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diff --git a/10726.txt b/10726.txt new file mode 100644 index 0000000..51415ac --- /dev/null +++ b/10726.txt @@ -0,0 +1,3582 @@ +The Project Gutenberg eBook, Outlines of Lessons in Botany, Part I; From +Seed to Leaf, by Jane H. Newell, Illustrated by H. P. Symmes + + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + + + + + + + +Title: Outlines of Lessons in Botany, Part I; From Seed to Leaf + +Author: Jane H. Newell + +Release Date: January 16, 2004 [eBook #10726] + +Language: English + +Character set encoding: US-ASCII + + +***START OF THE PROJECT GUTENBERG EBOOK OUTLINES OF LESSONS IN BOTANY, +PART I; FROM SEED TO LEAF*** + + +E-text prepared by Juliet Sutherland, Keren Vergon, Leonard D. Johnson, +and Project Gutenberg Distributed Proofreaders + + + +OUTLINES OF LESSONS IN BOTANY. + +PART I.: FROM SEED TO LEAF + +FOR THE USE OF TEACHERS, OR MOTHERS STUDYING WITH THEIR CHILDREN. + +BY + +JANE H. NEWELL. + +ILLUSTRATED BY H.P. SYMMES + +1888. + + + + + + + +PART I + +TABLE OF CONTENTS + + +I. PLANTS AND THEIR USES + 1. Food + 2. Clothing + 3. Purification of the Air + 4. Fuel + +II. SEEDLINGS + 1. Directions for raising in the Schoolroom + 2. Study of Morning-Glory, Sunflower, Bean, and Pea + 3. Comparison with other Dicotyledons + 4. Nature of the Caulicle + 5. Leaves of Seedlings + 6. Monocotyledons + 7. Food of Seedlings + +III. ROOTS + 1. Study of the Roots of Seedlings + 2. Fleshy Roots + 3. Differences between Stem and Root + 4. Root-hairs + 5. Comparison of a Carrot, an Onion, and a Potato + +IV BUDS AND BRANCHES + 1. Horsechestnut + Magnolia + Lilac + Beech + American Elm + Balm of Gilead + Tulip-tree + Cherry + Red Maple + Norway Spruce + 2. Vernation + 3. Phyllotaxy + +V STEMS + 1. Forms + 2. Movements + 3. Structure + +VI LEAVES + 1. Forms and Structure + 2. Descriptions + 3. Transpiration + 4. Assimilation + 5. Respiration + + + + +PREFACE. + + +In this study, as in all scientific teaching, the teacher's aim should +be to foster in his pupils the power of careful observation and clear +expression. The actual amount of knowledge gained at school must needs be +small, and often quickly forgotten, but the habit of right study is an +invaluable possession. + +The former method of teaching Botany was confined almost wholly to dry, +technical classification. The pupil learned to find the name and order of +a plant, but its structure, its habits, its life in short, were untouched +by him. We know now that Nature is the best text-book. The pupil should +first ask his questions of her and try to interpret her answers; then he +may learn with profit what those who better understand her speech have to +tell him. + +This method of teaching, however, requires much, very much, of the +teacher. He must be himself intelligent, well trained, and able to give +time to the preparation of his lessons. It seems to us, who are but +amateurs, as if it were impossible to teach thus without a thorough +comprehension of the whole field. Our own ignorance oppresses us so much +that we feel tempted to say that we cannot attempt it. But if the work of +leading children to observe the wonders about them is to be done at all, +it must be done by us, who are not masters of our subject, and we must +find out for ourselves how we can best accomplish this result, since we +have so little to guide us. + +It is with the hope that the experience of one who has tried to do +this with some fair amount of success may be of use to other puzzled +experimenters, that I venture to write out some outlines of lessons in +Botany for beginners. + +The method of beginning with the simpler forms of life is one that appeals +to the scientific tendencies of the day. It seems logical to begin with +lower forms and work up to the higher. But this method is only suitable +for mature minds. We do not teach a child English by showing him the +sources of the language; he learns it by daily use. So also the beginning +of the study of any Natural Science by the young should be the observation +of the most obvious things about them, the things which they can see, and +handle, and experiment upon naturally, without artificial aids. Therefore +this book concerns itself only with the Flowering Plants. + +The author believes that the simplest botanical study should afford the +means of identifying plants, as a large part of the student's pleasure in +the science will be the recognition of the things about him. The present +volume affords the basis for future classification, which Part II, on +flowers, will develop. It is, doubtless, as good a way, perhaps the best, +to begin with a single plant, and study root, stem, leaves, and flowers +as belonging to a whole, but the problem is complicated by practical +difficulties. In our climate there are but two months of the school year +when flowers are easily obtained. On the other hand, the material for +these lessons can be got throughout the winter, and the class, well +trained in methodical work, will begin the study of flowers at the season +when every day brings some fresh wonder of beauty. + +The author will receive gladly any criticisms or suggestions. + +JANE H. NEWELL. + +175 Brattle St., Cambridge + + + + +INTRODUCTION. + + +The lessons here outlined are suitable for children of twelve years of +age, and upwards. For younger pupils they would require much adaptation, +and even then they would not be so good as some simpler method, such as +following the growth of one plant, and comparing it with others at every +step. The little ones profit most by describing the very simple things +that they see, without much reference to theories. + +The outlines follow the plan of Dr. Gray's First Lessons and How Plants +Grow, and are intended to be used in connection with either of those +books. The necessary references will be found at the end of every section. +The book contains also references to a course of interesting reading in +connection with the subjects of the lessons. + +The lessons may begin, like the text-books, with the subject of +Germination, if the seeds are planted before they are required for use, +but it is generally preferable to use the first recitation with the class +for planting the seeds, in order to have them under the direct care of the +pupils. Some general talks about plants are therefore put at the beginning +to occupy the time until the seedlings are ready for study. + +Some Nasturtiums (_Tropaeolum majus_) and Morning-Glories should be planted +from the first in boxes of earth and allowed to grow over the window, as +they are often used for illustrations. + + + + +I. + +PLANTS AND THEIR USES.[1] + + +[Footnote 1: This section may be omitted, and the lessons begun with +Seedlings, if the teacher prefer.] + +What is Botany? The pupils are very apt to say at first that it is +learning about _flowers_. The teacher can draw their attention to the fact +that flowers are only a part of the plant, and that Botany is also the +study of the leaves, the stem, and the root. Botany is the science of +_plants_. Ask them what the Geranium is. Tell them to name some other +plants. The teacher should keep a few growing plants in the schoolroom for +purposes of illustration. + +Ask them what else there is in the world besides plants. By this question +the three kingdoms, animal, vegetable, and mineral, are brought up. It +will give occasion for a discussion of the earth and what it contains, the +mountains, formed of rocks and soil, the plants growing on the earth, +and the animals that inhabit it, including man. Let them name the three +kingdoms with some example of each. Which of these kingdoms contain living +things? The words _organic_ and _inorganic_ can be brought in here. An +_organ_ ([Greek: Ergon], meaning work) is any part that does a special +work, as the leaves, the stem of a plant, and the eye, the ear of animals. +An _organism_ is a living being made up of such organs. The inorganic +world contains the mineral kingdom; the organic world includes the +vegetable and animal kingdoms. + +One's aim in these lessons should always be to tell the pupils as little +as possible. Try to lead them to think out these things for themselves. + +Ask them how plants differ from animals. They will say that plants are +fixed to one place, while animals can move about; that plants have no will +or consciousness, and that animals have. These answers are true when we +compare the higher animals with plants, but the differences become lost as +we descend in the scale and approach the border land where botanist and +zoologist meet on a common ground. Sea-anemones are fixed to the rock on +which they grow, while some of the lower plants are able to move from +place to place, and it is hardly safe to affirm that a jelly-fish is more +conscious of its actions than is a Sensitive Plant, the leaves of which +close when the stem is touched. + +There is no real division between animals and plants. We try to classify +the objects about us into groups, according to the closeness of their +relationships, but we must always remember that these hard lines are ours, +not Nature's. We attempt, for purposes of our own convenience, to divide a +whole, which is so bound together that it cannot be separated into parts +that we can confidently place on different sides of a dividing line. + + +1. _Plants as Food-Producers_.--The chief distinguishing characteristic of +plants is one that the pupils may be led to think out for themselves by +asking them what animals feed upon. To help them with this, ask them what +they had for breakfast. Oatmeal is mentioned, perhaps. This is made from +oats, which is a plant. Coffee and tea, bread made from wheat, potatoes, +etc., all come from plants.[1] Beef, butter and milk come from the cow, +but the cow lives upon grass. The plant, on the other hand, is nourished +upon mineral or inorganic matter. It can make its own food from the soil +and the air, while animals can only live upon that which is made for +them by plants. These are thus the link between the mineral and animal +kingdoms. Ask the scholars if they can think of anything to eat or drink +that does not come from a plant. With a little help they will think of +salt and water. These could not support life. So we see that animals +receive all their food through the vegetable kingdom. One great use of +plants is that they are _food-producers_. + +[Footnote 1: Reader in Botany, for use in Schools. Selected and adapted +from well-known authors. Ginn & Co., Boston, New York and Chicago, 1889. +I. Origin of Cultivated Plants.] + +This lesson may be followed by a talk on food and the various plants used +for food.[2] + +[Footnote 2: The Flour Mills of Minneapolis: Century Magazine, May, 1886. +Maize: Popular Science News, Nov. and Dec., 1888.] + + +2. _Clothing_.--Plants are used for clothing. Of the four great clothing +materials, cotton, linen, silk, and woollen, the first two are of +vegetable, the last two of animal origin. Cotton is made from the hairs of +the seed of the cotton plant.[1] Linen is made of the inner fibre of +the bark of the flax plant. It has been cultivated from the earliest +historical times. + +[Footnote 1: Reader in Botany. II. The Cotton Plant.] + + +3. _Purification of the Air_.--The following questions and experiments are +intended to show the pupils, first, that we live in an atmosphere, the +presence of which is necessary to support life and combustion (1) and (2); +secondly, that this atmosphere is deprived of its power to support life +and combustion by the actions of combustion (2), and of respiration (3); +thirdly, that this power is restored to the air by the action of plants +(4). + +We have the air about us everywhere. A so-called empty vessel is one +where the contents are invisible. The following experiment is a good +illustration of this. + +(1) Wrap the throat of a glass funnel with moistened cloth or paper so +that it will fit tightly into the neck of a bottle, and fill the funnel +with water. If the space between the funnel and the bottle is air-tight, +the water will not flow into the bottle. + +[Illustration: FIG. 1.] + +Do not explain this in advance to the pupils. Ask them what prevents +the water from flowing into the bottle. If they are puzzled, loosen the +funnel, and show them that the water will now flow in. In the first case, +as the air could not escape, the water could not flow in; in the second, +the air was displaced by the heavier water. + +Ask the pupils why the air in a crowded room becomes so difficult to +breathe. Could a person live if he were shut up in an air-tight room for a +long time? Fresh air is necessary to life. The teacher may explain that it +is the oxygen in the air that supports life. Air is composed one-fifth of +this gas and four-fifths of nitrogen. The gases are mixed and the nitrogen +simply dilutes the oxygen, as it were. + +Fresh air is necessary to support combustion as well as life. Ask them why +we put out a fire by throwing a blanket or a rug over it. The following +experiment illustrates this. + +(2) Take a small, wide-mouthed bottle, covered with a card or cork. To +this cover fasten a piece of bent wire with a taper on the end. Light the +taper and lower it into the jar. It will burn a few seconds and then go +out. Raise and light it again, and it will be extinguished as soon as it +is plunged into the bottle. This shows that the oxygen of the air is used +up by burning substances, as it is by breathing animals. + +[Illustration: FIG. 2.] + +The following experiment shows that fire will not burn in an atmosphere of +gas from our lungs. + +(3) Fill a bottle with gas by breathing into it through a bit of glass +tubing, passed through a card or cork, and reaching to the bottom of the +bottle. The bottle will be dimmed with moisture, showing the presence of +aqueous vapor. A lighted match plunged into the bottle will be immediately +extinguished. A better way, which, however, takes some skill in +manipulation, is to fill the bottle with water, cover it with a flat piece +of glass, and invert the bottle in a dish of water, taking care that no +air bubbles enter. Then, through a bit of glass tubing, blow into the +bottle till the water is expelled. Cover the mouth with the glass under +water, and holding it tightly down, invert the bottle quickly. Set it +down, light a match, take away the glass, and at the same instant plunge +in the match. If no air has been allowed to enter, the match will go out +at once. No animal could live in an atmosphere which could not support +combustion. + +From these experiments the pupils have seen that the life-sustaining +quality of the air is used up by combustion and respiration. To bring in +the subject of purification by plants, ask them why all the oxygen in +the world is not exhausted by the people and the fires in it. After the +subject has been explained, the following experiment can be prepared and +put aside till the next lesson. + +(4) Fill two bottles with air from the lungs, as in (3) having previously +introduced a cutting from a plant into one of the bottles. Allow them to +stand in the sun for a day or two. Then test both bottles with a burning +match. If properly done, the result will be very striking. The end of +the cutting should be in the water of the dish. This experiment will not +succeed excepting with bottles such as are used for chemicals, which have +their mouths carefully ground. Common bottles allow the air to enter +between the bottle and the glass.[1] + +[Footnote 1: See note on page 13.] + +[Illustration: FIG. 3.] + + +4. _Fuel_.--Light a match and allow it to burn until half charred. Blow it +out gently, so as to leave a glowing spark. When this spark goes out it +will leave behind a light, gray ash. We have to consider the flame, the +charred substance, and the ash. + +Flame is burning gas. In all ordinary fuels, carbon and hydrogen, in +various combinations and free, make the principal part. The first effect +of the heat is to set free the volatile compounds of carbon and hydrogen. +The hydrogen then begins to unite with the oxygen of the air, forming +water, setting free the carbon, which also unites with oxygen, forming +carbonic acid gas. The burning gases cause the flame. The following +experiment will illustrate this. + +[Illustration: Fig. 4.] + +(5) Fit a test-tube with a tight cork, through which a bit of glass +tubing, drawn out into a jet, is passed, the tubing within being even with +the cork. Place some bits of shaving in the tube, cork it, and make the +cork perfectly air-tight by coating it with bees wax or paraffine. Heat +the test-tube gently over an alcohol lamp. The wood turns black, and vapor +issues from the jet, which may be lighted (Fig. 4). Care should be taken +to expel all the air before lighting. + +(6) That the burning hydrogen forms water by uniting with the oxygen of +the air, may be shown by holding a cold glass tumbler over the jet, or +over any flame. The glass will be dimmed by drops of moisture. + +The charred part of the wood is charcoal, which is one form of carbon. +Our ordinary charcoal is made by driving off all the gases from wood, by +burning it under cover where only a little air can reach it. The volatile +gases burn more readily than the carbon, and are the first substances to +be driven off, so that the carbon is left behind nearly pure. In the same +way we have driven off all the gases from the half-burned match and left +the carbon. The teacher should have a piece of charcoal to show the +pupils. It still retains all the markings of the wood. + +If the combustion is continued, the carbon also unites with the oxygen of +the air, till it is all converted into carbonic acid gas. This was the +case with the match where we left the glowing spark. The gray ash that was +left behind is the mineral matter contained in the wood. + +(7) We can show that this gas is formed by pouring lime water into a +bottle in which a candle has been burned as in (2). The water becomes +milky from a fine white powder formed by the union of the carbonic acid +gas with the lime, forming carbonate of lime. This is a chemical test. + +The wood of the match is plainly of vegetable origin; so also is the +charcoal, which is nearly pure carbon. Coal is also carbon, the remains of +ancient forests, from which the gases have been slowly driven off by heat +and pressure. All the common fuels are composed principally of carbon and +hydrogen. When these elements unite with oxygen, carbonic acid gas and +water are formed.[1] + +[Footnote 1: [Transcriber's Note: This note is missing from original +text.]] + +(8) The same products are formed by respiration. We breathe out carbonic +acid gas and water from our lungs. Breathe on a cold glass. It is bedewed +exactly as it is by the candle flame. Breathe through a bit of glass +tubing into a bottle of lime water. It becomes milky, showing the presence +of carbonic acid gas. Why is this? + +Every act or thought is accompanied by a consumption of material in the +body, which thus becomes unfit for further use. These waste substances, +composed chiefly of carbon and hydrogen, unite with oxygen breathed in +from the air, forming carbonic acid gas and water, which are breathed +out of the system. The action is a process of slow combustion, and it is +principally by the heat thus evolved that the body is kept warm. As we are +thus constantly taking oxygen from the air, a close room becomes unfit to +live in and a supply of fresh air is indispensable. The cycle of changes +is completed by the action of plants, which take in carbonic acid gas, use +the carbon, and return most of the oxygen to the atmosphere. + +APPARATUS FOR EXPERIMENTS.