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right: 84%; text-align: right;} -.fnanchor { - vertical-align: super; - font-size: .8em; - text-decoration: - none; -} - -.transnote {background-color: #E6E6FA; - color: black; - font-size:smaller; - padding:0.5em; - margin-bottom:5em; - font-family:sans-serif, serif; } - -.ws2 {display: inline; margin-left: 0em; padding-left: 2em;} -.ws3 {display: inline; margin-left: 0em; padding-left: 3em;} -.ws4 {display: inline; margin-left: 0em; padding-left: 4em;} - - @media handheld { - .pagenum {display:none;} - .epubonly {display:none;} -} - - </style> - </head> -<body> - -<div style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of Elementary Botany, by George Francis Atkinson</div> - -<div style='display:block; margin:1em 0'> -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world 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 <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you -are not located in the United States, you will have to check the laws of the -country where you are located before using this eBook. -</div> - -<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: Elementary Botany</div> - -<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Author: George Francis Atkinson</div> - -<div style='display:block; margin:1em 0'>Release Date: February 20, 2021 [eBook #64601]</div> - -<div style='display:block; margin:1em 0'>Language: English</div> - -<div style='display:block; margin:1em 0'>Character set encoding: UTF-8</div> - -<div style='display:block; margin-left:2em; text-indent:-2em'>Produced by: Sonya Schermann and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)</div> - -<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK ELEMENTARY BOTANY ***</div> -<hr class="chap" /> - -<div class="figcenter"> - <img src="images/frontis.jpg" alt="" width="600" height="369" /> - <div class="blockquot"> - <p class="center"><span class="smcap">Cycas revoluta</span> (<a href="#Page_311">see page 311</a>).</p> - <p class="author">(<i>Frontispiece.</i>)</p> - </div> -</div> -<hr class="chap" /> -<h1>ELEMENTARY BOTANY</h1> - -<p class="f90 space-above3">BY</p> -<p class="center">GEORGE FRANCIS ATKINSON, <span class="smcap">Ph.B.</span></p> -<p class="f90"><i>Professor of Botany in Cornell University</i></p> - -<p class="center space-above2 space-below2"><i>THIRD EDITION, REVISED</i></p> - -<div class="figcenter"> - <img src="images/logo.jpg" alt="" width="150" height="129" /> -</div> - -<p class="center space-above2">NEW YORK<br />HENRY HOLT AND COMPANY<br />1905</p> - -<p class="center space-above2 space-below2 ">Copyright, 1898, 1905<br />BY<br /> -HENRY HOLT AND COMPANY</p> - -<p class="center space-below2">ROBERT DRUMMOND, PRINTER, NEW YORK</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_iii" id="Page_iii">[Pg iii]</a></span></p> - -<div class="chapter"><h2 class="nobreak">PREFACE.</h2></div> - -<p>The present book is the result of a revision and elaboration of the -author’s “Elementary Botany,” New York, 1898. The general plan of the -parts on physiology and general morphology remains unchanged. A number -of the chapters in the physiological part are practically untouched, -while others are thoroughly revised and considerable new matter is -added, especially on the subjects of nutrition and digestion. The -principal chapters on general morphology are unchanged or only slightly -modified, the greatest change being in a revision of the subject of -the morphology of fertilization in the gymnosperms and angiosperms in -order to bring this subject abreast of the discoveries of the past few -years. One of the greatest modifications has been in the addition of -chapters on the classification of the algæ and fungi with studies of -additional examples for the benefit of those schools where the time -allowed for the first year’s course makes desirable the examination of -a broader range of representative plants. The classification is also -carried out with greater definiteness, so that the regular sequence -of classes, orders, and families is given at the close of each of the -subkingdoms. Thus all the classes, all the orders (except a few in the -algæ), and many of the families, are given for the algæ, fungi, mosses, -liverworts, pteridophytes, gymnosperms, and angiosperms.</p> - -<p>But by far the greatest improvement has been in the complete -reorganization, rewriting, and elaboration of the part dealing with -ecology, which has been made possible by studies of the past few years, -so that the subject can be presented in a more logical and coherent -<span class="pagenum"><a name="Page_iv" id="Page_iv">[Pg iv]</a></span> -form. As a result the subject-matter of the book falls naturally into -three parts, which may be passed in review as follows:</p> - -<p>Part I. <i>Physiology.</i> This deals with the life processes of plants, -as absorption, transpiration, conduction, photosynthesis, nutrition, -assimilation, digestion, respiration, growth, and irritability. Since -protoplasm is fundamental to all the life work of the plant, this -subject is dealt with first, and the student is led through the study -of, and experimentation with, the simpler as well as some of the higher -plants, to a general understanding of protoplasm and the special way in -which it enables the plant to carry on its work and to adjust itself to -the conditions of its existence. This study also serves the purpose of -familiarizing the pupil with some of the lower and unfamiliar plants.</p> - -<p>Some teachers will prefer to begin the study with general morphology -and classification, thus studying first the representatives of the -great groups of plants, and others will prefer to dwell first on the -ecological aspects of vegetation. This can be done in the use of this -book by beginning with Part II or with Part III.</p> - -<p>But the author believes that morphology can best be comprehended after -a general study of life processes and functions of the different parts -of plants, including in this study some of the lower forms of plant -life where some of these processes can more readily be observed. The -pupil is then prepared for a more intelligent consideration of general -and comparative morphology and relationships. Even more important is -a first study of physiology before taking up the subject of ecology. -The great value to be derived from a study of plants in their relation -to environment lies in the ability to interpret the different states, -conditions, behavior, and associations of the plant, and for this -physiology is indispensable. It is true that a considerable measure -of success can be obtained by a good teacher in beginning with either -subject, but the writer believes that measure of success would be -greater if the subjects were taken up in the order presented here. -<span class="pagenum"><a name="Page_v" id="Page_v">[Pg v]</a></span></p> - -<p>Part II. <i>Morphology and life history of representative plants.</i> This -includes a rather careful study of representative examples among the -algæ, fungi, liverworts, mosses, ferns and their allies, gymnosperms -and angiosperms, with especial emphasis on the form of plant parts, -and a comparison of them in the different groups, with a comparative -study of development, reproduction, and fertilization, rounding out -the work with a study of life histories and noting progression and -retrogression of certain organs and phases in proceeding from the -lower to the higher plants. Thus, in the algæ a first critical study -is made of four examples which illustrate in a marked way progressive -stages of the plant body, sexual organs, and reproduction. Additional -examples are then studied for the purpose of acquiring a knowledge of -variations from these types and to give a broader basis for the brief -consideration of general relationships and classification.</p> - -<p>A similar plan is followed in the other great groups. The processes of -fertilization and reproduction can be most easily observed in the lower -plants like the algæ and fungi, and this is an additional argument in -favor of giving emphasis to these forms of plant life as well as the -advantage of proceeding logically from simpler to more complex forms. -Having also learned some of these plants in our study of physiology, -we are following another recognized rule of pedagogy, i.e., proceeding -from known objects to unknown structures and processes. Through -the study of the organs of reproduction of the lower plants and by -general comparative morphology we have come to an understanding of the -morphology of the parts of the flower, and of the true sexual organs -of the seed plants, and no student can hope to properly interpret the -significance of the flower, or the sexual organs of the seed plants who -neglects a careful study of the general morphology of the lower plants.</p> - -<p>Part III. <i>Plant members in relation to environment.</i> This part deals -with the organization of the plant body as a whole in its relation to -environment, the organization of plant tissues with a discussion of -the principal tissues and a descriptive synopsis of the same. This is -<span class="pagenum"><a name="Page_vi" id="Page_vi">[Pg vi]</a></span> -followed by a complete study from a biological standpoint of the -different members of the plant, their special function and their -special relations to environment. The stem, root, leaf, flower, etc., -are carefully examined and their ecological relations pointed out. This -together with the study of physiology and representatives in the groups -of plants forms a thorough basis for pure plant ecology, or the special -study of vegetation in its relation to environment.</p> - -<p>There is a study of the factors of environment or ecological factors, -which in general are grouped under the physical, climatic, and biotic -factors. This is followed by an analysis of vegetation forms and -structures, plant formations and societies. Then in order are treated -briefly forest societies, prairie societies, desert societies, arctic -and alpine societies, aquatic societies, and the special societies of -sandy, rocky, and marshy places.</p> - -<p><i>Acknowledgments.</i> The author wishes to express his gratefulness to -all those who have given aid in the preparation of this work, or of -the earlier editions of Elementary Botany; to his associates, Dr. -E. J. Durand, Dr. K. M. Wiegand, and Professor W. W. Rowlee, of the -botanical department, and to Professor B. M. Duggar of the University -of Missouri, Professor J. C. Arthur of Purdue University, and Professor -W. F. Ganong of Smith College, for reading one or more portions of the -text; as well as to all those who have contributed illustrations.</p> - -<p><i>Illustrations.</i> The large majority of the illustrations are new -(or are the same as those used in earlier editions of the author’s -Elementary Botany) and were made with special reference to the method -of treatment followed in the text. Many of the photographs were made -by the author. Others were contributed by Professor Rowlee of Cornell -University; Mr. John Gifford of New Jersey; Professor B. M. Duggar, -University of Missouri; Professor C. E. Bessey, University of Nebraska; -Dr. M. B. Howe, New York Botanical Garden; Mr. Gifford Pinchot, Chief -of the Bureau of Forestry; Mr. B. T. Galloway, Chief of the Bureau of -Plant Industry; Professor Tuomey of Yale University; and Mr. E. H. -Harriman, who through Dr. C. H. Merriam of the National Museum allowed -<span class="pagenum"><a name="Page_vii" id="Page_vii">[Pg vii]</a></span> -the use of several of his copyrighted photographs from Alaska. To those -who have contributed drawings the author is indebted as follows: to -Professor Margaret C. Ferguson, Wellesley College; Professor Bertha -Stoneman of Huguenot College, South Africa; Mr. H. Hasselbring of -Chicago; Dr. K. Miyake, formerly of Cornell University and now of -Doshisha College, Japan; and Professors Ikeno and Hirase of the Tokio -Imperial University. The author is also indebted to Ginn & Co., Boston, -for the privilege to use from his “First Studies of Plant Life” the -following figures: 28, 29, 46, 48, 49, 56, 62, 66, 67, 87, 102, 103, -422-426, 429, 430, 438-440, 443, 444, 448, 449, 452, 472-475. A few -others are acknowledged in the text.</p> - -<p><span class="smcap">Cornell University</span>, April, 1905.</p> -<p><span class="pagenum"><a name="Page_viii" id="Page_viii">[Pg viii]</a></span></p> -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_ix" id="Page_ix">[Pg ix]</a></span></p> - -<div class="chapter"><h2 class="nobreak">TABLE OF CONTENTS.</h2></div> - -<table border="0" cellspacing="0" summary="TOC" cellpadding="0" > - <tbody><tr> - <td class="tdc lgfnt150" colspan="2">PART I. PHYSIOLOGY.</td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER I.</td> - </tr><tr> - <td class="tdr " colspan="2"><small>PAGE</small></td> - </tr><tr> - <td class="tdl"><span class="smcap">Protoplasm.</span></td> - <td class="tdr"><a href="#CHAPTER_I"> 1</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER II.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Absorption, Diffusion, Osmose.</span></td> - <td class="tdr"><a href="#CHAPTER_II">13</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER III.</td> - </tr><tr> - <td class="tdl"><span class="smcap">How Plants Obtain Water.</span></td> - <td class="tdr"><a href="#CHAPTER_III">22</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER IV.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Transpiration, or the Loss of Water by Plants.</span></td> - <td class="tdr"><a href="#CHAPTER_IV">35</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER V.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Path of Movement of Water in Plants.</span></td> - <td class="tdr"><a href="#CHAPTER_V">48</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER VI.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Mechanical Uses of Water.</span></td> - <td class="tdr"><a href="#CHAPTER_VI">56</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER VII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Starch and Sugar Formation.</span></td> - <td class="tdr"><a href="#CHAPTER_VII">60</a></td> - </tr><tr> - <td class="tdl_ws1">1. The Gases Concerned.</td> - <td class="tdr"><a href="#VII_1">60</a></td> - </tr><tr> - <td class="tdl_ws1">2. Where Starch is Formed.</td> - <td class="tdr"><a href="#VII_2">64</a></td> - </tr><tr> - <td class="tdl_ws1">3. Chlorophyll and the Formation of Starch.</td> - <td class="tdr"><a href="#VII_3">67</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER VIII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Starch and Sugar Concluded; Analysis of Plant Substance.</span></td> - <td class="tdr"><a href="#CHAPTER_VIII">73</a></td> - </tr><tr> - <td class="tdl_ws1">1. Translocation of Starch.</td> - <td class="tdr"><a href="#VIII_1">73</a></td> - </tr><tr> - <td class="tdl_ws1">2. Sugar, and Digestion of Starch.</td> - <td class="tdr"><a href="#VIII_2">75</a> - <span class="pagenum"><a name="Page_x" id="Page_x">[Pg x]</a></span></td> - </tr><tr> - <td class="tdl_ws1">3. Rough Analysis of Plant Substance.</td> - <td class="tdr"><a href="#VIII_3">79</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER IX.</td> - </tr><tr> - <td class="tdl"><span class="smcap">How Plants Obtain their Food, I.</span></td> - <td class="tdr"><a href="#CHAPTER_IX">81</a></td> - </tr><tr> - <td class="tdl_ws1">1. Sources of Plant Food.</td> - <td class="tdr"><a href="#IX_1">81</a></td> - </tr><tr> - <td class="tdl_ws1">2. Parasites and Saprophytes.</td> - <td class="tdr"><a href="#IX_2">83</a></td> - </tr><tr> - <td class="tdl_ws1">3. How Fungi Obtain their Food.</td> - <td class="tdr"><a href="#IX_3">86</a></td> - </tr><tr> - <td class="tdl_ws1">4. Mycorhiza.</td> - <td class="tdr"><a href="#IX_4">91</a></td> - </tr><tr> - <td class="tdl_ws1">5. Nitrogen gatherers.</td> - <td class="tdr"><a href="#IX_5">92</a></td> - </tr><tr> - <td class="tdl_ws1">6. Lichens.</td> - <td class="tdr"><a href="#IX_6">93</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER X.</td> - </tr><tr> - <td class="tdl"><span class="smcap">How Plants Obtain their Food, II.</span></td> - <td class="tdr"><a href="#CHAPTER_X">97</a></td> - </tr><tr> - <td class="tdl_ws1"> Seedlings,</td> - <td class="tdr"><a href="#X_1">97</a></td> - </tr><tr> - <td class="tdl_ws1"> Digestion,</td> - <td class="tdr"><a href="#X_2">107</a></td> - </tr><tr> - <td class="tdl_ws1"> Assimilation</td> - <td class="tdr"><a href="#X_3">109</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XI.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Respiration.</span></td> - <td class="tdr"><a href="#CHAPTER_XI">110</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Growth.</span></td> - <td class="tdr"><a href="#CHAPTER_XII">118</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XIII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Irritability.</span></td> - <td class="tdr"><a href="#CHAPTER_XIII">125</a></td> - </tr><tr> - <td class="tdc_space-above2 lgfnt150" colspan="2">PART II. MORPHOLOGY AND LIFE HISTORY<br /> - OF REPRESENTATIVE PLANTS.</td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XIV.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Spirogyra.</span></td> - <td class="tdr"><a href="#CHAPTER_XIV">136</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XV.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Vaucheria.</span></td> - <td class="tdr"><a href="#CHAPTER_XV">142</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XVI.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Œdogonium.</span></td> - <td class="tdr"><a href="#CHAPTER_XVI">147</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XVII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Coleochæte.</span></td> - <td class="tdr"><a href="#CHAPTER_XVII">153</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XVIII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Classification and Additional Studies of the Algæ.</span></td> - <td class="tdr"><a href="#CHAPTER_XVIII">158</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XIX.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Fungi: Mucor and Saprolegnia.</span></td> - <td class="tdr"><a href="#CHAPTER_XIX">177</a> - <span class="pagenum"><a name="Page_xi" id="Page_xi">[Pg xi]</a></span></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XX.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Fungi Continued</span> (“Rusts” Uredineæ).</td> - <td class="tdr"><a href="#CHAPTER_XX">187</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXI.</td> - </tr><tr> - <td class="tdl"><span class="smcap">The Higher Fungi.</span></td> - <td class="tdr"><a href="#CHAPTER_XXI">195</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Classification of the Fungi.</span></td> - <td class="tdr"><a href="#CHAPTER_XXII">213</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXIII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Liverworts</span> (Hepaticæ).</td> - <td class="tdr"><a href="#CHAPTER_XXIII">222</a></td> - </tr><tr> - <td class="tdl_ws1">Riccia,</td> - <td class="tdr"><a href="#XXIII_1">222</a></td> - </tr><tr> - <td class="tdl_ws1">Marchantia.</td> - <td class="tdr"><a href="#XXIII_2">226</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXIV.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Liverworts Continued.</span></td> - <td class="tdr"><a href="#CHAPTER_XXIV">231</a></td> - </tr><tr> - <td class="tdl_ws1">Sporogonium of Marchantia.</td> - <td class="tdr"><a href="#XXIV_1">231</a></td> - </tr><tr> - <td class="tdl_ws1">Leafy-stemmed Liverworts.</td> - <td class="tdr"><a href="#XXIV_2">236</a></td> - </tr><tr> - <td class="tdl_ws1">The Horned Liverworts.</td> - <td class="tdr"><a href="#XXIV_3">240</a></td> - </tr><tr> - <td class="tdl_ws1">Classification of the Liverworts.</td> - <td class="tdr"><a href="#XXIV_4">242</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXV.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Mosses</span> (Musci).</td> - <td class="tdr"><a href="#CHAPTER_XXV">243</a></td> - </tr><tr> - <td class="tdl_ws1">Classification of Mosses.</td> - <td class="tdr"><a href="#XXV_1">248</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXVI.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Ferns.</span></td> - <td class="tdr"><a href="#CHAPTER_XXVI">251</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXVII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Ferns Continued.</span></td> - <td class="tdr"><a href="#CHAPTER_XXVII">262</a></td> - </tr><tr> - <td class="tdl_ws1">Gametophyte of Ferns.</td> - <td class="tdr"><a href="#XXVII_1">262</a></td> - </tr><tr> - <td class="tdl_ws1">Sporophyte.</td> - <td class="tdr"><a href="#XXVII_2">268</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXVIII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Dimorphism of Ferns.</span></td> - <td class="tdr"><a href="#CHAPTER_XXVIII">273</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXIX.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Horsetails.</span></td> - <td class="tdr"><a href="#CHAPTER_XXIX">280</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXX.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Club mosses.</span></td> - <td class="tdr"><a href="#CHAPTER_XXX">284</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXI.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Quillworts</span> (Isoetes).</td> - <td class="tdr"><a href="#CHAPTER_XXXI">289</a> - <span class="pagenum"><a name="Page_xii" id="Page_xii">[Pg xii]</a></span></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Comparison of Ferns and their Relatives.</span></td> - <td class="tdr"><a href="#CHAPTER_XXXII">292</a></td> - </tr><tr> - <td class="tdl_ws1">Classification of the Pteridophytes.</td> - <td class="tdr"><a href="#XXXII_1">295</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXIII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Gymnosperms.</span></td> - <td class="tdr"><a href="#CHAPTER_XXXIII">297</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXIV.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Further Studies on Gymnosperms.</span></td> - <td class="tdr"><a href="#CHAPTER_XXXIV">311</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXV.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Morphology of the Angiosperms: Trillium; Dentaria.</span></td> - <td class="tdr"><a href="#CHAPTER_XXXV">318</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXVI.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Gametophyte and Sporophyte of Angiosperms.</span></td> - <td class="tdr"><a href="#CHAPTER_XXXVI">325</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXVII.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Morphology of the Nucleus and Significance of</span></td> - <td class="tdr"> </td> - </tr><tr> - <td class="tdl_ws1"><span class="smcap">Gametophyteand Sporophyte.</span></td> - <td class="tdr"><a href="#CHAPTER_XXXVII">340</a></td> - </tr> - </tbody> -</table> - -<table border="0" cellspacing="0" summary="TOC" cellpadding="0" > - <tbody><tr> - <td class="tdc_space-above2 lgfnt150" colspan="3">PART III. PLANT MEMBERS IN RELATION<br /> TO ENVIRONMENT.</td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XXXVIII.</td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">The Organization of the Plant.</span></td> - <td class="tdr"><a href="#CHAPTER_XXXVIII">349</a></td> - </tr><tr> - <td class="tdr">I.</td> - <td class="tdl_toc">Organization of Plant Members.</td> - <td class="tdr"><a href="#XXXVIII_1">349</a></td> - </tr><tr> - <td class="tdr">II.</td> - <td class="tdl_toc">Organization of Plant Tissues.</td> - <td class="tdr"><a href="#XXXVIII_2">356</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XXXIX.</td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">The Different Types of Stems.</span></td> - <td class="tdr"><a href="#CHAPTER_XXXIX">365</a></td> - </tr><tr> - <td class="tdr">I.</td> - <td class="tdl_toc">Erect Stems.</td> - <td class="tdr"><a href="#XXXIX_1">365</a></td> - </tr><tr> - <td class="tdr">II.</td> - <td class="tdl_toc">Creeping, Climbing, and Floating Stems.</td> - <td class="tdr"><a href="#XXXIX_2">369</a></td> - </tr><tr> - <td class="tdr">III.</td> - <td class="tdl_toc">Specialized Shoots and Shoots for Storage of Food.</td> - <td class="tdr"><a href="#XXXIX_3">372</a></td> - </tr><tr> - <td class="tdr">IV.</td> - <td class="tdl_toc">Annual Growth and Winter Protection of Shoots and Buds.</td> - <td class="tdr"><a href="#XXXIX_4">374</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XL.</td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">Foliage Leaves.</span></td> - <td class="tdr"><a href="#CHAPTER_XL">383</a></td> - </tr><tr> - <td class="tdr">I.</td> - <td class="tdl_toc">General Form and Arrangement of Leaves.</td> - <td class="tdr"><a href="#XL_1">383</a></td> - </tr><tr> - <td class="tdr">II.</td> - <td class="tdl_toc">Protective Modifications of Leaves.</td> - <td class="tdr"><a href="#XL_2">392</a></td> - </tr><tr> - <td class="tdr">III.</td> - <td class="tdl_toc">Protective Positions.</td> - <td class="tdr"><a href="#XL_3">395</a></td> - </tr><tr> - <td class="tdr">IV.</td> - <td class="tdl_toc">Relation of Leaves to Light.</td> - <td class="tdr"><a href="#XL_4">397</a></td> - </tr><tr> - <td class="tdr">V.</td> - <td class="tdl_toc">Leaf Patterns.</td> - <td class="tdr"><a href="#XL_5">404</a> - <span class="pagenum"><a name="Page_xiii" id="Page_xiii">[Pg xiii]</a></span></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLI.</td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">The Root.</span></td> - <td class="tdr"><a href="#CHAPTER_XLI">410</a></td> - </tr><tr> - <td class="tdr">I.</td> - <td class="tdl_toc">Function of Roots.</td> - <td class="tdr"><a href="#XLI_1">410</a></td> - </tr><tr> - <td class="tdr">II.</td> - <td class="tdl_toc">Kinds of Roots.</td> - <td class="tdr"><a href="#XLI_2">415</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLII.</td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">The Floral Shoot.</span></td> - <td class="tdr"><a href="#CHAPTER_XLII">419</a></td> - </tr><tr> - <td class="tdr">I.</td> - <td class="tdl_toc">The Parts of the Flower.</td> - <td class="tdr"><a href="#XLII_1">419</a></td> - </tr><tr> - <td class="tdr">II.</td> - <td class="tdl_toc">Kinds of Flowers.</td> - <td class="tdr"><a href="#XLII_2">421</a></td> - </tr><tr> - <td class="tdr">III.</td> - <td class="tdl_toc">Arrangement of Flowers, or Mode of Inflorescence.</td> - <td class="tdr"><a href="#XLII_3">426</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLIII.</td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">Pollination.</span></td> - <td class="tdr"><a href="#CHAPTER_XLIII">433</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLIV.</td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">The Fruit.</span></td> - <td class="tdr"><a href="#CHAPTER_XLIV">450</a></td> - </tr><tr> - <td class="tdr">I.</td> - <td class="tdl_toc">Parts of the Fruit.</td> - <td class="tdr"><a href="#XLIV_1">450</a></td> - </tr><tr> - <td class="tdr">II.</td> - <td class="tdl_toc">Indehiscent Fruits.</td> - <td class="tdr"><a href="#XLIV_2">451</a></td> - </tr><tr> - <td class="tdr">III.</td> - <td class="tdl_toc">Dehiscent Fruits.</td> - <td class="tdr"><a href="#XLIV_3">452</a></td> - </tr><tr> - <td class="tdr">IV.</td> - <td class="tdl_toc">Fleshy and Juicy Fruits.</td> - <td class="tdr"><a href="#XLIV_4">454</a></td> - </tr><tr> - <td class="tdr">V.</td> - <td class="tdl_toc">Reinforced, or Accessory, Fruits.</td> - <td class="tdr"><a href="#XLIV_5">455</a></td> - </tr><tr> - <td class="tdr">VI.</td> - <td class="tdl_toc">Fruits of Gymnosperms.</td> - <td class="tdr"><a href="#XLIV_6">456</a></td> - </tr><tr> - <td class="tdr">VII.</td> - <td class="tdl_toc">“Fruit” of Ferns, Mosses, etc.</td> - <td class="tdr"><a href="#XLIV_7">457</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLV.</td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">Seed Dispersal.</span></td> - <td class="tdr"><a href="#CHAPTER_XLV">458</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLVI.</td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">Vegetation in Relation to Environment.</span></td> - <td class="tdr"><a href="#CHAPTER_XLVI">464</a></td> - </tr><tr> - <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLVII.</td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">Classification of Angiosperms.</span></td> - <td class="tdr"><a href="#CHAPTER_XLVII">487</a></td> - </tr><tr> - <td class="tdl" colspan="2"><br /><span class="smcap">Index.</span></td> - <td class="tdr"><a href="#INDEX">503</a></td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> -<div class="chapter"> -<h2 class="nobreak">PART I.<br /> PHYSIOLOGY.</h2> -<hr class="r5" /> -<h3 class="nobreak"><a name="CHAPTER_I" id="CHAPTER_I">CHAPTER I.</a><br /> -<span class="h_subtitle">PROTOPLASM.</span> -<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></h3> -</div> - -<p><b>1.</b> In the study of plant life and growth, it will be found -convenient first to inquire into the nature of the substance which we -call the living material of plants. For plant growth, as well as some -of the other processes of plant life, are at bottom dependent on this -living matter. This living matter is called in general <i>protoplasm</i>.</p> - -<p><b>2.</b> In most cases protoplasm cannot be seen without the help of -a microscope, and it will be necessary for us here to employ one if we -wish to see protoplasm, and to satisfy ourselves by examination that -the substance we are dealing with <i>is</i> protoplasm.</p> - -<p><b>3.</b> We shall find it convenient first to examine protoplasm -in some of the simpler plants; plants which from their minute size -and simple structure are so transparent that when examined with the -microscope the interior can be seen.</p> - -<p>For our first study let us take a plant known as <i>spirogyra</i>, though -there are a number of others which would serve the purpose quite as -well, and may quite as easily be obtained for study. -<span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span></p> - -<h4>Protoplasm in spirogyra.</h4> - -<p><b>4. The plant spirogyra.</b>—This plant is found in the water of -pools, ditches, ponds, or in streams of slow-running water. It is green -in color, and occurs in loose mats, usually floating near the surface. -The name “pond-scum” is sometimes given to this plant, along with -others which are more or less closely related. It is an <i>alga</i>, and -belongs to a group of plants known as <i>algæ</i>. If we lift a portion of -it from the water, we see that the mat is made up of a great tangle of -green silky threads. Each one of these threads is a plant, so that the -number contained in one of these floating mats is very great.</p> - -<p>Let us place a bit of this thread tangle on a glass slip, and examine -with the microscope and we will see certain things about the plant -which are peculiar to it, and which enable us to distinguish it from -other minute green water plants. We shall also wish to learn what these -peculiar parts of the plant are, in order to demonstrate the protoplasm -in the plant.<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a></p> - -<p><b>5. Chlorophyll bands in spirogyra.</b>—We first observe the -presence of bands; green in color, the edges of which are usually -very irregularly notched. These bands course along in a spiral manner -near the surface of the thread. There may be one or several of these -spirals, according to the species which we happen to select for -study. This green coloring matter of the band is <i>chlorophyll</i>, and -this substance, which also occurs in the higher green plants, will -be considered in a later chapter. At quite regular intervals in the -chlorophyll band are small starch grains, grouped in a rounded mass -enclosing a minute body, the <i>pyrenoid</i>, which is peculiar to many algæ. -<span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span></p> - -<div class="figright_20"> - <img src="images/fig01.jpg" alt="" width="75" height="435" /> - <div class="blockquot"> - <p class="center">Fig. 1.</p> - <p class="center">Thread of spirogyra, showing long cells, chlorophyll band, nucleus, - strands of protoplasm, and the granular wall layer of protoplasm.</p> - </div> -</div> - -<p><b>6. The spirogyra thread consists of cylindrical cells end to -end.</b>—Another thing which attracts our attention, as we examine a -thread of spirogyra under the microscope, is that the thread is made up -of cylindrical segments or compartments placed end to end. We can see a -distinct separating line between the ends. Each one of these segments -or compartments of the thread is a <i>cell</i>, and the boundary wall is -in the form of a cylinder with closed ends.</p> - -<p><b>7. Protoplasm.</b>—Having distinguished these parts of the plant -we can look for the protoplasm. It occurs within the cells. It is -colorless (i.e., hyaline) and consequently requires close observation. -Near the center of the cell can be seen a rather dense granular body -of an elliptical or irregular form, with its long diameter transverse -to the axis of the cell in some species; or triangular, or quadrate in -others. This is the <i>nucleus</i>. Around the nucleus is a granular layer -from which delicate threads of a shiny granular substance radiate in a -starlike manner, and terminate in the chlorophyll band at one of the -pyrenoids. A granular layer of the same substance lines the inside of -the cell wall, and can be seen through the microscope if it is properly -focussed. This granular substance in the cell is <i>protoplasm</i>.</p> - -<p><b>8. Cell-sap in spirogyra.</b>—The greater part of the interior -space of the cell, that between the radiating strands of protoplasm, is -occupied by a watery fluid, the “cell-sap.”</p> - -<p><b>9. Reaction of protoplasm to certain reagents.</b>—We can employ -certain tests to demonstrate that this granular substance which we have -seen is protoplasm, for it has been found, by repeated experiments with -a great many kinds of plants, that protoplasm gives a definite reaction -in response to treatment with certain substances called reagents. Let -us mount a few threads of the spirogyra in a drop of a solution of -<span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span> -iodine, and observe the results with the aid of the microscope. The -iodine gives a yellowish-brown color to the protoplasm, and it can be -more distinctly seen. The nucleus is also much more prominent since it -colors deeply, and we can perceive within the nucleus one small rounded -body, sometimes more, the <i>nucleolus</i>. The iodine here kills and stains -the protoplasm. The protoplasm, however, in a living condition will -resist for a time some other reagents, as we shall see if we attempt -to stain it with a one per cent aqueous solution of a dye known as -<i>eosin</i>. Let us mount a few living threads in such a solution of eosin, -and after a time wash off the stain. The protoplasm remains uncolored. -Now let us place these threads for a short time, two or three minutes, -in strong alcohol, which kills the protoplasm. Then mount them in -the eosin solution. The protoplasm now takes the eosin stain. After -the protoplasm has been killed we note that the nucleus is no longer -elliptical or angular in outline, but is rounded. The strands of -protoplasm are no longer in tension as they were when alive.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig02.jpg" alt="" width="200" height="303" /> - <p class="center">Fig. 2.<br /> Cell of spirogyra before<br /> - treatment with iodine.</p> - </div> - <div class="figsub"> - <a><img src="images/fig03.jpg" alt="" width="200" height="296" /></a> - <p class="center">Fig. 3.<br /> Cell of spirogyra after<br /> - treatment with alcohol and iodine.</p> - </div> -</div> - -<p><b>10.</b> Let us now take some fresh living threads and mount them in -water. Place a small drop of dilute glycerine on the slip at one side -of the cover glass, and with a bit of filter paper at the other side -draw out the water. The glycerine will flow under the cover glass and -come in contact with the spirogyra threads. Glycerine absorbs water -promptly. Being in contact with the threads it draws water out of the -<span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span> -cell cavity, thus causing the layer of protoplasm which lines the -inside of the cell wall to collapse, and separate from the wall, -drawing the chlorophyll band inward toward the center also. The wall -layer of protoplasm can now be more distinctly seen and its granular -character observed.</p> - -<p>We have thus employed three tests to demonstrate that this substance -with which we are dealing shows the reactions which we know by -experience to be given by protoplasm. We therefore conclude that this -colorless and partly granular, slimy substance in the spirogyra cell -is protoplasm, and that when we have performed these experiments, and -noted carefully the results, we have <i>seen</i> protoplasm.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig04.jpg" alt="" width="110" height="340" /> - <p class="center">Fig. 4.</p> - <p class="center">Cell of spirogyra before<br /> treatment with glycerine.</p> - </div> - - <div class="figsub"> - <a><img src="images/fig05.jpg" alt="" width="250" height="343" /></a> - <p class="center">Fig. 5.</p> - <p class="center">Cells of spirogyra after<br /> treatment with glycerine.</p> - </div> -</div> - -<div class="blockquot"> -<p><b>11. Earlier use of the term protoplasm.</b>—Early students of the -living matter in the cell considered it to be alike in substance, but -differing in density; so the term protoplasm was applied to all of this -living matter. The nucleus was looked upon as simply a denser portion -of the protoplasm, and the nucleolus as a still denser portion. Now it -is believed that the nucleus is a distinct substance, and a permanent -organ of the cell. The remaining portion of the protoplasm is now -usually spoken of as the <i>cytoplasm</i>.</p> - -<p>In spirogyra then the cytoplasm in each cell consists of a layer -which lines the inside of the cell wall, a nuclear layer, which -surrounds the nucleus, and radiating strands which connect the nucleus -and wall layers, thus suspending the nucleus near the center of the -cell. But it seems best in this elementary study to use the term -protoplasm in its general sense.</p> -</div> - -<p><span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span></p> -<h4>Protoplasm in mucor.</h4> - -<p><b>12.</b> Let us now examine in a similar way another of the simple -plants with the special object in view of demonstrating the protoplasm. -For this purpose we may take one of the plants belonging to the group -of <i>fungi</i>. These plants possess no chlorophyll. One of several species -of <i>mucor</i>, a common mould, is readily obtainable, and very suitable -for this study.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a></p> - -<p><b>13. Mycelium of mucor.</b>—A few days after sowing in some -gelatinous culture medium we find slender, hyaline threads, which are -very much branched, and, radiating from a central point, form circular -colonies, if the plant has not been too thickly sown, as shown in -<a href="#FIG_06">fig. 6</a>. These threads of the fungus form the <i>mycelium</i>. -From these characters of the plant, which we can readily see without the aid -of a microscope, we note how different it is from spirogyra.</p> - -<p>To examine for protoplasm let us lift carefully a thin block of -gelatine containing the mucor threads, and mount it in water on a -glass slip. Under the microscope we see only a small portion of the -branched threads. In addition to the absence of chlorophyll, which we -have already noted, we see that the mycelium is not divided at short -intervals into cells, but appears like a delicate tube with branches, -which become successively smaller toward the ends.</p> - -<p><b>14. Appearance of the protoplasm.</b>—Within the tube-like thread -now note the protoplasm. It has the same general appearance as that -which we noted in spirogyra. It is slimy, or semi-fluid, partly -hyaline, and partly granular, the granules consisting of minute -particles (the <i>microsomes</i>). While in mucor the protoplasm has the -same general appearance as in spirogyra, its arrangement is very -<span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span> -different. In the first place it is plainly continuous throughout the -tube. We do not see the prominent radiations of strands around a large -nucleus, but still the protoplasm does not fill the interior of the -threads. Here and there are rounded clear spaces termed <i>vacuoles</i>, -which are filled with the watery fluid, cell-sap. The nuclei in mucor -are very minute, and cannot be seen except after careful treatment with -special reagents.</p> - -<div class="figcenter"> - <img id="FIG_06" src="images/fig06.jpg" alt="" width="600" height="471" /> - <div class="blockquot"> - <p class="center">Fig. 6.<br /> Colonies of mucor.</p> - </div> -</div> - -<p><b>15. Movement of the protoplasm in mucor.</b>—While examining the -protoplasm in mucor we are likely to note streaming movements. Often a -current is seen flowing slowly down one side of the thread, and another -flowing back on the other side, or it may all stream along in the same -direction.</p> - -<p><b>16. Test for protoplasm.</b>—Now let us treat the threads with -a solution of iodine. The yellowish-brown color appears which is -<span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span> -characteristic of protoplasm when subject to this reagent. If we -attempt to stain the living protoplasm with a one per cent aqueous -solution of eosin it resists it for a time, but if we first kill the -protoplasm with strong alcohol, it reacts quickly to the application of -the eosin. If we treat the living threads with glycerine the protoplasm -is contracted away from the wall, as we found to be the case with -spirogyra. While the color, form and structure of the plant mucor is -different from spirogyra, and the arrangement of the protoplasm within -the plant is also quite different, the reactions when treated by -certain reagents are the same. We are justified then in concluding that -the two plants possess in common a substance which we call protoplasm.</p> - -<div class="figcenter"> - <img src="images/fig07.jpg" alt="" width="600" height="190" /> - <div class="blockquot"> - <p class="center">Fig. 7.<br /> Thread of mucor, showing protoplasm and vacuoles.</p> - </div> -</div> - -<h4>Protoplasm in nitella.</h4> - -<p><a id="PARA_17" name="PARA_17"><b>17.</b></a> One of the most interesting plants for the study of one -remarkable peculiarity of protoplasm is <i>Nitella</i>. This plant belongs -to a small group known as stoneworts. They possess chlorophyll, and, -while they are still quite simple as compared with the higher plants, -they are much higher in the scale than spirogyra or mucor.</p> - -<p><b>18. Form of nitella.</b>—A common species of nitella is <i>Nitella -flexilis</i>. It grows in quiet pools of water. The plant consists of a -main axis, in the form of a cylinder. At quite regular intervals are -whorls of several smaller thread-like outgrowths, which, because of -their position, are termed “leaves,” though they are not true leaves. -These are branched in a characteristic fashion at the tip. The main -axis also branches, these branches arising in the axil of a whorl, -usually singly. The portions of the axis where the whorls arise are the -<i>nodes</i>. Each node is made up of a number of small cells definitely -arranged. The portion of the axis between two adjacent whorls is an -<span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span> -internode. These internodes are peculiar. They consist of but a single -“cell,” and are cylindrical, with closed ends. They are sometimes 5-10 -cm. long.</p> - -<div class="figright"> - <img id="FIG_08" src="images/fig08.jpg" alt="" width="200" height="307" /> - <p class="center">Fig. 8.</p> - <p class="center">Portion of plant<br /> nitella.</p> -</div> - -<p><b>19. Internode of nitella.</b>—For the study of an internode of -nitella, a small one, near the end, or the ends of one of the “leaves” -is best suited, since it is more transparent. A small portion of the -plant should be placed on the glass slip in water with the cover glass -over a tuft of the branches near the growing end. Examined with the -microscope the green chlorophyll bodies, which form oval or oblong -discs, are seen to be very numerous. They lie quite closely side by -side and form in perfect rows along the inner surface of the wall. -One peculiar feature of the arrangement of the chlorophyll bodies is -that there are two lines, extending from one end of the internode to -the other on opposite sides, where the chlorophyll bodies are wanting. -These are known as neutral lines. They run parallel with the axis of -the internode, or in a more or less spiral manner as shown in <a href="#FIG_09">fig. 9</a>.</p> - -<p><b>20. Cyclosis in nitella.</b>—The chlorophyll bodies are stationary -on the inner surface of the wall, but if the microscope be properly -focussed just beneath this layer we notice a rotary motion of particles -in the protoplasm. There are small granules and quite large masses of -granular matter which glide slowly along in one direction on a given -side of the neutral line. If now we examine the protoplasm on the other -side of the neutral line, we see that the movement is in the opposite -direction. If we examine this movement at the end of an internode -the particles are seen to glide around the end from one side of the -neutral line to the other. So that when conditions are favorable, such -as temperature, healthy state of the plant, etc., this gliding of the -particles or apparent streaming of the protoplasm down one side of -the “cell,” and back upon the other, continues in an uninterrupted -rotation, or <i>cyclosis</i>. There are many nuclei in an internode of -nitella, and they move also.</p> - -<p><b>21. Test for protoplasm.</b>—If we treat the plant with a solution -of iodine we get the same reaction as in the case of spirogyra and -mucor. The protoplasm becomes yellowish-brown. -<span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span></p> - -<div class="figleft"> - <img id="FIG_09" src="images/fig09.jpg" alt="" width="200" height="64" /> - <p class="center">Fig. 9.<br /> Cyclosis in nitella.</p> -</div> - -<p><b>22. Protoplasm in one of the higher plants.</b>—We now wish to -examine, and test for, protoplasm in one of the higher plants. Young -or growing parts of any one of various plants—the petioles of young -leaves, or young stems of growing plants—are suitable for study. -Tissue from the pith of corn (Zea mays) in young shoots just back of -the growing point or quite near the joints of older but growing corn -stalks furnishes excellent material.</p> - -<p>If we should place part of the stem of this plant under the microscope -we should find it too opaque for observation of the interior of the -cells. This is one striking difference which we note as we pass from -the low and simple plants to the higher and more complex ones; not -only in general is there an increase of size, but also in general an -increase in thickness of the parts. The cells, instead of lying end to -end or side by side, are massed together so that the parts are quite -opaque. In order to study the interior of the plant we have selected -it must be cut into such thin layers that the light will pass readily -through them.</p> - -<p>For this purpose we section the tissue selected by making with a razor, -or other very sharp knife, very thin slices of it. These are mounted in -water in the usual way for microscopic study. In this section we notice -that the cells are polygonal in form. This is brought about by mutual -pressure of all the cells. The granular protoplasm is seen to form a -layer just inside the wall, which is connected with the nuclear layer -by radiating strands of the same substance. The nucleus does not always -lie at the middle of the cell, but often is near one side. If we now -apply an alcohol solution of iodine the characteristic yellowish-brown -color appears. So we conclude here also that this substance is -identical with the living matter in the other very different plants -which we have studied.</p> - -<p><b>23. Movement of protoplasm in the higher plants.</b>—Certain -parts of the higher plants are suitable objects for the study of the -so-called streaming movement of protoplasm, especially the delicate -<span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span> -hairs, or thread-like outgrowths, such as the silk of corn, or the -delicate staminal hairs of some plants, like those of the common -spiderwort, tradescantia, or of the tradescantias grown for ornament in -greenhouses and plant conservatories.</p> - -<p>Sometimes even in the living cells of the corn plant which we have just -studied, slow streaming or gliding movements of the granules are seen -along the strands of protoplasm where they radiate from the nucleus. -<a href="#NOTE_1">See note</a> at close of this chapter.</p> - -<p><b>24. Movement of protoplasm in cells of the staminal hair of -“spiderwort.”</b>—A cell of one of these hairs from a stamen of a -tradescantia grown in glass houses is shown in <a href="#FIG_10">fig. 10</a>. The -nucleus is quite prominent, and its location in the cell varies considerably in -different cells and at different times. There is a layer of protoplasm -all around the nucleus, and from this the strands of protoplasm extend -outward to the wall layer. The large spaces between the strands are, as -we have found in other cases, filled with the cell-sap.</p> - -<div class="figcenter"> - <img id="FIG_10" src="images/fig10.jpg" alt="" width="600" height="125" /> - <p class="center">Fig. 10.<br /> Cell from stamen hair of tradescantia - showing movement of the protoplasm.</p> -</div> - -<p class="blockquot">An entire stamen, or a portion of the stamen, -having several hairs attached, should be carefully mounted in water. -Care should be taken that the room be not cold, and if the weather is -cold the water in which the preparation is mounted should be warm. With -these precautions there should be little difficulty in observing the -streaming movement.</p> - -<p>The movement is detected by observing the gliding of the granules. -These move down one of the strands from the nucleus along the wall -layer, and in towards the nucleus in another strand. After a little the -direction of the movement in any one portion may be reversed.</p> - -<p><b>25. Cold retards the movement.</b>—While the protoplasm is moving, -if we rest the glass slip on a block of ice, the movement will become -<span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span> -slower, or will cease altogether. Then if we warm the slip gently, the -movement becomes normal again. We may now apply here the usual tests -for protoplasm. The result is the same as in the former cases.</p> - -<p><b>26. Protoplasm occurs in the living parts of all plants.</b>—In -these plants representing such widely different groups, we find a -substance which is essentially alike in all. Though its arrangement -in the cell or plant body may differ in the different plants or in -different parts of the same plant, its general appearance is the same. -Though in the different plants it presents, while alive, varying -phenomena, as regards mobility, yet when killed and subjected to -well known reagents the reaction is in general identical. Knowing -by the experience of various investigators that protoplasm exhibits -these reactions under given conditions, we have demonstrated to -our satisfaction that we have seen protoplasm in the simple alga, -spirogyra, in the common mould, mucor, in the more complex stonewort, -nitella, and in the cells of tissues of the highest plants.</p> - -<p><b>27.</b> By this simple process of induction of these facts -concerning this substance in these different plants, we have learned an -important method in science study. Though these facts and deductions -are well known, the repetition of the methods by which they are -obtained on the part of each student helps to form habits of scientific -carefulness and patience, and trains the mind to logical processes in -the search for knowledge.</p> - -<p><b>28.</b> While we have by no means exhausted the study of protoplasm, -we can, from this study, draw certain conclusions as to its occurrence -and appearance in plants. Protoplasm is found in the living and growing -parts of all plants. It is a semi-fluid, or slimy, granular, substance; -in some plants, or parts of plants, the protoplasm exhibits a streaming -or gliding movement of the granules. It is irritable. In the living -condition it resists more or less for some time the absorption of -certain coloring substances. The water may be withdrawn by glycerine. -The protoplasm may be killed by alcohol. When treated with iodine it -becomes a yellowish-brown color.</p> - -<p class="blockquot"><a name="NOTE_1" id="NOTE_1"><i>Note.</i></a> -In some plants, like elodea for example, it has been found that -the streaming of the protoplasm is often induced by some injury or -stimulus, while in the normal condition the protoplasm does not move.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_II" id="CHAPTER_II">CHAPTER II.</a><br /> -<span class="h_subtitle">ABSORPTION, DIFFUSION, OSMOSE.</span></h3> -</div> - -<p><b>29.</b> We may next endeavor to learn how plants absorb water or -nutrient substances in solution. There are several very instructive -experiments, which can be easily performed, and here again some of the -lower plants will be found useful.</p> - -<p><b>30. Osmose in spirogyra.</b>—Let us mount a few threads of this -plant in water for microscopic examination, and then draw under the -cover glass a five per cent solution of ordinary table salt (NaCl) -with the aid of filter paper. We shall soon see that the result is -similar to that which was obtained when glycerine was used to extract -the water from the cell-sap, and to contract the protoplasmic membrane -from the cell wall. But the process goes on evenly and the plant is not -injured. The protoplasmic layer contracts slowly from the cell wall, -and the movement of the membrane can be watched by looking through the -microscope. The membrane contracts in such a way that all the contents -of the cell are finally collected into a rounded or oval mass which -occupies the center of the cell.</p> - -<p>If we now add fresh water and draw off the salt solution, we can see -the protoplasmic membrane expand again, or move out in all directions, -and occupy its former position against the inner surface of the cell -wall. This would indicate that there is some pressure from within while -this process of absorption is going on, which causes the membrane to -move out against the cell wall.</p> - -<p>The salt solution draws water from the cell-sap. There is thus a -tendency to form a vacuum in the cell, and the pressure on the outside -<span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span> -of the protoplasmic membrane causes it to move toward the center of the -cell. When the salt solution is removed and the thread of spirogyra is -again bathed with water, the movement of the water is <i>inward</i> in the -cell. This would suggest that there is some substance dissolved in the -cell-sap which does not readily filter out through the membrane, but -draws on the water outside. It is this which produces the pressure from -within and crowds the membrane out against the cell wall again.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig11.jpg" alt="" width="50" height="299" /> - <p class="center">Fig. 11.</p> - <p class="center">Spirogyra before placing<br /> in salt solution.</p> - </div> - <div class="figsub"> - <img src="images/fig12.jpg" alt="" width="150" height="260" /> - <p class="center space-above2">Fig. 12.</p> - <p class="center">Spirogyra in<br /> 5% salt solution.</p> - </div> - <div class="figsub"> - <img src="images/fig13.jpg" alt="" width="90" height="278" /> - <p class="center">Fig. 13.</p> - <p class="center">Spirogyra from salt<br /> solution into water.</p> - </div> -</div> - -<p><b>31. Turgescence.</b>—Were it not for the resistance which the cell -<span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span> -wall offers to the pressure from within, the delicate protoplasmic -membrane would stretch to such an extent that it would be ruptured, and -the protoplasm therefore would be killed. If we examine the cells at -the ends of the threads of spirogyra we shall see in most cases that -the cell wall at the free end is arched outward. This is brought about -by the pressure from within upon the protoplasmic membrane which itself -presses against the cell wall, and causes it to arch outward. This is -beautifully shown in the case of threads which are recently broken. -The cell wall is therefore <i>elastic</i>; it yields to a certain extent to -the pressure from within, but a point is soon reached beyond which it -will not stretch, and an equilibrium then exists between the pressure -from within on the protoplasmic membrane, and the pressure from without -by the elastic cell wall. This state of equilibrium in a cell is -<i>turgescence</i>, or such a cell is said to be <i>turgescent</i>, or <i>turgid</i>.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig14.jpg" alt="" width="150" height="173" /> - <p class="center">Fig. 14.</p> - <p class="center">Before treatment with<br /> salt solution.</p> - </div> - <div class="figsub"> - <img src="images/fig15.jpg" alt="" width="160" height="174" /> - <p class="center">Fig. 15.</p> - <p class="center">After treatment with<br /> salt solution.</p> - </div> - <div class="figsub"> - <img src="images/fig16.jpg" alt="" width="200" height="170" /> - <p class="center">Fig. 16.</p> - <p class="center">From salt solution placed<br /> in water.</p> - </div> - <p class="center space-below1">Figs. 14-16.—Osmosis in threads of mucor.</p> -</div> - -<p><b>32. Experiment with beet in salt and sugar solutions.</b>—We may -now test the effect of a five per cent salt solution on a portion of -the tissues of a beet or carrot. Let us cut several slices of equal -size and about 5mm in thickness. Immerse a few slices in water, a few -in a five per cent salt solution and a few in a strong sugar solution. -It should be first noted that all the slices are quite rigid when an -attempt is made to bend them between the fingers. In the course of one -<span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span> -or two hours or less, if we examine the slices we shall find that those in water -remain, as at first, quite rigid, while those in the salt and sugar solutions -are more or less flaccid or limp, and readily bend by pressure -between the fingers, the specimens in the salt solution, -perhaps, being more flaccid than those in the sugar solution. -The salt solution, we judge after our experiment with spirogyra, -withdraws some of the water from the cell-sap, the cells thus -losing their turgidity and the tissues becoming limp or flaccid -from the loss of water.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig17.jpg" alt="" width="150" height="130" /> - <p class="center">Fig. 17.</p> - <p class="center">Before treatment with<br /> salt solution.</p> - </div> - <div class="figsub"> - <img src="images/fig18.jpg" alt="" width="140" height="136" /> - <p class="center">Fig. 18.</p> - <p class="center">After treatment with<br /> salt solution.</p> - </div> - <div class="figsub"> - <img src="images/fig19.jpg" alt="" width="140" height="135" /> - <p class="center">Fig. 19.</p> - <p class="center">From salt solution into<br /> water again.</p> - </div> - <p class="center space-below1">Figs. 17-19.—Osmosis in cells of Indian corn.</p> -</div> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig20.jpg" alt="" width="150" height="325" /> - <p class="center">Fig. 20.</p> - <p class="center">Rigid condition of<br /> fresh beet section.</p> - </div> - <div class="figsub"> - <p class="space-above2"> </p> - <img src="images/fig21.jpg" alt="" width="150" height="245" /> - <p class="center">Fig. 21.</p> - <p class="center">Limp condition after<br /> lying in salt<br /> solution.</p> - </div> - <div class="figsub"> - <img src="images/fig22.jpg" alt="" width="150" height="367" /> - <p class="center">Fig. 22.</p> - <p class="center">Rigid again after<br /> lying again in water.</p> - </div> - <p class="center space-below1">Figs. 20-22.—Turgor and osmosis in slices of beet.</p> -</div> - -<p><span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span> -<b>33.</b> Let us now remove some of the slices of the beet from the -sugar and salt solutions, wash them with water and then immerse them in -fresh water. In the course of thirty minutes to one hour, if we examine -them again, we find that they have regained, partly or completely, -their rigidity. Here again we infer from the former experiment with -spirogyra that the substances in the cell-sap now draw water inward; -that is, the diffusion current is inward through the cell walls and the -protoplasmic membrane, and the tissue becomes turgid again.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_23" src="images/fig23.jpg" alt="" width="150" height="179" /> - <p class="center">Fig. 23.</p> - <p class="center">Before treatment with<br /> salt solution.</p> - </div> - <div class="figsub"> - <img id="FIG_24" src="images/fig24.jpg" alt="" width="150" height="184" /> - <p class="center">Fig. 24.</p> - <p class="center">After treatment with<br /> salt solution.</p> - </div> - <div class="figsub"> - <img id="FIG_25" src="images/fig25.jpg" alt="" width="150" height="185" /> - <p class="center">Fig. 25.</p> - <p class="center">Later stage of<br /> the same.</p> - </div> - <p class="center space-below1">Figs. 23-25.—Cells from beet treated with salt solution to<br /> - show osmosis and movement of the protoplasmic membrane.</p> -</div> - -<p><b>34. Osmose in the cells of the beet.</b>—We should now make a -section of the fresh tissue of a red colored beet for examination with -the microscope, and treat this section with the salt solution. Here we -can see that the effect of the salt solution is to draw water out of -the cell, so that the protoplasmic membrane can be seen to move inward -from the cell wall just as was observed in the case of spirogyra.<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a> -Now treating the section with water and removing the salt solution, the -<span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span> -diffusion current is in the opposite direction, that is inward through -the protoplasmic membrane, so that the latter is pressed outward until -it comes in contact with the cell wall again, which by its elasticity -soon resists the pressure and the cells again become turgid.</p> - -<p><b>35. The coloring matter in the cell-sap does not readily escape -from the living protoplasm of the beet.</b>—The red coloring matter, -as seen in the section under the microscope, does not escape from the -cell-sap through the protoplasmic membrane. When the slices are placed -in water, the water is not colored thereby. The same is true when the -slices are placed in the salt or sugar solutions. Although water is -withdrawn from the cell-sap, this coloring substance does not escape, -or if it does it escapes slowly and after a considerable time.</p> - -<p><b>36. The coloring matter escapes from dead protoplasm.</b>—If, -however, we heat the water containing a slice of beet up to a point -which is sufficient to kill the protoplasm, the red coloring matter -in the cell-sap filters out through the protoplasmic membrane and -colors the water. If we heat a preparation made for study under the -microscope up to the thermal death point we can see here that the red -coloring matter escapes through the membrane into the water outside. -This teaches that certain substances cannot readily filter through -the living membrane of protoplasm, but that they can filter through -when the protoplasm is dead. A very important condition, then, for -the successful operation of some of the physical processes connected -with absorption in plants is that the protoplasm should be in a living -condition.</p> - -<p><b>37. Osmose experiments with leaves.</b>—We may next take the leaves -of certain plants like the geranium, coleus or other plant, and place -them in shallow vessels containing water, salt, and sugar solutions -respectively. The leaves should be immersed, but the petioles should -project out of the water or solutions. Seedlings of corn or beans, -especially the latter, may also be placed in these solutions, so that -the leafy ends are immersed. After one or two hours an examination -shows that the specimens in the water are still turgid. But if we lift -a leaf or a bean plant from the salt or sugar solution, we find that -it is flaccid and limp. The blade, or lamina, of the leaf droops as if -wilted, though it is still wet. The bean seedling also is flaccid, the -succulent stem bending nearly double as the lower part of the stem is -held upright. This loss of turgidity is brought about by the loss of -water from the tissues, and judging from the experiments on spirogyra -and the beet, we conclude that the loss of turgidity is caused by the -withdrawal of some of the water from the cell-sap by the strong salt solution.</p> - -<p><b>38.</b> Now if we wash carefully these leaves and seedlings, which -have been in the salt and sugar solutions, with water, and then immerse -them in fresh water for a few hours, they will regain their turgidity. -Here again we are led to infer that the diffusion current is now inward -through the protoplasmic membranes of all the living cells of the leaf, -and that the resulting turgidity of the individual cells causes the -turgidity of the leaf or stem. -<span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span></p> - -<div class="figleft"> - <img src="images/fig26.jpg" alt="" width="150" height="81" /> - <p class="center">Fig. 26.<br /> - Seedling of radish,<br /> showing root hairs.</p> -</div> - -<p><b>39. Absorption by root hairs.</b>—If we examine seedlings, which -have been grown in a germinator or in the folds of paper or cloths so -that the roots will be free from particles of soil, we see near the -growing point of the roots that the surface is covered with numerous -slender, delicate, thread-like bodies, the root hairs. Let us place a -portion of a small root containing some of these root hairs in water on -a glass slip, and prepare it for examination with the microscope. We -see that each thread, or root hair, is a continuous tube, or in other -words it is a single cell which has become very much elongated. The -protoplasmic membrane lines the wall, and strands of protoplasm extend -across at irregular intervals, the interspaces being occupied by the -cell-sap.</p> - -<div class="figcenter"> - <img src="images/fig27.jpg" alt="" width="600" height="145" /> - <p class="center">Fig. 27.<br /> - Root hair of corn before and after treatment with 5% salt solution.</p> -</div> - -<p>We should now draw under the cover glass some of the five per cent salt -solution. The protoplasmic membrane moves away from the cell wall at -certain points, showing that <i>plasmolysis</i> is taking place, that is, -the diffusion current is outward so that the cell-sap loses some of its -water, and the pressure from the outside moves the membrane inward. -We should not allow the salt solution to work on the root hairs long. -It should be very soon removed by drawing in fresh water before the -protoplasmic membrane has been broken at intervals, as is apt to be the -case by the strong diffusion current and the consequent strong pressure -from without. The membrane of protoplasm now moves outward as the -diffusion current is inward, and soon regains its former position next -the inner side of the cell wall. The root hairs then, like other parts -<span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span> -of the plant which we have investigated, have the power of taking up -water under pressure.</p> - -<p><b>40. Cell-sap a solution of certain substances.</b>—From these -experiments we are led to believe that certain substances reside in the -cell-sap of plants, which behave very much like the salt solution when -separated from water by the protoplasmic membrane. Let us attempt to -interpret these phenomena by recourse to diffusion experiments, where -an animal membrane separates two liquids of different concentration.</p> - -<p><b>41. An artificial cell to illustrate turgor.</b>—Fill a small -wide-mouthed vial with a <i>very strong</i> sugar solution. Over the mouth -tie firmly a piece of <i>bladder</i> membrane. Be certain that as the -membrane is tied over the open end of the vial, the sugar solution -fills it in order to keep out air bubbles. Sink the vial in a vessel of -fresh water and leave it there for twenty-four hours. Remove the vial -and note that the membrane is arched outward. Thrust a sharp needle -through the membrane when it is arched outward, and quickly pull it -out. The liquid spurts out because of the inside pressure.</p> - -<div class="figcenter"> - <img src="images/fig28.jpg" alt="" width="600" height="240" /> - <p class="center">Fig. 28.<br /> - Puncturing a make-believe cell after it has been lying in water.</p> - <img src="images/fig29.jpg" alt="" width="600" height="184" /> - <p class="center">Fig. 29.<br /> - Same as Fig. 28 after needle is removed.</p> -</div> - -<p><b>42. Diffusion through an animal membrane.</b>—For this experiment -we may use a thistle tube, across the larger end of which should be -stretched and tied tightly a piece of a bladder membrane. A strong -sugar solution (three parts sugar to one part water) is now placed in -<span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span> -the tube so that the bulb is filled and the liquid extends part way in -the neck of the tube. This is immersed in water within a wide-mouth -bottle, the neck of the tube being supported in a perforated cork in -such a way that the sugar solution in the tube is on a level with the -water in the bottle or jar. In a short while the liquid begins to -rise in the thistle tube, in the course of several hours having risen -several centimeters. The diffusion current is thus stronger through the -membrane in the direction of the sugar solution, so that this gains -more water than it loses.</p> - -<p>We have here two liquids separated by an animal membrane, water on -the one hand which diffuses readily through the membrane, while on -the other is a solution of sugar which diffuses through the animal -membrane with difficulty. The water, therefore, not containing any -solvent, according to a general law which has been found to obtain in -such cases, diffuses more readily through the membrane into the sugar -solution, which thus increases in volume, and also becomes more dilute. -The bladder membrane is what is sometimes called a diffusion membrane, -since the diffusion currents travel through it.</p> - -<p><b>43.</b> In this experiment then the bulk of the sugar solution is -increased, and the liquid rises in the tube by this pressure above -the level of the water in the jar outside of the thistle tube. The -diffusion of liquids through a membrane is <i>osmosis</i>.</p> - -<p><b>44. Importance of these physical processes in plants.</b>—Now if -we recur to our experiment with spirogyra we find that exactly the -same processes take place. The protoplasmic membrane is the diffusion -membrane, through which the diffusion takes place. The salt solution -which is first used to bathe the threads of the plant is a stronger -solution than that of the cell-sap within the cell. Water therefore -is drawn out of the cell-sap, but the substances in solution in -the cell-sap do not readily move out. As the bulk of the cell-sap -diminishes the pressure from the outside pushes the protoplasmic -membrane away from the wall. Now when we remove the salt solution and -bathe the thread with water again, the cell-sap, being a solution of -certain substances, diffuses with more difficulty than the water, and -the diffusion current is inward, while the protoplasmic membrane moves -out against the cell wall, and turgidity again results. Also in the -experiments with salt and sugar solutions on the leaves of geranium, -on the leaves and stems of the seedlings, on the tissues and cells of -the beet and carrot, and on the root hairs of the seedlings, the same -processes take place.</p> - -<p>These experiments not only teach us that in the protoplasmic membrane, -the cell wall, and the cell-sap of plants do we have structures which -are capable of performing these physical processes, but they also show -that these processes are of the utmost importance to the plant; not -only in giving the plant the power to take up solutions of nutriment -from the soil, but they serve also other purposes, as we shall see later.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_III" id="CHAPTER_III">CHAPTER III.</a><br /> -<span class="h_subtitle">HOW PLANTS OBTAIN WATER.</span></h3> -</div> - -<p>In connection with the study of the means of absorption from the soil -or water by plants, it will be found convenient to observe carefully -the various forms of the plant. Without going into detail here, the -suggestion is made that simple thread forms like spirogyra, œdogonium, -and vaucheria; expanded masses of cells as are found in the thalloid -liverworts, the duckweed, etc., be compared with those liverworts, and -with the mosses, where leaf-like expansions of a central axis have been -differentiated. We should then note how this differentiation, from the -physiological standpoint, has been carried farther in the higher land plants.</p> - -<p><b>45. Absorption by Algæ and Fungi.</b>—In the simpler forms of -plant life, as in spirogyra and many of the algæ and fungi, the plant -body is not differentiated into parts.<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a> -In many other cases the only differentiation is between the growing -part and the fruiting part. In the algæ and fungi there is no -differentiation into stem and leaf, though there is an approach to it -in some of the higher forms. Where this simple plant body is flattened, -as in the sea-wrack, or ulva, it is a <i>frond</i>. The Latin word for -frond is <i>thallus</i>, and this name is applied to the plant body of all -the lower plants, the algæ and fungi. The algæ and fungi together -are sometimes called the <i>thallophytes</i>, or <i>thallus plants</i>. The -word thallus is also sometimes applied to the flattened body of the -liverworts. In the foliose liverworts and mosses there is an axis with -leaf-like expansions. These are believed by some to represent true -stems and leaves, by others to represent a flattened thallus in which -the margins are deeply and regularly divided, or in which the expansion -has only taken place at regular intervals.</p> - -<p>In nearly all of the algæ the plant body is submerged in water. In these -<span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span> -cases absorption takes place through all portions of the surface in -contact with the water, as in spirogyra, vaucheria, and all of the -larger seaweeds. Comparatively few of the algæ grow on the surfaces -of rocks or trees. In these examples it is likely that at times only -portions of the plant body serve in the process of absorption of water -from the substratum. A few of the algæ are parasitic, living in the -tissues of higher plants, where they are surrounded by the water or -liquids within the host. Absorption takes place in the same way in many -of the fungi. The aquatic fungi are immersed in water. In other forms, -like mucor, a portion of the mycelium is within the substratum, and -being bathed by the water or watery solutions absorbs the same, while -the fruiting portion and the aerial mycelium obtain their water and -food solutions from the mycelium in the substratum. In higher fungi, -like the mushrooms, the mycelium within the ground or decaying wood -absorbs the water necessary for the fruiting portion; while in the case -of the parasitic fungi the mycelium lies in the water or liquid within -the host.</p> - -<div class="figright"> - <a id="FIG_30" name="FIG_30"> </a> - <img src="images/fig30.jpg" alt="" width="200" height="177" /> - <p class="center">Fig. 30.<br />Thallus of Riccia lutescens.</p> -</div> - -<p><b>46. Absorption by liverworts.</b>—In many of the plants termed -liverworts the vegetative part of the plant is a thin, flattened, more -or less elongated green body known as a thallus.</p> - -<p><i>Riccia.</i>—One of these, belonging to the genus riccia, is shown in -<a href="#FIG_30">fig. 30</a>. Its shape is somewhat like that of a minute ribbon -which is forked at intervals in a dichotomous manner, the characteristic kind of -branching found in these thalloid liverworts. This riccia (known as R. -lutescens) occurs on damp soil; long, slender, hair-like processes grow -out from the under surface of the thallus which resemble root hairs and -serve the same purpose in the processes of absorption. Another species -of riccia (R. crystallina) is shown in <a href="#FIG_252">fig. 252</a>. This -plant is quite circular in outline and occurs on muddy flats. Some species float -on the water.</p> - -<p><b>47. Marchantia.</b>—One of the larger and coarser liverworts is -<a href="#FIG_31">figured at 31</a>. This is a very common liverwort, growing in -very damp and muddy places and also along the margins of streams, on the mud or -<span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span> -upon the surfaces of rocks which are bathed with the water. This is -known as <i>Marchantia polymorpha</i>. If we examine the under surface of -the marchantia we see numerous hair-like processes which attach the -plant to the soil. Under the microscope we see that some of these are -similar to the root hairs of the seedlings which we have been studying, -and they serve the purpose of absorption. Since, however, there are no -roots on the marchantia plant, these hair-like outgrowths are usually -termed here <i>rhizoids</i>. In marchantia they are of two kinds, one kind -the simple ones with smooth walls, and the other kind in which the -inner surfaces of the walls are roughened by processes which extend -inward in the form of irregular tooth-like points. Besides the hairs on -the under side of the thallus we note especially near the growing end -that there are two rows of leaf-like scales, those at the end of the -thallus curving up over the growing end, thus serving to protect the -delicate tissues at the growing point.</p> - -<div class="figcenter"> - <a id="FIG_31" name="FIG_31"> </a> - <img src="images/fig31.jpg" alt="" width="600" height="364" /> - <p class="center">Fig. 31.<br /> - Marchantia plant with cupules and gemmæ; rhizoids below.</p> -</div> - -<p><span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span></p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_32" src="images/fig32.jpg" alt="" width="100" height="248" /> - <p class="center">Fig. 32.</p> - <p class="center">Portion of plant<br /> of Frullania,<br /> a foliose<br /> liverwort.</p> - </div> - <div class="figsub"> - <img id="FIG_33" src="images/fig33.jpg" alt="" width="150" height="245" /> - <p class="center">Fig. 33.</p> - <p class="center">Portion of same<br /> more highly<br /> magnified, showing<br /> overlapping leaves.</p> - </div> - <div class="figsub"> - <img id="FIG_34" src="images/fig34.jpg" alt="" width="150" height="257" /> - <p class="center">Fig. 34.</p> - <p class="center">Under side,<br /> showing forked<br /> under row of<br /> - leaves and lobes<br /> of lateral leaves.</p> - </div> -</div> - -<p><b>48. Frullania.</b>—In <a href="#FIG_32">fig. 32</a> is shown another liverwort, -which differs greatly in form from the ones we have just been studying in -that there is a well-defined axis with lateral leaf-like outgrowths. -Such liverworts are called foliose liverworts. Besides these two quite -prominent rows of leaves there is a third row of poorly developed -leaves on the under surface. Also from the under surface of the axis we -see here and there slender outgrowths, the rhizoids, through which much -of the water is absorbed.</p> - -<div class="figcenter"> - <img src="images/fig35.jpg" alt="" width="600" height="337" /> - <p class="center">Fig. 35.<br />Foliose liverwort (bazzania) showing<br /> - dichotomous branching and overlapping leaves.</p> -</div> - -<p><b>49. Absorption by the mosses.</b>—Among the mosses, which are -usually common in moist and shaded situations, examples are abundant -which are suitable for the study of the organs of absorption. If we -take for example a plant of mnium (M. affine), which is illustrated in -<a href="#FIG_36">fig. 36</a>, we note that it consists of a slender axis with thin flat, -<span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span> -green, leaf-like expansions, Examining with the microscope the lower -end of the axis, which is attached to the substratum, there are seen -numerous brown-colored threads more or less branched.</p> - -<div class="figleft"> - <img id="FIG_36" src="images/fig36.jpg" alt="" width="100" height="297" /> - <p class="center">Fig. 36.<br /><br />Female plant (gametophyte)<br /> - of a moss (mnium), showing<br />rhizoids below, and the<br /> - tuft of leaves above,<br /> which protect the<br />archegonia.</p> -</div> - -<p><b>50. Absorption by the higher aquatic plants.</b>—Examples of -the water plants which are entirely submerged in water are the -water-crowfoots, some of the pondweeds, elodea or water-weeds, the -tape-grass, vallisneria, etc. In these plants all parts of the body -being submerged, they absorb water with which they are in contact. In -other aquatic plants, like the water-lilies, some of the pondweeds, the -duck-meats, etc., are only partially submerged in the water; the upper -surface of the leaf or of the leaf-like expansion being exposed to the -air, while the under surface lies in close contact with the water, and -the stems and the petioles of the leaves are also immersed in water. In -these plants absorption takes place through those parts in contact with -the water.</p> - -<p><a id="PARA_51" name="PARA_51"><b>51. Absorption by the duck-meats.</b></a>—These -plants are very curious examples of the higher plants.</p> - -<p class="blockquot"><i>Lemna.</i>—One of these is illustrated in <a href="#FIG_37">fig. 37</a>. -This is the common duckweed, <i>Lemna trisulca</i>. It is very peculiar -in form and in its mode of growth. Each one of the lateral leaf-like -expansions extends outwards by the elongation of the basal part, -which becomes long and slender. Next, two new lateral expansions are -formed on these by prolification from near the base, and thus the -plant continues to extend. The plant occurs in ponds and ditches and -is sometimes very common and abundant. It floats on the surface of the -water. While the flattened part of the plant resembles a leaf, it is -really the stem, no leaves being present. This expanded green body is -usually termed a “frond.” A single rootlet grows out from the under -side and is destitute of root hairs. Absorption of water therefore -takes place through this rootlet and through the under side of the “frond.” -<span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span></p> - -<div class="figcenter"> - <img id="FIG_37" src="images/fig37.jpg" alt="" width="600" height="302" /> - <p class="center">Fig. 37.<br />Fronds of the duckweed (Lemna trisculca).</p> -</div> -<div class="figcenter"> - <img id="FIG_38" src="images/fig38.jpg" alt="" width="400" height="301" /> - <p class="center">Fig. 38.<br />Spirodela polyrhiza.</p> -</div> - -<p><b>52. Spirodela polyrhiza.</b>—This is a very curious plant, closely -related to the lemna and sometimes placed in the same genus. It occurs -in similar situations, and is very readily grown in aquaria. It reminds -one of a little insect as seen in <a href="#FIG_38">fig. 38</a>. There are several -rootlets on the under side of the frond. Absorption of water takes place here in -the same way as in lemna.</p> - -<p><b>53. Absorption in wolffia.</b>—Perhaps the most curious of these -modified water plants is the little wolffia, which contains the -smallest specimens of the flowering plants. Two species of this genus -are shown in <a href="#FIG_39">figs. 39-41</a>. The plant body is reduced to -nothing but a rounded or oval green body, which represents the stem. No leaves or -roots are present. The plants multiply by “prolification,” the new -fronds growing out from a depression on the under side of one end. -Absorption takes place through the under surface.</p> - -<p><a id="PARA_54" name="PARA_54"><b>54. Absorption by land plants.</b></a>—<i>Water cultures.</i>—In connection -<span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span> -with our inquiry as to how land plants obtain their water, it will be -convenient to prepare some water cultures to illustrate this and which -can also be used later in our study of nutrition (<a href="#CHAPTER_IX">Chapter IX</a>).</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_39" src="images/fig39.jpg" alt="" width="150" height="237" /> - <p class="center space-above3">Fig. 39.<br /> Young frond of wolffia<br /> growing out of older one.</p> - </div> - <div class="figsub"> - <img id="FIG_40" src="images/fig40.jpg" alt="" width="150" height="269" /> - <p class="center space-above1">Fig. 40.<br /> Young frond of wolffia<br /> separating from older one.</p> - </div> - <div class="figsub"> - <img id="FIG_41" src="images/fig41.jpg" alt="" width="150" height="293" /> - <p class="center">Fig. 41.<br /> Another species of<br /> wolffia, the two fronds<br /> still connected.</p> - </div> -</div> - -<p>Chemical analysis shows that certain mineral substances are common -constituents of plants. By growing plants in different solutions of -these various substances it has been possible to determine what ones -are necessary constituents of plant food. While the proportion of the -mineral elements which enter into the composition of plant food may -vary considerably within certain limits, the concentration of the -solutions should not exceed certain limits. A very useful solution is -one recommended by Sachs, and is as follows:</p> - -<p><b>55. Formula for water cultures</b>:</p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl">Water</td> - <td class="tdr_ws1">1000</td> - <td class="tdc">cc.</td> - </tr><tr> - <td class="tdl">Potassium nitrate</td> - <td class="tdr_ws1">0.5</td> - <td class="tdc">gr.</td> - </tr><tr> - <td class="tdl">Sodium chloride</td> - <td class="tdr_ws1">0.5</td> - <td class="tdc">“</td> - </tr><tr> - <td class="tdl">Calcium sulphate</td> - <td class="tdr_ws1">0.5</td> - <td class="tdc">“</td> - </tr><tr> - <td class="tdl">Magnesium sulphate   </td> - <td class="tdr_ws1">0.5</td> - <td class="tdc">“</td> - </tr><tr> - <td class="tdl">Calcium phosphate</td> - <td class="tdr_ws1">0.5</td> - <td class="tdc">“</td> - </tr> - </tbody> -</table> - -<p>The calcium phosphate is only partly soluble. The solution which is not -in use should be kept in a dark cool place to prevent the growth of -minute algæ.</p> - -<p><b>56.</b> Several different plants are useful for experiments in water -cultures, as peas, corn, beans, buckwheat, etc. The seeds of these -plants may be germinated, after soaking them for several hours in warm -<span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span> -water, by placing them between the folds of wet paper on shallow trays, -or in the folds of wet cloth. The seeds should not be kept immersed in -water after they have imbibed enough to thoroughly soak and swell them. -At the same time that the seeds are placed in damp paper or cloth for -germination, one lot of the soaked seeds should be planted in good soil -and kept under the same temperature conditions, for control. When the -plants have germinated one series should be grown in distilled water, -which possesses no plant food; another in the nutrient solution, and -still another in the nutrient solution to which has been added a few -drops of a solution of iron chloride or ferrous sulphate. There would -then be four series of cultures which should be carried out with the -same kind of seed in each series so that the comparisons can be made on -the same species under the different conditions. The series should be -numbered and recorded as follows:</p> - -<ul class="index"> -<li class="isub1">No. 1, soil.</li> -<li class="isub1">No. 2, distilled water.</li> -<li class="isub1">No. 3, nutrient solution.</li> -<li class="isub1">No. 4, nutrient solution with a few drops of iron solution added.</li> -</ul> - -<div class="figright"> - <img src="images/fig42.jpg" alt="" width="200" height="304" /> - <p class="center">Fig. 42.<br />Culture cylinder to<br /> - show position of corn<br /> seedling (Hansen).</p> -</div> - -<p><b>57.</b> Small jars or wide-mouth bottles, or crockery jars, can be -used for the water cultures, and the cultures are set up as follows: A -cork which will just fit in the mouth of the bottle, or which can be -supported by pins, is perforated so that there is room to insert the -seedling, with the root projecting below into the liquid. The seed can -be fastened in position by inserting a pin through one side, if it is a -large one, or in the case of small seeds a cloth of a coarse mesh can -be tied over the mouth of the bottle instead of using the cork. After -properly setting up the experiments the cultures should be arranged -in a suitable place, and observed from time to time during several -weeks. In order to obtain more satisfactory results several duplicate -series should be set up to guard against the error which might arise -from variation in individual plants and from accident. Where there are -several students in a class, a single series set up by several will -act as checks upon one another. If glass jars are used for the liquid -cultures they should be wrapped with black paper or cloth to exclude -the light from the liquid, otherwise numerous minute algæ are apt to -grow and interfere with the experiment. Or the jars may be sunk in pots -of earth to serve the same purpose. If crockery jars are used they will -not need covering.</p> - -<p><b>58.</b> For some time all the plants grow equally well, until the -nutriment stored in the seed is exhausted. The numbers 1, 3 and 4, in -<span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span> -soil and nutrient solutions, should outstrip number 2, the plants in -the distilled water. No. 4 in the nutrient solution with iron, having a -perfect food, compares favorably with the plants in the soil.</p> - -<p><b>59. Plants take liquid food from the soil.</b>—From these -experiments then we judge that such plants take up the food they -receive from the soil in the form of a liquid, the elements being in -solution in water.</p> - -<p>If we recur now to the experiments which were performed with the salt -solution in producing plasmolysis in the cells of spirogyra, in the -cells of the beet or corn, and in the root hairs of the corn and bean -seedlings, and the way in which these cells become turgid again when -the salt solution is removed and they are again bathed with water, we -shall have an explanation of the way in which plants take up nutrient -solutions of food material through their roots.</p> - -<div class="figcenter"> - <img id="FIG_43" src="images/fig43.jpg" alt="" width="600" height="467" /> - <p class="center">Fig. 43.<br /> Section of corn root, showing rhizoids<br /> - formed from elongated epidermal cells.</p> -</div> - -<p><b>60. How food solutions are carried into the plant.</b>—We can see -<span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span> -how water and food solutions are carried into the plant, and we must -next turn our attention to the way in which these solutions are carried -farther into the plant. We should make a section across the root of a -seedling in the region of the root hairs and examine it with the aid -of a microscope. We here see that the root hairs are formed by the -elongation of certain of the surface cells of the root. These cells -elongate perpendicularly to the root, and become <i>3mm</i> to <i>6mm</i> long. -They are flexuous or irregular in outline and cylindrical, as shown in -<a href="#FIG_43">fig. 43</a>. The end of the hair next the root fits in between -the adjacent superficial cells of the root and joins closely to the next deeper -layer of cells. In studying the section of the young root we see that -the root is made up of cells which lie closely side by side, each with -its wall, its protoplasm and cell-sap, the protoplasmic membrane lying -on the inside of each cell wall.</p> - -<p><b>61.</b> In the absorption of the watery solutions of plant food -by the root hairs, the cell-sap, being a more concentrated solution, -gains some of the former, since the liquid of less concentration flows -through the protoplasmic membrane into the more concentrated cell-sap, -increasing the bulk of the latter. This makes the root hairs turgid, -and at the same time dilutes the cell-sap so that the concentration is -not so great. The cells of the root lying inside and close to the base -of the root hairs have a cell-sap which is now more concentrated than -the diluted cell-sap of the hairs, and consequently gain some of the -food solutions from the latter, which tends to lessen the content of -the root hairs and also to increase the concentration of the cell-sap -of the same. This makes it possible for the root hairs to draw on -the soil for more of the food solutions, and thus, by a variation in -the concentration of the substances in solution in the cell-sap of -the different cells, the food solutions are carried along until they -reach the <i>vascular bundles</i>, through which the solutions are carried -to distant parts of the plant. Some believe that there is a rhythmic -action of the elastic cell walls in these cells between the root hairs -and the vascular bundles. This occurs in such a way that, after the -cell becomes turgid, it contracts, thus reducing the size of the cell -and forcing some of the food solutions into the adjacent cells, when -by absorption of more food solutions, or water, the cell increases in -turgidity again. This rhythmic action of the cells, if it does take -place, would act as a pump to force the solutions along, and would form -one of the causes of root pressure.</p> - -<p><b>62. How the root hairs get the watery solutions from the -soil.</b>—If we examine the root hairs of a number of seedlings which -are growing in the soil under normal conditions, we shall see that a -large quantity of soil readily clings to the roots. We should note also -that unless the soil has been recently watered there is no free water -<span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span> -in it; the soil is only moist. We are curious to know how plants can -obtain water from soil which is not wet. If we attempt to wash off the -soil from the roots, being careful not to break away the root hairs, -we find, that small particles cling so tenaciously to the root hairs -that they are not removed. Placing a few such root hairs under the -microscope it appears as if here and there the root hairs were glued to -the minute soil particles.</p> - -<div class="figcenter"> - <img src="images/fig44.jpg" alt="" width="600" height="415" /> - <p class="center">Fig. 44.<br /> Root hairs of corn seedling with - soil particles adhering closely.</p> -</div> - -<p><b>63.</b> If now we take some of the soil which is only moist, weigh -it, and then permit it to become quite dry on exposure to dry air, and -weigh again, we find that it loses weight in drying. Moisture has been -given off. This moisture, it has been found, forms an exceedingly thin -film on the surface of the minute soil particles. Where these soil -particles lie closely together, as they usually do when massed together -in the pot or elsewhere, this thin film of moisture is continuous from -the surface of one particle to that of another. Thus the soil particles -which are so closely attached to the root hairs connect the surface -of the root hairs with this film of moisture. As the cell-sap of the -root hairs draws on the moisture film with which they are in contact, -the tension of this film is sufficient to draw moisture from distant -particles. In this way the roots are supplied with water in soil which -is only moist.</p> - -<p><b>64. Plants cannot remove all the moisture from the soil.</b>—If we -now take a potted plant, or a pot containing a number of seedlings, -place it in a moderately dry room, and do not add water to the soil we -find in a few days that the plant is wilting. The soil if examined will -appear quite dry to the sense of touch. Let us weigh some of this soil, -<span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span> -then dry it by artificial heat, and weigh again. It has lost in weight. -This has been brought about by driving off the moisture which still -remained in the soil after the plant began to wilt. This teaches that -while plants can obtain water from soil which is only moist or which is -even rather dry, they are not able to withdraw all the moisture from -the soil.</p> - -<div class="figleft"> - <img id="FIG_45" src="images/fig45.jpg" alt="" width="150" height="366" /> - <p class="center">Fig. 45.<br /> Experiment to show<br /> root pressure<br /> - (Detmer).</p> -</div> - -<p><b>65. “Root pressure” or exudation pressure.</b>—It is a very common -thing to note, when certain shrubs or vines are pruned in the spring, -the exudation of a watery fluid from the cut surfaces. In the case of -the grape vine this has been known to continue for a number of days, -and in some cases the amount of liquid, called “sap,” which escapes is -considerable. In many cases it is directly traceable to the activity -of the roots, or root hairs, in the absorption of water from the soil. -For this reason the term <i>root pressure</i> has been used to denote the -force exerted in supplying the water from the soil. But there are some -who object to the use of this term “root pressure.” The principal -objection is that the pressure which brings about the phenomenon -known as “bleeding” by plants is not present in the roots alone. This -pressure exists under certain conditions in all parts of the plant. The -term exudation pressure has been proposed in lieu of root pressure. It -should be remembered that the movement of water in the plant is started -by the pressure which exists in the root. If the term “root pressure” -is used, it should be borne clearly in mind that it does not express -the phenomenon exactly in all cases.</p> - -<p><b>Root pressure may be measured.</b>—It is possible to measure -not only the amount of water which the roots will raise in a given -time, but also to measure the force exerted by the roots during root -pressure. It has been found that root pressure in the case of the -nettle is sufficient to hold a column of water about 4.5 meters (15 -ft.) high (Vines), while the root pressure of the vine (Hales, 1721) -will hold a column of water about 10 meters (36.5 ft.) high, and the -birch (Betula lutea) (Clark, 1873) has a root pressure sufficient to -hold a column of water about 25 meters (84.7 ft.) high.</p> - -<p><b>66. Experiment to demonstrate root pressure.</b>—By a very simple -method this lifting of water by root pressure is shown. During the -<span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span> -summer season plants in the open may be used if it is preferred, but -plants grown in pots are also very serviceable, and one may use a -potted begonia or balsam, the latter being especially useful. The -plants are usually convenient to obtain from the greenhouses, to -illustrate this phenomenon. The stem is cut off rather close to the -soil and a long glass tube is attached to the cut end of the stem, -still connected with the roots, by the use of rubber tubing, as shown -in <a href="#FIG_45">figure 45</a>, and a very small quantity of water may be poured -in to moisten the cut end of the stem. In a few minutes the water begins to -rise in the glass tube. In some cases it rises quite rapidly, so that -the column of water can readily be seen to extend higher and higher up -in the tube when observed at quite short intervals. (To measure the -force of root pressure is rather difficult for elementary work. To -measure it see Ganong, Plant Physiology, pp. 67, 68, or some other book -for advanced work.)</p> - -<p><b>67.</b> In either case where the experiment is continued for -several days it is noticed that the column of water or of mercury -rises and falls at different times during the same day, that is, the -column stands at varying heights; or in other words the root pressure -varies during the day. With some plants it has been found that the -pressure is greatest at certain times of the day, or at certain -seasons of the year. Such variation of root pressure exhibits what -is termed a periodicity, and in the case of some plants there is a -daily periodicity; while in others there is in addition an annual -periodicity. With the grape vine the root pressure is greatest in -the forenoon, and decreases from 12-6 <span class="smcap">p.m.</span>, -while with the sunflower it is greatest before 10 <span class="smcap">a.m.</span>, -when it begins to decrease. Temperature of the soil is one of the most -important external conditions affecting the activity of root pressure.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_IV" id="CHAPTER_IV">CHAPTER IV.</a><br /> -<span class="h_subtitle">TRANSPIRATION, OR THE LOSS OF WATER<br /> BY PLANTS.</span></h3> -</div> - -<p><b>68.</b> We should now inquire if all the water which is taken up in -excess of that which actually suffices for turgidity is used in the -elaboration of new materials of construction. We notice when a leaf -or shoot is cut away from a plant, unless it is kept in quite a moist -condition, or in a damp, cool place, that it becomes flaccid, and -droops. It wilts, as we say. The leaves and shoot lose their turgidity. -This fact suggests that there has been a loss of water from the shoot -or leaf. It can be readily seen that this loss is not in the form of -drops of water which issue from the cut end of the shoot or petiole. -What then becomes of the water in the cut leaf or shoot?