. Would the same effect be likely to occur in the case of very oily
+seeds, such as flax and castor beans? Why? (Suggestion: try the effect
+of putting water on a piece of oiled paper.)</p>
+
+<p>19. Explain why many seeds cannot germinate successfully without
+air. (<a href="#p-30">30</a>, <a href="#p-31">31</a>; <a href="#exp-25">Exp. 25</a>.)</p>
+
+<p>20. Mention some of the practical advantages that a farmer, a gardener,
+or a careful housewife might gain from experiments like those made in this
+section.</p>
+
+<p>21. Explain why seeds can endure so much greater extremes of temperature
+than growing plants. (<a href="#p-23">23</a>, <a href="#p-33">33</a>.)</p>
+</div>
+
+
+<h3 id="CH_II_III">III. DEVELOPMENT OF THE SEEDLING</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Seedlings of various kinds in different stages of growth.
+It is recommended that the same species be used that were studied in
+Section III, Chapter I, or such equivalents as may have been substituted
+for them. Enough should be provided to give each pupil three or four
+specimens in different stages of development. Seeds, even of the same kind,<span class="pagenum" id="Page_41">[Pg 41]</span>
+develop at such different rates that it will probably not be necessary to
+make more than two plantings of each sort, from 2 to 5 days apart.
+Soaked seeds of corn and wheat will germinate in from 3 to 7 days,
+according to the temperature; oats in 1 to 4; beans in 4 to 6;
+squash and castor beans in from 8 to 10. Very obdurate ones may
+be hastened by clipping. Keep the germinators in an even temperature,
+at about 70° to 80° F.</p>
+
+<p>Pine is a very difficult seed to germinate, requiring usually from 18 to 21
+days. By soaking the mast for twenty-four hours and planting in damp
+sand or sawdust kept at an even temperature of 23° C. or about 75° F.,
+specimens may be obtained.</p>
+</div>
+
+<figure class="figright illowp25" id="i_051" style="max-width: 18.75em;">
+  <img class="w100" src="images/i_051.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 54, 55.</span>—Seedling
+of corn (<i>after</i> <span class="smcap">Gray</span>): 54, early stage
+of germination; 55, later stage.</p></figcaption>
+</figure>
+
+<p id="p-36"><b>36. Seedlings of monocotyls.</b>—Examine a seedling of
+corn that has just begun to sprout; from which side does the
+seedling spring, the plain or the grooved one? Refer to your
+sketch of the dry grain and see if this
+agrees with the position of the embryo as
+observed in the seed. Make sketches of
+four or five seedlings in different stages of
+advancement, until you reach one with a
+well-developed blade. From what part of
+the embryo has each part of the seedling
+developed? Which part first appeared
+above ground? Is it straight, or bent in
+any way? In what direction does the
+plumule grow? The hypocotyl? Does the
+cotyledon appear above ground at all? Slip
+off the husk and see if there is any difference
+in the size and appearance of the
+contents as you proceed from the younger
+to the older plants. How would you account
+for the difference?</p>
+
+<p id="p-37"><b>37. The root.</b>—Examine the lower end of the hypocotyl
+and find where the roots originate; would you say that they
+are an outgrowth from the stem, or the stem from the root?
+Observe that the root of the corn does not continue to grow
+in a single main axis like that of the castor bean, but that
+numerous adventitious and secondary roots spring from<span class="pagenum" id="Page_42">[Pg 42]</span>
+various points near the base of the hypocotyl and spread out
+in every direction, thus giving rise to the fibrous roots of
+grains and grasses.</p>
+
+<p id="p-38"><b>38. Root hairs.</b>—Notice the grains of sand or sawdust
+that cling to the rootlets of plants grown in a bedding of that
+kind. Examine with a lens and see if you
+can account for their presence. Lay the root
+in water on a bit of glass, hold up to the light
+and look for root hairs; on what part are they
+most abundant?</p>
+
+<figure class="figleft illowp10" id="i_52" style="max-width: 19.1875em;">
+  <img class="w100" src="images/i_052.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 56.</span>—Seedling
+of wheat, with
+root hairs.</p></figcaption>
+</figure>
+
+<p>The hairs are the chief agents in absorbing
+moisture from the soil. They do not last
+very long, but are constantly dying and being
+renewed in the younger and tenderer parts of
+the root. These are usually broken away in
+tearing the roots from the soil, so that it is not
+easy to detect the hairs except in seedlings,
+even with a microscope. In oat, maple, and radish seedlings
+they are very abundant and clearly visible to the naked eye.
+The amount of absorbing surface on a
+root is greatly increased by their presence.</p>
+
+<figure class="figright illowp25" id="i_052a" style="max-width: 18.75em;">
+  <img class="w100" src="images/i_052a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 57.</span>—Diagrammatic
+section of a root
+tip: <i>a</i>, cortex; <i>b</i>, central
+cylinder in which the
+conducting vessels are
+situated; <i>c</i>, root cap; <i>g</i>,
+growing point.</p></figcaption>
+</figure>
+
+<p id="p-39"><b>39. The root cap.</b>—Look at the tip of
+the root through your lens and notice the
+soft, transparent crescent or horseshoe-shaped
+mass in which it terminates. This
+is the root cap and serves to protect the
+tender parts behind it as the roots burrow
+their way through the soil. Being soft
+and yielding, it is not so likely to be injured
+by the hard substances with which
+it comes in contact as would be the more
+compact tissue of the roots. It is composed
+of loose cells out of which the solid root
+substance is being formed; the growing point of the root,
+<i>g</i>, is at the extremity of the tip just behind the cap, <i>c</i> (<a href="#i_052a">Fig. 57</a>).
+The cap is very apparent in a seedling of corn, and can easily<span class="pagenum" id="Page_43">[Pg 43]</span>
+be seen with the naked eye, especially if a thin longitudinal
+section is made. It is also well seen in the water roots of the
+common duckweed (<i>Lemna</i>), and on those developed by a
+cutting of the wandering Jew, when placed in water. Are
+there any hairs on the root cap? Can you account for their
+absence?</p>
+
+<div class="blockquot">
+
+<p><span class="smcap">Note.</span>—For a minute study of the structure of roots, see <b><a href="#p-67">67</a></b>.</p>
+</div>
+
+<p id="p-40"><b>40. Organs of vegetation.</b>—The three parts, root, stem,
+and leaf, are called organs of vegetation in contradistinction to
+the flower and fruit, which constitute
+the organs of reproduction. The former
+serve to maintain the plant’s individual
+existence, the latter to produce
+seed for the propagation of the species,
+so we find that the seed is both the beginning
+and the end of vegetable life.</p>
+
+<figure class="figright illowp30" id="i_053" style="max-width: 12.5em;">
+  <img class="w100" src="images/i_053.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 58.</span>—Seedlings of bean
+in different stages of growth:
+<i>cc</i>, cotyledons, showing the
+plumule and hypocotyl before
+germination; <i>a</i>, <i>b</i>, <i>d</i>, and <i>e</i>,
+successive stages of advancement.
+At <i>d</i> the arch of the
+hypocotyl is beginning to
+straighten; at <i>e</i> it has entirely
+erected itself.</p></figcaption>
+</figure>
+
+<p id="p-41"><b>41. Definitions.</b>—Organ is a general
+name for any part of a living thing,
+whether animal or vegetable, set apart
+to do a certain work, as the heart for
+pumping blood, or the stem and leaves
+of a plant for conveying and digesting
+sap. By “function” is meant the
+particular work or office that an organ
+has to perform.</p>
+
+<p id="p-42"><b>42. Seedlings of dicotyls. The bean.</b>—Sketch, without
+removing it, a bean seedling that has just begun to show
+itself above ground; what part is it that protrudes first?
+Sketch in succession four or five others in different stages of
+advancement. Notice how the hypocotyl is arched where
+it breaks through the soil. Does this occur in the monocotyls
+examined? Do the cotyledons of the bean appear above
+ground? How do they get out? Can you perceive any
+advantage in their being dragged out of the ground backwards
+in this way rather than pushed up tip foremost?<span class="pagenum" id="Page_44">[Pg 44]</span>
+What changes have the cotyledons undergone in the successive
+seedlings? Remove from the earth a seedling just
+beginning to sprout and sketch it. From what point does
+the hypocotyl protrude through the coats? Does this agree
+with its position as sketched in your study of the seed?
+In which part of the embryo does the first growth take place?</p>
+
+<p>Remove in succession the several seedlings you have
+sketched and note their changes. How does the root differ
+from that of the corn and oats? The first root formed by the
+extension of the hypocotyl is the <em>primary</em> root and should be
+so labeled in your drawings; the branches that spring from
+it are <em>secondary</em> roots. Look for root hairs; if there are
+any, where do they occur?</p>
+
+<figure class="figcenter illowp80" id="i_054" style="max-width: 50em;">
+  <img class="w100" src="images/i_054.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 59.</span>—Stages in the germination of a typical seedling of the squash family:
+<i>a</i>, a seed before germination; <i>b</i>, <i>c</i>, <i>e</i>, the same in different stages of growth; <i>d</i>, the
+empty testa, with kernel removed; <i>hi</i>, hilum; <i>m</i>, micropyle; <i>p</i>, <i>p</i>, the peg in the heel;
+<i>h</i>, <i>h</i>, <i>h</i>, the hypocotyl; <i>ar</i>, arch of the hypocotyl; <i>co</i>, cotyledons; <i>pl</i>, plumule; <i>pr</i>,
+primary root; <i>sc</i>, secondary roots.</p></figcaption>
+</figure>
+
+<p id="p-43"><b>43. Germination of the squash.</b>—How does the manner
+of breaking through the soil compare with that of the bean?
+With the corn? From which end of the seed, the large or
+the small one, does the hypocotyl spring? Do the cotyledons
+come above ground? How do they get out of the seed coat?
+Notice the thick protuberance developed by the hypocotyl
+and pressing against the lower half of the coat at the point
+where the hypocotyl breaks through. This is called the<span class="pagenum" id="Page_45">[Pg 45]</span>
+“peg”; can you tell its use? Could the cotyledons get out
+of their hard covering without it? Slip the peg below the
+coat in one of your growing specimens, leave it in the soil,
+and see what will happen. How do the cotyledons of the
+squash differ from those of the bean as they come out of the
+seed cover? Do they act as foliage leaves? Do you see
+any difference in the development of the plumule in the two
+seeds (<a href="#i_024a">Figs. 19</a>, <a href="#i_027">25</a>) to account for the different behavior of
+the cotyledons? Sketch three seedlings in different stages,
+labeling correctly the parts observed. Make a similar study
+of the castor bean, or other seedling selected by your teacher,
+and illustrate by drawings.</p>
+
+<p id="p-44"><b>44. Arched and straight hypocotyls.</b>—This difference in
+the manner of getting above ground is an important one.
+That by means of the arched hypocotyl is, in general, characteristic
+of the process of germination in which the cotyledons
+come above ground, while the straight kind, which was illustrated
+in the corn and wheat, is the prevailing
+method when the cotyledons remain
+below ground. Can you give a reason for
+the difference?</p>
+
+<figure class="figright illowp25" id="i_055" style="max-width: 29.25em;">
+  <img class="w100" src="images/i_055.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 60.</span>—Pine
+seedling (<i>After</i> <span class="smcap">Gray</span>).</p></figcaption>
+</figure>
+
+<p id="p-45"><b>45. Polycotyledons; germination of the
+pine.</b>—Examine a pine seedling just beginning
+to sprout. What part emerges first
+from the seed coat? Where does it break
+through? Where did you find the micropyle
+in the pine seed? (15.) Can you give a
+reason why the hypocotyl in seeds should
+break through the coats at this point? How
+do the cotyledons get out of the testa? Is
+the hypocotyl arched or straight in germination? How does
+it compare with the bean and squash in this respect? With
+the corn? Is any endosperm left in the testa after the cotyledons
+have come out? What has become of it? Do the
+cotyledons function as leaves? How many of them <a id="tn_45">have</a> the
+specimen you are studying? Notice the little knob or button<span class="pagenum" id="Page_46">[Pg 46]</span>
+at the upper end of the hypocotyl, just above the point where
+the cotyledons are attached; this is the <em>epicotyl</em>, or part
+above the cotyledons, here identical with the plumule; does
+it develop as rapidly as in the other seedlings you have examined?</p>
+
+<p id="p-46"><b>46. Relation of parts in the seedling.</b>—Before leaving this
+subject, it is important to fix clearly in mind the different
+parts of the germinating seedling and their relation to both
+the embryo from which they originated and the plant into
+which they are to develop. The part labeled “hypocotyl”
+in your sketches is all that portion of the embryo below the
+point of attachment of the cotyledons. In germination its
+upper part will become the stem, and in the embryo constitutes
+the <em>caulicle</em>, or stemlet, while its lower part, from
+which the root will develop, is the <em>radicle</em>, or rootlet; hence
+the term “hypocotyl” includes both the future root and
+stem. The plumule is that part of the embryo between the
+cotyledons and <em>above</em> their point of attachment to the caulicle.
+It is the upward growing point of the young plant, and hence
+the place of attachment of the cotyledon is the first <em>node</em>, or
+point of leaf origin, on the stem.</p>
+
+<p>The epicotyl, in contradistinction to the hypocotyl, is all
+that part of the plant <em>above</em> the insertion of the cotyledons.
+Before germination it is identical with the plumule. As the
+seedling grows, the epicotyl advances its growing point by
+adding new nodes and <em>internodes</em>, as the spaces between the
+successive points of leaf insertion are called.</p>
+
+<p id="p-47"><b>47. Botanical terms.</b>—As the prefixes <em>hypo</em> and <em>epi</em> are
+of frequent occurrence in botanical works, it will aid in
+understanding their various compounds if you will remember
+that <em>hypo</em> always refers to something below or beneath,
+and <em>epi</em>, to something over or above. With this idea in mind
+you will see that botanical terms are a labor-saving device,
+since it is much easier, in making notes, to use a single descriptive
+word than to write out the long English equivalent,
+such as “the part under (or over) the cotyledons.”</p>
+
+<p><span class="pagenum" id="Page_47">[Pg 47]</span></p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Do the cotyledons, as a general thing, resemble the mature leaves of
+the same plants?</p>
+
+<p>2. Name some plants in which you have observed differences, and account
+for them; could convenience of packing in the seed coats, for instance,
+or of getting out of them, have any bearing on the matter?</p>
+
+<p>3. Does the position in which seeds are planted in the ground have
+anything to do with the position of the seedlings as they appear above the
+surface?</p>
+
+<p>4. Is this fact of any importance to the farmer?</p>
+
+<p>5. Will grain that has begun to germinate make good meal or flour?
+Why? (<a href="#p-27">27</a>, <a href="#p-36">36</a>; <a href="#exp-25">Exp. 25</a>.)</p>
+</div>
+
+
+<h3 id="CH_II_IV">IV. GROWTH</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Two young potted plants; some lily or hyacinth bulbs;
+seedlings of different kinds,—some with well-developed
+taproots,—apple, cotton, and maple
+are good examples.</p>
+
+<p><span class="smcap">Appliances.</span>—A small flat dish, some mercury,
+and a piece of cork.</p>
+
+<figure class="figright illowp30" id="i_057" style="max-width: 20.25em;">
+  <img class="w100" src="images/i_057.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 61, 62.</span>—Seedling
+of corn, marked to
+show region of growth:
+61, early stage of germination;
+62, later stage.</p></figcaption>
+</figure>
+
+<p id="exp-34"><span class="smcap">Experiment 34. How does the root increase
+in length?</span>—Mark off the root of a very
+young corn seedling into sections by moistening a
+piece of sewing thread with indelible ink and
+applying it to the surface of the root at intervals
+of about two millimeters (⅒ of an inch), or by
+tying a thread lightly around it at the same intervals.
+Lay the seedling on a moist bedding between
+two panes of glass kept apart by a sliver of
+wood to prevent their injuring the root by pressure.
+Watch for a day or two, and you will see that
+growth takes place from a point just back of the
+tip (<a href="#i_057">Figs. 61, 62</a>).</p>
+
+<p>Mark off a seedling of the bean in the same
+way and watch to see whether it increases in the same manner as the corn.</p>
+
+<p id="exp-35"><span class="smcap">Experiment 35. How does the stem increase in length?</span>—Mark
+off a portion of the stem of a bean seedling as explained in the last experiment,
+and find out how it grows. Allow a seedling to develop until it
+has put forth several leaves and measure daily the spaces between them.
+Label these spaces in your drawings, “internodes,” and the points where the
+leaves are attached, “nodes.” Does an internode stop growing when the<span class="pagenum" id="Page_48">[Pg 48]</span>
+one next above it has formed? When is growth most rapid? Reverse the
+position of a number of seedlings that have just begun to sprout and watch
+what will happen. After a few days reverse again and note the effect.</p>
+
+<figure class="figcenter illowp100" id="i_058x" style="max-width: 40em;">
+  <img class="w100" src="images/i_058x.jpg" alt="">
+  <figcaption>
+<table class="autotable">
+<tr>
+<td class="tdl wd50"><p><span class="smcap">Figs.</span> 63, 64.—Root of bean seedling, measured to show region of growth: 63,
+early stage of germination; 64, later stage.</p></td>
+<td class="tdl"><p><span class="smcap">Figs.</span> 65, 66.—Stem of bean seedling, measured to show region of growth: 65,
+early stage of growth; 66, later stage.</p></td>
+</tr>
+</table>
+</figcaption>
+</figure>
+
+<p id="exp-36"><span class="smcap">Experiment 36. Can plants grow and lose weight at the same
+time?</span>—Remove the scales from a white
+lily bulb, weigh them, and lay in a warm,
+but not too damp place, away from the
+light. After a time bulblets will form at
+the bases of the scales. Weigh them again,
+and if there has been any loss, account
+for it. The experiment may be tried by
+allowing a potato tuber or a hyacinth bulb
+to germinate without absorbing moisture
+enough to affect its weight.</p>
+
+<figure class="figleft illowp30" id="i_058" style="max-width: 29.75em;">
+  <img class="w100" src="images/i_058.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 67, 68.</span>—Experiment showing
+the direction of growth in stems:
+67, young potato planted in an inverted
+position; 68, the same after
+an interval of eight days.</p></figcaption>
+</figure>
+
+<p id="exp-37"><span class="smcap">Experiment 37. Is the direction of
+growth a matter of any importance?</span>—Plant
+in a pot suspended as shown in
+<a href="#i_058">Fig. 67</a>, a healthy seedling of some kind,
+two or three inches high, so that the
+plumule shall point downward through
+the drain hole and the root upward into
+the soil. Watch the action of the stem<span class="pagenum" id="Page_49">[Pg 49]</span>
+for six or eight days, and sketch it at successive intervals. After the stem
+has directed itself well upward, invert the pot again, and watch the growth.
+After a week remove the plant and notice the direction of the root. Sketch
+it entire, showing the changes in direction of growth.</p>
+
+<p>At the same time that this experiment is arranged, lay another pot with a
+rapidly growing plant on one side, and every forty-eight hours reverse the
+position of the pot, laying it on the opposite side. At the end of ten or
+twelve days remove the plant and examine. How has the growth of root
+and stem been affected?</p>
+
+<p>What do we learn from these experiments and from <a href="#exp-35">Exp. 35</a> as to the
+normal direction of growth in these two organs respectively? Can you
+think of any natural force that might influence this direction?</p>
+
+<figure class="figright illowp30" id="i_059" style="max-width: 20em;">
+  <img class="w100" src="images/i_059.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 69.</span>—Experiment
+showing the root of a seedling
+forcing its way downward
+through mercury.</p></figcaption>
+</figure>
+
+<p id="exp-38"><span class="smcap">Experiment 38. To show that plants will exert force rather
+than change their direction of growth.</span>—Pin a sprouted bean to a
+cork and fasten the cork to the side of a flat dish,
+as shown in <a href="#i_059">Fig. 69</a>. Cover the bottom of the dish
+with mercury at least half an inch deep, and over
+the mercury pour a layer of water. Cover the
+whole with a pane of glass to keep the moisture in,
+and leave for several days. The root will force its
+way downward into the mercury, although the
+latter is fourteen times heavier than an equal
+bulk of the bean root substance, and the root must thus overcome a
+resistance equal to at least fourteen times its own weight.</p>
+</div>
+
+<p id="p-48"><b>48. What growth is.</b>—With the seedling begins the
+growth of the plant. Most people understand by this
+word mere increase in size; but growth is something more
+than this. It involves a change of form, usually, but not
+necessarily, accompanied by increase in bulk. Mere mechanical
+change is not growth, as when we bend or stretch
+an organ by force, though if it can be kept in the altered
+position till such position becomes permanent, or as we say
+in common speech, “till it grows that way,” the change
+may become growth. To constitute true growth, the change
+of form must be permanent, and brought about, or maintained,
+by forces within the plant itself.</p>
+
+<p id="p-49"><b>49. Conditions of growth.</b>—The internal conditions depend
+upon the organization of the plant. The essential
+external conditions are the same as those required for germination:<span class="pagenum" id="Page_50">[Pg 50]</span>
+food material, water, oxygen, and a sufficient
+degree of warmth. It may be greatly influenced by other
+circumstances, such as light, gravitation, pressure, and
+(probably) electricity; but the four first named are the essential
+conditions without which no growth is possible.</p>
+
+<p id="p-50"><b>50. Cycle of growth.</b>—When an organ becomes rigid
+and its form fixed, there is no further growth, but only nutrition
+and repair,—processes which must not be confounded
+with it. Every plant and part of a plant has its period of
+beginning, maximum, decline, and cessation of growth. The
+cycle may extend over a few hours, as in some of the fungi, or,
+in the case of large trees, over thousands of years.</p>
+
+<p id="p-51"><b>51. Geotropism.</b>—The general tendency of the growing
+axes of plants to take an upward and downward course as
+shown in <a href="#exp-37">Exp. 37</a>—in other words, to point to and from the
+center of the earth—is called <em>geotropism</em>. It is <em>positive</em> when
+the growing organs point downward, as most primary roots
+do; <em>negative</em> when they point upward, as in most primary
+stems; and <em>transverse</em>, or <em>lateral</em>, when they extend horizontally,
+as is the case with most secondary roots and branches.</p>
+
+<p id="p-52"><b>52. Gravity and growth.</b>—It cannot be proved directly
+that geotropism is due to gravity, because it is not possible
+to remove plants from its influence so as to see how they
+would behave in its absence. The effect of gravity may be
+neutralized, however, by arranging a number of sprouting
+seeds on the vertical disk of a clinostat, an instrument
+fitted with a clockwork movement by means of which they
+may be kept revolving steadily for several days. By this
+constant change of position gravity is made to act on them
+in all directions alike, which is the same in some respects as
+if it did not act at all. If the disk is made to revolve
+rapidly, the growing root tips turn toward the axis of motion,
+without showing a tendency to grow downward. We may
+then conclude that geotropism is a reaction to gravity.</p>
+
+<p id="p-53"><b>53. Geotropism an active force.</b>—It must be noted,
+however, that the force here alluded to is not the mere mechanical<span class="pagenum" id="Page_51">[Pg 51]</span>
+effect of gravity, due to weight of parts, as when the
+bough of a fruit tree is bent under the load of its crop, but
+a certain stimulus to which the plant reacts by a spontaneous
+adjustment of its growing parts. In other words, geotropism
+is an active, not a passive function, and the plant will
+overcome considerable resistance in response to it. (<a href="#exp-38">Exp. 38</a>).</p>
+
+<p id="p-54"><b>54. Other factors.</b>—The direction of growth is influenced
+by many other factors, such as light, heat, moisture,
+contact with other bodies, and perhaps by
+electricity. The result of all these forces is an
+endless variety in the forms and growth of
+organs that seems to defy all law.</p>
+
+<figure class="figcenter illowp100" id="i_061" style="max-width: 30em;">
+  <img class="w100" src="images/i_061.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 70.</span>—A piece of a haulm of millet that has been laid horizontally, righting
+itself through the influence of negative geotropism.</p></figcaption>
+</figure>
+
+<p>Heat, unless excessive, generally stimulates
+growth; contact sometimes stimulates it,
+causing the stem to curve away from the disturbing
+object, and sometimes retards it, causing
+the stem to curve toward the object of contact
+by growing more rapidly on the opposite side,
+as in the stems of twining vines. Light stimulates nutrition,
+but generally retards growth. The movements of plants
+toward the light are effected in this way; growth being
+checked on that side, the plant bends toward the light.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Why do stems of corn, wheat, rye, etc., straighten themselves after
+being prostrated by the wind? (<a href="#p-51">51</a>, <a href="#p-54">54</a>.)</p>
+
+<p>2. Do plants grow more rapidly in the daytime, or at night? (<a href="#p-54">54</a>.)</p>
+
+<p>3. Reconcile this with the fact that green plants will die if deprived
+of light.</p>
+
+<p><span class="pagenum" id="Page_52">[Pg 52]</span></p>
+
+<p>4. Which grows more rapidly, a young shoot or an old one? (<a href="#p-31">31</a>, <a href="#p-50">50</a>.)</p>
+
+<p>5. Which, as a general thing, are the more rapid growers, annuals or
+perennials? Herbaceous or woody-stemmed plants?</p>
+
+<p>6. Name some of the most rapid growers you know.</p>
+
+<p>7. Of what advantage is this habit to them?</p>
+
+<p>8. Why do roots form only on the under side of subterraneous stems?
+(<a href="#p-51">51</a>.)</p>
+
+<p>9. Why do new twigs develop most freely on the upper side of horizontal
+branches? (<a href="#p-51">51</a>.)</p>
+</div>
+
+
+<h4 id="CH_II_FIELD">Field Work</h4>
+
+<div class="blockquot">
+
+<p>(1) Notice the various seedlings met with in your walks and see how
+many you can recognize by their resemblance to the mature plants. Account
+for any differences you may observe between seedlings and older
+plants of the same species. Observe the cotyledons as they come up and
+their manner of getting out of the ground, and notice the ways in which
+this is influenced by moisture, light, and the nature of the soil. Where
+the cotyledons do not appear, dig into the ground and find out the reason.
+Notice which method of emergence occurs in each case, the arched, or
+straight, and account for it. Observe particularly the behavior of seedlings
+in hard, sunbaked soil. If you see any of them lifting cakes of earth,
+compare the size and weight of the cake with that of the seed; if there is
+any disparity, what does this imply? What is the force called which the
+plant exercises in lifting the weight? (51.)</p>
+
+<p>(2) Notice if there are any seeds germinating successfully on top of
+the ground, and find out by what means their roots get into the soil.
+Observe what effect sun and shade, moisture and drought, and the nature
+of the soil have on the process. Find out whether roots exercise force in
+penetrating the soil; what kinds they penetrate most readily, and what
+kinds, if any, they fail to penetrate at all. Notice whether seedlings with
+taproots, like the turnip and castor bean, or those with fibrous roots, like
+corn and wheat, are more successful in working their way downward.</p>
+
+<p>(3) Look for tree seedlings. Explain why seedlings of fruit trees are so
+much more widely distributed in cultivated districts, and so much easier
+to find than those of forest trees. Where do the latter occur, as a general
+thing? Account for the fact that seedling trees are so much more rare
+than germinating herbs, and why trees like the oak and chestnut and
+black walnut propagate so much more slowly, in a state of nature, than
+the pine, cedar, ash, and maple.</p>
+
+<p>(4) Observe the direction of growth in plants on the sides of gullies and
+ravines, and tell how it is influenced by geotropism. Notice whether there
+are other influences at work; for instance, light, or in the case of roots,
+the attraction of moisture.</p>
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_53">[Pg 53]</span></p>
+
+<h2 class="nobreak" id="CH_III">CHAPTER III. THE ROOT</h2>
+</div>
+
+
+<h3 id="CH_III_I">I. OSMOSIS AND THE ACTION OF THE CELL</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—For experiments in osmosis provide fresh and boiled
+slices of red beet, a fresh egg, a piece of ox bladder or some parchment
+paper; glass tubing, thread, twine, elastic bands, salt and sugar solutions.
+A common medicine dropper with the small end cut off will answer instead
+of tubing for making an artificial cell; or an eggshell may be used, by
+blowing out the contents through a puncture in the small end, and carefully
+chipping away a portion of the shell at the big end, leaving the lining
+membrane intact. The different liquids can be put into the shell and the
+exposed membrane placed in contact with the liquid
+in the glass, by fitting over the latter a piece of cardboard
+with a hole in the center large enough for the
+exposed surface to protrude sufficiently to touch the
+water.</p>
+</div>
+
+<figure class="figright illowp25" id="i_063" style="max-width: 14.75em;">
+  <img class="w100" src="images/i_063.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 71.</span>—Artificial
+cell.</p></figcaption>
+</figure>
+
+<p id="p-55"><b>55. Object of the experiments.</b>—In order
+to understand clearly the action of roots
+in absorbing nutrients from the soil, it will
+be necessary to learn something about the
+movement of liquids through the cells, upon
+which the physiological processes of the
+plant depend. For this purpose make an
+artificial cell by tying a piece of ox bladder
+or parchment paper tightly over one end of
+a small glass tube, as shown in <a href="#i_063">Fig. 71</a>.</p>
+
+<div class="blockquot">
+
+<p id="exp-39"><span class="smcap">Experiment 39. How does absorption take
+place in the cell?</span>—(<i>a</i>) Put some salt water in
+a wineglass, partly fill the tube of the artificial cell
+with fresh water, and mark on the outside of both
+vessels the height at which the contained liquid stands. Set the tube
+in the glass of salt water and wait for results, having first tested carefully
+to make sure that there are no leaks in the membrane. After half
+an hour, notice whether there is any increase of water in the glass, as
+indicated by the mark. If so, where did it come from? Is there any loss<span class="pagenum" id="Page_54">[Pg 54]</span>
+of water in the tube? What has become of it? How did it get out?
+Taste it to see if any of the salt water has got in. Which is the heavier,
+salt water, or fresh? (If you do not know, weigh an equal quantity of
+each.) In which direction did the principal flow take place; from the
+heavier to the lighter, or from the lighter to the heavier liquid?</p>
+
+<p>(<i>b</i>) Put a sugar or salt solution in the tube, and clear, fresh water in
+the glass, marking the height in each as before. Does the liquid rise or
+fall in the tube? Does any of it escape into the water of the glass, and if
+so, is it more or less than before? Which now contains the denser fluid,
+the tube or the glass? What principle governs the course of the liquid?
+Try the same experiment with (<i>c</i>), the same liquid in both vessels, and
+notice whether there is a greater flow in one direction than the other, as
+indicated by a comparison with the marks on the outside. (<i>d</i>) Put in
+the tube some of the white of a raw egg, insert in a glass of pure water, and
+note the effect. (<i>e</i>) Reverse, with water in the tube and white of egg
+in the glass. Does the water rise in the tube as before? Test the contents
+for proteins; has any of the albumin passed through the membrane into
+the tube?</p>
+
+<p id="exp-40"><span class="smcap">Experiment 40. To test the behavior of living and dead cells.</span>—Slice
+a fresh piece of red beet into a vessel of water and of a boiled one into
+another vessel of the same liquid at the same temperature. What difference
+do you notice? Can you think of any reason why the boiled one gives
+up its juices and the other one does not?</p>
+</div>
+
+<p id="p-56"><b>56. Osmosis.</b>—The passage of liquids or of solids in solution
+through membranes is known as <em>osmosis</em>. Our experiments
+have shown that the principles governing the osmotic
+movement are: (1) the passage of water from the thinner
+liquid toward the denser takes place more rapidly than in
+the opposite direction; (2) the rapidity of the transfer depends
+on the difference in density; (3) crystallizable substances
+in solution, like sugar and salt, osmose readily;
+(4) albuminous or gelatinous substances, such as the white
+of an egg, osmose so slowly that the cell wall may be regarded
+as practically impermeable to them.</p>
+
+<p id="p-57"><b>57. Osmosis a form of diffusion.</b>—Osmosis is related to
+diffusion as a part to the whole. In other words, it is a name
+given to the process when it takes place through a membrane,
+whether solid, as the outer wall of the cell, or semi-fluid,
+as the inner wall of living protoplasm. Diffusion may<span class="pagenum" id="Page_55">[Pg 55]</span>
+therefore take place without osmosis, that is, in the absence
+of a membrane, as, for example, when we sweeten our tea or
+coffee by allowing sugar to diffuse through it. Many membranes
+offer little resistance to the osmotic movement of
+crystallizable substances. Such membranes are said to be
+<em>permeable</em>. Membranes which are not permeable to the dissolved
+solids, are called <em>semi-permeable</em>, since they allow the
+diffusion of water but not of the substances in solution.
+Living protoplasm is of this class. It is only very slightly
+permeable to many substances toward which, when dead, it
+acts as a permeable membrane.</p>
+
+<p id="p-58"><b>58. Absorption in living and dead cells.</b>—There is one
+great difference between the action of the artificial cell used
+in the foregoing experiments and that of the cells of which
+a living body is built up. The living cell always has at least
+two membranes. One of these, the cell wall, is readily permeable,
+while the other, the protoplasm, is semi-permeable—that
+is, substances in solution usually diffuse more or less
+slowly, while water diffuses rapidly. Hence in the living cell
+the protoplasm exercises a power of absorption independent
+of the cell wall, sometimes rejecting substances admitted by
+the latter, sometimes retaining others to which it is permeable,
+as shown in <a href="#exp-40">Exp. 40</a>. In the boiled beet the protoplasm
+had been killed and the red coloring matter passed through
+it unhindered, while in the living one it was held back
+by the protoplasmic lining, which is thus seen to control the
+absorptive properties of the cell.</p>
+
+<p id="p-59"><b>59. Plasmolysis.</b>—Cells can be killed or injured in other
+ways than by heat; for example, by cold, by poisons, by
+starvation, and by overfeeding through the use of too much
+fertilizer or too rich a one. In this last case, the soil water
+becomes impregnated with soluble matter from the manure,
+which may render it denser than the sap in the roots. When
+this happens, it will cause the osmotic flow to set outward
+and thus deplete the cell of its water; whence we have
+the paradox that a cell, or even a whole plant, may be starved<span class="pagenum" id="Page_56">[Pg 56]</span>
+by overfeeding. This action of osmosis in withdrawing
+the contents from a cell is termed <em>plasmolysis</em>, and you can
+easily understand how very important a knowledge of the
+principles governing it is to the farmer in determining the
+application of fertilizers to his crops.</p>
+
+<p>Dead cells, although powerless to carry on the life processes
+of a plant, have nevertheless important uses in serving the
+purposes of mechanical support and also to some extent in
+assisting in the work of absorption, though their function
+here is a purely mechanical one.</p>
+
+<figure class="figright illowp60" id="i_066" style="max-width: 51.0625em;">
+  <img class="w100" src="images/i_066.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 72.</span>—Root of a tree enveloping a rock.
+The large sycamore, whose base is partly concealed
+by the trumpet creeper on the left of the picture,
+is growing in very hard, stony soil, and one of
+its main roots has molded itself so completely to the
+ledge of rock protruding on the right, that when a
+portion of it was torn away, as shown where the light
+streak ends at <i>a</i>, the impress of its fibers was so
+strongly marked on the rock as to give the latter the
+appearance of a petrified root.</p></figcaption>
+</figure>
+
+<p id="p-60"><b>60. Selective absorption.</b>—Different plants through
+their roots absorb different substances from the soil water, or
+the same substance
+in varying degrees.
+Hence, one kind of
+crop will exhaust
+the soil of certain
+minerals while leaving
+other kinds intact,
+or very little
+diminished; and <i>vice
+versa</i>, another kind
+will take up abundantly
+what its predecessor
+has rejected.
+In this sense, plants
+are said to exercise a
+selective power in
+the absorption of nutrients.
+The expression
+must not be understood, however, as implying any kind
+of volitional discrimination. It is merely a short and convenient
+way of saying that the cells of different plants possess
+different degrees of permeability to certain substances, some
+being more permeable to one thing, some to another. But
+beyond this rejection of untransmissible substances there is no<span class="pagenum" id="Page_57">[Pg 57]</span>
+active power of discrimination, any substance that can pass
+through the cell wall and its protoplasmic lining being taken
+in, whether useful, unnecessary, or even harmful. These may,
+however, be got rid of by excretion, as the superfluous water
+taken in with dissolved minerals is exhaled from the leaves;
+or if incapable of passing out by osmosis, rendered harmless
+and retained in the
+form of the curious
+“crystalloids” found
+in various parts of
+plants. But while
+the kind of selection
+exercised by vegetable
+cells implies no
+power of choice, as a
+matter of fact those
+substances most
+used by the plant in
+carrying on its life
+processes are absorbed
+in much
+greater quantities
+than others, being
+transferred to parts
+where growth or
+other changes in the
+plant tissues are going
+on, and there
+used up in the work of nutrition, or excreted in part as waste
+products. In either case their passage from cell to cell will
+give rise to a continuous osmotic current in that direction,
+and the absorption of new matter will go on in proportion to
+the amounts used up.</p>
+
+<figure class="figcenter illowp50" id="i_067" style="max-width: 38.75em;">
+  <img class="w100" src="images/i_067.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 73.</span>—Roots of elm and sycamore contending for
+possession of the soil on a rocky bluff on the Potomac.</p></figcaption>
+</figure>
+
+<p id="p-61"><b>61. Definition.</b>—Tissue is a word used to denote any
+animal or vegetable substance having a uniform structure
+organized to perform a particular office or function. Thus,<span class="pagenum" id="Page_58">[Pg 58]</span>
+for instance, we have bony tissue and muscular tissue in
+animals; that is, tissue made of bone substance and muscle
+substance and doing the work of bone and muscle respectively.
+Likewise in plants, we have strengthening tissue
+made up of hard, thick-walled cells, serving mainly for purposes
+of mechanical support, and vascular tissue, made up of
+conducting vessels for conveying sap—and so on, for every
+separate function.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Why do raspberries and strawberries have a flabby, wilted look if
+sugar has been put on them too long before they are served? (<a href="#p-7">7</a>, <a href="#p-56">56</a>.)</p>
+
+<p>2. Where has the juice gone? What caused it to go out of the berries?
+(<a href="#p-56">56</a>, <a href="#p-59">59</a>.)</p>
+
+<p>3. Is a knowledge of the principles governing osmosis of any practical
+use to the housekeeper?</p>
+
+<p>4. Why cannot roots absorb water as freely in winter as in summer?
+(Suggestion: which is the heavier, cold or warm water?)</p>
+
+<p>5. Why does fertilizing too heavily sometimes injure a crop? (<a href="#p-59">59</a>.)</p>
+
+<p>6. Do you see any apparent contradiction between the action of plasmolysis
+and the selective power of protoplasm? Can you reconcile it?</p>
+
+<p>7. If a piece of beet that has been frozen is placed in water it will behave
+just as the slice of boiled beet did in <a href="#exp-40">Exp. 40</a>; explain. (<a href="#p-58">58</a>, <a href="#p-59">59</a>.)</p>
+</div>
+
+
+<h3 id="CH_III_II">II. MINERAL NUTRIMENTS ABSORBED BY PLANTS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A dozen or two each of different kinds of seeds and grains.
+A small portion from a growing shoot of a woody and a herbaceous land
+plant, and of some kind of succulent water or marsh plant, such as arrow
+grass (<i>Sagittaria</i>), water plantain, etc.</p>
+
+<p><span class="smcap">Appliances.</span>—A pair of scales; a lamp, stove, or other means of burning
+away the perishable parts of the specimens to be studied.</p>
+
+<p id="exp-41"><span class="smcap">Experiment 41.—Do the tissues of plants contain mineral
+matter?</span>—Take about a dozen each of grains and seeds of different kinds,
+weigh each kind separately, and then dry them at a high temperature, but
+not high enough to scorch or burn them. After they have become perfectly
+dry, weigh them again. What proportion of the different seeds was water,
+as indicated by their loss of weight in drying?</p>
+
+<p>Burn all the solid part that remains, and then weigh the ash. What
+proportion of each kind of seed was of incombustible material? What
+proportion of the solid material was destroyed by combustion?</p>
+
+<p><span class="pagenum" id="Page_59">[Pg 59]</span></p>
+
+<p id="exp-42"><span class="smcap">Experiment 42.—Do they contain different kinds and quantities
+of minerals?</span>—Test in the same way the fresh, active parts of any
+kind of ordinary land plant (sunflower, hollyhock, pea vines, etc.), and
+of some kind of succulent water or marsh plant (Sagittaria, water lily,
+fern). Do you notice any difference in the amount of water given off and
+of solid matter left behind? In the character of the ashes left? Have
+you observed in general any difference between the ashes of different
+woods; as, for instance, hickory, pine, oak? Compare with the residue
+left in <a href="#exp-21">Exp. 21</a>; would you judge that the residual substances are of the
+same composition?</p>
+</div>
+
+<figure class="figright illowp30" id="i_069" style="max-width: 19.75em;">
+  <img class="w100" src="images/i_069.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 74.</span>—Water cultures
+of buckwheat, showing
+effect of the lack of the
+different food elements:
+1, with all the elements;
+2, without potassium; 3,
+with soda instead of potash;
+4, without calcium;
+5, without nitrates or ammonia
+salts.</p></figcaption>
+</figure>
+
+<p id="p-62"><b>62. Essential constituents.</b>—The composition of the
+ash of any particular plant will depend upon two things:
+the absorbent capacity of the plant itself
+and the nature of the substances contained
+in the soil in which it grows. But
+chemical analysis has shown that however
+the ashes may vary, they always
+contain some proportion of the following
+substances: potassium (potash),
+calcium (lime), magnesium, phosphorus,
+and (in green plants) iron. These elements
+occur in all plants, and if any one
+of them is absent, growth becomes abnormal
+if not impossible.</p>
+
+<p>The part of the dried substances that
+was burned away after expelling the
+water consists, in all plants, mainly of
+carbon, hydrogen, oxygen, nitrogen, and
+sulphur, in varying proportions. These
+five rank first in importance among the
+essential elements of vegetable life, and
+without them the plant cell itself, the physiological unit of
+vegetable structure, could not exist. They compose the
+greater part of the substance of every plant, carbon alone
+usually forming about one half the dry weight. Other substances
+may be present in varying proportions, but the two
+groups named above are found in all plants without exception,<span class="pagenum" id="Page_60">[Pg 60]</span>
+and so we may conclude that (with the possible addition
+of chlorine) they form the indispensable elements of plant
+food. Carbon, hydrogen, oxygen, nitrogen, sulphur, and
+phosphorus compose the structure of which the plant is built.
+The other four ingredients do not enter into the substance as
+component parts, but aid in the chemical processes by which
+the life functions of the plant are carried on, and are none
+the less essential elements of its food. <a href="#i_069">Figure 74</a> shows the
+difference between a plant grown in a solution where all
+the food elements are present, and others in which some of
+them are lacking.</p>
+
+<figure class="figright illowp40" id="i_070" style="max-width: 39.0625em;">
+  <img class="w100" src="images/i_070.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 75.</span>—Roots of soy bean bearing
+tubercle-forming bacteria.</p></figcaption>
+</figure>
+
+<p id="p-63"><b>63. How plants obtain their food material.</b>—Plants
+obtain their supply of the various mineral salts from solutions
+in the soil water which
+they absorb through their
+roots. With a few doubtful
+exceptions, they cannot assimilate
+their food unless it
+is in a liquid or gaseous form.
+Of the gases, carbon dioxide,
+oxygen, and hydrogen can
+be freely absorbed from the
+air, or from water with various
+substances in solution,
+but most plants are so constituted
+that they cannot absorb free nitrogen from the air;
+they can take it only in the form of compounds from nitrates
+dissolved in the soil, and hence the importance of ammonia
+and other nitrogenous compounds in artificial fertilizers.
+Some of the pea family, however, bear on their roots little
+tubers formed by minute organisms called bacteria, which
+have the power of extracting nitrogen directly from the
+free air mingled with the soil; and hence the soil in which
+these tuber-bearing legumes decay is enriched with nitrogen
+in a form ready for use.</p>
+
+<p><span class="pagenum" id="Page_61">[Pg 61]</span></p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Could any normal plant grow in a soil from which nitrogen was lacking?
+Potash? Lime? Phosphorus? (<a href="#p-62">62</a>.)</p>
+
+<p>2. Could it live in an atmosphere devoid of oxygen? Nitrogen? Carbon
+dioxide? (<a href="#p-62">62</a>.)</p>
+
+<p>3. Why are cow peas or other legumes planted on worn-out soil to renew
+it? (<a href="#p-63">63</a>.)</p>
+
+<p>4. Is the same kind of fertilizer equally good for all kinds of soil? For
+all kinds of plants? (<a href="#p-60">60</a>, <a href="#p-62">62</a>.)</p>
+
+<p>5. Why does too much watering interfere with the nourishment of
+plants? (<a href="#exp-26">Exps. 26</a>, <a href="#exp-27">27</a>.)</p>
+
+<p>6. Are ashes fit for fertilizers after being leached for lye? (<a href="#p-62">62</a>.)</p>
+
+<p>7. Why will plants die, or make very slow growth, in pots, unless the
+soil is renewed occasionally? (<a href="#p-60">60</a>, <a href="#p-62">62</a>.)</p>
+</div>
+
+
+<h3 id="CH_III_III">III. STRUCTURE OF THE ROOT</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Taproot of a young woody plant not over one or two
+years old; apple and cherry shoots make good specimens. For showing
+root hairs, seedlings of radish, turnip, or oat are good, also roots of wandering
+Jew grown in water; for the rootcap, corn, sunflower, squash.</p>
+</div>
+
+<figure class="figright illowp40" id="i_071" style="max-width: 33.5em;">
+  <img class="w100" src="images/i_071.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 76.</span>—Cross section of a young
+taproot; <i>a</i>, <i>a</i>, root hairs; <i>b</i>, epidermis;
+<i>c</i>, cortical layer; <i>d</i>, fibrovascular
+cylinder. Note the absence of medullary
+rays during the first year of
+growth.</p></figcaption>
+</figure>
+
+<p id="p-64"><b>64. Gross anatomy of the root.</b>—Cut a cross section of
+any woody taproot, about halfway between the tip and the
+ground level, examine it with a lens, and sketch. Label
+the dark outer covering, <em>epidermis</em>, the soft layer just within
+that, <em>cortex</em>, the hard, woody axis
+that you find in the center, <em>vascular
+cylinder</em>, and the fine silvery
+lines that radiate from the
+center to the cortex, <em>medullary
+rays</em> (in a very young root these
+will not appear). Cut a section
+through a root that has stood in
+coloring fluid for about three
+hours and note the parts colored
+by the fluid. What portion of
+the root, would you judge from
+this, acts as a conductor of the
+water absorbed from the ground?</p>
+
+<p><span class="pagenum" id="Page_62">[Pg 62]</span></p>
+
+<p>Make a longitudinal section passing through the central
+portion of the root and extending an inch or two into the
+lower part of the stem. Do you find any sharp line of division
+between them? Notice the hard, woody axis that runs
+through the center. This is the vascular cylinder and contains
+the conducting vessels, the cut ends of which were
+shown in cross section in <a href="#i_071">Fig. 76</a>.</p>
+
+<figure class="figright illowp20" id="i_072" style="max-width: 25em;">
+  <img class="w100" src="images/i_072.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 77.</span>—Verti-section
+of branching
+root, showing the
+branches, <i>n</i>, <i>n</i>, originating
+in the central
+axis, <i>f</i>, and passing
+through the cortex,
+<i>r</i>, <i>r</i>.</p></figcaption>
+</figure>
+
+<p id="p-65"><b>65. Distinctions between root and stem.</b>—Pull off a
+branch from the stem and one from the root; which comes
+off the more easily? Examine the points of
+attachment of the two and see why this is so.
+This mode of branching from the central
+axis instead of from the external layers, as
+in the stem, is one marked distinction between
+the structure of the two organs. In
+stems, moreover, branches occur normally
+above the points of leaf insertion at the
+nodes <a href="#p-46">(46)</a>, while in the root they tend to
+arrange themselves in straight vertical rows.
+The shoots and cions that often originate
+from them are not normal root branches,
+but outgrowths from irregular or <em>adventitious</em> buds, that
+may occur on any part of a plant. The root is not divided
+into nodes like the stem,
+and never bears leaves.</p>
+
+<figure class="figright illowp40" id="i_072a" style="max-width: 38.6875em;">
+  <img class="w100" src="images/i_072a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 78.</span>—Root of a tree on the side of
+a gulley, acting as stem.</p></figcaption>
+</figure>
+
+
+<p id="p-66"><b>66. The active part of
+the root.</b>—It is only the
+newest and most delicate
+parts of the root that produce
+hairs and are engaged
+in the active work of absorption,
+the older parts acting
+mainly as carriers. Hence,
+old roots lose much of their
+characteristic structure and
+take on more and more of<span class="pagenum" id="Page_63">[Pg 63]</span>
+the office of the stem, until there is practically no difference
+between them. On the sides of gullies, where the earth
+has been washed from around the trees, we often see the
+upper portion of the root covered with a thick bark and fulfilling
+every office of a true stem.</p>
+
+<p id="p-67"><b>67. Minute structure of the root.</b>—(<i>a</i>) Mount in water
+and place under the microscope a portion of the root of an
+oat or radish seedling containing a number of hairs. In
+studying the thin, transparent roots of very young seedlings
+a section will not be necessary. Observe whether the hairs
+originate from the epidermis or
+from the interior. Are they true
+roots, or mere outgrowths from
+the cells of the epidermis? Do
+they consist of a single cell or a
+number of cells each? Notice
+what very thin cell walls the
+hairs have; is there any advantage
+in this? The interior, transparent
+portion of the hair contains
+the sap, and the protoplasm
+forms a thin lining on the inner
+surface of the wall; why not
+the sap next the wall and the
+protoplasm in the interior? (<a href="#p-58">58</a>,
+<a href="#p-60">60</a>.)</p>
+
+<figure class="figright illowp30" id="i_073" style="max-width: 32.75em;">
+  <img class="w100" src="images/i_073.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 79.</span>—Longitudinal section
+through the tip of a young root, somewhat
+diagrammatic: <i>h</i>, <i>h</i>, root hairs;
+<i>ep</i>, epidermis; <i>a</i>, cortex; <i>b</i>, central
+cylinder; <i>e</i>, sheath of the cylinder
+(endodermis); <i>g</i>, growing point; <i>c</i>,
+root cap; <i>d</i>, dead and dying cells loosened
+from the extremity of the cap.</p></figcaption>
+</figure>
+
+<p>(<i>b</i>) Next examine a portion
+of the body of the root and try to make out the parts as
+shown in <a href="#i_073">Fig. 79</a>, and compare them with your observations
+in 64. The light line running through the middle is
+the <em>central cylinder</em>, up which the water passes, as was shown
+by the colored liquid in 64. Outside this is a darker portion
+(<i>a</i>, <a href="#i_073">Fig. 79</a>), corresponding to the cortex (<i>rr</i>, <a href="#i_072">Fig. 77</a>).
+Besides other uses, the cortex serves to prevent the loss
+of water as it passes up to the stem, and also, in fleshy
+roots like the carrot and turnip, for the storage of nourishment.<span class="pagenum" id="Page_64">[Pg 64]</span>
+Its innermost row of cells is thickened into the
+sheath, or <em>endodermis</em> (<i>e</i>), which serves as an additional
+protection to the conducting tissues. The extreme outer
+layer, from the cells of which the root hairs are developed,
+is, as already stated, the epidermis, and in the older and
+more exposed parts of perennial roots is displaced by the
+bark, which becomes indistinguishable from that of the
+stem. (66.)</p>
+
+<p>(<i>c</i>) Look at the tip of the root for a loose structure (<i>c</i>)
+fitting over it like a thimble. This is the rootcap. Do you
+see any loose cells that seem to have broken away from it?
+These are old cells that have been pushed to the front by
+the formation of new growth back of them, and, being of no
+further use, are rubbed off by friction as the root bores its
+way through the soil. Draw a longitudinal section of the
+root as it appears under the microscope, labeling all the parts.
+If they cannot be made out distinctly in the specimen examined,
+use sections of young corn or bean roots, which are
+larger and show the parts more distinctly.</p>
+
+<figure class="figleft illowp30" id="i_074" style="max-width: 33.5em;">
+  <img class="w100" src="images/i_074.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 80.</span>—Cross section of a young root,
+magnified: <i>h</i>, hairs; <i>a</i>, cortex; <i>b</i>, central
+cylinder; <i>e</i>, sheath or endodermis; <i>ep</i>, epidermis;
+<i>sp</i>, cut ends of the ducts.</p></figcaption>
+</figure>
+
+<p>(<i>d</i>) Place under the microscope a thin cross section
+through the hairy portion of a primary root of a bean or pea
+seedling, and try to make
+out the parts noted above
+and shown in cross section in
+<a href="#i_074">Fig. 80</a>. Make a sketch of
+what you see, labeling all
+the parts you can recognize.
+Show in your drawing the
+differences in the size and
+shape of the cells composing
+the different tissues. Notice
+in the central cylinder
+(<a href="#i_074">Fig. 80</a>) several groups of
+what look in the section like
+little round pits, or holes, <i>sp</i>. These are the cut ends of
+large-sized tubes or <em>ducts</em> that convey the water absorbed<span class="pagenum" id="Page_65">[Pg 65]</span>
+by the roots to the stem. Each set of these tubes, together
+with a number of smaller ones belonging to the same group,
+constitutes a <em>fibrovascular bundle</em>—a very important element
+in the structure of all roots and stems, as these bundles
+make up the conducting system of the plant body.</p>
+
+
+<h3 id="CH_III_IV">IV. THE WORK OF ROOTS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Germinating seedlings of radish, bean, corn, etc.; a
+potted plant of calla, fuchsia, tropæolum, touch-me-not (<i>Impatiens</i>), or
+corn; a plant that has been growing for some time in a porous earthen
+jar.</p>
+
+<p><span class="smcap">Appliances.</span>—Glass tumblers; coloring fluid; wax; some coarse netting;
+dark wrapping paper, or a long cardboard box; a sheet of oiled
+paper; some half-inch glass tubing; a few inches of rubber tubing; an
+ounce of mercury; some blue litmus paper; a flower pot full of earth;
+a few handfuls of sand, clay, and vegetable mold; a pair of scales; a
+half dozen straight lamp chimneys, or long-necked bottles from which
+the bottoms have been removed as directed in <a href="#exp-53">Exp. 53</a>.</p>
+
+<p id="exp-43"><span class="smcap">Experiment 43. Use of the epidermis.</span>—Cut away the lower end
+of a taproot; seal the cut surface with wax so as to make it perfectly
+water-tight, and insert it in red ink for at least half the remaining length,
+taking care that there is no break in the epidermis. Cut an inch or two
+from the tip of the lower piece, or if material is abundant, from another
+root of the same kind, and without sealing the cut surface, insert it in red
+ink, beside the other. At the end of three or four hours, examine longitudinal
+sections of both pieces. Has the liquid been absorbed equally by
+both? If not, in which has it been absorbed the more freely? What conclusion
+would you draw from this, as to the passage of liquids through
+the epidermis?</p>
+
+<p>From this experiment we see that the epidermis, besides protecting the
+more delicate parts within from mechanical injury by hard substances
+contained in the soil, serves by its comparative imperviousness to prevent
+evaporation, or the escape of the sap by osmosis as it flows from the root
+hairs up to the stem and leaves.</p>
+
+<p id="exp-44"><span class="smcap">Experiment 44. To show that roots absorb moisture.</span>—Fill two
+pots with damp earth, put a healthy plant in one, and set them side by
+side in the shade. After a few days examine by digging into the soil with
+a fork and see in which pot it is drier. Where has the moisture gone?
+How did it get out?</p>
+
+<p><span class="pagenum" id="Page_66">[Pg 66]</span></p>
+
+<p id="exp-45"><span class="smcap">Experiment 45. To show that roots shun the light.</span>—Cover the
+top of a glass of water with thin netting, and lay on it sprouting mustard
+or other convenient seed. Allow the roots to pass through the netting into
+the water, noting the position of root and stem. Envelop the sides of
+the glass in heavy wrapping paper, admitting a little ray of light through
+a slit in one side, and after a few days again observe the relative position
+of the two organs. How is each affected by the light?</p>
+
+<p id="exp-46"><span class="smcap">Experiment 46. To find out whether roots need air.</span>—Remove
+a plant from a porous earthenware pot in which it has been growing for
+some time; the roots will be found spread out in contact with the walls
+of the pot instead of embedded in the soil at the center. Why is this?</p>
+
+<p id="exp-47"><span class="smcap">Experiment 47. To show that roots seek water.</span>—Stretch some
+coarse netting covered with moist batting over the top of an empty tumbler.
+Lay on it some seedlings, as in <a href="#exp-45">Exp. 45</a>, allowing the roots to pass through the
+meshes of the netting. Keep the batting moist, but take care not to let
+any of the water run into the vessel. Observe the position of the roots
+at intervals, for twelve to twenty-four hours, then fill the glass with water
+to within 10 millimeters (a half inch, nearly) or less of the netting, let
+the batting dry, and after eight or ten hours again observe the position
+of the roots. What would you infer from this experiment as to the affinity
+of roots for water?</p>
+
+<p id="exp-48"><span class="smcap">Experiment 48. What becomes of the water absorbed by roots.</span>—Cover
+a calla lily, young cornstalk, sunflower, tropæolum, or other
+succulent herb with a cap of oiled paper to prevent evaporation from the
+leaves, set the pot containing it in a pan of tepid water, and keep the temperature
+unchanged. After a few hours look for water drops on the leaves.
+Where did this water come from? How did it get up into the leaves?</p>
+
+<p id="exp-49"><span class="smcap">Experiment 49. To show the force of root pressure.</span>—Cut off
+the stem of the plant 6 or 8 centimeters (3 or 4 inches) from the base.
+Slip over the part remaining in the soil a bit of rubber tubing of about
+the same diameter as the stem, and tie tightly just below the cut. Pour
+in a little water to keep the stem moist, and slip in above, a short piece
+of tightly fitting glass tubing. Watch the tube for several days and note
+the rise of water in it. The same phenomenon may be observed in the
+“bleeding” of rapidly growing, absorbent young shoots, such as grape,
+sunflower, gourd, tobacco, etc., if cut off near the ground in spring when
+the earth is warm and moist. By means of an arrangement like that shown
+in <a href="#i_077">Fig. 81</a>, the force of the pressure exerted can be measured by the displacement
+of the mercury. This flow cannot be due to the giving off of
+moisture by the leaves, since they have been removed. Their action,
+when present, by causing a deficiency of moisture in certain places may<span class="pagenum" id="Page_67">[Pg 67]</span>
+influence the direction and rapidity of the
+current, but does not furnish the motive
+power, which evidently comes, in part at
+least, from the roots, and is the expression
+of their absorbent activity.</p>
+
+<figure class="figright illowp30" id="i_077" style="max-width: 21em;">
+  <img class="w100" src="images/i_077.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 81.</span>—Arrangement for
+estimating the force of root pressure:
+<i>s</i>, stub of the cut stem; <i>g</i>,
+glass tubing joined by means of
+the rubber tubing, <i>t</i>, to the stem;
+<i>m</i>, mercury forced up the glass
+tube by water, <i>w</i>, pumped from
+the soil by the roots.</p></figcaption>
+</figure>
+
+<p id="exp-50"><span class="smcap">Experiment 50. To show that roots
+cause the occurrence of acids.</span>—Lay
+a piece of blue litmus paper on a board or
+on a piece of glass slightly tilted at one end
+to secure drainage. Cover the surface with
+an inch of moist sand and plant in it a
+number of healthy seedlings. Acids have
+the property of changing blue litmus to
+red; hence, if you find any red stains on
+the paper where the roots have penetrated,
+what are you to conclude?</p>
+
+<p>Carbon dioxide has a slight acid reaction
+and is caused to form in varying
+quantities by all roots. Probably other
+substances, and these not a few, are actually
+excreted.</p>
+
+<p id="exp-51"><span class="smcap">Experiment 51. Can the absorbent
+power of roots be interfered with?</span>—Place
+the roots of a number of seedlings
+with well-developed hairs in a weak solution of saltpeter—10 grams (about
+⅓ of an ounce) to a pint of water, and others in a stronger solution—say
+30 grams, or 1 ounce, to a pint. Try the same experiment with weak
+and strong solutions of any conveniently obtainable liquid fertilizer.
+After 45 minutes or an hour examine the roots under a lens and note the
+change that has taken place. What has gone out of them? What caused
+the loss of the contained sap?</p>
+
+<p id="exp-52"><span class="smcap">Experiment 52. To test the weight of soils.</span>—Thoroughly dry
+and powder a pint each of sand and clay, measure accurately, and balance
+against each other in a pair of scales. Which weighs more, bulk for bulk,
+a “light” soil, or a “heavy” one? (77.)</p>
+
+<p id="exp-53"><span class="smcap">Experiment 53. To test the capacity of soils for absorbing and
+retaining moisture.</span>—Arrange, as shown in <a href="#i_078">Fig. 82</a>, a number of long-necked
+bottles from which the bottom has been removed. This can be
+done by making a small indentation with a file at the point desired and
+leading the break round the circumference with the end of a glowing wire
+or a red-hot poker. The crack will follow the heated object with sufficient<span class="pagenum" id="Page_68">[Pg 68]</span>
+regularity to answer the purpose. Tie a piece of thin cloth over the mouth
+of each bottle and invert with the necks extending an inch or two into
+empty tumblers placed beneath. Fill all to the same height with soils of
+different kinds—sand, clay, gravel, loam, vegetable mold, etc.—and pour
+over each the same quantity of water from above. Watch the rate at
+which the liquid filters through into the tumblers. Which loses its moisture
+soonest? Which retains it longest?</p>
+
+<figure class="figcenter illowp75" id="i_078" style="max-width: 50em;">
+  <img class="w100" src="images/i_078.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 82.</span>—Apparatus for testing the capacity of soils to take in and retain
+moisture.</p></figcaption>
+</figure>
+
+<p>Next leave the soils in the bottles dry, fill the tumblers up to the necks
+of the bottles, and watch the rate at which the water rises in the different
+ones. The power of soils to absorb moisture is called <em>capillarity</em>. Which
+of your samples shows the highest capillarity? Which the lowest? Do
+you observe any relation between the capillarity of a soil and its power of
+retention?</p>
+</div>
+
+
+<p id="p-68"><b>68. Roots as holdfasts.</b>—One use of ordinary roots is
+to serve as props and stays for anchoring plants to the soil.
+Tall herbs and shrubs, and vegetation generally that is
+exposed to much stress of weather, are apt to have large,
+strong roots. Even plants of the same species will develop
+systems of very different strength according as they grow
+in sheltered or exposed places.</p>
+
+<p><span class="pagenum" id="Page_69">[Pg 69]</span></p>
+
+<figure class="figright illowp60" id="i_079" style="max-width: 44.75em;">
+  <img class="w100" src="images/i_079.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 83.</span>—Dandelion: <i>a</i>, common form, grown in plains
+region at low altitude; <i>b</i>, alpine form.</p></figcaption>
+</figure>
+
+<p id="p-69"><b>69. Root pull.</b>—Roots are not mere passive holdfasts,
+but exert an active downward pull upon the stem. Notice
+the rooting end
+of a strawberry or
+raspberry shoot
+and observe how
+the stem appears
+to be drawn into
+the ground at the
+rooting point.
+In the leaf rosettes
+of herbs
+growing flat on
+the ground or in
+the crevices of walls and pavements, the strong depression
+observable at the center is due to root pull. (<a href="#i_079a">Fig. 84</a>.)</p>
+
+<p class='cb'></p>
+
+<figure class="figleft illowp30" id="i_079a" style="max-width: 30.25em;">
+  <img class="w100" src="images/i_079a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 84.</span>—Raspberry stolon
+showing root pull.</p></figcaption>
+</figure>
+
+<p id="p-70"><b>70. Storage of food.</b>—Another office
+of roots is to store up food for the
+use of the plant. This is done chiefly
+in the tissues of fleshy roots and tubers,
+and gives to them their great
+economic value. Next to grains and
+cereals, roots probably furnish a larger
+portion of food to the human race
+than any other crop. In addition to
+this they are also the source of valuable
+drugs, condiments, and dyes.</p>
+
+<p id="p-71"><b>71. Absorption and conveyance of
+sap.</b>—But the most important function
+of roots is that of absorption.
+By their action the soil water and the
+minerals contained in it are drawn up
+into the plant body and made available
+for conversion by the leaves into
+organic foods, as will be explained in another chapter. From
+the nature of their function, most roots have naturally a<span class="pagenum" id="Page_70">[Pg 70]</span>
+strong affinity for water, and its presence or absence has a
+marked influence on their direction of growth, being often
+sufficient to overcome that of geotropism (<a href="#exp-47">Exp. 47</a>). There
+are many trees and shrubs, notably willow, sweet bay, red
+birch, and the like, that grow best on the banks of streams
+and ponds, where their roots can have direct access to water.
+Excess of moisture, however, is injurious to most land plants
+by preventing the roots from getting sufficient air for respiration.</p>
+
+<p id="p-72"><b>72. The conditions of absorption.</b>—The sap in the root
+cells is normally denser than the water in the soil, so there is
+a continuous flow from the latter to the former. But if,
+for any reason, the density of the liquids should be reversed,
+the flow would set in the opposite direction, and if continued
+long enough, the strength of the plant would be literally
+“sapped” by the exhaustion of its tissues, so that it would
+die. What is this process of cell exhaustion called?</p>
+
+<p id="p-73"><b>73. The use of acid secretions to the root.</b>—It was
+shown in <a href="#exp-50">Exp. 50</a> that carbon dioxide and probably other substances
+occur in the immediate
+vicinity of roots.
+Carbon dioxide is an active
+agent in dissolving
+the various mineral matters
+contained in the soil,
+and as these last can be
+absorbed only in a liquid
+or a gaseous state <a href="#p-63">(63)</a>,
+the advantage to the
+root as an absorbent organ,
+of being able to secrete
+such active solvents,
+is obvious.</p>
+
+<figure class="figleft illowp40" id="i_080" style="max-width: 39.875em;">
+  <img class="w100" src="images/i_080.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 85.</span>—A natural root etching,
+found on a piece of slate.</p></figcaption>
+</figure>
+
+<p id="p-74"><b>74. Relation of roots
+to the soil.</b>—In order to
+perform their work of absorption,<span class="pagenum" id="Page_71">[Pg 71]</span>
+roots must have access to a suitable soil. To produce
+the best results a soil must contain (1) all the essential
+mineral constituents <a href="#p-62">(62)</a>; (2) moisture for dissolving these
+materials; and (3) air enough to supply the oxygen which is
+necessary to the life processes of all green plants.</p>
+
+<p id="p-75"><b>75. Composition of soils.</b>—Sand, clay, and humus, or
+vegetable mold, with the various substances dissolved in
+them, constitute the basis of cultivated soils. A mixture
+of sand, clay, and humus is called loam. When the proportion
+of humus is very large and well decomposed, the mixture
+is called <em>muck</em>. Pure sand contains but little nourishing
+matter and is too porous to retain water well. Pure clay
+is too compact to be easily permeable to either air or water.
+Most soils are composed of a mixture of the two with vegetable
+mold in varying proportions, giving a sandy loam, or
+a clay loam, as the case may be.</p>
+
+<p id="p-76"><b>76. Tillage.</b>—The advantages of tillage are: (<i>a</i>) that by
+breaking up the hard lumps it renders the soil more permeable
+to air and water and more easily penetrable by the
+roots in their search for food; (<i>b</i>) the covering of loose,
+friable earth left by the plow and the harrow acts as a mulch,
+and by shading the soil below, prevents too rapid a loss of
+water by evaporation. Where the essential food ingredients
+are present, good tillage counts for more in making a crop
+than the original quality of the soil.</p>
+
+<p id="p-77"><b>77. Light and heavy soils.</b>—These terms are used by
+farmers not in relation to the weight of soils, but in reference
+to the ease or difficulty with which they are worked. Light
+soils contain a preponderance of sand; heavy ones, of clay.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Will plants grow better in an earthen pot or a wooden box than
+in a vessel of glass or metal? Why? (<a href="#exp-46">Exp. 46</a>.)</p>
+
+<p>2. Which absorb more from the soil, plants with light roots and abundant
+foliage, or those with heavy roots and scant foliage? (Suggestion:
+roots absorb from the soil; leaves, mainly from the air.)</p>
+
+<p><span class="pagenum" id="Page_72">[Pg 72]</span></p>
+
+<p>3. Why are willows so generally selected for planting along the
+borders of streams in order to protect the banks from washing? (<a href="#p-71">71</a>.)</p>
+
+<p>4. Why are the conducting tissues of roots at the center instead of
+near the surface as in stems? (<a href="#p-67">67</a>, <i>b</i>.)</p>
+
+<p>5. Why does corn never grow well in swampy ground? (<a href="#p-74">74</a>; <a href="#exp-46">Exp. 46</a>.)</p>
+
+<p>6. Why are fleshy roots so much larger in cultivated plants than in
+wild ones of the same species? (<a href="#p-74">74</a>, <a href="#p-76">76</a>.)</p>
+
+<p>7. When the use of a particular kind of fertilizer causes the leaves
+of the plants to which it has been applied to turn brown, so that the
+farmer says they have been “burned” by it, to what cause is the trouble
+due? (<a href="#p-59">59</a>, <a href="#p-72">72</a>.)</p>
+
+<p>8. Why do farmers speak of turnips and other root crops as “heavy
+feeders”? (<a href="#p-70">70</a>, <a href="#p-71">71</a>.)</p>
+
+<p>9. Which is more exhausting to the soil, a crop of beets, or one of oats?
+Onions, or green peas? (See 2, suggestion.)</p>
+
+<p>10. Why will inserting the end of a wilted twig in warm water sometimes
+cause it to revive? (<a href="#exp-48">Exps. 48</a>, <a href="#exp-49">49</a>.)</p>
+</div>
+
+
+<h3 id="CH_III_V">V. DIFFERENT FORMS OF ROOTS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Examples of taproots: bean, pea, cotton, maple seedlings,
+or any kind of very young woody root. Fibrous: any kind of grass or
+grain. Fleshy: parsnip, turnip, carrot, dahlia, sweet potato. Water:
+duckweed, pondweed, or a cutting of wandering Jew grown in water.
+Parasitic: mistletoe, dodder, beech drops. Aërial and adventitious: the
+aërial roots of old scuppernong vines, climbing roots of ivy and trumpet
+vine, prop roots from the lower nodes of cornstalks and sugar cane.</p>
+</div>
+
+<p id="p-78"><b>78. Basis of distinction.</b>—Roots vary in form and external
+structure according to their origin, function, and
+surroundings. In reference to the first, they are classed
+as primary or secondary; in regard to the second, as dry or
+fleshy; while as to surroundings, they may be adapted to
+either the soil, water, air, or the parasitic habit. Soil roots
+are the normal form. According to their mode of growth
+they are either fibrous or axial.</p>
+
+<figure class="figcenter illowp51" id="i_083" style="max-width: 58.25em;">
+  <img class="w100" src="images/i_083.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 3.</span>—Aërial roots of a Mexican “strangling” fig, enveloping the trunk
+of a palm (<i>From</i> “Rep’t. Mo. Bot. Garden”).</p></figcaption>
+</figure>
+
+<p id="p-79"><b>79. Taproots.</b>—These are the common form of the axial
+type. Compare the root of any young hardwood cion a
+year or two old with one of a mature stalk of corn or
+other grain, and with the roots of seedlings of the same
+species. Notice the difference in their mode of growth. In
+the first kind a single stout prolongation called a taproot
+proceeds from the lower end of the hypocotyl and continues
+the axis of growth straight downward, unless turned aside
+by some external influence. A taproot may be either simple,
+as in the turnip, radish, and dandelion,
+or branched, as in most shrubs and
+trees. In the latter case the main axis
+is called the primary root, and the
+branches are secondary ones.</p>
+
+<p><a id="Page_73"></a><span class="pagenum" id="Page_74">[Pg 74]</span></p>
+
+<figure class="figleft illowp30" id="i_084" style="max-width: 22.5625em;">
+  <img class="w100" src="images/i_084.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 86.</span>—Branched taproot
+of maple.</p></figcaption>
+</figure>
+
+<p id="p-80"><b>80. Fibrous and fascicled roots.</b>—Where
+the main axis fails to develop,
+as in the corn and grasses generally,
+a number of independent branches take
+its place, forming what are known as
+fibrous roots. Both fibrous and taproots
+may be either hard or fleshy.
+The turnip and carrot are examples of
+fleshy taproots, the dahlia and rhubarb of fascicled roots.
+The function of both is the storage of nourishment. The
+sweet potato is an example of a tuberous root.</p>
+
+<p id="p-81"><b>81. Practical importance of this distinction.</b>—The difference
+between axial and fibrous roots has important bearings
+in agriculture. The first kind,
+which are characteristic of most dicotyls,
+strike deep and draw their nourishment
+from the lower strata of the
+soil, while the fibrous and fascicled, or
+radial kinds, as we may call them for
+want of a better name, spread out near
+the surface and are more dependent on
+external conditions.</p>
+
+<figure class="figright illowp30" id="i_084a" style="max-width: 21.1875em;">
+  <img class="w100" src="images/i_084a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 87.</span>—Fibrous root.</p></figcaption>
+</figure>
+
+<p id="p-82"><b>82. Roots that grow above ground.</b>—The kinds of
+roots that have just been considered are all subterranean,
+and bring the plant into relation with the earth, whether for
+the purpose of absorbing nourishment, or of mechanical support,
+or, as in the majority of cases, for both. Many plants,<span class="pagenum" id="Page_75">[Pg 75]</span>
+however, do not get their mineral nutrients directly from
+the soil, and these give rise to various forms suited to other
+conditions of alimentation.</p>
+
+<p id="p-83"><b>83. Adventitious roots.</b>—This name applies to any kinds
+of roots that occur on stems, or in other unusual positions.
+They may be considered as intermediate between the two
+classes named in 81; for while their starting point is above
+ground, they generally end by fixing themselves in the soil,
+where they often function as normal roots. Familiar examples
+are the roots that put out from the lower nodes of corn and
+sugar cane stalks, and serve both to supply additional moisture
+and to anchor the plant more firmly to the soil. Most
+plants will develop adventitious roots if covered with earth,
+or even if merely kept in contact with the ground. The
+gardener takes advantage of this capacity when he propagates
+by cuttings and layers.</p>
+
+<p id="p-84"><b>84. Water roots.</b>—These are generally white and threadlike
+and more tender and succulent than ordinary soil roots,
+because they have less work to do. Floating and immersed
+plants, such as bladderwort and hornwort (<i>Ceratophyllum</i>)
+have no need of absorbent roots, since the greater part of
+their surface is in contact with water and can absorb directly
+what is needed.</p>
+
+<p>Land plants will often develop water roots and thrive
+for a time if the liquid holds in solution a sufficient quantity
+of air and mineral nutrients. Place a cutting of wandering
+Jew in a glass of clear water, and in from four to six days it
+will develop beautiful water roots in which both hairs and
+cap are clearly visible to the naked eye.</p>
+
+<p id="p-85"><b>85. Haustoria</b>, from a Latin word meaning to drain,
+or exhaust, is a name given to the roots of parasitic plants,
+or such as live by attaching themselves to some other living
+organism, from which they draw their nourishment ready
+made. Their roots are adapted to penetrating the substance
+of the <em>host</em>, as their victim is called, and absorbing
+the sap from it. Dodder and mistletoe are the best-known<span class="pagenum" id="Page_76">[Pg 76]</span>
+examples of plant parasites, though the latter is only partially
+parasitic, as it merely takes up the sap from the host and
+manufactures its own food
+by means of its green leaves.</p>
+
+<figure class="figright illowp30" id="i_086" style="max-width: 18.75em;">
+  <img class="w100" src="images/i_086.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 88.</span>—Beech root: <i>A</i>, grown in
+unsterilized wood humus: <i>p</i>, strands of
+fungal hyphæ, associated at <i>a</i>, with
+humus; <i>B</i>, grown in wood humus freed
+from fungus by sterilization—it is not
+provided with fungal hyphæ, and has
+root hairs, <i>h</i>. (<i>A</i> and <i>B</i> both several
+times magnified.)</p></figcaption>
+</figure>
+
+<p id="p-86"><b>86. Saprophytes.</b>—Akin
+to parasites are saprophytes,
+which live on dead and decaying
+vegetable matter. They
+are only partially parasitic
+and do not bear the haustoria
+of true parasites. Many of
+them, of which the Indian
+pipe (<i>Monotropa</i>) and coral
+root are familiar examples,
+obtain their nourishment in
+part, at least, by association with certain saprophytic fungi,
+which enmesh their roots in a growth of threadlike fibers
+that take the place of root hairs and absorb organic food
+from the rich humus in
+which these plants grow.
+Such growths are called
+<em>mycorrhiza</em>, meaning
+“fungal roots.” Similar
+associations are formed
+by some of the higher
+plants also. The rootlets
+of the common beech
+and of certain of the
+pine family, for instance,
+are often enveloped in
+a network of fungus fibers,
+and in this case root
+hairs are developed very
+poorly, or not at all. Besides greatly increasing the absorbent
+surface by their ramification through the soil, the mycorrhizal
+threads may possibly benefit the plant in other ways also, as,<span class="pagenum" id="Page_77">[Pg 77]</span>
+for instance, by bringing
+about chemical changes
+that might aid in the
+work of nutrition.</p>
+
+<figure class="figcenter illowp76" id="i_086a_2" style="max-width: 56.4375em;">
+  <img class="w100" src="images/i_086a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 89.</span>—An air plant (<i>Tillandsia</i>), growing
+on the underside of a bough.</p></figcaption>
+</figure>
+
+<figure class="figright illowp30" id="i_087" style="max-width: 25em;">
+  <img class="w100" src="images/i_087.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 90.</span>—A single strand of <i>Tillandsia
+usneoides</i>, a rootless epiphyte belonging to the
+pineapple family; better known as the “Spanish
+moss” that drapes the boughs of trees so
+conspicuously in the warm parts of America.
+Two-thirds natural size. (Photographed by C.
+F. O’Keefe.)</p></figcaption>
+</figure>
+
+<p id="p-87"><b>87. Epiphytes, or air
+plants.</b>—In the proper
+meaning of the word
+these are not parasitic,
+but use their host merely
+as a mechanical support
+to bring them into better
+light relations. The
+name, however, is loosely
+applied to all plants that
+find a lodgment on the
+trunks and branches of
+trees, whether parasites
+or true epiphytes that
+draw no nourishment
+from the host. Not infrequently
+the latter is
+killed by them through
+suffocation, overweighting,
+or the constriction
+of the stems by close
+clinging twiners.</p>
+
+<p id="p-88"><b>88. Aërial roots</b> are
+such as have no connection
+at all with the soil or
+with any host plant, except
+as they may lodge
+upon the trunks and
+branches of trees for a
+support. In other than
+purely epiphytic plants,
+which get all their nourishment<span class="pagenum" id="Page_78">[Pg 78]</span>
+from the air, they are generally subsidiary to soil
+roots, like the long dangling cords that hang from some
+species of old grapevines; or they subserve other purposes
+altogether than absorbing nourishment, as the climbing
+roots of the trumpet vine and poison ivy. A very remarkable
+development of aërial roots takes place in the “strangling
+fig” of Mexico and Florida, which begins life as a small
+epiphyte, from seeds dropped by birds on the boughs or
+trunks of trees. When it gets well started, the young plant
+sends down enormous aërial roots, which find their way to
+the ground, and in time so completely envelop the host that
+it is literally strangled to death (<a href="#i_083">Plate 3</a>, p. 73). When this
+support is removed, the sheathing roots take its place and
+become to all intents
+and purposes the stem
+of the fig tree, which
+now leads an independent
+life.</p>
+
+<figure class="figright illowp40" id="i_088" style="max-width: 39.6875em;">
+  <img class="w100" src="images/i_088.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 91.</span>—Root system of a tobacco plant.</p></figcaption>
+</figure>
+
+<p id="p-89"><b>89. The root system.</b>—The
+entire mass of
+roots belonging to a
+plant, with all its ramifications
+and subdivisions, composes a root
+system. The extent of root expansion is in general about
+equal to that of the crown, thus bringing the new and
+active parts under the drip of the boughs where the moisture
+is most abundant. Some plants have root systems out of
+all seeming proportion to their size. A catalpa seedling
+six months old showed, by actual measurement, 250 feet
+of root growth, and it is estimated that the roots of a thrifty
+cornstalk, if laid end to end, would extend a mile. In the
+development of the root system, a great deal depends upon
+external conditions. In a poor, dry soil, the roots have to
+travel farther in search of a livelihood, and so a larger system
+has to be developed than in a more favorable location.</p>
+
+<p><span class="pagenum" id="Page_79">[Pg 79]</span></p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Which is better to succeed a crop of turnips on the same land, hay
+or carrots? (<a href="#p-81">81</a>.)</p>
+
+<p>2. Write out what you think would be a good rotation for four or
+five successive crops based on the forms of the roots.</p>
+
+<p>3. Study the following rotations and give your opinion about them,
+on the same principle. Suggest any improvements that may occur to
+you, and give a reason for the change. Beets, barley, clover, wheat;
+cotton, oats, peas, corn; oats, melons, turnips; cotton, oats, corn and
+peas mixed, melons; cotton, hay, corn, peas.</p>
+
+<p>4. Give three good reasons in favor of a rotation over a single-crop
+system. (<a href="#p-24">24</a>, <a href="#p-60">60</a>, <a href="#p-62">62</a>, <a href="#p-81">81</a>.)</p>
+
+<p>5. Which will require deeper tillage, a bed of carrots or one of strawberries?
+(<a href="#p-81">81</a>.)</p>
+
+<p>6. Explain why some plants keep green and fresh when the surface
+of the soil is dry, while others wilt or die. (<a href="#p-81">81</a>, <a href="#p-89">89</a>.)</p>
+
+<p>7. Which will better withstand drought, a crop of alfalfa or one of
+Indian corn? Why? (<a href="#p-81">81</a>.)</p>
+
+<p>8. Which will interfere less with the trees if planted in an orchard,
+beets or onions? (<a href="#p-81">81</a>.)</p>
+
+<p>9. Ought a crop of hemp and tobacco to succeed each other on the
+same land? (<a href="#p-81">81</a>, <a href="#p-89">89</a>.)</p>
+
+<p>10. Why does a gardener manure a grass plot by scattering the fertilizer
+on the surface, while he digs around the roses and lilacs and deposits
+it under ground? (<a href="#p-81">81</a>.)</p>
+
+<p>11. Do the adventitious roots of such climbers as ivy and trumpet vine
+draw any nourishment from the objects to which they cling? (<a href="#p-83">83-88</a>.)</p>
+
+<p>12. How can you tell?</p>
+
+<p>13. Do partial dependents of this kind injure trees by climbing upon
+them; and if so, how? (<a href="#p-87">87</a>, <a href="#p-88">88</a>.)</p>
+
+<p>14. What is the use of the aërial roots of the scuppernong grape? (<a href="#p-88">88</a>.)</p>
+
+<p>15. Is the resurrection fern (<i>Polypodium incanum</i>), that grows on tree
+trunks in our Southern States, a parasite or an air plant? (<a href="#p-87">87</a>.)</p>
+
+<p>16. On what plants in your neighborhood does mistletoe grow most
+abundantly? Dodder?</p>
+
+<p>17. Is mistletoe injurious to the host? (<a href="#p-85">85</a>.)</p>
+
+<p>18. Name some plants that are propagated mainly, or solely, by roots
+and cuttings.</p>
+
+<p>19. Where do aërial roots get their nourishment? (<a href="#p-88">88</a>.)</p>
+
+<p>20. Would they be of any use to a plant in a very cold or dry climate?</p>
+
+<p>21. Where should manure be placed to benefit a tree or shrub with
+wide-spreading roots? (<a href="#p-66">66</a>, <a href="#p-89">89</a>.)</p>
+
+<p><span class="pagenum" id="Page_80">[Pg 80]</span></p>
+
+<p>22. Is it a wise practice to mulch a tree by raking up dead leaves and
+piling them around the base of the trunk, as is often done? Why, or why
+not? (<a href="#p-66">66</a>, <a href="#p-89">89</a>.)</p>
+</div>
+
+
+<h4 id="CH_III_FIELD">Field Work</h4>
+
+<div class="blockquot">
+
+<p>(1) Examine the underground parts of hardy winter herbs in your neighborhood,
+also of any weeds or grasses that are particularly troublesome,
+and see if there is anything about the structure of these parts to account
+for their persistence. Note the difference between roots of the same species
+in low, moist places and in dry ones; between those of the same kind of
+plants in different soils; in sheltered and in exposed situations. Study
+the direction and position of the roots of trees and shrubs with reference
+to any stream or body of water in the neighborhood. (The elm, fig,
+mulberry, and willow are good subjects for such observations.) Notice
+also whether there is any relation between the underground parts and the
+leaf systems of plants in reference to drainage and transpiration.</p>
+
+<p>(2) Observe the effect of root pull upon low herbs. Look along washes
+and gullies for roots doing the office of stems, and note any changes of
+structure consequent thereon. Study the relative length and strength
+of the root systems of different plants, with reference to their value as
+soil binders, or their hurtfulness in damaging the walls of cellars, wells,
+sewers, etc. Dig your trowel a few inches into the soil of any grove
+or copse you happen to visit, note the inextricable tangle of roots, and
+consider the fierce competition for living room in the vegetable world that
+it implies.</p>
+
+<p>(3) Tests might be made of the different soils in the neighborhood of
+the schoolhouse by planting seeds of various kinds and noting the rate of
+germination; first, without fertilizers, then by adding the different elements
+in succession to see what is lacking. The field for study suggested
+by this subject is almost inexhaustible.</p>
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_81">[Pg 81]</span></p>
+
+<h2 class="nobreak" id="CH_IV">CHAPTER IV. THE STEM</h2>
+</div>
+
+
+<h3 id="CH_IV_I">I. FORMS AND GROWTH OF STEMS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Vigorous young hop or beau seedlings grown in pots;
+a fresh dandelion stalk; a stem of pea, squash, cucumber, grape, or passion
+flower vine, with tendrils.</p>
+
+<p><span class="smcap">Appliances.</span>—A bowl of fresh water; rods of different sizes and
+smoothness for testing the hold of climbers.</p>
+
+<p id="exp-54"><span class="smcap">Experiment 54. To show the movements of twining stems.</span>—Raise
+a young hop or bean seedling in the schoolroom and allow it to grow
+about two decimeters—8 to 10 inches—in length before providing it
+with a support. Does the stem form any coils? Bring it in contact
+with a suitable upright support and watch for a day or two. What
+happens? Notice whether it starts to coil from right to left or from left
+to right and see if you can coax it to turn in the opposite direction. When
+it has reached the end of its stake, allow it to grow about five centimeters
+(two inches, approximately) beyond, and watch the revolution of the tip.
+Cut a hole through the center of a piece of cardboard about 14 centimeters
+(five to six inches) in diameter, slip it over the loose end of the stem,
+and fasten it to the stake in a horizontal position, with a pin. Note the
+position of the stem tip at regular intervals and mark on the cardboard;
+how long does it take to complete a revolution? Does it continue to coil,
+or to coil as readily, after leaving its stake as before? What would you
+infer from this as to the effect of contact in stimulating it to coil?</p>
+
+<p>Find out by experiment if it can climb well by means of a glass or other
+smooth rod; by a fine wire; a broomstick; a large, smooth post. See
+whether it does better on a horizontal or an upright support.</p>
+
+<p id="exp-55"><span class="smcap">Experiment 55. To illustrate the coiling of stems.</span>—Run a
+gathering thread in one side of a narrow strip of muslin and notice how
+the ruffle thus drawn will curl into a spiral when allowed to dangle from
+the needle. Can you think of any cause that might act on a stem in the
+same way? Suppose, for instance, that one side should grow faster than
+the other; what would be the effect? (54.)</p>
+
+<p>Split the stem of a fresh dandelion, or other herbaceous scape, longitudinally,
+and immerse it in a pan of fresh water for a few minutes. Notice
+how the two halves curve outward, or even coil up like the strip of muslin.
+This is due to the tension caused by the more rapid absorption of the<span class="pagenum" id="Page_82">[Pg 82]</span>
+thinner walled cells of the internal tissues. These, when relieved of the
+resistance of the thicker walled outer tissues, swell on their free side, but
+are held back on the other by the non-absorbent outer parts, as one side
+of the muslin ruffle was held by the gathering thread.</p>
+
+<p id="exp-56"><span class="smcap">Experiment 56. To find out whether the direction of stem
+growth is influenced by light.</span>—Place two rapidly growing young
+pea, bean, sunflower, or squash plants, each with several well-developed
+leaves, in a room or box with a light exposure on one side only. After two
+or three days, notice the position of the stems in regard to the light. Does
+either one show a more decided inclination toward it than the other?</p>
+
+<p id="exp-57"><span class="smcap">Experiment 57. Is the light relation of the stem influenced
+by the leaves?</span>—Cut the leaves from one of the plants used in <a href="#exp-56">Exp. 56</a>,
+covering the cut surfaces with vaseline to prevent “bleeding”; reverse
+the positions of both with regard to the light, and watch for two or three
+days. In which is the response to light the more rapid? What does this
+indicate as one object of the stem in seeking light? What is the best
+position of a stem, ordinarily, for getting its leaves into the light?</p>
+</div>
+
+<figure class="figright illowp40" id="i_092" style="max-width: 39.6875em;">
+  <img class="w100" src="images/i_092.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 92.</span>—Stems of red oak and hickory that
+have grafted themselves.</p></figcaption>
+</figure>
+
+<p id="p-90"><b>90. Classification.</b>—Stems are classed according to
+(1) duration, as annuals, biennials, and perennials; (2) with
+reference to hardness or
+softness of structure, as
+herbaceous and woody;
+(3) in regard to position
+and direction of growth,
+as erect, prostrate, climbing,
+inclined, declined,
+underground, etc.</p>
+
+<p id="p-91"><b>91. Annuals</b> complete
+their life cycle in a
+single season and then
+die down as soon as they
+have perfected their
+seed. Many of our most
+troublesome weeds belong
+to this class and
+might be exterminated by the simple expedient of mowing
+them down before their time of flowering.</p>
+
+<p><span class="pagenum" id="Page_83">[Pg 83]</span></p>
+
+<p id="p-92"><b>92. Biennials</b>, as the name implies, live for two years.
+Their energy during the first season is spent chiefly in laying
+by a store of nourishment,
+usually in the tissues of
+fleshy roots <a href="#p-70">(70)</a>. By this
+means they get a good start
+in the second season and
+mature their seeds early.
+Many of our common garden
+vegetables, such as turnips,
+carrots, parsnips, and
+cabbage, belong to this
+class. Where is the nourishment
+stored in the cabbage?</p>
+
+<figure class="figright illowp40" id="i_093" style="max-width: 39.25em;">
+  <img class="w100" src="images/i_093.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 93.</span>—A biennial plant, mullein, in
+winter condition with stem reduced to
+little more than a disk supporting a rosette
+of leaves. Notice how close they cling to
+the earth, and compare them with their
+fruiting condition a few months later as
+shown in <a href="#i_191a">Fig. 237</a>.</p></figcaption>
+</figure>
+
+<p id="p-93"><b>93. Perennials</b> are plants
+that live on indefinitely, like
+most of our forest trees
+and woody-stemmed shrubs.
+Woody stems are usually perennial and may live for hundreds
+and even thousands of years, as those of the giant
+sequoias of California, and the famous chestnut of Mt.