[1] + +[Footnote 1: The glass apparatus required, including an alcohol lamp, may +be obtained for one dollar by sending to the Educational Supply Co., No. 6 +Hamilton Place, Boston.] + +Two small wide-mouthed bottles. A narrow-necked bottle. A glass funnel. A +bit of bent glass-tubing. A bit of straight glass-tubing. A flat piece of +glass. A test-tube, with jet. An alcohol lamp. A bent wire with taper. +A card. A slip of a plant. A dish and pitcher of water. Beeswax or +paraffine. Shavings. Lime water. Matches. + +_Gray's First Lessons. Revised edition_. Sect. XVI, 445-7, 437. + +_How Plants Grow_. Chap. III, 279-288. + + + + +II. + +SEEDLINGS. + + +1. _Directions for raising in the Schoolroom_.--The seeds should be +planted in boxes tilled with clean sand. Plates or shallow crockery pans +are also used, but the sand is apt to become caked, and the pupils are +likely to keep the seeds too wet if they are planted in vessels that +will not drain. The boxes should be covered with panes of glass till the +seedlings are well started, and should be kept at a temperature of from +65 deg. to 70 deg. Fahr. It is very important to keep them covered while +the seeds are germinating, otherwise the sand will be certain to become +too dry if kept in a sufficiently warm place. Light is not necessary, and +in winter time the neighborhood of the furnace is often a very convenient +place to keep them safe from frost. They should not be in the sun while +germinating. When the first sprouts appear above the ground let another +set be planted, and so on, till a series is obtained ranging from plants +several inches high to those just starting from the seed. The seeds +themselves should be soaked for a day and the series is then ready +for study. The time required for their growth varies according to the +temperature, moisture, etc. Dr. Goodale says they should be ready in ten +days.[1] + +[Footnote 1: Concerning a few Common Plants, by G.L. Goodale, Boston, D.C. +Heath & Co. This little book, which is published, in pamphlet form, for +fifteen cents, will be found exceedingly useful.] + +I have never been able to raise them so quickly in the schoolroom, nor +have the pupils to whom I have given them to plant done so at home. +Generally, it is three weeks, at least, before the first specimens are as +large as is desirable. + +Germinating seeds need warmth, moisture and air. The necessary conditions +are supplied in the very best way by growing them on sponge, but it would +be difficult to raise enough for a large class in this manner. Place a +piece of moist sponge in a jelly-glass, or any glass that is larger at the +top, so that the sponge may not sink to the bottom, and pour some water +into the glass, but not so much as to touch the sponge. The whole should +be covered with a larger inverted glass, which must not be so close as +to prevent a circulation of air. The plants can thus be watched at every +stage and some should always be grown in this way. The water in the +tumbler will keep the sponge damp, and the roots, after emerging from +the sponge, will grow well in the moist air. Seeds can also be grown on +blotting paper. Put the seeds on several thicknesses of moist blotting +paper on a plate, cover them with more moist paper, and invert another +plate over them, taking care to allow the free entrance of air. + +If possible, it is by far the best way to have the seeds growing in the +schoolroom, and make it a regular custom for the pupils to observe them +every morning and take notes of their growth. + +These lessons on seeds are suitable for pupils of every age, from adults +to the youngest children who go to school. The difference should be only +in the mode of treatment; but the same principles should be brought out, +whatever the age and power of comprehension of the pupil. + +For these lessons the following seeds should be planted, according to the +above directions: + +Morning-Glory, Sunflower or Squash, Bean, Pea, Red Clover, Flax, Corn, +Wheat, and Oats.[1] If they can be procured plant also acorns, Pine-seeds, +Maple-seeds, and horsechestnuts. + +[Footnote 1: A package of these seeds may be obtained for fifty cents, +from Joseph Breck & Son, Boston, Mass. They will be sent by mail, postage +paid.] + + +2. _Study of Morning-Glory, Sunflower, Bean, and Pea_.--For reasons +hereafter given, I consider the Morning-Glory the best seedling to begin +upon. Having a series, as above described, before them, the pupils should +draw the seedlings. When the drawings are made, let them letter alike the +corresponding parts, beginning with the plantlet in the seed, and using +new letters when a new part is developed. The seed coats need not be +lettered, as they do not belong to the plantlet. + +[Illustration: FIG. 5.--Germination of Morning Glory, _a_, caulicle; _b_, +cotyledons; _c_, plumule; _d_, roots.] + +[Illustration: FIG. 6.--Germination of Sunflower.] + +After drawing the Morning-Glory series, let them draw the Sunflower or +Squash in the same way, then the Bean, and finally the Pea. Let them write +answers to the following questions: + +MORNING-GLORY.[1] + +[Footnote 1: It has been objected that the Morning-Glory seed is too small +to begin upon. If the teacher prefer, he may begin with the Squash, Bean, +and Pea. The questions will require but little alteration, and he can take +up the Morning-Glory later.] + +Tell the parts of the Morning-Glory seed. + +What part grows first? + +What becomes of the seed-covering? + +What appears between the first pair of leaves? + +Was this to be seen in the seed? + +How many leaves are there at each joint of stem after the first pair? + +How do they differ from the first pair? + +SUNFLOWER OR SQUASH. + +What are the parts of the seed? + +What is there in the Morning-Glory seed that this has not? + +How do the first leaves change as the seedling grows? + + +BEAN. + +What are the parts of the seed? + +How does this differ from the Morning-Glory seed? + +How from the Sunflower seed? + +How do the first pair of leaves of the Bean change as they grow? + +How many leaves are there at each joint of stem?[1] + +[Footnote 1: There are two simple leaves at the next node to the +cotyledons; after these there is one compound leaf at each node.] + +How do they differ from the first pair? + + +PEA. + +What are the parts of the seed? Compare it with the Morning-Glory, +Sunflower, and Bean. + +How does it differ in its growth from the Bean? + +What have all these four seeds in common? + +[Illustration: FIG. 7.--Germination of Pea. _a_, caulicle; _b_, +cotyledons; _c_, plumule; _d_, roots.] + +[Illustration: FIG. 8.--Germination of Bean.] + +What has the Morning-Glory seed that the others have not? + +What have the Bean and Pea that the Morning-Glory has not? + +How does the Pea differ from all the others in its growth? + +What part grows first in all these seeds? + +From which part do the roots grow? + +What peculiarity do you notice in the way they come up out of the +ground?[1] + +[Footnote 1: This question refers to the arched form in which they come +up. In this way the tender, growing apex is not rubbed.] + +The teacher must remember that, unless the pupils have had some previous +training, they will first have to learn to use their eyes, and for this +they will need much judicious help. They should be assisted to see what is +before them, not told what is there. It is absolutely necessary that these +questions should be thoroughly understood and correctly answered before +any conclusions are drawn from them. For this purpose abundant material is +indispensable. It is better not to attempt these lessons on seeds at +all, unless there is material enough for personal observation by all the +pupils. + +After this preliminary work has been done, the names of the parts can +be given to the pupils. They may be written under each drawing +thus,--A=Caulicle;[1] B=Cotyledons; C=Roots; D=Plumule. The whole plantlet +in the seed is the _embryo_ or _germ_, whence the sprouting of seeds is +called _germination_. + +[Footnote 1: The term radicle is still in general use. The derivation +(little root) makes it undesirable. Dr. Gray has adopted caulicle (little +stem) in the latest edition of his text-book, which I have followed. Other +writers use the term hypocotyl, meaning under the cotyledons.] + +I consider this the best order to study the seeds because in the +Morning-Glory the cotyledons are plainly leaves in the seed; and in the +Squash or Sunflower[2] the whole process is plainly to be seen whereby +a thick body, most unlike a leaf, becomes an ordinary green leaf with +veins.[3] In the Sunflower the true leaves are nearly the same shape as +the cotyledons, so that this is an especially good illustration for the +purpose. Thus, without any hint from me, my pupils often write of the +Bean, "it has two thick leaves and two thin leaves." In this way the Bean +and Pea present no difficulty. The cotyledons in the first make apparently +an unsuccessful effort to become leaves, which the second give up +altogether. + +[Footnote 2: The large Russian Sunflower is the best for the purpose.] + +[Footnote 3: These lessons are intended, as has been said, for children +over twelve years of age. If they are adapted for younger ones, it is +especially important to begin with a seed where the leaf-like character +of the cotyledons is evident, or becomes so. Maple is excellent for the +purpose. Morning-Glory is too small. Squash will answer very well. I think +it characteristic of the minds of little children to associate a term with +the first specimen to which it is applied. If the term cotyledon be given +them first for those of the Bean and Pea they will say when they come to +the Morning-Glory, "but those are _leaves_, not cotyledons. Cotyledons are +large and round." It will be very difficult to make them understand that +cotyledons are the first seed-leaves, and they will feel as if it were a +forced connection, and one that they cannot see for themselves.] + +The teacher's object now is to make the pupils understand the meaning of +the answers they have given to these questions. In the first place, they +should go over their answers and substitute the botanical terms they have +just learned for the ones they have used. + + +COMPARISON OF THE PARTS OF THE SOAKED SEEDS. + +_Morning-Glory_. A seed covering. Some albumen. Two cotyledons. A +caulicle. + +_Sunflower_. An outer covering.[1] An inner covering. Two cotyledons. A +caulicle.[2] + +[Footnote 1: The so-called seed of Sunflower is really a fruit. The outer +covering is the wall of the ovary, the inner the seed-coat. Such closed, +one-seeded fruits are called akenes.] + +[Footnote 2: The plumule is sometimes visible in the embryo of the +Sunflower.] + +_Bean_. A seed covering. Two cotyledons. A caulicle. A plumule. + +_Pea_. The same as the Bean. + +They have also learned how the first leaves in the last three differ from +those of the Morning-Glory, being considerably thicker in the Sunflower, +and very much thicker in the Bean and Pea. Why should the Morning-Glory +have this jelly that the others have not? Why do the first leaves of the +Sunflower change so much as the seedling grows? What becomes of their +substance? Why do those of the Bean shrivel and finally drop off? By this +time some bright pupil will have discovered that the baby-plant needs food +and that this is stored around it in the Morning-Glory, and in the leaves +themselves in the others. It is nourished upon this prepared food, until +it has roots and leaves and can make its own living. The food of the +Morning-Glory is called _albumen_; it does not differ from the others in +kind, but only in its manner of storage.[1] + +[Footnote 1: Reader in Botany. III. Seed-Food.] + +Also the questions have brought out the fact that the Bean and Pea +have the plumule ready formed in the seed, while the Morning-Glory and +Sunflower have not. Why should this be? It is because there is so much +food stored in the first two that the plumule can develop before a root is +formed, while in the others there is only nourishment sufficient to enable +the plantlet to form its roots. These must make the second leaves by their +own labor. + + +3. _Comparison with other Dicotyledons_.--The pupils should now have other +seeds to compare with these four. Let them arrange Flax, Four o-clock, +Horsechestnut, Almond, Nasturtium, Maple-seeds, etc., under two heads. + +_Seeds with the Food stored _Seeds with the Food stored +outside the plantlet in the embryo itself +(Albuminous)_. (Exalbuminous)_. + +Flax. Four-o'clock. Acorn. Horsechestnut. Almond. +Morning-Glory. Maple. Sunflower. Squash. + Bean. Pea. Nasturtium. + +They may also be divided into those with and without the plumule. + +_Without Plumule_. _With Plumule_. + +Flax. Maple. Sunflower. Acorn. Horsechestnut. +Four-o'clock. Almond. Bean. Pea. +Morning-Glory. Squash. Nasturtium. + +Those with plumules will be seen to have the most abundant nourishment. In +many cases this is made use of by man. + +These last can be again divided into those in which the cotyledons come up +into the air and those where they remain in the ground. + +_In the Air_. _In the Ground_. + +Bean. Almond. Squash. Acorn. Horsechestnut. + Pea. Nasturtium. + +In the latter the cotyledons are so heavily gorged with nourishment that +they never become of any use as leaves. As Darwin points out, they have +a better chance of escaping destruction by animals by remaining in the +ground. + +The cotyledons are very good illustrations of the different uses to which +a single organ may be put, and the thorough understanding of it will +prepare the pupils' minds for other metamorphoses, and for the theory that +all the various parts of a plant are modified forms of a very few members. + + +4. _Nature of the Caulicle_.--Probably some of the pupils will have called +the caulicle the root. It is, however, of the nature of stem. The root +grows only at the end, from a point just behind the tip; the stem +elongates throughout its whole length. This can be shown by marking the +stem and roots of a young seedling with ink. India ink must be used, as +common ink injures the plants. Dip a needle in the ink and prick a row +of spots at equal distances on a young root. Corn is very good for this +purpose, but Morning-Glory or Bean is better for experiments on the +stem. The plants should then be carefully watched and the changes in +the relative distance of the spots noted. The experiment is very easily +conducted with the seedlings growing on sponge, with their roots in the +moist air of the tumbler, as before described. + +Dr. Goodale says of this experiment,--"Let a young seedling of corn be +grown on damp paper in the manner described in No. 1,[1] and when the +longest root is a few centimetres long let it be marked very carefully by +means of India ink, or purple ink, put on with a delicate camel's-hair +pencil just one centimetre apart. Plants thus marked are to be kept under +favorable conditions with respect to moisture and warmth, so that growth +will be as rapid as possible. The marks on the older part of the root +will not change their relative distance, but the mark at the tip will be +carried away from the one next it, showing that the growth has taken place +only at this point. Such experiments as the one described are perfectly +practicable for all classes of pupils except the very youngest. How far +the details of these experiments should be suggested to the pupils, or +rather how far they should be left to work out the problem for themselves, +is a question to be settled by the teacher in each case. The better plan +generally is to bring the problem in a very clear form before the whole +class, or before the whole school, and ask whether anybody can think of a +way in which it can be solved; for instance, in this case how can it be +found out whether roots grow only at their tip or throughout their whole +length. If the way is thought out by even a single pupil the rest will be +interested in seeing whether the plan will work successfully." + +[Footnote 1: Concerning a Few Common Plants, page 25.] + +I have been more successful in pricking the roots than in marking them +with a brush. + +The caulicle can be proved by the manner of its growth to be of the nature +of stem, not root. The main root grows from its naked end. Roots can also +grow from the sides of the caulicle, as in Indian Corn. In this, it acts +precisely as does the stem of a cutting. It can be prettily shown with the +seedlings by breaking off a bean at the ground and putting the slip in +water. It will throw out roots and the pupil will readily understand that +the caulicle does the same thing. + +Darwin has made very interesting experiments on the movements of +seedlings. If the teacher wishes to repeat some of the experiments he will +find the details very fully given in "The Power of Movement of Plants."[1] +The pupils can observe in their growing seedlings some of the points +mentioned and have already noticed a few in their answers. They have said +that the caulicle was the part to grow first, and have spoken of the +arched form of the young stem. Their attention should also be drawn to the +root-hairs, which are well seen in Corn, Wheat, and Oats. They absorb the +liquid food of the plants. A secondary office is to hold the seed firmly, +so that the caulicle can enter the ground. This is shown in Red Clover, +which may be sown on the surface of the ground. It puts out root-hairs, +which attach themselves to the particles of sand and hold the seed. These +hairs are treated more fully in the lessons on roots. + +[Footnote 1: The Power of Movement in Plants. By Charles Darwin. London. +John Murray, 1880.] + +[Footnote 1: Reader in Botany. IV. Movements of Seedlings.] + + +5. _Leaves of Seedlings_.--Coming now to the question as to the number of +leaves at each joint of the stem, the Morning-Glory, Sunflower, and Bean +will present no difficulty, but probably all the pupils will be puzzled by +the Pea. The stipules, so large and leaf-like, look like two leaves, +with a stem between, bearing other opposite leaves, and terminating in a +tendril, while in the upper part it could not be told by a beginner which +was the continuation of the main stem. For these reasons I left this out +in the questions on the Pea, but it should be taken up in the class. How +are we to tell what constitutes a single leaf? The answer to this question +is that buds come in the _axils_ of single leaves; that is, in the inner +angle which the leaf makes with the stem. If no bud can be seen in the +Pea, the experiment may be tried of cutting off the top of the seedling +plant. Buds will be developed in the axils of the nearest leaves, and it +will be shown that each is a compound leaf with two appendages at its +base, called stipules, and with a tendril at its apex. Buds can be forced +in the same way to grow from the axils of the lower scales, and even from +those of the cotyledons, and the lesson may be again impressed that organs +are capable of undergoing great modifications. The teacher may use his own +judgment as to whether he will tell them that the tendril is a modified +leaflet. + +[Illustration: FIG. 9. 1. Grain of Indian Corn. 2. Vertical section, +dividing the embryo, _a_, caulicle: _b_, cotyledon; _c_, plumule. 3. +Vertical section, at right angles to the last.] + + +6. _Monocotyledons_.