</p> - -<p><b>69. Loss of water from excised leaves.</b>—Let us take a handful of -<span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span> -fresh, green, rather succulent leaves, which are free from water on -the surface, and place them under a glass bell jar, which is tightly -closed below but which contains no water. Now place this in a brightly -lighted window, or in sunlight. In the course of fifteen to thirty -minutes we notice that a thin film of moisture is accumulating on the -inner surface of the glass jar. After an hour or more the moisture has -accumulated so that it appears in the form of small drops of condensed -water. We should set up at the same time a bell jar in exactly the same -way but which contains no leaves. In this jar there is no condensed -moisture on the inner surface. We thus are justified in concluding that -the moisture in the former jar comes from the leaves. Since there is no -visible water on the surfaces of the leaves, or at the cut ends, before -it may have condensed there, we infer that the water escapes from the -leaves in the form of <i>water vapor</i>, and that this water vapor, when -it comes in contact with the surface of the cold glass, condenses and -forms the moisture film, and later the drops of water. The leaves of -these cut shoots therefore lose water in the form of water vapor, and -thus a loss of turgidity results.</p> - -<div class="figcenter"> - <img src="images/fig46.jpg" alt="" width="600" height="188" /> - <p class="center">Fig. 46.<br />To show loss of water from leaves, - the leaves just covered.</p> - <img src="images/fig47.jpg" alt="" width="600" height="181" /> - <p class="center">Fig. 47.<br />After a few hours drops of water have accumulated<br /> - on the inside of the jar covering the leaves.</p> -</div> - -<p><b>70. Loss of water from growing plants.</b>—Suppose we now take a -small and actively growing plant in a pot, and cover the pot and the -<span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span> -soil with a sheet of rubber cloth or flexible oilcloth which fits -tightly around the stem of the plant so that the moisture from the soil -or from the surface of the pot cannot escape. Then place a bell jar -over the plant, and set in a brightly lighted place, at a temperature -suitable for growth. In the course of a few minutes on a dry day a -moisture film forms on the inner surface of the glass, just as it did -in the case of the glass jar containing the cut shoots and leaves. -Later the moisture has condensed so that it is in the form of drops. If -we have the same leaf surface here as we had with the cut shoots, we -shall probably find that a larger amount of water accumulates on the -surface of the jar from the plant that is still attached to its roots.</p> - -<p><b>71. Water escapes from the surfaces of living leaves in the form of -water vapor.</b>—This living plant then has lost water, which also -escapes in the form of water vapor. Since here there are no cut places -on the shoots or leaves, we infer that the loss of water vapor takes -place from the surfaces of the leaves and from the shoots. It is also -to be noted that, while this plant is losing water from the surfaces of -the leaves, it does not wilt or lose its turgidity. The roots by their -activity and pressure supply water to take the place of that which is -given off in the form of water vapor. This loss of water in the form of -water vapor by plants is <i>transpiration</i>.</p> - -<p><b>72. A test for the escape of water vapor from plants.</b>—Make -a solution of cobalt chloride in water. Saturate several pieces of -filter paper with it. Allow them to dry. The water solution of cobalt -chloride is red. The paper is also red when it is moist, but when it -is thoroughly dry it is blue. It is very sensitive to moisture and the -moisture of the air is often sufficient to redden it. Before using dry -the paper in an oven or over a flame.</p> - -<p><b>73.</b> Take two bell jars, as shown in <a href="#FIG_49">fig. 49</a>. Under -one place a potted plant, the pot and earth being covered by oiled paper. Or cover -the plant with a fruit jar. To a stake in the pot pin a piece of the -<span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span> -dried cobalt paper, and at the same time pin to a stake, in another -jar covering no plant, another piece of cobalt paper. They should both -be put under the jars at the same time. In a few moments the paper in -the jar with the plant will begin to redden. In a short while, ten or -fifteen minutes, probably, it will be entirely red, while the paper -under the other jar will remain blue, or be only slightly reddened. The -water vapor passing off from the living plant comes in contact with -the sensitive cobalt chloride in the paper and reddens it before there -is sufficient vapor present to condense as a film of moisture on the -surface of the jar.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_48" src="images/fig48.jpg" alt="" width="200" height="387" /> - <p class="center">Fig. 48.</p> - </div> - <div class="figsub"> - <img id="FIG_49" src="images/fig49.jpg" alt="" width="400" height="378" /> - <p class="center">Fig. 49.</p> - </div> - <div class="blockquot"> - <p>Fig. 48.—Water vapor is given off by the leaves when attached to the - living plant. It condenses into drops of water on the cool surface of - the glass covering the plant.</p> - <p>Fig. 49.—A good way to show that the water passes off - from the leaves in the form of water vapor.</p> - </div> -</div> - -<p><b>74. Experiment to compare loss of water in a dry and a humid -atmosphere.</b>—We should now compare the escape of water from the -leaves of a plant covered by a bell jar, as in the last experiment, -<span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span> -with that which takes place when the plant is exposed in a normal way -in the air of the room or in the open. To do this we should select -two plants of the same kind growing in pots, and of approximately the -same leaf surface. The potted plants are placed one each on the arms -of a scale. One of the plants is covered in this position with a bell -jar. With weights placed on the pan of the other arm the two sides are -balanced. In the course of an hour, if the air of the room is dry, -moisture has probably accumulated on the inner surface of the glass jar -which is used to cover one of the plants. This indicates that there has -here been a loss of water. But there is no escape of water vapor into -the surrounding air so that the weight on this arm is practically the -same as at the beginning of the experiment. We see, however, that the -other arm of the balance has risen. We infer that this is the result of -the loss of water vapor from the plant on that arm. Now let us remove -the bell jar from the other plant, and with a cloth wipe off all the -moisture from the inner surface, and replace the jar over the plant. We -note that the end of the scale which holds this plant is still lower -than the other end.</p> - -<p><b>75. The loss of water is greater in a dry than in a humid -atmosphere.</b>—This teaches us that while water vapor escaped from -the plant under the bell jar, the air in this receiver soon became -saturated with the moisture, and thus the farther escape of moisture -from the leaves was checked. It also teaches us another very important -fact, viz., that plants lose water more rapidly through their leaves in -a dry air than in a humid or moist atmosphere. We can now understand -why it is that during the very hot and dry part of certain days plants -often wilt, while at nightfall, when the atmosphere is more humid, they -revive. They lose more water through their leaves during the dry part -of the day, other things being equal, than at other times.</p> - -<p><b>76. How transpiration takes place.</b>—Since the water of -transpiration passes off in the form of water vapor we are led to -inquire if this process is simply <i>evaporation</i> of water through the -surface of the leaves, or whether it is controlled to any appreciable -<span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span> -extent by any condition of the living plant. An experiment which is -instructive in this respect we shall find in a comparison between the -transpiration of water from the leaves of a cut shoot, allowed to lie -unprotected in a dry room, and a similar cut shoot the leaves of which -have been killed.</p> - -<p><b>77.</b> Almost any plant will answer for the experiment. For this -purpose I have used the following method. Small branches of the locust -(Robinia pseudacacia), of sweet clover (Melilotus alba), and of a -heliopsis were selected. One set of the shoots was immersed for a -moment in hot water near the boiling point to kill them. The other set -was immersed for the same length of time in cold water, so that the -surfaces of the leaves might be well wetted, and thus the two sets of -leaves at the beginning of the experiment would be similar, so far as -the amount of water on their surfaces is concerned. All the shoots were -then spread out on a table in a dry room, the leaves of the killed -shoots being separated where they are inclined to cling together. In -a short while all the water has evaporated from the surface of the -living leaves, while the leaves of the dead shoots are still wet on -the surface. In six hours the leaves of the dead shoots from which the -surface water had now evaporated were beginning to dry up, while the -leaves of the living plants were only becoming flaccid. In twenty-four -hours the leaves of the dead shoots were crisp and brittle, while those -of the living shoots were only wilted. In twenty-four hours more the -leaves of the sweet clover and of the heliopsis were still soft and -flexible, showing that they still contained more water than the killed -shoots which had been crisp for more than a day.</p> - -<p><b>78.</b> It must be then that during what is termed transpiration -the living plant is capable of holding back the water to some extent, -which in a dead plant would escape more rapidly by evaporation. It is -also known that a body of water with a surface equal to that of a given -leaf surface of a plant loses more water by evaporation during the same -length of time than the plant loses by transpiration.</p> - -<p><b>79. Structure of a leaf.</b>—We are now led to inquire why it is -that a living leaf loses water less rapidly than dead ones, and why -less water escapes from a given leaf surface than from an equal surface -of water. To understand this it will be necessary to examine the minute -structure of a leaf. For this purpose we may select the leaf of an ivy, -though many other leaves will answer equally well. From a portion of -the leaf we should make very thin cross-sections with a razor or other -sharp instrument. These sections should be perpendicular to the surface -<span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span> -of the leaf and should be then mounted in water for microscopic -examination.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a></p> - -<p><b>80. Epidermis of the leaf.</b>—In this section we see that the -green part of the leaf is bordered on what are its upper and lower -surfaces by a row of cells which possess no green color. The walls of -the cells of each row have nearly parallel sides, and the cross walls -are perpendicular. These cells form a single layer over both surfaces -of the leaf and are termed the <i>epidermis</i>. Their walls are quite stout -and the outer walls are <i>cuticularized</i>.</p> - -<div class="figcenter"> - <img src="images/fig50.jpg" alt="" width="200" height="252" /> - <p class="center">Fig. 50.<br /> Section through ivy leaf showing<br /> communication between stomate<br /> - and the large intercellular spaces<br /> of the leaf, stoma closed.</p> -</div> -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_51" src="images/fig51.jpg" alt="" width="250" height="228" /> - <p class="center">Fig. 51.<br /> Stoma open.</p> - </div> - <div class="figsub"> - <img id="FIG_52" src="images/fig52.jpg" alt="" width="250" height="223" /> - <p class="center">Fig. 52.<br /> Stoma closed.</p> - </div> - <p class="center">Figs. 51, 52.—Section through stomata of ivy leaf.</p> -</div> - -<p><b>81. Soft tissue of the leaf.</b>—The cells which contain the green -chlorophyll bodies are arranged in two different ways. Those on the -upper side of the leaf are usually long and prismatic in form and -lie closely parallel to each other. Because of this arrangement of -these cells they are termed the <i>palisade</i> cells, and form what is -called the <i>palisade layer</i>. The other green cells, lying below, vary -greatly in size in different plants and to some extent also in the same -plant. Here we notice that they are elongated, or oval, or somewhat -irregular in form. The most striking peculiarity, however, in their -arrangement is that they are not usually packed closely together, but -each cell touches the other adjacent cells only at certain points. This -arrangement of these cells forms quite large spaces between them, the -intercellular spaces. If we should examine such a section of a leaf -<span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span> -before it is mounted in water we would see that the intercellular -spaces are not filled with water or cell-sap, but are filled with air -or some gas. Within the cells, on the other hand, we find the cell-sap -and the protoplasm.</p> - -<p><b>82. Stomata.</b>—If we examine carefully the row of epidermal cells -on the under surface of the leaf, we find here and there a peculiar -arrangement of cells shown at figs. <a href="#FIG_51">51</a>, <a href="#FIG_52">52</a>. This -opening through the epidermal layer is a <i>stoma</i>. The cells which immediately surround -the openings are the <i>guard cells</i>. The form of the guard cells can be -better seen if we tear a leaf in such a way as to strip off a short -piece of the lower epidermis, and mount this in water. The guard cells -are nearly crescent-shaped, and the stoma is elliptical in outline. The -epidermal cells are very irregular in outline in this view. We should -also note that while the epidermal cells contain no chlorophyll, the -guard cells do.</p> - -<div class="figcenter"> - <img src="images/fig53.jpg" alt="" width="600" height="305" /> - <p class="center">Fig. 53.<br /> Portion of epidermis of ivy, showing irregular<br /> - epidermal cells, stoma and guard cells.</p> -</div> - -<p><b>82</b><i>a</i>. In the ivy leaf the guard cells are quite plain, but in -most plants the form as seen in cross-section is irregular in outline, -as shown in <a href="#FIG_53A">fig. 53<i>a</i></a>, which is from a section of a -wintergreen leaf. This leaf is interesting because it shows the characteristic structure -of leaves of many plants growing in soil where absorption of water by -the roots is difficult owing to the cold water, acids, or salts in the -water or soil, or in dry soil (see Chapters <a href="#CHAPTER_XLVII">47</a>, -54, 55). The cuticle over the upper epidermis is quite thick. This -lessens the loss of water by the leaf. The compact palisades of cells -are in two to three cell layers, also reducing the loss of water.</p> - -<p><b>83. The living protoplasm retards the evaporation of water from the -leaf.</b>—If we now take into consideration a few facts which we have -<span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span> -learned in a previous chapter, with reference to the physical -properties of the living cell, we shall be able to give a partial -explanation of the comparative slowness with which the water escapes -from the leaves. The inner surfaces of the cell walls are lined with -the membrane of protoplasm, and within this is the cell-sap. These -cells have become turgid by the absorption of the water which has -passed up to them from the roots. While the protoplasmic membrane of -the cells does not readily permit the water to filter through, yet it -is saturated with water, and the elastic cell wall with which it is in -contact is also saturated. From the cell wall the water evaporates into -the intercellular spaces. But the water is given up slowly through the -protoplasmic membrane, so that the water vapor cannot be given off as -rapidly from the cell walls as it could if the protoplasm were dead. -The living protoplasmic membrane then which is only slowly permeable to -the water of the cell-sap is here a very important factor in checking -the too rapid loss of water from the leaves.</p> - -<div class="figcenter"> - <img id="FIG_53A" src="images/fig53a.jpg" alt="" width="600" height="437" /> - <p class="center">Fig. 53<i>a</i>.<br /> Cross-section of leaf of wintergreen. <i>Cu.</i>, cuticle; <i>Epid.</i>,<br /> - epidermis; <i>v.d.</i>, vascular duct; <i>Int. c. sp.</i>, intercellular space;<br /> - <i>L. ep.</i>, lower epidermis; <i>St.</i>, stoma.</p> -</div> - -<p><span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span> -By an examination of our leaf section we see that the intercellular -spaces are all connected, and that the stomata, where they occur, open -also into intercellular spaces. There is here an opportunity for the -water vapor in the intercellular spaces to escape when the stomata are -open.</p> - -<p><b>84. Action of the stomata.</b>—The guard cells serve an important -function in regulating transpiration. During normal transpiration the -guard cells are turgid and their peculiar form then causes them to arch -away from each other, allowing the escape of water vapor. When the air -becomes too dry transpiration is in excess of absorption by the roots. -The guard cells lose some of their water, and collapse so that their -inner faces meet in a straight line and close the stoma. Thus the rapid -transpiration is checked. Some evaporation of water vapor, however, -takes place through the epidermal cells, and if the air remains too -dry, the leaves eventually become flaccid and droop. During the day -the effect of sunlight is to increase certain sugars or salts in the -guard cells so that they readily become turgid and open the stomates, -but at night the cell-sap is less concentrated and the stomates are -usually closed. Light therefore favors transpiration, while in darkness -transpiration is checked.</p> - -<p><b>85. Compare transpiration from the two surfaces of the -leaf.</b>—This can be done by using the cobalt chloride paper. This -paper can be kept from year to year and used repeatedly. It is thus a -very simple matter to make these experiments. Provide two pieces of -glass (discarded glass negatives, cleaned, are excellent), two pieces -of cobalt chloride paper, and some geranium leaves entirely free from -surface water. Dry the paper until it is blue. Place one piece of the -paper on a glass plate; place the geranium leaf with the under side on -the paper. On the upper side of the leaf now place the other cobalt -paper, and next the second piece of glass. On the pile place a light -weight to keep the parts well in contact. In fifteen or twenty minutes -open and examine. The paper next the under side of the geranium leaf -is red where it lies under the leaf. The paper on the upper side is -only slightly reddened. The greater loss of water, then, is through the -under side of the geranium leaf. This is true of a great many leaves, -but it is not true of all.</p> - -<p><b>86. Negative pressure.</b>—This is not only indicated by the -drooping of the leaves, but may be determined in another way. If the -shoot of such a plant be cut underneath mercury, or underneath a strong -solution of eosin, it will be found that some of the mercury or eosin, -as the case may be, will be forcibly drawn up into the stem toward the -roots. This is seen on quickly splitting the cut end of the stem. When -plants in the open cannot be obtained in this condition, one may take -a plant like a balsam plant from the greenhouse, or some other potted -plant, knock it out of the pot, free the roots from the soil and allow -to partly wilt. The stem may then be held under the eosin solution and cut. -<span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span></p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_54" src="images/fig54.jpg" alt="" width="150" height="236" /> - <p class="center">Fig. 54.<br /> Experiment to show lifting<br /> power of transpiration.</p> - </div> - <div class="figsub"> - <a><img id="FIG_55" src="images/fig55.jpg" alt="" width="350" height="226" /></a> - <p class="center">Fig. 55.<br /> Estimation of the amount of transpiration. The tubes are filled with<br /> - water, and as the water transpires from the leaf surface its movement<br /> - in the tube from <i>a</i> to <i>b</i> can be measured. (After Mangin.)</p> - </div> -</div> - -<p><b>87. Lifting power of transpiration.</b>—Not only does transpiration -go on quite independently of root pressure, as we have discovered -from other experiments, but transpiration is capable of exerting a -lifting power on the water in the plant. This may be demonstrated in -the following way: Place the cut end of a leafy shoot in one end of a -U tube and fit it water-tight. Partly fill this arm of the U tube with -water, and add mercury to the other arm until it stands at a level in -the two arms as in <a href="#FIG_54">fig. 54</a>. In a short time -we note that the mercury is rising in the tube.</p> - -<p><b>88. Root pressure may exceed transpiration.</b>—If we cover small -actively growing plants, such as the pea, corn, wheat, bean, etc., -with a bell jar, and place them in the sunlight where the temperature -is suitable for growth, in a few hours, if conditions are favorable, -we shall see that there are drops of water standing out on the margins -of the leaves. These drops of water have exuded through the ordinary -stomata, or in other cases what are called water stomata, through the -influence of root pressure. The plant being covered by the glass jar, -the air soon becomes saturated with moisture and transpiration is -checked. Root pressure still goes on, however, and the result is shown -in the exuding drops. Root pressure is here in excess of transpiration. -This phenomenon is often to be observed during the summer season in the -case of low-growing plants. During the bright warm day transpiration -equals, or may be in excess of, root pressure, and the leaves are -consequently flaccid. As nightfall comes on the air becomes more -moist, and the conditions of light are such also that transpiration -is lessened. Root pressure, however, is still active because the soil -is still warm. In these cases drops of water may be seen exuding from -the margins of the leaves due to the excess of root pressure over -transpiration. Were it not for this provision for the escape of the -excess of water raised by root pressure, serious injury by lesions, as -a result of the great pressure, might result. The plant is thus to some -extent a self-regulatory piece of apparatus so far as root pressure and -transpiration are concerned.</p> - -<p><b>89. Injuries caused by excessive root pressure.</b>—Some varieties -of tomatoes when grown in poorly lighted and poorly ventilated -<span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span> -greenhouses suffer serious injury through lesions of the tissues. -This is brought about by the cells at certain parts becoming charged -so full with water through the activity of root pressure and lessened -transpiration, assisted also probably by an accumulation of certain -acids in the cell-sap which cannot be got rid of by transpiration. -Under these conditions some of the cells here swell out, forming -extensive cushions, and the cell walls become so weakened that they -burst. It is possible to imitate the excess of root pressure in the -case of some plants by connecting the stems with a system of water -pressure, when very quickly the drops of water will begin to exude from -the margins of the leaves.</p> - -<div class="figleft"> - <img src="images/fig56.jpg" alt="" width="250" height="402" /> - <p class="center">Fig. 56.<br /> The roots are lifting more water into the plant than<br /> - can be given off in the form of water vapor, so it is<br /> - pressed out in drops. From “First Studies Plant Life.”</p> -</div> - -<p><b>90.</b> It should be stated that in reality there is no difference -between transpiration and evaporation, if we bear in mind that -evaporation takes place more slowly from living plants than from dead -ones, or from an equal surface of water.</p> - -<p><b>91.</b> The escape of water vapor is not the only function of the -stomata. The exchange of gases takes place through them as we shall -later see. A large number of experiments show that normally the stomata -are open when the leaves are turgid. But when plants lose excessive -quantities of water on dry and hot days, so that the leaves become -flaccid, the guard cells automatically close the stomata to check the -escape of water vapor. Some water escapes through the epidermis of many -plants, though the cuticularized membrane of the epidermis largely -prevents evaporation. In arid regions plants are usually provided -with an epidermis of several layers of cells to more securely prevent -evaporation there. In such cases the guard cells are often protected by -being sunk deeply in the epidermal layer.</p> - -<p><b>92. Demonstration of stomates and intercellular air spaces.</b>—A -good demonstration of the presence of stomates in leaves, as well as -the presence and intercommunication of the intercellular spaces, can be -made by blowing into the cut end of the petiole of the leaf of a calla -<span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span> -lily, the lamina being immersed in water. The air is forced out -through the stomata and rises as bubbles to the surface of the water. -At the close of the experiment some of the air bubbles will still be -in contact with the leaf surface at the opening of the stomata. The -pressure of the water gradually forces this back into the leaf. Other -plants will answer for the experiment, but some are more suitable than -others.</p> - -<p><b>92a. Number of stomata.</b>—The larger number of stomata are on the -under side of the leaf. (In leaves which float on the surface of the -water all of the stomata are on the upper side of the leaf, as in the -water-lily.) It has been estimated by investigation that in general -there are 40-300 stomata to the square millimeter of surface. In some -plants this number is exceeded, as in the olive, where there are 625. -In an entire leaf of Brassica rapa there are about 11,000,000 stomata, -and in an entire leaf of the sunflower there are about 13,000,000 stomata.</p> - -<p><b>92b. Amount of water transpired by plants.</b>—The amount of water -transpired by plants is very great. According to careful estimates a -sunflower 6 feet high transpires on the average about one quart per -day; an acre of cabbages 2,000,000 quarts in four months; an oak tree -with 700,000 leaves transpires about 180 gallons of water per day. -According to von Höhnel, a beech tree 110 years old transpired about -2250 gallons of water in one summer. A hectare of such trees (about 400 -on 2½ acres) would at the same rate transpire about 900,000 gallons, or -about 30,000 barrels in one summer.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_V" id="CHAPTER_V">CHAPTER V.</a><br /> -<span class="h_subtitle">PATH OF MOVEMENT OF WATER IN PLANTS.</span></h3> -</div> - -<p><b>93.</b> In our study of root pressure and transpiration we have -seen that large quantities of water or solutions move upward through -the stems of plants. We are now led to inquire through what part of the -stems the liquid passes in this upward movement, or in other words, -what is the path of the “sap” as it rises in the stem. This we can -readily see by the following trial.</p> - -<p><b>94. Place the cut ends of leafy shoots in a solution of some of -the red dyes.</b>—We may cut off leafy shoots of various plants and -insert the cut ends in a vessel of water to which have been added a few -crystals of the dye known as fuchsin to make a deep red color (other -red dyes may be used, but this one is especially good). If the study is -made during the summer, the “touch-me-not” (impatiens) will be found a -very useful plant, or the garden balsam, which may also be had in the -winter from conservatories. Almost any plant will do, however, but we -should also select one like the corn plant (zea mays) if in the summer, -or the petioles of a plant like caladium, which can be obtained from -the conservatory. If seedlings of the castor-oil bean are at hand we -may cut off some shoots which are 8-10 inches high, and place them in -the solution also.</p> - -<p><b>95. These solutions color the tracts in the stem and leaves through -which they flow.</b>—After a few hours in the case of the impatiens, -or the more tender plants, we can see through the stem that certain -tracts are colored red by the solution, and after 12 to 24 hours there -<span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span> -may be seen a red coloration of the leaves of some of the plants -used. After the shoots have been standing in the solution for a few -hours, if we cut them at various places we will note that there are -several points in the section where the tissues are colored red. In -the impatiens perhaps from four to five, in the sunflower a larger -number. In these plants the colored areas on a cross-section of the -stem are situated in a concentric ring which separates more or less -completely an outer ring of the stem from the central portion. If we -now split portions of the stem lengthwise we see that these colored -areas continue throughout the length of the stem, in some cases even -up to the leaves and into them.</p> - -<div class="figcenter"> - <img id="FIG_57" src="images/fig57.jpg" alt="" width="600" height="373" /> - <p class="center">Fig. 57.<br /> Broken corn stalk, showing fibrovascular bundles.</p> -</div> - -<p><b>96.</b> If we cut across the stem of a corn plant which has been -in the solution, we see that instead of the colored areas being in -a concentric ring they are irregularly scattered, and on splitting -the stem we see here also that these colored areas extend for long -distances through the stem. If we take a corn stem which is mature, or -an old and dead one, cut around through the outer hard tissues, and -then break the stem at this point, from the softer tissue long strings -of tissue will pull out as shown in <a href="#FIG_57">fig. 57</a>. These strings of -denser tissue correspond to the areas which are colored by the dye. They are -in the form of minute bundles, and are called <i>vascular bundles</i>. -<span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span></p> - -<p><b>97.</b> We thus see that instead of the liquids passing through the -entire stem they are confined to definite courses. Now that we have -discovered the path of the upward movement of water in the stem, we are -curious to see what the structure of these definite portions of the -stem is.</p> - -<div class="figcenter"> - <img id="FIG_58" src="images/fig58.jpg" alt="" width="600" height="349" /> -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdc" colspan="3">Fig. 58.</td> - </tr><tr> - <td class="tdl">Xylem portion of bundle.  </td> - <td class="tdc">Cambium portion of bundle.  </td> - <td class="tdr"> Bast portion of bundle.</td> - </tr><tr> - <td class="tdc" colspan="3">Section of vascular bundle of sunflower stem.</td> - </tr> - </tbody> -</table> -</div> - -<p><b>98. Structure of the fibrovascular bundles.</b>—We should now -make quite thin cross-sections, either free hand and mount in water -for microscopic examination, or they may be made with a microtome and -mounted in Canada balsam, and in this condition will answer for future -study. To illustrate the structure of the bundle in one type we may -take the stem of the castor-oil bean. On examining these cross-sections -we see that there are groups of cells which are denser than the ground -tissue. These groups correspond to the colored areas in the former -experiments, and are the vascular bundles cut across. These groups are -somewhat oval in outline, with the pointed end directed toward the -center of the stem. If we look at the section as a whole we see that -there is a narrow continuous ring<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a> -of small cells situated at the same distance from the center of the -stem as the middle part of the bundles, and that it divides the bundles -into two groups of cells.</p> - -<p><span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span> -<b>99. Woody portion of the bundle.</b>—In that portion of the bundle -on the inside of the ring, i.e., toward the “pith,” we note large, -circular, or angular cavities. The walls of these cells are quite thick -and woody. They are therefore called wood cells, and because they -are continuous with cells above and below them in the stem in such a -way that long tubes are formed, they are called woody vessels. Mixed -in with these are smaller cells, some of which also have thick walls -and are wood cells. Some of these cells may have thin walls. This -is the case with all when they are young, and they are then classed -with the fundamental tissue or soft tissue (parenchyma). This part of -the bundle, since it contains woody vessels and fibres, is the <i>wood -portion</i> of the bundle, or technically the <i>xylem</i>.</p> - -<p><b>100. Bast portion of the bundle.</b>—If our section is through a -part of the stem which is not too young, the tissues of the outer part -of the bundle will show either one or several groups of cells which -have white and shiny walls, that are thickened as much or more than -those of the wood vessels. These cells are <i>bast</i> cells, and for this -reason this part of the bundle is the <i>bast</i> portion, or the <i>phloem</i>. -Intermingled with these, cells may often be found which have thin -walls, unless the bundle is very old. Nearer the center of the bundle -and still within the bast portion are cells with thin walls, angular -and irregularly arranged. This is the softer portion of the bast, and -some of these cells are what are called <i>sieve</i> tubes, which can be -better seen and studied in a longitudinal section of the stem.</p> - -<p><b>101. Cambium region of the bundle.</b>—Extending across the center -of the bundle are several rows of small cells, the smallest of the -bundle, and we can see that they are more regularly arranged, usually -in quite regular rows, like bricks piled upon one another. These cells -have thinner walls than any others of the bundle, and they usually take -a deeper stain when treated with a solution of some of the dyes. This -is because they are younger, and are therefore richer in protoplasmic -contents. This zone of young cells across the bundle is the <i>cambium</i>. -Its cells grow and divide, and thus increase the size of the bundle. -By this increase in the number of the cells of the cambium layer, the -outermost cells on either side are continually passing over into the -phloem, on the one hand, and into the wood portion of the bundle, on -the other hand.</p> - -<p><b>102. Longitudinal section of the bundle.</b>—If we make thin -longisections of the vascular bundle of the castor-oil seedling (or -other dicotyledon) so that we have thin ones running through a bundle -radially, as shown in <a href="#FIG_59">fig. 59</a>, we can see the -structure of these parts of the bundle in side view. We see here that -the form of the cells is very different from what is presented in a -cross-section of the same. The walls of the various ducts have peculiar -markings on them. These markings are caused by the walls being -<span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span> -thicker in some places than in others, and this thickening takes place -so regularly in some instances as to form regular spiral thickenings. -Others have the thickenings in the form of the rounds of a ladder, -while still others have pitted walls or the thickenings are in the form -of rings.</p> - -<div class="figcenter"> - <img id="FIG_59" src="images/fig59.jpg" alt="" width="600" height="308" /> - <div class="blockquot"> - <p class="center">Fig. 59.</p> - <p class="center">Longitudinal section of vascular bundle of sunflower - stem; spiral, scalariform and pitted vessels at left; next are wood - fibers with oblique cross walls; in middle are cambium cells with - straight cross walls, next two sieve tubes, then phloem or bast cells.</p> - </div> -</div> - -<p><b>103. Vessels or ducts.</b>—One way in which the cells in side view -differ greatly from an end view, in a cross-section in the bundle, is -that they are much longer in the direction of the axis of the stem. The -cells have become elongated greatly. If we search for the place where -two of these large cells with spiral, or ladder-like, markings meet end -to end, we see that the wall which formerly separated the cells has -nearly or quite disappeared. In other words the two cells have now an -open communication at the ends. This is so for long distances in the -stem, so that long columns of these large cells form tubes or vessels -through which the water rises in the stems of plants.</p> - -<p><b>104.</b> In the bast portion of the bundle we detect the cells of -the bast fibers by their thick walls. They are very much elongated and -the ends taper out to thin points so that they overlap. In this way -they serve to strengthen the stem.</p> - -<p><b>105. Sieve tubes.</b>—Lying near the bast cells, usually toward -the cambium, are elongated cells standing end to end, with delicate -markings on their cross walls which appear like finely punctured plates -or sieves. The protoplasm in such cells is usually quite distinct, and -sometimes contracted away from the side walls, but attached to the -cross walls, and this aids in the detection of the sieve tubes (<a href="#FIG_59">fig. 59</a>.) -The granular appearance which these plates present is caused by minute -perforations through the wall so that there is a communication -between the cells. The tubes thus formed are therefore called sieve -tubes and they extend for long distances through the tube so that there -<span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span> -is communication throughout the entire length of the stem. (The -function of the sieve tubes is supposed to be that for the downward -transportation of substances elaborated in the leaves.)</p> - -<p><b>106.</b> If we section in like manner the stem of the sunflower we -shall see similar bundles, but the number is greater than eight. In -the garden balsam the number is from four to six in an ordinary stem -3-4<i>mm</i> diameter. Here we can see quite well the origin of the vascular -bundle. Between the larger bundles we can see especially in free-hand -sections of stems through which a colored solution has been lifted by -transpiration, as in our former experiments, small groups of the minute -cells in the cambial ring which are colored. These groups of cells -which form strands running through the stem are <i>pro-cambium strands</i>. -The cells divide and increase just like the cambium cells, and the -older ones thrown off on either side change, those toward the center -of the stem to wood vessels and fibers, and those on the outer side to -bast cells and sieve tubes.</p> - -<p><b>107. Fibrovascular bundles in the Indian corn.</b>—We should now -make a thin transection of a portion of the center of the stem of -Indian corn, in order to compare the structure of the bundle with that -of the plants which we have just examined. In <a href="#FIG_60">fig. 60</a> is -represented a fibrovascular bundle of the stem of the Indian corn. The large -cells are those of the spiral and reticulated and annular vessels. This is -the woody portion of the bundle or xylem. Opposite this is the bast -portion or phloem, marked by the lighter colored tissue at <i>i</i>. The -larger of these cells are the sieve tubes, and intermingled with them -are smaller cells with thin walls. Surrounding the entire bundle are -small cells with thick walls. These are elongated and the tapering ends -overlap. They are thus slender and long and form fibers. In such a -bundle all of the cambium has passed over into permanent tissue and is -said to be closed.</p> - -<div class="figcenter"> - <img id="FIG_60" src="images/fig60.jpg" alt="" width="600" height="357" /> - <div class="blockquot"> - <p class="center">Fig. 60.</p> - <p class="center">Transection of fibrovascular bundle of Indian corn. <i>a</i>, toward - periphery of stem; <i>g</i>, large pitted vessels; <i>s</i>, spiral vessel; <i>r</i>, - annular vessel; <i>l</i>, air cavity formed by breaking apart of the cells;<i>i</i>, - soft bast, a form of sieve tissue; <i>p</i>, thin-walled parenchyma. (Sachs.)</p> - </div> -</div> - -<p><b>108. Rise of water in the vessels.</b>—During the movement of the -water or nutrient solutions upward in the stem the vessels of the wood -portion of the bundle in certain plants are nearly or quite filled, -if root pressure is active and transpiration is not very rapid. If, -however, on dry days transpiration is in excess of root pressure, as -often happens, the vessels are not filled with the water, but are -<span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span> -partly filled with certain gases because the air or other gases in -the plant become rarefied as a result of the excessive loss of water. -There are then successive rows of air or gas bubbles in the vessels -separated by films of water which also line the walls of the vessels. -The condition of the vessel is much like that of a glass tube through -which one might pass the “froth” which is formed on the surface of -soapy water. This forms a chain of bubbles in the vessels. This chain -has been called Jamin’s chain because of the discoverer.</p> - -<p><b>109.</b> Why water or food solutions can be raised by the plant -to the height attained by some trees has never been satisfactorily -explained. There are several theories propounded which cannot be -discussed here. It is probably a very complex process. Root pressure -and transpiration both play a part, or at least can be shown, as we -have seen, to be capable of lifting water to a considerable height. In -addition to this, the walls of the vessels absorb water by diffusion, -and in the other elements of the bundle capillarity comes also into -play, as well as osmosis.</p> - -<p>See Organization of Tissues, <a href="#CHAPTER_XXXVIII">Chapter 38</a>.</p> - -<p><b>110. Flow of sap in the spring.</b>—The cause of the bleeding of -trees and the flow of sap in the spring is little understood. One of -the remarkable cases is the flow of sap in maple trees. It begins -in early spring and ceases as the buds are opening, and seems to be -initiated by alternation of high and low temperatures of day and night. -It has been found that the pressures inside of the tree at this time -are enormously increased during the day, when the temperature rises -after a cold night. This has led to the belief that the pressure is -caused by the expansion of the gases in the vascular ducts. The warming -up of the twigs and branches of the tree would take place rapidly -during the day, while the interior of the trunk would be only slightly -affected. The pressures then would cause the sap to flow downward -during the day, and at night the branches becoming cool, sap would flow -back again from the roots and trunk.</p> - -<p>Recent experiments by Jones <i>et al.</i> show that while some of the -pressure is due to the expansion of gas in the tree by the rise of -temperature, this cannot account for the enormous pressures which are -often present, for example, when after a rise in the temperature of 2° -C. there was an increase of 20 lbs. pressure.</p> - -<p>Then again, after the cessation of the flow in late spring there are -often as great differences between night and day temperatures. It -therefore seems reasonable to conclude that the expansion of gases by a -rise in temperature is not the direct cause.</p> - -<p><b>Activities of the cells.</b>—It has been suggested by some that -the rise in temperature exercises an influence on the protoplasts, -or living cells, so that they are stimulated to a special activity -resulting in an exudation pressure from the individual cells, which is -<span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span> -known to take place. With the fall of temperature at night this -activity would cease and there might result a lessened pressure in -the cells. Since the specific activities of cells are known to vary -in different plants, and in the same plant at different seasons, some -support is gained for this theory, though it is generally believed that -the activities of the living cells in the stems are not necessary for -the upward flow of water. It must be admitted, however, that at present -we know very little about this interesting problem.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_VI" id="CHAPTER_VI">CHAPTER VI.</a><br /> -<span class="h_subtitle">MECHANICAL USES OF WATER.</span></h3> -</div> - -<p><b>111. Turgidity of plant parts.</b>—As we have seen by the -experiments on the leaves, turgescence of the cells is one of the -conditions which enables the leaves to stand out from the stem, and the -lamina of the leaves to remain in an expanded position, so that they -are better exposed to the light, and to the currents of air. Were it -not for this turgidity the leaves would hang down close against the stem.</p> - -<div class="figleft"> - <img id="FIG_61" src="images/fig61.jpg" alt="" width="200" height="312" /> - <p class="center">Fig. 61.<br /> Restoration<br /> of turgidity<br /> (Sachs).</p> -</div> - -<p><b>112. Restoration of turgidity in shoots.</b>—If we cut off a living -stem of geranium, coleus, tomato, or “balsam,” and allow the leaves -to partly wilt so that the shoot loses its turgidity, it is possible -for this shoot to regain turgidity. The end may be freshly cut again, -placed in a vessel of water, covered with a bell jar and kept in a room -where the temperature is suitable for the growth of the plant. The -shoot will usually become turgid again from the water which is absorbed -through the cut end of the stem and is carried into the leaves where -the individual cells become turgid, and the leaves are again expanded. -Such shoots, and the excised leaves also, may often be made turgid -again by simply immersing them in water, as one of the experiments with -the salt solution would teach.</p> - -<p><b>113.</b> Turgidity may be restored more certainly and quickly in a -partially wilted shoot in another way. The cut end of the shoot may be -inserted in a U tube as shown in <a href="#FIG_61">fig. 61</a>, the end of the tube around -<span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span> -the stem of the plant being made air-tight. The arm of the tube in -which the stem is inserted is filled with water and the water is -allowed to partly fill the other arm. Into this other arm is then -poured mercury. The greater weight of the mercury causes such pressure -upon the water that it is pushed into the stem, where it passes up -through the vessels in the stems and leaves, and is brought more -quickly and surely to the cells which contain the protoplasm and -cell-sap, so that turgidity is more quickly and certainly attained.</p> - -<p><b>114. Tissue tensions.</b>—Besides the turgescence of the cells -of the leaves and shoots there are certain tissue tensions without -which certain tender and succulent shoots, etc., would be limp, and -would droop. There are a number of plants usually accessible, some at -one season and some at others, which may be used to illustrate tissue -tension.</p> - -<p><b>115. Longitudinal tissue tension.</b>—For this in early summer one -may use the young and succulent shoots of the elder (sambucus); or the -petioles of rhubarb during the summer and early autumn; or the petioles -of richardia. Petioles of caladium are excellent for this purpose, and -these may be had at almost any season of the year from the greenhouses, -and are thus especially advantageous for work during late autumn or -winter. The tension is so strong that a portion of such a petiole -10-15<i>cm</i> long is ample to demonstrate it. As we grasp the lower end of -the petiole of a caladium, or rhubarb leaf, we observe how rigid it is, -and how well it supports the heavy expanded lamina of the leaf.</p> - -<p><b>116.</b> The ends of a portion of such a petiole or other object -which may be used are cut off squarely. With a knife a strip from -2-3<i>mm</i> in thickness is removed from one side the full length of the -object. This strip we now find is shorter than the larger part from -which it was removed. The outer tissue then exerts a tension upon the -petiole which tends to shorten it. Let us remove another strip lying -next this one, and another, and so on until the outer tissues remain -only upon one side. The object will now bend toward that side. Now -remove this strip and compare the length of the strips removed with the -<span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span> -central portion. We find that they are much shorter now. In other words -there is also a tension in the tissue of the central portion of the -petiole, the direction of which is opposite to that of the superficial -tissue. The parts of the petiole now are not rigid, and they easily -bend. These two longitudinal tissue tensions acting in opposition to -each other therefore give rigidity to the succulent shoot. It is only -when the individual cells of such shoots or petioles are turgid that -these tissue tensions in succulent shoots manifest themselves or are -prominent.</p> - -<div class="figleft"> - <img id="FIG_62" src="images/fig62.jpg" alt="" width="200" height="287" /> - <p class="center">Fig. 62.<br /> Strip from dandelion<br /> stem made - to<br /> imitate a plant tendril.</p> -</div> - -<p><b>117.</b> To demonstrate the efficiency of this tension in giving -support, let us take a long petiole of caladium or of rhubarb. Hold it -by one end in a horizontal position. It is firm and rigid, and does not -droop, or but little. Remove all of the outer portion of the tissues, -as described above, leaving only the central portion. Now attempt to -hold it in a horizontal position by one end. It is flabby and droops -downward because the longitudinal tension is removed.</p> - -<p><b>118. Longitudinal tension in dandelion stems.</b>—Take long -and fresh dandelion stems. Split them. Note that they coil. The -longitudinal tension is very great. Place some of these strips in fresh -water. They coil up into close curls because by the absorption of water -by the cells the turgescence of the individual cells is increased, and -this increases the tension in the stem. Now place them in salt water (a -5 per cent solution). Why do they uncoil?</p> - -<p><b>119. To imitate the coiling of a tendril.</b>—Cut out a narrow -strip from a long dandelion stem. Fasten to a piece of soft wood, with -the ends close together, as shown in <a href="#FIG_62">fig. 62</a>. Now place it -in fresh water and watch it coil. Part of it coils one way and part another way, -<span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span> -just as a tendril does after the free end has caught hold of some place -for support.</p> - -<p><b>120. Transverse tissue tension.</b>—To illustrate this one may take -a willow shoot 3-5 <i>cm</i> diameter and saw off sections about 2 cm long. -Cut through the bark on one side and peel it off in a single strip. Now -attempt to replace it. The bark will not quite cover the wood again, -since the ends will not meet. It must then have been held in transverse -tension by the woody part of the shoot.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_VII" id="CHAPTER_VII">CHAPTER VII.</a><br /> -<span class="h_subtitle">STARCH AND SUGAR FORMATION.</span></h3> -</div> - -<h4><a name="VII_1" id="VII_1">1. The Gases Concerned.</a></h4> - -<p><b>121. Gas given off by green plants in the sunlight.</b>—Let us take -some green alga, like spirogyra, which is in a fresh condition, and -place one lot in a beaker or tall glass vessel of water and set this in -the direct sunlight or in a well lighted place. At the same time cover -a similar vessel of spirogyra with black cloth so that it will be in -the dark, or at least in very weak light.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig63.jpg" alt="" width="200" height="328" /> - <p class="center">Fig. 63.<br /> Oxygen gas given<br /> off by spirogyra.</p> - </div> - <div class="figsub"> - <img src="images/fig64.jpg" alt="" width="275" height="321" /> - <p class="center">Fig. 64.<br /> Bubbles of oxygen gas given off from<br /> - elodea in presence of sunlight. (Oels.)</p> - </div> -</div> - -<p><b>122.</b> In a short time we note that in the first vessel small -bubbles of gas are accumulating on the surface of the threads of the -spirogyra, and now and then some free themselves and rise to the -surface of the water. Where there is quite a tangle of the threads the -gas is apt to become caught and held back in larger bubbles, which on -agitation of the vessel are freed.</p> - -<p>If we now examine the second vessel we see that there are no bubbles, -or only a very few of them. We are led to believe then that sunlight -has had something to do with the setting free of this gas from the -plant.</p> - -<p><b>123.</b> We may now take another alga-like vaucheria and perform the -experiment in the same way, or to save time the two may be set up at -<span class="pagenum"><a name="Page_61" id="Page_61">[Pg 61]</a></span> -once. In fact if we take any of the green algæ and treat them as -described above gas will be given off in a similar manner.</p> - -<p><b>124.</b> We may now take one of the higher green plants, an aquatic -plant like elodea, callitriche, etc. Place the plant in the water with -the cut end of the stem uppermost, but still immersed, the plant being -weighted down by a glass rod or other suitable object. If we place the -vessel of water containing these leafy stems in the bright sunlight, -in a short time bubbles of gas will pass off quite rapidly from the -cut end of the stem. If in the same vessel we place another stem, from -which the leaves have been cut, the number of bubbles of gas given -off will be very few. This indicates that a large part of the gas is -furnished by the leaves.</p> - -<p><b>125.</b> Another vessel fitted up in the same way should be placed -in the dark or shaded by covering with a box or black cloth. It will -be seen here, as in the case of spirogyra, that very few or no bubbles -of gas will be set free. Sunlight here also is necessary for the rapid -escape of the gas.</p> - -<p><b>126.</b> We may easily compare the rapidity with which light of -varying intensity effects the setting free of this gas. After cutting -the end of the stem let us plunge the cut surface several times in -melted paraffine, or spread over the cut surface a coat of varnish. -Then prick with a needle a small hole through the paraffine or varnish. -Immerse the plant in water and place in sunlight as before. The gas now -comes from the puncture through the coating of the cut end, and the -number of bubbles given off during a given period can be ascertained by -counting. If we duplicate this experiment by placing one plant in weak -light or diffused sunlight, and another in the shade, we can easily -compare the rapidity of the escape of the gas under the different -conditions, which represent varying intensities of light. We see then -that not only is sunlight necessary for the setting free of this gas, -but that in diffused light or in the shade the activity of the plant in -this respect is less than in direct sunlight.</p> - -<p><b>127. What this gas is.</b>—If we take quite a quantity of the -plants of elodea and place them under an inverted funnel which is -immersed in water, the gas will be given off in quite large quantities -<span class="pagenum"><a name="Page_62" id="Page_62">[Pg 62]</a></span> -and will rise into the narrow exit of the funnel. The funnel should be -one with a short tube, or the vessel one which is quite deep so that -a small test tube which is filled with water may in this condition be -inverted over the opening of the funnel tube. With this arrangement -of the experiment the gas will rise in the inverted test tube, slowly -displace a portion of the water, and become collected in a sufficient -quantity to afford us a test. When a considerable quantity has -accumulated in the test tube, we may close the end of the tube in -the water with the thumb, lift it from the water and invert. The gas -will rise against the thumb. A dry soft-pine splinter should be then -lighted, and after it has burned a short time, extinguish the flame by -blowing upon it, when the still burning end of the splinter should be -brought to the mouth of the tube as the thumb is quickly moved to one -side. The glowing of the splinter shows that the gas is <i>oxygen</i>.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig65.jpg" alt="" width="250" height="381" /> - <p class="center">Fig. 65.<br /> Apparatus for collecting quantity<br /> - of oxygen from elodea.<br /> (Detmer.)</p> - </div> - <div class="figsub"> - <img src="images/fig66.jpg" alt="" width="250" height="359" /> - <p class="center">Fig. 66.<br /> Ready to see what the gas is.</p> - </div> -</div> - -<p><b>128.</b> It is better to allow the apparatus to stand several days -in the sunlight in order to catch a full tube of the gas. Or on a sunny -day carbon dioxide gas can be led into the water in the jar from a -generator, such an one as is used for the evolution of CO₂. The CO₂ -can be produced by the action of hydrochloric acid on bits of marble. -The CO₂ should not be run below the funnel. The test tube should be -fastened so that the light oxygen gas will not raise it off the funnel. -With the tube full of gas the test for oxygen can be made by lifting -<span class="pagenum"><a name="Page_63" id="Page_63">[Pg 63]</a></span> -the tube with one hand and quickly thrusting the glowing end of the -splinter in with the other hand. If properly handled, the splinter will -flame again. If it is necessary to keep the apparatus standing for more -than one day it is well to add fresh water in the place of most of the -water in the jar. Do not use leaves of land plants in this experiment, -since the bubbles which rise when these leaves are placed in water are -not evidence that this process is taking place.</p> - -<div class="figcenter"> - <img src="images/fig67.jpg" alt="" width="600" height="194" /> - <p class="center">Fig. 67.<br /> The splinter lights again - in the presence of oxygen gas.</p> -</div> - -<p class="blockquot"><b>129. Oxygen given off by green land plants -also.</b>—If we should extend our experiments to land plants we should -find that oxygen is given off by them under these conditions of light. -Land plants, however, will not do this when they are immersed in -water, but it is necessary to set up rather complicated apparatus and -to make analyses of the gases at the beginning and at the close of -the experiments. This has been done, however, in a sufficiently large -number of cases so that we know that all green plants in the sunlight, -if temperature and other conditions are favorable, give off oxygen.</p> - -<p><b>130. Absorption of carbon dioxide.</b>—We have next to inquire -where the oxygen comes from which is given off by green plants when -exposed to the sunlight, and also to learn something more of the -conditions necessary for the process. We know that water which has been -for some time exposed to the air and soil, and has been agitated, like -running water of streams, or the water of springs, has mixed with it a -considerable quantity of oxygen and carbon dioxide.</p> - -<p>If we boil spring water or hydrant water which comes from a stream -containing oxygen and carbon dioxide, for about 20 minutes, these -gases are driven off. We should set this aside where it will not be -agitated, until it has cooled sufficiently to receive plants without -injury. Let us now place some spirogyra or vaucheria, and elodea, or -other green water plant, in this boiled water and set the vessel in the -bright sunlight under the same conditions which were employed in the -experiments for the evolution of oxygen. No oxygen is given off. -<span class="pagenum"><a name="Page_64" id="Page_64">[Pg 64]</a></span></p> - -<p>Can it be that this is because the oxygen was driven from the water in -boiling? We shall see. Let us take the vessel containing the water, -or some other boiled water, and agitate it so that the air will be -thoroughly mixed with it. In this way oxygen is again mixed with the -water. Now place the plant again in the water, set in the sunlight, and -in several minutes observe the result. No oxygen or but little is given off. -There must be then some other requisite for the evolution of the oxygen.</p> - -<p><b>132. The gases are interchanged in the plants.</b>—We will now -introduce carbon dioxide again in the water. This can be done by -leading CO₂ from a gas generator into the water. Broken bits of marble -are placed in the generator, acted upon by hydrochloric acid, and the -gas is led over by glass tubing. Now if we place the plant in the water -and set the vessel in the sunlight, in a few minutes the oxygen is -given off rapidly.</p> - -<p><b>133. A chemical change of the gas takes place within the plant -cell.</b>—This leads us to believe then that CO₂ is in some way -necessary for the plant in this process. Since oxygen is given off -while carbon dioxide, a different gas, is necessary, it would seem that -a chemical change takes place in the gases within the plant. Since the -process takes place in such simple plants as spirogyra as well as in -the more bulky and higher plants, it appears that the changes go on -within the cell, in fact within the protoplasm.</p> - -<p><b>134. Gases as well as water can diffuse through the protoplasmic -membrane.</b>—Carbon dioxide then is absorbed by the plant while -oxygen is given off. We see therefore that gases as well as water can -diffuse through the protoplasmic membrane of plants under certain -conditions.</p> - -<h4><a name="VII_2" id="VII_2">2. Where Starch is Formed.</a></h4> - -<p>We have found by these simple experiments that some chemical change -takes place within the protoplasm of the green cells of plants during -the absorption of carbon dioxide and the giving off of oxygen. We -should examine some of the green parts of those plants used in the -<span class="pagenum"><a name="Page_65" id="Page_65">[Pg 65]</a></span> -experiments, or if they are not at hand we should set up others in -order to make this examination.</p> - -<p><b>135. Starch formed as a result of this process.</b>—We may take -spirogyra which has been standing in water in the bright sunlight for -several hours. A few of the threads should be placed in alcohol for a -short time to kill the protoplasm. From the alcohol we transfer the -threads to a solution of iodine in potassium iodide. We find that -at certain points in the chlorophyll band a bluish tinge, or color, -is imparted to the ring or sphere which surrounds the pyrenoid. In -our first study of the spirogyra cell we noted this sphere as being -composed of numerous small grains of starch which surround the pyrenoid.</p> - -<p><b>136. Iodine used as a test for starch.</b>—This color reaction -which we have obtained in treating the threads with iodine is the -well-known reaction, or test, for starch. We have demonstrated then -that starch is present in spirogyra threads which have stood in the -sunlight with free access to carbon dioxide.</p> - -<p>If we examine in the same way some threads which have stood in the -dark for a few days we obtain no reaction for starch, or at best only -a slight reaction. This gives us some evidence that a chemical change -does take place during this process (absorption of CO₂ and giving off -of oxygen), and that starch is a product of that chemical change.</p> - -<p><b>137. Schimper’s method of testing for the presence of -starch.</b>—Another convenient and quick method of testing for the -presence of starch is what is known as Schimper’s method. A strong -solution of chloral hydrate is made by taking 8 grams of chloral -hydrate for every 5<i>cc</i> of water. To this solution is added a little -of an alcoholic tincture of iodine. The threads of spirogyra may be placed -directly in this solution, and in a few moments mounted in water on the -glass slip and examined with the microscope. The reaction is strong and -easily seen.</p> - -<p>We should also examine the leaves of elodea, or one of the higher green -plants which has been for some time in the sunlight. We may use here -Schimper’s method by placing the leaves directly in the solution of -<span class="pagenum"><a name="Page_66" id="Page_66">[Pg 66]</a></span> -chloral hydrate and iodine. The leaves are made transparent by the -chloral hydrate so that the starch reaction from the iodine is easily -detected.</p> - -<p>The following is a convenient and safe method of extracting chlorophyll -from leaves. Fill a large pan, preferably a dishpan, half full of -hot water. This may be kept hot by a small flame. On the water float -an evaporating dish partly filled with alcohol. The leaves should be -first immersed in the hot water for several minutes, then placed in the -alcohol, which will quickly remove the chlorophyll. Now immerse the -leaves in the iodine solution.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_68" src="images/fig68.jpg" alt="" width="250" height="328" /> - <p class="center">Fig. 68.<br /> Leaf of coleus showing green and white<br /> - areas, before treatment with iodine.</p> - </div> - <div class="figsub"> - <img id="FIG_69" src="images/fig69.jpg" alt="" width="250" height="334" /> - <p class="center">Fig. 69.<br /> Similar leaf treated with iodine,<br /> - the starch reaction only showing<br /> where the leaf was green.</p> - </div> -</div> - -<p><b>138. Green parts of plants form starch when exposed to -light.</b>—Thus we find that in the case of all the green plants we -have examined, starch is present in the green cells of those which have -been standing for some time in the sunlight where the process of the -absorption of CO₂ and the giving off of oxygen can go on, and that in -<span class="pagenum"><a name="Page_67" id="Page_67">[Pg 67]</a></span> -the case of plants grown in the dark, or in leaves of plants which have -stood for some time in the dark, starch is absent. We reason from this -that starch is the product of the chemical change which takes place in -the green cells under these conditions. The CO₂ which is absorbed by -the plant mixes with the water (H₂O) in the cell and immediately forms -carbonic acid. The chlorophyll in the leaf absorbs radiant energy from -the sun which splits up the carbonic acid, and its elements then are -put together into a more complex compound, starch. This process of -putting together the elements of an organic compound is a <i>synthesis</i>, -or a <i>synthetic assimilation</i>, since it is done by the living plant. -It is therefore a synthetic assimilation of carbon dioxide. Since -the sunlight supplies the energy it is also called <i>photosynthesis</i>, -or <i>photosynthetic assimilation</i>. We can also say carbon dioxide -assimilation, or CO₂ assimilation (<a href="#X_3">see paragraph on assimilation at -close of Chapter 10</a>).</p> - -<p><b>139. Starch is formed only in the green parts of variegated -leaves.</b>—If we test for starch in variegated leaves like the leaf -of a coleus plant, we shall have an interesting demonstration of the -fact that the green parts of plants only form starch. We may take -a leaf which is partly green and partly white, from a plant which -has been standing for some time in bright light. <a href="#FIG_68">Fig. 68</a> is -from a photograph of such a leaf. We should first boil it in alcohol to remove -the green color. Now immerse it in the potassium iodide of iodine -solution for a short time. The parts which were formerly green are -now dark blue or nearly black, showing the presence of starch in -those portions of the leaf, while the white part of the leaf is still -uncolored. This is well shown in <a href="#FIG_69">fig. 69</a>, which is -from a photograph of another coleus leaf treated with the iodine solution.</p> - -<h4><a name="VII_3" id="VII_3">3. Chlorophyll and the Formation of Starch.</a></h4> - -<p><b>140.</b> In our experiments thus far in treating of the absorption -of carbon dioxide and the evolution of oxygen, with the accompanying -formation of starch, we have used green plants. -<span class="pagenum"><a name="Page_68" id="Page_68">[Pg 68]</a></span></p> - -<p><b>141. Fungi cannot form starch.</b>—If we should extend our -experiments to the fungi, which lack the green color so characteristic -of the majority of plants, we should find that photosynthesis does not -take place even though the plants are exposed to direct sunlight. These -plants cannot then form starch, but obtain carbohydrates for food from -other sources.</p> - -<p><b>142. Photosynthesis cannot take place in etiolated -plants.</b>—Moreover photosynthesis is usually confined to the green -plants, and if by any means one of the ordinary green plants loses its -green color this process cannot take place in that plant, even when -brought into the sunlight, until the green color has appeared under the -influence of light.</p> - -<p>This may be very easily demonstrated by growing seedlings of the -bean, squash, corn, pea, etc. (pine seedlings are green even when -grown in the dark), in a dark room, or in a dark receiver of some -kind which will shut out the rays of light. The room or receiver must -be quite dark. As the seedlings are “coming up,” and as long as they -remain in the dark chamber, they will present some other color than -green; usually they are somewhat yellowed. Such plants are said to be -<i>etiolated</i>. If they are brought into the sunlight now for a few hours -and then tested for the presence of starch the result will be negative. -But if the plant is left in the light, in a few days the leaves -begin to take on a green color, and then we find that carbon dioxide -assimilation begins.</p> - -<p><b>143. Chlorophyll and chloroplasts.</b>—The green substance in -plants is then one of the important factors in this complicated -process of forming starch. This green substance is <i>chlorophyll</i>, -and it usually occurs in definite bodies, the chlorophyll bodies, or -<i>chloroplasts</i>.</p> - -<p class="blockquot">The material for new growth of plants grown in the -dark is derived from the seed. Plants grown in the dark consist largely -of water and protoplasm, the walls being very thin.</p> - -<p><b>144. Form of the chlorophyll bodies.</b>—Chlorophyll bodies vary in -<span class="pagenum"><a name="Page_69" id="Page_69">[Pg 69]</a></span> -form in some different plants, especially in some of the lower -plants. This we have already seen in the case of spirogyra, where the -chlorophyll body is in the form of a very irregular band, which courses -around the inner side of the cell wall in a spiral manner. In zygnema, -which is related to spirogyra, the chlorophyll bodies are star-shaped. -In the desmids the form varies greatly. In œdogonium, another of the -thread-like algæ, illustrated in <a href="#FIG_144">fig. 144</a>, the chlorophyll -bodies are more or less flattened oval disks. In vaucheria, too, a branched -thread-like alga shown in <a href="#FIG_138">fig. 138</a>, the chlorophyll bodies -are oval in outline. These two plants, œdogonium and vaucheria, should be examined -here if possible, in order to become familiar with their form, since -they will be studied later under morphology (see chapters on <a href="#CHAPTER_XVI">œdogonium</a> -and <a href="#CHAPTER_XV">vaucheria</a>, for the occurrence and form of these plants). The form -of the chlorophyll body found in œdogonium and vaucheria is that which -is common to many of the green algæ, and also occurs in the mosses, -liverworts, ferns, and the higher plants. It is a more or less rounded, -oval, flattened body.</p> - -<div class="figcenter"> - <img src="images/fig69a.jpg" alt="" width="600" height="257" /> - <p class="center">Fig. 69<i>a</i>.<br /> Section of ivy leaf, palisade cells above, loose parenchyma,<br /> - with large intercellular spaces in center. Epidermal cells<br /> - on either edge, with no chlorophyll bodies.</p> -</div> - -<p><b>145. Chlorophyll is a pigment which resides in the -chloroplast.</b>—That the chlorophyll is a coloring substance which -resides in the chloroplastid, and does not form the body itself, can -be demonstrated by dissolving out the chlorophyll when the framework -of the chloroplastid is apparent. The green parts of plants which have -<span class="pagenum"><a name="Page_70" id="Page_70">[Pg 70]</a></span> -been placed for some time in alcohol lose their green color. The -alcohol at the same time becomes tinged with green. In sectioning such -plant tissue we find that the chlorophyll bodies, or chloroplastids as -they are more properly called, are still intact, though the green color -is absent. From this we know that chlorophyll is a substance distinct -from that of the chloroplastid.</p> - -<p><b>146. Chlorophyll absorbs energy from sunlight for -photosynthesis.</b>—It has been found by analysis with the -spectroscope that chlorophyll absorbs certain of the rays of the -sunlight. The energy which is thus obtained from the sun, called -<i>kinetic</i> energy, acts on the molecules of CH₂O₃, separating them into -molecules of C, H, and O. (When the CO₂ from the air enters the plant -cell it immediately unites with some of the water, forming carbonic -acid = CH₂O₃.) After a series of complicated chemical changes starch is -formed by the union of carbon, oxygen, and hydrogen. In this process -of the reduction of the CH₂O₃ and the formation of starch there is a -surplus of oxygen, which accounts for the giving off of oxygen during -the process.</p> - -<p><b>147. Rays of light concerned in photosynthesis.</b>—If a solution -of chlorophyll be made, and light be passed through it, and this -light be examined with the spectroscope, there appear what are called -absorption bands. These are dark bands which lie across certain -portions of the spectrum. These bands lie in the red, orange, yellow, -green, blue, and violet, but the bands are stronger in the red, which -shows that chlorophyll absorbs more of the red rays of light than of -the other rays. These are the rays of low refrangibility. The kinetic -energy derived by the absorption of these rays of light is transformed -into potential energy. That is, the molecule of CH₂O₃ is broken up, and -then by a different combination of certain elements starch is formed.<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a></p> - -<p><b>148. Starch grains formed in the chloroplasts.</b>—During -photosynthesis the starch formed is deposited generally in small grains -within the green chloroplast in the leaf. We can see this easily by -examining the leaves of some moss-like funaria which has been in the -light, or in the chloroplasts of the prothallia of ferns, etc. Starch -grains may also be formed in the chloroplasts from starch which was -<span class="pagenum"><a name="Page_71" id="Page_71">[Pg 71]</a></span> -formed in some other part of the plant, but which has passed in -solution. Thus the functions of the chloroplast are twofold, that of -photosynthesis and the formation of starch grains.</p> - -<p><b>149.</b> In the translocation of starch when it becomes stored up in -various parts of the plant, it passes from the state of solution into -starch grains in connection with plastids similar to the chloroplasts, -but which are not green. The green ones are sometimes called -<i>chloroplasts</i>, while the colorless ones are termed <i>leucoplasts</i>, -and those possessing other colors, as red and yellow, in floral leaves, the -root of the carrot, etc., are called <i>chromoplasts</i>.</p> - -<p><b>150. Photosynthesis in other than green plants.</b>—While -carbohydrates are usually only formed by green plants, there are some -exceptions. Apparent exceptions are found in the blue-green algæ, like -oscillatoria, nostoc, or in the brown and red sea weeds like fucus, -rhabdonia, etc. These plants, however, possess chlorophyll, but it is -disguised by another pigment or color. There are plants, however, which -do not have chlorophyll and yet form carbohydrates with evolution of -oxygen in the presence of light, as for example a purple bacterium, -in which the purple coloring substance absorbs light, though the rays -absorbed most energetically are not the red.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_70" src="images/fig70.jpg" alt="" width="250" height="169" /> - <p class="center">Fig. 70.<br /> Cell exposed to weak diffused light showing<br /> - chlorophyll bodies along the horizontal walls.</p> - </div> - <div class="figsub"> - <img id="FIG_71" src="images/fig71.jpg" alt="" width="250" height="148" /> - <p class="center">Fig. 71.<br /> Same cell exposed to strong light,<br /> - showing chlorophyll bodies have<br /> - moved to perpendicular walls.</p> - </div> - <p class="center space-below2">Figs. 70, 71.—Cell of prothallium of fern.</p> -</div> - -<p><b>151. Influence of light on the movement of chlorophyll -bodies.</b>—<i>In fern prothallia</i>.—If we place fern prothallia in -weak light for a few hours, and then examine them under the microscope, -we find that the most of the chlorophyll bodies in the cells are -arranged along the inner surface of the horizontal wall. If now the -same prothallia are placed in a brightly lighted place for a short -time most of the chlorophyll bodies move so that they are arranged -along the surfaces of the perpendicular walls, and instead of having -the flattened surfaces exposed to the light as in the former case, the -edges of the chlorophyll bodies are now turned toward the light. -<span class="pagenum"><a name="Page_72" id="Page_72">[Pg 72]</a></span> -(See figs. <a href="#FIG_70">70</a>, <a href="#FIG_71">71</a>.) The same phenomenon has been -observed in many plants. Light then has an influence on chlorophyll bodies, to some extent -determining their position. In weak light they are arranged so that the -flattened surfaces are exposed to the incidence of the rays of light, -so that the chlorophyll will absorb as great an amount as possible -of kinetic energy; but intense light is stronger than necessary, and -the chlorophyll bodies move so that their edges are exposed to the -incidence of the rays. This movement of the chlorophyll bodies is -different from that which takes place in some water plants like elodea. -The chlorophyll bodies in elodea are free in the protoplasm. The -protoplasm in the cells of elodea streams around the inside of the cell -wall much as it does in nitella and the chlorophyll bodies are carried -along in the currents, while in nitella they are stationary.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_73" id="Page_73">[Pg 73]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_VIII" id="CHAPTER_VIII">CHAPTER VIII.</a><br /> -<span class="h_subtitle">STARCH AND SUGAR CONCLUDED.<br /> -ANALYSIS OF PLANT SUBSTANCE.</span></h3> -</div> - -<h4><a name="VIII_1" id="VIII_1">1. Translocation of Starch.</a></h4> - -<p><b>152. Translocation of starch.</b>—It has been found that leaves of -many plants grown in the sunlight contain starch when examined after -being in the sunlight for several hours. But when the plants are left -in the dark for a day or two the leaves contain no starch, or a much -smaller amount. This suggests that starch after it has been formed may -be transferred from the leaves, or from those areas of the leaves where -it has been formed.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_72" src="images/fig72.jpg" alt="" width="150" height="238" /> - <p class="center">Fig. 72.<br /> Leaf of tropæolum<br /> - with portion covered<br /> - with corks to prevent<br /> - the formation of starch.<br /> - (After Detmer.)</p> - </div> - <div class="figsub"> - <img id="FIG_73" src="images/fig73.jpg" alt="" width="250" height="247" /> - <p class="center">Fig. 73.<br /> Leaf of tropæolum treated with<br /> - iodine after removal of cork, to<br /> - show that starch is removed from<br /> - the leaf during the night.</p> - </div> -</div> - -<p>To test this let us perform an experiment which is often made. We may -take a plant such as a garden tropæolum or a clover plant, or other -land plant in which it is easy to test for the presence of starch. Pin -a piece of circular cork, which is smaller than the area of the leaf, -on either side of the leaf, as in <a href="#FIG_72">fig. 72</a>, but allow free -circulation of air between the cork and the under side of the leaf. Place the plant -where it will be in the sunlight. On the afternoon of the following -day, if the sun has been shining, test the entire leaf for starch. The -part covered by the cork will not give the reaction for starch, as -shown by the absence of the bluish color, while the other parts of the -leaf will show it. The starch which was in that part of the leaf the -day before was dissolved and removed during the night, and then during -the following day, the parts being covered from the light, no starch -was formed in them. -<span class="pagenum"><a name="Page_74" id="Page_74">[Pg 74]</a></span></p> - -<p><b>153. Starch in other parts of plants than the leaves.</b>—We may -use the iodine test to search for starch in other parts of plants than -the leaves. If we cut a potato tuber, scrape some of the cut surface -into a pulp, and apply the iodine test, we obtain a beautiful and -distinct reaction showing the presence of starch. Now we have learned -that starch is only formed in the parts containing chlorophyll. We -have also learned that the starch which has been formed in the leaves -disappears from the leaf or is transferred from the leaf. We judge -therefore that the starch which we have found in the tuber of the -potato was formed first in the green leaves of the plant, as a result -of photosynthesis. From the leaves it is transferred in solution to -the underground stems, and stored in the tubers. The starch is stored -here by the plant to provide food for the growth of new plants from the -tubers, which are thus much more vigorous than the plants would be if -grown from the seed.</p> - -<p><b>154. Form of starch grains.</b>—Where starch is stored as a reserve -material it occurs in grains which usually have certain characters -peculiar to the species of plant in which they are found. They vary -in size in many different plants, and to some extent in form also. -If we scrape some of the cut surface of the potato tuber into a pulp -and mount a small quantity in water, or make a thin section for -microscopic examination, we find large starch grains of a beautiful -structure. The grains are oval in form and more or less irregular in -outline. But the striking peculiarity is the presence of what seem to -be alternating dark and light lines in the starch grain. We note that -the lines form irregular rings, which are smaller and smaller until -we come to the small central spot termed the “hilum” of the starch -grain. It is supposed that these apparent lines in the starch grain are -caused by the starch substance being deposited in alternating dense -and dilute layers, the dilute layers containing more water than the -dense ones; others think that the successive layers from the hilum -outward are regularly of diminishing density, and that this gives the -appearance of alternating lines. The starch formed by plants is one of -the organic substances which are manufactured by plants, and it (or -glucose) is the basis for the formation of other organic substances in -the plant. Without such organic substances green plants cannot make any -appreciable increase of plant substance, though a considerable increase -in size of the plant may take place.</p> - -<p class="blockquot"><span class="smcap">Note.</span>—The organic -compounds resulting from photosynthesis, since they are formed by the -union of carbon, hydrogen, and oxygen in such a way that the hydrogen -<span class="pagenum"><a name="Page_75" id="Page_75">[Pg 75]</a></span> -and oxygen are usually present in the same proportion as in water, are -called <i>carbohydrates</i>. The most common carbohydrates are sugars (cane -sugar, C₁₂H₂₂O₁₁ for example, in beet roots, sugar cane, sugar maple, -etc.), starch, and cellulose.</p> - -<p><b>155. Vaucheria.</b>—The result of carbon dioxide assimilation in -the threads of Vaucheria is not clearly understood. Starch is absent or -difficult to find in all except a few species, while oil globules are -present in most species. These oil globules are spherical, colorless, -globose and highly refringent. Often small ones are seen lying against -chlorophyll bodies. Oil is a <i>hydrocarbon</i> (containing C, H, and O, -but the H and O are in different proportions from what they are in H₂O) -and until recently it was supposed that this oil in Vaucheria was the -direct result of photosynthesis. But the oil does not disappear when -the plant is kept for a long time in the dark, which seems to show -that it is not the direct product of carbon dioxide assimilation, and -indicates that it comes either from a temporary starch body or from -glucose. Schimper found glucose in several species of Vaucheria, and -Waltz says that some starch is present in Vaucheria sericea, while -in V. tuberosa starch is abundant and replaces the oil. To test for -oil bodies in Vaucheria treat the threads with weak osmic acid, or -allow them to stand for twenty-four hours in Fleming’s solution (which -contains osmic acid). Mount some threads and examine with microscope. -The oil globules are stained black.</p> - -<h4><a name="VIII_2" id="VIII_2">2. Sugar, and Digestion of -Starch.</a><a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a></h4> - -<p><a name="PARA_156" id="PARA_156"><b>156.</b></a> It is probable that -some form of sugar is always produced as the result of photosynthesis. -The sugar thus formed may be stored as such or changed to starch. In -general it may be said that sugar is most common in the green parts of -monocotyledonous plants, while starch is most frequent in dicotyledons. -Plant sugars are of three general kinds: cane sugar abundant in the -sugar cane, sugar beet, sugar maple, etc.; glucose and fruit sugar, -found in the fruits of a majority of plants, and abundant in some, as -in apples, pears, grapes, etc.; and maltose, a variety produced in -germinating seeds, as in malted barley.</p> - -<p><b>157. Test for sugar.</b>—A very pretty experiment maybe made by -taking two test tubes, placing in one a solution of commercial grape -sugar (glucose), in the other one of granulated cane sugar, and adding -to each a few drops of Fehling’s solution.<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a> -After these tubes have stood in a warm place for half an hour, it will -<span class="pagenum"><a name="Page_76" id="Page_76">[Pg 76]</a></span> -be found that a bright orange brown or cinnabar-colored precipitate -of copper and cuprous oxide has formed in the tube containing grape -sugar, while the other solution is unchanged. Grape sugar or glucose, -therefore, reduces Fehling’s solution, while cane sugar as such has no -effect upon it.</p> - -<p>Cane sugar may be changed or converted to glucose by being boiled for a -short time with a dilute acid, or by adding Fehling’s solution to the -sugar solution and boiling. In the latter case the change is brought -about by the alkali and the precipitate of copper and cuprous oxide -forms.</p> - -<p><b>158. Tests for sugar in plant tissue.</b>—(<i>a</i>) Scrape out a little -of the tissue from the inside of a ripe apple or pear, place it with a -little water in a test tube, and add a few drops of Fehling’s solution. -After standing half an hour the characteristic precipitate of copper -and cuprous oxide appears, showing that grape sugar is present in -quantity.</p> - -<p>Make thin sections of the apple and mount in a drop of Fehling’s -solution on a slide. After half an hour examine with the microscope. -The granules of cuprous oxide are present in the cells of the tissue in -great abundance.</p> - -<p>(<i>b</i>) Cut up several leaves of a young vigorous corn seedling, -cover with water in a test tube and boil for a minute. After the -decoction has cooled add the Fehling’s solution and allow to stand. -The precipitate will appear. For comparison take similar corn leaves, -remove the chlorophyll with alcohol and test with iodine. No starch -reaction appears. The carbohydrate in corn leaves is therefore glucose -and not starch. If now the corn seed be examined the cells will be -found to be full of starch grains which give the beautiful blue -reaction with iodine. This experiment shows that grape sugar is formed -in the leaves of the corn plant, but is changed to starch when stored -in the seed.</p> - -<p>(<i>c</i>) Take two leaves of bean seedling or coleus, test one for sugar -and the other for starch. Both are present.</p> - -<p>(<i>d</i>) Procure some maple sap in the spring, or in the winter months -make a decoction of the broken tips of young branches of the sugar -maple by boiling them in water in a test tube. To the sap or cool -decoction add Fehling’s solution. No precipitate appears after -<span class="pagenum"><a name="Page_77" id="Page_77">[Pg 77]</a></span> -standing. Now heat the same solution to the boiling point, and the -precipitate forms, showing the presence of cane sugar in the maple -sap which was converted to glucose and fruit sugar by boiling in the -presence of an alkali.</p> - -<p>(<i>e</i>) Scrape out some of the tissue from a sugar beet root, cover with -water in a test tube and add Fehling’s solution. No change takes place -after standing. Boil the same solution and the precipitate forms, -showing the presence of cane sugar, inverted to grape sugar and fruit -sugar by the hot alkali.</p> - -<p><b>159. How starch is changed to sugar.</b>—We have seen that in -many plants the carbohydrate formed as the result of carbon dioxide -assimilation is stored as starch. This substance being insoluble -in water must be changed to sugar, which is soluble before it can -be used as food or transported to other parts of the plant. This -is accomplished through the action of certain enzymes, principally -diastase. This substance has the power of acting upon starch under -proper conditions of temperature and moisture, causing it to take up -the elements of water, and so to become sugar.</p> - -<p>This process takes place commonly in the leaves where starch is formed, -but especially in seeds, tubers (during the sprouting, etc.), and -other parts which the plant uses as storehouses for starch food. It is -probable that the same conditions of temperature and moisture which -favor germination or active growth are also favorable to the production -of diastase.</p> - -<p><b>160. Experiments to show the action of diastase.</b>—(<i>a</i>) Place -a bit of starch half as large as a pea in a test tube, and cover with -a weak solution<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a> -(about ⅕ per cent) of commercial taka diastase. After it has stood in -a warm place for five or ten minutes test with Fehling’s solution. The -precipitate of cuprous oxide appears showing that some of the starch -has been changed to sugar. By using measured quantities, and by testing -with iodine at frequent intervals, it can be determined just how long -it takes a given quantity of diastase to change a known quantity of -starch. In this connection one should first test a portion of the same -starch with Fehling’s solution to show that no sugar is present.</p> - -<p>(<i>b</i>) Repeat the above experiment using a little tissue from a potato, -and some from a corn seed.</p> - -<p>(<i>c</i>) Take 25 germinating barley seeds in which the radicle is just -appearing. Grind up thoroughly in a mortar with about three parts of -water. After this has stood for ten or fifteen minutes, filter. Fill a -test tube one-third full of water, add a piece of starch half the size -of a pea or less, and boil the mixture to make starch-paste. Add the -barley extract. Put in a warm place and test from time to time with -iodine. The first samples so treated will be blue, later ones violet, -<span class="pagenum"><a name="Page_78" id="Page_78">[Pg 78]</a></span> -brown, and finally colorless, showing that the starch has all -disappeared. This is due to the action of the diastase which was -present in the germinating seeds, and which was dissolved out and added -to the starch mixture. The office of this diastase is to change the -starch in the seeds to sugar. Germinating wheat is sweet, and it is a -matter of common observation that bread made from sprouted wheat is sweet.</p> - -<p>(<i>d</i>) Put a little starch-paste in a test tube and cover it with saliva -from the mouth. After ten or fifteen minutes test with Fehling’s -solution. A strong reaction appears showing how quickly and effectively -saliva acts in converting starch to sugar. Successive tests with iodine -will show the gradual disappearance of the starch.</p> - -<p><b>161. These experiments have shown us that diastase</b> from three -different sources can act upon starch converting it into sugar. The -active principle in the saliva is an <i>animal</i> diastase (<i>ptyalin</i>), -which is necessary as one step in the digestion of starch food in -animals. The <i>taka</i> diastase is derived from a fungus (Eurotium oryzæ) -which feeds on the starch in rice grains converting it into sugar -which the fungus absorbs for food. The <i>malt</i> diastase and <i>leaf</i> -diastase are formed by the seed plants. That in seeds converts the -starch to sugar which is absorbed by the embryo for food. That in the -leaf converts the starch into sugar so that it can be transported to -other parts of the plant to be used in building new tissue, or to be -stored again in the form of starch (example, the potato, in seeds, -etc.). The starch is formed in the leaf during the daylight. The light -renders the leaf diastase inactive. But at night the leaf diastase -becomes active and converts the starch made during the day. Starch is -not soluble in water, while the sugar is, and the sugar in solution is -thus easily transported throughout the plant. In those green plants -which do not form starch in their leaves (sugar beet, corn, and many -monocotyledons), grape sugar and fruit sugar are formed in the green -parts as the result of photosynthesis. In some, like the corn, the -grape sugar formed in the leaves is transported to other parts of the -plant, and some of it is stored up in the seed as starch. In others -like the sugar beet the glucose and fruit sugar formed in the leaves -flow to other parts of the plant, and much of it is stored up as cane -sugar in the beet root. The process of photosynthesis probably proceeds -in the same way in all cases up to the formation of the grape sugar and -fruit sugar in the leaves. In the beet, corn, etc., the process stops -here, while in the bean, clover, and most dicotyledons the process is -carried one step farther in the leaf and starch is formed. -<span class="pagenum"><a name="Page_79" id="Page_79">[Pg 79]</a></span></p> - -<h4><a name="VIII_3" id="VIII_3">3. Rough Analysis of Plant Substance.</a></h4> - -<p><b>162. Some simple experiments to indicate the nature of plant -substance.</b>—After these building-up processes of the plant, it is -instructive to perform some simple experiments which indicate roughly -the nature of the plant substance, and serve to show how it can be -separated into other substances, some of them being reduced to the -form in which they existed when the plant took them as food. For exact -experiments and results it would be necessary to make chemical analyses.</p> - -<p><b>163. The water in the plant.</b>—Take fresh leaves or leafy shoots -or other fresh plant parts. Weigh. Permit them to remain in a dry room -until they are what we call “dry.” Now weigh. The plants have lost -weight, and from what we have learned in studies of transpiration this -loss in weight we know to result from the loss of water from the plant.</p> - -<p><b>164. The dry plant material contains water.</b>—Take air-dry -leaves, shavings, or other dry parts of plants. Place them in a test -tube. With a holder rest the tube in a nearly horizontal position, -with the bottom of the tube in the flame of a Bunsen burner. Very -soon, before the plant parts begin to “burn,” note that moisture is -accumulating on the inner surface of the test tube. This is water -driven off which could not escape by drying in air, without the -addition of artificial heat, and is called “hygroscopic water.”</p> - -<p><b>165. Water formed on burning the dry plant material.</b>—Light a -soft-pine or basswood splinter. Hold a thistle tube in one hand with the -bulb downward and above the flame of the splinter. Carbon will be -deposited over the inner surface of the bulb. After a time hold the -tube toward the window and look through it above the carbon. Drops of -water have accumulated on the inside of the tube. This water is formed -by the rearrangement of some of the hydrogen and oxygen, which is set -free by the burning of the plant material, where they were combined -with carbon, as in the cellulose, and with other elements.</p> - -<p><b>166. Formation of charcoal by burning.</b>—Take dried leaves, and -shavings from some soft wood. Place in a porcelain crucible, and cover -about 3 cm. deep with dry fine earth. Place the crucible in the flame -of a Bunsen burner and let it remain for about fifteen minutes. Remove -and empty the contents. If the flame was hot the plant material will be -reduced to a good quality of charcoal. The charcoal consists largely of -carbon.</p> - -<p><b>167. The ash of the plant.</b>—Place in the porcelain crucible -dried leaves and shavings as before. Do not cover with earth. Place the -crucible in the flame of the Bunsen burner, and for a moment place on -the porcelain cover; then remove the cover, and note the moisture on -the under surface from the escaping water. Permit the plant material to -burn; it may even flame for a time. In the course of fifteen minutes it -<span class="pagenum"><a name="Page_80" id="Page_80">[Pg 80]</a></span> -is reduced to a whitish powder, much smaller in bulk than the charcoal -in the former experiment. This is the ash of the plant.</p> - -<p><b>168. What has become of the carbon?</b>—In this experiment the air -was not excluded from the plant material, so that oxygen combined with -carbon as the water was freed, and formed carbon dioxide, passing off -into the air in this form. This it will be remembered is the form in -which the plant took the carbon-food in through the leaves. Here the -carbon dioxide met the water coming from the soil, and the two united -to form, ultimately, starch, cellulose, and other compounds of carbon; -while with the addition of nitrogen, sulphur, etc., coming also from -the soil, still other plant substances were formed.</p> - -<p><b>169.</b> The carbohydrates are classed among the non-nitrogenous -substances. Other non-nitrogenous plant substances are the organic -acids like oxalic acid (H₂C₂O₄), malic acid (H₂C₄H₄O₅), etc.; the fats -and fixed oils, which occur in the seeds and fruits of many plants. Of -the nitrogenous substances the proteids have a very complex chemical -formula and contain carbon, hydrogen, oxygen, nitrogen, sulphur, etc. -(example, <i>aleuron</i>, or proteid grains, found in seeds). The proteids -are the source of nitrogenous food for the seedling during germination. -Of the amides, <i>asparagin</i> (C₄H₈N₂O₃) is an example of a nitrogenous -substance; and of the alkaloids, nicotin (C₁₀H₁₄N₂) from tobacco.</p> - -<p>All living plants contain a large per cent of water. According to -Vines “ripe seeds dried in the air contain 12 to 15 per cent of water, -herbaceous plants 60 to 80 per cent, and many water plants and fungi as -much as 95 per cent of their weight.” When heated to 100° C. the water -is driven off. The dry matter remaining is made up partly of organic -compounds, examples of which are given above, and inorganic compounds. -By burning this dry residue the organic substances are mostly changed -into volatile products, principally carbonic acid, water, and nitrogen. -The inorganic substances as a result of combustion remain as a white or -gray powder, the <i>ash</i>.</p> - -<p>The amount of the ash increases with the age of the plant, though the -percentage of ash may vary at different times in the different members -of the plant. The following table taken from Vines will give an idea of -the amount and composition of the ash in the dry solid of a few plants:</p> - -<p class="f120 space-above2">CONTENT OF 1000 PARTS OF DRY SOLID MATTER.</p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" rules="cols" > - <thead><tr> - <th class="tdc bb" colspan="7"> </th> - </tr><tr> - <th class="tdc bb"> </th> - <th class="tdc bb"> Clover, in <br /> blossom</th> - <th class="tdc bb"> Wheat, <br /> grain</th> - <th class="tdc bb"> Wheat, <br /> straw</th> - <th class="tdc bb"> Potato <br />tubers</th> - <th class="tdc bb"> Apples </th> - <th class="tdc bb"> Peas<br /> (the seed)</th> - </tr> - </thead> - <tbody><tr> - <td class="tdl">Ash</td> - <td class="tdr_ws1">68.3 </td> - <td class="tdr_ws1">19.7 </td> - <td class="tdr_ws1">53.7 </td> - <td class="tdr_ws1">37.7 </td> - <td class="tdr_ws1">14.4</td> - <td class="tdr">27.3 </td> - </tr><tr> - <td class="tdl">Potash.</td> - <td class="tdr_ws1">21.96</td> - <td class="tdr_ws1">6.14</td> - <td class="tdr_ws1">7.33</td> - <td class="tdr_ws1">22.76</td> - <td class="tdr_ws1">5.14</td> - <td class="tdr">11.41</td> - </tr><tr> - <td class="tdl">Soda.</td> - <td class="tdr_ws1">1.39</td> - <td class="tdr_ws1">0.44</td> - <td class="tdr_ws1">0.74</td> - <td class="tdr_ws1">0.99</td> - <td class="tdr_ws1">3.76</td> - <td class="tdr">0.26</td> - </tr><tr> - <td class="tdl">Lime.