+Etna.</p>
+
+<p id="p-94"><b>94. Herbaceous stems</b> are more or less succulent and die
+down after fruiting. They are usually annuals, though some
+kinds, like the garden geraniums and the common St.-John’s-wort,
+show a tendency to become woody, especially at the
+base, and live on from year to year. Others, such as the
+hawkweed and dahlia, die down above ground in winter,
+but are enabled to keep their underground parts alive indefinitely,
+through the nourishment stored in them, and are
+thus perennial below ground and annual above. Woody-stemmed
+annuals, such as the cotton and castor oil plant,
+are not, properly speaking, herbs. In the tropical countries
+to which they belong they are perennial shrubs, or even
+small trees, but on being transplanted to colder regions<span class="pagenum" id="Page_84">[Pg 84]</span>
+have been compelled to take on the annual habit as an
+adaptation to climate.</p>
+
+<table class='autotable'>
+<tr><td class='vab'>
+<figure class="figcenter illowp90" id="fig94" style="max-width: 31.25em;">
+  <img class="w100" src="images/i_094_94.jpg" alt="">
+  <figcaption>
+    <p><span class="smcap">Fig. 94.</span>—Orange hawkweed with runners.</p>
+  </figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp90" id="fig95" style="max-width: 56.75em;">
+  <img class="w100" src="images/i_094_95.jpg" alt="">
+  <figcaption>
+    <p><span class="smcap">Fig. 95.</span>—Prostrate stem of Lycopodium with assurgent branches.</p>
+  </figcaption>
+</figure></td></tr></table>
+
+<figure class="figright illowp20" id="i_094" style="max-width: 25em;">
+  <img class="w100" src="images/i_094.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 96.</span>—Diagram
+of stem growth: <i>ps</i>,
+surface of the ground;
+<i>e</i>, erect position; <i>d</i>,
+declined; <i>a</i>, assurgent;
+<i>p</i>, prostrate; <i>u</i>, vertical
+direction underground.</p></figcaption>
+</figure>
+
+<p id="p-95"><b>95. Direction and habit of growth.</b>—As to manner of
+growth, there are many forms, from the upright boles of
+the beech and pine to the trailing, prostrate, and creeping
+stems of which we have examples in the
+running periwinkle, the prostrate spurge
+and the creeping partridge berry (<i>Mitchella
+repens</i>), respectively. Trailing and prostrate
+stems are very apt to become
+creepers by the development of adventitious
+roots at their nodes wherever they
+come in contact with the soil. The rooting
+stems of dewberries, the runners and
+stolons of strawberries and currants, are
+familiar examples.</p>
+
+<p>Between the extremes of prostrate and
+upright, stems may be inclined or bent in
+various degrees. As shown in <a href="#i_094">Fig. 96</a>,
+there are two modes of inclination: <em>assurgent</em>,
+<i>a</i>, from the prostrate, <i>p</i>, toward the
+upright, <i>e</i>; and <em>declined</em>, <i>d</i>, from the upright<span class="pagenum" id="Page_85">[Pg 85]</span>
+toward the prostrate. Below the surface, <i>ps</i>, occur only
+underground stems. Is the prostrate habit an advantageous
+one for light exposure? Can you think of any compensating
+advantages a plant might derive from it; for example,
+in regard to warmth and moisture?</p>
+
+<figure class="figright illowp40" id="i_095" style="max-width: 26em;">
+  <img class="w100" src="images/i_095.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 97.</span>—Twining stems:
+<i>A</i>, hop twining with the sun;
+<i>B</i>, convolvulus twining against
+the sun.</p></figcaption>
+</figure>
+
+<p id="p-96"><b>96. Climbing stems.</b>—These are such as lift themselves
+from the ground and attain the advantages of the upright
+position by clinging to supports of
+various kinds—usually, in a state
+of nature, the stems and boughs of
+other plants. The means of climbing
+may be: (1) by merely leaning
+upon or propping themselves up by
+the aid of the supporting object—examples,
+the rose, wistaria, star jessamine
+(<i>Jasminum officinalis</i>); (2) by
+coiling their main axes spirally
+around the support—hop, bean,
+morning-glory; (3) by means of adventitious
+roots—poison ivy, common
+English ivy, trumpet vine
+(<i>Tecoma radicans</i>); (4) by organs specially developed for
+the purpose, called tendrils—gourd, cucumber, grape, passion
+flower.</p>
+
+<figure class="figright illowp40" id="i_096" style="max-width: 29.375em;">
+  <img class="w100" src="images/i_096.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 98.</span>—Leaf of common pea,
+showing upper leaflets reduced to
+tendrils.</p></figcaption>
+</figure>
+
+<p id="p-97"><b>97. Tendrils.</b>—The part assigned to do the work of climbing
+may be a secondary branch, a flower stem, a leafstalk, a
+leaf, a leaflet, or a group of leaflets (<a href="#i_096">Fig. 98</a>). Tendrils behave
+in general very much like twining stems, except that they
+are more sensitive and respond more quickly to any cause
+that may influence their movement. While young, their
+tips revolve just as do the tips of twining stems, until they
+meet with an object round which they can coil. When this
+happens, not only the part in contact with the object coils,
+but the free part between it and the main axis will usually
+respond by twisting itself into a helix (<a href="#i_096a">Fig. 99</a>). As the
+distance between the base and tip of the tendril is shortened<span class="pagenum" id="Page_86">[Pg 86]</span>
+by coiling, the body of the plant
+is drawn upward proportionally.
+It will be observed that the helix
+is interrupted at one or more
+points, above and below which
+the coils turn in opposite directions.
+This is because the tendril
+is attached at both ends and
+cannot adjust itself to the opposite
+strains of torsion. Twist
+with your fingers a piece of tape
+so attached, and you will see
+that on one side of your hand it
+turns from right to left and on
+the other from left to right.</p>
+
+<p id="p-98"><b>98. The cause of twining.</b>—Botanists
+are not fully agreed
+on this point. The explanation
+most generally accepted at present is that the twining of
+stems is due to the combined action of lateral and negative
+geotropism <a href="#p-51">(51)</a>. The first
+causes one side to grow
+more rapidly than the other,
+thus forming a succession of coils, while the
+second, by stimulating the upward growth
+of the axis, stretches it into a spiral, and in
+this way draws it more tightly round the
+support. For this reason twining stems do
+best on an upright support.</p>
+
+<figure class="figcenter illowp77" id="i_096a" style="max-width: 54.0625em;">
+  <img class="w100" src="images/i_096a.jpg" alt="">
+  <figcaption><p class='center'><span class="smcap">Fig. 99.</span>—Stems
+of a passion flower transformed into
+tendrils. (<i>After</i>
+<span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p>In tendrils, the twining is thought to be
+due not to gravity, but to contact with a
+solid body, which, by inducing unequal development
+on opposite sides of the tendril,
+causes it to turn about an available object.
+The coiling of the free part of the twining
+organ is in response to the stimulus transmitted<span class="pagenum" id="Page_87">[Pg 87]</span>
+from the part in contact—<em>stimulus</em>, in this sense,
+denoting the influence of any external agent that calls forth
+a responsive adjustment on the part of the plant.</p>
+
+<figure class="figright illowp40" id="i_097" style="max-width: 38.75em;">
+  <img class="w100" src="images/i_097.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 100.</span>—Showing the economy of
+labor and building material effected by the
+climbing habit. Notice how the grapevine
+coils like an anaconda around the tree
+boles, and overtops their tallest branches.
+Compare the diameter of the vine with that
+of the trees.</p></figcaption>
+</figure>
+
+<p id="p-99"><b>99. The object of the
+various habits of stem
+growth.</b>—To bring the
+growing parts of the plant
+into the best possible relations
+with light and air is
+one of the special functions
+of the stem, and the
+various habits of growth
+described in this section
+have been developed with
+reference to this function.
+In the case of prostrate
+and underground stems
+other factors may intervene;
+can you name some of the
+causes that might influence
+the position of the stem in
+such cases?</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Why is the normal direction of most stems upright? (<a href="#exp-56">Exp. 56</a>.)</p>
+
+<p>2. Name a dozen woody-stemmed plants; a dozen with herbaceous
+stems.</p>
+
+<p>3. Name all the plants you can think of that have prostrate stems, or
+leaf rosettes that hug the earth, like mullein and dandelion. Which of
+these are wintergreen plants? Which are hot-weather growers?</p>
+
+<p>4. Can you explain in what ways both hot-weather and cold-weather
+plants may be advantaged by the habit of clinging close to the earth?
+(<a href="#p-94">94</a>, <a href="#p-95">95</a>.)</p>
+
+<p>5. Is there any difference in the height of the stem of a dandelion flower
+and a dandelion ball?</p>
+
+<p>6. Of what advantage is this to the plant? (<a href="#exp-17">Exp. 17</a>.)</p>
+
+<p>7. Name all the means you can think of by which a stem may climb,
+and give an example of each.</p>
+
+<p><span class="pagenum" id="Page_88">[Pg 88]</span></p>
+
+<p>8. Why do we support peas with brush, and hops or beans with poles?
+(<a href="#p-98">98</a>; <a href="#exp-54">Exp. 54</a>.)</p>
+
+<p>9. Are the vines of gourds, watermelons, squashes, and pumpkins
+normally climbing or prostrate? How can you tell? (<a href="#p-96">96</a>, <a href="#p-97">97</a>.)</p>
+
+<p>10. Why does not the gardener provide them with poles or trellises to
+climb on?</p>
+
+<p>11. Do twining plants grow equally well on horizontal and upright
+supports? (<a href="#p-98">98</a>; <a href="#exp-54">Exp. 54</a>.)</p>
+
+<p>12. If there is any difference, which do they seem to prefer?</p>
+
+<p>13. Can you give any reasons for thinking that the climbing habit
+might lead to parasitism? (<a href="#p-83">83</a>, <a href="#p-85">85</a>, <a href="#p-87">87</a>.)</p>
+
+<p>14. What method of climbing would be most favorable to the development
+of such a habit? (Suggestion: What mode of climbing brings the
+stem into closest contact with its support?)</p>
+
+<p>15. Name some plants the stems of which are used as food.</p>
+
+<p>16. Name some from which gums and medicines are obtained.</p>
+
+<p>17. Explain how it can benefit a plant to have its leaves, or some of
+them, modified into tendrils. (<a href="#p-99">99</a>.)</p>
+
+<p>18. In what way is the loss of the normal function of the leaves so modified,
+compensated for? (<a href="#exp-57">Exp. 57</a>.)</p>
+
+<p>19. Suppose the vine shown in <a href="#i_097">Fig. 100</a> had to lift itself without the aid
+of a support; could it reach the same height and carry the same weight
+of foliage and flowers with the same expenditure of labor and building
+material?</p>
+</div>
+
+
+<h3 id="CH_IV_II">II. MODIFICATIONS OF THE STEM</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A shoot of asparagus; thorny branches of locust, plum,
+or haw; a cactus plant; bulbs of lily and hyacinth or onion; tubers of
+potato; rootstocks of iris, fern, or violet. If fresh specimens are not accessible,
+dried rootstocks of the sweet flag and Florentine iris may be obtained
+at the drug stores under the names of calamus and “orris” root.</p>
+</div>
+
+<p id="p-100"><b>100. How to recognize modified parts.</b>—Stems, like
+roots, are often modified to serve other than their normal
+purpose, and in adapting themselves to these new functions
+they sometimes undergo such changes of form and structure
+that it would be impossible to recognize their true nature
+from appearances alone. The safest tests in such cases
+are: (1) by a comparison of the parts of the modified structure
+with those of known organs of the same kind; and (2) by
+observing its position in reference to other parts. For<span class="pagenum" id="Page_89">[Pg 89]</span>
+instance, we know that the stem is the part of the plant which
+normally bears leaves and flowers, and if either of these,
+or if the small scales which often take the place of leaves,
+are found growing on any plant structure, we may usually
+take for granted that it is a stem. Then, again, as will be
+shown in the next chapter, buds and branches naturally
+appear only at the nodes, in or near the <i>axil</i>, or inner angle
+made by a leaf with the stem. Hence, if you see any growth
+springing from such a position, you may generally conclude
+it to be a stem.</p>
+
+<figure class="figright illowp30" id="i_099" style="max-width: 26.5em;">
+  <img class="w100" src="images/i_099.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 101.</span>—Stem-leaves
+(cladophylls) of a ruscus, bearing
+flowers.</p></figcaption>
+</figure>
+
+<p id="p-101"><b>101. Stems as foliage.</b>—The connection between stem
+and leaf is so intimate that we need not be surprised to find
+a frequent interchange of function
+between them, the leaf, or some part
+of it, doing the work of the stem
+(<a href="#i_096">Fig. 98</a>), the stem more often taking
+upon itself the office of the leaf. A
+common example is the garden asparagus.
+Examine one of the young
+shoots sold in the market, and notice
+that it bears a number of small scales
+in place of leaves. On an older
+shoot that has gone to seed, the
+green, threadlike appendages, which
+are usually taken for foliage, will be
+found to spring each from the axil
+of one of these scales. What, therefore, are we to conclude
+that it is?</p>
+
+<p>In the butcher’s-broom of Europe, the transformation has
+gone so far that the branches of the stem have assumed the
+flattened appearance of leaves (<a href="#i_099">Fig. 101</a>), but their real
+nature is evident both from their position in the axils of
+leaf scales, and from the fact that they bear flower clusters
+in the axil of a scale on their upper face. Another example
+of this sort of modification is seen in the pretty little <i>myrsiphyllum</i>
+of the greenhouses (wrongly called smilax), which<span class="pagenum" id="Page_90">[Pg 90]</span>
+is so much used for decoration.
+The delicate green blades are
+merely altered stems, shortened
+and flattened to simulate leaves.</p>
+
+<figure class="figleft illowp30" id="i_100" style="max-width: 29.0625em;">
+  <img class="w100" src="images/i_100.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 102.</span>—Thorn branches of
+<i>Holocantha Emoryi</i>, a plant growing
+in arid regions.</p></figcaption>
+</figure>
+
+<p id="p-102"><b>102. Weapons of defense.</b>—Conspicuous
+examples of these
+are the bristling thorns of the
+honey locust. Is their frequent
+branching any indication of their
+real nature? Does it <em>prove</em> anything,
+or must you look for other
+evidence? What further indications
+might you expect to
+find, if they are true branching
+stems? <a href="#p-100">(100.)</a> On old haw,
+plum, crab, and pear trees, stems can be found in all stages
+of transition, from stubby, ill-developed branches, to well-defined
+thorns.</p>
+
+<figure class="figright illowp25" id="i_100a" style="max-width: 14.3125em;">
+  <img class="w100" src="images/i_100a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 103.</span>—Melon
+cactus, showing
+greatly condensed
+stem for the storage
+and preservation of
+moisture.</p></figcaption>
+</figure>
+
+<p id="p-103"><b>103. Storage of nourishment.</b>—This is
+one of the most frequent causes of modification
+in both roots and stems. Of stems
+that grow above ground, the sugar cane
+probably comes first in economic importance
+on this account. In hot, arid regions, where
+the moisture drawn from the earth would,
+during prolonged drought, be too rapidly
+dissipated by an expanded surface of leaves,
+the whole plant, as in the case of the cactus,
+is sometimes compacted into a greatly thickened
+stem, which fills the triple office of leaf,
+stalk, and water reservoir.</p>
+
+<figure class="figright illowp25" id="i_101" style="max-width: 15.25em;">
+  <img class="w100" src="images/i_101.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 104.</span>—Rootstock
+of creeping
+panic grass.</p></figcaption>
+</figure>
+
+
+<p id="p-104"><b>104. The uses of underground stems.</b>—It
+is in these that the storage of nourishment
+most frequently takes place, and the modifications
+that stems undergo for this purpose
+are in some cases so great that their real<span class="pagenum" id="Page_91">[Pg 91]</span>
+nature becomes apparent only after a careful examination.
+But while the chief function of underground stems is the
+storage of nourishment, they serve other purposes also. In
+plants requiring a great deal of moisture,
+like the ferns, and in others growing in dry
+places and needing to husband moisture
+carefully, like the blackberry lily, underground
+stems may be useful in preventing
+the too rapid evaporation that would take
+place through aërial stems. Defense against
+frost, cold, heat, and other dangers, as well
+as quickness of propagation, are also attained
+or assisted by this means.</p>
+
+<p id="p-105"><b>105. Rootstocks and rhizomes.</b>—From a
+prostrate stem like that shown in <a href="#fig95">Fig. 95</a> to a
+creeping rootstock like the one in <a href="#i_101">Fig. 104</a>, the
+transition is so easy that we find no difficulty
+in accounting for it. From the prostrate rootstock to the
+thickened storage rhizome (<a href="#i_101a">Fig. 105</a>) of such plants as the iris,
+puccoon, bulrush, and Solomon’s-seal, is a longer step, but
+the bud with its leaf scales at the growing tip, <i>a</i>, the remains
+of the flower stem at the node, <i>b</i>, and the roots from the under
+surface sufficiently indicate its nature.
+The peculiar scars from which
+the Solomon’s-seal takes its name
+are caused by the falling away
+each year of the flowering stem
+of the season after its work is done,
+leaving behind the node of the underground
+stem from which it originated.
+In this way the rhizome lives on indefinitely,
+growing and increasing at one end as fast as it dies at
+the other. Test a little of the substance of the rhizome
+with iodine. Of what does it consist? Of what use is it
+to the plant?</p>
+
+<figure class="figcenter illowp100" id="i_101a" style="max-width: 15.0em;">
+  <img class="w100" src="images/i_101a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 105.</span>—Rhizome of Solomon’s-seal:
+<i>a</i>, growing bud at the tip; <i>b</i>, remains of the past
+season’s flower stem; <i>c</i>, <i>c</i>, <i>c</i>, scars
+of old stems. (<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<figure class="figright illowp30" id="i_102" style="max-width: 33.5em;">
+  <img class="w100" src="images/i_102.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 106.</span>—Potato tuber showing lenticels,
+<i>A</i>, <i>A</i>, or pores for air on the surface;
+<i>S</i>, leaf scale, or scar.</p></figcaption>
+</figure>
+
+<p id="p-106"><b>106. The tuber.</b>—A still further thickening and shortening<span class="pagenum" id="Page_92">[Pg 92]</span>
+of the rhizome gives rise to the tuber, of which the
+potato and the Jerusalem artichoke are familiar examples.
+Can you give any evidence to show that the potato is a
+modified stem? Find the
+point of attachment of the
+tuber to its stem and stand
+it on this end, which is its
+natural base. Notice that
+the eye sits in the axil of
+the little scale that forms
+the eyelid. What does the
+scale represent? What is
+the eye? <a href="#p-100">(100.)</a> Do the
+scales occur in any regular
+order—that is, opposite, or alternating with, each other, like
+the leaves on a stem? Look on the surface for a number of
+small, lens-shaped dots (<i>A</i>, <i>A</i>, <a href="#i_102">Fig. 106</a>) scattered irregularly
+over it. These are aërating pores called <i>lenticels</i>, and are
+found in most dicotyl
+stems. Does their
+presence help to throw
+light on the real nature
+of the tuber? If any
+sprouts occur on your
+specimen, where do
+they originate? Where
+do buds and sprouts
+originate on plants
+above ground? Make
+a sketch of the outside
+of a potato, showing
+the lenticels, eyes, and
+scales, or the scars left
+by the scales in case they have fallen away, as has probably
+happened, if your specimen is an old one.</p>
+
+<figure class="figright illowp40" id="i_102x" style="max-width: 30em;">
+  <img class="w100" src="images/i_102x.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 107, 108.</span>—Transverse
+and longitudinal
+sections of the
+potato: <i>A</i>, skin; <i>B</i>,
+cortical layer; <i>C</i>, outer
+pith layer; <i>D</i>, inner pith
+layer.</p></figcaption>
+</figure>
+
+<p>Cut a small slice from the stem end of two potatoes, stand<span class="pagenum" id="Page_93">[Pg 93]</span>
+them in coloring fluid for four or five hours, then divide into
+cross and vertical sections, as shown in <a href="#i_102x">Figs. 107, 108</a>, and
+draw, labeling the parts that you can make out. Through
+which has the liquid ascended most rapidly? Test with
+iodine and find out in which part nourishment is most abundant.
+It is this abundant store of food that makes the
+potato such a valuable crop in cold countries like Norway
+and Iceland, where the seasons are too short to admit of the
+slow process of developing the plant from the seed.</p>
+
+<figure class="figright illowp40" id="i_103x" style="max-width: 30em;">
+  <img class="w100" src="images/i_103x.jpg" alt="">
+  <figcaption>
+<table class="autotable">
+<tr>
+<td class="tdl wd50 vat"><p><span class="smcap">Fig.</span> 109.—Scaly bud of oak, enlarged.</p></td>
+<td class="tdl vat"><p><span class="smcap">Fig.</span> 110.—Scaly bulb of lily (<span class="smcap">Gray</span>).</p></td>
+</tr>
+</table>
+</figcaption>
+</figure>
+
+<p>Compare a common potato with a sweet potato. Are
+there any eyes or buds on the latter? Is there a scale below
+them? Do they occur in any regular order? Do you see
+any lenticels? The common potato and the sweet potato
+are both tubers; can you give some of the reasons why the
+one is regarded as a modified
+branch, and the other
+as a root? <a href="#p-100">(100.)</a> Compare
+their food contents;
+which contains most
+starch? Which most
+sugar? How can you
+judge about the sugar without
+a chemical test?</p>
+
+<p id="p-107"><b>107. The bulb</b> is a form of underground stem reduced to a
+single bud. Get the scaly bulb of a lily, and sketch it from
+the outside and in cross and vertical section. Compare it
+with the scaly winter buds of the oak and hickory, or other
+common deciduous tree. Make an enlarged sketch of the
+latter on the same scale as the lily bulb, and the resemblance
+will at once become apparent. The scales of the bulb are, in
+fact, only thick, fleshy leaves closely packed around a short
+axis that has become dilated into a flat disk. From the center
+of the disk, which is the terminal node of this transformed
+stem, rises the flower stalk, or <em>scape</em>, as it is called, of the
+season. After blossoming, the scape perishes with its bulb,
+and their place is taken by new ones which are developed<span class="pagenum" id="Page_94">[Pg 94]</span>
+from the axils of the scales, thus revealing their leaflike
+nature.</p>
+
+<figure class="figright illowp20" id="i_104" style="max-width: 12.5em;">
+  <img class="w100" src="images/i_104.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 111.</span>—Leaf
+of an onion divided
+lengthwise showing
+the base enlarged
+into the coat of a
+bulb.</p></figcaption>
+</figure>
+
+<p>That bulbs are only modified buds is further shown by
+the bulblets that sometimes appear among the flowers of the
+onion, and in the leaf axils of certain lilies.
+They never develop into branches, but drop
+off and grow into new plants just as the
+subterranean bulbs do.</p>
+
+<p>The bulbs of the onion and hyacinth are
+still further modifications, in which the scales
+consist of the thickened bases of leafstalks
+that are dilated until each one completely
+envelops the growing parts within.</p>
+
+<p id="p-108"><b>108. Morphology</b> is the part of botany
+that treats of the origin, form, and uses
+of the different organs of plants, and of
+the modifications they undergo in adapting themselves to
+changes of condition or function. Organs or parts that
+have the same origin but have become adapted to different
+functions, like the flattened stems of the butcher’s-broom
+or the bulb scales of the lily, are said to be
+<em>homologous</em>; those that are different in origin but adapted
+to the same function, as the sweet and common potatoes,
+are <em>analogous</em>. In other words, homologous organs
+are morphologically alike, but may be physiologically different;
+analogous organs are alike physiologically, but
+differ morphologically.</p>
+
+<p id="p-109"><b>109. Economic value of stems.</b>—We probably get a
+greater variety of economic products from the stem than
+from any other part of the plant. Consider the vast
+amount of food stored in underground stems like the potato;
+the resins, gums, and sugar found in the sap of plants
+like the sugar cane, the pine, and India-rubber trees; the
+medicines, dyes, and extracts obtained from the tissues; the
+valuable fibers, such as flax, jute, and hemp, furnished by
+the bast; the wood pulp for making paper; and the timber<span class="pagenum" id="Page_95">[Pg 95]</span>
+for building and furnishing our houses that we get from the
+woody trunks of trees. When we think of all these things,
+it seems hardly possible to overestimate the importance of
+this part of the vegetable kingdom to man, or to exert
+ourselves too strenuously to regulate and prevent the destruction
+of these invaluable natural resources.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Would you judge from the observations made in the foregoing section,
+that the work of an organ determines its form, or that the form determines
+its work? (<a href="#p-99">99</a>, <a href="#p-100">100</a>, <a href="#p-108">108</a>.)</p>
+
+<p>2. Which is the more important, form or function?</p>
+
+<p>3. Name some plants that are propagated by rootstocks; by runners
+or stolons; by rhizomes; by tubers; by bulbs.</p>
+
+<p>4. What is the advantage of propagating in this way over planting the
+seed? (<a href="#p-104">104</a>, <a href="#p-106">106</a>.)</p>
+
+<p>5. Mention any other advantages that the various plants named may
+gain from the development of their underground parts. <a href="#p-104">(104.)</a></p>
+
+<p>6. What makes the nut grass so troublesome to farmers in some parts
+of the country?</p>
+
+<p>7. Is its “nut” a root or a tuber? How can you tell? <a href="#p-106">(106.)</a></p>
+
+<p>8. Suggest some ways for destroying weeds that are propagated in this
+way.</p>
+
+<p>9. Could you get rid of wild onions in a pasture by mowing them down?
+By digging them up? <a href="#p-107">(107.)</a></p>
+
+<p>10. Is it wise for farmers to neglect the appearance of such a weed
+in their neighborhood, even though it does not infest their own land?</p>
+
+<p>11. Name any plants of your neighborhood, either wild or cultivated,
+that are valued for their rhizomes; for their tubers.</p>
+
+<p>12. What part of the plants named below do we use for food or other
+purposes? Ginger, angelica, ginseng, cassava, arrowroot, garlic, onion,
+sweet flag, iris, sweet potato, Cuba yam, artichoke.</p>
+
+<p>13. Why are the true roots of bulbous and rhizome-bearing plants
+generally so much smaller in proportion to the other parts than those of
+ordinary plants? (<a href="#p-89">89</a>, <a href="#p-104">104</a>.)</p>
+
+<p>14. If the Canada thistle grows in your vicinity, examine the roots and
+see if there is anything about them that will help to account for its hardihood
+and persistency.</p>
+
+<p>15. If you live in the region of the horse nettle (<i>Solanum Carolinense</i>),
+explain how it is helped by its root system. (<a href="#p-89">89</a>.)</p>
+</div>
+
+<p><span class="pagenum" id="Page_96">[Pg 96]</span></p>
+
+
+<h3 id="CH_IV_III">III. STEM STRUCTURE</h3>
+
+
+<h4 id="CH_IV_III_A">A. <span class="smcap">Monocotyls</span></h4>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Fresh cornstalks with several well-developed nodes,
+some of which should have stood in coloring fluid from 1 to 3 hours. If
+fresh specimens cannot be obtained from the fields, a number of seedlings
+may be grown in boxes of rich earth and cared for by the pupils either at
+home or in the schoolroom; they should be planted 4 or 5 weeks before
+needed. Asparagus and smilax sprouts may be used, or the stem of any
+large grass, or of wheat and other grains, but stalks of corn or sugar cane
+make the best subjects for study where they can be obtained.</p>
+
+<p><span class="smcap">Appliances.</span>—A compound microscope will be needed for detailed
+study. Prepared slides can be used, but it is better for students to make
+their own sections where practicable.</p>
+</div>
+
+<figure class="figright illowp25" id="i_106" style="max-width: 17.375em;">
+  <img class="w100" src="images/i_106.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 112.</span>—Cross
+section of a cornstalk
+(reduced): <i>v</i>, fibrovascular
+bundles; <i>c</i>, cortex;
+<i>p</i>, pith.</p></figcaption>
+</figure>
+
+<p id="p-110"><b>110. Gross anatomy of a monocotyl stem.</b>—Obtain a
+fresh cornstalk,—preferably one that has begun to tassel,—and
+observe its external characters. How are the internodes
+divided from one another? What
+is the use of the very firm, smooth epidermis?
+Notice a hollow, grooved channel
+running down one side between the <em>joints</em>,
+or nodes; does it occur in all of them?
+Is it on the same side or on the opposite
+sides of alternate internodes? Follow one
+of these grooves to the node from which
+it originates; what do you find there?
+After studying the internal structure of the stalk, you will
+understand why this groove should occur on the side of an
+internode bearing a bud or fruit.</p>
+
+<p>Cut a cross section midway between two nodes, and observe
+the composition of the interior; of what does the bulk
+of it appear to consist? Notice the arrangement of the
+little dots, like the ends of cut-off threads, that are scattered
+through the pith; where are they most abundant, toward the
+center or the circumference?</p>
+
+<figure class="figright illowp25" id="i_107" style="max-width: 12.5em;">
+  <img class="w100" src="images/i_107.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 113.</span>—Vertical
+section of cornstalk
+(reduced): <i>g</i>,
+groove; <i>c</i>, cortex; <i>v</i>,
+fibrovascular bundles
+mingled with parenchyma;
+<i>b</i>, bud; <i>n</i>,
+node.</p></figcaption>
+</figure>
+
+<p>Make a vertical section through one of the nodes. Cut a
+thin slice of the pith, hold it up to the light, and examine<span class="pagenum" id="Page_97">[Pg 97]</span>
+with a hand lens. Observe that it is composed of a number
+of oblong cells packed together like bricks in a wall. These
+are filled with protoplasm and cell sap, and constitute what is
+known to botanists as the <i>parenchyma</i> or
+fundamental tissue from which all the other
+tissues are derived. Apply the iodine test;
+in what parts does starch occur most abundantly?</p>
+
+<p>Draw out one of the woody threads running
+through the pith. Break away a bit of
+the epidermis, and see how very closely they
+are packed on its inner surface. Trace the
+course of the veins in the bases of the leaves;
+find their point of union with the stem;
+with what part of it do they appear to be
+continuous? Has this anything to do with
+the greater abundance of fibers near the epidermis?
+Can you follow the fibers through
+the nodes, or do they become confused and intermixed with
+other threads there? (If a stalk of sugar cane can be
+obtained, the ring of scars left by the vascular bundles as
+they pass from the leaves into the stem will be seen beautifully
+marked just above the nodes.)</p>
+
+<p>If there is an eye or bud at the node, see if any of
+the threads go into it. Can you account now for the depression
+that occurs in the internode above the eye?</p>
+
+<p>Make drawings of both cross and vertical sections, showing
+the points brought out in your examination of the cornstalk.</p>
+
+<p id="p-111"><b>111. The vascular system.</b>—To find out the use of the
+threads that you have been tracing, examine a piece of a
+living stem that has stood in red ink for three to twenty-four
+hours. Notice the course the coloring fluid has taken; what
+would you infer from this as to the use of the woody fibers?</p>
+
+<p>These threads constitute what is called the <em>vascular system</em>
+of the stem, because they are made up of <em>vessels</em> or <em>ducts</em>,
+along which the sap is conveyed from the roots to the leaves<span class="pagenum" id="Page_98">[Pg 98]</span>
+and back from the leaves to the parts where it is needed after
+it has contributed to the elaboration of food.</p>
+
+<p>On account of this double line of communication which
+they have to maintain, the vascular threads, or <em>bundles</em>, as
+they are technically called, are double; one part composed
+of larger vessels, carrying water up, the other consisting of
+smaller ones, bringing back the food. Can you give a reason
+for their difference in size?</p>
+
+<figure class="figright illowp20" id="i_108" style="max-width: 12.5em;">
+  <img class="w100" src="images/i_108.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 114.</span>—Longitudinal
+section
+through the stem
+of a palm, showing
+the curved course of
+the fibrovascular
+bundles (<span class="smcap">Gray</span>, <i>after</i>
+<span class="smcap">Falkenberg</span>).</p></figcaption>
+</figure>
+
+<p id="p-112"><b>112. Woody monocotyls.</b>—Examine sections of yucca,
+smilax, or of palmetto from the handle of a fan, and compare
+them with your sketches of the cornstalk.
+In which are the vascular fibers most abundant?
+Which is the toughest and strongest?
+Why? Trace the course of the leaf fibers
+from the point of insertion to the interior.
+How does it differ from that of the fibers
+in a cornstalk?</p>
+
+<p id="p-113"><b>113. Growth of monocotyl stems.</b>—After
+tracing the course of the leaf veins at the
+nodes of the cornstalk, you will have no
+difficulty in identifying these veins as part of
+the vascular system. In jointed stems like
+those of the corn and sugar cane and other
+grasses, their intercalation between the vascular
+bundles of the stem takes place, as we
+have seen, at the nodes, forming the hard
+rings known as joints; but in other monocotyls
+the fibers entering the stem from the
+leaves usually tend first downward, toward the interior
+(<a href="#i_108">Fig. 114</a>), then bend outward, toward the surface, where they
+become entwined with others and form the tough, inseparable
+cortex that gives to palmetto and bamboo stems their great
+strength. Generally, monocotyl stems do not increase in diameter
+after a certain point, and as they can contain only a
+limited number of vascular fibers, they are incapable of supporting
+an extended system of leaves and branches. Hence
+plants of this class, with a few exceptions, like smilax and
+asparagus, are characterized by simple, columnar stems and
+a limited spread of leaves. Such plant forms are admirably
+adapted by their structure to the purposes of mechanical
+support. It is a well-known law of mechanics that a hollow
+cylinder is a great deal stronger than the same mass would
+be in solid form, as may easily be tested by the simple experiment
+of breaking in your fingers a cedar pencil and a
+joint of cane or a stem of smilax of the same weight. In
+stems that may be technically classed as solid in structure,
+like the corn and palmetto, the interior is so light compared
+with the hard epidermis that the result is practically a hollow
+cylinder.</p>
+
+<p><span class="pagenum" id="Page_99">[Pg 99]</span></p>
+
+<figure class="figcenter illowp51" id="i_109" style="max-width: 50em;">
+  <img class="w100" src="images/i_109.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 4.</span>—Forest of bamboo, showing the tall, straight, branchless habit of
+monocotyl stems.</p></figcaption>
+</figure>
+
+
+<p><span class="pagenum" id="Page_100">[Pg 100]</span></p>
+
+<p id="p-114"><b>114. Minute study of a monocotyl stem.</b>—Place under
+the microscope a very thin transverse section of a cornstalk.
+The little dots that looked like
+the cut ends of threads to the
+naked eye will now appear as
+the complex group of cells shown in <a href="#i_110">Fig. 115</a>. The same parts
+are shown longitudinally in <a href="#i_110a">Fig. 116</a>. As seen in cross section,<span class="pagenum" id="Page_101">[Pg 101]</span>
+their arrangement suggests a grotesque resemblance to
+the face of an old woman wearing a pair of enormous spectacles
+and surrounded by a cap frill of netting with very wide
+meshes. These are parenchyma cells, <i>f</i>, <i>f</i>, <a href="#i_110">Fig. 115</a>, and
+constitute the greater portion of the living tissues.</p>
+
+<table><tr>
+<td class='tdc vab'>
+<figure class="figcenter illowp90" id="i_110" style="max-width: 38.6875em;">
+  <img class="w100" src="images/i_110.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 115.</span>—Transverse section through
+the fibrovascular bundle of a cornstalk:
+<i>a</i>, annular tracheid; <i>sp</i>, spiral tracheid;
+<i>m</i> and <i>m′</i>, ducts; <i>l</i>, air space; <i>v</i>, sieve
+tubes; <i>s</i>, companion cells; <i>vg</i>, strengthening
+fibers; <i>cp</i>, bast; <i>f</i>, <i>f</i>, parenchyma.</p></figcaption>
+</figure>
+</td><td class='tdc vab'>
+<figure class="figcenter illowp90" id="i_110a" style="max-width: 40.0625em;">
+  <img class="w100" src="images/i_110a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 116.</span>—Vertical section of the same;
+<i>a</i> and <i>a′</i>, rings of a decomposed annular
+tracheid; <i>v</i>, sieve tubes; <i>s</i>, companion
+cells; <i>cp</i>, bast; <i>l</i>, air space; <i>vg</i>, strengthening
+tissue; <i>sp</i>, spiral duct.</p></figcaption>
+</figure>
+</td></tr></table>
+
+<p>The two large openings, <i>m</i>, <i>m′</i>, that represent the spectacles,
+are ducts for carrying water <em>up</em> the stem. They are called
+pitted ducts on account of the bordered pits which cover
+their outer surface. The two smaller openings between and
+slightly below the pitted ducts are also vessels for carrying
+liquids up the stem. The lower one, <i>a</i>, is called the annular
+<i>tracheid</i> because its tube is strengthened by rings on the
+inside. The upper, smaller one, <i>sp</i>, is known as the spiral
+tracheid, because its walls are reinforced by spiral thickenings.
+Can you think what is the use of these strengthening contrivances
+in the walls of conducting cells? (Suggestion: What
+is the use of the spiral wire on a garden hose?) The large,
+irregular opening below the ducts is an air space. What is
+its object? Why has it no surrounding wall?</p>
+
+<p>Next look above the ducts for a group of rhomboidal or
+hexagonal cells, <i>v</i>, <i>v</i>, with smaller ones, <i>s</i>, between them. The
+larger of these are <em>sieve tubes</em>, the smaller
+ones, <em>companion cells</em>. The sieve tubes
+carry sap <em>down</em> the stem after it has been
+made into food by the leaves. They get
+their name from the sievelike openings
+between the connecting walls of the cells
+which form them—as if a row of pepper
+boxes with perforations at both top and
+bottom were placed end to end, so as to
+form a long tube divided into compartments
+by perforated walls. Can you give a reason why the
+cells of ducts that carry elaborated nutriment should have a
+more open line of communication than those carrying crude
+sap? [<a href="#p-56">56</a> (2).] Which one of the organic food substances was
+shown by <a href="#exp-39">Exp. 39</a> to be unable, or nearly so, to pass through<span class="pagenum" id="Page_102">[Pg 102]</span>
+the cell wall by osmosis? [<a href="#p-56">56</a> (4).] The
+conducting cells are surrounded by a mass
+of strengthening fibers separating them
+from the parenchyma, <i>f</i>, and constituting
+with them a <em>fibrovascular bundle</em>. The
+larger vessels, <i>m</i>, <i>m′</i>, <i>a</i>, and <i>sp</i>, compose
+the <i>xylem</i>, the harder, more woody part
+of the bundle, and the smaller ones, <i>v</i>, <i>s</i>,
+the <i>phloëm</i>, or softer part. Notice also
+that there is no parenchyma in contact
+with the xylem and phloëm in the fibrovascular
+bundles of a monocotyl, to supply
+material for new growth, but they are
+entirely surrounded by a sheath of strengthening
+tissue, whence such bundles are said
+to be <em>closed</em>, and are incapable of further
+growth by the addition of new cells.</p>
+
+<table class='autotable'><tr><td class='tdc'>
+<figure class="figcenter illowp50" id="i_111" style="max-width: 17.75em;">
+  <img class="w100" src="images/i_111.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 117.</span>—Horizontal
+view of the sieve tube
+of a gourd stem, showing
+perforations.</p></figcaption>
+</figure>
+</td><td class='tdc'>
+<figure class="figcenter illowp50" id="i_112" style="max-width: 21.625em;">
+  <img class="w100" src="images/i_112.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 118.</span>—Side
+view of the sieve
+tube of a gourd stem:
+<i>pr</i>, protoplasm layer;
+<i>u</i>, albuminous contents,
+forming mucilaginous
+strand.</p></figcaption>
+</figure></td></tr></table>
+
+
+
+<h4 id="CH_IV_III_B">B. <span class="smcap">Herbaceous Dicotyls</span></h4>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Young stems of sunflower, hollyhock, burdock, ragweed,
+cocklebur, castor bean, or any large herbaceous plant. In schools unprovided
+with compound microscopes, the minute anatomy can be studied
+with some degree of profit by the aid of pictures.</p>
+</div>
+
+<p id="p-115"><b>115. Gross anatomy.</b>—Examine the outside of a young
+stem of sunflower, burdock, or other herbaceous dicotyl.
+Notice whether it is smooth, or roughened with hairs, scales,
+ridges, or grooves. If hairy, observe the nature of the hairs,
+whether bristly, downy, sticky, etc. Notice the color of the
+epidermis, whether uniform, or splotched or striped with
+other colors, as, for example, jimson weed, and pigweed
+(amarantus). If there are any buds, branches, or flower
+stems, notice where they originate; what is the angle between
+the leaf and stem called? <a href="#p-100">(100.)</a></p>
+
+<p>Make a transverse cut through a portion of the stem that
+has stood for a time in coloring fluid and examine with a lens.
+Four regions can easily be distinguished: (1) the epidermis,<span class="pagenum" id="Page_103">[Pg 103]</span>
+<i>e</i>, <a href="#i_113">Fig. 119</a>; (2) the primary cortex, <i>c</i>; (3) a ring of fibrovascular
+bundles, <i>f</i>; and (4) a central cylinder of parenchyma,
+<i>p</i>. In some specimens there will be a fifth region, the
+pith, which will appear in
+the section as a white circular
+spot in the center of
+the parenchyma.</p>
+
+<figure class="figright illowp30" id="i_113" style="max-width: 39.75em;">
+  <img class="w100" src="images/i_113.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 119.</span>—Transverse section of a
+very young stem of burdock, showing fibrovascular
+bundles not completely united
+into a ring: <i>e</i>, epidermis; <i>c</i>, primary cortex;
+<i>f</i>, a ring of fibrovascular bundles;
+<i>p</i>, central cylinder of parenchyma.</p></figcaption>
+</figure>
+
+<p>In specimens a little older
+than the one shown in <a href="#i_113">Fig.
+119</a>, a narrow circular line
+will be seen running through
+the ring of bundles nearly
+midway between their inner
+and outer extremities, connecting
+them into an unbroken
+circle around the
+central cylinder. This is
+the <i>cambium</i> layer, which supplies the vascular region with
+materials for new growth, and thus enables dicotyl stems to
+increase in diameter by the successive addition of fresh
+vascular rings from year to year.</p>
+
+<p>Examine in the same way a vertical section, and find the
+parts corresponding to those shown in <a href="#i_113">Fig. 119</a>. Make enlarged
+sketches of both sections, labeling the various parts
+observed.</p>
+
+<p id="p-116"><b>116. Minute structure of a dicotyl stem.</b>—Place successively
+under a high power of the microscope thin transverse
+and longitudinal sections of the stem just examined, or
+such other specimen as the teacher may provide. Bring one
+of the fibrovascular bundles into the field, and try to make
+out the parts shown in <a href="#i_114">Figs. 120 and 121</a>. The corresponding
+parts in the two sections are indicated by the same letters.
+Notice the cortex, <i>R</i>, on the outside and the pith, <i>M</i>, on the
+inside; between these, the cambium, <i>C</i>, the <i>xylem</i>, or woody
+tissue, included between the radiating lines <i>X</i>, and the newer
+tissues composing the <i>phloëm</i> between the lines <i>P</i>. The
+cambium and pith, which includes the medullary rays so conspicuous
+in perennial stems, are composed of live parenchyma
+cells, from which alone growth can take place; they
+are the active part of the stem. The xylem contains the
+large vessels, <i>t</i> and <i>s</i>, that convey water <em>up</em> the stem, together
+with the wood fibers, <i>h</i>. These are the permanent tissues.
+After completing their growth the cells of the xylem gradually
+lose their protoplasm, and all vitality ceases. Even the
+cell sap disappears, and sometimes the walls of the ducts are
+disintegrated, leaving a mere air space like that shown at <i>l</i> in
+<a href="#i_110">Figs. 115</a> and <a href="#i_110a">116</a>. The dead cells and tissues, however, are
+by no means useless. They constitute the heartwood that
+is so valuable for timber, and serve an important purpose as
+a mechanical support for the stem. The phloëm contains
+on its outer face a mass of hard fibers, <i>b</i>, called bast, and
+toward the interior, the sieve tubes, <i>sb</i>, with a number of
+smaller vessels that convey <em>down</em> the stem the sap containing
+the food made in the leaves. It is separated from the cortex
+by the bundle sheath, <i>e</i>, and on its other side, from the exterior
+face of the xylem by the cambium, <i>C</i>. In this position
+the growing cambium adds new cells to the inner side of the
+phloëm, and to the outer side of the xylem, so that the former
+grows on its inner face and the latter on its outer. In perennial
+plants, as new rings are added to the xylem from season
+to season, the older ones die and are changed into heartwood,
+which thus gradually increases in thickness till in some of the
+giant redwoods and eucalypti, it may attain a diameter of
+thirty-five or forty feet. In the phloëm, on the other hand,
+as new cells are added from within, the older ones are
+gradually changed into hard bast, <i>b</i>, then into bark, and
+are finally sloughed off and fall to the ground. It is this
+free line of communication with the active cambium that
+enables dicotyl stems to grow on indefinitely, the sheath, <i>e</i>,
+being formed on the exterior face of the bundles only, leaving
+the other free, whence they are said to be <em>open</em>.</p>
+
+<p><span class="pagenum" id="Page_104">[Pg 104]</span></p>
+
+<figure class="figcenter illowp75" id="i_114" style="max-width: 50em;">
+  <img class="w100" src="images/i_114.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 120-121.</span>—Transverse and longitudinal sections of a fibrovascular bundle
+in the stem of a sunflower. The two sections are lettered to correspond: <i>M</i>, pith
+(parenchyma); <i>X</i>, xylem region; <i>P</i>, phloëm; <i>R</i>, cortex; <i>s</i>, spiral ducts; <i>s′</i>, annular
+ducts; <i>t</i>, <i>t</i>, pitted ducts; <i>C</i>, cambium between the phloëm and xylem regions; <i>sb</i>,
+sieve tubes; <i>b</i>, bast; <i>e</i>, bundle sheath; <i>ic</i>, cambium (parenchyma) cells; <i>h</i>, wood fibers.</p></figcaption>
+</figure>
+
+
+<p>Make drawings of cross and vertical sections of a dicotyl
+<span class="pagenum" id="Page_105">[Pg 105]</span>
+stem as it appears under the microscope, labeling correctly
+all the parts observed. Show the shape and relative size of
+the different cells. Compare
+your drawings with
+those made in your study
+of monocotyl stems, and
+write in your notebook the
+essential points of difference
+between the two.</p>
+
+<p><span class="pagenum" id="Page_106">[Pg 106]</span></p>
+
+<figure class="figcenter illowp75" id="i_116" style="max-width: 50em;">
+  <img class="w100" src="images/i_116.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 122.</span>—Internal structure of a pine stem, showing longitudinal section of a
+fibrovascular bundle through a medullary ray, <i>sm</i>, <i>sm′</i>; <i>s</i>, tracheids; <i>t</i>, bordered
+pits, surface view; <i>c</i>, cambium; <i>v</i>, sieve tubes; <i>vt</i>, sieve pits, analogous to the
+sieve plates in dicotyl stems.</p></figcaption>
+</figure>
+
+<figure class="figcenter illowp60" id="i_116a" style="max-width: 40.125em;">
+  <img class="w100" src="images/i_116a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 123.</span>—Internal structure of a pine
+stem, showing transverse section of a tracheid:
+<i>i</i>, cell walls; <i>m</i>, intermediate layer
+between walls of adjoining cells; <i>m′</i>, intercellular
+space here occupied by substance
+of intermediate layer; <i>b</i>, bordered pit in
+section at right angles to the surface; <i>t</i>,
+membrane for closing the pit canal.</p></figcaption>
+</figure>
+
+<p id="p-117"><b>117. The stems of conifers</b>,
+the group of Gymnosperms
+to which the pine
+belongs, do not differ greatly
+from those of dicotyls, the
+chief difference being that
+the vascular bundles contain
+tracheids only, corresponding
+to the smaller vessels of<span class="pagenum" id="Page_107">[Pg 107]</span>
+the phloëm, <i>s</i> and <i>s′</i>, shown in <a href="#i_114">Fig. 121</a>. These tracheids
+have large sunken places in their walls, called bordered pits
+(<a href="#i_116a">Fig. 123</a>), closed by a very thin membrane through which
+water and dissolved food materials can more readily percolate.
+In all other essentials, the internal structure of pine
+stems is like that of dicotyls. (See <a href="#i_118">Plate 5</a>.)</p>
+
+
+<h4 id="CH_IV_III_C">C. <span class="smcap">Woody Stemmed Dicotyl</span></h4>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Elm, basswood, mulberry, leatherwood, and pawpaw
+show the bast well; sassafras, slippery elm, and (in spring) hickory and
+willow show the cambium; grape and trumpet vine, the ducts. Some
+of the specimens used should be placed in coloring fluid from 3 to 8 hours
+before the lesson begins. The rate at which the liquid is absorbed varies
+with the kind of stem and the season. It is more rapid in spring and slower
+in winter. If a cutting stands too long in the fluid, the dye will gradually
+percolate through all parts of it; care should be taken to guard against this.</p>
+</div>
+
+<figure class="figright illowp35" id="i_117" style="max-width: 18.75em;">
+  <img class="w100" src="images/i_117.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 124.</span>—Part of a
+young China tree shoot,
+showing, <i>A</i>, lenticels; <i>B</i>,
+leaf scar; <i>C</i>, <i>C</i>, traces left
+by the broken ends of
+fibrovascular bundles that
+passed from the stem into
+the leaf. Natural size.</p></figcaption>
+</figure>
+
+<p id="p-118"><b>118. The external layer.</b>—While the primary structures,
+as shown in the last section, are essentially the same in all
+dicotyl stems, the continued yearly
+growth of perennials causes them to develop
+a number of secondary structures
+and variations of detail that differentiate
+them in a marked degree from soft-stemmed
+annuals. Take a piece of a
+three-year-old shoot of cherry, horse
+chestnut, or any convenient hardwood
+tree, and notice that the soft, green
+epidermis has given place to a thicker,
+harder, and usually darker colored bark.
+Notice the presence of lenticels <a href="#p-106">(106)</a> and
+their porous, corky texture for the admission
+of air to the interior. They
+are slightly raised above the surface of
+the bark, and are usually round, or
+more or less elongated in different directions,
+according as they are stretched vertically or horizontally
+by the growth of the axis. The characteristic markings
+of birch bark, which make it so ornamental, are due to the
+lenticels. In most trees they disappear on the older parts,
+where the bark is constantly breaking away and sloughing off.</p>
+
+<p><span class="pagenum" id="Page_108">[Pg 108]</span></p>
+
+<figure class="figcenter illowp51" id="i_118" style="max-width: 57em;">
+  <img class="w100" src="images/i_118.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 5.</span>—Stem of a conifer, <i>Sequoia gigantea</i>, Mariposa Grove, California. The
+first branch, 6 feet in diameter, leaves the parent trunk 125 feet above the ground.
+The photographer sitting on one of the exposed roots affords a good standard for
+comparison. The tree is noted for its massive limbs. The smaller trees in the
+background show the characteristic mode of branching in trees of this class.</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_109">[Pg 109]</span></p>
+
+<p id="p-119"><b>119. Internal structures.</b>—Cut a transverse section
+through your specimen, and notice under the epidermis a
+greenish layer of young bark; beneath this a layer of rather
+tough, stringy bast fibers, and beyond these a harder woody
+substance that constitutes the bulk of the interior; within this,
+at the very center of the axis, we find a cylinder of lighter
+texture, the pith, or medulla, occupying the place of the soft
+parenchyma which fills this space in very young stems.</p>
+
+<p>Between the woody axis and the bark notice a more or
+less soft and juicy ring.</p>
+
+<p id="p-120"><b>120. The cambium layer.</b>—This is not always easily
+distinguishable with a hand lens, but is conspicuous in the
+stems of sassafras, slippery elm, and aristolochia. If some
+of these cannot be obtained, the presence of the cambium
+can be recognized by observing the tendency of most stems
+to “bleed,” when cut, between the wood and bark. The
+reason for this is because the cambium is the active part of
+the stem, in which growth is taking place, and consequently
+it is most abundantly supplied with sap. In spring, especially,
+it becomes so full of sap that if a rod of hickory
+or elder is pounded, the pulpy cambium is broken up and the
+bark may be slipped off whole from the wood.</p>
+
+<p id="p-121"><b>121. Medullary rays.</b>—Observe the whitish, silvery lines
+that radiate in every direction from the center, like the
+spokes of a wheel from the hub. These are the medullary
+rays, and consist of threads of pith that serve as lines of communication
+between the “central cylinder” and the growing
+cambium layer. In old stems the central pith frequently
+disappears and its office is filled by the medullary rays, which
+become quite conspicuous.</p>
+
+<figure class="figcenter illowp75" id="i_120" style="max-width: 50em;">
+  <img class="w100" src="images/i_120.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 125, 126.</span>—Cross sections of twigs: 125, section across a young twig of box
+elder, showing the four stem regions: <i>e</i>, epidermis, represented by the heavy bounding
+line; <i>c</i>, cortex; <i>w</i>, vascular cylinder; <i>p</i>, pith; 126, section across a twig of box elder
+three years old, showing three annual growth rings, in the vascular cylinder. The
+radiating lines (<i>m</i>), which cross the vascular region (<i>w</i>), represent the pith rays, the
+principal ones extending from the pith to the cortex (<i>c</i>). (<i>From</i> <span class="smcap">Coulter’s</span> “Plant
+Relations.”)</p></figcaption>
+</figure>
+
+<p id="p-122"><b>122. Structural regions of a woody stem.</b>—Sketch cross
+and vertical sections of your specimen, as seen under the lens,
+labeling the different parts. Refer to <a href="#i_120">Figs. 125, 126</a>, if you<span class="pagenum" id="Page_110">[Pg 110]</span>
+have any difficulty in distinguishing the parts. In a year-old
+shoot (<a href="#i_120">Fig. 125</a>), the structural regions correspond closely to
+those shown in <a href="#i_113">Fig. 119</a>, except that the ring of fibrovascular
+bundles is here compact and woody, and crossed by the
+radiating lines of the medullary rays. In a three-year-old
+shoot (<a href="#i_120">Fig. 126</a>), the main divisions are the same, but the
+soft parenchyma of the central cylinder is replaced by the
+pith, and the vascular ring is composed of three layers corresponding
+to the three years of growth. In general, mature
+dicotyl stems may be said to include four well-defined regions:
+(1) the epidermis, or the bark; (2) the cortex, made
+up of bast and certain other tissues; (3) the cambium;
+(4) the woody vascular cylinder, made up of concentric
+rings, each representing a year’s growth. The pith, or medulla,
+constitutes a fifth region, but is obvious only in young
+stems. Notice the little pores or cavities that dot the woody
+part in the cross section; where are they largest and most
+abundant? How are the rings marked off from one another?<span class="pagenum" id="Page_111">[Pg 111]</span>
+These pores are the sections of ducts. They are very large
+in the grapevine, and a cutting two or three years old will
+show them distinctly. Examine sections of a twig that has
+stood in red ink from three to twelve hours, and observe the
+course the fluid has taken. How does this accord with the
+facts observed in your study of the conducting tissues in
+monocotyl and herbaceous stems? (<a href="#p-111">111</a>, <a href="#p-115">115</a>, <a href="#p-116">116</a>.)</p>
+
+<figure class="figright illowp20" id="i_121" style="max-width: 12.5em;">
+  <img class="w100" src="images/i_121.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 127.</span>—Diagram
+illustrating the
+annual growth of
+dicotyledons.</p></figcaption>
+</figure>
+
+<p id="p-123"><b>123. The rings</b> into which the woody cylinder is divided
+mark the yearly additions to the growth of the stem, which
+increases by the constant accession of new
+material to the outside of the permanent
+tissues <a href="#p-116">(116)</a>. The cambium constantly
+advances outward, beginning every spring
+a new season’s growth, and leaving behind
+the ring of ducts and woody fibers made
+the year before. As the work of the plant is
+most active and its growth most vigorous
+in spring, the largest ducts are formed then,
+the tissue becoming closer and finer as the
+season advances, thus causing the division
+into annual rings that is so characteristic of
+woody dicotyl stems. Each new stratum of
+growth is made up of the fibrovascular
+bundles that supply the leaves and buds and
+branches of the season. In this way we see
+that the increase of dicotyl trunks and
+branches is approximately in an elongated
+cone (<a href="#i_121">Fig. 127</a>), the number of rings gradually diminishing
+toward the top till at the terminal bud of each bough it is
+reduced to a single one, as in the stems of annuals.</p>
+
+<p>Sometimes a late autumn, succeeding a very dry summer,
+will cause trees to take on a second growth, and thus form two
+layers of wood in a single season. On this account we cannot
+always rely absolutely upon the number of rings in estimating
+the age of a tree, though the method is sufficiently
+exact for all practical purposes.</p>
+
+<p><span class="pagenum" id="Page_112">[Pg 112]</span></p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Old Fort Moultrie near Charleston was built originally of palmetto
+logs; was this good engineering or not? Why? <a href="#p-113">(113.)</a></p>
+
+<p>2. Explain the advantages of structure in a culm of wheat; a stalk of
+corn; a reed. <a href="#p-113">(113.)</a></p>
+
+<p>3. Would the same quality be of advantage to an oak? Why, or why
+not?</p>
+
+<p>4. Is it of any advantage to the farmer that grain straw is so light?</p>
+
+<p>5. Explain why boys can slip the bark from certain kinds of wood in
+spring to make whistles. <a href="#p-120">(120.)</a></p>
+
+<p>6. Why cannot they do this in autumn or winter? <a href="#p-123">(123.)</a></p>
+
+<p>7. Name some of the plants commonly used for this purpose.</p>
+
+<p>8. Is the spring, after the buds begin to swell, a good time to prune
+fruit trees and hedges? <a href="#p-120">(120.)</a></p>
+
+<p>9. What is the best time, and why?</p>
+
+<p>10. Why are grapevines liable to bleed to death if pruned too late in
+spring? (<a href="#p-120">120</a>, <a href="#p-123">123</a>.)</p>
+
+<p>11. Why are nurserymen, in grafting, so careful to make the cambium
+layer of the graft hit that of the stock? <a href="#p-120">(120.)</a></p>
+
+<p>12. In calculating the age of a tree or bough from the rings of annual
+growth, should we take a section from near the tip, or from the base?
+Why? <a href="#p-123">(123.)</a></p>
+</div>
+
+
+<h3 id="CH_IV_IV">IV. THE WORK OF STEMS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Leafy shoots of grape, balsam, peach, or other active
+young stems; a cutting of willow, currant, or any kind of easily rooting
+stem. Two bottles of water and some linseed or cottonseed oil.</p>
+
+<figure class="figright illowp30" id="i_123" style="max-width: 32.75em;">
+  <img class="w100" src="images/i_123.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 128.</span>—Experiment showing
+that moisture is thrown off by the
+leaves of plants.</p></figcaption>
+</figure>
+
+<p id="exp-58"><span class="smcap">Experiment 58. Do the leaves have any active part in effecting
+the movement of sap in the stem?</span>—Take two healthy young shoots of
+the same kind—grape, peach, corn, tropæolum, calla lily absorb rapidly.
+Trim the leaves from one shoot and close the cut surfaces with a little vaseline
+or gardener’s wax to prevent loss of water by evaporation. Place the
+lower end of each in a glass jar or tumbler filled to the same height with
+water. Cut off <em>under water</em> a half inch from the bottom of each shoot,
+to get a fresh absorbing surface. This is necessary because exposure to
+air for even a second greatly hinders absorption by permitting the entrance
+of air into the severed ends of the ducts. Pour a little oil on the water in
+both jars to prevent evaporation. (Do not use kerosene; it is injurious
+to plants.) At the end of twenty-four hours, which vessel has lost the
+more water? How do you account for the difference?</p>
+
+<p><span class="pagenum" id="Page_113">[Pg 113]</span></p>
+
+<p id="exp-59"><span class="smcap">Experiment 59. What becomes of the water that goes into the
+leaves?</span>—Cover the top of the vessel containing the leafy twig used in the
+last experiment with a piece of cardboard,
+having first cut a slit in one side,
+as shown in <a href="#i_123">Fig. 128</a>, so that it can be
+slid into place without injuring the
+stem. Invert over the twig a tumbler
+that has first been thoroughly dried,
+and leave in a warm, dry place. After
+an hour or two, what do you see on the
+<em>inside</em> of the tumbler? Where did the
+moisture come from?</p>
+
+<figure class="figleft illowp20" id="i_123a" style="max-width: 13em;">
+  <img class="w100" src="images/i_123a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 129.</span>—A
+twig which had been
+kept standing in
+water after the removal
+of a ring of
+cortical tissue: <i>a</i>,
+level of the water;
+<i>b</i>, swelling formed at
+the upper denudation;
+<i>c</i>, roots.</p></figcaption>
+</figure>
+
+<p id="exp-60"><span class="smcap">Experiment 60. Through what
+part of the stem does the sap flow
+upward?</span>—Remove a ring of the cortical
+layer from a
+twig of any readily
+rooting dicotyl,
+such as willow,
+being careful to
+leave the woody
+part, with the cambium, intact. Place the end <em>below</em>
+the cut ring in water, as shown in <a href="#i_123a">Fig. 129</a>. The leaves
+above the girdle will remain fresh. How is the water
+carried to them? How does this agree with the
+movement of red ink observed in 115 and 122?</p>
+
+<p id="exp-61"><span class="smcap">Experiment 61. Through what part does the
+sap come down?</span>—Next prune away the leaves and
+protect the girdled surface with tin foil, or insert it
+below the neck of a deep bottle to prevent evaporation,
+and wait until roots develop. Do they come more
+abundantly from above or below the decorticated
+ring?</p>
+</div>
+
+<p id="p-124"><b>124. The three principal functions of the
+stem</b> are:—(1) to serve as a mechanical support
+and framework for binding the other
+organs together and bringing them into the best attainable
+relations with light and air; (2) as a water carrier, or pipe
+line, for conveying the sap from the roots to the parts where
+it is needed; and (3) as a receptacle for the storage of foods.</p>
+
+<p><span class="pagenum" id="Page_114">[Pg 114]</span></p>
+
+<p id="p-125"><b>125. Movement of water.</b>—It has already been shown
+(71, 111) that a constant interchange of liquid is taking place
+through the stem, between the roots, where it is absorbed from
+the ground, and the leaves, where it is used partly in the manufacture
+of food. Just what causes the rise of sap in the stem
+is one of the problems of vegetable physiology that botanists
+have not yet been able to
+solve. There are, however,
+certain forces at
+work in the plant, which,
+though they may not account
+for all the phenomena
+of the movement,
+undoubtedly influence
+them to a great extent.
+From experiments 58-61,
+we can obtain an
+idea of what some of
+these forces may be.</p>
+
+<figure class="figcenter illowp50" id="i_124" style="max-width: 50em;">
+  <img class="w100" src="images/i_124.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 130.</span>—The stump of a large oak that
+was injured by lightning many years ago. The
+interior is completely decayed, leaving only
+a hollow shell of living tissue, from which
+branches continue to put forth leaves year
+after year.</p></figcaption>
+</figure>
+
+<p id="p-126"><b>126. Direction of the
+current.</b>—These experiments
+show that the upward
+movement of crude
+sap toward the leaves is
+mainly through the ducts
+in the woody portion of
+the stem, while the downward
+flow of elaborated
+sap from the leaves takes
+place chiefly through the
+soft bast and certain other vessels of the cortical layer. The
+action of the leaves in giving off part of the water absorbed, as
+shown in <a href="#exp-59">Exp. 59</a>, probably has also an important influence
+on the course of sap movement. If loss of water takes place
+in any organ through growth or other cause, the osmotic flow
+of the thinner sap from the roots will set in that direction.</p>
+
+<p><span class="pagenum" id="Page_115">[Pg 115]</span></p>
+
+<p id="p-127"><b>127. Ringing fruit trees.</b>—The course of the sap explains
+why farmers sometimes hasten the ripening of fruit by the
+practice of <em>ringing</em>. As the food material cannot pass below
+the denuded ring, the parts above become gorged, and a process
+of forcing takes place. The practice, however, is not to
+be commended, except in rare cases, as it generally leads to
+the death of the ringed stem. The portion below the ring
+can receive no nourishment from above, and will gradually
+be so starved that it cannot even act as a carrier of crude
+sap to the leaves, and so the whole bough will perish.</p>
+
+<figure class="figright illowp30" id="i_125" style="max-width: 25em;">
+  <img class="w100" src="images/i_125.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 131.</span>—Diagram showing
+general movement of sap.</p></figcaption>
+</figure>
+
+<p id="p-128"><b>128. Sap movement not circulation.</b>—It must not be
+supposed that this flow of sap in plants is analogous to the
+circulation of the blood in animals,
+though frequently spoken of in popular
+language as the “circulation of
+the sap.” There is no central organ
+like the heart to regulate its flow, and
+the water taken up by the roots does
+not make a continual circuit of the
+plant body as the blood does of ours,
+but is dispersed by a process of general
+diffusion, partly into the air through
+the leaves and partly through the plant
+body as food, wherever it is needed.
+<a href='#i_125'>Figure 131</a> gives a good general idea
+of the movement of sap in trees, the
+arrows indicating the direction of the
+movement of the different substances.</p>
+
+<p id="p-129"><b>129. Unexplained phenomena.</b>—Though the forces
+named above undoubtedly exert a powerful influence over
+sap movement, their combined action has not been proved
+capable of lifting the current to a height of more than 200
+feet, while in the giant redwoods of California and the towering
+blue gums of Australia, it is known to reach a height of
+more than 400 feet. The active force exerted by the cell
+protoplasm has been suggested as an efficient cause, but as<span class="pagenum" id="Page_116">[Pg 116]</span>
+the upward flow takes place through the cells of the xylem,
+which contain no protoplasm <a href="#p-116">(116)</a>, this explanation is inadequate,
+and we must be content, in the present state of our
+knowledge, to accept the fact as one which science has yet to
+account for.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Why will a leafy shoot heal more quickly than a bare one? (<a href="#p-125">125</a>,
+<a href="#p-126">126</a>; <a href="#exp-58">Exp. 58</a>.)</p>
+
+<p>2. Why does a transverse cut heal more slowly than a vertical one?
+(<a href="#p-126">126</a>, <a href="#p-127">127</a>.)</p>
+
+<p>3. Why does a ragged cut heal less rapidly than a smooth one?</p>
+
+<p>4. Why does the formation of wood proceed more rapidly as the amount
+of water given off by the leaves is increased? (<a href="#p-126">126</a>; <a href="#exp-59">Exp. 59</a>.)</p>
+
+<p>5. Why do nurserymen sometimes split the cortex of young trees in
+summer to promote the formation of wood? (<a href="#p-116">116</a>, <a href="#p-118">118</a>.)</p>
+
+<p>6. What is the advantage of scraping the stems of trees?</p>
+
+<p>7. Explain the frothy exudation that often appears at the cut ends of
+firewood, and the singing noise that accompanies it. [<a href="#p-120">120</a>, <a href="#p-124">124</a> (2).]</p>
+
+<p>8. Of what advantage is it to high climbing plants, like grape and
+trumpet vine (<i>Tecoma</i>), to have such large ducts? (<a href="#p-111">111</a>, <a href="#p-116">116</a>, <a href="#p-122">122</a>.)</p>
+
+<p>9. Why is the process of layering more apt to be successful if the shoot
+is bent or twisted at the point where it is desired to make it root? (<a href="#p-127">127</a>;
+<a href="#exp-60">Exps. 60</a>, <a href="#exp-61">61</a>.)</p>
+
+<p>10. Why do oranges become dry and spongy if allowed to hang on the
+tree too long? (<a href="#p-72">72</a>, <a href="#p-126">126</a>; <a href="#exp-60">Exps. 60</a>, <a href="#exp-61">61</a>.)</p>
+
+<p>11. Why will corn and fodder be richer in nourishment if, at harvest,
+the whole stalk is cut down and both fodder and grain are allowed to
+mature upon it? (<a href="#p-126">126</a>, <a href="#p-127">127</a>; <a href="#exp-60">Exps. 60</a>, <a href="#exp-61">61</a>.)</p>
+
+<p>12. Is the injury done to plants by freezing due, as a general thing,
+to mechanical, or to chemical action? <a href="#p-33">(33.)</a></p>
+
+<p>13. Why in pruning a branch is it best to make the cut just above a
+bud? (<a href="#exp-60">Exps. 60</a>, <a href="#exp-61">61</a>.)</p>
+
+<p>14. Why is the rim of new bark, or callus, that forms on the upper side
+of a horizontal wound, thicker than that on the lower side? (126, 127;
+<a href="#exp-60">Exps. 60</a>, <a href="#exp-61">61</a>.)</p>
+
+<p>15. Why is it that the medicinal or other special properties of plants
+are found mostly in the leaves and bark, or in the parts immediately
+under the bark? (<a href="#p-120">120</a>, <a href="#p-126">126</a>.)</p>
+
+<p>16. Why does twisting the footstalk of a bunch of grapes, just before
+ripening, make them sweeter? (<a href="#p-127">127</a>.)</p>
+</div>
+
+<p><span class="pagenum" id="Page_117">[Pg 117]</span></p>
+
+<figure class="figcenter illowp54" id="i_127" style="max-width: 50em;">
+  <img class="w100" src="images/i_127.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 6.</span>—A white oak, one of the monarchs of the dicotyl type. The owner of
+the ground on which this noble tree stands left a clause in his will bequeathing it in
+perpetuity a territory of 8 feet in every direction from its base. Refer to <a href="#p-89">89</a> and
+decide whether such an amount of standing room is sufficient to secure the preservation
+of this beautiful object.</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_118">[Pg 118]</span></p>
+
+<div class="blockquot">
+
+<p>17. Is it a mere superstition to drive nails into the stems of plum and
+peach trees to make them bear larger or more abundant fruit? (<a href="#p-126">126</a>, <a href="#p-127">127</a>.)</p>
+
+<p>18. Why is a living corn stalk heavier than a dry one? <a href="#p-124">(124.)</a></p>
+
+<p>19. Why is a stalk of sugar cane heavier than one of corn? Suggestion:
+Which is the heavier, pure water, or water holding solids in solution?</p>
+</div>
+
+
+<h3 id="CH_IV_V">V. WOOD STRUCTURE IN ITS RELATION TO INDUSTRIAL USES</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Select from the billets of wood cut for the fire, sticks of
+various kinds; hickory, ash, oak, chestnut, maple, walnut, cherry, pine,
+cedar, tulip tree, all make good specimens. Red oak shows the medullary
+rays well. Get sticks of green wood, if possible, and have them planed
+smooth at the ends. Collect also, where they can be obtained, waste bits
+of dressed lumber from a carpenter or joiner. If nothing better is available,
+any pieces of unpainted woodwork about the schoolroom will furnish
+subjects for study.</p>
+</div>
+
+<p id="p-130"><b>130. Detailed structure of a woody stem.</b>—Select a
+good-sized billet of hard wood, and count the rings of annual
+growth. How old was the tree or the bough from which it
+was taken? Was its growth uniform from year to year?
+How do you know? Are the rings broader, as a general
+thing, toward the center or the circumference? How do
+you account for this? Is each separate ring of uniform
+thickness all the way round? Mention some of the circumstances
+that might cause a tree to grow less on one side
+than on the other. Are the rings of the same thickness in
+all kinds of wood? Which are the more rapid growers, those
+with broad or with narrow rings? Do you notice any difference
+in the texture of the wood in rapid and in slow growing
+trees? Which makes the better timber as a general
+thing, and why?</p>
+
+<p id="p-131"><b>131. Heartwood and sapwood.</b>—Notice that in some
+of your older specimens (cedar, black walnut, barberry,
+black locust, chestnut, oak, Osage orange, show the difference
+distinctly) the central part is different in color and texture
+from the rest. This is because the sap gradually abandons
+the center (<a href="#p-116">116</a>, <a href="#p-123">123</a>) to feed the outer layers, where growth
+in dicotyls takes place; hence, the outer part of the stem
+usually consists of sapwood, which is soft and worthless as
+timber, while the dead interior forms the durable heartwood
+so prized by lumbermen. The heartwood is useful to
+the plant principally in giving strength and firmness to the
+axis. It will now be seen why girdling a stem,—that is, chipping
+off a ring of the softer parts all round, will kill it, while
+vigorous and healthy trees are often seen with the center of
+the trunk entirely hollow.</p>
+
+<p><span class="pagenum" id="Page_119">[Pg 119]</span></p>
+
+<figure class="figcenter illowp50" id="i_129" style="max-width: 50em;">
+  <img class="w100" src="images/i_129.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 132.</span>—Cross section through a black oak, showing heartwood
+and sapwood. (<i>From</i> <span class="smcap">Pinchot</span>, U. S. Dept. of Agr.)</p></figcaption>
+</figure>
+
+<figure class="figcenter illowp60" id="i_129a" style="max-width: 50em;">
+  <img class="w100" src="images/i_129a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 133.</span>—Vertical section through a black oak. (<i>From</i> <span class="smcap">Pinchot</span>,
+U. S. Dept. of Agr.)</p></figcaption>
+</figure>
+
+<figure class="figright illowp40" id="i_130" style="max-width: 25em;">
+  <img class="w100" src="images/i_130.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 134-136.</span>—Diagrams of sections
+of timber: 134, cross section;
+135, radial; 136, tangential. (<i>From</i>
+<span class="smcap">Pinchot</span>, U. S. Dept. of Agr.)</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_120">[Pg 120]</span></p>
+
+<p id="p-132"><b>132. Different ways of cutting.</b>—In studying the vertical
+arrangement of stems, two sections are necessary, a radial and
+a tangential one. The former passes along the axis, splitting
+the stem into halves (<a href="#i_130">Fig. 135</a>); the latter cuts between the
+axis and the perimeter, splitting
+off a segment from one
+side (<a href="#i_130">Fig. 136</a>). The appearance
+of the wood used in carpentry
+and joiner’s work is due
+largely to the manner in which
+the planks are cut.</p>
+
+<p id="p-133"><b>133. The cross cut.</b>—The
+section seen at the end of a log
+(<a href="#i_129">Figs. 132</a>, <a href="#i_130">134</a>) is called by
+carpenters a cross cut. It
+passes at right angles to the
+grain of the wood, and severs what important structures?
+(<a href="#p-116">116</a>, <a href="#p-119">119</a>, <a href="#p-122">122</a>.) Examine a cross cut at the end of a rough
+plank, or the top of
+a stump or an old
+fence post, and tell
+why this kind of cut
+is seldom used in
+carpentry.</p>
+
+<figure class="figright illowp40" id="i_130a" style="max-width: 25em;">
+  <img class="w100" src="images/i_130a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 137.</span>—Tangential section of mountain ash, showing
+ends of the medullary rays.</p></figcaption>
+</figure>
+
+<p id="p-134"><b>134. The tangent
+cut</b> is so called because
+it is made at
+right angles to the<span class="pagenum" id="Page_121">[Pg 121]</span>
+radius of a log. Repeat the geometrical
+principle upon which such
+a cut is described as “tangential.”
+It passes through the medullary
+rays and the annual rings diagonally
+(<a href="#i_130">Fig. 136</a>), and is the cheapest way
+of cutting timber, since the entire
+log is made into planks and there
+is no waste except the “slabs” and
+“edgings,” as shown in <a href="#i_131">Fig. 138</a>.
+The cut ends of the medullary rays
+appear on the surface as small lines
+or slits (<a href="#i_130a">Fig. 137</a>), and give to this
+kind of plank its peculiar graining.
+The wavy or “watered”
+appearance of the annual rings
+(<a href="#i_129a">Figs. 133</a>, <a href="#i_130">136</a>, <a href="#i_132">140</a>, <a href="#i_132a">141</a>), so often
+seen in cheap furniture and in the woodwork of cheaply
+constructed houses, is caused by the tangential cut, which
+strikes them at various angles.</p>
+
+<table class='autotable'>
+<tr><td class='tdc'>
+<figure class="figcenter illowp80" id="i_131" style="max-width: 35em;">
+  <img class="w100" src="images/i_131.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 138.</span>—Diagram to show
+the common method of sawing a
+log. The circles represent rings
+of annual growth: <i>R</i>, <i>R</i>, diameter
+of the log; <i>r</i>, <i>r</i>, <i>r</i> and <i>t</i>, <i>t</i>, <i>t</i>,
+boards cut perpendicular to it,
+giving for the two or three central
+ones radial, for the others,
+tangential, cuts. The waste portions
+are the “slabs” and “edgings,”
+shown in the dark segments
+at <i>R</i>, <i>R</i>, and the small
+triangular blocks, <i>e</i>, <i>e</i>, <i>e</i>.</p></figcaption>
+</figure>
+</td><td class='tdc'>
+<figure class="figcenter illowp80" id="i_131a" style="max-width: 35em;">
+  <img class="w100" src="images/i_131a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 139.</span>—Diagram illustrating
+the “quartered” cut: <i>d</i>, <i>d</i> and
+<i>d′</i>, <i>d′</i>, radial cuts (diameters) by
+which the log is “quartered”;
+<i>c</i>, center of the log; <i>r</i>, <i>r</i>, radii
+passing through the middle of
+each quarter, parallel to which
+the planks <i>t</i>, <i>t</i>, <i>t</i> are cut. The
+circles represent rings of annual
+growth.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-135"><b>135. The radial, or quartered cut</b>,
+familiar to most of us in the “quartered
+oak” of commerce, passes
+through the center of the log and
+cuts the rings of annual growth perpendicularly,
+giving it the “striped”
+appearance (<a href="#i_130">Fig. 135</a>) seen in the
+best woodwork. It gets its name
+from the practice of dealers in first
+sawing a log into quarters and then
+cutting parallel to the radius passing
+through the middle of each
+quarter, as shown in <a href="#i_131a">Fig. 139</a>. In
+this way each cut strikes the rings
+perpendicularly, but except in the
+case of very large logs, only narrow<span class="pagenum" id="Page_122">[Pg 122]</span>
+planks can be obtained in this manner. A better way of
+treating small logs is shown in <a href="#i_131">Fig. 138</a>, where the three
+central planks, <i>r</i>, <i>r</i>, <i>r</i>, on and near the diameter, will give the
+“quartered” effect, while the rest can be used for the cheaper
+tangential cuttings. Examine a piece of quartered board, or
+a log of wood that has been split down the center, and notice
+that the medullary rays appear as silvery bands or plates
+(<a href="#i_132">Figs. 140</a>, <a href="#i_132a">141</a>). This is because the cut runs parallel to
+them. It is the medullary rays chiefly that give to commercial
+woods their characteristic graining. Knots, buds, and
+other adventitious causes also influence it in various degrees.</p>
+
+<figure class="figcenter illowp75" id="i_132" style="max-width: 54em;">
+  <img class="w100" src="images/i_132.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 140.</span>—Sections of sycamore wood: <i>a</i>, tangential; <i>b</i>, radial;
+<i>c</i>, cross. (<i>From</i> <span class="smcap">Pinchot</span>, U. S. Dept. of Agr.)</p></figcaption>
+</figure>
+
+<figure class="figcenter illowp70" id="i_132a" style="max-width: 52em;">
+  <img class="w100" src="images/i_132a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 141.</span>—Section of white pine wood. (<i>From</i> <span class="smcap">Pinchot</span>,
+U. S. Dept. of Agr.)</p></figcaption>
+</figure>
+
+<figure class="figright illowp25" id="i_133" style="max-width: 15.5em;">
+  <img class="w100" src="images/i_133.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 142.</span>—Section
+of tree trunk showing
+knot.</p></figcaption>
+</figure>
+
+<p id="p-136"><b>136. The swelling and shrinking of timber.</b>—The capacity
+possessed by certain substances of bringing about an<span class="pagenum" id="Page_123">[Pg 123]</span>
+increase of volume by the absorption of liquids is termed
+<em>imbibition</em>. Care must be taken not to confound imbibition
+with capillarity. (<a href="#exp-53">Exp. 53</a>.) When liquids are carried
+into a body by capillary attraction, they
+merely fill up vacant spaces already existing
+between small particles of the substance,
+and therefore do not cause any swelling or
+increase in size. When imbibition takes
+place, the <em>molecules</em>, or chemical units of the
+liquid, force their way between those of the
+imbibing substance, and thus, in making
+room for themselves, bring about an increase
+in volume of the imbibing body.
+To this cause is due the alternate swelling and shrinking of
+timber in wet and dry weather.</p>
+
+<figure class="figright illowp30" id="i_133a" style="max-width: 21.25em;">
+  <img class="w100" src="images/i_133a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 143-144.</span>—Diagrams
+of tree trunks, showing
+knots of different ages:
+143, from tree grown in
+the open; 144, from tree
+grown in a dense forest.</p></figcaption>
+</figure>
+
+<p id="p-137"><b>137. Knots.</b>—Look for a billet with a knot in it. Notice
+how the rings of growth are disturbed
+and displaced in its neighborhood. If
+the knot is a large one, it will itself
+have rings of growth. Count them, and
+tell what its age was when it ceased to
+grow. Notice where it originates.
+Count the rings from its point of origin
+to the center of the stem. How old was
+the tree when the knot began to form?
+Count the rings from the origin of the
+knot to the circumference of the stem;
+how many years has the tree lived since
+the knot was formed? Does this agree
+with the age of the knot as deduced
+from its own rings? As the tree may
+continue to live and grow indefinitely
+after the bough which formed the knot
+died or was cut away, there will probably be no correspondence
+between the two sets of rings, especially in the
+case of old knots that have been covered up and embedded in<span class="pagenum" id="Page_124">[Pg 124]</span>
+the wood. The longer a dead branch remains on a tree the
+more rings of growth will form around it before covering it up,
+and the greater will be the disturbance caused by it. Hence,
+timber trees should be pruned while very young, and the
+parts removed should be cut as close as possible to the main
+branch or trunk. Sometimes knots injure lumber very much
+by falling out and leaving the holes that are often seen in pine
+boards. In other cases, however, when the knots are very
+small, the irregular markings caused by them add greatly
+to the beauty of the wood. The peculiar marking of bird’s-eye
+maple is caused by abortive buds buried in the wood.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Is the swelling of wood a physical or a physiological process?</p>
+
+<p>2. Does wood swell equally with the grain and across it? (Suggestion:
+test by keeping a block under water for 10 to 20 days, measuring its dimensions
+before and after immersion.)</p>
+
+<p>3. In building a fence, what is the use of “capping” the posts? <a href="#p-133">(133.)</a></p>
+
+<p>4. In laying shingles, why are they made to touch, if the work is done
+in wet weather, and placed somewhat apart, if in dry weather? <a href="#p-136">(136.)</a></p>
+
+<p>5. What is the difference between timber and lumber? Between a
+plank and a board? Between a log, stick, block, and billet?</p>
+
+<p>6. Why does sapwood decay more quickly than heartwood? <a href="#p-131">(131.)</a></p>
+
+<p>7. Explain the difference between osmosis, diffusion, capillarity, and
+imbibition. (<a href="#p-9">9</a>, <a href="#p-56">56</a>, <a href="#p-57">57</a>, <a href="#p-136">136</a>; <a href="#exp-53">Exp. 53</a>.)</p>
+</div>
+
+
+<h3 id="CH_IV_VI">VI. FORESTRY</h3>
+
+<p id="p-138"><b>138. Practical bearings.</b>—This part of our subject is
+closely related to lumbering and forestry. The business of
+the lumberman is to manufacture growing trees into merchantable
+timber, and to do this successfully he must understand
+enough about the structure of wood to cut his boards
+to the best advantage, both for economy and for bringing out
+the grain so as to produce the most desirable effects for
+ornamental purposes.</p>
+
+<p><span class="pagenum" id="Page_125">[Pg 125]</span></p>
+
+<figure class="figcenter illowp48" id="i_135" style="max-width: 53em;">
+  <img class="w100" src="images/i_135.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 7.</span>—Timber tree spoiled by standing too much alone in early youth.
+Notice how the crowded young timber in the background is righting itself, the lower
+branches dying off early from overshading, leaving tall, straight, clean boles. (<i>From</i>
+<span class="smcap">Pinchot</span>, U. S. Dept. of Agr.)</p></figcaption>
+</figure>
+
+<figure class="figright illowp40" id="i_136" style="max-width: 25em;">
+  <img class="w100" src="images/i_136.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 145.</span>—After the forest fire.</p></figcaption>
+</figure>
+
+<p id="p-139"><b>139. Forestry has for its object</b>: (1) the preservation
+and cultivation of existing forests; (2) the planting of new
+ones, or the reforestation of tracts from which the timber has
+been destroyed. Forests may be either <em>pure</em>, that is, composed
+mainly of one
+kind of tree, as a pine
+or a fir wood; or <em>mixed</em>,
+being made up of a variety
+of different growths,
+as are most of our common
+hardwood forests.</p>
+
+<p><span class="pagenum" id="Page_126">[Pg 126]</span></p>
+
+<figure class="figright illowp30" id="i_136a" style="max-width: 25em;">
+  <img class="w100" src="images/i_136a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 146.</span>—Oyster fungus on linden.</p></figcaption>
+</figure>
+
+<p id="p-140"><b>140. Enemies of the
+forest.</b>—The first step
+in the preservation of
+our forests is to know
+the dangers to be
+guarded against. The
+chief of these are:
+(1) fires; (2) the ignorance
+or recklessness of
+man in cutting for
+commercial purposes;
+(3) fungi; (4) injurious insects; (5) sheep, hogs, and other
+animals that eat the seeds and the young, tender growth.</p>
+
+<p id="p-141"><b>141. How to protect the
+forests.</b>—The annual destruction
+of forests by fires
+probably exceeds that from
+all other causes combined.
+The only effectual safeguard
+against this danger is watchfulness
+on the part of <em>everybody</em>.
+We can each one of
+us help in this work by at
+least being careful ourselves
+never to kindle a fire in the
+woods without taking every
+precaution against its<span class="pagenum" id="Page_127">[Pg 127]</span>
+spreading. A single match, or the glowing stump of a cigar,
+carelessly thrown among dry leaves or grass, may start a
+conflagration that will destroy millions of dollars’ worth of
+standing timber.</p>
+
+<p>To prevent the spread of fungi, dead trees should be removed,
+and broken or decayed branches trimmed off and the
+cut surfaces painted. Birds which destroy insects should be
+protected; sheep and hogs should be kept out, and dead
+leaves left on the ground to cover the roots and fertilize the
+soil with the humus created by their decay. Finally, none
+but mature trees should be cut for industrial purposes, and
+the cutting ought to be done in such a way that the young
+surrounding growth will not be injured by the falling
+trunks.</p>
+
+<p id="p-142"><b>142. The usefulness of forests.</b>—Aside from the value
+of their products, forests are useful in many other ways.
+They influence climate beneficially by acting as windbreaks,
+by giving off moisture (<a href="#exp-58">Exp. 58</a>), by shading the soil, and
+thus preventing too rapid evaporation. Their roots also
+help to retain the water in the soil, and by this means tend
+to prevent the washing of the land by heavy rains and to
+restrain the violence of freshets.</p>
+
+<p id="p-143"><b>143. Forests and water supply.</b>—It is especially important
+that the watershed of any region should be well
+protected by forests, to prevent contamination of the streams
+and to insure an unfailing supply of water by checking the
+escape of the rainfall from the soil.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Explain the difference between a forest, grove, copse, wood, woodland.</p>
+
+<p>2. In pruning a tree why ought the branch to be cut as close to the stock
+as possible? <a href="#p-137">(137.)</a></p>
+
+<p>3. Name the principal timber trees of your neighborhood. What gives
+to each its special value?</p>
+
+<p>4. Name six trees that produce timber valuable for ornament; for
+toughness and strength.</p>
+
+<p><span class="pagenum" id="Page_128">[Pg 128]</span></p>
+
+<p>5. Which is the better for timber, a tree grown in the open, or one
+grown in a forest, and why? (<a href="#i_135">Plate 7</a>.)</p>
+
+<p>6. What are the objects to be attained in pruning timber trees? Orchard
+and ornamental trees?</p>
+
+<p>7. Is the outer bark of any use to a tree, and if so, what?</p>
+
+<p>8. Why should pruning not be done in wet weather? [<a href="#p-140">140</a> (3), <a href="#p-141">141</a>.]</p>
+
+<p>9. Why should vertical shoots be cut off obliquely? [<a href="#p-133">133</a>, <a href="#p-140">140</a> (3),
+<a href="#p-141">141</a>.]</p>
+</div>
+
+
+<h4 id="CH_IV_FIELD">Field Work</h4>
+
+<div class="blockquot">
+
+<p>(1) Make a study of the various climbing plants of your neighborhood
+with reference to their modes of ascent, and the effect, injurious, or other,
+upon the plants to which they attach themselves. Note the origin and
+position of tendrils, and try to make out what modification has taken
+place in each case. Consider the twining habit in reference to parasitism,
+especially in the case of soft-stemmed twiners when brought into contact
+with soft-stemmed annuals. Observe the various habits of stem growth:
+prostrate, declined, ascending, etc., and decide what adaptation to circumstances
+may have influenced each case.</p>
+
+<p>(2) Notice the shape of the different stems met with, and learn to
+recognize the forms peculiar to certain of the great families. Observe
+the various appliances for defense and protection with which they are
+provided, and try to find out the meaning of the numerous grooves, ridges,
+hairs, prickles, and secretions that are found on stems. Always be on the
+alert for modifications, and learn to recognize a stem under any disguise,
+whether thorn, tendril, foliage, water holder, rootstock, or tuber.</p>
+
+<p>(3) Note the color and texture of the bark of the different trees you see
+and learn to distinguish the most important kinds:</p>
+
+<div class="blockquot">
+
+<p>(<i>a</i>) scaly—peeling off annually in large plates, as sycamore, shagbark-hickory;</p>
+
+<p>(<i>b</i>) fibrous—detached in stiff threads and fibers, as grape;</p>
+
+<p>(<i>c</i>) fissured—split into large, irregular cracks by the growth of the
+stem in thickness, as oak, chestnut, and most of our large forest
+trees;</p>
+
+<p>(<i>d</i>) membranous—separating in dry films and ribbons, as common
+birch (<i>Betula alba</i>).</p>
+</div>
+
+<p>Observe the difference in texture and appearance of the bark on old
+and young boughs of the same species. Try to account for the varying
+thickness of the bark on different trees and on different parts of the same
+tree. Notice the difference in the timber of the same species when grown
+in different soils, at different ages of the tree, and in healthy and weakly
+specimens. Find examples of self-pruning trees (<a href="#i_135">Plate 7</a>), and explain
+how the pruning was brought about.</p>
+
+<p><span class="pagenum" id="Page_129">[Pg 129]</span></p>
+
+<p>(4) Select a small plot, about a fourth of an acre, of any wooded tract
+in your neighborhood, and make a study of all the trees and shrubs it contains.
+Make a list of the different kinds, with the number of each. Take
+note of those that show themselves, by vigor and abundance of growth,
+best adapted to the situation. These are the “climax” or dominant
+vegetation of the plot. Find out, if you can, to what cause their superiority
+is due.</p>
+</div>
+
+<p><span class="pagenum" id="Page_130">[Pg 130]</span></p>
+
+<figure class="figcenter illowp90" id="i_140" style="max-width: 50em;">
+  <img class="w100" src="images/i_140.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 8.</span>—The American elm—a perfect type of deliquescent branching.</p></figcaption>
+</figure>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_131">[Pg 131]</span></p>
+
+
+<h2 class="nobreak" id="CH_V">CHAPTER V. BUDS AND BRANCHES</h2>
+</div>
+
+<h3 id="CH_V_I">I. MODES OF BRANCHING</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—For determinate growth, have twigs of an alternate and
+an opposite-leaved plant showing well-developed terminal buds: hickory,
+sweet gum, cottonwood, poplar, chestnut, are good examples of the
+first; maple, ash, horse-chestnut, viburnum, of the second; for the two-forked
+kind, mistletoe, buckeye, horse-chestnut, jimson weed, lilac. For
+showing indefinite growth: rose, willow, sumach, and ailanthus are good
+examples. Gummy buds, like horse-chestnut and poplar, should be
+soaked in warm water before dissecting, to soften the gum; the
+same treatment may be applied when the scales are too brittle to be
+handled without breaking. Buds with heavy fur on the scales cannot
+very well be studied in section; the parts must be taken out and
+examined separately.</p>
+</div>
+
+<table class='autotable'>
+<tr><td class='tdc'>
+<figure class="figcenter illowp100" id="i_141" style="max-width: 14em;">
+  <img class="w100" src="images/i_141.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 147.</span>—Diagram
+of excurrent
+growth.</p></figcaption>
+</figure>
+</td><td class='tdc'>
+<figure class="figcenter illowp100" id="i_141a" style="max-width: 19.5em;">
+  <img class="w100" src="images/i_141a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 148.</span>—Diagram
+of deliquescent growth.</p></figcaption>
+</figure></td></tr></table>
+
+
+<p id="p-144"><b>144. Modes of branching.</b>—Compare the arrangement
+of the boughs on a pine, cedar, magnolia, etc., with those
+of the elm, maple, apple, or any of our
+common deciduous trees. Draw a diagram
+of each, showing the two modes of growth.