--These are more difficult. Perhaps it is not worth +while to attempt to make the pupils see the embryo in Wheat and Oats. But +the embryo of Indian Corn is larger and can be easily examined after long +soaking. Removing the seed-covering, we find the greater part of the seed +to be albumen. Closely applied to one side of this, so closely that it +is difficult to separate it perfectly, is the single cotyledon. This +completely surrounds the plumule and furnishes it with food from the +albumen. There is a line down the middle, and, if we carefully bend back +the edges of the cotyledon, it splits along this line, showing the +plumule and caulicle within. The plumule consists of successive layers of +rudimentary leaves, the outer enclosing the rest (Fig. 10, 1, _c_). The +latter is the first leaf and remains undeveloped as a scaly sheath (Fig. +10, 2, _c_). In Wheat and Oats the cotyledon can be easily seen in the +largest seedlings by pulling off the dry husk of the grain. The food will +he seen to have been used up. + +[Illustration: FIG. 10. 1. Germination of Indian corn. 2. Same more +advanced. _a_, caulicle; _c_1, first leaf of the plumule, sheathing the +rest; _c_2, second leaf; _c_3, third leaf of the plumule; _d_, roots.] + +The series of Corn seedlings, at least, should be drawn as before and +the parts marked, this time with their technical terms. The following +questions should then be prepared. + +CORN. + +What are the parts of the seed? + +Compare these parts with the Morning-Glory, Sunflower, Bean, and Pea. + +Where is the food stored? + +How many cotyledons have Corn, Wheat, and Oats? + +How many have Bean, Pea, Morning-Glory, and Sunflower? + +Compare the veins of the leaves of each class and see what difference you +can find. + +This will bring up the terms dicotyledon and monocotyledon. _Di_ means +two, _mono_ means one. This difference in the veins, netted in the first +class, parallel in the second, is characteristic of the classes. Pupils +should have specimens of leaves to classify under these two heads. +Flowering plants are divided first into these two classes, the +Dicotyledons and the Monocotyledons. + +If Pine-seeds can be planted, the polycotyledonous embryo can also be +studied. + + +7. _Food of seedlings_.--The food of the Wheat seedling may be shown in +fine flour. [1]"The flour is to be moistened in the hand and kneaded until +it becomes a homogeneous mass. Upon this mass pour some pure water and +wash out all the white powder until nothing is left except a viscid lump +of gluten. This is the part of the crushed wheat-grains which very closely +resembles in its composition the flesh of animals. The white powder washed +away is nearly pure wheat-starch. Of course the other ingredients, such as +the mineral matter and the like, might be referred to, but the starch at +least should be shown. When the seed is placed in proper soil, or upon a +support where it can receive moisture, and can get at the air and still be +warm enough, a part of the starch changes into a sort of gum, like that on +postage stamps, and finally becomes a kind of sugar. Upon this sirup the +young seedling feeds until it has some good green leaves for work, and as +we have seen in the case of some plants it has these very early." + +[Footnote 1: Concerning a Few Common Plants, page 18.] + +The presence of starch can be shown by testing with a solution of iodine. +Starch is turned blue by iodine and may thus be detected in flour, in +seeds, in potatoes, etc. + +After all this careful experimental work the subject may be studied in the +text-book and recited, the recitation constituting a thorough review of +the whole. + +A charming description of the germination of a seed will be found in the +Reader. V. The Birth of Picciola. + +_Gray's Lessons_. Sect. II, 8-14. III. _How Plants Grow_. Sect. I, 22, 23. +II. + + + + +III + +ROOTS. + + +This subject can be treated more conveniently while the young seedlings +are still growing, because their roots are very suitable for study. It +seems best, therefore, to take it up before examining the buds. + + +1. _Study of the Roots of Seedlings_.--One or two of the seedlings should +be broken off and the slips put into a glass of water. They will be +studied later. Bean and Sunflower are the best for the purpose. + +Begin by telling the pupils to prepare for their first lesson a +description of the roots of their seedlings. Those grown on sponge or +paper will show the development of the root-hairs, while those grown on +sand are better for studying the form of the root. Give them also some +fleshy root to describe, as a carrot, or a radish; and a spray of English +Ivy, as an example of aerial roots. + +Throughout these lessons, the method is pursued of giving pupils specimens +to observe and describe before teaching them botanical terms. It is better +for them to name the things they see than to find examples for terms +already learned. In the first case, they feel the difficulty of expressing +themselves and are glad to have the want of exact terms supplied. This +method is discouraging at first, especially to the younger ones; but, +with time and patience, they will gradually become accustomed to describe +whatever they can see. They have, at any rate, used their eyes; and, +though they may not understand the real meaning of anything they have +seen, they are prepared to discuss the subject intelligently when they +come together in the class. If they will first write out their unassisted +impressions and, subsequently, an account of the same thing after they +have had a recitation upon it, they will be sure to gain something in the +power of observation and clear expression. It cannot be too strongly +urged that the number of facts that the children may learn is not of the +slightest consequence, but that the teacher should aim to cultivate the +quick eye, the ready hand, and the clear reason. + +The root of the Morning-Glory is _primary_; it is a direct downward growth +from the tip of the caulicle. It is about as thick as the stem, tapers +towards the end, and has short and fibrous branches. In some plants the +root keeps on growing and makes a _tap-root_; in the Bean, it soon becomes +lost in the branches. These are all simple, that is, there is but one +primary root. Sometimes there are several or many, and the root is then +said to be _multiple_. The Pumpkin is an example of this. The root of +the Pea is described in the older editions of Gray's Lessons as being +multiple, but it is generally simple. Indian Corn, also, usually starts +with a single root, but this does not make a tap-root, and is soon +followed by many others from any part of the caulicle, or even from the +stem above, giving it the appearance of having a multiple root. + +The root of the Radish is different from any of these; it is _fleshy_. +Often, it tapers suddenly at the bottom into a root like that of +the Morning-Glory with some fibres upon it. It is, in fact, as the +Morning-Glory would be if the main root were to be thickened up by +food being stored in it. It is a primary tap-root. The radish is +_spindle-shaped_, tapering at top and bottom, the carrot is _conical_, the +turnip is called _napiform_; some radishes are shaped like the turnip. + +The aerial roots of the English Ivy answer another purpose than that of +giving nourishment to the plant. They are used to support it in climbing. +These are an example of _secondary_ roots, which are roots springing +laterally from any part of the stem. The Sweet Potato has both fleshy and +fibrous roots and forms secondary roots of both kinds every year.[1] Some +of the seedlings will probably show the root-hairs to the naked eye. These +will be noticed hereafter. + +[Footnote 1: Gray's Lessons, p. 35, Fig. 86.] + +[Illustration: FIG. 11.--1. Tap-root. 2. Multiple root of Pumpkin. 3. +Napiform root of Turnip. 4. Spindle-shaped root of Radish. 5. Conical root +of Carrot. 6. Aerial roots of Ivy.] + +It is my experience that pupils always like classifying things under +different heads, and it is a good exercise. The following table may be +made of the roots they have studied, adding other examples. Dr. Gray says +that ordinary roots may be roughly classed into fibrous and fleshy.[1] +Thome classes them as woody and fleshy.[2] + +[Footnote 1: Gray's Lessons, p. 34.] + +[Footnote 2: Text-book of Structural and Physiological Botany. Otto Thome. +Translated and edited by Alfred W. Bennett, New York. John Wiley and Sons. +1877. Page 75.] + + ROOTS. + | + ------------------------------------------ + | | + _Primary_. _Secondary_. + | | + -------------------------------- | + | | | + _Fibrous_. _Fleshy_. Roots of cuttings + | Aerial roots. + ------------------- Sweet potatoes.[3] + | | + _Simple_. _Multiple_. _Simple_. + + Morning Glory. Pumpkin Carrot. + Sunflower. Radish. + Pea. Turnip. + Bean. Beet. + Corn. Corn. + +[Footnote 3: The Irish potato will very likely be mentioned as an example +of a fleshy root. The teacher can say that this will be explained later.] + + +2. _Fleshy Roots_.--The scholars are already familiar with the storing +of food for the seedling in or around the cotyledons, and will readily +understand that these roots are storehouses of food for the plant. The +Turnip, Carrot, and Beet are _biennials_; that is, their growth is +continued through two seasons. In the first year, they make a vigorous +growth of leaves alone, and the surplus food is carried to the root in the +form of a syrup, and there stored, having been changed into starch, or +something very similar. At the end of the first season, the root is filled +with food, prepared for the next year, so that the plant can live on its +reserve fund and devote its whole attention to flowering. These roots +are often good food for animals. There are some plants that store their +surplus food in their roots year after year, using up in each season the +store of the former one, and forming new roots continually. The Sweet +Potato is an example of this class. These are _perennials_. The food in +perennials, however, is usually stored in stems, rather than in roots, as +in trees. _Annuals_ are generally fibrous-rooted, and the plant dies after +its first year. The following experiment will serve as an illustration of +the way in which the food stored in fleshy roots is utilized for growth. + +Cut off the tapering end of a carrot and scoop out the inside of the +larger half in the form of a vase, leaving about half of the flesh behind. +Put strings through the upper rim, fill the carrot cup with water, and +hang it up in a sunny window. Keep it constantly full of water. The +leaf-buds below will put forth, and grow into leafy shoots, which, turning +upwards, soon hide the vase in a green circle. This is because the dry, +starchy food stored in the carrot becomes soft and soluble, and the supply +of proper food and the warmth of the room make the leaf-buds able to grow. +It is also a pretty illustration of the way in which stems always grow +upward, even though there is enough light and air for them to grow +straight downwards. Why this is so, we do not know. + + +3. _Differences between the Stem and the Root.--_Ask the pupils to tell +what differences they have found. + +_Stems_. _Roots_. + +Ascend into the air. Descend into the ground. +Grow by a succession of similar Grow only from a point + parts, each part when young just behind the tip. + elongating throughout. +Bear organs. Bear no organs. + +There are certain exceptions to the statement that roots descend into the +ground; such as aerial roots and parasitic roots. The aerial roots of the +Ivy have been mentioned. Other examples of roots used for climbing are +the Trumpet Creeper _(Tecoma radicans)_, and the Poison Ivy _(Rhus +Toxicodendron)_. Parasitic roots take their food ready-made from the +plants into which they strike. The roots of air-plants, such as certain +orchids, draw their nourishment from the air. + +The experiment of marking roots and stem has been already tried, but it +should be repeated. Repetition of experiments is always desirable, as it +fixes his conclusions in the pupil's mind. The stem grows by a succession +of similar parts, _phytomera_, each part, or _phyton_, consisting of node, +internode, and leaf. Thus it follows that stems must bear leaves. The +marked stems of seedlings show greater growth towards the top of the +growing phyton. It is only young stems that elongate throughout. The older +parts of a phyton grow little, and when the internode has attained a +certain length, variable for different stems and different conditions, it +does not elongate at all. + +The root, on the contrary, grows only from a point just behind the tip. +The extreme tip consists of a sort of cap of hard tissue, called the +root-cap. Through a simple lens, or sometimes with the naked eye, it can +be distinguished in most of the roots of the seedlings, looking like a +transparent tip. "The root, whatever its origin in any case may be, grows +in length only in one way; namely, at a point just behind its very +tip. This growing point is usually protected by a peculiar cap, which +insinuates its way through the crevices of the soil. If roots should grow +as stems escaping from the bud-state do,--that is, throughout their whole +length--they would speedily become distorted. But, since they grow at the +protected tips, they can make their way through the interstices of soil, +which from its compactness would otherwise forbid their progress."[1] + +[Footnote 1: Concerning a few Common Plants, p. 25.] + +The third difference is that, while the stem bears leaves, and has buds +normally developed in their axils, roots bear no organs. The stem, +however, especially when wounded, may produce buds anywhere from the +surface of the bark, and these buds are called _adventitious_ buds. In the +same manner, roots occasionally produce buds, which grow up into leafy +shoots, as in the Apple and Poplar.[1] + +[Footnote 1: See Gray's Structural Botany, p. 29.] + +It should be made perfectly clear that the stem is the axis of the plant, +that is, it bears all the other organs. Roots grow from stems, not steins +from roots, except in certain cases, like that of the Poplar mentioned +above. This was seen in the study of the seedling. The embryo consisted of +stem and leaves, and the roots were produced from the stem as the seedling +grew. + +For illustration of this point, the careful watching of the cuttings +placed in water will be very instructive. After a few days, small, hard +lumps begin to appear under the skin of the stem of the broken seedling +Bean. These gradually increase in size until, finally, they rupture the +skin and appear as rootlets. Roots are always thus formed under the outer +tissues of the stem from which they spring, or the root from which they +branch. In the Bean, the roots are in four long rows, quartering the stem. +This is because they are formed in front of the woody bundles of the stem, +which in the seedling Bean are four. In the Sunflower the roots divide the +circumference into six parts. In some of my cuttings of Beans, the stem +cracked in four long lines before the roots had really formed, showing the +parenchyma in small hillocks, so to speak. In these the gradual formation +of the root-cap could be watched throughout, with merely a small lens. I +do not know a better way to impress the nature of the root on the pupil's +mind. These forming roots might also be marked very early, and so be shown +to carry onward their root-cap on the growing-point. + + +4. _Root-hairs_. These are outgrowths of the epidermis, or skin of the +root, and increase its absorbing power. In most plants they cannot be seen +without the aid of a microscope. Indian Corn and Oats, however, show them +very beautifully, and the scholars have already noticed them in their +seedlings. They are best seen in the seedlings grown on damp sponge. In +those grown in sand, they become so firmly united to the particles of +soil, that they cannot be separated, without tearing the hairs away from +the plant. This will suggest the reason why plants suffer so much from +careless transplanting. + +The root-hairs have the power of dissolving mineral matters in the soil +by the action of an acid which they give out. They then absorb these +solutions for the nourishment of the plant. The acid given out was first +thought to be carbonic acid, but now it is supposed by some experimenters +to be acetic acid, by others to vary according to the plant and the time. +The action can be shown by the following experiment, suggested by Sachs. + +[Illustration: Fig. 12. I. Seedling of _Sinapis alba_ showing root-hairs. +II. Same, showing how fine particles of sand cling to the root-hairs. +(Sachs.)] + +Cover a piece of polished marble with moist sawdust, and plant some seeds +upon it. When the seedlings are somewhat grown, remove the sawdust, and +the rootlets will be found to have left their autographs behind. Wherever +the roots, with their root-hairs have crept, they have eaten into the +marble and left it corroded. The marks will become more distinct if the +marble is rubbed with a little vermilion. + +In order that the processes of solution and absorption may take place, it +is necessary that free oxygen should be present. All living things must +have oxygen to breathe, and this gas is as needful for the germination of +seeds, and the action of roots and leaves, as it is for our maintenance of +life. It is hurtful for plants to be kept with too much water about their +roots, because this keeps out the air. This is the reason why house-plants +are injured if they are kept too wet. + +A secondary office of root-hairs is to aid the roots of seedlings to enter +the ground, as we have before noticed. + +The root-hairs are found only on the young parts of roots. As a root grows +older the root-hairs die, and it becomes of no further use for absorption. +But it is needed now for another purpose, as the support of the growing +plant. In trees, the old roots grow from year to year like stems, and +become large and strong. The extent of the roots corresponds in a general +way to that of the branches, and, as the absorbing parts are the young +rootlets, the rain that drops from the leafy roof falls just where it is +needed by the delicate fibrils in the earth below.[1] + +[Footnote 1: Reader in Botany. VI. The Relative Positions of Leaves and +Rootlets.] + + +5. _Comparison of a Carrot, an Onion, and a Potato_.