</td> - <td class="tdr_ws1">24.06</td> - <td class="tdr_ws1">0.66</td> - <td class="tdr_ws1">3.09</td> - <td class="tdr_ws1">0.97</td> - <td class="tdr_ws1">0.59</td> - <td class="tdr">1.36</td> - </tr><tr> - <td class="tdl">Magnesium.</td> - <td class="tdr_ws1">7.44</td> - <td class="tdr_ws1">2.36</td> - <td class="tdr_ws1">1.33</td> - <td class="tdr_ws1">1.77</td> - <td class="tdr_ws1">1.26</td> - <td class="tdr">2.17</td> - </tr><tr> - <td class="tdl">Ferric Oxide.</td> - <td class="tdr_ws1">0.72</td> - <td class="tdr_ws1">0.26</td> - <td class="tdr_ws1">0.33</td> - <td class="tdr_ws1">0.45</td> - <td class="tdr_ws1">0.2 </td> - <td class="tdr">0.16</td> - </tr><tr> - <td class="tdl">Phosphoric Acid. </td> - <td class="tdr_ws1">6.74</td> - <td class="tdr_ws1">9.26</td> - <td class="tdr_ws1">2.58</td> - <td class="tdr_ws1">6.53</td> - <td class="tdr_ws1">1.96</td> - <td class="tdr">9.95</td> - </tr><tr> - <td class="tdl">Sulphuric Acid.</td> - <td class="tdr_ws1">2.06</td> - <td class="tdr_ws1">0.07</td> - <td class="tdr_ws1">1.32</td> - <td class="tdr_ws1">2.45</td> - <td class="tdr_ws1">0.88</td> - <td class="tdr">0.95</td> - </tr><tr> - <td class="tdl">Silica.</td> - <td class="tdr_ws1">1.62</td> - <td class="tdr_ws1">0.42</td> - <td class="tdr_ws1">36.25</td> - <td class="tdr_ws1">0.8 </td> - <td class="tdr_ws1">0.62</td> - <td class="tdr">0.24</td> - </tr><tr> - <td class="tdl">Chlorine.</td> - <td class="tdr_ws1">2.66</td> - <td class="tdr_ws1">0.04</td> - <td class="tdr_ws1">0.9 </td> - <td class="tdr_ws1">1.17</td> - <td class="tdr_ws1">....</td> - <td class="tdr">0.42</td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_81" id="Page_81">[Pg 81]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_IX" id="CHAPTER_IX">CHAPTER IX.</a><br /> -<span class="h_subtitle">HOW PLANTS OBTAIN THEIR FOOD. I.</span></h3> -</div> - -<h4><a name="IX_1" id="IX_1">1. Sources of Plant Food.</a></h4> - -<p><b>170. The necessary constituents of plant food.</b>—As indicated in -<a href="#CHAPTER_III">Chapter 3</a>, investigation has taught us the principal constituents of -plant food. Some suggestion as to the food substances is derived by a -chemical analysis of various plants. In <a href="#CHAPTER_VIII">Chapter 8</a> it was noted that -there are two principal kinds of compounds in plant substances, the -organic compounds and the inorganic compounds or mineral substances. -The principal elements in the organic compounds are <i>hydrogen</i>, -<i>carbon</i>, <i>oxygen</i> and <i>nitrogen</i>. The elements in the inorganic -compounds which have been found indispensable to plant growth are -<i>calcium</i>,<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a> -<i>potassium</i>, <i>magnesium</i>, <i>phosphorus</i>, <i>sulphur</i> and -<i>iron</i>. (<a href="#PARA_54">See paragraphs 54-58</a>, and complete observations -on water cultures.) Other elements are found in the ash of plants; and while -they are not absolutely necessary for growth, some<a name="FNanchor_13_13" id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a> -of them are beneficial in one way or another.</p> - -<p><b>171.</b> The carbohydrates are derived, as we have learned, from -the CO₂ of the air, and water in the plant tissue drawn from the soil; -though in the case of aquatic plants entirely submerged, all the -constituents are absorbed from the surrounding water.</p> - -<p><b>172. Food substances in the soil.</b>—Land plants derive their -mineral food from the soil, the soil received the mineral substances -from dissolving and disintegrating rocks. Nitrogenous food is chiefly -derived from the same source, but under a variety of conditions which -will be discussed in later paragraphs, but the nitrogen comes primarily -from the air. Some of the mineral substances, those which are soluble -as well as some of the nitrogenous substances, are found in solution in -the soil. These are absorbed by the plant, as needed, along with water, -through the root hairs. -<span class="pagenum"><a name="Page_82" id="Page_82">[Pg 82]</a></span></p> - -<p><b>173. Absorption of soluble substances.</b>—Since these substances -are dissolved in the water of the soil, it is not necessary for us -to dwell on the process of absorption. This in general is dwelt upon -in <a href="#CHAPTER_III">Chapter 3</a>. It should be noted, however, that food substances in -solution, during absorption, diffuse through the protoplasmic membrane -independently of each other and also independently of the rate of -movement of the water from the soil into the root hairs and cells of -the root.</p> - -<p>When the cells have absorbed a certain amount of a given substance, -no more is absorbed until the concentration of the cell-sap in that -particular substance is reduced. This, however, does not interfere -with the absorption of water, or of other substances in solution by -the same cells. Plants have therefore a certain selective power in the -absorption of food substances.</p> - -<p><b>174. Action of root hairs on insoluble substances. Acidity of root -hairs.</b>—If we take a seedling which has been grown in a germinator, -or in the folds of cloths or paper, so that the roots are free from the -soil, and touch the moist root hairs to blue litmus paper, the paper -becomes red in color where the root hairs have come in contact. This -is the reaction for the presence of an acid salt, and indicates that -the root hairs excrete certain acid substances. This acid property of -the root hairs serves a very important function in the preparation -of certain of the elements of plant food in the soil. Certain of the -chemical compounds of potash, phosphoric acid, etc., become deposited -on the soil particles, and are not soluble in water. The acid of the -root hairs dissolves some of these compounds where the particles of -soil are in close contact with them, and the solutions can then be -taken up by the roots. Carbonic acid and other acids are also formed in -the soil, and aid in bringing these substances into solution.</p> - -<p><b>175.</b> This corrosive action of the roots can be shown by the -well-known experiment of growing a plant on a marble plate which is -covered by soil. In lieu of the marble plate, the peas may be planted -in clam or oyster shells, which are then buried in the soil of the -pot, so that the roots of the seedlings will come in contact with the -smooth surface of the shell. After a few weeks, if the soil be washed -from the marble where the roots have been in close contact, there will -be an outline of this part of the root system. Several different acid -substances are excreted from the roots of plants which have been found -to redden blue litmus paper by contact. Experiments by Czapek show, -however, that the carbonic acid excreted by the roots has the power of -<span class="pagenum"><a name="Page_83" id="Page_83">[Pg 83]</a></span> -directly bringing about these corrosion phenomena. The acid salts are -the substances which are most actively concerned in reddening the blue -litmus paper. They do not directly aid in the corrosion phenomena. In -the soil, however, where these compounds of potash, phosphoric acid, -etc., are which are not soluble in water, the acid salt (primary acid -potassium phosphate) which is most actively concerned in reddening -the blue litmus paper may act indirectly on these mineral substances, -making them available for plant food. This salt soon unites with -certain chlorides in the soil, making among other things small -quantities of hydrochloric acid.</p> - -<p><b>176.</b> <span class="smcap">Note.</span>—It is a general rule that plants -cannot take solid food into their bodies, but obtain all food in either a -liquid or gaseous state. The only exception to this is in the case of -the plasmodia of certain <i>Myxomycetes</i> (Slime Moulds), and also perhaps -some of the Flagellates and other very low forms, which engulf solid -particles of food. It is uncertain, however, whether these organisms -belong to the plant or animal kingdom, and they probably occupy a more -or less intermediate position.</p> - -<p><b>177. Action of nitrite and nitrate bacteria.</b>—Many of the -higher green plants prefer their nitrogenous food in the form of -nitrates. (Example, nitrate of soda, potassium nitrate, saltpetre.) -Nitrates are constantly being formed in soil by the action of certain -bacteria. The nitrite bacteria (Nitromonas) convert ammonia in the -soil to <i>nitrous acid</i> (a <i>nitrite</i>), while at this point the nitrate -bacteria (Nitrobacter) convert the nitrites into nitrates. The fact -that this nitrification is going on constantly in soil is of the utmost -importance, for while commercial nitrates are often applied to the -soil, the nitrates are easily washed from the soil by heavy rains. -These nitrite and nitrate bacteria require oxygen for their activity, -and they are able to obtain their carbohydrates by decomposing organic -matter in the soil, or directly by assimilating the CO₂ in the soil, -deriving the energy for the assimilation of the carbon dioxide from -the chemical process of nitrification. This kind of carbon dioxide -assimilation is called <i>chemosynthetic</i> assimilation.</p> - -<h4><a name="IX_2" id="IX_2">2. Parasites and Saprophytes.</a></h4> - -<p><b>178. Parasites among the fungi.</b>—A parasite is an organism -which derives all or a part of its food directly from another living -organism (its host) and at the latter’s expense. The larger number -of plant parasites are found among the fungi (rusts, smuts, mildews, -etc.). (<a href="#PARA_185">See Nutrition of the Fungi, paragraph 185</a>.) Some -of these are not capable of development unless upon their host, and are called -<i>obligate</i> parasites. Others can grow not only as parasites but at -other times can also grow on dead organic matter, and are called -<i>facultative</i> parasites, i.e. they can choose either a parasitic life -or a saprophytic one.</p> - -<p><a id="PARA_179" name="PARA_179"><b>179. Parasites among the seed plants.</b></a>—<i>Cuscuta.</i>—There are, -however, parasites among the seed plants; for example, the dodder -<span class="pagenum"><a name="Page_84" id="Page_84">[Pg 84]</a></span> -(Cuscuta), parasitic on clover, and a great variety of other plants. -There is food enough in the seed for the young plant to take root and -develop a slender stem until it takes hold of its host. It then twines -around the stem of its host sending wedge-shaped haustoria into the -stem to obtain food. The part then in connection with the ground dies.</p> - -<p>The haustoria of the dodder form a complete junction with the vascular -bundles of its host so that through the vessels water and salts are -obtained, while through the junction of sieve tubes the elaborated -organic food is obtained. The union of the dodder with its host is like -that between a graft and the graft stock. The beech drops (Epiphegus) -is another example of a parasitic seed plant. It is parasitic on the -roots of the beech.</p> - -<div class="figcenter"> - <img src="images/fig74.jpg" alt="" width="500" height="556" /> - <p class="center">Fig. 74.<br /> Dodder.</p> -</div> - -<p><b>180. The mistletoe</b> (Viscum album), which grows on the branches -of trees, sends its roots into the branches, and only the vessels -of the vascular system are fused according to some. If this is true -then it probably obtains only water and salts from its host. But the -mistletoe has green leaves and is thus able to assimilate carbon -<span class="pagenum"><a name="Page_85" id="Page_85">[Pg 85]</a></span> -dioxide and manufacture its own organic substances. It is claimed by -some, however, that the host derives some food from the parasite during -the winter when the host has shed its leaves, and if this is true it -would seem that organic food could also be derived during the summer -from the host by the mistletoe.</p> - -<p><b>181. Saprophytes.</b>—A saprophyte is a plant which is enabled -to obtain its food, especially its organic food, directly from dead -animals or plants or from dead organic substances. Many fungi are -saprophytes, as the moulds, mushrooms, etc. (<a href="#PARA_185">See Nutrition of the Fungi</a>.)</p> - -<p><a id="PARA_182" name="PARA_182"><b>182. Humus saprophytes.</b></a>—The -action of fungi as described in the preceding chapter, as well as of -certain bacteria, gradually converts the dead plants or plant parts -into the finely powdered brown substance known as <i>humus</i>. In general -the green plants cannot absorb organic food from humus directly. But -plants which are devoid of chlorophyll can live saprophytically on this -humus. They are known as <i>humus saprophytes</i>. Many of the mushrooms -and other fungi, as well as some seed plants which lack chlorophyll or -possess only a small quantity, are able to absorb all their organic -food from humus. It is uncertain whether any seed plants can obtain -all of their organic food directly from humus, though it is believed -that many can so obtain a portion of it. But a number of seed plants, -like the Indian-pipe (Monotropa) and certain orchids, obtain organic -food from humus. These plants lack chlorophyll and cannot therefore -manufacture their own carbohydrate food. Not being parasitic on plants -which can, as in the case of the dodder and beech drops mentioned -above, they undoubtedly derive their organic food from the humus. But -fungus mycelium growing in the humus is attached to their roots, and -in some orchids enters the roots and forms a nutritive connection. The -fungus mycelium can absorb organic food from the humus and in some -cases at least can transfer it over to the roots of the higher plant -(<a href="#IX_4">see Mycorhiza</a>).</p> - -<p><b>183. Autotrophic, heterotrophic, and mixotrophic plants.</b>—An -<i>autotrophic</i> plant is one which is self-nourishing, i.e. it is -provided with an abundant chlorophyll apparatus for carbon dioxide -assimilation and with absorbing organs for obtaining water and salts. -Heterotrophic plants are not provided with a chlorophyll apparatus -sufficient to assimilate all the carbon dioxide necessary, so they -nourish themselves by other means. <i>Mixotrophic</i> plants are those -which are intermediate between the other two, i.e. they have some -chlorophyll but not enough to provide all the organic food necessary, -so they obtain a portion of it by other means. Evidently there are all -gradations of mixotrophic plants between the two other kinds (example, -the mistletoe).</p> - -<p><b>184. Symbiosis.</b>—Symbiosis means a living with or living -together, and is said of those organisms which live so closely in -connection with each other as to be influenced for better or worse, -especially from a nutrition standpoint. <i>Conjunctive</i> symbiosis has -<span class="pagenum"><a name="Page_86" id="Page_86">[Pg 86]</a></span> -reference to those cases where there is a direct interchange of -food material between the two organisms (lichens, mycorhiza, etc.). -<i>Disjunctive</i> symbiosis has reference to an inter-life relation without -any fixed union between them (example, the relations between flowers -and insects, ants and plants, and even in a broad sense the relation -between saprophytic plants in reducing organic matter to a condition -in which it may be used for food by the green plants, and these in -turn provide organic matter for the saprophytes to feed upon, etc.). -<i>Antagonistic</i> symbiosis is shown in the relation of parasite to its -host, <i>reciprocal</i> symbiosis, or <i>mutualistic</i> symbiosis is shown -in those cases where both symbionts derive food as a result of the union -(lichens, mycorhiza, etc.).</p> - -<h4><a name="IX_3" id="IX_3">3. How Fungi Obtain their Food.</a></h4> - -<div class="figleft"> - <img id="FIG_75" src="images/fig75.jpg" alt="" width="200" height="349" /> - <p class="center">Fig. 75.<br /> Carnation rust on leaf<br /> - and flower stem.<br /> From photograph.</p> -</div> - -<p><a id="PARA_185" name="PARA_185"><b>185. Nutrition of moulds.</b></a>—In -our study of mucor, as we have seen, the growing or vegetative part of -the plant, the mycelium, lies within the substratum, which contains the -food materials in solution, and the slender threads are thus bathed on -all sides by them. The mycelium absorbs the watery solutions throughout -the entire system of ramifications. When the upright fruiting threads -are developed they derive the materials for their growth directly from -the mycelium with which they are in connection. The moulds which grow -on decaying fruit or on other organic matter derive their nutrient -materials in the same way. The portion of the mould which we usually -see on the surface of these substances is in general the fruiting part. -The larger part of the mycelium lies hidden within the substratum.</p> - -<p><a id="PARA_186" name="PARA_186"> </a><b>186. Nutrition of parasitic fungi.</b>—Certain -of the fungi grow on or within the higher plants and derive their food materials from them -and at their expense. Such a fungus is called a <i>parasite</i>, and there -<span class="pagenum"><a name="Page_87" id="Page_87">[Pg 87]</a></span> -are a large number of these plants which are known as <i>parasitic -fungi</i>. The plant at whose expense they grow is called the “<i>host</i>.”</p> - -<p>One of these parasitic fungi, which it is quite easy to obtain in -greenhouses or conservatories during the autumn and winter, is the -carnation rust (<i>Uromyces caryophyllinus</i>), since it breaks out in -rusty dark brown patches on the leaves and stems of the carnation (see -<a href="#FIG_75">fig. 75</a>). If we make thin cross-sections through one of these -spots on a leaf, and place them for a few minutes in a solution of chloral -hydrate, portions of the tissues of the leaf will be dissolved. After -a few minutes we wash the sections in water on a glass slip, and stain -them with a solution of eosin. If the sections were carefully made, and -thin, the threads of the mycelium will be seen coursing between the -cells of the leaf as slender threads. Here and there will be seen short -branches of these threads which penetrate the cell wall of the host and -project into the interior of the cell in the form of an irregular knob. -Such a branch is a <i>haustorium</i>. By means of this haustorium, which is -<span class="pagenum"><a name="Page_88" id="Page_88">[Pg 88]</a></span> -here only a short branch of the mycelium, nutritive substances are -taken by the fungus from the protoplasm or cell-sap of the carnation. -From here it passes to the threads of the mycelium. These in turn -supply food material for the development of the dark brown gonidia, -which we see form the dark-looking powder on the spots. Many other -fungi form haustoria, which take up nutrient matters in the way -described for the carnation rust. In the case of other parasitic fungi -the threads of the mycelium themselves penetrate the cells of the host, -while in still others the mycelium courses only between the cells of -the host (fungus of peach leaf curl for example) and derives food -materials from the protoplasm or cell-sap of the host by the process of -osmosis.</p> - -<div class="figcenter"> - <img src="images/fig76.jpg" alt="" width="600" height="139" /> - <p class="center">Fig. 76.<br /> Several teleutospores, showing the variations in form.</p> -</div> -<div class="figcenter"> - <img src="images/fig77.jpg" alt="" width="600" height="348" /> - <p class="center">Fig. 77.<br /> Cells from the stem of a rusted carnation,<br /> - showing the intercellular mycelium and haustoria.<br /> - Object magnified 30 times more than the scale.</p> -</div> -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig78.jpg" alt="" width="150" height="252" /> - <p class="center">Fig. 78.<br /> Cell from carnation leaf,<br /> - showing haustorium of rust<br /> mycelium grasping the<br /> - nucleus of the host. <i>h</i>,<br /> haustorium; <i>n</i>,<br /> - nucleus of host.</p> - </div> - <div class="figsub"> - <img src="images/fig79.jpg" alt="" width="300" height="281" /> - <p class="center">Fig. 79.<br /> Intercellular mycelium with haustoria entering the cells.<br /> - <i>A</i>, of Cystopus candidus (white rust); <br /> - <i>B</i>, of Peronospora calotheca. (De Bary.)<br /></p> - </div> -</div> - -<p><b>187. Nutrition of the larger fungi.</b>—If we select some one of -the larger fungi, the majority of which belong to the mushroom family -and its relatives, which is growing on a decaying log or in the soil, -we shall see on tearing open the log, or on removing the bark or part -of the soil, as the case may be, that the stem of the plant, if it have -one, is connected with whitish strands. During the spring, summer, or -autumn months, examples of the mushrooms connected with these strands -may usually be found readily in the fields or woods, but during the -<span class="pagenum"><a name="Page_89" id="Page_89">[Pg 89]</a></span> -winter and colder parts of the year often they may be seen in forcing -houses, especially those cellars devoted to the propagation of the -mushroom of commerce.</p> - -<p><b>188.</b> These strands are made up of numerous threads of the -mycelium which are closely twisted and interwoven into a cord or -strand, which is called a mycelium strand, or <i>rhizomorph</i>. These are -well shown in <a href="#FIG_236">fig. 236</a>, which is from a photograph of the -mycelium strands, or “spawn” as the grower of mushrooms calls it, of Agaricus -campestris. The little knobs or enlargements on the strands are the -young fruit bodies, or “buttons.”</p> - -<div class="figcenter"> - <img id="FIG_80" src="images/fig80.jpg" alt="" width="500" height="460" /> - <p class="center">Fig. 80.<br /> Sterile mycelium on wood props in coal mine,<br /> - 400 feet below surface.</p> - <p class="author">(Photographed by the author.)</p> -</div> - -<p><b>189.</b> While these threads or strands of the mycelium in the -<span class="pagenum"><a name="Page_90" id="Page_90">[Pg 90]</a></span> -decaying wood or in the decaying organic matter of the soil are not -true roots, they function as roots, or root hairs, in the absorption -of food materials. In old cellars and on damp soil in moist places we -sometimes see fine examples of this vegetative part of the fungi, the -mycelium. But most magnificent examples are to be seen in abandoned -mines where timber has been taken down into the tunnels far below -the surface of the ground to support the rock roof above the mining -operations. I have visited some of the coal mines at Wilkesbarre, Pa., -and here on the wood props and doors, several hundred feet below the -surface, and in blackest darkness, in an atmosphere almost completely -saturated at all times, the mycelium of some of the wood destroying -fungi grows in a profusion and magnificence which is almost beyond -belief. <a href="#FIG_80">Fig. 80</a> is from a flash-light photograph of a beautiful -example 400 feet below the surface of the ground. This was growing over the -surface of a wood prop or post, and the picture is much reduced. On -the doors in the mine one can see the strands of the mycelium which -radiate in fan-like figures at certain places near the margin of -growth, and farther back the delicate tassels of mycelium which hang -down in fantastic figures, all in spotless white and rivalling the most -beautiful fabric in the exquisiteness of its construction.</p> - -<p><b>190. How fungi derive carbohydrate food.</b>—The fungi being -devoid of chlorophyll cannot assimilate the CO₂ from the air. They -are therefore dependent on the green plants for their carbohydrate -food. Among the saprophytes, the leaf and wood destroying fungi -excrete certain substances (known as <i>enzymes</i>) which dissolve the -carbohydrates and certain other organic compounds in the woody or -leafy substratum in which they grow. They thus produce a sort of -extracellular digestion of carbohydrates, converting them into a -soluble form which can be absorbed by the mycelium. The parasitic -fungi also obtain their carbohydrates and other organic food from the -host. The mycelium of certain parasitic, and of wood destroying fungi, -excretes enzymes (<i>cytase</i>) which dissolve minute perforations in the -cell walls of the host and thus aid the hypha during its boring action -in penetrating cell walls.</p> - -<p><span class="smcap">Note.</span>—Certain wood destroying fungi growing in oaks absorb -tannin directly, i.e. in an unchanged form. One of the pine destroying -fungi (<i>Trametes pini</i>) absorbs the xylogen from the wood cells, -leaving the pure cellulose in which the xylogen was filtrated; while -<i>Polyporus mollis</i> absorbs the cellulose, leaving behind only the wood element. -<span class="pagenum"><a name="Page_91" id="Page_91">[Pg 91]</a></span></p> - -<h4><a name="IX_4" id="IX_4">4. Mycorhiza.</a></h4> - -<p><b>191.</b> While such plants as the Indian-pipe (Monotropa), some -of the orchids, etc., are <i>humus saprophytes</i> and some of them are -possibly able to absorb organic food from the humus, many of them have -fungus mycelium in close connection with their roots, and these fungus -threads aid in the absorption of organic food. The roots of plants -which have fungus mycelium intimately associated in connection with -the process of nutrition, are termed <i>mycorhiza</i>. There is a mutual -interchange of food between the fungus and the host, a <i>reciprocal -symbiosis</i>.</p> - -<p><b>192. Mycorhiza are of two kinds</b> as regards the relation of -the fungus to the root; <i>ectotrophic</i> (or <i>epiphytic</i>), where the -mycelium is chiefly on the outside of the root, and <i>endotrophic</i> (or -<i>endophytic</i>) where the mycelium is chiefly within the tissue of the root.</p> - -<p><b>193. Ectotrophic mycorhiza.</b>—Ectotrophic mycorhiza occur on the -roots of the oak, beech, hornbean, etc., in forests where there is a -great deal of humus from decaying leaves and other vegetation. The -young growing roots of these trees become closely covered with a thick -felt of the mycelium, so that no root hairs can develop. The terminal -roots also branch profusely and are considerably thickened. The fungus -serves here as the absorbent organ for the tree. It also acts on the -humus, converting some of it into available plant food and transferring -it over to the tree.</p> - -<p><b>194. Endotrophic mycorhiza.</b>—These are found on many of the -humus saprophytes, which are devoid of chlorophyll, as well as on those -possessing little or even on some plants possessing an abundance, of -chlorophyll. Examples are found in many orchids (see the coral root -orchid, for example), some of the ferns (Botrychium), the pines, -leguminous plants, etc. In endotrophic mycorhiza the mycelium is more -abundant within the tissues of the root, though some of the threads -extend to the outside. In the case of the mycorhiza on the humus -saprophytes which have no chlorophyll, or but little, it is thought -by some that the fungus mycelium in the humus assists in converting -organic substances and carbohydrates into a form available for food -by the higher plant and then conducts it into the root, thus aiding -also in the process of absorption, since there are few or no root -hairs on the short and fleshy mycorhiza. The roots, however, of some -of these humus saprophytes have the power of absorbing a portion of -their organic compounds from the humus. It is thought by some, though -not definitely demonstrated, that in the case of the oaks, beeches, -hornbeans, and other chlorophyll-bearing symbionts, the fungus threads -do not absorb any carbohydrates for the higher symbiont, but that they -actually derive their carbohydrates from it.<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" class="fnanchor">[14]</a> -But it is reasonably certain that the fungus threads do assimilate from -<span class="pagenum"><a name="Page_92" id="Page_92">[Pg 92]</a></span> -the humus certain unoxidized, or feebly oxidized, nitrogenous -substances (ammonia, for example), and transfer them over to the host, -for the higher plants with difficulty absorb these substances, while -they readily absorb nitrates which are not abundant in humus. This is -especially important in the forest. It is likely therefore.</p> - -<h4><a name="IX_5" id="IX_5">5. Nitrogen gatherers.</a></h4> - -<div class="figleft"> - <img id="FIG_81" src="images/fig81.jpg" alt="" width="150" height="225" /> - <p class="center">Fig. 81.<br /> Root of the<br /> common vetch,<br /> - showing root<br /> tubercles.</p> -</div> - -<p><b>195. How clovers, peas, and other legumes gather nitrogen.</b>—It -has long been known that clover plants, peas, beans, and many other -leguminous plants are often able to thrive in soil where the cereals -do but poorly. Soil poor in nitrogenous plant food becomes richer in -this substance where clovers, peas, etc., are grown, and they are often -planted for the purpose of enriching the soil. Leguminous plants, -especially in poor soil, are almost certain to have enlargements, in -the form of nodules, or “root-tubercles.” A root of the common vetch -with some of these root-tubercles is shown in <a href="#FIG_81">fig. 81</a>.</p> - -<p><b>196. A fungal or bacterial organism in these root-tubercles.</b>—If -we cut one of these root-tubercles open, and mount a small portion -of the interior in water for examination with the microscope, we -shall find small rod-shaped bodies, some of which resemble bacteria, -while others are more or less forked into forms like the letter Y, as -shown in <a href="#FIG_82">fig. 82</a>. These bodies are rich in nitrogenous -substances, or proteids. They are portions of a minute organism, of a fungus or -bacterial nature, which attacks the roots of leguminous plants and -causes these nodular outgrowths. The organism (Phytomyxa leguminosarum) -exists in the soil and is widely distributed where legumes grow. -<span class="pagenum"><a name="Page_93" id="Page_93">[Pg 93]</a></span></p> - -<p><b>197. How the organism gets into the roots of the legumes.</b>—This -minute organism in the soil makes its way through the wall of a root -hair near the end. It then grows down the interior of the root hair in -the form of a thread. When it reaches the cell walls it makes a minute -perforation, through which it grows to enter the adjacent cell, when it -enlarges again. In this way it passes from the root hair to the cells -of the root and down to near the center of the root. As soon as it -begins to enter the cells of the root it stimulates the cells of that -portion to greater activity. So the root here develops a large lateral -nodule, or “root-tubercle.” As this “root-tubercle” increases in size, -the fungus threads branch in all directions, entering many cells. The -threads are very irregular in form, and from certain enlargements it -appears that the rod-like bodies are formed, or the thread later breaks -into myriads of these small “bacteroids.”</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_82" src="images/fig82.jpg" alt="" width="250" height="165" /> - <p class="center">Fig. 82.<br /> Root-tubercle organism from<br /> vetch, old condition.</p> - </div> - <div class="figsub"> - <img id="FIG_83" src="images/fig83.jpg" alt="" width="250" height="151" /> - <p class="center">Fig. 83.<br /> Root-tubercle organism from<br /> Medicago denticulata.</p> - </div> -</div> - -<p><b>198. The root organism assimilates free nitrogen for its -host.</b>—This organism assimilates the free nitrogen from the air -in the soil, to make the proteid substance which is found stored in -the bacteroids in large quantities. Some of the bacteroids, rich in -proteids, are dissolved, and the proteid substance is made use of by -the clover or pea, as the case may be. This is why such plants can -thrive in soil with a poor nitrogen content. Later in the season some -of the root-tubercles die and decay. In this way some of the proteid -substance is set free in the soil. The soil thus becomes richer in -nitrogenous plant food.</p> - -<p>The forms of the bacteroids vary. In some of the clovers they are oval, -in vetch they are rod-like or forked, and other forms occur in some of -the other genera.</p> - -<p class="blockquot"><b>199.</b> <span class="smcap">Note.</span>—So -far as we know the legume tubercle organism does not assimilate free -nitrogen of the air unless it is within the root of the legume. But -there are microörganisms in the soil which are capable of assimilating -free nitrogen independently. Example, a bacterium, <i>Clostridium -pasteurianum</i>. Certain bacteria and algæ live in <i>contact symbiosis</i> -in the soil, the bacteria fixing free nitrogen, while in return for the -combined nitrogen, the algæ furnish the bacteria with carbohydrates. -It seems that these bacteria cannot fix the free nitrogen of the air -unless they are supplied with carbohydrates, and it is known that -<i>Clostridium pasteurianum</i> cannot assimilate free nitrogen unless -sugar is present.</p> - -<h4><a name="IX_6" id="IX_6">6. Lichens.</a></h4> - -<p><a id="PARA_200" name="PARA_200"><b>200. Nutrition of lichens.</b></a>—Lichens are very -curious plants which grow on rocks, on the trunks and branches of trees, and on the -soil. They form leaf-like expansions more or less green in color, or -brownish, or gray, or they occur in the form of threads, or small -<span class="pagenum"><a name="Page_94" id="Page_94">[Pg 94]</a></span> -tree-like formations. Sometimes the plant fits so closely to the rock -on which it grows that it seems merely to paint the rock a slightly -different color, and in the case of many which occur on trees there -appears to be to the eye only a very slight discoloration of the bark -of the trunk, with here and there the darker colored points where fruit -bodies are formed. The most curious thing about them is, however, -that while they form plant bodies of various form, these bodies are -of a “dual nature” as regards the organisms composing them. The plant -bodies, in other words, are formed of two different organisms which, -woven together, exist apparently as one. A fungus on the one hand grows -around and encloses in the meshes of its mycelium the cells or threads -of an alga, as the case may be.</p> - -<div class="figcenter"> - <img src="images/fig84.jpg" alt="" width="600" height="345" /> - <p class="center">Fig. 84.<br /> Frond of lichen (peltigera), showing rhizoids.</p> -</div> - -<p>If we take one of the leaf-like forms known as peltigera, which grows -on damp soil or on the surfaces of badly decayed logs, we see that the -plant body is flattened, thin, crumpled, and irregularly lobed. The -color is dull greenish on the upper side, while the under side is white -or light gray, and mottled with brown, especially the older portions. -Here and there on the under surface are quite long slender blackish -strands. These are composed entirely of fungus threads and serve as -organs of attachment or holdfasts, and for the purpose of supplying -the plant body with mineral substances which are in solution in the -water of the soil. If we make a thin section of the leaf-like portion -of a lichen as shown in <a href="#FIG_85">fig. 85</a>, we shall see that it is -composed of a mesh of colorless threads which in certain definite portions contain -entangled green cells. The colorless threads are those of the fungus, -while the green cells are those of the alga. These green cells of the -alga perform the function of chlorophyll bodies for the dual organism, -while the threads of the fungus provide the mineral constituents of -<span class="pagenum"><a name="Page_95" id="Page_95">[Pg 95]</a></span> -plant food. The alga, while it is not killed in the embrace of the -fungus, does not reach the perfect state of development which it -attains when not in connection with the fungus. On the other hand the -fungus profits more than the alga by this association. It forms fruit -bodies, and perfects spores in the special fruit bodies, which are so -very distinct in the case of so many of the species of the lichens. -These plants have lived for so long a time in this close association -that the fungi are rarely found separate from the algæ in nature, but -in a number of cases they have been induced to grow in artificial -cultures separate from the alga. This fact, and also the fact that the -algæ are often found to occur separate from the fungus in nature, is -regarded by many as an indication that the plant body of the lichens is -composed of two distinct organisms, and that the fungus is parasitic on -the alga.</p> - -<div class="figcenter"> - <img id="FIG_85" src="images/fig85.jpg" alt="" width="600" height="412" /> - <p class="center">Fig. 85.<br /> Lichen (peltigera), section of thallus; dark zone of rounded<br /> - bodies made up largely of the algal cells. Fungus cells<br /> - above, and threads beneath and among the algal cells.</p> -</div> - -<p><b>201.</b> Others regard the lichens as autonomous plants, that is, -the two organisms have by this long-continued community of existence -become unified into an individualized organism, which possesses a habit -<span class="pagenum"><a name="Page_96" id="Page_96">[Pg 96]</a></span> -and mode of life distinct from that of either of the organisms forming -the component parts. This community of existence between two different -organisms is called by some <i>mutualism</i>, or <i>symbiosis</i>. While -the alga enclosed within the meshes of the fungus is not so free to develop, -and probably does not attain the full development which it would alone -under favorable conditions, still it is very likely that it is often -preserved from destruction during very dry periods, within the tough -thallus, on the surface of bare rocks.</p> - -<div class="figcenter"> - <img id="FIG_86" src="images/fig86.jpg" alt="" width="600" height="331" /> - <p class="center">Fig. 86.<br /> Section of fruit body or apothecium - of lichen (parmelia),<br /> showing asci and spores of the fungus.</p> -</div> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_97" id="Page_97">[Pg 97]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_X" id="CHAPTER_X">CHAPTER X.</a><br /> -<span class="h_subtitle">HOW PLANTS OBTAIN THEIR FOOD, II.</span></h3> -</div> - -<h4><a name="X_1" id="X_1">Seedlings.</a></h4> - -<p><b>202.</b> It is evident from some of the studies which we have made -in connection with germination of seeds and nutrition of the plant -that there is a period in the life of the seed plants in which they -are able to grow if supplied with moisture, but may entirely lack any -supply of food substance from the outside, though we understand that -growth finally comes to a standstill unless they are supplied with food -from the outside. In connection with the study of the nutrition of the -plant, therefore, it will be well to study some of the representative -seeds and seedlings to learn more accurately the method of germination -and nutrition in seedlings during the germinating period.</p> - -<p><b>203. To prepare seeds for germination.</b>—Soak a handful of -seeds (or more if the class is large) in water for 12 to 24 hours. -Take shallow crockery plates, or ordinary plates, or a germinator -with a fluted bottom. Place in the bottom some sheets of paper, and -if sphagnum moss is at hand scatter some over the paper. If the moss -is not at hand, throw the upper layer of paper into numerous folds. -Thoroughly wet the paper and moss, but do not have an excess of water. -Scatter the seeds among the moss or the folds of the paper. Cover -with some more wet paper and keep in a room where the temperature is -about 20°C. to 25°C. The germinator should be looked after to see that -the paper does not become dry. It may be necessary to cover it with -another vessel to prevent the too rapid evaporation of the water. The -germinator should be started about a week before the seedlings are -wanted for study. Some of the soaked seeds should be planted in soil in -pots and kept at the same temperature, for comparison with those grown -in the germinator.</p> - -<div class="figleft"> - <img src="images/fig87.jpg" alt="" width="250" height="55" /> - <p class="center">Fig. 87.<br /> Section of corn seed; at upper<br /> - right of each is the plantlet,<br /> - next the cotyledon, at left<br /> the endosperm.</p> -</div> - -<p><b>204. Structure of the grain of corn.</b>—Take grains of corn that -<span class="pagenum"><a name="Page_98" id="Page_98">[Pg 98]</a></span> -have been soaked in water for 24 hours and note the form and difference -in the two sides (in all of these studies the form and structure of -the seed, as well as the stages in germination, should be illustrated -by the student). Make a longisection of a grain of corn through the -middle line, if necessary making several in order to obtain one which -shows the structures well near the smaller end of the grain. Note -the following structures: 1st, the hard outer “wall” (formed of the -consolidated wall of the ovary with the integuments of the ovules—see -Chapters <a href="#CHAPTER_XXXV">35</a> and <a href="#CHAPTER_XXXVI">36</a>); -2d, the greater mass of starch and other plant food (the endosperm) -in the centre; 3d, a somewhat crescent-shaped body (the <i>scutellum</i>) -lying next the endosperm and near the smaller end of the grain; 4th, -the remaining portion of the young embryo lying between the scutellum -and the seed coat in the depression. When good sections are made one -can make out the radicle at the smaller end of the seed, and a few -successive leaves (the plumule) which lie at the opposite end of the -embryo shown by sharply curved parallel lines. Observe the attachment -of the scutellum to the caulicle at the point of junction of the -plumule and the radicle. The scutellum is a part of the embryo and -represents a cotyledon. The endosperm is also called <i>albumen</i>, and -such a seed is <i>albuminous</i>.</p> - -<p>Dissect out an embryo from another seed, and compare with that seen -in the section.</p> - -<p><b>205.</b> In the germination of the grain of corn the endosperm -supplies the food for the growth of the embryo until the roots are -well established in the soil and the leaves have become expanded and -green, in which stage the plant has become able to obtain its food from -the soil and air and live independently. The starch in the endosperm -cannot of course be used for food by the embryo in the form of starch. -It is first converted into a soluble form and then absorbed through -the surface of the scutellum or cotyledon and carried to all parts of -the embryo. An enzyme developed by the embryo acts upon the starch, -converting it into a form of sugar which is in solution and can thus -be absorbed. This enzyme is one of the so-called diastatic “ferments” -which are formed during the germination of all seeds which contain food -stored in the form of starch. In some seedlings, this diastase formed -is developed in much greater abundance than in others, for example, -in barley. Examine grains of corn still attached to seedlings several -weeks old and note that a large part of their content has been used up. -The action of diastase on starch is described in <a href="#CHAPTER_VIII">Chapter 8</a>. -<span class="pagenum"><a name="Page_99" id="Page_99">[Pg 99]</a></span></p> - -<p><b>206. Structure of the pumpkin seed.</b>—The pumpkin seed has a -tough papery outer covering for the protection of the embryo plant -within. This covering is made up of the seed coats. When the seed is -opened by slitting off these coats there is seen within the “meat” -of the pumpkin seed. This is nothing more than the embryo plant. The -larger part of this embryo consists of two flattened bodies which -are more prominent than any other part of the plantlet at this time. -These two flattened bodies are the two first leaves, usually called -<i>cotyledons</i>. If we spread these cotyledons apart we see that they are -connected at one end. Lying between them at this point of attachment -is a small bud. This is the <i>plumule</i>. The plumule consists of the -very young leaves at the end of the stem which will grow as the seed -germinates. At the other end where the cotyledons are joined is a small -projection, the young root, often termed the <i>radicle</i>.</p> - -<p><b>207. How the embryo gets out of a pumpkin seed.</b>—To see how the -embryo gets out of the pumpkin seed we should examine seeds germinated -in the folds of damp paper or on damp sphagnum, as well as some which -have been germinated in earth. Seeds should be selected which represent -several different stages of germination.</p> - -<div class="figcenter"> - <img src="images/fig88.jpg" alt="" width="600" height="192" /> - <p class="center">Fig. 88.<br /> Germinating seed of pumpkin, showing how the heel<br /> - or “peg” catches on the seed coat to cast it off.</p> -</div> -<div class="figcenter"> - <img src="images/fig89.jpg" alt="" width="500" height="460" /> - <p class="center">Fig. 89.<br /> Escape of the pumpkin seedling from the seed coats.</p> -</div> - -<p><b>208. The peg helps to pull the seed coats apart.</b>—The root -pushes its way out from between the stout seed coats at the smaller -<span class="pagenum"><a name="Page_100" id="Page_100">[Pg 100]</a></span> -end, and then turns downward unless prevented from so doing by a hard -surface. After the root is 2-4 <i>cm</i> long, and the two halves of the -seed coats have begun to be pried apart, if we look in this rift at the -junction of the root and stem, we shall see that one end of the seed -coat is caught against a heel, or “peg,” which has grown out from the -stem for this purpose. Now if we examine one which is a little more -advanced, we shall see this heel more distinctly, and also that the -stem is arching out away from the seed coats. As the stem arches up -its back in this way it pries with the cotyledons against the upper -seed coat, but the lower seed coat is caught against this heel, and -the two are pulled gradually apart. In this way the embryo plant pulls -itself out from between the seed coats. In the case of seeds which are -planted deeply in the soil we do not see this contrivance unless we dig -down into the earth. The stem of the seedling arches through the soil, -pulling the cotyledons up at one end. Then it straightens up, the green -cotyledons part, and open out their inner faces to the sunlight, as -shown in <a href="#FIG_90">fig. 90</a>. If we dig into the soil we shall see that this -same heel is formed on the stem, and that the seed coats are cast off into the soil. -<span class="pagenum"><a name="Page_101" id="Page_101">[Pg 101]</a></span></p> - -<div class="figcenter"> - <img id="FIG_90" src="images/fig90.jpg" alt="" width="600" height="382" /> - <p class="center">Fig. 90.<br /> Pumpkin seedling rising from the ground.</p> -</div> - -<p><b>209. Parts of the pumpkin seedling.</b>—During the germination of -the seed all parts of the embryo have enlarged. This increase in size -of a plant is one of the peculiarities of growth. The cotyledons have -elongated and expanded somewhat, though not to such a great extent -as the root and the stem. The cotyledons also have become green on -exposure to the light. Very soon after the main root has emerged from -the seed coats, other lateral roots begin to form, so that the root -soon becomes very much branched. The main root with its branches makes -up the root system of the seedling. Between the expanded cotyledons is -seen the plumule. This has enlarged somewhat, but not nearly so much as -the root, or the part of the stem which extends below the cotyledons. -This part of the stem, i.e., that part below the cotyledons and -extending to the beginning of the root, is called in all seedlings the -<i>hypocotyl</i>, which means “below the cotyledon.”</p> - -<p><b>210. The common garden bean.</b>—The common garden bean, or the -lima bean, may be used for study. The garden bean is not so flattened -or broadened as the lima bean. It is rounded compressed, elongate -slightly curved, slightly concave on one side and convex on the other, -and the ends are rounded. At the middle of the concave side note the -distinct scar (the hilum) formed where the bean seed separates from -its attachment to the wall of the pod. Upon one side of this scar is a -slight prominence which is continued for a short distance toward the -end of the bean in the form of a slight ridge. This is the <i>raphe</i>, and -represents that part of the stalk of the ovule which is joined to the -<span class="pagenum"><a name="Page_102" id="Page_102">[Pg 102]</a></span> -side of the ovule when the latter is curved around against it (see -<a href="#CHAPTER_XXXVI">Chapter 36</a>), and at the outer end of the raphe is -the <i>chalaza</i>, the point where the stalk is joined to the end of the ovule, -best understood in a straight ovule. Upon the opposite side of the scar -and close to it can be seen a minute depression, the <i>micropyle</i>. -Underneath the seed coat and lying between this point and the end of -the seed is the <i>embryo</i>, which gives greater prominence to the bean -at this point, but it is especially more prominent after the bean has been -soaked in water. Soak the beans in water and as they are swelling note -how the seed coats swell faster than the inner portion of the seed, -which causes them to wrinkle in a curious way, but finally the inner -portion swells and fills the seed coat out smooth again. Sketch a bean -showing all the external features both in side view and in front. Split -one lengthwise and sketch the half to which the embryo clings, noting -the young root, stem, and the small leaves which were lying between -the cotyledons. There is no endosperm here now, since it was all used -up in the growth of the embryo, and a large part of its substance was -stored up in the cotyledons. As the seed germinates the young plant -gets its first food from that stored in the cotyledons. The hypocotyl -elongates, becomes strongly arched, and at last straightens up, lifting -the cotyledons from the soil. As the cotyledons become exposed to the -light they assume a green color. Some of the stored food in them goes -to nourish the embryo during germination, and they therefore become -smaller, shrivel somewhat, and at last fall off.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig91.jpg" alt="" width="150" height="196" /> - <p class="center">Fig. 91.<br /> Garden bean.<br /> - <i>m</i>, micropyle;<br /> <i>h</i>, hilum or scar;<br /> - <i>r</i>, raphe;<br /> <i>c</i>, point where<br /> chalaza lies.</p> - </div> - <div class="figsub"> - <img src="images/fig92.jpg" alt="" width="300" height="206" /> - <p class="center space-above2">Fig. 92.<br /> Bean seed split open<br /> - to show plantlet.</p> - </div> -</div> - -<p><b>211. The castor-oil bean.</b>—This is not a true bean, since it -belongs to a very different family of plants (Euphorbiaceæ). In the -germination of this seed a very interesting comparison can be made with -that of the garden bean. As the “bean” swells the very hard outer coat -generally breaks open at the free end and slips off at the stem end. -<span class="pagenum"><a name="Page_103" id="Page_103">[Pg 103]</a></span> -The next coat within, which is also hard and shining black, splits -open at the opposite end, that is at the stem end. It usually splits -open in the form of three ribs. Next within the inner coat is a very -thin, whitish film (the remains of the nucellus, and corresponding to -the perisperm) which shrivels up and loosens from the white mass, the -endosperm, within. In the castor-oil bean, then, the endosperm is not -all absorbed by the embryo during the formation of the seed. As the -plant becomes older we should note that the fleshy endosperm becomes -thinner and thinner, and at last there is nothing but a thin, whitish -film covering the green faces of the cotyledons. The endosperm has been -gradually absorbed by the germinating plant through its cotyledons and -used for food.</p> - -<div class="figcenter"> - <img src="images/fig93.jpg" alt="" width="500" height="389" /> - <p class="center space-below2">Fig. 93.<br /> How the garden bean comes out of the ground. First the looped<br /> - hypocotyl, then the cotyledons pulled out, next casting off the<br /> - seed coat, last the plant erect, bearing thick cotyledons,<br /> - the expanding leaves, and the plumule between them.</p> -</div> - -<p class="center"><b>Arisæma triphyllum.</b><a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15" class="fnanchor">[15]</a></p> - -<p><b>212. Germination of seeds of jack-in-the-pulpit.</b>—The ovaries -of jack-in-the-pulpit form large, bright red berries with a soft pulp -enclosing one to several large seeds. The seeds are oval in form. Their -<span class="pagenum"><a name="Page_104" id="Page_104">[Pg 104]</a></span> -germination is interesting, and illustrates one type of germination of -seeds common among monocotyledonous plants. If the seeds are covered -with sand, and kept in a moist place, they will germinate readily.</p> - -<div class="figcenter"> - <img src="images/fig94.jpg" alt="" width="600" height="343" /> - <p class="center space-below2">Fig. 94.<br /> Germination of castor-oil bean.</p> -</div> - -<p><b>213. How the embryo backs out of the seed.</b>—The embryo lies -within the mass of the endosperm; the root end, near the smaller end of -the seed. The club-shaped cotyledon lies near the middle of the seed, -surrounded firmly on all sides by the endosperm. The stalk, or petiole, -of the cotyledon, like the lower part of the petiole of the leaves, is -a hollow cylinder, and contains the younger leaves, and the growing end -of the stem or bud. When germination begins, the stalk, or petiole, of -the cotyledon elongates. This pushes the root end of the embryo out -at the small end of the seed. The free end of the embryo now enlarges -somewhat, as seen in the figures, and becomes the bulb, or corm, of the -young plant. At first no roots are visible, but in a short time one, -two, or more roots appear on the enlarged end.</p> - -<p><b>214. Section of an embryo.</b>—If we make a longisection of the -embryo and seed at this time we can see how the club-shaped cotyledon -is closely surrounded by the endosperm. Through the cotyledon, then, -the nourishment from the endosperm is readily passed over to the -growing embryo. In the hollow part of the petiole near the bulb can be -seen the first leaf. -<span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span></p> - -<div class="figcenter"> - <img src="images/fig95.jpg" alt="" width="600" height="443" /> - <p class="center space-below2">Fig. 95.<br /> Seedlings of castor-oil bean - casting the seed coats,<br /> and showing papery remnant of - the endosperm.</p> -</div> -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig96.jpg" alt="" width="200" height="277" /> - <p class="center">Fig. 96.<br /> Seedlings of jack-in-the-pulpit;<br /> - embryo backing out of the seed.</p> - </div> - <div class="figsub"> - <img src="images/fig97.jpg" alt="" width="250" height="202" /> - <p class="center">Fig. 97.<br /> Section of germinating embryos of<br /> - jack-in-the-pulpit, showing young<br /> leaves inside the petiole of the<br /> - cotyledon. At the left cotyledon<br /> shown surrounded by the endosperm<br /> - in the seed; at right endosperm<br /> removed to show the club-shaped<br /> - cotyledon.</p> - </div> -</div> - -<p><span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span> -<b>215. How the first leaf appears.</b>—As the embryo backs out of -the seed, it turns downward into the soil, unless the seed is so lying -that it pushes straight downward. On the upper side of the arch thus -formed, in the petiole of the cotyledon, a slit appears, and through -this opening the first leaf arches its way out. The loop of the petiole -comes out first, and the leaf later, as shown in <a href="#FIG_98">fig. 98</a>. -The petiole now gradually straightens up, and as it elongates the leaf expands.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_98" src="images/fig98.jpg" alt="" width="100" height="320" /> - <p class="center">Fig. 98.<br /> Seedlings of<br /> jack-in-the-pulpit,<br /> - first leaf arching<br /> out of the<br /> petiole of<br /> the cotyledon.</p> - </div> - <div class="figsub"> - <img id="FIG_99" src="images/fig99.jpg" alt="" width="150" height="329" /> - <p class="center">Fig. 99.<br /> Embryos of<br /> jack-in-the-pulpit<br /> - still attached to <br /> the endosperm<br /> in seed coats,<br /> and showing<br /> the - simple<br /> first leaf.</p> - </div> - <div class="figsub"> - <img id="FIG_100" src="images/fig100.jpg" alt="" width="100" height="339" /> - <p class="center">Fig. 100.<br /> Seedling of<br /> jack-in-the-pulpit;<br /> - section of the<br /> endosperm<br /> and cotyledon.</p> - </div> -</div> - -<p><b>216. The first leaf of the jack-in-the-pulpit is a simple -one.</b>—The first leaf of the embryo jack-in-the-pulpit is very -different in form from the leaves which we are accustomed to see on -<span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span> -mature plants. If we did not know that it came from the seed of this -plant we would not recognize it. It is simple, that is it consists -of one lamina or blade, and not of three leaflets as in the compound -leaf of the mature plant. The simple leaf is ovate and with a broad -heart-shaped base. The jack-in-the-pulpit, then, as trillium, and some -other monocotyledonous plants which have compound leaves on the mature -plants, have simple leaves during embryonic development. The ancestral -monocotyledons are supposed to have had simple leaves. Thus there is in -the embryonic development of the jack-in-the-pulpit, and others with -compound leaves, a sort of recapitulation of the evolutionary history -of the leaf in these forms.</p> - -<p><b>216</b><i>a</i>. <b>Germination of the pea.</b>—Compare with the bean. -Note especially that the cotyledons are not lifted above the soil as in -the beans. Compare germination of acorns.</p> - -<h4><a name="X_2" id="X_2">Digestion.</a></h4> - -<p><a name="PARA_216" id="PARA_216"><b>216</b></a><i>b</i>. <b>To test for stored food substance in the seedlings -studied.</b>—The pumpkin, squash, and castor-oil bean are examples -of what are called oily seeds, since considerable oil is stored up -in the protoplasm in the cotyledons. To test for this, remove a -small portion of the substance from the cotyledon of the squash and -crush it on a glass slip in a drop or two of osmic acid.<a name="FNanchor_16_16" id="FNanchor_16_16"></a><a href="#Footnote_16_16" class="fnanchor">[16]</a> -Put on a cover glass and examine with a microscope. The black amorphous matter -shows the presence of oil in the protoplasm. The small bodies which are -stained yellow are <i>aleurone</i> grains, a form of protein or albuminous -substance. Both the oil and the protein substance are used by the -seedling during germination. The oil is converted into an available -food form by the action of an enzyme called <i>lipase</i>, which splits up -the fatty oil into glucose and other substances. Lipase has been found -in the endosperm of the castor-oil, cocoanut, and in the cotyledons -of the pumpkin, as well as in other seeds containing oil as a stored -product. The aleurone is made available by an enzyme of the nature of -trypsin. Test the endosperm of the castor-oil bean in the same way. -Make another test of both the squash and castor-oil seeds with iodine -to show that starch is not present.</p> - -<p>Test the cotyledon of the bean with iodine for the presence of -starch. If the endosperm of corn seed has not been tested do so now -with iodine. The endosperm consists largely of starch. The starch is -<span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span> -converted to glucose by a diastatic “ferment” formed by the seedling as -it germinates. Make a thin cross-section of a grain of wheat, including -the seed coat and a portion of the interior, treat with iodine and -mount for microscopic examination. Note the abundance of starch in the -internal portion of endosperm. Note a layer of cells on the outside of -the starch portions filled with small bodies which stain yellow. These -are aleurone grains. The cellulose in the cell walls of the endosperm -is dissolved by another enzyme called <i>cytase</i>, and some plants store -up cellulose for food. For example, in the endosperm of the <i>date</i> the -cell walls are very much thickened and pitted. The cell walls consist of -reserve cellulose and the seedling makes use of it for food during growth.</p> - -<p><b>216</b><i>c</i>. <b>Albuminous and exalbuminous seeds.</b>—In seeds -where the food is stored outside of the embryo they are called -<i>albuminous</i>; examples, corn, wheat and other cereals, Indian turnip, -etc. In those seeds where the food is stored up in the embryo they are -called <i>exalbuminous</i>; examples, bean, pea, pumpkin, squash, etc.</p> - -<p><b>217. Digestion</b> has a well-defined meaning in animal physiology -and relates to the conversion of solid food, usually within the -stomach, into a soluble form by the action of certain gastric juices, -so that the liquid food may be absorbed into the circulatory system. -The term is not often applied in plant physiology, since the method -of obtaining food is in general fundamentally different in plants and -animals. It is usually applied to the process of the conversion of -starch into some form of sugar in solution, as glucose, etc. This we -have found takes place in the leaf, especially at night, through the -action of a diastatic ferment developed more abundantly in darkness. As -a result, the starch formed during the day in the leaves is digested -at night and converted into sugar, in which form it is transferred to -the growing parts to be employed in the making of new tissues, or it is -stored for future use; in other cases it unites with certain inorganic -substances, absorbed by the roots and raised to the leaf, to form -proteids and other organic substances. In tubers, seeds, parts of stems -or leaves where starch is stored, it must first be “digested” by the -action of some enzyme before it can be used as food by the sprouting -tubers or germinating seeds.</p> - -<p>For example, starch is converted to a glucose by the action of a -diastase. Cellulose is converted to a glucose by cytase. Albuminoids -are converted into available food by a tryptic ferment. Fatty oils are -converted into glucose and other products by lipase.</p> - -<p>Inulin, a carbohydrate closely related to starch, is stored up for -food in solution in many composite plants, as in the artichoke, the -root tuber of dahlia, etc. When used for food by the growing plant -it is converted into glucose by an enzyme, inulase. Make a section -of a portion of a dahlia tuber or artichoke and treat with alcohol. -The inulin is precipitated into sphæro crystals. (See also paragraphs -<a href="#PARA_156">156-161</a> and <a href="#PARA_216">216<i>b</i></a>.) -<span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span></p> - -<p><b>218.</b> Then there are certain fungi which feed on starch or other -organic substances whether in the host or not, which excrete certain -enzymes to dissolve the starch, etc., to bring it into a soluble -form before they can absorb it as food. Such a process is a sort of -<i>extracellular digestion</i>, i.e., the organism excretes the enzyme and -digests the solid outside, since it cannot take the food within its -cells in the solid form. To a certain degree the higher plants perform -also extracellular digestion in the action of root hair excretion on -insoluble substances, and in the case of the humus saprophytes. But for -them soluble food is largely prepared by the action of acids, etc., in -the soil or water, or by the work of fungi and bacteria as described in -<a href="#CHAPTER_IX">Chapter 9</a>.</p> - -<p><a name="X_3" id="X_3"><b>219. Assimilation.</b></a>—In plant -physiology the term assimilation has been chiefly used for the process -of carbon dioxide assimilation (= photosynthesis). Some objections -have been raised against the use of assimilation here as one of the -life processes of the plant, since its inception stages are due to the -combined action of light, an external factor, and chlorophyll in the -plant along with the living chloroplastid. So long, however, as it -is not known that this process can take place without the aid of the -living plant, it does not seem proper to deny that it is altogether -not a process of assimilation. It is not necessary to restrict the -term assimilation to the formation of new living matter in the plant -cell; it can be applied also to the synthetic processes in the -formation of carbohydrates, proteids, etc., and called synthetic -assimilation. The sun supplies the energy, which is absorbed by the -chlorophyll, for splitting up the carbonic acid, and the living -chloroplast then assimilates by a synthetic process the carbon, -hydrogen, and oxygen. This process then can be called <i>photosynthetic -assimilation</i>. The nitrite and nitrate bacteria derive energy in -the process of nitrification, which enables them to assimilate CO₂ -from the air, and this is called <i>chemosynthetic assimilation</i>. The -inorganic material in the form of mineral salts, nitrates, etc., -absorbed by the root, and carried up to the leaves, here meets with -the carbohydrates manufactured in the leaf. Under the influence of -the protoplasm synthesis takes place, and proteids and other organic -compounds are built up by the union of the salts, nitrates, etc., with -the carbohydrates. This is also a process of synthetic assimilation. -These are afterward stored as food, or assimilated by the protoplasm in -the making of new living matter, or perhaps without the first process -of synthetic assimilation some of the inorganic salts, nitrates, and -carbohydrates meeting in the protoplasm are assimilated into new living -matter directly.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XI" id="CHAPTER_XI">CHAPTER XI.</a><br /> -<span class="h_subtitle">RESPIRATION.</span></h3> -</div> - -<p><b>220.</b> One of the life processes in plants which is extremely -interesting, and which is exactly the same as one of the life processes -of animals, is easily demonstrated in several ways.</p> - -<p><b>221. Simple experiment to demonstrate the evolution of CO₂ during -germination.</b>—Where there are a number of students and a number of -large cylinders are not at hand, take bottles of a pint capacity and -place in the bottom some peas soaked for 12 to 24 hours. Cover with -a glass plate which has been smeared with vaseline to make a tight -joint with the mouth of the bottle. Set aside in a warm place for 24 -hours. Then slide the glass plate a little to one side and quickly -pour in a little baryta water so that it will run down on the inside -of the bottle. Cover the bottle again. Note the precipitate of barium -carbonate which demonstrates the presence of CO₂ in the bottle. Lower a -lighted taper. It is extinguished because of the great quantity of CO₂. -If flower buds are accessible, place a small handful in each of several -jars and treat the same as in the case of the peas. Young growing -mushrooms are excellent also for this experiment, and serve to show -that respiration takes place in the fungi. -<span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span></p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_101" src="images/fig101.jpg" alt="" width="200" height="349" /> - <p class="center space-above2">Fig. 101.<br /> Test for presence of carbon dioxide in<br /> - vessel with germinating peas. (Sachs.)</p> - </div> - <div class="figsub"> - <img id="FIG_102" src="images/fig102.jpg" alt="" width="250" height="408" /> - <p class="center">Fig. 102.<br /> Apparatus to show respiration<br /> of germinating wheat.</p> - </div> -</div> - -<p><b>222.</b> If we now take some of the baryta water and blow our -“breath” upon it the same film will be formed. The carbon dioxide which -we exhale is absorbed by the baryta water, and forms barium carbonate, -just as in the case of the peas. In the case of animals the process by -which oxygen is taken into the body and carbon dioxide is given off is -<i>respiration</i>. The process in plants which we are now studying is the -same, and also is respiration. The oxygen in the vessel was partly used -up in the process, and carbon dioxide was given off. (It will be seen -that this process is exactly the opposite of that which takes place in -carbon dioxide assimilation.)</p> - -<p><b>223. To show that oxygen from the air is used up while plants -respire.</b>—Soak some wheat for 24 hours in water. Remove it from -the water and place it in the folds of damp cloth or paper in a moist -vessel. Let it remain until it begins to germinate. Fill the bulb of -a thistle tube with the germinating wheat. By the aid of a stand and -clamp, support the tube upright, as shown in <a href="#FIG_102">fig. 102</a>. -Let the small end of the tube rest in a strong solution of caustic potash (one stick -caustic potash in two-thirds tumbler of water) to which red ink has -been added to give a deep red color. Place a small glass plate over the -rim of the bulb and seal it air-tight with an abundance of vaseline. -Two tubes can be set up in one vessel, or a second one can be set up in -strong baryta water colored in the same way.</p> - -<p><b>224. The result.</b>—It will be seen that the solution of caustic -potash rises slowly in the tube; the baryta water will also, if that is -<span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span> -used. The solution is colored so that it can be plainly seen at some -distance from the table as it rises in the tube. In the experiment -from which the figure was made for the accompanying illustration, the -solution had risen in 6 hours to the height shown in <a href="#FIG_102">fig. 102</a>. -In 24 hours it had risen to the height shown in <a href="#FIG_103">fig. 103</a>.</p> - -<p><b>225. Why the solution of caustic potash rises in the -tube.</b>—Since no air can get into the thistle tube from above or -below, it must be that some part of the air which is inside of the -tube is used up while the wheat is germinating. From our study of -germinating peas, we know that a suffocating gas, carbon dioxide, is -given off while respiration takes place. The caustic potash solution, -or the baryta water, whichever is used, absorbs the carbon dioxide. The -carbon dioxide is heavier than air, and so it settles down in the tube -where it can be absorbed.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_103" src="images/fig103.jpg" alt="" width="100" height="239" /> - <p class="center">Fig. 103.<br /> Apparatus to show<br /> - respiration of<br /> germinating wheat.</p> - </div> - <div class="figsub"> - <img id="FIG_104" src="images/fig104.jpg" alt="" width="200" height="263" /> - <p class="center">Fig. 104.<br /> Pea seedlings; the one at the left<br /> - had no oxygen and little growth took<br /> - place, the one at the right in oxygen<br /> and growth was evident.</p> - </div> -</div> - -<p><b>226. Where does the carbon dioxide come from?</b>—We know it -comes from the growing seedlings. The symbol for carbon dioxide is -CO₂. The carbon comes from the plant, because there is not enough in -the air. Nitrogen could not join with the carbon to make CO₂. Some -oxygen from the air or from the protoplasm of the growing seedlings -(more probably the latter) joins with some of the carbon of the plant. -These break away from their association with the living substance and -unite, making CO₂. The oxygen absorbed by the plant from the air unites -with the living substance, or perhaps first with food substances, and -from these the plant is replenished with carbon and oxygen. After the -demonstration has been made, remove the glass plate which seals the -thistle tube above, and pour in a small quantity of baryta water. The -white precipitate formed affords another illustration that carbon -dioxide is released. -<span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span></p> - -<div class="figcenter"> - <img src="images/fig105.jpg" alt="" width="400" height="426" /> - <p class="center">Fig. 105.</p> - <p class="blockquot">Experiment to show that growth takes place more rapidly in presence of - oxygen than in absence of oxygen. The two tubes in the vessel represent - the condition at the beginning of the experiment. At the close of the - experiment the roots in the tube at the left were longer than those - in the tube filled at the start with mercury. The tube outside of - the vessel represents the condition of things where the peas grew in - absence of oxygen; the carbon dioxide given off has displaced a portion - of the mercury. This also shows <i>anaerobic</i> respiration.</p> -</div> - -<p><b>227. Respiration is necessary for growth.</b>—After performing -experiment in paragraph 221, if the vessel has not been open too -long so that oxygen has entered, we may use the vessel for another -experiment, or set up a new one to be used in the course of 12 to 24 -hours, after some oxygen has been consumed. Place some folded damp -filter paper on the germinating peas in the jar. Upon this place -one-half dozen peas which have just been germinated, and in which the -roots are about 20-25 <i>mm</i> long. The vessel should be covered tightly -again and set aside in a warm room. A second jar with water in the -bottom instead of the germinating peas should be set up as a check. -Damp folded filter paper should be supported above the water, and on -this should be placed one-half dozen peas with roots of the same length -as those in the jar containing carbon dioxide.</p> - -<p><b>228.</b> In 24 hours examine and note how much growth has taken -place. It will be seen that the roots have elongated but very little -or none in the first jar, while in the second one we see that the -roots have elongated considerably, if the experiment has been carried -on carefully. Therefore in an atmosphere devoid of oxygen very little -growth will take place, which shows that normal respiration with access -of oxygen (aerobic respiration) is necessary for growth.</p> - -<p><b>229. Another way of performing the experiment.</b>—If we wish we -may use the following experiment instead of the simple one indicated -above. Soak a handful of peas in water for 12-24 hours, and germinate -so that twelve with the radicles 20-25 <i>mm</i> long may be selected. Fill -a test tube with mercury and carefully invert it in a vessel of mercury -<span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span> -so that there will be no air in the upper end. Now nearly fill another -tube and invert in the same way. In the latter there will be some air. -Remove the outer coats from the peas so that no air will be introduced -in the tube filled with the mercury, and insert them one at a time -under the edge of the tube beneath the mercury, six in each tube, -having first measured the length of the radicles. Place in a warm -room. In 24 hours measure the roots. Those in the air will have grown -considerably, while those in the other tube will have grown but little -or none.</p> - -<p><b>230. Anaerobic respiration.</b>—The last experiment is also an -excellent one to show <i>anaerobic</i> respiration. In the tube filled -with mercury so that when inverted there will be no air, it will be -seen after 24 hours that a gas has accumulated in the tube which has -crowded out some of the mercury. With a wash bottle which has an exit -tube properly curved, some water may be introduced in the tube. Then -insert underneath a small stick of caustic potash. This will form a -solution of potash, and the gas will be partly or completely absorbed. -This shows that the gas was carbon dioxide. This evolution of carbon -dioxide by living plants when there is no access of oxygen is anaerobic -respiration (sometimes called intramolecular respiration). It occurs -markedly in oily seeds and especially in the yeast plant.</p> - -<div class="figleft"> - <img src="images/fig106.jpg" alt="" width="400" height="302" /> - <p class="center">Fig. 106.</p> - <p class="blockquot">Test for liberation of carbon dioxide from - leafy plant during respiration. Baryta water in smaller - vessel. (Sachs.)</p> -</div> - -<p><b>231. Energy set free during respiration.</b>—From what we have -learned of the exchange of gases during respiration we infer that the -plant loses carbon during this process. If the process of respiration -is of any benefit to the plant, there must be some gain in some -direction to compensate the plant for the loss of carbon which takes -place.</p> - -<p>It can be shown by an experiment that during respiration there is a -slight elevation of the temperature in the plant tissues. The plant -then gains some heat during respiration. Energy is also manifested by -growth.</p> - -<p><b>232. Respiration in a leafy plant.</b>—We may take a potted plant -which has a well-developed leaf surface and place it under a tightly -fitting bell jar. Under the bell jar there also should be placed a -small vessel containing baryta water. A similar apparatus should be set -up, but with no plant, to serve as a check. The experiment must be set -up in a room which is not frequented by persons, or the carbon dioxide -in the room from respiration will vitiate the experiment. The bell jar -containing the plant should be covered with a black cloth to prevent -carbon assimilation. In the course of 10 or 12 hours, if everything has -worked properly, the baryta water under the jar with the plant will -show the film of barium carbonate, while the other one will show none. -Respiration, therefore, takes place in a leafy plant as well as in -germinating seeds. -<span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span></p> - -<p><b>233. Respiration in fungi.</b>—If several large actively growing -mushrooms are accessible, place them in a tall glass jar as described -for determining respiration in germinating peas. In the course of 12 -hours test with the lighted taper and the baryta water. Respiration -takes place in fungi as well as in green plants.</p> - -<p><b>234. Respiration in plants in general.</b>—Respiration is general -in all plants, though not universal. There are some exceptions in the -lower plants, notably in certain of the bacteria, which can only grow -and thrive in the absence of oxygen.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig107.jpg" alt="" width="200" height="487" /> - <p class="center">Fig. 107.<br /> Fermentation tube<br /> with culture of yeast.</p> - </div> - <div class="figsub"> - <img src="images/fig108.jpg" alt="" width="220" height="454" /> - <p class="center space-above1">Fig. 108.<br /> Fermentation tube<br /> - filled with CO₂ from<br /> action of yeast in a<br /> sugar solution.</p> - </div> -</div> - -<p><b>235. Respiration a breaking-down process.</b>—We have seen that -in respiration the plant absorbs oxygen and gives off carbon dioxide. -We should endeavor to note some of the effects of respiration on the -plant. Let us take, say, two dozen dry peas, weigh them, soak for 12-24 -hours in water, and, in the folds of a cloth kept moist by covering -with wet paper or sphagnum, germinate them. When well germinated and -before the green color appears dry well in the sun, or with artificial -heat, being careful not to burn or scorch them. The aim should be to -get them about as dry as the seeds were before germination. Now weigh. -The germinated seeds weigh less than the dry peas. There has then been -a loss of plant substance during respiration.</p> - -<div class="figcenter"> - <img src="images/fig108a.jpg" alt="" width="400" height="250" /> - <p class="center">Fig. 108<i>a</i>.</p> - <p class="blockquot">Yeast. Saccharomyces ceriviseæ. <i>a</i>, - small colony; <i>b</i>, single cell budding; <i>c</i>, - single cell forming an ascus with four spores; <i>d</i>, - spores free from the ascus. (After Rees.)</p> -</div> - -<p><b>236. Fermentation of yeast.</b>—Take two fermentation tubes. Fill -the closed tubular parts of each with a weak solution of grape sugar, -or with potato decoction, leaving the open bulb nearly empty. Into the -liquid of one of the tubes place a piece of compressed yeast as large -as a pea. If the tubes are kept in a warm place for 24 hours bubbles -of gas may be noticed rising in the one in which the yeast was placed, -while in the second tube no such bubbles appear, especially if the -filled tubes are first sterilized. The tubes may be kept until the -first is entirely filled with the gas. Now dissolve in the liquid a -small piece of caustic potash. Soon the gas will begin to be absorbed, -and the liquid will rise until it again fills the tube. The gas was -carbon dioxide, which was chiefly produced during the anaerobic -respiration of the rapidly growing yeast cells. In bread making this -gas is produced in considerable quantities, and rising through the -dough fills it with numerous cavities containing gas, so that the bread -“rises.” When it is baked the heat causes the gas in the cavities to -<span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span> -expand greatly. This causes the bread to “rise” more, and baked in this -condition it is “light.” There are two special processes accompanying -the fermentation by yeast: 1st, the evolution of carbon dioxide as -shown above; and, 2d, the formation of alcohol. The best illustration -of this second process is the brewing of beer, where a form of the same -organism which is employed in “bread rising” is used to “brew beer.”</p> - -<p><a id="PARA_237" name="PARA_237"><b>237. The yeast plant.</b></a>—Before the -caustic potash is placed in the tube some of the fermented liquid should be taken -for study of the yeast plant, unless separate cultures are made for this purpose. -Place a drop of the fermented liquid on a glass slip, place on this -a cover glass, and examine with the microscope. Note the minute oval -cells with granular protoplasm. These are the yeast plant. Note in -some a small “bud” at one side of the end. These buds increase in size -and separate from the parent plant. The yeast plant is one-celled, -and multiplies by “budding” or “sprouting.” It is a fungus, and some -species of yeast like the present one do not form any mycelium. Under -certain conditions, which are not very favorable for growth (example, -when the yeast is grown in a weak nutrient substance on a thin layer of -a plaster Paris slab), several spores are formed in many of the yeast -cells. After a period of rest these spores will sprout and produce the -yeast plant again. Because of this peculiar spore formation some place -the yeast among the sac fungi. (<a href="#CHAPTER_XXII">See classification of the fungi</a>.)</p> - -<p><b>238. Organized ferments and unorganized ferments.</b>—An organism -like the yeast plant which produces a fermentation of a liquid with -evolution of gas and alcohol is sometimes called a <i>ferment</i>, or -<i>ferment organism</i>, or an <i>organized</i> ferment. On the other hand -the diastatic ferments or enzymes like diastase, taka diastase, animal -diastase (ptyalin in the saliva), cytase, etc., are <i>unorganized</i> -ferments. In the case of these it is better to say <i>enzyme</i> and leave -the word ferment for the ferment organisms. -<span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span></p> - -<p><b>239. Importance of green plants in maintaining purity of -air.</b>—By respiration, especially of animals, the air tends to -become “foul” by the increase of CO₂. Green plants, i.e., plants -with chlorophyll, purify the air during photosynthesis by absorbing -CO₂ and giving off oxygen. Animals absorb in respiration large -quantities of oxygen and exhale large quantities of CO₂. Plants -absorb a comparatively small amount of oxygen in respiration and -give off a comparatively small amount of CO₂. But they absorb during -photosynthesis large quantities of CO₂ and give off large quantities of -oxygen. In this way a balance is maintained between the two processes, -so that the percentage of CO₂ in the air remains approximately the -same, viz., about four-tenths of one per cent, while there are -approximately 21 parts oxygen and 79 parts nitrogen.</p> - -<p><b>239a. Comparison of respiration and photosynthesis.</b></p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdc bb" colspan="2"> </td> - </tr><tr> - <td class="tdc br bb" rowspan="5">Starch formation or Photosynthesis.</td> - <td class="tdl_ws1"><p class="neg-indent">Carbon dioxide is taken in by the plant and oxygen is liberated.</p></td> - </tr><tr> - <td class="tdl_ws1"><p class="neg-indent">Starch is formed as a result of the metabolism, or chemical change.</p></td> - </tr><tr> - <td class="tdl_ws1"><p class="neg-indent">The process takes place only in green plants, and in the green - parts of plants, that is, in the presence of the chlorophyll. - (Exception in purple bacterium.)</p></td> - </tr><tr> - <td class="tdl_ws1"><p class="neg-indent">The process only takes place under the influence of sunlight.</p></td> - </tr><tr> - <td class="tdl_ws1 bb"><p class="neg-indent">It is a building-up process, because new plant substance is formed.</p></td> - </tr><tr> - <td class="tdc br" rowspan="5">Respiration.</td> - <td class="tdl_ws1"><p class="neg-indent">Oxygen is taken in by the plant and carbon dioxide is liberated.</p></td> - </tr><tr> - <td class="tdl_ws1"><p class="neg-indent">Carbon dioxide is formed as a result of the - metabolism, or chemical change.</p></td> - </tr><tr> - <td class="tdl_ws1"><p class="neg-indent">The process takes place in all plants whether they possess - chlorophyll or not. (Exceptions in anaerobic bacteria).</p></td> - </tr><tr> - <td class="tdl_ws1"><p class="neg-indent">The process takes place in the dark as well as in the sunlight.</p></td> - </tr><tr> - <td class="tdl_ws1"><p class="neg-indent">It is a breaking-down process, because disintegration of plant substance occurs.</p></td> - </tr><tr> - <td class="tdc bt" colspan="2"> </td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XII" id="CHAPTER_XII">CHAPTER XII.</a><br /> -<span class="h_subtitle">GROWTH.</span></h3> -</div> - -<p>By growth is usually meant an increase in the bulk of the plant -accompanied generally by an increase in plant substance. Among the -lower plants growth is easily studied in some of the fungi.</p> - -<p><b>240. Growth in mucor.</b>—Some of the gonidia (often called spores) -may be sown in nutrient gelatine or agar, or even in prune juice. If -the culture has been placed in a warm room, in the course of 24 hours, -or even less, the preparation will be ready for study.</p> - -<p><b>241. Form of the gonidia.</b>—It will be instructive if we first -examine some of the gonidia which have not been sown in the culture -medium. We should note their rounded or globose form, as well as -their markings if they belong to one of the species with spiny walls. -Particularly should we note the size, and if possible measure them with -the micrometer, though this would not be absolutely necessary for a -comparison, if the comparison can be made immediately. Now examine some -of the gonidia which were sown in the nutrient medium. If they have not -already germinated we note at once that they are much larger than those -which have not been immersed in a moist medium.</p> - -<p><b>242. The gonidia absorb water and increase in size before -germinating.</b>—From our study of the absorption of water or watery -solutions of nutriment by living cells, we can easily understand the -cause of this enlargement of the gonidium of the mucor when surrounded -by the moist nutrient medium. The cell-sap in the spore takes up more -<span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span> -water than it loses by diffusion, thus drawing water forcibly through -the protoplasmic membrane. Since it does not filter out readily, the -increase in quantity of the water in the cell produces a pressure from -within which stretches the membrane, and the elastic cell wall yields. -Thus the gonidium becomes larger.</p> - -<div class="figcenter"> - <img src="images/fig109.jpg" alt="" width="600" height="209" /> - <p class="center">Fig. 109.<br /> Spores of mucor, and different stages of germination.</p> -</div> - -<p><b>243. How the gonidia germinate.</b>—We should find at this time -many of the gonidia extended on one side into a tube-like process the -length of which varies according to time and temperature. The short -process thus begun continues to elongate. This elongation of the plant -is <i>growth</i>, or, more properly speaking, one of the phenomena of growth.</p> - -<p><b>244. The germ tube branches and forms the mycelium.</b>—In the -course of a day or so branches from the tube will appear. This branched -form of the threads of the fungus is, as we remember, the mycelium. We -can still see the point where growth started from the gonidium. Perhaps -by this time several tubes have grown from a single one. The threads of -the mycelium near the gonidium, that is, the older portions of them, -have increased in diameter as they have elongated, though this increase -in diameter is by no means so great as the increase in length. After -increasing to a certain extent in diameter, growth in this direction -ceases, while apical growth is practically unlimited, being limited -only by the supply of nutriment.</p> - -<p><b>245. Growth in length takes place only at the end of the thread.</b>—If -<span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span> -there were any branches on the mycelium when the culture was first -examined, we can now see that they remain practically the same distance -from the gonidium as when they were first formed. That is, the older -portions of the mycelium do not elongate. Growth in length of the -mycelium is confined to the ends of the threads.</p> - -<p><b>246. Protoplasm increases by assimilation of nutrient -substances.</b>—As the plant increases in bulk we note that there -is an increase in the protoplasm, for the protoplasm is very easily -detected in these cultures of mucor. This increase in the quantity -of the protoplasm has come about by the assimilation of the nutrient -substance, which the plant has absorbed. The increase in the -protoplasm, or the formation of additional plant substance, is another -phenomenon of growth quite different from that of elongation, or -increase in bulk.</p> - -<p><b>247. Growth of roots.</b>—For the study of the growth of roots we -may take any one of many different plants. The seedlings of such plants -as peas, beans, corn, squash, pumpkin, etc., serve excellently for this -purpose.</p> - -<p><b>248. Roots of the pumpkin.</b>—The seeds, a handful or so, are -soaked in water for about 12 hours, and then placed between layers of -paper or between the folds of cloth, which must be kept quite moist but -not very wet, and should be kept in a warm place. A shallow crockery -plate, with the seeds lying on wet filter paper, and covered with -additional filter paper, or with a bell jar, answers the purpose well.</p> - -<p>The primary or first root (radicle) of the embryo pushes its way out -between the seed coats at the small end. When the seeds are well -germinated, select several which have the root 4-5 <i>cm</i> long. With a -crow-quill pen we may now mark the terminal portion of the root off -into very short sections as in <a href="#FIG_110">fig. 110</a>. The first mark should -be not more than 1 <i>mm</i> from the tip, and the others not more than 1mm -apart. Now place the seedlings down on damp filter paper, and cover -with a bell jar so that they will remain moist, and if the season is -cold place them in a warm room. At intervals of 8 or 10 hours, if -convenient, observe them and note the farther growth of the root. -<span class="pagenum"><a name="Page_121" id="Page_121">[Pg 121]</a></span></p> - -<div class="figcenter"> - <img id="FIG_110" src="images/fig110.jpg" alt="" width="600" height="266" /> - <p class="center">Fig. 110.<br /> Root of germinating pumpkin, showing region - of elongation just back of the tip.</p> -</div> - -<p><b>249. The region of elongation.</b>—While the root has elongated, -the region of elongation <i>is not at the tip of the root. It lies a -little distance back from the tip</i>, beginning at about 2mm from the tip -and extending over an area represented by from 4-5 of the millimeter -marks. The root shown in <a href="#FIG_110">fig. 110</a> was marked at 10 <span class="smcap">a.m.</span> on -July 5. At 6 <span class="smcap">p.m.</span> of the same day, 8 hours later, growth had -taken place as shown in the middle figure. At 9 <span class="smcap">a.m.</span> on the -following day, 15 hours later, the growth is represented in the lower -one. Similar experiments upon a number of seedlings give the same -result: the region of elongation in the growth of the root is situated -a little distance back from the tip. Farther back very little or no -elongation takes place, but growth in diameter continues for some time, -as we should discover if we examined the roots of growing pumpkins, or -other plants, at different periods.</p> - -<p><b>250. Movement of region of greatest elongation.</b>—In the region -of elongation the areas marked off do not all elongate equally at the -same time. The middle spaces elongate most rapidly and the spaces -marked off by the 6, 7, and 8 <i>mm</i> marks elongate slowly, those -farthest from the tip more slowly than the others, since elongation -has nearly ceased here. The spaces marked off between the 2-4 <i>mm</i> -marks also elongate slowly, but soon begin to elongate more rapidly, -since that region is becoming the region of greatest elongation. Thus -the region of greatest elongation moves forward as the root grows, and -remains approximately at the same distance behind the tip.</p> - -<p><b>251. Formative region.</b>—If we make a longitudinal section of the -tip of a growing root of the pumpkin or other seedling, and examine it -<span class="pagenum"><a name="Page_122" id="Page_122">[Pg 122]</a></span> -with the microscope, we see that there is a great difference in the -character of the cells of the tip and those in the region of elongation -of the root. First there is in the section a V-shaped cap of loose -cells which are constantly being sloughed off. Just back of this tip -the cells are quite regularly isodiametric, that is, of equal diameter -in all directions. They are also very rich in protoplasm, and have -thin walls. This is the region of the root where new cells are formed -by division. It is the <i>formative region</i>. The cells on the outside -of this area are the older, and pass over into the older parts of the -root and root cap. If we examine successively the cells back from this -<i>formative</i> region we find that they become more and more elongated in -the direction of the axis of the root. The elongation of the cells in -this older portion of the root explains then why it is that this region -of the root elongates more rapidly than the tip.</p> - -<p><b>252. Growth of the stem.</b>—We may use a bean seedling growing -in the soil. At the junction of the leaves with the stem there are -enlargements. These are the <i>nodes</i>, and the spaces on the stem between -successive nodes are the <i>internodes</i>. We should mark off several of -these internodes, especially the younger ones, into sections about 5 -<i>mm</i> long. Now observe these at several times for two or three days, -or more. The region of elongation is greater than in the case of the -roots, and extends back farther from the end of the stem. In some young -garden bean plants the region of elongation extended over an area of 40 -<i>mm</i> in one internode. See also Chapters <a href="#CHAPTER_XXXVIII">38</a>, -<a href="#CHAPTER_XXXIX">39</a>.</p> - -<p><b>253. Force exerted by growth.</b>—One of the marvelous things -connected with the growth of plants is the force which is exerted by -various members of the plant under certain conditions. Observations on -seedlings as they are pushing their way through the soil to the air -often show us that considerable force is required to lift the hard soil -and turn it to one side. A very striking illustration may be had in the -case of mushrooms which sometimes make their way through the hard and -packed soil of walks or roads. That succulent and tender plants should -be capable of lifting such comparatively heavy weights seems incredible -until we have witnessed it. Very striking illustrations of the force -of roots are seen in the case of trees which grow in rocky situations, -where rocks of considerable weight are lifted, or small rifts in large -rocks are widened by the lateral pressure exerted by the growth of a -root, which entered when it was small and wedged its way in.</p> - -<p><b>254. Zone of maximum growth.</b>—Great variation exists in the -rapidity of growth even when not influenced by outside conditions. In -our study of the elongation of the root we found that the cells just -<span class="pagenum"><a name="Page_123" id="Page_123">[Pg 123]</a></span> -back of the formative region elongated slowly at first. The rapidity of -the elongation of these cells increases until it reaches the maximum. -Then the rapidity of elongation lessens as the cells come to lie -farther from the tip. The period of maximum elongation here is the -<i>zone of maximum growth</i> of these cells.</p> - -<div class="figcenter"> - <img src="images/fig111.jpg" alt="" width="400" height="387" /> - <p class="center">Fig. 111.<br /> Lever auxanometer (Oels) for measuring<br /> - elongation of the stem during growth.</p> -</div> - -<p><b>255.</b> Just as the cells exhibit a zone of maximum growth, so -the members of the plant exhibit a similar zone of maximum growth. -In the case of leaves, when they are young the rapidity of growth -is comparatively slow, then it increases, and finally diminishes in -rapidity again. So it is with the stem. When the plant is young the -growth is not so rapid; as it approaches middle age the rapidity of -growth increases; then it declines in rapidity at the close of the -season.</p> - -<p><b>256. Energy of growth.</b>—Closely related to the zone of maximum -growth is what is termed the energy of growth. This is manifested in -the comparative size of the members of a given plant. To take the -sunflower for example, the lower and first leaves are comparatively -small. As the plant grows larger the leaves are larger, and this -increase in size of the leaves increases up to a maximum period, when -the size decreases until we reach the small leaves at the top of the -stem. The zone of maximum growth of the leaves corresponds with the -maximum size of the leaves on the stem. The rapidity and energy of -growth of the stem is also correlated with that of the leaves, and the -zone of maximum growth is coincident with that of the leaves. It would -be instructive to note it in the case of other plants and also in the -case of fruits.</p> - -<p><b>257. Nutation.</b>—During the growth of the stem all of the cells -of a given section of the stem do not elongate simultaneously. For -example the cells at a given moment on the south side are elongating -more rapidly than the cells on the other side. This will cause the -stem to bend slightly to the north. In a few moments later the cells -on the west side are elongating more rapidly, and the stem is turned -to the east; and so on, groups of cells in succession around the stem -elongate more rapidly than the others. This causes the stem to describe -a circle or ellipse about a central point. Since the region of greatest -elongation of the cells of the stem is gradually moving toward the apex -of the growing stem, this line of elongation of the cells which is -<span class="pagenum"><a name="Page_124" id="Page_124">[Pg 124]</a></span> -traveling around the stem does so in a spiral manner. In the same way, -while the end of the stem is moving upward by the elongation of the -cells, and at the same time is slowly moved around, the line which the -end of the stem describes must be a spiral one. This movement of the -stem, which is common to all stems, leaves, and roots, is <i>nutation</i>.</p> - -<p><b>258.</b> The importance of nutation to twining stems in their search -for a place of support, as well as for the tendrils on leaves or stems, -will be seen. In the case of the root it is of the utmost importance, -as the root makes its way through the soil, since the particles of soil -are more easily thrust aside. The same is also true in the case of many -stems before they emerge from the soil.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_125" id="Page_125">[Pg 125]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XIII" id="CHAPTER_XIII">CHAPTER XIII.</a><br /> -<span class="h_subtitle">IRRITABILITY.</span></h3> -</div> - -<p><b>259.</b> We should now examine the movements of plant parts in -response to the influence of certain stimuli. By this time we have -probably observed that the direction which the root and stem take upon -germination of the seed is not due to the position in which the seed -happens to lie. Under normal conditions we have seen that the root -grows downward and the stem upward.</p> - -<p><b>260. Influence of the earth on the direction of growth.</b>—When -the stem and root have been growing in these directions for a short -time let us place the seedling in a horizontal position, so that the -end of the root extends over an object of support in such a way that it -will be free to go in any direction. It should be pinned to a cork and -placed in a moist chamber. In the course of twelve to twenty-four hours -the root which was formerly horizontal has turned the tip downward -again. If we should mark off millimeter spaces beginning at the tip of -the root, we should find that the motor zone, or region of curvature, -lies in the same region as that of the elongation of the root.</p> - -<p>Knight found that the stimulus which influences the root to turn -downward is the force of gravity. The reaction of the root in response -to this stimulus is geotropism, a turning influenced by the earth. This -term is applied to the growth movements of plants influenced by the -earth with regard to direction. While the motor zone lies back of the -root-tip, the latter receives the stimulus and is the perceptive zone. -If the root-tip is cut off, the root is no longer geotropic, and will -not turn downward when placed in a horizontal position. Growth toward -<span class="pagenum"><a name="Page_126" id="Page_126">[Pg 126]</a></span> -the earth is <i>progeotropism</i>. The lateral growth of secondary roots is -<i>diageotropism</i>.