+The first represents the
+<em>excurrent</em> kind, from the
+Latin <i>excurrere</i>, to run
+out; the second, in which
+the trunk seems to divide
+at a certain point
+and flow away, losing
+itself in the branches,
+is called <em>deliquescent</em>,
+from the Latin <i lang="la">deliquescere</i>,
+to melt or flow away.
+The great majority of stems, as a little observation will
+show, present a combination of the two modes.</p>
+
+<p><span class="pagenum" id="Page_132">[Pg 132]</span></p>
+
+<figure class="figright illowp20" id="i_142" style="max-width: 12.5em;">
+  <img class="w100" src="images/i_142.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 149.</span>—Winter
+twig of sugar maple:
+<i>t</i>, terminal bud; <i>ax</i>,
+axillary buds; <i>ls</i>, leaf
+scars; <i>tr</i>, leaf traces;
+<i>l</i>, lenticels; <i>rs</i>, ring of
+scars left by bud scales
+of preceding season.</p></figcaption>
+</figure>
+
+<p id="p-145"><b>145. Terminal and axillary buds.</b>—Notice the large bud
+at the end of a twig of hickory, sweet gum, beech, cottonwood,
+etc. This is called the <em>terminal</em> bud because it terminates
+its branch. Notice the scars left by the leaves of
+the season as they fell away, and look for small buds just
+above them. These are <em>lateral</em>, or <em>axillary</em>, buds, so called
+because they spring from the axils of the leaves. How
+many leaves did your twig bear? What
+difference in size do you notice between
+the terminal and lateral buds?</p>
+
+<p id="p-146"><b>146. The leaf scars.</b>—Examine the leaf
+scars with a hand lens, and observe the
+number and position of the little dots in
+them. Ailanthus, varnish tree, sumach,
+and China tree show these very distinctly.
+They are called <em>leaf traces</em>, and mark the
+points where the fibrovascular bundles
+from the leaf veins passed into the stem.
+Look on the bark, or epidermis, for lenticels.</p>
+
+<p id="p-147"><b>147. Bud scales and scars.</b>—Notice the
+stout, hard scales by which the winter buds
+are covered in most of our hardy trees and
+shrubs. Remove these from the terminal
+one of your specimen, and notice the ring
+of scars left around the base. Look lower down on your
+twig for a ring of similar scars left from last year’s bud.
+Is there any difference in the appearance of the bark above
+and below this ring? If so, what is it, and how do you account
+for it? Is there more than one of these rings of scars
+on your twig, and if so, how many? How old is the twig
+and how much did it grow each year? Has its growth been
+uniform, or did it grow more in some years than in others?</p>
+
+<figure class="figright illowp25" id="i_143" style="max-width: 15.25em;">
+  <img class="w100" src="images/i_143.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 150.</span>—Diagram
+of opposite bud
+scales.</p></figcaption>
+</figure>
+
+<p id="p-148"><b>148. Arrangement and use of the scales.</b>—Notice the
+manner in which the scales overlap so as to “break joints,”
+like shingles on the roof of a house. Where the leaves are
+opposite, the manner of superposition is very simple. Remove<span class="pagenum" id="Page_133">[Pg 133]</span>
+the scales one by one, representing the number and
+position of the pairs by a diagram after the model given in
+<a href="#i_143">Fig. 150</a>. In the bud of an alternately branched twig the
+order will be different, and the diagram must be varied accordingly.
+Do you observe any difference
+as to size and texture between the outer
+and inner scales? Notice how the former
+inclose the tenderer parts within like a
+protecting wall. In cold climates the outer
+scales are frequently
+coated with gum, as in
+the horse-chestnut, for
+greater security against
+the weather. The hickory and various
+other trees have the inner scales covered
+with fur or down that envelops the tender
+bud like a warm blanket.</p>
+
+<p id="p-149"><b>149. Nature of the scales.</b>—The position
+of the scales shows that they occupy
+the place of leaves or of some part of a
+leaf. In expanding buds of the lilac and
+many other plants, they can be found in
+all stages of transition, from scales to
+true leaves. In the buckeye and horse-chestnut,
+they will easily be recognized
+as modified leaf stalks (<a href="#i_143a">Fig. 151</a>). In the
+tulip tree, magnolia, India rubber tree,
+fig, elm, and many others, they represent
+appendages called <em>stipules</em>, often found at
+the bases of leaves. (See 165, 166.) In
+this case a pair of scales is attached with
+each separate leaflet, and as the growing axis lengthens in
+spring, they are carried apart by the elongation of the internodes
+so that the scars are separated, a pair at each node,
+making rings all along the stem, as shown in <a href="#i_144">Fig. 152</a>, instead
+of having them compacted into bands at the base of<span class="pagenum" id="Page_134">[Pg 134]</span>
+the bud. These scars are sometimes very persistent, and
+in the common fig and magnolia may often be traced on
+stems six to eight years old. Do they furnish
+any indication as to the relative age of the
+different parts of the stem, like the bands of
+scars on twigs of horse-chestnut and hickory?
+Give a reason for your answer. (<a href="#i_144">Fig. 152</a>.)</p>
+
+<table class='autotable double-image'>
+<tr>
+<td class='tdc'>
+<figure class="figcenter illowp50" id="i_143a" style="max-width: 20.5em;">
+  <img class="w100" src="images/i_143a.jpg" alt="">
+</figure>
+</td><td class='tdc'>
+<figure class="figcenter illowp50" id="i_144" style="max-width: 20.5em;">
+  <img class="w100" src="images/i_144.jpg" alt="">
+</figure></td></tr>
+<tr>
+<td class='tdl caption'><p><span class="smcap">Fig. 151.</span>—Development
+of the parts of
+the bud in the buckeye.
+(<i>After</i> <span class="smcap">Gray</span>.)</p></td>
+<td class='tdl caption'><p><span class="smcap">Fig. 152.</span>—Stem
+of tulip tree: <i>s</i>, <i>s</i>,
+scars left by stipular
+scales; <i>l</i>, <i>l</i>, leaf scars.</p></td></tr>
+</table>
+
+<p id="p-150"><b>150. Different rates of growth.</b>—Notice
+the very great difference between branches
+in this respect. Sometimes the main stem
+will have lengthened from twenty to fifty
+centimeters or more in a single season, while
+some of the lateral ones will have grown
+but an inch or two in four or five seasons.
+One reason for this is because the terminal
+bud, being on the great trunk line of sap
+movement, gets a larger share of nourishment
+than the others, and being stronger
+and better developed to begin with, starts out in life with
+better chances of success.</p>
+
+<p>Make a drawing of your specimen, showing all the points
+brought out in the examination just made. Cut sections
+above and below a set of bud scars and count the rings of
+annual growth in each section. What is the age of each?
+How does this agree with your calculation from the number
+of scar clusters left by the bud scales?</p>
+
+<p id="p-151"><b>151. Irregularities.</b>—Take a larger bough of the same
+kind that you have been studying, and observe whether the
+arrangement of branches on it corresponds with the arrangement
+of buds on the twig. Did all the buds develop into
+branches? Do those that did develop all correspond in size
+and vigor? If all the buds developed, how many branches
+would a tree produce every year?</p>
+
+<p>In the elm, linden, beech, hornbeam, hazelnut, willow, and
+various other plants, the terminal bud always dies and the
+one next in order takes its place, giving rise to the more or<span class="pagenum" id="Page_135">[Pg 135]</span>
+less zigzag axis that generally characterizes trees of these
+species. (<a href="#i_145">Fig. 153</a>.)</p>
+
+<figure class="figright illowp30" id="i_145" style="max-width: 28.75em;">
+  <img class="w100" src="images/i_145.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 153.</span>—Bud development
+of beech: <i>a</i>, as it is, many buds
+failing to develop; <i>b</i>, as it would
+be if all the buds were to live.</p></figcaption>
+</figure>
+
+<p id="p-152"><b>152. Forked stems.</b>—Take a twig of buckeye, horse-chestnut,
+or lilac, and make a careful
+sketch of it, showing all the
+points that were brought out in the
+examination of your previous specimen.
+Which is the larger, the lateral
+or the terminal bud? Is their
+arrangement alternate or opposite?
+What was the leaf arrangement?
+Count the leaf traces in the scars;
+are they the same in all? If all the
+buds had developed into branches,
+how many would spring from a
+node? Look for the rings of scars
+left by the last season’s bud scales.
+Do you find any twig of more
+than one year’s growth, as measured by the scar rings?</p>
+
+<figure class="figleft illowp15" id="i_145a" style="max-width: 12.5em;">
+  <img class="w100" src="images/i_145a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 154.</span>—Two-forked
+twig of horse-chestnut.</p></figcaption>
+</figure>
+
+<p>Look down between the forks of a branched stem for a
+round scar. This is not a leaf scar, as we can see by its
+shape, but one left by the last season’s
+flower cluster. The flower, as we know,
+dies after perfecting its fruit, and so a
+flower bud cannot continue the growth of
+its axis as other buds do, but has just the opposite
+effect and stops all further growth in
+that direction. Hence, stems and branches
+that end in a flower bud cannot continue
+to develop their main axis, but their growth
+is usually carried on, in alternate-leaved
+stems, by the nearest lateral bud, or in
+opposite-leaved ones, by the nearest pair
+of buds. In the first case there results the zigzag spray
+characteristic of such trees as the beech and elm (<a href="#i_146">Fig. 155</a>,
+<i>B</i>); in the second, the two-forked, or <em>dichotomous</em> branching,<span class="pagenum" id="Page_136">[Pg 136]</span>
+exemplified by the buckeye, horse-chestnut, jimson weed,
+mistletoe, and dogwood (<a href="#i_146">Fig. 155</a>, <i>A</i>).</p>
+
+<p>Draw a diagram of the buckeye, or
+other dichotomous stem, as it would be if
+all the buds developed into branches, and
+compare it with your diagrams of excurrent
+and deliquescent growth. Draw diagrams
+to illustrate the branching of the elm,
+beech, lilac, linden, rose, maple, or their
+equivalents.</p>
+
+<figure class="figleft illowp20" id="i_146" style="max-width: 14.625em;">
+  <img class="w100" src="images/i_146.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 155.</span>—Diagrams
+of two-forked
+branching. The
+pointed bodies in the
+forks shows where terminal
+flower buds or
+flower clusters have
+changed the direction
+of growth.</p></figcaption>
+</figure>
+
+<p id="p-153"><b>153. Definite and indefinite annual
+growth.</b>—The presence or absence of terminal
+buds gives rise to another important
+distinction in plant development—that
+of <em>definite</em> and <em>indefinite</em> annual growth.
+Compare with any of the twigs just
+examined, a branch of rose, honey locust,
+sumac, mulberry, etc., and note the difference
+in their modes of termination. The first kind, where
+the bough completes its season’s increase in a definite time
+and then devotes its energies to developing a strong
+terminal bud to begin the next year’s work with, are said
+to make a <em>definite or determinate annual growth</em>. Those
+plants, on the other hand, which make no provision for
+the future, but continue to grow till the cold comes
+and literally nips them in the bud, are <em>indefinite</em>, or <em>indeterminate</em>
+annual growers. Notice the effect of this habit
+upon their mode of branching. The buds toward the end
+of each shoot, being the youngest and tenderest, are most
+readily killed off by frost or other accident, and hence new
+branches spring mostly from the older and stronger buds
+near the base of the stem. It is their mode of branching that
+gives to plants of this class their peculiar bushy aspect.
+Such shrubs generally make good hedges on account of their
+thick undergrowth. The same effect can be produced artificially
+by pruning.</p>
+
+<p><span class="pagenum" id="Page_137">[Pg 137]</span></p>
+
+<figure class="figright illowp40" id="i_147" style="max-width: 38.5em;">
+  <img class="w100" src="images/i_147.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 156.</span>—A mixed wood in winter, showing
+the trend of the branches.</p></figcaption>
+</figure>
+
+<p id="p-154"><b>154. Differences in the branching of trees.</b>—We are now
+prepared to understand something about the causes of that
+endless variety in the
+spread of bough and
+sweep of woody spray
+that makes the winter
+woods so beautiful.
+Where the terminal bud
+is undisputed monarch
+of the bough, as in the
+pine and fir, or where it
+is so strong and vigorous
+as to overpower its
+weaker brethren and
+keep the lead, as in the
+magnolia, tulip tree, and holly, we have excurrent growth.
+In plants like the oak and apple, where all the buds have
+a more nearly equal chance, the lateral
+branches show more vigor, and the result
+is either deliquescent growth, or a mixture
+of the two kinds. In the elm and beech,
+where the usurping pseudo-terminal bud
+keeps the mastery, but does not completely
+overpower its fellows, we find the long,
+sweeping, delicate spray characteristic of
+those species. Examine a sprig of elm,
+and notice further that the flower buds are
+all down near the base of the stem, while
+the leaf buds are near the tip. The chief
+development of the season’s growth is thus
+thrown toward the end of the branch, giving
+rise to that fine, feathery spray which
+makes the elm an even more beautiful
+object in winter than in summer (<a href="#i_148">Fig. 158</a>).</p>
+
+<p>An examination of the twigs of other trees will bring out the
+various peculiarities that affect their mode of branching. The<span class="pagenum" id="Page_138">[Pg 138]</span>
+angle, for instance, which a twig makes with its bough has a
+great effect in shaping the contour of the tree. Compare in
+this respect the elm and hackberry;
+the tulip tree and willow; ash and hickory.
+As a general thing, acute angles
+produce slender, flowing effects; right
+or obtuse angles, more bold and rugged
+outlines.</p>
+
+<table class='autotable double-image'>
+<tr>
+  <td class='tdc wd60'>
+
+<figure class="figcenter illowp34" id="i_147a" style="max-width: 16.75em;">
+  <img class="w100" src="images/i_147a.jpg" alt="Fig. 157.—Winter
+spray of ash, an opposite-leaved
+tree.">
+</figure>
+</td>
+<td class='tdc wd40'>
+<figure class="figcenter illowp64" id="i_148" style="max-width: 18.75em;">
+  <img class="w100" src="images/i_148.jpg" alt="Fig. 158.—Winter spray
+of elm.">
+</figure>
+</td>
+</tr>
+<tr>
+<td class='tdc captionx'><span class="smcap">Fig. 157.</span>—Winter
+spray of ash, an opposite-leaved
+tree.</td>
+<td class='tdc caption'><span class="smcap">Fig. 158.</span>—Winter spray
+of elm.</td>
+</tr>
+</table>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Has the arrangement of leaves on a twig
+anything to do with the way a tree is branched?
+(<a href="#p-145">145</a>, <a href="#p-151">151</a>, <a href="#p-152">152</a>.)</p>
+
+<p>2. Why do most large trees tend to assume
+the excurrent, or axial, mode of growth if let
+alone? (<a href="#p-150">150</a>, <a href="#p-154">154</a>.)</p>
+
+<p>3. If you wished to alter the mode of growth, or to produce what nurserymen
+call a low-headed tree, how would you prune it? (<a href="#p-152">152</a>, <a href="#p-153">153</a>.)</p>
+
+<p>4. Would you top a timber tree? (<a href="#p-152">152</a>, <a href="#p-153">153</a>.)</p>
+
+<p>5. Are low-headed or tall trees best for an orchard? Why?</p>
+
+<p>6. Why is the growth of annuals generally indefinite?</p>
+
+<p>7. Name some trees of your neighborhood that are conspicuous for
+their graceful winter spray.</p>
+
+<p>8. Name some that are characterized by sharpness and boldness of outline.</p>
+
+<p>9. Account for the peculiarities in each case.</p>
+</div>
+
+
+<h3 id="CH_V_II">II. BUDS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Expanding leaf and flower buds in different stages of
+development; large ones show the parts best and should be used where
+attainable. Some good examples for the opposite arrangement are
+horse-chestnut, maple, lilac, ash; for the alternate: hickory, sweet gum,
+balsam poplar, beech, elm. Where material is scarce, the twigs used in the
+last section may be placed in water and kept till the buds begin to expand.</p>
+</div>
+
+<p id="p-155"><b>155. Folding of the leaves.</b>—Remove the scales from a
+bud of horse-chestnut nearly ready to open, and notice the
+manner in which the young leaves are folded. This is called
+<em>vernation</em>, or <em>prefoliation</em>, words meaning respectively “spring
+condition” and “condition preceding the leaf.” Leaves
+are packed in the bud so as to occupy the least space possible,
+and in different plants they will be found folded in a great<span class="pagenum" id="Page_139">[Pg 139]</span>
+many different ways, according to the shape
+and texture of the leaf and
+the space available for it in
+the bud. When doubled back
+and forth like a fan, or crumpled
+and folded as in the
+buckeye, horse-chestnut, and
+maple, the vernation is <em>plicate</em>
+(<a href="#i_149b">Figs. 160</a>, <a href="#i_149a">162</a>).</p>
+
+<table class='double-image autotable'>
+<tr>
+<td class='tdc'>
+<figure class="figcenter illowp40" id="i_149" style="max-width: 16.5em;">
+  <img class="w100" src="images/i_149.jpg" alt="Fig. 159.—Expanding
+bud of English walnut,
+showing twice conduplicate
+vernation.">
+</figure>
+</td>
+<td class='tdc'>
+<figure class="figcenter illowp25" id="i_149b" style="max-width: 9.75em;">
+  <img class="w100" src="images/i_149b.jpg" alt="Fig. 160.—A
+partly expanded
+leaf of beech,
+showing plicate-conduplicate
+vernation.">
+</figure>
+</td></tr>
+<tr>
+<td class='tdl caption'><p><span class="smcap">Fig. 159.</span>—Expanding
+bud of English walnut,
+showing twice conduplicate
+vernation.</p></td>
+<td class='tdl caption'><p><span class="smcap">Fig. 160.</span>—A
+partly expanded
+leaf of beech,
+showing plicate-conduplicate
+vernation.</p></td>
+</tr>
+</table>
+
+<p id="p-156"><b>156. Position of the flower
+cluster.</b>—What do you find
+within the circle of leaves?
+Examine one of the smaller
+axillary buds, and see if you find the same object within it.
+If you are in any doubt as to what this object is, examine
+a bud that is more expanded, and you will have no difficulty
+in recognizing it as a rudimentary flower
+cluster. Notice its position with reference
+to the scales and leaves. If at the
+center of the bud, it will, of course, terminate
+its axis when the
+bud expands, and the
+growth of the branch
+will culminate in the
+flower. The branching
+of any kind of stem
+that bears a central
+flower cluster must,
+then, be of what order?
+Compare your drawings
+with the section of
+a hyacinth bulb or
+jonquil, and note the
+similarity in position
+of the flower clusters.
+In a bud of the hickory,<span class="pagenum" id="Page_140">[Pg 140]</span>
+walnut, oak, etc., the position of the
+flower clusters is different from that of
+flowers in the buds of lilac and horse-chestnut.
+Look for a bud containing them, and
+find out where they occur. Can the axis continue
+to grow after flowering, in this kind of
+stem? Give a reason for your answer. Make
+sketches in transverse and longitudinal section
+(see <a href="#i_149a">Figs. 162</a>, <a href="#i_149c">163</a>) of two different
+kinds of buds, illustrating the terminal and
+axillary position of the flower cluster.</p>
+
+<table class='autotable double-image'>
+<tr><td class='tdc'>
+<figure class="figcenter illowp30" id="i_149a" style="max-width: 20em;">
+  <img class="w100" src="images/i_149a.jpg" alt="Figs. 161, 162.</span>—Buds
+of maple: 161, vertical
+section of a twig; 162,
+cross section through
+bud, showing folded
+leaves in center and scales
+surrounding them.">
+</figure>
+</td><td class='tdc'>
+<figure class="figcenter illowp40" id="i_149c" style="max-width: 20em;">
+  <img class="w100" src="images/i_149c.jpg" alt="Fig. 163.</span>—Vertical
+section of hickory
+bud: <i>a</i>, furry inner
+scales; <i>b</i>, outer
+scales; <i>l</i>, folded leaf;
+<i>r</i>, receptacle.">
+</figure>
+</td></tr>
+<tr>
+<td class='tdl caption'><p><span class="smcap">Figs. 161, 162.</span>—Buds
+of maple: 161, vertical
+section of a twig; 162,
+cross section through
+bud, showing folded
+leaves in center and scales
+surrounding them.</p></td>
+<td class='tdl caption'><p><span class="smcap">Fig. 163.</span>—Vertical
+section of hickory
+bud: <i>a</i>, furry inner
+scales; <i>b</i>, outer
+scales; <i>l</i>, folded leaf;
+<i>r</i>, receptacle.</p></td>
+</tr>
+</table>
+
+<p id="p-157"><b>157. Dormant buds.</b>—A bud may often
+lie dormant for months or even years, and
+then, through the injury or destruction of its
+stronger rivals, or some other favoring cause,
+develop into a branch. Such buds are said
+to be <em>latent</em> or <em>dormant</em>. The sprouts that
+often put up from the stumps of felled trees
+originate from this source.</p>
+
+<figure class="figright illowp29" id="i_150" style="max-width: 25em;">
+  <img class="w100" src="images/i_150.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 164.</span>—Twig
+of red maple, showing
+supernumerary
+bud, <i>b</i>; <i>rs</i>, ring of
+scars left by last
+year’s bud scales.
+(<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p id="p-158"><b>158. Supernumerary buds.</b>—Where more
+than one bud develops at a node, as is so
+often the case in the oak, maple, honey
+locust, etc., all except the normal one in the
+axil are <em>supernumerary</em> or <em>accessory</em>. These must not be confounded
+with <em>adventitious</em> buds—those that occur elsewhere
+than at a node.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Would protected buds be of any use to annuals? Why, or why not?</p>
+
+<p>2. Of what use is the gummy coating found on the buds of the horse-chestnut
+and balm of Gilead? (<a href="#p-148">148</a>.)</p>
+
+<p>3. Can you name any plants the buds of which serve as food for man?</p>
+
+<p>4. How do flower buds differ in shape from leaf buds?</p>
+
+<p>5. At what season can the leaf bud and the flower bud first be distinguished?
+Is it the same for all flowering plants?</p>
+
+<p>6. Watch the different trees about your home, and see when the buds
+that are to develop into leaves and flowers the next season are formed in
+each species.</p>
+</div>
+
+<p><span class="pagenum" id="Page_141">[Pg 141]</span></p>
+
+
+<h3 id="CH_V_III">III. THE BRANCHING OF FLOWER STEMS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Typical flower clusters illustrating the definite and
+indefinite modes of inflorescence. Some of those mentioned in the text
+are:—</p>
+
+<p>Indefinite: hyacinth, shepherd’s purse, wallflower, carrot, lilac, blue
+grass, smartweed (<i>Polygonum</i>), wheat, oak, willow, clover.</p>
+
+<p>Definite: chickweed, spurge (<i>Euphorbia</i>), comfrey, dead nettle, etc.
+Any examples illustrating the principal kinds of cluster will answer.</p>
+</div>
+
+<p id="p-159"><b>159. Inflorescence</b> is a term
+used to denote the position and
+arrangement of flowers on the
+stem. It is merely a mode of
+branching, and follows the same
+laws that govern the branching
+of ordinary stems.</p>
+
+<p>The stalk that bears a flower
+is called the <em>peduncle</em>. In a
+cluster the main axis is the common
+peduncle, and the separate
+flower stalks are <em>pedicels</em>. A simple
+leafless flower stalk that rises
+directly from the ground, like
+those of the dandelion and daffodil,
+is called a <em>scape</em> (<a href="#i_151">Fig. 165</a>).</p>
+
+
+<table class='autotable'>
+<tr>
+<td class='tdc'>
+<figure class="figcenter illowp50" id="i_151" style="max-width: 37em;">
+  <img class="w100" src="images/i_151.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 165.</span>—Solitary terminal
+flower of a lily.</p></figcaption>
+</figure>
+</td><td class='tdc'>
+<figure class="figcenter illowp100" id="i_151a" style="max-width: 19.5em;">
+  <img class="w100" src="images/i_151a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 166.</span>—Indeterminate
+inflorescence of moneywort.
+(<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+</td></tr></table>
+
+<p id="p-160"><b>160. Two kinds of inflorescence.</b>—The
+growth of flower stems, like that of leaf stems,
+is of two principal kinds, definite and
+indefinite, or, as it is frequently expressed,
+determinate and indeterminate.
+The simplest kind of each is
+the solitary, a single flower either
+terminating the main axis, as the
+tulip, daffodil, trillium, magnolia,
+etc., or springing singly from the axils, as the running periwinkle,
+moneywort, and cotton.</p>
+
+<p><span class="pagenum" id="Page_142">[Pg 142]</span></p>
+
+<table class='autotable'>
+<tr>
+<td class='wd50'>
+<figure class="figcenter illowp50" id="i_152" style="max-width: 30.9375em;">
+  <img class="w100" src="images/i_152.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 167.</span>—Raceme
+of milk vetch (<i>Astragalus</i>).</p></figcaption>
+</figure>
+</td><td class='wd50'>
+<figure class="figcenter illowp100" id="i_152a" style="max-width: 25em;">
+  <img class="w100" src="images/i_152a.jpg" alt="">
+  <figcaption><p class='center'><span class="smcap">Fig, 168.</span>—Catkins of aspen.</p></figcaption>
+</figure>
+</td></tr></table>
+
+<p id="p-161"><b>161. Indeterminate inflorescence</b> is always axillary,
+since the production of a terminal flower would stop further
+growth in that direction and thus terminate the development
+of the axis. The <em>raceme</em> is the typical
+flower cluster of the indefinite sort. In
+such an arrangement the oldest flowers
+are at the lower nodes, new ones appearing
+only as the axis lengthens and produces
+new internodes. The little scale or
+<em>bract</em> usually found at the base of the pedicel
+in flower clusters of this sort is a reduced
+leaf, and the fact that the flower
+stalk springs from the axil shows it to be
+of the essential nature of a branch.
+When the flowers are sessile and crowded
+on the axis in various degrees, the cluster
+produced may be a <em>spike</em>, as seen in the
+plantain, knotweed, etc., or a <em>head</em>, like
+that of the clover, buttonwood, and sycamore.
+The <em>catkins</em> that form the characteristic inflorescence
+of most of our forest trees are merely pendant spikes. The
+<em>corymb</em> is a modification
+of the raceme in which
+the lower pedicels are
+elongated so as to place
+their flowers on a level
+with those of the upper
+nodes, making a convex,
+or more or less flat-topped
+cluster, as in the
+wallflower and hawthorn.
+The <em>umbel</em> differs
+from the corymb in
+having the pedicels with
+their bracts all gathered
+at the top of the peduncle,<span class="pagenum" id="Page_143">[Pg 143]</span>
+from which they spread in every direction like the
+rays of an umbrella, as the name implies. This is the prevalent
+type of flower cluster in the parsley family, which takes
+its botanical name, <i>Umbelliferæ</i>, from
+its characteristic
+form of inflorescence.
+The pedicels
+of an umbel
+are called <em>rays</em>, and
+the circle of bracts
+at the base of the
+cluster is an <em>involucre</em>.</p>
+
+<table class='autotable'>
+<tr>
+<td class='wd50'>
+<figure class="figcenter illowp60" id="i_153" style="max-width: 20em;">
+  <img class="w100" src="images/i_153.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 169.</span>—Corymb
+of plum blossoms.</p></figcaption>
+</figure>
+</td><td class='wd50'>
+<figure class="figcenter illowp60" id="i_153a" style="max-width: 20em;">
+  <img class="w100" src="images/i_153a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 170.</span>—Umbel of milkweed.</p></figcaption>
+</figure>
+</td>
+</tr><tr>
+<td>
+<figure class="figcenter illowp60" id="i_153b" style="max-width: 18em;">
+  <img class="w100" src="images/i_153b.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 171.</span>—Panicle
+of grass, a compound
+cluster of the racemose
+type.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp60" id="i_153c" style="max-width: 20em;">
+  <img class="w100" src="images/i_153c.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 172.</span>—Flat-topped
+cyme of sneezeweed.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-162"><b>162. Determinate,
+or cymose,
+inflorescence.</b>—In the <em>cyme</em>, the typical cluster of the determinate
+kind, the older blossoms in the center, being terminal,
+stop the axis of growth in that direction and force the
+stem, in continuing its growth, to send out side branches
+from the axils of the topmost leaves, in
+a manner precisely
+similar to the two-forked
+branching of
+stems like the horse-chestnut
+and jimson
+weed. When the older
+peduncles are lengthened
+as described in
+<a href="#p-161">161</a>, a flat-topped cyme
+is produced, which is
+distinguished from the
+corymb by its order of
+flowering, the oldest
+blossoms being at the
+center, while in the corymb they appear in the reverse
+order. A peculiar form of cyme is found in the scorpioid<span class="pagenum" id="Page_144">[Pg 144]</span>
+or coiled inflorescence of the pink-root (<i>Spigelia</i>), heliotrope,
+comfrey, etc. Its structure will be made clear by an inspection
+of <a href="#i_154a">Figs. 174-176</a>.</p>
+
+<figure class="figcenter illowp60" id="i_154" style="max-width: 50em;">
+  <img class="w100" src="images/i_154.jpg" alt="">
+  <figcaption><p class='center'><span class="smcap">Fig. 173.</span>—Scorpioid cyme.</p></figcaption>
+</figure>
+
+<p id="p-163"><b>163. The nature of flower stems.</b>—A comparison of
+the types of inflorescence with the modes of branching in
+ordinary stems (<a href="#p-144">144</a>, <a href="#p-152">152</a>, <a href="#p-153">153</a>) will show a strict correspondence
+between them. Both bear leaves and buds, and
+the individual flowers of a cluster usually spring from the<span class="pagenum" id="Page_145">[Pg 145]</span>
+axils of leaves or from bracts, which are merely reduced
+leaves. What, then, is the essential nature of flower stems?</p>
+
+<figure class="figcenter illowp80" id="i_154a" style="max-width: 50em;">
+  <img class="w100" src="images/i_154a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 174-176.</span>—Diagrams of cymose inflorescence, with flowers numbered in the
+order of their development: 174, cyme half developed (scorpioid); 175, a flat-topped
+or corymbose cyme; 176, development of a typical cyme.</p></figcaption>
+</figure>
+
+<p id="p-164"><b>164. Significance of the clustered arrangement.</b>—As a
+general thing the clustered arrangement marks a higher stage
+of development than the solitary, just as in human life the
+rudest social state is a distinct advance upon the isolated
+condition of the savage. In plant life it is the beginning of
+a system of coöperation and division of labor among the associated
+members of the flower cluster, as will be seen later
+when we take up the study of the flower.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Name as many solitary flowers as you can think of.</p>
+
+<p>2. Do you, as a rule, find very small flowers solitary, or in clusters?</p>
+
+<p>3. Would the separate flowers of the clover, parsley, or grape be readily
+distinguished by the eye among a mass of foliage?</p>
+
+<p>4. Should you judge from these facts that it is, in general, advantageous
+to plants for their flowers to be conspicuous?</p>
+</div>
+
+
+<h4 id="CH_V_FIELD">Field Work</h4>
+
+<div class="blockquot">
+
+<p>(1) In connection with <a href="#p-144">144-154</a>, the characteristic modes of branching
+among the common trees and shrubs of each neighborhood should be
+observed and accounted for. The naked branches of the winter woods
+afford exceptional opportunities for studies of this kind, which cannot
+well be carried on except out of doors. Note the effect of the mode of
+branching upon the general outline of the tree; compare the direction and
+mode of growth of the larger boughs with that of small twigs in the same
+species, and see if there is any general correspondence between them; note
+the absence of fine spray on the boughs of large-leaved trees, and account
+for it. Account for the flat sprays of trees like the elm, beech, hackberry,
+etc.; the irregular stumpy branches of the oak and walnut; the stiff
+straight twigs of the ash; the zigzag switches of the black locust, Osage
+orange, elm, and linden. Measure the twigs on various species, and see
+if there is any relation between the length and thickness of branches.
+Notice the different trend of the upper, middle, and lower boughs in most
+trees, and account for it. Observe the mode of branching of as many
+different species as possible of some of the great botanical groups of trees;
+the oaks, hickories, hawthorns, and pines, for instance, and notice whether
+it is, as a general thing, uniform among the species of the same group, and
+how it differs from that of other groups.</p>
+
+<p><span class="pagenum" id="Page_146">[Pg 146]</span></p>
+
+<p>(2) In connection with <a href="#p-155">155-158</a>, buds of as many different kinds as
+possible should be examined with reference to their means of protection,
+their vernation and leaf arrangement, and the resulting modes of growth.
+Compare the folding of the cotyledons in the seed with the vernation of
+the same plants, and observe whether the folding is the same throughout
+a whole group of related plants, or only for the same species. Notice which
+modes seem to be most prevalent. Select a twig on some tree near your
+home or your schoolhouse, and keep a record of its daily growth from the
+first sign of the unfolding of its principal bud to the full development of
+its leaves. Any study of buds should include an observation of them in
+all stages of development.</p>
+
+<p>(3) With <a href="#p-160">160-165</a>, study the inflorescence of the common plants and
+weeds that happen to be in season, until you have no difficulty in distinguishing
+between the definite and indefinite sorts, and can refer any
+ordinary cluster to its proper form. Notice whether there is any tendency
+to uniformity in the mode of inflorescence among flowers of the same family.
+Consider how each kind is adapted to the shape and habit of the
+flowers composing it, and what particular advantage each of the specimens
+examined derives from the way its flowers are clustered. In cases of mixed
+inflorescence, see if you can discover any reason for the change from one
+form to the other.</p>
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_147">[Pg 147]</span></p>
+
+<h2 class="nobreak" id="CH_VI">CHAPTER VI. THE LEAF</h2>
+</div>
+
+
+<h3 id="CH_VI_I">I. THE TYPICAL LEAF AND ITS PARTS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Leaves of different kinds showing the various modes of
+attachment, shapes, texture, etc. For stipules, leaves on very young
+twigs should be selected, as these bodies often fall away soon after the
+leaves expand. The rose, Japan quince, willow, strawberry, pea, pansy,
+and young leaves of beech, apple, elm, tulip tree, India rubber tree,
+magnolia, knotweed, furnish good examples of stipules. For the different
+orders of leaf arrangement, lilac, maple, spurge, trillium, cleavers (Galium)
+show the opposite and whorled kinds. Elm, basswood, grasses; alder,
+birch, sedges; peach, apple, cherry, show respectively for each group the
+three principal orders of alternate arrangement.</p>
+</div>
+
+<p id="p-165"><b>165. Parts of the leaf.</b>—Examine a young, healthy leaf
+of apple, quince, or elm, as it stands upon the stem, and
+notice that it consists of three parts: a
+broad expansion called the <em>blade</em>; a leaf
+stalk or <em>petiole</em> that attaches it to the
+stem; and two little leaflike or bristle-like
+bodies at the base, known
+as <em>stipules</em>. Make a
+sketch of any leaf provided
+with all these parts,
+and label them, respectively,
+blade, petiole, and
+stipules. These three parts make up a perfect
+or typical leaf, but as a matter of fact,
+one or more of them is usually wanting.</p>
+
+<table class='autotable'>
+<tr>
+<td>
+<figure class="figcenter illowp70" id="i_157" style="max-width: 15.75em;">
+  <img class="w100" src="images/i_157.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 177.</span>—A typical
+leaf and its parts:
+<i>b</i>, blade; <i>p</i>, petiole;
+<i>s</i>, <i>s</i>, stipules.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp60" id="i_157a" style="max-width: 12.5em;">
+  <img class="w100" src="images/i_157a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 178.</span>—Spiny
+stipules of clotbur.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-166"><b>166. Stipules.</b>—The office of stipules,
+when present, is generally to subserve in
+some way the purposes of protection. In many cases, as in
+the fig, elm, beech, oak, magnolia, etc., they appear only as
+protective scales that cover the bud during winter, and fall<span class="pagenum" id="Page_148">[Pg 148]</span>
+away as soon as the leaf expands. When <em>persistent</em>, that is,
+enduring, they take various forms according to the purposes
+they serve. But under whatever guise they occur, their
+true nature may be recognized by their position on each side
+of the base of the petiole, and not in the <em>axil</em>, or angle formed
+by the leaf with the stem. (<a href="#p-149">149</a>.)</p>
+
+<table class='autotable'>
+<tr>
+<td class='vat'>
+<figure class="figcenter illowp70" id="i_158a" style="max-width: 31.5625em;">
+  <img class="w100" src="images/i_158a.jpg" alt="">
+  <figcaption>
+    <span class="smcap">Fig. 179.</span>—Adnate
+    stipules of clover.
+  </figcaption>
+</figure>
+</td><td class='vat'>
+<figure class="figcenter illowp70" id="i_158b" style="max-width: 30.25em;">
+  <img class="w100" src="images/i_158b.jpg" alt="">
+  <figcaption>
+    <span class="smcap">Fig. 180.</span>—Leaves of smilax, showing stipular tendrils.
+  </figcaption>
+</figure>
+</td><td class='wd33 vat'>
+<figure class="figcenter illowp70" id="i_158c" style="max-width: 25.125em;">
+  <img class="w100" src="images/i_158c.jpg" alt="">
+  <figcaption>
+    <span class="smcap">Fig. 181.</span>—Leafy stipules of Japan quince.
+  </figcaption>
+</figure></td></tr></table>
+
+
+<p id="p-167" class='cb'><b>167. Leaf attachment.</b>—The normal use of the petiole is
+to secure a better light exposure for the leaves, but, like other
+parts, it is subject to modifications, and is often wanting
+altogether. In this case the leaf is said to be <em>sessile</em>, that is,
+<em>seated</em>, on the stem, and the leaf bases are designated by
+various terms descriptive of their mode of attachment. The
+meaning of these terms, when not self-explanatory, can best
+be learned by a comparison of living specimens with <a href="#i_159">Figs.
+184-187</a>.</p>
+
+<p id="p-168"><b>168. Arrangement of leaves on the stem.</b>—The mode
+of attachment is something quite distinct from the mode of
+leaf arrangement on the stem, or <em>phyllotaxy</em>, as it is termed
+by botanists. It was seen in <a href="#p-148">148</a> that this takes place in two
+different ways, the alternate and opposite. These two kinds
+of arrangement represent the principal forms of leaf disposition<span class="pagenum" id="Page_149">[Pg 149]</span>
+on the stem, the different varieties of each depending on
+the manner in which the leaves are distributed.</p>
+
+<figure class="figcenter illowp70" id="i_159" style="max-width: 99.7em;">
+  <img class="w100" src="images/i_159.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 182-187.</span>—Petioles, and leaf attachment: 182, petioles of jasmine nightshade
+(<i>Solanum jasminoides</i>) acting as tendrils; 183, acacia, showing petiole
+transformed to leaf blade; 184, sessile leaves of epilobium; 185, clasping leaf of
+lactuca; 186, perfoliate leaves of uvularia; 187, peltate leaf of tropæolum. (182 and
+186 <i>after</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p>Where three or more occur at a node, as in the trillium
+and cleavers (<i>Galium</i>), they constitute a whorl, which is only
+a variant of the opposite arrangement. There is no limit to
+the number of leaves that may be in a whorl except the space
+around the stem to accommodate them.</p>
+
+<p>The phyllotaxy of alternate leaves is more complicated.<span class="pagenum" id="Page_150">[Pg 150]</span>
+The different forms are characterized by
+the angular distance between the points
+of leaf insertion around the stem. In the
+elm, basswood, and most grasses, they are
+distributed in two rows or ranks on opposite
+sides of the stem, each just half
+way round the circumference from the
+one next in succession (<a href="#i_160a">Fig. 189</a>), the
+third in vertical order standing directly
+over the first. In most of our common
+trees and shrubs five leaves are passed
+in making two turns round the stem,
+the sixth leaf in vertical order standing
+over the first. This is called the five-ranked arrangement,
+and is the most
+common order among
+dicotyls.</p>
+
+<table class='autotable'>
+<tr><td>
+<figure class="figcenter illowp55" id="i_160" style="max-width: 29.5em;">
+  <img class="w100" src="images/i_160.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 188.</span>—Whorled
+leaves of Indian cucumber.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp55" id="i_160a" style="max-width: 60.8em;">
+  <img class="w100" src="images/i_160a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 189.</span>—Twig of a hackberry (<i>Celtis cinerea</i>),
+showing the two-ranked arrangement. Notice how
+the position of the stems and branches of the main
+axis corresponds to that of the leaves.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-169"><b>169. Relation between
+the shape and
+arrangement of leaves.</b>—Phyllotaxy
+is of importance
+chiefly on account
+of its influence
+on the light relation of
+leaves. A compact,
+close-ranked arrangement
+tends to shut off
+the light from the lower
+nodes, and hence, in
+plants where it prevails,
+the leaves are apt
+to be long and narrow
+in proportion to the
+frequency of the vertical
+rows. The yucca,
+oleander, Canada fleabane
+and bitterweed (<i>Helenium
+tenuifolium</i>), illustrate this relation.</p>
+
+<p><span class="pagenum" id="Page_151">[Pg 151]</span></p>
+
+<figure class="figcenter illowp75" id="i_161" style="max-width: 50em;">
+  <img class="w100" src="images/i_161.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 9.</span>—Vegetation of a moist, shady ravine. Notice the expanded surface of
+the leaf blades and the long internodes that separate the individual leaves. (From
+Rep’t. Mo. Botanical Garden.)</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_152">[Pg 152]</span></p>
+
+<figure class="figright illowp30" id="i_162" style="max-width: 24.625em;">
+  <img class="w100" src="images/i_162.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 190.</span>—Narrow leaves
+in crowded vertical rows.</p></figcaption>
+</figure>
+
+<p>On the other hand, when the leaves
+are large and rounded in outline, as
+those of the sunflower, hollyhock, and
+catalpa, they are usually separated
+by longer internodes, or their blades
+are cut and incised so that the sunlight
+easily strikes through to the
+lower ones.</p>
+
+<p id="p-170"><b>170. Other external characteristics</b>
+to be observed in leaves are:—</p>
+
+<p>(1) General Outline: whether round, oval, heart-shaped,
+etc. (<a href="#i_162a">Figs. 191-197</a>).</p>
+
+<p>(2) Margins: whether unbroken (<em>entire</em>), or variously
+toothed and indented. (<a href="#i_163">Figs. 198-202</a>.)</p>
+
+<p>(3) Texture: whether thick, thin, soft, hard, fleshy,
+leathery, brittle.</p>
+
+<p>(4) Surface: smooth, shining, dull, wrinkled, hairy, or
+otherwise roughened.</p>
+
+<figure class="figcenter illowp75" id="i_162a" style="max-width: 50em;">
+  <img class="w100" src="images/i_162a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 191-197.</span>—Shapes of leaves: 191, lanceolate; 192, spatulate; 193, oval;
+194, obovate; 195, kidney-shaped; 196, deltoid; 197, lyrate. (191-195 <i>after</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_153">[Pg 153]</span></p>
+
+<p>Not only do leaves of different
+kinds exhibit these characteristics
+in varying degrees, but young and
+old leaves, or those on young and
+old plants of the same kind, often
+differ from each other in color, size,
+shape, texture, mode of attachment,
+and the like, to such a degree (<a href="#i_163a">Figs.
+203, 204</a>) that one not familiar
+with them in both stages would
+hardly recognize them as belonging to the same species.
+The young leaves
+of eucalyptus, mulberry,
+and some oaks
+afford conspicuous
+examples of such
+differences, and they
+exist between the
+cotyledons and mature
+leaves of most
+plants.</p>
+
+<p>Can you see any
+benefit, in the case
+of the plant whose
+leaves you are studying,
+that could be
+derived from such of
+the characteristics
+named above as
+they may exhibit?</p>
+
+<table class='autotable'>
+<tr><td class='tdc wd50'>
+<figure class="figcenter illowp60" id="i_163" style="max-width: 21.75em;">
+  <img class="w100" src="images/i_163.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 198-202.</span>—Margins of
+leaves: 198, serrate; 199, dentate;
+200, crenate; 201, undulate;
+202, sinuate. (<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+</td><td class='tdc wd50'>
+<figure class="figcenter illowp60" id="i_163a" style="max-width: 54.75em;">
+  <img class="w100" src="images/i_163a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 203, 204.</span>—Leaves of paper mulberry tree:
+203, leaf from an old tree; 204, leaf from a two-year-old
+sprout.</p></figcaption>
+</figure></td></tr></table>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Tell the nature and use of the stipules in such of the following plants
+as you can find: tulip tree; fig; beech; apple; willow; pansy; garden
+pea; Japan quince (<i>Pyrus Japonica</i>); sycamore; rose; paper mulberry
+(<i>Broussonetia</i>).</p>
+
+<p><span class="pagenum" id="Page_154">[Pg 154]</span></p>
+
+<p>2. How would you distinguish between a chinquapin, a chestnut, a
+chestnut oak, and a horse-chestnut tree by their leaves alone? By their
+bark and branches? Between a hickory, ash, common elder, box elder,
+ailanthus, sumach? Between beech, birch, elm, hackberry, alder?</p>
+
+<p>(Any other sets of leaves may be substituted for those named, the object
+being merely to form the habit of distinguishing readily the differences
+and resemblances among those that bear some general likeness to one
+another.)</p>
+
+<p>3. From the study of these or similar specimens, would you conclude
+that resemblances in leaves are confined to those of closely related kinds?</p>
+
+<p>4. Name some causes independent of botanical relationship that might
+influence them. (<a href="#p-169">169</a>, <a href="#p-170">170</a>; <a href="#exp-48">Exps. 48</a>, <a href="#exp-57">57</a>.)</p>
+
+<p>5. Do you find, as a general thing, more leaves with stipules or without?</p>
+
+<p>6. Is their absence from a mature leaf always a sign that it is really
+exstipulate? (<a href="#p-166">166</a>.)</p>
+
+<p>7. Can you trace any line of development through intervening forms
+from a merely sessile leaf, like that of the pimpernel or specularia, to a
+peltate one? (<a href="#i_159">Figs. 184-187</a>, and observation of living specimens.)</p>
+
+<p>8. Does the leaf determine the position of the node, or the node the
+position of the leaf?</p>
+
+<p>9. Strip the leaves from a twig of one order of arrangement and replace
+them with foliage from a twig of a different order; for instance, place
+basswood upon white oak, birch upon lilac, elm upon pear, honeysuckle
+upon barberry, etc. Is the same amount of surface exposed as in the
+natural order?</p>
+
+<p>10. What disadvantage would it be to a plant if the leaves were arranged
+so that they stood directly over one another? (<a href="#p-169">169</a>.)</p>
+
+<p>11. Why are the internodes of vigorous young shoots, or scions, generally
+so long? (<a href="#p-150">150</a>.)</p>
+
+<p>12. If the upward growth of a stem or branch is stopped by pruning,
+what effect is produced upon the parts below, and why? (<a href="#p-152">152</a>, <a href="#p-153">153</a>.)</p>
+
+<p>13. Give some of the reasons why corn grows so small and stunted when
+sown broadcast for forage? (<a href="#p-60">60</a>, <a href="#p-63">63</a>, <a href="#p-169">169</a>.)</p>
+
+<p>14. What is the use of “chopping” (<i>i.e.</i> thinning out) cotton?</p>
+</div>
+
+
+<h3 id="CH_VI_II">II. THE VEINING AND LOBING OF LEAVES</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Leaves of any monocotyl and dicotyl will show the difference
+between parallel and net-veining. To illustrate the palmate and
+pinnate kinds, the leaves of grasses and arums may be used for monocotyls,
+and for dicotyls, those of ivy, maple, grape, elm, peach, cherry, etc.; for
+division, examine lobed and compound leaves of as many kinds as are
+attainable. A specimen showing each kind of veining should be placed in<span class="pagenum" id="Page_155">[Pg 155]</span>
+coloring fluid a short time before the lesson begins. The leafstalks of
+celery and plantain are excellent for showing the relation between the leaf
+veins and vascular system of the plant.</p>
+</div>
+
+<p id="p-171"><b>171. Parallel and net veining.</b>—Compare a leaf of the
+wandering Jew, lily, or any kind of grass, with one of grape,
+ivy, or willow. Hold each up to the light,
+and note the veins or little threads of woody
+substance that run through it. Make a drawing
+of each so as to show plainly the direction
+and manner of veining. Write under the
+first, <em>parallel-veined</em>, and under the second,
+<em>net-veined</em>. This distinction of leaves into
+parallel and net-veined corresponds
+with the two great
+classes into which seed-bearing
+plants are divided, monocotyls,
+as a general thing,
+being characterized by the
+first kind, and dicotyls by
+the second.</p>
+
+<table class='autotable'>
+<tr><td>
+<figure class="figcenter illowp60" id="i_165" style="max-width: 17.25em;">
+  <img class="w100" src="images/i_165.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 205.</span>—Parallel-veined
+leaf of
+lily of the valley
+(<i>After</i> <span class="smcap">Gray</span>).</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp60" id="i_165a" style="max-width: 17.75em;">
+  <img class="w100" src="images/i_165a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 206.</span>—Net-veined
+leaf of a willow.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp60" id="i_165b" style="max-width: 16.75em;">
+  <img class="w100" src="images/i_165b.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 207.</span>—Pinnately
+parallel-veined
+leaf of calla
+lily (<i>After</i> <span class="smcap">Gray</span>).</p></figcaption>
+</figure></td></tr></table>
+
+<figure class="figright illowp30" id="i_166" style="max-width: 27.75em;">
+  <img class="w100" src="images/i_166.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 208.</span>—Palmately net-veined
+leaf of wild ginger.</p></figcaption>
+</figure>
+
+
+<p id="p-172"><b>172. Pinnate and palmate veining.</b>—Next,
+compare a leaf of the canna, calla lily,
+or any kind of arum, with one of the elm,
+peach, cherry, etc. What resemblances do
+you notice between the two? What differences?
+Which is parallel-veined and which
+is net-veined? Make a drawing of each, and
+compare with the first two. Notice that in
+leaves of this kind, the petiole is continued
+in a large central vein, called the <em>midrib</em>,
+from which the secondary veins branch off
+on either side like the pinnæ of a feather;
+whence such leaves are said to be <em>pinnately</em>,
+or <em>feather</em> veined, as in <a href="#i_165a">Figs. 206</a>, <a href="#i_165b">207</a>. In
+the cotton, maple, ivy, etc., on the other
+hand, the petiole breaks up at the base of the<span class="pagenum" id="Page_156">[Pg 156]</span>
+leaf (<a href="#i_166">Fig. 208</a>) into a number of primary veins or ribs, which
+radiate in all directions like the fingers from the palm of the
+hand; hence, such a leaf is said to be <em>palmately</em> veined.
+Net-veined leaves—the plantain
+(<a href="#i_166a">Fig. 209</a>), wild smilax, beech, dogwood—are
+sometimes ribbed in a
+way that might lead an inexperienced
+observer to confound them
+with parallel-veined ones, but the
+reticulations between the ribs show
+that they belong to the net-veined
+class.</p>
+
+<figure class="figright illowp20" id="i_166a" style="max-width: 20em;">
+  <img class="w100" src="images/i_166a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 209.</span>—Ribbed
+leaf of plantain.</p></figcaption>
+</figure>
+
+<p id="p-173"><b>173. Veins as a mechanical support.</b>—Hold
+up a stiff, firm leaf of any kind, like the magnolia,
+holly, or India rubber, to the light, having first scraped
+away a little of the under surface, and examine it with a lens.
+Compare it with one of softer texture, like
+the peach, maple, or clover. In which are
+the veins the closer and stronger? Which
+is the more easily torn and wilted? Tear a
+blade of grass longitudinally and then cross-wise;
+in which direction does it give way
+the more readily? Tear apart gently a leaf
+of maple, or ivy, and one of elm or other
+pinnately veined plant; in which direction
+does each give way with least resistance?
+What would you judge from these facts as
+to the mechanical use of the veins?</p>
+
+<p id="p-174"><b>174. Effect upon shape.</b>—By comparing
+a number of leaves of each kind it will be seen that the
+feather-veined ones tend to assume elongated outlines (<a href="#i_162a">Figs.
+197</a>, <a href="#i_165b">207</a>); the palmate-veined ones, broad and rounded forms
+(<a href="#i_162a">Figs. 195</a>, <a href="#i_166">208</a>). Notice also that the straight, unbroken
+venation of parallel-veined leaves is generally accompanied by
+smooth, unbroken margins, while the irregular, open meshes
+of net-veined leaves are favorable to breaks and indentations.</p>
+
+<p><span class="pagenum" id="Page_157">[Pg 157]</span></p>
+
+<p id="p-175"><b>175. Veins as water carriers.</b>—Examine a leaf from a
+stem that has stood in red ink for an hour or two. Do you
+see evidence that it has absorbed any of the liquid? Cut
+across the blade and examine with a lens. What course has
+the absorbed liquid followed? What use does this indicate
+for the veins, besides the one already noted? Observe the
+point of insertion on the stem, and examine the scar with a
+lens: do you see any evidence of a connection between the
+leaf veins and the fibrovascular bundles of the stem? (<a href="#p-111">111</a>,
+<a href="#p-125">125</a>, <a href="#p-126">126</a>.) Notice where and how the veins end. Are they
+of the same size all the way, or do they grow smaller toward
+the tip? Are they separate and distinct, or are they connected
+throughout their ramifications, like the veins and
+arteries of the human body? How do you know? Do you
+see any of the coloring fluid in the small reticulations between
+the veins? How did it get there?</p>
+
+<p id="p-176"><b>176. The nature and office of veins.</b>—We learn from <a href="#p-173">173</a>
+and <a href="#p-175">175</a> that the veining serves two important purposes in the
+economy of the leaf: first, as a skeleton or framework, to support
+the expanded blade; and second, as a system of water
+pipes, for conveying the sap out of which its food is manufactured.
+In other words the veins are a continuation of the
+fibrovascular bundles into the leaves, by means of which the
+latter are put in communication with the body of the plant.</p>
+
+<p id="p-177"><b>177. The relation between veining and lobing.</b>—Compare
+the outline of a leaf of maple or ivy with one of oak or
+chrysanthemum. Do you perceive any correspondence between
+the manner of lobing or indentation of their margins,
+and the direction of the veins? (<a href="#i_168_210">Figs. 210</a>, <a href="#i_168_211">211</a>.) To what
+class would you refer each one?</p>
+
+<p>The lobes themselves may be variously cut, as in the
+fennel and rose geranium, thus giving rise to twice-cleft,
+thrice-cleft (<a href="#i_168_212">Fig. 212</a>), four-cleft, or even still more intricately
+divided blades.</p>
+
+<p id="p-178"><b>178. Compound leaves.</b>—Compare with the specimens
+just examined a leaf of horse-chestnut, clover, or Virginia
+creeper, and one of rose, black locust, or vetch. Notice that
+each of these last is made up of entirely separate divisions or
+leaflets, thus forming a <em>compound leaf</em>. Notice also that the
+two kinds of compound leaves correspond to the two kinds of
+veining and lobing, so that we have palmately and pinnately
+compound ones. In pinnate leaves the continuation of the
+common petiole along which the leaflets are ranged is called
+the <em>rhachis</em>.</p>
+
+<p><span class="pagenum" id="Page_158">[Pg 158]</span></p>
+
+<table class='autotable'>
+<tr><td class='vab'>
+<figure class="figcenter illowp50" id="i_168_210" style="max-width: 21.3125em;">
+  <img class="w100" src="images/i_168_210.jpg" alt="" data-role="presentation">
+  <figcaption><p>
+    <span class="smcap">Fig. 210.</span>—Pinnately
+    lobed leaf of horse nettle.</p>
+  </figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp56" id="i_168_211" style="max-width: 18.1875em;">
+  <img class="w100" src="images/i_168_211.jpg" alt="" data-role="presentation">
+  <figcaption><p>
+    <span class="smcap">Fig. 211.</span>—Palmately
+    lobed leaf of grape.</p>
+  </figcaption>
+</figure></td></tr></table>
+
+<table class='autotable'>
+<tr><td class='vab'>
+<figure class="figcenter illowp70" id="i_168_212" style="max-width: 44.4375em;">
+  <img class="w100" src="images/i_168_212.jpg" alt="" data-role="presentation">
+  <figcaption><p>
+    <span class="smcap">Fig. 212.</span>—Palmately parted leaf of a buttercup.
+  </p></figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp70" id="i_168_213" style="max-width: 25.5em;">
+  <img class="w100" src="images/i_168_213.jpg" alt="" data-role="presentation">
+  <figcaption><p>
+    <span class="smcap">Fig. 213.</span>—Pinnately compound leaf of black locust.
+  </p></figcaption>
+</figure></td></tr></table>
+
+<table class='autotable'>
+<tr><td class='vab'>
+<figure class="figcenter illowp70" id="i_168_214" style="max-width: 37.0625em;">
+  <img class="w100" src="images/i_168_214.jpg" alt="">
+  <figcaption><p>
+    <span class="smcap">Fig. 214.</span>—Palmately compound leaf of horse-chestnut.</p>
+  </figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp70" id="i_168_215" style="max-width: 26.6875em;">
+  <img class="w100" src="images/i_168_215.jpg" alt="">
+  <figcaption><p>
+    <span class="smcap">Fig. 215.</span>—Pinnately trifoliolate leaf of a desmodium.</p>
+  </figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp70" id="i_168_216" style="max-width: 26.5em;">
+  <img class="w100" src="images/i_168_216.jpg" alt="">
+  <figcaption><p>
+    <span class="smcap">Fig. 216.</span>—Palmately trifoliolate leaf of wood sorrel.</p>
+  </figcaption>
+</figure></td></tr></table>
+
+
+<p><span class="pagenum" id="Page_159">[Pg 159]</span></p>
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. In selecting leaves for decorations that are to remain several hours
+without water, which of the following would you prefer, and why:
+smilax or Madeira vine (<i>Boussingaultia</i>); ivy or Virginia creeper;
+magnolia or maple; maidenhair or shield fern (<i>Aspidium</i>)? (<a href="#p-173">173</a>.)</p>
+
+<p>2. Would you select very young leaves, or more mature ones, and why?</p>
+
+<p>3. Can you name any parallel-veined leaves that have their margins
+lobed, or indented in any way?</p>
+
+<p>4. Which are the more common, parallel-veined or net-veined leaves?</p>
+
+<p>5. Why do the leaves of corn and other grains not shrivel lengthwise in
+withering, but roll inward from side to side? (<a href="#p-173">173</a>.)</p>
+
+<p>6. Can you name any palmately veined leaves in which the secondary
+veins are pinnate? Any pinnately veined ones in which the secondary
+veins are palmate?</p>
+
+<p>7. Lay one of each kind before you; try to draw a pinnate leaf with
+palmate divisions. Do you see any reason now why these so seldom occur
+in nature?</p>
+
+<p>8. Name some advantages to a plant in having its leaves cut-lobed or
+compound. (<a href="#p-169">169</a>.)</p>
+
+<p>9. Mention some circumstances under which it might be advantageous
+for a plant to have large, entire leaves. (<a href="#p-169">169</a>; <a href="#i_161">Plate 9</a>.)</p>
+
+<p>10. How would the floating qualities of the leaves of the pond lily be
+affected if their blades were cut-lobed or compound?</p>
+
+<p>11. Do the leaves of the red cedar and arbor vitæ contribute to their
+value as shade trees?</p>
+
+<p>12. Name some of the favorite shade trees of your neighborhood; do
+they, as a general thing, have their leaves entire, or lobed and compound?</p>
+
+<p>13. Which of the following are the best shade trees, and why: pine,
+white oak, mimosa (<i>Albizzia</i>), sycamore, locust, horse-chestnut, fir, maple,
+linden, China tree, cedar, ash?</p>
+
+<p>14. Which would shade your porch best, and why: cypress vine,
+grape, gourd, morning-glory, wistaria, clematis, smilax, kidney bean,
+Madeira vine, rose, yellow jasmine, passion flower?</p>
+</div>
+
+<p><span class="pagenum" id="Page_160">[Pg 160]</span></p>
+
+
+<h3 id="CH_VI_III">III. TRANSPIRATION</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Leafy twigs of actively growing young plants. Sunflower,
+corn, peach, grape, calla, and arums in general transpire rapidly;
+thick-leaved evergreens and hairy or rough species, like mullein and horehound
+more slowly. For <a href="#exp-63">Exp. 63</a>, small-leaved, large-leaved, and thick-leaved
+kinds will be needed.</p>
+
+<p><span class="smcap">Appliances.</span>—Glass jars and bottles with air-tight stoppers; a little
+vaseline, oil, gardener’s wax, thread, cardboard, and a pair of scales.</p>
+
+<p id="exp-62"><span class="smcap">Experiment 62. To show why leaves wither.</span>—Dry two self-sealing
+jars thoroughly, by holding them over a stove or a lighted lamp
+for a short time to prevent “sweating.” Place in one a freshly cut leafy
+sprig of any kind, leaving the other empty. Seal both jars and set them
+in the shade. Place beside them, but without covering of any kind, a
+twig similar to the one in the jar. Both twigs should have been cut at
+the same time, and their cut ends covered with wax or vaseline, to prevent
+access of air. Look at intervals to see if there is any moisture deposited
+on the inside of either jar. If there is none, set them both in a refrigerator
+or cover with a wet cloth and allow to cool for half an hour, and then examine
+again. In which jar is there a greater deposit of dew? How do you
+account for it? Take the twig out of the jar and compare its leaves with
+those of the one left outside; which have withered the more, and why?</p>
+
+<p id="exp-63"><span class="smcap">Experiment 63. To measure the rate at which water is
+given off by leaves of different kinds.</span>—Fill three glass vessels of
+the same size with water and cover with oil to prevent evaporation.
+Insert into one the end of a healthy twig of peach or cherry; into the
+second a twig of catalpa, grape, or any large-leaved plant, and into
+the third, one of magnolia, holly, or other thick-leaved evergreen, letting
+the stems of all reach well down into the water. Care must be taken to
+select twigs of approximately the same size and age, since the absorbent
+properties of very young stems are more injured by cutting and exposure
+than those of older ones. All specimens should be cut under water as
+directed in <a href="#exp-58">Exp. 58</a>. Weigh all three vessels, and at the end of twenty-four
+hours, weigh again, taking note of the quantity of liquid that has disappeared
+from each glass. This will represent approximately the amount
+absorbed by the leaves from the twigs to replace that given off. Which
+twig has lost most? Which least? Note the condition of the leaves
+on the different twigs; have they all absorbed water about as rapidly
+as they have lost it? How do you know this? Pluck the leaves from
+each twig, one by one, lay them on a flat surface that has been previously
+measured off, into square inches or centimeters, and thus form a rough
+estimate of the area covered by each specimen. Make the best estimate<span class="pagenum" id="Page_161">[Pg 161]</span>
+you can of the number of leaves on each tree, and calculate the number
+of kilograms of water it would give off at that rate in a day.</p>
+
+<p id="exp-64"><span class="smcap">Experiment 64. Through what part of the leaf does the water
+get out?</span>—Take some healthy leaves of tulip tree, grape, tropæolum,
+or any large, soft kind attainable. Cover with vaseline the <em>leafstalk</em> and
+<em>upper</em> surface of one; the stalk and <em>under</em> surface of a second; the stalk
+and <em>both</em> surfaces of a third, and leave a fourth one untreated. Suspend
+all four in a dry place by means of a thread attached to the petioles so
+that both surfaces may be equally exposed. The leaves must be all of
+the same species, and as nearly as possible of the same age, size, and vigor,
+and care must be taken that none of the vaseline is rubbed off in handling.
+Examine at intervals of a few hours. Which of the leaves withers soonest?
+Which keeps fresh longest? From what part would you conclude, judging
+by this experiment, that the water escapes most rapidly?</p>
+</div>
+
+<p id="p-179"><b>179. Transpiration, nutrition, and growth.</b>—We learn
+from the foregoing, and from <a href="#exp-58">Exps. 58</a> and <a href="#exp-59">59</a>, that plants
+give off moisture very much as animals do by perspiration.
+The two processes must not be classed together, however,
+for they are physiologically different. The action, in plants,
+is called <em>transpiration</em>. It is usually assumed that a large
+amount of water must pass through the plant in order to
+bring to it the necessary supply of food material; but since
+the entrance of mineral salts is brought about by osmosis,
+conditioned by the living cells of the root; and since osmosis
+of salts may take place in a direction opposite to that of the
+greater movement of water, it follows that the entrance of
+salts is independent of transpiration.</p>
+
+<p>Inasmuch, however, as a certain amount of water is
+necessary to bring the living cells into a condition of turgor
+(7) so that they may grow, it follows that there is a relation
+between transpiration and growth. If transpiration exceeds
+absorption for any length of time, the tissues will be depleted
+of their moisture, as is shown by the wilting of crops
+in dry, hot weather; and if the unequal movement continues
+long enough, the plant will die. Hence, a knowledge of the
+laws governing this important function is necessary to all
+who are interested in cultivating agricultural products.</p>
+
+<p><span class="pagenum" id="Page_162">[Pg 162]</span></p>
+
+<figure class="figright illowp50" id="i_172_2" style="max-width: 70.5em;">
+  <img class="w100" src="images/i_172.jpg" alt="">
+  <figcaption>
+    <p><span class="smcap">Fig. 217.</span>—A “weeping tree,” showing the effect where
+    absorption exceeds transpiration. Notice the position of
+    the tree near the water where the roots have unlimited
+    moisture. (<i>After</i> <span class="smcap">Francé</span>.)</p>
+  </figcaption>
+</figure>
+
+<p id="p-180"><b>180. Magnitude of the work of transpiration.</b>—Few
+people have any idea of the enormous quantities of water
+given off by leaves. It has been calculated that a healthy
+oak may have as many as 700,000 leaves, and that 111,225
+kilograms of water—equal to about 244,700 pounds—may
+pass from its surface in the five active months from June
+to October. At
+this rate 226
+times its own
+weight may pass
+through it in a
+year, and it
+would transpire
+water enough
+during that time
+to cover the
+ground shaded
+by it to a depth
+of 20 feet!<a id="FNanchor_2" href="#Footnote_2" class="fnanchor">[2]</a>
+Lawn grass gives
+off water at such
+a rate that a vacant
+lot of 150 ×
+50 feet, if well
+turfed, would be
+capable of transpiring
+over a ton
+of water a day. Compare these figures with the average yearly
+rainfall in our Gulf States—53 inches, approximately—and
+you can form some estimate of the injury done to a growing
+crop from this cause alone. The moisture is drawn from the
+surface by shallow rooted weeds <a href="#p-81">(81)</a> and dissipated through
+the leaves. In the case of forest trees the effect is different.
+Their roots, striking deep into the soil, draw up water from
+the lower strata and distribute it to the thirsty air in summer.</p>
+
+<p><span class="pagenum" id="Page_163">[Pg 163]</span></p>
+
+<p>As the water given off by transpiration is in the form of
+vapor, it must draw from the plant the amount of heat
+necessary for its vaporization, and thus has the effect of
+making the leaves and the air in contact with them cooler
+than the surrounding medium. At the same time the coolness
+and moisture of the air tend to check the loss by
+evaporation from the surface soil. It is partly to this cause,
+and not alone to their shade, that the coolness of forests is
+due. Measurements at various weather bureau stations in
+the United States show that in summer the temperature of
+oak woods is 4° C. lower during the day than in the open,
+and as much higher at night. In a beech wood in Germany
+the difference between the forest and the general temperature
+amounted to as much as 7° C.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Is there any foundation in fact for the accounts of “weeping trees”
+and “rain trees” that we sometimes read about in the papers? (<a href="#p-180">180</a>;
+<a href="#exp-48">Exp. 48</a>.)</p>
+
+<p>2. Can you explain the fact, sometimes noticed by farmers, that in
+wooded districts, springs which have failed or run low during a dry spell
+sometimes begin to flow again in autumn when the trees drop their leaves,
+even though there has been no rain? (<a href="#p-180">180</a>; <a href="#exp-63">Exp. 63</a>.)</p>
+
+<p>3. Other things being equal, which would have the cooler, pleasanter
+atmosphere in summer, a well-wooded region or a treeless one? (<a href="#p-180">180</a>.)</p>
+
+<p>4. Could you keep a bouquet fresh by giving it plenty of fresh air?
+(<a href="#exp-62">Exp. 62</a>.)</p>
+
+<p>5. Why does a withered leaf become soft and flabby, and a dried one
+hard and brittle? (<a href="#p-7">7</a>; <a href="#exp-62">Exp. 62</a>.)</p>
+
+<p>6. Why do large-leaved plants, as a general thing, wither more quickly
+than those with small leaves? (<a href="#exp-63">Exp. 63</a>.)</p>
+
+<p>7. Is the amount of water absorbed always a correct indication of the
+amount transpired? Explain. (<a href="#p-179">179</a>.)</p>
+
+<p>8. Explain the difference between the withering caused by excessive
+transpiration and the shrinkage of cells due to plasmolysis. Are both of
+these physiological processes?</p>
+
+<p>9. Why is it best to trim a tree close when it is transplanted? (<a href="#p-179">179</a>,
+<a href="#p-180">180</a>.)</p>
+
+<p>10. Why should transplanting be done in winter or very early spring,
+before the leaves appear? (<a href="#p-180">180</a>.)</p>
+</div>
+
+<p><span class="pagenum" id="Page_164">[Pg 164]</span></p>
+
+
+<h3 id="CH_VI_IV">IV. ANATOMY OF THE LEAF</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—For study of the epidermis, leaves of the white garden
+lily (<i>Lilium album</i>) are best, as the stomata can be seen on their lower
+surface with the naked eye. Wandering Jew, Spanish bayonet (<i>Yucca
+aloifolia</i>), anemone, narcissus, iris, canna, show them under a hand lens,
+but less distinctly. For sections, beet, mustard, and beech leaves may
+be used, or ready-mounted specimens obtained of a dealer.</p>
+
+<p>A compound microscope is needed for a minute study of the leaf
+structure.</p>
+</div>
+
+<figure class="figright illowp30" id="i_174" style="max-width: 17.75em;">
+  <img class="w100" src="images/i_174.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 218, 219.</span>—Stomata
+of white lily
+leaf: 218, closed; 219,
+open. (<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p id="p-181"><b>181. Stomata.</b>—It was shown in <a href="#exp-64">Exp. 64</a> that the water
+of transpiration escapes most rapidly, as a general thing, from
+the under surface of leaves. To find out why this is so, a
+careful study of the epidermis will be necessary. For this
+purpose procure, if possible, the leaf of a white garden lily
+(<i>Lilium album</i>), wandering Jew, Spanish bayonet (<i>Yucca
+aloifolia</i>), anemone, narcissus, iris, or canna. The first-named
+is preferable, as the transpiration
+pores can be seen on it with the naked eye.
+Examine the under surface with a hand
+lens, and you will see that it is covered with
+small eye-shaped dots like those shown in
+<a href="#i_174">Figs. 218 and 219</a>. Strip off a portion of
+the epidermis, hold it up to the light on a
+piece of moistened glass, and they can be
+seen quite clearly with a lens. These dots
+are the pores through which the water vapor escapes in
+transpiration, and through which air finds its way into the
+tissues of the leaf. They are called <em>stomata</em> (sing., <em>stoma</em>),
+from a Greek word meaning “a mouth.” Look for stomata
+on the upper epidermis; do you find any, and if so, are there
+as many as on the under surface? Do you see any relation
+between this fact and the results obtained from <a href="#exp-64">Exp. 64</a>?
+Can you see any good reasons why the stomata should be
+placed on the under side in preference to the upper? Are they
+as much exposed to excessive light and heat, or as liable to
+be choked by dust, rain, and dew here as on the upper side?</p>
+
+<p><span class="pagenum" id="Page_165">[Pg 165]</span></p>
+
+<p id="p-182"><b>182. Distribution of stomata.</b>—While stomata are generally
+more abundant on the under side of leaves, this is not
+always the case. In vertical leaves, like those of the iris,
+which have both sides equally exposed to the sun, they are
+distributed equally on both sides. In plants like the water
+lily, where the under surface lies upon the
+water, they occur only on the upper side.
+Succulent leaves, as a general thing, have
+very few, because they need to conserve
+all their moisture. Submerged leaves
+have none at all; why?</p>
+
+<table class='autotable'>
+<tr><td class='vab'>
+<figure class="figcenter illowp50" id="i_175" style="max-width: 20em;">
+  <img class="w100" src="images/i_175.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 220.</span>—A small
+piece of the under epidermis
+of an oak leaf, highly
+magnified to show the
+stomata, <i>g</i>, and minute
+hairs, <i>h</i>.</p></figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp50" id="i_175a" style="max-width: 18.5em;">
+  <img class="w100" src="images/i_175a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 221.</span>—Under
+epidermis of an oat leaf,
+showing stomata.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-183"><b>183. Minute study of a leaf epidermis.</b>—Place
+a bit of the lower epidermis of
+a leaf under the microscope, and examine
+with a high power. It will appear, if a
+monocotyl, to be composed of long, flat,
+rectangular spaces (<a href="#i_175a">Fig. 221</a>); if the leaf
+of a dicotyl is used, they will be more or less irregular (<a href="#i_175">Fig.
+220</a>), with the outlines fitting into each other like the tiling
+of a floor or the blocks of a Chinese puzzle.
+These spaces are the cells of the epidermis,
+and the lines are the cell walls. Can you
+find any of the cell contents? The cell
+sap is not often visible; do you see the
+nuclei? Can you give a reason why the
+epidermal cells are so thin and flat? Between
+some of the cells you will see two
+kidney-shaped bodies placed with their
+concave sides together so as to leave a
+lenticular opening between them. This
+is a <em>stoma</em>, and the kidney-shaped bodies
+(<a href="#i_174">Figs. 218, 219</a>) are <em>guard cells</em>. They
+are given this name because they open
+or close the mouth of the stoma. If
+you will imagine a toy balloon made in the form of a hollow
+ring, like the tire of a bicycle, you can easily see, from<span class="pagenum" id="Page_166">[Pg 166]</span>
+<a href="#i_174">Figs. 218, 219</a>, that when the ring is strongly inflated, it
+will expand, and in enlarging its own circumference, will at
+the same time increase the diameter of the opening in the
+center. When the expansive
+force is removed,
+it collapses, thus closing,
+or greatly reducing, the
+aperture.</p>
+
+<figure class="figleft illowp50" id="i_176" style="max-width: 39.6875em;">
+  <img class="w100" src="images/i_176.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 222.</span>—Outline of a stoma of hellebore
+in vertical section. The darker lines show the
+shape assumed by the guard cells when the stoma
+is open; the lighter lines, when the stoma is
+closed. The cavities of the guard cells with the
+stoma closed are shaded, and are distinctly
+smaller than when the stoma is open.</p></figcaption>
+</figure>
+
+<p>In the same way the
+guard cells, when there
+is abundance of water in
+them, expand, thus opening
+the stoma so that the
+water vapor passes out
+more readily. But when
+there is a dearth of
+moisture, or when, by reason of chemical action in the soil,
+the roots fail to supply it, the leaves wilt, the guard cells,
+losing their water, collapse, closing the pore, and transpiration
+is thus prevented or greatly retarded. (<a href="#i_176">Fig. 222</a>.)</p>
+
+<p>Sketch a portion of the epidermis as it appears under the microscope,
+labeling the parts. If stomata can be found in both
+conditions, make sketches showing them both open and closed.</p>
+
+<p id="p-184"><b>184. Internal structure of a leaf.</b>—Roll a leaf blade, or
+fold it tightly to facilitate cutting, and with a scalpel, or a very
+sharp razor, cut the thinnest possible slice through the roll.
+This will give a section at right angles to the epidermis.
+It should be so thin as to appear almost transparent. Put a
+small bit of a section in a drop of water on a slide, place under
+the microscope, using a high power, and look for the parts
+shown in <a href="#i_177">Fig. 223</a>. Notice the horizontally flattened cells of the
+upper epidermis, <i>e</i>, and of the lower epidermis, <i>e′</i>; also the vertically
+elongated palisade cells, <i>p</i>, filled with particles of green
+coloring matter. These particles are the chlorophyll bodies,
+to which the green color of the leaf is due. They are the
+active agents in the manufacture of plant food, and in a leaf<span class="pagenum" id="Page_167">[Pg 167]</span>
+removed from the plant during the day time and viewed
+under a high power, the chlorophyll bodies, on treatment
+with iodine, will be seen to contain granules of starch which
+they are in the act of elaborating. The collecting cells, <i>t</i>,
+receive the assimilated product from the
+palisade cells and pass it on through the
+spongy parenchyma, <i>sch</i>, to the fibrovascular
+bundles. Notice how much more abundant
+the green matter is in the upper part of the
+leaf than in the lower; has this anything to
+do with the deeper color of the upper surfaces
+of leaves? Notice the opening, <i>st</i>,
+lower epidermis; do you recognize it? (See
+<a href="#i_176">Fig. 222</a>.) It is a stoma, seen in vertical
+section. Notice the intercellular air spaces,
+<i>i</i>, <i>i</i>, in the spongy parenchyma, and the much larger one, <i>a</i>,
+just behind the stoma. Why is this last so much larger?</p>
+
+<figure class="figcenter illowp85" id="i_177" style="max-width: 50em;">
+  <img class="w100" src="images/i_177.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 223.</span>—Transverse section through a leaf of beet: <i>e</i>, upper epidermis; <i>e′</i>,
+lower epidermis; <i>st</i>, stoma; <i>a</i>, air space; <i>p</i>, palisade cells; <i>t</i>, collecting cells; <i>sch</i>,
+spongy parenchyma; <i>i</i>, <i>i</i>, intercellular air spaces; <i>Fbv</i>, section of a vein (fibrovascular
+bundle).</p></figcaption>
+</figure>
+
+<figure class="figright illowp20" id="i_177a" style="max-width: 12.5em;">
+  <img class="w100" src="images/i_177a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 224.</span>—Chlorophyll
+bodies containing
+starch grains
+in the course of formation.
+Magnified
+250 times.</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_168">[Pg 168]</span></p>
+
+<p>Sketch the section of your specimen as it appears under
+the microscope. It will perhaps differ in some details from
+the one shown in the figure, but you can recognize and label
+the corresponding parts. Be sure that your drawing represents
+accurately the relative size and shapes of the different
+kinds of cells.</p>
+
+<p>It is in the upper surface, where the chlorophyll particles
+abound, that the manufacture of food goes on most actively,
+and from the under surface, where the stomata are situated,
+that transpiration takes place and air and other gases pass
+to and from the interior. These facts have important bearings
+on the growth and external characters of leaves.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Explain why a plant cannot thrive if its stomata are clogged with
+foreign matter. (<a href="#p-179">179</a>; <a href="#exp-64">Exp. 64</a>; <a href="#p-184">184</a>.)</p>
+
+<p>2. Mention some of the ways in which this might happen. (<a href="#p-181">181</a>.)</p>
+
+<p>3. Why must the leaves of house plants be washed occasionally to keep
+them healthy? (<a href="#p-179">179</a>, <a href="#p-181">181</a>.)</p>
+
+<p>4. Why is it so hard for trees and hedges to remain healthy in a large
+manufacturing town?</p>
+</div>
+
+
+<h3 id="CH_VI_V">V. FOOD MAKING</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A sprig of pondweed, mare’s-tail (<i>Hippuris</i>), hornwort
+(<i>Ceratophyllum</i>), marsh St.-John’s-wort (<i>Elodea</i>), or other green aquatic
+plant; bean or tropæolum, or other green leaves gathered from plants
+growing in the sunshine; a healthy potted plant; a small, fresh cutting.</p>
+
+<p><span class="smcap">Appliances.</span>—A shallow dish of water and two glass tumblers or wide-mouthed
+jars; a bent glass or rubber tube; a piece of black cloth or paper;
+a half pint of alcohol; iodine solution; a glass funnel or a long-necked
+bottle from which the bottom has been removed.</p>
+
+<p id="exp-65"><span class="smcap">Experiment 65. Is there any relation between sunlight
+and the green color of leaves?</span>—Place a seedling of oats, or other
+rapidly growing shoot, in the dark for a few days, and note its loss of
+color. Leave it in the dark indefinitely, and it will lose all color and die.
+Hence we may conclude that there is some intimate connection between
+the action of light and the green coloring matter of leaves.</p>
+
+<p id="exp-66"><span class="smcap">Experiment 66. Do leaves give off anything else besides
+water?</span>—Submerge a green water plant, with the cut end uppermost, in<span class="pagenum" id="Page_169">[Pg 169]</span>
+a glass vessel full of water, and invert over it a glass funnel, or a long-necked
+bottle from which the bottom has been removed as directed in <a href="#exp-53">Exp.
+53</a>. Expel the air from the neck of the funnel—or
+bottle—by submerging and corking under water
+so as to make it air-tight. Place in the sunlight and
+notice the bubbles that begin to rise from the cut
+end of the plant. When they have partly filled the
+neck of the funnel, remove the stopper and thrust
+in a glowing splinter. If it bursts into flame, or
+glows more brightly, what is the gas that was given
+off? (<a href="#exp-22">Exp. 22</a>.)</p>
+
+<p>As oxygen is not a product of respiration, some
+other process must be at work here, during which
+oxygen is set free, and some other substance used
+up. (Exps. 24 and 25.)</p>
+
+<table>
+<tr><td>
+<figure class="figcenter illowp50" id="i_179a" style="max-width: 15.5em;">
+  <img class="w100" src="images/i_179a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 225.</span>—Experiment
+showing that
+green plants give off
+oxygen in sunlight.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp50" id="i_179" style="max-width: 25em;">
+  <img class="w100" src="images/i_179.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 226.</span>—Experiment
+for showing that leaves absorb
+carbon dioxide from the atmosphere.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="exp-67"><span class="smcap">Experiment 67. What is the substance taken
+in when oxygen is given off?</span>—Fill two glass
+jars, or two tumblers, with water, to expel the
+air, and invert in a shallow dish of water, having
+first introduced a freshly cut sprig of some healthy
+green plant into one of them. Then, by means
+of a bent tube, blow into the mouth of each tumbler
+till all the water is expelled by the impure air
+from the lungs. Set the dish in the sunshine and
+leave it, taking care that the end of the cutting is in
+the water of the dish. After forty-eight hours remove
+the tumblers by running under the mouth of
+each, before lifting from the dish, a piece of glass well coated with vaseline
+(lard will answer), and pressing it down tight so that no air can enter.
+Place the tumblers in an upright position,
+keeping them securely covered. Fasten a
+lighted taper or match to the end of a wire,
+plunge it quickly first into one tumbler, then
+into the other, and note the result. What
+was the gas blown from your lungs into the
+jars? (Exps. 23, 24.) Why did the taper not
+go out in the second jar? What had become
+of the carbon dioxide?</p>
+
+<p id="exp-68"><span class="smcap">Experiment 68. To show that light
+is necessary for a plant to absorb carbon dioxide and give off
+oxygen.</span>—Repeat <a href="#exp-66">Exp. 66</a>, keeping the plant in a dark or shady place;
+do you see any bubbles? Test with a glowing match; is any oxygen<span class="pagenum" id="Page_170">[Pg 170]</span>
+formed in the tube of the funnel? Move back into the sunlight and
+leave for a few hours; what happens when you thrust a glowing splinter
+into the tube?</p>
+
+<p id="exp-69"><span class="smcap">Experiment 69. Is any food product found in leaves?</span>—Crush
+a few leaves of bean, sunflower, or tropæolum, and soak in alcohol until all
+the chlorophyll is dissolved out. Rinse them in water, and soak the
+leaves thus treated in a weak solution of iodine for a few minutes, then
+wash them and hold them up to the light. If
+there are any blue spots on the leaves, what are
+you to conclude? If a test for sugar is to be
+made, use sap pressed from fresh leaves; for
+oils and fats, leaves should be dried without
+being placed in alcohol.</p>
+
+<figure class="figright illowp25" id="i_180" style="max-width: 23.625em;">
+  <img class="w100" src="images/i_180.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 227.</span>—Leaf arranged
+with a piece of tin foil to exclude
+light from a portion of
+the surface.</p></figcaption>
+</figure>
+
+<p id="exp-70"><span class="smcap">Experiment 70. Has the presence or
+absence of light anything to do with the
+occurrence of starch in leaves?</span>—Exclude
+the light from parts of healthy leaves on a growing
+plant of tropæolum, bean, etc., by placing
+patches of black cloth or paper over them.
+Leave in a bright window, or preferably out of
+doors, for several hours, and then test for starch
+as in the last experiment; do you find any in
+the shaded spots?</p>
+
+<p id="exp-71"><span class="smcap">Experiment 71. Is the presence of air necessary for the
+production of starch?</span>—Cover the blades and the petioles of several
+leaves with vaseline or other oily substance so as to exclude the air, and
+after a day or two test as before.</p>
+</div>
+
+<p id="p-185"><b>185. Influence of plants on the atmosphere.</b>—These
+experiments show that leaves cannot do their work without
+light and air. The particular element of the atmosphere
+used by them in the process of food making is carbon dioxide.
+Their action in absorbing this gas and giving off oxygen
+tends to counterbalance the opposite action of respiration,
+decomposition, and combustion of all kinds, by which the
+proportion of it in the atmosphere tends to be constantly
+increased. In this way they help to regulate the quantity
+of it present and have a beneficial effect in ridding the air of
+one source of impurity.</p>
+
+<p><span class="pagenum" id="Page_171">[Pg 171]</span></p>
+
+<p id="p-186"><b>186. Photosynthesis.</b>—In our examination of the internal
+structure of the leaf, the chlorophyll bodies <a href="#p-184">(184)</a> were found
+to contain small granules of starch which the chlorophyll,
+under the stimulus of light, had elaborated as a nutriment for
+the plant tissues. Hence, the leaf may be regarded as a
+factory in which vegetable food, mainly starch, is manufactured
+out of the water brought up from the soil, and the carbon
+dioxide derived through the stomata from the atmosphere.
+In this process carbon dioxide (CO<sub>2</sub>) is combined with water
+(H<sub>2</sub>O) in such proportions that part of the oxygen is returned
+to the surrounding air. This is a fundamental food-forming
+process characteristic of green plants, and can take place
+only in the light. For this reason it has been named <em>Photosynthesis</em>,
+a word which means “building up by means of
+light,” just as <em>photography</em> means “drawing or engraving
+by means of light.”</p>
+
+<p>In carrying on the operation of photosynthesis, sunshine
+is the power, the chlorophyll bodies the working machinery,
+carbon dioxide and water the raw materials, and starch or oil
+the finished product, while oxygen and the water of transpiration
+represent the waste or by-products.</p>
+
+<p id="p-187"><b>187. How the new combination is effected.</b>—It may
+seem strange that a gas and a liquid should combine to make
+something so different from either as starch, but their chemical
+constituents are the same in different proportions. Water
+is made up of 2 parts hydrogen and 1 part oxygen; carbon
+dioxide, of 1 part carbon and 2 parts oxygen, while starch
+contains carbon, hydrogen, and oxygen, in the ratios of 6,
+10, and 5, respectively. Hence, by taking sufficient quantities
+of water and carbon dioxide and combining them in the
+proper proportions, the leaf factory can turn them into
+starch. If we use the letters C, H, and O, to represent Carbon,
+Hydrogen, and Oxygen, respectively, the new combination
+of materials can be expressed by an equation; thus:—</p>
+
+
+<table class="autotable">
+<tr class="fs80">
+<td class="tdc"><i>water</i></td>
+<td class="tdc"><i>carbon dioxide</i></td>
+<td class="tdc"><i>starch</i></td>
+<td class="tdc" colspan="2"><i>by-products</i></td>
+</tr>
+<tr>
+<td class="tdc">5 (H<sub>2</sub>O)</td>
+<td class="tdc">+ &nbsp;&nbsp; 6 (CO<sub>2</sub>) &nbsp;&nbsp; =  </td>
+<td class="tdc">&nbsp; (C<sub>6</sub>H<sub>10</sub>O<sub>5</sub>) &nbsp;</td>
+<td class="tdc">+ &nbsp;&nbsp; 6 (O<sub>2</sub>)</td>
+<td class="tdc">= &nbsp;&nbsp; 12 (O).</td>
+</tr>
+</table>
+
+<p><span class="pagenum" id="Page_172">[Pg 172]</span></p>
+
+<p>The water not used up in the process is given off as a waste
+product in transpiration, while the oxygen is returned to the
+air, as shown by <a href="#exp-66">Exp. 66</a>. This equation is not to be understood
+as representing the chemical changes that actually take
+place in the leaf. These are too complicated, and at present
+too imperfectly known, to be considered here. It will serve,
+however, to give a fair idea of the final result from the process
+of photosynthesis, however brought about.</p>
+
+<p>Simple as the operation appears, the chemist has not, as
+yet, been able to imitate it. He can analyze starch into its
+original constituents, but while he has the ingredients at
+hand in abundance, and knows the exact proportions of their
+combination, it is beyond his power, in the present state of
+our knowledge, to put them together. Hence, both man
+and the lower animals are dependent on plants for this most
+important food element. The so-called factories that supply
+the starch of commerce do not <em>make</em> starch any more than
+the miller makes wheat, but merely separate and render
+available for use that already elaborated by plants.</p>
+
+<p id="p-188"><b>188. Proteins.</b>—Foods of this class are mainly instrumental
+in furnishing material for the growth and repair of
+the tissues out of which the bodies of both plants and animals
+are built up. They embrace a great variety of substances,
+but their chemical nature is very complex and very imperfectly
+understood. Nitrogen is an important element in
+their composition, whence they are commonly distinguished
+as “nitrogenous foods.” Besides nitrogen, there are present
+carbon, hydrogen, oxygen, and sulphur, and traces of the
+mineral salts absorbed from the soil are found in varying
+quantities in the ash of different proteins. The percentages
+in which these ingredients are combined and the processes
+concerned in their formation are at present a matter of pure
+hypothesis. Botanists are not agreed even as to whether
+they are made in the leaf or in some other part or parts of
+the plant, though the weight of opinion inclines to the view
+that their construction takes place in the leaf.</p>
+
+<p><span class="pagenum" id="Page_173">[Pg 173]</span></p>
+
+<p id="p-189"><b>189. The activities of leaves.</b>—As there are only 4 parts
+of CO<sub>2</sub> to every 10,000 parts of ordinary free air, it has been
+estimated that in order to supply the leaf factory with the
+raw material it needs, an active leaf surface of one square
+meter—a little over one square yard—uses up, during
+every hour of sunshine, the CO<sub>2</sub> contained in 1000 liters
+(1000 quarts, approximately) of air. Suppose an oak tree
+to bear 500,000 leaves, each having a surface of 16 sq. cm., or
+4 sq. in., and working 12 hours a day for 6 months in the
+year; you will then have some idea of the enormous quantity
+of air that passes each season through its leaf system. Add
+to this the almost incredible volume of water transpired in
+the same time <a href="#p-180">(180)</a>, and we may well stand amazed at the
+tremendous activities of these silent workers that we are in
+the habit of regarding as mere passive elements in the
+general landscape.</p>
+
+<p id="p-190"><b>190. The economic value of leaves.</b>—Besides their importance
+as sanitary and food-making agencies, leaves have
+a direct commercial value as food products in the hay and
+fodder they supply for our domestic animals, the tea and
+salads with which they provide our tables, the aromatic
+flavors and seasonings contained in them, and the drugs,
+medicines, and dyes of various kinds for which they furnish
+the ingredients.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Why do gardeners “bank” celery? (<a href="#exp-65">Exp. 65</a>.)</p>
+
+<p>2. Why are the buds that sprout on potatoes in the cellar, white? (<a href="#exp-65">Exp.
+65</a>.)</p>
+
+<p>3. Why does young cotton look pale and sickly in long-continued wet
+or cloudy weather? (<a href="#exp-65">Exp. 65</a>.)</p>
+
+<p>4. Why do parasitic plants generally have either no leaves or very
+small, scalelike ones? (<a href="#p-85">85</a>, <a href="#p-186">186</a>, <a href="#p-187">187</a>.)</p>
+
+<p>5. The mistletoe is an exception to this; explain why, in the light of
+your answer to question 4.</p>
+
+<p>6. Could an ordinary nonparasitic plant live without green leaves?