--It is a good +exercise for a class to take a potato, an onion, and a carrot or radish to +compare, writing out the result of their observations. + +The carrot is a fleshy root, as we have already seen. The onion consists +of the fleshy bases of last year's leaves, sheathed by the dried remains +of the leaves of former years, from which all nourishment has been drawn. +The parallel veining of the leaves is distinctly marked. The stem is a +plate at the base, to which these fleshy scales are attached. In the +centre, or in the axils of the scales, the newly-forming bulbs can be +seen, in onions that are sprouting. If possible, compare other bulbs, as +those of Tulip, Hyacinth, or Snowdrop, and the bulb of a Crocus, in which +the fleshy part consists of the thickened base of the stem, and the leaves +are merely dry scales. This is called a _corm_. + +The potato is a thickened stem. It shows itself to be a stem, because it +bears organs. The leaves are reduced to little scales (eyelids), in the +axils of which come the buds (eyes). The following delightful experiment +has been recommended to me. + +In a growing potato plant, direct upwards one of the low shoots and +surround it with a little cylinder of stiff carpet paper, stuffed with +sphagnum and loam. Cut away the other tuber-disposed shoots as they +appear. The enclosed shoot develops into a tuber which stands more or less +vertical, and the scales become pretty little leaves. Removing the paper, +the tuber and leaves become green, and the latter enlarge a little. A +better illustration of the way in which organs adapt themselves to their +conditions, and of the meaning of morphology, could hardly be found. + +_Gray's First Lessons_. Sect. v, 65-88. _How Plants Grow_. Chap. I, 83-90. + + + + +IV. + +BUDS AND BRANCHES. + + +1. There is an astonishing amount to be learned from naked branches, +and, if pursued in the right way, the study will be found exceedingly +interesting. Professor Beal, in his pamphlet on the New Botany,[1] says:-- + +"Before the first lesson, each pupil is furnished or told where to procure +some specimen for study. If it is winter, and flowers or growing plants +cannot be had, give each a branch of a tree or shrub; this branch may be +two feet long. The examination of these is made during the usual time for +preparing lessons, and not while the class is before the teacher. For the +first recitation each is to tell what he has discovered. The specimens are +not in sight during the recitation. In learning the lesson, books are not +used; for, if they are used, no books will contain a quarter of what the +pupil may see for himself. If there is time, each member of the class is +allowed a chance to mention anything not named by any of the rest. The +teacher may suggest a few other points for study. The pupils are not told +what they can see for themselves. An effort is made to keep them working +after something which they have not yet discovered. If two members +disagree on any point, on the next day, after further study, they are +requested to bring in all the proofs they can to sustain their different +conclusions. For a second lesson, the students review the first lesson, +and report on a branch of a tree of another species which they have +studied as before. Now they notice any point of difference or of +similarity. In like manner new branches are studied and new comparisons +made. For this purpose, naked branches of our species of elms, maples, +ashes, oaks, basswood, beech, poplars, willows, walnut, butternut, +hawthorns, cherries, and in fact any of our native or exotic trees or +shrubs are suitable. A comparison of the branches of any of the evergreens +is interesting and profitable. Discoveries, very unexpected, are almost +sure to reward a patient study of these objects. The teacher must not +think time is wasted. No real progress can be made, till the pupils begin +to learn to see; and to learn to see they must keep trying to form the +habit from the very first; and to form the habit they should make the +study of specimens the main feature in the course of training." + +[Footnote 1: The New Botany. By W.J. Beal. Philadelphia, C.H. Marot, 814 +Chestnut St., 1882. Page 5.] + +HORSECHESTNUT (_AEsculus Hippocastanum_). + +We will begin with the study of a branch of Horsechestnut.[1] The pupils +should examine and describe their specimens before discussing them in the +class-room. They will need some directions and hints, however, to enable +them to work to any advantage. Tell them to open both large and small +buds. It is not advisable to study the Horsechestnut bud by cutting +sections, as the wool is so dense that the arrangement cannot be seen in +this way. The scales should be removed with a knife, one by one, and the +number, texture, etc., noted. The leaves and flower-cluster will remain +uncovered and will be easy to examine. The gum may be first removed by +pressing the bud in a bit of paper. The scholars should study carefully +the markings on the stem, in order to explain, if possible, what has +caused them. The best way to make clear the meaning of the scars is to +show them the relation of the bud to the branch. They must define a bud. +Ask them what the bud would have become the next season, if it had been +allowed to develop. It would have been a branch, or a part of one. A bud, +then, is an undeveloped branch. They can always work out this definition +for themselves. Conversely, a branch is a developed bud, or series of +buds, and every mark on the branch must correspond to something in the +bud. Let them examine the specimens with this idea clearly before their +minds. The lesson to prepare should be to write out all they can observe +and to make careful drawings of their specimens. Ask them to find a way, +if possible, to tell the age of the branch. + +[Footnote 1: The pupils should cut their names on their branches and keep +them. They will need them constantly for comparison and reference.] + +At the recitation, the papers can be read and the points mentioned +thoroughly discussed. This will take two lesson-hours, probably, and the +drawing may be left, if desired, as the exercise to prepare for the second +recitation. + +[1]The buds of Horsechestnut contain the plan of the whole growth of the +next season. They are scaly and covered, especially towards the apex, with +a sticky varnish. The scales are opposite, like the leaves. The outer +pairs are wholly brown and leathery, the succeeding ones tipped with +brown, wherever exposed, so that the whole bud is covered with a thick +coat. The inner scales are green and delicate, and somewhat woolly, +especially along the lapping edges. There are about seven pairs of +scales. The larger terminal buds have a flower-cluster in the centre, and +generally two pairs of leaves; the small buds contain leaves alone, two or +three pairs of them. The leaves are densely covered with white wool, to +protect them from the sudden changes of winter. The use of the gum is to +ward off moisture. The flower-cluster is woolly also. + +[Footnote 1: All descriptions are made from specimens examined by me. +Other specimens may differ in some points. Plants vary in different +situations and localities.] + +The scars on the stem are of three kinds, leaf, bud-scale, and +flower-cluster scars. The pupils should notice that the buds are always +just above the large triangular scars. If they are still in doubt as to +the cause of these marks, show them some house-plant with well-developed +buds in the axils of the leaves, and ask them to compare the position of +these buds with their branches. The buds that spring from the inner angle +of the leaf with the stem are _axillary_ buds; those that crown the stems +are _terminal_. Since a bud is an undeveloped branch, terminal buds carry, +on the axis which they crown, axillary buds give rise to side-shoots. The +leaf-scars show the leaf-arrangement and the number of leaves each year. +The leaves are opposite and each pair stands over the intervals of the +pair below. The same is observed to be true of the scales and leaves +of the bud.[1] All these points should be brought out by the actual +observation of the specimens by the pupils, with only such hints from the +teacher as may be needed to direct their attention aright. The dots on the +leaf-scar are the ends of woody bundles (fibro-vascular bundles) which, in +autumn, separated from the leaf. By counting these we can tell how many +leaflets there were in the leaf, three, five, seven, nine, or occasionally +six or eight. + +[Footnote 1: Bud-scales are modified leaves and their arrangement is +therefore the same as the leaves. This is not mentioned in the study of +the Horsechestnut bud, because it cannot be proved to the pupils, but the +transition is explained in connection with Lilac, where it may be clearly +seen. The scales of the bud of Horsechestnut are considered to be +homologous with petioles, by analogy with other members of the same +family. In the Sweet Buckeye a series can be made, exhibiting the gradual +change from a scale to a compound leaf. See the Botanical Text-Book, Part +I, Structural Botany. By Asa Gray. Ivison, Blakeman, Taylor and Co., New +York, 1879. Plate 233, p. 116.] + +[Illustration: FIG. 13.--Horsechestnut. I. Branch in winter state: _a_, +leaf-scars; _b_, bud-scars; _c_, flower-scars. 2. An expanding leaf-bud. +3. Same, more advanced.] + +_The Bud Scale-Scars_. These are rings left by the scales of the bud and +may be seen in many branches. They are well seen in Horsechestnut. If the +pupils have failed to observe that these rings show the position of former +buds and mark the growth of successive years, this point must be brought +out by skilful questioning. There is a difference in the color of the more +recent shoots, and a pupil, when asked how much of his branch grew the +preceding season, will be able to answer by observing the change in color. +Make him see that this change corresponds with the rings, and he will +understand how to tell every year's growth. Then ask what would make the +rings in a branch produced from one of his buds, and he can hardly fail to +see that the scales would make them. When the scholars understand that the +rings mark the year's growth, they can count them and ascertain the age +of each branch. The same should be done with each side-shoot. Usually the +numbers will be found to agree; that is, all the buds will have the +same number of rings between them and the cut end of the branch, but +occasionally a bud will remain latent for one or several seasons and then +begin its growth, in which case the numbers will not agree; the difference +will be the number of years it remained latent. There are always many buds +that are not developed. "The undeveloped buds do not necessarily perish, +but are ready to be called into action in case the others are checked. +When the stronger buds are destroyed, some that would else remain dormant +develop in their stead, incited by the abundance of nourishment which the +former would have monopolized. In this manner our trees are soon reclothed +with verdure, after their tender foliage and branches have been killed by +a late vernal frost, or consumed by insects. And buds which have remained +latent for several years occasionally shoot forth into branches from the +sides of old stems, especially in certain trees."[1] + +[Footnote 1: Structural Botany, p. 48.] + +The pupils can measure the distance between each set of rings on the main +stem, to see on what years it grew best. + +_The Flower-Cluster Scars_. These are the round, somewhat concave, scars, +found terminating the stem where forking occurs, or seemingly in the +axils of branches, on account of one of the forking branches growing more +rapidly and stoutly than the other and thus taking the place of the main +stem, so that this is apparently continued without interruption. If the +pupils have not understood the cause of the flower-cluster scars, show +them their position in shoots where they are plainly on the summit of the +stem, and tell them to compare this with the arrangement of a large +bud. The flower-cluster terminates the axis in the bud, and this scar +terminates a branch. When the terminal bud is thus prevented from +continuing its growth, the nearest axillary buds are developed.[1] One +shoot usually gets the start, and becomes so much stronger that it throws +the other to one side. The tendency of the Horsechestnut to have its +growth carried on by the terminal buds is so strong that I almost feel +inclined to say that vigorous branches are never formed from axillary +buds, in old trees, except where the terminal bud has been prevented from +continuing the branch. This tendency gives to the tree its characteristic +size of trunk and branches, and lack of delicate spray. On looking closely +at the branches also, they will be seen to be quite irregular, wherever +there has been a flower-cluster swerving to one side or the other. + +[Footnote 1: The first winter that I examined Horsechestnut buds I found, +in many cases, that the axillary shoots had from a quarter of an inch to +an inch of wood before the first set of rings. I could not imagine what +had formed this wood, and it remained a complete puzzle to me until the +following spring, when I found in the expanding shoots, that, wherever +a flower-cluster was present, there were one or two pairs of leaflets +already well developed in the axils, and that the next season's buds were +forming between them, while the internodes of these leaflets were making +quite a rapid growth. Subsequently, I found the leaflets also in the buds +themselves. I found these leaflets developed on the tree only in the +shoots containing flower-clusters, where they would be needed for the +future growth of the branches. I suppose the reason must be that the +flower-cluster does not use all the nourishment provided and that +therefore the axillary buds are able to develop. It would be interesting +to know what determines the stronger growth of the one which eventually +becomes the leader.] + +There is one thing more the pupils may have noticed. The small round dots +all over the young stem, which become long rifts in the older parts, are +breaks in the epidermis, or skin of the stem, through which the inner +layers of bark protrude. They are called lenticels. They provide a passage +for gases in and out of the stem. In some trees, as the Birch, they are +very noticeable. + +After discussing the subject thoroughly in the class-room, the pupils +should rewrite their papers, and finally answer the following questions, +as a species of review. I have thus spent three recitations on the +Horsechestnut. The work is all so new, and, if properly presented, +so interesting, that a good deal of time is required to exhaust its +possibilities of instruction. If the teacher finds his scholars wearying, +however, he can leave as many of the details as he pleases to be treated +in connection with other branches. + + +QUESTIONS ON THE HORSECHESTNUT. + +How many scales are there in the buds you have examined? + +How are they arranged? + +How many leaves are there in the buds? + +How are they arranged? + +Where does the flower-cluster come in the bud? + +Do all the buds contain flower-clusters? + +What is the use of the wool and the gum? + +Where do the buds come on the stem? + +Which are the strongest? + +How are the leaves arranged on the stem? + +Do the pairs stand directly over each other? + +What are the dots on the leaf-scars? + +How old is your branch? + +How old is each twig? + +Which years were the best for growth? + +Where were the former flower-clusters? + +What happens when a branch is stopped in its growth by flowering? + +What effect does this have on the appearance of the tree? + +In some parts of the country the Horsechestnut is not so commonly planted +as in New England. In the southern states the Magnolia may be used in its +stead, but it is not nearly so simple an example of the main points to be +observed.[1] + +[Footnote 1: Reader in Botany. VII. Trees in Winter.] + + +MAGNOLIA UMBRELLA. + +The bud may be examined by removing the scales with a knife, as in +Horsechestnut, and also by cutting sections. The outer scales enfold the +whole bud, and each succeeding pair cover all within. They are joined, +and it is frequently difficult to tell where the suture is, though it can +generally be traced at the apex of the bud. On the back is a thick +stalk, which is the base of the leaf-stalk. Remove the scales by cutting +carefully through a single pair, opposite the leaf-stalk, and peeling +them off. The scales are modified stipules, instead of leaf-stalks, as in +Horsechestnut. The outer pair are brown and thick, the inner green, and +becoming more delicate and crumpled as we proceed toward the centre of the +bud. The leaves begin with the second or third pair of scales. The first +one or two are imperfect, being small, brown, and dry. The leaves grow +larger towards the centre of the bud. They are covered with short, +silky hairs, and are folded lengthwise, with the inner surface within +(_conduplicate_). In the specimens I have examined I do not see much +difference in size between the buds with flowers and those without. In +every bud examined which contained a flower, there was an axillary bud in +the axil of the last, or next to the last, leaf. This bud is to continue +the interrupted branch in the same way as in Horsechestnut. + +There are from six to ten good leaves, in the buds that I have seen. Those +without flowers contain more leaves, as in Horsechestnut. In the centre of +these buds the leaves are small and undeveloped. The flower is very easy +to examine, the floral envelopes, stamens and pistils, being plainly +discernible. The bud may also be studied in cross-section. This shows the +whole arrangement. The plan is not so simple as in Horsechestnut, where +the leaves are opposite. The subject of leaf-arrangement should be passed +over until phyllotaxy is taken up. + +The scars on the stem differ from Horsechestnut in having no distinct +bands of rings. The scales, being stipules, leave a line on each side of +the leaf-scar, and these are separated by the growth of the internodes. +In the Beech, the scales are also stipules; but, whereas in the Magnolia +there are only one or two abortive leaves, in the Beech there are eight or +nine pairs of stipules without any leaves at all. The rings thus become +separated in Magnolia, while in the Beech the first internodes are not +developed, leaving a distinct band of rings, to mark the season's growth. +The Magnolia is therefore less desirable to begin upon. The branches are +swollen at the beginning of a new growth, and have a number of leaf-scars +crowded closely together. The leaf-scars are roundish, the lower line more +curved. They have many dots on them. From each leaf-scar runs an irregular +line around the stem. This has been left by the stipules. + +The flower-scar is on the summit of the axis, and often apparently in the +axil of a branch, as in Horsechestnut. Sometimes the nearest axillary bud +is developed; sometimes there are two, when the branch forks. The axillary +buds seldom grow unless the terminal bud is interrupted. The tree +therefore has no fine spray. + + +LILAC _(Syringa vulgaris_). + +Ask the scholars to write a description of their branches and to compare +them with Horsechestnut. These papers should be prepared before coming +into the class, as before. + +The buds are four-sided. The scales and leaves are opposite, as in +Horsechestnut. The outer pair sometimes have buds in their axils. Remove +the scales one by one with a knife, or better, with a stout needle. The +scales gradually become thinner as we proceed, and pass into leaves, so +that we cannot tell where the scales end and leaves begin. After about six +pairs are removed, we come, in the larger buds, to leaves with axillary +flower-clusters. The leaves grow smaller and the flower-clusters +larger till we come to the centre, where the axis is terminated by a +flower-cluster. There is a great difference in the buds on different +bushes and on shoots of the same bush, some being large, green, and easy +to examine, others small, hard, and dark-colored. It is better, of course, +to select as soft and large buds as possible for examination. + +[Illustration: FIG. 14.--Lilac. I. Branch in winter state: _a_, leaf-scar; +_b_, bud-scar (reduced). 2. Same, less reduced. 3. Branch, with leaf-buds +expanded. 4. Series in a single bud, showing the gradual transition from +scales to leaves.] + +That the scales are modified leaves is plainly shown by the gradual +transition they undergo, and also by the fact that buds are developed in +their axils. If any of these can be shown to the pupils, remind them of +the experiment where the top of a seedling Pea was cut off and buds forced +to develop in the axils of the lower scales.