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig112.jpg" alt="" width="250" height="141" /> - <p class="center">Fig. 112.<br /> Germinating pea placed in<br /> a horizontal position.</p> - </div> - <div class="figsub"> - <img src="images/fig113.jpg" alt="" width="300" height="140" /> - <p class="center">Fig. 113.<br /> In 24 hours gravity has caused<br /> the root to turn downward.</p> - </div> - <p class="center space-below2">Figs. 112, 113.—Progeotropism of the pea root.</p> -</div> - -<p>The stem, on the other hand, which was placed in a horizontal position -has become again erect. This turning of the stem in the upward -direction takes place in the dark as well as in the light, as we can -see if we start the experiment at nightfall, or place the plant in the -dark. This upward growth of the stem is also influenced by the earth, -and therefore is a case of geotropism. The special designation in the -case of upright stems is <i>negative geotropism</i>, or <i>apogeotropism</i>, or -the stems are said to be <i>apogeotropic</i>. If we place a rapidly growing -potted plant in a horizontal position by laying the pot on its side, -the ends of the shoots will soon turn upward again when placed in a -horizontal position. Young bean plants growing in a pot began within -two hours to turn the ends of the shoots upward.</p> - -<div class="figcenter"> - <img src="images/fig114.jpg" alt="" width="600" height="358" /> - <p class="center">Fig. 114.<br /> Pumpkin seedling showing apogeotropism.<br /> - Seedling at the left placed horizontally,<br /> in 24 hours the stem has become erect.</p> -</div> - -<p><span class="pagenum"><a name="Page_127" id="Page_127">[Pg 127]</a></span> -Horizontal leaves and shoots can be shown to be subject to the same -influence, and are therefore <i>diageotropic</i>.</p> - -<p><b>261. Influence of light.</b>—Not only is light a very important -factor for plants during photosynthesis, it exerts great influence on -plant growth and movement.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p> </p> - <img src="images/fig115.jpg" alt="" width="300" height="250" /> - <p class="center">Fig. 115.<br /> Radish seedlings grown in the<br /> dark, long, slender, not green.</p> - </div> - <div class="figsub"> - <img src="images/fig116.jpg" alt="" width="150" height="286" /> - <p class="center">Fig. 116.<br /> Radish seedlings grown in the<br /> - light, shorter, stouter, and green<br /> in color. Growth retarded by light.</p> - </div> -</div> - -<p><b>262. Growth in the absence of light.</b>—Plants grown in the -dark are subject to a number of changes. The stems are often longer, -more slender and weaker since they contain a larger amount of water -in proportion to building material which the plant obtains from -carbohydrates manufactured in the light. On many plants the leaves are -very small when grown in the dark.</p> - -<p><b>263. Influence of light on direction of growth.</b>—While we are -growing seedlings, the pots or boxes of some of them should be placed -so that the plants will have a one-sided illumination. This can be -done by placing them near an open window, in a room with a one-sided -illumination, or they may be placed in a box closed on all sides but -one which is facing the window or light. In 12-24 hours, or even in a -much shorter time in some cases, the stems of the seedlings will be -directed toward the source of light. This influence exerted by the rays -of light is <i>heliotropism</i>, a turning influenced by the sun or sunlight. -<span class="pagenum"><a name="Page_128" id="Page_128">[Pg 128]</a></span></p> - -<div class="figcenter"> - <img src="images/fig117.jpg" alt="" width="500" height="448" /> - <p class="center">Fig. 117.<br /> Seedling of castor-oil bean,<br /> - before and after a one-sided illumination.</p> -</div> -<div class="figcenter"> - <img src="images/fig118.jpg" alt="" width="500" height="206" /> - <p class="center">Fig. 118.<br /> Dark chamber with opening at one side to<br /> - show heliotropism. (After Schleichert.)</p> -</div> - -<p><b>264. Diaheliotropism.</b>—Horizontal leaves and shoots are -<i>diaheliotropic</i> as well as <i>diageotropic</i>. The general direction -which leaves assume under this influence is that of placing them with the -upper surface perpendicular to the rays of light which fall upon them. -Leaves, then, exposed to the brightly lighted sky are, in general, -horizontal. This position is taken in direct response to the stimulus -of light. The leaves of plants with a one-sided illumination, as can be -seen by trial, are turned with their upper surfaces toward the source -of light, or perpendicular to the incidence of the light rays. In this -way light overcomes for the time being the direction which growth -gives to the leaves. The so-called “sleep” of plants is of course -not sleep, though the leaves “nod,” or hang downward, in many cases. -There are many plants in which we can note this drooping of the leaves -at nightfall, and in order to prove that it is not determined by the -time of day we can resort to a well-known experiment to induce this -condition during the day. The plant which has been used to illustrate -<span class="pagenum"><a name="Page_129" id="Page_129">[Pg 129]</a></span> -this is the sunflower. Some of these plants, which were grown in a box, -when they were about 35 <i>cm</i> high were covered for nearly two days, -so that the light was excluded. At midday on the second day the box -was removed, and the leaves on the covered plants are well represented -by <a href="#FIG_119">fig. 119</a>, which was made from one of them. The leaves -of the other plants in the box which were not covered were horizontal, as shown by -<a href="#FIG_120">fig. 120</a>. Now on leaving these plants, which had exhibited -induced “sleep” movements, exposed to the light they gradually assumed the -horizontal position again.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_119" src="images/fig119.jpg" alt="" width="150" height="250" /> - <p class="center">Fig. 119.<br /> Sunflower plant. Epinastic condition of<br /> - leaves induced during the day in darkness.</p> - </div> - <div class="figsub"> - <img id="FIG_120" src="images/fig120.jpg" alt="" width="300" height="233" /> - <p class="center">Fig. 120.<br /> Sunflower plant removed from darkness,<br /> - leaves extending under influence of light<br /> (diaheliotropism.)</p> - </div> -</div> - -<p><b>265. Epinasty and hyponasty.</b>—During the early stages of growth -of many leaves, as in the sunflower plant, the direction of growth is -different from what it is at a later period. The under surface of the -young leaves grows more rapidly in a longitudinal direction than the -upper side, so that the leaves are held upward close against the bud -at the end of the stem. This is termed <i>hyponasty</i>, or the leaves are -said to be <i>hyponastic</i>. Later the growth is more rapid on the upper -side and the leaves turn downward or away from the bud. This is termed -<i>epinasty</i>, or the leaves are said to be <i>epinastic</i>. This is shown by -<span class="pagenum"><a name="Page_130" id="Page_130">[Pg 130]</a></span> -the night position of the leaves, or in the induced “sleep” of the -sunflower plant in the experiment detailed above. The day position of -the leaves on the other hand, which is more or less horizontal, is -induced because of their irritability under the influence of light, the -inherent downward or epinastic growth is overcome for the time. Then -at nightfall or in darkness, the stimulus of light being removed, the -leaves assume the position induced by the direction of growth.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_121" src="images/fig121.jpg" alt="" width="200" height="263" /> - <p class="center">Fig. 121.<br /> Squash seedling. Position<br /> of cotyledons in light.</p> - </div> - <div class="figsub"> - <img id="FIG_122" src="images/fig122.jpg" alt="" width="150" height="266" /> - <p class="center">Fig. 122.<br /> Squash seedling. Position<br /> of cotyledons in the dark.</p> - </div> -</div> - -<p><b>266.</b> In the case of the cotyledons of some plants it would seem -that the growth was hyponastic even after they have opened. The day -position of the cotyledons of the pumpkin is more or less horizontal, -as shown in <a href="#FIG_121">fig. 121</a>. At night, or if we darken the plant -by covering with a tight box, the leaves assume the position shown in -<a href="#FIG_122">fig. 122</a>.</p> - -<p>While the horizontal position is the general one which is assumed -by plants under the influence of light, their position is dependent -to a certain extent on the intensity of the light as well as on the -incidence of the light rays. Some plants are so strongly heliotropic -that they change their positions all during the day. -<span class="pagenum"><a name="Page_131" id="Page_131">[Pg 131]</a></span></p> - -<div class="figleft"> - <img id="FIG_123" src="images/fig123.jpg" alt="" width="200" height="407" /> - <p class="center">Fig. 123.<br /> Coiling tendril<br /> of bryony.</p> -</div> - -<p><b>267. Leaves with a fixed diurnal position.</b>—Leaves of some -plants when they are developed have a fixed diurnal position and are -not subject to variation. Such leaves tend to arrange themselves in a -vertical or paraheliotropic position, in which the surfaces are not -exposed to the incidence of light of the greatest intensity, but to the -incidence of the rays of diffused light. Interesting cases of the fixed -position of leaves are found in the so-called compass plants (like -Silphium laciniatum, Lactuca scariola, etc.). In these the horizontal -leaves arrange themselves with the surfaces vertical, and also pointing -north and south, so that the surfaces face east and west.</p> - -<p><b>268. Importance of these movements.</b>—Not only are the leaves -placed in a position favorable for the absorption of the rays of light -which are concerned in making carbon available for food, but they -derive other forms of energy from the light, as heat, which is absorbed -during the day. Then with the nocturnal position, the leaves being -drooped down toward the stem, or with the margin toward the sky, or -with the cotyledons as in the pumpkin, castor-oil bean, etc., clasped -upward together, the loss of heat by radiation is less than it would be -if the upper surfaces of the leaves were exposed to the sky.</p> - -<p><b>269. Influence of light on the structure of the leaf.</b>—In our -study of the structure of a leaf we found that in the ivy leaf the -palisade cells were on the upper surface. This is the case with a great -many leaves, and is the normal arrangement of “dorsiventral” leaves -which are diaheliotropic. Leaves which are paraheliotropic tend to have -palisade cells on both surfaces. The palisade layer of cells as we -have seen is made up of cells lying very close together, and they thus -prevent rapid evaporation. They also check to some extent the entrance -of the rays of light, at least more so than the loose spongy parenchyma -cells do. Leaves developed in the shade have looser palisade and -parenchyma cells. In the case of some plants, if we turn over a very -young leaf, so that the under side will be uppermost, this side will -develop the palisade layer. This shows that light has a great influence -on the structure of the leaf.</p> - -<p><b>270. Movement influenced by contact.</b>—In the case of tendrils, -twining leaves, or stems, the irritability to contact is shown in a -movement of the tendril, etc., toward the object in touch. This causes -the tendril or stem to coil around the object for support. The stimulus -is also extended down the part of the tendril below the point of -<span class="pagenum"><a name="Page_132" id="Page_132">[Pg 132]</a></span> -contact (see <a href="#FIG_123">fig. 123</a>), and that part coils up like a wire -coil spring, thus drawing the leaf or branch from which the tendril grows closer to -the object of support. This coil between the object of support and the -plant is also very important in easing up the plant when subject to -violent gusts of wind which might tear the plant from its support were -it not for the yielding and springing motion of this coil.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_124" src="images/fig124.jpg" alt="" width="300" height="193" /> - <p class="center">Fig. 124.<br /> Sensitive plant leaf<br /> in normal position.</p> - </div> - <div class="figsub"> - <img id="FIG_125" src="images/fig125.jpg" alt="" width="115" height="199" /> - <p class="center">Fig. 125.<br /> Pinnæ folding up<br /> after stimulus.</p> - </div> -</div> -<div class="figcenter"> - <img id="FIG_126" src="images/fig126.jpg" alt="" width="500" height="399" /> - <p class="center">Fig. 126.<br /> Later all the pinnæ folded and leaf drooped.</p> -</div> - -<p><b>271. Sensitive plants.</b>—These plants are remarkable for the -rapid response to stimuli. Mimosa pudica is an excellent plant to study -for this purpose.</p> - -<p><b>272. Movement in response to stimuli.</b>—If we pinch with the -forceps one of the terminal leaflets, or tap it with a pencil, the two -end leaflets fold above the “vein” of the pinna. This is immediately -followed by the movement of the next pair, and so on as shown in <a href="#FIG_125">fig. 125</a>, -until all the leaflets on this pinna are closed, then the stimulus -travels down the other pinnæ in a similar manner, and soon the pinnæ -approximate each other and the leaf then drops downward as shown in -<a href="#FIG_126">fig. 126</a>. The normal position of the leaf is shown in <a href="#FIG_124">fig. 124.</a> -If we jar the plant by striking it or by jarring the pot in which it is grown -all the leaves quickly collapse into the position shown in <a href="#FIG_126">fig. 126</a>. -If we examine the leaf now we see minute cushions at the base of each -leaflet, at the junction of the pinnæ with the petiole, and a larger -one at the junction of the petiole with the stem. We shall also note -that the movement resides in these cushions. -<span class="pagenum"><a name="Page_133" id="Page_133">[Pg 133]</a></span></p> - -<p><b>273. Transmission of the stimulus.</b>—The transmission of the -stimulus in this mimosa from one part of the plant has been found to be -along the cells of the bast.</p> - -<p><b>274. Cause of the movement.</b>—The movement is caused by a sudden -loss of turgidity on the part of the cells in one portion of the -pulvinus, as the cushion is called. In the case of the large pulvinus -at the base of the petiole this loss of turgidity is in the cells of -the lower surface. There is a sudden change in the condition of the -protoplasm of the cells here so that they lose a large part of their -water. This can be seen if with a sharp knife we cut off the petiole -just above the pulvinus before movement takes place. A drop of liquid -exudes from the cells of the lower side.</p> - -<p><b>275. Paraheliotropism of the leaves of the sensitive plant.</b>—If -the mimosa plant is placed in very intense light the leaflets will -turn their edges toward the incidence of the rays of light. This is -also true of other plants in intense light, and is <i>paraheliotropism</i>. -Transpiration is thus lessened, and chlorophyll is protected from too -intense light.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p> </p> - <img src="images/fig126a.jpg" alt="" width="250" height="333" /> - <p class="center">Fig. 126<i>a</i>.<br /> Leaf of Venus fly-trap (Dionæa muscipula),<br /> - showing winged petiole and toothed lobes.</p> - </div> - <div class="figsub"> - <img src="images/fig127.jpg" alt="" width="250" height="358" /> - <p class="center">Fig. 127.<br /> Leaf of Drosera rotundifolia, some of the<br /> - glandular hairs folding inward as a result<br /> of a stimulus.</p> - </div> -</div> - -<p>We thus see that variations in the intensity of light have an important -influence in modifying movements. Variations in temperature also exert -a considerable influence, rapid elevation of temperature causing -certain flowers to open, and falling temperature causing them to close.</p> - -<p><b>276. Sensitiveness of insectivorous plants.</b>—The Venus fly-trap -(Dionæa muscipula) and the sundew (drosera) are interesting examples of -sensitive plants, since the leaves close in response to the stimulus -from insects.</p> - -<p><b>277. Hydrotropism.</b>—Roots are sensitive to moisture. They will -turn toward moisture. This is of the greatest importance for the -well-being of the plant, since the roots will seek those places in the -<span class="pagenum"><a name="Page_134" id="Page_134">[Pg 134]</a></span> -soil where suitable moisture is present. On the other hand, if the soil -is too wet there is a tendency for the roots to grow away from the -soil which is saturated with water. In such cases roots are often seen -growing upon the surface of the soil so that they may obtain oxygen, -which is important for the root in the processes of absorption and -growth. Plants then may be injured by an excess of water as well as by -a lack of water in the soil.</p> - -<p><b>278. Temperature.</b>—In the experiments on germination thus -far made it has probably been noted that the temperature has much -to do with the length of time taken for seeds to germinate. It also -influences the rate of growth. The effect of different temperatures -on the germination of seed can be very well noted by attempting to -germinate some in rooms at various temperatures. It will be found, -other conditions being equal, that in a moderately warm room, or even -in one quite warm, 25-30 degrees centigrade, germination and growth -goes on more rapidly than in a cool room, and here more rapidly than in -one which is decidedly cold. In the case of most plants in temperate -climates, growth may go on at a temperature but little above freezing, -but few will thrive at this temperature.</p> - -<p><b>279.</b> If we place dry peas or beans in a temperature of about -70° C. for 15 minutes they will not be killed, but if they have been -thoroughly soaked in water and then placed at this temperature they -will be killed, or even at a somewhat lower temperature. The same seeds -in the dry condition will withstand a temperature of 10° C. below, but -if they are first soaked in water this low temperature will kill them.</p> - -<p><b>280.</b> In order to see the effect of freezing we may thoroughly -freeze a section of a beet root, and after thawing it out place it in -water. The water is colored by the cell-sap which escapes from the -cells, just as we have seen it does as a result of a high temperature, -while a section of an unfrozen beet placed in water will not color it -if it was previously washed.</p> - -<p>If the slice of the beet is placed at about -6° C. in a shallow glass -vessel, and covered, ice will be formed over the surface. If we examine -it with the microscope ice crystals will be seen formed on the outside, -and these will not be colored. The water for the formation of the -crystals came from the cell-sap, but the concentrated solutions in the -sap were not withdrawn by the freezing over the surface.</p> - -<p><b>281.</b> If too much water is not withdrawn from the cells of many -plants in freezing, and they are thawed out slowly, the water which was -withdrawn from the cells will be absorbed again and the plant will not -be killed. But if the plant is thawed out quickly the water will not -be absorbed, but will remain on the surface and evaporate. Some will -also remain in the intercellular spaces, and the plant will die. Some -<span class="pagenum"><a name="Page_135" id="Page_135">[Pg 135]</a></span> -plants, however, no matter how slowly they are thawed out, are killed -after freezing, as the leaves of the pumpkin, dahlia, or the tubers of -the potato.</p> - -<p><b>282.</b> It has been found that as a general rule when plants, or -plant parts, contain little moisture they will withstand quite high -degrees of temperature, as well as quite low degrees, but when the -parts are filled with sap or water they are much more easily killed. -For this reason dry seeds and the winter buds of trees, and other -plants, because they contain but little water, are better able to -resist the cold of winters. But when growth begins in the spring, and -the tissues of these same parts become turgid and filled with water, -they are quite easily killed by frosts. It should be borne in mind, -however, that there is great individual variation in plants in this -respect, some being more susceptible to cold than others. There is -also great variation in plants as to their resistance to the cold of -winters, and of arctic climates, the plants of the latter regions -being able to resist very low temperatures. We have examples also in -the arctic plants, and those which grow in arctic climates on high -mountains, of plants which are able to carry on all the life functions -at temperatures but little above freezing.</p> - -<p>For further discussion as to relation of plants to temperature, see -Chapters <a href="#CHAPTER_XLVI">46</a>, 48, 49, and 53.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_136" id="Page_136">[Pg 136]</a></span></p> -<div class="chapter"> -<h2 class="nobreak">PART II.<br /> -MORPHOLOGY AND LIFE HISTORY<br /> OF REPRESENTATIVE PLANTS.</h2> -<hr class="r5" /> -<h3 class="nobreak"><a name="CHAPTER_XIV" id="CHAPTER_XIV">CHAPTER XIV.</a><br /> -<span class="h_subtitle">SPIROGYRA.</span></h3> -</div> - -<p><b>283.</b> In our study of protoplasm and some of the processes of -plant life we became acquainted with the general appearance of the -plant spirogyra. It is now a familiar object to us. And in taking up -the study of representative plants of the different groups, we shall -find that in knowing some of these lower plants the difficulties of -understanding methods of reproduction and relationship are not so great -as they would be if we were entirely ignorant of any members of the -lower groups.</p> - -<div class="figcenter"> - <img id="FIG_128" src="images/fig128.jpg" alt="" width="600" height="102" /> - <p class="center">Fig. 128.<br /> Thread of spirogyra, showing long cells, chlorophyll band,<br /> - nucleus, strands of protoplasm, and the granular wall layer<br /> of protoplasm.</p> -</div> - -<p><b>284. Form of spirogyra.</b>—We have found that the plant spirogyra -consists of simple threads, with cylindrical cells attached end to -end. We have also noted that each cell of the thread is exactly alike, -with the exception of certain “holdfasts” on some of the species. If -we should examine threads in different stages of growth we should find -that each cell is capable of growth and division, just as it is capable -of performing all the functions of nutrition and assimilation. The -cells of spirogyra then multiply by division. Not simply the cells at -the ends of the threads but any and all of the cells divide as they -grow, and in this way the threads increase in length.</p> - -<p><b>285. Multiplication of the threads.</b>—In studying living material -of this plant we have probably noted that the threads often become -broken by two of the adjacent cells of a thread becoming separated. -<span class="pagenum"><a name="Page_137" id="Page_137">[Pg 137]</a></span> -This may be and is accomplished in many cases without any injury to the -cells. In this manner the threads or plants of spirogyra, if we choose -to call a thread a plant, multiply, or increase. In this breaking of a -thread the cell wall which separates any two cells splits. If we should -examine several species of spirogyra we would probably find threads -which present two types as regards the character of the walls at the -ends of the cells. In <a href="#FIG_128">fig. 128</a> we see that the -ends are plain, that is, the cross walls are all straight. But in some other species -the inner wall of the cells presents a peculiar appearance. This inner wall at -the end of the cell is at first straight across. But it soon becomes -folded back into the interior of its cell, just as the end of an empty -glove finger may be pushed in. Then the infolded end is pushed partly -out again, so that a peculiar figure is the result.</p> - -<p><b>286. How some of the threads break.</b>—In the separation of the -cells of a thread this peculiarity is often of advantage to the plant. -The cell-sap within the protoplasmic membrane absorbs water and the -pressure pushes on the ends of the infolded cell walls. The inner -wall being so much longer than the outer wall, a pull is exerted on -the latter at the junction of the cells. Being weaker at this point -the outer wall is ruptured. The turgidity of the two cells causes -these infolded inner walls to push out suddenly as the outer wall is -ruptured, and the thread is snapped apart as quickly as a pipe-stem may -be broken.</p> - -<div class="figcenter"> - <img id="FIG_129" src="images/fig129.jpg" alt="" width="600" height="241" /> - <p class="center">Fig. 129.<br /> Zygospores of spirogyra.</p> -</div> - -<p><b>287. Conjugation of spirogyra.</b>—Under certain conditions, when -vegetative growth and multiplication cease, a process of reproduction -takes place which is of a kind termed sexual reproduction. If we select -mats of spirogyra which have lost their deep green color, we are likely -to find different stages of this sexual process, which in the case of -spirogyra and related plants is called <i>conjugation</i>. A few threads -of such a mat we should examine with the microscope. If the material -is in the right condition we see in certain of the cells an oval or -elliptical body. If we note carefully the cells in which these oval -bodies are situated, there will be seen a tube at one side which -<span class="pagenum"><a name="Page_138" id="Page_138">[Pg 138]</a></span> -connects with an empty cell of a thread which lies near as shown in -<a href="#FIG_129">fig. 129</a>. If we search through the material we may see other -threads connected in this ladder fashion, in which the contents of the cells -are in various stages of collapse from what we have seen in the growing -cell. In some the protoplasm and chlorophyll band have moved but little -from the wall; in others it forms a mass near the center of the cell, -and again in others we will see that the contents of the cell of one -of the threads has moved partly through the tube into the cell of the -thread with which it is connected.</p> - -<p><b>289.</b> This suggests to us that the oval bodies found in the cells -of one thread of the ladder, while the cells of the other thread were -empty, are formed by the union of the contents of the two cells. In -fact that is what does take place. This kind of union of the contents -of two similar or nearly similar cells is <i>conjugation</i>. The oval -bodies which are the result of this conjugation are <i>zygotes</i>, or -<i>zygospores</i>. When we are examining living material of spirogyra in -this stage it is possible to watch this process of conjugation. <a href="#FIG_130">Fig. 130</a> -represents the different stages of conjugation of spirogyra.</p> - -<p><b>290. How the threads conjugate, or join.</b>—The cells of two -threads lying parallel put out short processes. The tubes from two -opposite cells meet and join. The walls separating the contents of the -two tubes dissolve so that there is an open communication between the -two cells. The content of each one of these cells which take part in -the conjugation is a <i>gamete</i>. The one which passes through the tube to -<span class="pagenum"><a name="Page_139" id="Page_139">[Pg 139]</a></span> -the receiving cell is the <i>supplying gamete</i>, while that of the -receiving cell is the <i>receiving gamete</i>.</p> - -<div class="figcenter"> - <img id="FIG_130" src="images/fig130a.jpg" alt="" width="600" height="193" /> - <img src="images/fig130b.jpg" alt="" width="600" height="201" /> - <p class="center">Fig. 130.</p> - <p class="blockquot space-below2">Conjugation in spirogyra; from left - to right beginning in the upper row is shown the gradual passage - of the protoplasm from the supplying gamete to the receiving gamete.</p> -</div> - -<p><b>291. How the protoplasm moves from one cell to another.</b>—Before -any movement of the protoplasm of the supplying cell takes place we can -see that there is great activity in its protoplasm. Rounded vacuoles -appear which increase in size, are filled with a watery fluid, and -swell up like a vesicle, and then suddenly contract and disappear. -As the vacuole disappears it causes a sudden movement or contraction -of the protoplasm around it to take its place. Simultaneously with -the disappearance of the vacuole the membrane of the protoplasm is -separated from a part of the wall. This is probably brought about by a -sudden loss of some of the water in the cell-sap. These activities go -on, and the protoplasmic membrane continues to slip away from the wall. -Every now and then there is a movement by which the protoplasm is moved -a short distance. It is moved toward the tube and finally a portion of -it with one end of the chlorophyll band begins to move into the tube. -About this time the vacuoles can be seen in an active condition in the -<span class="pagenum"><a name="Page_140" id="Page_140">[Pg 140]</a></span> -receptive cell. At short intervals movement continues until the content -of the supplying cell has passed over into that of the receptive cell. -The protoplasm of this one is now slipping away from the cell wall, -until finally the two masses round up into the one zygospore.</p> - -<p><b>292. The zygospore.</b>—This zygospore now acquires a thick wall -which eventually becomes brown in color. The chlorophyll color fades -out, and a large part of the protoplasm passes into an oily substance -which makes it more resistant to conditions which would be fatal to the -vegetative threads. The zygospores are capable therefore of enduring -extremes of cold and dryness which would destroy the threads. They -pass through a “resting” period, in which the water in the pond may be -frozen, or dried, and with the oncoming of favorable conditions for -growth in the spring or in the autumn they germinate and produce the -green thread again.</p> - -<p><b>293. Life cycle.</b>—The growth of the spirogyra thread, the -conjugation of the gametes and formation of the zygospore, and the -growth of the thread from the zygospore again, makes what is called a -complete <i>life cycle</i>.</p> - -<p><b>294. Fertilization.</b>—While conjugation results in the fusion of -the two masses of protoplasm, fertilization is accomplished when the -nuclei of the two cells come together in the zygospore and fuse into a -single nucleus. The different stages in the fusion of the two nuclei of -a recently formed zygospore are shown in <a href="#FIG_131">figure 131</a>.</p> - -<p>In the conjugation of the two cells, the chlorophyll band of the -supplying cell is said to degenerate, so that in the new plant the -number of chlorophyll bands in a cell is not increased by the union of -the two cells.</p> - -<div class="figcenter"> - <img id="FIG_131" src="images/fig131.jpg" alt="" width="600" height="153" /> - <p class="center">Fig. 131.</p> - <p class="blockquot space-below2">Fertilization in spirogyra; shows different stages of fusion of - the two nuclei, with mature zygospore at right. (After Overton.)</p> -</div> - -<p><b>295. Simplicity of the process.</b>—In spirogyra any cell of the -thread may form a gamete (excepting the holdfasts of some species). -Since all of the cells of a thread are practically alike, there is no -structural difference between a vegetative cell and a cell about to -conjugate. The difference is a physiological one. All the cells are -capable of conjugation if the physiological conditions are present. All -the cells therefore are potential gametes. (Strictly speaking the wall -of the cell is the <i>garnetangium</i>, while the content forms the gamete.)</p> - -<p>While there is sometimes a slight difference in size between the -<span class="pagenum"><a name="Page_141" id="Page_141">[Pg 141]</a></span> -conjugating cells, and the supplying cell may be the smaller, this is -not general. We say, therefore, that there is no differentiation among -the gametes, so that usually before the protoplasm begins to move one -cannot say which is to be the supplying and which the receiving gamete.</p> - -<p><b>296. Position of the plant spirogyra.</b>—From our study then we -see that there is practically no differentiation among the vegetative -cells, except where holdfasts grow out from some of the cells -for support. They are all alike in form, in capacity for growth, -division, or multiplication of the threads. Each cell is practically -an independent plant. There is no differentiation between vegetative -cell and conjugating cell. All the cells are potential gametes. -Finally there is no structural differentiation between the gametes. -This indicates then a simple condition of things, a low grade of -organization.</p> - -<p><b>297.</b> The alga spirogyra is one of the representatives of the -lower algæ belonging to the group called <i>Conjugatæ</i>. Zygnema with -star-shaped chloroplasts, mougeotia with straight or sometimes twisted -chlorophyll bands, belong to the same group. In the latter genus only -a portion of the protoplasm of each cell unites to form the zygospore, -which is located in the tube between the cells.</p> - -<div class="figcontainer"> - <div class="figsub"> - <a id="FIG_132-137" name="FIG_132-137"> </a> - <img src="images/fig132.jpg" alt="" width="100" height="388" /> - <p class="center">Fig. 132.<br /> Closterium.</p> - </div> - <div class="figsub"> - <img src="images/fig133.jpg" alt="" width="200" height="333" /> - <p class="center">Fig. 133.<br /> Micrasterias.</p> - </div> - <div class="figsub"> - <img src="images/fig134.jpg" alt="" width="200" height="332" /> - <p class="center">Fig. 134.<br /> Xanthidium.</p> - </div> -</div> -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig135.jpg" alt="" width="200" height="270" /> - <p class="center">Fig. 135.<br /> Staurastrum.</p> - </div> - <div class="figsub"> - <img src="images/fig136.jpg" alt="" width="200" height="261" /> - <p class="center">Fig. 136.<br /> Euastrum.</p> - </div> - <div class="figsub"> - <img src="images/fig137.jpg" alt="" width="200" height="272" /> - <p class="center">Fig. 137.<br /> Cosmarium.</p> - </div> -</div> - -<p><b>298.</b> The desmids also belong to the same group. The desmids -usually live as separate cells. Many of them are beautiful in form. -They grow entangled among other algæ, or on the surface of aquatic -plants, or on wet soil. Several genera are illustrated in <a href="#FIG_132-137">figures 132-137</a>.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_142" id="Page_142">[Pg 142]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XV" id="CHAPTER_XV">CHAPTER XV.</a><br /> -<span class="h_subtitle">VAUCHERIA.</span></h3> -</div> - -<p><b>299.</b> The plant vaucheria we remember from our study in an -earlier chapter. It usually occurs in dense mats floating on the water -or lying on damp soil. The texture and feeling of these mats remind one -of “felt,” and the species are sometimes called the “green felts.” The -branched threads are continuous, that is there are no cross walls in -the vegetative threads. This plant multiplies itself in several ways -which would be too tedious to detail here. But when fresh bright green -mats can be obtained they should be placed in a large vessel of water -and set in a cool place. Only a small amount of the alga should be -placed in a vessel, since decay will set in more rapidly with a large -quantity. For several days one should look for small green bodies which -may be floating at the side of the vessel next the lighted window.</p> - -<div class="figcenter"> - <img id="FIG_138" src="images/fig138.jpg" alt="" width="400" height="410" /> - <p class="center">Fig. 138.<br /> Portion of branched thread of vaucheria.</p> -</div> - -<p><b>300. Zoogonidia of vaucheria.</b>—If these minute floating green -bodies are found, a small drop of water containing them should be -<span class="pagenum"><a name="Page_143" id="Page_143">[Pg 143]</a></span> -mounted for examination. If they are rounded, with slender hair-like -appendages over the surface, which vibrate and cause motion, they very -likely are one of the kinds of reproductive bodies of vaucheria. The -hair-like appendages are <i>cilia</i>, and they occur in pairs, several of -them distributed over the surface. These rounded bodies are <i>gonidia</i>, -and because they are motile they are called <i>zoogonidia</i>.</p> - -<p>By examining some of the threads in the vessel where they occurred we -may have perhaps an opportunity to see how they are produced. Short -branches are formed on the threads, and the contents are separated from -those of the main thread by a septum. The protoplasm and other contents -of this branch separate from the wall, round up into a mass, and escape -through an opening which is formed in the end. Here they swim around in -the water for a time, then come to rest, and germinate by growing out -into a tube which forms another vaucheria plant. It will be observed -that this kind of reproduction is not the result of the union of two -different parts of the plant. It thus differs from that which is termed -sexual reproduction. A small part of the plant simply becomes separated -from it as a special body, and then grows into a new plant, a sort of -multiplication. This kind of reproduction has been termed <i>asexual -reproduction</i>.</p> - -<div class="figcenter"> - <img id="FIG_139" src="images/fig139.jpg" alt="" width="400" height="265" /> - <p class="center">Fig. 139.<br /> Young antheridium and oogonium of Vaucheria sessilis,<br /> - before separation from contents of thread by a septum.</p> -</div> - -<p><b>301. Sexual reproduction in vaucheria.</b>—The organs which -are concerned in sexual reproduction in vaucheria are very readily -obtained for study if one collects the material at the right season. -They are found quite readily during the spring and autumn, and may be -preserved in formalin for study at any season, if the material cannot -be collected fresh at the time it is desired for study. Fine material -for study often occurs on the soil of pots in greenhouses during the -winter. While the zoogonidia are more apt to be found in material which -is quite green and freshly growing, the sexual organs are usually more -abundant when the threads appear somewhat yellowish, or yellow green.</p> - -<p><b>302. Vaucheria sessilis; the sessile vaucheria.</b>—In this plant -the sexual organs are sessile, that is they are not borne on a stalk -as in some other species. The sexual organs usually occur several in a -group. <a href="#FIG_139">Fig. 139</a> represents a portion of a fruiting plant. -<span class="pagenum"><a name="Page_144" id="Page_144">[Pg 144]</a></span></p> - -<p><b>303. Sexual organs of vaucheria. Antheridium.</b>—The antheridia -are short, slender, curved branches from a main thread. A septum is -formed which separates an end portion from the stalk. This end cell -is the <i>antheridium</i>. Frequently it is collapsed or empty as shown in -<a href="#FIG_140">fig. 140</a>. The protoplasm in the antheridium forms numerous -small oval bodies each with two slender lashes, the cilia. When these are formed -the antheridium opens at the end and they escape. It is after the -escape of these spermatozoids that the antheridium is collapsed. Each -spermatozoid is a male gamete.</p> - -<div class="figcenter"> - <img id="FIG_140" src="images/fig140.jpg" alt="" width="600" height="222" /> - <p class="center space-below2">Fig. 140.<br /> Vaucheria sessilis, - one antheridium between two oogonia.</p> -</div> -<div class="figcenter"> - <img src="images/fig141.jpg" alt="" width="400" height="205" /> - <p class="center">Fig. 141.</p> - <p class="blockquot">Vaucheria sessilis; oogonium opening and emitting a bit - of protoplasm; spermatozoids; spermatozoids entering - oogonium. (After Pringsheim and Goebel.)</p> -</div> - -<p><b>304. Oogonium.</b>—The oogonia are short branches also, but -they become large and somewhat oval. The septum which separates the -protoplasm from that of the main thread is as we see near the junction -of the branch with the main thread. The oogonium, as shown in the -figure, is usually turned somewhat to one side. When mature the pointed -end opens and a bit of the protoplasm escapes. The remaining protoplasm -forms the large rounded egg-cell which fills the wall of the oogonium. -In some of the oogonia which we examine this egg is surrounded by a -<span class="pagenum"><a name="Page_145" id="Page_145">[Pg 145]</a></span> -thick brown wall, with starchy and oily contents. This is the -fertilized egg (sometimes called here the oospore). It is freed from -the oogonium by the disintegration of the latter, sinks into the mud, -and remains here until the following autumn or spring, when it grows -directly into a new plant.</p> - -<div class="figcenter"> - <img src="images/fig142.jpg" alt="" width="600" height="206" /> - <p class="center">Fig. 142.</p> - <p class="blockquot">Fertilization in vaucheria, <i>mn</i>, male nucleus; - <i>fn</i>, female nucleus. Male nucleus entering the - egg and approaching the female nucleus. (After Oltmans.)</p> -</div> - -<p><b>305. Fertilization.</b>—Fertilization is accomplished by the -spermatozoids swimming in at the open end of the oogonium, when one of -them makes its way down into the egg and fuses with the nucleus of the egg.</p> - -<div class="figcenter"> - <img id="FIG_143" src="images/fig143.jpg" alt="" width="600" height="154" /> - <p class="center">Fig. 143.</p> - <p class="blockquot">Fertilization of vaucheria. <i>fn</i>, female nucleus; <i>mn</i>, - male nucleus. The different figures show various stages in the fusion of the nuclei.</p> -</div> - -<p><b>306. The twin vaucheria (V. geminata).</b>—Another species of -vaucheria is the twin vaucheria. This is also a common one, and may be -used for study instead of the sessile vaucheria if the latter cannot -be obtained. The sexual organs are borne at the end of a club-shaped -branch. There are usually two oogonia, and one antheridium between them -which terminates the branch. In a closely related species, instead of -the two oogonia there is a whorl of them with the antheridium in the -center.</p> - -<p><b>307. Vaucheria compared with spirogyra.</b>—In vaucheria we have a -plant which is very interesting to compare with spirogyra in several -<span class="pagenum"><a name="Page_146" id="Page_146">[Pg 146]</a></span> -respects. Growth takes place, not in all parts of the thread, but is -localized at the ends of the thread and its branches. This represents a -distinct advance on such a plant as spirogyra. Again, only specialized -parts of the plant in vaucheria form the sexual organs. These are -short branches. Farther there is a great difference in the size of the -two organs, and especially in the size of the gametes, the supplying -gametes (spermatozoids) being very minute, while the receptive gamete -is large and contains all the nutriment for the fertilized egg. In -spirogyra, on the other hand, there is usually no difference in size -of the gametes, as we have seen, and each contributes equally in the -matter of nutriment for the fertilized egg. Vaucheria, therefore, -represents a distinct advance, not only in the vegetative condition of -the plant, but in the specialization of the sexual organs. Vaucheria, -with other related algæ, belongs to a group known as the <i>Siphoneæ</i>, so -called because the plants are tube-like or <i>siphon</i>-like.</p> - -<div class="figcenter"> - <img src="images/fig143a.jpg" alt="" width="500" height="534" /> - <p class="center">Fig. 143<i>a</i>.</p> - <p class="blockquot">Botrydium granulatum. <i>A</i>, the whole plant; <i>B</i>, swarm spore; - <i>C</i>, planogametes; <i>a</i>, a single gamete; <i>b</i>-<i>e</i>, - two gametes in process of fusion; <i>f</i>, zygote.</p> -</div> - -<p><b>308. Botrydium granulatum.</b>—An example of one of the simpler -members of the Siphoneæ is Botrydium granulatum. It is found sometimes -in abundance on wet ground which is colored green or red by its -presence, according to the stage of development. The plant body is long -pear-shaped, the smaller end attached to the ground by slender branched -rhizoids (<a href="#FIG_143">Fig. 143</a>). The protoplasm contains many nuclei and -lines the inside of the wall. When multiplication takes place large numbers of -small zoospores with one cilium each are formed in the protoplasm, and -escape at free end. Reproduction takes place by two-ciliated gametes, -which fuse in pairs to form zygospores. In dry seasons the protoplasm -in the pear-shaped plant passes down into the rhizoids and forms -small rounded <i>planospores</i>. All the stages of development are too -complicated to describe here.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_147" id="Page_147">[Pg 147]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XVI" id="CHAPTER_XVI">CHAPTER XVI.</a><br /> -<span class="h_subtitle">ŒDOGONIUM.</span></h3> -</div> - -<p><b>309.</b> Œdogonium is also an alga. The plant is sometimes -associated with spirogyra, and occurs in similar situations. Our -attention was called to it in the study of chlorophyll bodies. These we -recollect are, in this plant, small oval disks, and thus differ from -those in spirogyra.</p> - -<p><b>310. Form of œdogonium.</b>—Like spirogyra, œdogonium forms simple -threads which are made up of cylindrical cells placed end to end. But -the plant is very different from any member of the group to which -spirogyra belongs. In the first place each cell is not the equivalent -of an individual plant as in spirogyra. Growth is localized or confined -to certain cells of the thread which divide at one end in such a way -as to leave a peculiar overlapping of the cell walls in the form of a -series of shallow caps or vessels (<a href="#FIG_144">fig. 144</a>), and this is one -of the characteristics of this genus. Other differences we find in the manner -of reproduction.</p> - -<p><b>311. Fruiting stage of œdogonium.</b>—Material in the fruiting -stage is quite easily obtainable, and may be preserved for study in -formalin if there is any doubt about obtaining it at the time we need -it for study. This condition of the plant is easily detected because of -the swollen condition of some of the cells, or by the presence of brown -bodies with a thick wall in some of the cells.</p> - -<p><b>312. Sexual organs of œdogonium. Oogonium and egg.</b>—The enlarged -cell is the oogonium, the wall of the cell being the wall of the -<span class="pagenum"><a name="Page_148" id="Page_148">[Pg 148]</a></span> -oogonium. (See <a href="#FIG_145">fig. 145</a>.) The protoplasm inside, before -fertilization, is the egg-cell. In those cases where the brown body with a thick -wall is present fertilization has taken place, and this body is the -<i>fertilized egg</i>, or <i>oospore</i>. It contains large quantities of an oily -substance, and, like the fertilized egg of spirogyra and vaucheria, is -able to withstand greater changes in temperature than the vegetative -stage, and can endure drying and freezing for some time without injury.</p> - -<div class="figcenter"> - <img id="FIG_144" src="images/fig144.jpg" alt="" width="600" height="111" /> - <p class="center space-below2">Fig. 144.<br /> Portion of thread of œdogonium, showing chlorophyll<br /> - grains, and peculiar cap cell walls.</p> -</div> -<div class="figcenter"> - <img id="FIG_145" src="images/fig145.jpg" alt="" width="600" height="376" /> - <p class="center">Fig. 145.<br /> Œdogonium undulatum, with oogonia and dwarf males;<br /> - the upper oogonium at the right has a mature oospore.</p> -</div> - -<p>In the oogonium wall there can frequently be seen a rift near the -<span class="pagenum"><a name="Page_149" id="Page_149">[Pg 149]</a></span> -middle of one side, or near the upper end. This is the opening through -which the spermatozoid entered to fecundate the egg.</p> - -<p><b>313. Dwarf male plants.</b>—In some species there will also be seen -peculiar club-shaped dwarf plants attached to the side of the oogonium, -or near it, and in many cases the end of this dwarf plant has an open -lid on the end.</p> - -<p><b>314. Antheridium.</b>—The end cell of the dwarf male in such -species is the <i>antheridium</i>. In other species the spermatozoids are -developed in different cells (antheridia) of the same thread which -bears the oogonium, or on a different thread.</p> - -<div class="figcenter"> - <img id="FIG_146" src="images/fig146.jpg" alt="" width="500" height="382" /> - <p class="center">Fig. 146.</p> - <p class="blockquot">Zoogonidia of œdogonium escaping. At the right one is germinating - and forming the holdfasts, by means of which these algæ attach - themselves to objects for support. (After Pringsheim.)</p> -</div> - -<p><b>315. Zoospore stage of œdogonium.</b>—The egg after a period of -rest starts into active life again. In doing so it does not develop -the thread-like plant directly as in the case of vaucheria and -spirogyra. It first divides into four zoospores which are exactly like -the zoogonidia in form. (See <a href="#FIG_152">fig. 152</a>.) These germinate and -develop the thread form again. This is a quite remarkable peculiarity of -œdogonium when compared with either vaucheria or spirogyra. It is the -introduction of an intermediate stage between the fertilized egg and -that form of the plant which bears the sexual organs, and should be -kept well in mind.</p> - -<p><b>316. Asexual reproduction.</b>—Material for the study of this stage -of œdogonium is not readily obtainable just when we wish it for study. -But fresh plants brought in and placed in a quantity of fresh water may -yield suitable material, and it should be examined at intervals for -several days. This kind of reproduction takes place by the formation -of <i>zoogonidia</i>. The entire contents of a cell round off into an oval -body, the wall of the cell breaks, and the zoogonidium escapes. It has -a clear space at the small end, and around this clear space is a row or -crown of cilia as shown in <a href="#FIG_146">fig. 146</a>. By the vibration of -these cilia the zoogonidium swims around for a time, then settles down on some -object of support, and several slender holdfasts grow out in the form -of short rhizoids which attach the young plant.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_147" src="images/fig147.jpg" alt="" width="150" height="315" /> - <p class="center">Fig. 147.<br /> Portion of thread of œdogonium<br /> - showing antheridia.</p> - </div> - <div class="figsub"> - <img id="FIG_148" src="images/fig148.jpg" alt="" width="250" height="308" /> - <p class="center">Fig. 148.<br /> Portion of thread of œdogonium<br /> - showing upper half of egg open,<br /> and a spermatozoid ready<br /> - to enter. (After Klebahn).</p> - </div> -</div> - -<p><b>317. Sexual reproduction. Antheridia.</b>—The antheridia are short -cells which are formed by one of the ordinary cells dividing into a -number of disk-shaped ones as shown in <a href="#FIG_147">fig. 147</a>. The protoplasm in each -<span class="pagenum"><a name="Page_150" id="Page_150">[Pg 150]</a></span> -antheridium forms two spermatozoids (sometimes only one) which are of -the same form as the zoogonidia but smaller, and yellowish instead of -green. In some species a motile body intermediate in size and color -between the spermatozoids and zoogonidia is first formed, which after -swimming around comes to rest on the oogonium, or near it, and develops -what is called a “dwarf male plant” from which the real spermatozoid is -produced.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig149.jpg" alt="" width="150" height="121" /> - <p class="center">Fig. 149.<br /> Male nucleus<br /> just entering<br /> egg at left side.</p> - </div> - <div class="figsub"> - <img src="images/fig150.jpg" alt="" width="150" height="136" /> - <p class="center">Fig. 150.<br /> Male nucleus<br /> fusing with<br /> female nucleus.</p> - </div> - <div class="figsub"> - <img src="images/fig151.jpg" alt="" width="150" height="118" /> - <p class="center">Fig. 151.<br /> The two nuclei<br /> fused, and<br /> fertilization<br /> complete.</p> - </div> - <p class="center">Figs. 149-151.—Fertilization in œdogonium. (After Klebahn).</p> -</div> - -<p><b>318. Oogonia.</b>—The oogonia are formed directly from one of the -vegetative cells. In most species this cell first enlarges in diameter, -so that it is easily detected. The protoplasm inside is the egg-cell. -The oogonium wall opens, a bit of the protoplasm is emitted, and the -spermatozoid then enters and fertilizes it (<a href="#FIG_148">fig. 148</a>). -Now a hard brown wall is formed around it, and, just as in spirogyra and vaucheria, -it passes through a resting period. At the time of germination it does -not produce the thread-like plant again directly, but first forms four -zoospores exactly like the zoogonidia (<a href="#FIG_152">fig. 152</a>). -These zoospores then germinate and form the plant.</p> - -<p><b>319. Œdogonium compared with spirogyra.</b>—Now if we compare -œdogonium with spirogyra, as we did in the case of vaucheria, we find -here also that there is an advance upon the simple condition which -exists in spirogyra. Growth and division of the thread is limited to -certain portions. The sexual organs are differentiated. They usually -differ in form and size from the vegetative cells, though the oogonium -<span class="pagenum"><a name="Page_151" id="Page_151">[Pg 151]</a></span> -is simply a changed vegetative cell. The sexual organs are -differentiated among themselves, the antheridium is small, and the -oogonium large. The gametes are also differentiated in size, and the -male gamete is motile, and carries in its body the nucleus which fuses -with the nucleus of the egg-cell.</p> - -<div class="figcenter"> - <img id="FIG_152" src="images/fig152.jpg" alt="" width="600" height="170" /> - <p class="center">Fig. 152.</p> - <p class="blockquot">Fertilized egg of œdogonium after a period of rest escaping - from the wall of the oogonium, and dividing into the four zoospores. (After Juranyi.)</p> -</div> - -<p>But a more striking advance is the fact that the fertilized egg does -not produce the vegetative thread of œdogonium directly, but first -forms four zoospores, each of which is then capable of developing into -the thread. On the other hand we found that in spirogyra the zygospore -develops directly into the thread form of the plant.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_153" src="images/fig153.jpg" alt="" width="140" height="346" /> - <p class="center">Fig. 153.<br /> Tuft of chætophora,<br /> natural size.</p> - </div> - <div class="figsub"> - <img id="FIG_154" src="images/fig154.jpg" alt="" width="250" height="341" /> - <p class="center">Fig. 154.<br /> Portion of chætophora<br /> showing branching.</p> - </div> -</div> - -<p><b>320. Position of œdogonium.</b>—Œdogonium is one of the true -thread-like algæ, green in color, and the threads are divided into -distinct cells. It, along with many relatives, was once placed -in the old genus conferva. These are all now placed in the group -<i>Confervoideæ</i>, that is, the <i>conferva-like algæ</i>.</p> - -<p><b>321. Relatives of œdogonium.</b>—Many other genera are related -to œdogonium. Some consist of simple threads, and others of branched -threads. An example of the branched forms is found in chætophora, -represented in figures <a href="#FIG_153">153</a>, <a href="#FIG_154">154</a>. This plant grows in -quiet pools or in slow-running water. It is attached to sticks, rocks, or to larger -aquatic plants. Many threads spring from the same point of attachment -and radiate in all directions. This, together with the branching of the -<span class="pagenum"><a name="Page_152" id="Page_152">[Pg 152]</a></span> -threads, makes a small, compact, greenish, rounded mass, which is held -firmly together by a gelatinous substance. The masses in this species -are about the size of a small pea, or smaller. Growth takes place in -chætophora at the ends of the threads and branches. That is, growth is -apical. This, together with the branched threads and the tendency to -form cell masses, is a great advance of the vegetative condition of the -plant upon that which we find in the simple threads of œdogonium.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_153" id="Page_153">[Pg 153]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XVII" id="CHAPTER_XVII">CHAPTER XVII.</a><br /> -<span class="h_subtitle">COLEOCHÆTE.</span></h3> -</div> - -<p><b>322.</b> Among the green algæ coleochæte is one of the most -interesting. Several species are known in this country. One of these at -least should be examined if it is possible to obtain it. It occurs in -the water of fresh lakes and ponds, attached to aquatic plants.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_155" src="images/fig155.jpg" alt="" width="125" height="347" /> - <p class="center">Fig. 155.<br /> Stem of aquatic plant<br /> showing coleochæte,<br /> natural size.</p> - </div> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_156" src="images/fig156.jpg" alt="" width="300" height="276" /> - <p class="center">Fig. 156.<br /> Thallus of Coleochæte scutata.</p> - </div> -</div> - -<p><b>323. The shield-shaped coleochæte.</b>—This plant (C. scutata) is -in the form of a flattened, circular, green plate, as shown in <a href="#FIG_156">fig. 156</a>. -<span class="pagenum"><a name="Page_154" id="Page_154">[Pg 154]</a></span> -It is attached near the center on one side to rushes and other -plants, and has been found quite abundantly for several years in the -waters of Cayuga Lake at its southern extremity. As will be seen it -consists of a single layer of green cells which radiate from the center -in branched rows to the outside, the cells lying so close together as -to form a continuous plate. The plant started its growth from a single -cell at the central point, and grew at the margin in all directions. -Sometimes they are quite irregular in outline, when they lie quite -closely side by side and interfere with one another by pressure. If the -surface is examined carefully there will be found long hairs, the base -of which is enclosed in a narrow sheath. It is from this character that -the genus takes its name of coleochæte (sheathed hair).</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_157" src="images/fig157.jpg" alt="" width="250" height="271" /> - <p class="center">Fig. 157.<br /> Portion of thallus of Coleochæte scutata,<br /> - showing empty cells from which zoogonidia<br /> - have escaped, one from each cell;<br /> - zoogonidia at the left. (After Pringsheim.)</p> - </div> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_158" src="images/fig158.jpg" alt="" width="250" height="289" /> - <p class="center">Fig. 158.<br /> Portion of thallus of Coleochæte<br /> - scutata, showing four antheridia<br /> formed from one thallus cell; a<br /> - single spermatozoid at the right.<br /> (After Pringsheim.)</p> - </div> -</div> - -<p><b>324. Fruiting stage of coleochæte.</b>—It is possible at some -seasons of the year to find rounded masses of cells situated near the -margin of this green disk. These have developed from a fertilized egg -which remained attached to the plant, and probably by this time the -parent plant has lost its color.</p> - -<p><b>325. Zoospore stage.</b>—This mass of tissue does not develop -directly into the circular green disk, but each of the cells forms a -zoospore. Here then, as in œdogonium, we have another stage of the -plant interpolated between the fertilized egg and that stage of the -plant which bears the gametes. But in coleochæte we have a distinct -advance in this stage upon what is present in œdogonium, for in -coleochæte the fertilized egg develops first into a several-celled mass -of tissue before the zoospores are formed, while in œdogonium only four -zoospores are formed directly from the egg.</p> - -<p><b>326. Asexual reproduction.</b>—In asexual reproduction any of the -green cells on the plant may form zoogonida. The contents of a cell -<span class="pagenum"><a name="Page_155" id="Page_155">[Pg 155]</a></span> -round off and form a single zoogonidium which has two cilia at the -smaller end of the oval body, <a href="#FIG_157">fig. 157</a>. After swimming -around for a time they come to rest, germinate, and produce another plant.</p> - -<p><b>327. Sexual reproduction.—Oogonium.</b>—The oogonium is formed by -the enlargement of a cell at the end of one of the threads, and then -the end of the cell elongates into a slender tube which opens at the -end to form a channel through which the spermatozoid may pass down to -the egg. The egg is formed of the contents of the cell (<a href="#FIG_159">fig. 159</a>). -Several oogonia are formed on one plant, and in such a plant as C. -scutata they are formed in a ring near the margin of the disk.</p> - -<div class="figcenter"> - <img id="FIG_159" src="images/fig159.jpg" alt="" width="600" height="341" /> - <p class="center">Fig. 159.</p> - <p class="blockquot">Coleochæte soluta; at left branch bearing oogonium (<i>oog</i>); - antheridia (<i>ant</i>); egg in oogonium and surrounded by - enveloping threads; at center three antheridia open, and one - spermatozoid; at right sporocarp, mature egg inside sporocarp wall.</p> -</div> -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig160.jpg" alt="" width="250" height="273" /> - <p class="center">Fig. 160.<br /> Two sporocarps<br /> still surrounded<br /> by thallus.<br /> - Thallus finally<br /> decays and sets<br /> sporocarp free.</p> - </div> - <div class="figsub"> - <img src="images/fig161.jpg" alt="" width="250" height="252" /> - <p class="center">Fig. 161.<br /> Sporocarp ruptured by growth<br /> of egg to form cell - mass.<br /> Cells of this sporophyte<br /> forming zoospores.</p> - </div> - <p class="center space-below2">Figs. 160, 161. C. scutata.</p> -</div> - -<p><b>328. Antheridia.</b>—In C. scutata certain of the cells of the -plant divide into four smaller cells, and each one of these becomes -an antheridium. In C. soluta the antheridia grow out from the end of -terminal cells in the form of short flasks, sometimes four in number or -less (<a href="#FIG_159">fig. 159</a>). A single spermatozoid is formed from the contents. -<span class="pagenum"><a name="Page_156" id="Page_156">[Pg 156]</a></span> -It is oval and possesses two long cilia. After swimming around it passes -down the tube of the oogonium and fertilizes the egg.</p> - -<p><b>329. Sporocarp.</b>—After the egg is fertilized the cells of the -threads near the egg grow up around it and form a firm covering one -cell in thickness. This envelope becomes brown and hard, and serves -to protect the egg. This is the “fruit” of the coleochæte, and is -sometimes called a sporocarp (spore-fruit). The development of the cell -mass and the zoospores from the egg has been described above.</p> - -<p>Some of the species of coleochæte consist of branched threads, while -others form circular cushions several layers in thickness. These forms -together with the form of our plant C. scutata make an interesting -series of transitional forms from filamentous structures to an expanded -plant body formed of a mass of cells. -<span class="pagenum"><a name="Page_157" id="Page_157">[Pg 157]</a></span></p> - -<p class="space-above2"><b>330. COMPARATIVE TABLE FOR SPIROGYRA, VAUCHERIA, -ŒDOGONIUM, COLEOCHÆTE.</b></p> - -<table class="smallfont" border="0" cellspacing="0" summary=" " cellpadding="0" rules="cols" > - <thead><tr> - <th class="tdc bb2" colspan="10"> </th> - </tr><tr> - <th class="tdc bb2" rowspan="3"> </th> - <th class="tdc bb2" colspan="7">GAMETOPHYTE. (Bears the sexual organs and gonidia.)</th> - <th class="tdc bb2" rowspan="2">SPOROPHYTE<br />Bears spores</th> - <th class="tdc bb2" rowspan="3"><span class="smcap">How Veg. Phase<br />of Gametophyte<br /> is Developed.</span></th> - </tr><tr> - <th class="tdc bb2" rowspan="2"><span class="smcap">Vegetative<br />Phase</span></th> - <th class="tdc bb2" rowspan="2"><span class="smcap">Growth.</span></th> - <th class="tdc bb2" rowspan="2"><span class="smcap">Mulitipl-<br />ication.</span></th> - <th class="tdc bb2" colspan="4"><span class="smcap">Sexual Reproduction.</span></th> - </tr><tr> - <th class="tdc bb2" colspan="2"><span class="smcap">Sexual Organs.</span></th> - <th class="tdc bb2" colspan="2"><span class="smcap">Gametes.</span></th> - <th class="tdc bb2"><span class="smcap">Fruit.</span></th> - </tr> - </thead> - <tbody><tr> - <td class="tdl bb" rowspan="2">Spirogyra.</td> - <td class="tdl_table bb" rowspan="2"><p>Simple threads of cylindrical cells.</p></td> - <td class="tdl_table bb" rowspan="2"><p>All cells divide and grow.</p></td> - <td class="tdl_table bb" rowspan="2"><p>By breaking up of threads.</p></td> - <td class="tdc greyish" colspan="2">Undifferentiated.</td> - <td class="tdc greyish" colspan="2">Undifferentiated.</td> - <td class="tdl_table bb" rowspan="2"><p>Zygospore<br />Rests.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Develops vegetative phase directly.</p></td> - </tr><tr> - <td class="tdl_table bb" colspan="2"><p>Any cell of thread. Conjugate by tube.</p></td> - <td class="tdl_table bb" colspan="2"><p>Entire contents of cojugating cells.</p></td> - </tr><tr> - <td class="tdl bb" rowspan="2">Vaucheria.</td> - <td class="tdl_table bb" rowspan="2"><p>Branched threads, continuous.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Limited to ends of threads and branches.</p></td> - <td class="tdl_table bb" rowspan="2"><p>By multiciliate zoogonidia, and other cells, from terminal portions.</p></td> - <td class="tdc greyish" colspan="2">Differentiated.</td> - <td class="tdc greyish" colspan="2">Differentiated.</td> - <td class="tdl_table bb" rowspan="2"><p>Egg (or oospore). Rests.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Develops vegetative phase directly.</p></td> - </tr><tr> - <td class="tdl_table bb"><p>Antheridia slender cells on special branches.</p></td> - <td class="tdl_table bb"><p>Oogonium, large rounded cell on special branch, opens and emits bit of protoplasm.</p></td> - <td class="tdl_table bb"><p>Small two-ciliated spermatozoids.</p></td> - <td class="tdc bb"> Large <br /> egg<br /> cell.</td> - </tr><tr> - <td class="tdl bb" rowspan="2">Œdogonium.</td> - <td class="tdl_table bb" rowspan="2"><p>Simple threads of cylindrical cells.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Limited to certain portions of thread.</p></td> - <td class="tdl_table bb" rowspan="2"><p>By oval zoogonidia, with crown of cilia. - Any cell may form a single zoogonidium.</p></td> - <td class="tdc greyish" colspan="2">Differentiated.</td> - <td class="tdc greyish" colspan="2">Differentiated.</td> - <td class="tdl_table bb" rowspan="2"><p>Egg (or oospore). Rests.</p></td> - <td class="tdl_table bb" rowspan="2"><p></p>Divides into four cells; - each forms zoospore which develops veg.phase again.</td> - </tr><tr> - <td class="tdl_table bb"><p>Antheridia disk-shaped, several from one vegetative cell. - Sometimes on dwarf males.</p></td> - <td class="tdl_table bb"><p>Oogonium, changed vegetative cell, opens and emits bit of protoplasm.</p></td> - <td class="tdl_table bb"><p>Oval spermatozoids with crown of cilia. Two from each antheridium.</p></td> - <td class="tdc bb">Large<br /> egg<br /> cell.</td> - </tr><tr> - <td class="tdl bb" rowspan="2">Coleochæte.</td> - <td class="tdl_table bb" rowspan="2"><p>Branched threads, or compact circular plates.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Terminal or marginal.</p></td> - <td class="tdl_table bb" rowspan="2"><p>By zoogonidia with two cilia. - Any cell may form a single zoogonidium.</p></td> - <td class="tdc greyish" colspan="2">Differentiated.</td> - <td class="tdc greyish" colspan="2">Differentiated.</td> - <td class="tdl_table bb" rowspan="2"><p>Egg (surrounded by wall from gametophyte). - Rests. Divides and grows to form a mass of cells.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Each forms a zoospore. - Zoospore develops veg. phase again.</p></td> - </tr><tr> - <td class="tdl_table bb"><p>Antheridia, four or several from single veg. cell.</p></td> - <td class="tdl_table bb"><p>Oogonium, enlarged veg. cell, with long tube through - opening of which spermatozoid enters. After fertilization wall of enveloping threads - surrounds oogonium.</p></td> - <td class="tdl_table bb"><p>Oval, biciliate spermatozoid, one from each ntheridium.</p></td> - <td class="tdc bb">Large<br /> egg<br /> cell.</td> - </tr><tr> - <td class="tdc bt2" colspan="10"> </td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_158" id="Page_158">[Pg 158]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XVIII" id="CHAPTER_XVIII">CHAPTER XVIII.</a><br /> -<span class="h_subtitle">CLASSIFICATION AND ADDITIONAL<br /> STUDIES OF THE ALGÆ.</span></h3> -</div> - -<p>In order to show the general relationship of the algæ studied, the -principal classes are here enumerated as well as some of the families. -In some of the groups not represented by the examples studied above, a -few species are described which may serve as the basis of additional -studies if desired. The principal classes<a name="FNanchor_17_17" id="FNanchor_17_17"></a><a href="#Footnote_17_17" class="fnanchor">[17]</a> -of algæ are as follows:</p> - -<p class="center"><b>Class Chlorophyceæ.</b></p> - -<p><b>331.</b> These are the green algæ, so called because the chlorophyll -green is usually not masked by other pigments, though in some forms it -is. There are three subclasses.</p> - -<p><b>332. Subclass PROTOCOCCOIDEÆ.</b>—In the Protococcoideæ are found -the simplest green plants. Many of them consist of single cells which -live an independent life. Others form “colonies,” loose aggregations -of individuals not yet having attained the permanency of even a simple -plant body, for the cells often separate readily and are able to form -new colonies. The colonies are often held together by a gelatinous -membrane, or matrix. Some are motile, while others are non-motile. A -few of the families are here enumerated.</p> - -<p><b>333. Family Volvocaceæ.</b>—These are all motile, during the -vegetative stage. The individuals are single or form more or less -globose colonies.</p> - -<p><b>334. The “red snow” plant (Sphærella nivalis).</b>—This is often -found in arctic and alpine regions forming a red covering over more or -less large areas of snow or ice. For this reason it is called the “red -snow plant.”</p> - -<p><b>335. Sphærella lacustris</b>, a closely related species, is very -widely distributed in temperate regions along streams or on the borders -<span class="pagenum"><a name="Page_159" id="Page_159">[Pg 159]</a></span> -of lakes and ponds. Here in dry weather it is often found closely -adhering to the dry rock surface, and giving it a reddish color as -if the rock were painted. This is especially the case in the shallow -basins formed over the uneven surface of the rock near the water’s -edge. These places during heavy rains or in high water are provided -with sufficient water to fill the basins. During such times the red -snow plant grows and multiplies, loses its red color and becomes green, -and, being motile, is free swimming. It is a single-celled plant, -oval in form, surrounded by a gelatinous sheath and with two cilia or -flagella at the smaller end, by the vibration of which it moves (<a href="#FIG_162">fig. 162).</a> -The single cell multiplies by dividing into two cells. When the -water dries out of the basin, the motile plant comes to rest, and many -of the cells assume the red color. To obtain the plant for study, -scrape some of the red covering from these rock basins and place it in -fresh spring water, and in a day or so the swarmers are likely to be -found. Under certain conditions small microzoids are formed.</p> - -<div class="figcenter"> - <img id="FIG_162" src="images/fig162.jpg" alt="" width="600" height="230" /> - <p class="center">Fig. 162.</p> - <p class="blockquot">Sphærella lacustris (Girod.) Wittrock. <i>A</i>, mature free swimming - individual with central red spot. <i>B</i>, division of mother individual to - form two. <i>C</i>, division of a red one to form four. <i>D</i>, division into - eight. <i>E</i>, a typical resting cell, red. <i>F</i>, same beginning to divide. - <i>G</i>, one of four daughter zoospores after swimming around for a time - losing its red color and becoming green. (After Hazen.)</p> -</div> - -<p><b>336. Chlamydomonas</b> is a very interesting genus of motile -one-celled green algæ, because the species are closely related to -the Flagellates among the lower animals. The plant is oval, with a -single chloroplast and surrounded by a gelatinous envelope through -which the two cilia or flagella extend. One-celled organisms of this -kind are sometimes called <i>monads</i>, i.e., a one-celled being. This -one has a gelatinous cloak and is, therefore, a <i>cloaked monad</i> -(<i>Chlamydomonas</i>). The species often are found as a very thin green -film on fresh water. C. pulvisculus is shown in <a href="#FIG_163">fig. 163</a>. When -it multiplies the single cell divides into two, as shown in <i>B</i>. Sometimes -a non-motile palmella stage is formed, as shown in <i>C</i> and <i>D</i>. -<span class="pagenum"><a name="Page_160" id="Page_160">[Pg 160]</a></span> -Reproduction takes place by gametes which are of unequal size, the -smaller one representing the sperm and the larger one the egg, as in -<i>E</i> and <i>F</i>. These conjugate as in <i>G</i> and <i>H</i>, the -protoplasm of the smaller one passing over into the larger one, and a -zygospore is thus formed.</p> - -<div class="figcenter"> - <img id="FIG_163" src="images/fig163.jpg" alt="" width="600" height="137" /> - <p class="center">Fig. 163.</p> - <p class="blockquot"><i>Chlamydomonas pulvisculus</i> (Müll.) Ehrb. <i>A</i>, an old motile - individual; <i>n</i>, nucleus; <i>p</i>, pyrenoid; <i>s</i>, red eye spot; <i>v</i>, - contractile vacuole; <i>B</i>, motile individual has drawn in its cilia - and divided into two; <i>C</i>, mother plant has drawn in its cilia and - divided into four non-motile cells; <i>D</i>, pamella stage; <i>E</i>, female - gamete—egg; <i>F</i>, male gamete—sperm; <i>G</i>, early stage of conjugation; - <i>H</i>, zygospore with conjugating tube and empty male cell attached. (After Wille.)</p> -</div> - -<p><b>337. Of those which form colonies</b>, Pandorina morum is widely -distributed and not rare. It consists of a sphere formed of sixteen -individuals enclosed in a thin gelatinous membrane. Each cell possesses -two cilia (or flagella), which extend from the broader end out through -the enveloping membrane. By the movement of these flagella the colony -goes rolling around in the water. When the plant multiplies each -individual cell divides into sixteen small cells, which then grow and -form new colonies. Reproduction takes place when the individual cells -of the young colonies separate, and usually a small individual unites -with a larger one and a zygospore is formed (see <a href="#FIG_164">fig. 164</a>). -Eudorina elegans is somewhat similar, but when the gametes are formed certain -mother cells divide into sixteen small motile males or sperms, and -certain other mother cells divide into sixteen large motile females or -eggs. These separate from the colonies, and the sperms pair with the -eggs and fuse to form zygospores. This plant as well as Chlamydomonas -pulvisculus foreshadows the early differentiation of sex in plants. -<span class="pagenum"><a name="Page_161" id="Page_161">[Pg 161]</a></span></p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_164" src="images/fig164.jpg" alt="" width="400" height="480" /> - <p class="center">Fig. 164.<br />Pandorina morum (Müll.) Bory.</p> -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdr">I, </td> - <td class="tdl">motile colony;</td> - </tr><tr> - <td class="tdr">II, </td> - <td class="tdl">colony divided into</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl">  16 daughter colonies;</td> - </tr><tr> - <td class="tdr">III, </td> - <td class="tdl">sexual colony, gametes escaping;</td> - </tr><tr> - <td class="tdr">IV, V, </td> - <td class="tdl">conjugating gametes;</td> - </tr><tr> - <td class="tdr">VI, VII, </td> - <td class="tdl">young and old zygospore;</td> - </tr><tr> - <td class="tdr">VIII, </td> - <td class="tdl">zygospore forming a large swarm</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl">  spore, which is free in IX;</td> - </tr><tr> - <td class="tdr">X, </td> - <td class="tdl">same large swarm spore divided</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl">  to form young colony.</td> - </tr><tr> - <td class="tdr"> </td> - <td class="tdl">(After Pringsheim.)</td> - </tr> - </tbody> -</table> -</div> - <div class="figsub"> - <p class="space-below3"> </p> - <img id="FIG_165" src="images/fig165.jpg" alt="" width="200" height="401" /> - <p class="center">Fig. 165.<br /> Pleurococcus<br /> (protococcus)<br /> vulgaris.</p> - </div> -</div> - -<p><b>338. Family Tetrasporaceæ.</b>—This family is well represented by -Tetraspora lubrica forming slimy green net-like sheets attached to -objects in slow-running water. It is really a single-celled plant. The -rounded cells divide by cross walls into four cells, and these again, -and so on, large numbers being held in loose sheets by the slime in -which they are imbedded.</p> - -<p><b>339. Family Pleurococcaceæ.</b>—The members of this family are -all non-motile in the vegetative stage. They consist of single -individuals, or of colonies. Pleurococcus vulgaris (Protococcus -vulgaris) is a single-celled alga, usually obtained with little -difficulty. It is often found on the shaded, and cool, or moist side of -trees, rocks, walls, etc., in damp places. This plant is not motile. It -multiplies by fission (<a href="#FIG_165">Fig. 165</a>) into two, then four, etc. -These cells remain united for a time, then separate. Sometimes the cells are found -growing out into filaments, and it is thought by some that P. vulgaris -may be only a simple stage of a higher alga. Eremosphæra viridis is -another single-celled alga found in fresh water among filamentous -forms. The cells are large and globose.</p> - -<div class="figcenter"> - <img id="FIG_166" src="images/fig166.jpg" alt="" width="600" height="264" /> - <div class="blockquot"> - <p class="center">Fig. 166.</p> - <p>Pediastrum boryanum. <i>A</i>, mature colony, most of the young colonies - have escaped from their mother cells; at <i>g</i>, a young colony is - escaping; <i>sp</i>, empty mother cells; <i>B</i>, young colony; <i>C</i>, - same colony with spores arranged in order. (After Braun.)</p> - </div> -</div> - -<p><b>340. Family Hydrodictyaceæ.</b>—These plants form colonies of -cells. Hydrodictyon reticulatum, the water net, is made up of large -numbers of cylindrical cells so joined at their ends as to form a large -open mesh or net. Pediastrum forms circular flat colonies, as shown in -<a href="#FIG_166">fig. 166</a>. Both of these plants are rather common in fresh-water -pools, the latter one intermingled with filamentous algæ, while the former -forms large sheets or nets. Multiplication in Hydrodictyon takes place -<span class="pagenum"><a name="Page_162" id="Page_162">[Pg 162]</a></span> -by the protoplasm in one of the cells dividing into thousands of minute -cells, which gradually arrange themselves in the form of a net, escape -together from the mother cell, and grow into a large net. In Pediastrum -multiplication takes place in a similar way, but the protoplasm in each -cell usually divides into sixteen small cells, and escaping together -from the mother cell arrange themselves and grow to full size (<a href="#FIG_166">fig. 166</a>).</p> - -<p><b>341. The Conjugateæ</b> include several families of green algæ, -which probably should be included among the Chlorophyceæ. They have -probably had their origin from some of the more simple members of the -Protococcoideæ. They are represented by Spirogyra, Zygnema, and the -desmids, studied in <a href="#CHAPTER_XIV">Chapter 14</a>.</p> - -<p><b>342. Subclass CONFERVOIDEÆ.</b>—These are mostly filamentous algæ, -the filaments being composed of cells firmly united, and, with the -exception of the simplest forms, there is a definite growing point. A -few of the families are as follows:</p> - -<p><b>343. Family Ulvaceæ.</b>—These contain the sea wracks, or sea -lettuce, like Ulva, forming expanded green, ribbon-like growths in the sea.</p> - -<div class="figcenter"> - <img id="FIG_167" src="images/fig167.jpg" alt="" width="500" height="388" /> - <div class="blockquot"> - <p class="center">Fig. 167.</p> - <p>Ulothrix zonata. <i>A</i>, base of thread. <i>B</i>, cells with zoospores, <i>C</i>, - one cell with zoospores escaping another cell with small biciliate - gametes escaping and some fusing to form zygospores, <i>E</i>, zoospores - germinating and forming threads: <i>F</i>, <i>G</i>, zygospore growing and - forming zoospores. (After Caldwell and Dodel-Port.)</p> - </div> -</div> - -<p><b>344. Family Ulotrichaceæ</b>, represented by Ulothrix zonata, not -uncommon in slow-running water or in ponds of fresh water attached -to rocks or wood. It consists of simple threads of short cells. -Multiplication takes place by zoospores. Reproduction takes place by -motile sexual cells (gametes) which fuse to form a zygospore (<a href="#FIG_167">fig. 167</a>).</p> - -<p><b>345. Family Chætophoraceæ</b>, represented by Chætophora (in <a href="#CHAPTER_XV">Chapter -15</a>) and Drapernaudia in fresh water.</p> - -<p><b>346. Family Œdogoniaceæ</b>, represented by Œdogonium (<a href="#CHAPTER_XVI">Chapter 16</a>).</p> - -<p><b>347. Family Coleochætaceæ</b>, represented by Coleochæte (<a href="#CHAPTER_XVII">Chapter 17</a>).</p> - -<p><b>348. Subclass SIPHONEÆ.</b>—There are several families.</p> - -<p><b>349. Family Botrydiaceæ.</b>—This is represented by Botrydium -granulatum (Chapter 15, <a href="#Page_146">p. 146</a>).</p> - -<p><b>350. Family Vaucheriaceæ</b>, represented by Vaucheria (<a href="#CHAPTER_XV">Chapter 15</a>), -with quite a large number of species, is widely distributed. -<span class="pagenum"><a name="Page_163" id="Page_163">[Pg 163]</a></span></p> - -<p class="center"><b>Class Schizophyceæ</b> (= Cyanophyceæ).</p> - -<div class="figright"> - <img id="FIG_168" src="images/fig168.jpg" alt="" width="200" height="211" /> - <p class="center">Fig. 168.<br /> Glœocapsa.</p> -</div> - -<p><b>351. The Blue-Green Algæ</b>, or <b>Cyanophyceæ</b> form slimy -looking thin mats on damp wood or the ground, or floating mats or -scum on the water. The color is usually bluish green, but in some -species it is purple, red or brown. All have chlorophyll, but it is -not in distinct chloroplasts and is more or less completely guised -by the presence of other pigments. Two orders and eight families are -recognized. The following include some of our common forms:</p> - -<p><b>352. ORDER COCCOGONALES (COCCOGONEÆ).</b>—Single-celled plants, -occurring singly or in colonies, in some forms forming short threads. -One of the two families is mentioned.</p> - -<p><b>353. Family Chroococcaceæ.</b>—The plants multiply only through cell -division. Chroococcus, forms rounded, blue-green cells enclosed in a -thick gelatinous coat, in fresh water and in damp places; certain -species form “lichen-gonidia” in some genera of lichens. Glœocapsa is -similar to Chroococcus, but the colonies are surrounded by an additional -common gelatinous envelope (<a href="#FIG_168">fig. 168</a>); on damp rocks, etc.</p> - -<div class="figcenter"> - <img src="images/fig169.jpg" alt="" width="500" height="382" /> - <div class="blockquot"> - <p class="center">Fig. 169.</p> - <p><i>A</i>, Oscillatoria princeps, <i>a</i>, terminal cell; <i>b</i>, <i>c</i>, - portions from the middle of a filament. In <i>c</i>, a dead cell is shown between - the living cells; <i>B</i>, Oscillatoria froelichii, <i>b</i>, with granules along - the partition walls.</p> - </div> -</div> - -<p class="space-above2"><b>354. ORDER HORMOGONALES (HORMOGONEÆ).</b>—Plants filamentous, -simple celled or with false or true branching, usually several celled -(Spirulina is single celled). Multiplication takes place through -<i>hormogones</i>, short sections of the threads becoming free; also through -resting cells. Two of the six families are mentioned.</p> - -<p><b>355. Family Oscillatoriaceæ.</b>—This family is represented by -the genus Oscillatoria, and by several other genera common and widely -distributed. Oscillatoria contains many species. They are found on the -damp ground or wood, or floating in mats in the water. They often form -<span class="pagenum"><a name="Page_164" id="Page_164">[Pg 164]</a></span> -on the soil at the bottom of the pool, and as gas becomes entangled -in the mat of threads, it is lifted from the bottom and floated to -the surface of the water. The plant is thread-like, and divided up -into many short cells. The threads often show an oscillating movement, -whence the name <i>Oscillatoria</i>.</p> - -<p><b>356. Family Nostocaceæ.</b>—This family is represented by Nostoc, -which forms rounded, slimy, blue-green masses on wet rocks. The -individual plants in the slimy ball resemble strings of beads, each -cell being rounded, and several of these arranged in chains as shown -in <a href="#FIG_170">fig. 170</a>. Here and there are often found larger cells -(heterocysts) in the chain. Nostoc punctiforme lives in the intercellular spaces -of the roots of cycads (often found in greenhouses), and in the -stems of Gunnera. N. sphæricum lives in the spaces between the cells -in many species of liverworts (in the genera Anthoceros, Blasia, -Pellia, Aneura, Riccia, etc.), and in the perforated cells of Sphagnum -acutifolium. Anabæna is another common and widely distributed genus. -The species occur in fresh or salt water, singly or in slimy masses. -Anabæna azollæ lives endophytically in the leaves of the water fern, Azolla.</p> - -<div class="figcenter"> - <img id="FIG_170" src="images/fig170.jpg" alt="" width="400" height="380" /> - <div class="blockquot"> - <p class="center">Fig. 170.</p> - <p>Nostoc linckii. <i>A</i>, filament with two heterocysts (<i>h</i>), and a large - number of spores (<i>sp</i>); <i>B</i>, isolated spore beginning to germinate; - <i>C</i>, young filament developed from spore. (After Bornet.)</p> - </div> -</div> -<div class="figcenter"> - <img src="images/fig171.jpg" alt="" width="600" height="208" /> - <div class="blockquot"> - <p class="center">Fig. 171.</p> - <p>Bacteria. <i>A</i>, Bacillus subtilis. Spores in threads, unstained rods, - and stained rods showing cilia; <i>B</i>, Bacillus tetani, the tetanus - or lockjaw bacillus, found in garden soil and on old rusty nails. - Spores in club-shaped ends. <i>C</i>, Micrococcus; <i>D</i>, Sarcina; <i>E</i>, - Streptococcus; <i>F</i>, Spirillum. (After Migula.)</p> - </div> -</div> - -<p class="center"><b>Class Schizomycetes.</b></p> - -<p><b>357. Bacteriales.</b>—The bacteria are sometimes classified -with the Cyanophyceæ, under the name Schizophyta, and represent the -subdivision Schizomycetes, or fission fungi, because many of them -multiply by a division of the cells just as the blue-green algæ do. -For example, Bacillus forms rods which increase in length and divide -into two rods, or it may grow into a long thread of many short rods. -Micrococcus consists of single rounded cells. Streptococcus forms -chains of rounded cells, Sarcina forms irregular cubes of rounded -cells, while others like Spirillum are spiral in form. Bacillus -<span class="pagenum"><a name="Page_165" id="Page_165">[Pg 165]</a></span> -subtilis may be obtained by making an infusion from hay and allowing -it to stand for several days. Bacillus tetani occurs in the soil, on -old rusty nails, etc. It is called the tetanus bacillus because it -causes a permanent spasm of certain muscles, as in “lockjaw.” This -bacillus grows and produces this result on the muscles when it occurs -in deep and closed wounds such as are caused by stepping on an old nail -or other object which pierces the flesh deeply. In such a deep wound -oxygen is deficient, and in this condition the bacillus is virulent. -Opening the wounds to admit oxygen and washing them out with a solution -of bichloride of mercury prevents the tetanus. Many bacteria are of -great importance in bringing about the decay of dead animal and plant -matter, returning it to a condition for plant food. (See also nitrate -and nitrite bacteria, <a href="#CHAPTER_IX">Chapter IX</a>.) While most bacteria -are harmless there are many which cause very serious diseases of man and animals, -as typhoid fever, diphtheria, tuberculosis, etc., while some others -produce disease in plants. Others aid in certain fermentations of -liquids and are employed for making certain kinds of wines or other -beverages. Some work in symbiosis with yeasts, as in the kephir yeast, -used in fermenting certain crude beverages by natives of some countries.</p> - -<p><b>357</b><i>a</i>. <b>Myxobacteriales (Myxobacteriaceæ -Thaxter<a name="FNanchor_18_18" id="FNanchor_18_18"></a><a href="#Footnote_18_18" class="fnanchor">[18]</a>).</b>—These -plants consist of colonies of bacteria-like organisms, motile rods, -which multiply by cross-division and secrete a gelatinous substance or -matrix which surrounds the colonies. They form plasmodium-like masses -which superficially resemble the slime moulds. In the fruiting stage -some species become elevated from the substratum into cylindrical, -clavate, or branched forms, which bear cysts of various shapes -containing the rods in a resting stage, or the rods are converted into -spore-like masses. Ex., Chondromyces crocatus on decaying plant parts, -Myxobacter aureus on wet wood and bark, Myxococcus rubescens on dung, -decaying lichens, paper, etc.</p> - -<p class="center"><b>Class Flagellata.</b></p> - -<p><b>358. The flagellates</b> are organisms of very low organization -resembling animals as much as they do plants. They are single celled -and possess two cilia or flagella, by the vibration of which they -move. Some are without a cell wall, while others have a well-defined -membrane, but it rarely consists of cellulose. Some have chromatophores -and are able to manufacture carbohydrates like ordinary green plants. -These are green in Euglena, and brown in Hydrurus. Some possess a -mouth-like opening and are able to ingest solid particles of food -(more like animals), while others have no such opening and absorb food -substances dissolved in water (more like plants). The Euglena viridis is not -uncommon in stagnant water, often forming a greenish film on the water. -<span class="pagenum"><a name="Page_166" id="Page_166">[Pg 166]</a></span></p> - -<p class="center"><b>Class Peridineæ.</b></p> - -<p><b>358</b><i>a</i>. These are peculiar one-celled organisms provided -with two flagella and show some relationship to the Flagellates. They -usually are provided with a cellulose membrane, which in some forms -consists of curiously sculptured plates. In the higher forms this -cellulose membrane consists of two valves fitting together in such a -way as to resemble some of the diatoms. Like the Flagellates, some -have green chromatophores, which in some are obscured by a yellow or -brown pigment (resembling the diatoms), while still others have no -chlorophyll. The Peridineæ are abundant in the sea, while some are -found in fresh water.</p> - -<p class="center"><b>Class Diatomaphyceæ<br /> (Bacillariales, Diatomaceæ).</b></p> - -<div class="figcenter"> - <img src="images/fig171a.jpg" alt="" width="600" height="300" /> - <div class="blockquot"> - <p class="center">Fig. 171<i>a</i>.</p> - <p>A group of Diatoms: <i>c</i> and <i>d</i>, top and side views of the same form; - <i>e</i>, colony of stalked forms attached to an alga; <i>f</i> and <i>g</i>, top and - side views of the form shown at <i>e</i>; <i>h</i>, a colony; <i>i</i>, a colony, the - top and side view shown at <i>k</i> and <i>n</i>, forming auxospores. (After Kerner.)</p> - </div> -</div> - -<p><b>358</b><i>b</i>. <b>The diatoms</b> are minute and peculiar organisms -believed to be algæ. They live in fresh, brackish, and salt water. They -are often found covering the surface of rocks, sticks, or the soil -in thin sheets. They occur singly and free, or several individuals -may be joined into long threads, or other species may be attached to -objects by slender gelatinous stalks. Each protoplast is enclosed in a -silicified skeleton in the form of a box with two halves, often shaped -like an old-fashioned pill box, one half fitting over the other like -the lid of a box. It is evident that in this condition the plant cannot -increase much in size.</p> - -<p>They multiply by fission. This takes place longitudinally, i.e., in the -direction of the two halves or <i>valves</i> of the box. Each new plant then -has a valve only on one side. A new valve is now formed over the naked -half, and fits inside the old valve. At each division the individuals -thus become smaller and smaller until they reach a certain point, when -the valves are cast off and the cell forms an <i>auxospore</i>, i.e., it -grows alone, or after conjugation with another, to the full size again, -<span class="pagenum"><a name="Page_167" id="Page_167">[Pg 167]</a></span> -and eventually provides itself with new valves. The valves are often -marked, with numerous and fine lines, often making beautiful figures, -and some are used for test objects for microscopes.</p> - -<p>The free forms are capable of movement. The movement takes place in the -longitudinal direction of the valves. They glide for some time in one -direction, and then stop and move back again. It is not a difficult -thing to mount them in fresh water and observe this movement.</p> - -<p>The diatoms have small chlorophyll plates, but the green color is -disguised by a brownish pigment called diatomin. The relationships of -the diatoms are uncertain, but some, because of the color, think they -are related to the Phæophyceæ.</p> - -<p class="center"><b>Class Phæophyceæ.</b></p> - -<p><b>359. The brown algæ. (Phæophyceæ).</b>—The members of this class -possess chlorophyll, but it is obscured by a brown pigment. The plants -are accessible at the seashore, and for inland laboratories may be -preserved in formalin (2½ per cent). (See also Chapter LVI.)</p> - -<div class="figcenter"> - <img id="FIG_172" src="images/fig172.jpg" alt="" width="500" height="474" /> - <div class="blockquot"> - <p class="center">Fig. 172.</p> - <p><i>A</i>, Ectocarpus siliculosus; <i>B</i>, branch with a young and a ripe - plurilocular sporangium; <i>E</i>, gametes fusing to form zygospore, (<i>B</i>, - after Thuret; <i>E</i>, after Berthold.)</p> - </div> -</div> - -<p><b>360. Ectocarpus.</b>—The genus Ectocarpus represents well some -of the simpler forms of the brown algæ (<a href="#FIG_172">fig. 172</a>). They are -slender, filamentous branched algæ growing in tufts, either epiphytic on other -marine algæ (often on Fucaceæ), or on stones. The slender threads are -only divided crosswise, and thus consist of long series of short cells. -<span class="pagenum"><a name="Page_168" id="Page_168">[Pg 168]</a></span> -The sporangia are usually plurilocular (sometimes unilocular), and -usually occur in the place of lateral branches. The zoospores escape -from the apex of the sporangium and are biciliate, and they fuse to -form zygospores.</p> - -<p><b>361. Sphacelaria.</b>—The species of this genus represent an -advance in the development of the thallus. While they are filamentous -and branched, division takes place longitudinally as well as crosswise -(<a href="#FIG_173">fig. 173</a>).</p> - -<p><b>362. Leathesia difformis</b> represents an interesting type because -the plant body is small, globose, later irregular and hollow, and -consists of short radiately arranged branches, the surface ones in the -form of short, crowded, but free, trichome-like green branches. This -trichothallic body recalls the similar form of Chætophora pisiformis -(<a href="#CHAPTER_XVI">Chapter 16</a>) among the Chlorophyceæ.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_173" src="images/fig173.jpg" alt="" width="300" height="469" /> - <p class="center">Fig. 173.<br /> Sphacelaria, portion of plant<br /> - showing longitudinal division<br /> - of cells, and brood bud<br /> (plurilocular sporangium).</p> - </div> - <div class="figsub"> - <img id="FIG_174" src="images/fig174.jpg" alt="" width="270" height="469" /> - <p class="center">Fig. 174.<br /> Laminaria digitata, forma cloustoni,<br /> North Sea. (Reduced.)</p> - </div> -</div> - -<p><b>363. The Giant Kelps.</b>—Among the brown algæ are found the -largest specimens, some of the laminarias or giant kelps, rivaling in -size the largest land plants, and some of them have highly developed -tissues. <i>Postelsia palmæformis</i> has a long, stout stem, from the -free end of which extend numerous large and long blades, while the -stem is attached to the rocks by numerous “root” like outgrowths, the -holdfasts. It occurs along the northern Pacific coast, and appears to -flourish where it receives the shock of the surf beating on the shore. -Several species of Laminaria occur on our north Atlantic coast. In L. -digitata, the stem expands at the end into a broad blade, which becomes -split into several smaller blades (<a href="#FIG_174">fig. 174</a>). <i>Macrocystis pyrifera</i> -inhabits the ocean in the southern hemisphere, and sometimes is found -along the north American coast. It is said to reach a length of 200-300 -meters.</p> - -<p><b>364. Fucus, or Rockweed.</b>—This plant is a more or less branched -and flattened thallus or “frond.” One of them, illustrated in <a href="#FIG_119">fig. 119</a>, -measures 15-30 <i>cm</i> (6-12 inches) in length. It is attached to rocks -and stones which are more or less exposed at low tide. From the base -of the plant are developed several short and more or less branched -expansions called “holdfasts,” which, as their name implies, are organs -of attachment. Some species (F. vesiculosus) have vesicular swellings -in the thallus. -<span class="pagenum"><a name="Page_169" id="Page_169">[Pg 169]</a></span></p> - -<p>The fruiting portions are somewhat thickened as shown in the figure. -Within these portions are numerous oval cavities opening by a circular -pore, which gives a punctate appearance to these fruiting cushions. -Tufts of hairs frequently project through them.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig175.jpg" alt="" width="210" height="266" /> - <p class="center">Fig. 175.<br /> Portion of plant of Fucus<br /> - showing conceptacles in<br /> enlarged ends; and below<br /> - the vesicles<br /> (Fucus vesiculosus).</p> - </div> - <div class="figsub"> - <img src="images/fig176.jpg" alt="" width="300" height="261" /> - <p class="center">Fig. 176.<br /> Section of conceptacle<br /> of Fucus, showing oogonia,<br /> - and tufts of antheridia.</p> - </div> -</div> - -<p><b>365. Structure of the conceptacles.</b>—On making sections of the -fruiting portions one finds the walls of the cavities covered with -outgrowths. Some of these are short branches which bear a large rounded -terminal sac, the oogonium, at maturity containing eight egg-cells. -More slender and much-branched threads bear narrowly oval antheridia. -In these are developed several two-ciliated spermatozoids.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig177.jpg" alt="" width="250" height="384" /> - <p class="center">Fig. 177.<br /> Oogonium of Fucus<br /> with ripe eggs.</p> - </div> - <div class="figsub"> - <img src="images/fig178.jpg" alt="" width="300" height="373" /> - <p class="center">Fig. 178.<br /> Antheridia of Fucus,<br /> on branched threads.</p> - </div> -</div> - -<p><b>366. Fertilization.</b>—At maturity the spermatozoids and egg-cells -float outside of the oval cavities, where fertilization takes place. -<span class="pagenum"><a name="Page_170" id="Page_170">[Pg 170]</a></span> -The spermatozoid sinks into the protoplasm of the egg-cell, makes its -way to the nucleus of the egg, and fuses with it as shown in <a href="#FIG_181">fig. 181</a>. -The fertilized egg then grows into a new plant. Nearly all the brown -algæ are marine.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig179.jpg" alt="" width="250" height="392" /> - <p class="center">Fig. 179.<br /> Antheridia of Fucus with<br /> escaping spermatozoids.</p> - </div> - <div class="figsub"> - <img src="images/fig180.jpg" alt="" width="250" height="378" /> - <p class="center">Fig. 180.<br /> Eggs of Fucus surrounded<br /> by spermatozoids.</p> - </div> -</div> -<div class="figcenter"> - <img id="FIG_181" src="images/fig181.jpg" alt="" width="600" height="185" /> - <div class="blockquot"> - <p class="center">Fig. 181.</p> - <p>Fertilization in Fucus; <i>fn</i>, female nucleus; <i>mn</i>, male nucleus; - <i>n</i>, nucleolus. In the left figure the male nucleus is shown moving - down through the cytoplasm of the egg; in the remaining figures the - cytoplasm of the egg is omitted. (After Strasburger.)</p> - </div> -</div> - -<p><b>367. The Gulf weed</b> (<b>Sargassum bacciferum</b>) in the warmer -Atlantic ocean unites in great masses which float on the water, whence -comes the name “Sargassum Sea.” The Sargassum grows on the coast where -it is attached to the rocks, but the beating of the waves breaks many -specimens loose and these float out into the more quiet waters, where -they continue to grow and multiply vegetatively.</p> - -<p><b>368. Uses.</b>—Laminaria japonica and L. angustata are used as food -by the Chinese and Japanese. Some species of the Laminariaceæ are used -as food for cattle and are also used for fertilizers, while L. digitata -is sometimes employed in surgery. -<span class="pagenum"><a name="Page_171" id="Page_171">[Pg 171]</a></span></p> - -<p><i>Classification.</i>—Kjellman divides the Phæophyceæ into two orders.</p> - -<p><b>369. Order Phæosporales (Phæosporeæ)</b> including 18 families. -One of the most conspicuous families is the Laminariaceæ, including -among others the Giant Kelps mentioned above (Laminaria, Postelsia, -Macrocystis, etc.).</p> - -<p><b>370. Order Cyclosporales (Cyclosporeæ).</b>—This includes one -family, the <i>Fucaceæ</i> with Ectocarpus, Sphacelaria, Læathesia, Fucus, -Sargassum, etc.</p> - -<p class="center"><b>Class Rhodophyceæ.</b></p> - -<p><b>371. The red algæ (Rhodophyceæ).</b>—The larger number of the -so-called red algæ occur in salt water, though a few genera occur in -fresh water. The plants possess chlorophyll, but it is usually obscured -by a reddish or purple pigment.