+(<a href="#p-186">186</a>, <a href="#p-187">187</a>.)</p>
+
+<p>7. Are abundance and color of foliage any indication of the health of
+a plant? (<a href="#p-186">186</a>, <a href="#p-187">187</a>; <a href="#exp-65">Exp. 65</a>.)</p>
+
+<p><span class="pagenum" id="Page_174">[Pg 174]</span></p>
+
+<p>8. Is the practice of lopping and pruning very closely, as in the process
+called “pollarding,” beneficial to a tree under ordinary conditions? (<a href="#p-186">186</a>,
+<a href="#p-189">189</a>; <a href="#exp-63">Exp. 63</a>.)</p>
+
+<p>9. Name some plants of your neighborhood that grow well in the shade.</p>
+
+<p>10. Compare in this respect Bermuda grass and Kentucky blue grass;
+cotton and maize; horse nettle (<i>Solanun Carolinense</i>) and dandelion;
+beech, oak, red maple, dogwood, pine, cedar, holly, magnolia, etc.</p>
+
+<p>11. Name all the aromatic leaves you can think of; all that are used as
+food, beverages, drugs, and dyes.</p>
+
+<p>12. What is the use of aromatic and medicinal leaves to the plant itself?
+(Suggestion: Why does the housewife put lavender or tobacco leaves in
+her woolen chest?)</p>
+
+<p>13. Which would be richer in nourishment, hay cut in the evening or
+in the morning, and why? (<a href="#p-54">54</a>, <a href="#p-186">186</a>; <a href="#exp-70">Exp. 70</a>.)</p>
+
+<p>14. Mention three important sanitary services that are rendered by a
+tree like that shown in <a href="#i_127">plate 6</a> or <a href="#i_140">8</a>. (<a href="#p-180">180</a>, <a href="#p-185">185</a>, <a href="#p-189">189</a>.)</p>
+
+<p>15. Name some of the plants employed in the manufacture of starch.</p>
+</div>
+
+
+<h3 id="CH_VI_VI">VI. THE LEAF AN ORGAN OF RESPIRATION</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A number of vigorous, freshly cut green leaves; a liter
+or two (one or two quarts) of expanding flower or leaf buds.</p>
+
+<p><span class="smcap">Appliances.</span>—Some wide-mouthed jars of one or two liters’ capacity;
+two small open vials of limewater.</p>
+
+<p id="exp-72"><span class="smcap">Experiment 72. Do leaves give off carbon dioxide?</span>—Cover
+the bottoms of two wide-mouthed jars with water about two centimeters
+(1 inch) deep. Place in one a number of healthy green leaves with
+their stalks in the water, and insert among them a small open vial containing
+limewater. In the other jar place only a vial of limewater in the
+clear water at the bottom, this last being merely to make the conditions
+in both vessels the same. Seal both tight and keep together in the dark
+for about 48 hours, and then examine. In which jar does the limewater
+indicate the greater accumulation of CO<sub>2</sub>? (It may show a slight
+milkiness in the other vessel due to gas derived from the inclosed air and
+water.) From this experiment, what process would you conclude has
+been going on among the leaves in jar No. 1? (<a href="#exp-25">Exp. 25</a>.)</p>
+
+<figure class="figright illowp25" id="i_185" style="max-width: 17.25em;">
+  <img class="w100" src="images/i_185.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 228.</span>—Arrangement
+of apparatus to
+show that heat and carbon
+dioxide are given off
+by leaf buds.</p></figcaption>
+</figure>
+
+<p id="exp-73"><span class="smcap">Experiment 73. Is the exhalation of carbon dioxide accompanied
+by any other concomitant of respiration?</span>—In <a href="#exp-24">Exps. 24</a>,
+<a href="#exp-25">25</a>, it was shown that respiration is accompanied by heat; hence, if the
+production of carbon dioxide by the leaf is due to this cause, it should be
+attended by the evolution of heat. To find out whether this is the case,
+partly fill a glass jar of two liters’ capacity with unfolding leaf buds arranged<span class="pagenum" id="Page_175">[Pg 175]</span>
+in layers alternating with damp cotton batting
+or blotting paper (<a href="#i_185">Fig. 228</a>); close the jar
+tightly and leave from 12 to 24 hours in the dark
+to prevent the action of photosynthesis. Then
+insert a thermometer and note the rise in temperature.
+If a lighted taper is plunged in, it will
+quickly be extinguished, showing that respiration
+has been going on.</p>
+</div>
+
+<p id="p-191"><b>191. Respiration in leaves.</b>—We see
+from experiments like the foregoing that
+the leaf, besides carrying on the functions
+of digestion, photosynthesis, and transpiration,
+is also an active agent in the
+work of respiration. In this function
+oxygen is used up and carbon dioxide
+given off, just as in the respiration of animals; but the
+process is so slow in plants that it is much more difficult
+to detect than the contrary action in photosynthesis, and is,
+in fact, not perceptible at all while the latter is going on,
+though it does not cease even then.</p>
+
+<p>But while the leaf is the principal organ of respiration, the
+process is carried on in other parts of the plant as well,
+else it could not survive during the leafless months of
+winter. It <em>appears</em> to be most active at night, but this is
+only because it is not obscured then, as during the day, by
+the more active function of photosynthesis. Indeed, it was
+for a long time supposed that plants “breathed” only at
+night, and it was thought to be unwholesome to keep them
+in a bedroom. It is now known, however, that respiration
+goes on at all times and in all living parts of the plant, but
+the quantity of oxygen taken in is so small from a hygienic
+point of view that it may be disregarded.</p>
+
+<p id="p-192"><b>192. Distinctions between respiration and photosynthesis.</b>—While
+these two functions are contrasting and antipodal,
+so to speak, in their action, they are mutually complementary
+and interdependent, the one manufacturing food and the
+other using it up, or rather marking the activity of those<span class="pagenum" id="Page_176">[Pg 176]</span>
+life processes by which it is used up. The difference between
+them will be made clear by a comparison of the two processes
+as summarized in the following statement:</p>
+
+
+<table class="autotable fs80 wd80 statement">
+<tr>
+<th class="tdc smcap wd50">Photosynthesis</th>
+<th class="tdc smcap wd50 pl1">Respiration</th>
+</tr>
+<tr>
+<td class="tdl vat pr1"><p>Goes on only in sunlight and in the green parts of plants.</p></td>
+<td class="tdl vat pl1"><p>Goes on at all times and in all parts of the plant.</p></td>
+</tr>
+<tr>
+<td class="tdl vat pr1"><p>Produces starch and sugar.</p></td>
+<td class="tdl vat pl1"><p>Releases energy (heat and working power).</p></td>
+</tr>
+<tr>
+<td class="tdl vat pr1"><p>Gives off, as by-product, oxygen.</p></td>
+<td class="tdl vat pl1"><p>Gives off, as by-products, CO<sub>2</sub> and water.</p></td>
+</tr>
+<tr>
+<td class="tdl vat pr1"><p>A constructive process, in which energy is used up to make food.</p></td>
+<td class="tdl vat pl1"><p>A destructive, or consumptive process, in which food is used up in expending energy.</p></td>
+</tr>
+</table>
+
+
+<p id="p-193"><b>193. Metabolism.</b>—The total of all the life processes of
+plants, including growth, waste, repair, etc., is summed up
+under the general term <em>metabolism</em>. It is a <em>constructive</em> or
+building-up process when it results in the making of new
+tissues out of food material absorbed from the earth and air,
+and the consequent increase of the plant in size or numbers.
+But, as in the case of animals, so with plants, not all the
+food provided is converted into new tissue, part being used
+as a source of energy, and part decomposed and excreted
+as waste. In this sense, metabolism is said to be <em>destructive</em>.
+The waste in healthy growing plants is always, of course, less
+than the gain, and a portion of the food material is laid by
+as a reserve store. For this reason, photosynthesis, being a
+constructive process, is usually more energetic than respiration,
+which is the measure of the destructive change of
+materials that attends all life processes.</p>
+
+<p>It is evident also, from what has been said, that growth and
+repair of tissues can take place only so long as the plant has
+sufficient oxygen for respiration, since the energy liberated
+by it is necessary for the assimilation of nourishment by
+the tissues.</p>
+
+<p>Thus we see that plants are dependent on air not only for
+respiration, but for nutrition, and none of their life processes
+can be carried on without it.</p>
+
+<p><span class="pagenum" id="Page_177">[Pg 177]</span></p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Can a plant be suffocated, and if so, in what ways? (<a href="#p-87">87</a>, <a href="#p-193">193</a>;
+Exps. 26, 27.)</p>
+
+<p>2. The roots on the palm shown in <a href="#i_083">plate 3</a> are not drawing any sap
+from it as parasites; why does their continued growth bring about the
+death of the tree? (<a href="#p-87">87</a>, <a href="#p-193">193</a>.)</p>
+
+<p>3. Is it unwholesome to keep flowering plants in a bedroom? Leafy
+ones? Why, in each case? (<a href="#p-191">191</a>.)</p>
+
+<p>4. Would there be any more reason for objecting to the presence of
+flowers by night than by day? Explain. (<a href="#p-191">191</a>.)</p>
+
+<p>5. Why is respiration much less marked in plants than in animals?
+(<a href="#p-30">30</a>, <a href="#p-31">31</a>.)</p>
+</div>
+
+
+<h3 id="CH_VI_VII">VII. THE ADJUSTMENT OF LEAVES TO EXTERNAL
+RELATIONS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A potted plant of oxalis, spotted medick, white clover,
+or other sensitive species. The subject is better suited for outdoor observation
+than for laboratory work.</p>
+
+<p id="exp-74"><span class="smcap">Experiment 74. To show that leaves adjust themselves to
+changes in intensity of light.</span>—Keep a healthy potted plant of oxalis,
+white clover, or spotted medick in
+your room for observation. Note
+the daily changes of position the
+leaves undergo. Sketch one as it
+appears at night and in the morning.</p>
+
+<figure class="figright illowp40" id="i_187" style="max-width: 30em;">
+  <img class="w100" src="images/i_187.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 229, 230.</span>—Leaves of a peanut
+plant: 229, in day position; 230, in
+night position.</p></figcaption>
+</figure>
+
+<p>In order to determine whether
+these changes are due to want of light
+or of warmth, put your plant in a dark
+closet in the middle of the day, without
+change of temperature. After
+several hours note results. Transfer
+to a refrigerator, or in winter place
+outside a window where it will be exposed
+to a temperature of about 5° C. (40° F.) for several hours, and see if
+any change takes place. Next put it at night in a well-lighted room and
+note the effect. If practicable, keep a specimen for several weeks in some
+place where electric lights are burning continuously all night, and watch
+the results.</p>
+
+<p id="exp-75"><span class="smcap">Experiment 75. To show that the fall of the leaf may result
+from other causes than cold or frost.</span>—Wrap some leaves of ailanthus,
+Kentucky coffee tree, ash, walnut, or hickory in a damp towel and<span class="pagenum" id="Page_178">[Pg 178]</span>
+keep them in the dark for several days; the leaflets will fall away, leaving
+a clear scar like those on winter twigs.</p>
+
+<p id="exp-76"><span class="smcap">Experiment 76. To show that adjustments to temperature may
+be made by chemical means.</span>—Place a small twig of oleander, laurestinus,
+or other broad-leaved evergreen in a 5 to 10 per cent solution
+of sugar, and transfer it at the end of a few days to a temperature of
+6° to 8° below freezing. On comparison with a similar twig that has
+stood for the same length of time in pure water, it will be found to possess
+a greater power of resistance to cold.</p>
+</div>
+
+<figure class="figright illowp30" id="i_188" style="max-width: 20em;">
+  <img class="w100" src="images/i_188.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 231.</span>—A
+plant that has been
+growing near an open
+window, showing the
+leaves all turned
+toward the light.</p></figcaption>
+</figure>
+
+<p id="p-194"><b>194. The light relation.</b>—The principal external conditions
+to which leaves have to adjust themselves are light,
+air, moisture, gravity, temperature, and the attacks of animals.
+From the knowledge of their work and function
+gained in the preceding sections, it will be clear that the primary
+relation of the leaf is a light relation, and to this, first of
+all, it must adjust itself.</p>
+
+<p>It was shown in Exps. 56 and 57 how promptly leaves respond
+to changes in the direction of light,
+and a little observation (<a href="#exp-74">Exp. 74</a>) will convince
+us that they are equally sensitive to
+changes in intensity and periodicity of illumination.</p>
+
+<p id="p-195"><b>195. Phototropism.</b>—The movement of
+plants in response to light is called <em>phototropism</em>—a
+word that means “turning
+toward or away from light.” It includes
+all kinds of light adjustments, and examples
+of it are to be met with everywhere in the
+disposition of leaves with reference to their
+light exposure.</p>
+
+<p id="p-196"><b>196. Horizontal and vertical adjustment.</b>—Take two
+sprigs, one upright, the other horizontal, from any convenient
+shrub or tree—and notice the difference in the position of
+the leaves. Examine their points of attachment and see how
+this is brought about, whether by a twist of the petiole or of
+the base of the leaf blades, or by a half twist of the stem
+between two consecutive leaves, or by some other means.</p>
+
+<p><span class="pagenum" id="Page_179">[Pg 179]</span></p>
+
+<figure class="figcenter illowp52" id="i_189" style="max-width: 75em;">
+  <img class="w100" src="images/i_189.jpg" alt="">
+  <figcaption><p class='pm0'><span class="smcap">Plate 10.</span>—A mosaic of moonseed leaves, showing adjustment for light exposure.</p>
+  <p class='center pm0'>(<i>From</i> Mo. Botanical Garden Rep’t.)</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_180">[Pg 180]</span></p>
+
+<p>Observe both branches in their natural position; what part
+of the leaf is turned upward, the edge or the surface of the
+blade? Change the position of the two sprigs, placing the
+vertically growing one horizontal, and the horizontal one
+vertical. What part of the leaves is turned upward in each?</p>
+
+<figure class="figcenter illowp75" id="i_190" style="max-width: 52.6875em;">
+  <img class="w100" src="images/i_190.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 232, 233.</span>—Adjustment of leaves to different positions:
+232, upright; 233, procumbent.</p></figcaption>
+</figure>
+
+<figure class="figright illowp30" id="i_190a" style="max-width: 21.875em;">
+  <img class="w100" src="images/i_190a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 234.</span>—Leaf mosaic
+of elm.</p></figcaption>
+</figure>
+
+<p id="p-197"><b>197. Leaf mosaics.</b>—Trees with horizontal or drooping
+branches, like the elm and beech, and vines growing along
+walls or trailing on the ground, generally display their foliage
+in flat, spreading layers, each leaf fitting
+in between the interstices of the
+others like the stones in a mosaic,
+whence this has been called the <em>mosaic</em>
+arrangement. (<a href="#i_189">Plate 10</a>.) In plants of
+more upright or bunchy habit, the
+leaves are placed at all angles, giving
+the appearance of a rosette when viewed
+from above, whence this is called the
+<em>rosette</em> arrangement.</p>
+
+<p>A variety of the same disposition is
+seen in the pyramidal shape assumed
+by plants with large, undivided leaves
+like the mullein and burdock (<a href="#i_191a">Fig. 237</a>), in which access of
+light is secured by a mutual adjustment between the size
+and position of leaves, the upper ones becoming successively
+smaller.</p>
+
+<p><span class="pagenum" id="Page_181">[Pg 181]</span></p>
+
+<p id="p-198"><b>198. Heliotropism</b>—“turning
+with the sun”—is
+the name given to the daily
+movement of plants like the
+cotton and sunflower in
+turning their leaves or their
+blossoms to face the sun. If you live where cotton is grown,
+notice the leaves in a field about ten o’clock on a bright
+sunny morning, and again from the same
+point of view at about four or five in the
+afternoon. Do you perceive any difference
+in their general disposition?
+Watch on a
+cloudy day and see if
+any change takes place.
+Find out by observation
+whether the “heliotrope”
+of the hothouses is really
+heliotropic.</p>
+
+<figure class="figcenter illowp90" id="i_191" style="max-width: 99em;">
+  <img class="w100" src="images/i_191.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 235, 236.</span>—Horse-chestnut leaves: 235, leaf rosette seen from above;
+236, the same seen sidewise, showing the formation of rosettes by the lengthening
+of the lower petioles.</p></figcaption>
+</figure>
+
+<table class='autotable'>
+<tr><td>
+<figure class="figcenter illowp70" id="i_191a" style="max-width: 25em;">
+  <img class="w100" src="images/i_191a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 237.</span>—Leaf
+pyramid of mullein.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp70" id="i_191b" style="max-width: 28em;">
+  <img class="w100" src="images/i_191b.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 238, 239.</span>—A
+compass plant, rosinweed
+(<i>Silphium laciniatum</i>):
+238, seen from
+the east; 239, seen
+from the south.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-199"><b>199. Adjustment
+against too great intensity
+of light.</b>—Plants frequently
+have to protect
+themselves against excess
+of light and heat. An<span class="pagenum" id="Page_182">[Pg 182]</span>
+interesting example of this kind of adjustment is furnished
+by the rosinweed, or compass plant (<i>Silphium laciniatum</i>,
+<a href="#i_191b">Figs. 238, 239</a>), which grows in the prairies of Alabama and
+westward, where it is exposed to intense sunlight. The
+leaves not only stand vertical, but have a tendency to turn
+their edges north and south so that the blades are exposed
+only to the gentler morning and evening rays. The prickly
+lettuce manifests the same habit in a less marked degree.</p>
+
+<figure class="figright illowp50" id="i_192" style="max-width: 38em;">
+  <img class="w100" src="images/i_192.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 240, 241.</span>—A plant of the guayule
+(<i>Parthenium argentatum</i>), to the leaves of which
+indexes have been affixed to show their day and
+night position: 240, day position; 241, night
+position. (<i>From</i> photographs by Prof. F. E.
+Lloyd.)</p></figcaption>
+</figure>
+
+<p id="p-200"><b>200. Night and day adjustments.</b>—These are movements
+in response to changes in the degree of illumination
+and temperature, as evidenced by the fact that they become
+feeble and soon cease altogether if the plant is kept a sufficient
+time under uniform conditions as to these two factors.
+(<a href="#exp-74">Exp. 74</a>.) They are called “nyctitropic” or sleep movements,
+because they are most obvious in certain plants that
+undergo periodic adjustments to the alternations of day and
+night suggestive of an imaginary likeness to the sleep of animals.
+Examples are
+most frequently met
+with among members of
+the pea family (<i>Leguminosæ</i>),
+the spurges
+(<i>Euphorbiaceæ</i>), and the
+sorrel (<i>Oxalis</i>) family.
+They are found among
+other species also, and
+indeed are much more
+general than is usually
+supposed, most plants
+showing signs of them
+if carefully tested. A
+simple way of doing this
+is by attaching bristles about two inches long to the tips of
+two leaves on opposite sides of the stem, as in <a href="#i_192">Figs. 240, 241</a>,
+and comparing the divergence of the bristles during the day
+and at nightfall. In this way a change of position in the<span class="pagenum" id="Page_183">[Pg 183]</span>
+leaves, too slight to attract attention otherwise, will be made
+apparent. The positions assumed vary in different plants,
+and even in the parts of the same compound leaf; in the
+kidney bean, for instance, the common petiole turns up at
+night, while the individual leaflets turn down. One of the
+common pigweeds (<i>Amaranthus Palmeri</i>, <a href="#i_193">Figs. 242-244</a>) is
+heliotropic in the day time and nyctitropic at night.</p>
+
+<figure class="figcenter illowp90" id="i_193" style="max-width: 50em;">
+  <img class="w100" src="images/i_193.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 242-244.</span>—Showing the movements of <i>Amaranthus Palmeri</i>: 242, 243,
+position at sunrise and sunset (heliotropic); 244, night position (nyctitropic) half an
+hour after sunset. (<i>From</i> photographs by Prof. F. E. Lloyd.)</p></figcaption>
+</figure>
+
+<p>The very striking nyctitropic adjustments of the wild
+senna (<i>Cassia tora</i>) photographed by Professor Francis<span class="pagenum" id="Page_184">[Pg 184]</span>
+E. Lloyd of the Alabama Polytechnic Institute (<a href="#i_193a">Figs. 245-250</a>),
+though obviously influenced by the sun, are not
+directed toward it as in those of truly heliotropic plants.</p>
+
+<figure class="figcenter illowp90" id="i_193a" style="max-width: 53.25em;">
+  <img class="w100" src="images/i_193a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 245-250.</span>—Wild senna (<i>Cassia tora</i>), showing the nyctitropic adjustments
+of its leaves. The upper figures show their horizontal arrangement; those below,
+the vertical: 245, 248, position of the leaves at 9 <span class="allsmcap">A.M.</span>; 246, 249, at 3 <span class="allsmcap">P.M.</span>; 247,
+250, at 6.30 <span class="allsmcap">P.M.</span> (<i>From</i> photographs by Prof. F. E. Lloyd.)</p></figcaption>
+</figure>
+
+<p>These movements are common also among flowers, many
+of them having regular hours for opening and closing, as indicated
+by such names as “morning-glory” and “four-o’clock.”
+In these cases, however, other causes (<a href="#p-277">277</a>, <a href="#p-280">280</a>)
+than the light relation must be taken into account.</p>
+
+<p id="p-201"><b>201. Irritability</b> is a general term applied to the power in
+plants of receiving and responding by spontaneous movements
+to impressions from without. In its widest acceptation,
+irritability includes, besides the various forms of
+adjustment described in this section and the next, all movements
+due to geotropism, those of roots seeking air and moisture,
+the revolution of twining stems and tendrils, the circulation
+of protoplasm in the cell—any movement, in short,
+that is made in response to an impression from the environment
+is a manifestation of irritability. It may be of various
+degrees, but is possessed to some extent by every living vegetable
+organism.</p>
+
+<p>The term is usually applied, however, more especially to
+those obvious and pronounced responses made by plants to
+their surroundings, as exemplified in the cases just given.
+Still more marked instances are to be found in the movements
+of the tentacles of insectivorous plants, and the sensitive
+leaflets of the mimosa that close at the slightest touch. The
+tendrils of the passion flower are said to appreciate and
+respond to a pressure that cannot be distinguished even by
+the human tongue, and many plants will detect and respond
+to the ultra-violet rays of light, which are entirely invisible
+to man.</p>
+
+<p>This faculty of irritability among plants corresponds, in an
+imperfect, rudimentary way, to what we recognize in animals
+as nervous excitability. By this it is not meant to imply
+that the two things are identical in their ultimate manifestations,
+though we may regard them as fundamentally the<span class="pagenum" id="Page_185">[Pg 185]</span>
+same in that they are both to be referred to the property
+inherent in protoplasm of responding to stimuli. There is
+no indication, however, that irritability in the vegetable
+kingdom is accompanied by anything like consciousness or
+volition, or that plants possess any power of initiative.
+While the movements in response to stimuli are in many
+cases eminently adapted to a purpose, we have no evidence
+of a controlling power behind them. The movement comes
+automatically in response to the stimulus, whether the effect
+at the moment be advantageous or the
+reverse.</p>
+
+<p id="p-202"><b>202. Adjustments in relation to
+moisture.</b>—These adjustments may
+be—(1) To guard against excess of
+moisture; <i>e.g.</i> glands for excreting water
+and salts; scales, wax, down, etc., on
+the surface of leaves. These may serve
+also for protection against cold, insects,
+excess of light and heat. (2) For the
+conservation of moisture; <i>e.g.</i> the revolute
+leaf margins of grasses and sand plants growing along
+the seashore; the fleshy leaves of stonecrops and purselanes;
+the hard epidermis of yuccas and aloes; the scales, scurf, and
+down, by which the moisture absorbed from the soil by plants
+growing in dry and barren
+places is prevented
+from escaping too
+rapidly through the
+stomata; the leaf cups
+and holders sometimes
+formed by winged
+petioles and clasping
+leaf bases for retaining
+dew or rain water.
+(3) For leaf drainage,
+or the conduction of<span class="pagenum" id="Page_186">[Pg 186]</span>
+moisture, by means of grooves, channels, and taper-pointed
+leaves, which act as natural gutters and drain pipes.</p>
+
+<table>
+<tr><td>
+<figure class="figcenter illowp90" id="i_195" style="max-width: 21.25em;">
+  <img class="w100" src="images/i_195.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 251.</span>—Cross sections
+of the leaf of sand
+grass: <i>a</i>, unrolled in its ordinary
+position; <i>b</i> and <i>c</i>,
+rolled up to prevent too
+rapid transpiration.</p></figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp90" id="i_195_252" style="max-width: 24.375em;">
+  <img class="w100" src="images/i_195_252.jpg" alt="">
+  <figcaption>
+    <p><span class="smcap">Fig. 252.</span>—Winged petiole of <i>Polymnia</i>.</p>
+  </figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp90" id="i_195_253" style="max-width: 24.375em;">
+  <img class="w100" src="images/i_195_253.jpg" alt="">
+  <figcaption>
+    <p><span class="smcap">Fig. 253.</span>—Water cups of <i>Silphium perfoliatum</i>.</p>
+  </figcaption>
+</figure></td></tr></table>
+
+<figure class="figright illowp50" id="i_196" style="max-width: 50.75em;">
+  <img class="w100" src="images/i_196.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 254.</span>—Fallen leaves. Notice how they cover
+the ground with a warm mulch, protecting the soil
+from denudation, and the roots and seeds from frost.</p></figcaption>
+</figure>
+
+<p id="p-203"><b>203. The fall of the leaf.</b>—This is, in effect, an adjustment
+to change of temperature, but that it is not directly due
+to cold is shown by <a href="#exp-75">Exp. 75</a>, and also by the fact that leaves
+in the tropics and those of evergreens, while they do not fall
+at stated periods like the bulk of the foliage in the temperate
+zones, are cut off just the same and replaced by new ones,
+whenever, for any
+reason, they are unable
+to perform their
+function. In cold
+climates they fall at
+the approach of
+winter, not because
+the frost loosens
+them, but because
+the roots are not able
+to absorb enough
+moisture to supply
+them with material
+for making food.
+The needles and the
+scale-leaves characteristic
+of evergreens
+in cold regions are
+enabled to persist indefinitely by reason of their contracted
+surface. This prevents the dissipation of moisture and affords
+no lodging for the accumulations of sleet and snow that
+would otherwise cumber and perhaps break the boughs with
+their weight. Trees and shrubs that shed their leaves in winter
+are said to be <em>deciduous</em>, from a Latin word meaning “to
+fall.” Can you mention some advantages of the deciduous
+habit to a plant with broad, expanded leaves, growing in
+a cold climate?</p>
+
+<p>The mechanical means by which the leaf fall is accomplished<span class="pagenum" id="Page_187">[Pg 187]</span>
+is through the growth of a corky layer of loose
+cells that forms at the base of the petiole and cuts it away
+from the stem, leaving a smooth, clean scar. Tear some
+fresh young leaves from a growing twig and compare the
+scars with those on a winter bough. Do you see any
+difference? This corky layer can be made to form in
+some plants artificially, by depriving them of working material.
+(<a href="#exp-75">Exp. 75</a>.)</p>
+
+<p id="p-204"><b>204. The protection of wintergreen leaves.</b>—A great
+many, perhaps the majority of broad-leaved evergreens,
+bear no obvious protection against cold, while a large proportion,
+such as chickweed, violet, fumitory, groundsel
+(<i>Senecio</i>), and dead nettle (<i>Lamium</i>), would seem peculiarly
+unfitted, by their delicate structure, to withstand it. But
+recent investigations by the Swedish botanist, Lidforss,
+have shown that all wintergreen leaves, with the exception
+of those on submerged water plants, which are sufficiently
+protected by the medium in which they live, lose their
+starch in winter and contain instead an increased percentage
+of sugar. The same is true of other vegetable structures
+also, where starch is present, such as roots, stems, tubers,
+and winter fruits—nuts, haws, persimmons, and the like,
+which, as every schoolboy knows, become perceptibly sweeter
+after frost.</p>
+
+<p>The presence of certain substances, of which sugar is the
+most frequent, enables plants to withstand a greater degree
+of cold than they could otherwise endure (<a href="#exp-76">Exp. 76</a>). This
+effect, as shown by Lidforss’s experiments, is due to the
+action of sugar in counteracting, or retarding, the “salting
+out” of proteins by cold, as explained in 33.</p>
+
+<p>As sugar is readily reconverted into starch by exposure to
+a moderately high temperature for even a few days, we may
+find here an explanation of the fact that plants which have
+survived the prolonged cold of winter are often killed by a
+single sharp night frost following a few warm days in early
+spring, before the tender new growth has appeared. The<span class="pagenum" id="Page_188">[Pg 188]</span>
+plant suffers, not from the direct effects of cold, but from
+the warmth preceding it, which stimulated the transformation
+into starch of the sugar that would have prevented the
+loss of proteins. On the same principle we may account for
+the puzzling fact that the sunny southern side of trees and
+shrubs usually suffers more from the effects of sudden frost
+than the shaded and colder northern face.</p>
+
+<p>In apparent conflict with this reasoning is the fact that
+sugar cane and the sugar beet are peculiarly susceptible to
+cold. This, however, does not invalidate the premises established
+by Lidforss’s researches, but merely emphasizes
+the need of further investigation, which may either reconcile
+all the facts, or modify their interpretation.</p>
+
+<p id="p-205"><b>205. The colors of autumn leaves.</b>—These are due to
+the breaking up and disappearance of the chlorophyll when
+the leaf factory has to “shut down” for want of raw material
+to work with <a href="#p-203">(203)</a>. It is closely connected with the
+appearance of frost, since the same changes of temperature
+which produce frost cause the cessation of sap flow that
+brings about the disorganization of the chlorophyll and the
+formation of various pigments derived from it. Besides
+these, leaves may contain other coloring matters that are
+perceptible only when the chlorophyll disappears; and in
+the sap there is a reddish pigment which becomes either a
+very bright red, or a dark purplish maroon, from the effect
+of chemicals that combine with it in the leaves. With these
+coloring materials at command it is easy to see how the
+autumn woods can assume such splendid hues.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. How would you explain the fact that the outer twigs of trees generally
+are the most leafy? (<a href="#p-99">99</a>, <a href="#p-194">194</a>; <a href="#exp-57">Exps. 57</a>, <a href="#exp-74">74</a>.)</p>
+
+<p>2. Is the common sunflower a compass plant? Is cotton?</p>
+
+<p>3. Are there any such plants in your neighborhood?</p>
+
+<p>4. Compare the leaves of half a dozen shade-loving plants of your neighborhood
+with those of as many sun-loving ones; which, as a general thing,
+are the larger and less incised?</p>
+
+<p><span class="pagenum" id="Page_189">[Pg 189]</span></p>
+
+<p>5. Give a reason for the difference. (<a href="#p-169">169</a>.)</p>
+
+<p>6. Why do most leaves—notably grasses—curl their edges backward
+in withering? (<a href="#p-182">182</a>.)</p>
+
+<p>7. What advantage is gained by doing this? (<a href="#p-202">202</a>.)</p>
+
+<p>8. Observe such of the following plants as are found in your neighborhood,
+and report any changes of position that may take place in their
+leaves and the causes to which such changes should be ascribed: wood
+sorrel, mimosa, honey locust, wild senna, partridge pea, wild sensitive plant,
+redbud, bush clover, Japan clover, Kentucky coffee tree, sensitive brier
+(<i>Schrankia</i>), peanut, kidney bean.</p>
+
+<p>9. Which of the trees named below shed their leaves from base to tip
+of the bough (centripetally), and which in the reverse order: ash, beech,
+hazel, hornbeam, lime, willow, poplar, pear, peach, sweet gum, elm, sycamore,
+mulberry, China tree, sumac, chinquapin?</p>
+
+<p>10. Account for the fact that evergreen trees and shrubs have generally
+thick, hard, and shiny leaves, like those of the holly and magnolia, or scales
+and needles, as the cedar and pine. (<a href="#p-203">203</a>.)</p>
+
+<p>11. Why do many plants which are deciduous at the North tend to become
+evergreen at the South? (<a href="#p-203">203</a>.)</p>
+
+<p>12. Why are evergreens more abundant in cold than in warm climates?
+(<a href="#p-203">203</a>.)</p>
+
+<p>13. There is an apparent inconsistency between questions 11 and 12;
+can you reconcile it? (<a href="#p-203">203</a>.)</p>
+
+<p>14. Why is it more important to protect the south side of trees against
+exposure to frost than the northern side? (<a href="#p-33">33</a>, <a href="#p-204">204</a>.)</p>
+
+<p>15. Explain why peach orchards on the tops and northern slopes of elevated
+areas are less liable to have their fruit destroyed by late frost than
+those in the valleys and on the southern slopes. (<a href="#p-33">33</a>, <a href="#p-204">204</a>.)</p>
+</div>
+
+
+<h3 id="CH_VI_VIII">VIII. MODIFIED LEAVES</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Get from a florist a potted plant of sundew, Venus’s-flytrap,
+sarracenia, or, if possible, one of all three, and keep in the schoolroom
+for observation. The subject can be studied best in a well-stocked
+greenhouse, if one is accessible.</p>
+</div>
+
+<figure class="figright illowp40" id="i_200" style="max-width: 37.375em;">
+  <img class="w100" src="images/i_200.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 255.</span>—Spearlike leaves of Spanish
+bayonet.</p></figcaption>
+</figure>
+
+<p id="p-206"><b>206. Modification and adaptation.</b>—Modification is
+structural adjustment, or adaptation, carried so far as to
+obscure the original form of an organ. Its true nature,
+however, can generally be determined by some of the tests
+mentioned in <a href="#p-100">100</a>.</p>
+
+<p>Examples of the modification of leaves to do the work of<span class="pagenum" id="Page_190">[Pg 190]</span>
+other organs have already been noticed, as also their entire
+disappearance in certain cases (<a href="#p-97">97</a>, <a href="#p-101">101</a>, <a href="#p-149">149</a>) and replacement
+by other parts; it is
+unnecessary, therefore, to
+revert to this branch of the
+subject here.</p>
+
+<p id="p-207"><b>207. Protective modifications.</b>—The
+most general
+protective modifications
+that leaves undergo are
+(1) for the conservation of
+moisture, as explained in
+<a href="#p-202">202</a>, and (2) for protection
+against animals. Many of
+the adaptations for the
+former purpose serve incidentally
+for defense against
+animals also. Spines, hairs,
+scales, sticky exudations,
+water holders, clasping and
+perfoliate leaves bar the way to crawling insects; horny
+cuticles, as well as offensive odors, bitter secretions, and
+poisonous juices warn leaf-eating cattle and bugs away.
+These devices are merely protective, however, and adapted
+to a passive attitude of self-defense.</p>
+
+<figure class="figcenter illowp90" id="i_200a" style="max-width: 50em;">
+  <img class="w100" src="images/i_200a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 256-258.</span>—Protective hairs magnified: 256, mullein; 257, cinque-foil
+258, Shepherdia.</p></figcaption>
+</figure>
+
+<p id="p-208"><b>208. Insectivorous leaves.</b>—But sometimes a plant<span class="pagenum" id="Page_191">[Pg 191]</span>
+becomes the aggressor, and instead of standing on the defensive
+or suffering itself to be quietly devoured, proceeds to
+capture and devour small game on its own account, and in
+this case, the leaf sometimes becomes a deadly weapon of
+destruction.</p>
+
+<p id="p-209"><b>209. Pitcher plants.</b>—The sarracenia, or trumpet leaf,
+is a familiar example of this class. The lower part of the
+leaf blade is transformed
+into a hollow vessel for
+holding water, and the
+top is rounded into a
+broad flap called the
+<em>lamina</em>. Sometimes the
+lamina stands erect, as
+in the common yellow
+trumpets of our coast
+regions, and when this is
+the case, it is brilliantly
+colored and attracts insects
+(<a href="#i_201">Fig. 259</a>). Sometimes,
+as in the parrot-beaked
+and the spotted
+trumpet leaf, it is bent
+over the top of the water
+vessel like a lid, and the
+back of the leaf, near the foot of the lamina, is dotted with
+transparent specks that serve to decoy foolish flies away
+from the true opening and tempt them to wear themselves
+out in futile efforts to escape, as we often see them do against
+a window pane.</p>
+
+<table>
+<tr><td>
+<figure class="figcenter illowp80" id="i_201" style="max-width: 43.75em;">
+  <img class="w100" src="images/i_201.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 259.</span>—Yellow trumpets (<i>Sarracenia flava</i>).
+(<i>From</i> the Mo. Botanical Garden Rep’t.)</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp80" id="i_202" style="max-width: 28.75em;">
+  <img class="w100" src="images/i_202.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 260.</span>—Plant of sundew.</p></figcaption>
+</figure></td></tr></table>
+
+<p>If the contents of one of these leaves are examined with a
+lens, there will generally be found mixed with the water at the
+bottom the remains of the bodies of a large number of insects.
+The hairs on the outside all point up, toward the
+rim of the pitcher, while those on the inside turn down,
+thus smoothing the way to destruction, but making return<span class="pagenum" id="Page_192">[Pg 192]</span>
+impossible to a small insect when once it is ensnared.
+When we remember that these plants are generally found
+in poor, barren soil, we can appreciate
+the value to them of the animal
+diet thus obtained.</p>
+
+<figure class="figcenter illowp90" id="i_202a" style="max-width: 50em;">
+  <img class="w100" src="images/i_202a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 261-263.</span>—Leaves of sundew magnified: 261, leaf expanded; 262, leaf
+closing over captured insect; 263, leaf digesting a meal.</p></figcaption>
+</figure>
+
+<p id="p-210"><b>210. Flytraps.</b>—The most remarkable
+examples of insect-catching
+leaves are the Venus’s-flytrap,
+found in the seacoast region of
+North Carolina, and the sundew
+(<i>Drosera rotundifolia</i>), common on
+the margins of sandy bogs and
+ponds. The latter is a delicate,
+innocent-looking little plant, and
+owes its poetic name to the dewlike
+appearance of a shining, sticky
+fluid exuded from glands on its
+leaves, which glitter in the sun like dewdrops. It is, however,
+a most voracious carnivorous plant, the sticky leaves acting
+as so many bits of fly paper by means of which it catches its
+prey. When a fly has been trapped, the tentacles close
+upon it, the edges of the leaf curve inward, making a sort of
+stomach, from the glands of which an acid juice exudes and<span class="pagenum" id="Page_193">[Pg 193]</span>
+digests the meal. After a number of days, varying according
+to the digestibility of the diet, the blades slowly unfold again
+and are ready for another capture.</p>
+
+<figure class="figcenter illowp90" id="i_203" style="max-width: 50em;">
+  <img class="w100" src="images/i_203.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 264.</span>—Bladderwort, showing finely dissected submerged leaves
+bearing bladders for capturing animalculæ.</p></figcaption>
+</figure>
+
+<p>The bladderwort, common in pools and still waters nearly
+everywhere, has its petioles transformed into floats, while
+the finely dissected, rootlike blades bear little bladders which,
+when examined under the microscope, are found to contain
+the decomposed remains of captured animalculæ.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Can you find any kind of leaf that is not preyed upon by something?
+If so, how do you account for its immunity?</p>
+
+<p>2. Make a list of some of the most striking of the protected leaves of
+your neighborhood.</p>
+
+<p>3. What is the nature of the protective organ in each case?</p>
+
+<p>4. For protection against what does it seem to be specially adapted?</p>
+
+<p>5. Are the plants in your list for the most part useful ones, or troublesome
+weeds?</p>
+
+<p><span class="pagenum" id="Page_194">[Pg 194]</span></p>
+
+<p>6. Examine the leaves of the worst weeds that you know of and see
+if these will help in any way to account for their persistency.</p>
+</div>
+
+
+<h4 id="CH_VI_FIELD">Field Work</h4>
+
+<div class="blockquot">
+
+<p>(1) In connection with Sections I and II, observe the effect of the lobing
+and branching of leaves in letting the sunlight through. Notice any
+general differences that may appear as to shape, margin, and texture in the
+leaves of sun plants, shade plants, and water plants, and account for them.
+Study the arrangement of leaves on stems of various kinds, with reference
+to the size and shapes of leaves and their light relations. Consider the
+value of the various kinds of foliage for shade; for ornament; as producers
+of moisture; as food; as insect destroyers, etc.</p>
+
+<p>Make a special study of the twelve principal deciduous trees of your
+neighborhood. Compare the leaves, bark, and branches of the same
+trees so that you will be able to recognize them by any one of these means
+alone.</p>
+
+<p>(2) In connection with Sections III and V, consider the effects upon soil
+moisture of transpiration from the leaves of forest trees and from those
+of shallow-rooted herbs and weeds that draw their water supply from
+the surface. Consider the value of forests in protecting crops from excessive
+evaporation by acting as wind breaks. Study the effect of the fall of
+leaves upon the formation of soil. In any undisturbed forest tract turn up
+a few inches of soil with a garden trowel and see what it is composed of.
+Notice what kind of plants grow in it. Note the absence of weeds and
+account for it. Compare the appearance of trees scattered along windy
+hillsides, where the fallen leaves are constantly blown away, or in any
+position where the soil is unrenewed, with those in an undisturbed forest,
+and then give an opinion as to the wisdom of hauling away the leaves every
+year from a timber lot.</p>
+
+<p>(3) In Section VII, observe, in different kinds of leaf mosaics, the means
+by which the adjustment has been brought about and the purpose it subserves.
+Make a list of plants illustrating the two habits. Notice the form
+and position of petioles of different leaves, and their effect upon light exposure,
+drainage, etc., and the behavior of the different kinds in the wind.
+Look for compass plants in your neighborhood, and for other examples of
+adjustment to heat and light. Study the position of leaves at different
+times of day and in different kinds of weather and note what changes occur
+and to what they are due.</p>
+
+<p>Make a list of ten plants that seem to you to have best worked out the
+problem of leaf adjustment, giving the reasons for your opinion.</p>
+
+<p>Study the drainage system of different plants and observe whether there
+is any general correspondence between the leaf drainage and the root systems.<span class="pagenum" id="Page_195">[Pg 195]</span>
+This will lead to interesting questions in regard to irrigation and
+manuring. Where plants are crowded, the growth of both roots and
+leaves is complicated with so many other factors that it is best to select
+for observations of this sort specimens growing in more or less isolated
+situations.</p>
+
+<p>Notice the time of the expansion and shedding of the leaves of different
+plants, and whether the early leafers, as a general thing, shed early or late;
+in other words, whether there seems to be any general time relation between
+the two acts of leaf expansion and leaf fall.</p>
+
+<p>(4) Under Section VIII, look for instances of modified leaves; study
+the nature of the different modifications you find, and try to understand
+their meaning and object. Make a collection (<i>a</i>) of all the leaves you can
+find modified to serve other than their normal purposes; (<i>b</i>) of all the
+organs of other kinds that have been modified to serve as leaves; (<i>c</i>) of
+all the modified parts of leaves—stipules and petioles—that you can
+find. Keep the collections separate, labeling each specimen with the
+name of the plant it belongs to, what part it is, what use it serves,
+when and where found. These collections need not be made individually,
+but by the class as a whole and kept for the use of the school.</p>
+
+<p>Observe also (<i>d</i>) the differences between young and old leaves of the
+same kind, and the leaves of young and old plants or parts of plants of the
+same kind; (<i>e</i>) resemblances between young leaves belonging to plants of
+different species; (<i>f</i>) between young leaves of one species and mature ones
+of one or more different species. Make a collection of all the specimens you
+can find illustrating the three points mentioned, referring each to its proper
+head, and giving the name and relative age—old or young—of all specimens
+collected.</p>
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_196">[Pg 196]</span></p>
+
+<h2 class="nobreak" id="CH_VII">CHAPTER VII. THE FLOWER</h2>
+</div>
+
+
+<h3 id="CH_VII_I">I. DISSECTION OF TYPES WITH SUPERIOR OVARY</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—For monocotyls, any flower of the lily family, such as
+tulip, dogtooth violet (<i>Erythronium</i>), trillium, star-of-Bethlehem, yucca,
+bear’s grass, and the like. The large garden lilies make particularly good
+examples, but they are for the most part spring bloomers. For autumn,
+spiderwort (<i>Tradescantia</i>), arrow grass (<i>Sagittaria</i>), or late specimens of
+colchicum and tiger lily may be used. Any of these will meet the essential
+conditions of the analysis given in the text, but care should be taken not to
+select for this exercise lily-like flowers of the iris and amaryllis families,
+which have the <em>ovary inferior</em>.</p>
+
+<p>For examples of hypogynous dicotyls, flax, linden, pinks, corn cockle,
+wood sorrel, poppies, tomato blossoms, and other common flowers can
+usually be obtained without difficulty. In autumn, the geraniums so
+largely cultivated for ornament will meet all the conditions of the analysis.
+Specimens of the cress family—wallflower, cabbage, mustard, turnip—can
+generally be found everywhere and at all seasons, and they possess
+the advantage of having their flowers throughout the order put up on so
+nearly the same pattern that a description of one species will answer, even
+in details, for the rest.</p>
+
+<p>For sympetalous specimens of the hypogynous type, hyacinth, lily of
+the valley, bearberry, huckleberry, or other equivalent forms may be
+used.</p>
+
+<p><span class="smcap">Appliances.</span>—A compound microscope may be needed for examining
+minute objects, such as pollen grains and ovules; but for all other purposes,
+a good hand lens, with the pupil’s ordinary laboratory equipment
+of drawing-materials, notebook, and dissecting needles, will be sufficient
+for the studies outlined in this and the four succeeding sections.</p>
+</div>
+
+<figure class="figcenter illowp90" id="i_207" style="max-width: 50em;">
+  <img class="w100" src="images/i_207.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 265-267.</span>—Flower of a monocotyl (star-of-Bethlehem), with superior
+ovary dissected: 265, entire flower, showing the different sets of organs: <i>pet</i>,
+petals; <i>sep</i>, sepals; <i>sta</i>, stamens; <i>pist</i>, pistil; <i>ped</i>, peduncle; 266, side view with
+all the petals and sepals but two removed to show order of the parts: <i>r</i>, receptacle;
+<i>o</i>, ovary; <i>sty</i>, style; <i>stig</i>, stigma—parts composing the pistil; <i>f</i>, filament;
+<i>a</i>, anther—parts composing the stamen; 267, cross section of the ovary: <i>c</i>, <i>c</i>, carpels;
+<i>ov</i>, ovules; <i>pl</i>, placenta.</p></figcaption>
+</figure>
+
+<p id="p-211"><b>211. The floral envelopes.</b>—Make a sketch of your
+specimen flower from the outside. Is it solitary, or one of a
+cluster? If the latter, refer to <a href="#p-160">160-162</a> and tell the nature
+of the cluster. Notice the color; is it conspicuous enough
+to attract attention or not? Can this have anything to do
+with its clustered or solitary position? Label the head of
+the peduncle that supports the flower, <em>receptacle</em>; the outer<span class="pagenum" id="Page_197">[Pg 197]</span>
+greenish leaves, <em>sepals</em>; the inner, lighter-colored ones,
+<em>petals</em>. The sepals taken together form the <em>calyx</em>, and the
+petals, the <em>corolla</em>. Where the petals and sepals are all
+separate and distinct, as in the tulip and the star-of-Bethlehem,
+the corolla is said to be <em>polypetalous</em> and the calyx
+<em>polysepalous</em>, words meaning, respectively, many-petaled
+and many-sepaled. <em>Monopetalous</em> and <em>monosepalous</em>, or
+<em>sympetalous</em> and <em>synsepalous</em>, are terms used to describe a
+condition in which the petals or sepals are all united into
+one, as in the morning-glory and lily of the valley. In many<span class="pagenum" id="Page_198">[Pg 198]</span>
+flowers, there is little or no difference between the two sets of
+organs. In such cases the calyx and corolla together are
+called the <em>perianth</em>, but the distinction of parts is always
+observed, the outer divisions being regarded as sepals, the
+inner ones as petals. These two sets of organs constitute
+the <em>floral envelopes</em>, and are not essential parts of the flower,
+as it can fulfill its office of producing fruit and seed without
+them. Note their number, mode of attachment to the
+receptacle, and how they alternate with each other. Remove
+one of the sepals and one of the petals, and notice any
+differences between them as to size, shape, or color. Which is
+most like a foliage leaf? Hold each up to the light and try
+to make out the veining. Is it the same as that of the foliage
+leaves? If a light-colored flower is used, examine a specimen
+that has stood in coloring fluid. How many of each set are
+there?</p>
+
+<figure class="figcenter illowp90" id="i_207a" style="max-width: 50em;">
+  <img class="w100" src="images/i_207a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 268-269.</span>—Yucca blossom: 268, external view: <i>br</i>, bract; <i>pd</i>, peduncle;
+<i>r</i>, receptacle; <i>s</i>, sepal; <i>pet</i>, petal; 269, vertical section: <i>ped</i>, peduncle; <i>br</i>, bract;
+<i>r</i>, receptacle; <i>per</i>, perianth; <i>sta</i>, stamen; <i>o</i>, ovary; <i>sty</i>, style; <i>stg</i>, stigma. The
+last three parts named compose the pistil.</p></figcaption>
+</figure>
+
+<figure class="figright illowp35" id="i_208" style="max-width: 36.3125em;">
+  <img class="w100" src="images/i_208.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 270-274.</span>—Stamens: 270, a
+typical stamen with the terminal anther,
+<i>b</i>, surmounting the filament, <i>a</i>,
+and opening in the normal manner
+down the outer side of each cell; 271,
+stamen of tulip tree, with adnate extrorse
+anther; 272, stamen of an evening
+primrose (<i>Œnothera</i>) with versatile
+anther; 273, stamen of pyrola, the
+anther cells opening by chinks or pores
+at the top; 274, stamen of a cranberry,
+with the anther cells prolonged into a
+tube and opening by a pore at the apex.
+(<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p id="p-212"><b>212. The essential organs.</b>—Next sketch the flower on
+its inner face, labeling the appendages just within the petals,
+<em>stamens</em>, and the central organ
+within the ring of stamens,
+<em>pistil</em>. These are called essential
+<em>organs</em> because they are
+necessary to the production of
+fruit and seed. Note their
+mode of insertion, three of the
+stamens in a flower like the
+star-of-Bethlehem alternating
+with the petals, and the other
+three with these and with the
+lobes of the base of the pistil.</p>
+
+<p id="p-213"><b>213. The stamens.</b>—Notice
+whether the stamens are
+all alike, or whether there are
+differences as to size, height,
+shape, color, etc. Do these
+differences, if there are any,<span class="pagenum" id="Page_199">[Pg 199]</span>
+occur indiscriminately and without order, or in regular succession
+between the alternating stamens? Examine one of
+the little powdery yellow bodies at the tip of the stamens,
+and see whether they face toward the pistil or away from it.</p>
+
+<p>Remove one of the stamens and sketch as it appears under
+the lens, labeling the powdery yellow body at the top,
+<em>anther</em>, and the stalklike body supporting it, <em>filament</em>. Usually
+the filaments are threadlike, whence their name, but
+sometimes, as in the star-of-Bethlehem, they are flattened
+and look like altered petals. See if you can find such a one.
+What would you infer from this fact as to the possible origin
+of the stamens? (<a href="#p-100">100</a>.)</p>
+
+<figure class="figright illowp40" id="i_209" style="max-width: 39.25em;">
+  <img class="w100" src="images/i_209.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 275-278.</span>—Forms of pollen: 275,
+from <i>mimulus</i>; 276, star cucumber; 277
+wild balsam apple; 278, <i>hibiscus</i>. (<i>After</i>
+<span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p>Notice the two little sacs or pouches that compose the
+anther, as to their shape and manner of opening, or dehiscing,
+to discharge the powder
+contained in them. This
+powder is called <em>pollen</em>, and
+will be seen under the lens
+to consist of little yellow
+grains. These are of different
+shapes, colors, and sizes,
+in different plants, and their surface often appears beautifully
+grooved and striate when sufficiently magnified. Place some
+of the pollen under the microscope and draw two of the
+grains, with their markings. In the hibiscus and others of
+the mallow family, they are large enough to be seen with a
+hand lens.</p>
+
+<p id="p-214"><b>214. The pistil.</b>—Remove the stamens and sketch the
+pistil as it stands on the receptacle. Label the round or
+oval enlargement at the base, <em>ovary</em>, the threadlike appendage
+rising from its center, <em>style</em>, and the tip end of the style,
+<em>stigma</em>. In some specimens the style may be very short, or
+wanting. In this case the stigma is <em>sessile</em>, and the pistil
+consists of stigma and ovary alone. If the stigma is lobed
+or parted, count the divisions and see if there is any correspondence
+between them and the number of petals and sepals,<span class="pagenum" id="Page_200">[Pg 200]</span>
+or of the lobes of the ovary. Examine the tip with a lens
+and notice the sticky, mucilaginous exudation that moistens
+it. Can you think of any use for this? If not, touch one of
+the powdery anthers to it, and examine it again with a lens.
+What do you see? Can you blow or dust the pollen from
+the stigma?</p>
+
+<p id="p-215"><b>215. Pollination</b>, or the transfer of pollen from the anther
+to the stigma, is a matter of great importance, as the pistil
+cannot develop seed without it, except in the case of a few
+plants like the Alpine everlasting, some species of meadow
+rue (<i>Thalictrum</i>), and <i>Alchemilla</i>, which have the unusual
+faculty of perfecting seeds in the absence of pollen. Note
+the relative position of pistils and stamens and see if it is
+such that the pollen can reach the stigma without external
+agency.</p>
+
+<p id="p-216"><b>216. The ovary.</b>—Observe the shape of the ovary, and
+the number of ridges, or grooves, that divide the surface.
+Select a flower which has begun to
+wither, so that the ovary is well
+developed, cut a cross section near
+the middle, and try to make out the
+number of <em>locules</em>, or internal divisions.
+Do you perceive any correspondence
+in number between these
+and the ridges or lobes outside (<a href="#i_210">Fig.
+280</a>)? Between them and the lobes
+of the stigma? The walls that
+inclose the cavities of the ovary
+are called <em>carpels</em>, and the ridges or
+depressions that mark their point
+of union on the outside are the
+<em>sutures</em>, or seams. The little round
+bodies in the locules, as the compartments of the ovary are
+called, are the <em>ovules</em>, which will later be developed into seeds.
+Their place of attachment is the <em>placenta</em>. If they are
+attached to the walls of the carpels (<a href="#i_211">Fig. 281</a>), the placenta<span class="pagenum" id="Page_201">[Pg 201]</span>
+is <em>parietal</em>; if to a central axis formed by the edges of the
+carpels projecting inwards (<a href="#i_211">Fig. 282</a>), it is central and axial;
+if instead of being attached to the carpels, the ovules are
+borne on a projection from the receptacle, the placenta is a
+<em>free central</em> one (<a href="#i_211">Fig. 283</a>). If your cross section shows a
+central placenta, make
+a vertical cut down to
+the receptacle and find
+out whether it is free,
+or axial. What appears
+to be the primary
+office of the ovary?
+Make an enlarged
+sketch of your specimen
+in both vertical and horizontal section, labeling correctly
+all the parts observed.</p>
+
+<table class='wd90'>
+<tr><td class='pr1'>
+<figure class="figright illowp100" id="i_210" style="max-width: 27.375em;">
+  <img class="w100" src="images/i_210.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 279, 280.</span>—Ovary of
+yucca, a hypogynous monocotyl,
+dissected: 279, vertical
+section; <i>ov</i>, ovules; 280, diagram
+of a horizontal section of the
+same, enlarged, showing the
+three carpels and six locules;
+<i>ds</i>, dorsal sutures; <i>vs</i>, ventral
+sutures; <i>ov</i>, ovules; <i>pl</i>, placenta.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figright illowp100" id="i_211" style="max-width: 50em;">
+  <img class="w100" src="images/i_211.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 281-283.</span>—Different kinds of placenta:
+281, parietal; 282, central and axial; 283, free
+central. 281 and 282 are horizontal sections; 283,
+vertical.</p></figcaption>
+</figure></td></tr></table>
+
+<figure class="figright illowp25" id="i_211a" style="max-width: 20em;">
+  <img class="w100" src="images/i_211a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 284.</span>—Horizontal
+diagram of a
+flower of the lily kind.
+The dot represents the
+growing axis of
+the plant.</p></figcaption>
+</figure>
+
+<p id="p-217"><b>217. Numerical plan.</b>—Make a horizontal diagram
+of the plan of the whole flower, after the model given in
+<a href="#i_211a">Fig. 284</a>, showing the order of attachment of the different
+cycles,—sepals, petals, stamens, and pistils,—the number
+of organs in each set, and their mode of alternation with the
+organs of the other cycles. Notice that the
+parts of each set are in threes, or multiples
+of three. This is called the numerical plan
+of the flower, and is the prevailing number
+among monocotyls. It is expressed in botanical
+language by saying that the flower is
+<em>trimerous</em>, a word meaning measured, or
+divided off, into parts for three.</p>
+
+<p id="p-218"><b>218. Vertical order.</b>—Next make a vertical
+diagram of your specimen after the
+manner shown in <a href="#i_207a">Fig. 269</a>, and note carefully that the ovary
+stands <em>above</em> the other organs (this is true of all the lily
+family), and is entirely separate and distinct from them. In
+such cases the ovary is said to be <em>free</em>, or <em>superior</em>, and the
+other organs <em>inferior</em>, or <em>hypogynous</em>, a word meaning “inserted<span class="pagenum" id="Page_202">[Pg 202]</span>
+under the pistil.” These terms should be remembered,
+as the distinction is an important one in plant evolution.</p>
+
+<p id="p-219"><b>219. Summary of observations.</b>—In the flower just examined,
+we found that there were four sets of floral organs
+present—sepals, petals, stamens, and pistil; that the individual
+organs in each set were alike in size and shape; that
+there were the same number, or multiples of the same
+number of parts in each set, and that all the parts of each set
+were entirely separate and disconnected, the one from the
+other, and from those of the other cycles. Such a flower is
+said to be:—</p>
+
+<p><em>Perfect</em>, that is, provided with both kinds of organs essential
+to the production of seed—stamens and pistil.</p>
+
+<p><em>Complete</em>, having all the kinds of organs that a flower can
+have: viz. two sets of essential organs, and two sets of
+floral envelopes.</p>
+
+<p><em>Symmetrical</em>, having the same number of organs, or multiples
+of the same number, in each set.</p>
+
+<p><em>Regular</em>, having all the parts of each set of the same size
+and shape, as in the wild rose and bellflower, or if different,
+arranged in regular order or pairs, so that there will be a
+correspondence between the two sides of the flower, as in the
+violet, sweet pea, sage, and larkspur. For convenience, the
+two kinds may be distinguished as <em>complete</em> and <em>bilateral
+regularity</em>, respectively.</p>
+
+<p>The opposites of these terms are: <em>imperfect</em>, <em>incomplete</em>,
+<em>asymmetrical</em> or <em>unsymmetrical</em>, and <em>irregular</em>.</p>
+
+<p>Note that regularity refers to form, symmetry to number
+of parts, and that a flower may be perfect without being
+complete.</p>
+
+<figure class="figcenter illowp80" id="i_213" style="max-width: 50em;">
+  <img class="w100" src="images/i_213.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 285-288.</span>—A flower of the cress family: 285, side view; 286, view from
+above; 287, diagram of parts: <i>p</i>, petals; <i>s</i>, sepals; <i>st</i>, stamens; <i>pi</i>, pistil; <i>cl</i>, claw
+of petal; +, +, position of the missing stamens; 288, pistil and stamens, enlarged.
+(<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<figure class="figright illowp30" id="i_214" style="max-width: 37.625em;">
+  <img class="w100" src="images/i_214.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 289.</span>—Section of a tomato flower, showing
+the hypogynous arrangement: <i>cx</i>, calyx;
+<i>c</i>, corolla; <i>s</i>, stamens; <i>p</i>, pistil; <i>o</i>, ovary; <i>st</i>,
+stigma. (Twice natural size.)</p></figcaption>
+</figure>
+
+<p id="p-220"><b>220. Dissection of a typical dicotyl flower.</b>—(Poppy,
+flax, pink, tomato, linden, etc., can be substituted for the
+specimen used in the text.) Gently remove the sepals and
+petals from a wallflower, stock, mustard, or other cress
+flower, lay them on the table before you in exactly the order
+in which they grew on the stem, and sketch them. How<span class="pagenum" id="Page_203">[Pg 203]</span>
+many of each are there, and how do they alternate with one
+another? Sketch the pistil and stamens as they stand on
+the receptacle; how many of the latter are there? Notice
+that two of the six are outside and a little below the others,
+alternate with the petals, while the other four stand opposite
+them, as is natural, if they were alternating with another
+ring of stamens between themselves and the corolla. Put a
+dot before two of the sepals in your first drawing to indicate
+the position of the two outer stamens, and a cross before
+the other two to show where stamens are wanting to complete
+the symmetry of this set, as in <a href="#i_213">Fig. 287</a>. When parts
+necessary to complete the plan of a flower are wanting, as
+in this case, they are said to be <em>obsolete</em>, <em>suppressed</em>, or
+<em>aborted</em>. Place dots before the petals to represent the other
+four stamens. Sketch one of the anthers as it appears
+under a lens, showing the arrow-shaped base, and the
+mode of attachment to the filament. Is it such that the
+pollen can reach the stigma without external agency? In
+what manner do the anthers open to discharge their pollen?
+Are the anthers and stigma mature at the same time?
+Remove all the stamens from a flower and sketch the pistil,
+showing the long, slender ovary, the very short style, and the<span class="pagenum" id="Page_204">[Pg 204]</span>
+<em>capitate</em> (that is, round and knoblike) stigma. Make cross
+and vertical sections of one of the older pistils lower down
+on the stem. How many
+ovules does it contain?
+How are they attached?
+Represent the position
+of the pistil by a small
+circle in the center of
+your sketch of the separate
+parts. You have
+now a complete ground
+plan of the flower. Diagram
+a vertical section,
+as in <a href="#i_214">Fig. 289</a>, showing
+the position of the ovary
+with reference to the
+other parts, and report
+in your notebook as to the following points:—</p>
+
+<table class="autotable fs80">
+<tr>
+<td class="tdl">Numerical plan</td>
+<td class="tdl">Presence or absence of parts</td>
+</tr>
+<tr>
+<td class="tdl">Symmetry</td>
+<td class="tdl">Union of parts</td>
+</tr>
+<tr>
+<td class="tdl">Regularity (complete or bilateral) &nbsp; &nbsp;</td>
+<td class="tdl">Position of ovary</td>
+</tr>
+</table>
+
+
+<h3 id="CH_VII_II">II. DISSECTION OF TYPES WITH INFERIOR OVARY</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—For monocotyls: in spring and early summer, iris, snowflake,
+freesia, crocus, narcissus, daffodil, can be used; in autumn, gladiolus,
+blackberry lily, fall crocus, star grass (<i>Hypoxys</i>). For dicotyls: in spring,
+flowers of apple, pear, quince, gooseberry, squash, gourd, melon (with both
+male and female flowers); in late summer and autumn, fuchsia, evening
+primrose (<i>Œnothera</i>), willow-herb (<i>Epilobium</i>).</p>
+</div>
+
+<p id="p-221"><b>221. Study of a monocotyl flower.</b>—Compare with the
+specimens examined in the last section, a narcissus, snowflake,
+or iris flower. What difference do you notice in the
+position of the ovary? Would you call it <em>inferior</em> (below the
+other parts) or <em>superior</em> (above them)? How was it in the
+lily and the hyacinth? If your specimen is an iris, notice
+that it is sessile in the axil of a large bract called a <em>spathe</em>,<span class="pagenum" id="Page_205">[Pg 205]</span>
+which conceals the lower part of the flower. Remove the
+spathe and observe that the lower part of the perianth is
+united into a long, narrow tube, from
+the top of which the sepals and petals
+extend as long, curving lobes.</p>
+
+<table>
+<tr><td>
+<figure class="figcenter illowp80" id="i_215" style="max-width: 20em;">
+  <img class="w100" src="images/i_215.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 290.</span>—Iris flower:
+<i>sp</i>, spathes; <i>s</i>, sepals + <i>p</i>,
+petals = perianth.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp80" id="i_215a" style="max-width: 20em;">
+  <img class="w100" src="images/i_215a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 291.</span>—Vertical
+section of iris flower:
+<i>ov</i>, ovules; <i>pl</i>, placenta;
+<i>tu</i>, tube of the perianth
+inclosing the style; <i>sta</i>,
+stamen; <i>sti</i>, stigma: <i>o</i>,
+ovary. (<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure></td></tr></table>
+
+<table>
+<tr><td>
+<figure class="figcenter illowp80" id="i_215b" style="max-width: 20em;">
+  <img class="w100" src="images/i_215b.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 292.</span>—Vertical
+section of iris flower, with
+perianth removed, showing
+a stamen and three stigmas:
+<i>su</i>, stigmatic surface.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp80" id="i_215c" style="max-width: 21.25em;">
+  <img class="w100" src="images/i_215c.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 293.</span>—Cross section
+of ovary of iris flower:
+<i>c</i>, <i>c</i>, carpels; <i>l</i>, <i>l</i>, locules;
+<i>ov</i>, ovules; <i>pl</i>, placenta.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-222"><b>222. Arrangement of parts.</b>—Sketch
+the outside
+of the flower,
+labeling the oblong,
+three-lobed
+enlargement at
+the base, <em>ovary</em>;
+the prolongation
+above it, <em>tube of
+the perianth</em>; the
+three outer lobes
+with the broad
+sessile bases,
+<em>sepals</em>; the others,
+with their bases
+narrowed and bent inward, <em>petals</em>. Now turn the flower over
+and sketch the inside, labeling the three large, petal-like expansions
+in the center,
+<em>stigmas</em>. Do you
+see any stamens?
+Remove one of
+the sepals and
+look under the
+stigma; what do
+you find there?
+Notice the little
+honey pockets at
+the foot of the
+stamen. Run the
+head of your pencil into them and see what would happen
+to the head of an insect probing for honey.</p>
+
+<p><span class="pagenum" id="Page_206">[Pg 206]</span></p>
+
+<p>Remove the perianth and sketch the remaining organs in
+profile, showing the position of the stamens. Do you see
+any advantage in their position? Can you determine the
+use of the crest of hairlike filaments on the upper side of the
+sepals? Remove a stamen and sketch it.</p>
+
+<p id="p-223"><b>223. The pistil.</b>—Remove as much of the upper part of
+the perianth tube as you can without injuring the pistil,
+and with a sharp knife cut a vertical section down through
+the ovary so as to show the long style and its connection with
+the placenta. Make a sketch of this longitudinal section
+(see <a href="#i_215a">Fig. 291</a>), labeling the parts observed. Notice whether
+the placenta is central or parietal. Draw a cross section of
+the ovary; how many locules has it? How many ovules in
+each? Where are they attached? Is the placenta free
+central or axial (<a href="#i_215c">Fig. 293</a>)? Examine with a lens the little
+flap at the base of the two-cleft apex of one of the stigmas, and
+look for a moist spot to which the pollen will adhere. Label
+this in your sketch, <em>stigmatic surface</em>. No seeds can be matured
+unless some of the pollen reaches this surface; can you
+think by what agency it is carried there? What insects
+have you seen hovering about the iris? Notice that in
+drawing his head <em>out</em> of the flower, an insect would not
+touch the stigmatic surface, since it is on the <em>upper</em> side of
+the flap and he would be probing <em>under</em> it. But in entering
+the next flower that he visits, he is likely to
+strike his head against the flap and turn it
+under, thus dusting it with pollen brought
+from another flower.</p>
+
+<figure class="figright illowp25" id="i_216" style="max-width: 20em;">
+  <img class="w100" src="images/i_216.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 294.</span>—Horizontal
+diagram of iris
+flower.</p></figcaption>
+</figure>
+
+<p id="p-224"><b>224. Diagrams.</b>—Draw diagrams showing
+the horizontal and vertical arrangement
+of parts in the iris or other specimen examined,
+and compare with those made of
+the monocotyl studied in the preceding section.
+In what respect does it differ from them? How do
+you account for the difference in the number of stamens, if
+there is any? (<a href="#p-220">220</a>.)</p>
+
+<p><span class="pagenum" id="Page_207">[Pg 207]</span></p>
+
+<p id="p-225"><b>225. The vertical order.</b>—The difference in vertical
+arrangement is an important one. Bear in mind that flowers
+of this type have the ovary <em>inferior</em>, that is, inserted <em>under</em>
+the other organs (<a href="#i_217">Figs. 296</a>, <a href="#i_219a">304</a>), which are then said to be
+superior, or <em>epigynous</em>, a word which, as you know from the
+prefix <i>epi</i> <a href="#p-47">(47)</a>, means over or above the pistil. To make the
+matter clear, the two sets of terms employed for describing
+the position of the ovary are given below in parallel columns:</p>
+
+<table class="autotable fs80">
+<tr>
+<td class="tdl">Hypogynous</td>
+<td class="tdl">Epigynous</td>
+</tr>
+<tr>
+<td class="tdl">Ovary superior</td>
+<td class="tdl">Ovary inferior</td>
+</tr>
+<tr>
+<td class="tdl">Calyx or perianth inferior</td>
+<td class="tdl">Calyx or perianth superior</td>
+</tr>
+</table>
+
+<p>The epigynous arrangement is considered as marking a
+higher stage of floral development than the hypogynous,
+which is characteristic of a more
+simple and primitive structure.</p>
+
+<figure class="figcenter illowp75" id="i_217" style="max-width: 50em;">
+  <img class="w100" src="images/i_217.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 295-296.</span>—Evening primrose, dicotyl flower with inferior
+ovary: 295, exterior view; 296, longitudinal section,
+showing vertical arrangement of parts.</p></figcaption>
+</figure>
+
+<p id="p-226"><b>226. Dissection of a dicotyl
+flower.</b>—Sketch a blossom of
+quince or apple, fuchsia, evening
+primrose, etc., first from the outside,
+then from the inside, and
+then in vertical section, labeling
+the parts as in
+your other
+sketches. Notice
+in the pear
+or apple how
+the ovary is
+sunk in the
+hollowed-out
+receptacle.
+Where are the
+other parts
+attached? Are they inferior or superior? Hold up a petal
+to the light and examine its venation through a lens. (Use
+for this purpose a petal from a flower that has stood in red
+ink for two or three hours.) Is it parallel-veined or net-veined?<span class="pagenum" id="Page_208">[Pg 208]</span>
+If the flowers are clustered, what is the order of
+inflorescence? Does the position of the flowers on their
+branch correspond to that of
+the leaf axils on the same
+kind of plant?</p>
+
+<table>
+<tr><td>
+<figure class="figcenter illowp50" id="i_218" style="max-width: 39.0625em;">
+  <img class="w100" src="images/i_218.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 297-300.</span>—Flower and sections
+of pear: 297, cluster of blossoms, showing
+inflorescence; 298, vertical section of a
+flower; 299, ground plan of a flower; 300,
+vertical section of fruit.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp80" id="i_219" style="max-width: 20em;">
+  <img class="w100" src="images/i_219.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 301.</span>—Vertical
+section of an almond
+blossom with
+petals removed, showing
+the perigynous
+arrangement.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-227"><b>227. The stamens.</b>—Remove
+the petals from a flower
+and examine the stamens
+with a lens. Notice the attachment
+and shape of the
+anthers. Are they all of the
+same color? How do you
+account for the difference, if
+there is any? Is the position
+of the pistil and stamens
+such that the pollen from
+the anthers can readily reach
+the stigmas without external
+aid? Examine the pistil in
+flowers of different ages, and
+see if the stigma is mature (that is, moist and sticky) at the
+same time that the anthers are discharging their pollen.
+Make an enlarged sketch of a stamen showing the shape of
+the anther and the method of opening to discharge pollen.</p>
+
+<p id="p-228"><b>228. The pistils.</b>—How many pistils do you find in the
+apple blossom (or other flower under examination)? Are they
+distinct, or united? Find where the styles originate; what
+do you see there? Make a cross section of the ovary and
+count the locules; how does their number compare with
+that of the styles? Can you make out the number of ovules
+in each? If not, use a young fruit; as it is only an enlarged
+ovary, it will show the parts correctly. Compare it with a
+ripe fruit and see if all the ovules matured. Can you think
+of any reasons why some of them might fail? Do you see
+any signs of nourishment stored in the ovary? Name all
+the ways you can think of in which the ovary can benefit the<span class="pagenum" id="Page_209">[Pg 209]</span>
+ovules and seeds. Draw the ovary in cross and vertical
+sections, labeling correctly all the parts.</p>
+
+<figure class="figcenter illowp80" id="i_219a" style="max-width: 50em;">
+  <img class="w100" src="images/i_219a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 302-304.</span>—Diagrams showing arrangement of parts with reference to the
+ovary: <i>bd</i>, receptacle; <i>k</i>, calyx; <i>kr</i>, corolla; <i>st</i>, stamens; <i>fr</i>, ovary; <i>g</i>, style; <i>n</i>,
+stigma; 302, perigynous; 303, hypogynous; 304, epigynous.</p></figcaption>
+</figure>
+
+<p id="p-229"><b>229. The numerical plan of dicotyls.</b>—Diagram the plan
+of the flower in cross and vertical section. How many parts
+are there in each set? Can you tell readily
+the number of stamens? When the individuals
+of any set or cycle of organs are too
+numerous to be easily counted, like the
+stamens of the apple, pear, and peach, or
+the petals of the water lily, they are said
+to be <em>indefinite</em>. It is very seldom that perfect
+symmetry is found in all parts of the
+flower. The stamens and pistil, in particular,
+show a great tendency to variation, so
+that the numerical plan is generally determined
+by the calyx and corolla. Where the
+parts are in fives, as in the pear, quince, and wild rose, the
+flower is said to be <em>pentamerous</em>, or in sets of five. This is the
+prevailing number among dicotyls, though other orders are
+not uncommon. In the mustard family <a href="#p-220">(220)</a> and other
+well-known species, the fourfold order prevails, while some
+of the saxifrages have their parts in twos, and the magnolia
+and the pawpaw have a threefold arrangement.</p>
+
+<p><span class="pagenum" id="Page_210">[Pg 210]</span></p>
+
+<p id="p-230"><b>230. Intermediate types.</b>—Flowers like the peach and
+rose represent an intermediate type in which the calyx,
+petals, and stamens are attached to a prolongation of the
+receptacle that extends above the ovary, but is not united
+with it (<a href="#i_219">Fig. 301</a>). In general, a flower is not considered as
+belonging to the epigynous kind unless the ovary is more or
+less consolidated with the parts around it (<a href="#i_219a">Fig. 304</a>).</p>
+
+
+<h3 id="CH_VII_III">III. STUDY OF A COMPOSITE FLOWER</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—The largest heads attainable should be selected, as the
+florets are small at best, and difficult to handle. The large cultivated sunflower
+(<i>Helianthus annuus</i>) makes an ideal specimen, if accessible. Oxeye
+daisy and dandelion can be obtained throughout the season almost everywhere,
+but the former has no pappus, and the latter does not show the
+tubular disk flowers. Other common specimens are: for spring, mayweed,
+Jerusalem artichoke, coreopsis, arnica; for late summer and autumn,
+China aster, golden aster (<i>Chrysopsis</i>), sneezeweed, elecampane—and,
+in fact, the great majority of flowers to be found at this season are of the
+composite family. Oxeye daisy is used as a model in the text on account
+of its general accessibility, but almost any specimen of the radiate kind
+will meet all essential conditions of the analysis.</p>
+</div>
+
+<figure class="figcenter illowp80" id="i_220" style="max-width: 53.75em;">
+  <img class="w100" src="images/i_220.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 305-308.</span>—An oxeye daisy: 305, a flower head;
+306, vertical section of a head; 307, disk flower; 308, ray
+flower, enlarged.</p></figcaption>
+</figure>
+
+<p id="p-231"><b>231. The ray flowers.</b>—Examine the upper side of an oxeye
+daisy through a lens. Of what is the yellow button in the
+center composed? Count the narrow, petal-like rays disposed
+around
+the center. To
+decide what they
+are, look for a
+small two-cleft
+body at the base
+of the ray; this
+is the pistil.
+Do you see any
+stamens in the
+ray? An examination
+will show
+that all rays<span class="pagenum" id="Page_211">[Pg 211]</span>
+contain pistils, but no stamens; they are, therefore, not petals,
+but the corollas of imperfect flowers. Look at the upper edge
+of a ray of sneezeweed, coreopsis, arnica, chicory, etc., for
+small teeth or notches; these represent the lobes of a sympetalous
+corolla. Split one of the tubular corollas of the disk
+down one side and open it out flat; does it throw any light
+on the morphology of the ray? In many composite plants,
+as the sunflower, coneflower, coreopsis, the rays are all <em>neutral</em>;
+that is, they have neither pistil nor stamens. Are they of any
+use in such cases? If you are in doubt, remove all the rays
+from a head; would the disk be noticeable enough to attract
+attention without them? What is the principal office of
+the rays?</p>
+
+<p id="p-232"><b>232. The involucre.</b>—Look at the cluster of green, leafy
+scales on the under side of the head. It is not a calyx, but
+a collection of bracts, called an <em>involucre</em>. Have you ever
+noticed the bracts under the separate flowers on a raceme?
+(<a href="#p-161">161</a>.) What would be the position of the bracts if all the
+flowers of the raceme were compacted into a head like the
+daisy or sunflower? Is the involucre of any use? Cut it
+away gently so as not to disturb the other organs and see
+what happens to the rays.</p>
+
+<p id="p-233"><b>233. The disk flowers.</b>—Cut a vertical section through
+the head of a flower and notice the broad, flat receptacle (in
+some cases round or columnar) on which the tiny florets
+are seated. Observe whether it is naked, or whether it
+bears chaffy scales inclosing the florets. Make an enlarged
+drawing of this section, showing the insertion of the different
+parts and labeling them all correctly. What differences
+do you observe between the disk and the ray flowers?</p>
+
+<p id="p-234"><b>234. The pappus.</b>—Open one of the disk flowers with a
+dissecting needle and observe the small striate (in some
+specimens, hairy) body to which the base of the style is attached.
+This is the ovary, inclosed in the lower part of the
+calyx, which has become incorporated with it. When mature,
+it will form a small, one-seeded fruit called an <em>akene</em>. Can<span class="pagenum" id="Page_212">[Pg 212]</span>
+you see the ovule? Where is it attached? (Use a mature
+akene for this purpose.) In most plants of this family, the
+akene is surmounted by delicate hairy bristles, as in the
+dandelion, wild lettuce, and groundsel; or by small chaffy
+scales, as in the sneezeweed and sunflower, and sometimes
+by hooks and barbed hairs, like those of the tickseed, bur
+marigold, and cocklebur. These appendages constitute the
+<em>pappus</em>. They are modifications
+of the sepals, and serve an important
+purpose in aiding the distribution
+of the seed. Can you
+suggest some of the ways in which they may aid in accomplishing
+this object?</p>
+
+<figure class="figcenter illowp90" id="i_222" style="max-width: 50em;">
+  <img class="w100" src="images/i_222.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 309-314.</span>—Akenes of the composite family: 309, mayweed (no
+pappus); 310, chicory (pappus a shallow cup); 311, sunflower (pappus of two
+deciduous scales); 312, sneezeweed (<i>Helenium</i>, pappus of five scales); 313, sow
+thistle (pappus of delicate downy hairs); 314, dandelion, tapering below the
+pappus into a long beak. (<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<figure class="figright illowp40" id="i_223" style="max-width: 50em;">
+  <img class="w100" src="images/i_223.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 315-317.</span>—Flowers of <i>Arnica
+montana</i>, showing successive stages in pollination:
+315, pistil just extruding from
+anther tube, covered with pollen, but with
+stigmatic surfaces closed; 316, stigma
+opened and mature; 317, stigma recurved
+to receive pollen from its own or neighboring
+anthers if foreign pollen has not
+reached it.</p></figcaption>
+</figure>
+
+<p id="p-235"><b>235. The stamens and pistil.</b>—Remove the corolla of a
+disk flower carefully so as not to disturb the inclosed organs,
+and notice how the stamens are united into a tube by their
+anthers. Flatten out the tube and make an enlarged sketch
+of it, showing the long, narrow shape of the anthers and their
+mode of attachment. Can you make out how they open to
+discharge their pollen? Examine one of the younger florets
+near the center of the disk, and observe that the tip of the
+style is inclosed in the anther tube with the lobes of the
+stigma pressed tightly together by their inner faces (<a href="#i_223">Fig. 315</a>),
+so that it is impossible for any of the pollen to reach the stigmatic<span class="pagenum" id="Page_213">[Pg 213]</span>
+surface. It remains in this position till the anthers have
+shed their pollen, then, as may be seen by examining an older
+flower, the style begins to elongate, pushing up the pollen
+that has fallen on the hairy outside of the closed stigma, and
+forcing it out of the corolla tube, where it can be scattered
+by insects among the other
+flowers of the cluster. When
+the pollen of its own floret
+has been thus disposed of, the
+stigma lobes open and curl
+outward, ready to receive the
+pollen from other flowers.
+This arrangement is practically
+universal among plants
+of the composite family; can
+you divine its object? It
+will be shown later, that much
+larger and stronger seeds are
+produced when the pistil is
+pollinated from a different
+flower, or, better still, from a
+different plant of the same
+species; hence, you see what
+a useful adaptation this is.</p>
+
+<p id="p-236"><b>236. Nature of a composite flower.</b>—It will be evident,
+from the examination just made, that the daisy, dandelion,
+sunflower, etc., are not single flowers, but compact heads
+of small blossoms so closely united as to appear like a single
+individual; hence they are said to be <em>composite</em>, or compound.
+They are the most numerous and widely disseminated
+of all plants, comprising one seventh of the entire
+flowering vegetation of the globe, and are regarded by
+botanists as representing the most advanced stage of floral
+evolution. Can you point out some of the adaptations to
+which their success in solving the problems of plant life is
+due? (<a href="#p-164">164</a>.)</p>
+
+<p><span class="pagenum" id="Page_214">[Pg 214]</span></p>
+
+
+<h3 id="CH_VII_IV">IV. SPECIALIZED FLOWERS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—For spring and early summer: sweet pea, black locust,
+wistaria, lupine, or any of the characteristic butterfly-shaped flowers of
+the pea family. For autumn or late summer: tropæolum, monkshood,
+or a bilabiate flower—snapdragon, digitalis, dead nettle, salvia, catalpa,
+etc.—of the mint or figwort family.</p>
+</div>
+
+<p id="p-237"><b>237. Irregularity and specialization.</b>—Irregularity and
+bilateral regularity are, as a rule, indicative of specialization,
+or adaptation to a particular purpose, such as the ready
+distribution of pollen, or its protection against injury. These
+adaptations are more noticeable in the corolla than in other
+parts, and hence flowers of this kind are usually classed
+according to the shape of their corollas. The most highly
+specialized flowers in this respect are the orchids, but they
+are too rare and difficult of access to be available objects for
+study. The most familiar and widely distributed kinds of
+specialized corollas are the <em>bilabiate</em>, or two-lipped, and the
+<em>papilionaceous</em>, or butterfly, forms. The first is characteristic
+of the mint and figwort families, of which the toadflax,
+sage, and catalpa are familiar examples. The second comprises
+the well-known papilionaceous flowers of the pea
+family, named from the Latin word <i>papilio</i>, a butterfly, on
+account of their general resemblance to that insect.</p>
+
+<p id="p-238"><b>238. Dissection of a papilionaceous flower.</b>—Sketch a
+blossom of any kind of pea or vetch as it appears on the
+outside. Are the sepals all of the same length and
+shape? If not, which are the shorter, the upper or the
+lower ones?</p>
+
+<p>Turn the flower over and examine its inner face. Notice
+the large, round, and usually upright petal at the back, the
+two smaller ones on each side, and the boat-shaped body
+between them, formed of two small petals more or less united
+at the apex. Press the side petals gently down with the
+thumb and forefinger and notice how the essential organs are
+forced out from the little boat in which they are concealed.<span class="pagenum" id="Page_215">[Pg 215]</span>
+Observe how the end of the style is bent over so as to bring
+the stigma uppermost when the petals are depressed. Imagine
+the legs of a bee or a butterfly resting there as he probed
+for honey; with what organ would his body first come in
+contact when he alighted? If his thorax and abdomen had
+previously become dusted with pollen when visiting another
+flower, where would the pollen be deposited? Do you notice
+anything in the color, shape, or odor of this flower that would
+be likely to attract insects? Have you ever observed insects
+hovering around flowers of this kind; for example, in clover
+and pea fields, and about locust trees and wistaria vines?
+What kind of insects, chiefly, have you seen about them?</p>
+
+<figure class="figcenter illowp90" id="i_225" style="max-width: 50em;">
+  <img class="w100" src="images/i_225.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 318-322.</span>—Dissection of a papilionaceous flower: 318, front view of a
+corolla; 319, the petals displayed: <i>v</i>, vexillum, or standard; <i>w</i>, wings; <i>k</i>, keel;
+320, side view with all except one of the lower petals removed, showing the essential
+organs protected in the keel: <i>l</i>, loose stamen; <i>st</i>, stamen tube; 321, side view,
+showing how the anthers protrude when the keel is depressed; 322, ground plan.
+(<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p>Remove the sepals and petals from one side, and sketch
+the flower in longitudinal section, showing the position of the
+pistil and stamens. Then remove all the petals, and spread
+in their natural order on the table before you, and sketch as
+they lie (<a href="#i_225">Fig. 319</a>). Label the large, round upper one,
+<em>standard</em> or <em>vexillum</em>; the smaller pair on each side, <em>wings</em>,
+and the two more or less coherent ones in which the pistil
+and stamens are contained, <em>keel</em>.</p>
+
+<p id="p-239"><b>239. The stamens.</b>—Count the stamens, and notice
+how they are united into two sets of nine and one. Stamens<span class="pagenum" id="Page_216">[Pg 216]</span>
+united in this way, no matter what the number in each set,
+are said to be <em>diadelphous</em>, that is, in two brotherhoods.
+Notice the position of the lone brother, whether below the
+pistil—next to the keel—or above, facing the <em>vexillum</em>.
+Would the projection of the pistil, when the wings are depressed,
+be facilitated to the same extent if the opening in the
+stamen tube were on the other side, or if the filaments were
+<em>monadelphous</em>—all united into one set? Flatten out the
+stamen tube, or sheath, formed by the united filaments, and
+sketch it.</p>
+
+<p id="p-240"><b>240. The pistil.</b>—Remove all the parts from around the
+pistil, and sketch it as it stands upon the receptacle. Look
+through your lens for the stigmatic surface <a href="#p-223">(223)</a>. See if
+there are any hairs on the style, and if so, whether they
+are on the front, the back, or all around. Can you think of a
+use for these hairs? Notice how the long, narrow ovary is
+attached to the receptacle; is it sessile, or raised on a short
+footstalk? If the latter, label the footstalk, <em>stipe</em>. Select a
+well-developed pistil from one of the lower flowers, open the
+ovary parallel with its flattened sides, and sketch the two
+halves as they appear under the lens. Notice to which side
+the ovules are attached, the upper (toward the vexillum) or
+the lower, and label it, placenta. How many locules has the
+ovary? How many carpels? How can you tell <a href="#p-216">(216)</a>?</p>
+
+<p id="p-241"><b>241. Plan of the flower.</b>—Diagram the flower in horizontal
+and vertical section, and decide upon the following
+points:—</p>
+
+<table class='autotable'>
+<tr>
+<td class='tdl'>Numerical plan</td>
+</tr><tr>
+<td class='tdl'>Symmetry</td>
+</tr><tr>
+<td class='tdl'>Regularity</td>
+</tr><tr>
+<td class='tdl'>Union of parts</td>
+</tr><tr>
+<td class='tdl'>Position of the ovary</td>
+</tr></table>
+
+<figure class="figright illowp60" id="i_227" style="max-width: 50em;">
+  <img class="w100" src="images/i_227.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 323, 324.</span>—Salvia: 323, a newly opened
+flower, showing the pollen-covered anther striking
+the back of a visiting bee; 324, an older flower,
+with the protruding pistil rubbing against the back
+of a bee covered with pollen from a younger flower.</p></figcaption>
+</figure>
+
+<p id="p-242"><b>242. Significance of these distinctions.</b>—These distinctions
+are important to remember, not only because they are
+very useful in grouping and classifying plants, but because
+they mark successive stages in the evolution of the flower.
+In general, flowers of a primitive type and less advanced<span class="pagenum" id="Page_217">[Pg 217]</span>
+organization are characterized by having their organs free
+and hypogynous, while the more highly developed forms show
+a tendency to consolidation and union of parts, and the
+epigynous mode of
+insertion. Irregularity
+also, since it indicates
+specialization
+and adaptation to a
+particular purpose,
+may be regarded as a
+mark of advanced
+evolution.</p>
+
+<figure class="figcenter illowp80" id="i_227a" style="max-width: 50em;">
+  <img class="w100" src="images/i_227a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 325, 326.</span>—Salvia: 325, longitudinal section through a flower, showing
+the rocking connective which is struck at <i>a</i> by a visiting insect; 326, section of the
+same flower after being visited, showing the lower arm of the connective pushed
+back and lowering the anther.</p></figcaption>
+</figure>
+
+<p id="p-243"><b>243. Dissection of
+a bilabiate flower.</b>—Make
+a similar study
+of the flower of a
+salvia, dead nettle,
+catalpa, or other specimen
+of the bilabiate
+kind. Make diagrams
+and report as to (1) numerical plan; (2) presence or absence
+of parts; (3) regularity; (4) union of parts; (5) position of
+ovary. Observe especially the relative position of stigma
+and anthers; is it such that the pollen can reach the stigma
+without external aid? Does the peculiar shape of the corolla
+serve any other purpose than to attract the attention of<span class="pagenum" id="Page_218">[Pg 218]</span>
+insect visitors by its conspicuous appearance? What is the
+use of the projecting underlip? Is it any convenience to a
+bee, for instance, to have a platform to rest on while gathering
+pollen or honey? What is the use of the arched upper
+lip? Cut it away and notice the exposed condition of the
+stamens and pistil. Turn a flower upside down; what
+would be the effect on a visiting bee or butterfly? (<a href="#exp-83">Exps.
+83</a>, <a href="#exp-84">84</a>.)</p>
+
+<table>
+<tr><td>
+<figure class="figcenter illowp90" id="i_228" style="max-width: 30em;">
+  <img class="w100" src="images/i_228.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 327.</span>—Staminodia, transformed
+stamens of canna simulating
+petals: <i>pet</i>, petals; <i>st</i>,
+staminodia.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp50" id="i_228a" style="max-width: 20em;">
+  <img class="w100" src="images/i_228a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 328.</span>—Flower
+of a cactus
+(<i>cereus greggii</i>),
+showing transition
+from scales to
+petals.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-244"><b>244. Morphology of the flower.</b>—We have seen that the
+venation of petals and sepals corresponds in a general way
+with that of foliage leaves of the class to
+which they belong, and that their arrangement
+around their axis is analogous to the
+arrangement of foliage leaves on the branch.
+In our study of
+inflorescence, it
+was observed that
+flowers and flower
+buds occur in the
+same positions
+where leaf buds
+occur, and that
+they are subject
+to the same laws
+of arrangement
+and growth. We
+learned, also, in our study of leaves, something
+about the wonderful modifications that
+these organs are capable of undergoing; and
+finally, an examination of a number of different flowers has
+shown them capable of undergoing modifications to an equal
+or even greater extent, and examples of the transition of
+almost any floral organ into another may be observed by one
+who will take the trouble to look for it. Stamens and petals
+are found in all stages of transformation, from the slightly
+flattened filament of the star-of-Bethlehem, or the yellow<span class="pagenum" id="Page_219">[Pg 219]</span>
+pollen speck on the petal of a rose, to the brilliant staminodia,
+or transformed stamens of the canna (<a href="#i_228">Fig. 327</a>), which simulate
+petals so perfectly that their real nature is never suspected
+by the ordinary observer. The transition from spines
+and bracts to the brilliant corolla of the cactus (<a href="#i_228a">Fig. 328</a>)
+is so gradual that we are hardly aware of it till we examine a
+specimen and see it actually going on before our eyes.</p>
+
+<p>It must not be supposed, however, that an organ is ever
+developed as one thing and then deliberately changed into
+something else. When we speak loosely of one organ being
+modified into another, the meaning is merely that it has developed
+into one thing instead of into something else that it
+was equally capable of developing into.</p>
+
+<p id="p-245"><b>245. The course of floral evolution.</b>—For the reasons
+mentioned, the flower is regarded as merely a branch with
+modified leaves and the internodes indefinitely shortened so
+as to bring the successive cycles into close contact, the whole
+being greatly altered and specialized to serve a particular
+purpose. With this conception of the nature of the flower,
+we can readily see that the less specialized its organs are and
+the more nearly they approach in structure and arrangement
+to the condition of an undifferentiated branch, the more
+primitive and undeveloped is the type to which it belongs.