[1] The transition from scales +to leaves can be well studied by bringing branches into the house, where +they will develop in water, and towards spring may even be made to +blossom. Cherry, Apple, Forsythia, and other blossoming trees and shrubs +can be thus forced to bloom. Place the branches in hot water, and cut off +a little of their ends under water. If the water is changed every day, +and the glass kept near the register or stove, they will blossom out very +quickly. These expanded shoots may be compared with the buds. The number +of leaves in the bud varies. + +[Footnote 1: See p. 31.] + +The leaf-scars of Lilac are horseshoe-shaped and somewhat swollen. It can +often be plainly seen that the outer tissue of the stem runs up into the +scar. It looks as if there were a layer of bark, ending with the scar, +fastened over each side of the stem. These apparent layers alternate as +well as the scars. The epidermis, or skin of the leaves, is in fact always +continuous with that of the stem. There are no dots on the leaf-scars. + +The rings are not nearly so noticeable as in Horsechestnut, but they can +be counted for some years back. + +The flower-cluster can often be traced by a dried bit of stem remaining on +the branch. + +The terminal bud in the Lilac does not usually develop, and the two +uppermost axillary buds take its place, giving to the shrub the forked +character of its branching. In all these bud studies, the pupil should +finish by showing how the arrangement of the buds determines the growth of +the branches. + + +QUESTIONS ON THE LILAC. + +How do the scales differ from those of Horsechestnut? + +How many scales and leaves are there? + +How are they arranged? + +Where does the flower-cluster come in the bud? + +Do all the buds contain flower-clusters? + +How does the arrangement of leaves and flower-clusters differ from that of +Horsechestnut? + +How old is your branch? + +Which buds develop most frequently? + +How does this affect the appearance of the shrub? + + +COPPER BEECH (_Fagus sylvatica, var. purpurea_). + +The buds are long and tapering, the scales thin and scarious, the outer +naked, the inner with long, silky hairs. Remove the scales one by one, as +in Lilac. The outer four or six pairs are so minute that the arrangement +is not very clear, but as we proceed we perceive that the scales are in +alternate pairs, as in Horsechestnut; that is, that two scales are exactly +on the same plane. But we have learned in the Lilac that the scales are +modified leaves, and follow the leaf-arrangement of the species. The +Beech is alternate-leaved, and we should therefore expect the scales to +alternate. The explanation is found as we go on removing the scales. At +the eighth or ninth pair we come upon a tiny, silky leaf, directly between +the pair of scales, and, removing these, another larger leaf, opposite the +first but higher up on the rudimentary stem, and so on, with the rest of +the bud. There are five or more leaves, each placed between a pair of +scales. Our knowledge of the parts of a leaf shows us at once that the +scales must be modified stipules, and that therefore they must be in +pairs.[1] Other examples of scales homologous with stipules are the +American Elm, Tulip-tree, Poplar and Magnolia. The leaves are plaited +on the veins and covered with long, silky hairs. The venation is very +distinct. The outer leaves are smaller and, on examining the branch, it +will be seen that their internodes do not make so large a growth as the +leaves in the centre of the bud. + +[Footnote 1: See the stipules of the Pea, p. 31.] + +[Illustration: FIG. 15.--Copper Beech. 1. Branch in winter state: _a_, +leaf-scar; _b_, bud-scar. 2. Branch, with leaf-buds expanding, showing the +plicate folding of the leaves.] + +The leaf-scars are small, soon becoming merely ridges running half round +the stem. + +The bud-rings are very plain and easily counted. For this reason, and +because it branches freely, it is a good tree for measurements of growth, +as is seen in the following tables. Nos. 1, 2, 3 and 4: were made by a +class of girls, from fourteen to sixteen, from a tree on my lawn. No. 5 +was made by a pupil, whom I taught by correspondence, from a tree of the +same species in another town. No. 6 was made by myself from my own tree. +The measurements of the first four tables were somewhat revised by me, as +they were not perfectly accurate. The pupils should always be cautioned +to measure from the beginning of one set of rings to the beginning of the +next.[1] + +[Footnote 1: Care must be taken to select branches well exposed to the +light. Of course there are many circumstances that may aid or hinder the +growth of any particular branch.] + +NO. 1. + +YEARS. GROWTH OF 1ST BRANCH. 2nd BRANCH. 3RD BRANCH 4TH BRANCH. + MAIN AXIS. +---------------------------------------------------------------- + in. +'79 8-1/2 -- -- -- -- +'80 4-1/2 2 1-7/8 -- -- +'81 3-1/2 1-1/8 2-5/8 -- -- +'82 6 5/8 4-1/4 5-7/8 -- +'83 7-3/8 3-3/8 5-1/4 4 5-3/4 +'84 2 1/2 3/4 3/8 5-3/8 +'85 5/8 1/4 3/8 1/2 1 +'86 5-5/8 7/8 4-3/8 3-1/8 5 + + +NO. 2. + +YEARS. GROWTH of 1ST 2nd 3RD 4TH 5TH + MAIN AXIS. BRANCH BRANCH BRANCH BRANCH BRANCH +---------------------------------------------------------------- + in. +'79 8 -- -- -- -- -- -- +'80 3-1/2 5-1/4 5-1/2 5-5/8 -- -- -- +'81 4-3/4 3/4 1/2 2-1/2 2 -- -- +'82 5-3/4 7/8 2 3/4 3/8 1/2 -- +'83 5-1/4 4-3/4 5-1/2 4 3-1/4 2-3/8 1-3/4 -- +'84 1/2 1 3/4 3/8 1 3/4 1 3/8 +'85 2-3/4 1-3/4 4-3/8 3/4 3/4 2-1/8 3-1/4 1-1/4 +'86 7-1/2 5-1/2 6-3/4 3 3 4-1/2 3-1/8 5 + + +NO. 3. + +YEARS. GROWTH of 1ST 2nd 3RD 4TH 5TH + MAIN AXIS. BRANCH BRANCH BRANCH BRANCH BRANCH +----------------------------------------------------- + in. +'80 8-1/4 -- -- -- -- -- +'81 4-1/2 3-1/2 3-3/4 -- -- -- +'82 5-1/2 3/4 1-1/2 1 -- -- +'83 3-1/4 3-3/4 4-1/2 3/4 2 1-1/4 +'84 5-1/2 1/2 3/4 1 1/2 3 +'85 1/2 1-3/4 1/2 3/8 1 1/2 +'86 4-1/4 3-3/8 2-3/8 1-1/4 2-1/4 1-1/2 + + +NO. 4. + +YEARS GROWTH 1ST 2nd 3RD 4TH + of MAIN BRANCH BRANCH BRANCH BRANCH + AXIS +----------------------------------------- + in. +'81 7-3/4 -- -- -- -- +'82 8-3/4 6 6 -- -- +'83 6-3/4 5-1/4 4 4-3/4 5-1/2 +'84 4-1/2 5/8 1-5/8 2-1/4 3-1/4 +'85 2 5/8 3/16 2 3/4 +'86 10-3/4 1-3/4 1/4 7-1/4 3-1/2 + + +NO. 4. (cont.) + +YEARS 5TH 6TH 7TH 8TH 9TH + BRANCH BRANCH BRANCH BRANCH BRANCH + ----------------------------------- + in. +'81 -- -- -- -- -- +'82 -- -- -- -- -- +'83 -- -- -- -- -- +'84 3/4 2-1/2 -- -- -- +'85 7/8 5/8 1/4 3/4 -- +'86 4-3/4 6-3/8 1 2-1/4 6-1/2 + + +NO. 5. + +YEARS GROWTH 1ST 2nd 3RD 4TH 5TH 6TH + of MAIN BRANCH BRANCH BRANCH BRANCH BRANCH BRANCH + AXIS +----------------------------------------------------- + in. +'82 6-7/8 --- --- --- --- --- --- +'83 6-1/2 4-3/4 4-1/4 --- --- --- --- +'84 4-3/4 1/4 1-3/4 3-1/2 --- --- --- +'85 4-1/2 3/4 1 2-3/4 2-3/4 --- --- +'86 6-1/4 2-1/4 4-3/4 6-3/4 2-3/4 5-3/4 --- +'87 6-3/4 1-1/8 3-1/4 4 2-1/4 3 5-1/2 + + +NO. 6. + +YEARS MAIN 1ST 2ND 2ND 2ND 3RD 4TH + AXIS BRANCH BRANCH BRANCH BRANCH BRANCH BRANCH +----------------------------------------------------- + in. 1st 2nd + side side +'80 6-1/4 --- --- shoot. shoot. --- --- +'81 8-3/4 6-3/4 --- --- --- --- --- +'82 8-1/2 6-1/4 6-7/8 --- --- --- . +'83 4-3/4 1-1/2 2-3/8 --- --- 4 . +'84 3-1/2 3-1/8 5-1/8 --- --- 1-3/4 7/8 +'85 4-1/2 3/8 4-3/4 2-1/4 --- 6 1 +'86 6+ 6-3/4 12-1/8 5-1/2 10-1/2 8-7/8 5-1/8 +'87 bough 2-1/2 8-3/4 4-1/4 4-1/4 4-6/8 3-3/4 + broken. + +One question brought up by these measurements is whether there is any +correspondence in growth between the main axis and its branches. It +appears in these tables that there is a general correspondence, in this +tree at least. In the recitation of the class, whose tables are given +above (Nos. 1, 2, 3 and 4), we took all the measurements of these four +branches for the year 1885 and added them. We did the same for 1886, and +compared the results. The total growth for 1885 was 31-15/16 inches; for +1886, leaving out the measurement of the twig whose entire growth was in +that year, 109-3/4 inches or nearly 3-1/2 times as much. The proportion +held in a general way throughout, there being only a single case of a +branch where the growth was greater in the first year.[1] But there is a +point that must not be overlooked in this connection. The branches of the +Beech seem to grow about equally well in the first, second, third, or any +succeeding year. In some trees, as the Ash, the axillary buds make a large +growth, and the succeeding terminal buds carry on the branch much more +slowly; in other trees, as the Cherry, a branch grows very slowly in the +first few years and then suddenly takes a start. These facts would appear +in tables of growth, made from branches of these trees, but the addition +of results for any particular year would have no significance. + +[Footnote 1: The spring of 1880 was a remarkably early one. Thus I find in +my diary of that year the following entries:-- + +April 17. The red maples are in full bloom, the elms almost over. The +leaves of the Horsechestnut are quite large. The lilacs are nearly in +leaf. April 24. We went up to Waverley and found bloodroot up, spice bush +out, violets, dog-tooths and anemones, also caltha. April 28. All the +cherries are in full bloom. April 29. Picked an apple blossom in bud, +beautifully pink. + +The season was nearly three weeks earlier than usual. 1885 on the other +hand was a late spring.] + +In table No. 5, the addition of the measurements for 1885 and 1886 shows +the growth in the latter year to be about twice that of the former. This +branch came from a tree in another town. We have tried also to discover +whether the number of leaves each year has any relation to growth. I +cannot see that it has, but it requires many experiments to determine +these points. To study this, make tables of the number of leaves on the +branch each year. I think teachers would find it interesting to keep all +data of this kind of work done by their classes, with a view to tabulation +and comparison. The scholars themselves are exceedingly interested in +anything that partakes of the nature of an original investigation.[1] + +[Footnote 1: The class, previously mentioned, were much interested in the +addition of their results. One of them asked me whether this subject of +measurements had been treated in any book. I replied that I had never seen +it mentioned. My attention was afterwards called to "What may be learned +from a Tree," by Prof. Harlan Couitas. D. Appleton & Co., New York, 1863. +I found, greatly to my surprise, that he had not only given diagrams of +growth, but that he also had selected a Copper Beech as his example.] + +The leaf-arrangement of the Beech is alternate, on the one-half plan. The +small twigs turn upwards, so that all the spray is on the upper side, +giving a flat appearance to the branch.[1] This gives the leaves a better +exposure to the light. Both the terminal and axillary buds grow freely, +thus forming long, straight limbs, with many branches and much fine spray. + +[Footnote 1: Phyllotaxy is treated later, by a comparison and study of +many branches, but the teacher can draw the pupils' attention to the fact +that each Beech leaf and twig is on exactly the opposite side of the +branch from the preceding one. This allows all the twigs to grow towards +one side of the branch, whereas in trees on the two-fifths plan, as the +Apple, Poplar, Oak, etc., no such regularity would be possible, on account +of their many different angles with the stem.] + +The bark of the Beech is beautifully smooth. The extreme straightness of +the trunk and limbs is very striking, and may be compared to the crooked +limbs of the Horsechestnut, where the branch is continually interrupted by +the flower-cluster. In the Beech the flowers are axillary. + + +QUESTIONS ON THE BEECH. + +How are the scales of the Beech bud arranged? + +How many leaves are there in the bud? + +How does the arrangement of the scales and leaves in the bud differ from +that of the Horsechestnut? + +How are the leaves folded in the bud? + +What is the arrangement of the leaves on the stem? + +How does this differ from Horsechestnut and Lilac? + +How old is your branch? + +How old is each twig? + +What years were the best for growth? + +How does the growth of the branches differ from that of Horsechestnut? +From Lilac? + +Explain these differences with reference to the growth and arrangement of +the buds? + +In what direction do the twigs grow? + +How does this affect the appearance of the tree? + +Compare the amount of spray of the Beech and Horsechestnut and explain the +reason of the difference. + +These questions are only intended for review, they are never to be used +for the first study of the specimen. + + +AMERICAN ELM (_Ulmus Americana_). + +The buds are covered with brown scales, which are hairy on the edges. The +flower-buds are larger than the leaf-buds and are in the axils of the +lower leaves of the preceding year. Each leaf in the bud is enclosed by +a pair of scales. They are so small that the pupils, unused to delicate +work, will hardly discover them. Under a glass they can be seen to be +ovate, folded on the midrib with the inner face within (_conduplicate_), +and with an ovate scale joined to the base of the leaf on either side. The +scales thus show themselves to be modified stipules. The venation of the +leaves is very plain. The scales are much larger than the leaves. The +flower-buds contain a cluster of flowers, on slender green pedicels. The +calyx is bell-shaped, unequal, and lobed. The stamens and pistil can +be seen. The flower-clusters do not seem to leave any mark which is +distinguishable from the leaf-scar. + +[Illustration: FIG. 16.--American Elm. 1. Branch in winter state: _a_, +leaf-scars; _b_, bud-scars; _d_, leaf-buds; _e_, flower-buds. 2. Branch, +with staminate flower-buds expanding. 3. Same, more advanced. 4. Branch, +with pistillate flowers, the leaf-bud also expanding.] + +The leaf-scars are small and extend about half around the stem. The +arrangement is alternate on the one-half plan. There are three dots on the +scar. + +The rings are quite plain. The tree can be used to make tables of growth, +like those of the Beech. + +The buds will probably be too small for examination by the pupils, at +present, but their position and development can be studied, and are very +instructive. As the leaf-buds are all on the ends of the branchlets, the +twigs and branches will be just below the bud-rings, and then there will +be a space where no twigs nor branches will be found, till the next set +of rings is reached. This gives the branches more room to develop +symmetrically. The terminal buds do not develop in the Elm, in old trees, +the bud axillary to the last leaf of the season taking its place, and most +of the other axillary buds growing also. This makes the tree break out +into very fine spray. A tree like the Elm, where the trunk becomes lost in +the branches, is called _deliquescent_; when the trunk is continued to the +top of the tree, as in the Spruce, it is _excurrent_. + +The small, feathery twigs and branches that are often seen on the trunks +and great limbs of the elm grow from buds which are produced anywhere on +the surface of the wood. Such buds are called _adventitious_ buds. They +often spring from a tree when it is wounded. + +"The American elm is, in most parts of the state, the most magnificent +tree to be seen. From a root, which, in old trees, spreads much above +the surface of the ground, the trunk rises to a considerable height in a +single stem. Here it usually divides into two or three principal branches, +which go off by a gradual and easy curve. Theses stretch upwards and +outwards with an airy sweep, become horizontal, the extreme half of the +limb, pendent, forming a light and regular arch. This graceful curvature, +and absence of all abruptness, in the primary limbs and forks, and all the +subsequent divisions, are entirely characteristic of the tree, and enable +an observer to distinguish it in the winter and even by night, when +standing in relief against the sky, as far as it can be distinctly +seen."[1] + +[Footnote 1: A Report on the Trees and Shrubs growing naturally in the +Forests of Massachusetts. By Geo. B. Emerson, Boston, Little, Brown and +Co., 1875. + +This book will be found very useful, containing careful descriptions of +many trees and shrubs, and interesting facts about them.] + + +QUESTIONS ON THE AMERICAN ELM. + +How do the flower-buds differ from the leaf-buds in position and +appearance? + +What is the arrangement of the leaves? + +What other tree that you have studied has this arrangement? + +How old is your branch? + +Where would you look to see if the flower-cluster had left any mark? + +Why is it that several twigs grow near each other, and that then comes a +space without any branches? + +What buds develop most frequently? + +How does this affect the appearance of the tree? + +What is a tree called when the trunk is lost in the branches? + + +BALM OF GILEAD (_Populus balsamifera, var. candicans_). + +The buds are pointed: the terminal slightly angled, the axillary flattened +against the stem.[1] Some of the axillary buds contain leaves and some +flowers; the appearance of the leaf-buds and flower-buds being the same. +The scales of the bud are modified stipules. The terminal buds have about +three pairs of the outer scales brown and leathery. The inner scales, as +well as the leaves, are coated with resinous matter, which has a strong +odor and a nauseous taste. The smaller outer scales have no corresponding +leaf, and apparently are modified stipules of the leaves of the preceding +year, but the larger ones have a leaf to each pair of scales. The outer +and inner leaves are small, the middle ones larger. Comparing the branch, +it will be seen that these leaves make the largest growth of internode. +The leaves are rolled towards the midrib on the upper face (_involute_). +There are about ten which are easily seen and counted, the inner ones +being very small, with minute scales. The axillary buds have a short +thick scale on the outer part of the bud, then about three pairs of large +scales, each succeeding one enwrapping those within, the outer one brown +and leathery. The scales of the flower-buds are somewhat gummy, but not +nearly so much so as those of the leaf-buds. Within is the catkin. Each +pistil, or stamen (they are on separate trees, _dioecious_) is in a little +cup and covered by a scale, which is cut and fringed. + +[Footnote 1: These buds cannot be satisfactorily examined in cross +section, on account of the resin. The scales must be removed one by one, +with a knife, with a complete disregard of the effect upon the hands.] + +The leaf-scars are somewhat three-lobed on the young parts, with three +dots, indicating the fibro-vascular bundles, which ran up into the leaf. +The scars are swollen, making the young branches exceedingly rough. In +the older parts the scars become less noticeable. Strong young shoots, +especially those which come up from the root, are strongly angled, +with three ridges running up into each leaf-scar, making them almost +club-shaped. There are often from twenty to thirty leaves in one year's +growth, in such shoots, and all the leaves are not rudimentary in the bud. +The growth in this case is said to be _indefinite_. Usually in trees with +scaly buds the plan of the whole year's growth is laid down in the bud, +and the term _definite_ is applied. Branches, like the Rose, that go on +growing all summer grow indefinitely. + +The bud-scale scar is quite different from the other trees which we have +examined. It is not composed of definite rings, but of leaf-scars with +long ridges running from each side of them, showing the scales to be +modified stipules. The leaf-scars have become somewhat separated by the +growth of the internodes. In the Beech, there are eight, or more, pairs of +scales with no leaves, so that the internodes do not develop, and a ring +is left on the branch. + +The flower-cluster leaves a concave, semicircular scar, in the leaf-axil. + +[Illustration: FIG. 17.--Balm-of-Gilead. 1. Branch in winter state: _a_, +leaf-scar; _b_, bud-scar. 2. Branch, with leaf-buds expanded. 