</p> - -<p><b>372. Nemalion.</b>—This is one of the lower marine forms, though -its thallus is not one of the simplest in structure. The plant body -consists of a slender cylindrical branched shoot, sometimes very -profusely branched. The central strand is rather firm, while the cortex -is composed of rather loose filaments.</p> - -<div class="figcenter"> - <img src="images/fig182.jpg" alt="" width="400" height="371" /> - <div class="blockquot"> - <p class="center">Fig. 182.</p> - <p>A red alga (Nemalion). <i>A</i>, sexual branches, showing antheridia (<i>a</i>); - carpogonium or procarp (<i>o</i>) with its trichogyne (<i>t</i>), to which are - attached two spermatia (<i>s</i>); <i>B</i>, beginning of a cystocarp (<i>o</i>), - the trichogyne (<i>t</i>) still showing; <i>C</i>, an almost mature cystocarp - (<i>o</i>), with the disorganizing trichogyne (<i>t</i>). (After Vines.)</p> - </div> -</div> - -<p><b>373. Batrachospermum.</b>—This genus occurs in fresh water, and the -species are found in slow-running water of shallow streams or ditches. -There is a central slender strand which is more or less branched, -and on these branches are whorls of densely crowded slender branches -occurring at regular intervals. The plants are usually very slippery. -Gonidia are formed on the ends of some of these branches in globose -sporangia, called monosporangia, since but a single spore or gonidium -is developed in each. Other branches often terminate in long slender -hyaline setæ.</p> - -<p><b>374. Lemanea.</b>—This genus also occurs in fresh water. The -species develop only during the cold winter months in rapids of streams -or where the water from falls strikes the rocks and is thoroughly -aerated. They form tufts of greenish threads, cylindrical or whiplike, -which in the summer are usually much broken down. The threads are -<span class="pagenum"><a name="Page_172" id="Page_172">[Pg 172]</a></span> -hollow and have a firm cortex. These are the sexual shoots, and they arise -as branches from a sterile filamentous-branched, Chantransia-like form.</p> - -<p><b>375. Fertilization in the lower red algæ.</b>—The sexual organs in -the red algæ consist of antheridia and carpogonia. The antheridia are -usually borne in crowded clusters, or surfaces, and bear terminally -the small non-motile sperm cells. The carpogonium is a branch of one -or several cells, the terminal cell (procarp) extending into a long -slender process, the trichogyne. The sperm cell comes in contact with -the trichogyne, and in the case of Nemalion and some others the nucleus -has been found to pass down the inside and fuse with the nucleus of the -procarp.</p> - -<div class="figcenter"> - <img src="images/fig183.jpg" alt="" width="600" height="513" /> - <div class="blockquot"> - <p class="center">Fig. 183.</p> - <p><i>A</i>, part of a shoot showing whorls of branches with clusters of - carpospores. <i>B</i>, carpogonic branch or procarp. <i>c</i>, procarp cell; - <i>tr</i>, trichogyne. <i>C</i>, same with sperm (<i>sp</i>) uniting with trichogyne. - <i>D</i>, same with carpospores developing from procarp cell. <i>E</i>, male - branch with one-celled antheridia. <i>F</i>, same with some of antheridia - empty. (After Schmitz.)</p> - </div> -</div> - -<p>From this point in the lower red algæ like Nemalion, Batrachospermum -and Lemanea the formation of the spores is very simple. The procarp -is stimulated to growth, and buds in different directions, producing -branched chains of spores (carpospores). The carpospores form a rather -<span class="pagenum"><a name="Page_173" id="Page_173">[Pg 173]</a></span> -compact cluster called the sporocarp, which means spore-fruit or -spore-fruit body. In Batrachospermum it is seen as a compact tuft in -the loose branching, in Nemalion it lies in the surface of the cortex, -while in Lemanea the sporocarps lie at different positions in the -hollow tube of the sexual shoot.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_184" src="images/fig184.jpg" alt="" width="300" height="293" /> - <p class="center">Fig. 184.<br /> A red alga (Callithamnion),<br /> showing sporangium <i>A</i>, and<br /> - the tetraspores discharged <i>B</i>.<br /> (After Thuret.)</p> - </div> - <div class="figsub"> - <img id="FIG_185" src="images/fig185.jpg" alt="" width="150" height="301" /> - <p class="center">Fig. 185.<br /> Gracilaria, portion of frond,<br /> showing position of cystocarps.</p> - </div> -</div> - -<div class="figleft"> - <img src="images/fig186.jpg" alt="" width="200" height="206" /> - <p class="center">Fig. 186.<br /> Gracilaria, section of<br /> cystocarp showing spores.</p> -</div> - -<p><b>376. Gonidia in the red algæ.</b>—The common type of gonidium -in the red algæ is found in the <i>tetraspores</i>. A single mother cell -divides into four cells arranged usually in the form of tetrads within -the <i>tetrasporangium</i>. In Callithamnion the tetrasporangium is exposed. -In Polysiphonia, Rhabdonia, Gracilaria, etc., it is imbedded in the -cortex. In Batrachospermum there are monosporangia, each monosporangium -containing a single gonidium, while in Lemanea, and according to some -also in Nemalion, gonidia are wanting. -<span class="pagenum"><a name="Page_174" id="Page_174">[Pg 174]</a></span></p> - -<p><b>377. Gracilaria.</b>—Gracilaria is one of the marine forms, and -one species is illustrated in <a href="#FIG_185">fig. 185</a>. It measures 15-20<i>cm</i> -or more long, and is profusely branched in a palmate manner. The parts of the -thallus are more or less flattened. The fruit is a cystocarp, which -is characteristic of the Rhodophyceæ (Florideæ). In Gracilaria these -fruit bodies occur scattered over the thallus. They are somewhat -flask-shaped, are partly sunk in the thallus, and the conical end -projects strongly above the surface. The carpospores are grouped in -radiating threads within the oval cavity of the cystocarp. These -cystocarps are developed as a result of fertilization. Other plants -bear gonidia in groups of four, the so-called <i>tetraspores</i>.</p> - -<p><b>378. Rhabdonia.</b>—This plant is about the same size as the -gracilaria, though it possesses more filiform branches. The cystocarps -form prominent elevations, while the carpospores lie in separated -groups around the periphery of a sterile tissue within the cavity. (See -figs. <a href="#FIG_187">187</a>, <a href="#FIG_187">188</a>.) Gonidia -in the form of tetraspores are also developed in Rhabdonia.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_187" src="images/fig187.jpg" alt="" width="200" height="343" /> - <p class="center">Fig. 187.<br /> Rhabdonia, branched portion<br /> of frond showing cystocarps.</p> - </div> - <div class="figsub"> - <img id="FIG_188" src="images/fig188.jpg" alt="" width="250" height="320" /> - <p class="center">Fig. 188.<br /> Section of cystocarp of<br /> rhabdonia, showing spores.</p> - </div> -</div> - -<p><b>379. Fertilization of the higher red algæ.</b>—The process of -fertilization in most of the red algæ is very complicated, chiefly -because the fertilized egg-cell (procarp) does not develop the spores -<span class="pagenum"><a name="Page_175" id="Page_175">[Pg 175]</a></span> -directly, as in Nemalion, Lemanea, etc., but fuses directly, or by a -short cell or long filament with one or more auxiliary cells before -the sporocarp is finally formed. Examples are Rhabdonia, Polysiphonia, -Callithamnion, Dudresnaya, etc. (<a href="#FIG_189">fig. 189</a>). The auxiliary cell -then develops the sporocarp. See fig. 189 for conjugation of a filament from -the fertilized procarp with an auxiliary cell.</p> - -<div class="figcenter"> - <img id="FIG_189" src="images/fig189.jpg" alt="" width="500" height="413" /> - <div class="blockquot"> - <p class="center">Fig. 189.</p> - <p>Dudresnaya purpurifera. <i>tr</i>, trichogyne, with spermatozoids attached; - <i>ct</i>, connecting-tube which grows out from below the base of the - trichogyne, and comes in contact with the fertile branches <i>f</i>, <i>f</i>; - <i>ct′</i>, young connecting-tube. (After Thuret and Bornet.)</p> - </div> -</div> - -<p><b>380. Uses of the red algæ.</b>—Many species produce a great amount -of gelatinous substance in their tissues, and several of these are used -for food, for the manufacture of gelatines and agar-agar. Some of these -are Gracilaria lichenoides and wrightii, the former species occurring -along the coast of India and China. The plant is easily converted into -gelatinous substance (agar-agar). Chondrus crispus, widely distributed -in the northern Atlantic is known as “Irish” moss and is used for food -and for certain medicinal purposes. Gigartina mamillosa in the Atlantic -and Arctic oceans is similarly employed. The following orders are -recognized in the red algæ:</p> - -<p><b>381. Order Bangiales.</b>—Example, Bangia atropurpurea (= Conferva -atropurpurea) in springs and brooks in North America and Europe. -Porphyra contains a number of species forming broad, thin, leaf-like -purple sheets in the sea.</p> - -<p><b>382. Order Nemalionales.</b>—Including Lemanea, Batrachospermum, -Nemalion, described above, and many others.</p> - -<p><b>383. Order Gigartinales.</b>—In this order occurs the common -Iceland moss (Chondrus crispus) in the sea, and Rhabdonia and Gigartina -mentioned above.</p> - -<p><b>384. Order Rhodomeniales.</b>—In this order occurs Gracilaria and -Polysiphonia mentioned above, also the beautiful marine forms like -Ceramium.</p> - -<p><b>385. Order Cryptonemiales.</b>—Examples are Dudresnaya, Melobesia, -Corallina, etc., the last two genera include many species with a wide distribution. -<span class="pagenum"><a name="Page_176" id="Page_176">[Pg 176]</a></span></p> - -<p class="center"><b>Class Charophyceæ,<br /> Order Charales.</b></p> - -<p><b>386.</b> The Charales are by some thought to represent a distinct -class of algæ standing near the mosses, perhaps, because of the -biciliate character of the spermatozoids. There is one family, the -Characeæ. The plants occur in fresh and brackish water. Aside from the -peculiarity of the reproductive organs they are remarkable for the -large size of the cells of the internodes and of the “leaves,” and the -protoplasm exhibits to a remarkable degree the phenomenon of “cyclosis” -(<a href="#PARA_17">see paragraphs 17-20</a>). Three of the genera are found -in North America (Chara, Nitella (<a href="#FIG_08">Fig. 8</a>) and Tolypella).</p> - -<div class="figcenter"> - <img src="images/fig172a.jpg" alt="" width="500" height="443" /> - <div class="blockquot"> - <p class="center">Fig. 172<i>a</i>.</p> - <p>Reproductive organs of <i>Chara fragilis</i>. <i>A</i>, a central portion of a - leaf, <i>b</i>, with an antheridium, <i>a</i>, and a carpogonium, <i>s</i>, surrounded - by the spirally twisted enveloping cells; <i>c</i>, crown of five cells at - apex; β, sterile lateral leaflets; β′, large lateral leaflet near the - fruit; β″, bracteoles springing from the basal node of the reproductive - organs. <i>B</i>, a young antheridium, <i>a</i>, and a young carpogonium, <i>sk</i>; - <i>w</i>, nodal cell of leaf; <i>u</i>, intermediate cell between <i>w</i> and the - basal-node cell of the antheridium; <i>l</i>, cavity of the internode of - the leaf; <i>br</i>, cortical cells of the leaf. <i>A</i> × about 33; <i>B</i> × 240. - (After Sachs.)</p> - </div> -</div> - -<p><b>386a.</b> The complicated structure of the sexual organs shows a -higher state of organization than any of the other living algæ known. -While the internodes in Nitella are composed of a single, stout cell, -some times a foot or more in length, the nodes in all are composed of -a group of smaller cells. From the lateral cells of this group lateral -axes (sometimes called leaves) arise in whorls.</p> - -<p>In Nitella the internodes are naked, but in most species of Chara -they are <i>corticated</i>, i.e., they are covered by a layer of numerous -elongated cells which grow downward from the nodes at the base of the -whorl of lateral shoots.</p> - -<p><b>386b.</b> The sexual organs are situated at the nodes of the whorled -lateral shoots, and consist of antheridia and carpogonia. Most of the -plants are monœcious, and both antheridia and carpogonia are often -attached to the same node, the antheridium projecting downward while -the carpogonium is more or less ascending. The sexual organs are -visible to the unaided eye. The antheridium is a globose red body of -an exceedingly complicated structure. The sperms are borne in several -very long coiled slender threads which are divided transversely into -numerous cells. The carpogonium is oval or elliptical in outline, the -wall of which is composed of several closely coiled spiral threads -enclosing the large egg.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_177" id="Page_177">[Pg 177]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XIX" id="CHAPTER_XIX">CHAPTER XIX.</a><br /> -<span class="h_subtitle">FUNGI: MUCOR AND SAPROLEGNIA.</span></h3> -</div> - -<p class="center"><b>Mucor.</b></p> - -<p><b>387.</b> In the chapter on growth, and in our study of protoplasm, -we have become familiar with the vegetative condition of mucor. We now -wish to learn how the plant multiplies and reproduces itself. For this -study we may take one of the mucors. Any one of several species will -answer. This plant may be grown by placing partially decayed fruits, -lemons, or oranges, from which the greater part of the juice has been -removed, in a moist chamber; or often it occurs on animal excrement -when placed under similar conditions. In growing the mucor in this way -we are likely to obtain Mucor mucedo, or another plant sometimes known -as Mucor stolonifer, or Rhizopus nigricans, which is illustrated in -<a href="#FIG_191">fig. 191</a>. This latter one is sometimes very injurious to -stored fruits or vegetables, especially sweet potatoes or rutabagas. -<a href="#FIG_190">Fig. 190</a> is from a photograph of this fungus on a banana.</p> - -<p><b>388. Asexual reproduction.</b>—On the decaying surface of the -vegetable matter where the mucor is growing there will be seen numerous -small rounded bodies borne on very slender stalks. These heads contain -the gonidia, and if we sow some of them in nutrient gelatine or agar -in a Petrie dish the material can be taken out very readily for -examination under the microscope. Or we may place glass slips close -to the growing fungus in the moist chamber, so that the fungus will -develop on them, though cultures in a nutrient medium are much better. -Or we may take the material directly from the substance on which it is -<span class="pagenum"><a name="Page_178" id="Page_178">[Pg 178]</a></span> -growing. After mounting a small quantity of the mycelium bearing these -heads, if we have been careful to take it where the heads appear -quite young, it may be possible to study the early stages of their -development. We shall probably note at once that the stalks or upright -threads which support the heads are stouter than the threads of the -mycelium.</p> - -<div class="figcenter"> - <img id="FIG_190" src="images/fig190.jpg" alt="" width="600" height="405" /> - <p class="center">Fig. 190.<br /> Portion of banana with a mould - (Rhizopus nigricans) growing on one end.</p> -</div> - -<p>These upright threads soon have formed near the end a cross wall which -separates the protoplasm in the end from the remainder. This end cell -now enlarges into a vesicle of considerable size, the head as it -appears, but to which is applied the name of <i>sporangium</i> (sometimes -called gonidangium), because it encloses the <i>gonidia</i>.</p> - -<p>At the same time that this end cell is enlarging the cross wall is -arching up into the interior. This forms the <i>columella</i>. All the -protoplasm in the sporangium now divides into gonidia. These are -<span class="pagenum"><a name="Page_179" id="Page_179">[Pg 179]</a></span> -small-rounded or oval bodies. The wall of the sporangium becomes -dissolved, except a small collar around the stalk which remains -attached below the columella (fig. 192). By this means the -gonidia are freed. These gonidia germinate and produce the mycelium again.</p> - -<div class="figcenter"> - <img id="FIG_191" src="images/fig191.jpg" alt="" width="600" height="356" /> - <p class="center">Fig. 191.<br /> Group of sporangia of a mucor (Rhizopus nigricans) showing<br /> - rhizoids and the stolon extending from an older group.</p> -</div> - -<p><b>389. Sexual stage.</b>—This stage is not so frequently found, but -may sometimes be obtained by growing the fungus on bread.</p> - -<p>Conjugation takes place in this way. Two threads of the mycelium which -lie near each other put out each a short branch which is clavate in -form. The ends of these branches meet, and in each a septum is formed -which cuts off a portion of the protoplasm in the end from that of the -rest of the mycelium. The meeting walls of the branches now dissolve -and the protoplasm of each gamete fuses into one mass. A thick wall -is now formed around this mass, and the outer layer becomes rough and -brown. This is the <i>zygote</i> or <i>zygospore</i>. The mycelium dies and -it becomes free often with the suspensors, as the stalks of these sexual -branches are called, still attached. This zygospore passes through -a period of rest, when with the entrance of favorable conditions of -growth it germinates, and usually produces directly a sporangium with -gonidia. This completes the normal life cycle of the plant.</p> - -<p><b>390. Gemmæ.</b>—Gemmæ, as they are sometimes called, are often -formed on the mycelium. A short cell with a stout wall is formed on the -<span class="pagenum"><a name="Page_180" id="Page_180">[Pg 180]</a></span> -side of a thread of the mycelium. In other cases large portions of the -threads of the mycelium may separate into chains of cells. Both these -kinds of cells are capable of growing and forming the mycelium again. -They are sometimes called <i>chlamydospores</i>.</p> - -<div class="figcenter"> - <img src="images/fig194.jpg" alt="" width="600" height="345" /> - <div class="blockquot"> - <p class="center">Fig. 194.</p> - <p>A mucor (Rhizopus nigricans); at left nearly mature sporangium with - columella showing within; in the middle is ruptured sporangium with - some of the gonidia clinging to the columella; at right two ruptured - sporangia with everted columella.</p> - </div> -</div> - -<p><b>390</b><i>a</i>. The Mucorineæ according to their manner of zygospore -formation are of two kinds: 1st, the <i>homothallic</i> (monœcious), in -which all of the colonies of thalli developed from different spores -are the same, and both gametes may be developed from the mycelium -from a single spore, as in Sporodinia grandis, a mould common on old -mushrooms; 2d, the <i>heterothallic</i> (diœcious), in which certain plants -are of a male nature and small in comparison with those of perhaps a -female nature which are larger or more vigorous. When grown separately -each of these two kinds of thalli, or colonies of mycelium, produce -their own kind but only sporangia. If the two kinds are brought -together, however, branches from one conjugate with branches from -the other and zygospores are produced, as in Rhizopus nigricans, the -common bread or fruit mould. This is one reason why we rarely find this -fungus forming zygospores. (See Blakeslee, Sexual Reproduction in the -Mucorineæ, Proc. Am. Acad. Arts and Sci., <b>40</b>, 205-319, pl. 1-4, 1904.) -<span class="pagenum"><a name="Page_181" id="Page_181">[Pg 181]</a></span></p> - -<p class="center"><b>Water Moulds</b><br /> (Saprolegnia).</p> - -<p><b>391.</b> The water moulds are very interesting plants to study -because they are so easy to obtain, and it is so easy to observe a type -of gonidium here to which we have referred in our studies of the algæ, -the motile gonidium, or zoogonidium. (See appendix for directions for -cultivating this mould.)</p> - -<p><b>392. Appearance of the saprolegnia.</b>—In the course of a few days -we are quite certain to see in some of the cultures delicate whitish -threads, radiating outward from the body of the fly in the water. A few -threads should be examined from day to day to determine the stage of -the fungus.</p> - -<div class="figcenter"> - <img id="FIG_195" src="images/fig195.jpg" alt="" width="600" height="386" /> - <p class="center">Fig. 195.<br /> Sporangia of saprolegnia, one showing the escape of the zoogonidia.</p> -</div> - -<p><b>393. Sporangia of saprolegnia.</b>—The sporangia of saprolegnia -can be easily detected because they are much stouter than the ordinary -threads of the mycelium. Some of the threads should be mounted in fresh -water. Search for some of those which show that the protoplasm is -divided up into a great number of small areas, as shown in <a href="#FIG_195">fig. 195</a>. -With the low power we should watch some of the older appearing ones, and if -after a few minutes they do not open, other preparations should be made. -<span class="pagenum"><a name="Page_182" id="Page_182">[Pg 182]</a></span></p> - -<div class="figcenter"> - <img id="FIG_196" src="images/fig196.jpg" alt="" width="600" height="181" /> - <p class="center">Fig. 196.<br /> Branch of saprolegnia showing oogonia with<br /> - oospores, eggs matured parthenogenetically.</p> -</div> -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_197" src="images/fig197.jpg" alt="" width="250" height="412" /> - <p class="center">Fig. 197.<br /> Downy mildew of grape (Plasmopora viticola),<br /> - showing tuft of gonidiophores bearing gonidia,<br /> also intercellular mycelium. - (After Millardet.)</p> - </div> - <div class="figsub"> - <img id="FIG_198" src="images/fig198.jpg" alt="" width="300" height="407" /> - <p class="center">Fig. 198.<br /> Phytophthora infestans showing<br /> - peculiar branches; gonidia below.</p> - </div> -</div> - -<p><b>394. Zoogonidia of saprolegnia.</b>—The sporangium opens at the -end, and the zoogonidia swirl out and swim around for a short time, -when they come to rest. With a good magnifying power the two cilia on -<span class="pagenum"><a name="Page_183" id="Page_183">[Pg 183]</a></span> -the end may be seen, or we may make them more distinct by treatment -with Schultz’s solution, drawing some under the cover glass. The -zoogonidium is oval and the cilia are at the pointed end. After they -have been at rest for some time they often slip out of the thin wall, -and swim again, this time with the two cilia on the side, and then the -zoogonidium is this time more or less bean-shaped or reniform.</p> - -<div class="figcenter"> - <img id="FIG_199" src="images/fig199.jpg" alt="" width="600" height="174" /> - <div class="blockquot"> - <p class="center">Fig. 199.<br /> </p> - <p>Fertilization in saprolegnia, tube of antheridium carrying in the - nucleus of the sperm cell to the egg. In the right-hand figure a - smaller sperm nucleus is about to fuse with the nucleus of the egg. - (After Humphrey and Trow.)</p> - </div> -</div> -<div class="figcontainer"> - <div class="figsub"> - <p> </p> - <img id="FIG_200" src="images/fig200.jpg" alt="" width="250" height="449" /> - <p class="center">Fig. 200.<br /> Branching hypha of<br /> Peronospora alsinearum.</p> - </div> - <div class="figsub"> - <img id="FIG_201" src="images/fig201.jpg" alt="" width="250" height="466" /> - <p class="center">Fig. 201.<br /> Branched hypha of downy mildew<br /> - of grape showing peculiar branching<br /> (Plasmopara viticola).</p> - </div> -</div> - -<p><span class="pagenum"><a name="Page_184" id="Page_184">[Pg 184]</a></span> -<b>395. Sexual reproduction of saprolegnia.</b>—When such cultures are -older we often see large rounded bodies either at the end of a thread, -or of a branch, which contain several smaller rounded bodies as shown -in <a href="#FIG_196">fig. 196</a>. These are the oogonia (unless the plant is attacked -by a parasite), and the round bodies inside are the egg-cells, if before -fertilization, or the eggs, if after this process has taken place. -Sometimes the slender antheridium can be seen coiled partly around the -oogonium, and one end entering to come in contact with the egg-cell. -But in some species the antheridium is not present, and that is the -case with the species <a href="#FIG_196">figured at 196</a>. In this case the -eggs mature without fertilization. This maturity of the egg without fertilization -is called <i>parthenogenesis</i>, which occurs in other plants also, but is -a rather rare phenomenon.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_202" src="images/fig202.jpg" alt="" width="300" height="195" /> - <p class="center">Fig. 202.<br /> Gonidiophores and gonidia of potato blight<br /> - (Phytophthora infestans). <i>b</i>, an older stage<br /> - showing how the branch enlarges where it<br /> - grows beyond the older gonidium.<br /> (After de Bary.)</p> - </div> - <div class="figsub"> - <img id="FIG_203" src="images/fig203.jpg" alt="" width="125" height="197" /> - <p class="center">Fig. 203.<br /> Gonidia of potato blight forming<br /> zoogonidia. - (After de Bary.)</p> - </div> -</div> - -<p><b>396.</b> In <a href="#FIG_199">fig. 199</a> is shown the oogonium and an -antheridium, and the antheridium is carrying in the male nucleus to the egg-cell. -Spermatozoids are not developed here, but a nucleus in the antheridium -reaches the egg-cell. It sinks in the protoplasm of the egg, comes -in contact with the nucleus of the egg, and fuses with it. Thus -fertilization is accomplished. -<span class="pagenum"><a name="Page_185" id="Page_185">[Pg 185]</a></span></p> - -<p class="center"><b>Downy Mildews.</b></p> - -<p><b>397.</b> The downy mildews make up a group of plants which are -closely related to the water moulds, but they are parasitic on land -plants, and some species produce very serious diseases. The mycelium -grows between the cells of the leaves, stems, etc., of their hosts, -and sends haustoria into the cells to take up nutriment. Gonidia are -formed on threads which grow through the stomates to the outside and -branch as shown in <a href="#FIG_198">figs. 198</a>-<a href="#FIG_201">201</a>. -The gonidia are borne on the tips of the branches. The kind of branching bears some -relation to the different genera. <a href="#FIG_200">Fig. 200</a> is from Peronospora -alsinearum on leaves of cerastium; <a href="#FIG_197">figs. 197</a> and <a href="#FIG_199">199</a> are Plasmopara -viticola, the grape mildew, while <a href="#FIG_198">figs. 198</a> and <a href="#FIG_202">202</a> -are from Phytophthora infestans which causes a disease known as potato -blight. The gonidia of peronospora germinate by a germ tube, those of -plasmopara first form zoogonidia, while in phytophthora the gonidium -may either germinate forming a thread, or each gonidium may first form -several zoogonidia, as shown in <a href="#FIG_203">fig. 203</a>.</p> - -<div class="figcenter"> - <img id="FIG_204" src="images/fig204.jpg" alt="" width="600" height="206" /> - <div class="blockquot"> - <p class="center">Fig. 204.<br /> </p> - <p>Fertilization in Peronospora alsinearum; tube from antheridium carrying - in the sperm nucleus in figure at the left, female nucleus near; fusion - of the two nuclei shown in the two other figures. (After Berlese.)</p> - </div> -</div> -<div class="figcenter"> - <img src="images/fig205.jpg" alt="" width="400" height="339" /> - <p class="center">Fig. 205.<br /> Ripe oospore of Peronospora alsinearum.</p> -</div> - -<p><b>398.</b> In sexual reproduction oogonia and antheridia are developed -on the mycelium within the tissues. <a href="#FIG_204">Fig. 204</a> represents the antheridium -<span class="pagenum"><a name="Page_186" id="Page_186">[Pg 186]</a></span> -entering the oogonium, and the male nucleus fusing with the female -nucleus in fertilization. The sexual organs of Phytophthora infestans -are not sufficiently known.</p> - -<p><b>399.</b> Mucor, saprolegnia, peronospora, and their relatives -have few or no septa in the mycelium. In this respect they resemble -certain of the algæ like vaucheria, but they lack chlorophyll. They are -sometimes called the alga-like fungi and belong to a large group called -<i>Phycomycetes</i>.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_187" id="Page_187">[Pg 187]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XX" id="CHAPTER_XX">CHAPTER XX.</a><br /> -<span class="h_subtitle">FUNGI CONTINUED.</span></h3> -</div> - -<p class="center"><b>“Rusts”</b> (Uredineæ).</p> - -<p><b>400.</b> The fungi known as “rusts” are very important ones to -study, since all the species are parasitic, and many produce serious -injuries to crops.</p> - -<div class="figcontainer"> - <a id="FIG_206-210" name="FIG_206-210"> </a> - <div class="figsub"> - <img src="images/fig206.jpg" alt="" width="100" height="215" /> - <p class="center">Fig. 206.<br /> Wheat leaf<br /> with red-rust,<br /> natural size.</p> - </div> - <div class="figsub"> - <img src="images/fig207.jpg" alt="" width="100" height="224" /> - <p class="center">Fig. 207.<br /> Portion of<br /> leaf enlarged<br /> to show sori.</p> - </div> - <div class="figsub"> - <img src="images/fig208.jpg" alt="" width="100" height="230" /> - <p class="center">Fig. 208.<br /> Natural size.</p> - </div> - <div class="figsub"> - <img src="images/fig209.jpg" alt="" width="100" height="263" /> - <p class="center">Fig. 209.<br /> Enlarged.</p> - </div> - <div class="figsub"> - <img src="images/fig210.jpg" alt="" width="100" height="219" /> - <p class="center">Fig. 210.<br /> Single sorus.</p> - </div> - <p class="center">Figs. 206, 207.—Puccinia graminis, red-rust stage (uredo stage).  </p> - <p class="center space-below2">Figs. 208-210.—Black rust of wheat, showing sori of teleutospores.</p> -</div> - -<p><b>401. Wheat rust (Puccinia graminis).</b>—The wheat rust is one of -the best known of these fungi, since a great deal of study has been -given to it. One form of the plant occurs in long reddish-brown or -reddish pustules, and is known as the “red-rust” (<a href="#FIG_206-210">figs. 206, 207</a>). -Another form occurs in elongated black pustules, and this form is the -<span class="pagenum"><a name="Page_188" id="Page_188">[Pg 188]</a></span> -one known as the “black rust” (<a href="#FIG_206-210">figs. 208</a>-<a href="#FIG_211">211</a>). -These two forms occur on the stems, blades, etc., of the wheat, also on -oats, rye, and some of the grasses.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_211" src="images/fig211.jpg" alt="" width="210" height="401" /> - <p class="center">Fig. 211.<br /> Head of wheat showing<br /> black rust spots on<br /> the chaff and awns.</p> - </div> - <div class="figsub"> - <img id="FIG_212" src="images/fig212.jpg" alt="" width="150" height="253" /> - <p class="center">Fig. 212.<br /> Teleutospores of wheat<br /> rust, showing two cells<br /> and the pedicel.</p> - <img id="FIG_213" src="images/fig213.jpg" alt="" width="150" height="93" /> - <p class="center">Fig. 213.<br /> Uredospores of wheat<br /> rust, one showing<br /> remnants of the<br /> pedicel.</p> - </div> -</div> - -<p><b>402. Teleutospores of the black rust form.</b>—If we scrape off -some portion of one of the black pustules (sori), tease it out in water -on a slide, and examine with a microscope, we see numerous gonidia, -composed of two cells, and having thick, brownish walls as shown -in <a href="#FIG_212">fig. 212</a>. Usually there is a slender brownish stalk -on one end. These gonidia are called <i>teleutospores</i>. They are somewhat oblong -or elliptical, a little constricted where the septum separates the two -cells, and the end cell varies from ovate to rounded. The mycelium of -<span class="pagenum"><a name="Page_189" id="Page_189">[Pg 189]</a></span> -the fungus courses between the cells, just as is found in the case of -the carnation rust, which belongs to the same family (<a href="#PARA_186">see Parag. 186</a>).</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_214" src="images/fig214.jpg" alt="" width="200" height="485" /> - <p class="center">Fig. 214.<br /> Barberry leaf with<br /> two diseased spots,<br /> natural size.</p> - </div> - <div class="figsub"> - <img id="FIG_215" src="images/fig215.jpg" alt="" width="100" height="409" /> - <p class="center">Fig. 215.<br /> Single spot<br /> showing<br /> cluster-cups<br /> enlarged.</p> - </div> - <div class="figsub"> - <img id="FIG_216" src="images/fig216.jpg" alt="" width="110" height="403" /> - <p class="center">Fig. 216.<br /> Two cluster-cups<br /> more - enlarged,<br /> showing<br /> split margin.</p> - </div> - <p class="center">Figs. 214-216.—Cluster-cup stage of wheat rust.</p> -</div> - -<p><b>403. Uredospores of the red-rust form.</b>—If we make a similar -preparation from the pustules of the red-rust form we see that instead -of two-celled gonidia they are one-celled. The walls are thinner -and not so dark in color, and they are covered with minute spines. -They have also short stalks, but these fall away very easily. These -one-celled gonidia of the red-rust form are called “uredospores.” The -uredospores and teleutospores are sometimes found in the same pustule.</p> - -<p>It was once supposed that these two kinds of gonidia belonged to -different plants, but now it is known that the one-celled form, the -uredospores, is a form developed earlier in the season than the teleutospores.</p> - -<p><b>404. Cluster-cup form on the barberry.</b>—On the barberry is found -still another form of the wheat rust, the “<i>cluster-cup</i>” stage. The -pustules on the under side of the barberry leaf are cup-shaped, the -cups being partly sunk in the tissue of the leaf, while the rim is more -or less curved backward against the leaf, and split at several places. -These cups occur in clusters on the affected spots of the barberry leaf -as shown in <a href="#FIG_215">fig. 215</a>. Within the cups numbers of one-celled -gonidia (orange in color, called æcidiospores) are borne in chains from short -branches of the mycelium, which fill the base of the cup. In fact the -<span class="pagenum"><a name="Page_190" id="Page_190">[Pg 190]</a></span> -wall of the cup (peridium) is formed of similar rows of cells, which, -instead of separating into gonidia, remain united to form a wall. These -cups are usually borne on the under side of the leaf.</p> - -<p><b>405. Spermagonia.</b>—Upon the upper side of the leaves in the -same spot occur small, orange-colored pustules which are flask-shaped. -They bear inside, minute, rod-like bodies on the ends of slender -threads, which ooze out on the surface of the leaf. These flask-shaped -pustules are called <i>spermagonia</i>, and the minute bodies within them -<i>spermatia</i>, since they were once supposed to be the male element of -the fungus. Their function is not known. They appear in the spots at an -earlier time than the cluster-cups.</p> - -<div class="figcenter"> - <img src="images/fig217.jpg" alt="" width="600" height="397" /> - <p class="center">Fig. 217.<br /> Section of an æcidium (cluster-cup) - from barberry leaf.<br /> (After Marshall-Ward.)</p> -</div> - -<p><b>406. How the cluster-cup stage was found to be a part of the wheat -rust.</b>—The cluster-cup stage of the wheat rust was once supposed -also to be a different plant, and the genus was called <i>æcidium</i>. -The occurrence of wheat rust in great abundance on the leeward side -of affected barberry bushes in England suggested to the farmers that -wheat rust was caused by barberry rust. It was later found that the -æcidiospores of the barberry, when sown on wheat, germinate and the -thread of mycelium enters the tissues of the wheat, forming mycelium -between the cells. This mycelium then bears the uredospores, and later -the teleutospores. -<span class="pagenum"><a name="Page_191" id="Page_191">[Pg 191]</a></span></p> - -<p><b>407. Uredospores can produce successive crops of -uredospores.</b>—The uredospores are carried by the wind to other -wheat or grass plants, germinate, form mycelium in the tissues, -and later the pustules with a second crop of uredospores. Several -successive crops of uredospores may be developed in one season, so -this is the form in which the fungus is greatly multiplied and widely -distributed.</p> - -<div class="figcenter"> - <img src="images/fig218.jpg" alt="" width="600" height="269" /> - <p class="center">Fig. 218.<br /> Section through leaf of barberry at point affected with the cluster-cup<br /> - stage of the wheat rust; spermagonia above, æcidia below.<br /> - (After Marshall-Ward.)</p> -</div> -<div class="figcenter"> - <img src="images/fig219.jpg" alt="" width="600" height="391" /> - <p class="center">Fig. 219.<br /> <i>A</i>, section through sorus of black rust of wheat, showing teleutospores.<br /> - <i>B</i>, mycelium bearing both teleutospores and uredospores.<br /> (After de Bary.)</p> -</div> - -<p><span class="pagenum"><a name="Page_192" id="Page_192">[Pg 192]</a></span></p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig220.jpg" alt="" width="300" height="449" /> - <p class="center">Fig. 220.<br /> Germinating uredospore of wheat rust.<br /> (After Marshall-Ward.)</p> - </div> - <div class="figsub"> - <img src="images/fig221.jpg" alt="" width="230" height="443" /> - <p class="center">Fig. 221.<br /> Germ tube entering the<br /> leaf through a stoma.</p> - </div> -</div> - -<p><b>407a. Teleutospores the last stage of the fungus in the -season.</b>—The teleutospores are developed late in the season, or -late in the development of the host plant (in this case the wheat -is the host). They then rest during the winter. In the spring under -favorable conditions each cell of the teleutospore germinates, -producing a short mycelium called a <i>promycelium</i>, as shown -in figs. <a href="#FIG_222">222</a>, <a href="#FIG_223">223</a>. -This promycelium is usually divided into four cells. From -each cell a short, pointed process is formed called a “<i>sterigma</i>.” -Through this the protoplasm moves and forms a small gonidium on the -end, sometimes called a <i>sporidium</i>.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_222" src="images/fig222.jpg" alt="" width="150" height="347" /> - <p class="center">Fig. 222.<br /> Teleutospore<br /> germinating,<br /> forming<br /> promycelium.</p> - </div> - <div class="figsub"> - <img id="FIG_223" src="images/fig223.jpg" alt="" width="200" height="290" /> - <p class="center">Fig. 223.<br /> Promycelium<br /> of germinating<br /> teleutospore,<br /> forming sporidia.</p> - </div> - <div class="figsub"> - <img id="FIG_224" src="images/fig224.jpg" alt="" width="200" height="287" /> - <p class="center">Fig. 224.<br /> Germinating<br /> sporidia<br /> - entering<br /> leaf of<br /> barberry by<br /> mycelium.</p> - </div> - <p class="center">Figs. 222-224.—Puccinia graminis (wheat rust).<br /> (After Marshall-Ward.)</p> -</div> - -<p><b>408. How the fungus gets from the wheat back to the -barberry.</b>—If these sporidia from the teleutospores are carried by -<span class="pagenum"><a name="Page_193" id="Page_193">[Pg 193]</a></span> -the wind so that they lodge on -the leaves of the barberry, they germinate and produce the cluster-cup again. -The plant has thus a very complex life history. Because of the presence of -several different forms in the life cyle, it is called a <i>polymorphic</i> fungus.</p> - -<p>The presence of the barberry does not seem necessary in all cases for the -development of the fungus from one year to another.</p> - -<p><b>409. Synopsis of life history of wheat rust.</b></p> - -<p><i>Cluster-cup stage on leaf of barberry.</i></p> - -<div class="blockquot"> -<p class="neg-indent">Mycelium between cells of leaf in affected spots.</p> - -<p class="neg-indent">Spermagonia (sing. spermagonium), small -flask-shaped bodies sunk in upper side of leaf; contain “spermatia.”</p> - -<p class="neg-indent">Æcidia (sing. æcidium), cup-shaped bodies in -under side of leaf.</p> - -<p class="neg-indent">Wall or peridium, made up of outer layer of -fungus threads which are divided into short cells but remain united.</p> - -<p class="neg-indent">At maturity bursts through epidermis of leaf; -margin of cup curves outward and downward toward surface of leaf.</p> - -<p class="neg-indent">Central threads of the bundle are closely packed, -but free. Threads divide into short angular cells which separate and -become æcidiospores, with orange-colored content.</p> - -<p class="neg-indent">Æcidiospores carried by the wind to wheat, oats, -grasses, etc. Here they germinate, mycelium enters at stomate, and -forms mycelium between cells of the host.</p> -</div> - -<p><i>Uredo stage (red-rust) on wheat, oats, grasses, etc.</i></p> - -<div class="blockquot"> -<p class="neg-indent">Mycelium between cells of host.</p> - -<p class="neg-indent">Bears uredospores (1-celled) in masses under -epidermis, which is later ruptured and uredospores set free.</p> - -<p class="neg-indent">Uredospores carried by wind to other individual -hosts, and new crops of uredospores formed.</p> -</div> - -<p><i>Teleutospore stage (black rust), also on wheat, etc.</i></p> - -<div class="blockquot"> -<p class="neg-indent">Mycelium between cells of host.</p> - -<p class="neg-indent">Bears teleutospores (2-celled) in masses (sori) -under epidermis, which is later ruptured.</p> - -<p class="neg-indent">Teleutospores rest during winter. In spring each -<span class="pagenum"><a name="Page_194" id="Page_194">[Pg 194]</a></span> -cell germinates and produces a promycelium, a short thread, divided -into four cells.</p> - -<p class="neg-indent">Promycelium bears four sterigmata and four -gonidia (or sporidia), which in favorable conditions pass back to -the barberry, germinate, the tube enters between cells into the -intercellular spaces of the host to produce the cluster-cup again, and -thus the life cycle is completed.</p> -</div> - -<p><b>410. Other examples of the rusts.</b>—Some of the rusts do great -injury to fruit trees and also to forest trees. The “cedar apples” are -abnormal growths on the leaves and twigs of the cedar stimulated by the -presence of the mycelium of a rust known as Gymnosporangium macropus. -The teleutospores are two-celled and are formed in the tissue of the -“cedar apple” or gall. The teleutosori are situated at quite regular -intervals over the surface of the gall at small circular depressions, -and can be easily seen in late autumn and during the winter. A quantity -of gelatine is developed along with the teleutospores. In early spring -with the warm spring rains the gelatinous substance accompanying the -teleutospores swells greatly, and causes the teleutospores to ooze -out in long, dull, orange-colored strings, which taper gradually to -a slender point and bristle all over the “cedar apple.” Here the -teleutospores germinate and produce the sporidia. The sporidia are -carried to apple trees where they infect leaves and even the fruit, -producing here the cluster-cups. There are no uredospores.</p> - -<p>G. globosum is another species forming cedar apples, but the gelatinous -strings of teleutospores are short and clavate, and the cluster-cups -are formed on hawthorns. G. nidusavis forms “witches brooms” or “birds -nests” in the branches of the cedar. The mycelium in the branches -stimulates them to profuse branching so that numerous small branches -are developed close together. The teleutosori form small pustules -scattered over the branches. G. clavipes affects the branches of cedar -only slightly deforming them or not at all, and the cluster-cups are -formed on fruits, twigs, and leaves of the hawthorns or quinces, the -cluster-cups being long, tubular, and orange in color.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_195" id="Page_195">[Pg 195]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXI" id="CHAPTER_XXI">CHAPTER XXI.</a><br /> -<span class="h_subtitle">THE HIGHER FUNGI.</span></h3> -</div> - -<p><b>411. The series of the higher fungi.</b>—Of these there are two -large series. One of these is represented by the sac fungi, and the -other by the mushrooms, a good example of which is the common mushroom -(Agaricus campestris).</p> - -<p class="center"><b>Sac Fungi</b> (Ascomycetes).</p> - -<p><b>412. The sac fungi</b> may be represented by the “powdery mildews”; -examples, uncinula, microsphæra, podosphæra, etc. <a href="#FIG_225">Fig. 225</a> -is from a photograph of two willow leaves affected by one of these mildews. The -leaves are first partly covered with a whitish growth of mycelium, and -numerous chains of colorless gonidia are borne on short erect threads. -The masses of gonidia give the leaf a powdery appearance. The mycelium -lives on the outer surface of the leaf, but sends short haustoria into -the epidermal cells.</p> - -<p><b>413. Fruit bodies of the willow mildew.</b>—On this same mycelium -there appear later numerous black specks scattered over the affected -places of the leaf. These are the fruit bodies (<i>perithecia</i>). If -we scrape some of these from the leaf, and mount them in water for -microscopic examination, we shall be able to see their structure. -Examining these first with a low power of the microscope, each one is -seen to be a rounded body, from which radiate numerous filaments, the -<i>appendages</i>. Each one of these appendages is coiled at the end into -the form of a little hook. Because of these hooked appendages this -genus is called <i>uncinula</i>. This rounded body is the <i>perithecium</i>. -<span class="pagenum"><a name="Page_196" id="Page_196">[Pg 196]</a></span></p> - -<div class="figcenter"> - <img id="FIG_225" src="images/fig225.jpg" alt="" width="500" height="528" /> - <p class="center">Fig. 225.<br /> Leaves of willow showing willow mildew. The black dots are the<br /> - fruit bodies (perithecia) seated on the white mycelium.</p> -</div> - -<p><b>414. Asci and ascospores.</b>—While we are looking at a few of -these through the microscope with the low power, we should press on the -cover glass with a needle until we see a few of the perithecia rupture. -If this is done carefully we see several small ovate sacs issue, each -containing a number of spores, as shown in <a href="#FIG_227">fig. 227</a>. -Such a sac is an <i>ascus</i>, and the spores are <i>ascospores</i>. -<span class="pagenum"><a name="Page_197" id="Page_197">[Pg 197]</a></span></p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_226" src="images/fig226.jpg" alt="" width="100" height="232" /> - <p class="center">Fig. 226.<br /> Willow mildew;<br /> bit of mycelium<br /> with erect<br /> - conidiophores,<br /> bearing chain<br /> of gonidia;<br /> - gonidium<br /> at left<br /> germinating.</p> - </div> - <div class="figsub"> - <img id="FIG_227" src="images/fig227.jpg" alt="" width="250" height="281" /> - <p class="center">Fig. 227.<br /> Fruit of willow mildew,<br /> showing hooked - appendages.<br /> Genus uncinula.</p> - </div> - <div class="figsub"> - <img id="FIG_228" src="images/fig228.jpg" alt="" width="100" height="219" /> - <p class="center">Fig. 228.<br /> Fruit body<br /> of another<br /> mildew with<br /> dichotomous<br /> - appendages.<br /> Genus microsphæra.</p> - </div> - <p class="center">Figs. 227-228.—Perithecia (perithecium) of two powdery mildews, showing<br /> - escape of asci containing the spores from the crushed fruit bodies.</p> -</div> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig229.jpg" alt="" width="125" height="285" /> - <p class="center">Fig. 229.<br /> Contact of<br /> antheridium<br /> and carpogonium<br /> - (carpogonium<br /> the larger cell);<br /> beginning of<br /> fertilization.</p> - </div> - <div class="figsub"> - <img src="images/fig230.jpg" alt="" width="125" height="285" /> - <p class="center">Fig. 230.<br /> Disappearance of<br /> contact walls of<br /> - antheridium and<br /> carpogonium,<br /> and fusion of<br /> the two nuclei.</p> - </div> - <div class="figsub"> - <img src="images/fig231.jpg" alt="" width="250" height="291" /> - <p class="center">Fig. 231.<br /> Fertilized egg surrounded<br /> by the enveloping threads<br /> - which grow up around it.</p> - </div> - <p class="center">Figs. 229-231.—Fertilization in sphærotheca; one of the powdery - mildews.<br /> (After Harper.)</p> -</div> - -<p><b>415. Number of spores in an ascus.</b>—The ascus is the most -important character showing the general relationship of the members of -the sac fungi. While many of the powdery mildews have a variable number -of spores in an ascus, a large majority of the ascomycetes have just -<span class="pagenum"><a name="Page_198" id="Page_198">[Pg 198]</a></span> -8 spores in an ascus, while some have 4, others 16, and some an -indefinite number. The asci in a perithecium are more variable. In some -ascomycetes there is no perithecium.</p> - -<div class="figcenter"> - <img id="FIG_231A" src="images/fig231a.jpg" alt="" width="400" height="502" /> - <p class="center">Fig. 231<i>a</i>.<br /> Edible Morel. Morchella esculenta.<br /> - The asci, forming hymenium, cover the pitted surface.</p> -</div> - -<p><b>416. The black fungi.</b>—These are very common on dead logs, -branches, leaves, etc., and may be collected in the woods at almost any -season. The perithecia are often numerous, scattered or densely crowded -<span class="pagenum"><a name="Page_199" id="Page_199">[Pg 199]</a></span> -as in Rosellinia. Sometimes they are united to form a crust which is -partly formed from sterile elements as in Hypoxylon, or they form black -clavate or branched bodies as in Xylaria. The black knot of the plum -and cherry is also an example.</p> - -<p>The lichens are mostly ascomycetes like the black fungi or cup fungi, -while a few are basidiomycetes.</p> - -<p><b>417. The morels (Morchella).</b>—There are several species of -morels which are common in early spring on damp ground. Either one of -the species is suitable for use if it is desired to include this in -the study. <a href="#FIG_231A">Fig. 231a</a> illustrates the Morchella esculenta. -The stem is cylindrical and stout. The fruiting portion forms the “head,” and it -is deeply pitted. The entire pitted surface is covered by the asci, -which are cylindrical and eight spored. A thin section may be made of -a portion for study, or a small piece may be crushed under the cover -glass.</p> - -<p><b>418. The cup fungi.</b>—These fungi are common on damp ground or -on rotting logs in the summer. They may be preserved in 70 per cent -alcohol for study. Many of them are shaped like broad open cups or -saucers. The inner surface of the cup is the fruiting surface, and is -covered with the cylindrical asci, which stand side by side. A bit of -the cup may be sectioned or crushed under a cover glass for study.</p> - -<p class="center"><b>Mushrooms</b><br /> (Basidiomycetes).</p> - -<p><b>419. The large group of fungi</b> to which the mushroom belongs is -called the basidiomycetes because in all of them a structure resembling -a club, or basidium, is present, and bears a limited number of spores, -usually four, though in some genera the number is variable. Some place -the rusts (Uredineæ) in the same series (basidium series), because of -the short promycelium and four sporidia developed from each cell of the -teleutospore.</p> - -<p><b>420. The gill-bearing fungi (Agaricaceæ).</b>—A good example for -this study is the common mushroom (Agaricus campestris).</p> - -<p>This occurs from July to November in lawns and grassy fields. The -plant is somewhat umbrella-shaped, as shown in <a href="#FIG_232">fig. 232</a>, -and possesses a cylindrical stem attached to the under side of the convex cap -or pileus. On the under side of the pileus are thin radiating plates, -shaped somewhat like a knife blade. These are the gills, or lamellæ, -and toward the stem they are rounded on the lower angle and are not -attached to the stem. The longer ones extend from near the stem to the -margin of the pileus, and the V-shaped spaces between them are occupied -by successively shorter ones. Around the stem a little below the gills -is a collar, termed the ring or annulus. -<span class="pagenum"><a name="Page_200" id="Page_200">[Pg 200]</a></span></p> - -<div class="figcenter"> - <img id="FIG_232" src="images/fig232.jpg" alt="" width="600" height="360" /> - <p class="center">Fig. 232.<br /> Agaricus campestris. View of under side showing stem,<br /> - annulus, gills, and margin of pileus.</p> -</div> -<div class="figcenter"> - <img src="images/fig233.jpg" alt="" width="450" height="452" /> - <p class="center">Fig. 233.<br /> Agaricus campestris.<br /> Longitudinal section through stem and pileus.<br /> - <i>a</i>, pileus; <i>b</i>, portion of veil on margin of pileus;<br /> - <i>c</i>, gill; <i>d</i>, fragment of annulus; <i>e</i>, stipe.</p> -</div> - -<p><span class="pagenum"><a name="Page_201" id="Page_201">[Pg 201]</a></span></p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_234" src="images/fig234.jpg" alt="" width="300" height="307" /> - <p class="center">Fig. 234.<br /> Portion of section of lamella of Agaricus campestris.<br /> - <i>tr</i>, trama; <i>sh</i>, subhymenium; <i>b</i>, basidium;<br /> - <i>st</i>, sterigma (<i>pl.</i> sterigmata); <i>g</i>, basidiospore.</p> - </div> - <div class="figsub"> - <img id="FIG_235" src="images/fig235.jpg" alt="" width="150" height="301" /> - <p class="center">Fig. 235.<br /> Portion of hymenium<br /> of Coprinus micaceus,<br /> - showing large cystidium<br /> in the hymenium.</p> - </div> -</div> - -<p><b>421. Fruiting surface of the mushroom.</b>—The surface of these -gills is the fruiting surface of the mushroom, and bears the gonidia -of the mushroom, which are dark purplish brown when mature, and thus -the gills when old are dark in color. If we make a thin section across -a few of the gills, we see that each side of the gill is covered with -closely crowded club-shaped bodies, each one of which is a <i>basidium</i>. -In <a href="#FIG_234">fig. 234</a> a few of these are enlarged, so that the -structure of the gill can be seen. Each basidium of the common mushroom has two -spinous processes at the free end. Each one is a <i>sterig′ma</i> (plural -<i>sterig′mata</i>), and bears a gonidium. In a majority of the members of -the mushroom family each basidium bears four spores. When mature these -spores easily fall away, and a mass of them gives a purplish-black -color to objects on which they fall, so that a print of the under -surface of the cap showing the arrangement of the gills can be obtained -by cutting off the stem, and placing the pileus on white paper for a time. -<span class="pagenum"><a name="Page_202" id="Page_202">[Pg 202]</a></span></p> - -<div class="figcenter"> - <img id="FIG_236" src="images/fig236.jpg" alt="" width="600" height="327" /> - <p class="center">Fig. 236.<br /> Agaricus campestris.<br /> - Soil washed from “spawn” and “buttons,” showing the minute<br /> - young “buttons” attached to the strands of mycelium.</p> -</div> - -<p><span class="pagenum"><a name="Page_203" id="Page_203">[Pg 203]</a></span> -<b>422. How the mushroom is formed.</b>—The mycelium of the mushroom -lives in the ground, and grows here for several months or even years, -and at the proper seasons develops the mature mushroom plant. The -mycelium lives on decaying organic matter, and a large number of the -threads grow closely together forming strands, or cords, of mycelium, -which are quite prominent if they are uncovered by removing the soil, -as shown in <a href="#FIG_236">fig. 236</a>.</p> - -<div class="figcenter"> - <img id="FIG_237" src="images/fig237.jpg" alt="" width="600" height="313" /> - <p class="center">Fig. 237.<br /> Agaricus campestris; sections of “buttons” of different<br /> - sizes, showing formation of gills and veil covering them.</p> -</div> - -<p><b>423.</b> From these strands the buttons arise by numerous threads -growing side by side in a vertical direction, each thread growing -independently at the end, but all lying very closely side by side. When -the buttons are quite small the gills begin to form on the under margin -of the knob. They are formed by certain of the threads growing downward -in radiating ridges, just as many of these ridges being started as -there are to be gills formed. At the same time, threads of the stem -grow upward to meet those at the margin of the button in such a manner -that they cover up the forming gills, and thus enclose the gills in a -minute cavity. Sections of buttons at different ages will show this, as -is seen in <a href="#FIG_237">fig. 237</a>. This curtain of mycelium which is thus -stretched across the gill cavity is the veil. As the cap expands more and more -this is stretched into a thin and delicate texture as shown in <a href="#FIG_238">fig. 238</a>. -Finally, as shown in <a href="#FIG_239">fig. 239</a>, this veil is ruptured by the expansion -of the pileus, and it either clings to the stem as a collar, or a -portion of it remains clinging to the margin of the cap. When the -buttons are very young the gills are white, but they soon become pink -in color, and very soon after the veil breaks the spores mature, and -then the gills are dark brown. -<span class="pagenum"><a name="Page_204" id="Page_204">[Pg 204]</a></span></p> - -<div class="figcenter"> - <img id="FIG_238" src="images/fig238.jpg" alt="" width="600" height="406" /> - <p class="center">Fig. 238.<br /> Agaricus campestris; nearly mature plants, showing<br /> - veil still stretched across the gill cavity.</p> -</div> -<div class="figcenter"> - <img id="FIG_239" src="images/fig239.jpg" alt="" width="600" height="363" /> - <p class="center">Fig. 239.<br /> Agaricus campestris; under view of two plants just<br /> - after rupture of veil, fragments of the latter<br /> - clinging both to margin of pileus and to stem.</p> -</div> - -<p><span class="pagenum"><a name="Page_205" id="Page_205">[Pg 205]</a></span></p> - -<div class="figcenter"> - <img src="images/fig240.jpg" alt="" width="400" height="440" /> - <p class="center">Fig. 240.<br /> Agaricus campestris; plant in natural position just after<br /> - rupture of veil, showing tendency to double annulus on the<br /> - stem. Portions of the veil also dripping from margin of pileus.</p> -</div> -<div class="figcenter"> - <img src="images/fig241.jpg" alt="" width="400" height="385" /> - <p class="center">Fig. 241.<br /> Agaricus campestris; spore print.</p> -</div> - -<p><span class="pagenum"><a name="Page_206" id="Page_206">[Pg 206]</a></span></p> - -<div class="figcenter"> - <img src="images/fig242.jpg" alt="" width="600" height="364" /> - <p class="center">Fig. 242.<br /> “Fairy ring” formed by Agaricus arvensis (photograph by B. M. Duggar).<br /> - The mycelium spreads centrifugally each year, consuming the available<br /> - food, and thus the plants appear in a ring.</p> -</div> - -<p><span class="pagenum"><a name="Page_207" id="Page_207">[Pg 207]</a></span></p> - -<div class="figcenter"> - <img id="FIG_243" src="images/fig243.jpg" alt="" width="250" height="461" /> - <p class="center">Fig. 243.<br /> Amanita phalloides; white form,<br /> - showing pileus, stipe, annulus,<br /> and volva.</p> -</div> - -<p><b>424. Beware of the poisonous mushroom.</b>—The number of species -of mushrooms, or toadstools as they are often called, is very great. -<span class="pagenum"><a name="Page_208" id="Page_208">[Pg 208]</a></span> -Besides the common mushroom (Agaricus campestris) there are a large -number of other edible species. But one should be very familiar with -any species which is gathered for food, unless collected by one who -certainly knows what the plant is, since carelessness in this respect -sometimes results fatally from eating poisonous ones.</p> - -<div class="figcenter"> - <img src="images/fig244.jpg" alt="" width="600" height="312" /> - <p class="center">Fig. 244.<br /> Amanita phalloides;<br /> - plant turned to one side, after having been placed in a<br /> - horizontal position, by the directive force of gravity.</p> -</div> - -<p><b>425.</b> A plant very similar in structure to the Agaricus -campestris is the Lepiota naucina, but the spores are white, and thus -the gills are white, except that in age they become a dirty pink. This -plant occurs in grassy fields and lawns often along with the common -mushroom. Great care should be exercised in collecting and noting the -characters of these plants, for a very deadly poisonous species, the -deadly amanita (Amanita phalloides) is perfectly white, has white -spores, a ring, and grows usually in wooded places, but also sometimes -occurs in the margins of lawns. In this plant the base of the stem is -seated in a cup-shaped structure, the <i>volva</i>, shown in <a href="#FIG_243">fig. 243</a>. -One should dig up the stem carefully so as not to tear off this volva if -it is present, for with the absence of this structure the plant might -easily be mistaken for the lepiota, and serious consequences would result. -<span class="pagenum"><a name="Page_209" id="Page_209">[Pg 209]</a></span></p> - -<div class="figcenter"> - <img id="FIG_245" src="images/fig245.jpg" alt="" width="400" height="334" /> - <p class="center">Fig. 245.<br /> Edible Boletus. Boletus edulis.<br /> Fruiting - surface honey-combed on under side of cap.</p> -</div> - -<p><b>426. Tube-bearing fungi (Polyporaceæ).</b>—In the tube-bearing -fungi, the fruiting surface, instead of lying over the surface of -gills, lines the surface of tubes or pores on the under side of the -cap. The fruit-bearing portion therefore is “honey-combed.” The sulphur -polyporus (Polyporus sulphureus) illustrates one form. The tube-bearing -fungi are sometimes called “bracket” fungi, or “shelf” fungi, because -the pileus is attached to the tree or stump like a shelf or bracket. -One very common form in the woods is the plant so much sought by -“artists,” and often called Polyporus applanatus. It is hard and woody, -reddish brown, brown or grayish on the upper side, according to age, -and is marked by prominent and large concentric ridges. (This form is -probably P. leucophæus.) The under side is white and honey-combed by -numerous very minute pores. This plant is perennial, that is, it lives -from year to year. Each year a new layer is added to the under side, -and several new rings usually to the margin. If a plant two or three -years old is cut in two, there will be seen several distinct tube -layers or strata, each one representing a year’s growth.</p> - -<p>In some of these bracket fungi, each ring on the upper surface marks a -<span class="pagenum"><a name="Page_210" id="Page_210">[Pg 210]</a></span> -year’s growth as in the pine polyporus (P. pinicola). In the birch -polyporus (P. fomentarius) the tubes are quite large. It also occurs on -other trees. The beech polyporus (P. igniarius, also on other trees) -often becomes very old. I have seen one specimen over eighty years old. -Not all the tube-bearing fungi are bracket form. Some have a stem and -cap (see<a href="#FIG_245"> fig. 245</a>). Some are spread on the -surface of logs.</p> - -<div class="figcenter"> - <img id="FIG_246" src="images/fig246.jpg" alt="" width="600" height="503" /> - <p class="center">Fig. 246.<br /> Coral fungus. Hydnum coralloides,<br /> - spines hanging down from branches.</p> -</div> - -<p><b>427. Hedgehog fungi (Hydnaceæ).</b>—These plants are bracket in -form or have a stem and cap, or are spread on the surface of wood; but -the finest specimens resemble coral masses of fungus tissue (example, -Hydnum, <a href="#FIG_246">fig. 246</a>). In most of them there are slender processes -resembling teeth, spines or awls, which depend from the under surface -(<a href="#FIG_247">fig. 247</a>). The fruiting surface covers these spines.</p> - -<p><b>428. Coral fungi or fairy clubs (Clavariaceæ).</b>—These plants -stand upright from the wood, leaves, or soil, on which they grow -(example, Clavaria). The “coral” ones are branched, while the “fairy -clubs” are simple. The fruiting surface covers the entire exposed -surface of the plants (<a href="#FIG_248">fig. 248</a>). -<span class="pagenum"><a name="Page_211" id="Page_211">[Pg 211]</a></span></p> - -<div class="figcenter"> - <img id="FIG_247" src="images/fig247.jpg" alt="" width="450" height="508" /> - <p class="center">Fig. 247.<br /> Hydnum repandum, spines hanging down from under side of cap.</p> -</div> - -<p><span class="pagenum"><a name="Page_212" id="Page_212">[Pg 212]</a></span></p> - -<div class="figcenter"> - <img id="FIG_248" src="images/fig248.jpg" alt="" width="500" height="480" /> - <p class="center">Fig. 248.<br /> Clavaria botrytes.</p> -</div> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_213" id="Page_213">[Pg 213]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXII" id="CHAPTER_XXII">CHAPTER XXII.</a><br /> -<span class="h_subtitle">CLASSIFICATION OF THE FUNGI.</span></h3> -</div> - -<p><b>429. Classification of the fungi.</b>—Those who believe that the fungi represent -a natural group of plants arrange them in three large series related to -each other somewhat as follows:</p> - -<div class="blockquot"> -<p>The Gonidium Type or Series. The number of gonidia in the sporangium -is indefinite and variable. It may be very large or very small, or -even only one in a sporangium. To this series belong the lower fungi; -examples: mucor, saprolegnia, peronospora, etc.</p> - -<p>The Basidium Type or Series. The number of gonidia on a basidium is -limited and definite, and the basidium is a characteristic structure; -examples: uredineæ (rusts), mushrooms, etc.</p> - -<p>The Ascus Type or Series. The number of spores in an ascus is -limited and definite, and the ascus is a characteristic structure; -examples: leaf curl of peach (exoascus), powdery mildews, black knot of -plum, black rot of grapes, etc.</p> -</div> - -<p><b>430.</b> Others believe that the fungi do not represent a natural -group, but that they have developed off from different groups of -the algæ by becoming parasitic. As parasites they no longer needed -chlorophyll, and consequently lost it.</p> - -<p>According to this view the lower fungi have developed off from the -lower algæ (saprolegnias, mucors, peronosporas, etc., being developed -off from siphonaceous algæ like vaucheria), and the higher fungi being -developed off from the higher algæ (the ascomycetes perhaps from the -Rhodophyceæ).</p> - -<p><b>431. A very general outline of classification</b>,<a name="FNanchor_19_19" id="FNanchor_19_19"></a><a href="#Footnote_19_19" class="fnanchor">[19]</a> -according to the former of these views, might be presented here to show the general -<span class="pagenum"><a name="Page_214" id="Page_214">[Pg 214]</a></span> -relationships of the fungi studied, with the addition of a few more -in orders not represented above. It should be borne in mind that the -author in presenting this view of classification does not necessarily -commit himself to it. It is based on that presented in Engler & -Prantl’s Pflanzenfamilien. There are three classes.</p> - -<div class="figcenter"> - <img id="FIG_249" src="images/fig249.jpg" alt="" width="600" height="377" /> - <p class="center">Fig. 249.</p> - <p class="blockquot">Chytrids. <i>A</i>, Harpochytrium hedenii, parasitic on spirogyra threads; - <i>a</i>, sickle-form plant; <i>b</i>, the sporangium part with escaping - zoospores; <i>c</i>, old plant proliferating by forming new sporangium - in the old empty one; <i>d</i>, zoospore; <i>e</i>, two young plants just - beginning to grow. <i>B</i>, Rhizophidium globosum parasitic on spirogyra. - Globose sporangium with delicate threads inside of the host, zoospores - escaping from one. <i>C</i>, Olpidium pendulum, parasitic in spirogyra cell. - Elliptical sporangium with slender exit tube through which zoospores - are escaping. <i>D</i>, Lagenidium rabenhorstii parasitic in spirogyra cell. - Two slender sporangia with exit tubes through which protoplasm escapes - forming a rounded mass at the end of tube, this protoplasm forming - biciliate zoospores.</p> -</div> - -<p class="center"><b>I. Class Phycomycetes</b> (Alga-like Fungi).</p> - -<p class="center"><b>1. SUBCLASS OOMYCETES.</b></p> - -<p><b>432.</b> These are the egg-spore fungi. They include the water mold -(Saprolegnia), the downy mildew of the grape (Plasmopara), the potato -<span class="pagenum"><a name="Page_215" id="Page_215">[Pg 215]</a></span> -blight (Phytophthora), the white rust of cruciferous plants (Cystopus -= Albugo), the damping-off fungus (Pythium), and many parasites of -the algæ known as chytrids, as Olpidium, Rhizophidium, Lagenidium, -Chytridium, etc.</p> - -<p>The two following orders are sometimes placed in a separate subclass, -<i>Archimycetes</i>.</p> - -<div class="figcenter"> - <img id="FIG_250" src="images/fig250.jpg" alt="" width="400" height="391" /> - <p class="center">Fig. 250.</p> - <p class="blockquot">Monoblepharis insignis Thaxter. End of hypha bearing oogonium (<i>oog</i>) - and antheridium (<i>ant</i>). Sperms escaping from antheridium and creeping - up on the oogonium. (After Thaxter.)</p> -</div> - -<p><b>433. Order Chytridiales (Chytridineæ).</b>—These include the lowest -fungi. Many of them are parasitic on algæ and lack mycelium, the -swarm spore either with or without minute rhizoids, developing into -a globose sporangium (Rhizophidium, Chytridium, Olpidium, etc., <a href="#FIG_249">fig. 249</a>), -or the swarm spore attached to the wall of the host develops into -a long sword-shaped body with a sterile base, which proliferates and -forms a new sporangium in the old one (Harpochytrium), or with slight -development of mycelium in aquatic plants (Cladochytrium). Some are -parasitic in leaves and stems of land plants. Synchytrium decipiens is -very common on the trailing legume, Amphicarpæa monoica.</p> - -<p><b>434. Order Ancylistales (Ancylistineæ).</b>—The members of this -order have a slight development of mycelium and many are parasitic in -algæ (Lagenidium, <a href="#FIG_249">fig. 249</a>).</p> - -<p><b>435. Order Saprolegniales (Saprolegniineæ).</b>—These include the -water molds (Saprolegnia). See <a href="#CHAPTER_XIX">Chapter XIX</a>.</p> - -<p><b>436. Order Monoblepharidales (Monoblepharidineæ).</b>—These are -peculiar water molds, related to the Saprolegniales, but motile sperm -cells are formed (Monoblepharis, etc., <a href="#FIG_250">fig. 250</a>).</p> - -<p><b>437. Order Peronosporales (Peronosporineæ).</b>—These include the -downy mildews (Peronospora, Plasmopara, Phytopthora, etc.), and the -white rust of crucifers and other plants (Cystopus = Albugo), <a href="#CHAPTER_XIX">Chapter XIX</a>.</p> - -<p class="center"><b>2. SUBCLASS ZYGOMYCETES.</b></p> - -<p><b>438.</b> These are the conjugating fungi.</p> - -<p><b>439. Order Mucorales (Mucorineæ).</b>—This includes the black mold -and its many relatives (Mucor, Rhizopus, etc.). <a href="#CHAPTER_XIX">Chapter XIX</a>.</p> - -<p><b>440. Order Entomophthorales (Entomophthorineæ).</b>—This order -includes the “fly fungus” (Empusa) and its many relatives parasitic on -<span class="pagenum"><a name="Page_216" id="Page_216">[Pg 216]</a></span> -insects. In the autumn and winter dead flies are often found stuck to -window-panes, with a white ring of the conidia around each fly.</p> - -<p class="center"><b>II. Class Ascomycetes.</b> (The ascus series.)</p> - -<p class="center">1. SUBCLASS HEMIASCOMYCETES.</p> - -<div class="figcenter"> - <img id="FIG_251" src="images/fig251.jpg" alt="" width="400" height="449" /> - <p class="center">Fig. 251.</p> - <p class="blockquot">Dipodascus albidus. <i>A</i>, thread with sexual organs, ascogonium and - antheridium; <i>B</i>, fertilized ascogonium developing ascus; <i>C</i>, - ascus with spores; <i>D</i>, conidia. (After Lagerheim.)</p> -</div> - -<p><b>441. Order Hemiascales (Hemiascineæ).</b>—Fungi with a well -developed, septate mycelium, but with a sporangium-like ascus, i.e., -a large and indefinite number of spores in the ascus. Examples: -Protomyces macrosporus in stems of Umbelliferæ, or P. polysporus in -Ambrosia trifida. These two are by some placed in the Ustilagineæ. -Dipodascus albidus grows in the exuding sap of Bromeliaceæ in Brazil -and the sap of the beech in Sweden. The ascus is developed as the -result of the fertilization of an ascogonium with an antheridium (see -<a href="#FIG_251">fig. 251</a>).</p> - -<p class="center">2. SUBCLASS PROTOASCOMYCETES.</p> - -<p><b>442. The asci are well-defined</b> and usually with a limited and -definite number of spores (usually 8, sometimes 1, 2, 4, 16, or more). -Mycelium often well developed and septate. Asci scattered on the -mycelium, not associated in definite fields or groups.</p> - -<p><b>443. Order Protoascales (Protoascineæ).</b>—The asci are separate -cells, or are scattered irregularly in loose wefts of mycelium. -No fruit body. (The yeast, Saccharomyces, <a href="#PARA_237">see paragraph 237</a>; -and certain mold-like fungi, some of which are parasitic on mushrooms, as -Endomyces, are examples.) -<span class="pagenum"><a name="Page_217" id="Page_217">[Pg 217]</a></span></p> - -<p class="center">3. SUBCLASS EUASCOMYCETES.</p> - -<p>Asci associated in surfaces forming a hymenium, or in groups or -intermingled in the elements of a fruit body. Fruit body usually present.</p> - -<p>The following four or five orders comprise the Discomycetes, according -to the usual classification.</p> - -<p><b>444. Order Protodiscales (Protodiscineæ).</b>—The asci are exposed -and form large and indefinite groups, but there is no definite fruit -body. Examples: leaf curl of peach, plum pocket, etc. (Exoascus).</p> - -<p><b>445. Order Helvellales (Helvellineæ).</b>—The asci form large -fields over the upper portion of the fruit body. This order includes -the morels (<a href="#FIG_231A">fig. 231<i>a</i></a>), helvellas, -earth tongues (Geoglossum), etc.</p> - -<p><b>446. Order Pezizales (Pezizineæ).</b>—The asci form a definite -field or fruiting surface surrounded on the sides and below by a wall -of fungus tissue, forming a fruit body in the shape of a cup. These are -known as the cup fungi (Peziza, Lachnea, etc.).</p> - -<p><b>447. Order Phacidiales (Phacidiineæ).</b>—Fungi mostly saprophytic, -and fruit body similar to the cup fungi. Examples: Propolis in rotting -wood, Rhytisma forming black crusts on leaves (maple for example), -Urnula craterium, a large black beaker-shaped fungus on the ground.</p> - -<p><b>448. Order Hysteriales (Hysteriineæ).</b>—Fungi with a more or less -elongated fruit body with an enclosing wall opening by a long slit. In -some forms the fruit body has the appearance of a two-lipped body; in -others it is shaped like a clam shell, the asci being inside. Example, -Hysterographium common on dry, dead, decorticated sticks.</p> - -<p><b>449. Order Tuberales (Tuberineæ).</b>—The more or less rounded -fruit bodies are usually subterranean. The most important fungi in this -order are the truffles (Tuber). The mycelium of many species assists -in the formation of mycorhiza on the roots of oaks, etc., and several -species are partly cultivated, or protected, and collected for food. -This is especially the case with Tuber brumale and its forms; more than -a million francs worth of truffles are sold in France and Italy yearly. -Dogs and pigs are employed in the collection of truffles from the ground.</p> - -<p><b>450. Order Plectascales (Plectascineæ).</b>—The fruit body of these -plants is more or less globose, and contains the asci distributed -irregularly through the mycelium of the interior. Some are subterranean -(Elaphomyces), while others grow in decaying plants, or certain food -substances (Eurotium, Sterigmatocystis, Penicillium). Penicillium in -its conidial stage forms blue mold on fruit, bread, etc.</p> - -<p>The following four orders comprise the Pyrenomycetes, according to the -usual classification.</p> - -<p><b>451. Order Perisporiales.</b>—The powdery mildews are good examples -of this order (Uncinula, Microsphæra, etc., <a href="#CHAPTER_XXI">Chapter XXI</a>). -<span class="pagenum"><a name="Page_218" id="Page_218">[Pg 218]</a></span></p> - -<p><b>452. Order Hypocreales.</b><a name="FNanchor_20_20" id="FNanchor_20_20"></a><a href="#Footnote_20_20" class="fnanchor">[20]</a>—The -fruit bodies are colorless, or bright colored and entirely enclose the -asci, sometimes opening by an apical pore. Nectria cinnabarina has -clusters of minute orange oval fruit bodies, and is common on dead -twigs. Cordyceps with a number of species is parasitic on insects, and -on certain subterranean Ascomycetes, especially Elaphomyces (of the -order <i>Plectascales</i> = <i>Plectascineæ</i>).</p> - -<p><b>453. Order Dothidiales.</b><a name="FNanchor_21_21" id="FNanchor_21_21"></a><a href="#Footnote_21_21" class="fnanchor">[21]</a>—Fungi -with black stroma formed of mycelium in which are cavities containing -the asci. The cavities are usually shaped like a perithecium, but -there is no wall distinct from the tissue of the stroma (Dothidea, -Phyllachora, on grasses).</p> - -<p><b>454. Order Sphæriales.</b><a name="FNanchor_22_22" id="FNanchor_22_22"></a><a href="#Footnote_22_22" class="fnanchor">[22]</a>—These -contain the so-called black fungi, with separate or clustered, oval, -fruit bodies, black in color. The black wall encloses the asci, and -usually opens by an apical pore. Examples are found in the black knot -of plum and cherry, black rot of grapes, and in Rosellinia, Hypoxylon, -Xylaria, etc., on dead wood.</p> - -<p><b>455. Order Laboulbeniales (Laboulbineæ).</b>—These are peculiar -fungi attached to the legs and bodies of insects by a short stalk, and -provided with a sac-like fruit body which contains the asci. Example, -Laboulbenia.</p> - -<p class="center">III. Class Basidiomycetes. (The basidium series.)</p> - -<p class="center">1. SUBCLASS HEMIBASIDIOMYCETES.</p> - -<p><b>456. Order Ustilaginales (Ustilagineæ).</b>—This order includes the -well-known smuts on corn, wheat, oats, etc. (Ustilago, Tilletia, etc.).</p> - -<p class="center">2. SUBCLASS ÆCIDIOMYCETES.</p> - -<p><b>457. Order Uredinales</b><a name="FNanchor_23_23" id="FNanchor_23_23"></a><a href="#Footnote_23_23" class="fnanchor">[23]</a> (Uredineæ).—This -order includes the parasitic fungi known as rusts. Examples: wheat rust -(<a href="#CHAPTER_XX">Chapter XX</a>), the cedar apple, etc.</p> - -<p>The true Basidiomycetes include the following orders:</p> - -<p class="center">3. SUBCLASS PROTOBASIDIOMYCETES.</p> - -<p><b>458. Order Auriculariales.</b><a name="FNanchor_24_24" id="FNanchor_24_24"></a><a href="#Footnote_24_24" class="fnanchor">[24]</a>—This -order includes trembling fungi in which the basidium is long and -divided transversely into usually four cells (example, Auricularia), -and similar forms. Pilacre petersii on dead wood represents an -angiocarpous form.</p> - -<p><b>459. Order Tremellales (Tremellineæ)</b>, trembling or gelatinous -fungi with the globose basidium divided longitudinally into four cells (Tremella). -<span class="pagenum"><a name="Page_219" id="Page_219">[Pg 219]</a></span></p> - -<p class="center">4. SUBCLASS EUBASIDIOMYCETES.</p> - -<p><b>460. Order Dacryomycetales (Dacryomycetineæ).</b>—This order -includes certain fungi of a gelatinous or waxy consistency, usually -of bright colors. They resemble the Tremellales, but the basidia are -slender and fork into two long sterigmata. (Example, Dacryomyces.) -Gyrocephalus rufus is quite a large plant, 10-15 cm. high, growing on -the ground in woods.</p> - -<p><b>461. Order Exobasidiales (Exobasidiineæ).</b>—The fungus causing -azalea apples is an example (Exobasidium).</p> - -<p><b>462. Order Hymeniales (Hymenomycetineæ).</b>—In this order the -basidia are usually club-shaped and undivided, and bear usually four -spores on the end (sometimes two or six). There are several families.</p> - -<p><b>463. Family Thelephoraceæ.</b>—The fruit bodies are more or less -membranous and spread over wood or the ground, or somewhat leaf-like, -growing on wood or the ground. The fruiting surface is nearly or quite -even, and occupies the under side of the leaf-like bodies (Stereum, -Thelephora) or the outside of the forms spread out on wood (Corticium, -Coniophora).</p> - -<p><b>464. Family Clavariaceæ.</b>—This order includes the fairy clubs, -and some of the coral fungi. The larger number of species are in one -genus (Clavaria, <a href="#FIG_248">fig. 248</a>).</p> - -<p><b>465. Family Hydnaceæ.</b>—The fungi of this order are known as -“hedgehog” fungi, because of the numerous awl-like teeth or spines over -which the fruiting surface is spread, as in Hydnum (figs. <a href="#FIG_246">246</a>, -<a href="#FIG_247">247</a>).</p> - -<p><b>466. Family Polyporaceæ.</b>—The tube-bearing fungi (Polyporus, -Boletus, etc., <a href="#FIG_245">fig. 245</a>).</p> - -<p><b>467. Family Agaricaceæ.</b>—The gill-bearing fungi (Agaricus, -Amanita, etc., see <a href="#CHAPTER_XXI">Chapter XXI</a>).</p> - -<p>The above five orders, according to the earlier classification (still -used at the present time by some), made up the order Hymenomycetes, -while the following five orders made up the Gasteromycetes. The -Hymenomycetes, according to this system, included those plants in which -the fruiting portion (hymenium) is either exposed from the first, or -if covered by a veil or volva (as in Agaricus, Amanita, etc.) this -ruptures and exposes the fruiting surface before, or at the time of, -the ripening of the spores, while the Gasteromycetes included those in -which the fruit body is closed until after the maturity of the spores.</p> - -<p><b>468. Order Phallales (Phallineæ).</b>—The “stink-horn” fungi, or -“buzzard’s nose.” Usually foul-smelling fungi, the fruiting portion -borne aloft on a stout stalk, and dissolving (Dictyophora, Ithyphallus, -etc.).</p> - -<p><b>469. Order Hymenogastrales (Hymenogastrineæ).</b>—The basidia form -a distinct hymenium which does not break down at maturity. Some of -the plants resemble Boletus or Agaricus in the way the fruit bodies -open (Secotium, etc.), while others open irregularly on the surface -<span class="pagenum"><a name="Page_220" id="Page_220">[Pg 220]</a></span> -(Rhizopogon) or like an earth star (Sclerogaster), or portions of the -surface become gelatinized (Phallogaster). The last-named one grows on -very rotten wood, while most of the others grow on the ground.</p> - -<p><b>470. Order Lycoperdales (Lycoperdineæ).</b>—These include the -“puff-balls,” or “devil’s snuff-box” (Lycoperdon), and the earth stars -(Geaster). The basidia form a distinct hymenium, but at maturity the -entire inner portion of the plant (except certain peculiar threads, the -capillitium) disintegrates and with the spores forms a powdery mass.</p> - -<p><b>471. Order Nidulariales (Nidulariineæ).</b>—These are known -as bird-nest fungi. The fruit body when mature is cup-shaped, -or goblet-shaped, and contains minute flattened circular bodies -(peridiola) containing the spores. The intermediate portions of the -fruit body disintegrate and set the peridiola free, which then lie in -the cup-shaped base like eggs in a nest.</p> - -<p><b>472. Order Plectobasidiales (Plectobasidiineæ).</b>—The basidia -do not form a definite hymenium, but are interwoven with the threads -inside, or are collected into knot-like groups. (Examples: Calostoma, -Tulostoma, Astræus, Sphærobolus, etc.)</p> - -<p><b>472a. Lichens.</b>—The plant body of the lichens (<a href="#PARA_200">see paragraphs -200, 201</a>) consists of two component parts, the one a fungus, the other -an alga. The fructification is that of the fungus. The fruit body -shows the lichens to be related some to the Ascomycetes, others to -the Hymenomycetes, and Gasteromycetes. They are usually classified as -a distinct class or order from the fungi, but a natural arrangement -would distribute them in several of the orders above. Their special -relationship with these orders has not been satisfactorily worked out. -For the present they are arranged as follows:</p> - -<ul class="index"> -<li class="isub1"><b>Ascolichenes.</b></li> - -<li class="isub3"><i>Pyrenocarpous lichens</i> (those with a fruit body like the Pyrenomycetes).</li> - -<li class="isub3"><i>Gymnocarpous lichens</i> (those with a fruit body like the Discomycetes).</li> - -<li class="isub1"><b>Hymenolichenes</b> (those with a fruit body like the Hymenomycetes).</li> - -<li class="isub1"><b>Gasterolichenes</b> (those with a fruit body like the Gasteromycetes).</li> -</ul> - -<p>From a vegetative standpoint there are two types according to the -distribution of the elements.</p> - -<p>1st. Where the fungal and algal elements are evenly distributed in the -plant body the lichen is said to be <i>homoiomerous</i>. There are two types -of these:</p> - -<div class="blockquot"> -<p><i>a. Filamentous lichens</i>, example, Ephebe pubescens.</p> - -<p><i>b. Gelatinous lichens</i>, example, Collema (with the alga nostoc), -Physma (with the Chroococcaceæ).</p> -</div> - -<p>2d. Where the elements are stratified, as in Parmelia, etc., the lichen -is said to be <i>heteromerous</i>. In these there are three types:</p> - -<div class="blockquot"> -<p><i>a. Crustaceous lichens</i>, the plant body is in the form of a thin -incrustation on rocks, etc. -<span class="pagenum"><a name="Page_221" id="Page_221">[Pg 221]</a></span></p> - -<p><i>b. Foliaceous lichens</i>, the plant body is leaf-like and lobed and more -or less loosely attached by rhizoids: Parmelia, Peltigera, etc.</p> - -<p><i>c. Fruticose lichens</i>, the plant body is filamentous or band-like and -branched, as in Usnea, Cladonia, etc.</p> -</div> - -<div class="figcenter"> - <img src="images/fig251a.jpg" alt="" width="450" height="459" /> - <p class="center">Fig. 251<i>a</i>.<br /> Rock lichen (Parmelia contigua).</p> - -</div> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_222" id="Page_222">[Pg 222]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXIII" id="CHAPTER_XXIII">CHAPTER XXIII.</a><br /> -<span class="h_subtitle">LIVERWORTS (HEPATICÆ).</span></h3> -</div> - -<p><b>473.</b> We come now to the study of representatives of another -group of plants, a few of which we examined in studying the organs of -assimilation and nutrition. I refer to what are called the liverworts. -Two of these liverworts belonging to the genus riccia are illustrated -in figs. <a href="#FIG_30">30</a>, <a href="#FIG_252">252</a>.</p> - -<h4><a name="XXIII_1" id="XXIII_1">Riccia.</a></h4> - -<p><b>474. Form of the floating riccia (R. fluitans).</b>—The general -form of floating riccia is that of a narrow, irregular, flattened, -ribbon-like object, which forks repeatedly, in a dichotomous manner, -so that there are several lobes to a single plant. It receives its -name from the fact that at certain seasons of the year it may be found -floating on the water of pools or lakes. When the water lowers it comes -to rest on the damp soil, and rhizoids are developed from the under -side. Now the sexual organs, and later the fruit capsule, are developed.</p> - -<p><b>475. Form of the circular riccia (R. crystallina).</b>—The circular -riccia is shown in <a href="#FIG_252">fig. 252</a>. The form of this one is quite -different from the floating one, but the manner of growth is much the same. -The branching is more compact and even, so that a circular plant is -the result. This riccia inhabits muddy banks, lying flat on the wet -surface, and deriving its soluble food by means of the little rootlets -(rhizoids) which grow out from the under surface. -<span class="pagenum"><a name="Page_223" id="Page_223">[Pg 223]</a></span></p> - -<div class="figright"> - <img id="FIG_252" src="images/fig252.jpg" alt="" width="200" height="184" /> - <p class="center">Fig. 252.<br /> Thallus of<br /> Riccia crystallina.</p> -</div> - -<p>Here and there on the margin are narrow slits, which extend nearly to -the central point. They are not real slits, however, for they were -formed there as the plant grew. Each one of these V-shaped portions of -the thallus is a lobe, and they were formed in the young condition of -the plant by a branching in a forked manner. Since growth took place -in all directions radially the plant became circular in form. These -large lobes we can see are forked once or twice again, as shown by the -seeming shorter slits in the margin.</p> - -<p><b>476. Sexual organs.</b>—In order to study the sexual organs we -must make thin sections through one of these lobes lengthwise and -perpendicular to the thallus surface. These sections are mounted for -examination with the microscope.</p> - -<p><b>477. Archegonia.</b>—We are apt to find the organs in various -stages of development, but we will select one of the flask-shaped -structures shown in <a href="#FIG_253">fig. 253</a> for study. This flask-shaped -body we see is entirely sunk in the tissue of the thallus. This structure is the -female organ, and is what we term in these plants the <i>archegonium</i>. -It is more complicated in structure than the oogonium. The lower portion -is enlarged and bellied out, and is the venter of the archegonium, -while the narrow portion is the neck. We here see it in section. The -wall is one cell layer in thickness. In the neck is a canal, and in -the base of the venter we see a large rounded cell with a distinct and -large nucleus. This cell is the <i>egg</i> cell.</p> - -<p><b>478. Antheridia.</b>—The antheridia are also borne in cavities sunk -in the tissue of the thallus. There is here no illustration of the -antheridium of this riccia, but <a href="#FIG_259">fig. 259</a> represents an -antheridium of another liverwort, and there is not a great difference between -the two kinds. Each one of those little rectangular sperm mother cells in the -antheridium changes into a swiftly moving body like a little club with -two long lashes attached to the smaller end. By the violent lashing of -these organs the spermatozoid is moved through the water, or moisture -which is on the surface of the thallus. It moves through the canal of -the archegonium neck and into the egg, where it fuses with the nucleus -of the egg, and thus fertilization is effected. -<span class="pagenum"><a name="Page_224" id="Page_224">[Pg 224]</a></span></p> - -<p><b>479. Embryo.</b>—In the plants which we have selected thus far for -study, the egg, immediately after fecundation, we recollect, passed -into a resting state, and was enclosed by a thick protecting wall. -But in riccia, and in the other plants of the group which we are now -studying, this is not the case. The egg, on the other hand, after -acquiring a thin wall, swells up and fills the cavity of the venter. -Then it divides by a cross wall into two cells. These two grow, and -divide again, and so on until there is formed a quite large mass -of cells rounded in form and still contained in the venter of the -archegonium, which itself increases in size by the growth of the cells -of the wall.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_253" src="images/fig253.jpg" alt="" width="250" height="341" /> - <p class="center">Fig. 253.<br /> Archegonium of riccia, showing<br /> - neck, venter, and the egg;<br /> archegonium is partly<br /> - surrounded by the tissue of<br /> the thallus.<br /> - (Riccia crystallina.)</p> - </div> - <div class="figsub"> - <img id="FIG_254" src="images/fig254.jpg" alt="" width="200" height="338" /> - <p class="center">Fig. 254.<br /> Young embryo (sporogonium)<br /> - of riccia, within the<br /> venter of the archegonium;<br /> - the latter has now two<br /> layers of cells.<br /> - (Riccia crystallina.)</p> - </div> -</div> - -<p><b>480. Sporogonium of riccia.</b>—The fruit of riccia, which is -developed from the fertilized egg in the archegonium, forms a rounded -capsule still enclosed in the venter of the archegonium, which grows -also to provide space for it. Therefore a section through the plant at -this time, as described for the study of the archegonium, should show -this capsule. The capsule then is a rounded mass of cells developed -from the egg. A single outer layer of cells forms the wall, and -<span class="pagenum"><a name="Page_225" id="Page_225">[Pg 225]</a></span> -therefore is sterile. All the inner cells, which are richer in -protoplasm, divide into four cells each. Each of these cells becomes -a spore with a thick wall, and is shaped like a triangular pyramid -whose sides are of the same extent as the base (tetrahedral). These -cells formed in fours are the <i>spores</i>. At this time the wall of the -spore-case dissolves, the spores separate from each other and fill the -now enlarged venter of the archegonium. When the thallus dies they are -liberated, or escape between the loosely arranged cells of the upper surface.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig255.jpg" alt="" width="300" height="308" /> - <p class="center">Fig. 255.<br /> Nearly mature sporogonium of Riccia<br /> - crystallina; mature spore at the right.</p> - </div> - <div class="figsub"> - <img src="images/fig256.jpg" alt="" width="200" height="318" /> - <p class="center">Fig. 256.<br /> Riccia glauca; archegonium containing<br /> - nearly mature sporogonium. <i>sg</i>,<br /> spore-producing cells surrounded by<br /> - single layer of sterile cells, the<br /> wall of the sporogonium.</p> - </div> -</div> - -<p><b>481. A new phase in plant life.</b>—Thus we have here in the -sporogonium of <i>riccia</i> a very interesting phase of plant life, in -which the egg, after fertilization, instead of developing directly into -the same phase of the plant on which it was formed, grows into a quite -new phase, the sole function of which is the development of spores. -Since the form of the plant on which the sexual organs are developed -is called the <i>gametophyte</i>, this new phase in which the spores are -developed is termed the <i>sporophyte</i>.</p> - -<p>Now the spores, when they germinate, develop the <i>gametophyte</i>, or -<span class="pagenum"><a name="Page_226" id="Page_226">[Pg 226]</a></span> -thallus, again. So we have this very interesting condition of things, -the thallus (gametophyte) bears the sexual organs and the unfertilized -egg. The fertilized egg, starting as it does from a single-celled -stage, develops the sporogonium (sporophyte). Here the single-cell -stage is again reached in the spore, which now develops the thallus.</p> - -<p><b>482. Riccia compared with coleochæte, œdogonium, etc.</b>—We have -said that in the sporogonium of riccia we have formed a new phase in -plant life. If we recur to our study of coleochæte we may see that -there is here possibly a state of things which presages, as we say, -this new phase which is so well formed in riccia. We recollect that -after the fertilized egg passed the period of rest it formed a small -rounded mass of cells, each of which now forms a zoospore. The zoospore -in turn develops the normal thallus (gametophyte) of the coleochæte -again. In coleochæte then we have two phases of the plant, each having -its origin in a one-celled stage. Then if we go back to œdogonium, -we remember that the fertilized egg, before it developed into the -œdogonium plant again (which is the gametophyte), at first divides -into <i>four</i> cells which become zoospores. These then develop -the œdogonium plant.</p> - -<p class="blockquot">Note. Too much importance should not be attached -to this seeming homology of the sporophyte of œdogonium, coleochæte, -and riccia, for the nuclear phenomena in the formation of the zoospores -of œdogonium and coleochæte are not known. They form, however, a very -suggestive series.</p> - -<h4><a name="XXIII_2" id="XXIII_2">Marchantia.</a></h4> - -<p><b>483.</b> The marchantia (M. polymorpha) has been chosen for study -because it is such a common and easily obtained plant, and also for -the reason that with comparative ease all stages of development can -be obtained. It illustrates also very well certain features of the -structure of the liverworts.</p> - -<div class="figcenter"> - <img id="FIG_257" src="images/fig257.jpg" alt="" width="600" height="399" /> - <p class="center">Fig. 257.<br /> Male plant of marchantia bearing antheridiophores.</p> -</div> - -<p>The plants are of two kinds, male and female. The two different organs, -then, are developed on different plants. In appearance, however, before -the beginning of the structures which bear the sexual organs they -are practically the same. The thallus is flattened like nearly all -of the thalloid forms, and branches in a forked manner. The color is -dark green, and through the middle line of the thallus the texture is -different from that of the margins, so that it possesses what we term a -<span class="pagenum"><a name="Page_227" id="Page_227">[Pg 227]</a></span> -midrib, as shown in figs. <a href="#FIG_257">257</a>, <a href="#FIG_261">261</a>. -The growing point of the thallus is situated in the little depression -at the free end. If we examine the upper surface with a hand lens we -see diamond-shaped areas, and at the center of each of these areas are -the openings known as the stomates.</p> - -<div class="figcenter"> - <img id="FIG_258" src="images/fig258.jpg" alt="" width="600" height="183" /> - <div class="blockquot"> - <p class="center">Fig. 258.<br /> </p> - <p>Section of antheridial receptacle from male plant of Marchantia polymorpha, - showing cavities where the antheridia are borne.</p> - </div> -</div> - -<p><b>484. Antheridial plants.</b>—One of the male plants is figured at -257. It bears curious structures, each held aloft by a short stalk. -These are the antheridial receptacles (or male gametophores). Each -one is circular, thick, and shaped somewhat like a biconvex lens. The -upper surface is marked by radiating furrows, and the margin is -crenate. Then we note, on careful examination of the upper surface, -that there are numerous minute openings. If we make a thin section of -this structure perpendicular to its surface we shall be able to unravel -the mystery of its interior. Here we see, as shown in <a href="#FIG_258">fig. 258</a>, -that each one of these little openings on the surface is an entrance to quite -<span class="pagenum"><a name="Page_228" id="Page_228">[Pg 228]</a></span> -a large cavity. Within each cavity there is an oval or elliptical -body, supported from the base of the cavity on a short stalk. This is -an antheridium, and one of them is shown still more enlarged in <a href="#FIG_259">fig. 259</a>. -This shows the structure of the antheridium, and that there are -within several angular areas, which are divided by numerous straight -cross-lines into countless tiny cuboidal cells, the <i>sperm mother -cells</i>. Each of these, as stated in the former chapter, changes into a -swiftly moving body resembling a serpent with two long lashes attached -to its tail.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_259" src="images/fig259.jpg" alt="" width="300" height="386" /> - <p class="center">Fig. 259.<br /> Section of antheridium of marchantia,<br /> - showing the groups of sperm mother cells.</p> - </div> - <div class="figsub"> - <img id="FIG_260" src="images/fig260.jpg" alt="" width="250" height="345" /> - <p class="center">Fig. 260.<br /> Spermatozoids of marchantia,<br /> - uncoiling and one extended,<br /> showing the two cilia.</p> - </div> -</div> - -<p><b>485.</b> The way in which one of these sperm mother cells changes -into this spermatozoid is very curious. We first note that a coiled -spiral body is appearing within the thin wall of the cell, one end of -the coil larger than the other. The other end terminates in a slender -hair-like outgrowth with a delicate vesicle attached to its free end. -This vesicle becomes more and more extended until it finally breaks and -forms two long lashes which are clubbed at their free ends as shown in -<a href="#FIG_260">fig. 260</a>.</p> - -<div class="figcenter"> - <img id="FIG_261" src="images/fig261.jpg" alt="" width="500" height="458" /> - <p class="center">Fig. 261.<br /> Marchantia polymorpha, female plants bearing archegoniophores.</p> - -</div> -<div class="figleft"> - <img id="FIG_262" src="images/fig262.jpg" alt="" width="150" height="245" /> - <p class="center">Fig. 262.<br /> Marchantia polymorpha,<br /> showing origin of<br /> gametophore.</p> -</div> - -<p><b>486. Archegonial plants.</b>—In <a href="#FIG_261">fig. 261</a> we see one of -the female plants of marchantia. Upon this there are also very curious structures, -which remind one of miniature umbrellas. The general plan of the -<span class="pagenum"><a name="Page_229" id="Page_229">[Pg 229]</a></span> -archegonial receptacle (or female gametophore), for this is what these -structures are, is similar to that of the antheridial receptacle, -but the rays are more pronounced, and the details of structure are -quite different, as we shall see. Underneath the arms there hang down -delicate fringed curtains. If we make sections of this in the same -direction as we did of the antheridial receptacle, we shall be able to -find what is secreted behind these curtains. Such a section is figured -at 266. Here we find the archegonia, but instead of being sunk in -<span class="pagenum"><a name="Page_230" id="Page_230">[Pg 230]</a></span> -cavities their bases are attached to the under surface, while the -delicate, pendulous fringes afford them protection from drying. An -archegonium we see is not essentially different in marchantia from -what it is in riccia, and it will be interesting to learn whether the -sporogonium is essentially different from what we find in riccia.</p> - -<p><b>487. Homology of the gametophore of marchantia.</b>—To see the -relation of the gametophore to the thallus of marchantia take portions -of the thallus bearing the female receptacle. On the under side note -that the prominent midrib continues beyond the thin lateral expansions -and arches upward in the sinus or notch at the end, or at the side -where the branch of the thallus has continued to grow beyond. The stalk -of the gametophore is then a continuation of the midrib of the thallus. -On the apex of this are organized several radial growing points which -develop the digitate or ray-like receptacle. The gametophore is thus a -specialized branch of the thallus. When young, or in many cases when -nearly or quite mature, the gametophore, as one looks at the upper -surface of the thallus, appears to arise from the upper surface, as in -<a href="#FIG_261">fig. 261</a>. This is because the thin lateral expansions of -the thallus project forward and overlap in advance of the stalk. It is sometimes -necessary to tear these overlapping edges apart to see the real origin -of the gametophore. But in quite old plants these expanded portions are -farther apart and show clearly that the stalk arises from the midrib -below and arches upward in the sinus, as in <a href="#FIG_262">fig. 262</a>.