+On the other hand, if the parts are highly specialized and
+widely differentiated from the crude branch, a proportionately
+high stage of floral evolution is indicated.</p>
+
+
+<h3 id="CH_VII_V">V. FUNCTION AND WORK OF THE FLOWER</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—For this exercise, flowers of the mallow family—hollyhock,
+abutilon, mallow, hibiscus, cotton, okra, etc.—are particularly
+recommended because they have pollen grains so large that they can be
+studied fairly well with a hand lens. Lily, tulip, iris, etc., will also meet all
+essential conditions of the study outlined in the text. A strand of silk
+from a pollinated ear of corn is an excellent example for showing the
+growth of the pollen tube, under the microscope.</p>
+
+<p><span class="smcap">Appliances.</span>—A compound microscope; a watch crystal; sugar solution
+of 5 to 15 per cent.</p>
+
+<p><span class="pagenum" id="Page_220">[Pg 220]</span></p>
+
+<p id="exp-77"><span class="smcap">Experiment 77. To show the germination of pollen grains.</span>—Put
+a drop of 5 per cent sugar solution into a watch crystal or a concave
+slide, seal by smearing the edges with vaseline, and cover with a glass
+to keep out the dust. Examine at intervals of five minutes under the
+microscope (a hand lens will show the result with the specimens recommended,
+though not so well), and the pollen grains will be observed to send
+out long filaments or tubes into the sirup, as a germinating seedling sends
+its radicle into the soil.</p>
+</div>
+
+<p id="p-246"><b>246. Office of the flower.</b>—The one object of the flower
+is the production of fruit and seed, and all its wonderful
+specializations and variations of form and color tend either
+directly or indirectly to this end.</p>
+
+<p id="p-247"><b>247. Pollination and fertilization.</b>—It was stated in <a href="#p-215">215</a>
+that only in very exceptional cases can seed be developed
+unless some of the pollen reaches the stigma. This act,
+called <em>pollination</em>, is an essential step in seed production, but
+is not sufficient to secure that end unless it leads to the process
+known as <em>fertilization</em>. Successful pollination is a necessary
+preliminary to fertilization, and the one begins where the
+other ends.</p>
+
+<p id="p-248"><b>248. The next step toward fertilization.</b>—Examine with a
+lens the pollinated pistil of a mallow, lily, or other large
+flower, and notice the flabby, withered appearance of grains
+that have stood for some time on the stigma, as compared
+with those of a newly opened anther. Can you account
+for the difference? Touch the tip of your tongue
+to the stigma, or apply the proper chemical test, and it will
+be seen that the sticky fluid which it exudes, contains sugar.
+Refer to <a href="#exp-77">Exp. 77</a> and say what effect this substance has
+on the pollen.</p>
+
+<figure class="figright illowp43" id="i_231" style="max-width: 25em;">
+  <img class="w100" src="images/i_231.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 329.</span>—A
+pollen grain emitting
+a tube (magnified).</p></figcaption>
+</figure>
+
+<p id="p-249"><b>249. The pollen tube.</b>—The same thing happens when a
+pollen grain falls on the moist surface of the stigma. It
+begins to germinate by sending a little tube down into the
+substance of the pistil, and the withered appearance of the
+grains on the stigma results from the nourishment in them
+having been exhausted, just as the endosperm of the seed is
+exhausted when the embryo begins to germinate. Here, however,<span class="pagenum" id="Page_221">[Pg 221]</span>
+the analogy ends, for the pollen tube is not adapted, like
+the radicle of the seedling, to absorb and convey nourishment
+up to the other parts, but to feed and carry down to the ovary
+two small bodies called <em>generative cells</em>,
+which it discharges there, and then its work
+is done and it disappears. So it must be
+borne in mind that when we speak of the
+germination of the pollen grains, we mean
+something really very different from the
+germination of a seed.</p>
+
+<p id="p-250"><b>250. The course of the pollen tube.</b>—Cut
+the thinnest possible section through
+a freshly pollinated pistil and place under
+the microscope. Watch the pollen tubes
+from the grains on the stigma as they descend
+through the style toward the ovary.
+A pollinated strand of corn silk—which is
+only a very much elongated style—is excellent for this purpose.
+It is so thin and transparent that no section need be
+made, and the tube can be traced as it works its way down
+through the entire length of the threadlike style to the young
+grain, or ovary, on the cob. The time required for the tube
+to penetrate to the ovary varies in different flowers according
+to the distance traversed and the rate of growth. In the
+crocus it takes from one to three days; in the spotted calla,
+about five days; and in orchids, from ten to thirty days.
+As a rule, it occupies only a few hours. Sometimes the pistil
+is hollow, affording a free passage to the pollen tube;
+in other cases, it is solid, and the growing tube eats its way
+down, as it were, feeding on the substance of the pistil
+as it grows. How is it in the flower you are examining? It
+takes a grain of pollen to fertilize each ovule, and where more
+than one seed is produced to a carpel, as is commonly the
+case, at least as many pollen tubes must find their way to
+each locule of the ovary as there are ovules—provided all
+are fertilized.</p>
+
+<p><span class="pagenum" id="Page_222">[Pg 222]</span></p>
+
+<figure class="figright illowp40" id="i_232" style="max-width: 40em;">
+  <img class="w100" src="images/i_232.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 330.</span>—Diagram of a simple
+flower, showing course of the pollen
+tube: <i>a</i>, transverse section of an
+anther before its dehiscence; <i>b</i>, an
+anther dehiscing longitudinally, with
+pollen; <i>c</i>, filament; <i>d</i>, base of floral
+leaves; <i>e</i>, nectaries; <i>f</i>, wall of carpels;
+<i>g</i>, style; <i>h</i>, stigma; <i>i</i>, germinating
+pollen grains; <i>m</i>, a pollen tube which
+has reached and entered the micropyle
+of the ovule; <i>n</i>, stalk of ovule; <i>o</i>, base
+of the inverted ovule; <i>p</i>, outer
+integument or testa; <i>q</i>, inner integument;
+<i>t</i>, cavity of the embryo
+sac; <i>u</i>, its basal portion;
+<i>z</i>, oösphere.</p></figcaption>
+</figure>
+
+<p id="p-251"><b>251. Fertilization.</b>—When a pollen tube has penetrated
+to the ovary, it next enters one of the ovules, usually through
+the micropyle (<a href="#i_232">Fig. 330</a>, <i>m</i>).
+There it penetrates the wall of
+a baglike inclosure called the
+<em>embryo sac</em> (<a href="#i_232">Fig. 330</a>, <i>u</i>, <i>t</i>, <i>z</i>),
+where one of the generative
+cells emitted by the pollen tube
+fuses with a large cell contained
+in the embryo sac, known as
+the <em>germ cell</em>, or <em>egg cell</em> (<a href="#i_232">Fig.
+330</a>, <i>z</i>). The fusion of these
+two bodies is what constitutes
+fertilization. The cell formed
+by their union finally develops
+into the embryo, and the other
+contents of the sac into the
+endosperm, and the ripened
+ovules become seeds.</p>
+
+<p id="p-252"><b>252. Stability of the process
+of fertilization.</b>—The phenomena
+that characterize the
+functions of fertilization and
+reproduction are the most uniform
+and stable of all the life
+processes, varying little not
+only in different species and
+orders, but throughout the whole vegetable kingdom. And
+since these functions furnish a more reliable standard for
+judging of the real affinities of the different groups than do
+mere external resemblances, which are more liable to variation
+and may often be accidental, they have been chosen
+by botanists as the ultimate basis for the classification of
+plants.</p>
+
+<p id="p-253"><b>253. Embryology.</b>—The study of the developing plantlet,
+known as <em>embryology</em>, is a comparatively recent branch of<span class="pagenum" id="Page_223">[Pg 223]</span>
+science, and has greatly enlarged our knowledge of the life
+history of both plants and animals, by bringing to light resemblances
+that exist between the most widely divergent
+species in their earlier stages of development and thus
+showing traces of a common origin. It has shown further,
+that every individual plant or animal, in its development
+from the embryo to the mature state, passes briefly through
+stages apparently similar to those which the species has traversed
+in the course of its evolution. This summary repetition,
+by the individual, of the evolutionary progress of its
+kind is known as the <em>biogenetic law</em>, and through its intelligent
+application some of the most intricate problems in both
+physiology and psychology have been solved.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Does the biogenetic law throw any light on the resemblances sometimes
+observed between leaves of different ages in unlike species; for
+example, the fig and the mulberry? (<a href="#p-170">170</a>; Field Work, <a href="#Page_195">p. 195</a>.)</p>
+
+<p>2. Can you name any other examples of plants or parts of plants which
+show mutual resemblances in their early stages that do not exist at
+maturity?</p>
+
+<p>3. Are there other causes than those acting under the biogenetic law
+to which some of these resemblances may be referred; for instance, the
+down and waxy coating on young leaves and bud scales? (<a href="#p-148">148</a>, <a href="#p-207">207</a>.)</p>
+</div>
+
+
+<h3 id="CH_VII_VI">VI. HYBRIDIZATION</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Several potted plants of tulip, lily, or any attainable
+large flowered kind; or preferably a small plot in a garden or nursery.</p>
+
+<p><span class="smcap">Appliances.</span>—A pair of dissecting scissors, a camel’s-hair brush, and
+some paper bags.</p>
+
+<p id="exp-78"><span class="smcap">Experiment 78. Does it make any difference whether a flower
+has its ovules fertilized with its own pollen or with that of another
+flower of the same kind?</span>—Carefully remove the <em>unopened</em>
+anthers from a bud of a tulip, or other large flower just ready to unfold
+(<a href="#i_234">Fig. 331</a>), inclose the mutilated bud in a small paper bag until the stigma
+is mature, as shown by stickiness, then transfer to it with a camel’s-hair
+brush some pollen from another flower. On the stigma of a second flower
+of the same kind place some of its own pollen, and cover with a paper bag
+until the stigma withers, to keep foreign pollen from reaching it by means<span class="pagenum" id="Page_224">[Pg 224]</span>
+of wind or insects. Watch until seeds are matured. Which flower produces
+the more seeds or the better ones? Plant the seeds; which produce
+the more vigorous progeny?</p>
+
+<figure class="figcenter illowp90" id="i_234" style="max-width: 50em;">
+  <img class="w100" src="images/i_234.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 331-333.</span>—Flower of Lorillard tomato: 331, newly opened bud, showing
+stage in which the stamens should be removed; 332, mature flower: <i>cx</i>, calyx; <i>c</i>,
+corolla; <i>s</i>, stamens; <i>st</i>, stigma; 333, flower with stamens removed for pollination.
+(Natural size.)</p></figcaption>
+</figure>
+
+<p id="exp-79"><span class="smcap">Experiment 79. Can a flower be fertilized with pollen of a
+different kind?</span>—Dust the stigma of a tulip or a lily, from which the
+stamens have been removed, with pollen from a narcissus, iris, or amaryllis.
+Cover to protect from wind and insects. Are any seeds produced?</p>
+
+<p>Experiments of this kind, to be conclusive, ought to be performed on
+a sufficient number of plants and through at least three generations. This
+is hardly practicable for class work, but students who are specially interested
+in the subject may carry on experiments at home, or supply their
+place, to some extent, by observations out of doors, if there are any farms
+or gardens accessible.</p>
+</div>
+
+<figure class="figcenter illowp50" id="i_234a" style="max-width: 50em;">
+  <img class="w100" src="images/i_234a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 334-335.</span>—Seeds of Bartlett pear, showing
+the advantage of cross-fertilization: 334, cross-fertilized;
+335, self-fertilized.</p></figcaption>
+</figure>
+
+<p id="p-254"><b>254. Self-fertilization</b>
+takes place
+when a stigma is
+pollinated from the
+same flower. Horticulturists
+have
+long known that
+continued self-fertilization,
+or “in-breeding”
+as it is
+called by nurserymen,
+tends to deteriorate
+a stock; but<span class="pagenum" id="Page_225">[Pg 225]</span>
+Charles Darwin was the first to explain, by a series of pains-taking
+experiments, the meaning of those careful adjustments
+which the more highly organized plants, as a rule, have developed
+to guard against it.</p>
+
+<figure class="figcenter illowp75" id="i_235" style="max-width: 50em;">
+  <img class="w100" src="images/i_235.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 336.</span>—Showing the effect of in-breeding on corn in one generation. The
+two left-hand rows are from self-fertilized seed.</p></figcaption>
+</figure>
+
+<p id="p-255"><b>255. Cross-fertilization</b> is effected by the pollination of a
+stigma from another flower of the same variety or species.
+As used by practical horticulturists, the expression means
+that the two factors, pollen and ovule, belong to different
+plants. Since pollination is the necessary antecedent to
+fertilization, and the only means by which we can control it,
+the breeder’s part in crossing is concerned with this act only
+and nature does the rest. Darwin’s experiments—and they
+are confirmed by the experience of plant growers everywhere—prove<span class="pagenum" id="Page_226">[Pg 226]</span>
+that the offspring from crossing different plants of
+the same kind is usually stronger and more productive than
+that from self-fertilized ones; and if the parent stocks are
+grown in different places and under different conditions, the
+offspring is more vigorous than that from the same kind of
+plants grown under like conditions. For instance, plants
+from crossed seeds of morning-glory vines growing near each
+other exceeded in height those from self-fertilized seeds as
+100:76; while the offspring of plants growing under different
+conditions exceeded those of the other cross, in height, as
+100:78; in number of pods, as 100:57, and in weight of
+pods, as 100:51. Knowledge of this kind, when applied to
+the raising of fruits and grains for market, is of incalculable
+value to gardeners and farmers, and also to the amateur who
+raises fruits or flowers for pleasure.</p>
+
+<p id="p-256"><b>256. Hybridization</b> is the crossing of two plants of different
+species or of widely separated varieties of the same species.
+The resulting offspring is a <em>hybrid</em>. Hybridization can take
+place only within certain limits. If the species are too unlike,
+the pollen will either not take effect at all, or the resulting
+offspring will be too weak and spindling to live; or if they
+survive, will not be able to set seed (<a href="#exp-79">Exp. 79</a>).</p>
+
+<p><span class="pagenum" id="Page_227">[Pg 227]</span></p>
+
+<figure class="figcenter illowp45" id="i_237" style="max-width: 75em;">
+  <img class="w100" src="images/i_237.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 11.</span>—Hybrid between a red and a white carnation, showing characters
+intermediate between the two parents.</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_228">[Pg 228]</span></p>
+
+<p id="p-257"><b>257. Effects of hybridization.</b>—The most important practical
+uses of hybridizing are: (1) it “breaks the type” by
+causing plants to vary, and thus gives the breeder a fresh
+starting point for a new strain; and (2) when the parent
+species are not too unlike, it accentuates the good effects of
+crossing, and sometimes gives rise to offspring greatly surpassing
+either parent in size and vigor. In regard to variability
+it may act in three ways: (1) the hybrid may wholly
+resemble one parent or the other, in which case there is, of
+course, no variation; (2) it may resemble one parent more
+than the other; or (3) it may show a blending of the characters
+of the two, as when a cross between a red poppy and a
+white gives rise to a light pink, or a mixed red and white
+variety. In the first two cases, the characters of the parent
+that manifest themselves are said to be <em>dominant</em>; those
+which do not, <em>recessive</em>.</p>
+
+<figure class="figcenter illowp80" id="i_238" style="max-width: 50em;">
+  <img class="w100" src="images/i_238.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 337.</span>—Effect of hybridization between related species in imparting superior
+vigor to offspring: <i>M</i>, Californian black walnut (<i>Juglans californica</i>), male parent;
+<i>F</i>, Eastern black walnut (<i>J. nigra</i>), female parent; <i>H</i>, hybrid.</p></figcaption>
+</figure>
+
+<p id="p-258"><b>258. Mendel’s Law.</b>—So long ago as the middle of the last
+century it was discovered by Gregor Mendel, an Austrian
+investigator, that hybrids vary in certain cases according to
+a fixed law, by means of which the proportionate share of the
+characteristics of the two parent forms inherited by the offspring
+can be foretold with almost mathematical precision.
+The controversy over Darwin’s “Origin of Species,” which
+was raging at the time, caused Mendel’s discoveries to be
+overlooked for a generation, and it is only within the last
+few years that their importance has been realized. The
+principle of variation demonstrated by him in a series of
+experiments, and confirmed by later investigators is, briefly,<span class="pagenum" id="Page_229">[Pg 229]</span>
+this: If two parents differing in some fixed characteristic
+be crossed, the entire offspring, in the first generation, will be
+like the parent possessing the dominant quality. If all the
+seed of this generation is planted and carefully protected
+from foreign pollen, its offspring composing the second
+generation from the parents will vary in the proportion of
+¾ dominants (<i>D</i>, <i>D′</i>, line 2 of the diagram) to ¼ recessives (<i>R</i>).
+Planting <em>all</em> the seeds of the second generation and carefully
+shielding their progeny from foreign pollen, we get from <i>D</i>,
+line 2, all pure dominants (<i>D</i>, line 3)—that is, plants producing
+only their own type, and from <i>R</i>, line 2, all pure
+recessives (<i>R</i>, line 3). But from each of the two sets of dominants,
+<i>D′D′</i>, line 2, marked “impure” in the diagram, and
+so called because their seeds may produce both dominants
+and recessives, we get the same result as in the second generation,
+namely: pure dominants (<i>D′D′</i>, line 3), pure recessives
+(<i>R′R′</i>, line 3), and impure dominants (<i>D″D″</i>, <i>D″D″</i>, line
+3). If it were possible to distinguish the seeds of these impure
+dominants before germination and plant them only, for
+no matter how many generations, the result would always be
+approximately the same,—¼ pure dominants, ¼ pure recessives,
+and ²⁄₄ impure dominants capable of producing both
+dominants and recessives in the proportion of 3:1.</p>
+
+<figure class="figcenter illowp80" id="i_238a" style="max-width: 50em;">
+  <img class="w100" src="images/i_238a.jpg" alt="">
+  <figcaption><p class='center'>Diagram illustrating Mendel’s Law.</p></figcaption>
+</figure>
+
+<p id="p-259"><b>259. Practical applications.</b>—Four principles of great
+importance to plant breeders follow from this law in cases to
+which it applies: (1) the absence of variation in the first
+generation of hybrids is no sign that it may not occur later;
+(2) pure recessives always breed true; hence, if they show
+the desired character, no further selection is necessary for
+that character; (3) pure dominants always breed true, but
+the distinction between pure and impure is usually not
+apparent in one generation; (4) the descendants of “impure”
+parents cannot be depended upon to come true to
+either type, but impure dominants may breed recessives, and
+<i>vice versa</i>, with the presumption, however, of 3:1 in favor
+of dominants.</p>
+
+<p><span class="pagenum" id="Page_230">[Pg 230]</span></p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Would hybridization account for some of the diversities mentioned
+in <a href="#p-170">170</a>? (See <a href="#p-257">257</a>.)</p>
+
+<p>2. To what cases would it not apply? (<a href="#p-256">256</a>; <a href="#exp-79">Exp. 79</a>.)</p>
+
+<p>3. Would it be worth while to try to hybridize the potato and squash?
+The squash and pumpkin? The lily and rose? Sweetbrier and wild
+rose? Apple and peach? Wild crab and sweet apple? Blackberry and
+strawberry? Blackberry and raspberry? Lemon and watermelon?
+Lemon and orange? Why, or why not, in each case? (<a href="#p-256">256</a>; <a href="#exp-78">Exps.
+78</a>, <a href="#exp-79">79</a>.)</p>
+</div>
+
+
+<h3 id="CH_VII_VII">VII. PLANT BREEDING</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—If practicable, visit a market garden, a florist’s establishment,
+or, lacking these, the fruit and vegetable stalls of a city market.</p>
+</div>
+
+<p id="p-260"><b>260. Fixing the type.</b>—It is the tendency of plants to
+vary under the influence of climate, soil, food supply, crossing,
+and other causes perhaps unknown to us, that makes
+the plant breeder’s art possible. When a horticulturist sets
+out to produce a new fruit or vegetable, he first forms in his
+mind a clear idea of what he wants—whether increase of yield
+or size, resistance to cold, drought, or disease, improvement in
+flavor, color, shape, etc., or change in the time of maturing or
+flowering (early and late varieties). Suppose, for instance,
+he wishes to produce an oxeye daisy with all the disk florets
+changed to white ones like the rays. He will begin by selecting
+plants with the greatest number of rays and the most conspicuous
+ones that he can find, and sowing the seeds of the flowers
+which show the greatest tendency to the development of these
+qualities. He will continue this process from generation to
+generation, rigorously destroying all specimens that do not
+approach nearer the ideal sought, until all disposition to
+“rogue,” as the tendency to revert is called, has been eliminated.
+When variations cease to occur and the seed of the
+new variety always “come true,” the type is said to be <em>fixed</em>;
+though some care will always be necessary to keep it so,
+as the influence of changed surroundings and the danger of
+mixture with foreign pollen must always be provided against.</p>
+
+<p><span class="pagenum" id="Page_231">[Pg 231]</span></p>
+
+<figure class="figright illowp50" id="i_241" style="max-width: 50em;">
+  <img class="w100" src="images/i_241.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 338.</span>—A field of pumpkins grown from selected
+seed.</p></figcaption>
+</figure>
+
+<p id="p-261"><b>261. Survival of the fittest.</b>—In the fierce struggle
+continually going on among both plants and animals for
+food, shelter, and elbow room in the world, any individual
+that happens to vary in a way which adapts it to
+its surroundings a
+little better than its
+rivals, has an advantage
+that will enable
+it to survive when
+less favored members
+of the species
+will perish. Its offspring,
+or some of
+them, may inherit
+this quality and
+transmit it, with the
+attendant advantage,
+to their posterity,
+and so on, till
+that particular
+breed outstrips all
+competitors, and in
+time, as the less favored
+intervening
+forms die out, becomes
+differentiated
+as a new species. This is, in brief, the doctrine of natural
+selection and the survival of the fittest.</p>
+
+<p id="p-262"><b>262. Artificial selection.</b>—Artificial selection enables the
+breeder to accomplish more quickly what nature appears to
+do by the slow process of natural selection. It is by this
+means that our choicest fruits and vegetables have been developed
+from greatly inferior, and sometimes inedible, wild
+forms. Plants respond so readily to the influence of selection,
+and the changes brought about by it are so rapid,
+that new styles of fruits and flowers succeed each other in<span class="pagenum" id="Page_232">[Pg 232]</span>
+the market with almost as great frequency and in as ready
+response to demand as the new styles of women’s bonnets
+and gowns in the shop windows.</p>
+
+<figure class="figcenter illowp80" id="i_242" style="max-width: 50em;">
+  <img class="w100" src="images/i_242.jpg" alt="">
+  <figcaption><p class='center'><span class="smcap">Fig. 339.</span>—Variation in blackberry leaves due to hybridization.</p></figcaption>
+</figure>
+
+<p id="p-263"><b>263. Causes of variation.</b>—While man cannot directly
+force plants to vary in any given direction, he can hasten the
+process of variation by crossing, or by changing the conditions
+under which they are growing. This is called “breaking
+the type.” Hybridization furnishes the readiest means to
+this end. Change of food supply, especially if accompanied
+by excess of nourishment, is probably the expedient that
+ranks next in effectiveness. Light, temperature, moisture,
+character of the soil, exposure to wind, and the like, also
+have their influence; and in adapting themselves to changes
+in these various conditions, plants are apt to exhibit an
+unusual number of variations, when removed from one locality
+to another, especially if the difference in soil and climate
+is very marked. Now comes the breeder’s opportunity. By
+taking advantage of such variations as may occur either
+spontaneously, or as the result of his efforts to break the type,
+he will generally find some that will meet his requirements;
+and knowing the effect produced by different conditions, he
+can, to a certain extent, influence the course of variation in
+the direction desired, by subjecting his specimens to the<span class="pagenum" id="Page_233">[Pg 233]</span>
+conditions that tend to produce it. If he wishes to develop
+a dwarf variety, for instance, he will take notice that overcrowding,
+lack of nourishment, and cold tend to produce that
+result in nature, and by acting on this hint he can direct his
+efforts more intelligently. He will learn, too, not to waste
+time in trying to breed a plant contrary to its nature. He
+must not expect to gather figs from thistles by any art of
+selection or skill in culture. By attention to Mendel’s law,
+a still further saving of time and labor may be effected.</p>
+
+<p>It is obvious, from what has been said, that a breeder’s
+chance of finding what he wants will be greater in proportion
+to the number of individual plants he has to choose from.
+For this reason, a horticulturist sometimes uses thousands
+and hundreds of thousands of specimens of a single kind in
+conducting his experiments. In this way he compresses into
+a short space of time the advantage that nature can gain only
+by spreading her random experiments over a long series of
+years, or even centuries.</p>
+
+<figure class="figright illowp50" id="i_243" style="max-width: 50em;">
+  <img class="w100" src="images/i_243.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 340.</span>—Mutation in twin ears of corn,
+showing the sudden variations that sometimes
+occur, by which a new type may be provided
+without the labor of selection.</p></figcaption>
+</figure>
+
+<p id="p-264"><b>264. Mutation and variation.</b>—There are at least two
+ways in which changes in vegetable and animal forms are
+thought to occur: (1)
+by the preservation and
+fixation through selection
+and heredity, of
+slight differences that
+may appear from time to
+time, such divergences
+being called “fluctuating
+variations”; (2) by
+the appearance now and
+then, due to causes as
+yet unknown, of definite
+and sudden changes
+creating a new form at
+a single, though perhaps small, leap. When such a change
+is temporary and passes away with the individual in which<span class="pagenum" id="Page_234">[Pg 234]</span>
+it first appeared, it is called a “sport,” and leads to no
+important results; but when it is inherited by the offspring,
+so that it is capable of giving rise to a new species, it constitutes
+a “mutation.” The value of a mutation to breeders
+in saving time and trouble is obvious. Professor Hugo de
+Vries, a Dutch botanist, was the first to call attention to the
+importance of mutation and its bearing upon the production
+of new species.</p>
+
+<p id="p-265"><b>265. Factors in the evolution of species.</b>—Variation,
+heredity, and selection are the three principal agents underlying
+all changes, whether for the improvement or deterioration
+of living organisms. The influence of external surroundings
+in keeping up a variation once begun, or in starting new
+ones, is also a factor that cannot be disregarded. It is for
+this reason that natural species are so much more stable than
+those brought about by man. The former, being evolved in
+response to natural conditions, are liable to change only as
+alterations in their surroundings are brought about by the
+slow operation of natural causes. But the types resulting
+from the breeder’s art, produced as they often are in response
+to human demands and in direct opposition to the requirements
+of natural conditions, are in a sense purely artificial, and
+can be preserved only by keeping up the artificial surroundings
+by which they were developed. Hence, the importance
+of diligent cultivation and constant care and tillage, without
+which the most carefully selected stocks may quickly “run
+out” and degenerate into worthless forms.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Which are the more pliable to the breeder’s art, annuals or perennials?
+Why? (<a href="#p-91">91</a>, <a href="#p-93">93</a>, <a href="#p-262">262</a>, <a href="#p-263">263</a>.)</p>
+
+<p>2. What advantage is gained by using buds and grafts instead of
+seedlings in making new varieties of fruit trees? (<a href="#p-257">257</a>, <a href="#p-259">259</a>, <a href="#p-260">260</a>.)</p>
+
+<p>3. Would it be practicable to breed new varieties of slow-growing forest
+trees, like oak, cypress, redwood, from seeds? Why or why not? (93,
+<a href="#p-262">262</a>, <a href="#p-263">263</a>.)</p>
+
+<p>4. Can you account for the existence of the numerous intermediate
+forms between the different species of oaks found in nature? (<a href="#p-255">255</a>, <a href="#p-257">257</a>.)</p>
+
+<p><span class="pagenum" id="Page_235">[Pg 235]</span></p>
+
+<p>5. If a breeder wished to produce a sweet-scented daisy or pansy, how
+would he make his selections? (<a href="#p-260">260</a>.)</p>
+
+<p>6. Which would be the more useful for his purpose, a plant that showed
+a general tendency to variability, or one that remained steadily fixed to
+its type? (<a href="#p-260">260</a>.)</p>
+
+<p>7. What could he do to break the type? (<a href="#p-263">263</a>.)</p>
+
+<p>8. Would an intelligent breeder set out to produce edible roots and
+tubers from wheat or barley? (<a href="#p-263">263</a>.)</p>
+
+<p>9. Would he think it worth while to try to develop a fleshy fruit from
+a filbert or a walnut tree? From a haw? From sheepberry and black
+haw? From tupelo (ogeechee lime)? (<a href="#p-263">263</a>.)</p>
+
+<p>10. Suppose a florist should wish to change the color of a rose from pink
+to deep red; how could he hasten the process? (<a href="#p-257">257</a>, <a href="#p-263">263</a>.)</p>
+
+<p>11. Explain why it is so much easier to produce new varieties of plants
+when there are already many kinds in existence, as, for example, the rose,
+peach, and chrysanthemum. (<a href="#p-255">255</a>, <a href="#p-256">256</a>; <a href="#exp-78">Exps. 78</a>, <a href="#exp-79">79</a>.)</p>
+</div>
+
+
+<h3 id="CH_VII_VIII">VIII. ECOLOGY OF THE FLOWER</h3>
+
+
+<h4 id="CH_VII_VIII_A">A. <span class="smcap">The Prevention of Self-pollination</span></h4>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Any kind of unisexual flowers obtainable. Some good
+examples for illustrating points mentioned in the text are: for spring and
+early summer, catkins of almost any of our common forest trees,—oak,
+hickory, willow, poplar, etc.; tassels and young ears of early corn; for
+summer and early fall, flowers of late corn, and of melon, squash, pumpkin,
+or others of the gourd family. Examples of <em>dichogamy</em> are: evening
+primrose, showy primrose (<i>Œnothera speciosa</i>), willow herb (<i>Epilobium</i>),
+dandelion, artichoke, sunflower, or any of the composite family; of <i>dimorphism</i>:
+English primrose (<i>Primula</i>), loosestrife (<i>Pulmonaria</i>), bluets
+(<i>Houstonia</i>), partridge berry; <i>cleistogamic</i>: fringed polygala, violets.
+Peanuts, while not technically classed as cleistogamic, are strictly close-fertilized,
+and approach the type so nearly that they may be used as an
+illustration.</p>
+</div>
+
+<p id="p-266"><b>266. Ecology</b> is the study of plants and animals in relation
+to their surroundings. The principal modifications that
+flowers undergo in this respect are in adapting themselves
+for (1) pollination, and (2) protection.</p>
+
+<table class='autotable'>
+<tr><td>
+<figure class="figcenter illowp60" id="i_246" style="max-width: 28.8em;">
+  <img class="w100" src="images/i_246.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 341, 342.</span>—Unisexual
+flowers of willow:
+341, staminate;
+342, pistillate.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp60" id="i_246a" style="max-width: 39.1em;">
+  <img class="w100" src="images/i_246a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 343.</span>—Twig of oak with
+both kinds of flowers: <i>f</i>, fertile
+flowers; <i>s</i>, <i>s</i>, staminate; <i>a</i>, pistillate
+flower, enlarged; <i>b</i>, vertical
+section of pistillate flower,
+enlarged; <i>c</i>, portion of one of the
+sterile aments, enlarged, showing
+the clusters of stamens.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-267"><b>267. Unisexual flowers.</b>—The advantages of cross fertilization
+were shown in the last two sections. It was also<span class="pagenum" id="Page_236">[Pg 236]</span>
+shown that the first step taken by the breeder to secure this
+result is to render the flower incapable of self-fertilization,
+by removing the stamens. Nature accomplishes
+the same purpose by the more
+effectual expedient of providing imperfect,
+or <em>unisexual</em> flowers, in which stamens
+only, or pistils only, occur in the
+same flower. When the stamens alone
+are present, the flower is said to be staminate,
+or <em>sterile</em>, because it is incapable
+of producing seeds of its own, though its
+pollen is a necessary factor in seed production.
+If, on the other hand, the
+ovary is present and the stamens absent,
+the flower is pistillate and <em>fertile</em>; that is, capable of producing
+fruit when impregnated with pollen. Sometimes both
+stamens and pistils are wanting, as
+in the showy corollas of the garden
+“snowball,” the hydrangea, and
+the rays of the sunflower. Such
+blossoms are said to be <em>neutral</em>,
+from the Latin word <i>neuter</i>, meaning
+neither, because they have
+neither pistils nor stamens. They
+can, of course, have no direct part
+in the production of fruit, but are
+for show merely. (<a href="#p-231">231</a>.)</p>
+
+<p id="p-268"><b>268. Monœcious and diœcious
+plants.</b>—When both kinds of
+flowers, staminate and pistillate,
+are borne on the same plant, as in
+the oak, pine, hickory, and most of
+our common forest trees, they are
+said to be <em>monœcious</em>, a word which
+means “belonging to one household”; when borne on separate
+plants, as in the willow, sassafras, and black gum, they<span class="pagenum" id="Page_237">[Pg 237]</span>
+are <em>diœcious</em>, or “of two households.” Draw a flowering twig
+of oak, pine, or willow. Where are the fertile flowers situated?
+Notice how very much more numerous the staminate flowers
+are than the fertile ones. Why is this necessary? (<a href="#p-275">275</a>.)</p>
+
+<figure class="figcenter illowp60" id="i_247" style="max-width: 50em;">
+  <img class="w100" src="images/i_247.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 344, 345.</span>—Flower of fireweed (<i>Epilobium angustifolium</i>):
+344, with mature stamens and immature
+pistil; 345, the same a few days older, with expanded
+pistil after the anthers have shed their pollen. (<i>After</i>
+<span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p id="p-269"><b>269. Dichogamy</b> is the name applied to a condition where
+the stamens and
+pistils mature at
+different times,
+as in the evening
+primrose, oxeye
+daisy, and most
+of the composite
+family. It is a
+very common
+method in nature
+for preventing
+self-pollination, and quite as effective as the monœcious
+arrangement, since it renders the flowers practically unisexual.</p>
+
+<figure class="figright illowp30" id="i_247a" style="max-width: 30em;">
+  <img class="w100" src="images/i_247a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 346-347.</span>—Flower of pulmonaria:
+346, long styled; 347, short
+styled.</p></figcaption>
+</figure>
+
+<p id="p-270"><b>270. Dimorphism</b> denotes a condition in which the stamens
+and pistils are of different relative lengths in different
+flowers of the same species, the stamens being long and the
+pistils short in some, the pistils
+long and the stamens short in
+others. Flowers of this sort are
+said to be <em>dimorphous</em>, or <em>dimorphic</em>,
+that is, of two forms; and
+some species are even <em>trimorphic</em>,
+having the two sets of
+organs long, short, and medium,
+respectively, in different individuals.
+Examples of dimorphic flowers are the pretty little
+bluets (<i>Houstonia cœrulea</i>), the partridge berry, the swamp
+loosestrife, and the English cowslip. Of trimorphic flowers
+we have examples in the wood sorrel and the spiked loosestrife
+(<i>Lythrum salicaria</i>) of the gardens. These flowers were a
+great puzzle to botanists until the celebrated naturalist,<span class="pagenum" id="Page_238">[Pg 238]</span>
+Charles Darwin,
+proved by experiment
+that the seeds
+produced by pollinating
+a dimorphous
+flower with its own
+pollen, or with pollen
+from a flower of
+similar form, are of
+very inferior quality
+to those produced
+by impregnating a long-styled flower with pollen from a
+short-styled one, and <i>vice versa</i>.</p>
+
+<figure class="figcenter illowp70" id="i_248" style="max-width: 50em;">
+  <img class="w100" src="images/i_248.jpg" alt="">
+  <figcaption><p class='center'><span class="smcap">Figs. 348-350.</span>—Three forms of loosestrife (<i>Lythrum
+salicaria</i>).</p></figcaption>
+</figure>
+
+<p id="p-271"><b>271. “Nature abhors self-fertilization.”</b>—These are the
+three principal methods by which nature provides against
+self-fertilization. Other cases occur in which the relative
+position of the two organs is such that self-pollination is
+difficult, or impossible, as in the iris and bear’s grass; or the
+pollen may be incapable of acting on the stigma of the flower
+that produced it. This aversion to self-fertilization is so
+great that many flowers, even when capable of it, will give
+preference to the pollen of another plant of the same
+kind, if dusted with both. From his observations on the
+behavior of plants in reference to this function, Charles Darwin
+drew the conclusion that “Nature abhors perpetual
+self-fertilization.”</p>
+
+<p id="p-272"><b>272. Cleistogamic flowers.</b>—Apparent exceptions to this
+rule are the hidden flowers found on certain plants which
+seem to have been constructed with a special view to self-fertilization.
+They are called <i>cleistogamic</i>, or closed, because
+they never open, but are fertilized in the bud; and those of
+the fringed polygala do not even rise above ground at all.
+Flowers of this kind can be found on several species of
+violet, concealed under the leaves, close to the ground; and
+the flowers of the peanut, found in the same situation, while
+they open slightly, are close-fertilized and practically cleistogamic.<span class="pagenum" id="Page_239">[Pg 239]</span>
+They are much more prolific than ordinary flowers,
+but are not common, and seem to be a provision against
+accident, for the plants producing them are generally provided
+with other flowers of the usual kind,—some, as the
+violet, having elaborate special adaptations for cross fertilization.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Why does a strawberry bed sometimes fail to fruit well, although it
+may flower abundantly? (<a href="#p-267">267</a>, <a href="#p-268">268</a>.)</p>
+
+<p>2. Are berries found on all sassafras trees? On all buckthorns?
+Hollies?</p>
+
+<p>3. Would a solitary hop-vine produce fruit? A solitary ash tree?
+(<a href="#p-267">267</a>.)</p>
+
+<p>4. Why is a mistletoe bough with berries on it so much harder to find
+than one with foliage merely? (<a href="#p-267">267</a>, <a href="#p-268">268</a>.)</p>
+</div>
+
+
+<h4 id="CH_VII_VIII_B">B. <span class="smcap">Wind Pollination</span></h4>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—In spring, catkins of forest trees, staminate and pistillate
+flowers of pine. At nearly all seasons, heads of grain and panicles of various
+kinds of grass can be obtained. For experiment, a potted plant of
+any kind, just about to bloom, may be used.</p>
+
+<p id="exp-80"><span class="smcap">Experiment 80. To test the effect of shutting out external
+agencies.</span>—Tie paper bags over flower buds of different kinds when nearly
+ready to open and leave until the flowers have withered. On removing
+the bags, mark with colored threads the flowers that had been covered, and
+watch until seed time. Do you notice any difference in the number, size,
+or weight of the seed produced by them and by those of the same kind left
+exposed? How do you account for the difference, if there is any? By
+what agencies could foreign pollen have been carried to the stigmas of
+the exposed flowers? If any of the covered specimens wither and drop
+their seed vessels without any attempt to fruit, examine a fresh flower, and
+see if it is capable of self-pollination.</p>
+
+<p>As already explained, experiments of this kind, to be conclusive, should
+be tried on as many specimens as possible. The greater the number of
+species and individuals included, the better. Where it is not practicable
+to carry on experiments by the class, pupils who are interested can make
+them at home.</p>
+</div>
+
+<p id="p-273"><b>273. The problem of pollination.</b>—When a plant has provided
+against self-pollination, its problem is only half solved,<span class="pagenum" id="Page_240">[Pg 240]</span>
+as it must now depend upon the conveyance of pollen to the
+stigma by extraneous means.</p>
+
+<figure class="figright illowp40" id="i_250" style="max-width: 40em;">
+  <img class="w100" src="images/i_250.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 351.</span>—Feathery stigmas of a grass
+adapted to wind pollination.</p></figcaption>
+</figure>
+
+<p id="p-274"><b>274. Adaptations to wind pollination.</b>—A very large
+number of plants, among which are included nearly all our
+principal forest trees, grains,
+and grasses of every kind,
+depend exclusively upon the
+wind for the distribution of
+their pollen. This being
+the case, it is, of course, an
+advantage to them to get
+rid of all unnecessary appendages
+that might hinder
+a free play of the wind
+among their flowers, and so
+they consist, as a rule, of
+essential organs only (<a href="#i_246">Figs.
+341, 342</a>). Such flowers are
+often distinguished, however,
+especially among
+grasses and low herbs, by
+large, feathery stigmas that
+are well adapted to catch and hold any stray pollen grains
+which may be floating in the air. Place a stigma of oat or
+other grass under the microscope and you will probably see
+a number of pollen grains clinging to its branches.</p>
+
+<p id="p-275"><b>275. The disadvantages of wind pollination.</b>—This is a
+very clumsy and wasteful method, however, for so much
+pollen is lost by the haphazard mode of distribution that the
+plant is forced to spend its energies in producing a vast
+amount more than is actually needed, and great masses of it
+are frequently seen in spring floating like patches of sulphur
+on ponds and streams in the neighborhood of pine thickets.
+Like those that are self-pollinated, wind-pollinated flowers
+are generally very inconspicuous, devoid of odor, and of all
+attractions of form or color, because they have no need of<span class="pagenum" id="Page_241">[Pg 241]</span>
+these allurements to attract the visits of insects. Besides
+being wasteful, wind pollination is very uncertain. The
+pollen cannot be blown about very well unless it is dry, and
+in rainy weather it may all be rotted or washed away before
+it can reach the stigmas that are ready to receive it.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Why do the flowers of oak, willow, and other wind-fertilized plants
+generally appear before the leaves? (<a href="#p-274">274</a>.)</p>
+
+<p>2. Can you account for the showers of “sulphur” sometimes reported
+in the newspapers? (<a href="#p-275">275</a>.)</p>
+
+<p>3. Do you see any connection between the feathery stigmas of most
+grasses and their mode of pollination? (<a href="#p-274">274</a>.)</p>
+
+<p>4. Why are house plants not apt to seed so well as those left in the
+open? (<a href="#exp-80">Exp. 80</a>.)</p>
+
+<p>5. Why are the tassels of corn placed at the tip of the stalk? (<a href="#p-274">274</a>.)</p>
+
+<p>6. Can you trace any connection between the winds and the corn crop?
+(<a href="#p-274">274</a>.)</p>
+
+<p>7. If March winds should cease to blow, would vegetation be affected
+in any way? (<a href="#p-274">274</a>.)</p>
+
+<p>8. Why are wind-fertilized plants generally trees or tall herbs? (<a href="#p-274">274</a>.)</p>
+
+<p>9. Is it good husbandry to plant different varieties of corn or other
+grain in the same field, if it is desired to keep the strain pure? (<a href="#p-255">255</a>, <a href="#p-274">274</a>.)</p>
+
+<p>10. Is water a good pollen carrier? (<a href="#p-275">275</a>.)</p>
+
+<p>11. What is the only class of plants it is likely to reach?</p>
+
+<p>12. What is the only other agency, besides wind and water, by which
+this office can be performed?</p>
+</div>
+
+
+<h4 id="CH_VII_VIII_C">C. <span class="smcap">Insect Pollination</span></h4>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Half a dozen panes of glass, about 6 × 9; squares of
+bright-colored cloth or paper; a few spoonfuls of honey or sirup; perfumes
+of various kinds, preferably flower extracts; fetid and disagreeable
+smelling substances, such as a bit of decaying animal or vegetable matter.
+Observations on living plants can best be made out of doors or in a greenhouse,
+as opportunity offers.</p>
+
+<p id="exp-81"><span class="smcap">Experiment 81. Has the color of flowers any attraction for
+insects?</span>—Place half a dozen panes of ordinary window glass out of doors
+or in an open window to which insects can have free access. Lay under
+the first pane a piece of black paper or cloth, and under the others bright-colored
+pieces of red, blue, white, yellow, and purple. Drop on the center
+of each pane a little honey or sirup, and watch. Do insects show any
+color preferences? Which color attracts fewest visitors? Which most?</p>
+
+<p><span class="pagenum" id="Page_242">[Pg 242]</span></p>
+
+<p id="exp-82"><span class="smcap">Experiment 82. Does odor influence insects?</span>—Try the same
+experiment with different odors, removing the bright colors and sprinkling
+some kind of perfume on each pane. Try also the effect of decaying
+meat and other malodorous substances. Are any insects attracted by
+these? What kinds? Does this account for the noisome smells of the
+“carrion-flower” and skunk cabbage? What kinds of insects are attracted
+by sweet-smelling substances? Do the greater number appear to be attracted
+by these, or by foul odors? Are flowers of the sweet-smelling
+or the foul-smelling kind more common in nature? Do insects seem to
+be more strongly influenced by colors or by odors?</p>
+</div>
+
+<p id="p-276"><b>276. The color of flowers</b>, being an adaptation to changing
+external conditions, is a very unstable quality, and varies
+greatly within the limits of the same species. Even on the
+same stem, flowers of different colors are often found, due,
+probably, to hybridization. Yet, notwithstanding all this
+apparently random intermingling of hues, the range of color
+for each species is confined, approximately, within certain
+limits. Nobody has ever seen a blue rose or a yellow aster;
+and though the florist’s art is constantly narrowing the application
+of this law, it still remains true that in a state of
+nature, certain colors seem to be associated together in the
+floral art gamut. Yellow is considered the simplest and
+most primitive color in flowers, and blue the latest and
+most highly evolved. Yellow, white, and purple, in the
+order named, are the commonest flower colors in nature;
+blue, the rarest. Do you see any relation between these facts
+and the color preferences of insects?</p>
+
+<p id="p-277"><b>277. Advantages of insect pollination.</b>—It is evident that
+this is a much more certain as well as a more economical
+method of securing pollination than through the haphazard
+agency of wind or water. In probing around for the nectar
+or the pollen upon which they feed, these busy little creatures
+get themselves dusted with the fertilizing powder, which they
+unconsciously convey from the stamen of one flower to the
+pistil of another. Insects usually confine themselves, as far
+as possible, to the same species during their day’s work, and
+since less pollen is wasted in this way than would be done by<span class="pagenum" id="Page_243">[Pg 243]</span>
+the wind, it is clearly to the advantage of a plant to attract
+such visitors, even at the expense of a little honey, or of a
+liberal toll out of the pollen they distribute.</p>
+
+<p id="p-278"><b>278. Special partnerships.</b>—Some plants have adapted
+themselves to the visits of one particular kind of insect so
+completely that they would die out if that
+species were to become extinct. The well-known
+alliance between red clover and the
+bumblebee was brought to light when the
+plant was first introduced into Australia.
+It grew luxuriantly and blossomed profusely,
+but would never set seed till the
+bumblebee was introduced to
+keep it company.</p>
+
+<table class='autotable'>
+<tr>
+<td>
+<figure class="figcenter illowp70" id="i_253" style="max-width: 20em;">
+  <img class="w100" src="images/i_253.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 352.</span>—Pod
+of <i>yucca</i> pierced by
+the <i>Pronuba yuccasella</i>.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp70" id="i_253a" style="max-width: 15em;">
+  <img class="w100" src="images/i_253a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 353.</span>—Pronuba
+pollinating
+pistil of
+yucca.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp70" id="i_253b" style="max-width: 30em;">
+  <img class="w100" src="images/i_253b.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 354.</span>—Moth resting on yucca
+blossom.</p></figcaption>
+</figure></td></tr></table>
+
+<p>A remarkable partnership of
+this kind exists between the
+<i>pronuba</i>, or yucca moth, and
+the flowering yuccas, of which the bear’s grass
+and Spanish bayonet are familiar examples.
+The pods of these plants are never perfect, but
+all show a constriction at or near the middle,
+such as is sometimes
+seen in
+the sides of
+wormy plums
+and pears.
+This is caused by the larvæ
+of the moth, which feed upon
+the unripe seeds. A glance
+under the nodding perianth
+of a yucca blossom (<a href="#i_253b">Fig. 354</a>)
+will show that the short stamens are curved back from the
+pistil in such a manner that, under ordinary circumstances,
+the pollen cannot reach the stigma except by the rarest
+accident. But the yucca moth, as soon as she has deposited
+her eggs in the seed vessel, takes care to provide a crop of<span class="pagenum" id="Page_244">[Pg 244]</span>
+food for her offspring by gathering a ball of pollen in her
+antennæ and deliberately plastering it over the stigma (<a href="#i_253a">Fig.
+353</a>). In this way fertilization of the ovules and maturing
+of the fruit is secured. The larvæ feed on the unripe seeds
+for a time, but so few are
+destroyed in proportion to
+the number matured that
+the plant can well afford to
+pay the small toll charged
+in return for the service
+rendered.</p>
+
+<table class='autotable'>
+<tr><td class='wd60'>
+<figure class="figcenter illowp70" id="i_254" style="max-width: 50em;">
+  <img class="w100" src="images/i_254.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 355.</span>—Upper boughs of a caprifig
+tree, showing an abundant crop of
+spring fruit.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp70" id="i_254a" style="max-width: 30em;">
+  <img class="w100" src="images/i_254a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 356.</span>—Female wasps
+issuing from the galls of caprifigs,
+in which the eggs are
+laid.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-279"><b>279. Caprification of the
+fig.</b>—A more complicated
+case of specialization is that
+of the Smyrna fig of commerce—the
+only one of the
+species that is capable of
+perfecting seeds. The
+staminate flowers are borne on a separate tree, the caprifig,
+which grows wild in the countries bordering on the Mediterranean.
+The caprifigs, as the fruit of this tree is called,
+are worthless except as the breeding
+and nesting places of a small insect,
+the fig wasp. This insect is the
+necessary agent in conveying pollen
+from the stamens of the caprifig to
+the pistils of the Smyrna fig, which it
+penetrates at certain seasons of the
+year in the effort to lay its eggs. In
+order to insure <em>caprification</em>, as this process is called, the
+caprifigs are strung by hand on fillets of cord or raffia and
+hung about on the trees which are to be fertilized. In this
+case we have an example of a threefold partnership between
+man, the fig tree, and the wasp, which is necessary to the
+existence of two of the parties.</p>
+
+<p><span class="pagenum" id="Page_245">[Pg 245]</span></p>
+
+
+<h4 id="CH_VII_VIII_D">D. <span class="smcap">Protective Adaptation</span></h4>
+
+<div class="blockquot">
+
+<p id="exp-83"><span class="smcap">Experiment 83. Are the floral envelopes of any use?</span>—Carefully
+remove the calyx and corolla from a young flower bud on a growing
+plant and see what will happen. Remove them from a flower just unfolding.
+Mark each by tying a colored thread lightly around the petiole and
+see if it sets as many seeds, or as good ones, as the unmutilated flowers on
+the same plant.</p>
+
+<p id="exp-84"><span class="smcap">Experiment 84. Is the position of a flower on the stem of any
+importance?</span>—Invert a blossom of pea or sage, and see what parts would
+come in contact with the body of a visiting insect. How would its chances
+for pollination be affected? Try to make a flower grow in an inverted
+position by tying or weighting it down, and watch the effect on seed production.</p>
+
+<p id="exp-85"><span class="smcap">Experiment 85. Is the position of flowers on the stem influenced
+by light?</span>—Place a potted plant with expanding flower buds near a
+window so that the light will reach it from one side only, and notice the
+position of the buds. After a day or two reverse the position with regard
+to light, and watch whether any change of position takes place.</p>
+</div>
+
+<figure class="figcenter illowp90" id="i_255" style="max-width: 50em;">
+  <img class="w100" src="images/i_255.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 357-359.</span>—Flower of monkshood, showing the changes by which it returns
+to its original position under the influence of geotropism after the axis of inflorescence,
+s, has been inverted: 357, inverted position; 358, change due to negative geotropism;
+359, change due to lateral geotropism.</p></figcaption>
+</figure>
+
+<div class="blockquot">
+
+<p id="exp-86"><span class="smcap">Experiment 86. Is the position of flowers on the stem influenced
+by geotropism?</span>—Lay a potted plant of lily of the valley, larkspur,
+gladiolus, or digitalis in a horizontal position, tie the main stem to keep
+it from changing its direction of growth, and leave for two or three days
+in a place where it is lighted equally on all sides. How do the individual
+flowers behave? What part bends to turn them up? Vary the experiment<span class="pagenum" id="Page_246">[Pg 246]</span>
+by turning the pot bottom upwards so that the flowering axis will
+point downwards. This can be done by inclosing the pot in a bag of strong
+cheesecloth, with the string tied loosely but firmly around the foot of the
+stem to prevent the contents from falling out, and suspending the whole
+bottom upwards. In making these experiments, use flowers that grow
+in a long cluster, or raceme, and hold the main axis in a vertical position
+by tying or weighting it down. Watch the behavior of the individual
+flowers. Arrange another pot containing the same kind of plant, in the
+same way, and suspend one
+in a dark place, keeping the
+other in the light. Does the
+same movement take place in
+both? Is it in response to
+light, or to gravity?</p>
+</div>
+
+<table class='autotable'>
+<tr><td>
+<figure class="figcenter illowp80" id="i_256" style="max-width: 40em;">
+  <img class="w100" src="images/i_256.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 360, 361.</span>—Protection of pollen in the
+thistle: 360, position at night, or during wet
+weather; 361, position in sunshine.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp80" id="i_256a" style="max-width: 40em;">
+  <img class="w100" src="images/i_256a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 362, 363.</span>—A bell flower: 362, position
+in daylight; 363, position at night, or during wet
+weather.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-280"><b>280. Means of protection.</b>—Where
+plants
+have adapted themselves
+to insect pollination,
+it is, of course, important to shut out intruders that
+would not make good carriers. In general, small, creeping
+things, like ants and
+plant lice, are not such
+efficient pollen bearers
+as winged insects, and
+hence the various devices,
+such as hairs,
+scales, and constrictions,
+at the throat of
+the corolla, by means
+of which their access to
+the pollen is prohibited.
+To this class of adaptations
+belong the hairy
+filaments of the spiderwort,
+the sticky ring
+about the peduncles of
+the catchfly, the swollen lips of the snapdragon, the scales or
+hairs in the throat of the hound’s-tongue, the velvet petals<span class="pagenum" id="Page_247">[Pg 247]</span>
+of the partridge berry, and the recurved edges of corollas
+like those of the morning-glory and tobacco, over which small
+crawling insects cannot easily climb.</p>
+
+<p>Of flowers that are pollinated by night moths, some close
+during the day, as the four-o’clock and the evening primrose;
+and <i>vice versa</i>, the morning-glory, dandelion, and dayflower
+(<i>Commelyna</i>) unfold their beauties only in the sunlight.
+For similar reasons, night-blooming flowers are generally
+white or very light-colored, and shed their fragrance only after
+sunset. A nodding position is assumed by many flowers at
+night, or during a
+shower, to keep the
+pollen from being injured
+by dew or rain.</p>
+
+<figure class="figcenter illowp80" id="i_257" style="max-width: 40em;">
+  <img class="w100" src="images/i_257.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 364.</span>—A flower of the trumpet vine (<i>Tecoma
+radicans</i>) adapted to pollination by humming birds
+and humming bird moths, which has been pierced by
+a bee or bird for honey.</p></figcaption>
+</figure>
+
+<figure class="figcenter illowp80" id="i_257a" style="max-width: 40em;">
+  <img class="w100" src="images/i_257a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 365.</span>—Head of the swordbill, a bird
+adapted to feeding on nectar from long,
+tubular corollas.</p></figcaption>
+</figure>
+
+<p id="p-281"><b>281. Insect depredators.</b>—The
+secretion
+of honey is a
+common means of
+attracting insects,
+and various adaptations,
+such as spurs, sacs, and pockets, are provided for protecting
+it against unwelcome intruders. In general, plants
+that have long, tubular
+flowers, like the trumpet
+honeysuckle (<i>Lonicera sempervirens</i>)
+and the trumpet
+vine, are reserving their
+sweets for humming birds,
+or long-tongued moths and butterflies. This protective
+device is not always successful, however, against insect depredators,
+for it is not uncommon to find such corollas with
+a puncture near the base, made by wasps or bees, and sometimes
+by humming birds themselves, in their impatience to
+get at the feast before the flower is open. Through the breach
+thus made, a rabble of petty thieves can then find entrance.</p>
+
+<p><span class="pagenum" id="Page_248">[Pg 248]</span></p>
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Of what use is the brilliant coloring of the camellia? The large
+flowers of the magnolia? The perfume of the rose and the violet? The
+fetid odor of the ailanthus? (<a href="#p-277">277</a>; <a href="#exp-81">Exps. 81</a>, <a href="#exp-82">82</a>.)</p>
+
+<p>2. Are the tastes of insects in regard to odors always the same as ours?
+(<a href="#exp-82">Exp. 82</a>.)</p>
+
+<p>3. Have flowers any economic value except for decorative purposes?</p>
+
+<p>4. Can you name any that are used as food or beverages? Any that
+furnish spices and flavorings? Drugs, medicines, or dyes?</p>
+
+<p>5. What commercial food product is obtained almost entirely from
+flowers?</p>
+
+<p>6. Name some of the flowers that are most valued by the beekeeper.</p>
+
+<p>7. Mention another important industry that is entirely dependent on
+flowers.</p>
+
+<p>8. Name some of the flowers that are most important to the perfumer.</p>
+
+<p>9. Why do the seeds of fruit trees so seldom produce offspring true
+to the stock? (<a href="#p-256">256</a>, <a href="#p-257">257</a>, <a href="#p-271">271</a>, <a href="#p-277">277</a>.)</p>
+
+<p>10. Would you place a beehive near a field of buckwheat? Of clover?
+Near a strawberry bed? In a peach orchard? Near a fig tree? Under
+a grape arbor?</p>
+
+<p>11. Why are very conspicuous flowers, like the camellia, hollyhock, and
+pelargoniums, so frequently without odor?</p>
+
+<p>12. Why is the wallflower “sweetest by night”? (<a href="#p-280">280</a>.)</p>
+
+<p>13. What advantage can flowers like the morning-glory gain by their
+early closing? (<a href="#p-280">280</a>.)</p>
+
+<p>14. Of what use to the cotton plant, Japan honeysuckle, and hibiscus
+is the change of color their blossoms undergo a few hours after opening?
+(<a href="#p-277">277</a>, <a href="#p-278">278</a>, <a href="#p-280">280</a>.)</p>
+
+<p>15. Why does the Japan honeysuckle, which has run wild so abundantly
+in many parts of our country, produce so few berries? (<a href="#p-278">278</a>, <a href="#p-280">280</a>.)</p>
+
+<p>16. If the trumpet vine grows in your neighborhood, examine a number
+of corollas and account for the dead ants found in them. Account also
+for the large hole (sometimes three quarters of an inch in diameter) often
+found near the base of the tube. (<a href="#p-281">281</a>.)</p>
+
+<p>17. Do you see any connection between the greater freshness and beauty
+of flowers early in the morning, and the activity of bees, birds, and butterflies
+at that time?</p>
+
+<p>18. The flowers most frequented by humming birds are the trumpet
+honeysuckle, cardinal flower, trumpet vine, horsemint (<i>Monarda</i>), wild
+columbine, canna, fuchsia, etc.; what inference would you draw from
+this as to their color preferences?</p>
+</div>
+
+<p><span class="pagenum" id="Page_249">[Pg 249]</span></p>
+
+
+<h4 id="CH_VII_FIELD">Field Work</h4>
+
+<div class="blockquot">
+
+<p>1. The ecology of the flower is so suggestive a subject and so peculiarly
+appropriate to outdoor work that it seems hardly necessary to point out the
+many attractive fields of inquiry it opens to the student of nature. In this
+way alone can experiments in insect pollination be carried on to the best
+advantage. Try the effect of enveloping buds of various kinds in gauze so
+as to exclude the visits of insects, and note the result as to the production
+of fruit and seed. Envelop a cluster of milkweed blossoms in this way and
+notice how much longer the flowers so protected continue in bloom than do
+the others; why is this? Try the same experiment upon the blooms of
+cotton and hibiscus, if you live where they grow, and see whether the characteristic
+change in color occurs in flowers from which insects have been
+excluded, and whether good seed pods are produced by them. Try the
+effect upon fruit production of excluding insects from clusters of apple,
+pear, and peach blossoms.</p>
+
+<p>2. Make a list of all the outdoor plants, both wild and cultivated, that
+are found blooming in your neighborhood, keeping a record of the earliest
+specimens of each as you find them. The best way is to keep a sort of
+daily calendar, and at the end of each month give a summary of the species
+found in bloom during that period. In this way a fairly complete annual
+record of the flowering time of the different plants for that vicinity will be
+obtained. The record should be kept up the whole year round. Don’t
+stop in winter, but go straight on through the coldest as well as the hottest
+season, and you will make some surprising discoveries, especially if the
+record is continued year after year. Give the common name of each plant,
+adding the botanical one if you know it. Any facts that you may know
+or may discover in regard to particular plants, such as their medicinal or
+other uses, their poisonous or edible properties, the insects that visit them,
+and in the case of weeds, their origin and introduction, will greatly enhance
+the interest and value of the record.</p>
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_250">[Pg 250]</span></p>
+
+<h2 class="nobreak" id="CH_VIII">CHAPTER VIII. FRUITS</h2>
+</div>
+
+
+<h3 id="CH_VIII_I">I. HORTICULTURAL AND BOTANICAL FRUITS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Green ears of corn or wheat, fresh pods of beans, young
+fruits of apple, grape, tomato, melon, buckeye, chestnut, or pecan. A
+young fruiting stem of squash, gourd, or tomato.</p>
+
+<p><span class="smcap">Appliances.</span>—Coloring fluid, glasses of water, a piece of cardboard,
+tin-foil, vaseline.</p>
+
+<p id="exp-87"><span class="smcap">Experiment 87. Where do the food substances contained in
+fruits come from?</span>—Apply your food tests to the pulp of a young apple,
+squash, bean pod, chestnut, buckeye, or a “green” ear of corn or wheat,
+and see what it contains. Test the stem and roots of a plant of the same
+kind in the same way. Do you find the same foods in them? Where
+is the food stored?</p>
+
+<p id="exp-88"><span class="smcap">Experiment 88. Through what parts of the stem and fruit do
+water and nourishment travel to the seed?</span>—Cut a young squash
+or cucumber from the vine, leaving stem enough to insert by its cut end
+in a glass of eosin solution. Leave for two or three days, then make a
+vertical section through the stem and fruit. What course has the liquid
+followed? Can you trace some of it into each seed? Do you see now a
+use for the seed stalk and the rhaphe?</p>
+
+<p id="exp-89"><span class="smcap">Experiment 89. Does the surface of fruits give off water by
+transpiration?</span>—Try <a href="#exp-59">Exp. 59</a>, using in place of leaves a young squash,
+eggplant, or a bunch of grapes, and after a day or two notice whether
+any moisture has been given off. If the fruit skin gives off moisture,
+it is natural to expect that it would be provided with stomata, like other
+transpiring organs. To find out whether this is so, place a thin piece of
+the outer epidermis of a grape, tomato, plum, or apple under the microscope.
+Do you find stomata on any of them? Do you see anything else?
+Try the skin of an apple, and compare the corky dots you find there with
+those on the bark of a young dicotyl stem <a href="#p-118">(118)</a> and decide what they are.</p>
+
+<p id="exp-90"><span class="smcap">Experiment 90. Will fruits ripen well in the absence of light
+and air?</span>—Envelop a number of immature fruits in bags of dark cloth
+or paper so that no light can reach them. Keep a number of others well
+coated with oil or vaseline, and watch. Do the fruits so treated mature
+as quickly or develop as fully as those of the same kind left untreated?</p>
+</div>
+
+<p><span class="pagenum" id="Page_251">[Pg 251]</span></p>
+
+
+<figure class="figcenter illowp45" id="i_261" style="max-width: 75em;">
+  <img class="w100" src="images/i_261.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 12.</span>—The improvement of fruits by cultivation and selection: 1, the
+common wild gooseberry; 2, Houghton gooseberry, seedling of the wild form;
+3, Downing gooseberry, seedling of the Houghton. (All natural size, adapted from
+Bailey.)</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_252">[Pg 252]</span></p>
+
+<div class="blockquot">
+
+<p id="exp-91"><span class="smcap">Experiment 91. What is the use of the rind to the fruit?</span>—Select
+two apples of equal size, peel one, and weigh both. After 12 to 24
+hours, weigh them again. Which shows the greater loss in weight?
+Leave peeled and unpeeled fruits in an exposed place and see which is
+the more readily attacked by insects. Which decays the sooner? What
+are some of the uses of the rind?</p>
+</div>
+
+<p id="p-282"><b>282. What is a fruit?</b>—Horticulturally and commercially
+the distinction between a fruit and a vegetable depends very
+much upon the use we make of it—whether as food, or as a
+mere gratification of the palate. Broadly speaking, those
+fruits that are lacking in sugar, as the tomato and cucumber,
+are classed as vegetables. Botanically, a fruit is any
+ripened seed vessel, or ovary, with such connected parts as
+may have become incorporated with it; and hence, to the
+botanist, a boll of cotton, a tickseed, or a cocklebur is just
+as much a fruit as a peach or a watermelon.</p>
+
+<p id="p-283"><b>283. Classification of fruits.</b>—For convenience of description,
+fruits are classed as:</p>
+
+<p>(<i>a</i>) Dry or fleshy, according as they have a more or less
+hard and bony, or soft and fleshy, texture.</p>
+
+<p>(<i>b</i>) Dehiscent, or indehiscent, according as they open at
+maturity in a regular way to discharge their seed, or remain
+closed until the covering wears away or is burst by the germinating
+embryo.</p>
+
+<p>Fleshy fruits are very seldom dehiscent, though some few,
+as the balsam apple and the chayote, or one-seeded squash,
+discharge their seed when mature. The banana and some
+other fleshy fruits, when peeled, separate along regular lines,
+and in this respect behave very much as if they were fleshy
+pods.</p>
+
+<p id="p-284"><b>284. When is a fruit ripe?</b>—A fruit is ripe horticulturally,
+when it is good to eat; it is ripe botanically, when it has set
+its seed. Many of our choicest table fruits, such as the pineapple,
+banana, and most varieties of fig, seldom are botanically
+ripe, since they rarely produce perfect seeds.</p>
+
+<p>It is the constant effort of the horticulturist to develop<span class="pagenum" id="Page_253">[Pg 253]</span>
+those parts of a plant that are useful to man, while in a state
+of nature the plant seeks to develop such parts as best serve
+its own purpose in the struggle for existence. The plants
+most useful to man have, as a general thing, been subjected
+to a long course of artificial breeding and selection. They
+are forced developments, often monstrosities, from the plant’s
+point of view, if we could conceive of it as capable of having
+an opinion. Nature is continually striving to reclaim them;
+and if left to themselves, they must
+either obey “the call of the wild,”
+or die out.</p>
+
+<figure class="figright illowp30" id="i_263" style="max-width: 30em;">
+  <img class="w100" src="images/i_263.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 366.</span>—A seedless citrange,
+hybrid between the orange
+and the lemon.</p></figcaption>
+</figure>
+
+<p id="p-285"><b>285. Seedless fruits and vegetables.</b>—As
+the seed is the most
+important thing to the plant, the
+edible parts in wild fruits are, as a
+rule, subsidiary to its development.
+In a state of nature, fruits will generally
+wither and drop from the
+stem, if for any reason they have
+become incapable of perfecting their
+seed. It is only in a few kinds, limited to those which can
+successfully propagate themselves by other means, that the
+production of seed does not take place. Among cultivated
+species, however, where propagation is carefully provided
+for by man, the seed is of less importance, and sterile varieties
+that might soon die out under natural conditions, continue
+their existence indefinitely under his fostering hand.
+The seeds of edible fruits are, as a general thing, both indigestible
+and unpalatable <a href="#p-21">(21)</a>, and hence the efforts of the
+horticulturist are directed largely to getting rid of them, or
+to very greatly reducing their size and number in proportion
+to the edible parts.</p>
+
+<p id="p-286"><b>286. How seedless fruits arise.</b>—The perfecting of seed
+requires a great consumption of food and energy on the part
+of the plant, and when it is led, for any reason, to expend
+an unusual amount of force in some other function,—as<span class="pagenum" id="Page_254">[Pg 254]</span>
+for instance, in producing tubers or in growing bulbs,—it
+is apt to bear few seeds and to depend more or less completely
+upon other methods of reproduction.</p>
+
+<p>Among cultivated plants, selection on the part of man,
+whether conscious or unconscious, has perhaps contributed
+more than any other cause to bring about the same result.
+To this agency is probably due the development of our common
+domestic fig, of which over four hundred varieties that
+mature fruits without fertilization are cultivated in the United
+States alone. The fig was one of the earliest fruits known to
+cultivation; and the early navigators, ignorant of the processes
+of fertilization, would naturally, in choosing specimens to
+carry home with them, select only fruit-bearing trees. Such
+of these as matured fruits would be preserved and propagated,
+until, by repeated selection, hundreds of edible varieties have
+been developed that ripen fruits without caprification <a href="#p-279">(279)</a>.</p>
+
+<p id="p-287"><b>287. The use of the fruit to the plant.</b>—The object of
+the fruit is to furnish protection to the seeds during their
+period of development and inactivity, and to aid in various
+ways the work of dispersal. It probably takes part also in
+digesting and diffusing nourishment for the use of the developing
+seeds. It has been shown in previous chapters that plants,
+almost without exception, are in the habit of storing up
+food in various ways as a provision for fruiting. That a
+large portion of the stored nourishment is used up in the performance
+of this function is proved by its disappearance from
+those parts—for example, from fleshy roots, such as beets
+and turnips, after they have “gone to seed.”</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. What is the use of the down on the peach? The bloom of the plum
+and grape? [<a href="#p-202">202</a>, (1); <a href="#exp-91">Exp. 91</a>.]</p>
+
+<p>2. Why are apples, pears, plums, and other fleshy fruits nearly always
+rosier on one side than on the other? (<a href="#exp-90">Exp. 90</a>.)</p>
+
+<p>3. Can annuals be improved in any other way than by seed selection?</p>
+
+<p>4. Would a seedless annual be perpetuated under natural conditions?</p>
+
+<p><span class="pagenum" id="Page_255">[Pg 255]</span></p>
+
+<p>5. Why is decrease of moisture and increase of light desirable as the
+fruiting season approaches? (<a href="#p-126">126</a>, <a href="#p-127">127</a>; <a href="#exp-90">Exp. 90</a>.)</p>
+
+<p>6. Why are turnips, carrots, and other fleshy roots unfit to eat if left
+over till the plants have seeded? (<a href="#p-92">92</a>, <a href="#p-287">287</a>.)</p>
+</div>
+
+
+<h3 id="CH_VIII_II">II. FLESHY FRUITS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A specimen of each of the four principal kinds of fleshy
+fruits. Examples of the pome are: apple, pear, quince, rose hip, haw; of
+the berry: grape, tomato, cranberry, currant, gooseberry, lemon; of the
+pepo: melon, squash, pumpkin; of the drupe: peach, plum, cherry, dogwood.
+Specimens of the commoner kinds can nearly always be found in
+the market; if nothing better is available, pickled and dried ones may be
+used—figs, prunes, dates, raisins, etc.</p>
+</div>
+
+<figure class="figright illowp40" id="i_265" style="max-width: 50em;">
+  <img class="w100" src="images/i_265.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 367.</span>—Outside of an apple, showing
+lenticels on the skin.</p></figcaption>
+</figure>
+
+
+<p id="p-288"><b>288. Dissection of a pome fruit.</b>—Examine with a lens
+the outside of an apple or a pear. Can you make out the
+lenticels? What difference
+in color do you notice between
+the ripe and unripe
+fruit? What difference in
+taste? What substance
+would you judge from this,
+do ripe fruits contain
+which green ones do not?
+Test both kinds for sugar
+and starch; which contains
+the more of each? Strictly
+speaking, sugar and starch
+are merely different forms
+of the same chemical compound. In ripe fruits the starch
+has been cooked by the sun and converted into sugar.</p>
+
+<p>With the point of a pencil separate the little dry scales that
+cover the depression in the center of the fruit at the end opposite
+the stem. How many of them are there? How does this
+accord with the plan of the flower as outlined in <a href="#p-229">229</a>? They
+are the remains of the sepals, as will be more apparent on
+comparing them with the larger and more leaflike ones on
+a hip, which is clearly only the end of the footstalk enlarged<span class="pagenum" id="Page_256">[Pg 256]</span>
+and hollowed out with the calyx sepals at the top. Cut a
+cross section midway between the stem and the blossom end,
+and make an enlarged sketch of it. Label the thin, papery
+walls that inclose the seed, <em>carpels</em>.
+How many of them are there, and how
+many seeds does each contain? The
+carpels, together with all that portion
+of the fruit which surrounds and adheres
+to the ovary, constitute the <em>pericarp</em>,
+or wall of the seed vessel. The
+fleshy part of the apple is no part of
+the ovary proper, but consists merely
+of the receptacle, or end of the footstalk,
+which becomes greatly enlarged
+and thickened in fruit. Look for a
+ring of dots outside the carpels, connected (usually) by a
+faint scalloped line. How many of these dots are there? How
+do they compare in number with the carpels? With the remnants
+of the sepals adhering to the blossom end of the fruit?</p>
+
+<table class='autotable'>
+<tr><td>
+<figure class="figcenter illowp70" id="i_266" style="max-width: 30em;">
+  <img class="w100" src="images/i_266.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 368.</span>—Cross section
+of a pome: <i>pl</i>, placenta; <i>c</i>,
+carpels; <i>f</i>, fibrovascular bundles.</p></figcaption></figure>
+</td><td>
+<figure class="figcenter illowp60" id="i_266a" style="max-width: 50em;">
+  <img class="w100" src="images/i_266a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 369.</span>—Vertical section
+of a pome: <i>p</i>, peduncle; <i>f</i>,
+fibrovascular bundles; <i>s</i>, seeds;
+<i>pl</i>, placenta; <i>c</i>, carpel.</p></figcaption>
+</figure></td></tr></table>
+
+<p>Next make a vertical section
+through a fruit, and sketch, enlarging
+it sufficiently to show all the
+parts distinctly. Observe the line of
+woody fibers outside the carpels, inclosing
+the core of the apple. Compare
+this with your cross section; to
+what does it correspond? Where do
+these threads originate? Where do
+they end? Can you make out what
+they are? (<a href="#p-176">176</a>.) Notice how and
+where the stem is attached to the
+fruit. Label the external portion of
+the stem, <em>peduncle</em>; the upper part, from which the fibrovascular
+bundles branch, the <em>receptacle</em>. It is the enlargement
+of this which forms the fleshy part of the fruit. Try to find
+out, with the aid of your lens and dissecting pins, the exact<span class="pagenum" id="Page_257">[Pg 257]</span>
+spot at which the seeds are attached to the carpels, and
+label this point, <em>placenta</em>. Notice whether it is in the axis
+where the carpels all meet at their inner edges, or on the
+outer side. Observe, also, whether the seed is attached to
+the placenta by its big or its little end. If you can find a
+tiny thread that attaches the seed to the carpel; label it, seed
+stalk. Fruits of this kind are classed, botanically, as <em>pomes</em>.
+Write, from your analysis, a definition of the pome.</p>
+
+<figure class="figright illowp35" id="i_267" style="max-width: 40em;">
+  <img class="w100" src="images/i_267.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 370, 371.</span>—Enlarged
+receptacle of Carolina allspice
+(<i>Calycanthus</i>), containing fruits
+attached to its inner surface:
+370, exterior; 371, vertical section.</p></figcaption>
+</figure>
+
+<p id="p-289"><b>289. Modifications of the receptacle.</b>—Compare with the
+drawings you have made, a haw and a hip. What points of
+agreement do you see? What differences?
+Which of the two more
+closely resembles the typical pome?
+The receptacle is subject to a variety
+of modifications, and forms a
+part of many fruits, for example,
+the fig, lotus, and calycanthus
+(<a href="#i_267">Figs. 370, 371</a>); but a fruit is not
+a pome unless the containing receptacle
+becomes more or less soft
+and edible.</p>
+
+<p id="p-290"><b>290. The pepo, or melon.</b>—Next
+examine a gourd, cucumber, squash,
+or any kind of melon, and compare its blossom end with that
+of the apple or pear. Do you find any remains of a calyx,
+or other part of the flower? Examine the peduncle and observe
+how the fruit is attached to it. Can you tell what
+made the outer epidermis of the rind? Put a small piece
+under the microscope; do you see any stomata, or lenticels?
+Cut cross and vertical sections, and sketch them, labeling
+each part. There may be some difficulty in making out the
+carpels, for they are not separate and distinct as in the pome,
+but confluent with the enlarged receptacle, which in these
+fruits forms the outer portion of the rind, and also with each
+other at their edges, so as to form one unbroken circle, as if
+they had all grown together. And this is precisely what<span class="pagenum" id="Page_258">[Pg 258]</span>
+has happened. The placentas are greatly enlarged and
+modified, and it may be necessary to refer to the diagram,
+<a href="#i_268">Fig. 372</a>, <i>c</i>, in order to make them out. How many locules,
+or chambers, are there in your specimen? How many
+placentas? Notice that these are central
+and double, but extend to the pericarp before
+dividing so that they appear to be parietal,
+and twice their real number, which
+is only three. Are the seeds vertical, as in
+the apple, or horizontal? Look for the
+little stalk, or thread, that attaches them
+to the placenta.</p>
+
+<p><em>Pepo</em> is the name given by botanists to
+this kind of fruit. Write in your notebook
+a proper definition of it, from the specimens examined.</p>
+
+<table class='autotable'>
+<tr><td>
+<figure class="figcenter illowp60" id="i_268" style="max-width: 20em;">
+  <img class="w100" src="images/i_268.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 372.</span>—Cross
+section of gourd: <i>c</i>, one
+of the carpels in diagram.
+(<i>After</i> <span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp60" id="i_268a" style="max-width: 40em;">
+  <img class="w100" src="images/i_268a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 373, 374.</span>—A potato
+berry: 373, exterior; 374, cross
+section.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-291"><b>291. The berry.</b>—Examine a tomato, an eggplant, a
+grape, cranberry, lemon, or orange, in both cross and vertical
+section, and compare it with the melon and the apple.
+What differences and resemblances do you find? Cut a
+cross section, and draw, showing the attachment of the seeds.
+How many locules are there? Normally the tomato is a
+two-celled fruit, like the potato berry (<a href="#i_268a">Fig. 374</a>), but it has
+been so modified by cultivation that
+the original plan is not always easy
+to distinguish. See if you can make
+it out. Do the seeds in your specimen
+appear to be healthy and well
+developed, or are some of them small
+and aborted? How do you account
+for this? (<a href="#p-285">285</a>, <a href="#p-286">286</a>.) What difference
+do you notice in color between
+the ripe and unripe fruit? Write a
+definition of the berry from the study you have made of it.</p>
+
+<p>Berries are the commonest of all fleshy fruits, and the most
+variable and difficult to define. In general, any soft, pulpy,
+or juicy mass, like the grape and tomato, whether one or<span class="pagenum" id="Page_259">[Pg 259]</span>
+many seeded, inclosed in a containing envelope, whether
+skin or rind, is a berry. Its typical forms are such fruits as
+the grape, mistletoe, pokeberry, etc., though such diverse
+forms as the eggplant, persimmon, red pepper, orange, banana,
+and pomegranate have been classed as berries; and,
+in fact, the melon and the pumpkin are only greatly modified
+kinds of the same fruit. In popular language, any small,
+round, edible fruit is called a berry. This is a good commercial
+classification, though not botanically correct.</p>
+
+<figure class="figright illowp25" id="i_269" style="max-width: 20em;">
+  <img class="w100" src="images/i_269.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 375.</span>—Vertical
+section of a
+drupe. (<i>After</i>
+<span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p id="p-292"><b>292. The drupe, or stone fruit.</b>—Examine a section of a
+green plum, peach, or cherry, before the stone has hardened,
+and tell from what part it is formed. This stony covering,
+composed of the inner layer of the pericarp, and enveloping
+the seed like an outer coat, is the main distinction
+between the drupe and the berry,
+but it is not always possible to make out its
+real nature except by an examination of the
+young ovary. In a green drupe, before the
+stone has hardened, its connection with the
+fleshy part is very evident, and the ripe fruit
+will answer inquiries if we know how to put
+them. Open the stone, and the seed will be exposed with its
+own coverings inside. When a stone has more than one
+kernel,—for instance, an almond or peach stone, —the
+stone is not a seed coat, but the hardened inner wall of a
+seed vessel or ovary; for a seed coat can never contain more
+than one seed, any more than the same skin can contain
+more than one animal.</p>
+
+<p>All the fruits considered in this section belong to the fleshy
+class. These form the bulk of the fruits sold in the market,
+and are of special importance to the horticulturist.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Is the tomato horticulturally a fruit or a vegetable? the squash?
+eggplant? cranberry? olive? elderberry? pepper? date? maypop? crab
+apple? black haw? To what class does each belong? (<a href="#p-283">283</a>, <a href="#p-288">288-292</a>.)</p>
+
+<p><span class="pagenum" id="Page_260">[Pg 260]</span></p>
+
+<p>2. Of what use to the plant is the hard stone of the drupe? (21.)</p>
+
+<p>3. Is the pulp of fleshy fruits agreeable to the taste before they are
+ripe? After? What advantage is this to the plant? (21.)</p>
+
+<p>4. Are the seeds of edible fruits, as a general thing, digestible or agreeable
+to the palate?</p>
+
+<p>5. Is this an advantage to man? To the plant? (<a href="#p-21">21</a>, <a href="#p-284">284</a>, <a href="#p-285">285</a>.)</p>
+
+<p>6. What are the most common fleshy fruits in autumn?</p>
+
+<p>7. With what vegetative parts of the plant does the skin of many
+fruits present correspondences? Are these such as to indicate homology,
+or analogy only, between them? (<a href="#p-100">100</a>, <a href="#p-118">118</a>, <a href="#p-288">288</a>, <a href="#p-289">289</a>; <a href="#exp-89">Exp. 89</a>.)</p>
+
+<p>8. Name six of the most watery fruits that grow in your neighborhood.</p>
+
+<p>9. Under what conditions as to soil, heat, moisture, etc., does each
+thrive best?</p>
+
+<p>10. Would a gardener act wisely to infer that because a fruit contains
+a great deal of water it should be planted in a very wet place?</p>
+
+<p>11. Which contains more water, the fruit or the leaves of the apple?</p>
+
+<p>12. Why does not the fruit, when separated from the tree, wither as
+quickly as do the leaves? (<a href="#exp-91">Exp. 91</a>.)</p>
+</div>
+
+
+<h3 id="CH_VIII_III">III. DRY FRUITS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Some easily attainable specimens of dry fruits are (1) nuts:
+acorn, hickory nut, walnut, chestnut, pecan, filbert; (2) pods: pea and bean
+pods, capsules of larkspur, milkweed, jimson weed, cotton; (3) grains: corn,
+wheat, oats, rice; (4) akene: sunflower, thistle, dandelion, buckwheat,
+clematis.</p>
+</div>
+
+<p id="p-293"><b>293. Importance of dry fruits.</b>—Dry fruits are not in
+general so conspicuous or so attractive as fleshy ones, but on
+account of their great number and variety they offer a
+wide field for study. They are also of great interest from an
+economic point of view: (1) because they include the cereal
+grains that furnish so large a portion of our food, and (2)
+because the greater part of the troublesome weeds that infest
+our crops are scattered by fruits of this class.</p>
+
+<p id="p-294" class='cb'><b>294. Indehiscent fruits.</b>—These kinds are so simple that
+it will not be necessary to give much time to them. Compare
+an acorn, a chestnut, or a filbert with a ripe bean pod or with
+a capsule of morning-glory. Try to open each with your
+fingers; which <em>dehisces</em>, or opens, the more readily? Which is
+indehiscent, having no regular way of opening? How many<span class="pagenum" id="Page_261">[Pg 261]</span>
+seeds or kernels do you find in the dehiscent pod? How
+many in the indehiscent one? Would it be of any advantage
+for a one-seeded pod to open? Remove the kernel
+from the indehiscent fruit; has it any covering besides the
+shell? Which is the pericarp, and which the seed coat?</p>
+
+<table class='autotable'>
+<tr><td>
+<figure class="figcenter illowp80" id="i_271" style="max-width: 50em;">
+  <img class="w100" src="images/i_271.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 376, 377.</span>—Nut of the pecan
+tree: 376, exterior; 377, cross section.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp80" id="i_271a" style="max-width: 50em;">
+  <img class="w100" src="images/i_271a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 378, 379.</span>—Nutlike seeds:
+378, horse-chestnut; 379, seed of the
+fetid sterculia.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-295"><b>295. The nut</b> is easily recognized by its hard, bony covering,
+containing usually, when mature, a single large seed that
+fills the interior. Care should be taken not to confound with
+true nuts, large bony seeds, like those of the buckeye, horse-chestnut,
+date, and the Brazil nut sold in the markets. In
+the true nut, the hard covering is the seed vessel, or pericarp,
+and not a part of the seed itself, though it often adheres to it
+so closely as to seem so. In bony seeds, like those of the horse-chestnut
+and persimmon, the hard covering is the outer seed
+coat. The distinction is not always easy to make out unless
+the seed can be examined while still attached to the placenta
+of the fruit.</p>
+
+<table class='autotable'>
+<tr><td class='wd40'>
+<figure class="figcenter illowp80" id="i_271b" style="max-width: 30em;">
+  <img class="w100" src="images/i_271b.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 380, 381.</span>—Akenes
+(magnified): 380, of buckwheat;
+381, of cinque-foil.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp80" id="i_272" style="max-width: 40em;">
+  <img class="w100" src="images/i_272.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 382-384.</span>—Cremocarps, fruits of
+the parsley family.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-296"><b>296. The akene</b>, of which we have
+examples in the tailed fruit of the
+clematis, the tiny pits on the strawberry,
+and the so-called seeds of the
+thistle, dandelion, and sunflower, is a
+small, dry, one-seeded, indehiscent
+fruit, so like a naked seed that it is
+generally taken for one by persons not
+acquainted with botany. It is the<span class="pagenum" id="Page_262">[Pg 262]</span>
+commonest of all fruits, and there are so many kinds that
+special names have been applied to some of the most marked
+varieties. The akene of the
+composite family may generally
+be known by the
+various appendages in the
+form of scales, hooks, hairs,
+or chaff, that crown it (<a href="#i_222">Figs.
+309-314</a>). The fruits of the
+parsley family are merely a
+sort of double akene attached
+by the inner face
+to a slender stalk from which it separates at maturity.</p>
+
+<p>The <em>samara</em>, or key fruit, is an akene provided with a
+wing to aid in its dispersion
+by the wind. The
+maple, ash, and elm furnish
+familiar examples.</p>
+
+<table class='autotable'>
+<tr><td class='wd70'>
+<figure class="figcenter illowp80" id="i_272a" style="max-width: 40em;">
+  <img class="w100" src="images/i_272a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 385, 386.</span>—Samaras: 385, ailanthus;
+386, maple.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp80" id="i_272b" style="max-width: 20em;">
+  <img class="w100" src="images/i_272b.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 387, 388.</span>—Grain
+of wheat with husks on:
+387, front view; 388, back
+view.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-297"><b>297. The grain</b>, so familiar
+to us in all kinds of
+grasses, is economically
+the most important of all
+fruits. It is popularly
+classed as a seed, and for practical purposes may be treated
+as such, but it is really a modification of the akene in which
+the seed coats have so completely fused with the pericarp
+that they can no longer be distinguished
+as separate organs. Peel the husk from
+a grain of corn that has been soaked for
+twenty-four hours, and you will find the
+contents exposed without any covering;
+remove the shell of an acorn or a hickory
+nut, and the seed will still be enveloped
+by its own coats. Would it be of any
+advantage for the seed of an indehiscent fruit, like a grain of
+corn or oats, to have a separate special covering of its own?</p>
+
+<p><span class="pagenum" id="Page_263">[Pg 263]</span></p>
+
+<table class='autotable wd80'>
+<tr><td>
+<figure class="figcenter illowp50" id="i_273" style="max-width: 30em;">
+  <img class="w100" src="images/i_273.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 389.</span>—Follicle
+of milkweed.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp50" id="i_273a" style="max-width: 30em;">
+  <img class="w100" src="images/i_273a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 390.</span>—Leaflike
+follicle of Japan
+varnish tree: <i>S</i>,
+outer (dorsal) suture;
+<i>S′</i>, inner (ventral)
+suture.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-298"><b>298. Dehiscent fruits.</b>—<em>Pod</em>, or <em>capsule</em>, is the general
+name applied to all dehiscent fruits. The simplest possible
+kind of pod is the <em>follicle</em>, composed of a
+single carpel, like those of
+the larkspur, milkweed, and
+marsh marigold, and may be
+regarded as a modified leaf.
+Examine one of these pods
+and you will find that it
+splits down one side, which
+corresponds to the edges of
+the leaf brought together
+and turned inward to form
+a placenta for the attachment
+of the seed. This line
+of union is called a “suture,”
+from a Latin word
+meaning a “seam.”</p>
+
+<p id="p-299"><b>299. The legume.</b>—Get a pod of any kind of bean or
+pea, and observe that it differs
+from the follicle in having two
+sutures or lines of dehiscence.
+One of these runs along the back
+of the carpel and corresponds
+to the midrib of the leaf; the
+other, corresponding to the
+united edges of the carpellary
+leaf, always turns inward,
+toward the axis of the flower,
+and forms the placenta.</p>
+
+<table class='autotable'>
+<tr><td class='wd60'>
+<figure class="figcenter illowp60" id="i_273b" style="max-width: 40em;">
+  <img class="w100" src="images/i_273b.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 391-393.</span>—Legumes: 391,
+legume of bean: <i>v</i>, ventral suture;
+<i>d</i>, dorsal suture; 392, constricted
+legume of senna (<i>Cassia Nelsonia</i>); 393,
+legume of a pea, with partially constricted
+pod.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp80" id="i_274" style="max-width: 20em;">
+  <img class="w100" src="images/i_274.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 394.</span>—Loment of
+beggar-ticks.</p></figcaption>
+</figure></td></tr></table>
+
+<p>The beggar-ticks, so unpleasantly
+familiar to most of us,
+are merely a kind of legume constricted
+between the seeds and
+breaking up into separate joints
+at maturity. What kind of<span class="pagenum" id="Page_264">[Pg 264]</span>
+indehiscent fruits do the joints become
+when separated? (<a href="#p-296">296</a>.)</p>
+
+<figure class="figright illowp50" id="i_274a" style="max-width: 50em;">
+  <img class="w100" src="images/i_274a.jpg" alt="">
+  <figcaption>
+<table class="autotable">
+<tr>
+<td class="tdl wd50"><p><span class="smcap">Fig. 395.</span>—Cross section of one-celled syncarpous capsule of frostweed, with parietal placentæ.
+(<i>After</i> <span class="smcap">Gray</span>.)</p></td>
+<td class="tdl"><p><span class="smcap">Fig. 396.</span>—Follicles of larkspur borne on the same torus, but distinct.</p></td>
+</tr>
+</table>
+</figcaption>
+</figure>
+
+<p id="p-300"><b>300. Compound or syncarpous pods.</b>—The
+carpellary leaves may
+unite either by their open
+edges, as if a whorl like that
+represented in <a href="#i_160">Fig. 188</a> were
+to grow together by the
+margins (<a href="#i_274a">Fig. 395</a>); or each
+may first roll itself into a
+simple follicle like the larkspur
+and columbine (<a href="#i_274a">Fig. 396</a>), and then a number of
+these may unite by their ventral sutures into a single syncarpous
+capsule, with as many locules as there are carpels
+(<a href="#fig_398">Fig. 398</a>). The seed-bearing sutures being all brought together
+in the center, the placenta becomes <em>central</em> and <em>axial</em>.