3. Branch, +with catkin appearing from the bud.] + +The terminal buds are the strongest and not very many axillary buds +develop, so that the tree has not fine spray. + +The leaf-arrangement is alternate, on the 2/5 plan. Phyllotaxy is not yet +to be taken up, but the pupils should be shown the different angles of the +branching of the twigs, and told to compare them with Beech and Elm. + +QUESTIONS ON THE BALM OF GILEAD. + +In which buds are the flower-clusters? + +Are there flowers and leaves in the same buds? + +What are the scales of the bud? + +How are the leaves folded in the bud? + +How do the axillary and terminal buds differ? + +What are the dots on the leaf-scars? + +Why is there no distinct band of rings as in Beech? + +How old is your branch? + +Where do you look for flower-cluster scars? + +Which buds are the strongest? + +How does this affect the appearance of the tree? + +What makes the ends of the branches so rough? + +Compare the arrangement of the twigs and branches with Beech and Elm, with +Horsechestnut and Lilac. + + +TULIP-TREE (_Liriodendron Tulipifera_). + +The buds are small, flat, and rounded at the apex. They are sheathed by +scales, each leaf being covered by a pair, whose edges cohere. The outer +pair are brown and are the stipules of the last leaf of the preceding +year. The leaves are conduplicate, as in Magnolia, and have the blade bent +inwards on the petiole (_inflexed_). Their shape is very clearly to be +seen, and no bud is more interesting in the closeness of its packing. +Axillary buds are often found within. The flowers grow high upon the trees +and towards the ends of the branches. + +The leaf-scars are round with many dots. The scar of the stipules is a +continuous line around the stem, as in Magnolia. + + +CHERRY _(Prunus Cerasus_). + +The leaf-buds are terminal, or in the axils of the upper leaves of the +preceding year; the flower buds are axillary. There is but one bud in each +axil, and usually two or three flowers in each bud, but the leaves on +the twigs are crowded and the flowers therefore appear in clusters. The +blossom-buds are larger and more rounded than the leaf-buds. + +The buds of the tree develop very easily in the house, and as they are +so small they can be better studied in watching them come out, than by +attempting to dissect them, unless the scholars are sufficiently advanced +to use the microscope easily. It is always bad for a pupil to attempt to +describe what he sees but imperfectly. He will be sure to jump at any +conclusions which he thinks ought to be correct. + +The leaf-scars are semicircular, small and swollen. + +The bud-rings are plain. The twigs make a very small growth in a season, +so that the leaf-scars and rings make them exceedingly rough. + +The flower-cluster scars are small circles, with a dot in the centre, in +the leaf-axils. The flowers come before the leaves. + +The leaf-arrangement is alternate on the 2/5 plan. The pupils may compare +the branching with that of their other specimens. + + +RED MAPLE (_Acer rubrum_). + +This is a good specimen for the study of accessory buds. There is usually +a bud in the axil of each lower scale of the axillary buds, making three +side by side. We have already noticed this as occurring sometimes in +Lilac. It is habitually the case with the Red Maple. The middle bud, which +is smaller and develops later, is a leaf-bud. The others are flower-buds. + +The leaf-scars are small, with three dots on each scar. The rings are very +plain. The flower-cluster leaves a round scar in the leaf-axil, as in +Cherry. + +The leaves are opposite and the tree branches freely. The twigs seem to +be found just below the bud-rings, as the upper leaf-buds usually develop +best and the lower buds are single, containing flowers only. + + +NORWAY SPRUCE (_Picea excelsa_). + +The buds are terminal, and axillary, from the axils of the leaves of the +preceding year, usually from those at the ends of the branchlets. They +are covered with brown scales and contain many leaves. + +[Illustration: FIG. 18.--Branch of Cherry in winter state: _a_, leaf-scar; +_b_, bud-scar; _c_, flower-scar.] + +[Illustration: FIG. 19.--Branch of Red Maple in winter state (reduced). 2. +Flower-buds] + +The leaves are needle-shaped and short.[1] They are arranged densely on +the branches, alternately on the 8/21 plan (see section on phyllotaxy). +When they drop off they leave a hard, blunt projection which makes the +stem very rough. As the terminal bud always develops unless injured, the +tree is excurrent, forming a straight trunk, throwing out branches on +every side. The axillary buds develop near the ends of the branchlets, +forming apparent whorls of branches around the trunk. In the smaller +branches, as the tree grows older, the tendency is for only two buds to +develop nearly opposite each other, forming a symmetrical branch. + +[Footnote 1: The pupils should observe how much more crowded the leaves +are than in the other trees they have studied. The leaves being smaller, +it is necessary to have more of them. Large-leaved trees have longer +internodes than those with small leaves.] + +The bud-scales are persistent on the branches and the growth from year to +year can be traced a long way back. + +The cones hang on the ends of the upper branches. They are much larger +than in our native species of Black and White Spruce. + +The Evergreens are a very interesting study and an excellent exercise in +morphology for the older scholars. + + +2. _Vernation_. This term signifies the disposition of leaves in the bud, +either in respect to the way in which each leaf is folded, or to the +manner in which the leaves are arranged with reference to each other. +The pupils have described the folding of the leaves in some of their +specimens. + +In the Beech, the leaf is _plicate_, or plaited on the veins. In the Elm, +Magnolia, and Tulip-tree, it is _conduplicate_, that is, folded on +the midrib with the inner face within. In the Tulip-tree, it is also +_inflexed_, the blade bent forwards on the petiole. In the Balm of Gilead, +the leaf is _involute_, rolled towards the midrib on the upper face. + +Other kinds of vernation are _revolute_, the opposite of involute, where +the leaf is rolled backwards towards the midrib; _circinate_, rolled from +the apex downwards, as we see in ferns; and _corrugate_, when the leaf is +crumpled in the bud. + +[Illustration: FIG. 20.--Branch of Norway Spruce.] + +In all the trees we have studied, the leaves simply succeed each other, +each leaf, or pair of leaves, overlapping the next in order. The names of +the overlapping of the leaves among themselves, _imbricated, convolute, +etc_., will not be treated here, as they are not needed. They will come +under _aestivation_, the term used to describe the overlapping of the +modified leaves, which make up the flower.[1] + +[Footnote 1: Reader in Botany. VIII. Young and Old Leaves.] + + +3. _Phyllotaxy_. The subject of leaf-arrangement is an extremely difficult +one, and it is best, even with the older pupils, to touch it lightly. The +point to be especially brought out is the disposition of the leaves so +that each can get the benefit of the light. This can be seen in any plant +and there are many ways in which the desired result is brought about. The +chief way is the distribution of the leaves about the stem, and this is +well studied from the leaf-scars. + +The scholars should keep the branches they have studied. It is well to +have them marked with the respective names, that the teacher may examine +and return them without fear of mistakes. + +In the various branches that the pupils have studied, they have seen that +the arrangement of the leaves differs greatly. The arrangement of leaves +is usually classed under three modes: the _alternate_, the _opposite_, +and the _whorled_; but the opposite is the simplest form of the whorled +arrangement, the leaves being in circles of two. In this arrangement, the +leaves of each whorl stand over the spaces of the whorl just below. The +pupils have observed and noted this in Horsechestnut and Lilac. In these +there are four vertical rows or ranks of leaves. In whorls of three leaves +there would be six ranks, in whorls of four, eight, and so on. + +When the leaves are alternate, or single at each node of the stem, they +are arranged in many different ways. Ask the pupils to look at all the +branches with alternate leaves that they have studied, and determine in +each case what leaves stand directly over each other. That is, beginning +with any leaf, count the number of leaves passed on the stem, till one is +reached that stands directly over the first.[1] In the Beech and the Elm +the leaves are on opposite sides of the stem, so that the third stands +directly over the first. This makes two vertical ranks, or rows, of +leaves, dividing the circle into halves. It is, therefore, called the +1/2 arrangement. Another way of expressing it is to say that the angular +divergence between the leaves is 180 deg., or one-half the circumference. + +[Footnote 1: The pupils must be careful not to pass the bud-rings when +they are counting the leaves.] + +The 1/3 arrangement, with the leaves in three vertical ranks, is not very +common. It may be seen in Sedges, in the Orange-tree, and in Black Alder +_(Ilex verticillata)_. In this arrangement, there are three ranks of +leaves, and each leaf diverges from the next at an angle of 120 deg., or +one-third of the circumference. + +By far the commonest arrangement is with the leaves in five vertical +ranks. The Cherry, the Poplar, the Larch, the Oak, and many other trees +exhibit this. In this arrangement there are five leaves necessary to +complete the circle. We might expect, then, that each leaf would occupy +one-fifth of the circle. This would be the case were it not for the fact +that we have to pass twice around the stem in counting them, so that each +leaf has twice as much room, or two-fifths of the circle, to itself. This +is, therefore, the 2/5 arrangement. This can be shown by winding a thread +around the stem, passing it over each leaf-scar. In the Beech we make one +turn of the stem before reaching the third leaf which stands over the +first. In the Apple the thread will wind twice about the stem, before +coming to the sixth leaf, which is over the first. + +Another arrangement, not very common, is found in the Magnolia, the Holly, +and the radical leaves of the common Plantain and Tobacco. The thread +makes three turns of the stem before reaching the eighth leaf which stands +over the first. This is the 3/8 arrangement. It is well seen in the +Marguerite, a greenhouse plant which is very easily grown in the house. + +Look now at these fractions, 1/2, 1/3, 2/5, and 3/8. The numerator of +the third is the sum of the numerators of the first and second, its +denominator, the sum of the two denominators. The same is true of the +fourth fraction and the two immediately preceding it. Continuing the +series, we get the fractions 5/13, 8/21, 13/34. These arrangements can +be found in nature in cones, the scales of which are modified leaves and +follow the laws of leaf-arrangement.[1] + +[Footnote 1: See the uses and origin of the arrangement of leaves in +plants. By Chauncey Wright. Memoirs Amer. Acad., IX, p. 389. This essay +is an abstruse mathematical treatise on the theory of phyllotaxy. The +fractions are treated as successive approximations to a theoretical angle, +which represents the best possible exposure to air and light. + +Modern authors, however, do not generally accept this mathematical view of +leaf-arrangement.] + +[1]"It is to be noted that the distichous or 1/2 variety gives the maximum +divergence, namely 180 deg., and that the tristichous, or 1/3, gives the +least, or 120 deg.; that the pentastichous, or 2/5, is nearly the mean +between the first two; that of the 3/8, nearly the mean between the two +preceding, etc. The disadvantage of the two-ranked arrangement is that the +leaves are soon superposed and so overshadow each other. This is commonly +obviated by the length of the internodes, which is apt to be much greater +in this than in the more complex arrangements, therefore placing them +vertically further apart; or else, as in Elms, Beeches, and the like, the +branchlets take a horizontal position and the petioles a quarter twist, +which gives full exposure of the upper face of all the leaves to the +light. The 1/3 and 2/5, with diminished divergence, increase the number of +ranks; the 3/8 and all beyond, with mean divergence of successive leaves, +effect a more thorough distribution, but with less and less angular +distance between the vertical ranks." + +[Footnote 1: Gray's Structural Botany, Chap, iv, p. 126.] + +For directions for finding the arrangement of cones, see Gray's Structural +Botany, Chap. IV, Sect. 1. + +The subject appears easy when stated in a text-book, but, practically, it +is often exceedingly difficult to determine the arrangement. Stems often +twist so as to alter entirely the apparent disposition of the leaves. The +general principle, however, that the leaves are disposed so as to get the +best exposure to air and light is clear. This cannot be shown by the study +of the naked branches merely, because these do not show the beautiful +result of the distribution.[1] Many house plants can be found, which will +afford excellent illustrations (Fig. 21). The Marguerite and Tobacco, both +easily grown in the house, are on the 3/8 plan. The latter shows the eight +ranks most plainly in the rosette of its lower leaves. The distribution is +often brought about by differences in the lengths of the petioles, as in +a Horsechestnut branch (Fig. 22) where the lower, larger leaves stand +out further from the branch than the upper ones; or by a twist in the +petioles, so that the upper faces of the leaves are turned up to the +light, as in Beech (Fig. 23). If it is springtime when the lessons are +given, endless adaptations can be found. + +[Footnote 1: Reader in Botany. IX. Leaf-Arrangement.] + +[Illustration: FIG. 21. Branch of Geranium, viewed from above.] + +[Illustration: FIG. 22.] + +[Illustration: FIG. 23.] + +_Gray's First Lessons_. Sect. IV. VII, sec. 4. _How Plants Grow_. Chap. I, +51-62; I, 153. + + + + +V. + +STEMS. + + +The stem, as the scholars have already learned, is the axis of the plant. +The leaves are produced at certain definite points called nodes, and the +portions of stem between these points are internodes. The internode, +node, and leaf make a single plant-part, and the plant is made up of a +succession of such parts. + +The stem, as well as the root and leaves, may bear plant-hairs. The +accepted theory of plant structure assumes that these four parts, root, +stem, leaves, and plant-hairs, are the only members of a flowering plant, +and that all other forms, as flowers, tendrils, etc., are modified from +these. While this idea is at the foundation of all our teaching, causing +us to lead the pupil to recognize as modified leaves the cotyledons of a +seedling and the scales of a bud, it is difficult to state it directly +so as to be understood, except by mature minds. I have been frequently +surprised at the failure of even bright and advanced pupils to grasp this +idea, and believe it is better to let them first imbibe it unconsciously +in their study. Whenever their minds are ready for it, it will be readily +understood. The chief difficulty is that they imagine that there is a +direct metamorphosis of a leaf to a petal or a stamen. + +Briefly, the theory is this: the beginnings of leaf, petal, tendril, etc., +are the same. At an early stage of their growth it is impossible to tell +what they are to become. They develop into the organ needed for the +particular work required of them to do. The organ, that under other +circumstances might develop into a leaf, is capable of developing into a +petal, a stamen, or a pistil, according to the requirements of the plant, +but no actual metamorphosis takes place. Sometimes, instead of developing +into the form we should normally find, the organ develops into another +form, as when a petal stands in the place of a stamen, or the pistil +reverts to a leafy branch. This will be more fully treated under flowers. +The study of the different forms in which an organ may appear is the study +of _morphology_. + + +1. _Forms of Stems_.--Stems may grow in many ways. Let the pupils compare +the habits of growth of the seedlings they have studied. The Sunflower and +Corn are _erect_. This is the most usual habit, as with our common trees. +The Morning Glory is _twining_, the stem itself twists about a support. +The Bean, Pea and Nasturtium are _climbing_. The stems are weak, and +are held up, in the first two by tendrils, in the last by the twining +leaf-stalks. The English Ivy, as we have seen, is also climbing, by means +of its aerial roots. The Red Clover is _ascending_, the branches rising +obliquely from the base. Some kinds of Clover, as the White Clover, are +_creeping_, that is, with prostrate branches rooting at the nodes and +forming new plants. Such rooting branches are called _stolons_, or when +the stem runs underground, _suckers_. The gardener imitates them in +the process called layering, that is, bending down an erect branch and +covering it with soil, causing it to strike root. When the connecting stem +is cut, a new plant is formed. Long and leafless stolons, like those of +the Strawberry are called _runners_. Stems creep below the ground as well +as above. Probably the pupil will think of some examples. The pretty +little Gold Thread is so named from the yellow running stems, which grow +beneath the ground and send up shoots, or suckers, which make new plants. +Many grasses propagate themselves in this way. Such stems are called +_rootstocks_. "That these are really stems, and not roots, is evident +from the way in which they grow; from their consisting of a succession of +joints; and from the leaves which they bear on each node, in the form +of small scales, just like the lowest ones on the upright stem next the +ground. They also produce buds in the axils of these scales, showing the +scales to be leaves; whereas real roots bear neither leaves nor axillary +buds."[1] Rootstocks are often stored with nourishment. We have already +taken up this subject in the potato, but it is well to repeat the +distinction between stems and roots. A thick, short rootstock provided +with buds, like the potato, is called a _tuber_. Compare again the corm of +Crocus and the bulb of Onion to find the stem in each. In the former, it +makes the bulk of the whole; in the latter, it is a mere plate holding the +fleshy bases of the leaves. + +[Footnote 1: Gray's First Lessons, revised edition, 1887, page 42.] + +2. _Movements of Stems.--_Let a glass thread, no larger than a coarse +hair, be affixed by means of some quickly drying varnish to the tip of the +laterally inclined stem of one of the young Morning-Glory plants in the +schoolroom. Stand a piece of cardboard beside the pot, at right angles to +the stem, so that the end of the glass will be near the surface of the +card. Make a dot upon the card opposite the tip of the filament, taking +care not to disturb the position of either. In a few minutes observe that +the filament is no longer opposite the dot. Mark its position anew, and +continue thus until a circle is completed on the cardboard. This is a +rough way of conducting the experiment. Darwin's method will be found in +the footnote.