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_231" id="Page_231">[Pg 231]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXIV" id="CHAPTER_XXIV">CHAPTER XXIV.</a><br /> -<span class="h_subtitle">LIVERWORTS CONTINUED.</span></h3> -</div> - -<div class="figcenter"> - <img src="images/fig263.jpg" alt="" width="600" height="370" /> - <div class="blockquot"> - <p class="center">Fig. 263.</p> - <p>Archegonial receptacles of marchantia bearing ripe sporogonia. The - capsule of the sporogonium projects outside, while the stalk is - attached to the receptacle underneath the curtain. In the left figure - two of the capsules have burst and the elaters and spores are escaping.</p> - </div> -</div> - -<p><a name="XXIV_1" id="XXIV_1"><b>488. Sporogonium of marchantia.</b></a>—If we examine the plant shown -in <a href="#FIG_181">fig. 181</a> we shall see oval bodies which stand out between the -rays of the female receptacle, supported on short stalks. These are -the sporogonia, or spore-cases. We judge at once that they are quite -different from those which we have studied in riccia, since those were -not stalked. We can see that some of the spore-cases have opened, the -wall splitting down from the apex in several lines. This is caused by -the drying of the wall. These tooth-like divisions of the wall now -curl backward, and we can see the yellowish mass of the spores in slow -<span class="pagenum"><a name="Page_232" id="Page_232">[Pg 232]</a></span> -motion, falling here and there. It appears also as if there were twisting -threads which aided the spores in becoming freed from the capsule.</p> - -<div class="figcenter"> - <img src="images/fig264.jpg" alt="" width="600" height="216" /> - <div class="blockquot"> - <p class="center">Fig. 264.</p> - <p>Section of archegonial receptacle of Marchantia polymorpha; ripe - sporogonia. One is open, scattering spores and elaters; two are still - enclosed in the wall of the archegonium. The junction of the stalk of - the sporogonium with the receptacle is the point of attachment of the - sporophyte of marchantia with the gametophyte.</p> - </div> -</div> -<div class="figcenter"> - <img src="images/fig265.jpg" alt="" width="600" height="415" /> - <div class="blockquot"> - <p class="center">Fig. 265.</p> - <p>Elater and spore of marchantia. <i>sp</i>, spore; - <i>mc</i>, mother cell of spores, showing partly formed spores.</p> - </div> -</div> - -<p><b>489. Spores and elaters.</b>—If we take a bit of this mass of -spores and mount it in water for examination with the microscope, we -shall see that, besides the spores, there are very peculiar thread-like -bodies, the markings of which remind one of a twisted rope. These are -very long cells from the inner part of the spore-case, and their walls -are marked by spiral thickenings. This causes them in drying, and also -when they absorb moisture, to twist and curl in all sorts of ways. They -thus aid in pushing the spores out of the capsule as it is drying.</p> - -<p><b>490. Sporophyte of marchantia compared with riccia.</b>—We must -recollect that the sporogonium in marchantia is larger than in riccia, -and that it is also not lying in the tissue of the thallus, but is only -<span class="pagenum"><a name="Page_233" id="Page_233">[Pg 233]</a></span> -attached to it at one side by a slender stalk. This shows us an -increase in the size and complex structure of this new phase of the -plant, the <i>sporophyte</i>. This is one of the very interesting things -which we have to note as we go on in the study of the higher plants.</p> - -<div class="figcenter"> - <img src="images/fig266.jpg" alt="" width="600" height="416" /> - <div class="blockquot"> - <p class="center">Fig. 266.</p> - <p>Marchantia polymorpha, archegonium at the left with egg; archegonium at - the right with young sporogonium; <i>p</i>, curtain which hangs down around - the archegonia; <i>e</i>, egg; <i>v</i>, venter of archegonium; <i>n</i>, - neck of archegonium; <i>sp</i>, young sporogonium.</p> - </div> -</div> - -<p><b>491. Sporophyte dependent on the gametophyte for its -nutriment.</b>—We thus see that at no time during the development of -the sporogonium is it independent from the gametophyte. This new phase -of plants then, the sporophyte, has not yet become an independent -plant, but must rely on the earlier phase for sustenance.</p> - -<p><b>492. Development of the sporogonium.</b>—It will be interesting -to note briefly how the development of the marchantia sporogonium -differs from that of riccia. The first division of the fertilized egg -is the same as in riccia, that is a wall which runs crosswise of the -axis of the archegonium divides it into two cells. In marchantia the -cell at the base develops the stalk, so that here there is a radical -difference. The outer cell forms the capsule. But here after the wall -is formed the inner tissue does not all go to make spores, as is the -case with riccia. But some of it forms the elaters. While in riccia -only the outside layer of cells of the sporogonium remained sterile, in -marchantia the basal half of the egg remains completely sterile and -<span class="pagenum"><a name="Page_234" id="Page_234">[Pg 234]</a></span> -develops the stalk, and in the outer half the part which is formed from -some of the inner tissue is also sterile.</p> - -<div class="figcenter"> - <img id="FIG_267" src="images/fig267.jpg" alt="" width="600" height="487" /> - <div class="blockquot"> - <p class="center">Fig. 267.</p> - <p>Section of developing sporogonia of marchantia; <i>nt</i>, nutritive tissue - of gametophyte; <i>st</i>, sterile tissue of sporophyte; <i>sp</i>, fertile part - of sporophyte; <i>va</i>, enlarged venter of archegonium.</p> - </div> -</div> - -<p><b>493. Embryo.</b>—In the development of the embryo we can see all -the way through this division line between the basal half, which is -completely sterile, and the outer half, which is the fertile part. In -<a href="#FIG_267">fig. 267</a> we see a young embryo, and it is nearly circular -in section although it is composed of numerous cells. The basal half is attached -to the base of the inner surface of the archegonium, and at this time -the archegonium still surrounds it. The archegonium continues to grow -then as the embryo grows, and we can see the remains of the shrivelled -neck. The portion of the embryo attached to the base of the archegonium -is the sterile part and is called the “foot,” and later develops the -stalk. The sporogonium during all the stages of its development derives -<span class="pagenum"><a name="Page_235" id="Page_235">[Pg 235]</a></span> -its nourishment from the gametophyte at this point of attachment at -the base of the archegonium. Soon, as shown in <a href="#FIG_267">fig. 267</a> at -the right, the outer portion of the sporogonium begins to differentiate into -the cells which form the elaters and those which form spores. These -lie in radiating lines side by side, and form what is termed the -<i>archesporium</i>. Each fertile cell forms four spores just as in riccia. -They are thus called the mother cells of the spores, or spore mother cells.</p> - -<p><b>494. How marchantia multiplies.</b>—New plants of marchantia are -formed by the germination of the spores, and growth of the same to the -thallus. The plants may also be multiplied by parts of the old ones -breaking away by the action of strong currents of water, and when they -lodge in suitable places grow into well-formed plants. As the thallus -lives from year to year and continues to grow and branch the older -portions die off, and thus separate plants may be formed from a former -single one.</p> - -<div class="figcenter"> - <img id="FIG_268" src="images/fig268.jpg" alt="" width="600" height="423" /> - <p class="center">Fig. 268.</p> - <p class="center">Marchantia plant with cupules and gemmæ; rhizoids below.</p> -</div> - -<p><b>495. Buds, or gemmæ, of marchantia.</b>—But there is another -way in which marchantia multiplies itself. If we examine the upper -surface of such a plant as that shown in <a href="#FIG_268">fig. 268</a>, we shall -see that there are minute cup-shaped or saucer-shaped vessels, and within them -minute green bodies. If we examine a few of these minute bodies with -the microscope we see that they are flattened, biconvex, and at two -opposite points on the margin there is an indentation similar to that -which appears at the growing end of the old marchantia thallus. These -are the growing points of these little buds. When they free themselves -<span class="pagenum"><a name="Page_236" id="Page_236">[Pg 236]</a></span> -from the cups they come to lie on one side. It does not matter on what -side they lie, for whichever side it is, that will develop into the -lower side of the thallus, and forms rhizoids, while the upper surface -will develop the stomates.</p> - -<h4><a name="XXIV_2" id="XXIV_2">Leafy-stemmed liverworts.</a></h4> - -<p><b>496.</b> We should now examine more carefully than we have done -formerly a few of the leafy-stemmed liverworts (called foliose liverworts).</p> - -<div class="figcenter"> - <img src="images/fig269.jpg" alt="" width="600" height="394" /> - <div class="blockquot"> - <p class="center">Fig. 269.</p> - <p>Section of thallus of marchantia. <i>A</i>, through the middle portion; <i>B</i>, - through the marginal portion; <i>p</i>, colorless layer; <i>chl</i>, chlorophyll - layer; <i>sp</i>, stomate; <i>h</i>, rhizoids; <i>b</i>, leaf-like outgrowths on - underside (Goebel).</p> - </div> -</div> - -<p><b>497. Frullania</b> (<a href="#FIG_32">Fig. 32</a>).—This plant grows on -the bark of logs, as well as on the bark of standing trees. It lives in quite dry -situations. If we examine the leaves we will see how it is able to do -this. We note that there are two rows of lateral leaves, which are very -close together, so close in fact that they overlap like the shingles -on a roof. Then, as the creeping stems lie very close to the bark of -the tree, these overlapping leaves, which also hug close to the stem -and bark, serve to retain moisture which trickles down the bark during -rains. If we examine these leaves from the under side as shown in <a href="#FIG_34">fig. 34</a>, -we see that the lower or basal part of each one is produced into a -peculiar lobe which is more or less cup-shaped. This catches water and -holds it during dry weather, and it also holds moisture which the plant -<span class="pagenum"><a name="Page_237" id="Page_237">[Pg 237]</a></span> -absorbs during the night and in damp days. There is so much moisture in -these little pockets of the under side of the leaf that minute animals -have found them good places to live in, and one frequently discovers -them in this retreat. There is here also a third row of poorly -developed leaves on the under side of the stem.</p> - -<p><b>498. Porella.</b>—Growing in similar situations is the plant known -as porella. Sometimes there are a few plants in a group, and at other -times large mats occur on the bark of a trunk. This plant, porella, -also has closely overlapping leaves in rows on opposite sides of the -stem, and the lower margin of each leaf is curved under somewhat as in -frullania, though the pocket is not so well formed.</p> - -<p>The larger plants are female, that is they bear archegonia, while -the male plants, those which bear antheridia, are smaller and the -antheridia are borne on small lateral branches. The antheridia -are borne in the axils of the leaves. Others of the leafy-stemmed -liverworts live in damp situations. Some of these, as Cephalozia, grow -on damp rotten logs. Cephalozia is much more delicate, and the leaves -are farther apart. It could not live in such dry situations where the -frullania is sometimes found. If possible the two plants should be -compared in order to see the adaptation in the structure and form to -their environment.</p> - -<div class="figcenter"> - <img src="images/fig270.jpg" alt="" width="500" height="409" /> - <div class="blockquot"> - <p class="center">Fig. 270.</p> - <p>Thallus of a thalloid liverwort (blasia) showing lobed margin - of the frond, intermediate between thalloid and foliose plant.</p> - </div> -</div> - -<p><b>499. Sporogonium of a foliose liverwort.</b>—The sporogonium of the -leafy-stemmed liverworts is well represented by that of several genera. -<span class="pagenum"><a name="Page_238" id="Page_238">[Pg 238]</a></span> -We may take for this study the one illustrated in <a href="#FIG_274">fig. 274</a>, -but another will serve the purpose just as well. We note here that it -consists of a rounded capsule borne aloft on a long stalk, the stalk -being much longer proportionately than in marchantia. At maturity the -capsule splits down into four quadrants, the wall forming four valves, -which spread apart from the unequal drying of the cells, so that the -spores are set free, as shown in <a href="#FIG_278">fig. 276</a>. Some of the -cells inside of the capsule develop elaters here also as well as spores. These are -illustrated in <a href="#FIG_278">fig. 278</a>.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p class="space-below1"> </p> - <img src="images/fig271.jpg" alt="" width="250" height="458" /> - <p class="center">Fig. 271.<br /> Foliose liverwort, male plant<br /> - showing antheridia in axils of<br /> the leaves (a jungermannia).</p> - </div> - <div class="figsub"> - <img src="images/fig272.jpg" alt="" width="175" height="230" /> - <p class="center">Fig. 272.<br /> Antheridium of a foliose<br /> liverwort (jungermannia).</p> - - <img src="images/fig273.jpg" alt="" width="140" height="228" /> - <p class="center">Fig. 273.<br /> Foliose liverwort,<br /> female plant with<br /> rhizoids.</p> - </div> -</div> - -<p><b>500.</b> In this plant we see that the sporophyte remains attached to -<span class="pagenum"><a name="Page_239" id="Page_239">[Pg 239]</a></span> -the gametophyte, and thus is dependent on it for sustenance. This is -true of all the plants of this group. The sporophyte never becomes -capable of an independent existence, and yet we see that it is becoming -larger and more highly differentiated than in the simple riccia.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_274" src="images/fig274.jpg" alt="" width="150" height="473" /> - <p class="center">Fig. 274.<br /> Fruiting plant of<br /> a foliose liverwort<br /> (jungermannia).<br /> - Leafy part is the<br /> gametophyte; stalk<br /> and capsule is<br /> - the sporophyte<br /> (sporogonium in<br /> the bryophytes).</p> - </div> - <div class="figsub"> - <p> </p> - <img id="FIG_275-277" src="images/fig275.jpg" alt="" width="100" height="111" /> - <p class="center">Fig. 275.<br /> Opening capsule<br /> showing escape<br /> of spores and<br /> elaters.</p> - - <img src="images/fig276.jpg" alt="" width="100" height="135" /> - <p class="center">Fig. 276.<br /> Capsule parted<br /> down to the<br /> stalk.</p> - - <img src="images/fig277.jpg" alt="" width="100" height="69" /> - <p class="center">Fig. 277.<br /> Four spores<br /> from mother<br /> cell held<br /> in a group.</p> - </div> - <div class="figsub"> - <img id="FIG_278" src="images/fig278.jpg" alt="" width="180" height="513" /> - <p class="center">Fig. 278.<br /> Elaters, at left<br /> showing the two<br /> - spiral marks, at<br /> right a branched<br /> elater.</p> - </div> - <p class="center">Figs. 275-278.—Sporogonium of liverwort (jungermannia) opening by - splitting into four parts,<br /> showing details of elaters and spores.</p> -</div> - -<p><span class="pagenum"><a name="Page_240" id="Page_240">[Pg 240]</a></span></p> - -<h4><a name="XXIV_3" id="XXIV_3">The Horned Liverworts.</a><a name="FNanchor_25_25" id="FNanchor_25_25"></a><a href="#Footnote_25_25" class="fnanchor">[25]</a></h4> - -<p><b>501. The horned liverworts</b> take their name from the shape of -the sporogonium. This is long, slender, cylindrical, pointed, and very -slightly curved, suggesting the shape of a minute horn. Anthoceros is -one of the most common and widely distributed species. The plant grows -on damp soil or on mud.</p> - -<p class="center">Anthoceros.</p> - -<p><b>502. The gametophyte.</b>—The gametophyte is thalloid. It is thin, -flattened, green, irregularly ribbon-shaped and branched. It lies on -the soil and is more or less crisped or wavy, or curled, the edges -nearly plane, or somewhat irregular, and with minute lobes, or notches, -especially near the growing end. The general form and branching can -be seen in <a href="#FIG_279">fig. 279</a>. Where the plants are much crowded the -thallus is more irregular, and often possesses numerous small lateral branches -in addition to the main lobes. Upon the under side are the slender -rhizoids, which attach to the soil. With a hand lens there can be seen -also upon the under side small dark, rounded and thickened spots, where -an alga (nostoc) is located.</p> - -<p class="center">Sexual Organs of Anthoceros.</p> - -<p><b>502. The sexual organs of anthoceros</b> differ considerably from -those of the other liverworts studied. In the first place they are -immersed in the true tissue of the thallus, i.e., they do not project -above the surface.</p> - -<div class="figcenter"> - <img id="FIG_279" src="images/fig279.jpg" alt="" width="450" height="463" /> - <div class="blockquot"> - <p class="center">Fig. 279.</p> - <p>Anthoceros gracilis. <i>A</i>, several gametophytes, on which sporangia - have developed; <i>B</i>, an enlarged sporogonium, showing its elongated - character and dehiscence by two valves, leaving exposed the slender - columella on the surface of which are the spores, <i>C</i>, <i>D</i>, <i>E</i>, <i>F</i>, - elaters of various forms, <i>G</i>, spores. (After Schiffner.)</p> - </div> -</div> - -<p><b>503. Antheridia.</b>—The antheridium arises from an internal cell -of the thallus, a cell just below the upper surface. This cell develops -<span class="pagenum"><a name="Page_241" id="Page_241">[Pg 241]</a></span> -usually a group of antheridia which lie in a cavity formed around this -cell as the thallus continues to grow. They are situated along the -middle line of the thallus, and can be seen by making a section in this -direction. The antheridia are oval or rounded, have a wall of one layer -of cells which contains the sperm cells, and each antheridium has a -slender stalk. The sperms are like those of the true liverworts.</p> - -<p><b>504. Archegonia.</b>—The archegonia are also borne along the -middle line of the thallus. Each one arises at an early stage in the -development of the tissue of the thallus from a superficial cell, -but the archegonium does not project above the surface. The venter -therefore which contains the egg is deep down in the thallus, the wall -of the neck is formed from cells indistinguishable from the adjoining -cells of the thallus and opens at the surface.</p> - -<p class="center">Sporophyte of Anthoceros.</p> - -<p><b>505. The Sporogonium.</b>—The sporogonium is developed from the -fertilized egg, fertilization resulting of course from the fusion of -one of the sperms with the nucleus of the egg. From the lower part -of the embryo certain cells elongate and push out like rhizoids into -the thallus (gametophyte), but never reach the outside so that the -sporogonium derives its nutriment from the gametophyte in a parasitic -manner like the true liverworts. It is surrounded at the base by a -sheath, an outgrowth of the gametophyte.</p> - -<p><b>506. Growing point of the sporogonium.</b>—A remarkable thing -about the sporogonium of anthoceros, and its relatives, is that the -growing point instead of being situated at the free end is located near -the base, just above the nourishing foot. Thus the upper part of the -sporogonium is older. In the old sporogonia there may be ripe spores -near the free end, young ones near the middle, and undifferentiated -growing tissue near the base. A longitudinal section of a sporogonium -just as the spores are ripening will show this.</p> - -<p><b>507. Structure of the sporogonium.</b>—A longitudinal section -of the sporogonium shows that the spore-bearing tissue occupies a -comparatively small portion of the sporogonium. In the section there -is a narrow layer (two cells thick) on either side and joined at the -top. In the entire sporogonium this fertile tissue is in the shape of -an inverted test tube situated inside of the sporogonium. The wall of -the sporogonium is about four cells thick. The sterile tissue inside -of the spore-bearing tube is the columella. The cells of the wall -contain chlorophyll, and there are true stomata with guard cells in the -epidermal layer.</p> - -<p><b>508. Spores and elaters.</b>—In the spore-bearing tissue there -are two layers of cells (the archesporium). Each cell is a potential -mother cell. The cells, however, of alternate tiers do not form spores. -<span class="pagenum"><a name="Page_242" id="Page_242">[Pg 242]</a></span> -They elongate some what and are somewhat irregular and sometimes divide -or branch. They are supposed to represent rudimentary <i>elaters</i>. The -cells in the other tiers are actual mother cells, and each one forms -four spores.</p> - -<p><b>509. The sporophyte of anthoceros</b> represents the highest type -found in the liverworts. The spongy green parenchyma forming the -wall, with the stomata in the epidermal layer, fits this tissue for -the process of photosynthesis, so that this part of the sporophyte -functions as the green leaf of the seed plants. It has been suggested -by some that if the rhizoids on the nourishing foot could only extend -outside and anchor in the soil, the sporophyte of anthoceros could live -an independent existence. But we see that it stops short of that.</p> - -<h4><a name="XXIV_4" id="XXIV_4">Classification of the Liverworts.</a></h4> - -<p class="center">CLASS HEPATICÆ.</p> - -<p><b>510. Order Marchantiales.</b><a name="FNanchor_26_26" id="FNanchor_26_26"></a><a href="#Footnote_26_26" class="fnanchor">[26]</a> -—There are two families represented in the United States.</p> - -<p>Family Ricciaceæ, including Riccia and Ricciocarpus.</p> - -<p>Family Marchantiaceæ, including Marchantia, Fegatella (= Conocephalus), -Fimbriaria, Targionia, etc.</p> - -<p><b>511. Order Jungermanniales.</b><a name="FNanchor_27_27" id="FNanchor_27_27"></a><a href="#Footnote_27_27" class="fnanchor">[27]</a>—There -are two subdivisions of this order. <i>The Anacrogynæ</i> include chiefly -thalloid forms with continued apical growth, the archegonia back of the -apical cell. Examples: Blasia, Aneura, Pellia, etc.</p> - -<p><i>The Acrogynæ</i> include chiefly foliose forms, the archegonia arising -from the apical cell and in such cases interrupting apical growth. -Examples: Cephalozia, Frullania, Bazzania, Jungermannia, Ptilidium, Porella, etc.</p> - -<p class="center">CLASS ANTHOCEROTES.</p> - -<p><b>512. The Anthocerotes</b> have formerly been placed with the -Hepaticæ as an order. But because of their wide divergence from -the other liverworts in the development of the sexual organs, and -especially in the structure of the sporophyte, they are now by some -separated as a distinct class. There is one order.</p> - -<p><b>Order Anthocerotales.</b><a name="FNanchor_28_28" id="FNanchor_28_28"></a><a href="#Footnote_28_28" class="fnanchor">[28]</a>—This -includes one family (Anthocerotaceæ) with Anthoceros and Notothylas in -Europe and North America, and Dendroceros in the tropics. The latter is epiphytic.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_243" id="Page_243">[Pg 243]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXV" id="CHAPTER_XXV">CHAPTER XXV.</a><br /> -<span class="h_subtitle">MOSSES (MUSCI).</span></h3> -</div> - -<p><b>513.</b> We are now ready to take up the more careful study of the -moss plant. There are a great many kinds of mosses, and they differ -greatly from each other in the finer details of structure. Yet there -are certain general resemblances which make it convenient to take for -study almost any one of the common species in a neighborhood, which -forms abundant fruit. Some, however, are more suited to a first study -than others. (Polytrichum and funaria are good mosses to study.)</p> - -<p><b>514. Mnium.</b>—We will select here the plant shown in <a href="#FIG_280">fig. 280</a>. -This is known as a mnium (M. affine), and one or another of the species -of mnium can be obtained without much difficulty. The mosses, as we -have already learned, possess an axis (stem) and leaf-like expansions, -so that they are leafy-stemmed plants also. Certain of the branches of -the mnium stand upright, or nearly so, and the leaves are all of the -same size at any given point on the stem, as seen in the figure. There -are three rows of these leaves, and this is true of most of the mosses.</p> - -<p><b>515.</b> The mnium plants usually form quite extensive and pretty -mats of green in shady moist woods or ravines. Here and there among the -erect stems are prostrate ones, with two rows of prominent leaves so -arranged that it reminds one of some of the leafy-stemmed liverworts. -If we examine some of the leaves of the mnium we see that the greater -part of the leaf consists of a single layer of green cells, just as -is the case in the leafy-stemmed liverworts. But along the middle -line is a thicker layer, so that it forms a distinct midrib. This is -<span class="pagenum"><a name="Page_244" id="Page_244">[Pg 244]</a></span> -characteristic of the leaves of mosses, and is one way in which they -are separated from the leafy-stemmed liverworts, the latter never -having a midrib.</p> - -<div class="figcenter"> - <img id="FIG_280" src="images/fig280.jpg" alt="" width="450" height="456" /> - <div class="blockquot"> - <p class="center">Fig. 280.</p> - <p>Portion of moss plant of Mnium affine, showing two sporogonia from one - branch. Capsule at left has just shed the cap or operculum; capsule at - right is shedding spores, and the teeth are bristling at the mouth. - Next to the right is a young capsule with calyptra still attached; next - are two spores enlarged.</p> - </div> -</div> - -<p><b>516. The fruiting moss plant.</b>—In <a href="#FIG_280">fig. 280</a> is -a moss plant “in fruit,” as we say. Above the leafy stem a slender stalk bears -the capsule, and in this capsule are borne the spores. The capsule then -belongs to the <i>sporophyte phase</i> of the moss plant, and we should -inquire whether the entire plant as we see it here is the sporophyte, -or whether part of it is gametophyte. If a part of it is gametophyte -and a part sporophyte, then where does the one end and the other begin? -If we strip off the leaves at the end of the leafy stem, and make a -longisection in the middle line, we should find that the stalk which -bears the capsule is simply stuck into the end of the leafy stem, and -is not organically connected with it. This is the dividing line, then, -between the gametophyte and the sporophyte. We shall find that here the -<span class="pagenum"><a name="Page_245" id="Page_245">[Pg 245]</a></span> -archegonium containing the egg is borne, which is a surer way of -determining the limits of the two phases of the plant.</p> - -<p><b>517. The male and female moss plants.</b>—The two plants of mnium -shown in figs. <a href="#FIG_281">281</a>, <a href="#FIG_281">282</a> are quite different, -as one can easily see, and yet they belong to the same species. One is a female plant, -while the other is a male plant. The sexual organs then in mnium, as in many -others of the mosses, are borne on separate plants. The archegonia are -borne at the end of the stem, and are protected by somewhat narrower -leaves which closely overlap and are wrapped together. They are similar -to the archegonia of the liverworts.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_281" src="images/fig281.jpg" alt="" width="200" height="459" /> - <p class="center">Fig. 281.<br /> Female plant (gametophyte) of<br /> - a moss (mnium), showing<br /> rhizoids below, and the<br /> - tuft of leaves above which<br /> protect the archegonia.</p> - </div> - <div class="figsub"> - <img id="FIG_282" src="images/fig282.jpg" alt="" width="235" height="456" /> - <p class="center">Fig. 282.<br /> Male plant (gametophyte) of<br /> - a moss (mnium) showing<br /> rhizoids below and the<br /> - antheridia at the center<br /> above surrounded by<br /> - the rosette of leaves.</p> - </div> -</div> - -<p>The male plants of mnium are easily selected, since the leaves at the -end of the stem form a broad rosette with the antheridia, and some -sterile threads packed closely together in the center. The ends of the -mass of antheridia can be seen with the naked eye, as shown in <a href="#FIG_282">fig. 282</a>. -<span class="pagenum"><a name="Page_246" id="Page_246">[Pg 246]</a></span> -When the antheridia are ripe, if we make a section through a -cluster, or if we merely tease out some from the end with a needle in -a drop of water on the slide, then prepare for examination with the -microscope, we can see the form of the antheridia. They are somewhat -clavate or elliptical in outline, as seen in <a href="#FIG_284">fig. 284</a>. -Between them there stand short threads composed of several cells containing -chlorophyll grains. These are sterile threads (paraphyses).</p> - -<p><b>518. Sporogonium.</b>—In <a href="#FIG_280">fig. 280</a> we see illustrated -a sporogonium of mnium, which is of course developed from the fertilized egg-cell -of the archegonium. There is a nearly cylindrical capsule, bent downward, -and supported on a long slender stalk. Upon the capsule is a peculiar -cap,<a name="FNanchor_29_29" id="FNanchor_29_29"></a><a href="#Footnote_29_29" class="fnanchor">[29]</a> -shaped like a ladle or spatula. This is the remnant of the old -archegonium, which, for a time surrounded and protected the young -embryo of the sporogonium, just as takes place in the liverworts. In -most of the mosses this old remnant of the archegonium is borne aloft -on the capsule as a cap, while in the liverworts it is thrown to one -side as the sporogonium elongates.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_283" src="images/fig283.jpg" alt="" width="300" height="319" /> - <p class="center">Fig. 283.<br /> Section through end of stem of<br /> - female plant of mnium, showing<br /> archegonia at the center. One<br /> - archegonium shows the egg. On<br /> the sides are sections of the<br /> - protecting leaves.</p> - </div> - <div class="figsub"> - <a><img id="FIG_284" src="images/fig284.jpg" alt="" width="140" height="321" /></a> - <p class="center">Fig. 284.<br /> Antheridium of mnium with<br /> - jointed paraphysis at the<br /> left; spermatozoids at<br /> - the right.</p> - </div> -</div> - -<p><b>519. Structure of the moss capsule.</b>—At the free end on the moss -<span class="pagenum"><a name="Page_247" id="Page_247">[Pg 247]</a></span> -capsule as shown in the case of mnium in <a href="#FIG_280">fig. 280</a>, after the -remnant of the archegonium falls away, there is seen a conical lid which fits -closely over the end. When the capsule is ripe this lid easily falls -away, and can be brushed off so that it is necessary to handle the -plants with care if it is desired to preserve this for study.</p> - -<p><b>520.</b> When the lid is brushed away as the capsule dries more we -see that the end of the capsule covered by the lid appears “frazzled.” -If we examine this end with the microscope we see that the tissue of -the capsule here is torn with great regularity, so that there are two -rows of narrow, sharp teeth which project outward in a ring around the -opening. If we blow our “breath” upon these teeth they will be seen to -move, and as the moisture disappears and reappears in the teeth, they -close and open the mouth of the capsule, so sensitive are they to the -changes in the humidity of the air. In this way all of the spores are -prevented to some extent from escaping from the capsule at one time.</p> - -<p><b>521.</b> Note. If we make a section longitudinal of the capsule of -mnium, or some other moss, we find that the tissue which develops the -spores is much more restricted than in the capsule of the liverworts -which we have studied. The spore-bearing tissue is confined to a single -layer which extends around the capsule some distance from the outside -of the wall, so that a central cylinder is left of sterile tissue. This -is the columella, and is present in nearly all the mosses. Each of the -cells of the fertile layer divides into four spores.</p> - -<div class="figcenter"> - <img id="FIG_285" src="images/fig285.jpg" alt="" width="350" height="500" /> - <div class="blockquot"> - <p class="center">Fig. 285.</p> - <p>Two different stages of young sporogonium of a moss, still within the - archegonium and wedging their way into the tissue of the end of the - stem. <i>h</i>, neck of archegonium; <i>f</i>, young sporogonium. This - shows well the connection of the sporophyte with the gametophyte.</p> - </div> -</div> - -<p><b>522. Development of the sporogonium.</b>—The egg-cell after -fertilization divides by a wall crosswise to the axis of the -archegonium. Each of these cells continues to divide for a time, so -that a cylinder pointed at both ends is formed. The lower end of -this cylinder of tissue wedges its way down through the base of the -archegonium into the tissue of the end of the moss stem as shown in -<span class="pagenum"><a name="Page_248" id="Page_248">[Pg 248]</a></span> -<a href="#FIG_285">fig. 285</a>. This forms the foot through which the nutrient -materials are passed from the gametophyte to the sporogonium. The upper part -continues to grow, and finally the upper end differentiates into the -mature capsule.</p> - -<p><b>523. Protonema of the moss.</b>—When the spores of a moss germinate -they form a thread-like body, with chlorophyll. This thread becomes -branched, and sometimes quite extended tangles of these threads are -formed. This is called the protonema, that is <i>first thread</i>. The older -threads become finally brown, while the later ones are green. From this -protonema at certain points buds appear which divide by close oblique -walls. From these buds the leafy stem of the moss plant grows. Threads -similar to these protonemal threads now grow out from the leafy stem, -to form the rhizoids. These supply the moss plant with nutriment, and -now the protonema usually dies, though in some few species it persists -for long periods.</p> - -<h4><a name="XXV_1" id="XXV_1">Classification of the Mosses.</a></h4> - -<p class="center">CLASS MUSCINEÆ (MUSCI).</p> - -<p><b>524. Order Sphagnales.</b><a name="FNanchor_30_30" id="FNanchor_30_30"></a><a href="#Footnote_30_30" class="fnanchor">[30]</a>—This -order includes the peat mosses. There is but one family (Sphagnaceæ) -and but a single genus (Sphagnum). The peat mosses are widely -distributed over the globe, chiefly occurring in moors, or “bogs,” -usually low ground around the shores of lakes, ponds, or along streams, -but they often occur on wet dripping rocks in cool shady places. Small -ponds are sometimes filled in by their growth. As the sphagnum growing -in such an abundance of water only partially decays, “ground” is built -up rather rapidly, and the sphagnum remains are known as “peat.” This -“ground”-building peculiarity of sphagnum sometimes enables the plant -(often in conjunction with others) to fill in ponds completely. (See -Atoll Moor, Chapter LV.)</p> - -<p>The gametophyte of sphagnum, like that of all the mosses, is dimorphic, -but the first part (or protonema) which develops from the spores is -thalloid, and therefore more like the thallose liverworts. The leafy -axis (or gametophore) which develops from the thalloid form is very -characteristic (see Chapter LV).</p> - -<p>The archegonia are borne on the free end of the main axis, while the -antheridia are borne on short branches which are brightly colored, red, -yellow, etc. The sporophyte (sporogonium) is globose and possesses a -broad foot anchored in the end of a naked prolongation of the end of -the leafy gametophore. This naked prolongation of the gametophore looks -like the stalk of the sporogonium, but a study of its connection with -the sporogonium shows that it is part of the gametophyte, which is only -developed after the fertilization of the egg in the archegonium. In the -sporogonium there is a short columella, and the archesporium is in the -form of an inverted cup. -<span class="pagenum"><a name="Page_249" id="Page_249">[Pg 249]</a></span></p> - -<p><b>525. Order Andreæales.</b><a name="FNanchor_31_31" id="FNanchor_31_31"></a><a href="#Footnote_31_31" class="fnanchor">[31]</a>—This -order includes the single genus Andreæa. The plants are small but form -extensive mats, growing on rocks in arctic or alpine regions usually. -They are sometimes found in great abundance on bare, rather dry rocks -on mountains. The protonema is somewhat thalloid. The sporogonium opens -by splitting longitudinally into four valves. An elongated columella -is present so that the archesporium is shaped like an inverted -test tube.</p> - -<p><b>526. Order Archidiales.</b><a name="FNanchor_32_32" id="FNanchor_32_32"></a><a href="#Footnote_32_32" class="fnanchor">[32]</a>—This -order contains the single genus Archidium, and by some is placed as -an aberrant genus in the Bryales. There is no columella in the simple -sporogonium. The archesporium occupies all the internal part of the -sporogonium, some cells being fertile and others sterile.</p> - -<p><b>527. Order Bryales.</b><a name="FNanchor_33_33" id="FNanchor_33_33"></a><a href="#Footnote_33_33" class="fnanchor">[33]</a>—These -include the higher mosses, and a very large number of genera and -species. The protonema is filamentous and branched except in a few -forms where it is partly thalloid as in Tetraphis (= Georgia). -(Tetraphis pellucida is a common moss on very rotten logs. The capsule -has four prominent teeth.) In a few of the lower genera (Phascum, -Pleuridium, etc.) the capsule opens irregularly, but in the larger -number the capsule opens by a lid (operculum). A cylindrical columella -is present, and the archesporium is in the form of a tube open at both -ends. (Examples: Polytrichum, Bryum, Mnium, Hypnum, etc.) -<span class="pagenum"><a name="Page_250" id="Page_250">[Pg 250]</a></span></p> - -<p><b>528.</b></p> -<p class="center">TABLE SHOWING RELATION OF GAMETOPHYTE AND<br /> - SPOROPHYTE IN THE LIVERWORTS AND MOSSES.</p> - -<table class="smallfont" border="0" cellspacing="0" summary=" " cellpadding="0" rules="cols" > - <thead><tr> - <th class="tdc bb2" colspan="9"> </th> - </tr><tr> - <th class="tdc bb2" rowspan="2"> </th> - <th class="tdc bb2" colspan="4">GAMETOPHYTE.<br /> (Prominent part of the plant.<br /> Leads an independent existence.)</th> - <th class="tdc bb2" colspan="3">SPOROPHYTE<br />(Attached to gametophyte and dependent on it for nourishment.)</th> - <th class="tdc bb2" rowspan="2"><span class="smcap">Beginning<br /> of<br /> Gametophyte.</span></th> - </tr><tr> - <th class="tdc bb2"><span class="smcap">Vegetative<br />Phase</span></th> - <th class="tdc bb2"><span class="smcap">Vegetative<br />Mulitipl-<br />ication.</span></th> - <th class="tdc bb2" colspan="2"> <span class="smcap">Sexual Organs.</span> </th> - <th class="tdc bb2"><span class="smcap">Beginning<br /> of<br /> Sporophyte.</span></th> - <th class="tdc bb2"><span class="smcap">Sterile Part.</span></th> - <th class="tdc bb2"><span class="smcap">Fertile Part.</span></th> - </tr> - </thead> - <tbody><tr> - <td class="tdl bb" rowspan="2"><span class="smcap">Riccia.</span></td> - <td class="tdl_table bb" rowspan="2"><p>Thallus flattened, ribbon-like, forked, or nearly circular.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Sometimes by branching and dying away of older parts.</p></td> - <td class="tdc" colspan="2"><p>Immersed by surrounding, upward growth of thallus.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops sporogonium.)</p></td> - <td class="tdl_table bb" rowspan="2"><p>Wall of sporogonium, of one-layer cells.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Central mass (archesporium) develops .....</p></td> - <td class="tdl bb" rowspan="2"> Spores.</td> - </tr><tr> - <td class="tdl_table bb"><p>Antheridia, with spermatozoids.</p></td> - <td class="tdl_table bb"><p>Archegonia, with egg in each.</p></td> - </tr><tr> - <td class="tdl bb" rowspan="2"><span class="smcap">Marchantia.</span></td> - <td class="tdl_table bb" rowspan="2"><p>Thallus flattened, ribbon-like, forked, - male and female plants bear gametophores.</p></td> - <td class="tdl_table bb" rowspan="2"><p>By dying away of older parts, and by gemmæ.</p></td> - <td class="tdc" colspan="2">Borne on special receptacles on different plants.</td> - <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops sporogonium.)</p></td> - <td class="tdl_table bb" rowspan="2"><p>Sterile part of stalked is stalk, wall of capsule - of several layers, elaters.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Central part of capsule (archesporium) - develops .....<br /> and elaters.</p></td> - <td class="tdl bb" rowspan="2"> Spores.</td> - </tr><tr> - <td class="tdl_table bb"><p>Antheridia, with spermatozoids, borne on antheridiphores, - or male gametophores.</p></td> - <td class="tdl_table bb"><p>Archegonia, borne on female gametophore (or archegoniophore), - each with an egg.</p></td> - </tr><tr> - <td class="tdl bb" rowspan="2"><span class="smcap">Jungermannia <br /> (or Cephalozia,<br /> Porella,</span> etc.)</td> - <td class="tdl_table bb" rowspan="2"><p>A plant with apparent leaves and stem; margins of thallus - have become cut into lobes. Male and female plants.</p></td> - <td class="tdl_table bb" rowspan="2"><p>By dying away of older parts.</p></td> - <td class="tdc" colspan="2">On different plants.</td> - <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops sporogonium.)</p></td> - <td class="tdl_table bb" rowspan="2"><p>Sterile part of stalked capsule is stalk, wall - of capsule of several layers, elaters.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Central part of capsule (archesporium) develops .....<br /> - and elaters.</p></td> - <td class="tdl bb" rowspan="2"> Spores.</td> - </tr><tr> - <td class="tdl_table bb"><p>Antheridia, with spermatozoids, in axils of leaves of male plant.</p></td> - <td class="tdl_table bb"><p>Archegonia, each with egg, on female plant.</p></td> - </tr><tr> - <td class="tdl bb" rowspan="2"><span class="smcap">Mosses.<br /> - Mnium,<br /> Polytrichum</span><br /> etc.</td> - <td class="tdl_table bb" rowspan="2"><p>Plant with apparent leafy axis, 3 rows of leaves - (similar to jungermannia), borne on an earlier protonemal stage. - Male and female plants.</p></td> - <td class="tdl_table bb" rowspan="2"><p>By branching, by growth of protonema from axis, leaves, - or even sporogonium. (In some genera by gemmæ.)</p></td> - <td class="tdc" colspan="2">On different plants.</td> - <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops sporogonium.)</p></td> - <td class="tdl_table bb" rowspan="2"><p>Sterile part of stalked capsule is stalk, wall - of capsule of several layers, columella, lid, teeth etc., of - the highly specialized capsule.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Cylindrical layer of cells around columella is the - archesporium; it develops .....</p></td> - <td class="tdl bb" rowspan="2"> Spores.</td> - </tr><tr> - <td class="tdl_table bb"><p>Antheridia, with spermatozoids, at end of stem of male plant.</p></td> - <td class="tdl_table bb"><p>Archegonia each with egg, on female plant. (Calyptra found on - sporogonium is remnant of archegonium.)</p></td> - </tr><tr> - <td class="tdc bt" colspan="9"> </td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_251" id="Page_251">[Pg 251]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXVI" id="CHAPTER_XXVI">CHAPTER XXVI.</a><br /> -<span class="h_subtitle">FERNS.</span></h3> -</div> - -<p><b>529.</b> In taking up the study of the ferns we find plants which -are very beautiful objects of nature and thus have always attracted -the interest of those who love the beauties of nature. But they are -also very interesting to the student, because of certain remarkable -peculiarities of the structure of the fruit bodies, and especially -because of the intermediate position which they occupy within the -plant kingdom, representing in the two phases of their development the -primitive type of plant life on the one hand, and on the other the -modern type. We will begin our study of the ferns by taking that form -which is the more prominent, the fern plant itself.</p> - -<p><b>530. The Christmas fern.</b>—One of the ferns which is very common -in the Northern States, and occurs in rocky banks and woods, is the -well-known Christmas fern (Aspidium acrostichoides) shown in <a href="#FIG_286">fig. 286</a>. -The leaves are the most prominent part of the plant, as is the case -with most if not all our native ferns. The stem is very short and -for the most part under the surface of the ground, while the leaves -arise very close together, and thus form a rosette as they rise and -gracefully bend outward. The leaf is elongate and reminds one somewhat -of a plume with the pinnæ extending in two rows on opposite sides of -the midrib. These pinnæ alternate with one another, and at the base of -each pinna is a little spur which projects upward from the upper edge. -Such a leaf is said to be pinnate. While all the leaves have the same -general outline, we notice that certain ones, especially those toward -<span class="pagenum"><a name="Page_252" id="Page_252">[Pg 252]</a></span> -the center of the rosette, are much narrower from the middle portion -toward the end. This is because of the shorter pinnæ here.</p> - -<div class="figcenter"> - <img id="FIG_286" src="images/fig286.jpg" alt="" width="450" height="471" /> - <p class="center">Fig. 286.<br /> Christmas fern<br /> (Aspidium acrostichoides).</p> -</div> - -<p><b>531. Fruit “dots” (sorus, indusium).</b>—If we examine the under -side of such short pinnæ of the Christmas fern we see that there -are two rows of small circular dots, one row on either side of the -pinna. These are called the “fruit dots,” or sori (a single one is a -sorus). If we examine it with a low power of the microscope, or with -a pocket lens, we see that there is a circular disk which covers more -or less completely very minute objects, usually the ends of the latter -projecting just beyond the edge if they are mature. This circular disk -is what is called the <i>indusium</i>, and it is a special outgrowth of the -epidermis of the leaf here for the protection of the spore-cases. These -minute objects underneath are the fruit bodies, which in the case of -the ferns and their allies are called <i>sporangia</i>. This indusium in the -case of the Christmas fern, and also in some others, is attached to the -<span class="pagenum"><a name="Page_253" id="Page_253">[Pg 253]</a></span> -leaf by means of a short slender stalk which is fastened to the middle -of the under side of this shield, as seen in cross-section in <a href="#FIG_292">fig. 292</a>.</p> - -<p><b>532. Sporangia.</b>—If we section through the leaf at one of the -fruit dots, or if we tease off some of the sporangia so that the stalks -are still attached, and examine them with the microscope, we can see -the form and structure of these peculiar bodies. Different views of a -sporangium are shown in <a href="#FIG_293">fig. 293</a>. The slender portion is -the stalk, and the larger part is the spore-case proper. We should examine the -structure of this spore-case quite carefully, since it will help us to -understand better than we otherwise could the remarkable operations -which it performs in scattering the spores.</p> - -<div class="figcenter"> - <img id="FIG_287" src="images/fig287.jpg" alt="" width="350" height="482" /> - <p class="center">Fig. 287.<br /> Rhizome with bases of leaves, and<br /> - roots of the Christmas fern.</p> -</div> - -<p><b>533. Structure of a sporangium.</b>—If we examine one of the -sporangia in side view as shown in <a href="#FIG_293">fig. 293</a>, we note a prominent -row of cells which extend around the margin of the dorsal edge from near -the attachment of the stalk to the upper front angle. The cells are -prominent because of the thick inner walls, and the thick radial walls -which are perpendicular to the inner walls. The walls on the back of -this row and on its sides are very thin and membranous. We should make -this out carefully, for the structure of these cells is especially -<span class="pagenum"><a name="Page_254" id="Page_254">[Pg 254]</a></span> -adapted to a special function which they perform. This row of cells is -termed the <i>annulus</i>, which means a little ring. While this is not a -complete ring, in some other ferns the ring is nearly complete.</p> - -<div class="figcenter"> - <img src="images/fig288.jpg" alt="" width="600" height="280" /> - <p class="center">Fig. 288.<br /> Rhizome of sensitive fern<br /> - (Onoclea sensibilis).</p> -</div> -<div class="figleft"> - <img src="images/fig289.jpg" alt="" width="200" height="199" /> - <p class="center">Fig. 289.<br /> Under side of pinna of<br /> - Aspidium spinulosum<br /> showing fruit dots<br /> (sori).</p> -</div> - -<p><b>534.</b> In the front of the sporangium is another peculiar group -of cells. Two of the longer ones resemble the lips of some creature, -and since the sporangium opens between them they are sometimes termed -the lip cells. These lip cells are connected with the upper end of the -annulus on one side and with the upper end of the stalk on the other -side by thin-walled cells, which may be termed connective cells, since -they hold each lip cell to its part of the opening sporangium. The -cells on the side of the sporangium are also thin-walled. If we now -examine a sporangium from the back, or dorsal edge as we say, it will -appear as in the left-hand figure. Here we can see how very prominent -the annulus is. It projects beyond the surface of the other cells of -<span class="pagenum"><a name="Page_255" id="Page_255">[Pg 255]</a></span> -the sporangium. The spores are contained inside this case.</p> - -<p><b>535. Opening of the sporangium and dispersion of the spores.</b>—If -we take some fresh fruiting leaves of the Christmas fern, or of any one -of many of the species of the true ferns just at the ripening of the -spores, and place a portion of it on a piece of white paper in a dry -room, in a very short time we shall see that the paper is being dusted -with minute brown objects which fly out from the leaf. Now if we take -a portion of the same leaf and place it under the low power of the -microscope, so that the full rounded sporangia can be seen, in a short -time we note that the sporangium opens, the upper half curls backward -as shown in <a href="#FIG_294">fig. 294</a>, and soon it snaps quickly, to near -its former position, and the spores are at the same time thrown for a considerable -distance. This movement can sometimes be seen with the aid of a good -hand lens.</p> - -<div class="figcenter"> - <img src="images/fig290.jpg" alt="" width="600" height="263" /> - <p class="center">Fig. 290.<br /> Four pinnæ of adiantum, showing recurved<br /> - margins which cover the sporangia.</p> -</div> -<div class="figcenter"> - <img id="FIG_291" src="images/fig291.jpg" alt="" width="600" height="348" /> - <p class="center">Fig. 291.<br /> Section through sorus of Polypodium vulgare - showing different<br /> stages of sporangium, and one multicellular capitate hair.</p> -</div> - -<p><b>536. How does this opening and snapping of the sporangium take -place?</b>—We are now more curious than ever to see just how this -opening and snapping of the sporangium takes place. We should now mount -some of the fresh sporangia in water and cover with a cover glass for -microscopic examination. A drop of glycerine should be placed at one -side of the cover glass on the slip so that the edge of the glycerine -will come in touch with the water. Now as one looks through the -<span class="pagenum"><a name="Page_256" id="Page_256">[Pg 256]</a></span> -microscope to watch the sporangia, the water should be drawn from under -the cover glass with the aid of some bibulous paper, like filter paper, -placed at the edge of the cover glass on the opposite side from the -glycerine. As the glycerine takes the place of the water around the -sporangia it draws the water out of the cells of the annulus, just as -it took the water out of the cells of the spirogyra as we learned some -time ago. As the water is drawn out of these cells there is produced -a pressure from without, the atmospheric pressure upon the glycerine. -This causes the walls of these cells of the annulus to bend inward, -because, as we have already learned, the glycerine does not pass -through the walls nearly so fast as the water comes out.</p> - -<div class="figcenter"> - <img id="FIG_292" src="images/fig292.jpg" alt="" width="600" height="158" /> - <p class="center">Fig. 292.<br /> Section through sorus and shield-shaped indusium of aspidium.</p> -</div> - -<p><b>537.</b> Now the structure of the cells of this annulus, as we have -seen, is such that the inner walls and the perpendicular walls are -stout, and consequently they do not bend or collapse when this pressure -<span class="pagenum"><a name="Page_257" id="Page_257">[Pg 257]</a></span> -is brought to bear on the outside of the cells. The thin membranous -walls on the back (dorsal walls) and on the sides of the annulus, -however, yield readily to the pressure and bend inward. This, as we -can readily see, pulls on the ends of each of the perpendicular walls -drawing them closer together. This shortens the outer surface of the -annulus and causes it to first assume a nearly straight position, then -curve backward until it quite or nearly becomes doubled on itself. The -sporangium opens between the lip cells on the front and the lateral -walls of the sporangium are torn directly across. The greater mass of -spores are thus held in the upper end of the open sporangium, and when -the annulus has nearly doubled on itself it suddenly snaps back again -in position. While treating with the glycerine we can see all this -movement take place. Each cell of the annulus acts independently, but -often they all act in concert. When they do not all act in concert, -some of them snap sooner than others, and this causes the annulus to -snap in segments.</p> - -<div class="figcenter"> - <img id="FIG_293" src="images/fig293.jpg" alt="" width="600" height="358" /> - <p class="center">Fig. 293.<br /> Rear, side, and front views of fern sporangium.<br /> - <i>d</i>, <i>e</i>, annulus; <i>a</i>, lip cells.</p> -</div> -<hr class="r25" /> -<div class="figcenter"> - <img id="FIG_294" src="images/fig294.jpg" alt="" width="600" height="529" /> - <p class="center">Fig. 294.<br /> Dispersion of spores from sporangium of Aspidium acrostichoides,<br /> - showing different stages in the opening and snapping of the annulus.</p> -</div> - -<p><span class="pagenum"><a name="Page_258" id="Page_258">[Pg 258]</a></span> -<b>538. The movements of the sporangium can take place in old and dried -material.</b>—If we have no fresh material to study the sporangium -with, we can use dried material, for the movements of the sporangia can -be well seen in dried material, provided it was collected at about the -time the sporangia are mature, that is at maturity, or soon afterward. -We take some of the dry sporangia (or we may wash the glycerine off -those which we have just studied) and mount them in water, and quickly -examine them with a microscope. We notice that in each cell of the -annulus there is a small sphere of some gas. The water which bathes the -walls of the annulus is absorbed by some substance inside these cells. -This we can see because of the fact that this sphere of gas becomes -<span class="pagenum"><a name="Page_259" id="Page_259">[Pg 259]</a></span> -smaller and smaller until it is only a mere dot, when it disappears in -a twinkling. The water has been taken in under such pressure that it -has absorbed all the gas, and the farther pressure in most cases closes -the partly opened sporangium more completely.</p> - -<p><b>539.</b> Now we should add glycerine again and draw out the water, -watching the sporangia at the same time. We see that the sporangia -which have opened and snapped once will do it again. And so they may -be made to go through this operation several times in succession. We -should now note carefully the annulus, that is after the sporangia have -opened by the use of glycerine. So soon as they have snapped in the -glycerine we can see those minute spheres of gas again, and since there -was no air on the outside of the sporangia, but only glycerine, this -gas must, it is reasoned, have been given up by the water before it was -all drawn out of the cells.</p> - -<p><b>540. The common polypody.</b>—We may now take up a few other ferns -for study. Another common fern is the polypody, one or more species of -which have a very wide distribution. The stem of this fern is also not -usually seen, but is covered with the leaves, except in the case of -those species which grow on the surface of rocks. The stem is slender -and prostrate, and is covered with numerous brown scales. The leaves -are pinnate in this fern also, but we find no difference between the -fertile and sterile leaves (except in some rare cases). The fruit dots -occupy much the same positions on the under side of the leaf that they -do in the Christmas fern, but we cannot find any indusium. In the place -of an indusium are club-shaped hairs as shown in <a href="#FIG_291">fig. 291</a>. -The enlarged ends of these clubs reaching beyond the sporangia give some protection -to them when they are young.</p> - -<p><b>541. Other ferns.</b>—We might examine a series of ferns to see -how different they are in respect to the position which the fruit -dots occupy on the leaf. The common brake, which sometimes covers -extensive areas and becomes a troublesome weed, has a stout and smooth -underground stem (rhizome) which is often 12 to 20 <i>cm</i> beneath the -surface of the soil. There is a long leaf stalk, which bears the -lamina, the latter being several times pinnate. The margins of the -fertile pinnæ are inrolled, and the sporangia are found protected -underneath in this long sorus along the margin of the pinna. The -beautiful maidenhair fern and its relatives have obovate pinnæ, and -the sori are situated in the same positions as in the brake. In other -ferns, as the walking fern, the sori are borne along by the side of the -veins of the leaf.</p> - -<p><b>542. Opening of the leaves of ferns.</b>—The leaves of ferns -open in a peculiar manner. The tip of the leaf is the last portion -<span class="pagenum"><a name="Page_260" id="Page_260">[Pg 260]</a></span> -developed, and the growing leaf appears as if it was rolled up as in -<a href="#FIG_287">fig. 287</a> of the Christmas fern. As the leaf -elongates this portion unrolls.</p> - -<p><b>543. Longevity of ferns.</b>—Most ferns live from year to year, by -growth adding to the advance of the stem, while by decay of the older -parts the stem shortens up behind. The leaves are short-lived, usually -dying down each year, and a new set arising from the growing end of the -stem. Often one can see just back or below the new leaves the old dead -ones of the past season, and farther back the remains of the petioles -of still older leaves.</p> - -<div class="figcenter"> - <img id="FIG_295" src="images/fig295.jpg" alt="" width="400" height="438" /> - <p class="center">Fig. 295.<br /> Cystopteris bulbifera, young plant growing from bulb.<br /> - At right is young bulb in axil of pinna of leaf.</p> -</div> - -<p><b>544. Budding of ferns.</b>—A few ferns produce what are called -bulbils or bulblets on the leaves. One of these, which is found -throughout the greater part of the eastern United States, is the -bladder fern (Cystopteris bulbifera), which grows in shady rocky -places. The long graceful delicate leaves form in the axils of the -pinnæ, especially near the end of the leaf, small oval bulbs as shown -in <a href="#FIG_295">fig. 295</a>. If we examine one of these bladder-like bulbs -we see that the bulk of it is made up of short thick fleshy leaves, smaller -ones appearing between the outer ones at the smaller end of the bulb. -This bulb contains a stem, young root, and several pairs of these -fleshy leaves. They easily fall to the ground or rocks, where, with -the abundant moisture usually present in localities where the fern is -found, the bulb grows until the roots attach the plant to the soil or -in the crevices of the rocks. A young plant growing from one of these -bulbils is shown in <a href="#FIG_295">fig. 295</a>.</p> - -<p><b>545. Greenhouse ferns.</b>—Some of the ferns grown in -conservatories have similar bulblets. <a href="#FIG_296">Fig. 296</a> represents -one of these which is found abundantly on the leaves of Asplenium bulbiferum. These -bulbils have leaves which are very similar to the ordinary leaf except -that they are smaller. The bulbs are also much more firmly attached to -the leaf, so that they do not readily fall away.</p> - -<p><b>546.</b> Plant conservatories usually furnish a number of very -interesting ferns, and one should attempt to make the acquaintance of -<span class="pagenum"><a name="Page_261" id="Page_261">[Pg 261]</a></span> -some of them, for here one has an opportunity during the winter season -not only to observe these interesting plants, but also to obtain -material for study. In the tree ferns which often are seen growing in -such places we see examples of the massive trunks and leaves of some of -the tropical species.</p> - -<div class="figcenter"> - <img id="FIG_296" src="images/fig296.jpg" alt="" width="400" height="295" /> - <p class="center">Fig. 296.<br /> Bulbil growing from leaf of asplenium<br /> (<i>A</i>, bulbiferum).</p> -</div> - -<p><b>547. The fern plant is a sporophyte.</b>—We have now studied -the fern plant, as we call it, and we have found it to represent -the spore-bearing phase of the plant, that is the <i>sporophyte</i> -(corresponding to the sporogonium of the liverworts and mosses).</p> - -<p><b>548. Is there a gametophyte phase in ferns?</b>—But in the -sporophyte of the fern, which we should not forget is the fern plant, -we have a striking advance upon the sporophyte of the liverworts and -mosses. In the latter plants the sporophyte remained attached to the -gametophyte, and derived its nourishment from it. In the ferns, as we -see, the sporophyte has a root of its own, and is attached to the soil. -Through the aid of root hairs of its own it takes up mineral solutions. -It possesses also a true stem, and true leaves in which carbon -conversion takes place. It is able to live independently, then. Does -a gametophyte phase exist among the ferns? Or has it been lost? If it -does exist, what is it like, and where does it grow? From what we have -already learned we should expect to find the gametophyte begin with the -germination of the spores which are developed on the sporophyte, that -is on the fern plant itself. We should investigate this and see.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_262" id="Page_262">[Pg 262]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXVII" id="CHAPTER_XXVII">CHAPTER XXVII.</a><br /> -<span class="h_subtitle">FERNS CONTINUED.</span></h3> -</div> - -<h4><a name="XXVII_1" id="XXVII_1">Gametophyte of ferns.</a></h4> - -<p><b>549. Sexual stage of ferns.</b>—We now wish to see what the sexual -stage of the ferns is like. Judging from what we have found to take -place in the liverworts and mosses we should infer that the form of the -plant which bears the sexual organs is developed from the spores. This -is true, and if we should examine old decaying logs, or decaying wood -<span class="pagenum"><a name="Page_263" id="Page_263">[Pg 263]</a></span> -in damp places in the near vicinity of ferns, we should probably find -tiny, green, thin, heart-shaped growths, lying close to the substratum. -These are also found quite frequently on the soil of pots in plant -conservatories where ferns are grown. Gardeners also in conservatories -usually sow fern spores to raise new fern plants, and usually one can -find these heart-shaped growths on the surface of the soil where they -have sown the spores. We may call the gardener to our aid in finding -them in conservatories, or even in growing them for us if we cannot -find them outside. In some cases they may be grown in an ordinary room -by keeping the surfaces where they are growing moist, and the air also -moist, by placing a glass bell jar over them.</p> - -<div class="figcenter"> - <img id="FIG_297" src="images/fig297.jpg" alt="" width="600" height="419" /> - <div class="blockquot"> - <p class="center">Fig. 297.</p> - <p>Prothallium of fern, under side, showing rhizoids, antheridia - scattered among and near them, and the archegonia near the sinus.</p> - </div> -</div> - -<p><b>550.</b> In <a href="#FIG_297">fig. 297</a> is shown one of these growths -enlarged. Upon the under side we see numerous thread-like outgrowths, the rhizoids, -which attach the plant to the substratum, and which act as organs for -the absorption of nourishment. The sexual organs are borne on the under -side also, and we will study them later. This heart-shaped, flattened, -thin, green plant is the <i>prothallium</i> of ferns, and we should now give -it more careful study, beginning with the germination of the spores.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p> </p> - <img id="FIG_298" src="images/fig298.jpg" alt="" width="150" height="155" /> - <p class="center">Fig. 298.<br /> Spore of Pteris serrulata<br /> showing the three-rayed<br /> - elevation along the side<br /> of which the spore wall<br /> cracks during germination.</p> - </div> - <div class="figsub"> - <img id="FIG_299" src="images/fig299.jpg" alt="" width="150" height="214" /> - <p class="center">Fig. 299.<br /> Spore of Aspidium<br /> acrostichoides with<br /> winged exospore.</p> - </div> - <div class="figsub"> - <img id="FIG_300" src="images/fig300.jpg" alt="" width="300" height="206" /> - <p class="center">Fig. 300.<br /> Spore crushed to remove exospore<br /> and show endospore.</p> - </div> -</div> - -<p><b>551. Spores.</b>—We can easily obtain material for the study of the -spores of ferns. The spores vary in shape to some extent. Many of them -are shaped like a three-sided pyramid. One of these is shown in <a href="#FIG_298">fig. 298</a>. -The outer wall is roughened, and on one end are three elevated -<span class="pagenum"><a name="Page_264" id="Page_264">[Pg 264]</a></span> -ridges which radiate from a given point. A spore of the Christmas fern -is shown in <a href="#FIG_299">fig. 299</a>. The outer wall here is more or less -winged. At <a href="#FIG_300">fig. 300</a> is a spore of the same species from -which the outer wall has been crushed, showing that there is an inner wall also. -If possible we should study the germination of the spores of some fern.</p> - -<p><b>552. Germination of the spores.</b>—After the spores have been -sown for about one week to ten days we should mount a few in water for -examination with the microscope in order to study the early stages. If -germination has begun, we find that here and there are short slender -green threads, in many cases attached to brownish bits, the old walls -of the spores. Often one will sow the sporangia along with the spores, -and in such cases there may be found a number of spores still within -the old sporangium wall that are germinating, when they will appear as -in <a href="#FIG_302">fig. 302</a>.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_301" src="images/fig301.jpg" alt="" width="150" height="233" /> - <p class="center">Fig. 301.<br /> Spores of asplenium;<br /> exospore - removed from<br /> the one at the right.</p> - </div> - <div class="figsub"> - <img id="FIG_302" src="images/fig302.jpg" alt="" width="200" height="297" /> - <p class="center">Fig. 302.<br /> Germinating spores<br /> of Pteris aquilina<br /> - still in the sporangium.</p> - </div> -</div> -<div class="figcenter"> - <img id="FIG_303" src="images/fig303.jpg" alt="" width="600" height="297" /> - <p class="center">Fig. 303.<br /> - Young prothallium of a fern (niphobolus).</p> -</div> - -<p><b>553. Protonema.</b>—These short green threads are called -<i>protonemal</i> threads, or <i>protonema</i>, which means a <i>first thread</i>, -and it here signifies that this short thread only precedes a larger growth -of the same object. In figs. <a href="#FIG_302">302</a>, <a href="#FIG_303">303</a> are -shown several stages of germination of different spores. Soon after the short germ tube emerges -<span class="pagenum"><a name="Page_265" id="Page_265">[Pg 265]</a></span> -from the crack in the spore wall, it divides by the formation of a -cross wall, and as it increases in length other cross walls are formed. -But very early in its growth we see that a slender outgrowth takes -place from the cell nearest the old spore wall. This slender thread is -colorless, and is not divided into cells. It is the first rhizoid, and -serves both as an organ of attachment for the thread, and for taking up -nutriment.</p> - -<p><b>554. Prothallium.</b>—Very soon, if the sowing has not been so -crowded as to prevent the young plants from obtaining nutriment -sufficient, we will see that the end of this protonema is broadening, -as shown in <a href="#FIG_303">fig. 303</a>. This is done by the formation of the -cell walls in different directions. It now continues to grow in this way, the end -becoming broader and broader, and new rhizoids are formed from the -under surface of the cells. The growing point remains at the middle of -the advancing margin, and the cells which are cut off from either side, -as they become old, widen out. In this way the “wings,” or margins of -the little, green, flattened body, are in advance of the growing point, -and the object is more or less heart-shaped, as shown in <a href="#FIG_297">fig. 297</a>. -Thus we see how the prothallium of ferns is formed.</p> - -<p><b>555. Sexual organs of ferns.</b>—If we take one of the prothallia -of ferns which have grown from the sowings of fern spores, or one of -<span class="pagenum"><a name="Page_266" id="Page_266">[Pg 266]</a></span> -those which may be often found growing on the soil of pots in -conservatories, mount it in water on a slip, with the under side -uppermost, we can then examine it for the sexual organs, for these are -borne in most cases on the under side.</p> - -<div class="figcenter"> - <img src="images/fig304.jpg" alt="" width="600" height="151" /> - <div class="blockquot"> - <p class="center">Fig. 304.</p> - <p>Male prothallium of a fern (niphobolus), in form of an alga - or protonema. Spermatozoids escaping from antheridia.</p> - </div> -</div> -<hr class="r25" /> -<div class="figcenter"> - <img id="FIG_305" src="images/fig305.jpg" alt="" width="500" height="425" /> - <div class="blockquot"> - <p class="center">Fig. 305.</p> - <p>Male prothallium of fern (niphobolus), showing opened and unopened - antheridia; section of unopened antheridium; spermatozoids escaping; - spermatozoids which did not escape from the antheridium.</p> - </div> -</div> - -<p><b>556. Antheridia.</b>—If we search among the rhizoids we see small -<span class="pagenum"><a name="Page_267" id="Page_267">[Pg 267]</a></span> -rounded elevations as shown in <a href="#FIG_297">fig. 297</a> or <a href="#FIG_305">305</a> -scattered over this portion of the prothallium. These are the antheridia. If the prothallia -have not been watered for a day or so, we may have an opportunity of -seeing the spermatozoids coming out of the antheridium, for when the -prothallia are freshly placed in water the cells of the antheridium -absorb water. This presses on the contents of the antheridium -and bursts the cap cell if the antheridium is ripe, and all the -spermatozoids are shot out. We can see here that each one is shaped -like a screw, with the coils at first close. But as the spermatozoid -begins to move this coil opens somewhat and by the vibration of the -long cilia which are on the smaller end it whirls away. In such -preparations one may often see them spinning around for a long while, -and it is only when they gradually come to rest that one can make out -their form.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_306" src="images/fig306.jpg" alt="" width="200" height="165" /> - <p class="center">Fig. 306.<br /> Section of antheridia<br /> showing sperm cells,<br /> - and spermatozoids in<br /> the one at the right.</p> - </div> - <div class="figsub"> - <img id="FIG_307" src="images/fig307.jpg" alt="" width="200" height="259" /> - <p class="center">Fig. 307.<br /> Different views of<br /> spermatozoids; in<br /> - a quiet condition;<br /> in motion<br /> (Adiantum concinnum).</p> - </div> - <div class="figsub"> - <img id="FIG_308" src="images/fig308.jpg" alt="" width="200" height="282" /> - <p class="center">Fig. 308.<br /> Archegonium of fern.<br /> Large cell in the center<br /> - is the egg, next is the<br /> ventral canal cell, and<br /> - in the canal of the neck<br /> are two nuclei of the<br /> - canal cell.</p> - </div> -</div> -<div class="figcenter"> - <img src="images/fig309.jpg" alt="" width="600" height="285" /> - <div class="blockquot"> - <p class="center">Fig. 309.</p> - <p>Mature and open archegonium of fern (Adiantum cuneatum) with - spermatozoids making their way down through the slime to the egg.</p> - </div> -</div> -<div class="figleft"> - <img src="images/fig310.jpg" alt="" width="250" height="165" /> - <p class="center">Fig. 310.<br /> Fertilization in a fern<br /> (Marattia).<br /> - <i>sp</i>, spermatozoid fusing with<br /> the nucleus of the egg.<br /> - (After Campbell.)</p> -</div> - -<p><b>557. Archegonia.</b>—If we now examine closely on the thicker part -of the under surface of the prothallium, just back of the “sinus,” we -may see longer stout projections from the surface of the prothallium. -<span class="pagenum"><a name="Page_268" id="Page_268">[Pg 268]</a></span> -These are shown in <a href="#FIG_297">fig. 297</a>. They are the archegonia. One -of them in longisection is shown in <a href="#FIG_308">fig. 308</a>. It is flask-shaped, -and the broader portion is sunk in the tissue of the prothallium. The egg is in the -larger part. The spermatozoids when they are swimming around over the -under surface of the prothallium come near the neck, and here they are -caught in the viscid substance which has oozed out of the canal of the -archegonium. From here they slowly swim down the canal, and finally one -sinks into the egg, fuses with the nucleus of the latter, and the egg -is then fertilized. It is now ready to grow and develop into the fern -plant. This brings us back to the sporophyte, which begins with the -fertilized egg.</p> - -<h4><a name="XXVII_2" id="XXVII_2">Sporophyte.</a></h4> - -<p><b>558. Embryo.</b>—The egg first divides into two cells as shown in -<a href="#FIG_228">fig. 228</a>, then into four. Now from each one of these quadrants -of the embryo a definite part of the plant develops, from one the first leaf, -<span class="pagenum"><a name="Page_269" id="Page_269">[Pg 269]</a></span> -from one the stem, from one the root, and from the other the organ -which is called the foot, and which attaches the embryo to the -prothallium, and transports nourishment for the embryo until it can -become attached to the soil and lead an independent existence. During -this time the wall of the archegonium grows somewhat to accommodate the -increase in size of the embryo, as shown in figs. <a href="#FIG_312">312</a>, -<a href="#FIG_313">313</a>. But soon the wall of the archegonium is -ruptured and the embryo emerges, the root attaches itself to the soil, -and soon the prothallium dies.</p> - -<div class="figcenter"> - <img src="images/fig311.jpg" alt="" width="500" height="433" /> - <p class="center">Fig. 311.<br /> Two-celled embryo of Pteris serrulata.<br /> - Remnant of archegonium neck below.</p> -</div> - -<p>The embryo is first on the under side of the prothallium, and the first -leaf and the stem curves upward between the lobes of the heart-shaped -body, and then grows upright as shown in <a href="#FIG_314">fig. 314</a>. Usually -only one embryo is formed on a single prothallium, but in one case I found a -prothallium with two well-formed embryos, which are <a href="#FIG_315">figured in 315</a>.</p> - -<p><b>559. Comparison of ferns with liverworts and mosses.</b>—In the -ferns then we have reached a remarkable condition of things as compared -with that which we found in the mosses and liverworts. In the mosses -<span class="pagenum"><a name="Page_270" id="Page_270">[Pg 270]</a></span> -and liverworts the sexual phase of the plant (gametophyte) was the -prominent one, and consisted of either a thallus or a leafy axis, -but in either case it bore the sexual organs and led an independent -existence; that is it was capable of obtaining its nourishment from the -soil or water by means of organs of absorption belonging to itself, and -it also performed the office of photosynthesis.</p> - -<div class="figcenter"> - <img id="FIG_312" src="images/fig312.jpg" alt="" width="500" height="422" /> - <div class="blockquot"> - <p class="center">Fig. 312.</p> - <p>Young embryo of fern (Adiantum concinnum) in enlarged venter of the archegonium. - <i>S</i>, stem; <i>L</i>, first leaf or cotyledon; <i>R</i>, root; <i>F</i>, foot.</p> - </div> -</div> - -<p><b>560.</b> The spore-bearing phase (sporophyte) of the liverworts -and mosses, on the other hand, is quite small as compared with the -sexual stage, and it is completely dependent on the sexual stage for -its nourishment, remaining attached permanently throughout all its -development, by means of the organ called a foot, and it dies after the -spores are mature.</p> - -<p><b>561.</b> Now in the ferns we see several striking differences. In -the first place, as we have already observed, the spore-bearing phase -<span class="pagenum"><a name="Page_271" id="Page_271">[Pg 271]</a></span> -(sporophyte) of the plant is the prominent one, and that which -characterizes the plant. It also leads an independent existence, and, -with the exception of a few cases, does not die after the development -of the spores, but lives from year to year and develops successive -crops of spores. There is a <i>distinct advance</i> here in the <i>size</i>, -<i>complexity</i>, and <i>permanency</i> of this phase of the plant.</p> - -<p><b>562.</b> On the other hand the sexual phase of the ferns -(gametophyte), while it still is capable of leading an independent -existence, is short-lived (with very few exceptions). It is also much -smaller than most of the liverworts and mosses, especially as compared -with the size of the spore-bearing phase. The gametophyte phase or -stage of the plants, then, is decreasing in size and durance as the -sporophyte stage is increasing. We shall be interested to see if this -holds good of the fern allies, that is of the plants which belong to -the same group as the ferns. And as we come later to take up the study -of the higher plants we must bear in mind to carry on this comparison, -and see if this progression on the one hand of the sporophyte -continues, and if the retrogression of the gametophyte continues also.</p> - -<div class="figcenter"> - <img id="FIG_313" src="images/fig313.jpg" alt="" width="600" height="366" /> - <div class="blockquot"> - <p class="center">Fig. 313.</p> - <p>Embryo of fern (Adiantum concinnum) still surrounded by the - archegonium, which has grown in size, forming the“calyptra.” - <i>L</i>, leaf; <i>S</i>, stem; <i>R</i>, root; <i>F</i>, foot.</p> - </div> -</div> - -<p><span class="pagenum"><a name="Page_272" id="Page_272">[Pg 272]</a></span></p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_314" src="images/fig314.jpg" alt="" width="200" height="435" /> - <p class="center">Fig. 314.<br /> Young plant of Pteris serrulata<br /> still attached to prothallium.</p> - </div> - <div class="figsub"> - <img id="FIG_315" src="images/fig315.jpg" alt="" width="200" height="437" /> - <p class="center">Fig. 315.<br /> Two embryos from one prothallium<br /> of Adiantum cuneatum.</p> - </div> -</div> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_273" id="Page_273">[Pg 273]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXVIII" id="CHAPTER_XXVIII">CHAPTER XXVIII.</a><br /> -<span class="h_subtitle">DIMORPHISM OF FERNS.</span></h3> -</div> - -<p><b>563.</b> In comparing the different members of the leaf series there -are often striking illustrations of the transition from one form to -another, as we have noted in the case of the trillium flower. This -occurs in many other flowers, and in some, as in the water-lily, these -transformations are always present, here showing a transition from the -petals to the stamens. In the bud-scales of many plants, as in the -butternut, walnut, currant, etc., there are striking gradations between -the form of the simple bud-scales and the form of the leaf. Some of the -most interesting of these transformations are found in the dimorphic ferns.</p> - -<p><b>564. Dimorphism in the leaves of ferns.</b>—In the common polypody -fern, the maidenhair, and in many other ferns, all the leaves are of -the same form. That is, there is no difference between the fertile leaf -and the sterile leaf. On the other hand, in the case of the Christmas -fern we have seen that the fertile leaves are slightly different from -the sterile leaves, the former having shorter pinnæ on the upper half -of the leaf. The fertile pinnæ are here the shorter ones, and perform -but little of the function of carbon conversion. This function is -chiefly performed by the sterile leaves and by the sterile portions of -the fertile leaves. This is a short step toward the division of labor -between the two kinds of leaves, one performing chiefly the labor of -carbon conversion, the other chiefly the labor of bearing the fruit.</p> - -<div class="figcenter"> - <img id="FIG_316" src="images/fig316.jpg" alt="" width="300" height="480" /> - <p class="center">Fig. 316.<br /> Sensitive fern; normal condition of<br /> - vegetative leaves and sporophylls.</p> -</div> - -<p><b>565. The sensitive fern.</b>—This division of labor is carried to -<span class="pagenum"><a name="Page_274" id="Page_274">[Pg 274]</a></span> -an extreme extent in the case of some ferns. Some of our native ferns -are examples of this interesting relation between the leaves like -the common sensitive fern (Onoclea sensibilis) and the ostrich fern -(O. struthiopteris) and the cinnamon-fern (Osmunda cinnamomea). The -sensitive fern is here shown in <a href="#FIG_316">fig. 316</a>. The sterile leaves -are large, broadly expanded, and pinnate, the pinnæ being quite large. The fertile -leaves are shown also in the figure, and at first one would not take -them for leaves at all. But if we examine them carefully we see that -the general plan of the leaf is the same: the two rows of pinnæ which -are here much shorter than in the sterile leaf, and the pinnules, or -<span class="pagenum"><a name="Page_275" id="Page_275">[Pg 275]</a></span> -smaller divisions of the pinnæ, are inrolled into little spherical -masses which lie close on the side of the pinnæ. If we unroll one -of these pinnules we find that there are several fruit dots within -protected by this roll. In fact when the spores are mature these -pinnules open somewhat, so that the spores may be disseminated.</p> - -<div class="figcenter"> - <img src="images/fig317.jpg" alt="" width="300" height="488" /> - <p class="center">Fig. 317.<br /> Sensitive fern; one fertile leaf<br /> - nearly changed to vegetative leaf.</p> -</div> - -<p>There is very little green color in these fertile leaves, and what -green surface there is is very small compared with that of the broad -expanse of the sterile leaves. So here there is practically a complete -<span class="pagenum"><a name="Page_276" id="Page_276">[Pg 276]</a></span> -division of labor between these two kinds of leaves, the general plan -of which is the same, and we recognize each as being a leaf.</p> - -<div class="figcenter"> - <img src="images/fig318.jpg" alt="" width="300" height="434" /> - <p class="center">Fig. 318.<br /> Sensitive fern, showing one vegetative leaf<br /> - and two sporophylls completely transformed.</p> -</div> - -<p><b>566. Transformation of the fertile leaves of onoclea to sterile -ones.</b>—It is not a very rare thing to find plants of the sensitive -fern which show intermediate conditions of the sterile and the -fertile leaf. A number of years ago it was thought by some that this -represented a different species, but now it is known that these -intermediate forms are partly transformed fertile leaves. It is a -very easy matter in the case of the sensitive fern to produce these -transformations by experiment. If one in the spring, when the sterile -leaves attain a height of 12 to 16 <i>cm</i> (8-10 inches), cuts them away, -and again when they have a second time reached the same height, some -of the fruiting leaves which develop later will be transformed. A few -<span class="pagenum"><a name="Page_277" id="Page_277">[Pg 277]</a></span> -years ago I cut off the sterile leaves from quite a large patch of -the sensitive fern, once in May, and again in June. In July, when -the fertile leaves were appearing above the ground, many of them -were changed partly or completely into sterile leaves. In all some -thirty plants showed these transformations, so that every conceivable -gradation was obtained between the two kinds of leaves.</p> - -<div class="figcenter"> - <img id="FIG_319" src="images/fig319.jpg" alt="" width="300" height="445" /> - <p class="center">Fig. 319.<br /> Normal and transformed sporophyll<br /> of sensitive fern.</p> -</div> - -<p><b>567.</b> It is quite interesting to note the form of these changed -leaves carefully, to see how this change has affected the pinnæ and the -sporangia. We note that the tip of the leaf as well as the tips of all -<span class="pagenum"><a name="Page_278" id="Page_278">[Pg 278]</a></span> -the pinnæ are more expanded than the basal portions of the same. -This is due to the fact that the tip of the leaf develops later -than the basal portions. At the time the stimulus to the change in -the development of the fertile leaves reached them they were partly -formed, that is the basal parts of the fertile leaves were more or less -developed and fixed and could not change. Those portions of the leaf, -however, which were not yet completely formed, under this stimulus, or -through correlation of growth, are incited to vegetative growth, and -expand more or less completely into vegetative leaves.</p> - -<p><b>568. The sporangia decrease as the fertile leaf expands.</b>—If -we now examine the sporangia on the successive pinnæ of a partly -transformed leaf we find that in case the lower pinnæ are not changed -at all, the sporangia are normal. But as we pass to the pinnæ which -show increasing changes, that is those which are more and more -expanded, we see that the number of sporangia decrease, and many of -them are sterile, that is they bear no spores. Farther up there are -only rudiments of sporangia, until on the more expanded pinnæ sporangia -are no longer formed, but one may still see traces of the indusium. -On some of the changed leaves the only evidences that the leaf began -once to form a fertile leaf are the traces of these indusia. In some of -these cases the transformed leaf was even larger than the sterile leaf.</p> - -<p><b>569. The ostrich fern.</b>—Similar changes were also produced in -the case of the ostrich fern, and in <a href="#FIG_319">fig. 319</a> is shown at -the left a normal fertile leaf, then one partly changed, and at the right one -completely transformed.</p> - -<p><b>570. Dimorphism in tropical ferns.</b>—Very interesting forms -of dimorphism are seen in some of the tropical ferns. One of these -is often seen growing in plant conservatories, and is known as the -staghorn fern (Platycerium alcicorne). This in nature grows attached to -the trunks of quite large trees at considerable elevations on the tree, -sometimes surrounding the tree with a massive growth. One kind of leaf, -which may be either fertile or sterile, is narrow, and branched in a -peculiar manner, so that it resembles somewhat the branching of the -<span class="pagenum"><a name="Page_279" id="Page_279">[Pg 279]</a></span> -horn of a stag. Below these are other leaves which are different in -form and sterile. These leaves are broad and hug closely around the -roots and bases of the other leaves. Here they serve to catch and -retain moisture, and they also catch leaves and other vegetable matter -which falls from the trees. In this position the leaves decay and then -serve as food for the fern.</p> - -<div class="figcenter"> - <img src="images/fig320.jpg" alt="" width="300" height="447" /> - <p class="center">Fig. 320.<br /> Ostrich fern, showing one normal sporophyll, one<br /> - partly transformed, and one completely transformed.</p> -</div> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_280" id="Page_280">[Pg 280]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXIX" id="CHAPTER_XXIX">CHAPTER XXIX.</a><br /> -<span class="h_subtitle">HORSETAILS.</span></h3> -</div> - -<p><b>571.</b> Among the relatives of the ferns are the horsetails, so -called because of the supposed resemblance of the branched stems of -some of the species to a horse’s tail, as one might infer from the -plant shown in <a href="#FIG_325">fig. 325</a>. They do not bear the least -resemblance to the ferns which we have been studying. But then -relationship in plants does not depend on mere resemblance of outward -form, or of the prominent part of the plant.</p> - -<div class="figcenter"> - <img id="FIG_321" src="images/fig321.jpg" alt="" width="600" height="136" /> - <p class="center">Fig. 321.<br /> Portion of fertile plant of Equisetum arvense<br /> - showing whorls of leaves and the fruiting spike.</p> -</div> - -<p><b>572. The field equisetum. Fertile shoots.</b>—<a href="#FIG_321">Fig. 321</a> -represents the common horsetail (Equisetum arvense). It grows in moist sandy -or gravelly places, and the fruiting portion of the plant (for this -species is dimorphic), that is the portion which bears the spores, -appears above the ground early in the spring. It is one of the first -things to peep out of the recently frozen ground. This fertile shoot -of the plant does not form its growth this early in the spring. Its -development takes place under the ground in the autumn, so that with -the advent of spring it pushes up without delay. This shoot is from -10 to 20 <i>cm</i>. high, and at quite regular intervals there are slight -enlargements, the nodes of the stem. The cylindrical portions between -the nodes are the internodes. If we examine the region of the -internodes carefully we note that there are thin membranous scales, -more or less triangular in outline, and connected at their bases into a -<span class="pagenum"><a name="Page_281" id="Page_281">[Pg 281]</a></span> -ring around the stem. Curious as it may seem, these are the leaves of -the horsetail. The stem, if we examine it farther, will be seen to -possess numerous ridges which extend lengthwise and which alternate -with furrows. Farther, the ridges of one node alternate with those of -the internode both above and below. Likewise the leaves of one node -alternate with those of the nodes both above and below.</p> - -<div class="figleft"> - <img id="FIG_322" src="images/fig322.jpg" alt="" width="200" height="180" /> - <p class="center">Fig. 322.<br /> Peltate sporophyll of<br /> equisetum (side view)<br /> - showing sporangia<br /> on under side.</p> -</div> - -<p><b>573. Sporangia.</b>—The end of this fertile shoot we see possesses -a cylindrical to conic enlargement. This is the <i>fertile spike</i>, and we -note that its surface is marked off into regular areas if the spores -have not yet been disseminated. If we dissect off a few of these -portions of the fertile spike, and examine one of them with a low -magnifying power, it will appear like the <a href="#FIG_322">fig. 322</a>. We see -here that the angular area is a disk-shaped body, with a stalk attached to its -inner surface, and with several long sacs projecting from its inner -face parallel with the stalk and surrounding the same. These elongated -sacs are the <i>sporangia</i>, and the disk which bears them, together with -the stalk which attaches it to the stem axis, is the <i>sporophyll</i>, and -thus belongs to the leaf series. These sporophylls are borne in close -whorls on the axis.</p> - -<p><b>574. Spores.</b>—When the spores are ripe the tissue of the -sporangium becomes dry, and it cracks open and the spores fall out. -If we look at <a href="#FIG_323">fig. 323</a> we see that the spore is covered -with a very singular coil which lies close to the wall. When the spore dries this -uncoils and thus rolls the spore about. Merely breathing upon these -spores is sufficient to make them perform very curious evolutions by -the twisting of these four coils which are attached to one place of the -wall. They are formed by the splitting up of an outer wall of the spore.</p> - -<p><b>575. Sterile shoot of the common horsetail.</b>—When the spores are -ripe they are soon scattered, and then the fertile shoot dies down. -Soon afterward, or even while some of the fertile shoots are still in -<span class="pagenum"><a name="Page_282" id="Page_282">[Pg 282]</a></span> -good condition, sterile shoots of the plant begin to appear above the -ground. One of these is shown in <a href="#FIG_325">fig. 325</a>. This has a much -more slender stem and is provided with numerous branches. If we examine the stem of -this shoot, and of the branches, we see that the same kind of leaves -are present and that the markings on the stem are similar. Since the -leaves of the horsetail are membranous and not green, the stem is green -in color, and this performs the function of photosynthesis. These green -shoots live for a great part of the season, building up material which -is carried down into the underground stems, where it goes to supply the -forming fertile shoots in the fall. On digging up some of these plants -we see that the underground stems are often of great extent, and that -both fertile and sterile shoots are attached to one and the same.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_323" src="images/fig323.jpg" alt="" width="100" height="193" /> - <p class="center">Fig. 323.<br /> Spore of equisetum<br /> with elaters<br /> coiled up.</p> - </div> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_324" src="images/fig324.jpg" alt="" width="200" height="178" /> - <p class="center">Fig. 324.<br /> Spore of equisetum with<br /> elaters uncoiled.</p> - </div> - <div class="figsub"> - <img id="FIG_325" src="images/fig325.jpg" alt="" width="150" height="337" /> - <p class="center">Fig. 325.<br /> Sterile plant of horsetail<br /> (Equisetum arvensis).</p> - </div> -</div> - -<p><b>576. The scouring rush, or shave grass.</b>—Another common species -of horsetail in the Northern States grows on wet banks, or in sandy -soil which contains moisture along railroad embankments. It is the -scouring rush (E. hyemale), so called because it was once used for -polishing purposes. This plant like all the species of the horsetails -<span class="pagenum"><a name="Page_283" id="Page_283">[Pg 283]</a></span> -has underground stems. But unlike the common horsetail, there is but -one kind of aerial shoot, which is green in color and fertile. The -shoots range as high as one meter or more, and are quite stout. The new -shoots which come up for the year are unbranched, and bear the fertile -spike at the apex. When the spores are ripe the apex of the shoot dies, -and the next season small branches may form from a number of the nodes.</p> - -<p><b>577. Gametophyte of equisetum.</b>—The spores of equisetum have -chlorophyll when they are mature, and they are capable of germinating -as soon as mature. The spores are all of the same kind as regards size, -just as we found in the case of the ferns. But they develop prothallia -of different sizes, according to the amount of nutriment which they -obtain. Those which obtain but little nutriment are smaller and develop -only antheridia, while those which obtain more nutriment become larger, -more or less branched, and develop archegonia. This character of an -independent prothallium (gametophyte) with the characteristic sexual -organs, and the also independent sporophyte, with spores, shows the -relationship of the horsetails with the ferns. We thus see that these -characters of the reproductive organs, and the phases and fruiting of -the plant, are more essential in determining relationships of plants -than the mere outward appearances.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_284" id="Page_284">[Pg 284]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXX" id="CHAPTER_XXX">CHAPTER XXX.</a><br /> -<span class="h_subtitle">CLUB MOSSES.</span></h3> -</div> - -<div class="figright"> - <img id="FIG_326" src="images/fig326.jpg" alt="" width="200" height="269" /> - <p class="center">Fig. 326.<br /> Lycopodium clavatum,<br /> branch bearing two<br /> - fruiting spikes; at<br /> right sporophyll with<br /> open sporangium;<br /> - single spore near it.</p> -</div> - -<p><b>578.</b> What are called the “club mosses” make up another group -of interesting plants which rank as allies of the ferns. They are not -of course true mosses, but the general habit of some of the smaller -species, and especially the form and size of the leaves, suggest a -resemblance to the larger of the moss plants.</p> - -<p><b>579. The clavate lycopodium.</b>—Here is one of the club mosses -(<a href="#FIG_326">fig. 326</a>) which has a wide distribution and which is well -entitled to hold the name of club because of the form of the upright club-shaped -branches. As will be seen from the illustration, it has a prostrate -stem. This stem runs for considerable distances on the surface of the -ground, often partly buried in the leaves, and sometimes even buried -beneath the soil. The leaves are quite small, are flattened-awl-shaped, -and stand thickly over the stem, arranged in a spiral manner, which -is the usual arrangement of the leaves of the club mosses. Here and -there are upright branches which are forked several times. The end of -one or more of these branches becomes produced into a slender upright -stem which is nearly leafless, the leaves being reduced to mere scales. -The end of this leafless branch then terminates in one or several -cylindrical heads which form the club. -<span class="pagenum"><a name="Page_285" id="Page_285">[Pg 285]</a></span></p> - -<p><b>580. Fruiting spike of Lycopodium clavatum.</b>—This club is the -fruiting spike or head (sometimes termed a <i>strobilus</i>). Here the -leaves are larger again and broader, but still not so large as the -leaves on the creeping shoots, and they are paler. If we bend down some -of the leaves, or tear off a few, we see that in the axil of the leaf, -where it joins the stem, there is a somewhat rounded, kidney-shaped -body. This is the spore-case or sporangium, as we can see by an -examination of its contents. There is but a single spore-case for each -of the fertile leaves (sporophyll). When it is mature, it opens by a -crosswise slit as seen in <a href="#FIG_326">fig. 326</a>. When we consider the -number of spore-cases in one of these club-shaped fruit bodies we see that the -number of spores developed in a large plant is immense. In mass the -spores make a very fine, soft powder, which is used for some kinds of -pyrotechnic material, and for various toilet purposes.</p> - -<div class="figcenter"> - <img id="FIG_327" src="images/fig327.jpg" alt="" width="400" height="467" /> - <div class="blockquot"> - <p class="center">Fig. 327.</p> - <p>Lycopodium lucidulum, bulbils in axils of leaves near - the top, sporangia in axils of leaves below them. At right - is a bulbil enlarged.</p> - </div> -</div> - -<p><b>581. Lycopodium lucidulum.</b>—Another common species is <a href="#FIG_327">figured -at 327</a>. This is Lycopodium lucidulum. The habit of the plant is quite -different. It grows in damp ravines, woods, and moors. The older -parts of the stem are prostrate, while the branches are more or less -ascending. It branches in a forked manner. The leaves are larger than -in the former species, and they are all of the same size, there being -no appreciable difference between the sterile and fertile ones. The -characteristic club is not present here, but the spore-cases occupy -certain regions of the stem, as shown at 327. In a single season one -region of the stem may bear spore-cases, and then a sterile portion -of the same stem is developed, which later bears another series of -spore-cases higher up.</p> - -<p><b>582. Bulbils on Lycopodium lucidulum.</b>—There is one curious way -in which this club moss multiplies. One may see frequently among the -upper leaves small wedge-shaped or heart-shaped green bodies but little -<span class="pagenum"><a name="Page_286" id="Page_286">[Pg 286]</a></span> -larger than the ordinary leaves. These are little buds which contain -rudimentary shoot and root and several thick green leaves. When they -fall to the ground they grow into new lycopodium plants, just as the -bulbils of cystopteris do which were described in the <a href="#CHAPTER_XXVI">chapter on ferns</a>.</p> - -<p><b>583.</b> Note.—The prothallia of the species of lycopodium which -have been studied are singular objects. In L. cernuum a cylindrical -body sunk in the earth is formed, and from the upper surface there -are green lobes. In L. phlegmaria and some others slender branched, -colorless bodies are formed which according to Treub grow as a -saphrophyte in decayed bark of trees. Many of the prothallia examined -have a fungus growing in their tissue which is supposed to play some -part in the nutrition of the prothallium.</p> - -<p class="center"><b>The little club mosses (selaginella).</b></p> - -<p><b>584.</b> Closely related to the club mosses are the selaginellas. -These plants resemble closely the general habit of the club mosses, but -are generally smaller and the leaves more delicate. Some species are -grown in conservatories for ornament, the leaves of such usually having -a beautiful metallic lustre. The leaves of some are arranged as in -lycopodium, but many species have the leaves in four to six rows. <a href="#FIG_328">Fig. 328</a> -represents a part of a selaginella plant (S. apus). The fruiting -spike possesses similar leaves, but they are shorter, and their -arrangement gives to the spike a four-sided appearance.