+In the first case (<a href="#i_274a">Fig. 395</a>) the open carpels form a one-chambered
+capsule, though the placentas sometimes project,
+as in the cotton, so far as to produce the effect of true
+partitions with a central axial placenta. In capsules with<span class="pagenum" id="Page_265">[Pg 265]</span>
+only one compartment, the number of carpels can generally
+be determined by the number of sutures or of placentas.</p>
+
+<table class='autotable wd90'>
+<tr>
+<td class='tdc vab pm0'>
+<figure class="figcenter illowp30 pmtb0" id="fig_397" style="max-width: 9.1875em;">
+  <img class="w100" src="images/fig_397.jpg" alt="">
+</figure>
+</td>
+<td class='tdc vab pm0'>
+<figure class="figcenter illowp35 pmtb0" id="fig_398" style="max-width: 10.5625em;">
+  <img class="w100" src="images/fig_398.jpg" alt="">
+</figure>
+</td>
+<td class='tdc vab pm0'>
+<figure class="figcenter illowp31 pmtb0" id="fig_399" style="max-width: 9.5625em;">
+  <img class="w100" src="images/fig_399.jpg" alt="">
+</figure>
+</td>
+</tr>
+<tr>
+<td class='tdl vat caption wd30'><p>
+<span class="smcap">Fig. 397.</span>—Pods of Echeveria, contiguous, but distinct.</p></td>
+<td class='tdl vat caption wd30'><p>
+<span class="smcap">Fig. 398.</span>—Capsule of
+Colchicum, with carpels
+united into a syncarpous
+pod.</p></td>
+<td class='tdl vat caption wd30'><p>
+<span class="smcap">Fig. 399.</span>—Capsule
+of corn cockle, with
+free central placenta.</p></td>
+</tr>
+</table>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. To what class of fruits does each of the following belong—rice;
+beggar-ticks; poppy; peanut; jimson weed; chinquapin; caraway?</p>
+
+<p>2. Is the coconut, as usually sold in the market, a fruit or a
+seed?</p>
+
+<p>Suggestion: carefully examine the “eyes,” from without and from
+within; if you can get a specimen with the husk on, it will help to a
+decision.</p>
+
+<p>3. Can you name any syncarpous, or compound capsule, that is single-seeded?</p>
+
+<p>4. Can you name any indehiscent fruit that has normally more than
+one seed?</p>
+
+<p>5. Give a reason for the difference. (23.)</p>
+
+<p>6. Name the weeds of your neighborhood that are most troublesome
+on account of their adhesive fruits.</p>
+
+<p>7. Do these fruits belong, as a rule, to the dehiscent or to the indehiscent
+class?</p>
+
+<p>8. Give a reason for the difference, if any is noted. (23.)</p>
+</div>
+
+
+<h3 id="CH_VIII_IV">IV. ACCESSORY, AGGREGATE, AND MULTIPLE FRUITS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—For autumn and winter, examples of accessory fruits
+are: pineapple, common apple, pear, rose hip; aggregate: magnolia,
+tulip tree, wild cucumber, sweet flag (<i>Calamus</i>); multiple: osage orange,
+sweet gum balls, pine cones, figs, fresh or dried.</p>
+
+<p>For spring and summer, examples of accessory fruits are: raspberry,
+strawberry, squash, cucumber; aggregate: strawberry, blackberry, Jack-in-the-pulpit;
+multiple: fig, mulberry. Most of those named will be
+found to belong to more than one class; the strawberry, for instance, is
+both accessory and aggregate; the fig and pineapple, accessory and
+multiple.</p>
+</div>
+
+<p id="p-301"><b>301.</b> Besides the varieties already named, all fruits,
+whether fleshy or dry, may be simple, accessory, aggregate,
+or collective. Fruits of the first kind need no explanation;
+they consist merely of a single ripened ovary,<span class="pagenum" id="Page_266">[Pg 266]</span>
+whether of one or more carpels, as the peach, cherry, bean,
+and lemon.</p>
+
+<figure class="figcenter illowp90" id="i_276" style="max-width: 50em;">
+  <img class="w100" src="images/i_276.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 400, 401.</span>—Vertical sections showing the relation between a strawberry
+flower and fruit: 400, the flower; 401, the fruit developed from it. The corresponding
+parts are indicated by connecting lines; <i>r</i>, receptacle; <i>a</i>, sepal; <i>b</i>, petal;
+<i>s</i>, stamens; <i>c</i>, carpel (akene in fruit); <i>p</i>, style of the pistil; <i>pl</i>, pulp of the fruit.</p></figcaption>
+</figure>
+
+<p id="p-302"><b>302. Accessory fruits</b> are so called because some other
+part than the seed vessel, or ovary proper, is coherent with,
+or accessory to it, in forming the fruit, as in the apple and
+the hip. The accessory part may consist of any organ, but
+is more frequently the calyx or the receptacle. In the strawberry,
+the little hard bodies, usually called seeds, that dot
+the surface are the true fruits (akenes). A vertical section
+through the center will show the edible part to consist
+wholly of the enlarged receptacle. In the pineapple, the
+edible stalk may be traced through a mass of flowers
+whose seed vessels have become enlarged and ripened into
+fruits.</p>
+
+<p id="p-303"><b>303. Aggregate fruits.</b>—Some accessory fruits, the strawberry
+and blackberry for example, are, at the same time,
+aggregate; that is, they are composed of a number of separate
+individual fruits produced from a single flower. The
+cone of the magnolia and of the tulip tree are aggregate
+fruits; can you name any others?</p>
+
+<p><span class="pagenum" id="Page_267">[Pg 267]</span></p>
+
+<figure class="figright illowp60" id="i_277" style="max-width: 50em;">
+  <img class="w100" src="images/i_277.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 402-404.</span>—Multiple fruit of the pineapple:
+402, external view of a ripe fruit, showing the prolonged
+receptacle growing into a new plant above, and the scaly
+bracted covering below; 403, vertical section through the
+axis of a fruit, showing <i>a</i>, the receptacle, with <i>b</i>, <i>b</i>, the
+fleshy ovaries cohering around it and forming the edible
+part of fruit; 404, a single “eye” or scale, somewhat
+reduced, showing the scaly bract from the axil of which
+the (generally) abortive flower originates.</p></figcaption>
+</figure>
+
+<p id="p-304"><b>304. Collective, or multiple, fruits.</b>—The pineapple is an
+example of both an accessory and a multiple fruit, being
+composed of the
+ripened ovaries of
+a number of separate
+flowers that
+have become
+more or less coherent.
+The osage
+orange, sweet
+gum balls, fig, and
+mulberry are
+other examples
+of this class.</p>
+
+<p id="p-305"><b>305. Dissection
+of a multiple fruit.</b>—Get
+one of the
+dried figs sold by
+the grocers. Look
+at the small end
+where the skin
+originates; of what
+part is it a modification?
+(<a href="#p-289">289</a>.)
+Can think of
+a reason for this
+curious, urnlike enlargement of the receptacle? Is there anything
+about the fig, for instance, that renders it peculiarly
+liable to be preyed upon by birds and insects? Could any
+but a very small insect get through the eye without injuring
+the fruit? Could it free itself from the sticky mass
+inside and get out again without difficulty? Would you
+judge from this that the caprification of the fig is easily
+effected <a href="#p-279">(279)</a>, even when the fig wasp is present? Can you
+now account for the fact that over four hundred varieties of
+cultivated figs ripen their fruit without fertilization?</p>
+
+<p><span class="pagenum" id="Page_268">[Pg 268]</span></p>
+
+<figure class="figleft illowp25" id="i_278" style="max-width: 30em;">
+  <img class="w100" src="images/i_278.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 405.</span>—Vertical section
+of a fig, showing the
+minute flowers inside the
+closed receptacle.</p></figcaption>
+</figure>
+
+<p>Open your specimen and examine the contents; what do
+you find? From a dried specimen it will hardly be practicable
+to make out clearly that the pulp of the fig consists of hundreds
+of tiny pistillate blossoms that line the inner face of the
+receptacle. The little grains usually
+taken for seeds are really small akenes—the
+ripened ovaries of flowers that
+have been pollinated from the caprifig
+(<a href="#p-279">279</a>, <a href="#p-286">286</a>). Crush one gently and examine
+with a lens, or under a low power of
+the microscope. It is these “botanically”
+ripe fruits <a href="#p-284">(284)</a> that give to the dried
+figs of commerce their plumpness and
+their pleasant, nutty flavor. Why are
+our native American figs lacking in these qualities <a href="#p-279">(279)</a>?
+Could this defect be remedied? Do you know of any
+efforts being made in that direction by American cultivators?</p>
+
+<figure class="figcenter illowp90" id="i_278a" style="max-width: 50em;">
+  <img class="w100" src="images/i_278a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 406-409.</span>—Non caprificated and caprificated figs: 406, outside appearance
+of non caprificated fig; 407, outside appearance of caprificated fig; 408, interior of
+caprificated fig; 409, interior of non caprificated fig.</p></figcaption>
+</figure>
+
+<p id="p-306"><b>306. Fruit clusters.</b>—Be careful not to confound aggregate
+and collective fruits with mere clusters, like a bunch
+of grapes or of sumac berries. The distinction is not always
+easy to make out. The clump of akenes that make up a dandelion
+ball, for instance, though held on a common receptacle,
+like the mulberry and other collective fruits, have
+so little connection with each other, and separate so completely
+at maturity, as to partake more of the nature of a<span class="pagenum" id="Page_269">[Pg 269]</span>
+cluster than of a collective fruit. The same is true of the
+clump of tailed akenes that make up the fruit of the clematis.
+Though the product of a single flower and thus technically
+an aggregate fruit, they are really only a compact head or
+cluster. Some degree of cohesion is necessary to constitute
+a cluster of matured ovaries into an aggregate or a multiple
+fruit.</p>
+
+<p id="p-307"><b>307. The individual fruits</b> that make up the various kinds
+just described may belong to any of the classes mentioned
+in the two preceding sections: those of the blackberry, for
+instance, are drupes; of the strawberry, akenes; of the
+sweet gum, capsules.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. To what class of fruits would you refer the following: a banana;
+a tickseed; a dewberry; a cocklebur; a string bean; a watermelon; a
+cantaloupe; a pomegranate; a black haw; a dogwood berry; a red
+pepper?</p>
+
+<p>2. Tell which of the following are aggregate or multiple fruits, and
+which are fruit clusters: an ear of corn; of wheat; a buttonwood or a
+sycamore ball; a hop; a dewberry; a pine cone; a prickly pear. (<a href="#p-303">303</a>,
+<a href="#p-304">304</a>, <a href="#p-306">306</a>.)</p>
+
+<p>3. Tell the nature of the individual fruits composing the different combinations
+mentioned in the last question.</p>
+
+<p>4. Can you suggest any advantage that might accrue to a species from
+having its fruits clustered or compound? (<a href="#p-21">21</a>, <a href="#p-23">23</a>, <a href="#p-24">24</a>, <a href="#p-287">287</a>.)</p>
+</div>
+
+
+<h4 id="CH_VIII_FIELD">Field Work</h4>
+
+<div class="blockquot">
+
+<p>1. Study the various edible fruits of your neighborhood with regard to
+their means of dissemination and protection. Consider the object of the
+protective adaptations in each case, whether against heat, cold, moisture,
+animals, etc. Notice the color of the different kinds, and trace its significance;
+for example, the bright red of the holly, the dull color of muscadine,
+black haw, and wild smilax. Account for the prevalence of red
+among autumn fruits. Notice the position of the fruit on the bough and
+explain its object; as, for instance, the clustering of dogwood at the end
+of the twig, the pendent position of grapes and honey locusts. Observe<span class="pagenum" id="Page_270">[Pg 270]</span>
+the relation between the color and size of fruits and their grouping. What
+advantage is it for sumac and bird haws to be gathered in large clusters?</p>
+
+<p>2. Compare wild with cultivated fruits and notice in what respects man
+has altered the latter for his own benefit. Note, for instance, the difference
+between cultivated apples and the wild crab, between the cultivated
+grains and wild grasses. Observe the great number of varieties of each
+kind in cultivation and try to account for it.</p>
+
+<p>3. Notice the situations in which different kinds of fruits grow, whether
+hot, dry, moist, windy, or sheltered, and how they are affected by their
+surroundings. For example, account for the difference between blackberries
+growing on a dry hillside, and those in moist land along the borders
+of a stream. Give the conclusions drawn from your observations in each
+case.</p>
+
+<p>4. Notice what animals feed upon the different kinds, and whether their
+visits are harmful or beneficial. Consider in what respects the interests
+of the plant itself, the interests of man, and the interests of other animals
+may clash or coincide. Examine the vegetation along the hedgerows and
+borders of fields and old fences. Notice the kind of plants that compose
+it—sumac, sassafras, cedars, cat brier, etc. The list will be slightly
+different for different localities, but this will not alter the general conclusion.
+What kinds of fruits and seeds do these shrubs produce? What
+kinds of living creatures frequent hedgerows and feed upon the seeds of
+such plants? Do you see any relation between these facts and one of the
+modes of seed dispersal?</p>
+
+<p>5. Classify all the fruits you have collected during your walk, under their
+proper heads, as fleshy or dry, dehiscent or indehiscent, simple, accessory,
+aggregate, collective. Be careful to distinguish between compact clusters,
+like the heads of clematis or buttonwood, and truly compound fruits.</p>
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_271">[Pg 271]</span></p>
+
+<h2 class="nobreak" id="CH_IX">CHAPTER IX. THE RESPONSE OF THE PLANT
+TO ITS SURROUNDINGS</h2>
+</div>
+
+
+<h3 id="CH_IX_I">I. ECOLOGICAL FACTORS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A number of small flowerpots filled with soils of as many
+different kinds as can be found in the neighborhood.</p>
+</div>
+
+<p id="p-308"><b>308. Definition.</b>—By <em>ecology</em> is meant the relation of
+plants to their surroundings, which may be considered under
+three general heads: their relations to inanimate nature,
+to other plants, and to animals. The subject has been
+touched upon repeatedly in the foregoing pages, and, in
+fact, it is impossible to treat of any branch of botany without
+some reference to it. All that was said about the adjustment
+of leaves for light and moisture, and their adaptations
+for protection and food storage, about the devices
+for pollination, and for fruit and seed dispersal, really
+belong to ecology.</p>
+
+<p id="p-309"><b>309. Symbiosis.</b>—The relations of plants to animate
+nature are <em>biological factors</em>, and may act in two ways:
+(1) through the destruction of vegetation by hungry animals
+and by parasitic and disease-producing organisms;
+and (2) by associations for mutual benefit, such as are
+described in section viii of chapter VII. Associations of
+this kind are included under the general term <em>symbiosis</em>,
+a word which means “living together.” In its broadest
+sense symbiosis refers to any sort of dependence or intimate
+organic relation between different kinds of individuals, and
+so may include the climbing and parasitic habits; but it
+is usually restricted to cases where the relation is one of
+mutual benefit. It may exist either between plants of one
+kind with those of another, between animals with animals,
+or between plants and animals, as in the case of the clover
+and bumblebee, and the yucca and pronuba.</p>
+
+<p><span class="pagenum" id="Page_272">[Pg 272]</span></p>
+
+<figure class="figcenter illowp50" id="i_282" style="max-width: 75em;">
+  <img class="w100" src="images/i_282.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 13.</span>—Showing the quick response of vegetation to surroundings. The
+upper cut shows the appearance of an irrigation canal in the arid plains region,
+when first completed; the lower cut, ten years after completion.</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_273">[Pg 273]</span></p>
+
+<p>The occurrence of root tubercles on certain of the leguminosæ
+<a href="#p-63">(63)</a> is a clear case of symbiosis, the microscopic
+organisms in the tubercles getting their food from the plant
+and at the same time enabling it to get food for itself from
+the air in a way that it could not otherwise do.</p>
+
+<p id="p-310"><b>310. Relations with inanimate nature.</b>—But it is to the
+relations of plants with inanimate nature, and their grouping
+into societies under the influence of such conditions,
+that the term “ecology” is more strictly applied. The
+external conditions that lead to the grouping are called
+<em>ecological factors</em>. The most important of these are temperature,
+moisture, soil, light, and air, including the direction
+and character of the prevailing winds. Each of these
+factors is complicated with the others and with conditions
+of its own in a way that often makes it difficult to determine
+just what effect any one of them may have in the formation
+of a given plant society.</p>
+
+<p id="p-311"><b>311. Temperature</b> may be even and steady, like that of
+most oceanic regions, or it may be subject to sudden caprices
+and variations, like the “heated terms” and “cold
+snaps” that afflict our Eastern coast region every few years.
+It is not the average temperature of a climate, but its
+extremes, especially of cold, that limit the character of
+vegetation.</p>
+
+<p>Temperature probably has more influence than any other
+factor upon the distribution of plants over the globe; but it
+can have little or no effect in evolving local differences in
+vegetation, because the temperature of any given locality,
+except on the sides of high mountains, will ordinarily be the
+same within a circuit of many miles.</p>
+
+<p id="p-312"><b>312. Moisture</b>, again, may be of all degrees, from the
+superabundance of lakes and rivers and standing swamps,
+to the arid dryness of the desert, and the water may be<span class="pagenum" id="Page_274">[Pg 274]</span>
+still and sluggish, or in rapid motion. It may exist more
+or less permanently in the atmosphere, as in moist climates
+like those of England and Ireland, where vegetation is
+characterized by great verdure; or it may come irregularly
+in the form of sudden floods, or at fixed intervals, causing
+an alternation of wet and dry seasons. Moreover, the
+moisture of the soil or the atmosphere may be impregnated
+with minerals or gases, which may affect the vegetation
+independently of the actual amount of water absorbed.</p>
+
+<figure class="figcenter illowp75" id="i_284" style="max-width: 50em;">
+  <img class="w100" src="images/i_284.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 410.</span>—The effect of cold—a Mt. Katahdin bog. (<i>From</i> Mo. Botanical
+Garden Rep’t.)</p></figcaption>
+</figure>
+
+<p>Snow is a form of water which may act in two entirely
+opposite ways: (1) by keeping the atmospheric precipitation
+locked up in a solid state and thus bringing about a
+condition analogous to drought—for example, in arctic deserts
+and Alpine snow fields; (2) by causing annual floods
+and overflows when it melts in the spring, as in the Nile
+and Mississippi valleys.</p>
+
+<p>In cold temperate regions it also influences vegetation<span class="pagenum" id="Page_275">[Pg 275]</span>
+to a considerable extent by covering the warm earth like
+a blanket during winter, and thus protecting tender seeds
+and shoots that otherwise would not be able to survive.</p>
+
+<figure class="figright illowp40" id="i_285" style="max-width: 40em;">
+  <img class="w100" src="images/i_285.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 411.</span>—Dogwood, a tree tolerant
+of shade, growing and blooming in a deeply
+wooded glen.</p></figcaption>
+</figure>
+
+<p id="p-313"><b>313. Light</b> may be of all
+degrees of intensity, from the
+blazing sun of the treeless
+plain to the darkness of caves
+and cellars where no green
+thing can exist. Between
+these extremes are numberless
+intermediate stages: the
+dark ravines on the northern
+side of mountains, the dense
+shade of beech and hemlock
+forests, and the light, lacy
+shadows of the pines,—each
+characterized by its peculiar
+form of vegetation. Absence
+of light, too, is usually accompanied by a lowering of temperature
+and a reduction of transpiration, factors which tend to
+accentuate the difference between sun plants and shade
+plants, giving to the latter some of the characteristics of
+aquatic vegetation. Generally, the
+tissues of these are thin and delicate,
+and having no need to guard
+against excessive transpiration, they
+wither rapidly when cut or exposed
+to too great intensity of heat and
+light.</p>
+
+<table class='autotable wd90'>
+<tr><td class='wd60'>
+<figure class="figcenter illowp60" id="i_285a" style="max-width: 30em;">
+  <img class="w100" src="images/i_285a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 412.</span>—A red cedar grown
+in a barren, wind-beaten situation.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp60" id="i_286" style="max-width: 20em;">
+  <img class="w100" src="images/i_286.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 413.</span>—A red
+cedar grown under
+normal conditions.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-314"><b>314. Winds</b> affect vegetation, not
+only as to the manner of seed distribution
+and the conveyance of pollen,
+but directly by increasing transpiration, and necessitating
+the development of strong holdfasts in plants growing
+upon mountain sides and in other exposed situations. The
+nature of the region from which they blow—whether moist,<span class="pagenum" id="Page_276">[Pg 276]</span>
+dry, hot, cold, etc.—is also an important
+factor. In a district open to sea breezes,
+live oaks, which require a salt atmosphere,
+may sometimes be found as far as a hundred
+miles from the coast.</p>
+
+<p id="p-315"><b>315. Soil.</b>—While water is the most important,
+soil is perhaps the most interesting
+of these factors to the farmer, because it is
+the one that he has it most largely in his
+power to modify. It is to be viewed under
+two aspects: first, as to its mechanical properties,
+whether soft, hard, compact, porous,
+light, heavy, etc.; secondly, as to its chemical
+composition and the amount of plant food-materials
+contained in it. The first can be
+regulated by tillage and drainage, the second by a proper
+use of fertilizers.</p>
+
+<div class="blockquot">
+
+<p id="exp-92"><span class="smcap">Experiment 92. To show the influence of soil as an ecological
+factor.</span>—Fill a number of small earthen pots with all the different kinds
+of soil that are to be found in your neighborhood. Keep well moistened
+and make a list of the plants that appear spontaneously in each. Is
+there any difference in the kinds produced by different soils? In vigor
+or abundance of the same or different kinds? Do more seedlings appear
+in any of the pots than could live if left alone? What becomes of a majority
+of the seedlings that come up in a state of nature?</p>
+
+<p>After a time, stop watering until all the plants are dead and new ones
+cease to appear. Notice the rate at which vegetation dies out in each
+and the kind of plants that can live longest without water. Which of the
+different soils is capable of sustaining vegetation longest without a fresh
+supply of moisture? To what quality of the soil is this due? (<a href="#exp-53">Exp. 53</a>.)</p>
+</div>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Is the relation between man and the plants cultivated by him a
+symbiosis? (<a href="#p-309">309</a>.)</p>
+
+<p>2. Why is it that plants of the same, or closely related species are found
+in such different localities as the shores of Lake Superior, the top of Mt.
+Washington, and the Black Mountains in North Carolina? (<a href="#p-311">311</a>, <a href="#p-330">330</a>.)</p>
+
+<p><span class="pagenum" id="Page_277">[Pg 277]</span></p>
+
+<p>3. Which of the five ecological factors mentioned in paragraphs <a href="#p-311">311-315</a>
+has probably most largely influenced their distribution?</p>
+
+<p>4. What is the prevailing character of the soil in your neighborhood?</p>
+
+<p>5. Is your climate moist or dry? Warm or cold?</p>
+
+<p>6. Can you trace any connection between these factors and the prevailing
+types of vegetation?</p>
+</div>
+
+
+<h3 id="CH_IX_II">II. PLANT ASSOCIATIONS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—The subject is not well suited to laboratory work, though,
+if time permits, it is recommended that a detailed study be made of at
+least one typical hydrophyte, halophyte, and xerophyte plant. Some
+good examples are: (1) Hydrophyte: pond weed, waterlily, pipewort (<i>Eriocaulon</i>),
+bladderwort, arrowhead (<i>Sagittaria</i>); (2) Halophyte: sea lavender,
+sea rocket, sea lettuce, water hyacinth; (3) Xerophyte: cactus, century
+plant, pineapple, stonecrop, purslane, lichen.</p>
+</div>
+
+<p id="p-316"><b>316. Modes of grouping.</b>—Plants group themselves in
+their favorite habitats, not according to their botanical relationships,
+but with regard to the predominance of one or
+more of the ecological factors that influence their growth.
+Sometimes one or two species will take practical possession
+of large areas, like the coarse grasses that spread over certain
+salt marshes, or the pines that formerly constituted the sole
+forest growth over extensive regions in North Carolina and
+Maine. Exclusive growths of this kind over limited areas
+are sometimes called plant <em>colonies</em>, and the individuals composing
+them belong, as a general thing, to the hardy, pushing
+sort known as “pioneers,” which are among the first to take
+possession of new soil and force their way into unoccupied
+territory. But more usually we find a great diversity of
+forms brought together by their common requirements as
+to shade, soil, moisture, and other external conditions.</p>
+
+<p>Any well-defined assemblage of plants, whether of one kind
+or many, originating in such a common response to the same
+influences, is called a <em>formation</em>. These associations are variously
+classed, according to the nature of their habitat,
+as salt water, fresh water, sand hill, swamp, bog, river bottom,
+or such other kinds as their ecological character may<span class="pagenum" id="Page_278">[Pg 278]</span>
+indicate. Local conditions in limited areas may lead to the
+segregation of smaller and more compact groups called <em>societies</em>.
+This term, however, is used rather loosely, being treated
+in some works as synonymous with formations, in others as
+analogous with what have here been defined as colonies.</p>
+
+<figure class="figcenter illowp75" id="i_288" style="max-width: 50em;">
+  <img class="w100" src="images/i_288.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 414.</span>—A colony of Alabama primroses (<i>Œnothera speciosa</i>).</p></figcaption>
+</figure>
+
+<p id="p-317"><b>317. Principles of subdivision.</b>—The mixed associations
+described in the last paragraph are quite independent of
+botanical relationships, and any of the factors named in
+<a href="#p-310">310</a>, or others of a different kind, could be made the basis of
+their classification. They might be grouped, for instance,
+according to their economic uses, or according to origin,
+whether native or introduced, as best suited the purpose of
+the classification in each case. The moisture factor, however,
+has been generally agreed upon as the one most convenient
+for ordinary purposes. Upon this principle plants are divided
+into three great groups:—</p>
+
+<p><span class="pagenum" id="Page_279">[Pg 279]</span></p>
+
+<p><b>Hydrophytes</b>, or water plants, those that require abundant
+moisture.</p>
+
+<p><b>Xerophytes</b>, or drought plants, those that have adapted
+themselves to desert or arid conditions.</p>
+
+<figure class="figright illowp25" id="i_289" style="max-width: 20em;">
+  <img class="w100" src="images/i_289.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 415.</span>—A water
+plant (<i>Limnophila</i>),
+with water leaves and
+air leaves and transitional
+forms.</p></figcaption>
+</figure>
+
+<p><b>Mesophytes</b>, plants that live in conditions intermediate
+between excessive drought and excessive
+moisture. To this class belong most of
+our ordinary cultivated plants and the
+greater part of the vegetation of the globe.</p>
+
+<p><b>Halophytes</b>, “salt plants,” is a term
+used to designate a fourth class, based not
+directly upon the water factor, but upon
+the presence of a particular mineral in the
+water or the soil which they can tolerate.
+They seem to bear a sort of double relation
+to hydrophytes on the one hand and
+to zerophytes on the other.</p>
+
+<p id="p-318"><b>318. Hydrophyte societies.</b>—These embrace
+a number of forms, from those inhabiting
+swamps and wet moors, to the
+submerged vegetation of lakes and rivers.
+An examination of almost any kind of
+water plant will show some of the physiological
+effects of unlimited moisture. Take
+a piece of pondweed, or other immersed
+plant, out of the water and notice how completely
+it collapses. This is because, being
+buoyed up by the water, it has no need to
+spend its energies in developing woody
+tissue. Floating and swimming plants will
+generally be found to have no root system
+or very small ones, because they absorb
+their nourishment through all parts of the
+epidermis directly from the medium in which they live.
+That they may absorb readily, the tissues are apt to be soft
+and succulent and the walls of the cells composing them<span class="pagenum" id="Page_280">[Pg 280]</span>
+very thin. In some of the pipeworts (<i>Eriocaulon</i>), the ells
+are so large as to be easily seen with the unaided eye. If
+you can obtain one of these, examine it
+with a lens and notice how very thin the
+walls are. Water plants also contain numerous
+air cavities, and often develop
+bladders and floats, as in the common bladderwort
+and many
+seaweeds. The leaves
+of submerged plants
+are usually either
+greatly reduced in size
+or very much cut and
+divided, while the ones
+that rise above water,
+like those of the water
+lily, are apt to be large
+and entire, to facilitate floating, and have
+stomata on their upper surface. Floating
+plants sometimes form such large
+colonies as to be a serious menace to
+navigation. Well-known instances of
+this are the water hyacinths in the St.
+John’s River, Florida, and the vast
+formations of swimming gulfweed from
+which the Sargasso Sea takes its name.</p>
+
+<table class='autotable wd80'>
+<tr><td>
+<figure class="figcenter illowp50" id="i_290a" style="max-width: 20em;">
+  <img class="w100" src="images/i_290.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 416.</span>—Seaweed
+(<i>sargassum</i>) with bladderlike
+floats.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp50" id="i_290" style="max-width: 20em;">
+  <img class="w100" src="images/i_290a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 417.</span>—A pioneer
+swamp colony of cattails.
+(<i>From</i> a photograph by
+Harry B. Shaw, U.S. Dept.
+Agr.)</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-319"><b>319. Swamp societies.</b>—These include
+what may be regarded as the amphibious
+portion of the hydrophyte
+group. They compose the sedge and
+cattail bogs, reed jungles, moss and fern
+thickets, forests of cypress, magnolia,
+black gum, pine, tamarack, balsam, and
+the like. The sedges and cattails are the pioneers of these
+societies, which tend constantly to encroach upon the water
+and so prepare the way for the advance of other colonists.<span class="pagenum" id="Page_281">[Pg 281]</span>
+Drawing their nourishment from the loose soil in which they
+are anchored, and lacking the support of a liquid medium,
+they develop roots and vascular stems. The roots of plants
+growing in swamps have difficulty in obtaining proper aëration
+on account of the water, which shuts off the air from
+them; hence they are furnished with large air cavities, and
+the bases of the stems are often greatly enlarged, as in the
+Ogeechee lime (<i>Nyssa capitata</i>) and cypress, to give room
+for the formation of air passages. The peculiar hollow projections
+known as “cypress knees” are arrangements for
+aërating the roots of these trees.</p>
+
+<figure class="figcenter illowp90" id="i_291" style="max-width: 50em;">
+  <img class="w100" src="images/i_291.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 418.</span>—A Southern cypress swamp, showing on the left the peculiar enlargements
+for aëration, known as “cypress knees.” (<i>From</i> Mo. Botanical Garden Rep’t.)</p></figcaption>
+</figure>
+
+<p id="p-320"><b>320. Xerophyte societies</b> are <a id="tn_281">adapted</a> to conditions the
+reverse of those affected by hydrophytes. The extreme of
+these conditions is presented by regions of perennial drought,
+like our Western arid plains and the great deserts of the interior
+of Asia and Africa. Under these conditions plants
+have two problems to solve,—to collect all the moisture they
+can and to keep it as long as they can. Hence, plants of
+such regions have a diminished evaporating surface, owing
+to the absence of foliage and the compacting of their tissues
+into the stem, after the manner of the cactus and prickly
+euphorbia; or their leaves may become thick and fleshy so
+as to resist evaporation and retain large amounts of moisture,
+as in the case of the yucca and century plant. They
+also frequently develop a thick, hard epidermis, or cover
+themselves with protective hairs and scales.</p>
+
+<p>The principal types of xerophyte plants are: (1) the lichens,
+mosses, and saxifrages found on bald rocks and mountain
+cliffs; (2) sand plants, such as cockspur grass, sand spurry,
+wiregrass, and the like, inhabiting sea beaches and pine
+barrens; (3) the sage brush, greasewood, and switch plants
+of our Western alkali plains; (4) the cactus and yuccas of
+southern California, Arizona, and Mexico; (5) the acacias,
+agaves, and hardy “chapparal” thickets of southern Texas
+and Mexico. The first class are of importance as the pioneers
+and pathfinders of the xerophyte community. In
+tropical and polar deserts alike they are the first settlers,
+and by aiding in the disintegration of rocks and their gradual
+conversion into soil, they pave the way for the coming of
+the higher plants, and it may be of man himself.</p>
+
+<p><span class="pagenum" id="Page_282">[Pg 282]</span></p>
+
+<figure class="figcenter illowp90" id="i_292" style="max-width: 50em;">
+  <img class="w100" src="images/i_292.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 14.</span>—A xerophyte formation of yuccas, cacti, and switch plants, near Zacatecas, Mexico.
+(<i>From</i> a photograph by Professor F. E. Lloyd.)</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_283">[Pg 283]</span></p>
+
+<p id="p-321"><b>321. Partial xerophytes.</b>—Plants exposed to periodic
+and occasional droughts frequently provide against hard
+times by laying up stores of nourishment in bulbs and rootstocks
+and retiring underground until the stress is over.
+This is known as the <em>geophilous</em>, or earth-loving, habit.
+Others, as some of the lichens, and the little resurrection
+fern (<i>Polypodium incanum</i>, <a href="#i_294">Figs. 419, 420</a>), so common on the
+trunks of oaks and elms in the Southern States, make no
+resistance, but wither away completely during dry weather,
+only to waken again to vigorous life with the first shower.</p>
+
+<figure class="figcenter illowp50" id="i_294" style="max-width: 50em;">
+  <img class="w100" src="images/i_294.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 419, 420.</span>—A resurrection fern: 419, in dry weather; 420, after a shower.</p></figcaption>
+</figure>
+
+<p id="p-322"><b>322. Physiological xerophytes.</b>—Plants growing in thin
+or poor soil, such as that on denuded hillsides, fresh railroad
+cuts, and newly graded streets, are apt to take on a more or
+less xerophytic character, even though there may be no lack
+of moisture. Such soils are called “new” because the
+mineral elements in them have not been exposed long enough<span class="pagenum" id="Page_284">[Pg 284]</span>
+to have become decomposed and mixed with humus, and the
+vegetation that first populates them has to do the pioneer
+work of disintegrating and impregnating the substratum with<span class="pagenum" id="Page_285">[Pg 285]</span>
+humus. For similar reasons the vegetation of sandy bogs
+and sea beaches, owing to the poverty of the soil in nitrogenous
+matter, usually develops xerophyte adaptations,
+even though there may be a superabundance of moisture.
+Plants growing on high mountain tops and in cold arctic
+bogs take on the same characteristics (<a href="#i_284">Fig. 410</a>). Such situations
+are said to be “physiologically dry,” because the
+moisture they have is not in a condition to be readily absorbed.
+The vegetation of arctic regions suffers more from
+physiological drought than from cold.</p>
+
+<figure class="figcenter illowp90" id="i_295" style="max-width: 50em;">
+  <img class="w100" src="images/i_295.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 421.</span>—A halophyte swamp of mangroves. Notice the tangle of adventitious
+prop roots assisting in the work of absorption from the brackish marsh soil.
+(<i>From</i> Mo. Botanical Garden Rep’t.)</p></figcaption>
+</figure>
+
+<p id="p-323"><b>323. Halophytes</b> include plants growing by the seashore
+and the vegetation around salt springs and lakes and that of
+alkali deserts. Seaweeds are in a sense halophytes, since
+they live in salt water, but as they are true aquatic plants
+and exhibit many of the peculiarities of hydrophytes in their
+mechanical structure, they are classed with them. The
+name <em>halophyte</em> applies more particularly to land plants<span class="pagenum" id="Page_286">[Pg 286]</span>
+that have adapted themselves to the presence in the soil
+or in the atmospheric vapor, of certain minerals, popularly
+known as salts, which cause them to take on many xerophyte
+characteristics. The reason for this, as was shown in
+Exp. 39, is because the mixture of salt in the water of the
+soil increases its density so that it is difficult for the plant to
+absorb as much as it needs, and thus halophytes are living
+under “physiologically” xerophyte conditions. If you have
+ever spent any time at the seashore, you cannot fail to have
+observed the thick and fleshy habit exhibited by many of
+the plants growing there, such as the samphire, sea purslane
+(<i>Sesuvium</i>), and sea rocket (<i>Cakile</i>). A form of goldenrod
+found by the seashore has thick, fleshy leaves, and is as hard
+to dry as some of the fleshy xerophytes.</p>
+
+<p>Another characteristic of desert plants that is common
+also to seaside vegetation is the frequent occurrence of a
+thick, hard epidermis, as in the sea lavender and saw grass.
+The live oaks, trees that love the salt air and never flourish
+well beyond reach of the sea breezes, have small, thick,
+hard leaves, very like those of the stunted oaks that grow on
+the dry hills of California. The presence of spines and
+hairs, it will be observed, is also very common; <i>e.g.</i> the salsola,
+the sea oxeye, and the low primrose (<i>Œnothera humifusa</i>).
+In other cases the leaf blades are so strongly involute
+or revolute <a href="#p-202">(202)</a> as to make them appear cylindrical. All
+these, it will be observed, are xerophyte adaptations, and the
+object in both cases is the same—the conservation of moisture.</p>
+
+<p id="p-324"><b>324. Mesophytes.</b>—These embrace the great body of
+plants growing under the ordinary conditions of temperate
+regions, which may vary from the liberal water supply of
+low meadows and shady forests to the almost desert barrenness
+of dusty lanes and gullied, treeless hillsides. The
+forms and conditions they present are so varied that it would
+be impracticable to consider them all in a work like this, but
+they may be summed up under the two general heads of<span class="pagenum" id="Page_287">[Pg 287]</span>
+(1) <em>open ground</em> and (2) <em>woodland</em>. Under the first are included:
+(<i>a</i>) all cultivated grounds—fields, meadows, lawns,
+pastures, and roadsides, with their characteristic shrubs,
+flowers, and grasses; (<i>b</i>) heaths and plains of northern or
+alpine regions, with their low, stunted perennials and bright,
+but fugacious, flowers. Under the second are classed all
+woods, thickets, and copses, with the shrubs and herbs that
+form their undergrowth. These may be grouped in three
+main divisions: (<i>c</i>) mixed forests of maple, ash, oak, hickory,
+birch, sweet gum, etc.; (<i>d</i>) pure forests of pine, balsam, fir,
+cypress, and the like; and finally (<i>e</i>), the perennial splendors
+of the tropical forest, where the vegetation of the globe
+reaches its climax in luxuriance and variety of growth.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Why do florists cultivate cactus plants in poor soil? (<a href="#p-320">320</a>.)</p>
+
+<p>2. What would be the effect on such a plant of copious watering and
+fertilizing?</p>
+
+<p>3. Why must an asparagus bed be sprinkled occasionally with salt?
+(<a href="#p-323">323</a>.)</p>
+
+<p>4. If a gardener wished to develop or increase a fleshy habit in a plant,
+to what conditions of soil and moisture would he subject it? (<a href="#p-320">320</a>, <a href="#p-323">323</a>.)</p>
+
+<p>5. What difference do you notice between blackberries and dewberries
+grown by the water and on a dry hillside?</p>
+
+<p>6. Are there corresponding differences in the root, stem, and leaves of
+plants growing in the two situations, and if so account for them?</p>
+
+<p>7. When a tract of dry land is permanently overflowed by the building
+of a dam or levee, why does all the original vegetation die, or take on a
+sickly appearance? (<a href="#p-319">319</a>.)</p>
+
+<p>8. Should plants with densely hairy leaves be given much water, as
+a general thing? (<a href="#p-202">202</a>, <a href="#p-320">320</a>.)</p>
+
+<p>9. A farmer planted a grove of pecan trees on a high, dry hilltop;
+had he paid much attention to ecology? Give a reason for your answer.</p>
+
+<p>10. Why do the branches of trees often die, or fail to develop, on the
+windward side? (<a href="#p-314">314</a>.)</p>
+
+<p>11. Why do trees grown in dry soil have harder wood than the same
+kind grown in wet soil? (<a href="#p-123">123</a>, <a href="#p-318">318</a>.)</p>
+</div>
+
+<p><span class="pagenum" id="Page_288">[Pg 288]</span></p>
+
+
+<h3 id="CH_IX_III">III. ZONES OF VEGETATION</h3>
+
+<figure class="figright illowp60 mth" id="i_298" style="max-width: 50em;">
+  <img class="w100" src="images/i_298.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 422.</span>—A pioneer colony of sumac growing on
+a railroad cutting. (<i>From</i> a photograph by J. M.
+Coulter.)</p></figcaption>
+</figure>
+
+<p id="p-325"><b>325. The origin of vegetable zones.</b>—The terms “zone”
+and “zonation” are used to express a general tendency of
+plant societies and formations to distribute themselves in
+more or less regular belts or strata, relatively to the varying
+intensity of the prevalent ecological factor of their habitat.
+In almost every locality there exists some special feature—a
+pond, a brook, a small ravine, an isolated hilltop, a deserted
+quarry, a gravel pit, or a railroad cut,—sufficiently distinct
+from the general surroundings to exercise a perceptible
+control over the
+vegetation in its
+immediate vicinity,
+and thus to become
+the starting point
+of a series of plant
+zones that mark the
+decreasing influence
+of the factor concerned,
+by their
+change of character
+as they recede from
+its point of greatest
+intensity. Starting
+from a barren, exposed hilltop, for example, with a covering
+of dry broom sedge (<i>Andropogon</i>) and fleabane, we encounter
+next an almost desert zone of washed and gullied slopes in
+whose hard, sunbaked soil nothing but a few scrub pines and
+brambles can gain a foothold. This will, perhaps, be succeeded,
+by a straggling belt of sassafras, sumac, and buckthorn, mixed
+with cat brier and blackberry canes, beyond which, at the foot
+of the hill, begins a stretch of meadow, or a bit of woodland
+crossed by a brook, or hollowed into a boggy depression.
+From this new factor originates a second series of zonations,
+passing through all the stages of bog, swamp, shade, and sun<span class="pagenum" id="Page_289">[Pg 289]</span>
+plants, back to the prevailing type of the region. Moisture
+is really the controlling factor in both cases, its influence
+in the first being negative,—that is, inversely,—and in the
+other, positive, or directly proportioned to the quantity
+present.</p>
+
+<p id="p-326"><b>326. Direction of zonation.</b>—When the direction in which
+the controlling factor changes is horizontal, as with soil and
+water, the zonation will be <em>horizontal</em>; when, as in the case
+of light, it is vertical, the zonation or stratification will be
+<em>vertical</em>. Examples of this can be observed in the growth of
+almost any forest area, the natural order of succession being:
+(1) a ground layer of mosses and fungi; (2) low, creeping
+vines,—partridge berry, trailing arbutus, twinflower (<i>Linnæa</i>);
+(3) small ferns and low flowering herbs—pyrola, clintonia,
+trillium; (4) a zone of tall herbs and low bushes—royal
+fern, cohosh (<i>Actæa</i>), blueberries; (5) tall herbs and shrubs,
+small trees, and climbing vines—kalmia, dogwood, farkleberry,
+smilax, Virginia creeper; (6) tall treetops towering up
+into full sunlight.</p>
+
+<p>When the physical cause of intensity is a central area, such
+as a pond or a hilltop, the zonation will be <em>concentric</em>; that is,
+the different belts will succeed each other in widening circles
+more or less complete. Where the controlling cause extends
+in a line, as a river, or a chain of mountains, the zones run in
+parallel belts on each side of it, and the zonation is <em>bilateral</em>.
+In any case, however, it is seldom regular, being frequently
+broken and interrupted through the intervention of other
+factors. Nor must precisely the same kind of plants be
+always looked for in similar situations, though their place is
+usually occupied by kindred species and genera. The common
+pitch pine, for instance, of the Northern sand barrens
+is represented in sandy districts farther south by the tall,
+long-leaved pine, a kindred species.</p>
+
+<p id="p-327"><b>327. Succession.</b>—Zonation is a regular succession of
+different kinds of plants in space; there is also an analogous
+succession in time, as, when the vegetation of a locality is<span class="pagenum" id="Page_290">[Pg 290]</span>
+killed off by fire or other cause, plants of an entirely different
+character will nearly always spring up to occupy its place. A
+forest of pine, for instance,
+is rarely followed
+by conifers,
+but by a growth of
+hardwood trees, and
+<i>vice versa</i>—nature
+thus giving an impressive
+example as
+to the effectiveness
+of a rotation of crops.</p>
+
+<figure class="figcenter illowp70" id="i_300" style="max-width: 50em;">
+  <img class="w100" src="images/i_300.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 423.</span>—A thicket of pines that has succeeded
+a mixed growth of hard wood trees.</p></figcaption>
+</figure>
+
+<p>Succession may be
+influenced by a variety
+of causes. Two
+of the most efficient are: (1) the exhaustion of the soil by the
+long-continued growth of one formation <a href="#p-60">(60)</a>, thus causing
+a deficiency of mineral material suited for the support of
+plants of that kind; (2) the migration of new species into
+the denuded territory where those which have different requirements
+as to mineral
+nutrients from the
+former inhabitants will,
+other things being equal,
+have the best chance to
+succeed.</p>
+
+<figure class="figcenter illowp60" id="i_300a" style="max-width: 50em;">
+  <img class="w100" src="images/i_300a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 424.</span>—A successful invasion—Japanese
+honeysuckle covering the banks of a ravine and
+climbing over shrubs and tree tops.</p></figcaption>
+</figure>
+
+<p id="p-328"><b>328. Invasion.</b>—A
+rapid and widespread
+occupation of any territory
+by a new species is
+called an <em>invasion</em>. Notable
+examples of invaders
+are those of the
+Russian thistle in the
+northwestern states of the Union, and the “bitterweed”
+(<i>Helenium tenuifolium</i>) that has almost driven out the hardy<span class="pagenum" id="Page_291">[Pg 291]</span>
+dog fennel (<i>Anthemis cotula</i>) which formerly held undisputed
+possession of arid places throughout the South Atlantic states.
+A still more remarkable instance is the invasion of the Japanese
+honeysuckle (<i>Lonicera Japonica</i>), originally introduced
+for ornament, but which has naturalized itself within the last
+thirty years and overrun waste places everywhere, from the
+Gulf to the Potomac, with a vigor and luxuriance equaled
+by few of our native species. As its beauty and fragrance
+are even more conspicuous in a state of nature than under
+cultivation, and as it can, <a id="tn_291">moreover</a>, be made very useful in
+stopping gullies and washes, its phenomenally rapid occupation
+of so large a territory has caused no alarm and
+consequently attracted little attention.</p>
+
+<p id="p-329"><b>329. Climatic zones.</b>—These are more general groupings
+than those we have been considering. They follow
+in a rough way the parallels of latitude, and are classed
+accordingly as: (1) tropical; (2) subtropical; (3) temperate;
+(4) boreal or (on mountains) subalpine; (5) arctic or (on
+high mountains) alpine. Taking the cultivated plants of
+our own country by way of illustration, we have the subtropical
+zone, embracing Florida and the southern portion
+of the Gulf states, where sugar cane, rice, and tropical
+fruits are the staple crops. Then comes the temperate
+zone, with three agricultural subdivisions: (<i>a</i>) the great
+cotton belt, with Indian corn, sweet potatoes, and the
+peach, melon, and fig as secondary products. Farther
+north, in the Central and Middle Atlantic states, we find
+(<i>b</i>) the region of maize, hemp, and tobacco, with grapes,
+apples, pears, cherries, and a great variety of garden vegetables
+as side crops. Finally comes (<i>c</i>) the great wheat-growing
+region of the North, with buckwheat, hay, and Irish
+potatoes as subsidiary crops.</p>
+
+<p>Technically, the distribution of the natural zones of vegetation
+from south to north is classed under the three general
+heads of Forest, Grass Land, and Arctic Desert, with numerous
+subdivisions in each.</p>
+
+<p><span class="pagenum" id="Page_292">[Pg 292]</span></p>
+
+<p id="p-330"><b>330. Boundaries of the zones.</b>—While the broad continental
+zones of vegetation follow, in a general way, the
+climatic zones outlined above, they are not sharply defined,
+but run into each other and overlap in various degrees, so
+that a map depicting the range of vegetation in any wide
+area would show a marked deviation from those of latitude.
+Various other geographical factors, such as mountain ranges
+and bodies of water, influence the direction and character of
+the prevailing winds and rains, and through them the moisture
+and temperature, to so great an extent that they become
+the controlling factors over wide areas. In countries bordering
+on the sea, the coast line always marks a belt of its own,
+and on the sides of a mountain range, all the climatic zones
+from the equator to the pole may be repeated during an
+ascent of a few miles.</p>
+
+<p>In our own country, where the mountain chains and coast
+lines run approximately north and south, the great continental
+zones have been superseded, for all practical purposes,
+by four regional divisions running almost at right angles to
+them. These are, disregarding minor subdivisions:—</p>
+
+<p>(1) The Forest region, occupying the eastern and south
+central portion of the Union. In classifying this territory
+as forest, it is not meant to imply that it is now, or ever
+was, one unbroken jungle, like parts of central Africa, but
+that it combines the conditions most favorable to a vigorous
+and varied forest growth.</p>
+
+<p>(2) The Plains region, extending from the very irregular
+western boundary of the forest region to the Rocky Mountains.</p>
+
+<p>(3) The Rocky Mountain region, including the Rockies
+and the Sierra Nevadas with the desert area between them.</p>
+
+<p>(4) The Pacific Slope, a narrow strip between the Sierras
+and the Pacific Ocean.</p>
+
+<p><span class="pagenum" id="Page_293">[Pg 293]</span></p>
+
+<figure class="figcenter illowp56" id="i_303" style="max-width: 75.0em;">
+  <img class="w100" src="images/i_303.jpg" alt="">
+  <figcaption><p><span class="smcap">Plate 15.</span>—This giant tulip tree is a relic of the primitive forest. It is twenty-seven
+feet in circumference, at a distance of four feet from the ground. Notice the
+sharp elbows of the large boughs, a mode of branching characteristic of this kind of
+tree.</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_294">[Pg 294]</span></p>
+
+<p>The boundaries of these regions, like those of the great
+continental zones, overlap in various ways, the plants of one
+region often appearing in another, like an arm of the sea
+projecting into the land. But the district where any class of
+plants reaches its highest development is its proper habitat,
+and as a general thing the one where its cultivation pays
+best. It would be a waste of time and money to try to raise
+cotton in Maine, or cranberries in Georgia.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Does the native wild growth of a region furnish any indication of
+the kind of crops which could be successfully grown there? (<a href="#p-325">325</a>, <a href="#p-326">326</a>.)</p>
+
+<p>2. Can you give a reason why the zones of cultivation may, in some
+cases, be more extensive than the natural range of wild plants in the same
+region? (<a href="#p-262">262</a>, <a href="#p-265">265</a>.)</p>
+
+<p>3. Can you give reasons why the reverse may sometimes be true? (<a href="#p-261">261</a>,
+<a href="#p-284">284</a>.)</p>
+
+<p>4. What crops are raised in different parts of your own state?</p>
+
+<p>5. Name some of the native plants characteristic of different parts of
+your state. What are its principal plant formations?</p>
+</div>
+
+
+<h4 id="CH_IX_FIELD">Field Work</h4>
+
+<div class="blockquot">
+
+<p>1. Ecology offers the most attractive subject for field work of all the
+departments of botany. It can be studied anywhere that a blade of vegetation
+is to be found. In riding along the railroad, there is an endless
+fascination in watching the different plant societies succeed one another
+and noting the variations they undergo with every change of soil or climate.</p>
+
+<p>2. Students in cities can find interesting subjects for study in the vegetation
+that springs up on vacant lots, around doorsteps and area railings,
+and even between the paving stones of the more retired streets. On a
+vacant lot near the public library in Boston, over thirty different kinds
+of weeds and herbs were found, and in the heart of Washington, D.C., on
+a vacant space of about twelve by twenty feet, nineteen different species
+were counted. Just where such things come from, how they get into
+such positions, and why they stay there, will be interesting questions for
+city students to solve.</p>
+
+<p>3. But the country always has been and always will be the happy hunting
+ground of the botanist. All the factors considered in the two preceding
+sections can hardly be found in any one locality, but by selecting
+areas traversed by brooks, or by gullies and ravines, very marked changes
+in the character of vegetation may often be observed. Barren, sandy,
+or rocky soils, the sunbaked clay of naked hillsides, and the borders of
+treeless, dusty roads will offer close approximations to xerophyte conditions.</p>
+
+<p><span class="pagenum" id="Page_295">[Pg 295]</span></p>
+
+<p>4. If there are any bodies of water in your neighborhood, examine their
+vegetation and see of what it consists. Notice the difference in the shape
+and size of floating and immersed leaves and account for it. Note the general
+absence of free-swimming plants in running water, and account for it.
+Note the difference between the swamp and border plants and those growing
+in the water, and what trees or shrubs grow in or near it. Compare
+the vegetation of different bogs and pools in your neighborhood, and
+account for any differences you may observe. Compare the water plants
+with those growing in the dryest and barrenest places in your vicinity,
+note their differences of structure, and try to find out what special adaptations
+have taken place in each case. Make a list of those in each location
+examined that you would class as pioneers.</p>
+
+<p>5. Draw a map of the vegetation of some locality in your neighborhood
+that presents a variety of conditions, such as a steep hillside, a field or
+meadow traversed by a brook, the slopes and borders of a ravine, or the
+change from cultivated ground to uncultivated moor or woodland. Represent
+the different zones and formations by different colored inks or crayons,
+or by different degrees of shading with the pencil.</p>
+
+<p>6. Draw a map of your state showing the different agricultural regions,
+as indicated by the character of the cultivated plants in each;
+use different colors, or light and dark shading, to define the boundaries.
+Notice any irregularities of outline and account for them—whether due
+to soil, moisture, geological formation, winds, or temperature. What is
+the controlling factor of each region?</p>
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_296">[Pg 296]</span></p>
+
+<h2 class="nobreak" id="CH_X">CHAPTER X. CRYPTOGAMS</h2>
+</div>
+
+
+<h3 id="CH_X_I">I. THEIR PLACE IN NATURE</h3>
+
+<p id="p-331"><b>331. Order of development.</b>—All the forms that have
+hitherto claimed our attention belong to the great division
+of Spermatophytes, or seed-bearing plants, designated also as
+<em>Phanerogams</em>, or flowering plants. They comprise the higher
+forms of vegetable life, and because they are more conspicuous
+and better known than the other groups, they have been
+taken up first, since it is more convenient, for ordinary purposes,
+to work our way backward from the familiar to the less
+known, rather than in the reverse order.</p>
+
+<p>But it must be understood that this is not the order of
+nature. The geological record shows that the simplest
+forms of life were the first to appear, and from these all the
+higher forms were gradually evolved. There is no sharp
+line of division between any of the orders and groups of
+plants, but the line of development can be traced through a
+succession of almost imperceptible changes from the lowest
+forms to the highest, and it is only by a study of the former
+that botanists have come to understand the true nature and
+structure of the latter.</p>
+
+<p id="p-332"><b>332. Basis of distinction.</b>—<em>Cryptogams</em>, or seedless
+plants as a whole, are distinguished from the phanerogams
+by their simpler structure and by their mode of propagation,
+which in the former is by means of spores, while in the
+phanerogams it is by seeds. A spore is a simple organic
+body, consisting usually of a single cell which separates from
+the parent plant at maturity and gives rise to a new individual.
+A seed is a complicated, many-celled structure, containing
+within itself the rudimentary structure of a new plant already
+organized.</p>
+
+<p><span class="pagenum" id="Page_297">[Pg 297]</span></p>
+
+<p>Beginning with the simplest forms, cryptogams are grouped
+in three great orders:—</p>
+
+<p id="p-333"><b>333. I. Thallophytes</b>, or thallus plants.—This group takes
+its name from the <em>thallus</em> structure that characterizes its
+vegetation. In its typical form, a thallus is
+a more or less flat, expanded body, of which
+the lichens and liverworts offer familiar examples
+among land plants, and the kelps and
+laminarias among seaweeds. It may be of
+any size and shape, however, and sometimes
+consists of a mere filament, as in the common
+brook silk, or even of a single cell (<a href="#i_310">Fig.
+429</a>). The term is applied in general to the
+simplest kinds of vegetable structure, in
+which there is no differentiation of tissues,
+and no true distinction of root, stem, and
+leaves. While it is not peculiar to the thallophytes,
+it has attained its most typical development among
+them, and the name is therefore retained as distinctive of
+that group. It embraces two great divisions,
+the Algæ and Fungi. The first
+includes seaweeds and the common freshwater
+brook silks and pond scums, besides
+numerous microscopic forms whose
+presence escapes the eye altogether, or is
+made known only by the discolorations
+and other changes caused by them in the
+water. To the fungi belong the mushrooms
+and puffballs, the molds, rusts,
+mildews, and the vast tribe of microscopic
+organisms called <em>bacteria</em>, which
+are so active in the production of fermentation, putrefaction,
+and disease.</p>
+
+<table class='autotable'>
+<tr><td class='vab'>
+<figure class="figcenter illowp45" id="i_307" style="max-width: 15em;">
+  <img class="w100" src="images/i_307.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 425.</span>—A seaweed
+with broad, expanded
+thallus.</p></figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp45" id="i_307a" style="max-width: 15em;">
+  <img class="w100" src="images/i_307a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 426.</span>—Anthoceros,
+a liverwort with flat,
+spreading thallus.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-334"><b>334. II. Bryophytes</b>, or moss plants.—This group likewise
+contains two main divisions, Mosses and Liverworts. Familiar
+examples of the latter are the flat, spreading green plants,
+<span class="pagenum" id="Page_298">[Pg 298]</span>
+bearing somewhat the aspect of lichens, met with everywhere
+on wet rocks and banks around shady watercourses. The
+name is a reminiscence of their former use
+in medicine as a specific for diseases of the
+liver, and not, as in the case of the liver leaf,
+of a fancied resemblance to that organ.</p>
+
+<p>Mosses are one of the best defined of
+botanical orders, and are easily recognized
+by their slender, leafy fruiting stalks, growing
+usually in dense, spreading mats, and
+presenting every appearance of a highly
+organized structure, well differentiated into
+root, stem, and leaves.</p>
+
+<p>The liverworts represent
+the more primitive division
+of the group, and in some
+of their forms approach so
+near the thallophytes that
+it is not difficult to recognize
+them as connecting
+links in the same chain of
+life. Their relationship to the next higher
+group is not clear, but while they represent
+a more primitive stage of evolution than
+the mosses, the development of the latter
+has followed a course divergent from the
+main line of evolutionary progress.</p>
+
+<table class='autotable'>
+<tr><td class='vab'>
+<figure class="figcenter illowp45" id="i_308" style="max-width: 25em;">
+  <img class="w100" src="images/i_308.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 427.</span>—A
+shoot of peat moss
+with ripe spore
+fruits, <i>f</i>, <i>f</i>.</p></figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp45" id="i_308a" style="max-width: 25em;">
+  <img class="w100" src="images/i_308a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 428.</span>—A common
+fern (<i>Polypodium
+vulgare</i>).</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-335"><b>335. III. Pteridophytes</b>, or fern plants, are
+classed roughly in the three divisions of
+ferns, horsetails, and club mosses. They
+differ greatly in structure, but all possess a
+vascular system, and a well-organized structure
+of root, stem, and leaves. They rank
+next to the spermatophytes in the order of
+development, and the group is of especial interest on account
+of its relationship to the higher plants. One of its divisions,<span class="pagenum" id="Page_299">[Pg 299]</span>
+the club mosses, has probably given rise to at least one section
+of the gymnosperms, while the ferns are regarded as the
+ancestors of the true flowering plants, which make up the
+great class of angiosperms, and represent the highest type of
+evolution yet attained in the vegetable kingdom.</p>
+
+
+<h3 id="CH_X_II">II. THE ALGÆ</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Simple forms of green algæ can be found on the shady
+side of tree trunks, damp walls, old fence palings, and the outside of flowerpots.
+<i>Pleurococcus</i>, one of the commonest kinds, occurs as a green,
+powdery mat or felt in damp places, and is often accompanied by <i>protococcus</i>,
+another good specimen for study. <i>Spirogyra</i> and other filamentous
+algæ can be found in stagnant pools and ditches and in old rain barrels.</p>
+
+<p><span class="smcap">Appliances.</span>—Eosin solution, nitric acid, alcohol, iodine solution;
+a white china plate; a hand lens; a compound microscope, and slides.</p>
+</div>
+
+<p id="p-336"><b>336. Variety of forms.</b>—This group embraces plants of
+the greatest diversity of form and structure, from the minute
+volvox and desmids that hover near the uncertain boundaries
+dividing the vegetable from the animal world, to the giant
+kelps of the ocean, which sometimes attain a length of from
+six hundred to one thousand feet. They are usually classed
+according to their color, as green, brown, and red algæ,
+including various subdivisions of each group. They all contain
+chlorophyll, by means of which they manufacture their
+own food, though in the red and brown divisions it is masked
+by the presence of other pigments—an adaptation to the
+modified light that reaches them at various depths under
+water. With few exceptions they can live only in the water,
+and unlike any other form of plant life, attain their highest
+development in the salty depths of the ocean. The freshwater
+forms are small and inconspicuous, and generally of a
+more simple type than the seaweeds. The great majority of
+them belong to the two classes of green and blue-green algæ.
+The former is believed to have furnished the type from
+which the higher plants have been evolved.</p>
+
+<figure class="figright illowp40" id="i_310" style="max-width: 20em;">
+  <img class="w100" src="images/i_310.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 429.</span>—Three stages in
+the division of a one-celled alga
+(<i>Glœocaspa polydermatica</i>): <i>A</i>,
+division of a cell just beginning;
+<i>B</i>, division further advanced;
+<i>C</i>, four cells after division, remaining
+in contact.</p></figcaption>
+</figure>
+
+<p id="p-337"><b>337. Study of a one-celled alga.</b>—Put a little of the green
+algæ in water on a glass slide. Hold up to the light, or<span class="pagenum" id="Page_300">[Pg 300]</span>
+over a sheet of white paper, and examine with a hand lens;
+then place under the microscope. It will probably be found
+to contain a number of minute organisms, but the pleurococci
+can be recognized as small round bodies of a bright green
+color, some of them separate, others adhering together in
+groups of two, four, or more, with the sides that are in contact
+slightly flattened. Each of these bodies is an individual
+plant consisting of a single cell, whence they are said to be
+<em>unicellular</em>. Draw one of the single cells and one of the
+groups, or colonies, as they appear
+under the microscope. Try to make
+out the cell wall and the nucleus, and
+label all the parts (see 7). If you
+have any difficulty in distinguishing
+the cell wall, drop a little glycerine
+or salt water on the slide. This will
+cause the cell contents to shrink by
+osmosis (56, 59). Can you make
+out the structure of the cell colonies?
+They have resulted from the peculiar
+mode of multiplication that prevails
+among this class of plants. A cell
+elongates, contracts in the middle,
+and divides into two parts, each of
+which becomes an independent plant like the mother cell.
+See if you can find one in the process of division. The
+daughter cells repeat the process, each one giving rise to two
+new individuals, and so on indefinitely. The new cells do
+not always separate immediately on their formation, but frequently
+adhere together for a time, in colonies, before falling
+away and beginning an independent existence.</p>
+
+<p id="p-338"><b>338. Reproduction by fission.</b>—This kind of reproduction
+is called <em>fission</em>, or cell division, and marks a very primitive
+stage of development. Under stress of adverse conditions
+the cells formed by division may remain inactive for a time.
+They are then called <em>resting spores</em>, and when more favorable<span class="pagenum" id="Page_301">[Pg 301]</span>
+circumstances arise, they begin again their work of reproduction
+and growth as actively as ever.</p>
+
+<p id="p-339"><b>339. Meaning of the name.</b>—The suffix <em>coccus</em> is a Latin
+noun (plural <em>cocci</em>) meaning a grain or berry, and is a general
+term applied to any small, round organism consisting of a
+single cell; hence, <em>micrococcus</em>, a minute round body; <em>protococcus</em>,
+a primitive form, or prototype of one-celled bodies;
+and <em>pleurococcus</em>, which may be freely translated “a one-sided
+little round body,” from the flattening of the adjacent
+sides during fission—<em>pleuro</em> meaning lateral, or pertaining
+to the side.</p>
+
+<p>It is important to remember this definition, as the term
+<em>coccus</em> is of very frequent occurrence in works of biology, as a
+suffix for designating small round bodies of various kinds.</p>
+
+<p id="p-340"><b>340. Examination of a filamentous alga.</b>—Place on a
+white dish a few drops of water containing some of the green
+pond scum common in stagnant pools and ditches. Examine
+with a hand lens; of what does it appear to consist?
+Are the filaments all alike, or are they of different lengths
+and thickness? Soak a number of them in alcohol for half
+an hour and examine again; where has the green matter
+gone? Do these algæ contain chlorophyll? (<a href="#p-336">336</a>; <a href="#exp-65">Exp. 65</a>.)
+This class are called filamentous algæ on account of their
+slender, threadlike thalli, which look like bits of fine floss
+floating about in the water. The bubbles of oxygen which
+they sometimes give off in great abundance cause the
+frothy appearance that has given rise to their popular
+name, “frog spit.”</p>
+
+<figure class="figright illowp45" id="i_312" style="max-width: 19em;">
+  <img class="w100" src="images/i_312.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 430, 431.</span>—<i>Spirogyra</i>
+(magnified): 430,
+two filaments beginning
+to conjugate; 431, formation
+of spores.</p></figcaption>
+</figure>
+
+<p id="p-341"><b>341. Spirogyra.</b>—The filamentous algæ are very numerous,
+and a drop of pond scum will probably contain several
+kinds. At least one of these, it is likely, will be a <i>Spirogyra</i>,
+as this is one of the commonest and most widely
+distributed of them all. Place a filament under the microscope
+and notice the spiral bands in which the chlorophyll
+is disposed within the cells. It is from this spiral arrangement
+that the species takes its name. Do you notice any<span class="pagenum" id="Page_302">[Pg 302]</span>
+roundish particles inclosed in the chlorophyll bands? Test
+with a little iodine solution and see what they contain.
+Each filament will be seen, when sufficiently magnified,
+to consist of a number of more or less cylindrical cells joined
+together in a vertical row, and thus forming the simple
+threadlike thallus which characterizes this
+class of algæ. Physiologically, each cell
+is an independent individual, and often
+exists as such. Can you see the cell
+nucleus? If not, place a few filaments
+in a solution of eosin and add a drop of
+acetic acid to give the solution a pale
+rose color. After twenty to thirty minutes,
+examine again; the nucleus will be
+stained a deep red. If you can find an
+unbroken filament, examine both ends to
+see whether there is any differentiation of
+base and apex.</p>
+
+<p id="p-342"><b>342. Conjugation.</b>—See if you can find two filaments
+sending out lateral protuberances toward each other.
+Watch and notice that after a time these projections come
+together and unite by breaking down the cell walls dividing
+them, the protoplasm in each contracts, the contents of
+one pass over into the other, and the two coalesce, forming
+a new cell but little, if any, larger than the original conjugating
+bodies. This cell germinates under favorable
+conditions and produces a new individual. This method
+of reproduction is known as <em>conjugation</em>. The cells thus produced
+by the union of the contents of two separate cells
+may either germinate at once, and give rise to new individuals,
+or remain quiescent for a time, as resting spores.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Are any of the green algæ parasitic? How do you know? (<a href="#p-186">186</a>,
+<a href="#p-336">336</a>.)</p>
+
+<p>2. Why is their presence in water regarded as denoting unhygienic
+conditions?</p>
+
+<p><span class="pagenum" id="Page_303">[Pg 303]</span></p>
+
+<p>3. Mention some of the ways in which their presence may contribute
+to the contamination of drinking water.</p>
+
+<p>4. Refer to <a href="#exp-66">Exp. 66</a>, and account for the bubbles and froth that usually
+accompany these plants in the water.</p>
+
+<p>5. Can you suggest any other causes than the evolution of oxygen that
+might produce the same effect?</p>
+
+<p>6. Is the presence of these gas bubbles of any use to floating plants?</p>
+</div>
+
+
+<h3 id="CH_X_III">III. FUNGI</h3>
+
+<figure class="figright illowp50" id="i_313" style="max-width: 37em;">
+  <img class="w100" src="images/i_313.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 432.</span>—A common form of mold, magnified,
+showing thallus modified into a fibrous mycelium:
+<i>a</i>, <i>a</i>, spore cases; <i>b</i>, mycelium. (<i>After</i> <span class="smcap">Kopf</span>, in part.)</p></figcaption>
+</figure>
+
+<p id="p-343"><b>343. Classification.</b>—In the fungi the thallus structure
+is greatly modified, appearing usually as a network of fine
+threads called the <em>mycelium</em>
+(pl., <em>mycelia</em>), from a Greek
+word meaning “fungus”
+<a href="#p-369">(369)</a>. These plants are
+all, with a few doubtful
+exceptions, parasites or
+saprophytes which contain
+no chlorophyll and are
+incapable of supporting an
+independent existence.
+Biologists are divided as to
+their position in the genealogical
+tree of life. The
+weight of authority
+at present inclines to
+the view that they are
+degenerate forms derived
+from the algæ,
+but they have been
+so modified by their
+parasitic habits as to
+render their position
+in the general scheme of life a doubtful one. They represent
+an offshoot, or side branch, as it were, of the great
+evolutionary line, and so may be considered for the present
+as standing apart in a class by themselves.</p>
+
+<p><span class="pagenum" id="Page_304">[Pg 304]</span></p>
+
+<p id="p-344"><b>344. Numbers and variety.</b>—Fungi exceed every other
+class of living organisms both in the number of species and
+of individuals composing them. They include such diverse
+forms as bacteria, molds, rusts, mildews, mushrooms, and
+the like, ranging in size all the way from the giant puffball,
+a foot or more in diameter, to the almost inconceivably
+minute influenza bacillus, of which nearly two thousand
+million can inhabit a single drop of water without inconvenient
+crowding!</p>
+
+<figure class="figcenter illowp100" id="i_314" style="max-width: 100em;">
+  <img class="w100" src="images/i_314.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 433.</span>—Cephalothecium, a fungus parasitic on rosehips—greatly magnified.
+(<i>From</i> Mo. Botanical Garden Rep’t. Photographed by Hedgcock.)</p></figcaption>
+</figure>
+
+<p id="p-345"><b>345. The parasitic habit.</b>—But while their life history
+is obscure and hard to trace, the fungi are, as a class, well
+differentiated by their parasitic habit. They contain no
+chlorophyll, can manufacture no food, and consequently
+have to obtain it ready-made from the tissues of living or
+dead animals and plants. On this account they are active
+agents in the production of disease and decay, especially
+certain of those manifold forms that have been grouped<span class="pagenum" id="Page_305">[Pg 305]</span>
+together under the general head of bacteria. While not responsible
+for all the disease known to be caused by living
+organisms,—some very serious ones, such as malaria and
+cattle fever, being due to animal parasites,—the majority of
+those that have been most carefully investigated are traced
+to the bacteria, or other fungi. After any of these parasites
+have found a lodgment in the body of an organism whose
+tissues furnish them a congenial habitat, they multiply with
+enormous rapidity, and through the action of certain poisons
+called <em>toxins</em>, which they excrete, give rise to the most destructive
+diseases in both animals and plants; and no rational
+sanitary science is possible without a knowledge of their
+habits and life history. Add to the vast amount of human
+suffering that is to be laid at their door the economic damage
+done by rust and smut fungi, by molds and blights and mildews,
+and we shall be tempted to conclude that the “battle
+of life” is largely a struggle against these invisible foes.</p>
+
+<figure class="figcenter illowp100" id="i_315" style="max-width: 99em;">
+  <img class="w100" src="images/i_315.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 434-437.</span>—Disease-producing bacteria: 434, bacteria of consumption
+(<i>Bacillus tuberculosis</i>); 435, cholera bacillus; 436, bacilli of anthrax, showing spores;
+437, typhoid bacillus.</p></figcaption>
+</figure>
+
+<p id="p-346"><b>346. Useful fungi.</b>—Not all fungi, however, are injurious.
+On the contrary, the great majority of them are harmless,
+and very many kinds are positively beneficial to man.
+Without the yeasts and bacteria of fermentation we could
+not have our bread and cheese. Other forms are active
+agents in the fertilization of soils, it having been estimated
+that there are 100,000 or more of these infinitesimal laborers
+at work in every cubic centimeter (about ¹⁄₁₆ of a
+cubic inch) of virgin soil! Even the bacteria of putrefaction,
+which we are accustomed to regard as the embodiment<span class="pagenum" id="Page_306">[Pg 306]</span>
+of all that is foul and loathesome, are engaged in an unceasing
+work as scavengers, without which life would no longer
+be possible on our globe, as will be shown in the following
+section.</p>
+
+
+<h4 id="CH_X_III_A">A. <span class="smcap">Bacteria</span></h4>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A vessel of water in which hay has been left to soak for
+several hours; a freshly boiled potato.</p>
+
+<p><span class="smcap">Appliances.</span>—A double boiler for sterilizing; a number of clean glass
+jars and bottles; cotton wool for stoppers; a compound microscope.</p>
+
+<p><span class="smcap">Culture Mediums.</span>—A freshly boiled potato answers very well for
+ordinary purposes. “Bread mash” can be made by drying some bread
+crumbs in an oven, then mashing and mixing them to a paste with boiling
+water; sterilize by three successive heatings in a double boiler. A sterilized
+preparation of gelatine solution is the medium most commonly used.</p>
+</div>
+
+<p id="p-347"><b>347. How to obtain specimens for observation.</b>—While
+bacteria are plentiful almost everywhere, it is not always
+easy to capture them just when and where you want them.
+For this purpose, put some hay in water and leave in a
+warm place away from the light until the liquid becomes
+cloudy or a film forms on the surface. This will show that
+bacteria are present. If it is desired to study any particular
+kind of bacterium, inoculate one of the culture mediums
+described under “material,” or a few drops of sterilized
+extract of beef, with a small quantity of the substance to be
+examined, or with dust or scrapings from the locality under
+consideration.</p>
+
+<div class="blockquot">
+
+<p id="exp-93"><span class="smcap">Experiment 93. By what means are bacteria commonly distributed?</span>—Put
+a slice of freshly boiled potato into each of three glass tumblers
+and cover with a filter of cotton wool held in place by tying tightly
+with a cord, or by an elastic band. Set them all in a vessel of water, bring
+it to a boil, and keep at that temperature for half an hour, to sterilize the
+air in the tumblers. When they have cooled, lift the cotton from (1) for
+a minute or two and then replace. Carefully pass the tip of a medicine
+dropper through the filter of (2) so as to prevent the entrance of unsterilized
+air, and put on the slice of potato a small quantity of the bacterial
+liquid prepared as directed in the last paragraph. Leave (3) unopened.
+Keep all together in a warm, dark place and observe at intervals of from
+12 to 24 hours. Do any bacteria appear in (3)? Do any appear on the<span class="pagenum" id="Page_307">[Pg 307]</span>
+potato in (2), where the liquid was dropped? Are they more, or less
+abundant than in (1)? Since cotton wool is entirely impervious to the
+smallest microörganisms known, would you judge from this experiment
+that bacteria can get into any place unless carried there by the air, or by
+some other means?</p>
+
+<p id="exp-94"><span class="smcap">Experiment 94. Can bacteria be carried by pure air?</span>—On a
+warm (and preferably cloudy) day, put a slice of potato on a plate, and
+leave uncovered in an unused room or closet, free from dust, and kept
+carefully closed. Put another slice arranged in exactly the same way
+in an open window on a dusty street, or in a room that is used and daily
+swept and dusted. Do bacteria appear in the first plate? In the second?
+Is air free from dust a good conveyor of bacteria?</p>
+
+<p id="exp-95"><span class="smcap">Experiment 95. What conditions are favorable to bacterial
+growth?</span>—Strain some of your culture liquid into half a dozen small
+bottles of the same size, filling each about half full. Put (1) in a dark,
+cool place—on ice, if the weather is warm; (2) in a dark, warm place;
+(3) in a warm, well-lighted place; into (4) put a drop of carbolic acid, formalin,
+corrosive sublimate, or boracic acid, and keep in a dark, warm place.
+Keep (5) in boiling water for half an hour or more, and then place beside
+(2). Keep (6) in a freezing mixture of salt and ice for several hours, then
+place with (2) and (5). Examine all at intervals of from 12 to 24 hours.
+In which bottles is the presence of bacteria indicated by cloudiness of the
+contained liquid, or the formation of a surface film? In which do they
+appear first? In which most abundantly? In which last, or not at all?
+What is the effect of light and darkness on their growth? Of heat and
+cold? Of disinfectants? Name the circumstances that tend to hinder
+their growth, in the order of their efficacy.</p>
+</div>
+
+<p id="p-348"><b>348. Microscopic study of bacteria.</b>—Put a drop of
+hay infusion on a slide and examine with the highest power
+of the microscope. You will see a multitude of very small
+glistening bodies including different kinds of bacteria, a
+majority of which are probably the hay bacillus, <i>B. subtilis</i>,
+shown in <a href="#i_319">Figs. 443, 444</a>. Notice that some forms
+move about freely, while others are non-motile. Which
+kind are the more numerous? The motion may be either mechanical,
+resembling that of the small dust particles we see
+dancing about in the sunshine, or apparently voluntary,
+and caused by the vibration of little whiplike cilia. Can
+you distinguish the two kinds? Try to make out clearly<span class="pagenum" id="Page_308">[Pg 308]</span>
+the different shapes you see. Some appear as slender
+chains or filaments, but this is due to the individual cells’
+adhering together for a time before breaking up and beginning
+an independent existence. The small, rounded bodies,
+like a period (<a href="#i_318">Fig. 438</a>), are <em>cocci</em>; the slender, rod-shaped
+ones—sometimes slightly curved (<a href="#i_318">Fig. 440</a>)—are <em>bacilli</em>
+(sing., <em>bacillus</em>); the comma-shaped ones, and those generally
+showing a slight spiral curvature, are <em>vibrios</em> (<a href="#i_318">Fig.
+441</a>); the spirally twisted ones, like a corkscrew (<a href="#i_318">Fig. 442</a>),
+are <em>spirilli</em> (sing., <em>spirillum</em>). These are the principal forms
+which it is important to distinguish and remember. The
+names are applied very loosely, however, in practice, bacillus
+being often used as a general term applicable to almost any
+kind,—the spirillum of cholera, for instance, being commonly
+known as the cholera bacillus, while by some authors
+vibrios are ranked as a variety of spirillum.</p>
+
+<figure class="figcenter illowp100" id="i_318" style="max-width: 50em;">
+  <img class="w100" src="images/i_318.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 438-442.</span>—Typical forms of bacteria: 438, coccus type; 439, the same,
+hanging together in chains; 440, rod-shaped bacteria (bacillus type), the clear areas
+in some of these are spores; 441, forms of vibrio; 442, forms of spirillum.</p></figcaption>
+</figure>
+
+<p id="p-349"><b>349. Life history of a typical bacterium.</b>—A pure culture
+of the <i>Bacillus subtilis</i> can easily be obtained by boiling
+some of the hay infusion for half an hour and then leaving<span class="pagenum" id="Page_309">[Pg 309]</span>
+in a warm place till the usual indications of the presence
+of bacteria appear <a href="#p-347">(347)</a>. The spores of this micro-organism
+are so resistant that they can withstand the temperature
+of boiling water for several hours, while those of
+most other forms of bacteria are killed by a few minutes’
+exposure to it; hence, the crop that develops after boiling
+will consist of a pure culture of the
+hay bacillus.</p>
+
+<figure class="figright illowp45" id="i_319" style="max-width: 31.25em;">
+  <img class="w100" src="images/i_319.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 443, 444.</span>—Hay bacillus (<i>B. subtilis</i>):
+443, a portion of the film from the culture
+liquid, the black lines, <i>e</i>, being bacteria
+in the vegetative state; 444, spore formation;
+<i>a</i>, <i>d</i>, motile cells and chain of cells: <i>b</i>,
+non-motile cells; <i>c</i>, spores and chain of
+spores from the film <i>e</i>.</p></figcaption>
+</figure>
+
+<p>In their active state these organisms
+will be seen to consist of single-celled,
+rod-shaped bodies, about
+three or four times as long as broad,
+and generally cohering in
+bands or filaments, as shown
+in <a href="#i_319">Fig. 444</a>, <i>c</i>. The black dots
+within the cells are the
+spores. Each individual
+bacterium produces but a
+single spore, or rather becomes
+a spore itself, by the
+contraction of its contents
+and the formation around
+them of a strong inclosing
+membrane. On germinating,
+the spores give rise to
+little ciliated, one-celled organisms
+called “swarm
+spores,” that swim about
+freely in the containing medium and multiply rapidly for a
+time by cell division. After this they pass again into the
+quiescent state, ready, whenever favorable conditions arise,
+to begin anew the repetition of their life cycle, which is an
+irregular alternation of cell division and spore formation.</p>
+
+<p id="p-350"><b>350. Resistance of spores.</b>—Bacteriologists are not fully
+agreed as to the cause of spore formation, some holding
+that it takes place only when conditions are most favorable<span class="pagenum" id="Page_310">[Pg 310]</span>
+for bacterial growth, others claiming the reverse. The
+consensus of opinion at present is toward the view that the
+spores are a provision for tiding over periods of stress and
+difficulty. They are capable of retaining their vitality
+for a long time, and are much harder to kill than the bacterial
+cells in their ordinary vegetative state, as was seen
+in the case of the hay bacillus. The spores of one species
+of potato bacillus have retained their vitality after four
+hours of boiling, and those of the typhoid bacillus after
+continuous exposure to a freezing temperature for more
+than three months. The majority of bacteria, in their
+vegetative state, are, however, either killed or rendered
+inert by temperatures ranging below 10° or above 50° centigrade—equivalent
+to about 50° and 122° Fahrenheit,
+respectively. It is easy to see what important bearing
+these facts have on the process of disinfection.</p>
+
+<p id="p-351"><b>351. Reproduction and multiplication.</b>—The ordinary
+mode of reproduction in bacteria, as in other unicellular
+organisms, is by fission (<a href="#p-337">337</a>, <a href="#p-338">338</a>). As each individual
+forms but a single spore, no increase in numbers could take
+place by this means alone. Hence, while the spores are
+an important factor in the preservation of the species by
+continuing its existence under conditions which the active
+organisms could not survive, their successful propagation
+depends on their power of rapid multiplication by division.
+If this process were to go on unchecked, every hour, in an
+unbroken geometrical progression, the progeny of a single
+bacterium would, in 24 hours, number nearly 17 million;
+in 25 hours, 34 million; in 26 hours, 68 million, and in five
+days they would cover the entire surface of the globe, land
+and sea, to a depth of 3 feet! In ordinary standard milk
+sold by dairymen, and containing, when examined, less
+than 10,000 microbes to the cubic centimeter,—about
+20 drops,—the number was found to have increased after
+24 hours to 600 million. It is comforting to know, however,
+that the majority of these are of the harmless kinds<span class="pagenum" id="Page_311">[Pg 311]</span>
+which are the active agents in the making of buttermilk
+and cheese.</p>
+
+<p>The effects of their rapid multiplication will be better
+appreciated when we consider that bacteria are the smallest
+of known living creatures. If 1000 of the influenza bacilli
+were spread out in a single layer with their sides touching,
+but not overlapping, they would not take up more room
+than one of the periods used in punctuating this book;
+and a coccus concerned in a tubercular disease prevalent
+among cattle in South America has recently been discovered,
+of which double that number could be accommodated in the
+same space.</p>
+
+<figure class="figcenter illowp100" id="i_321" style="max-width: 100em;">
+  <img class="w100" src="images/i_321.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 445, 446.</span>—Milk (highly magnified): 445, pure, fresh milk, showing fat
+globules; 446, milk that has stood for hours in a warm room in a dirty dish, showing
+fat globules and many forms of bacteria.</p></figcaption>
+</figure>
+
+<p id="p-352"><b>352. Distribution of bacteria.</b>—Ordinary air, when free
+from dust, contains, on the average, not more than five
+germs to the liter—equal to about 1 for every 12 cubic
+inches. Pathogenic, or disease-producing, germs seldom
+occur in ordinary fresh air, and even when present are, under
+ordinary circumstances, harmful only to people whose
+bodies, by reason of physical weakness or unhygienic habits,
+offer a congenial soil for their multiplication. Numerous instances
+are known in which perfectly healthy persons have
+carried about infectious disease germs in their bodies and
+even transmitted them to others without experiencing
+any inconvenience, or even being aware of their presence.<span class="pagenum" id="Page_312">[Pg 312]</span>
+Among others, the germs of pneumonia, diphtheria, and
+tuberculosis are often found in the mouth, nose, and sputum
+of perfectly healthy persons. There are also a number
+of bacteria that are regular inhabitants of the mouth, some
+of which are the cause of decayed teeth and foul breath.
+One form of bacterium, concerned in the production of inflammation
+and abscesses (<em>Staphylococcus</em>) is so constantly
+present on the human epidermis that one authority has
+declared it impossible to sterilize the skin so thoroughly
+as to free it entirely of this microbe. It is ordinarily not
+harmful unless it comes in contact with open wounds and
+abrasions.</p>
+
+<p id="p-353"><b>353. The economic importance of bacteria.</b>—It is hard
+to say whether these organisms concern us most on account
+of the damages attributable to them on the one hand, or
+the benefits we owe them on the other. If they were all
+as harmful as the pathogenic kinds, life would hardly be
+possible on the globe, while without their presence life
+as we know it would have ceased to be possible long ago.
+They are nature’s great army of scavengers, the sole agents
+of decomposition, without which dead organic matter would
+be subject only to the slow changes by which the rocks
+and mineral matter of the earth’s crust are disintegrated,
+and the undecomposed bodies of the vast procession of
+plants and animals that have existed since life first began
+on our globe would long ago have cumbered its surface to such
+an extent as to render impossible the continued development
+of life such as we know.</p>
+
+<p id="p-354"><b>354. Sterilization</b> is the process of ridding a substance
+of living microörganisms. To do this effectively, the process
+must be repeated several times at intervals, so as
+to give any spores that may have survived previous applications
+time to pass into the vegetative state, when their
+power of resistance is diminished and they are more easily
+destroyed. The incubation period, as the time required
+for the germination of the spores is called, is different for<span class="pagenum" id="Page_313">[Pg 313]</span>
+different kinds of bacteria; hence the importance, from a
+sanitary point of view, of a thorough knowledge of their life
+history.</p>
+
+<p id="p-355"><b>355. Disinfection</b> is sterilization on a large scale, and
+the same principles apply to both. Heat is the safest
+disinfectant for objects that will bear it, if continued long
+enough and repeated often enough at a sufficiently high
+temperature. Freezing will destroy some kinds of germs
+and check or retard the development of nearly all, but
+is not to be relied on as a permanent germicide, since
+even among flowering plants there are many kinds, not
+only of seeds, but of perennial vegetative forms that are
+capable of enduring an arctic temperature of many degrees
+below freezing for long continued periods.</p>
+
+<p>Chemical disinfectants act usually as microbe poisons,
+and are unsuitable as sterilizers for food, though valuable
+in the purification of houses, clothing, and utensils—especially
+the instruments employed in surgical operations.</p>
+
+<p>The prevention of the growth of bacteria, especially in
+wounds and surgical incisions, whether by means of chemical
+or physical agencies, is known as <em>antisepsis</em>.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Why should a person recovering from an ague continue for some
+time after to take quinine every third or every seventh day? (<a href="#p-350">350</a>, <a href="#p-354">354</a>.)</p>
+
+<p>2. Name some of the principal diseases produced by bacteria.</p>
+
+<p>3. What is the principle to be acted on in the avoidance of such diseases?
+(<a href="#exp-94">Exps. 94</a>, <a href="#exp-95">95</a>.)</p>
+
+<p>4. Are the same means equally effective for prevention and for cure?
+(<a href="#p-354">354</a>, <a href="#p-355">355</a>; <a href="#exp-93">Exps. 93-95</a>.)</p>
+
+<p>5. Why is “fresh air” beneficial in a sick room? (<a href="#p-352">352</a>; <a href="#exp-94">Exp. 94</a>.)</p>
+
+<p>6. Does it act as a disinfectant, or as a mere diluent of the infected
+air of the room? (<a href="#p-352">352</a>.)</p>
+
+<p>7. Why ought preserved fruits and vegetables to be scalding hot when
+put into the can? (<a href="#p-355">355</a>.)</p>
+
+<p>8. Why is it necessary to exclude the air from them? (<a href="#exp-93">Exps. 93</a>,
+<a href="#exp-94">94</a>.)</p>
+
+<p>9. Reconcile question 8 with question 5.</p>
+
+<p><span class="pagenum" id="Page_314">[Pg 314]</span></p>
+
+<p>10. Why does the use, for drinking purposes, of water that has been
+boiled render a person less liable to infectious diseases? (<a href="#p-355">355</a>.)</p>
+
+<p>11. Was the old-fashioned practice of handing the baby round to be
+promiscuously kissed by friends and neighbors a good one for the baby?
+(<a href="#p-352">352</a>.)</p>
+
+<p>12. Why is the spitting habit to be condemned? The use of common
+drinking cups in schoolrooms and other public places? (<a href="#p-352">352</a>.)</p>
+
+<p>13. Is it proper from a sanitary point of view that roommates at a boarding
+school, or even members of the same family, should use soap, towels,
+and other articles of the toilet in common? (<a href="#p-352">352</a>.)</p>
+</div>
+
+
+<h4 id="CH_X_III_B">B. <span class="smcap">Yeasts</span></h4>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A piece of fresh baker’s yeast, some warm water, and a
+little honey or sugar solution; a pipette, or a medicine dropper; three or
+four clean pint bottles or preserve jars.</p>
+
+<p>To raise a crop of yeast fungi for observation, rub one fourth of a fresh
+yeast cake in water enough to make a paste; add one pint of water, with
+a tablespoonful of honey or sugar, and stir well.</p>
+
+<p id="exp-96"><span class="smcap">Experiment 96. What conditions favor the growth of yeast?</span>—Pour
+equal parts of the liquid made as directed (see Material) into each
+of three pint bottles, stopper lightly, and label. Put (1) in a warm, dark
+place; (2) in a cool, dark place; and (3) in a bright light in a warm place.
+Observe at intervals of a few hours the changes that occur in each. Notice
+the bubbles that rise from the liquid. In which bottle do they form most
+rapidly? Lower a lighted match into it, or transfer some of the gas with
+a pipette into a vessel containing limewater, and tell what it is. Taste
+some of the fermenting liquid. Is it sweet? What has become of the
+sugar that was put into it?</p>
+</div>
+
+<p id="p-356"><b>356. Yeasts and ferments.</b>—Yeasts belong to a very different
+order of fungi from the bacteria, but on account of
+their simplicity of structure and the similarity of their action
+to that of some of the latter, it is usual to consider them together.
+They are the active agents of fermentation, and
+include a large number of species. The kind used for household
+purposes is the same as that employed in making beer.
+Of this species there are many varieties, each one of which
+gives a characteristic taste to the beer made from it; and
+brewers, by paying attention to the cultivation of yeasts,
+give their product the special flavors peculiar to the different<span class="pagenum" id="Page_315">[Pg 315]</span>
+brands. This kind of yeast is not known to exist except in
+a state of cultivation, and probably owes its survival and
+present condition of development to a symbiosis with man,
+on account of its usefulness in bread making, and still more,
+perhaps, to its part in the gratification of his bibulous propensities,
+for among savage tribes the manufacture of fermented
+liquors is practiced long before the wholesome art of
+bread making.</p>
+
+<figure class="figcenter illowp100" id="i_325" style="max-width: 100em;">
+  <img class="w100" src="images/i_325.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 447-449.</span>—Forms of common yeast (<i>Saccharomyces cerevisiæ</i>): 447,
+brewers’ yeast; 448, household yeast (the large grains are starch); 449, yeast from
+beer sediment, showing budding. (Figs. 447, 448 × 250; Fig. 449 × 1270.)</p></figcaption>
+</figure>
+
+<p>There are other yeasts existing in a state of nature, such as
+those on the surface of fruits, which cause the latter, under
+certain circumstances, to ferment and decay. For this reason
+artificial ferments are not needed in making wine and
+other alcoholic liquors from fruits. Fermentation is also
+caused by certain forms of bacteria, as in the formation of
+vinegar and the souring of milk. Such bacteria often contaminate
+the yeast ferments.</p>
+
+<p id="p-357"><b>357. Microscopic examination.</b>—Place a drop of the
+cultural liquid on a slide and examine under the highest
+power of the microscope. What do you see? These egg-shaped
+bodies are yeast plants, unicellular organisms like
+the pleurococcus. Do you see any chlorophyll? Are the
+yeasts parasitic? How do you know? What do they live
+on? (Suggestion: What food substance that has disappeared
+was put into the culture liquid?) In getting their nourishment
+from the sugar, these fungi disintegrate it into alcohol
+and carbon dioxide, which is a process of fermentation. It<span class="pagenum" id="Page_316">[Pg 316]</span>
+is the bubbles of gas that were seen rising in the liquid which
+cause beer to effervesce and bread to rise. They permeate
+the dough and by their expansion produce the sponginess
+peculiar to leavened bread. Look for a cell with a bud forming
+on it; from what part does it appear to grow? Where a
+number of buds remain for some time attached to the mother
+cell (<a href="#i_325">Fig. 449</a>), they form a <em>colony</em>. Make a sketch of a
+single cell and of a colony of two or more adherent ones,
+labeling all the parts. If the cell wall cannot be made out
+clearly, run a little glycerine, or salt water, under the cover
+glass with a medicine dropper. What causes the contents of
+the cell to contract and leave the wall? (<a href="#p-56">56</a>, <a href="#p-59">59</a>.)</p>
+
+<p id="p-358"><b>358. Reproduction.</b>—From time to time buds break away
+from the mother cell and form new individuals or colonies
+of their own. This process is called multiplication by budding,
+and is only another form of cell division.</p>
+
+<p>Whenever reproduction takes place by other means than
+seeds or spores, it is said to be <em>vegetative</em>. This sort of reproduction
+is not confined to unicellular plants, but exists also
+among the phanerogams, the propagation of species by means
+of buds, tubers, rootstocks, runners, grafting, and the like
+being variations of the same process. On the other hand,
+yeasts and bacteria and the unicellular algæ have the power,
+under extreme conditions, to form resting spores, which
+sometimes lie dormant for years and resume their activity
+when favorable conditions return.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. When is fermentation useful to man?</p>
+
+<p>2. What is the effect on canned fruits and vegetables if yeast cells get
+into them?</p>
+
+<p>3. Why does milk turn sour in warm weather? (<a href="#p-350">350</a>, <a href="#p-351">351</a>; <a href="#exp-96">Exp. 96</a>.)</p>
+
+<p>4. Why do buttermilk and clabber spoil if left standing too long?