[1] + +[Footnote 1: "Plants growing in pots were protected wholly from the light, +or had light admitted from above or on one side as the case might require, +and were covered above by a large horizontal sheet of glass, and with +another vertical sheet on one side. A glass filament, not thicker than a +horsehair, and from a quarter to three-quarters of an inch in length, +was affixed to the part to be observed by means of shellac dissolved in +alcohol. The solution was allowed to evaporate until it became so thick +that it set hard in two or three seconds, and it never injured the +tissues, even the tips of tender radicles, to which it was applied. To the +end of the glass filament an excessively minute bead of black sealing-wax +was cemented, below or behind which a bit of card with a black dot was +fixed to a stick driven into the ground.... The bead and the dot on the +card were viewed through the horizontal or vertical glass-plate (according +to the position of the object) and when one exactly covered the other, a +dot was made on the glass plate with a sharply pointed stick dipped in +thick India ink. Other dots were made at short intervals of time and these +were afterwards joined by straight lines. The figures thus traced were +therefore angular, but if dots had been made every one or two minutes, the +lines would have been more curvilinear."--The Power of Movement in Plants, +p. 6.] + +The use of the glass filament is simply to increase the size of the circle +described, and thus make visible the movements of the stem. All young +parts of stems are continually moving in circles or ellipses. "To learn +how the sweeps are made, one has only to mark a line of dots along the +upper side of the outstretched revolving end of such a stem, and to note +that when it has moved round a quarter of a circle, these dots will be on +one side; when half round, the dots occupy the lower side; and when the +revolution is completed, they are again on the upper side. That is, the +stem revolves by bowing itself over to one side,--is either pulled over or +pushed over, or both, by some internal force, which acts in turn all round +the stem in the direction in which it sweeps; and so the stem makes its +circuits without twisting."[1] + +[Footnote 1: How Plants Behave. By Asa Gray. Ivison, Blakeman, Taylor & +Co., New York, 1872. Page 13.] + +The nature of the movement is thus a successive nodding to all the points +of the compass, whence it is called by Darwin _circumnutation_. The +movement belongs to all young growing parts of plants. The great sweeps of +a twining stem, like that of the Morning-Glory, are only an increase in +the size of the circle or ellipse described.[1] + +[Footnote 1: "In the course of the present volume it will be shown +that apparently every growing part of every plant is continually +circumnutating, though often on a small scale. Even the stems of seedlings +before they have broken through the ground, as well as their buried +radicles, circumnutate, as far as the pressure of the surrounding earth +permits. In this universally present movement we have the basis or +groundwork for the acquirement, according to the requirements of the +plant, of the most diversified movements. Thus the great sweeps made by +the stems of the twining plants, and by the tendrils of other climbers, +result from a mere increase in the amplitude of the ordinary movement of +circumnutation."--The Power of Movement in Plants, p. 3.] + +When a young stem of a Morning-Glory, thus revolving, comes in contact +with a support, it will twist around it, unless the surface is too smooth +to present any resistance to the movement of the plant. Try to make +it twine up a glass rod. It will slip up the rod and fall off. The +Morning-Glory and most twiners move around from left to right like the +hands of a clock, but a few turn from right to left. + +While this subject is under consideration, the tendrils of the Pea and +Bean and the twining petioles of the Nasturtium will be interesting for +comparison. The movements can be made visible by the same method as was +used for the stem of the Morning-Glory. Tendrils and leaf petioles are +often sensitive to the touch. If a young leaf stalk of Clematis be rubbed +for a few moments, especially on the under side, it will be found in a day +or two to be turned inward, and the tendrils of the Cucumber vine will +coil in a few minutes after being thus irritated.[1] The movements of +tendrils are charmingly described in the chapter entitled "How Plants +Climb," in the little treatise by Dr. Gray, already mentioned. + +[Footnote 1: Reader in Botany. X. Climbing Plants.] + +The so-called "sleep of plants" is another similar movement. The Oxalis is +a good example. The leaves droop and close together at night, protecting +them from being chilled by too great radiation. + +The cause of these movements is believed to lie in changes of tension +preceding growth in the tissues of the stem.[1] Every stem is in a state +of constant tension. Naudin has thus expressed it, "the interior of every +stem is too large for its Jacket."[2] If a leaf-stalk of Nasturtium be +slit vertically for an inch or two, the two halves will spring back +abruptly. This is because the outer tissues of the stem are stretched, +and spring back like india-rubber when released. If two stalks twining +in opposite directions be slit as above described, the side of the stem +towards which each stalk is bent will spring back more than the other, +showing the tension to be greater on that side. A familiar illustration of +this tension will be found in the Dandelion curls of our childhood. + +[Footnote 1: See Physiological Botany. By Geo. L. Goodale. Ivison & Co., +New York, 1885. Page 406.] + +[Footnote 2: The following experiment exhibits the phenomenon of tension +very strikingly. "From a long and thrifty young internode of grapevine +cut a piece that shall measure exactly one hundred units, for instance, +millimeters. From this section, which measures exactly one hundred +millimeters, carefully separate the epidermal structures in strips, and +place the strips at once under an inverted glass to prevent drying; +next, separate the pith in a single unbroken piece wholly freed from the +ligneous tissue. Finally, remeasure the isolated portions, and compare +with the original measure of the internode. There will be found an +appreciable shortening of the epidermal tissues and a marked increase in +length of the pith."--Physiological Botany, p. 391.] + +The movements of the Sensitive Plant are always very interesting to +pupils, and it is said not to be difficult to raise the plants in the +schoolroom. The whole subject, indeed, is one of the most fascinating +that can be found, and its literature is available, both for students and +teachers. Darwin's essay on "Climbing Plants," and his later work on the +"Power of Movement in Plants," Dr. Gray's "How Plants Behave," and the +chapter on "Movements" in the "Physiological Botany," will offer a wide +field for study and experiment. + +3. _Structure of Stems_.--Let the pupils collect a series of branches of +some common tree or shrub, from the youngest twig up to as large a branch +as they can cut, and describe them. Poplar, Elm, Oak, Lilac, etc., will be +found excellent for the purpose. + +While discussing these descriptions, a brief explanation of +plant-structure may be given. In treating this subject, the teacher must +govern himself by the needs of his class, and the means at his command. +Explanations requiring the use of a compound microscope do not enter +necessarily into these lessons. The object aimed at is to teach the pupils +about the things which they can see and handle for themselves. Looking at +sections that others have prepared is like looking at pictures; and, while +useful in opening their eyes and minds to the wonders hidden from our +unassisted sight, fails to give the real benefit of scientific training. +Plants are built up of cells. The delicate-walled spherical, or polygonal, +cells which make up the bulk of an herbaceous stem, constitute cellular +tissue (_parenchyma_). This was well seen in the stem of the cutting of +Bean in which the roots had begun to form.[1] The strengthening fabric +in almost all flowering plants is made up of woody bundles, or woody +tissue.[2] The wood-cells are cells which are elongated and with thickened +walls. There are many kinds of them. Those where the walls are very thick +and the cavity within extremely small are _fibres_. A kind of cell, not +strictly woody, is where many cells form long vessels by the breaking away +of the connecting walls. These are _ducts_. These two kinds of cells +are generally associated together in woody bundles, called therefore +fibro-vascular bundles. We have already spoken of them as making the dots +on the leaf-scars, and forming the strengthening fabric of the leaves.[3] + +[Footnote 1: See page 46.] + +[Footnote 2: If elements of the same kind are untied, they constitute a +tissue to which is given the name of those elements; thus parenchyma cells +form parenchyma tissue or simply parenchyma; cork-cells form cork, etc. A +tissue can therefore be defined as a fabric of united cells which have had +a common origin and obeyed a common law of growth.--Physiological Botany. +p. 102.] + +[Footnote 3: See page 58.] + +We will now examine our series of branches. The youngest twigs, in spring +or early summer, are covered with a delicate, nearly colorless skin. +Beneath this is a layer of bark, usually green, which gives the color to +the stem, an inner layer of bark, the wood and the pith. The pith is soft, +spongy and somewhat sappy. There is also sap between the bark and the +wood. An older twig has changed its color. There is a layer of brown bark, +which has replaced the colorless skin. In a twig a year old the wood is +thicker and the pith is dryer. Comparing sections of older branches with +these twigs, we find that the pith has shrunk and become quite dry, and +that the wood is in rings. It is not practicable for the pupils to +compare the number of these rings with the bud-rings, and so find out for +themselves that the age of the branch can be determined from the wood, for +in young stems the successive layers are not generally distinct. But, in +all the specimens, the sap is found just between the wood and the bark, +and here, where the supply of food is, is where the growth is taking +place. Each year new wood and new bark are formed in this _cambium-layer_, +as it is called, new wood on its inner, new bark on its outer face. Trees +which thus form a new ring of wood every year are called _exogenous_, or +outside-growing. + +Ask the pupils to separate the bark into its three layers and to try +the strength of each. The two outer will easily break, but the inner is +generally tough and flexible. It is this inner bark, which makes the +Poplar and Willow branches so hard to break. These strong, woody fibres +of the inner bark give us many of our textile fabrics. Flax and Hemp come +from the inner bark of their respective plants (_Linum usitatissimum_ and +_Cannabis sativa_), and Russia matting is made from the bark of the Linden +(_Tilia Americana_). + +We have found, in comparing the bark of specimens of branches of various +ages, that, in the youngest stems, the whole is covered with a skin, or +_epidermis_, which is soon replaced by a brown outer layer of bark, called +the _corky layer_; the latter gives the distinctive color to the tree. +While this grows, it increases by a living layer of cork-cambium on its +inner face, but it usually dies after a few years. In some trees it goes +on growing for many years. It forms the layers of bark in the Paper Birch +and the cork of commerce is taken from the Cork Oak of Spain. The green +bark is of cellular tissue, with some green coloring matter like that of +the leaves; it is at first the outer layer, but soon becomes covered with +cork. It does not usually grow after the first year. Scraping the bark of +an old tree, we find the bark homogeneous. The outer layers have perished +and been cast off. As the tree grows from within, the bark is stretched +and, if not replaced, cracks and falls away piecemeal. So, in most old +trees, the bark consists of successive layers of the inner woody bark. + +Stems can be well studied from pieces of wood from the woodpile. The ends +of the log will show the concentric rings. These can be traced as long, +wavy lines in vertical sections of the log, especially if the surface is +smooth. If the pupils can whittle off different planes for themselves, +they will form a good idea of the formation of the wood. In many of +the specimens there will be knots, and the nature of these will be an +interesting subject for questions. If the knot is near the centre of the +log, lead back their thoughts to the time when the tree was as small as +the annular ring on which the centre of the knot lies. Draw a line on this +ring to represent the tree at this period of its growth. What could the +knot have been? It has concentric circles like the tree itself. It was a +branch which decayed, or was cut off. Year after year, new rings of wood +formed themselves round this broken branch, till it was covered from +sight, and every year left it more deeply buried in the trunk. + +Extremely interesting material for the study of wood will be found in thin +sections prepared for veneers. Packages of such sections will be of great +use to the teacher.[1] They show well the reason of the formation of a +dividing line between the wood of successive seasons. In a cross section +of Oak or Chestnut the wood is first very open and porous and then close. +This is owing to the presence of ducts in the wood formed in the spring. +In other woods there are no ducts, or they are evenly distributed, but +the transition from the close autumn wood, consisting of smaller and +more closely packed cells, to the wood of looser texture, formed in the +following spring, makes a line that marks the season's growth. + +[Footnote 1: Mr. Romeyn B. Hough, of Lowville, N.Y., will supply a package +of such sections for one dollar. The package will consist of several +different woods, in both cross and vertical section and will contain +enough duplicates for an ordinary class. + +He also issues a series of books on woods illustrated by actual and neatly +mounted specimens, showing in each case three distinct views of the grain. +The work is issued in parts, each representing twenty-five species, and +selling with text at $5, expressage prepaid; the mounted specimens alone +at 25 cts. per species or twenty-five in neat box for $4. He has also +a line of specimens prepared for the stereopticon and another for the +microscope. They are very useful and sell at 50 cts. per species or +twenty-five for $10.] + +Let each of the scholars take one of the sections of Oak and write a +description of its markings. The age is easily determined; the pith rays, +or _medullary rays_, are also plain. These form what is called the silver +grain of the wood. The ducts, also, are clear in the Oak and Chestnut. +There is a difference in color between the outer and inner wood, the older +wood becomes darker and is called the _heart-wood_, the outer is the +_sap-wood_. In Birds-eye Maple, and some other woods, the abortive buds +are seen. They are buried in the wood, and make the disturbance which +produces the ornamental grain. In sections of Pine or Spruce, no ducts +can be found. The wood consists entirely of elongated, thickened cells or +fibres. In some of the trees the pith rays cannot be seen with the naked +eye. + +Let the pupils compare the branches which they have described, with a +stalk of Asparagus, Rattan, or Lily. A cross section of one of these shows +dots among the soft tissue. These are ends of the fibro-vascular bundles, +which in these plants are scattered through the cellular tissue instead of +being brought together in a cylinder outside of the pith. In a vertical +section they appear as lines. There are no annular rings. + +If possible, let the pupils compare the leaves belonging to these +different types of stems. The parallel-veined leaves of monocotyledons +have stems without distinction of wood, bark and pith; the netted-veined +leaves of dicotyledons have exogenous stems. + +Dicotyledons have bark, wood, and pith, and grow by producing a new ring +of wood outside the old. They also increase by the growth of the woody +bundles of the leaves, which mingle with those of the stem.[1] Twist off +the leaf-stalk of any leaf, and trace the bundles into the stem. + +[Footnote 1: See note, p. 127, Physiological Botany.] + +Monocotyledons have no layer which has the power of producing new wood, +and their growth takes place entirely from the intercalation of new +bundles, which originate at the bases of the leaves. The lower part of a +stem of a Palm, for instance, does not increase in size after it has lost +its crown of leaves. This is carried up gradually. The upper part of the +stem is a cone, having fronds, and below this cone the stem does not +increase in diameter. The word _endogenous_, inside-growing, is not, +therefore, a correct one to describe the growth of most monocotyledons, +for the growth takes place where the leaves originate, near the exterior +of the stem. + +_Gray's First Lessons_. Sect. VI. Sect, XVI, sec. 1, 401-13. sec. 3. +sec. 6, 465-74. + +_How Plants Grow_. Chap. 1, 82, 90-118. + + + + +VI. + +LEAVES. + + +We have studied leaves as cotyledons, bud-scales, etc., but when we speak +of _leaves_, we do not think of these adapted forms, but of the green +foliage of the plant. + +1. _Forms and Structure_.--Provide the pupils with a number of green +leaves, illustrating simple and compound, pinnate and palmate, sessile and +petioled leaves. They must first decide the question, _What are the parts +of a leaf_? All the specimens have a green _blade_ which, in ordinary +speech, we call the leaf. Some have a stalk, or _petiole_, others are +joined directly to the stem. In some of them, as a rose-leaf, for +instance, there are two appendages at the base of the petiole, called +_stipules_. These three parts are all that any leaf has, and a leaf that +has them all is complete. + +Let us examine the blade. Those leaves which have the blade in one +piece are called _simple_; those with the blade in separate pieces are +_compound_. We have already answered the question, _What constitutes a +single leaf_?[1] Let the pupils repeat the experiment of cutting off the +top of a seedling Pea, if it is not already clear in their minds, and find +buds in the leaf-axils of other plants.[2] + +[Footnote 1: See page 31.] + +[Footnote 2: With one class of children, I had much difficulty in making +them understand the difference between simple and compound leaves. I did +not tell them that the way to tell a single leaf was to look for buds in +the axils, but incautiously drew their attention to the stipules at the +base of a rose leaf as a means of knowing that the whole was one. Soon +after, they had a locust leaf to describe; and, immediately, with the +acuteness that children are apt to develop so inconveniently to their +teacher, they triumphantly refuted my statement that it was one leaf, by +pointing to the stiples. There was no getting over the difficulty; and +although I afterwards explained to them about the position of the buds, +and showed them examples, they clung with true childlike tenacity to their +first impression and always insisted that they could not see why each +leaflet was not a separate leaf.] + +An excellent way to show the nature of compound leaves is to mount a +series showing every gradation of cutting, from a simple, serrate leaf to +a compound one (Figs. 24 and 25). A teacher, who would prepare in summer +such illustrations as these, would find them of great use in his winter +lessons. The actual objects make an impression that the cuts in the book +cannot give. + +[Illustration: FIG. 24.--Series of palmately-veined leaves.] + +[Illustration: FIG. 25.--Series of pinnately-veined leaves.] + +Let the pupils compare the distribution of the veins in their specimens. +They have already distinguished parallel-veined from netted-veined leaves, +and learned that this difference is a secondary distinction between +monocotyledons and dicotyledons.