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_328" src="images/fig328.jpg" alt="" width="200" height="318" /> - <p class="center">Fig. 328.<br /> Selaginella with three<br /> fruiting spikes.<br /> - (Selaginella apus.)</p> - </div> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_329" src="images/fig329.jpg" alt="" width="150" height="297" /> - <p class="center">Fig. 329.<br /> Fruiting spike<br /> showing large<br /> and small sporangia.</p> - </div> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_330" src="images/fig330.jpg" alt="" width="100" height="274" /> - <p class="center">Fig. 330.<br /> Large<br /> sporangium.</p> - </div> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_331" src="images/fig331.jpg" alt="" width="100" height="272" /> - <p class="center">Fig. 331.<br /> Small<br /> sporangium.</p> - </div> -</div> - -<p><span class="pagenum"><a name="Page_287" id="Page_287">[Pg 287]</a></span> -<b>585. Sporangia.</b>—On examining the fruiting spike, we find as -in lycopodium that there is but a single sporangium in the axil of a -fertile leaf. But we see that they are of two different kinds, small -ones in the axils of the upper leaves, and large ones in the axils of -a few of the lower leaves of the spike. The <i>microspores</i> are borne -in the smaller spore-cases and the <i>macrospores</i> in the larger ones. -<a href="#FIG_329">Figures 329-331</a> give the details. There are many microspores -in a single small spore-case, but 3-4 macrospores in a large spore-case.</p> - -<p><b>586. Male prothallia.</b>—The prothallia of selaginella are much -reduced structures. The microspores when mature are already divided -into two cells. When they grow into the mature prothallium a few more -cells are formed, and some of the inner ones form the spermatozoids, -as seen in <a href="#FIG_332">fig. 332</a>. Here we see that the antheridium itself -is larger than the prothallia. Only antheridia are developed on the prothallia -formed from the microspores, and for this reason the prothallia are -called <i>male prothallia</i>. In fact a male prothallium of selaginella -is nearly all antheridium, so reduced has the gametophyte become here.</p> - -<div class="figcenter"> - <img id="FIG_332" src="images/fig332.jpg" alt="" width="600" height="231" /> - <div class="blockquot"> - <p class="center">Fig. 332.</p> - <p>Details of microspore and male prothallium of selaginella; 1st, - microspore; 2d, wall removed to show small prothallial cell below; 3d, - mature male prothallium still within the wall; 4th, small cell below is - the prothallial cell, the remainder is antheridium with wall and four - sperm cells within; 5th spermatozoid. After Beliaieff and Pfeffer.</p> - </div> -</div> - -<p><b>587. Female prothallia.</b>—The female prothallia are developed -from the macrospores. The macrospores when mature have a rough, thick, -hard wall. The female prothallium begins to develop inside of the -macrospore before it leaves the sporangium. The protoplasm is richer -<span class="pagenum"><a name="Page_288" id="Page_288">[Pg 288]</a></span> -near the wall of the spore and at the upper end. Here the nucleus -divides a great many times, and finally cell walls are formed, so -that a tissue of considerable extent is formed inside the wall of the -spore, which is very different from what takes place in the ferns we -have studied. As the prothallium matures the spore is cracked at the -point where the three angles meet, as shown in <a href="#FIG_334">fig. 334</a>. -The archegonia are developed in this exposed surface, and several -can be seen in the illustration.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_333" src="images/fig333.jpg" alt="" width="150" height="211" /> - <p class="center">Fig. 333.<br /> Section of mature macrospore<br /> - of selaginella, showing female<br /> prothallium and archegonia.<br /> - After Pfeffer.</p> - </div> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_334" src="images/fig334.jpg" alt="" width="150" height="276" /> - <p class="center">Fig. 334.<br /> Mature female prothallium of<br /> selaginella, just bursting<br /> - open the wall of macrospore,<br /> exposing archegonia.<br /> After Pfeffer.</p> - </div> - <div class="figsub"> - <p class="space-below2"> </p> - <img id="FIG_335" src="images/fig335.jpg" alt="" width="150" height="369" /> - <p class="center">Fig. 335.<br /> Seedling of selaginella still<br /> - attached to the macrospore.<br /> After Campbell.</p> - </div> -</div> - -<p><b>588. Embryo.</b>—After fertilization the egg divides in such a way -that a long cell called a suspensor is cut off from the upper side, -which elongates and pushes the developing embryo down into the center -of the spore, or what is now the female prothallium. Here it derives -nourishment from the tissues of the prothallium, and eventually the -root and stem emerge, while a process called the “foot” is still -attached to the prothallium. When the root takes hold on the soil the -embryo becomes free.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_289" id="Page_289">[Pg 289]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXXI" id="CHAPTER_XXXI">CHAPTER XXXI.</a><br /> -<span class="h_subtitle">QUILLWORTS (ISOETES).</span></h3> -</div> - -<div class="figleft"> - <img id="FIG_336" src="images/fig336.jpg" alt="" width="100" height="234" /> - <p class="center">Fig. 336.<br /> Isoetes,<br /> mature plant,<br /> sporophyte stage.</p> -</div> - -<p><b>589.</b> The quillworts, as they are popularly called, are very -curious plants. They grow in wet marshy places. They receive their -name from the supposed resemblance of the leaf to a quill. <a href="#FIG_336">Fig. 336</a> -represents one of these quillworts (Isoetes engelmannii). The leaves -are the prominent part of the plant, and they are about all that can -be seen except the roots, without removing the leaves. Each leaf, it -will be seen, is long and needle-like, except the basal part, which -is expanded, not very unlike, in outline, a scale of an onion. These -expanded basal portions of the leaves closely overlap each other, and -the very short stem is completely covered at all times. <a href="#FIG_338">Fig. 338</a> -is from a longitudinal section of a quillwort. It shows the form of the -leaves from this view (side view), and also the general outline of the -short stem, which is triangular. The stem is therefore a very short object. -<span class="pagenum"><a name="Page_290" id="Page_290">[Pg 290]</a></span></p> - -<p><b>590. Sporangia of isoetes.</b>—If we pull off some of the leaves of -the plant we see that they are somewhat spoon-shaped as in <a href="#FIG_337">fig. 337</a>. -In the inner surface of the expanded base we note a circular depression -which seems to be of a different texture from the other portions of the -leaf. This is a <i>sporangium</i>. Beside the spores on the inside of the -sporangium, there are strands of sterile tissue which extend across the -cavity. This is peculiar to isoetes of all the members of the class -of plants to which the ferns belong, but it will be remembered that -sterile strands of tissue are found in some of the liverworts in the -form of elaters.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_337" src="images/fig337.jpg" alt="" width="200" height="385" /> - <p class="center">Fig. 337.<br /> Base of leaf of isoetes, showing<br /> - sporangium with macrospores.<br /> (Isoetes engelmannii.)</p> - </div> - <div class="figsub"> - <img id="FIG_338" src="images/fig338.jpg" alt="" width="300" height="360" /> - <p class="center">Fig. 338.<br /> Section of plant of Isoetes engelmannii,<br /> - showing cup-shaped stem, and longitudinal<br /> sections of the sporangia - in the thickened<br /> bases of the leaves.</p> - </div> -</div> - -<p><b>591.</b> The spores of isoetes are of two kinds, small ones -(microspores) and large ones (macrospores), so that in this respect -it agrees with selaginella, though it is so very different in other -<span class="pagenum"><a name="Page_291" id="Page_291">[Pg 291]</a></span> -respects. When one kind of spore is borne in a sporangium usually all -in that sporangium are of the same kind, so that certain sporangia -bear microspores, and others bear macrospores. But it is not uncommon -to find both kinds in the same sporangium. When a sporangium bears -only microspores the number is much greater than when one bears only -macrospores.</p> - -<p><b>592.</b> If we examine some of the microspores of isoetes we see -that they are shaped like the quarters of an apple, that is they are of -the bilateral type as seen in some of the ferns (asplenium).</p> - -<p><b>593. Male prothallia.</b>—In isoetes, as in selaginella, the -microspores develop only male prothallia, and these are very -rudimentary, one division of the spore having taken place before the -spore is mature, just as in selaginella.</p> - -<p><b>594. Female prothallia.</b>—These are developed from the -macrospores. The latter are of the tetrahedral type. The development -of the female prothallium takes place in much the same way as in -selaginella, the entire prothallium being enclosed in the macrospore, -though the cell divisions take place after it has left the sporangium. -When the archegonia begin to develop the macrospore cracks at the three -angles and the surface bearing the archegonia projects slightly as in -selaginella. Absorbing organs in the form of rhizoids are very rarely -formed.</p> - -<p><b>595. Embryo.</b>—The embryo lies well immersed in the tissue of the -prothallium, though there is no suspensor developed as in selaginella.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_292" id="Page_292">[Pg 292]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXXII" id="CHAPTER_XXXII">CHAPTER XXXII.</a><br /> -<span class="h_subtitle">COMPARISON OF FERNS AND<br /> THEIR RELATIVES.</span></h3> -</div> - -<p><b>596. Comparison of selaginella and isoetes with the ferns.</b>—On -comparing selaginella and isoetes with the ferns, we see that the -sporophyte is, as in the ferns, the prominent part of the plant. It -possesses root, stem, and leaves. While these plants are not so large -in size as some of the ferns, still we see that there has been a great -advance in the sporophyte of selaginella and isoetes upon what exists -in the ferns. There is a division of labor between the sporophylls, -in which some of them bear microsporangia with microspores, and some -bear macrosporangia with only macrospores. In the ferns and horsetails -there is only one kind of sporophyll, sporangium, and spore in a -species. By this division of labor, or differentiation, between the -sporophylls, one kind of spore, the microspore, is compelled to form -a male prothallium, while the other kind of spore, the macrospore, is -compelled to form a female prothallium. This represents a progression -of the sporophyte of a very important nature.</p> - -<p><b>597.</b> On comparing the gametophyte of selaginella and isoetes -with that of the ferns, we see that there has been a still farther -retrogression in size from that which we found in the independent and -large gametophyte of the liverworts and mosses. In the ferns, while it -is reduced, it still forms rhizoids, and leads an independent life, -absorbing its own nutrient materials, and assimilating carbon. In -selaginella and isoetes the gametophyte does not escape from the spore, -nor does it form absorbing organs, nor develop assimilative tissue. -The reduced prothallium develops at the expense of food stored by the -sporophyte while the spore is developing. Thus, while the gametophyte -is separate from the sporophyte in selaginella and isoetes, it is -really dependent on it for support or nourishment.</p> - -<p><b>598.</b> The important general characters possessed by the ferns -and their so-called allies, as we have found, are as follows: The -spore-bearing part, which is the fern plant, leads an independent -existence from the prothallium, and forms root, stem, and leaves. The -spores are borne in sporangia on the leaves. The prothallium also leads -an independent existence, though in isoetes and selaginella it has -<span class="pagenum"><a name="Page_293" id="Page_293">[Pg 293]</a></span> -become almost entirely dependent on the sporophyte. The prothallium -bears also well-developed antheridia and archegonia. The root, stem, -and leaves of the sporophyte possess vascular tissue. All the ferns and -their allies agree in the possession of these characters. The mosses -and liverworts have well-developed antheridia and archegonia, and the -higher plants have vascular tissue. But no plant of either of these -groups possesses the combined characters which we find in the ferns and -their relatives. The latter are, therefore, the fern-like plants, or -<i>pteridophyta</i>. The living forms of the pteridophyta are classified as -follows into families or orders. (<a href="#Page_295">See page 295</a>.) -<span class="pagenum"><a name="Page_294" id="Page_294">[Pg 294]</a></span></p> - -<p><b>599.</b></p> -<p class="center"> TABLE SHOWING RELATION OF GAMETOPHYTE<br /> -AND SPOROPHYTE IN THE PTERIDOPHYTES.</p> - -<table class="smallfont" border="0" cellspacing="0" summary=" " cellpadding="0" rules="cols" > - <thead><tr> - <th class="tdc bb2" colspan="9"> </th> - </tr><tr> - <th class="tdc bb2" colspan="5">GAMETOPHYTE.<br />(Becoming smaller, mostly independent.<br /> In selaginella - and isoetes becoming<br /> dependent on the sporophyte.)</th> - <th class="tdc bb2" colspan="3">SPOROPHYTE<br />(Largest part of the plant. The fern plant. Independent of,<br /> - and more hardy than, the gametophyte. Usually perennial.)</th> - <th class="tdc bb2" rowspan="2"><span class="smcap">Beginning<br /> of<br /> Gametophyte.</span></th> - </tr><tr> - <th class="tdc bb2"> </th> - <th class="tdc bb2" colspan="2"><span class="smcap">Vegetative Part.</span></th> - <th class="tdc bb2" colspan="2"> <span class="smcap">Sexual Organs.</span> </th> - <th class="tdc bb2"><span class="smcap">Beginning<br /> of<br /> Sporophyte.</span></th> - <th class="tdc bb2"><span class="smcap">Vegetative Part.</span></th> - <th class="tdc bb2"><span class="smcap">Fruiting Part.</span></th> - </tr> - </thead> - <tbody><tr> - <td class="tdl bb" rowspan="2"><span class="smcap">Ferns.</span> <br />(Polypodiaceæ.)</td> - <td class="tdl_table bb" colspan="2" rowspan="2"><p>A green, thin, expanded, heart-shaped growth, with rhizoids.</p></td> - <td class="tdc" colspan="2">Usually both kinds on<br /> the same prothallium.</td> - <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops into fern plant.)</p></td> - <td class="tdl_table bb" rowspan="2"><p>Root, stem, leaf.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Sporangia on leaf. All of one kind. Sporangium contains ....</p></td> - <td class="tdl bb" rowspan="2"> Spores.</td> - </tr><tr> - <td class="tdl_table bb"><p>Antheridia with spermatozoids.</p></td> - <td class="tdl_table bb"><p>Archegonia, each with egg.</p></td> - </tr><tr> - <td class="tdl bb" rowspan="2"><span class="smcap">Equisetum.</span></td> - <td class="tdl_table bb" colspan="2" rowspan="2"><p>A green, thin, expanded, lobed growth, with rhizoids.</p></td> - <td class="tdc" colspan="2">Usually the two kinds<br /> on different prothallia.</td> - <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops into equisetum plant.)</p></td> - <td class="tdl_table bb" rowspan="2"><p>Root, stem, leaf.</p></td> - <td class="tdl_table bb" rowspan="2"><p>Sporangia on sporophylls. All of one kind. Sporangium contains ....</p></td> - <td class="tdl bb" rowspan="2"> Spores.</td> - </tr><tr> - <td class="tdl_table bb"><p>Antheridia, on small male prothallia, with spermatozoids.</p></td> - <td class="tdl_table bb"><p>Archegonia on larger female prothallia, each with an egg.</p></td> - </tr><tr> - <td class="tdl bb" rowspan="2"><span class="smcap">Isoetes.</span></td> - <td class="tdl_table" colspan="2"><p>Colorless, rounded mass of cells, inside of spore wall, - usually no rhizoids, or but few. Two kinds.</p></td> - <td class="tdc" colspan="2">On different prothallia.</td> - <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops into isoetes plant.)</p></td> - <td class="tdl_table bb" rowspan="2"><p>Root, stem, leaf. Stem very short. Leaves bear sporangia in - cavities at base; outer leaves usually bear macrosporangia, inner ones microsporangia.</p></td> - <td class="tdl_table"><p>Sporangia of two kinds. Small ones contain ....</p></td> - <td class="tdl"> Microspores.</td> - </tr><tr> - <td class="tdl_table bb"><p>Small ones, male. Developed into small prothallial cell, - and antherid cell while still in sporangium.</p></td> - <td class="tdl_table bb"><p>Large ones, female. Developed from nutriment stored - in macrospore from sporophyte.</p></td> - <td class="tdl_table bb"><p>One antheridium, much larger than the single prothallial - cell. Antheridium with spermatozoids.</p></td> - <td class="tdl_table bb"><p>Few archegonia, in apex of oval colorless, female - prothallium, each with egg.</p></td> - <td class="tdl_table bb"><p>Large ones contain ....</p></td> - <td class="tdl bb"> Macrospores.</td> - </tr><tr> - <td class="tdl bb" rowspan="2"><span class="smcap">Selaginella.</span></td> - <td class="tdl_table" colspan="2"><p>Colorless, rounded mass of cells inside of spore wall, - no rhizoids, or but few. Two kinds.</p></td> - <td class="tdc" colspan="2">On different prothallia.</td> - <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops into selaginella plant.)</p></td> - <td class="tdl_table bb" rowspan="2"><p>Root, stem, leaf. Spore-bearing leaves grouped on - the end of stem in a spike. Lower ones bear macrosporangia, upper - ones bear microsporangia.</p></td> - <td class="tdl_table"><p>Sporangia of two kinds. Small ones contain ....</p></td> - <td class="tdl"> Microspores.</td> - </tr><tr> - <td class="tdl_table bb"><p>Small ones, male. Developed into small prothallial cell, and - antherid cell while in sporangium.</p></td> - <td class="tdl_table bb"><p>Large ones, female. Developed while still in sporangium and - dependent on sporophyte.</p></td> - <td class="tdl_table bb"><p>One antheridium, much larger than the single prothallial cell. - Antheridium with spermatozoids.</p></td> - <td class="tdl_table bb"><p>Few archegonia, in apex of oval, colorless, female prothallium, - each with egg.</p></td> - <td class="tdl_table bb"><p>Large ones contain ....</p></td> - <td class="tdl bb"> Macrospores.</td> - </tr><tr> - <td class="tdc bt" colspan="9"> </td> - </tr> - </tbody> -</table> - -<p><span class="pagenum"><a name="Page_295" id="Page_295">[Pg 295]</a></span></p> -<h4><a name="XXXII_1" id="XXXII_1">Classification of the Pteridophytes.</a></h4> - -<p class="center">Of the living pteridophytes four classes may be recognized.</p> - -<p class="center">CLASS FILICINEÆ.<a name="FNanchor_34_34" id="FNanchor_34_34"></a><a href="#Footnote_34_34" class="fnanchor">[34]</a></p> - -<p>This class includes the ferns. Four orders may be recognized.</p> - -<p><b>600. Order Ophioglossales.</b> (One Family, Ophioglossaceæ).—This -order includes the grapeferns (Botrychium), so called because of the -large botryoid cluster of sporangia, resembling roughly a cluster -of grapes; and the adder-tongue (Ophioglossum), the sporangia being -embedded in a long tongue-like outgrowth from the green leaf. -Botrychium and Ophioglossum are widely distributed. The roots are -fleshy, nearly destitute of root hairs, and contain an endophytic -fungus, so that the roots are mycorhiza. The gametophyte is -subterranean, and devoid of chlorophyll. In Botrychium virginianum, -an endophytic fungus has been found in the prothallium. Another genus -(Helminthostachys) with one species is limited to the East Indies.</p> - -<p><b>601. Order Marattiales</b> (One Family, Marattiaceæ).—These are -tropical ferns, with only four or five living genera (Marattia, Danæa, -etc.). They resemble the typical ferns, but the sporangia are usually -united, several forming a compound sporangium, or <i>synangium</i>.</p> - -<p>The Ophioglossales and Marattiales are known as eusporangiate ferns, -while the following order includes the leptosporangiate ferns.</p> - -<p><b>602. Order Filicales.</b>—This order includes the typical ferns. -Eight families are recognized.</p> - -<p><i>Family Osmundaceæ.</i>—Three genera are known in this family. Osmunda -has a number of species, three of which are found in the Eastern United -States; the cinnamon-fern (O. cinnamomea), the royal fern (O. regalis), -and Clayton’s fern (O. claytoniana). No species of this family are -found on the Pacific coast.</p> - -<p><i>Family Gleicheniaceæ.</i>—These ferns are found chiefly in the tropics, -and in the mountain regions of the temperate zones of South America. There -are two genera, Gleichenia containing all but one of the known species.</p> - -<p><i>Family Matoniaceæ.</i>—One genus, Matonia, in the Malayan region.</p> - -<p><i>Family Schizæceæ.</i>—These are chiefly tropical, but two species are -found in eastern North America, Schizæa pusilla and Lygodium palmatum, -the latter a climbing fern.</p> - -<p><i>Family Hymenophyllaceæ.</i>—These are known as the filmy ferns because -of their thin, delicate leaves. They grow only in damp or wet regions, -mostly in the tropics, but a few species occur in the southern United States. -<span class="pagenum"><a name="Page_296" id="Page_296">[Pg 296]</a></span></p> - -<p><i>Family Cyatheaceæ.</i>—These are known as the tree ferns, because of the -large size which many of them attain. They occur chiefly in tropical -mountainous regions, many of them palm-like and imposing because of the -large trunks and leaves. Dicksonia, Cyathea, Cibotium, Alsophila, are -some of the most conspicuous genera.</p> - -<p><i>Family Parkeriaceæ.</i>—There is a single species in this family -(Ceratopteris thalictroides), abundant in the tropics and extending -into Florida. It is aquatic.</p> - -<p><i>Family Polypodiaceæ.</i>—This family includes the larger number of -living ferns and many genera and species are found in North America. -Examples, Polypodium, Pteridium (= Pteris), Adiantum, etc.</p> - -<p><b>603. Order Hydropterales (or Salviniales).</b>—The members of this -order are peculiar, aquatic ferns, some floating on the water (Azolla, -Salvinia), while others are anchored to the soil by roots (Marsilia, -Pilularia). They are known as water ferns. The sporangia are of two -kinds, one containing large spores (macrospores) and the other small -spores (microspores). They are therefore heterosporous ferns.</p> - -<p><i>Family Salviniaceæ.</i>—There are two genera, Salvinia and Azolla.</p> - -<p><i>Family Marsiliaceæ.</i>—Two genera, Marsilia and Pilularia. In this -family the sporangia are enclosed in a sporocarp, which forms a -pod-like structure.</p> - -<p class="center">CLASS EQUISETINEÆ.<a name="FNanchor_35_35" id="FNanchor_35_35"></a><a href="#Footnote_35_35" class="fnanchor">[35]</a></p> - -<p><b>604. Order Equisetales.</b>—The single order contains a single -family, Equisetaceæ, among the living forms, and but a single genus, -Equisetum. There are about twenty-four species, with fourteen in the -United States (see <a href="#CHAPTER_XXIX">Chapter XXIX</a>).</p> - -<p class="center">CLASS LYCOPODIINEÆ.<a name="FNanchor_36_36" id="FNanchor_36_36"></a><a href="#Footnote_36_36" class="fnanchor">[36]</a></p> - -<p><b>605. Order Lycopodiales.</b>—The first two families of this order -include the homosporous Lycopodiineæ, while the Selaginellaceæ are -heterosporous.</p> - -<p><i>Family Lycopodiaceæ.</i>—There are two genera. Lycopodium (club moss) -includes many species, most of them tropical, but a number in temperate -and subarctic regions. The gametophyte of many species is tuberous, -lacks chlorophyll, and in some there lives an endophytic fungus. -Phylloglossum with one species is found in Australia.</p> - -<p><i>Family Psilotaceæ.</i>—There are two genera. Psilotum chiefly in the -tropics has one species (P. triquetrum) in the region of Florida.</p> - -<p><i>Family Selaginellaceæ.</i>—These include the little club mosses, with -one genus, Selaginella (see <a href="#CHAPTER_XXX">Chapter XXX</a>).</p> - -<p class="center">CLASS ISOETINEÆ.</p> - -<p><b>606. Order Isoetales</b>, with one family Isoetaceæ and one genus -Isoetes (see <a href="#CHAPTER_XXXI">Chapter XXXI</a>). There are about fifty species, -with about sixteen in the United States.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_297" id="Page_297">[Pg 297]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXXIII" id="CHAPTER_XXXIII">CHAPTER XXXIII.</a><br /> -<span class="h_subtitle">GYMNOSPERMS.</span></h3> -</div> - -<p class="center">The white pine.</p> - -<p><b>607. General aspect of the white pine.</b>—The white pine (Pinus -strobus) is found in the Eastern United States. In favorable situations -in the forest it reaches a height of about 50 meters (about 160 feet), -and the trunk a diameter of over 1 meter. In well-formed trees the -trunk is straight and towering; the branches where the sunlight has -access and the trees are not crowded, or are young, reaching out in -graceful arms, form a pyramidal outline to the tree. In old and dense -forests the lower branches, because of lack of sunlight, have died -away, leaving tall, bare trunks for a considerable height.</p> - -<p><b>608. The long shoots of the pine.</b>—The branches are of two -kinds. Those which we readily recognize are the long branches, so -called because the growth in length each year is considerable. The -terminal bud of the long branches, as well as of the main stem, -continues each year the growth of the main branch or shoot; while the -lateral long branches arise each year from buds which are crowded close -together around the base of the terminal bud. The lateral long branches -of each year thus appear to be in a whorl. The distance between each -false whorl of branches, then, represents one year’s growth in length -of the main stem or long branch.</p> - -<p><b>609. The dwarf shoots of the pine.</b>—The dwarf branches are all -lateral on the long branches, or shoots. They are scattered over the -year’s growth, and each bears a cluster of five long, needle-shaped, -green leaves, which remain on the tree for several years. At the base -of the green leaves are a number of chaff-like scales, the previous bud -scales. While the dwarf branches thus bear green leaves, and scales, -the long branches bear only thin scale-like leaves which are not green. -<span class="pagenum"><a name="Page_298" id="Page_298">[Pg 298]</a></span></p> - -<p><b>610. Spore-bearing leaves of the pine.</b>—The two kinds of -spore-bearing leaves of the pine, and their close relatives, are so -different from anything which we have yet studied, and are so unlike -the green leaves of the pine, that we would scarcely recognize them as -belonging to this category. Indeed there is great uncertainty regarding -their origin.</p> - -<div class="figcenter"> - <img id="FIG_339" src="images/fig339.jpg" alt="" width="450" height="474" /> - <p class="center">Fig. 339.<br /> Spray of white pine showing cluster of male cones<br /> - just before the scattering of the pollen.</p> - -</div> - -<p><b>611. Male cones, or male flowers.</b>—The male cones are borne in -clusters as shown in <a href="#FIG_339">fig. 339</a>. Each compact, nearly cylindrical, -or conical mass is termed a cone, or flower, and each arises in place of a -<span class="pagenum"><a name="Page_299" id="Page_299">[Pg 299]</a></span> -long lateral branch. One of these cones is shown considerably enlarged -in <a href="#FIG_340">fig. 340</a>. The central axis of each cone is a lateral -branch, and belongs to the stem series. The stem axis of the cone can be seen -in <a href="#FIG_341">fig. 341</a>. It is completely covered by stout, thick, -scale-like outgrowths. These scales are obovate in outline, and at the inner -angle of the upper end there are several rough, short spines. They -are attached by their inner lower angle, which forms a short stalk -or petiole, and continues through the inner face of the scale as -a “midrib.” What corresponds to the lamina of the scale-like leaf -bulges out on each side below and makes the bulk of the scale. These -prominences on the under side are the sporangia (microsporangia). There -are thus two sporangia on a sporophyll (microsporophyll). When the -spores (microspores), which here are usually called pollen grains, are -mature, each sporangium, or anther locule, splits down the middle as -shown in <a href="#FIG_342">fig. 342</a>, and the spores are set free.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_340" src="images/fig340.jpg" alt="" width="150" height="282" /> - <p class="center">Fig. 340.<br /> Staminate cone of white pine, with<br /> - bud scales removed on one side.</p> - </div> - <div class="figsub"> - <img id="FIG_341" src="images/fig341.jpg" alt="" width="150" height="273" /> - <p class="center">Fig. 341.<br /> Section of staminate cone,<br /> showing sporangia.</p> - </div> - <div class="figsub"> - <img id="FIG_342" src="images/fig342.jpg" alt="" width="100" height="259" /> - <p class="center">Fig. 342.<br /> Two sporophylls<br /> - removed, showing<br /> opening of sporangia.</p> - </div> -</div> -<div class="figleft"> - <img id="FIG_343" src="images/fig343.jpg" alt="" width="150" height="89" /> - <p class="center">Fig. 343.<br /> Pollen grain of<br /> white pine.</p> -</div> - -<p><b>612. Microspores of the pine, or pollen grains.</b>—A mature pollen -grain of the pine is shown in <a href="#FIG_343">fig. 343</a>. It is a queer-looking -object, possessing on two sides an air sac, formed by the upheaval of the outer -<span class="pagenum"><a name="Page_300" id="Page_300">[Pg 300]</a></span> -coat of the spore at these two points. When the pollen is mature, the -moisture dries out of the scale (or stamen, as it is often called here) -while it ripens. When a limb, bearing a cluster of male cones, is -jarred by the hand, or by currents of air, the split suddenly opens, -and a cloud of pollen bursts out from the numerous anther locules. The -pollen is thus borne on the wind and some of it falls on the female flowers.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_344" src="images/fig344.jpg" alt="" width="250" height="421" /> - <p class="center">Fig. 344.<br /> White pine, branch with cluster of<br /> - mature cones shedding the seed. A few<br /> young cones four months old are shown<br /> - on branch at the left.<br /> Drawn from photograph.</p> - </div> - <div class="figsub"> - <img id="FIG_345" src="images/fig345.jpg" alt="" width="300" height="462" /> - <p class="center">Fig. 345.<br /> Mature cone of white pine at<br /> - time of scattering of the seed,<br /> nearly natural size.</p> - </div> -</div> - -<p><b>613. Form of the mature female cone.</b>—A cluster of the -white pine cones is shown in <a href="#FIG_344">fig. 344</a>. These are mature, -and the scales have spread as they do when mature and becoming dry, in order that the -<span class="pagenum"><a name="Page_301" id="Page_301">[Pg 301]</a></span> -seeds may be set at liberty. The general outline of the cone is -lanceolate, or long oval, and somewhat curved. It measures about -10-15<i>cm</i> long. If we remove one of the scales, just as they are -beginning to spread, or before the seeds have scattered, we shall find -the seeds attached to the upper surface at the lower end. There are -two seeds on each scale, one at each lower angle. They are ovate in -outline, and shaped somewhat like a biconvex lens. At this time the -seeds easily fall away, and may be freed by jarring the cone. As the -seed is detached from the scale a strip of tissue from the latter is -peeled off. This forms a “wing” for the seed. It is attached to one end -and is shaped something like a knife blade. On the back of the scale is -a small appendage known as the cover scale.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig346.jpg" alt="" width="100" height="202" /> - <p class="center">Fig. 346.<br /> Sterile scale.<br /> Seeds undeveloped.</p> - </div> - <div class="figsub"> - <img src="images/fig347.jpg" alt="" width="100" height="184" /> - <p class="center">Fig. 347.<br /> Scale with<br /> well-developed<br /> seeds.</p> - </div> - <div class="figsub"> - <img src="images/fig348.jpg" alt="" width="100" height="191" /> - <p class="center">Fig. 348.<br /> Seeds have split<br /> off from scale.</p> - </div> - <div class="figsub"> - <img src="images/fig349.jpg" alt="" width="100" height="201" /> - <p class="center">Fig. 349.<br /> Back of scale<br /> with small<br /> cover scale.</p> - </div> - <div class="figsub"> - <img src="images/fig350.jpg" alt="" width="100" height="213" /> - <p class="center">Fig. 350.<br /> Winged seed<br /> free from<br /> scale.</p> - </div> - <p class="center">Figs. 346-350.—White pine showing details - of mature scales and seed.</p> -</div> -<div class="figcenter"> - <img id="FIG_351" src="images/fig351.jpg" alt="" width="600" height="221" /> - <p class="center">Fig. 351.<br /> Female cones of the pine at time<br /> - of pollination, about natural size.</p> -</div> - -<p><b>614. Formation of the female pine cone.</b>—The female flowers -begin their development rather late in the spring of the year. They -are formed from terminal buds of the higher branches of the tree. In -this way the cone may terminate the main shoot of a branch, or of the -lateral shoots in a whorl. After growth has proceeded for some time in -the spring, the terminal portion begins to assume the appearance of a -<span class="pagenum"><a name="Page_302" id="Page_302">[Pg 302]</a></span> -young female cone or flower. These young female cones, at about the -time that the pollen is escaping from the anthers, are long ovate, -measuring about 6-10 <i>mm</i> long. They stand upright as shown in <a href="#FIG_351">fig. 351</a>.</p> - -<p><b>615. Form of a “scale” of the female flower.</b>—If we remove one -of the scales from the cone at this stage we can better study it in -detail. It is flattened, and oval in outline, with a stout “rib,” if -it may be so called, running through the middle line and terminating -in a point. The scale is in two parts as shown in <a href="#FIG_354">fig. 354</a>, -which is a view of the under side. The small “outgrowth” which appears as an -appendage is the cover scale, for while it is smaller in the pine than -the other portion, in some of the relatives of the pine it is larger -than its mate, and being on the outside, covers it. (The inner scale is -sometimes called the ovuliferous scale, because it bears the ovules.)</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_352" src="images/fig352.jpg" alt="" width="125" height="443" /> - <p class="center">Fig. 352.<br /> Section of female cone<br /> of white pine, showing<br /> - young ovules<br /> (macrosporangia)<br /> at base of the<br /> ovuliferous scales.</p> - </div> - <div class="figsub"> - <img id="FIG_353" src="images/fig353.jpg" alt="" width="150" height="449" /> - <p class="center">Fig. 353.<br /> Scale of white pine<br /> with the two ovules<br /> - at base of<br /> ovuliferous scale.</p> - </div> - <div class="figsub"> - <img id="FIG_354" src="images/fig354.jpg" alt="" width="150" height="472" /> - <p class="center">Fig. 354.<br /> Scale of white pine seen<br /> - from the outside, showing<br /> the cover scale.</p> - </div> -</div> - -<p><b>616. Ovules, or macrosporangia, of the pine.</b>—At each of the -lower angles of the scale is a curious oval body with two curved, -forceps-like processes at the lower and smaller end. These are the -macrosporangia, or, as they are called in the higher plants, the -ovules. These ovules, as we see, are in the positions of the seeds on -<span class="pagenum"><a name="Page_303" id="Page_303">[Pg 303]</a></span> -the mature cones. In fact the wall of the ovule forms the outer coat of -the seed, as we will later see.</p> - -<div class="figcenter"> - <img src="images/fig355.jpg" alt="" width="500" height="491" /> - <div class="blockquot"> - <p class="center">Fig. 355.</p> - <p>Branch of white pine showing young female cones at time of - pollination on the ends of the branches, and one-year-old cones - below, near the time of fertilization.</p> - </div> -</div> - -<p><b>617. Pollination.</b>—At the time when the pollen is mature the -female cones are still erect on the branches, and the scales, which -during the earlier stages of growth were closely pressed against one -another around the axis, are now spread apart. As the clouds of pollen -burst from the clusters of the male cones, some of it is wafted by -the wind to the female cones. It is here caught in the open scales, -and rolls down to their bases, where some of it falls between these -forceps-like processes at the lower end of the ovule. At this time the -ovule has exuded a drop of a sticky fluid in this depression between -the curved processes at its lower end. The pollen sticks to this, and -later, as this viscid substance dries up, it pulls the pollen close up -<span class="pagenum"><a name="Page_304" id="Page_304">[Pg 304]</a></span> -in the depression against the lower end of the ovule. This depression -is thus known as the <i>pollen chamber</i>.</p> - -<p><b>618.</b> Now the open scales on the young female cone close up -again so tightly that water from rains is excluded. What is also very -curious, the cones, which up to this time have been standing erect, so -that the open scale could catch the pollen, now turn so that they hang -downward. This more certainly excludes the rains, since the overlapping -of the scales forms a shingled surface. Quantities of resin are also -formed in the scales, which exudes and makes the cone practically -impervious to water.</p> - -<p><b>619.</b> The female cone now slowly grows during the summer and -autumn, increasing but little in size during this time. During the -winter it rests, that is, ceases to grow. With the coming of spring, -growth commences again and at an accelerated rate. The increase in size -is more rapid. The cone reaches maturity in September. We thus see that -nearly eighteen months elapse from the beginning of the female flower -to the maturity of the cone, and about fifteen months from the time -that pollination takes place.</p> - -<div class="figleft"> - <img id="FIG_356" src="images/fig356.jpg" alt="" width="200" height="243" /> - <p class="center">Fig. 356.<br /> Macrosporangium of pine (ovule).<br /> - <i>int</i>, integument; <i>n</i>, nucellus;<br /> - <i>m</i>, macrospore; <i>pc</i>, pollen chamber;<br /> - <i>pg</i>, pollen grain; <i>an</i>, axile row;<br /> - <i>spt</i>, spongy tissue.<br /> (After Ferguson.)</p> -</div> - -<p><b>620. Female prothallium of the pine.</b>—To study this we must -make careful longitudinal sections through the ovule (better made with -the aid of a microtome). Such a section is shown in <a href="#FIG_358">fig. 358</a>. -The outer layer of tissue, which at the upper end (point where the scale -is attached to the axis of the cone) stands free, is the ovular coat, -or <i>integument</i>. Within this integument, near the upper end, there is -a cone-shaped mass of tissue. This mass of tissue is the <i>nucellus</i>, -or the <i>macrosporangium</i> proper. In the lower part of the nucellus in -<a href="#FIG_356">fig. 356</a> can be seen a rounded mass of “spongy tissue” (<i>spt</i>), -which is a special nourishing tissue of the nucellus, or sporangium, around -the macrospore. Within this can be seen an axile row of three cells -(<i>an: m</i>). The lowest one, which is larger than the other two, is the -<i>macrospore</i>. Sometimes there are four of these cells in the axile row. -This axile row of three or four cells is formed by the two successive -<span class="pagenum"><a name="Page_305" id="Page_305">[Pg 305]</a></span> -divisions of a mother cell in the nucellus. So it would appear that -these three or four cells are all spores.</p> - -<p>Only one of them, however, the lower one, develops; the others are -disorganized and disappear. The nucleus of the macrospore now divides -several times to form several free nuclei in the now enlarging cavity, -much as the nucleus of the macrospore in Selaginella and Isoetes -divides within the spore. The development thus far takes place during -the first summer, and now with the approach of winter the very young -female prothallium goes into rest about the stage shown in <a href="#FIG_358">fig. 358</a>. -The conical portion of the nucellus which lies above is the nucellar cap.</p> - -<div class="figcenter"> - <img id="FIG_357" src="images/fig357.jpg" alt="" width="600" height="350" /> - <div class="blockquot"> - <p class="center">Fig. 357.</p> - <p>Pollen grains of pine. One of them germinating. <i>p</i>¹ and <i>p</i>², the two - disintegrated prothallial cells, = sterile part of male gametophyte; - <i>a.c.</i>, central cell of antheridium; <i>v.n.</i>, vegetative nucleus or tube - nucleus of the single-wall cell of antheridium; <i>s.g.</i>, starch grains. - (After Ferguson.)</p> - </div> -</div> -<div class="figcenter"> - <img id="FIG_358" src="images/fig358.jpg" alt="" width="300" height="486" /> - <div class="blockquot"> - <p class="center">Fig. 358.</p> - <p>Section of ovule of white pine. <i>int</i>, integument; <i>pc</i>, pollen - chamber; <i>pt</i>, pollen tube; <i>n</i>, nucleus; <i>m</i>, macrospore cavity.</p> - </div> -</div> - -<p><b>621. Male prothallia.</b>—By the time the pollen is mature the -male prothallium is already partly formed. In <a href="#FIG_343">fig. 343</a> we can -see two well-formed cells. Two other cells are formed earlier, but they become -so flattened that it is difficult to make them out when the pollen -grain is mature. These are shown in <a href="#FIG_357">fig. 357</a>, <i>p</i>¹ and <i>p</i>², -and they are the only sterile cells of the male prothallium in the pines. The -large cell is the antheridium wall, its nucleus <i>v.n.</i> in <a href="#FIG_357">fig. 357</a>. -The smaller cell, <i>a.c.</i>, is the central cell of the antheridium. During -the summer and autumn the male prothallium makes some farther growth, -but this is slow. The larger cell, called the vegetative cell or tube -<span class="pagenum"><a name="Page_306" id="Page_306">[Pg 306]</a></span> -cell, which is in reality the wall of the antheridium, elongates by -the formation of a tube, forming a sac, known as the pollen tube. It -is either simple or branched. It grows down into the tissue of the -nucellus, and at a stage represented in <a href="#FIG_358">fig. 358</a>, winter -overtakes it and it rests. At this time the central cell has divided into two cells, -and the vegetative nucleus is in the pollen tube.</p> - -<div class="figcenter"> - <img id="FIG_359" src="images/fig359.jpg" alt="" width="450" height="460" /> - <div class="blockquot"> - <p class="center">Fig. 359.</p> - <p>Section of nucellus and endosperm of white pine. The inner layer - of cells of the integument shown just outside of nucellus; <i>arch</i>, - archegonium; <i>en</i>, egg nucleus. In the nucellar cap are shown three - pollen tubes. <i>vn</i>, vegetative nucleus or tube nucleus; <i>stc</i>, stalk - cell; <i>spn</i>, sperm nuclei, the larger one in advance is the one which - unites with the egg nucleus. The archegonia are in the endosperm or - female gametophyte. (After Ferguson.)</p> - </div> -</div> - -<p><b>622. The endosperm.</b>—In the following spring growth of all these -parts continues. The nuclei in the macrospore divide to form more, and -eventually cell walls are formed between them making a distinct tissue, -<span class="pagenum"><a name="Page_307" id="Page_307">[Pg 307]</a></span> -known as the <i>endosperm</i>. This endosperm continues to grow until a -large part of the nucellus is consumed for food.</p> - -<div class="figcenter"> - <img src="images/fig360.jpg" alt="" width="600" height="274" /> - <div class="blockquot"> - <p class="center">Fig. 360.</p> - <p>Last division of the egg in the white pine cutting off the ventral canal - cell at the apex of the archegonium. <i>End</i>, endosperm; <i>Arch</i>, archegonium.</p> - </div> -</div> - -<p><b>623. Female prothallium and archegonia.</b>—The endosperm is the -female prothallium. This is very evident from the fact that several -archegonia are developed in it usually on the side toward the pollen -chamber. The archegonia are sexual organs, and since the sexual organs -are developed on the gametophyte, therefore, the endosperm is the -female gametophyte, or prothallium. In <a href="#FIG_359">fig. 359</a> are -represented two archegonia in the endosperm and the pollen tubes are growing -down through the nucellus. The archegonia are quite large, the wall is a -sheath or jacket of cells which encloses the very large egg which has a -large nucleus in the center.</p> - -<p><b>624. Pollen tube and sperm cells.</b>—While the endosperm (female -prothallium) and archegonia are developing the pollen tube continues -its growth down through the nucellar cap, as shown in <a href="#FIG_359">fig. 359</a>. -At the same time the two cells which were formed in the pollen grain -(antheridium) from the central cell move down into the tube. One of -these is the “generative” cell, or “body” cell, and the other is called -the stalk cell, though it is more properly a sterile half of the -central cell. The nucleus of the generative cell, about the time the -archegonium is mature, divides to form two nuclei, which are the sperm -nuclei, and the one in advance is the larger, though it is much smaller -than the egg nucleus.</p> - -<p><b>625. Fertilization.</b>—Very soon after the archegonia are mature -(early in June in the northern United States) the pollen tube grows -through into the archegonium and empties the two sperm nuclei, the -vegetative nucleus and the stalk cell, into the protoplasm of the large -egg. The larger of the two sperm nuclei at once comes in contact with -the very large egg nucleus and sinks down into a depression of the -same, as shown in <a href="#FIG_361">fig. 361</a>. These two nuclei, in the pines, -do not fuse into a resting nucleus, but at once organize the nuclear figure for the -first division of the embryo. Two nuclei are thus formed, and these -divide to form four nuclei which sink to the bottom of the archegonium -<span class="pagenum"><a name="Page_308" id="Page_308">[Pg 308]</a></span> -and there organize the embryo which pushes its way into the endosperm -from which it derives its food (<a href="#FIG_362">fig. 362</a>).</p> - -<div class="figcenter"> - <img id="FIG_361" src="images/fig361.jpg" alt="" width="600" height="455" /> - <div class="blockquot"> - <p class="center">Fig. 361.</p> - <p>Archegonium of white pine at stage of fertilization, <i>en</i>, egg nucleus; - <i>spn</i>, sperm nucleus in conjugation with it; <i>nb</i>, nutritive bodies in - cytoplasm of large egg; <i>cpt</i>, cavity of pollen tube; <i>vn</i>, vegetative - nucleus or tube nucleus; <i>stc</i>, stalk cell; <i>spn</i>, second sperm - nucleus: <i>pr</i>, portion of prothallium or endosperm; <i>sg</i>, starch grains - in pollen tube. The sheath of jacket cells of the archegonium is not - shown. (After Ferguson.)</p> - </div> -</div> - -<p><b>626. Homology of the parts of the female cone.</b>—Opinions are -divided as to the homology of the parts of the female cone of the pine. -Some consider the entire cone to be homologous with a flower of the -angiosperms. The entire scale according to this view is a carpel, or -sporophyll, which is divided into the cover scale and the ovuliferous -scale. This division of the sporophyll is considered similar to that -which we have in isoetes, where the sporophyll has a ligule above the -sporangium, or as in ophioglossum, where the leaf is divided into a -fertile and a sterile portion.</p> - -<p>Others believe that the ovuliferous scale is composed of two leaves -situated laterally and consolidated representing a shoot in the axis of -the bract. There is some support for this in the fact that in certain -abnormal cones which show proliferation a short axis appears in the -<span class="pagenum"><a name="Page_309" id="Page_309">[Pg 309]</a></span> -axil of the bract and bears lateral leaves, and in some cases all -gradations are present between these lateral leaves on the axis and -their consolidation into an ovuliferous scale. In the normal condition -of the ovuliferous scale the axis has disappeared and the shoot is -represented only by the consolidated leaves, which would represent then -the macrosporophylls (or carpels) each bearing one macrosporangium (ovule).</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_362" src="images/fig362.jpg" alt="" width="150" height="288" /> - <p class="center">Fig. 362.<br /> Pine seed,<br /> section of,<br /> - <i>sc</i>, seed coat;<br /> <i>n</i>, remains of nucellus;<br /> - <i>end</i>, endosperm<br /> (= female gametophyte);<br /> - <i>emb</i>, embryo =<br /> young sporophyte.<br /> - Seed coat and nucellus =<br /> remains of old sporophyte.</p> - </div> - <div class="figsub"> - <img id="FIG_363" src="images/fig363.jpg" alt="" width="150" height="430" /> - <p class="center">Fig. 363.<br /> Embryo of white pine<br /> - removed from seed,<br /> showing several cotyledons.</p> - </div> - <div class="figsub"> - <img id="FIG_364" src="images/fig364.jpg" alt="" width="150" height="412" /> - <p class="center">Fig. 364.<br /> Pine seedling<br /> just emerging<br /> from the ground.</p> - </div> -</div> - -<p>One of the most interesting and plausible views is that of Celakovsky. -He believes that the axial shoot is reduced to two ovules, that the -ovules have two integuments, but the outer integument of each has -become proliferated into scales which are consolidated. In this -proliferation of the outer integument it is thrown off from the ovule -so that it only remains attached to one side and the larger part of the -ovule is thus left with only one integument. This view is supported -by the fact that in gingko, for example (another gymnosperm), the -outer integument (the “collar”) sometimes proliferates into a leaf. -Celakovsky’s view is, therefore, not very different from the second one -mentioned above. -<span class="pagenum"><a name="Page_310" id="Page_310">[Pg 310]</a></span></p> - -<div class="figcenter"> - <img src="images/fig365.jpg" alt="" width="450" height="463" /> - <p class="center">Fig. 365.<br /> White pine seedling casting seed coats.</p> -</div> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_311" id="Page_311">[Pg 311]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXXIV" id="CHAPTER_XXXIV">CHAPTER XXXIV.</a><br /> -<span class="h_subtitle">FURTHER STUDIES ON<br /> GYMNOSPERMS.</span></h3> -</div> - -<h4>Cycas.</h4> - -<div class="figleft"> - <img src="images/fig366.jpg" alt="" width="100" height="147" /> - <p class="center">Fig. 366.<br /> Macrosporophyll of<br /> Cycas revoluta.</p> -</div> - -<p><b>627.</b> In such gymnosperms as cycas, illustrated in the -frontispiece, there is a close resemblance to the members of the fern -group, especially the ferns themselves. This is at once suggested by -the form of the leaves. The stem is short and thick. The leaves have a -stout midrib and numerous narrow pinnæ. In the center of this rosette -of leaves are numerous smaller leaves, closely overlapping like bud -scales. If we remove one of these at the time the fruit is forming we -see that in general it conforms to the plan of the large leaves. There -are a midrib and a number of narrow pinnæ near the free end, the entire -leaf being covered with woolly hairs. But at the lower end, in place of -the pinnæ, we see oval bodies. These are the macrosporangia (ovules) -of cycas, and correspond to the macrosporangia of selaginella, and the -leaf is the macrosporophyll.</p> - -<p><b>628. Female prothallium of cycas.</b>—In figs. <a href="#FIG_367">367</a>, <a href="#FIG_368">368</a>, -are shown mature ovules, or macrosporangia, of cycas. In 368, which is a -roentgen-ray photograph of 367, the oval prothallium can be seen. So in -<span class="pagenum"><a name="Page_312" id="Page_312">[Pg 312]</a></span> -cycas, as in selaginella, the female prothallium is developed entirely -inside of the macrosporangium, and derives the nutriment for its growth -from the cycas plant, which is the sporophyte. Archegonia are developed -in this internal mass of cells. This aids us in determining that it is -the prothallium. In cycas it is also called endosperm, just as in the pines.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_367" src="images/fig367.jpg" alt="" width="250" height="316" /> - <p class="center">Fig. 367.<br /> Macrosporangium of<br /> Cycas revoluta.</p> - </div> - <div class="figsub"> - <img id="FIG_368" src="images/fig368.jpg" alt="" width="252" height="316" /> - <p class="center">Fig. 368.<br /> Roentgen photograph of same,<br /> showing female prothallium.</p> - </div> -</div> -<div class="figcenter"> - <img id="FIG_369" src="images/fig369.jpg" alt="" width="450" height="436" /> - <div class="blockquot"> - <p class="center">Fig. 369.</p> - <p>A sporophyll (stamen) of cycas; sporangia in groups on the under side. - <i>b</i>, group of sporangia; <i>c</i>, open sporangia. (From Warming.)</p> - </div> -</div> - -<p><b>629.</b> If we cut open one of the mature ovules, we can see the -endosperm (prothallium) as a whitish mass of tissue. Immediately -surrounding it at maturity is a thin, papery tissue, the remains of the -nucellus (macrosporangium), and outside of this are the coats of the -ovule, an outer fleshy one and an inner stony one.</p> - -<p><b>630. Microspores, or pollen, of cycas.</b>—The cycas plant -illustrated in the frontispiece is a female plant. Male plants also -<span class="pagenum"><a name="Page_313" id="Page_313">[Pg 313]</a></span> -exist which have small leaves in the center that bear only -microsporangia. These leaves, while they resemble the ordinary leaves, -are smaller and correspond to the stamens. Upon the under side, as -shown in <a href="#FIG_369">fig. 369</a>, the microsporangia are borne in groups -of three or four, and these contain the microspores, or pollen grains. The -arrangement of these microsporangia on the under side of the cycas -leaves bears a strong resemblance to the arrangement of the sporangia -on the under side of the leaves of some ferns.</p> - -<p><b>631. The gingko tree</b> is another very interesting plant belonging -to this same group. It is a relic of a genus which flourished in the -remote past, and it is interesting also because of the resemblance of -the leaves to some of the ferns like adiantum, which suggests that -this form of the leaf in gingko has been inherited from some fern-like -ancestor.</p> - -<div class="figcenter"> - <img src="images/fig370.jpg" alt="" width="400" height="387" /> - <p class="center">Fig. 370. <br />Zamia integrifolia, showing thick stem,<br /> - fern-like leaves, and cone of male flowers.</p> -</div> -<div class="figcenter"> - <img id="FIG_371" src="images/fig371.jpg" alt="" width="400" height="486" /> - <p class="center">Fig. 371. <br />Two spermatozoids in end of pollen tube of<br /> - cycas. (After drawing by Hirase and Ikeno.)</p> - -</div> - -<p><b>632.</b> While the resemblance of the leaves of some of the -gymnosperms to those of the ferns suggests fern-like ancestors for the -members of this group, there is stronger evidence of such ancestry -in the fact that a prothallium can well be determined in the ovules. -The endosperm with its well-formed archegonia is to be considered a -prothallium.</p> - -<p><b>633. Spermatozoids in some gymnosperms.</b>—But within the past two -years it has been discovered in gingko, cycas, and zamia, all belonging -<span class="pagenum"><a name="Page_314" id="Page_314">[Pg 314]</a></span> -to this group, that the sperm cells are well-formed spermatozoids. In -zamia each one is shaped somewhat like the half of a biconvex lens, and -around the convex surface are several coils of cilia. After the pollen -tube has grown down through the nucellus, and has reached a depression -at the end of the prothallium (endosperm) where the archegonia are -formed, the spermatozoids are set free from the pollen tube, swim -around in a liquid in this depression, and later fuse with the egg. In -gingko and cycas these spermatozoids were first discovered by Ikeno and -Hirase in Japan, and later in zamia by Webber in this country. In figs. -<a href="#FIG_371">371</a>-<a href="#FIG_374">374</a> the details -of the male prothallia and of fertilization are shown.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig372.jpg" alt="" width="250" height="273" /> - <p class="center">Fig. 372.<br /> Fertilization in cycas, small spermatozoid<br /> - fusing with the larger female nucleus of the<br /> - egg. The egg protoplasm fills the archegonium.<br /> - (From drawings by Hirase and Ikeno.)</p> - </div> - <div class="figsub"> - <img src="images/fig373.jpg" alt="" width="250" height="273" /> - <p class="center">Fig. 373.<br /> Spermatozoid of gingko.<br /> - Some abnormal forms have a tail.<br /> (After Ikeno and Hirase.)</p> - </div> -</div> - -<p><b>634. The sporophyte in the gymnosperms.</b>—In the pollen grains -of the gymnosperms we easily recognize the characters belonging to the -spores in the ferns and their allies, as well as in the liverworts and -mosses. They belong to the same series of organs, are borne on the -same phase or generation of the plant, and are practically formed in -the same general way, the variations between the different groups not -being greater than those within a single group. These spores we have -recognized as being the product of the sporophyte. We are able then to -identify the sporophyte as that phase or generation of the plant formed -from the fertilized egg and bearing ultimately the spores. We see from -this that the sporophyte in the gymnosperms is the prominent part of -the plant, just as we found it to be in the ferns. The pine tree, then, -as well as the gingko, cycas, yew, hemlock-spruce, black spruce, the -giant redwood of California, etc., are sporophytes.</p> - -<p>While the sporangia (anther sacs) of the male flowers open and permit -the spores (pollen) to be scattered, the sporangia of the female -flowers of the gymnosperms rarely open. The macrospore is developed -within sporangium (nucellus) to form the female prothallium (endosperm).</p> - -<p><b>635. The gametophyte has become dependent on the sporophyte.</b>—In -this respect the gymnosperms differ widely from the pteridophytes, -though we see suggestions of this condition of things in Isoetes and -Selaginella, where the female prothallium is developed within the -macrospore, and even in Selaginella begins, and nearly completes, its -development while still in the sporangium. -<span class="pagenum"><a name="Page_315" id="Page_315">[Pg 315]</a></span></p> - -<p>In comparing the female prothallium of the gymnosperms with that -of the fern group we see a remarkable change has taken place. The -female prothallium of the gymnosperms is very much reduced in size. -Especially, it no longer leads an independent existence from the -sporophyte, as is the case with nearly all the fern group. It remains -enclosed within the macrosporangium (in cycas if not fertilized it -sometimes grows outside of the macrosporangium and becomes green), and -derives its nourishment through it from the sporophyte, to which the -latter remains organically connected. This condition of the female -prothallium of the gymnosperms necessitated a special adaptation of the -male prothallium in order that the sperm cells may reach and fertilize -the egg-cell.</p> - -<div class="figcenter"> - <img id="FIG_374" src="images/fig374.jpg" alt="" width="500" height="466" /> - <div class="blockquot"> - <p class="center">Fig. 374.</p> - <p>Gingko biloba. <i>A</i>, mature pollen grain; <i>B</i>, germinating pollen grain, - the branched tube entering among the cells of the nucellus; <i>Ex</i>, - exine (outer wall of spore); <i>P</i>₁, prothallial cell; <i>P</i>₂, antheridial - cell (divides later to form stalk cell and generative cell); <i>P</i>₃, - vegetative cell; <i>Va</i>, vacuoles; <i>Nc</i>, nucellus. (After drawings by - Hirase and Ikeno.)</p> - </div> -</div> -<div class="figcenter"> - <img src="images/fig375.jpg" alt="" width="600" height="158" /> - <div class="blockquot"> - <p class="center">Fig. 375.</p> - <p>Gingko biloba, diagrammatic representation of the relation of pollen - tube to the archegonium in the end of the nucellus. <i>pt</i>, pollen tube; - <i>o</i>, archegonium. (After drawing by Hirase and Ikeno.)</p> - </div> -</div> - -<p><b>636. Gymnosperms are naked seed plants.</b>—The pine, as we have -seen, has naked seeds. That is, the seeds are not enclosed within the -<span class="pagenum"><a name="Page_316" id="Page_316">[Pg 316]</a></span> -carpel, but are exposed on the outer surface. All the plants of the -great group to which the pine belongs have naked seeds. For this reason -the name “<i>gymnosperms</i>” has been given to this great group.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig376.jpg" alt="" width="250" height="251" /> - <p class="center">Fig. 376.<br /> Spermatozoids of zamia<br /> in pollen tube;<br /> - <i>pg</i>, pollen grain;<br /> <i>a</i>, <i>a</i>, spermatozoids.<br /> - (After Webber.)</p> - </div> - <div class="figsub"> - <img src="images/fig377.jpg" alt="" width="250" height="269" /> - <p class="center">Fig. 377.<br /> Spermatozoid of zamia<br /> showing - spiral row of<br /> cilia. (After Webber.)</p> - </div> -</div> - -<p><b>637. Classification of gymnosperms.</b>—The gingko tree has until -recently been placed with the pines, yew, etc., in the order <i>Pinales</i>, -but the discovery of the spermatozoids in the pollen tube suggests -that it is not closely allied with the Pinales, and that it represents -an order coordinate with them. Engler arranges the living gymnosperms -somewhat as follows:</p> - -<h4>Class Gymnospermæ.</h4> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl">Order 1.</td> - <td class="tdl_ws1">Cycadales;</td> - <td class="tdl_ws1">family Cycadaceæ.</td> - <td class="tdl_ws1">Cycas, Zamia, etc.</td> - </tr><tr> - <td class="tdl">Order 2.</td> - <td class="tdl_ws1">Gingkoales;</td> - <td class="tdl_ws1">family Gingkoaceæ.</td> - <td class="tdl_ws1">Gingko.</td> - </tr><tr> - <td class="tdc" colspan="4"> </td> - </tr><tr> - <td class="tdl_top">Order 3.</td> - <td class="tdl_ws1">Pinales (or Coniferæ);</td> - <td class="tdl_ws1">family 1. Taxaceæ.</td> - <td class="tdl_table"><p class="no-indent">Taxus, the common yew in the eastern United States, - and Torreya, in the western United States, are examples.</p></td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdl_ws1"> </td> - <td class="tdl_ws1">family 2. Pinaceæ.</td> - <td class="tdl_table"><p class="no-indent">Sequoia (redwood of California), firs, spruces, - pines, cedars, cypress, etc.</p></td> - </tr><tr> - <td class="tdl_top">Order 4.</td> - <td class="tdl_ws1">Gnetales.</td> - <td class="tdl_table" colspan="2"><p class="no-indent">Welwitschia mirabilis, deserts of southwest - Africa; Ephedra, deserts of the Mediterranean and of West Asia. Gnetum, climbers (Lianas), - from tropical Asia and America.</p></td> - </tr> - </tbody> -</table> - -<p><span class="pagenum"><a name="Page_317" id="Page_317">[Pg 317]</a></span></p> - -<p><b>638.</b></p> -<p class="center"> TABLE SHOWING HOMOLOGIES OF SPOROPHYTE<br /> AND GAMETOPHYTE IN THE PINE.</p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <thead><tr> - <th class="tdc"> </th> - <th class="tdc bb"><span class="smcap">Terms Corresponding to those<br /> used in Pteridophytes.</span></th> - <th class="tdc bb"> </th> - <th class="tdc bb"><span class="smcap">Common Terms.</span></th> - </tr> - </thead> - <tbody><tr> - <td class="tdl br"> </td> - <td class="tdl_ws1">Sporophyte</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Pine tree.</td> - </tr><tr> - <td class="tdl br"> </td> - <td class="tdl_ws1">Spore-bearing part</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Male and female cones.</td> - </tr><tr> - <td class="tdl br bb bt" rowspan="2">Sporophyte</td> - <td class="tdl_ws1 bt">Microsporophyll</td> - <td class="tdc_ws1 bt">=</td> - <td class="tdl bt" colspan="2">Stamen.</td> - </tr><tr> - <td class="tdl_ws1 bb">Microsporangium</td> - <td class="tdc_ws1 bb">=</td> - <td class="tdl bb" colspan="2">Pollen sac.</td> - </tr><tr> - <td class="tdl bb br" rowspan="9">Male<br /> gametophyte</td> - <td class="tdl_ws1">Microspore</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Pollen grain.</td> - </tr><tr> - <td class="tdl_ws1"> Mature microspore is rudimentary male prothallium</td> - <td class="tdc_ws1" rowspan="2">=</td> - <td class="tdl" rowspan="2" colspan="2">Mature pollen grain.</td> - </tr><tr> - <td class="tdl_ws1">  with rudimentary antheridium</td> - </tr><tr> - <td class="tdl_ws1">Large cell (part of antheridium wall?)</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Vegetative cell of pollen grain.</td> - </tr><tr> - <td class="tdl_ws1">Antheridium cell</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Small cell of pollen</td> - </tr><tr> - <td class="tdl_ws1">Antheridium cell divides to form stalk cell and</td> - <td class="tdc_ws1" rowspan="2">=</td> - <td class="tdl" rowspan="2" colspan="2">Generative cell.</td> - </tr><tr> - <td class="tdl_ws1">  central cell of antheridium (male sexual organ)</td> - </tr><tr> - <td class="tdl_ws1">Central cell of antheridium divides to form</td> - <td class="tdc_ws1 bb" rowspan="2">=</td> - <td class="tdl" colspan="2">Paternal cells, or</td> - </tr><tr> - <td class="tdl_ws1 bb">  two sperm cells</td> - <td class="tdl bb" colspan="2">  generative cells.</td> - </tr><tr> - <td class="tdl br bb" rowspan="7">Sporophyte</td> - <td class="tdl_ws1">Macrosporophyll</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Ovuliferous scale (cover scale</td> - </tr><tr> - <td class="tdl_ws1"> </td> - <td class="tdc_ws1" rowspan="4"> </td> - <td class="tdl" colspan="2">and carpellary outgrowth); or</td> - </tr><tr> - <td class="tdl_ws1"> </td> - <td class="tdl" colspan="2">three carpels united into</td> - </tr><tr> - <td class="tdl_ws1"> </td> - <td class="tdl" colspan="2">ovuliferous scale, the central one</td> - </tr><tr> - <td class="tdl_ws1"> </td> - <td class="tdl" colspan="2"> sterile (in axil of cover scale).</td> - </tr><tr> - <td class="tdl_ws1">Macrosporangium covered by integument</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Nucellus covered by</td> - </tr><tr> - <td class="tdl_ws1 bb">  by integument</td> - <td class="tdc_ws1 bb"> </td> - <td class="tdl bb" colspan="2"> integument = ovule.</td> - </tr><tr> - <td class="tdl bb br" rowspan="6">Female<br /> gametophyte </td> - <td class="tdl_ws1">Macrospore (remains in sporangium)</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Large cell in center of nucellus</td> - </tr><tr> - <td class="tdl_ws1"> </td> - <td class="tdc_ws1"> </td> - <td class="tdl" colspan="2">which develops embryo sac and</td> - </tr><tr> - <td class="tdl_ws1"> </td> - <td class="tdc_ws1"> </td> - <td class="tdl" colspan="2">endosperm (remains in nucellus).</td> - </tr><tr> - <td class="tdl_ws1">Female prothallium (in sporangium)</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Endosperm, in nucellus.</td> - </tr><tr> - <td class="tdl_ws1">Archegonia (female sexual organs)</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Corpuscula, in endosperm.</td> - </tr><tr> - <td class="tdl_ws1 bb">Egg</td> - <td class="tdc_ws1 bb">=</td> - <td class="tdl bb" colspan="2">Maternal cell, or germ cell.</td> - </tr><tr> - <td class="tdl bb br" rowspan="7">Young<br /> sporophyte</td> - <td class="tdl_ws1">Egg (fertilized)</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Germ cell.</td> - </tr><tr> - <td class="tdl_ws1">Young sporophyte</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Pine embryo in nucellus</td> - </tr><tr> - <td class="tdl_ws1"> </td> - <td class="tdc_ws1"> </td> - <td class="tdl" colspan="2">  and integument.</td> - </tr><tr> - <td class="tdl_ws1">Young sporophyte</td> - <td class="tdc_ws1">=</td> - <td class="tdl br bt">Embryo</td> - <td class="tdl bb" rowspan="4"> Seed.</td> - </tr><tr> - <td class="tdl_ws1">In remains of gametophyte</td> - <td class="tdc_ws1">=</td> - <td class="tdl br">Endosperm</td> - </tr><tr> - <td class="tdl_ws1">And sporangium</td> - <td class="tdc_ws1">=</td> - <td class="tdl br">Nucellus</td> - </tr><tr> - <td class="tdl_ws1 bb">Surrounded by new growth of old sporophyte</td> - <td class="tdc_ws1 bb">=</td> - <td class="tdl bb br">Integument</td> - </tr><tr> - <td class="tdc" colspan="4"> </td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_318" id="Page_318">[Pg 318]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXXV" id="CHAPTER_XXXV">CHAPTER XXXV.</a><br /> -<span class="h_subtitle">MORPHOLOGY OF THE ANGIOSPERMS:<br /> TRILLIUM; DENTARIA.</span></h3> -</div> - -<h4>Trillium.</h4> - -<p><b>639. General appearance.</b>—As one of the plants to illustrate -this group we may take the wake-robin, as it is sometimes called, -or trillium. There are several species of this genus in the United -States; the commonest one in the eastern part is the “white wake-robin” -(Trillium grandiflorum). This occurs in or near the woods. A picture of -the plant is shown in <a href="#FIG_378">fig. 378</a>. There is a thick, fleshy, -underground stem, or rhizome as it is usually called. This rhizome is perennial, -and is marked by ridges and scars. The roots are quite stout and -possess coarse wrinkles. From the growing end of the rhizome each year -the leafy, flowering stem arises. This is 20-30<i>cm</i> (8-12 inches) in -height. Near the upper end is a whorl of three ovate leaves, and from -the center of this rosette rises the flower stalk, bearing the flower -at its summit.</p> - -<p><b>640. Parts of the flower. Calyx.</b>—Now if we examine the flower -we see that there are several leaf-like structures. These are arranged -also in threes just as are the leaves. First there is a whorl of three, -pointed, lanceolate, green, leaf-like members, which make up the -<i>calyx</i> in the higher plants, and the parts of the calyx are <i>sepals</i>, -that is, each leaf-like member is a <i>sepal</i>. But while the sepals are -part of the flower, so called, we easily recognize them as belonging to -the <i>leaf series</i>. -<span class="pagenum"><a name="Page_319" id="Page_319">[Pg 319]</a></span></p> - -<p><b>641. Corolla.</b>—Next above the calyx is a whorl of white or -pinkish members, in Trillium grandiflorum, which are also leaf-like in -form, and broader than the sepals, being usually somewhat broader at -the free end. These make up what is the <i>corolla</i> in the higher plants, -and each member of the corolla is a <i>petal</i>. But while they are parts -of the flower, and are not green, their form and position would suggest -that they also belong to the leaf series.</p> - -<div class="figcenter"> - <img id="FIG_378" src="images/fig378.jpg" alt="" width="250" height="462" /> - <p class="center">Fig. 378. <br /> Trillium grandiflorum.</p> -</div> - -<p><b>642. Andrœcium.</b>—Within and above the insertion of the corolla -is found another tier, or whorl, of members which do not at first -sight resemble leaves in form. They are known in the higher plants -as <i>stamens</i>. As seen in <a href="#FIG_379">fig. 379</a> each stamen -possesses a stalk (= filament), and extending along on either side for the greater -part of the length are four ridges, two on each side. This part of the stamen -is the <i>anther</i>, and the ridges form the anther sacs, or lobes. Soon -after the flower is opened, these anther sacs open also by a split in -the wall along the edge of the ridge. At this time we see quantities of -yellowish powder or dust escaping from the ruptured anther locules. If -<span class="pagenum"><a name="Page_320" id="Page_320">[Pg 320]</a></span> -we place some of this under the microscope we see that it is made up of -minute bodies which resemble spores; they are rounded in form, and the -outer wall is spiny. They are in fact spores, the microspores of the -trillium, and here, as in the gymnosperms, are better known as <i>pollen</i>.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_379" src="images/fig379.jpg" alt="" width="300" height="240" /> - <p class="center">Fig. 379.<br /> Sepal, petal, stamen, and pistil<br /> - of Trillium grandiflorum.</p> - </div> - <div class="figsub"> - <img id="FIG_380" src="images/fig380.jpg" alt="" width="150" height="273" /> - <p class="center">Fig. 380.<br /> Trillium grandiflorum,<br /> with the compound pistil<br /> - expanded into three leaf-like<br /> members. At the right these<br /> - three are shown in detail.</p> - </div> -</div> - -<p><b>643. The stamen a sporophyll.</b>—Since these pollen grains are -the spores, we would infer, from what we have learned of the ferns -and gymnosperms, that this member of the flower which bears them is -a sporophyll; and this is the case. It is in fact what is called the -<i>microsporophyll</i>. Then we see also that the anther sacs, since they -enclose the spores, would be the sporangia (microsporangia). From this -it is now quite clear that the stamens belong also to the leaf series. -They are just six in number, twice the number found in a whorl of -leaves, or sepals, or corolla. It is believed, therefore, that there -are two whorls of stamens in the flower of trillium.</p> - -<p><b>644. Gynœcium.</b>—Next above the stamens and at the center of the -flower is a stout, angular, ovate body which terminates in three long, -<span class="pagenum"><a name="Page_321" id="Page_321">[Pg 321]</a></span> -slender, curved points. This is the pistil, and at present the only -suggestion which it gives of belonging to the leaf series is the fact -that the end is divided into three parts, the number of parts in each -successive whorl of members of the flower. If we cut across the body of -this pistil and examine it with a low power we see that there are three -chambers or cavities, and at the junction of each the walls suggest to -us that this body may have been formed by the infolding of the margins -of three leaf-like members, the places of contact having then become -grown together. We see also that from the incurved margins of each -division of the pistil there stand out in the cavity oval bodies. These -are the <i>ovules</i>. Now the ovules we have learned from our study of the -gymnosperms are the <i>sporangia</i> (here the macrosporangia). It is now -more evident that this curious body, the pistil, is made up of three -leaf-like members which have fused together, each member being the -equivalent of a sporophyll (here the macrosporophyll). This must be a -fascinating observation, that plants of such widely different groups -and of such different grades of complexity should have members formed -on the same plan and belonging to the same series of members, devoted -to similar functions, and yet carried out with such great modifications -that at first we do not see this common meeting ground which a -comparative study brings out so clearly.</p> - -<div class="figcenter"> - <img id="FIG_381" src="images/fig381.jpg" alt="" width="500" height="343" /> - <div class="blockquot"> - <p class="center">Fig. 381.</p> - <p>Abnormal trillium. The nine parts of the perianth are green, and the - outer whorls of stamens are expanded into petal-like members.</p> - </div> -</div> -<div class="figleft"> - <img src="images/fig382.jpg" alt="" width="200" height="196" /> - <p class="center">Fig. 382.<br /> Transformed stamen of<br /> - trillium showing anther<br /> locules on the margin.</p> -</div> - -<p><b>645. Transformations of the flower of trillium.</b>—If anything -more were needed to make it clear that the parts of the flower of -trillium belong to the leaf series we could obtain evidence from the -<span class="pagenum"><a name="Page_322" id="Page_322">[Pg 322]</a></span> -transformations which the flower of trillium sometimes presents. In -<a href="#FIG_381">fig. 381</a> is a sketch of a flower of trillium, made from -a photograph. One set of the stamens has expanded into petal-like organs, with the -anther sacs on the margin. In <a href="#FIG_380">fig. 380</a> is shown a plant of -Trillium grandiflorum in which the pistil has separated into three distinct and -expanded leaf-like structures, all green except portions of the margin.</p> - -<h4>Dentaria.</h4> - -<p><b>646. General appearance.</b>—For another study we may take a plant -which belongs to another division of the higher plants, the common -“pepper root,” or “toothwort” (Dentaria diphylla) as it is sometimes -called. This plant occurs in moist woods during the month of May, and -is well distributed in the northeastern United States. A plant is shown -in <a href="#FIG_383">fig. 383</a>. It has a creeping underground rhizome, -whitish in color, fleshy, and with a few scales. Each spring the annual flower-bearing -stem rises from one of the buds of the rhizome, and after the ripening -of the seeds, dies down.</p> - -<p>The leaves are situated a little above the middle point of the stem. -They are opposite and the number is two, each one being divided into -three dentate lobes, making what is called a compound leaf.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_383" src="images/fig383.jpg" alt="" width="300" height="471" /> - <p class="center">Fig. 383.<br /> Toothwort (Dentaria diphylla).</p> - </div> - <div class="figsub"> - <img id="FIG_384" src="images/fig384.jpg" alt="" width="150" height="186" /> - <p class="center">Fig. 384.<br /> Flower of the toothwort<br /> (Dentaria diphylla).</p> - </div> -</div> - -<p><b>647. Parts of the flower.</b>—The flowers are several, and they -are borne on quite long stalks (pedicels) scattered over the terminal -portion of the stem. We should now examine the parts of the flower -beginning with the calyx. This we can see, looking at the under side -of some of the flowers, possesses four scale-like sepals, which easily -fall away after the opening of the flower. They do not resemble leaves -so much as the sepals of trillium, but they belong to the leaf series, -and there are two pairs in the set of four. The corolla also possesses -four petals, which are more expanded than the sepals and are whitish in -color. The stamens are six in number, one pair lower than the others, -<span class="pagenum"><a name="Page_323" id="Page_323">[Pg 323]</a></span> -and also shorter. The filament is long in proportion to the anther, the -latter consisting of two lobes or sacs, instead of four as in trillium. -The pistil is composed of two carpels, or leaves fused together. So we -find in the case of the pepper root that the parts of the flower are -in twos, or multiples of two. Thus they agree in this respect with the -leaves; and while we do not see such a strong resemblance between the -parts of the flower here and the leaves, yet from the presence of the -<span class="pagenum"><a name="Page_324" id="Page_324">[Pg 324]</a></span> -pollen (microspores) in the anther sacs (microsporangia) and of ovules -(macrosporangia) on the margins of each half of the pistil, we are, -from our previous studies, able to recognize here that all the members -of the flower belong to the leaf series.</p> - -<p><b>648.</b> In trillium and in the pepper root we have seen that the -parts of the flower in each apparent whorl are either of the same -number as the leaves in a whorl, or some multiple of that number. This -is true of a large number of other plants, but it is not true of all. A -glance at the spring-beauty (Claytonia virginiana), and at the anemone -(or Isopyrum biternatum, fig. 563) will serve to show that the number -of the different members of the flower may vary. The trillium and the -dentaria were selected as being good examples to study first, to make -it very clear that the members of the flower are fundamentally leaf -structures, or rather that they belong to the same series of members as -do the leaves of the plant.</p> - -<p><b>649. Synopsis of members of the sporophyte in angiosperms.</b></p> - -<table border="0" class="no-wrap" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl">Higher plant.</td> - <td class="tdc" colspan="8"> </td> - </tr><tr> - <td class="tdl">Sporophyte phase</td> - <td class="tdc" rowspan="2"><img src="images/cbl-2.jpg" alt="" width="9" height="32" /></td> - <td class="tdl_ws1">Root.</td> - <td class="tdc"> </td> - <td class="tdl_ws1"> </td> - <td class="tdc" rowspan="6"><img src="images/cbl-6.jpg" alt="" width="37" height="132" /></td> - <td class="tdl_ws1">Foliage leaves.</td> - <td class="tdc"> </td> - <td class="tdl_ws1"> </td> - </tr><tr> - <td class="tdl">(or modern phase) </td> - <td class="tdl_ws1">Shoot.</td> - <td class="tdc" rowspan="2"><img src="images/cbl-2.jpg" alt="" width="9" height="32" /></td> - <td class="tdl_ws1">Stem.</td> - <td class="tdl_ws1">Perianth leaves.</td> - <td class="tdc" rowspan="5"><img src="images/cbr-5.jpg" alt="" width="30" height="107" /></td> - <td class="tdl_ws1"> </td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdc"> </td> - <td class="tdl_ws1"> </td> - <td class="tdl_ws1"> Leaf.</td> - <td class="tdl_ws1">Spore-bearing leaves</td> - <td class="tdl_ws1"> </td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdc"> </td> - <td class="tdl_ws1"> </td> - <td class="tdc"> </td> - <td class="tdl_ws1"> </td> - <td class="tdl_ws1">  with sporangia.</td> - <td class="tdl_ws1">Flower.</td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdc"> </td> - <td class="tdl_ws1"></td> - <td class="tdc"> </td> - <td class="tdl_ws1"> </td> - <td class="tdl_ws1">(Sporangia sometimes</td> - <td class="tdl_ws1"> </td> - </tr><tr> - <td class="tdl"> </td> - <td class="tdc"> </td> - <td class="tdl_ws1"></td> - <td class="tdc"> </td> - <td class="tdl_ws1"> </td> - <td class="tdl_ws1">  on shoot.)</td> - <td class="tdl_ws1"> </td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_325" id="Page_325">[Pg 325]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXXVI" id="CHAPTER_XXXVI">CHAPTER XXXVI.</a><br /> -<span class="h_subtitle">GAMETOPHYTE AND SPOROPHYTE<br /> OF ANGIOSPERMS.</span></h3> -</div> - -<p><b>650. Male prothallium of angiosperms.</b>—The first division which -takes place in the nucleus of the pollen grain occurs, in the case of -trillium and many others of the angiosperms, before the pollen grain -is mature. In the case of some specimens of T. grandiflorum in which -the pollen was formed during the month of October of the year before -flowering, the division of the nucleus into two nuclei took place soon -after the formation of the four cells from the mother cell. The nucleus -divided in the young pollen grain is shown in <a href="#FIG_385">fig. 385</a>. -After this takes place the wall of the pollen grain becomes stouter, and minute -spiny projections are formed.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_385" src="images/fig385.jpg" alt="" width="150" height="101" /> - <p class="center">Fig. 385.<br /> Nearly mature pollen<br /> grain of trillium. The<br /> - smaller cell is the<br /> generative cell.</p> - </div> - <div class="figsub"> - <img id="FIG_386" src="images/fig386.jpg" alt="" width="300" height="253" /> - <p class="center">Fig. 386.<br /> Germinating spores (pollen grains) of peltandra;<br /> - generative nucleus in one undivided, in other<br /> - divided to form the two sperm nuclei; vegetative<br /> - nucleus in each near the pollen grain.</p> - </div> -</div> - -<p><b>651.</b> The larger cell is the vegetative cell of the prothallium, -while the smaller one, since it later forms the sperm cells, is -the generative cell. This generative cell then corresponds to the -central cell of the antheridium, and the vegetative cell perhaps -corresponds to a wall cell of the antheridium. If this is so, then the -male prothallium of angiosperms has become reduced to a very simple -antheridium. The farther growth takes place after fertilization. In -some plants the generative cell divides into the two sperm cells at -the maturity of the pollen grain. In other cases the generative cell -divides in the pollen tube after the germination of the pollen grain. -For study of the pollen tube the pollen may be germinated in a weak -<span class="pagenum"><a name="Page_326" id="Page_326">[Pg 326]</a></span> -solution of sugar, or on the cut surface of pear fruit, the latter -being kept in a moist chamber to prevent drying the surface.</p> - -<p><b>652.</b> In the spring after flowering the pollen escapes from the -anther sacs, and as a result of pollination is brought to rest on -the stigma of the pistil. Here it germinates, as we say, that is, it -develops a long tube which makes its way down through the style, and in -through the micropyle to the embryo sac, where, in accordance with what -takes place in other plants examined, one of the sperm cells unites -with the egg, and fertilization of the egg is the result.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig387.jpg" alt="" width="250" height="405" /> - <p class="center">Fig. 387.<br /> Section of pistil of trillium,<br /> - showing position of ovules<br /> (macrosporangia).</p> - </div> - <div class="figsub"> - <img src="images/fig388.jpg" alt="" width="250" height="482" /> - <p class="center">Fig. 388.<br /> Mandrake<br /> (Podophyllum peltatum).</p> - </div> -</div> - -<p><b>653. Macrospore and embryo sac.</b>—In trillium the three carpels -are united into one, and in dentaria the two carpels are also united -into one compound pistil. Simple pistils are found in many plants, for -example in the ranunculaceæ, the buttercups, columbine, etc. These -simple pistils bear a greater resemblance to a leaf, the margins of -which are folded around so that they meet and enclose the ovules or -sporangia.</p> - -<div class="figcenter"> - <img id="FIG_389" src="images/fig389.jpg" alt="" width="600" height="469" /> - <div class="blockquot"> - <p class="center">Fig. 389.</p> - <p>Young ovule (macrosporangium) of podophyllum. <i>n</i>, nucellus - containing the one-celled stage of the macrospore; <i>i.int</i>, inner - integument; <i>o.int</i>, outer integument.</p> - </div> -</div> - -<p><b>654.</b> If we cut across the compound pistil of trillium we -find that the infoldings of the three pistils meet to form three -partial partitions which extend nearly to the center, dividing off -three spaces. In these spaces are the ovules which are attached to -the infolded margins. If we make cross-sections of a pistil of the -<span class="pagenum"><a name="Page_327" id="Page_327">[Pg 327]</a></span> -May-apple (podophyllum) and through the ovules when they are quite young, we -shall find that the ovule has a structure like that shown in <a href="#FIG_389">fig. 389</a>. -At <i>m</i> is a cell much larger than the surrounding ones. This is -called the macrospore. The tissue surrounding it is called here the -nucellus, but because it contains the macrospore it must be the -macrosporangium. The two coats or integuments of the ovule are -yet short and have not grown out over the end of the nucellus. -This macrospore increases in size, forming first a cavity or sac -in the nucellus, the <i>embryo sac</i>. The nucleus divides several -times until eight are formed, four in the micropylar end of the -embryo sac and four in the opposite end. In some plants it -has been found that one nucleus from each group of four moves -toward the middle of the embryo sac. Here they fuse together -to form one nucleus, the <i>endosperm nucleus</i> or <i>definitive nucleus</i> -shown in <a href="#FIG_390">fig. 390</a>. One of the nuclei at the micropylar end is -<span class="pagenum"><a name="Page_328" id="Page_328">[Pg 328]</a></span> -the egg, while the two smaller ones nearer the end are the <i>synergids</i>. -The egg-cell is all that remains of the archegonium in this reduced prothallium. -The three nuclei at the lower end are the <i>antipodal</i> cells.</p> - -<div class="figcenter"> - <img id="FIG_390" src="images/fig390.jpg" alt="" width="600" height="326" /> - <div class="blockquot"> - <p class="center">Fig. 390.</p> - <p>Podophyllum peltatum, ovule containing mature embryo sac; two - synergids, and eggs at left, endosperm nucleus in center, three - antipodal cells at right.</p> - </div> -</div> -<div class="figleft"> - <img id="FIG_391" src="images/fig391.jpg" alt="" width="150" height="140" /> - <p class="center">Fig. 391.<br /> Macrospore<br /> (one-celled stage)<br /> of lilium.</p> -</div> - -<p><b>655. Embryo sac is the young female prothallium.</b>—In figs. -<a href="#FIG_391">391</a>-<a href="#FIG_393">393</a> are shown the different -stages in the development of the embryo sac in lilium. The embryo sac -at this stage is the young female prothallium, and the egg is the only -remnant of the female sexual organ, the archegonium, in this reduced -gametophyte.</p> - -<p><b>656. Fertilization.</b>—When the pollen tube has reached the embryo -sac (paragraph 652) it opens and the two sperm cells are emptied near -the egg. The first sperm nucleus enters the protoplasm surrounding the -egg nucleus and uniting with the latter brings about fertilization. The -second sperm nucleus often unites with the endosperm nucleus (or with -one or both of the “polar nuclei”), bringing about what some call a -second fertilization. Where this takes place in addition to the union -<span class="pagenum"><a name="Page_329" id="Page_329">[Pg 329]</a></span> -of the first sperm nucleus with the egg nucleus it is called <i>double -fertilization</i>. The sperm nucleus is usually smaller than the egg -nucleus, but often grows to near or quite the size of the egg nucleus -before union. See figs. <a href="#FIG_394">394</a> and <a href="#FIG_395">395</a>.</p> - -<div class="figcenter"> - <img src="images/fig392.jpg" alt="" width="500" height="429" /> - <div class="blockquot"> - <p class="center">Fig. 392.</p> - <p>Two-and four-celled stage of embryo sac of lilium. The middle one - shows division of nuclei to form the four-celled stage. (Easter lily.)</p> - </div> -</div> - -<p><b>657. Fertilization in plants is fundamentally the same as in -animals.</b>—In all the great groups of plants as represented by -spirogyra, œdogonium, vaucheria, peronospora, ferns, gymnosperms, and -in the angiosperms, fertilization, as we have seen, consists in the -fusion of a male nucleus with a female nucleus. Fertilization, then, in -plants is identical with that which takes place in animals.</p> - -<p><b>658. Embryo.</b>—After fertilization the egg develops into a short -row of cells, the <i>suspensor</i> of the embryo. At the free end the embryo -develops. In figs. <a href="#FIG_397">397</a> and <a href="#FIG_398">398</a> -is a young embryo of trillium.</p> - -<p><b>659. Endosperm, the mature female prothallium.</b>—During the -<span class="pagenum"><a name="Page_330" id="Page_330">[Pg 330]</a></span> -development of the embryo the endosperm nucleus divides into a great -many nuclei in a mass of protoplasm, and cell walls are formed -separating them into cells. This mass of cells is the <i>endosperm</i>, -and it surrounds the embryo. It is the <i>mature female prothallium</i>, -belated in its growth in the angiosperms, usually developing only when -fertilization takes place, and its use has been assured.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_393" src="images/fig393.jpg" alt="" width="150" height="455" /> - <p class="center">Fig. 393.<br /> Mature embryo sac<br /> (young prothallium) of<br /> - lilium. <i>m</i>, micropylar end;<br /> <i>S</i>, synergids; <i>E</i>, egg;<br /> - <i>Pn</i>, polar nuclei; <i>Ant</i>,<br /> antipodals. (Easter lily.)</p> - </div> - <div class="figsub"> - <img id="FIG_394" src="images/fig394.jpg" alt="" width="200" height="445" /> - <p class="center">Fig. 394.<br /> Section through nucellus and<br /> - upper part of embryo sac of<br /> cotton at time of entrance of<br /> - pollen tube. <i>E</i>, egg; <i>S</i>,<br /> synergids; <i>P</i>, pollen tube with<br /> - sperm cell in the end. (Duggar.)</p> - </div> -</div> - -<p><span class="pagenum"><a name="Page_331" id="Page_331">[Pg 331]</a></span> -<b>660. Seed.</b>—As the embryo is developing it derives its -nourishment from the endosperm (or in some cases perhaps from the -nucellus). At the same time the integuments increase in extent and -harden as the seed is formed.</p> - -<div class="figcenter"> - <img id="FIG_395" src="images/fig395.jpg" alt="" width="500" height="314" /> - <div class="blockquot"> - <p class="center">Fig. 395.</p> - <p>Fertilization of cotton. <i>pt</i>, pollen tube; <i>Sn</i>, - synergids; <i>E</i>, egg, with male and female nucleus fusing. - (Duggar.)</p> - </div> -</div> -<div class="figcenter"> - <img src="images/fig396.jpg" alt="" width="400" height="530" /> - <div class="blockquot"> - <p class="center">Fig. 396.</p> - <p>Diagrammatic section of ovary and ovule at time of fertilization in - angiosperm. <i>f</i>, funicle of ovule; <i>n</i>, nucellus; <i>m</i>, micropyle; <i>b</i>, - antipodal cells of embryo sac; <i>e</i>, endosperm nucleus; <i>k</i>, egg-cell - and synergids; <i>ai</i>, outer integument of ovule; <i>ii</i>, inner integument. - The track of the pollen tube is shown down through the style, walls of - the ovary to the micropylar end of the embryo sac.</p> - </div> -</div> - -<p><b>661. Perisperm.</b>—In most plants the nucellus is all consumed -in the development of the endosperm, so that only minute fragments -of disorganized cell walls remain next the inner integument. In some -plants, however, (the water-lily family, the pepper family, etc.,) -a portion of the nucellus remains intact in the mature seed. In such -seeds the remaining portion of the nucellus is the <i>perisperm</i>.</p> - -<p><b>662. Presence or absence of endosperm in the seed.</b>—In many of -the angiosperms all of the endosperm is consumed by the embryo during -its growth in the formation of the seed. This is the case in the rose -family, crucifers, composites, willows, oaks, legumes, etc., as in the -acorn, the bean, pea and others. In some, as in the bean, a large part -<span class="pagenum"><a name="Page_332" id="Page_332">[Pg 332]</a></span> -of the nutrient substance passing from the endosperm into the embryo is -stored in the cotyledons for use during germination. In other plants -the endosperm is not all consumed by the time the seed is mature. -Examples of this kind are found in the buttercup family, the violet, -lily, palm, jack-in-the-pulpit, etc. Here the remaining endosperm in -the seed is used as food by the embryo during germination.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_397" src="images/fig397.jpg" alt="" width="350" height="260" /> - <p class="center">Fig. 397.<br /> Section of one end of ovule of trillium,<br /> - showing young embryo in endosperm.</p> - </div> - <div class="figsub"> - <img id="FIG_398" src="images/fig398.jpg" alt="" width="100" height="238" /> - <p class="center">Fig. 398.<br /> Embryo<br /> enlarged.</p> - </div> -</div> -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig399.jpg" alt="" width="250" height="207" /> - <p class="center">Fig. 399.<br /> Seed of violet, external view,<br /> - and section. The section shows<br /> the embryo lying in the endosperm.</p> - </div> - <div class="figsub"> - <img src="images/fig400.jpg" alt="" width="250" height="183" /> - <p class="center">Fig. 400.<br /> Section of fruit of pepper (Piper nigrum),<br /> - showing small embryo lying in a small<br /> quantity of whitish endosperm at one end,<br /> - the perisperm occupying the larger part of<br /> the interior, surrounded by pericarp.</p> - </div> -</div> - -<p><b>663. Outer parts of the seed.</b>—While the embryo is forming within -<span class="pagenum"><a name="Page_333" id="Page_333">[Pg 333]</a></span> -the ovule and the growth of the endosperm is taking place, where this -is formed, other correlated changes occur in the outer parts of the -ovule, and often in adjacent parts of the flower. These unite in making -the “seed,” or the “fruit.” Especially in connection with the formation -of the seed a new growth of the outer coat, or integument, of the ovule -occurs, forming the outer coat of the seed, known as the <i>testa</i>, while -the inner integument is absorbed. In some cases the inner integument -of the ovule also forms a new growth, making an inner coat of the seed -(rosaceæ). In still other cases neither of the integuments develops -into a testa, and the embryo sac lies in contact with the wall of -the ovary. Again an additional envelope grows up around the seed; an -example of this is found in the case of the red berries of the “yew” -(taxus), the red outer coat being an extra growth, called an <i>aril</i>.</p> - -<p>In the willow and the milkweed an aril is developed in the form of -a tuft of hairs. (In the willow it is an outgrowth of the funicle, -= stalk of the ovule, and is called a funicular aril; while in the -milkweed it is an outgrowth of the micropyle, = the open end of the -ovule, and is called a micropylar aril.)</p> - -<p><b>664. Increase in size during seed formation.</b>—Accompanying this -extra growth of the different parts of the ovule in the formation of -the seed is an increase in the size, so that the seed is often much -greater in size than the ovule at the time of fertilization. At the -same time parts of the ovary, and in many plants, the adherent parts of -the floral envelopes, as in the apple; or of the receptacle, as in the -strawberry; or in the involucre, as in the acorn; are also stimulated -to additional growth, and assist in making the fruit. -<span class="pagenum"><a name="Page_334" id="Page_334">[Pg 334]</a></span></p> - -<p><b>665. Synopsis of the seed.</b></p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl br" rowspan="7"><i>The seed. </i></td> - <td class="tdc br"> </td> - <td class="tdl bt">Aril, rarely present.</td> - </tr><tr> - <td class="tdc br"> </td> - <td class="tdl_ws1"><p class="neg-indent2">Ovular coats (one or two usually present), the <i>testa</i>.</p></td> - </tr><tr> - <td class="tdc br"> </td> - <td class="tdl_ws1"><p class="neg-indent2"><i>Funicle</i> (stalk of ovule), <i>raphe</i> (portion of funicle when bent on to - the side of ovule), <i>micropyle</i>, <i>hilum</i> (scar where seed was attached - to ovary).</p></td> - </tr><tr> - <td class="tdr br"><i>Ripened ovule.</i><span class="ws4"> </span></td> - <td class="tdl_ws1 bb"><p class="neg-indent2"><i>Remnant of the nucellus</i> (central part of ovule); sometimes - nucellus remains as <i>Perisperm</i> in some albuminous seeds.</p></td> - </tr><tr> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdl_ws1"><i>Endosperm</i>, present in albuminous seeds.</td> - </tr><tr> - <td class="tdl_ws1"><p class="neg-indent2"><i>Embryo</i> within surrounded by endosperm when this - is present, or by the remnant of nucellus, and by the ovular coats - which make the <i>testa</i>. In many seeds (example, bean) the endospermis - transferred to the cotyledons which become fleshy(exalbuminous seeds).</p></td> - </tr> - </tbody> -</table> - -<p><b>666. Parts of the ovule.</b>—In <a href="#FIG_401">fig. 401</a> are represented -three different kinds of ovules, which depend on the position of the ovule -with reference to its stalk. The funicle is the stalk of the ovule, -the hilum is the point of attachment of the ovule with the ovary, the -raphe is the part of the funicle in contact with the ovule in inverted -ovules, the chalaza is the portion of the ovule where the nucellus and -the integuments merge at the base of the ovule, and the micropyle is -the opening at the apex of the ovule where the coats do not meet.</p> - -<div class="figcenter"> - <img id="FIG_401" src="images/fig401.jpg" alt="" width="600" height="221" /> - <div class="blockquot"> - <p class="center">Fig. 401.</p> - <p><i>A</i>, represents a straight (orthotropous) ovule of polygonum; <i>B</i>, the - inverted (anatropous) ovule of the lily; and <i>C</i>, the right-angled - (campylotropous) ovule of the bean. <i>f</i>, funicle; <i>c</i>, chalaza; - <i>k</i>, nucellus; <i>ai</i>, outer integument; <i>ii</i>, inner integument; <i>m</i>, - micropyle; <i>em</i>, embryo sac.</p> - </div> -</div> -<p><span class="pagenum"><a name="Page_335" id="Page_335">[Pg 335]</a></span></p> - -<p class="center"><b>Comparison of Organ and Member.</b></p> - -<p><b>667. The stamens and pistils are not the sexual organs.</b>—Before -the sexual organs and sexual processes in plants were properly -understood it was customary for botanists to speak of the stamens and -pistils of flowering plants as the sexual organs. Some of the early -botanists, a century ago, found that in many plants the seed would not -form unless first the pollen from the stamens came to be deposited on -the stigma of the pistil. A little further study showed that the pollen -germinated on the stigma and formed a tube which made its way down -through the pistil and into the ovule.</p> - -<p>This process, including the deposition of the pollen on the stigma, -was supposed to be fertilization, the stamen was looked on as the male -sexual organ, and the pistil as the female sexual organ. We have found -out, however, by further study, and especially by a comparison of the -flowering plants and the lower plants, that the stamens and pistils are -not the sexual organs of the flower.</p> - -<p><b>668. The stamens and pistils are spore-bearing leaves.</b>—The -stamen is the spore-bearing leaf, and the pollen grains are not -unlike spores; in fact they are the small spores of the angiosperms. -The pistil is also a spore-bearing leaf, the ovule the sporangium, -which contains the large spore called an <i>embryo sac</i>. In the ferns -we know that the spore germinates and produces the green heart-shaped -prothallium. The prothallium bears the sexual organs. Now the fern leaf -bears the spores and the spore forms the prothallium. So it is in the -flowering plants. The stamen bears the small spores—pollen grains—and -the pollen grain forms the prothallium. The prothallium in turn forms -the sexual organs. The process is in general the same as it is in the -ferns, but with this special difference: the prothallium and the sexual -organ of the flowering plants are very much reduced.</p> - -<p><b>669. Difference between organ and member.