+(<a href="#p-345">345</a>, <a href="#p-356">356</a>.)</p>
+
+<p>5. What causes bread to be “heavy”? (<a href="#p-356">356</a>, <a href="#p-357">357</a>.)</p>
+
+<p>6. Why will dough not rise unless kept in a warm place? (<a href="#exp-96">Exp. 96</a>.)</p>
+
+<p>7. Why is beer kept cold during fermentation? (<a href="#p-350">350</a>, <a href="#p-356">356</a>.)</p>
+</div>
+
+<p><span class="pagenum" id="Page_317">[Pg 317]</span></p>
+
+
+<h4 id="CH_X_III_C">C. <span class="smcap">Rusts</span></h4>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—A leaf of wheat affected with red rust; a leaf or a stalk
+with black rust. Some barberry leaves with yellowish pustules on the
+under side, which under the lens look like clusters of minute white corollas.
+These are popularly known as “cluster cups.” As the spots on barberry
+occur in spring, the red rust in summer, and the black rust in autumn,
+gather the specimens as they can be found, and preserve for use.</p>
+
+<figure class="figright illowp25" id="i_327" style="max-width: 20em;">
+  <img class="w100" src="images/i_327.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 450, 451.</span>—Leaf
+of wheat affected
+with orange
+leaf-rust (<i>Puccinia
+rubigo-vera</i>), uredo
+stage: 450, upper
+side of leaf; 451,
+under side.</p></figcaption>
+</figure>
+
+<p>The orange leaf, or brown, rust (<i>Puccinia rubigo-vera</i>) is more common
+in some parts of the country than the ordinary wheat rust (<i>Puccinia
+graminis</i>), but the two are so much alike that the directions given will
+do for either. If the orange leaf-rust (so named from its color, and not
+from any connection with orange leaves, the logical relation of the words
+being orange leaf-rust, and not orange-leaf rust) is used, the cups and
+pustules should be looked for on plants of the borage family—comfrey,
+hound’s-tongue, etc. The orange leaf-rust of apple is caused by a fungus
+which will serve to illustrate the same class of parasites.
+The “teleuto” stage of this will be found on cedar
+trees, in the excrescences commonly known as “cedar
+apples”; the “cluster cups” on the leaves of apple
+and haw trees affected with the disease.</p>
+</div>
+
+<p id="p-359"><b>359. Red rust.</b>—Uredo stage. Examine
+a leaf of “red rusted” wheat under the lens,
+and notice the little oblong brown dots that
+cover it. These are clusters of spore cases,
+and are the only part that appears above the
+surface. Viewed under the microscope, the
+red rust will be seen to consist of a mycelium
+(see <a href="#i_328">Fig. 452</a>), which ramifies through the
+tissues of the leaf and bears clusters of single-celled
+reddish spores that break through the
+epidermis and form the reddish brown spots
+and streaks from which the disease takes its
+name. These spores, falling upon other
+leaves, germinate in a few hours and form
+new mycelia, from which, in six to ten days,
+fresh spores arise. Formerly this was thought to complete the
+life history of the fungus, to which the name of <em>Uredo</em> was
+given. It is now known, however, that the red rust is merely a<span class="pagenum" id="Page_318">[Pg 318]</span>
+stage in the life cycle of the plant, and to this stage the old
+name uredo is applied, the spores being called <em>uredospores</em>.</p>
+
+<p id="p-360"><b>360. Black rust.</b>—Teleuto stage. Next examine with a
+lens a part of the plant attacked by black rust. Do you
+observe any
+difference except
+in the
+color? Do the
+two kinds of
+rust attack all
+parts of the
+plant equally?
+If not, what
+part does each
+seem to affect more particularly? At what season does the
+black rust appear most abundantly? Place a section of the
+diseased part under the microscope and notice that the difference
+in color is due to a preponderance of long, two-celled
+bodies with very thick, black walls (<a href="#i_328a">Fig. 453</a>). These
+are called <em>teleutospores</em>,
+a word
+meaning “final
+spores,” because
+they are
+formed only
+toward the end
+of the season.
+They are developed
+from
+the same mycelium
+with the
+uredospores,
+and are not a
+product of the latter, but collateral with them and belong to
+the same stage in the life history of the fungus. After they
+appear, the uredospores cease to be developed at all, and<span class="pagenum" id="Page_319">[Pg 319]</span>
+only the dark teleutospores are produced. These remain on
+the culms in the stubble fields over winter, ready to begin
+the work of reproduction in spring. For this reason the
+teleutos are popularly known as “winter spores” in contradistinction
+to the uredos, or “summer spores,” whose activity
+is confined to the warm months.</p>
+
+<figure class="figcenter illowp70" id="i_328" style="max-width: 50em;">
+  <img class="w100" src="images/i_328.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 452.</span>—Uredo spores of wheat rust (<i>Puccinia graminis</i>),
+magnified. (<i>From</i> <span class="smcap">Coulter’s</span> “Plant Structures.”)</p></figcaption>
+</figure>
+
+<figure class="figcenter illowp70" id="i_328a" style="max-width: 50em;">
+  <img class="w100" src="images/i_328a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 453.</span>—Teleutospores of wheat rust, magnified.
+(<i>From</i> <span class="smcap">Coulter’s</span> “Plant Structures.”)</p></figcaption>
+</figure>
+
+<figure class="figright illowp30" id="i_329" style="max-width: 20em;">
+  <img class="w100" src="images/i_329.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 454.</span>—Teleutospore
+germinating
+and forming sporidia,
+<i>s</i>, <i>s</i>. (<i>From</i> <span class="smcap">Coulter’s</span>
+“Plant Structures.”)</p></figcaption>
+</figure>
+
+<p>It was formerly supposed that black rust was caused by a
+different fungus from that producing red rust, and to it the
+name <em>Puccinia</em> was given. This has been
+retained as a general designation for all fungi
+undergoing these two phases, and the particular
+form of fungus that we are now considering
+is known in all its stages as <i>Puccinia
+graminis</i>.</p>
+
+<p id="p-361"><b>361. The nonparasitic stage.</b>—The formation
+of teleutospores completes that portion
+of the life history of the fungus during
+which it is parasitic on wheat and grasses of
+different kinds. In spring they begin to
+germinate on the ground, each cell producing
+a small filament, from which arise in turn
+several small branches. Upon the tip of
+each of these branches is developed a tiny
+sporelike body called a <em>sporidium</em> (<a href="#i_329">Fig. 454</a>),
+which continues the generation of the rust
+fungus through the next stage of its existence.
+The filament which bears these sporidia is not parasitic,
+but when the sporidia ripen and the spores contained
+in them are scattered by the wind, there begins a second
+parasitic phase, which forms the most curious part of this
+strange life history.</p>
+
+<p id="p-362"><b>362. The æcidium.</b>—Examine next the under side of
+some barberry leaves (or comfrey, etc., if orange leaf-rust
+is used) for clusters of small whitish bodies that appear
+under the lens like little white corollas with yellow anthers
+in the center. Examine a section of one of these under the<span class="pagenum" id="Page_320">[Pg 320]</span>
+microscope and notice that the yellow substance is composed
+of regular layers of colored spores. The corolla-like
+receptacles containing them, popularly known as “cluster
+cups,” are borne on a mycelium produced from the
+spores described in the last paragraph. This mycelium is
+parasitic on barberry or other leaves, according to the kind
+of fungus, and was long believed to be a distinct plant, to
+which the name <i>Æcidium</i>
+(pl., <i>Æcidia</i>) was
+given. This term is
+now applied to the
+cluster cups, and those
+fungi which at any
+period of their life history
+produce them are
+called æcidium fungi.</p>
+
+<figure class="figright illowp50" id="i_330" style="max-width: 50em;">
+  <img class="w100" src="images/i_330.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 455.</span>—Section through a barberry leaf,
+showing on the upper side two spermogonia, <i>s</i>, <i>s</i>;
+and on the under side, an æcidium, <i>æ</i>.</p></figcaption>
+</figure>
+
+<p id="p-363"><b>363. Spermogonia.</b>—On
+the upper surface
+of the leaves that
+bear the æcidia, notice
+some small black dots
+hardly larger than pin
+points, but which,
+when sufficiently magnified,
+appear as little
+flask-shaped bodies (<a href="#i_330">Fig. 455</a>) under the epidermis. These are
+known as <em>spermogonia</em>, or <em>pycnidia</em>. When mature, they
+break through the epidermis so that the necks protrude, and
+discharge a quantity of minute cells or spores, very like some
+that, later on, we shall find playing an important part in the
+reproductive processes of certain other fungi, and of mosses
+and liverworts. In the rust fungi, however, their function is
+not understood. They may possibly be survivals of organs
+which were once active in the life processes of the plant, but
+have become useless under changed conditions. Do such
+organs throw any light on the evolutionary history of plants?</p>
+
+<p><span class="pagenum" id="Page_321">[Pg 321]</span></p>
+
+<figure class="figright illowp60" id="i_331" style="max-width: 63em;">
+  <img class="w100" src="images/i_331.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 456.</span>—A species of “cedar apple” (<i>Gymnosporangum</i>),
+showing the uredo-teleuto stage of
+the apple rust fungus. (<i>From</i> a photograph by
+Prof. F. E. Lloyd.)</p></figcaption>
+</figure>
+
+<p id="p-364"><b>364. Connection between barberry and wheat rust.</b>—With
+the discharge of the æcidium spores, the part of the
+life cycle of the fungus spent on the barberry comes to an
+end, and it is ready to begin the uredo-teleuto stage over
+again as soon as it finds a suitable host. Where there are no
+barberries, it is capable of propagating without them, either
+by adapting itself to some other host plant, or by omitting
+the æcidium stage altogether.
+The parasitic
+habit being an
+acquired one, the
+fungus, like some animal
+organisms that
+we know of, can often
+be “educated” by
+force of circumstances
+into tolerating,
+and even thriving
+upon, foods which
+under other circumstances
+it would reject.
+The wheat rust
+is known to be capable
+of propagating
+year after year in the
+uredo stage, the
+spores surviving
+through the winter on volunteer grains and grasses; and in
+no other country in the world does rust do greater damage
+to the wheat crop than in Australia, where the barberry
+is practically unknown. This power of accommodation
+possessed by many parasites is one of the difficulties the
+agriculturist has to contend with in the development of rustproof
+varieties.</p>
+
+<p id="p-365"><b>365. Polymorphism.</b>—Plants that pass through different
+stages in their life history are said to be <em>polymorphic</em>, that<span class="pagenum" id="Page_322">[Pg 322]</span>
+is, of many forms. The habit is very common among the
+lower forms of vegetation. The fact that one or more of
+the phases are sometimes omitted, as the æcidium phase
+of wheat rust in warm climates, suggests the idea that it
+may be of use in helping the plant to tide over difficult
+conditions. Besides giving better chances of obtaining
+nourishment, it probably has the same effect as cross fertilization
+among flowering plants, in imparting increased
+strength and vitality to the succeeding generation. Wheat
+rust produced from barberry æcidia is said to be much more
+vigorous—and consequently more destructive—than when
+derived from a uredo that has reproduced itself for several
+generations.</p>
+
+<p id="p-366"><b>366. The damage done by rust</b> to the host is through the
+destruction of its tissues by the mycelium. The chlorophyll
+is destroyed so that the plant can no longer manufacture
+food, and is too starved to produce good grain. There are
+many varieties of wheat rust, which have been found on
+twenty-seven different kinds of grain. Most of them are
+specialized to a particular host plant and will not, ordinarily
+<a href="#p-364">(364)</a>, infest any other. Has this fact any bearing upon the
+production of rustproof varieties?</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Is a farmer wise to leave scabby and mildewed weeds and bushes
+in the neighborhood of his grain fields? (<a href="#p-364">364</a>, <a href="#p-365">365</a>.)</p>
+
+<p>2. Are there any objections to the presence of volunteer grain stalks
+along roadsides and in fence corners during winter? (<a href="#p-364">364</a>.)</p>
+
+<p>3. Should cedar trees be allowed to grow near an apple orchard? Give
+a reason for your answer. (p. <a href="#Page_317">317</a>, Material.)</p>
+
+<p>4. Should diseased plants be plowed under? (<a href="#p-361">361</a>.)</p>
+
+<p>5. What disposition should be made of them?</p>
+
+<p>6. Ought diseased fruits to be left hanging on the tree?</p>
+
+<p>7. Why is it necessary to pick over and discard from a crate or bin all
+decaying fruits and vegetables?</p>
+
+<p>8. Does a rotation of crops tend to prevent the spread of disease in
+plants? Give reasons for your answer.</p>
+
+<p>9. Are rustproof varieties to be relied on indefinitely? (<a href="#p-364">364</a>.)</p>
+</div>
+
+<p><span class="pagenum" id="Page_323">[Pg 323]</span></p>
+
+
+<h4 id="CH_X_III_D">D. <span class="smcap">Mushrooms</span></h4>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Any kind of gilled mushroom in different stages of development,
+with a portion of the substratum on which it grows, containing
+some of the so-called spawn. The common mushroom sold in the
+markets (<i>Agaricus campestris</i>) can usually be obtained without difficulty.
+Full directions for cultivating this fungus are given in Bulletin 53 of the
+U. S. Department of Agriculture. From 6 to 12 hours before the lesson
+is to begin, cut the stem from the cap of a mature specimen, close up to
+the gills, lay it, gills downward, on a piece of clean paper, cover with a bowl
+or pan to keep the spores from being blown about by the wind, and leave
+until a print (<a href="#i_337">Fig. 466</a>) has been formed.</p>
+</div>
+
+<p id="p-367"><b>367. Mushrooms and toadstools.</b>—The popular distinction
+which limits the term “mushroom” to a single species,
+the <i>Agaricus campestris</i>, and classes all others as toadstools,
+has no sanction in botany. All mushrooms are toadstools
+and all toadstools are mushrooms, whether poisonous or
+edible. The real distinction is between mushrooms and
+puffballs, the former term being more properly applied to
+fungi which have the spore-bearing surface exposed.</p>
+
+<p id="p-368"><b>368. Examination of a typical specimen.</b>—The most
+highly specialized of the fungi, and the easiest to observe on
+account of their size and abundance, are the mushrooms
+that are such familiar objects after every summer shower.
+The <em>gilled</em> kind—those with the rayed laminæ under the
+cap—are usually the most easily obtained. Specimens
+should be examined as soon after gathering as possible, since
+they decay very quickly.</p>
+
+<p id="p-369"><b>369. The mycelium.</b>—Examine some of the white fibrous
+substance usually called spawn through a lens. Notice
+that it is made up of fine white threads interlacing with each
+other, and often forming webby mats that ramify to a considerable
+distance through the substratum of rotten wood
+or other material upon which the fungus grows. This webby
+structure, often mistaken for root fibers, is the thallus or
+true vegetative body of the plant, the part rising above
+ground, and usually regarded as the mushroom, being only
+the fruit, or reproductive organ. Place some of the mycelium<span class="pagenum" id="Page_324">[Pg 324]</span>
+under the microscope and notice that it is
+composed of delicate filaments made up of
+single cells placed end to end, as in Spirogyra
+<a href="#p-341">(341)</a>. These filaments are called
+<em>hyphæ</em>.</p>
+
+<p id="p-370"><b>370. The button.</b>—Look on the mycelium
+for one of the small round bodies
+called buttons (<a href="#i_334">Fig. 457</a>). These are the
+beginning of the fruiting body popularly
+known as the mushroom, and are of various
+sizes, some of the youngest being
+barely visible to the naked eye. After a
+time they begin to elongate and make
+their way out of the substratum.</p>
+
+<table class='autotable'>
+<tr><td>
+<figure class="figcenter illowp90" id="i_334" style="max-width: 30em;">
+  <img class="w100" src="images/i_334.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 457.</span>—Mycelium
+of a mushroom (<i>Agaricus
+campestris</i>), with young
+buttons (fruiting organs)
+in different stages: 1, 2,
+3, 4, 5, sections of fructification
+at successive periods
+of development; <i>m</i>,
+mycelium; <i>st</i>, stipe; <i>p</i>,
+pileus; <i>l</i>, gill, or lamina;
+<i>v</i>, veil.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp90" id="i_334a" style="max-width: 30em;">
+  <img class="w100" src="images/i_334a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 458.</span>—Diagram of unexpanded
+<i>Amanita</i>, showing parts: <i>a</i>,
+volva; <i>b</i>, pileus; <i>c</i>, gills; <i>d</i>, veil; <i>e</i>,
+stipe; <i>m</i>, mycelium.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-371"><b>371. The veil and the volva.</b>—Make a
+vertical section through the center of one
+of the larger buttons after it is well above
+ground, and sketch. Notice whether it is
+entirely enveloped from root to cap in a covering membrane—the
+<em>volva</em> (<a href="#i_334a">Fig. 458</a>, <i>a</i>)—or
+whether the enveloping membrane
+extends only from the
+upper part of the stem to the
+margin of the cap—the <em>veil</em> (<a href="#i_334a">Fig.
+458</a>, <i>d</i>); whether it has both veil
+and volva, or finally, whether it
+is naked, that is, devoid of both.</p>
+
+<p id="p-372"><b>372. The stipe, or stalk.</b>—Notice
+this as to length, thickness,
+color, and position; that is,
+whether it is inserted in the
+center of the cap or to one side
+(excentric), or on one edge (lateral).
+Observe the base, whether
+bulbous, tapering, or straight,
+and whether surrounded by a<span class="pagenum" id="Page_325">[Pg 325]</span>
+cup, or merely by concentric rings or ragged
+bits of membrane (the remains of the
+volva). Look for the <em>annulus</em> or ring (remains
+of the veil) near the insertion of the
+stipe into the cap, and if there is one, notice
+whether it adheres to the stipe, or moves
+freely up and down (<a href="#i_335">Fig. 459</a>, <i>a</i>); whether
+it is thick and firm, or broad and membranous
+so that it hangs like a sort of curtain
+round the upper part of the stipe (<a href="#i_337a">Fig.
+467</a>, <i>a</i>). Break the stem and notice whether
+it is hollow or solid; observe also the texture,
+whether brittle, cartilaginous, fibrous, or
+fleshy.</p>
+
+<table class='autotable'>
+<tr><td class='wd50'>
+<figure class="figcenter illowp70" id="i_335" style="max-width: 13.25em;">
+  <img class="w100" src="images/i_335.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 459.</span>—Parasol
+mushroom (<i>Lepiota
+procera</i>), showing
+movable annulus: <i>st</i>,
+stipe; <i>a</i>, annulus, or
+ring; <i>u</i>, umbo; <i>p</i>, <i>p</i>,
+floccose patches left
+by volva.</p></figcaption>
+</figure>
+</td><td class='wd50'>
+<figure class="figleft illowp70" id="i_335a" style="max-width: 30em;">
+  <img class="w100" src="images/i_335a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 460.</span>—Chanterelle
+(<i>Cantharellus cibarius</i>), with
+infundibuliform pileus and
+decurrent gills.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-373"><b>373. The pileus, or cap.</b>—Observe this as
+to color and surface, whether dry, or moist
+and sticky; smooth, or covered with scurf
+or scales left by the remains of the volva, as it was stretched
+and broken up by the expanding cap (<a href="#i_335">Fig. 459</a>, <i>p</i>, <i>p</i>). Note
+also the size and shape, whether conical,
+expanded, funnel-shaped (<a href="#i_335a">Fig. 460</a>),
+or <em>umbonate</em>—having a protuberance
+at the apex (<a href="#i_335">Fig. 459</a>)—or whether the
+margin is turned up at the edge (revolute,
+<a href="#i_337a">Fig. 467</a>), or under (involute, <a href="#i_335">Fig. 459</a>).</p>
+
+<p id="p-374"><b>374. The gills, or laminæ.</b>—Look at
+the under surface and notice whether
+the gills are broad or narrow, whether
+they extend straight from stem to margin,
+or are rounded at the ends, or
+curved, toothed, or lobed in any way.
+Notice their attachment to the stipe,
+whether <em>free</em>, not touching it at all; <em>adnate</em>, attached squarely
+to the stem at their anterior ends; or <em>decurrent</em>, running
+down on the stem for a greater or less distance (<a href="#i_335a">Fig. 460</a>).</p>
+
+<p><span class="pagenum" id="Page_326">[Pg 326]</span></p>
+
+<table class='autotable'>
+<tr><td class='wd40'>
+<figure class="figcenter illowp100" id="i_336" style="max-width: 30em;">
+  <img class="w100" src="images/i_336.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 461-463.</span>—Section of a
+gilled mushroom: 461, through
+one side, showing sections of the
+pendent gills, <i>g</i>, <i>g</i> (slightly magnified);
+462, one of the gills
+more enlarged, showing the central
+tissue of the trama, <i>tr</i>, and
+the broad border formed by the
+hymenium, <i>h</i>; 463, a small section
+of one side of a gill very
+much enlarged, showing the
+club-shaped basidia, <i>b</i>, <i>b</i>, standing
+at right angles to the surface,
+bearing each two small branches
+with a spore, <i>s</i>, <i>s</i>, at the end.
+The sterile paraphyses, <i>p</i>, are
+seen mixed with the basidia.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp100" id="i_336a" style="max-width: 30em;">
+  <img class="w100" src="images/i_336a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 464, 465.</span>—A tube fungus (<i>Boletus edulis</i>):
+464, entire; 465, section, showing position of the
+tubes.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-375"><b>375. The hymenium.</b>—Cut a tangential section through
+one side of the pileus and sketch the section of the gills as
+they appear under a lens, or a low
+power of the microscope. Notice
+that the blade consists of a central
+portion called the <em>trama</em> (<i>tr</i>, <a href="#i_336">Fig. 462</a>)
+and a somewhat thickened portion,
+<i>h</i>, constituting the <em>hymenium</em>, or
+spore-bearing surface. Now examine,
+under a high power, a small section
+from the edge of a gill, including
+a bit of the trama. Notice that this
+last consists of a tissue of mycelial
+cells (<a href="#i_336">Fig. 463</a>) covered by the hymenium,
+or spore-bearing membrane,
+which is thickly clothed with a layer
+of elongated, club-shaped cells (<i>b</i>, <i>b</i>
+and <i>p</i>, <i>p</i>, <a href="#i_336">Fig. 463</a>) set upon it at right
+angles to the surface. Some of these
+put out from two to four, or in some
+species as many as eight, little
+prongs, each bearing a spore (<i>s</i>, <i>s</i>, <a href="#i_336">Fig.
+463</a>), while others remain
+sterile. The spore-bearing
+cells are called
+<em>basidia</em>; the sterile
+ones, <em>paraphyses</em>; and
+the whole spore-bearing surface together, the <em>hymenium</em>, from
+a Greek word meaning a membrane. It is from the presence<span class="pagenum" id="Page_327">[Pg 327]</span>
+of this expanded fruiting membrane that the class of mushrooms
+we are considering gets its botanical name, <i>Hymenomycetes</i>,
+membrane fungi. The hymenium is not always
+borne on gills, but is arranged in various ways which serve
+as a convenient basis for distinguishing the different orders.
+In the tube fungi, to which the edible
+boletus belongs (<a href="#i_336a">Figs. 464, 465</a>), the
+basidia are placed along the inside of
+little tubes that line the under side
+of the pileus, giving it the appearance
+of a honeycomb. In another
+order, the porcupine fungi, they are
+arranged on the outside of projecting
+spines or teeth, while in the
+morelles they are held in little cups
+or basins.</p>
+
+<table class='autotable'>
+<tr><td class='wd50'>
+<figure class="figcenter illowp80" id="i_337" style="max-width: 30em;">
+  <img class="w100" src="images/i_337.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 466.</span>—Spore print of a
+gilled mushroom.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp80" id="i_337a" style="max-width: 30em;">
+  <img class="w100" src="images/i_337a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 467.</span>—Deadly agaric
+(<i>Amanita phalloides</i>), showing
+the broad pendent annulus,
+<i>a</i>, formed by the ruptured
+veil; the cup at the
+base, <i>c</i>, and floccose patches
+on the pileus, left by the
+breaking up of the volva.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-376"><b>376. Spore prints.</b>—When the
+gills are ripe, they shed their spores in great abundance.
+Take up the pileus that was laid on paper, as directed under
+Material, on <a href="#Page_323">page 323</a>, and examine
+the print made by the discharged
+spores; it will be found to give an
+exact representation of the under side
+of the pileus.</p>
+
+<p id="p-377"><b>377. The spores.</b>—Notice the color
+of the spores as shown in the print.
+This is a matter of importance in distinguishing
+gill-bearing fungi, which are
+divided into five sections according to
+the color of the spores. One source of
+danger, at least, to mushroom eaters
+would be avoided if this difference was
+always attended to, for the deadly
+amanita (<i>Amanita phalloides</i>) and the
+almost equally dangerous fly mushroom
+(<i>A. muscaria</i>) both have white spores,<span class="pagenum" id="Page_328">[Pg 328]</span>
+while the favorite edible kind (<i>Agaricus campestris</i>), though
+white-gilled when young, produces dark, purple-brown spores
+that cannot fail to distinguish it clearly for any one who will
+take the trouble to make a print.</p>
+
+<p id="p-378"><b>378. Economic properties.</b>—Most of the wood-destroying
+fungi belong to this and allied orders. They are among
+the worst enemies the forester has to deal with <a href="#p-140">(140)</a>, and
+millions of feet of
+lumber are destroyed
+every year by them.</p>
+
+<figure class="figright illowp60" id="i_338" style="max-width: 50em;">
+  <img class="w100" src="images/i_338.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 468.</span>—Portion of the root of a maple affected
+with rot caused by the mycelium of a fungus that
+has penetrated to its interior.</p></figcaption>
+</figure>
+
+<p>Over seven hundred
+kinds of fungi
+growing in the United
+States have been described
+as edible, but
+the evil repute into
+which the whole class
+has been brought by
+the poisonous qualities
+of a few species,
+and the difficulty, to
+any but an expert, of
+distinguishing between
+these and the harmless kinds, has caused them to be
+generally neglected as articles of diet. While they are
+pleasant relishes and furnish an agreeable variety to our daily
+fare, their food value has been greatly exaggerated. They
+contain a large proportion of water, often over 90 per cent,
+and the most valued of them, the <i>Agaricus campestris</i>, is
+about equivalent to cabbage in nutrient properties.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Why are mushrooms generally grown in cellars? (<a href="#p-186">186</a>, <a href="#p-343">343</a>.)</p>
+
+<p>2. Name any fungi you know of that are good for food or medicine or
+any other purpose.</p>
+
+<p>3. Name the most dangerous ones you know of.</p>
+
+<p><span class="pagenum" id="Page_329">[Pg 329]</span></p>
+
+<p>4. Do you find fungi most abundant on young and healthy trees, or
+on old, decrepit ones? Account for the difference. (<a href="#p-141">141</a>, <a href="#p-343">343</a>, <a href="#p-378">378</a>.)</p>
+
+<p>5. Do you ever find them growing on perfectly sound wood anywhere?</p>
+
+<p>6. Are they ever beneficial to a tree? (<a href="#p-86">86</a>.)</p>
+
+<p>7. Is it wise to leave old, unhealthy trees and decaying trunks in a
+timber lot?</p>
+</div>
+
+
+<h3 id="CH_X_IV">IV. LICHENS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Specimens can be found almost everywhere, growing
+on rocks, walls, logs, stumps, and trees. Some of the more common kind
+are: <i>Parmelia</i>, recognizable by the shallow spore cups borne on the upper
+surface of the thallus; <i>Cladonia</i>, by the little stalked receptacles, like
+goblets, in which its spores are held; <i>Physcia</i>, by its bright orange color.
+Where practicable, it is well to have several different kinds for comparison.
+Iceland moss (<i>Cetraria islandica</i>) can generally be obtained from the
+grocers, and is a good example of an intermediate form between foliaceous
+and fruticose lichens.</p>
+
+<p>If the specimens are very dry, they will be too brittle to handle conveniently,
+and should be moistened by soaking a short time in water. This
+will render them quite flexible and also bring out the green color more
+clearly.</p>
+</div>
+
+<figure class="figcenter illowp100" id="i_339" style="max-width: 50em;">
+  <img class="w100" src="images/i_339.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 469.</span>—Foliaceous lichens: <i>A</i>, <i>Xanthoria (Physcia) parietina</i>; <i>B</i>, <i>Parmelia
+conspersa</i>; <i>a</i>, spore cups.</p></figcaption>
+</figure>
+
+<p id="p-379"><b>379. Examination of a typical specimen.</b>—The commonest
+kind of lichens, and generally the most easily obtained,
+are those that grow on rocks and tree trunks in flat,
+spreading patches. Their margins are much dented and<span class="pagenum" id="Page_330">[Pg 330]</span>
+curled, giving them a somewhat leaflike appearance, whence
+they are called “foliaceous” lichens. This broad, expanded
+body is the thallus, or vegetative part, as distinguished from
+its reproductive part. Examine carefully the thallus of
+your specimen. Note the size and shape of the indentations.
+Is there any order or regularity about them, such as was
+observed in the lobing of leaves? Is there any difference
+in color between the upper and under sides? What other
+differences do you notice? Do you see anything like hairs,
+or rootlets, on the under side? Mount one of them in water
+and place under the microscope. What does it look like?
+Compare with one of the hairs from a leaf of mullein, gromwell,
+blueweed, or other hairy plant, with the hypha of a
+fungus mycelium, and with your study of the root hair in
+<a href="#p-67">67</a> (<i>a</i>). Is it a hair or a root? These rootlike hairs are
+called <em>rhizoids</em>, and serve to anchor the lichen to its substratum.
+Look on the upper side for little cup-shaped or
+saucer-shaped receptacles. On what part of the thallus
+are they situated? Examine
+with a lens and see
+if you can make out what
+they contain. These cups
+are the spore cases. The
+lichen fungus belongs to
+the division of sac fungi,
+which produce their
+spores in closed sacs, or
+cups.</p>
+
+<figure class="figright illowp55" id="i_340" style="max-width: 40em;">
+  <img class="w100" src="images/i_340.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 470.</span>—Portion of the thallus of a lichen,
+magnified, showing imprisoned algæ.</p></figcaption>
+</figure>
+
+<p id="p-380"><b>380. Structure of the
+thallus.</b>—Make a thin
+section through a thallus and place under the microscope.
+Notice the small green bodies enveloped in the hyphæ of the
+fungus. Are they most abundant near the upper or the lower
+epidermis? Has their green color anything to do with this,
+and with the difference in color between the two surfaces of
+the thallus? (<a href="#p-184">184</a>.) Do they look like chlorophyll granules?<span class="pagenum" id="Page_331">[Pg 331]</span>
+Can you tell what they are? Compare with your study of
+the unicellular algæ <a href="#p-337">(337)</a> and with <a href="#i_310">Fig. 429</a>. Does this
+throw any light on their real nature?</p>
+
+<figure class="figcenter illowp80" id="i_341" style="max-width: 50em;">
+  <img class="w100" src="images/i_341.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 471.</span>—Artificial lichen mycelium, <i>m</i>, made by sowing spores of a fungus,
+<i>sp</i>, among alga cells, <i>a</i>.</p></figcaption>
+</figure>
+
+<p id="p-381"><b>381. The lichen thallus a composite body.</b>—You will
+probably have no difficulty in making out that these small
+round bodies are green algæ of some kind, but of what species
+will depend upon the kind of lichen with which it is associated.
+In Cladonia and the bearded lichen (<a href="#i_343">Fig. 473</a>), it is a protococcus;
+in other forms, a pleurococcus or a nostoc—and so
+on, each species of lichen fungus being specialized to a certain
+form of alga. The great botanist, De Bary, showed
+that it is even possible to produce a lichen thallus artificially
+by sowing the spores of a fungus among the cells of the particular
+alga with which it is able to unite. The spores will
+germinate without the alga, but soon perish unless they come
+in contact with the right one. It is thus made clear that the
+lichen plant as a whole is a combination of elements belonging
+to two distinct orders, the algæ and fungi, but so closely
+associated as to constitute practically a single individual.</p>
+
+<p><span class="pagenum" id="Page_332">[Pg 332]</span></p>
+
+<p id="p-382"><b>382. Slavery, or partnership?</b>—Now, what can be the
+object of this peculiar association? Is it a symbiosis, or
+a case of enslavement? The fungi, as we know, are all
+parasites, unable to manufacture their own food or to exist
+at all except at the expense of other organisms, living or dead.
+But the lichens have refined upon the gross rapacity of their
+order, and instead of indiscriminately destroying the hosts
+that furnish their nourishment, have used their victims to
+better purpose by converting them into contented, well-fed
+slaves! The imprisoned algæ perform for them the same
+service that the chlorophyll bodies do for the higher plants,
+and so the lichen fungi have the advantage of other parasites
+in getting their food manufactured at home, so to speak.
+And while the algæ have to do double work in order to feed
+both themselves and their masters, the fungus, in return,
+shelters them against cold and drought, and prolongs their
+growing period by giving them a more continuous supply
+of moisture and food materials,
+which it draws from the
+substratum by means of its
+rhizoids. In this way both
+plants are enabled to live in
+situations that neither could
+occupy without the other.</p>
+
+<figure class="figright illowp40" id="i_342" style="max-width: 30em;">
+  <img class="w100" src="images/i_342.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 472.</span>—A crustaceous lichen
+(<i>Graphis elegans</i>) growing on holly: <i>A</i>,
+natural size; <i>B</i>, slightly magnified.</p></figcaption>
+</figure>
+
+<p id="p-383"><b>383. Reproduction.</b>—The
+multiplication of the lichen
+algæ is exclusively vegetative.
+The fungus, on the other
+hand, reproduces normally
+by spores, and the fruiting
+bodies found on the thallus
+originate from the fungus
+mycelium.</p>
+
+<p id="p-384"><b>384. Classification.</b>—To
+be strictly accurate, the
+two kinds of vegetable bodies<span class="pagenum" id="Page_333">[Pg 333]</span>
+that make up the lichen thallus would probably have to be
+classified separately, as algæ or fungi, respectively, but as
+fructification is the generally accepted basis of classification,
+and the plant body is too intimately permeated with both
+kinds of tissue to be divided, each lichen body as a whole is
+classed with its particular kind of fungus. The entire group,
+on account of the distinctive characters that mark it, is
+placed in a separate order of its own. This includes three
+principal divisions, distributed according to the shape of the
+thallus, and its habit of growth: (1) <em>Crustaceous</em>, those that
+adhere closely to the substratum, as if glued or inscribed on
+it; (2) <em>Foliaceous</em>, with a broad, more or less lobed and leaflike
+thallus that adheres loosely to the substratum by means
+of rhizoids springing from its under surface; (3) <em>Fruticose</em>,
+with branching, stemlike thallus attached at the base like a
+regularly rooting plant (<a href="#i_343">Figs. 473, 474</a>). Among these are
+the Iceland moss, used as an article of food by man, and the
+reindeer moss (<i>Cladonia rangiferina</i>), which is the chief sustenance
+of the reindeer.</p>
+
+<figure class="figcenter illowp100" id="i_343" style="max-width: 50em;">
+  <img class="w100" src="images/i_343.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 473, 474.</span>—Fruticose lichens: 473, <i>Usnea barbata</i>, bearded lichen; 474,
+<i>Cladonia rangiferina</i>, reindeer moss: <i>A</i>, sterile; <i>B</i>, fruiting portion.</p></figcaption>
+</figure>
+
+<p><span class="pagenum" id="Page_334">[Pg 334]</span></p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Have lichens any economic value? (<a href="#p-384">384</a>.)</p>
+
+<p>2. In what way are they most useful? (<a href="#p-320">320</a>.)</p>
+
+<p>3. Do you find them, as a general thing, on healthy young trees and
+boughs, or on old ones, and those showing signs of decay?</p>
+
+<p>4. Do you ever find them growing on trees or other objects in densely
+inhabited areas,—cities, large towns, and manufacturing centers?</p>
+
+<p>5. Do they grow more thickly on the shady (northern) side of rocks,
+walls, and trees growing in the open, than on the sunny and (presumably)
+warmer sides?</p>
+
+<p>6. Mention some ways in which a growth of lichens might be beneficial
+to a tree.</p>
+
+<p>7. In what ways could it be harmful?</p>
+</div>
+
+
+<h3 id="CH_X_V">V. LIVERWORTS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Liverworts can generally be found growing with mosses
+in damp, shady places, and are easily recognized by their flat, spreading
+habit, which gives them the appearance of green lichens. <i>Marchantia
+polymorpha</i> (<a href="#i_345">Fig. 475</a>), one of the largest and best specimens for study,
+is common in shady, damp ground throughout the states. It is diœcious,
+and specimens bearing both male and female organs should be provided.
+<i>Lunularia</i>, a smaller species that can be recognized by the little crescent-shaped
+receptacles on some of the divisions of the thallus, is abundant
+in greenhouses on the floor, or on the sides of pots and boxes kept in damp
+places; but the spore-bearing receptacles are seldom or never present,
+the species being an introduced one and possibly rendered sterile by
+changed conditions. <i>Anthoceros</i> (<a href="#i_307a">Fig. 426</a>) and leafy liverworts, such
+as that shown in <a href="#i_352">Fig. 484</a>, also make good examples for study.</p>
+
+<p id="exp-97"><span class="smcap">Experiment 97. Why are the upper and under sides of a liverwort
+different?</span>—Plant a growing branch of marchantia, or of any
+flat, spreading liverwort, in moist earth so that the upper side will lie next
+the soil, and watch for a week or two, noting the changes that take place.
+What would you infer from these as to the cause of any differences that
+may have been observed between the two surfaces?</p>
+</div>
+
+<p id="p-385"><b>385. Examination of a typical liverwort</b>—The thallus.—The
+broad, flat, branching organ that forms the body of the
+plant is the thallus. Examine the end of each branch;
+what do you find there? Are the two forks into which the
+apex of the branches divides equal or unequal? Compare
+the growing end with the distal one; does it proceed from<span class="pagenum" id="Page_335">[Pg 335]</span>
+a true root? Notice that as the lower end dies, the growing
+branches go on increasing and reproducing the thallus.</p>
+
+<figure class="figcenter illowp82" id="i_345" style="max-width: 51em;">
+  <img class="w100" src="images/i_345.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 475, 476.</span>—Umbrella liverwort (<i>Marchantia polymorpha</i>): 475, portion of a
+female thallus about natural size, showing dichotomous branching; <i>f</i>, <i>f</i>, archegonial
+or female receptacles; <i>r</i>, rhizoids; 476, portion of a male thallus bearing an antheridial
+disk or receptacle, <i>d</i>, and gemmæ, <i>g</i>, <i>g</i>.</p></figcaption>
+</figure>
+
+<figure class="figright illowp30" id="i_346" style="max-width: 20em;">
+  <img class="w100" src="images/i_346.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 477.</span>—A portion
+of the upper epidermis
+of marchantia, magnified,
+showing rhomboidal
+plates with a stoma in
+each.</p></figcaption>
+</figure>
+
+<p>Do you find anything like a midrib? If so, trace it through
+the branches and body of the thallus; where does it end?
+Does it seem to be formed like the midrib of a leaf? Hold
+a piece of the thallus up to the light and see if you can detect
+any veins. Is it of the same color in all parts, and if there is
+a difference, can you give a reason for it? Examine the
+upper surface with a lens. Peel off a piece of the epidermis,
+place it under a low power of the microscope, or between
+two moistened bits of glass, and hold up to the light, keeping
+the upper surface toward you; what is its appearance?<span class="pagenum" id="Page_336">[Pg 336]</span>
+Observe a tiny dot near the center of the rhomboidal areas
+into which the epidermis is divided and compare it with
+your drawings of stomata (<a href="#p-181">181</a>, <a href="#p-183">183</a>).
+What would you judge that these dots
+are for? While differing in structure
+from the stomata of leaves, they serve
+the same purposes and may be regarded
+a more rudimentary form of the same
+organ.</p>
+
+<p id="p-386"><b>386. Rhizoids.</b>—Wash the dirt from
+the under side of a thallus and examine with a lens; how
+does it differ from the upper surface? Do you see anything
+like roots? Place one in a drop of water under the microscope.
+Compare with similar organs found on the lichen
+<a href="#p-379">(379)</a>. What are they? Would rhizoids be of any use on
+the upper side? stomata on the under side?</p>
+
+<p id="p-387"><b>387. Gemmæ.</b>—Look along the upper surface for little
+saucer-shaped (in lunularia, crescent-shaped) cupules (<i>g</i>, <i>g</i>,
+<a href="#i_345">Fig. 476</a>). Notice their shape and position, whether on a
+midrib or near the margin. Examine the contents with
+a lens and see if you can tell what they are. These little
+bodies, called <em>gemmæ</em>, are of the nature of buds, by which
+the plant propagates itself vegetatively somewhat as the
+onion and the tiger lily do by means of bulblets. Sow some
+of the gemmæ on moist sand, cover them with a tumbler
+to prevent evaporation, and watch them develop the thalloid
+structure.</p>
+
+<p id="p-388"><b>388. The fruiting receptacles.</b>—Procure, if possible,
+thalli with upright pedicels bearing flattened enlargements
+at the top (<a href="#i_345">Figs. 475, 476</a>). These are thallus branches
+modified into receptacles containing the reproductive organs,
+which, in marchantia, are diœcious, the two kinds growing
+on separate thalli. Notice their difference in shape, one
+kind being slightly lobed or scalloped, the other rayed like
+the spokes of a wheel. The first kind are known as <em>antheridial</em>,
+or male, receptacles; the second as <em>archegonial</em>, or female.</p>
+
+<p><span class="pagenum" id="Page_337">[Pg 337]</span></p>
+
+<p id="p-389"><b>389. The antheridia.</b>—Examine one of the male receptacles
+on both surfaces and in vertical section. Notice the
+tiny egg-shaped bodies sunk in little
+cavities between the lobes just under
+the upper epidermis (<a href="#i_347">Fig. 478</a>). These
+are antheridia. When mature, they
+rupture at the apex, and multitudes of
+extremely small bodies, called <em>antherozoids</em>,
+or <em>spermatozoids</em>, are discharged
+from them.</p>
+
+<table class='autotable'>
+<tr><td>
+<figure class="figcenter illowp75" id="i_347" style="max-width: 30em;">
+  <img class="w100" src="images/i_347.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 478.</span>—Longitudinal
+section of a male receptacle
+of marchantia polymorpha,
+magnified: <i>a</i>, antheridia;
+<i>t</i>, thallus; <i>s</i>, ventral scales;
+<i>r</i>, rhizoids.</p></figcaption>
+</figure>
+</td><td>
+<figure class="figcenter illowp75" id="i_347a" style="max-width: 30em;">
+  <img class="w100" src="images/i_347a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 479.</span>—Under side of an
+archegonial receptacle enlarged.
+The archegonia are borne
+among the hairs on the under
+surface, which is presented to
+view in the figure; <i>f</i>, a spore
+case.</p></figcaption>
+</figure></td></tr></table>
+
+<p id="p-390"><b>390. Archegonia.</b>—Next examine one
+of the female receptacles. Look on the
+under surface, between the narrow divisions
+of the receptacle, for radiating rows
+of flask-shaped bodies with their necks
+turned downward, and all surrounded
+by a toothed sheath or involucre (<a href="#i_347a">Fig.
+479</a>). These bodies are the archegonia,
+or female organs, and correspond, loosely speaking, to the
+ovaries of flowering plants. If the receptacle is a mature
+one, the archegonia will be replaced
+by the ripe spore cases (<em>sporangia</em>),
+as at <i>f</i>, <a href="#i_347a">Fig. 479</a>.</p>
+
+<p>Make enlarged drawings of the
+upper surface of a male and a female
+receptacle, and of a vertical section
+of each, passing through an antheridium
+in the male, and an archegonial
+row in the female receptacle.
+Label the parts observed in each.</p>
+
+<p id="p-391"><b>391. Minute study of an archegonium.</b>—Place
+under the microscope
+a very thin, longitudinal section
+through a ray of a receptacle containing
+a young archegonium, and observe that the latter
+consists of a lower portion, the <em>venter</em>, <i>v</i>, <a href="#i_348">Fig. 480</a>, and an<span class="pagenum" id="Page_338">[Pg 338]</span>
+upper part, the neck, which is perforated by the <em>neck canal</em>,
+<i>ca</i>. The venter contains the <em>egg cell</em>, <i>o</i>, and the ventral canal
+cell, <i>vc</i>. The neck canal is filled with small cells which,
+at maturity, dissolve into a mucilaginous substance that
+swells on being wet and discharges itself through the top
+of the neck, leaving an open passage to the venter, where
+the egg cell is ready to be fertilized.</p>
+
+<figure class="figright illowp40" id="i_348" style="max-width: 30em;">
+  <img class="w100" src="images/i_348.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 480, 481.</span>—480, young
+archegonium of M. polymorpha;
+<i>v</i>, ventral portion; <i>o</i>, egg
+cell; <i>vc</i>, ventral canal and cells;
+<i>ca</i>, neck canal with cells; 481,
+the same ready for fertilization
+after discharge of the mucilaginous
+fluid.</p></figcaption>
+</figure>
+
+<p>Make a drawing of the section as
+seen under the microscope, labeling
+all the parts.</p>
+
+<p id="p-392"><b>392. Fertilization.</b>—In the liverworts,
+and in cryptogams generally,
+this process has to take place under
+water, as the antherozoids are motile
+only in a liquid, but the amount required
+is so small that a few drops
+of rain or dew will enable them to
+make their journey to the archegonium.
+The mucilaginous substances
+discharged from the neck canal attract
+them to the mouth of the opening,
+one or more of them penetrates
+to the egg cell, and fertilization is accomplished.
+Do you see any analogies
+between this and the same
+function among flowering plants?
+(<a href="#p-250">250</a>, <a href="#p-251">251</a>.)</p>
+
+<p id="p-393"><b>393. The spore case.</b>—After fertilization the egg becomes
+an <em>oöspore</em>, capable of producing a new plant. Instead,
+however, of separating from the mother plant and giving
+rise to an independent growth, it germinates within the archegonium
+and produces there a small, stalked body, called
+a <em>sporogonium</em>, or <em>sporophyte</em>, which at length ripens into
+a spore case, as shown at <i>f</i>, <a href="#i_347a">Fig. 479</a>. At maturity this
+capsule-like sporophyte ruptures at the apex, and discharges<span class="pagenum" id="Page_339">[Pg 339]</span>
+a mass of spores, mingled with elongated filaments called
+<em>elators</em>, which, by their elastic movements, assist in disseminating
+the spores. These latter, on germinating, produce,
+not a simple sporophyte like that which bore them, but
+the thallus of the liverwort with all its complicated arrangement
+of antheridia and archegonia and vegetative organs
+that seem to foreshadow, by the analogies they suggest,
+the coming of the higher plants.</p>
+
+<p id="p-394"><b>394. Sexual and asexual reproduction.</b>—We find here
+a very marked change from the simple reproductive processes
+observed in the algæ and fungi. In the forms thus far considered,
+this function was carried on mainly by simple vegetative
+fission or budding, with a more or less irregular intervention
+of resting spores. If only one kind of spore is
+concerned, reproduction is said to be <em>asexual</em>. When two
+different kinds of cells, the egg and sperm cell, unite to form
+an oöspore, as in the liverworts, reproduction is said to be
+<em>sexual</em>. While sexual reproduction takes place to some
+extent among both algæ and fungi, the prevailing method
+among thallophytes is asexual, and may be carried on in
+three different ways: by fission (and budding), by resting
+spores, and by conjugation.</p>
+
+<p>Representing the plant body by <i>A</i> and the resting spores
+by <i>a</i>, the primitive asexual processes may be expressed to
+the eye by the accompanying formulas:—</p>
+
+<p class="noindent pad6">
+(1) Fission and budding: <i>A</i> → <i>A</i> → <i>A</i> → <i>A</i> →<br>
+(2) Resting spores: <i>A a</i> → <i>A a</i> → <i>A a</i> →<br>
+(3) Conjugation: <i>A</i> + <i>A</i> → <i>a</i> → <i>A</i> + <i>A</i> → <i>a</i> →</p>
+
+<p class="noindent">In (3), as was seen in the conjugating cells of the spirogyra
+<a href="#p-342">(342)</a>, the method is a little more complicated, showing an
+approach toward the sexual process. In each of these cases,
+however, there is only one kind of cell concerned, while in
+the liverworts there are not only different kinds, technically
+known as <em>gametes</em>, but specialized organs, archegonia
+and antheridia, for producing them. The thallus body
+bearing these organs is termed the <em>gametophyte</em>, because it<span class="pagenum" id="Page_340">[Pg 340]</span>
+bears the gametes, or sexual organs,—the suffix <em>phyte</em> meaning
+a plant; for example, <em>epiphyte</em>, on or upon plants; <em>spermophyte</em>,
+or <em>spermatophyte</em>, seed plant; <em>sporophyte</em>, spore plant.
+The <em>sporophyte</em>, produced within the archegonium, bears
+simple nonsexual spores that are capable of germinating
+independently. Structurally it is a separate, individual
+organism, though it does not appear as such in this class,
+but lives inclosed in the archegonium, as a parasite on the
+mother plant.</p>
+
+<p id="p-395"><b>395. Alternation of generations.</b>—If we represent the
+sporophyte by <i>S</i>, the thallus, or gametophyte, by <i>G</i>, the
+female gamete, or egg cell, by <i>fg</i>, the antherozoids (male
+gametes) by <i>mg</i>, the fertilized egg cell, or oöspore, resulting
+from their union by <i>oös</i>, and the asexual spores discharged
+from the sporophyte by <i>o</i>, this complicated mode
+of reproduction may be expressed diagrammatically as
+follows:—</p>
+
+<table class="autotable fs80 alternation">
+<tr>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>fg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>fg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"><i>G</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"> <i>oös</i> ⟶ <i>s</i> ⟶ <i>o</i> ⟶ <i>G</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>oös</i> ⟶ <i>s</i> ⟶ <i>o</i> ⟶ <i>G</i> ⟶ etc.</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>mg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>mg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+</tr>
+</table>
+
+<p>A glance at the diagram will show a continual interchange
+of the sexual and asexual modes of reproduction, in
+which each generation gives rise to its <em>opposite</em>, the asexual
+sporophyte producing the sexual gametophyte, and this in
+turn, through its gametes, giving rise to the asexual sporophyte.
+This regular recurrence in genealogical succession of
+two differing forms is what is meant by the expression “alternation
+of generations.” Analogous processes occur also
+among some of the thallophytes, but as there is no well-defined
+differentiation of sporophyte and gametophyte,
+alternation proper may be regarded as beginning with the
+bryophytes. The subject is a complicated one and somewhat
+difficult to grasp, but it is important to form a correct
+idea of it and to fix clearly in mind the different modes of
+reproduction as we proceed from the lower to the higher forms
+of vegetation, since in this way alone can their biological<span class="pagenum" id="Page_341">[Pg 341]</span>
+relationships and their order of succession in the evolutionary
+scale be made intelligible.</p>
+
+
+<h3 id="CH_X_VI">VI. MOSSES</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—One of the most widely distributed of mosses is the
+Sphagnum, or peat moss, so generally used by florists in packing plants for
+shipment, and it can be obtained from them at almost all times. It is
+rather difficult, however, to find specimens with the fruiting organs, since
+they are rarely to be met with except in late autumn or early spring.
+Other common forms are <i>Polytrichum</i>, <i>Funaria</i>, and <i>Mnium</i>, any of which
+will meet all essential conditions of the study outlined in the text.</p>
+</div>
+
+<figure class="figcenter illowp80" id="i_351" style="max-width: 50em;">
+  <img class="w100" src="images/i_351.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 482, 483.</span>—Protonema
+of a moss: 482, germinating spore; 483, protonema;
+<i>kn</i>, buds; <i>r</i>, rhizoids; <i>s</i>, spore.</p></figcaption>
+</figure>
+
+<p id="p-396"><b>396. The protonema or thallus stage.</b>—In mosses the
+sexual, or gametophyte generation differs from that of
+liverworts in undergoing two phases. The germinating
+cells of the sporophyte do not develop immediately into
+the leafy stem, which is the typical gametophyte of true
+mosses, but produce first a filamentous, creeping structure
+called the <em>protonema</em> (<a href="#i_351">Fig. 483</a>), that spreads over the
+ground and forms the tangled green felt usually observed
+where mosses are growing. Place a few of these filaments on
+a slide in water, and examine under the microscope. Do
+they remind you of any of the forms of algæ? Look near<span class="pagenum" id="Page_342">[Pg 342]</span>
+the base of the branches for knots or enlargements, like
+those seen at <i>kn</i>, <a href="#i_351">Fig. 483</a>. These are buds from which the
+leafy moss stems will develop. Do they correspond to anything
+observed among the thallophytes? Notice the rootlike
+filaments that extend under ground; how do they differ from
+the ones above ground? Why are they colorless? How
+do you know that they are not true roots? [<a href="#p-67">67</a> (<i>a</i>), <a href="#p-379">379</a>.]
+Sketch one of each kind of filament sufficiently enlarged to
+show the cells composing it.</p>
+
+<p>A protonema that arises directly from the spore is said
+to be <em>primary</em>, while those which sometimes spring from
+rhizoids above ground, or from stems or leaves, are
+<em>secondary</em>. The fact that a protonema can bud from parts
+of the fruiting stems shows that the two do not belong to
+different generations, but are merely successive stages of
+a single generation, and both together compose the gametophyte.</p>
+
+<p id="p-397"><b>397. The leafy stage.</b>—In their fully developed state
+the true mosses show a marked advance in organization over
+the liverworts. There is a distinct
+differentiation of the growing axis into
+stem and leaves, though no true roots
+are formed. The leaves are arranged
+spirally, on upright stems, while in the
+liverworts the vegetative body is
+either a flat, spreading thallus, or the
+leaves are arranged horizontally on
+opposite sides of a prostrate, or more
+or less inclined, axis. Sometimes a
+second set occurs, on the upper side
+of the axis, but in this case the leaves
+are usually much smaller and inclined
+to the horizontal arrangement, as
+shown in <a href="#i_352">Fig. 484</a>.</p>
+
+<table class='autotable'>
+<tr><td class="wd60">
+<figure class="figcenter illowp50" id="i_352" style="max-width: 30em;">
+  <img class="w100" src="images/i_352.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 484.</span>—Scapania, a
+liverwort with leafy thallus, approaching
+the form of mosses
+and lycopodiums. (<i>From</i> <span class="smcap">Coulter’s</span>
+“Plant Structures.”)</p></figcaption>
+</figure>
+</td><td rowspan='2'>
+<figure class="figcenter illowp60" id="i_353a" style="max-width: 30em;">
+  <img class="w100" src="images/i_353a.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 486.</span>—Fruiting
+stem of a moss
+(<i>Polytrichum commune</i>)
+with ripe capsules:
+<i>s</i>, seta, or footstalk;
+<i>c</i>, capsule with
+calyptra; <i>f</i>, capsule
+after the calyptra has
+fallen away; <i>d</i>, operculum,
+or lid.</p></figcaption>
+</figure></td>
+</tr>
+<tr><td>
+<figure class="figcenter illowp50" id="i_353" style="max-width: 30em;">
+  <img class="w100" src="images/i_353.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 485.</span>—Fruiting receptacle
+of a moss (<i>Phascum cuspidatum</i>),
+bearing both antheridia,
+<i>an</i>, and archegonia, <i>ar</i>, at
+the bifurcated apex; <i>b</i>, leaves;
+<i>p</i>, paraphyses.</p></figcaption>
+</figure>
+</td></tr></table>
+
+<p id="p-398"><b>398. The reproductive organs.</b>—The antheridia and
+archegonia are borne in groups at the end either of the main<span class="pagenum" id="Page_343">[Pg 343]</span>
+axes, or of lateral branches (<a href="#i_353">Figs. 485</a>, <a href="#i_353a">486</a>), but as a rule
+only one archegonium is fertilized, so the mature sporogonia
+are solitary. The plants may
+be either diœcious or monœcious, as
+in <a href="#i_353">Fig. 485</a>; and in
+the latter case, the
+reproductive organs
+may be borne on the
+same, or on different,
+receptacles. The
+antheridia and the
+archegonia are both
+mixed with club-shaped
+hairs called
+paraphyses (<a href="#i_353">Fig.
+485</a>).</p>
+
+<p id="p-399"><b>399. The sporophyte.</b>—An examination
+of the fruiting capsule of any of the true
+mosses will show that it consists of a long
+footstalk, the <em>seta</em>, <i>s</i>, <a href="#i_353a">Fig. 486</a>, bearing a
+capsule, or ripened sporogonium, <i>f</i>, which
+is at first surmounted by a cap or hood,
+known as the <em>calyptra</em>, <i>c</i>. The hood represents
+the excessively developed and often
+highly specialized wall of the archegonium.
+It falls away at maturity, and the spores are
+discharged through an opening made by the
+removal of the <em>operculum</em>, or lid, <i>d</i>. The
+spores and the capsule are both developed
+from the fertilized egg (oöspore), within the
+archegonium, in much the same manner as in
+the liverworts, and together constitute the
+sporophyte, or asexual generation. It never
+leads a completely independent existence, but remains a
+partial parasite on the mother plant, though the lower part
+of the young sporogonium is usually provided with stomata<span class="pagenum" id="Page_344">[Pg 344]</span>
+and chlorophyll so that it is capable of manufacturing food.
+In this respect it shows a distinct advance on the corresponding
+phase of the liverworts—if we except the single genus
+<i>Anthoceros</i>, which alone among the liverworts has the cells
+of the sporogonium provided with chlorophyll.</p>
+
+<p id="p-400"><b>400. Alternation of generations.</b>—The process of reproduction
+in mosses is so closely similar to that of liverworts
+that it is unnecessary to repeat the details. There are
+some minor variations, but in all essentials the processes
+are the same and may be represented to the eye by the
+same formula.</p>
+
+<p id="p-401"><b>401. Relative position of mosses and liverworts in the
+line of evolution.</b>—Though mosses, as a rule, show a higher
+degree of organization than liverworts, in both generations,
+their development has been <em>away</em> from the general course
+of evolution followed by the higher plants. This, as will
+be seen later, tends towards a decreasing complexity of
+the gametophyte with increasing complexity of the sporophyte,
+while the mosses show increasing complexity of <em>both</em>.
+Like the order of birds in the animal kingdom, they form
+a highly specialized and somewhat isolated group. While
+they may be regarded as descendants from a common ancestral
+stock with the ferns and club mosses, they have
+been switched off, so to speak, on a side track of the great
+evolutionary trunk line, and their advance on this side
+track has carried them to a point more remote from the
+course along which the higher forms of plant life have
+traveled than the distant junction at which they branched
+off from their less progressive kindred, the humble liverworts.</p>
+
+
+<h3 id="CH_X_VII">VII. FERN PLANTS</h3>
+
+<div class="blockquot">
+
+<p><span class="smcap">Material.</span>—Any kind of fern in the fruiting stage. Several different
+varieties should be cultivated in the schoolroom for observation. While
+gathering specimens, look along the ground under the fronds, or in greenhouses
+where ferns are cultivated, among the pots and on the floor, for
+a small, heart-shaped body like that represented in <a href="#i_359">Figs. 501, 502</a>, called
+a <em>prothallium</em>. It is found only in moist and shady places, and care should<span class="pagenum" id="Page_345">[Pg 345]</span>
+be taken in collecting specimens, as in their early stages the prothallia
+bear a strong resemblance to certain liverworts found in the same situations.
+The best way is for each class to raise its own specimens by scattering
+the spores of a fern in a glass jar, on the bottom of which is a bed
+of moist sand or blotting paper. Cover the jar loosely with a sheet of
+glass and keep it moist and warm, and not in too bright a light. Spores
+of the sensitive ferns (<i>Onoclea</i>) will germinate in from two to ten days,
+according to the temperature. Those of the royal fern (<i>Osmunda</i>) germinate
+promptly if sown as soon as ripe, but if kept even for a few weeks
+are apt to lose their vitality. The spores of sensitive fern can be kept
+for six months or longer, while those of the bracken (<i>Pteris</i>) and various
+other species require a rest before germinating, so that in these cases it
+is better to use spores of the previous season.</p>
+</div>
+
+<figure class="figright illowp50" id="i_355" style="max-width: 40em;">
+  <img class="w100" src="images/i_355.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 487-491.</span>—A fern plant: 487, fronds
+and rootstock; 488, fertile pinna: <i>s</i>, <i>s</i>, sori;
+489, cross section of a stipe, showing ends of the
+fibrovascular bundles; 490, a cluster of sporangia,
+magnified; 491, a single sporangium still more
+magnified, shedding its spores.</p></figcaption>
+</figure>
+
+<p id="p-402"><b>402. Study of a typical fern.</b>—Observe the size and
+general outline of the fronds, and note whether those of
+the same plant are all alike, or if they differ in any way,
+and how. Observe the
+shape and texture of the
+divisions or pinnæ composing
+the frond, their
+mode of attachment to
+the rachis, and whether
+they are simple, or
+notched, or branched in
+any way. Hold a pinna
+up to the light and notice
+the veining. Is it like any
+of the kinds described in
+<a href="#p-171">171</a>, <a href="#p-172">172</a>? In what respect
+is it different?
+This forked venation is
+a very general characteristic
+of ferns. When the
+forks do not reticulate or
+intercross, the veins are
+said to be free; are they
+free in your specimen, or
+reticulated? Make a<span class="pagenum" id="Page_346">[Pg 346]</span>
+sketch, labeling the primary branches of the frond, <em>pinnæ</em>
+(sing., <em>pinna</em>), the secondary ones, if any, <em>pinnules</em>, and the
+common stalk that supports them, <em>stipe</em>. Note the color,
+texture, and surface of the stipe. If any appendages are
+present, such as hairs, chaff, or scales (in Pteris, nectar
+glands), notice whether they are equally distributed. If not,
+where are they most abundant?</p>
+
+<p>Examine the mode of attachment of the stipes to their
+underground axis. Break one away and examine the scar.
+Compare with your drawings of leaf scars and with <a href="#i_101a">Fig.
+105</a>. Do the stipes grow from a root or a rhizome? How
+do you know? Do you find any remains of leafstalks of
+previous years? How does the rootstock increase in
+length? Measure some of the internodes; how much did
+it increase each year? Cut a cross section and look for
+the ends of the fibrovascular bundles. Trace their course
+through several internodes. Do they run straight, or do
+they turn or bend in any way at the nodes? If so, where
+do they go? Do you see anything like roots? Where do
+they originate? Put one of them under the microscope and
+find out whether they are roots or hairs.</p>
+
+<p>True roots are first developed in the pteridophytes. Since
+those of the fern spring from an underground stem, to what
+class of roots do they belong? (83.)</p>
+
+<p id="p-403"><b>403. Minute study of a fern stem.</b>—Place a very thin
+section of a fern rhizoma, or of the stipe of a frond, under
+the microscope. Except in very young stems the vascular
+bundles are arranged in a ring, or sometimes in two or
+more rings (<a href="#i_357">Fig. 492</a>), with plates of strengthening tissue,
+<i>l</i>, <i>l</i>, between the inner and outer rings. Notice the inner
+epidermal layer of hard brown tissue, and within that, the
+soft parenchyma, which fills the rest of the interior. Test
+it with iodine and observe how rich in starch it is. If the
+section of a petiole is under observation, the details will
+be somewhat different; would you expect to find as much
+starch in the stipe as in the rootstock? Why, or why not?</p>
+
+<p><span class="pagenum" id="Page_347">[Pg 347]</span></p>
+
+
+<p>Make a longitudinal
+section of a rhizome
+through the point
+where a leafstalk is
+attached and trace the
+course of the bundles.
+This will be facilitated
+if the specimen has
+stood in eosin solution
+a few hours. Make
+enlarged drawings of
+both sections, labeling
+all the parts.</p>
+
+<table class='autotable'>
+<tr><td class='wd60 vab'>
+<figure class="figcenter illowp95" id="i_357" style="max-width: 30em;">
+  <img class="w100" src="images/i_357.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 492.</span>—Diagram of a cross section through
+the stem of a fern (<i>Pteris</i>): <i>s</i>, <i>s</i>, <i>s</i>, rings of fibrovascular
+bundles; <i>l</i>, <i>l</i>, plates of strengthening tissue,
+with a ring of fibrovascular bundles between them;
+<i>lp</i>, zone of strengthening fibers; <i>r</i>, cortex; <i>e</i>,
+epidermis.</p></figcaption>
+</figure>
+</td><td class='vab'>
+<figure class="figcenter illowp95" id="i_357a" style="max-width: 30em;">
+  <img class="w100" src="images/i_357a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 493-494.</span>—Parts of
+fertile pinnæ: 493, of <i>polypodium</i>,
+enlarged, showing the sori
+without indusium; 494, of <i>pellea</i>,
+showing indusium formed by the
+revolute margin.</p></figcaption>
+</figure></td></tr></table>
+
+<p>Clearly differentiated
+conducting bundles
+occur in the mosses,
+but they are of much simpler structure than in the pteridophytes,
+consisting usually of a single central strand, and are
+found more frequently in the leaves
+than in the stems. A true vascular
+structure appears first in the pteridophytes,
+whence these plants are
+distinguished as <em>vascular cryptogams</em>.</p>
+
+<p id="p-404"><b>404. Fructification.</b>—Examine
+the back of a fruiting frond; what
+do you find there? These dots are
+the <em>sori</em> (sing., <em>sorus</em>), or spore clusters,
+and the fronds or pinnæ bearing
+them are said to be <em>fertile</em>. Are
+there any differences of size, shape,
+etc., between the fertile and the
+sterile fronds of your specimen?
+between the fertile and the sterile pinnæ? On what part
+of the frond are the fertile pinnæ borne? Notice the shape
+and position of the sori, and their relation to the veins,
+whether borne at the tips, in the forks, on the upper side<span class="pagenum" id="Page_348">[Pg 348]</span>
+(toward the margin), or the lower (toward the midrib).
+Look for a delicate membrane (<i>indusium</i>) covering the sori,
+and observe its shape and mode of attachment. If the
+specimen under examination
+is a polypodium, there will be
+no indusium; if a maidenhair,
+or a bracken, it will be
+formed of the revolute margin
+of the pinna. In lady
+fern and Christmas fern (<i>Aspidium</i>),
+the sori frequently
+become confluent, that is, so
+close together as to appear
+like a solid mass. Sketch a
+fertile pinna as it appears under the lens, bringing out all
+the points noted.</p>
+
+<figure class="figcenter illowp70" id="i_358" style="max-width: 30em;">
+  <img class="w100" src="images/i_358.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 495-496.</span>—Christmas fern (<i>Aspidium</i>):
+495, part of a fertile frond, natural
+size; 496, a pinna enlarged, showing the
+sori confluent under the peltate indusia.</p></figcaption>
+</figure>
+
+<figure class="figcenter illowp90" id="i_358a" style="max-width: 50em;">
+  <img class="w100" src="images/i_358a.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 497-500.</span>—Spores of pteridophytes, magnified:
+497, a fern spore; 498, 499, two views of a spore of a club
+moss; 500, spore of a common horsetail (<i>Equisetum arveuse</i>).</p></figcaption>
+</figure>
+
+<p id="p-405"><b>405. The spore cases.</b>—Look under the indusium at
+the cluster of little stalked circular appendages (<a href="#i_355">Fig. 490</a>).
+These are the <em>sporangia</em>, or spore cases, in which the reproductive
+bodies are borne. Place one of them under the
+microscope, and it will be found to consist of a little stalked
+circular body like a tennis racket (<a href="#i_355">Fig. 491</a>), surrounded
+by a jointed ring
+called the <em>annulus</em>.
+Watch a
+few moments and
+see if you can
+find out the use
+of the annulus.
+If not, warm the
+slide and you will probably see the ring straighten itself
+with a sudden jerk, rupturing the wall of the sporangium
+and discharging the spores with considerable force. If this
+does not happen, add a drop of strong glycerine to a specimen
+mounted in water; the rupture will be apt to follow
+quickly. What causes it, in either case? [<a href="#p-56">56</a>, (1); <a href="#exp-19">Exp. 19</a>.]</p>
+
+<p><span class="pagenum" id="Page_349">[Pg 349]</span></p>
+
+<p id="p-406"><b>406. The sporophyte.</b>—The spores found in such abundance
+on the fertile pinnæ; are all alike, and each one is
+capable of germinating and continuing the work of reproduction
+as effectually as the sexual spores of the bryophytes.
+The fertile frond, or part of a frond, on which they are borne
+is called a <em>sporophyll</em> (spore-bearing leaf), and the entire
+plant is the <em>sporophyte</em>, which, with its crop of spores, makes
+up one generation.</p>
+
+<p>It is important to observe that in the ferns and in all pteridophytes
+the sporophyte is the conspicuous and highly
+organized body that is commonly recognized as the normal
+growing plant; while with the bryophytes just the reverse
+holds true,—the sexual generation, or gametophyte, represents
+the normal plant structure, while the sporophyte is
+an insignificant appendage
+which never attains an
+independent existence.
+Broadly speaking, in bryophytes,
+it is a spore fruit;
+in the pteridophytes and
+spermatophytes a highly
+developed plant.</p>
+
+<figure class="figright illowp50" id="i_359" style="max-width: 50em;">
+  <img class="w100" src="images/i_359.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 501, 502.</span>—Prothallium of a common
+fern (<i>Aspidium</i>): 501, under surface, showing
+rhizoids, <i>rh</i>, antheridia, <i>an</i>, and archegonia,
+<i>ar</i>; 502, under surface of an older gametophyte,
+showing rhizoids, <i>rh</i>, young sporophyte,
+with root, <i>w</i>, and leaf, <i>b</i>.</p></figcaption>
+</figure>
+
+<p id="p-407"><b>407. The gametophyte.</b>—When
+one of these asexual
+spores germinates, it
+produces, not a fern plant
+like the one that bore it,
+but a small, heart-shaped
+body like that shown in <a href="#i_359">Fig. 501</a>. Examine one of these bodies
+carefully with a lens. Observe that there are no veins nor
+fibrovascular bundles, and the whole body of the plant seems
+to consist of one uniform tissue. Compare it with the forked
+apex of a branching thallus of a liverwort. Do you perceive
+any points of similarity? The two are, in fact, morphologically
+the same. This heart-shaped body is called a <em>prothallium</em>,
+and is the gametophyte of the fern. It may be of<span class="pagenum" id="Page_350">[Pg 350]</span>
+different shapes, and in some species is branching and filamentous,
+like the protonema of a moss. Generally, however, it
+is flat and more or less two-lobed, as shown in <a href="#i_359">Fig. 501</a>. It
+is small and inconspicuous and very short-lived, being of
+importance only in connection with the work of reproduction.</p>
+
+<p>Look with your lens for a cluster of small, bottle-shaped
+bodies just below the deep cleft in the heart. If you cannot
+make out what they are, put a thin section through
+a part of the prothallium containing one under the microscope,
+and you will see that they are the archegonia. Lower
+down among the rhizoids, near the pointed base, will be
+found the antheridia. In some species the prothalli are
+diœcious, one kind bearing antheridia, the other archegonia,
+but this is rare among the true ferns.</p>
+
+<figure class="figright illowp50" id="i_360" style="max-width: 30em;">
+  <img class="w100" src="images/i_360.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 503.</span>—Young archegonium of a fern,
+magnified: <i>K</i>, neck canal cell; <i>K′</i>, ventral
+canal cell: <i>O</i>, egg cell.</p></figcaption>
+</figure>
+
+<p id="p-408"><b>408. Fertilization.</b>—This process is the same in all essentials
+as in the bryophytes. As in other cryptogams, it can
+take place only under
+water,—a circumstance
+which points to an aquatic
+origin for this sub-kingdom,
+and through them to the
+entire flora of the globe.
+The archegonia differ
+somewhat in shape from
+those of the liverworts and
+mosses, but a section under
+the microscope will show
+that they consist of essentially
+the same parts. On
+account of the similarity of
+these organs, the pteridophytes
+and bryophytes are often classed together as <i>Archegoniates</i>.</p>
+
+<p id="p-409"><b>409. Alternation of generations.</b>—Among the section of
+ferns that we have been considering, the order of alternation
+corresponds in all essentials to that prevailing among the<span class="pagenum" id="Page_351">[Pg 351]</span>
+bryophytes, and may be represented by the same formula.
+The chief difference is in the relatively much greater importance
+of the sporophyte, which may be expressed by
+putting it first:—</p>
+
+<table class="autotable fs80 alternation">
+<tr>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>fg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>fg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"><i>S</i> ⟶ <i>o</i> ⟶ <i>G</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"> <i>oös</i> ⟶ <i>S</i> ⟶ <i>o</i> ⟶ <i>G</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>oös</i> ⟶ <i>S</i> ⟶ <i>o</i> ⟶ <i>G</i> etc.</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>mg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>mg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+</tr>
+</table>
+
+<p>But some of the pteridophytes—of which the Selaginella
+offers a conspicuous example—have differentiated their<span class="pagenum" id="Page_352">[Pg 352]</span>
+asexual spores (<i>o</i> of the formula) into two kinds, large and
+small, known respectively as <em>megaspores</em> and <em>microspores</em>.
+The prothallia developed by the former bear archegonia
+containing female gametes only; those by the latter, antheridia
+containing male gametes—while in the diœcious bryophytes,
+the archegonial and antheridial thalli are produced
+by spores of the same kind.</p>
+
+<figure class="figcenter illowp74" id="i_361" style="max-width: 75em;">
+  <img class="w100" src="images/i_361.jpg" alt="">
+  <figcaption><p><span class="smcap">Figs. 504.-508.</span>—A kind of pteridophyte (<i>Selaginella martensii</i>) with its organs of
+fructification: 504, a fruiting branch; 505, a microsporophyll with a microsporangium,
+showing microspores through a rupture in the wall; 506, a megasporophyll
+with a megasporangium; 507, megaspores; 508, microspores. (<i>From</i> <span class="smcap">Coulter’s</span>
+“Plant Structures.”)</p></figcaption>
+</figure>
+
+<p>The differentiation of the asexual spores in the higher
+pteridophytes gives rise to corresponding changes in the
+sporangia that bear them, and even in the sporophylls themselves,
+one kind bearing microsporangia only, the other
+megasporangia. In this way the differentiation of sex is
+pushed back, step by step, until it virtually begins with the
+sporophyte, or asexual generation.</p>
+
+<p>Using the same terms as before, and representing the microspores
+by the abbreviation <i>mo</i>, the megaspores by <i>Mo</i>,
+the archegonial gametophyte by <i>arG</i>, the antheridial by
+<i>anG</i>, the formula may be modified to express this more complicated
+process of alternation, as follows:—</p>
+
+<table class="autotable fs80 alternation">
+<tr>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>Mo</i> ⟶ <i>arG</i> ⟶ <i>fg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>Mo</i> ⟶ <i>arG</i> ⟶ <i>fg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"><i>S</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"> <i>oös</i> ⟶ <i>S</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>oös</i> ⟶ <i>S</i> etc.</td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>mo</i> ⟶ <i>anG</i> ⟶ <i>mg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>mo</i> ⟶ <i>anG</i> ⟶ <i>mg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+</tr>
+</table>
+
+<p class="noindent">Comparing this formula with the preceding, it will be seen
+that the increased complexity affects the sporophyte at the
+expense of the gametophyte, which has now become a mere
+dependent on the former.</p>
+
+<p id="p-410"><b>410. Advantages of alternation.</b>—This roundabout mode
+of reproduction would hardly have been developed unless it
+had been of some benefit to the plants in which it occurs.
+The chief advantage seems to be in more rapid multiplication
+and consequently better chance to propagate the species, as
+compared with the slow process of sexual reproduction were
+the plant confined to that method alone. Only one plant is
+produced by each oöspore, and if this were a gametophyte
+with its limited number of archegonia, multiplication would<span class="pagenum" id="Page_353">[Pg 353]</span>
+be slow; but the sporophyte with its millions of spores, each
+capable of producing a new individual, enables the species to
+multiply indefinitely. At the same time the interposition of
+a gametophyte, or sexual generation, secures the introduction
+of a new strain with effects analogous to those of cross
+fertilization.</p>
+
+<figure class="figright illowp20" id="i_363" style="max-width: 20em;">
+  <img class="w100" src="images/i_363.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 509.</span>—Part
+of the fruiting
+stem of a
+scouring rush,
+<i>Equisetum limosum</i>,
+showing the
+cone-like spore
+cluster. (<i>After</i>
+<span class="smcap">Gray</span>.)</p></figcaption>
+</figure>
+
+<p id="p-411"><b>411. Classification of pteridophytes.</b>—In our study of
+this group, the ferns have been taken as the type because
+they are the most familiar and most widely
+distributed of all the vascular cryptogams.
+But while they exceed in numbers, both of
+individuals and species, all the other orders
+combined, they form only one division of three
+great groups that make up the class Pteridophyta.
+These groups are: (1) ferns, under
+which are included, besides the true ferns, two
+widely differing orders, with the grape ferns
+and adder’s-tongue in one, and the water ferns
+in the other; (2) the club mosses, embracing
+the two subdivisions of <i>Lycopodium</i> and <i>Selaginella</i>;
+(3) the horsetail family, including
+horsetails and scouring rushes. Orders (2)
+and (3) are grouped together as cone-bearing
+(strobilaceous) pteridophytes, because their
+sporangia are clustered in oblong heads, or
+<em>strobiles</em> (<a href="#i_363">Fig. 509</a>), somewhat like the cones of
+the pine. The orders of pteridophytes differ
+greatly among themselves, but agree in possessing
+certain characteristics that point to
+their derivation from a common ancestry.</p>
+
+<p id="p-412"><b>412. Distinction between pteridophytes and
+bryophytes.</b>—In passing from the Thallophytes
+and Bryophytes to the vascular cryptogams, we cross
+the widest chasm in the vegetable kingdom—a gap relatively
+as great as that between vertebrates and invertebrates among
+animals. The most important modifications that discriminate<span class="pagenum" id="Page_354">[Pg 354]</span>
+the two groups are: (1) the presence in Pteridophytes
+of a highly organized vascular system accompanied by a
+well-marked differentiation of the plant body into root and
+stem; (2) increased importance and complexity of the sporophyte
+with proportionate diminution of the gametophyte.</p>
+
+<p>While vessels for conducting water occur in some of the
+bryophytes <a href="#p-403">(403)</a>, a well-defined vascular system and true
+roots are met with first in the Pteridophytes. The change
+in the relative importance of sporophyte and gametophyte
+is so marked that in Selaginella, the genus which approaches
+nearest in structure to the seed-bearing plants, the suppression
+of the gametophyte has proceeded so far that it never
+leads an independent existence at all and is difficult even to
+recognize as a distinct individual.</p>
+
+
+<h4>Practical Questions</h4>
+
+<div class="blockquot">
+
+<p>1. Have ferns any economic use—that is, are they good for food,
+medicines, etc.?</p>
+
+<p>2. What is their chief value?</p>
+
+<p>3. Under what ecological conditions do they grow?</p>
+
+<p>4. Are they often attacked by insects, or by blights and disease of
+any kind?</p>
+
+<p>5. Of what advantage is it to ferns to have their stems underground,
+in the form of rootstocks? (<a href="#p-321">321</a>.)</p>
+
+<p>6. What causes the young frond of ferns to unroll? (<a href="#p-54">54</a>, <a href="#p-98">98</a>.)</p>
+
+<p>7. Name the ferns indigenous to your neighborhood.</p>
+
+<p>8. Which of these are most ornamental, and to what peculiarities of
+structure do they owe that quality?</p>
+
+<p>9. Are cultivated ferns usually raised from the spores or in some
+other way? Why?</p>
+
+<p>10. After the great eruption of <a id="tn_354">Krakatoa</a> in 1883, by which the vegetation
+of the island was completely destroyed, ferns were the first plants
+to reappear. Explain why. (<a href="#p-19">19</a>; <a href="#exp-17">Exp. 17</a>.)</p>
+</div>
+
+
+<h3 id="CH_X_VIII">VIII. THE RELATION BETWEEN CRYPTOGAMS AND
+SEED PLANTS</h3>
+
+<p id="p-413"><b>413. No break in the chain of life.</b>—The great gap that
+was once supposed to exist between the cryptogams and
+phanerogams has been bridged over by the discovery of<span class="pagenum" id="Page_355">[Pg 355]</span>
+analogies in the reproductive processes of the two groups
+that connect them together as successive links in one continuous
+chain of vegetable life. It is therefore very important
+to have a clear understanding of the nature and meaning of
+these processes, for the chief turning points in the life history
+of the different groups of plants are connected with
+them, their natural relationships to each other, and their
+distribution according to their respective places in the evolutionary
+scale, being determined largely by a comparison of
+their modes of continuing the life of the group.</p>
+
+<p id="p-414"><b>414. Alternation of generations in seed plants.</b>—This
+process, so conspicuous among Bryophytes and Pteridophytes,
+and not unknown among Thallophytes, is universal
+among seed plants (Spermatophytes) also, though in so
+masked a form that it is not easy to recognize without a
+more detailed study than would be practicable within the
+limits of a book like this. Briefly, we may say that the
+stamens of spermatophytes, and the pistils, or rather the
+carpels, which we have seen to be transformed leaves <a href="#p-298">(298)</a>,
+represent the sporophylls <a href="#p-406">(406)</a> of the higher pteridophytes.
+The pollen sacs and ovules are sporangia, bearing microspores
+and megaspores <a href="#p-409">(409)</a>, represented respectively by
+the pollen grains in the anther and the embryo sac in the
+ovule. These go through a series of microscopic changes in
+the body of the ovule analogous to the production of the
+oöspore in the archegonia of ferns and liverworts, but the
+process is so obscure that to an ordinary observer the pollen
+grains and the ovule appear to be the real gametes, and were
+long supposed to be such. The fertilized germ cell in the
+embryo sac <a href="#p-251">(251)</a> corresponds to an oöspore; the embryo sac
+with the endosperm found in all seeds (previous to its absorption
+by the cotyledons) is a rudimentary gametophyte; and
+the embryo in the matured seed is the undeveloped sporophyte,
+destined, after germination and further growth, to
+produce a new generation with its recurrent cycle of alternating
+phases.</p>
+
+<p><span class="pagenum" id="Page_356">[Pg 356]</span></p>
+
+<figure class="figleft illowp50" id="i_366" style="max-width: 40em;">
+  <img class="w100" src="images/i_366.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 510.</span>—Diagrammatic section through the
+ovule of a gymnosperm belonging to the spruce
+family: <i>i</i>, integument covering the ovule; <i>e</i>, endosperm
+(corresponding to female gametophyte),
+which fills the embryo sac, containing two archegonia,
+<i>a</i>; <i>o</i>, egg cell; <i>p</i>, pollen grains; <i>t</i>, pollen
+tubes entering the neck, <i>c</i>, of the archegonia.</p></figcaption>
+</figure>
+
+<p>In the gymnosperms,—pines, yews, cycads, etc.,—which
+represent the most ancient and primitive type of existing
+seed-bearing plants,
+the similarity of these
+processes to those of
+certain of the pteridophytes
+is very striking,
+and it was through
+the study of these that
+the sequences of the
+process were traced in
+the much more obscure
+form in which they
+occur among the angiosperms.
+From the
+endosperm in the seeds
+of gymnosperms archegonia
+were found to be
+developed (<a href="#i_366">Fig. 510</a>) in
+much the same way as
+in Selaginella, from the
+prothallium, thus
+showing the endosperm
+to be a modified
+and greatly reduced
+gametophyte. In some cases, it has even been found to
+protrude a little way out of the embryo sac and to take on
+a slightly greenish tinge—another reminiscence of its origin.
+Fertilization, too, takes place in precisely the same manner
+as in the pteridophytes, except that in all but the ginkgo
+and the cycads, the fertilizing cells in the pollen grains are
+non-motile, and find their way to the ovule by growing down
+into the embryo sac with the pollen tube, instead of swimming
+to it—an adaptation probably brought about in response
+to changed condition during the course of evolution from
+aquatic to terrestrial life.</p>
+
+<p><span class="pagenum" id="Page_357">[Pg 357]</span></p>
+
+<p>The analogies between the sequence of alternations in the
+two classes will be made clearer by a comparison of the
+accompanying diagrams. The corresponding terms applied
+to the various organs stand in the same vertical row. Diagram
+(1) shows the process as it takes place in the more
+highly developed Pteridophytes; diagram (2) the corresponding
+phases in angiosperms.</p>
+
+<p class="center fs80 cb">PTERIDOPHYTES</p>
+
+<table class="autotable fs80 alternation">
+<tr>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>mospl</i> ⟶ <i>mic</i> ⟶ <i>mo</i> ⟶ <i>anG</i> ⟶ <i>ant</i> ⟶ <i>mg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc">(1) <i>S</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"> <i>öos</i> ⟶ <i>S</i></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>Mospl</i> ⟶ <i>Mgc</i> ⟶ <i>Mo</i> ⟶ <i>arG</i> ⟶ <i>arc</i> ⟶ <i>fg</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+</tr></table>
+
+<div class='mth'>
+<p class="fs80"><i>mospl</i>, microsporophyll; <i>mic</i>, microsporangium; <i>mo</i>, microspores; <i>anG</i>, male
+gametophyte; <i>ant</i>, antheridia; <i>mg</i>, antherozoids. The letters in the lower line
+stand for the corresponding female organs.</p></div>
+
+
+<p class="p2 center fs80">SPERMATOPHYTES</p>
+
+<table class="autotable fs80 gymnosperms">
+<tr>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc vac"><i>st</i> ⟶ <i>an</i> ⟶ <i>pol</i> ⟶ <i>fc</i> ⟶</td>
+<td class='tdc vac'><i>not<br>developed</i></td>
+<td class='tdc vac'> ⟶ <i>gc</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc">(2) <i>S</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"> <i>öos</i> ⟶ <i>S</i></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc">╲</td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc">╱</td>
+<td class="tdc"></td>
+</tr>
+<tr>
+<td class="tdc"></td>
+<td class="tdc"></td>
+<td class="tdc"><i>p</i> ⟶ <i>ov</i> ⟶ <i>em</i> ⟶ <i>end</i> ⟶</td>
+<td class='tdc vac'><i>developed<br>only in<br>gymnosperms</i></td>
+<td class='tdc vac'> ⟶ <i>ec</i></td>
+<td class="tdc"></td>
+<td class="tdc"></td>
+</tr></table>
+
+<p class="fs80"><i>st</i>, stamen; <i>an</i>, anther; <i>pol</i>, pollen; <i>fc</i>, food cells in pollen grain; <i>gc</i>, generative
+cell; <i>p</i>, pistil; <i>ov</i>, ovules; <i>em</i>, embryo sac; <i>end</i>, endosperm; <i>ec</i>, egg cell.</p>
+
+<p id="p-415"><b>415. Disappearance of the gametophyte.</b>—The seed is a
+comparatively recent development in plant evolution. It
+has no counterpart anywhere among the cryptogams, but is
+strictly characteristic of the three great orders of Spermophytes:
+Monocotyl, Dicotyl, and Gymnosperms, which
+compose the greater part of the vegetation of the globe.
+Structurally, it is a matured sporangium containing a rudimentary
+sporophyte (the embryo), and a reduced gametophyte
+(the embryo sac), which, under the form of endosperm,
+has dwindled to an insignificance that makes it difficult to
+recognize it as a phase in an alternation of generations.</p>
+
+<p id="p-416"><b>416. Significance of the sporophyte.</b>—The gametophyte
+is obviously a more ancient and primitive structure than the
+sporophyte, which first becomes prominent in the ferns and<span class="pagenum" id="Page_358">[Pg 358]</span>
+their allies. The sudden and violent break in the succession
+of vegetable life that accompanies the appearance of the
+pteridophytes <a href="#p-412">(412)</a> is probably to be explained by the
+development of a land flora and the necessity of adaptation to
+life in a new medium. The fact that no living cell, whether
+vegetable or animal, can absorb nourishment except in a
+liquid form, seems to point to an aquatic origin more or less
+remote for all life. This inference is further strengthened,
+in the case of plants, by the fact that even in so highly organized
+a group as the pteridophytes, fertilization cannot
+take place except in water. Such a requirement would
+manifestly be a great disadvantage to land plants, and one
+of the first steps in response to the demands of a new habitat
+would be to get rid, as far as possible, of the primitive gametophyte
+with its outgrown adaptations to a liquid medium,
+and to transfer the greater part of the work of reproduction
+to the asexual generation, in which the problem of fertilization
+did not have to be directly met, the asexual spores germinating
+without it. The greater the number of these
+produced, the better the chance that at least some of the
+gametes developed from them would meet the difficult conditions
+of fertilization, and the survival of the species be
+assured. At the same time, in order to meet the requirements
+of terrestrial life successfully, and to provide for continuing
+the sexual generation, correlative changes would have to
+take place in the gametophyte by which the increasing
+uncertainty of fertilization due to structural changes in the
+sporophyte, and the absence of a liquid medium for the conveyance
+of free swimming antherozoids would be avoided.
+This necessity has been met by the development of the pollen
+tube, which bores its way to the egg cell, carrying with it the
+generative cells, which in seed plants have taken the place
+of the more primitive antherozoids. With the concomitant
+reduction of the gametophyte and development of the seed
+habit, the adaptation to land conditions has been made
+complete.</p>
+
+<p><span class="pagenum" id="Page_359">[Pg 359]</span></p>
+
+<p>Roughly speaking, it may be said: (1) that Thallophytes
+are predominantly aquatic; (2) Archegoniates (Bryophytes
+and Pteridophytes), amphibious; (3) Spermophytes, terrestrial;
+(4) that the seed habit is a response to terrestrial
+conditions; and (5) that the increased development of the
+sporophyte was a necessary adaptation to meet those conditions.</p>
+
+
+<h3 id="CH_X_IX">IX. THE COURSE OF PLANT EVOLUTION</h3>
+
+<p id="p-417"><b>417. Plant genealogy.</b>—It has been shown by a study of
+existing forms of plant life that there is no hard and fast
+line of division anywhere between the different groups, but
+that they are all connected by ties of kinship more or less
+defined, according to their distance from a common ancestral
+stock. The geological record points to the same conclusion,
+and our classification of them into families, orders, and species
+is merely a very imperfect genealogical table of their
+supposed pedigrees. This does not mean, however, that we
+can assert positively that such and such a species is derived
+from such or such another, but that both are descended from
+some common intermediate form more or less remote. While
+we have reason to believe that the flowering plants are derived
+through pteridophyte and bryophyte types from some
+of the green algæ, no direct connection has ever been traced
+between any particular kind of flowering plant and any particular
+kind of alga,—or between a liverwort and an alga,
+for that matter,—and probably never will be, because the intermediate
+forms die out, or pass on by variation into other
+lines of development. But while this is true, all the evidence
+we possess does go to show that, since the beginning of life
+on the globe, there has been a general progressive evolution
+from lower and simpler to higher and more complex forms.</p>
+
+<p id="p-418"><b>418. Retrogressive evolution.</b>—While the general course
+of evolution has been upward and onward, the movement has
+not always followed a straight line, but, like a mountain road,<span class="pagenum" id="Page_360">[Pg 360]</span>
+shows many windings and deviations from the direct route.