[1] The veins in netted-veined leaves are +arranged in two ways. The veins start from either side of a single midrib +(_feather-veined_ or _pinnately-veined_), or they branch from a number of +ribs which all start from the top of the petiole, like the fingers from +the palm of the hand (_palmately-veined_). The compound leaves correspond +to these modes of venation; they are either pinnately or palmately +compound. + +[Footnote 1: See page 34.] + +These ribs and veins are the woody framework of the leaf, supporting the +soft green pulp. The woody bundles are continuous with those of the stem, +and carry the crude sap, brought from the roots, into the cells of every +part of the leaf, where it is brought into contact with the external +air, and the process of making food (_Assimilation_ 4) is carried on. +"Physiologically, leaves are green expansions borne by the stern, +outspread in the air and light, in which assimilation and the processes +connected with it are carried on."[1] + +[Footnote 1: Gray's Structural Botany, p. 85.] + +The whole leaf is covered with a delicate skin, or epidermis, continuous +with that of the stem.[1] + +[Footnote 1: Reader in Botany. XI. Protection of Leaves from the Attacks +of Animals.] + + +2. _Descriptions_.--As yet the pupils have had no practice in writing +technical descriptions. This sort of work may be begun when they come to +the study of leaves. In winter a collection of pressed specimens will be +useful. Do not attach importance to the memorizing of terms. Let them be +looked up as they are needed, and they will become fixed by practice. The +pupils may fill out such schedules as the following with any leaves that +are at hand. + +SCHEDULE FOR LEAVES. + + Arrangement _Alternate_[1] + + |Simple or compound. _Simple_ + |(arr. and no. of leaflets) + | + |Venation _Netted and + | feather-veined_ + |Shape _Oval_ +1. BLADE < + | Apex _Acute_ + | + | Base _Oblique_ + | + |Margin _Slightly wavy_ + | + |Surface _Smooth_ + +2. PETIOLE _Short; hairy_ + +3. STIPULES _Deciduous_ + +Remarks. Veins prominent and very straight. + +[Footnote 1: The specimen described is a leaf of Copper Beech.] + +In describing shapes, etc., the pupils can find the terms in the book as +they need them. It is desirable at first to give leaves that are easily +matched with the terms, keeping those which need compound words, such as +lance-ovate, etc., to come later. The pupils are more interested if they +are allowed to press and keep the specimens they have described. It is not +well to put the pressed leaves in their note books, as it is difficult to +write in the books without spoiling the specimens. It is better to mount +the specimens on white paper, keeping these sheets in brown paper covers. +The pupils can make illustrations for themselves by sorting leaves +according to the shapes, outlines, etc., and mounting them. + + +3. _Transpiration_.--This term is used to denote the evaporation of water +from a plant. The evaporation takes place principally through breathing +pores, which are scattered all over the surface of leaves and young stems. +The _breathing pores_, or _stomata_, of the leaves, are small openings +in the epidermis through which the air can pass into the interior of the +plant. Each of these openings is called a _stoma_. "They are formed by a +transformation of some of the cells of the epidermis; and consist usually +of a pair of cells (called guardian cells), with an opening between +them, which communicates with an air-chamber within, and thence with the +irregular intercellular spaces which permeate the interior of the leaf. +Through the stomata, when open, free interchange may take place between +the external air and that within the leaf, and thus transpiration be +much facilitated. When closed, this interchange will be interrupted or +impeded."[1] + +[Footnote 1: Gray's Structural Botany, page 89. For a description of the +mechanism of the stomata, see Physiological Botany, p. 269.] + +In these lessons, however, it is not desirable to enter upon subjects +involving the use of the compound microscope. Dr. Goodale says: "Whether +it is best to try to explain to the pupils the structure of these valves, +or stomata, must be left to each teacher. It would seem advisable to +pass by the subject untouched, unless the teacher has become reasonably +familiar with it by practical microscopical study of leaves. For a teacher +to endeavor to explain the complex structure of the leaf, without having +seen it for himself, is open to the same objection which could be urged +against the attempted explanation of complicated machinery by one who has +never seen it, but has heard about it. What is here said with regard to +stomata applies to all the more recondite matters connected with plant +structure."[1] + +[Footnote 1: Concerning a few Common Plants, p. 29.] + +There are many simple experiments which can be used to illustrate the +subject. + +(1) Pass the stem of a cutting through a cork, fitting tightly into the +neck of a bottle of water. Make the cork perfectly air-tight by coating it +with beeswax or paraffine. The level of the liquid in the bottle will be +lowered by the escape of water through the stem and leaves of the cutting +into the atmosphere. + +(2) Cut two shoots of any plant, leave one on the table and place the +other in a glass of water.[1] The first will soon wilt, while the other +will remain fresh. If the latter shoot be a cutting from some plant that +will root in water, such as Ivy, it will not fade at all. Also, leave one +of the plants in the schoolroom unwatered for a day or two, till it begins +to wilt. If the plant be now thoroughly watered, it will recover and the +leaves will resume their normal appearance. + +[Footnote 1: Lessons in Elementary Botany, by Daniel Oliver, London. +Macmillan & Co., 1864, pp. 14-15.] + +Evaporation is thus constantly taking place from the leaves, and if there +is no moisture to supply the place of what is lost, the cells collapse and +the leaf, as we say, wilts. When water is again supplied the cells swell +and the leaf becomes fresh. + +(3) Place two seedlings in water, one with its top, the other with its +roots in the jar. The latter will remain fresh while the first wilts and +dies. + +Absorption takes place through the roots. The water absorbed is drawn up +through the woody tissues of the stem (4), and the veins of the leaves +(5), whence it escapes into the air (6). + +(4) Plunge a cut branch immediately into a colored solution, such as +aniline red, and after a time make sections in the stem above the liquid +to see what tissues have been stained.[1] + +[Footnote 1: The Essentials of Botany, by Charles E. Bessey. New York, +Henry Holt & Co., 1884. Page 74. See also Physiological Botany, pp. +259-260.] + +(5) "That water finds its way by preference through the fibro-vascular +bundles even in the more delicate parts, is shown by placing the cut +peduncle of a white tulip, or other large white flower, in a harmless dye, +and then again cutting off its end in order to bring a fresh surface in +contact with the solution,[1] when after a short time the dye will mount +through the flower-stalk and tinge the parts of the perianth according to +the course of the bundles."[2] + +[Footnote 1: If the stems of flowers are cut under water they will last a +wonderfully long time. "One of the most interesting characteristics of the +woody tissues in relation to the transfer of water is the immediate change +which the cut surface of a stem undergoes upon exposure to the air, +unfitting it for its full conductive work. De Vries has shown that when a +shoot of a vigorous plant, for instance a Helianthus, is bent down under +water, care being taken not to break it even in the slightest degree, +a clean, sharp cut will give a surface which will retain the power of +absorbing water for a long time; while a similar shoot cut in the open +air, even if the end is instantly plunged under water, will wither much +sooner than the first."--Physiological Botany, p. 263.] + +[Footnote 2: Physiological Botany, p. 260.] + +(6) Let the leaves of a growing plant rest against the window-pane. +Moisture will be condensed on the cold surface of the glass, wherever the +leaf is in contact with it. This is especially well seen in Nasturtium +(Tropaeolum) leaves, which grow directly against a window, and leave the +marks even of their veining on the glass, because the moisture is only +given out from the green tissue, and where the ribs are pressed against +the glass it is left dry. + +Sometimes the water is drawn up into the cells of the leaves faster than +it can escape into the atmosphere.[1] This is prettily shown if we place +some of our Nasturtium seedlings under a ward-case. The air in the case is +saturated with moisture, so that evaporation cannot take place, but the +water is, nevertheless, drawn up from the roots and through the branches, +and appears as little drops on the margins of the leaves. That this is +owing to the absorbing power of the roots, may be shown by breaking off +the seedling, and putting the slip in water. No drops now appear on the +leaves, but as soon as the cutting has formed new roots, the drops again +appear. + +[Footnote 1: See Lectures on the Physiology of Plants. By Sidney Howard +Vines, Cambridge, England. University Press, 1886. Page 92.] + +This constant escape of water from the leaves causes a current to flow +from the roots through the stem into the cells of the leaves. The dilute +mineral solutions absorbed by the roots[1] are thus brought where they +are in contact with the external air, concentrated by the evaporation of +water, and converted in these cells into food materials, such as starch. +The presence of certain mineral matters, as potassium, iron, etc., are +necessary to this assimilating process, but the reason of their necessity +is imperfectly understood, as they do not enter in the products formed. + +[Footnote 1: See page 48.] + +The amount of water exhaled is often very great. Certain plants are used +for this reason for the drainage of wet and marshy places. The most +important of these is the Eucalyptus tree.[1] + +[Footnote 1: Reader in Botany. XII. Transpiration.] + +"The amount of water taken from the soil by the trees of a forest and +passed into the air by transpiration is not so large as that accumulated +in the soil by the diminished evaporation under the branches. Hence, there +is an accumulation of water in the shade of forests which is released +slowly by drainage.[1] But if the trees are so scattered as not materially +to reduce evaporation from the ground, the effect of transpiration in +diminishing the moisture of the soil is readily shown. It is noted, +especially in case of large plants having a great extent of exhaling +surface, such, for instance, as the common sunflower. Among the plants +which have been successfully employed in the drainage of marshy soil by +transpiration probably the species of Eucalyptus (notably _E_. _globulus_) +are most efficient."[2] + +[Footnote 1: Reader in Botany. XIII. Uses of the Forests.] + +[Footnote 2: Physiological Botany, page 283.] + + +4. _Assimilation_.--It is not easy to find practical experiments on +assimilation. Those which follow are taken from "Physiological Botany" (p. +305). + + Fill a five-inch test tube, provided with a foot, with fresh drinking + water. In this place a sprig of one of the following water + plants,--_Elodea Canadensis, Myriophyllum spicatum, M. + verticillatum_, or any leafy _Myriophyllum_ (in fact, any small- + leaved water plant with rather crowded foliage). This sprig should be + prepared as follows: Cut the stem squarely off, four inches or so + from the tip, dry the cut surface quickly with blotting paper, then + cover the end of the stein with a quickly drying varnish, for + instance, asphalt-varnish, and let it dry perfectly, keeping the rest + of the stem, if possible, moist by means of a wet cloth. When the + varnish is dry, puncture it with a needle, and immerse the stem in + the water in the test tube, keeping the varnished larger end + uppermost. If the submerged plant be now exposed to the strong rays + of the sun, bubbles of oxygen gas will begin to pass off at a rapid + and even rate, but not too fast to be easily counted. If the simple + apparatus has begun to give off a regular succession of small + bubbles, the following experiments can be at once conducted: + + (1) Substitute for the fresh water some which has been boiled a few + minutes before, and then allowed to completely cool: by the boiling, + all the carbonic acid has been expelled. If the plant is immersed in + this water and exposed to the sun's rays, no bubbles will be evolved; + there is no carbonic acid within reach of the plant for the + assimilative process. But, + + (2) If breath from the lungs be passed by means of a slender glass + tube through the water, a part of the carbonic acid exhaled from the + lungs will be dissolved in it, and with this supply of the gas the + plant begins the work of assimilation immediately. + + (3) If the light be shut off, the evolution of bubbles will presently + cease, being resumed soon after light again has access to the plant. + + (5) Place round the base of the test tube a few fragments of ice, in + order to appreciably lower the temperature of the water. At a certain + point it will be observed that no bubbles are given off, and their + evolution does not begin again until the water becomes warm. + +The evolution of bubbles shows that the process of making food is going +on. The materials for this process are carbonic acid gas and water. The +carbonic acid dissolved in the surrounding water is absorbed, the carbon +unites with the elements of water in the cells of the leaves, forming +starch, etc., and most of the oxygen is set free, making the stream of +bubbles. When the water is boiled, the dissolved gas is driven off and +assimilation cannot go on; but as soon as more carbonic acid gas is +supplied, the process again begins. We have seen by these experiments +that sunlight and sufficient heat are necessary to assimilation, and that +carbonic acid gas and water must be present. The presence of the green +coloring matter of the leaves (chlorophyll) is also essential, and some +salts, such as potassium, iron, etc., are needful, though they may not +enter into the compounds formed. + +The food products are stored in various parts of the plant for future use, +or are expended immediately in the growth and movements of the plant. In +order that they shall be used for growth, free oxygen is required, and +this is supplied by the respiration of the plant. + +Some plants steal their food ready-made. Such a one is the Dodder, which +sends its roots directly into the plant on which it feeds. This is a +_parasite_.[1] It has no need of leaves to carry on the process of making +food. Some parasites with green leaves, like the mistletoe, take the crude +sap from the host-plant and assimilate it in their own green leaves. +Plants that are nourished by decaying matter in the soil are called +_saprophytes_. Indian Pipe and Beech-Drops are examples of this. They need +no green leaves as do plants that are obliged to support themselves. + +[Footnote 1: Reader in Botany. XIV. Parasitic Plants.] + +Some plants are so made that they can use animal matter for food. This +subject of insectivorous plants is always of great interest to pupils. If +some Sundew (_Drosera_) can be obtained and kept in the schoolroom, it +will supply material for many interesting experiments.[1] That plants +should possess the power of catching insects by specialized movements and +afterwards should digest them by means of a gastric juice like that of +animals, is one of the most interesting of the discoveries that have been +worked out during the last thirty years.[2] + +[Footnote 1: See Insectivorous Plants, by Charles Darwin. New York: D. +Appleton and Co., 1875. + +How Plants Behave, Chap. III. + +A bibliography of the most important works on the subject will be found in +Physiological Botany, page 351, note.] + +[Footnote 2: Reader in Botany. XV. Insectivorous Plants.] + + +5. _Respiration_.--Try the following experiment in germination. + +Place some seeds on a sponge under an air-tight glass. Will they grow? +What causes them to mould? + + +Seeds will not germinate without free access of air. They must have free +oxygen to breathe, as must every living thing. We know that an animal +breathes in oxygen, that the oxygen unites with particles of carbon within +the body and that the resulting carbonic acid gas is exhaled.[1] The same +process goes on in plants, but it was until recently entirely unknown, +because it was completely masked during the daytime by the process of +assimilation, which causes carbonic acid to be inhaled and decomposed, and +oxygen to be exhaled.[2] In the night time the plants are not assimilating +and the process of breathing is not covered up. It has, therefore, long +been known that carbonic acid gas is given off at night. The amount, +however, is so small that it could not injure the air of the room, as +is popularly supposed. Respiration takes place principally through the +stomata of the leaves.[3] We often see plants killed by the wayside dust, +and we all know that on this account it is very difficult to make a hedge +grow well by a dusty road. The dust chokes up the breathing pores of the +leaves, interfering with the action of the plant. It is suffocated. + +The oxygen absorbed decomposes starch, or some other food product of the +plant, and carbonic acid gas and water are formed. It is a process of slow +combustion.[4] The energy set free is expended in growth, that is, in the +formation of new cells, and the increase in size of the old ones, and in +the various movements of the plant. + +[Footnote 1: See page 13.] + +[Footnote 2: This table illustrates the differences between the processes. + +ASSIMILATION PROPER. RESPIRATION. + +Takes place only in cells Takes place in all active cells. +containing chlorophyll. + +Requires light. Can proceed in darkness. + +Carbonic acid absorbed, Oxygen absorbed, carbonic +oxygen set free. acid set free. + +Carbohydrates formed. Carbohydrates consumed. + +Energy of motion becomes Energy of position becomes +energy of position. energy of motion. + +The plant gains in dry The plant loses dry weight. +weight. + +Physiological Botany, page 356.] + +[Transcriber's Note: Two footnote marks [3] and [4] above in original +text, but no footnote text was found in the book] + +This process of growth can take place only when living _protoplasm_ is +present in the cells of the plant. The substance we call protoplasm is +an albuminoid, like the white of an egg, and it forms the flesh of both +plants and animals. A living plant can assimilate its own protoplasm, an +animal must take it ready-made from plants. But a plant can assimilate its +food and grow only under the mysterious influence we call life. Life +alone brings forth life, and we are as far as ever from understanding +its nature. Around our little island of knowledge, built up through the +centuries by the labor of countless workers, stretches the infinite ocean +of the unknown. + +_Gray's First Lessons_. Sect. VII, XVI, sec. 2, sec. 4, sec. 5, sec. 6, +476-480. + +_How Plants Grow_. Chap. I, 119-153, Chap. III, 261-280. + + + + + + +***END OF THE PROJECT GUTENBERG EBOOK OUTLINES OF LESSONS IN BOTANY, PART +I; FROM SEED TO LEAF*** + + +******* This file should be named 10726.txt or 10726.zip ******* + + +This and all associated files of various formats will be found in: +https://www.gutenberg.org/1/0/7/2/10726 + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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