+The monocotyls furnish a conspicuous example of this departure
+from the general law of progression. It was formerly
+supposed, on account of their greater simplicity of structure,
+that they were a more ancient type than dicotyls, but recent
+investigations point to the conclusion that they are a later
+offshoot, derived from some primitive form of aquatic dicotyl,
+and represent, not an ancient and primitive stock, but a case
+of retrogressive evolution from a higher type. Strong presumptions
+in favor of this view are: (1) that various species
+of dicotyls show an unequal development of the seed leaves,
+amounting, in the bryony, to complete abortion of one of
+them, while some monocotyl seeds show morphological
+characters that can best be explained as survivals, or inheritances,
+from a dicotyl ancestor; (2) the structural resemblances
+between gymnosperms and dicotyls are closer than
+between gymnosperms and monocotyls, which could hardly
+be the case if the latter were the more ancient; (3) the geological
+record does not show them to have appeared before
+dicotyls; (4) the number of cotyledons furnishes no criterion
+as to the relative age of any plant group, since all three types
+are represented among the pteridophytes, where plants are
+found bearing one, two, or more cotyledons.</p>
+
+<p>The theory of their comparatively recent origin from an
+aquatic ancestor is further borne out by the many points of
+similarity between their internal structure and that of hydrophytes
+<a href="#p-318">(318)</a>, and also by the great proportion of aquatic
+plants among them, amounting to thirty-three per cent, while
+in dicotyls the proportion is only four per cent. Can you
+give any reasons, from your examination of their internal
+structure (<a href="#p-113">113</a>, <a href="#p-114">114</a>), for believing that the line of development
+which they have followed is a less effective one for
+meeting conditions now existing on the globe than that attained
+by dicotyls?</p>
+
+<p>We should remember, too, that while progressive evolution
+implies successful adjustment to surroundings, it is possible<span class="pagenum" id="Page_361">[Pg 361]</span>
+to conceive of a state, as our planet approaches the period
+of cosmic debility and decay, when the conditions of existence
+may become progressively more and more unfavorable. In
+this case the course of evolution would be reversed, the higher
+types gradually dying out as the struggle for life became
+more severe, and the tendency would be constantly toward
+lower and simpler forms, until finally all life would become
+extinct on our planet.
+We have no right, however,
+to assume that
+during such a course of
+retrogressive evolution
+the same forms would
+be repeated in reverse
+order as have already
+appeared, because
+there is no reason to
+believe that the conditions
+brought about by
+planetary decline and
+“old age” would be
+the same as those attending
+planetary
+birth and adolescence.</p>
+
+<figure class="figright illowp50" id="i_371" style="max-width: 40em;">
+  <img class="w100" src="images/i_371.jpg" alt="">
+  <figcaption><p><span class="smcap">Fig. 511.</span>—Diagram showing the supposed
+course of plant evolution.</p></figcaption>
+</figure>
+
+<p id="p-419"><b>419. Explanation of
+the diagram.</b>—An attempt
+to show the
+general course of plant
+evolution up to the present time is made in the accompanying
+diagram. The four great divisions, Thallophytes, Bryophytes,
+Pteridophytes, and Spermatophytes, are represented
+by spaces between four horizontal lines arranged one above
+the other in the order of their succession in time and complexity
+of organization. It should be borne in mind that
+these dividing lines are not sharply defined in nature, but
+overlap or indent the territory between them with varying<span class="pagenum" id="Page_362">[Pg 362]</span>
+degrees of irregularity, like the coast line on a map.
+The relative positions of the different orders we have
+been considering are represented by upright and diagonal
+lines, the general course of which, as indicated by the
+arrows, is intended to give an idea of the trend of evolutionary
+progress in the particular group represented by each
+line. No one of these lines is made to originate directly in
+any other, because, with the possible exception of the monocotyls,
+we have no authority for asserting that any such direct
+connection exists between plants as we know them, but only
+that certain types give evidence of descent from a common
+ancestry. This lack of certainty is expressed by placing the
+point of origin for any given line in more or less close proximity
+to the one which is supposed to be the nearest living
+representative of the common ancestor. The line of ferns,
+for instance, is depicted as originating in the region of the
+bryophytes, somewhere in the neighborhood of the liverworts,
+but the two lines nowhere come in contact, because there is
+no evidence that any fern, living or fossil, is directly descended
+from any particular kind of liverwort known to us.
+With these explanations, the diagram shows, in a rough way,
+the generally accepted view of plant relationships as based on
+the evidence at present before us. But in questions of this
+sort it is wise to keep in mind the blunt remark of a famous
+old American statesman, that “only fools and dead people
+never change their opinions.”</p>
+
+
+<h4 id="CH_X_FIELD">Field Work</h4>
+
+<div class="blockquot">
+
+<p>1. If you live in the country, study the appearance of plants affected
+with blights, smuts, rusts, and mildews, and learn to recognize the different
+kinds of disease by their signs. Notice which kinds are most prevalent in
+your neighborhood, and what plants are most affected by them.</p>
+
+<p>2. Notice the different kinds of mushrooms you find growing wild.
+Observe the difference between those that grow on the ground and those
+that grow on logs, stumps, and trees; between those found in the woods
+and those in open ground. Find out how those on the ground get their
+nourishment. Uncover the mycelium, and notice the extent of its surface.<span class="pagenum" id="Page_363">[Pg 363]</span>
+Examine the soil and find out if it contains anything upon which they
+could feed. Note the prevalence of shelf fungi on trees. Examine the
+condition of the wood where they grow, and decide in what ways they
+injure their hosts. Notice whether they abound most on healthy or on
+decaying trunks and boughs, and decide whether this is because the
+fungus prefers that kind of host, or whether the injury it does causes
+the decay, or whether both causes operate together. Notice what fungi
+grow on different trees, and study their preferences in this respect.</p>
+
+<p>3. Observe the different kinds of lichens found in your walks and try
+to distinguish the three classes. Which kind are most abundant in your
+neighborhood? Which least so? Note the situations in which you find
+each kind growing, whether on stumps, trees, rocks, or the ground. Consider
+how the algæ and fungi aid each other in the different positions;
+could either, for instance, exist independently on bald rocks? Notice on
+what kind of trees the different lichens seem to thrive best and on which
+poorly or not at all, and whether the character of the bark—rough,
+smooth, scaly—has anything to do with their choice of a habitat.</p>
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_364">[Pg 364]</span></p>
+
+<h2 class="nobreak" id="APPENDIX">APPENDIX</h2>
+</div>
+
+<h3 id="APP_1">SYSTEMATIC BOTANY</h3>
+
+
+<p><b>Taxonomy, or systematic botany</b>, deals with the family
+relationships of plants in the order of their nearness or remoteness
+with regard to a common line of descent. Its chief
+value is the insight it gives into the course of plant evolution
+and into the nature of the modifications that differentiate
+each group from the ancestral type. While it is not advisable
+to spend too much time in the mere identification of
+species, a sufficient number should be examined and described
+to familiarize the student with the distinctive
+characteristics of the principal botanical orders.</p>
+
+<p><b>Principles of classification.</b>—All the known plants in the
+world, numbering not less than one hundred and twenty
+thousand species of the seed-bearing kind alone, are ranged
+according to certain resemblances of structure, into a number
+of great groups known as families or orders. The names
+of these families are distinguished by the ending <em>aceæ</em>; the
+rose family, for instance, are the <i>Rosaceæ</i>; the pink family,
+<i>Caryophyllaceæ</i>; the walnut family, <i>Juglandaceæ</i>, etc. Each
+of these families is divided into lesser groups called <em>genera</em>
+(singular, <em>genus</em>), characterized by similarities showing a
+still greater degree of affinity than that which marks the
+larger groups or orders; and finally, when the differences
+between the individual plants of a kind are so small as to be
+disregarded, they are considered to form one species; all the
+common morning-glories, for instance, of whatever shade or
+color, belong to the species <i>Ipomea purpurea</i>. The small
+differences that arise within a species as to the color and<span class="pagenum" id="Page_365">[Pg 365]</span>
+size of flowers, and other minor points, constitute mere
+varieties, and have no special names applied to them. The
+line between varieties and species is not clearly defined, and
+in the nature of things can never be, since progressive development,
+through unceasing change, is the law of all
+life.</p>
+
+<p>In botanical descriptions, the name both of the species
+and the genus is given, just as in designating a person, like
+Mary Jones or John Robinson, we give both the surname
+and the Christian name. The genus, or generic name,
+answers to the surname, and that of the species to the
+Christian name—except that in botanical nomenclature
+the order is reversed, the generic, or surname, coming first,
+and the specific or individual name last; for example,
+<i>Ipomea</i> is the generic, or surname, of the morning-glories, and
+<i>purpurea</i> the specific one.</p>
+
+<p><b>How to use the key.</b>—Any good manual will answer the
+purpose. Gray’s “School and Field Book” is, perhaps, the
+best available at present for the states east of the Mississippi.
+Reference to the floral analyses in sections <b>I-IV</b> of
+Chapter VII will make its use clear. Suppose, for instance,
+we want to find out to what botanical species the morning-glory
+or the sweet potato belongs. Turning to the key,
+we find the sub-kingdom of Phænerogams—flowering or
+seed-bearing plants—divided into two great classes, Angiosperms
+and Gymnosperms, as explained in 18. A glance will
+show that our specimen belongs to the former class. Angiosperms,
+again, are divided into the two subclasses of Dicotyledons
+and Monocotyledons (<a href="#p-18">18</a>, <a href="#p-171">171</a>). We at once recognize
+our plant, by its net-veined leaves and pentamerous flowers,
+as a dicotyledon (<a href="#p-171">171</a>, <a href="#p-229">229</a>), and turning again to the key,
+we find this subclass divided into three great groups: Sympetalous
+<a href="#p-211">(211)</a>, called also Monopetalous and Gamopetalous;
+Apopetalous, or Polypetalous <a href="#p-211">(211)</a>, and Apetalous—having
+no petals or corolla. A glance will refer our blossom to the
+sympetalous or monopetalous group, which we find divided<span class="pagenum" id="Page_366">[Pg 366]</span>
+into two sections, characterized by the superior or inferior
+ovary (<a href="#p-218">218</a>, <a href="#p-225">225</a>). Further examination will show that the
+morning-glory belongs to the former class, which is in turn
+divided into two sections, according as the corolla is <em>regular</em>,
+or <em>more or less irregular</em>. We see at once that we must look
+for our specimen in the group having regular corollas. This
+we find again subdivided into four sections, according to the
+number and position of the stamens, and we find that the
+morning-glory falls under the last of these,—“Stamens as
+many as the lobes or parts of the corolla and alternate
+with them.” A very little further search brings us to the
+family <i>Convolvulaceæ</i>, and turning to that title in the descriptive
+analysis, we find under the genus, <i>Ipomea</i>, a full
+description of the common morning-glory, in the species
+<i>Ipomea purpurea</i>, and of the sweet potato in the species
+<i>Ipomea batatas</i>.</p>
+
+<p><b>Making collections.</b>—Mere labeled aggregations of species
+are not recommended, but the collection of examples illustrating
+special points in morphology and plant variation
+may be made with profit; such, for instance, as the adaptations
+observed in tendrils and stipular appendages, the
+various modifications of leaves and stems to serve other
+than their normal purposes, or the different forms of leaves
+and flowers on the same stem, or on different plants of the
+same species. A collection made with some specific object
+in view would also be instructive, and might prove of great
+value; for instance, to get together examples of all the
+troublesome weeds of a locality for the purpose of studying
+their habits and devising means for their eradication; or of
+all the native useful plants, with detailed analyses of their
+economic properties, and observations on their habits and the
+practicability of further developing them. In short, wherever
+collecting is carried on, it should be done with some object
+other than the mere identification of species, which often
+results in greater detriment to the wild plants of a neighborhood
+than profit to the collector.</p>
+
+<p><span class="pagenum" id="Page_367">[Pg 367]</span></p>
+
+
+<h3 id="APP_2">WEIGHTS, MEASURES, AND TEMPERATURES</h3>
+
+<p>As the metric system of weights and measures and the
+Centigrade appraisement of temperatures are universally
+employed in scientific works, the following tables showing
+the equivalents in our common English standards of those
+in most frequent use, are given for the convenience of
+students who have not already familiarized themselves with
+the subject. The values given are approximate only, but will
+answer for all practical purposes, except in cases where very
+great exactitude is required. The micron, or micrometer,
+is used principally by scientific investigators for measuring
+extremely minute objects seen under the microscope.</p>
+
+
+<p class="p2 center fs80"><span class="smcap">Measures of Length</span></p>
+
+
+<table class="autotable fs80 wd80">
+<tr><td class="bt" colspan="3"></td></tr>
+<tr><td class="bt" colspan="2"></td><td class="bt bl"></td></tr>
+<tr>
+<td class="tdc smcap" colspan="2">Metric</td>
+<td class="tdc bl smcap">English Equivalents</td>
+</tr>
+<tr><td class="bt"></td><td class="bt bl"></td><td class="bt bl"></td></tr>
+<tr>
+<td class="tdl">Kilometer</td>
+<td class="tdl bl wd20">km.</td>
+<td class="tdl bl wd50">⅔ of a mile.</td>
+</tr>
+<tr><td class="bt"></td><td class="bt bl"></td><td class="bt bl"></td></tr>
+<tr>
+<td class="tdl">Meter</td>
+<td class="tdl bl">m.</td>
+<td class="tdl bl">39 inches.</td>
+</tr>
+<tr><td class="bt"></td><td class="bt bl"></td><td class="bt bl"></td></tr>
+<tr>
+<td class="tdl">Decimeter</td>
+<td class="tdl bl">dm.</td>
+<td class="tdl bl">4 inches.</td>
+</tr>
+<tr><td class="bt"></td><td class="bt bl"></td><td class="bt bl"></td></tr>
+<tr>
+<td class="tdl">Centimeter</td>
+<td class="tdl bl">cm.</td>
+<td class="tdl bl">⅖ of an inch.</td>
+</tr>
+<tr><td class="bt"></td><td class="bt bl"></td><td class="bt bl"></td></tr>
+<tr>
+<td class="tdl">Millimeter</td>
+<td class="tdl bl">mm.</td>
+<td class="tdl bl">¹⁄₂₅ of an inch.</td>
+</tr>
+<tr><td class="bt"></td><td class="bt bl"></td><td class="bt bl"></td></tr>
+<tr>
+<td class="tdl">Micron</td>
+<td class="tdl bl">µ</td>
+<td class="tdl bl">¹⁄₂₅₀₀₀ of an inch.</td>
+</tr>
+<tr><td class="bb"></td><td class="bb bl"></td><td class="bb bl"></td></tr>
+</table>
+
+<p class="p2 center fs80"><span class="smcap">Capacity</span></p>
+
+<table class="autotable fs80 wd80">
+<tr><td class="bt" colspan="3"></td></tr>
+<tr>
+<td class="tdl">Liter</td>
+<td class="tdl bl wd20">l.</td>
+<td class="tdl bl wd50">61 cubic inches, or 1 quart, U.S. measure</td>
+</tr>
+<tr><td class="bt"></td><td class="bt bl"></td><td class="bt bl"></td></tr>
+<tr>
+<td class="tdl">Cubic centimeter</td>
+<td class="tdl bl">cc.</td>
+<td class="tdl bl">¹⁄₁₆ of a cubic inch.</td>
+</tr>
+<tr><td class="bb"></td><td class="bb bl"></td><td class="bb bl"></td></tr>
+</table>
+
+<p class="p2 center fs80"><span class="smcap">Weight</span></p>
+
+<table class="autotable fs80 wd80">
+<tr><td class="bt" colspan="3"></td></tr>
+<tr>
+<td class="tdl">Kilogram</td>
+<td class="tdl bl wd20">kg., or kilo.</td>
+<td class="tdl bl wd50">2⅕ pounds.</td>
+</tr>
+<tr><td class="bt"></td><td class="bt bl"></td><td class="bt bl"></td></tr>
+<tr>
+<td class="tdl" rowspan="2">Gram</td>
+<td class="tdl bl" rowspan="2">gm.</td>
+<td class="tdl bl">15½ grains avoirdupois.</td>
+</tr>
+<tr>
+<td class="tdl bl">¹⁄₂₈ of an ounce avoirdupois.</td>
+</tr>
+<tr><td class="bb"></td><td class="bb bl"></td><td class="bb bl"></td></tr>
+<tr><td class="bb" colspan="3"></td></tr>
+</table>
+
+<p><span class="pagenum" id="Page_368">[Pg 368]</span></p>
+
+
+<p class="p2 center fs80"><span class="smcap">Metric and English Scales</span></p>
+
+<figure class="figcenter illowp75" id="i_378" style="max-width: 50em;">
+  <img class="w100" src="images/i_378.jpg" alt="Rulers comparing millimeters to inches">
+  <figcaption><p class='center'>10 CENTIMETERS = 1 DECIMETER<br>
+  100 MILLIMETERS<br>
+  4 INCHES</p></figcaption>
+</figure>
+
+<p class="p2 center fs80"><span class="smcap">Temperature Equivalents</span></p>
+
+<p>The next table gives the Fahrenheit equivalent, in round
+numbers, for every tenth degree Centigrade from absolute
+zero to the boiling point of water. To find the corresponding
+F. for any degree C., multiply the given C. temperature
+by nine, divide by five, and add thirty-two. Conversely,
+to change F. to C. equivalent, subtract thirty-two, multiply
+by five, and divide by nine.</p>
+
+<table class="autotable fs80 wd20">
+<tr>
+<th class="tdc wd50">Cent.</th>
+<th class="tdc wd50">Fahr.</th>
+</tr>
+<tr><td class="bb" colspan="2"></td></tr>
+<tr>
+<td class="tdr">100</td>
+<td class="tdr">212</td>
+</tr>
+<tr>
+<td class="tdr">90</td>
+<td class="tdr">194</td>
+</tr>
+<tr>
+<td class="tdr">80</td>
+<td class="tdr">176</td>
+</tr>
+<tr>
+<td class="tdr">70</td>
+<td class="tdr">158</td>
+</tr>
+<tr>
+<td class="tdr">60</td>
+<td class="tdr">140</td>
+</tr>
+<tr>
+<td class="tdr">50</td>
+<td class="tdr">122</td>
+</tr>
+<tr>
+<td class="tdr">40</td>
+<td class="tdr">104</td>
+</tr>
+<tr>
+<td class="tdr">30</td>
+<td class="tdr">86</td>
+</tr>
+<tr>
+<td class="tdr">20</td>
+<td class="tdr">68</td>
+</tr>
+<tr>
+<td class="tdr">10</td>
+<td class="tdr">50</td>
+</tr>
+<tr>
+<td class="tdr">0</td>
+<td class="tdr">32</td>
+</tr>
+<tr>
+<td class="tdr">−10</td>
+<td class="tdr">14</td>
+</tr>
+<tr>
+<td class="tdr">−20</td>
+<td class="tdr">−4</td>
+</tr>
+<tr>
+<td class="tdr">−30</td>
+<td class="tdr">−22</td>
+</tr>
+<tr>
+<td class="tdr">−40</td>
+<td class="tdr">−40</td>
+</tr>
+<tr>
+<td class="tdr">−50</td>
+<td class="tdr">−58</td>
+</tr>
+<tr>
+<td class="tdr">−100</td>
+<td class="tdr">−148</td>
+</tr>
+<tr>
+<td class="tdc bt" colspan="2">Absolute zero.</td>
+</tr>
+<tr>
+<td class="tdr">-273</td>
+<td class="tdr">-459</td>
+</tr>
+</table>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<p><span class="pagenum" id="Page_369">[Pg 369]</span></p>
+
+<h2 class="p4 nobreak" id="INDEX">INDEX</h2>
+</div>
+
+<p>(The numbers, unless otherwise designated, refer to paragraphs.)</p>
+
+
+<ul class="index">
+<li class="ifrst">Aborted, <a href="#p-220">220</a>, <a href="#p-291">291</a>.</li>
+
+<li class="indx">Absorption, <a href="#p-58">58</a>, <a href="#p-71">71</a>, <a href="#p-72">72</a>;</li>
+<li class="isub1">Exp. <a href="#exp-39">39</a>.</li>
+<li class="isub1">selective, <a href="#p-60">60</a>.</li>
+
+<li class="indx">Accessory buds, <a href="#p-158">158</a>.</li>
+
+<li class="indx">Accessory fruits, <a href="#p-302">302</a>.</li>
+
+<li class="indx">Adaptation, <a href="#p-206">206</a>, <a href="#p-237">237</a>.</li>
+
+<li class="indx">Adhesive fruits, <a href="#p-20">20</a>;</li>
+<li class="isub1">Exp. <a href="#exp-20">20</a>.</li>
+
+<li class="indx">Adjustment of leaves, <a href="#p-196">196-202</a>.</li>
+
+<li class="indx">Adnate, <a href="#p-374">374</a>.</li>
+
+<li class="indx">Adventitious buds, <a href="#p-65">65</a>, <a href="#p-158">158</a>.</li>
+
+<li class="indx">Adventitious roots, <a href="#p-37">37</a>, <a href="#p-83">83</a>.</li>
+
+<li class="indx">Æcidium, <a href="#p-362">362</a>.</li>
+
+<li class="indx">Aëration, <a href="#p-319">319</a>.</li>
+
+<li class="indx">Aërial roots, <a href="#p-88">88</a>.</li>
+
+<li class="indx">Aggregate fruits, <a href="#p-301">301</a>, <a href="#p-303">303</a>.</li>
+
+<li class="indx">Air space, <a href="#p-114">114</a>, <a href="#p-116">116</a>, <a href="#p-184">184</a>.</li>
+
+<li class="indx">Akene, <a href="#p-234">234</a>, <a href="#p-296">296</a>, <a href="#p-302">302</a>, <a href="#p-305">305</a>.</li>
+
+<li class="indx">Albumin, <a href="#p-3">3</a>.</li>
+
+<li class="indx">Albuminous, <a href="#p-56">56</a>.</li>
+
+<li class="indx">Albuminous seed, <i>i.e.</i>, containing endosperm; Field work, p. <a href="#CH_I_FIELD">28</a>.</li>
+
+<li class="indx">Aleurone, <a href="#p-3">3</a>.</li>
+
+<li class="indx">Algæ, <a href="#p-333">333</a>, <a href="#p-336">336-342</a>.</li>
+
+<li class="indx">Alternate leaves, <a href="#p-168">168</a>.</li>
+
+<li class="indx">Alternation of generations, <a href="#p-395">395</a>, <a href="#p-400">400</a>, <a href="#p-409">409</a>, <a href="#p-414">414</a>.</li>
+
+<li class="indx">Analogous, <a href="#p-108">108</a>.</li>
+
+<li class="indx">Anatropous, Fig. <a href="#i_027a">26</a>.</li>
+
+<li class="indx">Angiosperms, <a href="#p-15">15</a>, <a href="#p-18">18</a>; Fig. <a href="#i_371">511</a>.</li>
+
+<li class="indx">Annuals, <a href="#p-91">91</a>.</li>
+
+<li class="indx">Annulus, <a href="#p-372">372</a>, <a href="#p-405">405</a>.</li>
+
+<li class="indx">Anther, <a href="#p-213">213</a>, <a href="#p-235">235</a>; Figs. <a href="#i_208">270-274</a>.</li>
+
+<li class="indx">Antheridia, <a href="#p-389">389</a>, <a href="#p-394">394</a>, <a href="#p-398">398</a>, <a href="#p-407">407</a>.</li>
+
+<li class="indx">Antheridial, <a href="#p-388">388</a>.</li>
+
+<li class="indx">Antherozoids, <a href="#p-389">389</a>, <a href="#p-392">392</a>, <a href="#p-395">395</a>, <a href="#p-416">416</a>.</li>
+
+<li class="indx">Antisepsis, <a href="#p-355">355</a>.</li>
+
+<li class="indx">Arch of the hypocotyl, <a href="#p-42">42</a>, <a href="#p-44">44</a>.</li>
+
+<li class="indx">Archegonia, <a href="#p-390">390</a>, <a href="#p-394">394</a>, <a href="#p-407">407</a>, <a href="#p-408">408</a>.</li>
+
+<li class="indx">Archegonial, <a href="#p-388">388</a>.</li>
+
+<li class="indx">Archegoniates, <a href="#p-408">408</a>, <a href="#p-416">416</a>.</li>
+
+<li class="indx">Archegonium, <a href="#p-391">391</a>, <a href="#p-394">394</a>, <a href="#p-398">398</a>.</li>
+
+<li class="indx">Asexual generation, <a href="#p-395">395</a>, <a href="#p-399">399</a>, <a href="#p-409">409</a>, <a href="#p-416">416</a>.</li>
+
+<li class="indx">Asexual reproduction, <a href="#p-394">394</a>, <a href="#p-395">395</a>.</li>
+
+<li class="indx">Asexual spore, <a href="#p-395">395</a>, <a href="#p-407">407</a>, <a href="#p-409">409</a>, <a href="#p-410">410</a>, <a href="#p-416">416</a>.</li>
+
+<li class="indx">Assurgent, <a href="#p-95">95</a>.</li>
+
+<li class="indx">Axial placenta, <a href="#p-216">216</a>, <a href="#p-300">300</a>.</li>
+
+<li class="indx">Axil, <a href="#p-100">100</a>, <a href="#p-166">166</a>.</li>
+
+<li class="indx">Axillary buds, <a href="#p-145">145</a>.</li>
+
+<li class="indx">Axis, <a href="#p-64">64</a>, <a href="#p-65">65</a>, <a href="#p-79">79</a>, <a href="#p-152">152</a>, <a href="#p-156">156</a>, <a href="#p-159">159</a>,
+    <a href="#p-161">161</a>.</li>
+
+
+<li class="ifrst">Bacillus, <a href="#p-348">348</a>, <a href="#p-349">349</a>.</li>
+
+<li class="indx">Bacteria, <a href="#p-333">333</a>, <a href="#p-345">345</a>, <a href="#p-347">347-353</a>.</li>
+
+<li class="indx">Bark, <a href="#p-118">118</a>, <a href="#p-119">119</a>, <a href="#p-122">122</a>, p. <a href="#p-128">128</a>, (3).</li>
+
+<li class="indx">Basidia, <a href="#p-375">375</a>.</li>
+
+<li class="indx">Bast, <a href="#p-116">116</a>, <a href="#p-119">119</a>, <a href="#p-122">122</a>.</li>
+
+<li class="indx">Berry, <a href="#p-291">291</a>.</li>
+
+<li class="indx">Biennial, <a href="#p-92">92</a>.</li>
+
+<li class="indx">Bilabiate, <a href="#p-237">237</a>, <a href="#p-243">243</a>.</li>
+
+<li class="indx">Bilateral regularity, <a href="#p-219">219</a>.</li>
+
+<li class="indx">Bilateral zonation, <a href="#p-326">326</a>.</li>
+
+<li class="indx">Black rust, <a href="#p-360">360</a>.</li>
+
+<li class="indx">Blade of leaf, <a href="#p-165">165</a>.</li>
+
+<li class="indx">Biogenetic law, <a href="#p-253">253</a>.</li>
+
+<li class="indx">Biological factors, <a href="#p-309">309</a>.</li>
+
+<li class="indx">Bordered pits, <a href="#p-114">114</a>, <a href="#p-117">117</a>; Fig. <a href="#i_116a">123</a>.</li>
+
+<li class="indx">Boreal, <a href="#p-329">329</a>.</li>
+
+<li class="indx">Bract, <a href="#p-161">161</a>.</li>
+
+<li class="indx">Bryophytes, <a href="#p-334">334</a>, <a href="#p-385">385-401</a>.</li>
+
+<li class="indx">Bud scales, <a href="#p-147">147-149</a>.</li>
+
+<li class="indx">Buds, <a href="#p-145">145</a>, <a href="#p-155">155-158</a>.</li>
+
+<li class="indx">Bulb, <a href="#p-107">107</a>.</li>
+
+<li class="indx">Button (of mushroom), <a href="#p-370">370</a>.</li>
+
+
+<li class="ifrst">Calyptra, <a href="#p-399">399</a>.</li>
+
+<li class="indx">Calyx, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Cambium, <a href="#p-115">115</a>, <a href="#p-116">116</a>, <a href="#p-120">120</a>, <a href="#p-123">123</a>.</li>
+
+<li class="indx">Cap, <a href="#p-372">372</a>, <a href="#p-373">373</a>.</li>
+
+<li class="indx">Capillarity, <a href="#p-136">136</a>; Exp. <a href="#exp-53">53</a>.</li>
+
+<li class="indx">Capitate, <a href="#p-220">220</a>.</li>
+
+<li class="indx">Caprification, <a href="#p-279">279</a>, <a href="#p-305">305</a>.</li>
+
+<li class="indx">Caprifig, <a href="#p-279">279</a>.</li>
+
+<li class="indx">Capsule, <a href="#p-298">298</a>.</li>
+
+<li class="indx">Carbon, <a href="#p-27">27</a>, <a href="#p-28">28</a>, <a href="#p-62">62</a>.</li>
+
+<li class="indx">Carbon dioxide, <a href="#p-29">29</a>, <a href="#p-63">63</a>, <a href="#p-185">185</a>, <a href="#p-186">186</a>, <a href="#p-187">187</a>, <a href="#p-189">189</a>;
+    Exps. <a href="#exp-23">23</a>, <a href="#exp-25">25</a>.</li>
+
+<li class="indx">Carpels, <a href="#p-216">216</a>, <a href="#p-288">288</a>.</li>
+
+<li class="indx">Caruncle, <a href="#p-13">13</a>.</li>
+
+<li class="indx">Catkin, <a href="#p-161">161</a>.</li>
+
+<li class="indx">Caulicle, <a href="#p-46">46</a>.</li>
+
+<li class="indx">Cedar apples, Fig. <a href="#i_331">456</a>.</li>
+
+<li class="indx">Cell, <a href="#p-6">6</a>, <a href="#p-7">7</a>.</li>
+<li class="isub1">collecting, <a href="#p-184">184</a>.</li>
+<li class="isub1">companion, <a href="#p-114">114</a>.</li>
+
+<li class="indx">Cell sap, <a href="#p-7">7</a>, <a href="#p-110">110</a>.</li>
+
+<li class="indx">Cell wall, <a href="#p-7">7</a>, <a href="#p-183">183</a>.</li>
+
+<li class="indx">Central cylinder, <a href="#p-67">67</a>.</li>
+
+<li class="indx">Central placenta, <a href="#p-216">216</a>, <a href="#p-300">300</a>.</li>
+
+<li class="indx">Chalaza, <a href="#p-13">13</a>.</li>
+
+<li class="indx"><span class="pagenum" id="Page_370">[Pg 370]</span>Chlorophyll, <a href="#p-186">186</a>, <a href="#p-341">341</a>, <a href="#p-366">366</a>.</li>
+
+<li class="indx">Chlorophyll bodies, <a href="#p-184">184</a>, <a href="#p-186">186</a>, <a href="#p-382">382</a>.</li>
+
+<li class="indx">Cion, <a href="#p-65">65</a>.</li>
+
+<li class="indx">Classification, <a href="#p-90">90</a>, <a href="#p-252">252</a>, <a href="#p-283">283</a>, <a href="#p-343">343</a>, <a href="#p-384">384</a>, <a href="#p-411">411</a>,
+    <a href="#p-417">417</a>.</li>
+
+<li class="indx">Cleistogamic flowers, <a href="#p-272">272</a>.</li>
+
+<li class="indx">Climatic zones, <a href="#p-329">329</a>.</li>
+
+<li class="indx">Climbing stems, <a href="#p-96">96-98</a>.</li>
+
+<li class="indx">Clipped seed, p. <a href="#Page_12">12</a> (material).</li>
+
+<li class="indx">Closed bundle, <a href="#p-114">114</a>.</li>
+
+<li class="indx">Close-fertilized, <a href="#p-272">272</a>.</li>
+
+<li class="indx">Cluster cups, <a href="#p-362">362</a>.</li>
+
+<li class="indx">Coccus (pl. cocci), <a href="#p-339">339</a>, <a href="#p-348">348</a>.</li>
+
+<li class="indx">Coiled inflorescence, <a href="#p-162">162</a>.</li>
+
+<li class="indx">Collective fruits, <a href="#p-304">304</a>.</li>
+
+<li class="indx">Colony, <a href="#p-316">316</a>, <a href="#p-337">337</a>, <a href="#p-357">357</a>.</li>
+
+<li class="indx">Color of flowers, <a href="#p-276">276</a>.</li>
+
+<li class="indx">Compass plants, <a href="#p-199">199</a>.</li>
+
+<li class="indx">Complete flower, <a href="#p-219">219</a>.</li>
+
+<li class="indx">Composite, <a href="#p-235">235</a>, <a href="#p-381">381</a>.</li>
+
+<li class="indx">Composite flower, <a href="#p-236">236</a>.</li>
+
+<li class="indx">Compound leaf, <a href="#p-178">178</a>.</li>
+
+<li class="indx">Conduplicate, Figs. <a href="#i_149">159</a>, <a href="#i_149b">160</a>.</li>
+
+<li class="indx">Confluent, <a href="#p-404">404</a>.</li>
+
+<li class="indx">Conifers, <a href="#p-117">117</a>, <a href="#p-327">327</a>.</li>
+
+<li class="indx">Conjugation, <a href="#p-342">342</a>, <a href="#p-394">394</a>.</li>
+
+<li class="indx">Corolla, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Cortex, <a href="#p-64">64</a>, <a href="#p-115">115</a>, <a href="#p-122">122</a>.</li>
+
+<li class="indx">Corymb, <a href="#p-161">161</a>.</li>
+
+<li class="indx">Cotyledon, <a href="#p-11">11</a>, <a href="#p-12">12</a>, <a href="#p-18">18</a>.</li>
+
+<li class="indx">Cross cut, <a href="#p-133">133</a>.</li>
+
+<li class="indx">Cross fertilization, <a href="#p-255">255</a>.</li>
+
+<li class="indx">Cross pollination, <a href="#p-255">255</a>.</li>
+
+<li class="indx">Crustaceous lichen, <a href="#p-384">384</a>.</li>
+
+<li class="indx">Cryptogam, <a href="#p-332">332</a>.</li>
+
+<li class="indx">Crystalloids, <a href="#p-60">60</a>.</li>
+
+<li class="indx">Culture medium, <a href="#p-347">347</a>; p. <a href="#p-306">306</a> (material).</li>
+
+<li class="indx">Cycle, <a href="#p-217">217</a>, <a href="#p-219">219</a>, <a href="#p-229">229</a>.</li>
+
+<li class="indx">Cycle of growth, <a href="#p-50">50</a>.</li>
+
+<li class="indx">Cyme, <a href="#p-162">162</a>.</li>
+
+<li class="indx">Cymose inflorescence, <a href="#p-162">162</a>.</li>
+
+<li class="indx">Cypress knees, <a href="#p-319">319</a>.</li>
+
+
+<li class="ifrst">Deciduous, <a href="#p-203">203</a>.</li>
+
+<li class="indx">Declined, <a href="#p-95">95</a>.</li>
+
+<li class="indx">Decurrent, <a href="#p-374">374</a>.</li>
+
+<li class="indx">Definite annual growth, <a href="#p-153">153</a>.</li>
+
+<li class="indx">Definite inflorescence, <a href="#p-160">160</a>, <a href="#p-162">162</a>.</li>
+
+<li class="indx">Dehiscent fruits, <a href="#p-283">283</a>, <a href="#p-298">298</a>.</li>
+
+<li class="indx">Deliquescent, <a href="#p-144">144</a>.</li>
+
+<li class="indx">Determinate growth, <a href="#p-153">153</a>.</li>
+
+<li class="indx">Determinate inflorescence, <a href="#p-160">160</a>, <a href="#p-162">162</a>.</li>
+
+<li class="indx">Diadelphous, <a href="#p-239">239</a>.</li>
+
+<li class="indx">Diastase, <a href="#p-9">9</a>.</li>
+
+<li class="indx">Dichogamy, <a href="#p-269">269</a>.</li>
+
+<li class="indx">Dichotomous, <a href="#p-152">152</a>; Fig. <a href="#i_146">155</a>.</li>
+
+<li class="indx">Dicotyl, <a href="#p-42">42</a>, <a href="#p-115">115</a>, <a href="#p-116">116</a>, <a href="#p-171">171</a>, <a href="#p-220">220</a>.</li>
+
+<li class="indx">Dicotyledonous, <a href="#p-12">12</a>.</li>
+
+<li class="indx">Differentiate, <a href="#p-245">245</a>, <a href="#p-345">345</a>, <a href="#p-409">409</a>.</li>
+
+<li class="indx">Diffusion, <a href="#p-9">9</a>, <a href="#p-57">57</a>.</li>
+
+<li class="indx">Digestion, <a href="#p-9">9</a>.</li>
+
+<li class="indx">Dimorphic, <a href="#p-270">270</a>.</li>
+
+<li class="indx">Dimorphism, <a href="#p-270">270</a>.</li>
+
+<li class="indx">Dimorphous, <a href="#p-270">270</a>.</li>
+
+<li class="indx">Diœcious, <a href="#p-268">268</a>.</li>
+
+<li class="indx">Disinfection, <a href="#p-355">355</a>.</li>
+
+<li class="indx">Disk flower, <a href="#p-233">233</a>.</li>
+
+<li class="indx">Dispersal of seed, <a href="#p-19">19-25</a>.</li>
+
+<li class="indx">Dominant, <a href="#p-257">257</a>, <a href="#p-258">258</a>.</li>
+
+<li class="indx">Dormant buds, <a href="#p-157">157</a>.</li>
+
+<li class="indx">Dorsal; Figs. <a href="#i_273a">390</a>, <a href="#i_273b">391</a>.</li>
+
+<li class="indx">Drupe, <a href="#p-292">292</a>.</li>
+
+<li class="indx">Dry fruits, <a href="#p-283">283</a>, <a href="#p-293">293-300</a>.</li>
+
+<li class="indx">Duct, <a href="#p-67">67</a>, <a href="#p-111">111</a>, <a href="#p-114">114</a>.</li>
+
+
+<li class="ifrst">Ecological factors, <a href="#p-310">310</a>.</li>
+
+<li class="indx">Ecology, <a href="#p-266">266</a>, <a href="#p-308">308</a>, <a href="#p-310">310</a>.</li>
+
+<li class="indx">Edgings, <a href="#p-134">134</a>.</li>
+
+<li class="indx">Egg cell, <a href="#p-251">251</a>, <a href="#p-391">391</a>.</li>
+
+<li class="indx">Elators, <a href="#p-393">393</a>.</li>
+
+<li class="indx">Embryo, <a href="#p-11">11</a>.</li>
+
+<li class="indx">Embryology, <a href="#p-253">253</a>.</li>
+
+<li class="indx">Embryo sac, <a href="#p-251">251</a>.</li>
+
+<li class="indx">Endodermis, <a href="#p-67">67</a> (b).</li>
+
+<li class="indx">Endosperm, <a href="#p-11">11</a>, <a href="#p-13">13</a>, <a href="#p-14">14</a>, <a href="#p-16">16</a>, <a href="#p-17">17</a>, <a href="#p-414">414</a>.</li>
+
+<li class="indx">Epicotyl, <a href="#p-45">45</a>, <a href="#p-46">46</a>, <a href="#p-47">47</a>.</li>
+
+<li class="indx">Epidermis, <a href="#p-64">64</a>, <a href="#p-115">115</a>, <a href="#p-122">122</a>, <a href="#p-183">183</a>.</li>
+
+<li class="indx">Epigynous, <a href="#p-225">225</a>, <a href="#p-230">230</a>.</li>
+
+<li class="indx">Epiphyte, <a href="#p-87">87</a>, <a href="#p-394">394</a>.</li>
+
+<li class="indx">Essential constituents, <a href="#p-62">62</a>.</li>
+
+<li class="indx">Essential organs, <a href="#p-212">212</a>.</li>
+
+<li class="indx">Evolution, <a href="#p-242">242</a>, <a href="#p-245">245</a>, <a href="#p-265">265</a>, <a href="#p-334">334</a>, <a href="#p-335">335</a>, <a href="#p-401">401</a>,
+    <a href="#p-414">414</a>, <a href="#p-415">415</a>, <a href="#p-417">417</a>, <a href="#p-418">418</a>, <a href="#p-419">419</a>.</li>
+
+<li class="indx">Evolutionary, <a href="#p-253">253</a>, <a href="#p-413">413</a>.</li>
+
+<li class="indx">Excentric attachment, <a href="#p-372">372</a>.</li>
+
+<li class="indx">Excurrent, <a href="#p-144">144</a>, <a href="#p-154">154</a>.</li>
+
+
+<li class="ifrst">Factors, <a href="#p-54">54</a>, <a href="#p-265">265</a>, <a href="#p-310">310</a>.</li>
+
+<li class="indx">Fall of the leaf, <a href="#p-203">203</a>.</li>
+
+<li class="indx">Fascicled roots, <a href="#p-80">80</a>, <a href="#p-81">81</a>.</li>
+
+<li class="indx">Fats, <a href="#p-1">1</a>, <a href="#p-3">3</a>, <a href="#p-4">4</a>.</li>
+
+<li class="indx">Feather-veined, <a href="#p-172">172</a>.</li>
+
+<li class="indx">Ferments, <a href="#p-9">9</a>, <a href="#p-356">356</a>.</li>
+
+<li class="indx">Fertile, <a href="#p-404">404</a>.</li>
+
+<li class="indx">Fertile flower, <a href="#p-267">267</a>.</li>
+
+<li class="indx">Fertilization, <a href="#p-247">247</a>, <a href="#p-251">251</a>, <a href="#p-252">252</a>, <a href="#p-392">392</a>, <a href="#p-408">408</a>,
+    <a href="#p-416">416</a>.</li>
+
+<li class="indx">Fibrous roots, <a href="#p-37">37</a>, <a href="#p-78">78</a>, <a href="#p-80">80</a>, <a href="#p-81">81</a>.</li>
+
+<li class="indx">Fibrovascular bundle, <a href="#p-67">67</a>, <a href="#p-114">114</a>, <a href="#p-116">116</a>, <a href="#p-176">176</a>, <a href="#p-288">288</a>.</li>
+
+<li class="indx">Fig wasp, <a href="#p-279">279</a>.</li>
+
+<li class="indx">Filament of the stamen, <a href="#p-213">213</a>;</li>
+<li class="isub1">a hairlike appendage, <a href="#p-341">341</a>, <a href="#p-361">361</a>, <a href="#p-369">369</a>, <a href="#p-393">393</a>, <a href="#p-396">396</a>.</li>
+
+<li class="indx">Filamentous algæ, <a href="#p-340">340</a>, <a href="#p-341">341</a>.</li>
+
+<li class="indx">Fission, <a href="#p-338">338</a>, <a href="#p-394">394</a>.</li>
+
+<li class="indx">Fleshy fruits, <a href="#p-283">283</a>, <a href="#p-288">288-292</a>.</li>
+
+<li class="indx">Floral envelopes, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Foliaceous lichen, <a href="#p-379">379</a>, <a href="#p-384">384</a>.</li>
+
+<li class="indx">Follicle, <a href="#p-298">298</a>.</li>
+
+<li class="indx">Forestry, <a href="#p-139">139-142</a>.</li>
+
+<li class="indx">Forked stems, <a href="#p-152">152</a>.</li>
+
+<li class="indx">Formation, <a href="#p-316">316</a>.</li>
+
+<li class="indx">Free, <a href="#p-218">218</a>, <a href="#p-374">374</a>.</li>
+
+<li class="indx">Free central placenta, <a href="#p-216">216</a>.</li>
+
+<li class="indx">Free gills, <a href="#p-374">374</a>.</li>
+
+<li class="indx">Free ovary, <a href="#p-218">218</a>.</li>
+
+<li class="indx">Free veining, <a href="#p-402">402</a>.</li>
+
+<li class="indx">Freezing, <a href="#p-33">33</a>.</li>
+
+<li class="indx">Frog’s spit, <a href="#p-340">340</a>.</li>
+
+<li class="indx">Frond, <a href="#p-402">402</a>.</li>
+
+<li class="indx">Fruit, <a href="#p-282">282</a>.</li>
+
+<li class="indx">Fruticose lichen, <a href="#p-384">384</a>.</li>
+
+<li class="indx">Function, <a href="#p-41">41</a>.</li>
+
+<li class="indx">Fungi, <a href="#p-333">333</a>, <a href="#p-343">343</a>, <a href="#p-344">344</a>, <a href="#p-345">345</a>, <a href="#p-346">346</a>,
+    <a href="#p-378">378</a>.</li>
+
+<li class="indx">Fungus, <a href="#p-86">86</a>, <a href="#p-364">364</a>.</li>
+
+
+<li class="ifrst">Gametes, <a href="#p-394">394</a>.</li>
+
+<li class="indx">Gametophyte, <a href="#p-394">394</a>, <a href="#p-395">395</a>, <a href="#p-396">396</a>, <a href="#p-406">406</a>, <a href="#p-407">407</a>, <a href="#p-410">410</a>,
+    <a href="#p-412">412</a>, <a href="#p-414">414</a>, <a href="#p-415">415</a>, <a href="#p-416">416</a>.</li>
+
+<li class="indx">Gemmæ, <a href="#p-387">387</a>.</li>
+
+<li class="indx">Generative cell, <a href="#p-249">249</a>, <a href="#p-416">416</a>.</li>
+
+<li class="indx">Geophilous, <a href="#p-321">321</a>.</li>
+
+<li class="indx">Geotropism, <a href="#p-51">51</a>, <a href="#p-52">52</a>, <a href="#p-53">53</a>.</li>
+
+<li class="indx">Germ, <a href="#p-2">2</a>, <a href="#p-11">11</a>.</li>
+
+<li class="indx">Germ cell, <a href="#p-251">251</a>, <a href="#p-414">414</a>.</li>
+
+<li class="indx">Germination, <a href="#p-32">32</a>, <a href="#p-35">35</a>; Exps. <a href="#exp-25">25</a>, <a href="#exp-26">26-29</a>.</li>
+
+<li class="indx">Germs, <a href="#p-352">352</a>, <a href="#p-355">355</a>.</li>
+
+<li class="indx">Gills (of mushroom), <a href="#p-374">374</a>.</li>
+
+<li class="indx">Girdling, <a href="#p-131">131</a>.</li>
+
+<li class="indx">Glutin, <a href="#p-3">3</a>.</li>
+
+<li class="indx">Gourd, <a href="#p-14">14</a>, <a href="#p-290">290</a>.</li>
+
+<li class="indx">Grain, <a href="#p-11">11</a>, <a href="#p-297">297</a>.</li>
+
+<li class="indx">Grain of timber, <a href="#p-133">133</a>, <a href="#p-134">134</a>, <a href="#p-135">135</a>.</li>
+
+<li class="indx">Gravity, <a href="#p-52">52</a>.</li>
+
+<li class="indx">Growth, <a href="#p-48">48-52</a>, <a href="#p-179">179</a>.</li>
+
+<li class="indx">Guard cell, <a href="#p-183">183</a>.</li>
+
+<li class="indx">Gymnosperms, <a href="#p-15">15</a>, <a href="#p-18">18</a>, <a href="#p-117">117</a>, <a href="#p-414">414</a>.</li>
+
+<li class="indx">Gymnosporangium, Fig. <a href="#i_331">456</a>.</li>
+
+
+<li class="ifrst">Halophyte, <a href="#p-317">317</a>, <a href="#p-323">323</a>.</li>
+
+<li class="indx">Haustoria, <a href="#p-85">85</a>.</li>
+
+<li class="indx">Hay bacillus, <a href="#p-348">348</a>, <a href="#p-349">349</a>.</li>
+
+<li class="indx">Head, <a href="#p-161">161</a>.</li>
+
+<li class="indx">Heartwood, <a href="#p-131">131</a>.</li>
+
+<li class="indx">Heliotropic, <a href="#p-200">200</a>.</li>
+
+<li class="indx">Heliotropism, <a href="#p-198">198</a>.</li>
+
+<li class="indx">Herbaceous, <a href="#p-90">90</a>, <a href="#p-94">94</a>, <a href="#p-115">115</a>, <a href="#p-116">116</a>.</li>
+
+<li class="indx">Heredity, <a href="#p-264">264</a>, <a href="#p-265">265</a>.</li>
+
+<li class="indx">Hilum, <a href="#p-12">12</a>, <a href="#p-13">13</a>, <a href="#p-14">14</a>.</li>
+
+<li class="indx">Homologous, <a href="#p-108">108</a>.</li>
+
+<li class="indx">Host plant, <a href="#p-85">85</a>.</li>
+
+<li class="indx">Humus, <a href="#p-75">75</a>, <a href="#p-86">86</a>.</li>
+
+<li class="indx">Hybrid, <a href="#p-256">256</a>.</li>
+
+<li class="indx">Hybridization, <a href="#p-256">256</a>, <a href="#p-257">257</a>, <a href="#p-263">263</a>.</li>
+
+<li class="indx">Hydrophytes, <a href="#p-317">317</a>, <a href="#p-318">318</a>, <a href="#p-319">319</a>.</li>
+
+<li class="indx">Hymenium, <a href="#p-375">375</a>.</li>
+
+<li class="indx">Hymenomycetes, <a href="#p-375">375</a>.</li>
+
+<li class="indx"><span class="pagenum" id="Page_371">[Pg 371]</span>Hyphæ (sing. hypha), <a href="#p-369">369</a>, <a href="#p-380">380</a>.</li>
+
+<li class="indx">Hypocotyl, <a href="#p-11">11</a>, <a href="#p-12">12</a>, <a href="#p-14">14</a>, <a href="#p-46">46</a>.</li>
+<li class="isub1">arched, <a href="#p-42">42</a>, <a href="#p-44">44</a>.</li>
+<li class="isub1">straight, <a href="#p-44">44</a>.</li>
+
+<li class="indx">Hypogynous, <a href="#p-218">218</a>, <a href="#p-225">225</a>.</li>
+
+
+<li class="ifrst">Imbibition, <a href="#p-136">136</a>.</li>
+
+<li class="indx">Imperfect flower, <a href="#p-219">219</a>, <a href="#p-231">231</a>, <a href="#p-267">267</a>.</li>
+
+<li class="indx">Impure hybrid, <a href="#p-258">258</a>, <a href="#p-259">259</a>.</li>
+
+<li class="indx">In-breeding, <a href="#p-254">254</a>.</li>
+
+<li class="indx">Incomplete flower, <a href="#p-219">219</a>.</li>
+
+<li class="indx">Incubation, <a href="#p-354">354</a>.</li>
+
+<li class="indx">Indefinite annual growth, <a href="#p-153">153</a>.</li>
+
+<li class="indx">Indefinite inflorescence, <a href="#p-160">160</a>, <a href="#p-161">161</a>.</li>
+
+<li class="indx">Indefinite number of parts, <a href="#p-229">229</a>.</li>
+
+<li class="indx">Indehiscent fruit, <a href="#p-283">283</a>, <a href="#p-294">294</a>.</li>
+
+<li class="indx">Indeterminate growth, <a href="#p-153">153</a>.</li>
+
+<li class="indx">Indeterminate inflorescence, <a href="#p-160">160</a>, <a href="#p-161">161</a>.</li>
+
+<li class="indx">Indusium, <a href="#p-404">404</a>.</li>
+
+<li class="indx">Inferior ovary, <a href="#p-221">221</a>, <a href="#p-225">225</a>.</li>
+
+<li class="indx">Inflorescence, <a href="#p-159">159</a>.</li>
+
+<li class="indx">Insectivorous plants, <a href="#p-208">208-210</a>.</li>
+
+<li class="indx">Internode, <a href="#p-46">46</a>, <a href="#p-110">110</a>; Exp. <a href="#exp-35">35</a>.</li>
+
+<li class="indx">Invasion, <a href="#p-328">328</a>.</li>
+
+<li class="indx">Inverted seed, <a href="#p-14">14</a>.</li>
+
+<li class="indx">Involucre, <a href="#p-161">161</a>, <a href="#p-232">232</a>.</li>
+
+<li class="indx">Involute, <a href="#p-373">373</a>; Fig. <a href="#i_195">251</a>.</li>
+
+<li class="indx">Iodine solution, Exp. <a href="#exp-3">3</a>.</li>
+
+<li class="indx">Irregular flower, <a href="#p-219">219</a>, <a href="#p-237">237</a>.</li>
+
+<li class="indx">Irritability, <a href="#p-201">201</a>.</li>
+
+
+<li class="ifrst">Joint, <a href="#p-110">110</a>, <a href="#p-113">113</a>.</li>
+
+
+<li class="ifrst">Keel, <a href="#p-238">238</a>.</li>
+
+<li class="indx">Knots, <a href="#p-137">137</a>.</li>
+
+
+<li class="ifrst">Lamina, <a href="#p-209">209</a>.</li>
+
+<li class="indx">Laminæ, <a href="#p-368">368</a>, <a href="#p-374">374</a>.</li>
+
+<li class="indx">Lateral, <a href="#p-372">372</a>, <a href="#p-398">398</a>.</li>
+
+<li class="indx">Lateral buds, <a href="#p-145">145</a>.</li>
+
+<li class="indx">Leaf attachment, <a href="#p-167">167</a>.</li>
+
+<li class="indx">Leaf cups, <a href="#p-202">202</a>.</li>
+
+<li class="indx">Leaf scars, <a href="#p-146">146</a>.</li>
+
+<li class="indx">Leaf traces, <a href="#p-146">146</a>.</li>
+
+<li class="indx">Legume, <a href="#p-299">299</a>.</li>
+
+<li class="indx">Lenticels, <a href="#p-106">106</a>, <a href="#p-118">118</a>, <a href="#p-288">288</a>.</li>
+
+<li class="indx">Lichen, <a href="#p-379">379</a>.</li>
+
+<li class="indx">Life cycle, <a href="#p-359">359</a>, <a href="#p-364">364</a>.</li>
+
+<li class="indx">Loam, <a href="#p-75">75</a>.</li>
+
+<li class="indx">Lobing, <a href="#p-177">177</a>; Figs. <a href="#i_168_210">210-212</a>.</li>
+
+<li class="indx">Locule, <a href="#p-216">216</a>.</li>
+
+<li class="indx">Loment, Fig. <a href="#i_274">394</a>.</li>
+
+<li class="indx">Lyrate, Fig. <a href="#i_162a">197</a>.</li>
+
+
+<li class="ifrst">Medulla, <a href="#p-119">119</a>, <a href="#p-122">122</a>.</li>
+
+<li class="indx">Medullary rays, <a href="#p-64">64</a>, <a href="#p-116">116</a>, <a href="#p-121">121</a>, <a href="#p-122">122</a>, <a href="#p-134">134</a>,
+    <a href="#p-135">135</a>.</li>
+
+<li class="indx">Megasporangia, <a href="#p-409">409</a>.</li>
+
+<li class="indx">Megaspore, <a href="#p-409">409</a>, <a href="#p-414">414</a>.</li>
+
+<li class="indx">Mendel’s law, <a href="#p-258">258</a>.</li>
+
+<li class="indx"><span class="pagenum" id="Page_372">[Pg 372]</span>Mesophyte, <a href="#p-317">317</a>, <a href="#p-324">324</a>.</li>
+
+<li class="indx">Metabolism, <a href="#p-193">193</a>.</li>
+
+<li class="indx">Microbe, <a href="#p-351">351</a>, <a href="#p-355">355</a>.</li>
+
+<li class="indx">Micrococcus, <a href="#p-339">339</a>.</li>
+
+<li class="indx">Micropyle, <a href="#p-12">12</a>, <a href="#p-13">13</a>, <a href="#p-14">14</a>, <a href="#p-15">15</a>, <a href="#p-45">45</a>.</li>
+
+<li class="indx">Microsporangia, <a href="#p-409">409</a>.</li>
+
+<li class="indx">Microspore, <a href="#p-409">409</a>, <a href="#p-414">414</a>.</li>
+
+<li class="indx">Midrib, <a href="#p-172">172</a>.</li>
+
+<li class="indx">Mixed forest, <a href="#p-139">139</a>, <a href="#p-324">324</a>.</li>
+
+<li class="indx">Modification, <a href="#p-100">100-108</a>, <a href="#p-206">206</a>, <a href="#p-207">207</a>, <a href="#p-289">289</a>.</li>
+
+<li class="indx">Molecule, <a href="#p-136">136</a>.</li>
+
+<li class="indx">Monadelphous, <a href="#p-239">239</a>.</li>
+
+<li class="indx">Monocotyl, <a href="#p-110">110</a>, <a href="#p-112">112</a>, <a href="#p-171">171</a>, <a href="#p-217">217</a>, <a href="#p-221">221</a>,
+    <a href="#p-418">418</a>.</li>
+
+<li class="indx">Monocotyledonous, <a href="#p-11">11</a>.</li>
+
+<li class="indx">Monœcious, <a href="#p-268">268</a>.</li>
+
+<li class="indx">Monopetalous, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Monosepalous, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Morphology, <a href="#p-108">108</a>.</li>
+<li class="isub1">of the flower, <a href="#p-244">244</a>.</li>
+
+<li class="indx">Mosaic (leaf), <a href="#p-197">197</a>.</li>
+
+<li class="indx">Mosses, <a href="#p-334">334</a>, <a href="#p-396">396-401</a>.</li>
+
+<li class="indx">Muck, <a href="#p-75">75</a>.</li>
+
+<li class="indx">Multiple fruit, <a href="#p-304">304</a>, <a href="#p-305">305</a>.</li>
+
+<li class="indx">Mushroom, <a href="#p-333">333</a>, <a href="#p-367">367</a>.</li>
+
+<li class="indx">Mutation, <a href="#p-264">264</a>.</li>
+
+<li class="indx">Mycelium, <a href="#p-343">343</a>, <a href="#p-359">359</a>, <a href="#p-369">369</a>.</li>
+
+<li class="indx">Mychorrhiza, <a href="#p-86">86</a>.</li>
+
+
+<li class="ifrst">Neck canal, <a href="#p-391">391</a>.</li>
+
+<li class="indx">Net-veined, <a href="#p-171">171</a>.</li>
+
+<li class="indx">Neuter, <a href="#p-267">267</a>.</li>
+
+<li class="indx">Neutral flower, <a href="#p-231">231</a>, <a href="#p-267">267</a>.</li>
+
+<li class="indx">Nitrogen, <a href="#p-62">62</a>, <a href="#p-63">63</a>, <a href="#p-188">188</a>.</li>
+
+<li class="indx">Nitrogenous food, <a href="#p-188">188</a>.</li>
+
+<li class="indx">Node, <a href="#p-46">46</a>, <a href="#p-65">65</a>, <a href="#p-110">110</a>, <a href="#p-113">113</a>.</li>
+
+<li class="indx">Nucleus, <a href="#p-7">7</a>, <a href="#p-341">341</a>.</li>
+
+<li class="indx">Numerical plan, <a href="#p-217">217</a>, <a href="#p-229">229</a>.</li>
+
+<li class="indx">Nut, <a href="#p-295">295</a>.</li>
+
+<li class="indx">Nutriment, <a href="#p-3">3</a>, <a href="#p-186">186</a>.</li>
+
+<li class="indx">Nutrition, <a href="#p-50">50</a>, <a href="#p-54">54</a>, <a href="#p-179">179</a>, <a href="#p-193">193</a>.</li>
+
+<li class="indx">Nyctitropic, <a href="#p-200">200</a>.</li>
+
+
+<li class="ifrst">Obsolete, <a href="#p-220">220</a>.</li>
+
+<li class="indx">Oil, <a href="#p-1">1</a>, <a href="#p-3">3</a>, <a href="#p-8">8</a>.</li>
+
+<li class="indx">Oöspore, <a href="#p-393">393</a>, <a href="#p-394">394</a>, <a href="#p-395">395</a>.</li>
+
+<li class="indx">Open bundle, <a href="#p-116">116</a>.</li>
+
+<li class="indx">Operculum, <a href="#p-399">399</a>.</li>
+
+<li class="indx">Opposite leaves, <a href="#p-168">168</a>.</li>
+
+<li class="indx">Organ, <a href="#p-41">41</a>.</li>
+
+<li class="indx">Organic foods, <a href="#p-4">4</a>.</li>
+
+<li class="indx">Organs of reproduction, <a href="#p-40">40</a>.</li>
+<li class="isub1">of vegetation, <a href="#p-40">40</a>.</li>
+
+<li class="indx">Osmosis, <a href="#p-56">56</a>, <a href="#p-57">57</a>.</li>
+
+<li class="indx">Ovary, <a href="#p-214">214</a>, <a href="#p-216">216</a>, <a href="#p-223">223</a>.</li>
+
+<li class="indx">Ovule, <a href="#p-216">216</a>.</li>
+
+<li class="indx">Oxidation, <a href="#p-27">27</a>; Exps. <a href="#exp-21">21</a>, <a href="#exp-22">22</a>.</li>
+
+<li class="indx">Oxygen, <a href="#p-62">62</a>, <a href="#p-63">63</a>, <a href="#p-186">186</a>, <a href="#p-187">187</a>; Exps. <a href="#exp-22">22</a>, <a href="#exp-66">66</a>.</li>
+
+
+<li class="ifrst">Palisade cells, <a href="#p-184">184</a>.</li>
+
+<li class="indx">Palmate veining, <a href="#p-172">172</a>.</li>
+
+<li class="indx">Panicle, Fig. <a href="#i_153b">171</a>.</li>
+
+<li class="indx">Papilionaceous, <a href="#p-237">237</a>, <a href="#p-238">238</a>.</li>
+
+<li class="indx">Pappus, <a href="#p-234">234</a>.</li>
+
+<li class="indx">Parallel veining, <a href="#p-171">171</a>.</li>
+
+<li class="indx">Paraphyses, <a href="#p-375">375</a>, <a href="#p-398">398</a>.</li>
+
+<li class="indx">Parasitic, <a href="#p-5">5</a>, <a href="#p-345">345</a>, <a href="#p-364">364</a>.</li>
+
+<li class="indx">Parasitic plants, <a href="#p-85">85</a>, <a href="#p-343">343</a>, <a href="#p-382">382</a>.</li>
+
+<li class="indx">Parenchyma, <a href="#p-110">110</a>, <a href="#p-114">114</a>, <a href="#p-115">115</a>.</li>
+
+<li class="indx">Parietal, <a href="#p-216">216</a>.</li>
+
+<li class="indx">Pathogenic, <a href="#p-352">352</a>, <a href="#p-353">353</a>.</li>
+
+<li class="indx">Pedicel, <a href="#p-159">159</a>.</li>
+
+<li class="indx">Peduncle, <a href="#p-159">159</a>, <a href="#p-288">288</a>.</li>
+
+<li class="indx">Pentamerous, <a href="#p-229">229</a>.</li>
+
+<li class="indx">Pepo, <a href="#p-290">290</a>.</li>
+
+<li class="indx">Perennial, <a href="#p-93">93</a>.</li>
+
+<li class="indx">Perfect flower, <a href="#p-219">219</a>.</li>
+
+<li class="indx">Perianth, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Pericarp, <a href="#p-288">288</a>.</li>
+
+<li class="indx">Perigynous, Figs. <a href="#i_219">301</a>, <a href="#i_219a">302</a>.</li>
+
+<li class="indx">Persistent, <a href="#p-166">166</a>.</li>
+
+<li class="indx">Petals, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Petiole, <a href="#p-165">165</a>.</li>
+
+<li class="indx">Phanerogams, <a href="#p-331">331</a>, <a href="#p-332">332</a>.</li>
+
+<li class="indx">Phloem, <a href="#p-114">114</a>, <a href="#p-116">116</a>.</li>
+
+<li class="indx">Photosynthesis, <a href="#p-186">186</a>, <a href="#p-192">192</a>, <a href="#p-193">193</a>.</li>
+
+<li class="indx">Phototropism, <a href="#p-195">195</a>.</li>
+
+<li class="indx">Phyllotaxy, <a href="#p-168">168</a>, <a href="#p-169">169</a>.</li>
+
+<li class="indx">Pileus, <a href="#p-373">373</a>.</li>
+
+<li class="indx">Pinna, <a href="#p-402">402</a>.</li>
+
+<li class="indx">Pinnate veining, <a href="#p-172">172</a>.</li>
+
+<li class="indx">Pinnule, <a href="#p-402">402</a>.</li>
+
+<li class="indx">Pioneer plant, <a href="#p-316">316</a>, <a href="#p-319">319</a>, <a href="#p-320">320</a>.</li>
+
+<li class="indx">Pistil, <a href="#p-212">212</a>, <a href="#p-214">214</a>, <a href="#p-223">223</a>, <a href="#p-228">228</a>, <a href="#p-240">240</a>.</li>
+
+<li class="indx">Pistillate, <a href="#p-267">267</a>.</li>
+
+<li class="indx">Pitcher plant, <a href="#p-209">209</a>.</li>
+
+<li class="indx">Pith, <a href="#p-110">110</a>, <a href="#p-115">115</a>, <a href="#p-116">116</a>, <a href="#p-119">119</a>, <a href="#p-121">121</a>,
+    <a href="#p-122">122</a>.</li>
+
+<li class="indx">Pitted ducts, <a href="#p-114">114</a>.</li>
+
+<li class="indx">Placenta, <a href="#p-216">216</a>, <a href="#p-288">288</a>, <a href="#p-298">298</a>, <a href="#p-300">300</a>.</li>
+
+<li class="indx">Plant society, <a href="#p-316">316</a>.</li>
+
+<li class="indx">Plasmolysis, <a href="#p-59">59</a>.</li>
+
+<li class="indx">Pleurococcus, <a href="#p-337">337</a>.</li>
+
+<li class="indx">Plicate, <a href="#p-155">155</a>.</li>
+
+<li class="indx">Plumule, <a href="#p-11">11</a>, <a href="#p-12">12</a>, <a href="#p-14">14</a>, <a href="#p-45">45</a>, <a href="#p-46">46</a>.</li>
+
+<li class="indx">Pod, <a href="#p-298">298</a>.</li>
+
+<li class="indx">Pollen, <a href="#p-213">213</a>.</li>
+
+<li class="indx">Pollen grains, <a href="#p-213">213</a>.</li>
+
+<li class="indx">Pollen sac, <a href="#p-213">213</a>.</li>
+
+<li class="indx">Pollen tubes, <a href="#p-249">249</a>, <a href="#p-250">250</a>.</li>
+
+<li class="indx">Pollination, <a href="#p-215">215</a>, <a href="#p-247">247</a>.</li>
+
+<li class="indx">Polycotyledons, <a href="#p-15">15</a>, <a href="#p-45">45</a>.</li>
+
+<li class="indx">Polymorphic, <a href="#p-365">365</a>.</li>
+
+<li class="indx">Polymorphism, <a href="#p-365">365</a>.</li>
+
+<li class="indx">Polypetalous, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Polysepalous, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Pome, <a href="#p-288">288</a>.</li>
+
+<li class="indx">Prefoliation, <a href="#p-155">155</a>.</li>
+
+<li class="indx">Primary, <a href="#p-396">396</a>.</li>
+
+<li class="indx">Primary root, <a href="#p-42">42</a>, <a href="#p-79">79</a>.</li>
+
+<li class="indx">Pronuba, <a href="#p-278">278</a>.</li>
+
+<li class="indx">Prostate, <a href="#p-95">95</a>.</li>
+
+<li class="indx">Protection, <a href="#p-199">199</a>, <a href="#p-204">204</a>, <a href="#p-207">207</a>, <a href="#p-280">280</a>, <a href="#p-287">287</a>.</li>
+
+<li class="indx">Proteins, <a href="#p-3">3</a>, <a href="#p-8">8</a>, <a href="#p-33">33</a>, <a href="#p-188">188</a>, <a href="#p-204">204</a>.</li>
+
+<li class="indx">Prothallium, <a href="#p-407">407</a>.</li>
+
+<li class="indx">Protonema, <a href="#p-396">396</a>.</li>
+
+<li class="indx">Protoplasm, <a href="#p-6">6</a>, <a href="#p-7">7</a>, <a href="#p-57">57</a>, <a href="#p-58">58</a>, <a href="#p-67">67</a>, <a href="#p-110">110</a>,
+    <a href="#p-116">116</a>.</li>
+
+<li class="indx">Pteridophytes, <a href="#p-335">335</a>, <a href="#p-411">411</a>, <a href="#p-412">412</a>.</li>
+
+<li class="indx">Puccinia, <a href="#p-360">360</a>.</li>
+
+<li class="indx">Pure dominant, <a href="#p-258">258</a>, <a href="#p-259">259</a>.</li>
+
+<li class="indx">Pure forest, <a href="#p-139">139</a>, <a href="#p-324">324</a>.</li>
+
+<li class="indx">Pure recessive, <a href="#p-258">258</a>, <a href="#p-259">259</a>.</li>
+
+<li class="indx">Pycnidia, <a href="#p-363">363</a>.</li>
+
+
+<li class="ifrst">Quartered cut, <a href="#p-135">135</a>.</li>
+
+
+<li class="ifrst">Raceme, <a href="#p-161">161</a>.</li>
+
+<li class="indx">Rhachis, <a href="#p-178">178</a>.</li>
+
+<li class="indx">Radial section, <a href="#p-132">132</a>, <a href="#p-135">135</a>.</li>
+
+<li class="indx">Radicle, <a href="#p-46">46</a>.</li>
+
+<li class="indx">Rhaphe, <a href="#p-13">13</a>.</li>
+
+<li class="indx">Ray, <a href="#p-161">161</a>, <a href="#p-391">391</a>.</li>
+
+<li class="indx">Ray flowers, <a href="#p-231">231</a>.</li>
+
+<li class="indx">Receptacle, <a href="#p-211">211</a>, <a href="#p-288">288</a>, <a href="#p-289">289</a>, <a href="#p-388">388</a>, <a href="#p-390">390</a>,
+    <a href="#p-398">398</a>.</li>
+
+<li class="indx">Recessive, <a href="#p-257">257</a>, <a href="#p-258">258</a>.</li>
+
+<li class="indx">Red rust, <a href="#p-359">359</a>.</li>
+
+<li class="indx">Regular flower, <a href="#p-219">219</a>.</li>
+
+<li class="indx">Reproduction, <a href="#p-338">338</a>, <a href="#p-351">351</a>, <a href="#p-358">358</a>, <a href="#p-383">383</a>.</li>
+
+<li class="indx">Respiration, <a href="#p-30">30</a>, <a href="#p-31">31</a>, <a href="#p-191">191</a>, <a href="#p-192">192</a>.</li>
+
+<li class="indx">Resting spore, <a href="#p-338">338</a>, <a href="#p-342">342</a>, <a href="#p-358">358</a>, <a href="#p-394">394</a>.</li>
+
+<li class="indx">Reticulation, <a href="#p-172">172</a>, <a href="#p-402">402</a>.</li>
+
+<li class="indx">Retrogressive evolution, <a href="#p-418">418</a>.</li>
+
+<li class="indx">Revolute, <a href="#p-373">373</a>, <a href="#p-404">404</a>.</li>
+
+<li class="indx">Rhizoids, <a href="#p-379">379</a>, <a href="#p-386">386</a>.</li>
+
+<li class="indx">Rhizome, <a href="#p-105">105</a>.</li>
+
+<li class="indx">Ringing, <a href="#p-127">127</a>.</li>
+
+<li class="indx">Rings of growth, <a href="#p-122">122</a>, <a href="#p-123">123</a>, <a href="#p-134">134</a>, <a href="#p-135">135</a>.</li>
+
+<li class="indx">Rogue, <a href="#p-260">260</a>.</li>
+
+<li class="indx">Root cap, <a href="#p-39">39</a>.</li>
+
+<li class="indx">Root hairs, <a href="#p-38">38</a>, <a href="#p-67">67</a>.</li>
+
+<li class="indx">Root pressure, Exp. <a href="#exp-49">49</a>.</li>
+
+<li class="indx">Root pull, <a href="#p-69">69</a>.</li>
+
+<li class="indx">Rootstock, <a href="#p-105">105</a>.</li>
+
+<li class="indx">Root system, <a href="#p-89">89</a>.</li>
+
+<li class="indx">Root tubercles, <a href="#p-63">63</a>, <a href="#p-300">300</a>.</li>
+
+<li class="indx">Rosette, <a href="#p-197">197</a>.</li>
+
+<li class="indx">Rotation of crops, <a href="#p-24">24</a>, <a href="#p-327">327</a>.</li>
+
+<li class="indx">Runner, <a href="#p-95">95</a>.</li>
+
+
+<li class="ifrst">Samara, <a href="#p-296">296</a>.</li>
+
+<li class="indx">Sap movement, <a href="#p-125">125</a>, <a href="#p-126">126</a>, <a href="#p-128">128</a>, <a href="#p-129">129</a>.</li>
+
+<li class="indx">Saprophyte, <a href="#p-86">86</a>.</li>
+
+<li class="indx">Sapwood, <a href="#p-131">131</a>.</li>
+
+<li class="indx">Scale leaves, <a href="#p-101">101</a>, <a href="#p-106">106</a>, <a href="#p-107">107</a>, <a href="#p-147">147-149</a>, <a href="#p-207">207</a>.</li>
+
+<li class="indx">Scape, <a href="#p-107">107</a>, <a href="#p-159">159</a>.</li>
+
+<li class="indx">Scorpioid inflorescence, <a href="#p-162">162</a>; Figs. <a href="#i_154">173-176</a>.</li>
+
+<li class="indx">Screenings, <a href="#p-20">20</a>; p. <a href="#Page_28">28</a>, Qn. 22.</li>
+
+<li class="indx">Secondary roots, <a href="#p-37">37</a>, <a href="#p-42">42</a>, <a href="#p-79">79</a>.</li>
+
+<li class="indx"><span class="pagenum" id="Page_373">[Pg 373]</span>Seed, <a href="#p-11">11-18</a>, <a href="#p-332">332</a>, <a href="#p-415">415</a>.</li>
+
+<li class="indx">Seed coat, <a href="#p-12">12</a>, <a href="#p-14">14</a>, <a href="#p-15">15</a>, <a href="#p-43">43</a>.</li>
+
+<li class="indx">Seedless fruits, <a href="#p-285">285</a>, <a href="#p-286">286</a>.</li>
+
+<li class="indx">Seedlings, <a href="#p-36">36</a>, <a href="#p-42">42</a>, <a href="#p-43">43</a>, <a href="#p-45">45</a>.</li>
+
+<li class="indx">Seed plants, <a href="#p-331">331</a>, <a href="#p-414">414</a>.</li>
+
+<li class="indx">Seed vessel, <a href="#p-282">282</a>.</li>
+
+<li class="indx">Selection, <a href="#p-260">260</a>, <a href="#p-265">265</a>, <a href="#p-286">286</a>.</li>
+<li class="isub1">artificial, <a href="#p-262">262</a>.</li>
+<li class="isub1">natural, <a href="#p-261">261</a>.</li>
+
+<li class="indx">Self-fertilization, <a href="#p-254">254</a>, <a href="#p-271">271</a>.</li>
+
+<li class="indx">Sepals, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Sessile, <a href="#p-167">167</a>, <a href="#p-214">214</a>.</li>
+
+<li class="indx">Seta, <a href="#p-399">399</a>.</li>
+
+<li class="indx">Sexual generation, <a href="#p-395">395</a>, <a href="#p-396">396</a>, <a href="#p-406">406</a>, <a href="#p-410">410</a>, <a href="#p-416">416</a>.</li>
+
+<li class="indx">Sexual reproduction, <a href="#p-394">394</a>, <a href="#p-395">395</a>, <a href="#p-410">410</a>.</li>
+
+<li class="indx">Sheath, <a href="#p-67">67</a>, <a href="#p-116">116</a>.</li>
+
+<li class="indx">Shrinking of timber, <a href="#p-136">136</a>.</li>
+
+<li class="indx">Sieve tube, <a href="#p-114">114</a>.</li>
+
+<li class="indx">Slabs, <a href="#p-134">134</a>.</li>
+
+<li class="indx">Sleep movements, <a href="#p-200">200</a>.</li>
+
+<li class="indx">Soils, <a href="#p-75">75</a>, <a href="#p-77">77</a>.</li>
+
+<li class="indx">Sori, <a href="#p-404">404</a>.</li>
+
+<li class="indx">Spathe, <a href="#p-221">221</a>.</li>
+
+<li class="indx">Specialization, <a href="#p-237">237</a>.</li>
+
+<li class="indx">Spermatophytes, <a href="#p-331">331</a>, <a href="#p-335">335</a>, <a href="#p-394">394</a>, <a href="#p-414">414</a>.</li>
+
+<li class="indx">Spermatozoid, <a href="#p-389">389</a>.</li>
+
+<li class="indx">Spermogonia, <a href="#p-363">363</a>.</li>
+
+<li class="indx">Spike, <a href="#p-161">161</a>.</li>
+
+<li class="indx">Spirillum, <a href="#p-348">348</a>.</li>
+
+<li class="indx">Spirogyra, <a href="#p-341">341</a>.</li>
+
+<li class="indx">Sporangia, <a href="#p-390">390</a>, <a href="#p-405">405</a>.</li>
+
+<li class="indx">Spore, <a href="#p-332">332</a>, <a href="#p-349">349</a>, <a href="#p-350">350</a>, <a href="#p-377">377</a>, <a href="#p-406">406</a>,
+    <a href="#p-410">410</a>.</li>
+
+<li class="indx">Spore case, <a href="#p-390">390</a>, <a href="#p-393">393</a>, <a href="#p-405">405</a>.</li>
+
+<li class="indx">Spore print, <a href="#p-376">376</a>.</li>
+
+<li class="indx">Sporidium, <a href="#p-361">361</a>.</li>
+
+<li class="indx">Sporogonium, <a href="#p-393">393</a>, <a href="#p-399">399</a>.</li>
+
+<li class="indx">Sporophyll, <a href="#p-406">406</a>, <a href="#p-414">414</a>.</li>
+
+<li class="indx">Sporophyte, <a href="#p-393">393-395</a>, <a href="#p-399">399</a>, <a href="#p-406">406</a>, <a href="#p-410">410</a>, <a href="#p-412">412</a>,
+    <a href="#p-414">414</a>, <a href="#p-416">416</a>.</li>
+
+<li class="indx">Sport, <a href="#p-264">264</a>.</li>
+
+<li class="indx">Stamen, <a href="#p-212">212</a>, <a href="#p-213">213</a>.</li>
+
+<li class="indx">Staminate, <a href="#p-267">267</a>, <a href="#p-268">268</a>.</li>
+
+<li class="indx">Staminodia, <a href="#p-244">244</a>.</li>
+
+<li class="indx">Standard, <a href="#p-238">238</a>.</li>
+
+<li class="indx">Starch, <a href="#p-3">3</a>, <a href="#p-4">4</a>, <a href="#p-187">187</a>, <a href="#p-204">204</a>, <a href="#p-288">288</a>;
+    Exps. <a href="#exp-69">69</a>, <a href="#exp-70">70</a>.</li>
+
+<li class="indx">Stems, <a href="#p-90">90-99</a>.</li>
+
+<li class="indx">Sterile flower, <a href="#p-267">267</a>.</li>
+
+<li class="indx">Sterilization, <a href="#p-354">354</a>.</li>
+
+<li class="indx">Stigma, <a href="#p-214">214</a>.</li>
+
+<li class="indx">Stigmatic surface, <a href="#p-223">223</a>.</li>
+
+<li class="indx">Stimulus, <a href="#p-98">98</a>, <a href="#p-186">186</a>, <a href="#p-201">201</a>.</li>
+
+<li class="indx">Stipe, <a href="#p-240">240</a>, <a href="#p-372">372</a>, <a href="#p-402">402</a>.</li>
+
+<li class="indx">Stipule, <a href="#p-149">149</a>, <a href="#p-165">165</a>, <a href="#p-166">166</a>.</li>
+
+<li class="indx">Stolon, <a href="#p-95">95</a>.</li>
+
+<li class="indx">Stoma, <a href="#p-181">181</a>, <a href="#p-182">182</a>, <a href="#p-183">183</a>.</li>
+
+<li class="indx">Stomata, <a href="#p-181">181</a>, <a href="#p-182">182</a>.</li>
+
+<li class="indx">Stone fruit, <a href="#p-292">292</a>.</li>
+
+<li class="indx">Storage of food, <a href="#p-2">2</a>, <a href="#p-3">3</a>, <a href="#p-4">4</a>, <a href="#p-17">17</a>, <a href="#p-70">70</a>, <a href="#p-103">103</a>,
+    <a href="#p-104">104-107</a>, <a href="#p-287">287</a>.</li>
+
+<li class="indx"><span class="pagenum" id="Page_374">[Pg 374]</span>Strangling fig, <a href="#p-88">88</a>.</li>
+
+<li class="indx">Strobile, <a href="#p-411">411</a>.</li>
+
+<li class="indx">Strobiliaceous, <a href="#p-411">411</a>.</li>
+
+<li class="indx">Style, <a href="#p-214">214</a>.</li>
+
+<li class="indx">Succession, <a href="#p-327">327</a>.</li>
+
+<li class="indx">Sugars, <a href="#p-3">3</a>, <a href="#p-4">4</a>, <a href="#p-204">204</a>, <a href="#p-288">288</a>.</li>
+
+<li class="indx">Summer spores, <a href="#p-360">360</a>.</li>
+
+<li class="indx">Sundew, <a href="#p-210">210</a>.</li>
+
+<li class="indx">Superior ovary, <a href="#p-218">218</a>, <a href="#p-221">221</a>, <a href="#p-225">225</a>.</li>
+
+<li class="indx">Supernumerary buds, <a href="#p-158">158</a>.</li>
+
+<li class="indx">Suppressed, <a href="#p-220">220</a>.</li>
+
+<li class="indx">Survival of the fittest, <a href="#p-261">261</a>.</li>
+
+<li class="indx">Suture, <a href="#p-216">216</a>, <a href="#p-298">298</a>, <a href="#p-299">299</a>.</li>
+
+<li class="indx">Swarm spore, <a href="#p-349">349</a>.</li>
+
+<li class="indx">Swelling of timber, <a href="#p-136">136</a>.</li>
+
+<li class="indx">Symbiosis, <a href="#p-309">309</a>, <a href="#p-382">382</a>.</li>
+
+<li class="indx">Symmetrical flower, <a href="#p-219">219</a>.</li>
+
+<li class="indx">Sympetalous, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Syncarpous, <a href="#p-300">300</a>.</li>
+
+<li class="indx">Synsepalous, <a href="#p-211">211</a>.</li>
+
+<li class="indx">Systematic botany, <i>see</i> <a href="#APPENDIX">Appendix</a>.</li>
+
+
+<li class="ifrst">Tangential cut, <a href="#p-132">132</a>, <a href="#p-134">134</a>.</li>
+
+<li class="indx">Tap root, <a href="#p-79">79</a>.</li>
+
+<li class="indx">Teleutospore, <a href="#p-360">360</a>.</li>
+
+<li class="indx">Tendril, <a href="#p-96">96</a>, <a href="#p-97">97</a>.</li>
+
+<li class="indx">Terminal bud, <a href="#p-145">145</a>, <a href="#p-154">154</a>.</li>
+
+<li class="indx">Testa, <a href="#p-14">14</a>.</li>
+
+<li class="indx">Thallophytes, <a href="#p-333">333</a>.</li>
+
+<li class="indx">Thallus, <a href="#p-333">333</a>, <a href="#p-341">341</a>, <a href="#p-343">343</a>, <a href="#p-379">379</a>, <a href="#p-380">380</a>, <a href="#p-381">381</a>,
+    <a href="#p-385">385</a>.</li>
+
+<li class="indx">Tillage, <a href="#p-76">76</a>.</li>
+
+<li class="indx">Tissue, <a href="#p-60">60</a>, <a href="#p-61">61</a>.</li>
+
+<li class="indx">Toadstools, <a href="#p-367">367</a>.</li>
+
+<li class="indx">Toxins, <a href="#p-345">345</a>.</li>
+
+<li class="indx">Tracheids, <a href="#p-114">114</a>, <a href="#p-117">117</a>.</li>
+
+<li class="indx">Trailing, <a href="#p-95">95</a>.</li>
+
+<li class="indx">Trama, <a href="#p-375">375</a>.</li>
+
+<li class="indx">Transpiration, <a href="#p-179">179</a>, <a href="#p-180">180</a>.</li>
+
+<li class="indx">Trifoliolate, Figs. <a href="#i_168_215">215</a>, <a href="#i_168_216">216</a>.</li>
+
+<li class="indx">Trimerous, <a href="#p-217">217</a>.</li>
+
+<li class="indx">Trimorphic, <a href="#p-270">270</a>.</li>
+
+<li class="indx">Tuber, <a href="#p-106">106</a>.</li>
+
+<li class="indx">Tumbleweeds, <a href="#p-23">23</a>.</li>
+
+<li class="indx">Turgidity, <a href="#p-7">7</a>.</li>
+
+<li class="indx">Turgor, <a href="#p-179">179</a>.</li>
+
+<li class="indx">Twining, cause of, <a href="#p-98">98</a>; Exp. <a href="#exp-55">55</a>.</li>
+
+<li class="indx">Twining stems, <a href="#p-96">96</a>; Exp. <a href="#exp-54">54</a>.</li>
+
+<li class="indx">Type, <a href="#p-18">18</a>, <a href="#p-260">260</a>, <a href="#p-263">263</a>, <a href="#p-265">265</a>, <a href="#p-336">336</a>, <a href="#p-411">411</a>.</li>
+
+
+<li class="ifrst">Umbel, <a href="#p-161">161</a>.</li>
+
+<li class="indx">Umbonate, <a href="#p-373">373</a>.</li>
+
+<li class="indx">Underground stems, <a href="#p-104">104-107</a>.</li>
+
+<li class="indx">Unicellular, <a href="#p-337">337</a>.</li>
+
+<li class="indx">Unisexual, <a href="#p-267">267</a>.</li>
+
+<li class="indx">Uredo, <a href="#p-359">359</a>.</li>
+
+<li class="indx">Uredospore, <a href="#p-359">359</a>, <a href="#p-360">360</a>.</li>
+
+
+<li class="ifrst">Variation, <a href="#p-263">263</a>, <a href="#p-264">264</a>, <a href="#p-265">265</a>.</li>
+
+<li class="indx">Vascular bundles, <a href="#p-111">111</a>.</li>
+
+<li class="indx">Vascular cryptogams, <a href="#p-403">403</a>, <a href="#p-411">411</a>, <a href="#p-412">412</a>.</li>
+
+<li class="indx">Vascular cylinder, <a href="#p-64">64</a>.</li>
+
+<li class="indx">Vascular system, <a href="#p-111">111</a>, <a href="#p-113">113</a>, <a href="#p-335">335</a>.</li>
+
+<li class="indx">Vegetative reproduction, <a href="#p-358">358</a>.</li>
+
+<li class="indx">Veil, <a href="#p-371">371</a>.</li>
+
+<li class="indx">Veins, <a href="#p-173">173-176</a>.</li>
+
+<li class="indx">Venter, <a href="#p-391">391</a>.</li>
+
+<li class="indx">Ventral, Figs. <a href="#i_273a">390</a>, <a href="#i_273b">391</a>.</li>
+
+<li class="indx">Vernation, <a href="#p-155">155</a>.</li>
+
+<li class="indx">Vessels, <a href="#p-111">111</a>.</li>
+
+<li class="indx">Vexillum, <a href="#p-238">238</a>, <a href="#p-239">239</a>.</li>
+
+<li class="indx">Vibrio, <a href="#p-348">348</a>.</li>
+
+<li class="indx">Vitality of seeds, <a href="#p-34">34</a>; Exp. <a href="#exp-30">30</a>.</li>
+
+<li class="indx">Volva, <a href="#p-371">371</a>.</li>
+
+
+<li class="ifrst">Water roots, <a href="#p-39">39</a>, <a href="#p-84">84</a>.</li>
+
+<li class="indx">Whorled leaves, <a href="#p-168">168</a>.</li>
+
+<li class="indx">Wind pollination, <a href="#p-274">274</a>, <a href="#p-275">275</a>.</li>
+
+<li class="indx">Wings, <a href="#p-238">238</a>.</li>
+
+<li class="indx">Winter spores, <a href="#p-360">360</a>.</li>
+
+
+<li class="ifrst">Xerophyte, <a href="#p-317">317</a>.</li>
+
+<li class="indx">Xerophyte societies, <a href="#p-317">317</a>, <a href="#p-320">320-322</a>.</li>
+
+<li class="indx">Xylem, <a href="#p-114">114</a>, <a href="#p-116">116</a>.</li>
+
+
+<li class="ifrst">Yeast, <a href="#p-356">356</a>.</li>
+
+<li class="indx">Yeast colony, <a href="#p-357">357</a>.</li>
+
+<li class="indx">Yellow trumpets, <a href="#p-209">209</a>.</li>
+
+<li class="indx">Yucca, <a href="#p-278">278</a>.</li>
+
+<li class="indx">Yucca moth, <a href="#p-278">278</a>.</li>
+
+
+<li class="ifrst">Zonation, <a href="#p-325">325</a>, <a href="#p-327">327</a>.</li>
+<li class="isub1">bilateral, <a href="#p-326">326</a>.</li>
+<li class="isub1">concentric, <a href="#p-326">326</a>.</li>
+<li class="isub1">horizontal, <a href="#p-326">326</a>.</li>
+<li class="isub1">vertical, <a href="#p-326">326</a>.</li>
+
+<li class="indx">Zones of vegetation, <a href="#p-325">325</a>.</li>
+</ul>
+
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+<h2 class="nobreak" id="FOOTNOTES">FOOTNOTES:</h2>
+</div>
+
+<div class="footnote">
+
+<p><a id="Footnote_1" href="#FNanchor_1" class="label">[1]</a> Vines, “Lectures on the Physiology of Plants,” p. 282. See also Sachs,
+“Physiology of Plants.”</p>
+
+</div>
+
+<div class="footnote">
+
+<p><a id="Footnote_2" href="#FNanchor_2" class="label">[2]</a> Marshall Ward, “The Oak.”</p>
+
+</div>
+<hr class="chap x-ebookmaker-drop">
+
+
+<div class="chapter transnote">
+<h2>TRANSCRIBER’S NOTE</h2>
+
+<p>Obvious typographical errors and punctuation errors have been
+corrected after careful comparison with other occurrences within
+the text and consultation of external sources.</p>
+
+<p>Some hyphens in words have been silently removed, some added,
+when a predominant preference was found in the original book.</p>
+
+<p>Except for those changes noted below, all misspellings in the text,
+and inconsistent or archaic usage, have been retained.</p>
+
+<table>
+<tr>
+<td class='tdr'><a href="#tn_45">p. &ensp;45</a>:</td>
+<td class='tdl'>‘many of them has’</td>
+<td class='tdl'>amended to ‘many of them have’</td>
+</tr>
+<tr>
+<td class='tdr'><a href="#tn_281">p. 281</a>:</td>
+<td class='tdl'> ‘are adpated’</td>
+<td class='tdl'> amended to ‘are adapted’</td>
+</tr>
+<tr>
+<td class='tdr'><a href="#tn_291">p. 291</a>:</td>
+<td class='tdl'>‘and as it can, moveover’</td>
+<td class='tdl'>amended to ‘and as it can, moreover’</td>
+</tr>
+<tr>
+<td class='tdr'><a href="#tn_354">p. 354</a>:</td>
+<td class='tdl'>‘eruption of Krakatao’</td>
+<td class='tdl'>amended to ‘eruption of Krakatoa’</td>
+</tr>
+</table>
+</div>
+
+<div style='text-align:center'>*** END OF THE PROJECT GUTENBERG EBOOK 78430 ***</div>
+</body>
+</html>
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diff --git a/LICENSE.txt b/LICENSE.txt
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+This book, including all associated images, markup, improvements,
+metadata, and any other content or labor, has been confirmed to be
+in the PUBLIC DOMAIN IN THE UNITED STATES.
+
+Procedures for determining public domain status are described in
+the "Copyright How-To" at https://www.gutenberg.org.
+
+No investigation has been made concerning possible copyrights in
+jurisdictions other than the United States. Anyone seeking to utilize
+this eBook outside of the United States should confirm copyright
+status under the laws that apply to them.
diff --git a/README.md b/README.md
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+Project Gutenberg (https://www.gutenberg.org) public repository for eBook #78430
+(https://www.gutenberg.org/ebooks/78430)