</b>—While it is not -<span class="pagenum"><a name="Page_336" id="Page_336">[Pg 336]</a></span> -strictly correct then to say that the stamen is a sexual organ, or male -organ, we might regard it as a <i>male member</i> of the flower, and we -should distinguish between <i>organ</i> and <i>member</i>. It is an <i>organ</i> when -we consider <i>pollen production</i>, but it is not a sexual organ. When we -consider <i>fertilization</i> it is <i>not a sexual organ, but a male member</i> -of the flower which bears the small spore.</p> - -<p>The following table will serve to indicate these relations.</p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl_top">Stamen</td> - <td class="tdc_top"> = </td> - <td class="tdl">spore-bearing leaf = male member of flower.</td> - </tr><tr> - <td class="tdl_top">Anther locule</td> - <td class="tdc_top"> = </td> - <td class="tdl">sporangium.</td> - </tr><tr> - <td class="tdl_top">Pollen grain</td> - <td class="tdc_top"> = </td> - <td class="tdl">small spore = reduced male prothallium and sexual organ.</td> - </tr> - </tbody> -</table> - -<p>So the pistil is not a sexual organ, but might be regarded as the -female member of the flower.</p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl_top">Pistil</td> - <td class="tdc_top"> = </td> - <td class="tdl">spore-bearing leaf = female member of flower.</td> - </tr><tr> - <td class="tdl_top">Ovule</td> - <td class="tdc_top"> = </td> - <td class="tdl">sporangium.</td> - </tr><tr> - <td class="tdl_top">Embryo sac</td> - <td class="tdc_top"> = </td> - <td class="tdl">large spore = female prothallium containing the egg.</td> - </tr><tr> - <td class="tdl_top">The egg</td> - <td class="tdc_top"> = </td> - <td class="tdl">a reduced archegonium = the female sexual organ.</td> - </tr> - </tbody> -</table> - -<p class="center"><b>Progression and Retrogression in<br /> Sporophyte and Gametophyte.</b></p> - -<p><b>670. Sporophyte is prominent and highly developed.</b>—In the -angiosperms then, as we have seen from the plants already studied, the -trillium, dentaria, etc., are sporophytes, that is they represent the -spore-bearing, or sporophytic, stage. Just as we found in the case of -the gymnosperms and ferns, this stage is the prominent one, and the -one by which we characterize and recognize the plant. We see also that -the plants of this group are still more highly specialized and complex -than the gymnosperms, just as they were more specialized and complex -than the members of the fern group. From the very simple condition -in which we possibly find the sporophyte in some of the algæ like -spirogyra, vaucheria, and coleochæte, there has been a gradual increase -in size, specialization of parts, and complexity of structure through -the bryophytes, pteridophytes, and gymnosperms, up to the highest types -of plant structure found in the angiosperms. Not only do we find that -these changes have taken place, but we see that, from a condition of -complete dependence of the spore-bearing stage on the sexual stage -(gametophyte), as we find it in the liverworts and mosses, it first -becomes free from the gametophyte in the members of the fern group, and -is here able to lead an independent existence. The sporophyte, then, -<span class="pagenum"><a name="Page_337" id="Page_337">[Pg 337]</a></span> -might be regarded as the modern phase of plant life, since it is that -which has become and remains the prominent one in later times.</p> - -<p><b>671. The gametophyte once prominent has become degenerate.</b>—On -the other hand we can see that just as remarkable changes have come -upon the other phase of plant life, the sexual stage, or gametophyte. -There is reason to believe that the gametophyte was the stage of plant -life which in early times existed almost to the exclusion of the -sporophyte, since the characteristic thallus of the algæ is better -adapted to an aquatic life than is the spore-bearing state of plants. -At least, we now find in the plants of this group as well as in the -liverworts, that the gametophyte is the prominent stage. When we reach -the members of the fern group, and the sporophyte becomes independent, -we find that the gametophyte is decreasing in size, in the higher -members of the pteridophytes, the male prothallium consisting of only a -few cells, while the female prothallium completes its development still -within the spore wall. And in selaginella it is entirely dependent on -the sporophyte for nourishment.</p> - -<p><b>672.</b> As we pass through the gymnosperms we find that the -condition of things which existed in the bryophytes has been reversed, -and the gametophyte is now entirely dependent on the sporophyte for -its nourishment, the female prothallium not even becoming free from -the sporangium, which remains attached to the sporophyte, while the -remnant of a male prothallium, during the stage of its growth, receives -nourishment from the tissues of the nucellus through which it bores its -way to the egg-cell.</p> - -<p><b>673.</b> In the angiosperms this gradual degradation of the male -and female prothallia has reached a climax in a one-celled male -prothallium with two sperm cells, and in the embryo sac with no clearly -recognizable traces of an archegonium to identify it as a female -prothallium. The development of the endosperm subsequent, in most -cases, to fertilization, providing nourishment for the sporophytic -embryo at one stage or another, is believed to be the last remnant of -the female prothallium in plants.</p> - -<p><b>674. The seed.</b>—The seed is the only important character -possessed by the higher plants (the gymnosperms and angiosperms) which -is not possessed by one or another of the lower great groups. With the -gradual evolution of the higher plants from the lower there has been -developed at certain periods organs or structural characters which -were not present in some of the lower groups. Thus the thallus is the -plant body of the algæ and fungi, so that these two groups of plants -are sometimes called <i>Thallophytes</i>. In the Bryophytes (liverworts and -mosses) the thallus is still present, but there is added the highly -organized archegonium in place of the simple female gamete or oogonium, -or carpogonium of the algæ and fungi, and the sporophyte has become -a distinct though still dependent structure. In the Pteridophytes -the thallus is still present as the prothallium, archegoina are also -present, and while both of these structures are retrograding the -sporophyte has become independent and has organized for the first time -<span class="pagenum"><a name="Page_338" id="Page_338">[Pg 338]</a></span> -a true vascular system for conduction of water and food. In the -gymnosperms and angiosperms the thallus is present in the endosperm; -distinct, though reduced, archegonia are present in most gymnosperms -and represented only by the egg in the angiosperms; the vascular system -is still more highly developed while the seed for the first time is -organized, and characterizes these plants so that they are called seed -plants, or <i>Spermatophytes</i>.</p> - -<p class="center"><b>Variation, Hybridization, Mutation.</b></p> - -<p><b>674a. Variation.</b>—It is a well-known fact that plants as well -as animals are subject to variation. Under certain conditions, some -of which are partly understood and others are unknown, the progeny of -plants differ in one or more characters from their parents. Some of -these variations are believed to be due to the influence of environment -(see Parts III and IV). Others are the result of the crossing of -individuals which show greater or lesser differences in one or more -characters, or the crossing of different species (<i>hybridization</i>). The -most profound variations are those which spring suddenly into existence -(<i>mutation</i>).</p> - -<p><b>674b. Hybridization.</b>—Two different species are “crossed” where -the egg-cell of one species is fertilized by the sperm of another -species. The progeny resulting from such a cross is a <i>hybrid</i>. Hybrids -sometimes resemble one parent, sometimes another, sometimes both. Where -the parents differ only in respect to one character of an organ or -structure, there is a regular law in respect to the progeny if they are -self-fertilized. In the first generation all the individuals are alike -and resemble one of the parents, and the special differential character -of that parent is called the <i>dominant</i> character. In the second -generation 75% possess the dominant character, while 25% resemble -the other original parent, and its differential character is called -<i>recessive</i>. These are <i>pure</i> recessives, since successive generations, -if self-fertilized, are always recessive. Of the 75% which show the -dominant character in the second generation, one-third (or 25% of the -whole number) are pure dominants if self-fertilization is continued, -while 50% are really “cross breds” like the first generation, and -if self-fertilized split up again into approximately 25 dominants, -50 cross breds, and 25 recessives. This is what is called Mendel’s -law. Where the original parents differ in respect to more than one -character, the result is more complicated (see Mendel’s Principles of -Heredity; also de Vries, Das Spaltungsgesetz der Bastarde, Ber. d. -deutsch. bot. Gesell., 18, 83, 1900).</p> - -<p><b>674c. Mutation.</b>—This term is applied to those variations which -appear so suddenly that some of the progeny of two like individuals -differ from all the others to a marked degree. Some of these mutations -are so different as to be regarded as new species. Some of the -primroses show mutations, and Œnothera gigas is a mutation from Œnothera -lamarkiana (see de Vries, Die Mutationstheorie, Leipzig). -<span class="pagenum"><a name="Page_339" id="Page_339">[Pg 339]</a></span></p> - -<p><b>675.</b></p> - -<p class="center">TABLE SHOWING HOMOLOGIES OF SPOROPHYTE AND<br /> -GAMETOPHYTE IN ANGIOSPERMS.</p> - -<p class="center"><span class="smcap">Terms Corresponding to those used in Pteridophytes.</span> <span class="smcap">Common Terms.</span></p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <thead><tr> - <th class="tdc"> </th> - <th class="tdc bb"><span class="smcap">Terms Corresponding to those<br /> used in Pteridophytes.</span></th> - <th class="tdc bb"> </th> - <th class="tdc bb" colspan="2"><span class="smcap">Common Terms.</span></th> - </tr> - </thead> - <tbody><tr> - <td class="tdl br"> </td> - <td class="tdl_ws1">Sporophyte</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Higher plant.</td> - </tr><tr> - <td class="tdl br"> </td> - <td class="tdl_ws1">Spore-bearing part</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Stamens and carpels.</td> - </tr><tr> - <td class="tdl br bt" rowspan="3">Sporophyte</td> - <td class="tdl bt" rowspan="2"> Microsporophyll</td> - <td class="tdc_ws1 bt" rowspan="2">=</td> - <td class="tdl bt br" rowspan="2">Stamen</td> - <td class="tdl bt">Anther</td> - </tr><tr> - <td class="tdl">Filament.</td> - </tr><tr> - <td class="tdl_ws1 ">Microsporangium</td> - <td class="tdc_ws1 ">=</td> - <td class="tdl " colspan="2">Pollen sac, usually two or four.</td> - </tr><tr> - <td class="tdl br bb bt" rowspan="9">Male gametophyte</td> - <td class="tdl_ws1 bt">Microspore at maturity usually of 2 or 3</td> - <td class="tdc_ws1 bt">=</td> - <td class="tdl bt" colspan="2">Pollen grain.</td> - </tr><tr> - <td class="tdl_ws1">  cells {young male prothallium}</td> - <td class="tdc_ws1"> </td> - <td class="tdl" colspan="2"> </td> - </tr><tr> - <td class="tdl"> 1. Large cell (part of antheridium wall?), with</td> - <td class="tdc_ws1"> </td> - <td class="tdl" colspan="2"> </td> - </tr><tr> - <td class="tdl_ws1">its nucleus surrounded by wall of spore</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Vegetative cell.</td> - </tr><tr> - <td class="tdl"> 2. Small cell with nucleus, no wall, floating</td> - <td class="tdc_ws1"> </td> - <td class="tdl" colspan="2"></td> - </tr><tr> - <td class="tdl_ws1">in protoplasm of large cell is the central</td> - <td class="tdc_ws1"> </td> - <td class="tdl" colspan="2"> </td> - </tr><tr> - <td class="tdl_ws1">cell of antheridium (male sexual organ)</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Generative cell.</td> - </tr><tr> - <td class="tdl_ws1">Mature male prothallium</td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Pollen grain with tube.</td> - </tr><tr> - <td class="tdl_ws1 bb">Antheridium cell divided, 2 sperm cells</td> - <td class="tdc_ws1 bb">=</td> - <td class="tdl bb" colspan="2">Paternal cells, or generative cells.</td> - </tr><tr> - <td class="tdl br bb" rowspan="4">Sporophyte</td> - <td class="tdl " rowspan="2"> Macrosporophyll</td> - <td class="tdc_ws1" rowspan="2">=</td> - <td class="tdl br" rowspan="2">Carpel or simple pistil</td> - <td class="tdl" rowspan="2">Stigma.<br />Style.<br />Ovary.</td> - </tr><tr> - <td class="tdc" colspan="5"> </td> - </tr><tr> - <td class="tdl_ws1 bb" rowspan="2">Macrosporangium, covered by 1 or 2 coats</td> - <td class="tdc_top bb" rowspan="2">=</td> - <td class="tdl bb" rowspan="2" colspan="2">Nucellus, covered by 1 or 2 coats = ovule.</td> - </tr><tr> - <td class="tdc" colspan="5"> </td> - </tr><tr> - <td class="tdl br bb" rowspan="5">Female gametophyte</td> - <td class="tdl_ws1"><p class="no-indent">Macrospore, cell in end of macrosporangium, - does not become free, cavity enlarges</p></td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Uninuclear state of embryo sac.</td> - </tr><tr> - <td class="tdl_ws1"><p class="no-indent">Macrospore divides into - 8 cells to form young female prothallium</p></td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Embryo sac.</td> - </tr><tr> - <td class="tdl_ws1"><p class="no-indent">Remnant of archegonium, egg (female sexual organ)</p></td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Maternal cell, or germ cell.</td> - </tr><tr> - <td class="tdl_ws1"><p class="no-indent">Growing part of prothallium</p></td> - <td class="tdc_ws1">=</td> - <td class="tdl" colspan="2">Two polar nuclei fused, making endosperm nucleus.</td> - </tr><tr> - <td class="tdl_ws1 bb"><p class="no-indent">Mature female prothallium</p></td> - <td class="tdc_ws1 bb">=</td> - <td class="tdl bb" colspan="2">Endosperm, developed by many divisions of endosperm nucleus.</td> - </tr><tr> - <td class="tdl_ws1 br bb"><p class="no-indent">Young sporophyte surrounded by parts of the gametophyte - and new growth of old sporophyte</p></td> - <td class="tdl_ws1 bb"><p class="no-indent">After fecundation of egg, egg divides to form embryo. - Embryo in endosperm (sometimes latter nearly or quite absent) surrounded - by coats</p></td> - <td class="tdc_ws1 bb">=</td> - <td class="tdl bb" colspan="2">Seed.</td> - </tr><tr> - <td class="tdl_ws1" colspan="3"><p class="no-indent">Young sporophyte surrounded by remnants - of gametophyte and new parts of old sporophyte (remains of endosperm and - of nucellus, and ovular coat) = the seed.</p></td> - <td class="tdl" colspan="2"> </td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_340" id="Page_340">[Pg 340]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXXVII" id="CHAPTER_XXXVII">CHAPTER XXXVII.</a><br /> -<span class="h_subtitle">MORPHOLOGY OF THE NUCLEUS AND SIGNIFICANCE<br /> - OF GAMETOPHYTE AND SPOROPHYTE.</span></h3> -</div> - -<p><b>676.</b> In the development of the spores of the liverworts, -mosses, ferns, and their allies, as well as in the development of the -microspores of the gymnosperms and angiosperms, we have observed that -four spores are formed from a single mother cell. These mother cells -are formed as a last division of the fertile tissue (archesporium) of -the sporangium. In ordinary cell division the nucleus always divides -prior to the division of the cell. In many cases it is directly -connected with the laying down of the dividing cell wall.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig402.jpg" alt="" width="250" height="220" /> - <p class="center">Fig. 402.<br /> Forming spores in mother cells<br /> - (Polypodium vulgare).</p> - </div> - <div class="figsub"> - <img src="images/fig403.jpg" alt="" width="250" height="229" /> - <p class="center">Fig. 403.<br /> Spores just mature and wall of mother<br /> - cell broken (Asplenium bulbiferum).</p> - </div> -</div> - -<p><b>677. Direct division of the nucleus.</b>—The nucleus divides in two -different ways. On the one hand the process is very simple. The nucleus -simply fragments, or cuts itself in two. This is direct division.</p> - -<p><b>678. Indirect division of the nucleus.</b>—On the other hand very -<span class="pagenum"><a name="Page_341" id="Page_341">[Pg 341]</a></span> -complicated phenomena precede and attend the division of the nucleus, -giving rise to a succession of nuclear figures presented by a definite -but variable series of evolutions on the part of the nuclear substance. -This is <i>indirect division</i> of the nucleus, or <i>karyokinesis</i>. -Indirect division of the nucleus is the usual method, and it occurs in the -normal growth and division of the cell. The nuclear figures which are -formed in the division of the mother cell into the four spores are -somewhat different from those occurring in vegetative division, but -their study will serve to show the general character of the process.</p> - -<p><b>679. Chromatin and linin of the nucleus.</b>—In <a href="#FIG_404">figure 404</a> -is represented a pollen mother cell of the May-apple (podophyllum). The -nucleus is in the resting stage. There is a network consisting of very -delicate threads, the <i>linin</i> network. Upon this network are numerous -small granules, and at the junction of the threads are distinct knots. -The nucleolus is quite large and prominent. The numerous small granules -upon the linin stain very deeply when treated with certain dyes used in -differentiating the nuclear structure. This deeply staining substance -is the <i>chromatin</i> of the nucleus.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_404" src="images/fig404.jpg" alt="" width="150" height="297" /> - <p class="center">Fig. 404.<br /> Pollen mother cell of podophyllum,<br /> - resting nucleus. Chromatin forming<br /> a network.</p> - </div> - <div class="figsub"> - <img id="FIG_405" src="images/fig405.jpg" alt="" width="175" height="281" /> - <p class="center">Fig. 405.<br /> Spirem stage of nucleus. <i>nu</i>,<br /> - nuclear cavity; <i>n</i>, nucleolus;<br /> <i>Sp</i>, spirem.</p> - </div> - <div class="figsub"> - <img id="FIG_406" src="images/fig406.jpg" alt="" width="150" height="269" /> - <p class="center">Fig. 406.<br /> Forming spindle, threads from<br /> - protoplasm with several poles,<br /> roping the chromosomes up to<br /> - nuclear plate.</p> - </div> -<p class="center space-below1">(Figures 404-406 after Mottier.)</p> -</div> - -<p><span class="pagenum"><a name="Page_342" id="Page_342">[Pg 342]</a></span> -<b>680. The chromatin skein.</b>—One of the first nuclear figures -in the preparatory stages of division is the chromatin <i>skein</i> or -<i>spirem</i>. The chromatin substance unites to form this. The -spirem is in the form of a narrow continuous ribbon, or band, -woven into an irregular skein, or gnarl, as shown in <a href="#FIG_405">figure 405</a>. -This band splits longitudinally into two narrow ones, and then -each divides into a definite number of segments, about eight in -the case of podophyllum. Sometimes the longitudinal splitting of -the band appears to take place after the separation into the chromatin -segments. The segments remain in pairs until they separate -at the nuclear plate.</p> - -<div class="figcenter"> - <img id="FIG_407" src="images/fig407.jpg" alt="" width="600" height="253" /> - <div class="blockquot"> - <p class="center">Fig. 407.</p> - <p>Karyokinesis in pollen mother cells of podophyllum. At the left the spindle with the - chromosomes separating at the nuclear plate; in the middle figure the chromosomes have - reached the poles of the spindle, and at the right the chromosomes are forming the daughter - nuclei. (After Mottier.)</p> - </div> -</div> - -<p><b>681. Chromosomes, nuclear plate, and nuclear spindle.</b>—Each -one of these rod-like chromatin segments is a <i>chromosome</i>. -The pairs of chromosomes arrange themselves in a median plane -of the nucleus, radiating somewhat in a stellate fashion, forming -the <i>nuclear plate</i>, or <i>monaster</i>. At the same time threads of -the protoplasm (kinoplasm) become arranged in the form of a spindle, -the axis of which is perpendicular to the nuclear plate of chromosomes, -as shown in <a href="#FIG_407">figure 407</a>, at left. Each pair of -chromosomes now separate in the line of the division of the original -spirem, one chromosome of each pair going to one pole of the spindle, -<span class="pagenum"><a name="Page_343" id="Page_343">[Pg 343]</a></span> -while the other chromosome of each pair goes to the opposite pole. -The chromosomes here unite to form the daughter nuclei. Each of these -nuclei now divide as shown in <a href="#FIG_409">figure 409</a> (whether the -chromosomes in this second division in the mother cell split longitudinally or -divide transversely has not been definitely settled), and four nuclei are -formed in the pollen mother cell. The protoplasm about each one of these -four nuclei now surrounds itself with a wall and the spores are formed.</p> - -<div class="figcenter"> - <img src="images/fig408.jpg" alt="" width="500" height="265" /> - <div class="blockquot"> - <p class="center">Fig. 408.</p> - <p>Different stages in the separation of divided U-shaped chromosomes - at the nuclear plate. (After Mottier.) In podophyllum.</p> - </div> -</div> -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_409" src="images/fig409.jpg" alt="" width="200" height="371" /> - <p class="center">Fig. 409.<br /> Second division of nuclei<br /> - in pollen mother cell of<br /> podophyllum, chromosomes<br /> - at poles.</p> - </div> - <div class="figsub"> - <img id="FIG_410" src="images/fig410.jpg" alt="" width="250" height="352" /> - <p class="center">Fig. 410.<br /> Chromosomes uniting at<br /> - poles to form the nuclei<br /> of the four spores.<br /> - (After Mottier.)</p> - </div> -</div> - -<p><b>The number of chromosomes usually the same in a given species -throughout one phase of the plant.</b>—In those plants which have been -carefully studied, the number of chromosomes in the dividing nucleus -has been found to be fairly constant in a given species, through all -the divisions in that stage or phase of the plant, especially in the -embryonic, or young growing parts. For example, in the prothallium, or -gametophyte, of certain ferns, as osmunda, the number of chromosomes -in the dividing nucleus is always twelve. So in the development of the -pollen of lilium from the mother cells, and in the divisions of the -antherid cell to form the generative cells or sperm cells, there are -always twelve chromosomes so far as has been found. In the development -of the egg of lilium from the macrospore there are also twelve chromosomes. -<span class="pagenum"><a name="Page_344" id="Page_344">[Pg 344]</a></span></p> - -<p><b>When fertilization takes place the number of chromosomes is doubled -in the embryo.</b>—In the spermatozoid of osmunda then, as well as in -the egg, since these are developed on the gametophyte, there are twelve -chromosomes each. The same is true in the sperm cell (generative cell) -of lilium, and also in the egg-cell. When these nuclei unite, as they -do in fertilization, the paternal nucleus with the maternal nucleus, -the number of chromosomes in the fertilized egg, if we take lilium as -an example, is twenty-four instead of twelve; the number is doubled. -The fertilized egg is the beginning of the sporophyte, as we have seen. -Curiously throughout all the divisions of the nucleus in the embryonic -tissues of the sporophyte, so far as has been determined, up to the -formation of the mother cells of the spores, the number of chromosomes -is usually the same.</p> - -<div class="figcenter"> - <img id="FIG_411" src="images/fig411.jpg" alt="" width="600" height="390" /> - <div class="blockquot"> - <p class="center">Fig. 411.</p> - <p>Karyokinesis in sporophyte cells of podophyllum (twice the number of - chromosomes here that are found in the dividing spore mother cells).</p> - </div> -</div> - -<p><b>682. Reduction of the number of chromosomes in the nucleus.</b>—If -there were no reduction in the number of chromosomes at any point in -the life cycle of plants, the number would thus become infinitely -<span class="pagenum"><a name="Page_345" id="Page_345">[Pg 345]</a></span> -large. A reduction, however, does take place. This usually occurs, -either in the mother cell of the spores or in the divisions of its -nucleus, at the time the spores are formed. In the mother cells a sort -of pseudo-reduction is effected by the chromatin band separating into -one half the usual number of nuclear segments. So that in lilium during -the first division of the nucleus of the mother cell the chromatin band -divides into twelve segments, instead of twenty-four as it has done -throughout the sporophyte stage. So in podophyllum during the first -division in the mother cell it separates into eight instead of into -sixteen. Whether a qualitative reduction by transverse division of the -spirem band, unaccompanied by a longitudinal splitting, takes place -during the first or second karyokinesis is still in doubt. Qualitative -reduction does take place in some plants according to Beliaieff and -others. Recently the author has found that it takes place in Trillium -grandiflorum during the second karyokinesis, and in Arisæma triphyllum -the chromosomes divide both transversely and longitudinally during -the first karyokinesis forming four chromosomes, and a qualitative -reduction takes place here.</p> - -<p><b>683. Significance of karyokinesis and reduction.</b>—The precision -with which the chromatin substance of the nucleus is divided, when -in the spirem stage, and later the halves of the chromosomes are -distributed to the daughter nuclei, has led to the belief that this -substance bears the hereditary qualities of the organism, and that -these qualities are thus transmitted with certainty to the offspring. -In reduction not only is the original number of chromosomes restored, -it is believed by some that there is also a qualitative reduction of -the chromatin, i.e. that each of the four spores possesses different -qualitative elements of the chromatin as a result of the reducing -division of the nucleus during their formation.</p> - -<p>The increase in number of chromosomes in the nucleus occurs with the -beginning of the sporophyte, and the numerical reduction occurs at the -beginning of the gametophyte stage. The full import of karyokinesis and -reduction is perhaps not yet known, but there is little doubt that a -profound significance is to be attached to these interesting phenomena -in plant life. -<span class="pagenum"><a name="Page_346" id="Page_346">[Pg 346]</a></span></p> - -<p><b>684. The gametophyte may develop directly from the tissue of the -sporophyte.</b>—If portions of the sporophyte of certain of the -mosses, as sections of a growing seta, or of the growing capsule, be -placed on a moist substratum, under favorable conditions some of the -external cells will grow directly into protonemal threads. In some -of the ferns, as in the sensitive fern (onoclea), when the fertile -leaves are expanding into the sterile ones, protonemal outgrowths occur -among the aborted sporangia on the leaves of the sporophyte. Similar -rudimentary protonemal growths sometimes occur on the leaves of the -common brake (pteris) among the sporangia, and some of the rudimentary -sporangia become changed into the protonema. In some other ferns, as -in asplenium (A. filix-fœmina, var. clarissima), prothallia are borne -among the aborted sporangia, which bear antheridia and archegonia. In -these cases the gametophyte develops from the tissue of the sporophyte -without the intervention or necessity of the spores. This is <i>apospory</i>.</p> - -<div class="figright"> - <img src="images/fig412.jpg" alt="" width="200" height="180" /> - <p class="center">Fig. 412.<br /> Apogamy in Pteris cretica.</p> -</div> - -<p><b>685. The sporophyte may develop directly from the tissue of the -gametophyte.</b>—In some of the ferns, Pteris cretica for example, -the embryo fern sporophyte arises directly from the tissue of the -prothallium, without the intervention of sexual organs, and in some -cases no sexual organs are developed on such prothallia. Sexual organs, -then, and the fusion of the spermatozoid and egg nucleus are not here -necessary for the development of the sporophyte. This is <i>apogamy</i>. -Apogamy occurs in some other species of ferns, and in other groups of -plants as well, though it is in general a rare occurrence except in -certain species, where it may be the general rule. -<span class="pagenum"><a name="Page_347" id="Page_347">[Pg 347]</a></span></p> - -<p><b>686. Types of nuclear division.</b>—The nuclear figures in the -vegetative cells are usually different from those in the spore -mother cells. In the spore mother cells there are two types of -nuclear division. (1) The first division in the mother cell is called -<i>heterotypic</i>. The early stages of this division usually extend over a -longer period than the second, and the figures are more complex. Before -the chromosomes arrive at the nuclear plate they are often in the form -of rings, or tetrads, or in the form of X, V, or Y, and the number is -usually one half the number in the preceding cells of the sporophyte. -(2) The <i>homotypic</i> division immediately follows the heterotypic and -the figures are simpler, often the chromosomes being of a hook form, -or sometimes much stouter than in the heterotypic division. In the -vegetative cells (sometimes called somatic cells, or body cells in -contrast with reproductive cells) there is another type, called by some -the <i>vegetative type</i>. The chromosomes here are often in the form of -the letter U, and the figures are much simpler than in the heterotypic -division. In the somatic cells of the sporophyte, as stated above, -the number of chromosomes is double that found in the heterotypic -and homotypic divisions of the mother cells and in the somatic cells -of the gametophyte, <a href="#FIG_411">Fig. 411</a> represents a late stage in -the division of somatic cells in the sporophyte of podophyllum. The root-tips of -various plants as the onion, lily, etc., are excellent places in which -to study nuclear division in the somatic cells of the sporophyte.</p> - -<p><b>687. Comparison with animals.</b>—In animals there does not seem -to be anything which corresponds with the gametophyte of plants unless -the sperm cells and eggs themselves represent it. Heterotypic and -homotypic division with the accompanying reduction of the number of the -chromosomes takes place in animals usually in the mother cells of the -sperms and eggs. At the time of fertilization the number of chromosomes -is doubled, so that all the somatic cells (except in rare instances) -from the fertilized egg to the mother cells of sperms and eggs have the -doubled number of chromosomes. Reduction, therefore, takes place in -<span class="pagenum"><a name="Page_348" id="Page_348">[Pg 348]</a></span> -animals just prior to the formation of the gametes, while in plants it -takes place just prior to the formation of the gametophytes.</p> - -<p><b>688. Perhaps there is not a fundamental difference between -gametophyte and sporophyte.</b>—This development of sporophyte, or -leafy-stemmed plant of the fern (parag. 685), from the tissue of the -gametophyte is taken by some to indicate that there is not such a great -difference between the gametophyte and sporophyte of plants as others -contend. In accordance with this view it has been suggested that the -leafy-stemmed moss plant, as well as the leafy stem of the liverworts, -is homologous with the sporophyte or leafy stem of the fern plant; that -it arises by budding from the protonema; and that the sexual organs are -borne then on the sporophyte.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_349" id="Page_349">[Pg 349]</a></span></p> -<div class="chapter"> -<h2 class="nobreak">PART III.<br /> -PLANT MEMBERS IN RELATION<br /> TO ENVIRONMENT.</h2> -<h3 class="nobreak"><a name="CHAPTER_XXXVIII" id="CHAPTER_XXXVIII">CHAPTER XXXVIII.</a><br /> -<span class="h_subtitle">THE ORGANIZATION OF THE PLANT.</span></h3> -</div> - -<h4><a name="XXXVIII_1" id="XXXVIII_1">I. Organization of Plant Members.</a><a name="FNanchor_37_37" id="FNanchor_37_37"></a><a href="#Footnote_37_37" class="fnanchor">[37]</a></h4> - -<p><b>689.</b> It is now generally conceded that the earliest plants to -appear in the world were very simple in form and structure. Perhaps the -<span class="pagenum"><a name="Page_350" id="Page_350">[Pg 350]</a></span> -earliest were mere bits of naked protoplasm, not essentially different -from early animal life. The simplest ones which are clearly recognized -as plants are found among the lower algæ and fungi. These are single -cells of very minute size, roundish, oval, or oblong, existing -during their growing period in water or in a very moist substratum -or atmosphere. Examples are found in the red snow plant (<i>Sphærella -nivalis</i>), the Pleurococcus, the bacteria; and among small colonies of -these simple organisms (Pandorina) or the thread-like forms (Spirogyra, -Œdogonium, etc.). It is evident that some of the life relations of such -very simple organisms are very easily obtained—that is, the adjustment -to environment is not difficult. All of the living substance is very -closely surrounded by food material in solution. These food solutions -are easily absorbed. Because of the minute size of the protoplasts and -of the plant body, they do not have to solve problems of transport of -food to distant parts of the body. When we pass to more bulky organisms -consisting of large numbers of protoplasts closely compacted together, -the problem of relation to environment and of food transport become -felt; the larger the organism usually the greater are these problems. -A point is soon reached at which there is a gain by a differentiation -in the work of different protoplasts, some for absorption, some for -conduction, some for the light relation, some for reproduction, and -so on. There is also a gain in splitting the form of the plant body -up into parts so that a larger surface is exposed to environment -with an economy in the amount of building material required. In this -differentiation of the plant body into parts, there are two general -problems to be solved, and the plant to be successful in its struggle -for existence must control its development in such a way as to preserve -the balance between them. (1) A ready display of a large surface to -environment for the purpose of acquiring food and the disposition of -waste. (2) The protection of the plant from injuries incident to an -austere environment.</p> - -<p>It is evident with the great variety of conditions met with in -different parts of the same locality or region, and in different parts -of the globe, that the plant has had very complex problems to meet and -<span class="pagenum"><a name="Page_351" id="Page_351">[Pg 351]</a></span> -in the solution of them it has developed into a great variety of forms. -It is also likely that different plants would in many cases meet these -difficulties in different ways, sometimes with equal success, at other -times with varied success. Just as different persons, given some one -piece of work to do, are likely to employ different methods and reach -results that are varied as to their value. While we cannot attribute -consciousness or choice to plants in the sense in which we understand -these qualities in higher animals, still there is something in their -“constitution” or “character” whereby they respond in a different -manner to the same influences of environment. This is, perhaps, -imperceptible to us in the different individuals of the same species, -but it is more marked in different species. Because of our ignorance of -this occult power in the plant, we often speak of it as an “inherent” quality.</p> - -<div class="blockquot"> -<p>Perhaps the most striking examples one might use to illustrate the -different line of organization among plants in two regions where the -environment is very different are to be found in the adaptation of the -cactus or the yucca to desert regions, and the oak or the cucurbits -to the land conditions of our climate. The cactus with stem and leaf -function combined in a massive trunk, or the yucca with bulky leaves -expose little surface in comparison to the mass of substance, to the -dry air. They have tissue for water storage and through their thick -epidermis dole it out slowly since there is but little water to obtain -from dry soil.</p> - -<p>The cucurbits and the oak in their foliage leaves expose a very -large surface in proportion to the mass of their substance, to an -atmosphere not so severely dry as that of the desert, while the -roots are able to obtain an abundant supply of water from the moist -soil. The cactus and the yucca have differentiated their parts in a -very different way from the oak or the cucurbits, in order to adapt -themselves to the peculiar conditions of the environment.</p> - -<p>When we say that certain plants have the power to adapt themselves -to certain conditions of environment, we do not mean to say that if the -cucurbits were transferred to the desert they would take on the form -of the cactus or the yucca. They could do neither. They would perish, -since the change would be too great for their organization. Nor do we -mean, that, if the cactus or yucca were transferred from the desert to -our climate, they would change into forms with thin foliage leaves. -They could not. The fact is that they are enabled to live in our -<span class="pagenum"><a name="Page_352" id="Page_352">[Pg 352]</a></span> -climate when we give them some care, but they show no signs of assuming -characters like those of our vegetation. What we do mean is, that where -the change is not too great nor too sudden, some of the plants become -slightly modified. This would indicate that the process of organization -and change of form is a very slow one, and is therefore a question of -time—ages it may be—in which change in environment and adaptation in -form and structure have gone on slowly hand in hand.</p> -</div> - -<p><b>690. Members of the plant body.</b>—The different parts into which -the plant body has become differentiated are from one point of view, -spoken of as members. It is evident that the simplest forms of life -spoken of above do not have members. It is only when differentiation -has reached the stage in which certain more or less prominent parts -perform certain functions for the plant that members are recognized. -In the algæ and fungi there is no differentiation into stem and leaf, -though there is an approach to it in some of the higher forms. Where -this simple plant body is flattened, as in the sea-wrack, or ulva, it -is a <i>frond</i>. The Latin word for frond is <i>thallus</i>, and this name -is applied to the plant body of all the lower plants, the algæ and fungi. -The algæ and fungi together are sometimes called <i>thallophytes</i>, or -<i>thallus plants</i>. The word thallus is also sometimes applied to the -flattened body of the liverworts. In the foliose liverworts and mosses -there is an axis with leaf-like expansions. These are believed by some -to represent true stems and leaves; by others to represent a flattened -thallus in which the margins are deeply and regularly divided, or in -which the expansion has only taken place at regular intervals.</p> - -<p>In the higher plants there is usually great differentiation of the -plant body, though in many forms, as in the duckweeds, it is in the -form of a frond. While there is a great variety in the form and -function of the members of the plant body, they are all reducible to a -few fundamental members. Some reduce these forms to three, the <i>root</i>, -<i>stem</i>, <i>leaf</i>; while others to two, the <i>root</i>, and <i>shoot</i>, -which is perhaps the best primary subdivision, and the shoot is then divided -into stem and leaf, the leaf being a lateral outgrowth of the stem, and -can be indicated by the following diagram: -<span class="pagenum"><a name="Page_353" id="Page_353">[Pg 353]</a></span></p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl" rowspan="4"><br />Plant body···· </td> - <td class="tdc"> </td> - <td class="tdr_ws1"> </td> - <td class="tdc" rowspan="3"><img src="images/cbl-3.jpg" alt="" width="16" height="57" /></td> - <td class="tdr_ws1">Stem.</td> - </tr><tr> - - <td class="tdc" rowspan="3"><img src="images/cbl-3.jpg" alt="" width="16" height="57" /></td> - <td class="tdl">Shoot···· </td> - <td class="tdr_ws1"> </td> - </tr><tr> - - <td class="tdr_ws1"> </td> - <td class="tdr_ws1">Leaf.</td> - </tr><tr> - <td class="tdl">Root.</td> - </tr> - </tbody> -</table> - -<p class="center">KINDS OF SHOOTS.</p> - -<p><b>691.</b> Since it is desirable to consider the shoot in its relation -to environment, for convenience in discussion we may group shoots into -four prominent kinds: (1) <i>Foliage shoots</i>; (2) <i>Shoots without foliage -leaves</i>; (3) <i>Floral shoots</i>; (4) <i>Winter conditions of shoots and -buds.</i> Topic (4) will be treated in <a href="#XXXIX_4">Chapter XXXIX, section IV</a>.</p> - -<div class="figcenter"> - <img src="images/fig413.jpg" alt="" width="400" height="378" /> - <p class="center">Fig. 413.<br /> - Lupinus perennis.<br /> Foliage shoot and floral shoot.</p> -</div> - -<p><b>692. (1st) Foliage shoots.</b>—Foliage shoots are either aerial, -when their relation is to both light and air; or they are aquatic, -when their relation is to both light and water. They bear green -leaves, and whether in the air or water we see that light is one of -the necessary relations for all. Naturally there are several ways in -which a shoot may display its leaves to the light and air or water. -Because of the great variety of conditions on the face of the earth -and the multitudinous kinds of plants, there is the greatest diversity -presented in the method of meeting these conditions. There is to be -considered the problem of support to the shoot in the air, or in the -water. The methods for solving this problem are fundamentally different -in each case, because of the difference in the density of air and -water, the latter being able to buoy up the plant to a great degree, -particularly when the shoot is provided with air in its intercellular -<span class="pagenum"><a name="Page_354" id="Page_354">[Pg 354]</a></span> -spaces or air cavities. In the solution of the problem in the relation -of the shoot to aerial environment, stem and leaf have in most cases -coöperated;<a name="FNanchor_38_38" id="FNanchor_38_38"></a><a href="#Footnote_38_38" class="fnanchor">[38]</a> -but in view of the great variety of stems and their -modifications, as well as of leaves, it will be convenient to discuss -them in separate chapters.</p> - -<div class="figcenter"> - <img id="FIG_413A" src="images/fig413a.jpg" alt="" width="600" height="255" /> - <p class="center">Fig. 413<i>a</i>.<br /> - Burrowing type, the mandrake,<br /> a “rhizome.”</p> -</div> - -<p><b>693. (2d) Shoots without foliage leaves.</b>—These are subterranean -or aerial. Nearly all subterranean shoots have also aerial shoots, -the latter being for the display of foliage leaves (foliage-shoots), -and also for the display of flowers (flower-shoots). The subterranean -kinds bear scale leaves, i.e., the leaves not having a light relation -are reduced in size, being small, and they lack chlorophyll. Examples -are found in Solomon’s seal, mandrake (<a href="#FIG_413A">fig. 413<i>a</i></a>), etc. -Here the scale leaves are on the bud at the end of the underground stem from -which the foliage shoot arises. Aerial shoots which lack foliage -leaves are the dodder, Indian-pipe-plant, beech drops, etc. These -plants are saprophytes or parasites (see <a href="#CHAPTER_IX">Chapter IX</a>). -Deriving their carbohydrate food from other living plants, or from humus, they -do not need green leaves. The leaves have, therefore, probably been reduced -in size to mere scales, and accompanying this there has been a loss of -the chlorophyll. Other interesting examples of aerial shoots without -<span class="pagenum"><a name="Page_355" id="Page_355">[Pg 355]</a></span> -foliage leaves are the cacti where the stem has assumed the leaf -function and the leaves have become reduced to mere spines. The various -modifications which shoots have undergone accompanying a change in -their leaf relation will be discussed under stems in <a href="#CHAPTER_XXXIX">Chapter XXXIX</a>.</p> - -<p><b>694. (3d) Floral shoots.</b>—The floral shoot is the part of the -plant bearing the flower. As interpreted here it may consist of but a -single flower with its stalk, as in Trillium, mandrake, etc., or of -the clusters of flowers on special parts of the stem, termed flower -clusters, as the <i>catkin</i>, <i>raceme</i>, <i>spike</i>, <i>umbel</i>, -<i>head</i>, etc. In the floral shoot as thus interpreted there are several -peculiarities to observe which distinguish it from the foliage shoot and -adapt it to its life relations.</p> - -<p>The floral shoot in many respects is comparable to the foliage shoot, -as seen from the following peculiarities:</p> - -<div class="blockquot"> -<p>(1) It usually possesses, beside the flowers, small green leaves -which are in fact foliage though they are very much reduced in size, -because the function of the shoot as a foliage shoot is subordinated -to the function of the floral shoot. These small leaves on the floral -shoot are termed <i>bracts</i>.</p> - -<p>(2) It may be (<i>a</i>) unbranched, when it would consist of a single -flower, or (<i>b</i>) branched, when there would be several to many flowers -in the flower cluster.</p> - -<p>(3) The flower bud has the same origin on the shoot as the leaf bud; -it is either terminal or axillary, or both.</p> - -<p>(4) The members of the flower belong to the leaf series, i.e., they -are leaves, but usually different in color from foliage leaves, because -of the different life relation which they have to perform. Evidence of -this is seen in the transition of sepals, petals, stamens, or pistils, -to foliage leaves in many flowers, as in the pond lily, the abnormal -forms of trillium, and many monstrosities in other flowers -(see <a href="#CHAPTER_XXXIV">Chapter XXXIV</a>).</p> - -<p>(5) The position of the members of the flower on its axis, though -usually more crowded, in many cases follows the same plan as the leaves -on the stem.</p> -</div> - -<p>The various kinds of floral shoots or flower clusters will be discussed -in <a href="#CHAPTER_XLII">Chapter XLII</a>, on the Floral Shoot. -<span class="pagenum"><a name="Page_356" id="Page_356">[Pg 356]</a></span></p> - -<h4><a name="XXXVIII_2" id="XXXVIII_2">II. Organization of Plant Tissues.</a></h4> - -<p><b>695.</b> A tissue is a group of cells of the same kind having a -similar position and function. In large and bulky plants different -kinds of tissue are necessary, not only because the work of the plant -can be more economically performed by a division of labor, but also -cells in the interior of the mass or at a distance from the source -of the food could not be supplied with food and air unless there -were specialized channels for conducting food and specialized tissue -for support of the large plant body. In these two ways most of the -higher plants differ from the simple ones. The tissues for conduction -are sometimes called collectively the <i>mestome</i>, while tissues for -mechanical support are called <i>stereome</i>. Division of labor has -gone further also so that there are special tissues for absorption, -assimilation, perception, reproduction, and the like. The tissues of -plants are usually grouped into three systems: (1) The Fundamental -System, (2) The Fibrovascular System, (3) The Epidermal System. Some of -the principal tissues are as follows:</p> - -<p class="center">1. THE FUNDAMENTAL SYSTEM.</p> - -<p><b>696. Parenchyma.</b>—Tissue composed of thin-walled cells which -in the normal state are living. Parenchyma forms the loose and spongy -tissue in leaves, as well as the palisade tissue (see <a href="#CHAPTER_IV">Chapter IV</a>); -the soft tissue in the cortex of root and stem (<a href="#FIG_414">Fig. 414</a>); as well -as that of the pith, of the pith-rays or medullary rays of the stem; and is -mixed in with the other elements of the vascular bundle where it is -spoken of as wood parenchyma and bast parenchyma; and it also includes -the undifferentiated tissue (meristem) in the growing tips of roots and -shoots; also the “intrafascicular” cambium (i.e., between the bundles, -some also include the cambium within the bundle).</p> - -<p><b>697. Collenchyma.</b>—This is a strengthening tissue often found -in the cortex of certain shoots. It also is composed of living cells. -The cells are thickened at the angles, as in the tomato and many other -herbs (<a href="#FIG_414">fig. 414</a>).</p> - -<p><b>698. Sclerenchyma, or stone-tissue.</b>—This is also a -strengthening tissue and consists of cells which do not taper at the -ends and the walls are evenly thickened, sometimes so thick that the -inside (lumen) of the cell has nearly disappeared. Usually such cells -contain no living contents at maturity. Sclerenchyma is very common in -<span class="pagenum"><a name="Page_357" id="Page_357">[Pg 357]</a></span> -the hard parts of nuts, and underneath the epidermis of stems and -leaves of many plants, as in the underground stems of the bracken fern, -the leaves of pines (<a href="#FIG_415">fig. 415</a>), etc.</p> - -<div class="figcenter"> - <img id="FIG_414" src="images/fig414.jpg" alt="" width="500" height="448" /> - <div class="blockquot"> - <p class="center">Fig. 414.</p> - <p>Transverse section of portion of tomato stem. <i>ep</i>, epidermis; <i>ch</i> - chlorophyll-bearing cells; <i>co</i>, collenchyma; <i>cp</i>, parenchyma.</p> - </div> -</div> -<div class="figcenter"> - <img id="FIG_415" src="images/fig415.jpg" alt="" width="400" height="388" /> - <div class="blockquot"> - <p class="center">Fig. 415.</p> - <p>Margin of leaf of Pinus pinaster, transverse section, <i>c</i>, - cuticularized layer of outer wall of epidermis; <i>i</i>, inner - non-cuticularized layer; <i>c´</i>, thickened outer wall of marginal - cell; <i>g</i>, <i>i´</i>, hypoderma of elongated sclerenchyma; <i>p</i>, - chlorophyll-bearing parenchyma; <i>pr</i>, contracted protoplasmic contents. - ×800. (After Sachs.)</p> - </div> -</div> -<div class="figcenter"> - <img id="FIG_416" src="images/fig416.jpg" alt="" width="500" height="300" /> - <div class="blockquot"> - <p class="center">Fig. 416.</p> - <p>Section through a lenticel of Betula alba showing stoma at top, - phellogen below producing rows of flattened cells, the cork. (After De Bary.)</p> - </div> -</div> - -<p><b>699. Cork.</b>—In many cases there is a development of “cork” -tissue underneath the epidermis. Cork tissue is developed by repeated -division of parenchyma cells in such a way that rows of parallel cells -are formed toward the outside. These are in distinct layers, soon lose -their protoplasm and die; there are no intercellular spaces and the -cells are usually of regular shape and fit close to each other. In -some plants the cell walls are thin (cork oak), while in others they -are thickened (beech). The tissue giving rise to cork is called “cork -cambium,” or phellogen, and may occur in other parts of the plant. For -example, where plants are wounded the living exposed parenchyma cells -often change to cork cambium and develop a protective layer of cork. -The walls of cork cells contain a substance termed <i>suberin</i>, which -renders them nearly waterproof. -<span class="pagenum"><a name="Page_358" id="Page_358">[Pg 358]</a></span></p> - -<p><b>700. Lenticels.</b>—These are developed quite abundantly underneath -stomates on the twigs of birch, cherry, beech, elder, etc. The -phellogen underneath the stoma develops a cushion of cork which presses -outward in the form of an elevation at the summit of which is the stoma -(<a href="#FIG_416">fig. 416</a>). The lenticels can easily be seen.</p> - -<p class="center">2. THE FIBROVASCULAR SYSTEM.</p> - -<p><b>701. Fibrous tissue.</b><a name="FNanchor_39_39" id="FNanchor_39_39"></a><a href="#Footnote_39_39" class="fnanchor">[39]</a>—This -consists of thick-walled cells, usually without living contents which -are elongated and taper at the ends so that the cells, or fibers, -overlap. It is common as one of the elements of the vascular bundles, -as wood fibers and bast fibers.</p> - -<p><b>702. Vascular tissue, or tracheary tissue.</b>—This consists of the -vessels or ducts, and tracheides, which are so characteristic of the -vascular bundle (see <a href="#CHAPTER_V">Chapter V</a>) and forms a conducting tissue -for the flow of water. The vascular tissue contains spiral, annular, pitted, -and scalariform vessels and tracheides according to the marking on the -walls (figs. <a href="#FIG_58">58</a>, <a href="#FIG_59">59</a>). These -are all without protoplasmic contents when mature. There are also -thin-walled living cells intermingled called wood parenchyma. In -the conifers (pines, etc.) the tracheary tissue is devoid of true -vessels except a few spiral vessels in the young stage, while it is -characterized by tracheides with peculiar markings. These marks on the -tracheides are due to the “bordered” pits appearing as two concentric -rings one within the other. These can be easily seen in a longitudinal -section of wood of conifers.</p> - -<p><b>703. Sieve tissue.</b>—This consists of elongated tubular cells -connected at the ends, the cross walls being perforated at the ends. -These are in the phloem part of the bundle, and serve to conduct -downwards the dissolved substances elaborated in the leaves.</p> - -<p><b>704. Fascicular cambium.</b>—This is the living, cell-producing -tissue in the vascular bundle, which in the open bundle adds to the -phloem on one side and the xylem on the other.</p> - -<p class="center">3. THE EPIDERMAL SYSTEM.</p> - -<p><b>705.</b> To the epidermal system belong the epidermis and the -various outgrowths of its cells in the form of hairs, or <i>trichomes</i>, -as well as the guard cells of the stomates, and probably some of the -reproductive organs.</p> - -<p><b>706. The epidermis.</b>—The epidermis proper consists of a -single layer of external cells originating from the outer layer of -parenchyma cells at the growing apex of the stem or root. These cells -undergo various modifications of form. In many cases they lose their -protoplasmic contents. In many cases the outer wall becomes thickened, -<span class="pagenum"><a name="Page_359" id="Page_359">[Pg 359]</a></span> -especially in plants growing in dry situations or where they are -exposed to drying conditions. The epidermal cells generally become -considerably flattened, and are usually covered with a more or less -well developed waterproof cuticle, a continuous layer over the -epidermis. In many plants the cuticle is covered with a waxy exudation -in the form of a thin layer, or of rounded grains, or slender rods, -or grains and needles in several layers. These waxy coverings are -sometimes spoken of as “bloom” on leaves and fruit.</p> - -<p><b>707. Trichomes.</b>—Trichome is a general term including various -hair-like outgrowths from the epidermis, as well as scales, prickles, -etc. These include root hairs, rhizoids, simple or branched hairs, -glandular hairs, glandular scales, etc. Glandular hairs are found on -many plants, as tomato, verbena, primula, etc.; glandular scales on -the hop; simple-celled hairs on the evening primrose, cabbage, etc.; -many-celled hairs on the primrose, pumpkin; branched hairs on the -shepherd’s-purse, mullein, etc., stellate hairs on some oak leaves.</p> - -<p>For stomates see <a href="#CHAPTER_IV">Chapter IV</a>.</p> - -<p class="center">4. ORIGIN OF THE TISSUES.</p> - -<p><b>708. Meristem tissue.</b>—The various tissues consisting of cells -of dissimilar form are derived from young growing tissue known as -<i>meristem</i>. Meristem tissue consists of cells nearly alike in form, -with thin cell walls and rich in protoplasm. It is situated at the -growing regions of the plants. In the higher plants these regions in -general are three in number, the stem and root apex, and the cambium -cylinder beneath the cortex. Tissues produced from the stem and root -apex are called <i>primary</i>, those from the cambium <i>secondary</i>. -In most cases the main bulk of the plant is secondary tissue, while in -the corn plant it is all primary.</p> - -<div class="figcenter"> - <img id="FIG_417" src="images/fig417.jpg" alt="" width="500" height="271" /> - <div class="blockquot"> - <p class="center">Fig. 417.</p> - <p>Section through growing point of stem, <i>d</i>, - dermatogen; <i>p</i>, plerome; periblem between. (After De Bary.)</p> - </div> -</div> - -<p><b>709. Origin of stem tissues.</b>—Just back of the apical meristem -in a longitudinal section of a growing point it can be seen that the -cells are undergoing a change in form, and here are organized three -formative regions. The outer layer of cells is called <i>dermatogen</i> -(skin producer), because later it becomes the epidermis. The central -group of elongating cells is the <i>plerome</i> (to fill). This later -develops the <i>central cylinder</i>, or <i>stele</i>, as it is called -<span class="pagenum"><a name="Page_360" id="Page_360">[Pg 360]</a></span> -(<a href="#FIG_417">fig. 417</a>). Surrounding the plerome and filling the space between -it and the dermatogen is the third formative tissue called the <i>periblem</i>, -which later forms the cortex (bark or rind), and consists of -parenchyma, collenchyma, sclerenchyma, or cork, etc., as the case may -be. It should be understood that all these different forms and kinds -of cells have been derived from meristem by gradual change. In the -mature stems, therefore, there are three distinct regions, the central -cylinder or stele, the cortex, and the epidermis.</p> - -<div class="figcenter"> - <img id="FIG_418" src="images/fig418.jpg" alt="" width="600" height="365" /> - <div class="blockquot"> - <p class="center">Fig. 418.</p> - <p>Concentric bundle from stem of Polypodium vulgare. Xylem in the - center, surrounded by phloem, and this by the endodermis. (From the - author’s Biology of Ferns.)</p> - </div> -</div> - -<p><b>710. Central cylinder or stele.</b>—As the central cylinder is -organized from the plerome it becomes differentiated into the vascular -bundles, the pith, the pith-rays (medullary rays) which radiate from -the pith in the center between the bundles out to the cortex, and -the pericycle, a layer of cells lying between the central cylinder -and the cortex. The bundles then are farther organized into the -xylem and phloem portions with their different elements, and the -fascicular cambium (meristem) separating the xylem and phloem, as -described in <a href="#CHAPTER_V">Chapter V</a>. Such a bundle, where the xylem -and phloem portions are separated by the cambium is called an open bundle (as -in <a href="#FIG_58">fig. 58</a>). Where the phloem and xylem lie side by side in -the same radius the bundle is a <i>collateral</i> one. Dicotyledons and conifers -are characterized by open collateral bundles. This is why trees and many -<span class="pagenum"><a name="Page_361" id="Page_361">[Pg 361]</a></span> -other perennial plants continue to grow in diameter each year. -The cambium in the open bundle forms new tissue each spring and -summer, thus adding to the phloem on the outside and the xylem on -the inside. In the spring and early summer the large vessels in the -xylem predominate, while in late summer wood fibers and small vessels -predominate and this part of the wood is firmer. Since the vascular -bundles in the stem form a circle in the cylinder, this difference -in the size of the spring and late summer wood produces the “annual” -rings, so evident in the cross-section of a tree trunk. Branches -originate at the surface involving epidermis, cortex, and the bundles.</p> - -<p>In monocotyledonous plants (corn, palm, etc.) the bundles are not -regularly arranged to form a hollow cylinder, but are irregularly -situated through the stele. There is no meristem, or cambium, left -between the xylem and phloem portions of the bundle and the bundle is -thus <i>closed</i> (as in<a href="#FIG_60"> fig. 60</a>), since it all passes over -into permanent tissue. In most monocotyledons there is, therefore, practically no -annual increase in diameter of the stem.</p> - -<div class="figright"> - <img id="FIG_419" src="images/fig419.jpg" alt="" width="200" height="150" /> - <p class="center">Fig. 419.<br /> Section of stem (rhizome)<br /> - of Pteris aquilina.<br /> <i>sc</i>, thick-walled sclerenchyma;<br /> - <i>a</i>, thin-walled sclerenchyma;<br /> - <i>par</i>, parenchyma.<br /></p> -</div> - -<p><b>711. Ferns.</b>—In the ferns and most of the Pteridophytes an -apical meristem tissue is wanting, its place being taken by a single -apical cell from the several sides of which cells are successively -cut off, though Isoetes and many species of Lycopodium have an apical -meristem group. In most of the Pteridophytes also the bundles are -<i>concentric</i> instead of collateral. <a href="#FIG_418">Fig. 418</a> represents -one of the bundles from the stem of the polypody fern. The xylem is in the center, -this surrounded by the phloem, the phloem by the phloem sheath, and -this in turn by the endodermis, giving a concentric arrangement of the -component tissues. A cross-section of the stem (<a href="#FIG_419">fig. 419</a>) -shows two large areas of sclerenchyma, which gives the chief mechanical support, -the bundles being comparatively weak.</p> - -<p><b>712. Origin of root tissues.</b>—A similar apical meristem exists -in roots, but there is in addition a fourth region of formative -tissue in front of the meristem called <i>calyptrogen</i> (<a href="#FIG_420">fig. 420</a>). -This gives rise to the “root cap” which serves to protect the meristem. -The vascular cylinder in roots is very different from that of the -stem. There is a solid central cylinder in which the groups of xylem -radiate from the center and groups of phloem alternate with them but -do not extend so near the center (<a href="#FIG_421">fig. 421</a>). As the root -ages, changes take place which obscure this arrangement more or less. Branches of -the roots arise from the central cylinder. In fern roots the apical -<span class="pagenum"><a name="Page_362" id="Page_362">[Pg 362]</a></span> -meristem is replaced by a single four-sided (tetrahedral) apical cell, -the root cap being cut off by successive divisions of the outer face, -while the primary root tissues are derived from the three lateral faces.</p> - -<div class="figcenter"> - <img id="FIG_420" src="images/fig420.jpg" alt="" width="400" height="482" /> - <div class="blockquot"> - <p class="center">Fig. 420.</p> - <p>Median longitudinal section of the apex of a root of the barley, - Hordeum vulgare. <i>k</i>, calyptrogen; <i>d</i>, dermatogen; <i>c</i>, its - thickened wall; <i>pr</i>, periblem; <i>pl</i>, plerome; <i>en</i>, endodermis; <i>i</i>, - intercellular air-space in process of formation; <i>a</i>, cell row destined - to form a vessel; <i>r</i>, exfoliated cells of the root cap. - (After Strasburger.)</p> - </div> -</div> -<div class="figcenter"> - <img id="FIG_421" src="images/fig421.jpg" alt="" width="500" height="411" /> - <div class="blockquot"> - <p class="center">Fig. 421.</p> - <p>Cross-section of fibrovascular bundle in - adventitious root of Ranunculus repens. <i>w</i>, pericycle; <i>g</i>, four - radial plates of xylem; alternating with them are groups of phloem. - This is a radial bundle. (After De Bary.)</p> - </div> -</div> - -<p><b>Function of the root cap.</b>—The root cap serves an important -function in protecting the delicate meristem or cambium at the tip of -the root. These cells are, of course, very thin-walled, and while there -is not so much danger that they would be injured from dryness, since -the soil is usually moist enough to prevent evaporation, they would be -liable to injury from friction with the rough particles of soil. No -similar cap is developed on the end of the stem, but the meristem here -is protected by the overlapping bud-scales. One of the most striking -illustrations of a root cap may be seen in the case of the Pandanus, or -screw-pine, often grown in conservatories (see <a href="#FIG_447">fig. 447</a>). -On the prop roots which have not yet reached the ground the root caps can readily -be seen, since they are so large that they fit over the end of the root -like a thimble on the finger. -<span class="pagenum"><a name="Page_363" id="Page_363">[Pg 363]</a></span></p> - -<p><b>713.</b></p> -<p class="center"><b>Descriptive Classification of Tissues.</b></p> -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl br" rowspan="9">Epidermal<br /> System.····</td> - <td class="tdl_ws1" colspan="3">Epidermis.<br /> </td> - </tr><tr> - <td class="tdc_ws1 br" rowspan="7">Trichomes.</td> - <td class="tdl_ws1 bt" colspan="2">Simple hairs.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Many-celled hairs.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Branched hairs, often stellate.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Clustered, tufted hairs.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Glandular hairs.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Root hairs.</td> - </tr><tr> - <td class="tdl_ws1 bb" colspan="2">Prickles.</td> - </tr><tr> - <td class="tdl_ws1" colspan="3"> <br />Guard cells of stomates.</td> - </tr><tr> - <td class="tdc" colspan="4"> </td> - </tr><tr> - <td class="tdl br" rowspan="12">Fibrovascular<br /> System.····</td> - <td class="tdc_ws1 br" rowspan="7">Xylem (wood).</td> - <td class="tdl_ws1 bt" colspan="2">Spiral vessels.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Pitted vessels.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Scalariform vessels.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Annular vessels.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Tracheides.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Wood fibers.</td> - </tr><tr> - <td class="tdl_ws1 bb" colspan="2">Wood parenchyma.</td> - </tr><tr> - <td class="tdl_ws1" colspan="3"> <br />Cambium (fascicular).<br /> </td> - </tr><tr> - <td class="tdc_ws1 br" rowspan="4">Phloem (bast).</td> - <td class="tdl_ws1 bt" colspan="2">Sieve tubes.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Bast fibers.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Companion cells.</td> - </tr><tr> - <td class="tdl_ws1 bb" colspan="2">Bast parenchyma.</td> - </tr><tr> - <td class="tdc" colspan="4"> </td> - </tr><tr> - <td class="tdc_ws1 br" rowspan="25">Fundamental<br />System.····</td> - <td class="tdc_ws1 br" rowspan="16">Stem and root.</td> - <td class="tdc_ws1 br" rowspan="5">Cortex.····</td> - <td class="tdl_ws1 bt">Cork.</td> - </tr><tr> - <td class="tdl_ws1">Collenchyma.</td> - </tr><tr> - <td class="tdl_ws1">Parenchyma.</td> - </tr><tr> - <td class="tdl_ws1">Fibers.</td> - </tr><tr> - <td class="tdl_ws1 bb">Milk tissue.</td> - </tr><tr> - <td class="tdl_ws1"> </td> - </tr><tr> - <td class="tdc_ws1 br" rowspan="2">Pith-ray.··</td> - <td class="tdl_ws1 bt">Parenchyma.</td> - </tr><tr> - <td class="tdl_ws1 bb">Intrafascicular cambium.</td> - </tr><tr> - <td class="tdl_ws1"> </td> - </tr><tr> - <td class="tdl_ws1"> </td> - </tr><tr> - <td class="tdc_ws1 br" rowspan="2">Pith.······</td> - <td class="tdl_ws1 bt">Parenchyma.</td> - </tr><tr> - <td class="tdl_ws1 bb">Sclerenchyma.</td> - </tr><tr> - <td class="tdl_ws1"> </td> - </tr><tr> - <td class="tdl_ws1" colspan="2">Bundle-sheath.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2"><br />Endodermis.</td> - </tr><tr> - <td class="tdl_ws1" colspan="3"> </td> - </tr><tr> - <td class="tdl_ws1" colspan="3"> </td> - </tr><tr> - <td class="tdc_ws1 br" rowspan="2">Leaves.</td> - <td class="tdl_ws1 bt" colspan="2">Palisade tissue.</td> - </tr><tr> - <td class="tdl_ws1 bb" colspan="2">Spongy parenchyma.</td> - </tr><tr> - <td class="tdl_ws1" colspan="3"> </td> - </tr><tr> - <td class="tdl_ws1" colspan="3">Reproductive Organs (mainly fundamental).</td> - </tr> - </tbody> -</table> - -<p class="space-above2"><span class="pagenum"><a name="Page_364" id="Page_364">[Pg 364]</a></span> -<b>714. Physiological Classification of Tissues.</b></p> - -<p><i>Formative Tissue.</i></p> - -<p>Thin-walled cells composing the meristem, capable of division and from -which other tissues are formed.</p> - -<p><i>Protective Tissue.</i></p> - -<p><i>Tegumentary System.</i>—Epidermis, periderm, bark protecting the plant -from external contact.</p> - -<p><i>Mechanical System.</i>—Bast tissue, bast-like tissue, collenchyma, -sclerenchyma, afford protection against harmful bending, pulling, etc.</p> - -<p><i>Nutritive Tissues.</i></p> - -<p><i>Absorptive System.</i>—Root hairs and cells, rhizoids, aerial root -tissue, absorptive leaf glands, absorptive organs in seeds, haustoria -of parasites, etc.</p> - -<p><i>Assimilatory System.</i>—Assimilating cells in leaf and stem.</p> - -<p><i>Conductive System.</i>—Sieve tissue, tracheary tissue, milk tissue, -conducting parenchyma, etc.</p> - -<p><i>Food-storing System.</i>—Water reservoir, water tissue, slime tissue, -fleshy roots and stems, endosperm and cotyledons, etc.</p> - -<p><i>Aerating System.</i>—Air spaces and tubes, special air tissue, -air-seeking roots, stomates, lenticels, etc.</p> - -<p><i>Secretory and Excretory System.</i>—Water glands, digestive glands, -resin glands, nectaries, tannin, pitch and oil receptacles, etc.</p> - -<p><i>Apparatus and Tissues for Special Duties.</i></p> - -<p>Holdfasts.</p> - -<p>Tissues of movement, parachute hairs, floating tissue, hygroscopic -tissue, living tissue.</p> - -<p>For perceiving stimuli.</p> - -<p>For conducting stimuli, etc.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_365" id="Page_365">[Pg 365]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XXXIX" id="CHAPTER_XXXIX">CHAPTER XXXIX.</a><br /> -<span class="h_subtitle">THE DIFFERENT TYPES OF STEMS.<br /> WINTER SHOOTS AND BUDS.</span></h3> -</div> - -<h4><a name="XXXIX_1" id="XXXIX_1">I. Erect Stems.</a></h4> - -<p><b>715. Columnar type.</b>—The columnar type of stem may be simple or -branched. When branching occurs the branches are usually small and in -general subordinate to the main axis. The sunflower (Helianthus annuus) -is an example. The foliage part is mainly simple. The main axis remains -unbranched during the larger part of the growth-period. The principal -flowerhead terminates the stem. Short branches bearing small heads -then arise in the axils of a few of the upper leaves. In dry, poor -soil, or where other conditions are unfavorable, there may be only the -single terminal flowerhead, when the stem is unbranched. The mullein -is another columnar stem. The foliage part is rarely branched, though -branches sometimes occur where the main axis has become injured or -broken. The flower stem is terminal. The corn plant and the Easter lily -are good illustrations also of the columnar stem.</p> - -<p>Among trees the Lombardy poplar (Populus fastigiata) is an excellent -example of the columnar type. Though this is profusely branched, the -branches are quite slender and small in contrast with the main axis, -unless by some injury or other cause two large axes may be developed. -As the technical name indicates, the branching is fastigiate, i.e., the -branches are crowded close together and closely surround the central -axis. The royal palm and some of the tree ferns have columnar, simple -<span class="pagenum"><a name="Page_366" id="Page_366">[Pg 366]</a></span> -stems, but the large, wide-spreading leaves at the top of the stem give -the plant anything but a cylindrical habit. Some cedars and arbor-vitæ -are also columnar.</p> - -<p>The advantages of the columnar habit of stem are three: (1) That the -plant stands above other neighboring ones of equal foliage area and -thus is enabled to obtain a more favorable light relation; (2) where -large numbers of plants of the same species are growing close together, -they can maintain practically the same habit as where growing alone; -(3) the advantage gained by other types in their neighborhood in less -shading than if the type were spreading. The cylindrical type can, -therefore, grow between other types with less competition for existence.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_422" src="images/fig422.jpg" alt="" width="150" height="429" /> - <p class="center">Fig. 422.<br /> Cylindrical stem<br /> of mullein.</p> - </div> - <div class="figsub"> - <img id="FIG_423" src="images/fig423.jpg" alt="" width="300" height="445" /> - <p class="center">Fig. 423.<br /> Conical type of larch.</p> - </div> -</div> - -<p><b>716. The cone type.</b>—This is well exampled in the larches, -spruces, the gingko tree, some of the pines, cedars, and other -gymnosperms. In the cone type, the main axis extends through the system -of branches like a tall shaft, i.e., the trunk is <i>excurrent</i>. The -lower branches are wide-spreading, and the branches become successively -shorter, usually uniformly, as one ascends the stem. The branching is -of two types: (1) the branches are in false whorls; (2) the branches are -<span class="pagenum"><a name="Page_367" id="Page_367">[Pg 367]</a></span> -distributed along the stem. To the first type belong the pines, Norway -spruce, Douglas spruce, etc. <i>The white pine</i> is an exquisite example, -and in young and middle-aged trees shows the style of branching to -very good advantage. The branches are nearly horizontal, with a -slight sigmoid graceful curve, while towards the top the branches are -ascending. This direction of the branches is due to the light relation. -The few whorls at the top are ascending because of the strong light -from above. They soon become extended in a horizontal direction as the -main source of light is shifting to the side by the shading of the top. -The ascending direction first taken by the upper branches and their -subsequent turning downward, while the ends often still have a slight -ascending direction gives to the older branches their sigmoid curve.</p> - -<p>The young vernal shoots of the pines show some very interesting -growth movements. There are two growth periods: (1) the elongation of -the shoot, and (2) the elongation of the leaves. The elongation of the -shoot takes place first and is completed in about six weeks or two -months’ time. The direction of the shoot in the first period seems to -be entirely influenced by geotropism. It grows directly upward and -stands up as a very conspicuous object in strong contrast with the dark -green foliage of the more or less horizontal shoots. When the second -period of growth takes place, and the leaves elongate, the shoot bends -downward and outward in a lateral direction.</p> - -<p>The rate of growth of the pines can be very easily observed since each -<span class="pagenum"><a name="Page_368" id="Page_368">[Pg 368]</a></span> -whorl of branches (between the whorls of long shoots there are short -shoots bearing the needle leaves), whether on the main axis or on the -lateral branches, marks a year, the new branches arising each year -at the end of the shoot of the previous year. The rate of growth is -sometimes as high as twelve to twenty-four inches or more per year.</p> - -<p>The <i>spruces</i> form a more perfect cone than the pines. The long -branches are mostly in whorls, but often there are intermediate ones, -though the rate of growth per year can usually be easily determined. In -the <i>hemlock-spruce</i>, the branching is distributed. The <i>larch</i> has a -similar mode of branching, but it is deciduous, shedding its leaves in -the autumn, and it has a tall, conical form.</p> - -<p>It would seem that trees of the cone type possessed certain advantages -in some latitudes or elevations over other trees. (1) A conical tree, -like the spruces and larches and the pines, and hemlocks also, before -they get very old, meets with less injury during high winds than trees -of an oval or spreading type. The slender top of the tree where the -force of the wind is greatest presents a small area to the wind, while -the trunk and short slender branches yield without breaking. Perhaps -this is one reason why trees of this type exist in more northern -latitudes and at higher elevations in mountainous regions, and why -the spruce type reaches a higher latitude and altitude even than the -pines. (2) The form of the tree is such as to admit light to a large -foliage area, even where the trees are growing near each other. The -evergreen foliage, persistent for several years, on the wide-spreading -lower branches, probably affords some protection to the trees since -this cover would aid in maintaining a more equable temperature in the -forest cover than if the trees were bare during the winter. (3) There -is less danger of injury from the weight of snow since the greater -load of snow would lie on the lower branches. The form of the branches -also, especially in the spruces, permits them to bend downward without -injury, and if necessary unload the snow if the load becomes too heavy.</p> - -<p><b>717. The oval type.</b>—This type is illustrated by the oak, -<span class="pagenum"><a name="Page_369" id="Page_369">[Pg 369]</a></span> -chestnut, apple, etc. The trees are usually deciduous, i.e., cast -their leaves with the approach of winter. The main axis is sometimes -maintained, but more often disappears (trunk is <i>deliquescent</i>), -because of the large branches which maintain an ascending direction, -and thus lessen the importance of the central axis which is so marked -in the cone type. Trees of this type, and in fact all deciduous trees, -exhibit their character or habit to better advantage during the winter -season when they are bare. Trees of this type are not so well adapted -to conditions in the higher altitudes and latitudes as the cone type, -for the reason given in the discussion of that type. The deciduous -habit of the oaks, etc., enables them to withstand heavy winds far -better than if they retained their foliage through the winter, even -were the foliage of the needle kind and adapted to endure cold.</p> - -<p><b>718. The deliquescent type.</b>—The elm is a good illustration of -this type. The main axes and the branches fork by a false dichotomy, so -that a trunk is not developed except in the forest. The branches rise -at a narrow angle, and high above diverge in the form of an arch. The -chief foliage development is lofty and spreading.</p> - -<p>Trees possess several advantages over vegetation less lofty. They may -start their growth later, but in the end they outgrow the other kinds, -shade the ground and drive out the sun-loving kinds.</p> - -<h4><a name="XXXIX_2" id="XXXIX_2">II. Creeping, Climbing, and Floating Stems.</a></h4> - -<p><b>719. Prostrate type.</b>—This type is illustrated by creeping or -procumbent stems, as the strawberry, certain roses, of which a good -type is one of the Japanese roses (Rosa wichuriana), which creeps very -close to the ground, some of the raspberries, the cucurbits like the -squash, pumpkin, melons, etc. These often cover extensive areas by -branching and reaching out radially on the ground or climbing over low -objects. The cucurbits should perhaps be classed with the climbers, -since they are capable of climbing where there are objects for support, -<span class="pagenum"><a name="Page_370" id="Page_370">[Pg 370]</a></span> -but they are prostrate when grown in the field or where there are no -objects high enough to climb upon. In the prostrate type, there is -economy in stem building. The plants depend on the ground for support, -and it is not necessary to build strong, woody trunks for the display -of the foliage which would be necessary in the case of an erect plant -with a foliage area as great as some of the prostrate stems. This -gain is offset, at least to a great extent, by the loss in ability to -display a great amount of foliage, which can be done only on the upper -side of the stem.</p> - -<div class="figcenter"> - <img src="images/fig424.jpg" alt="" width="500" height="318" /> - <p class="center">Fig. 424.<br /> Prostrate type of the water fern (<i>marsilia</i>).</p> -</div> - -<p>Other advantages gained by the prostrate stems are protection from -wind, from cold in the more rigorous climates, and some propagate -themselves by taking root here and there, as in certain roses, the -strawberry plant, etc. Some plants have erect stems, and then send -out runners below which take root and aid the plant in spreading and -multiplying its numbers.</p> - -<p><b>720. The decumbent type.</b>—In this type the stem is first erect, -but later bends down in the form of an arch, and strikes root where the tip -touches the ground. Some of the raspberries and blackberries are of this type. -<span class="pagenum"><a name="Page_371" id="Page_371">[Pg 371]</a></span></p> - -<p><b>721. The climbing type.</b>—The grapes, clematis, some roses, the -ivies, trumpet-creeper, the climbing bittersweet, etc., are climbing -stems. Like the prostrate type, the climbers economize in the material -for stem building. They climb over shrubs, up the trunks of trees and -often reach to a great height and acquire the power of displaying a -great amount of foliage by sending branches out on the limbs of the -trees, sometimes developing an amount of foliage sufficient to cover -and nearly smother the foliage of large trees; while the main stem of -the vine may be not over two inches in diameter and the trunk of the -supporting tree may be three feet in diameter.</p> - -<p><b>722. Floating stems.</b>—These are necessarily found in aquatic -plants. The stems may be ascending or horizontal. The stems are -usually not very large, nor very strong, since the water bears them -up. The plants may grow in shallow water, or in water 10-12 feet or -more deep, but the leaves are usually formed at or near the surface of -the water in order to bring them near the light. Various species of -Potamogeton, Myriophyllum, and other plants common along the shores of -lakes, in ponds, sluggish streams, etc., are examples. Among the algæ -are examples like Chara, Nitella, etc., in fresh water; Sargassum, -Macrocystis, etc., in the ocean. In these plants, however, the plant -body is a thallus, which is divided into stem-like (<i>caulidium</i>) -and leaf-like (<i>phyllidium</i>) structures.</p> - -<p><b>723. The burrowing type, or rhizomes.</b>—These are horizontal, -subterranean stems. The bracken fern, sensitive fern, the mandrake -(see <a href="#FIG_413A">fig. 413<i>a</i></a>), Solomon’s seal, Trillium, Dentaria, -and the like, are examples. The subterranean habit affords them protection from the -cold, the wind, and from injury by certain animals. Many of these stems -act as reservoirs for the storage of food material to be used in the -rapid growth of the short-lived aerial shoot. In the ferns mentioned, -the subterranean is the only shoot, and this bears scale leaves which -are devoid of chlorophyll, and foliage leaves which are larger, and the -only member of the plant body which is aerial. The foliage leaf has -<span class="pagenum"><a name="Page_372" id="Page_372">[Pg 372]</a></span> -assumed the function of the aerial shoot. The latter is not necessary -since flowers are not formed. The mandrake, Solomon’s seal, Trillium, -etc., have scale leaves on the fleshy underground stems, while foliage -leaves are formed on the aerial stems, the latter also bearing the -flowers. Some of the advantages of the rhizomes are protection from -injury, food storage for the rapid development of the aerial shoot, -and propagation.</p> - -<p>Many of the grasses have subterranean stems which ramify for great -distances and form a dense turf. For the display of foliage and for -flower and seed production, aerial shoots are developed from these -lateral upright branches.</p> - -<h4><a name="XXXIX_3" id="XXXIX_3">III. Specialized Shoots and Shoots for Storage of Food.</a><a name="FNanchor_40_40" id="FNanchor_40_40"></a><a href="#Footnote_40_40" class="fnanchor">[40]</a></h4> - -<p><b>724. The bulb.</b>—The bulb is in the form of a bud, but the scale -leaves are large, thick, and fleshy, and contain stored in them food -products manufactured in the green aerial leaves and transported to -the underground bases of the leaves. Or when the bulb is aerial in its -formation, it is developed as a short branch of the aerial stem from -which the reserve food material is transported. Examples are found -in many lilies, as Easter lily, Chinese lilies, onion, tulip, etc. -The thick scale leaves are closely overlapped and surround the short -stem within (also called a <i>tunicated</i> stem). In many lilies there -is a sufficient<span class="pagenum"><a name="Page_373" id="Page_373">[Pg 373]</a></span> -amount of food to supply the aerial stem for the development of flower -and seed. There are roots, however, from the bulb and these acquire -water for the aerial shoot, and when planted in soil additional food is -obtained by them.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p> </p> - <img src="images/fig425.jpg" alt="" width="300" height="279" /> - <p class="center">Fig. 425.<br /> Bulb of hyacinth.</p> - </div> - <div class="figsub"> - <img src="images/fig426.jpg" alt="" width="225" height="300" /> - <p class="center">Fig. 426.<br /> Corm of Jack-in-the-pulpit.</p> - </div> -</div> - -<p><b>725. Corm.</b>—A corm is a thick, short, fleshy, underground stem. -A good example is found in the jack-in-the-pulpit (Arisæma).</p> - -<p><b>726. Tubers.</b>—These are thickened portions of the subterranean -stems. The most generally known example is the potato tuber (“Irish” -potato, not the sweet potato, which is a root). The “eyes” of the -potato are buds on the stem from which the aerial shoots arise when the -potato sprouts. The potato tuber is largely composed of starch which is -used for food by the young sprouts.</p> - -<p><b>726</b><i>a</i>. <b>Phylloclades.</b>—These are trees, shrubs, or -herbs in which the leaves are reduced to mere bracts and stems, -are not only green and function as leaves, but some or all of the -branches are flattened and resemble leaves in form as in Phyllanthus, -Ruscus, Semele, Asparagus, etc. The flowers are borne directly on -these flattened axes. The prickly-pear cactus (Opuntia) is also -a phylloclade. Examples of phylloclades are often to be found in -greenhouses.</p> - -<p><b>727. Undifferentiated stems</b> are found in such plants as the -duckweed, or duckmeat (Lemna, Wolffia, etc.<a href="#CHAPTER_III"> See Chapter III</a>). -<span class="pagenum"><a name="Page_374" id="Page_374">[Pg 374]</a></span></p> - -<h4><a name="XXXIX_4" id="XXXIX_4">IV. Annual Growth and Winter Protection of Shoots and Buds.</a><a name="FNanchor_41_41" id="FNanchor_41_41"></a><a href="#Footnote_41_41" class="fnanchor">[41]</a></h4> - -<p><b>728. Winter conditions.</b><a name="FNanchor_42_42" id="FNanchor_42_42"></a><a href="#Footnote_42_42" class="fnanchor">[42]</a>—While -herbs are subjected only to the damp warm atmosphere of summer, woody -plants are also exposed during the cold dry winter, and must protect -themselves against such conditions. The air is dryer in winter than in -summer; while at the same time root absorption is much retarded by the -cold soil. Then, too, the osmotic activity of the dormant twig-cells -being much reduced, the water-raising forces are at a minimum. It -is easy to see, therefore, that a tree in winter is practically -under desert conditions. Moreover, it has been found by various -investigators, contrary to the general belief, that cold in freezing is -only indirectly the cause of death. The real cause is the abstraction -of water from the cell by the ice crystals forming in the intercellular -spaces. Death ensues because the water content is reduced below the -danger-point for that particular cell. It was formerly thought that on -freezing, the cells in the tissue were ruptured. This is not so. Ice -almost never forms within the cell, but in the spaces between. Freezing -then is really a drying process, and dryness, not cold, causes death -in winter. To protect themselves in winter, trees provide various -waterproof coverings for the exposed surfaces and reduce the activity -of the protoplasm so that it will be less easily harmed by the loss of -water abstracted by the freezing process.</p> - -<div class="figcenter"> - <img src="images/fig427.jpg" alt="" width="600" height="100" /> - <div class="blockquot"> - <p class="center">Fig. 427.</p> - <p>Two-year-old twig of horse-chestnut, showing buds and leaf-scars. (A - twig with a terminal bud should have been selected for this figure.)</p> - </div> -</div> - -<p><b>729. Protection of the twig.</b>—Woody plants protect the living -cells within the twigs by the production of a dull or rough corky bark, -<span class="pagenum"><a name="Page_375" id="Page_375">[Pg 375]</a></span> -or by a thick glossy epidermis over the entire surface. At intervals -occur small whitish specks called lenticels, which here perform nearly -the same function as do stomates in the leaf.</p> - -<p><b>730. Bark of trunk.</b>—A similar service is performed by the -bark for the main trunk and branches of the tree. To admit of growth -in diameter the old bark is constantly being thrown off in strips, -flakes, etc., and replaced by a new but larger cylinder of young bark. -The external appearance thus produced enables experienced persons to -recognize many kinds of trees by the trunk alone.</p> - -<p><b>731. Leaf-scars and bundle-scars.</b>—The presence of foliage -leaves during the winter would greatly increase the transpiring surface -without being of use to the plant; hence they are usually thrown off on -the approach of winter. The scars left by the fallen leaves are termed -leaf-scars. The small dots on the leaf-scars left by the vascular -bundles which extended through the petiole into the twig are termed -bundle-scars. Sometimes stipule-scars are left on each side of the -leaf-scar by the fallen stipules.</p> - -<p><b>732. Nodes and internodes.</b>—The region upon a stem where a leaf -is borne is termed a node. The space between two nodes is an internode.</p> - -<div class="figcenter"> - <img src="images/fig428.jpg" alt="" width="600" height="99" /> - <div class="blockquot"> - <p>Fig. 428.—Shoot of butternut showing leaf-scars, axillary buds, - and adventitious buds (buds coming from above the axils).</p> - </div> -</div> -<div class="figcenter"> - <img src="images/fig429.jpg" alt="" width="600" height="81" /> - <p class="center space-below2">Fig. 429.—Shoot and bud of white oak.</p> -</div> - -<p><b>733. Phyllotaxy.</b>—Investigation of a horse-chestnut or willow -twig will show that the leaf-scars occupy definite positions which -are constant for each plant but different for the two species. -The arrangement of the leaves on the stem in any plant is termed -phyllotaxy. In the horse-chestnut we find two scars placed at the same -node, but on opposite sides of the stem. Somewhat higher up we find two -more similarly placed, but in a position perpendicular to that of the -first pair. Such phyllotaxy is termed opposite. If in any plant several -leaves occur at a node, the phyllotaxy is whorled. If but one at each -node, as in the willow, the phyllotaxy is alternate. The opposite and -alternate types are very commonly met with. Closer observation will -show that in the willow, if a line be drawn connecting the successive -leaf-scars, it will pass spirally up the twig until at length a scar is -reached directly over the one taken as a starting-point. Such spiral -arrangement always accompanies alternate phyllotaxy. The section of the -spiral thus delineated is termed a cycle. We express the nature of the -<span class="pagenum"><a name="Page_376" id="Page_376">[Pg 376]</a></span> -cycle by the fractions ½, ⅓, ⅖, ⅜, ⁵/₁₃, etc., in which the numerator -denotes the number of turns around the stem in each cycle, and the -denominator the number of leaf-scars in the same distance. In a general -way we find in plants only such arrangements as are represented by -the fractions given above. These fractions show the curious condition -that the numerator and denominator of each is equal to the sum of -the numerator or denominator of the two preceding fractions. Much -speculation has been indulged in regarding the significance of these -definite laws of leaf arrangement. In part they may be due to the -desire that each leaf receive the maximum amount of light. Only certain -definite geometrical conditions will insure this. More likely it is due -to the economy of space allotted to the leaf-fundaments in the bud. -Here, again, geometrical laws govern this economy. The phyllotaxy is -nearly constant for a given species.</p> - -<p><b>734. Buds.</b>—The growing point of the stem or branch together -with its leaf or flower fundaments and protective structures is termed -a bud. Winter buds on woody plants are terminal when inclosing the -growing point of the main axis of the twig; lateral when the growing -point is that of a branch of the main axis. Lateral buds are always -axillary, i.e., situated on the upper angle between a leaf and the main axis.</p> - -<p><b>735. Buds occupying special positions.</b>—Several species of trees -and shrubs produce more than one bud in each leaf-axil. The additional -<span class="pagenum"><a name="Page_377" id="Page_377">[Pg 377]</a></span> -ones are termed accessory or supernumerary buds. These may be lateral -to one another or they may be superposed as in the walnut or butternut. -In such cases some of the buds usually contain simply floral shoots and -are termed flower buds. In some species buds are frequently produced -on the side of the branches and trunk at some distance from the -leaf-axils, and entirely without regard for the latter; or more rarely -may occur upon the root. Such buds are termed adventitious, and are the -source of the feathery branchlets upon the trunks of the American elm.</p> - -<p><b>736. Branching follows the phyllotaxy.</b>—Since the lateral or -branch-producing buds are always located in the axil of a leaf, the -branches necessarily follow the same arrangement upon the main axis -as do the leaves. Since, however, many of the axillary buds fail to -develop, this arrangement may be more or less obscured.</p> - -<div class="figleft"> - <img src="images/fig430.jpg" alt="" width="200" height="400" /> - <p class="center">Fig. 430.<br /> Bud of European elm<br /> - in section, showing<br /> overlapping of scales.<br /></p> -</div> - -<p><b>737. Coverings of winter buds.</b>—These are of two sorts, hair -and cork, or scales. Buds protected simply by dense hair or sunk in -the cork of the twig are termed naked buds, and are comparatively -rare. Most species protect their buds by the addition of an imbricated -covering of closely appressed scales, the whole frequently being -rendered still more waterproof by the excretion of resin between the -scales or over the whole surface. The scales when studied carefully -are found to be much reduced leaves or parts of leaves. In some cases -they represent a modified whole leaf, when they are said to be laminar, -or a leaf-petiole, when they are petiolar, or stipular, when they are -much-specialized stipules of a leaf which itself is usually absent. The -latter type is much the less common. The form of the bud, the nature -and form of the scales, when combined with characters furnished by the -leaf- and bundle-scars, enable one to recognize and classify the winter -twigs of the various woody species.</p> - -<p><b>738. Phyllotaxy of the bud-scales.</b>—Since the bud-scales are -leaves, they follow a definite phyllotaxy. This may or may not be -the same as that of the foliage leaves. Twigs with opposite leaves -have opposite bud-scales, or if with alternate leaves, then alternate -bud-scales, but the fractions vary. If the scales are stipular, then -there are of course two at each node. -<span class="pagenum"><a name="Page_378" id="Page_378">[Pg 378]</a></span></p> - -<p><b>739. Function of the bud coverings.</b>—It is popularly believed -that the scales and hairy coverings serve to keep the bud warm. -Research, however, shows this to be almost entirely erroneous, and that -the thin bud coverings are entirely inadequate to keep out the cold of -winter. They cannot keep the bud even a degree or two warmer than the -outside air, except when the changes are very rapid. Experiment also -shows that the modifying effect of the covering when the bud thaws -out is so slight as to be almost negligible. Indeed, a thermometer -bulb covered with scales taken from a horse-chestnut bud warmed up -more rapidly than a naked one when exposed to sunshine. The wool in -the horse-chestnut bud is not for the purpose of keeping it warm, but -to protect the young shoot from too great transpiration after the bud -opens the following spring. Research has also shown that such tempering -of the heat conditions is not especially beneficial to the plant, -as was once thought. Neither can we find the main function in the -prevention of water from entering the bud. This might be accomplished -in much simpler ways, even if we could demonstrate the desirability of -keeping the water out at all.</p> - -<p>The true functions of the bud-scales are two in number: Firstly, the -prevention of too great loss of water from the young and delicate -parts within; and secondly, the protection of these same parts from -mechanical injury. Without some such protection the delicate young -structures would be beaten off by the wind, or become the food for -hungry birds during the long winter months. -<span class="pagenum"><a name="Page_379" id="Page_379">[Pg 379]</a></span></p> - -<div class="figcenter"> - <img src="images/fig431.jpg" alt="" width="400" height="508" /> - <p class="center space-below2">Fig. 431.<br /> Opening buds of hickory.</p> -</div> - -<p><b>740. Opening of the buds.</b>—When the young shoot begins to -grow in the spring, the bud-scales are forced apart or open of their -own accord. During the young condition the shoot is very soft and -brittle, and also possesses a very thin, little cutinized epidermis. -In this condition it is especially liable to mechanical injury and to -injury from drying out. We find, therefore, a tendency for the inner -bud-scales to elongate during vernation, thus forming a tube around the -delicate tissue much like the opening out of a telescope. The young -<span class="pagenum"><a name="Page_380" id="Page_380">[Pg 380]</a></span> -leaves and internodes themselves are often provided with a woody or -hairy covering to retard transpiration. When the epidermis becomes more -efficient the hairy covering often falls away.</p> - -<p>In the case of naked buds protection is afforded in other ways: by -the protection of hairy covering, by physiological adaptation of the -tissue, or in many cases by the late appearance of the shoot in spring -after the very dry April and May winds have ceased.</p> - -<p><b>741. Bud-scars, and how to tell the age of the plant.</b>—In -general the bud-scales when they fall away in the spring leave scars -termed scale-scars, and the whole aggregate of scale-scars makes up the -bud-scar. The position of the buds of previous winters is, therefore, -marked. It becomes an easy matter to determine the age of a branch, -since all that is necessary is to follow back from one bud-scar to -another, the portion of the stem between representing, except in rare -cases, one year’s growth.</p> - -<p>A woody plant grows in height only by the formation of new sections -of stem added to the apex or side of similar sections produced the -previous season, never, as is commonly supposed, by the further -elongation of the previous year’s growth. Hence a branch once formed -upon a tree is fixed as regards its distance from the ground. The -apparent rise of the branches away from the ground in forest trees is -an illusion caused by the dying away of the lower branches.</p> - -<p><b>742. Definite and indefinite growth.</b>—With the opening of the -buds in spring, growth begins. In some cases, when all the members -for the season were formed, but still minute, within the bud, such -growth consists solely in the expansion of parts already formed; in -others only a few members are thus present to expand, while new ones -are produced by the growing point as the season progresses. In most -cases growth is completed by the middle of July, soon after which buds -are formed for next year’s growth. Such a method of growth is termed -definite.</p> - -<p>In a few woody plants, as, for example, sumach, locust, and raspberry, -growth continues until late in the autumn. In such cases the most -recently formed nodes and internodes are unable to become sufficiently -<span class="pagenum"><a name="Page_381" id="Page_381">[Pg 381]</a></span> -“hardened” before winter sets in, and are killed back more or less. -Next season’s shoot is a branch from some axillary bud. Such growth is -termed indefinite.</p> - -<div class="figcenter"> - <img src="images/fig432.jpg" alt="" width="400" height="482" /> - <p class="center space-below2">Fig. 432.<br /> Three-year-old twig of the American ash,<br /> - with sections of each year’s growth<br /> showing annual rings.</p> -</div> - -<p><b>743. Structure of woody stems.</b>—If we make a cross-section of a -woody twig three general regions are presented to view. On the outside -is the rather soft, often greenish “bark,” so called, made up of -sieve tubes, ordinary parenchyma cells, and in many cases long fibrous -cells composing the “fibrous bark.” From a growing layer in this region, -termed the phellogen, the true corky bark of the older trunk is formed.</p> - -<p>Next within the bark we find the so-called “woody” portion of the -twig. This is strong and resistant to both breaking and cutting. The -microscope shows it to be composed of the ordinary already known woody -elements,<a name="FNanchor_43_43" id="FNanchor_43_43"></a><a href="#Footnote_43_43" class="fnanchor">[43]</a> -wood fibers, for strengthening purposes, pitted and spiral vessels as -conducting tissue; and intermixed with these some living parenchyma -cells. A cross-section of the stem also shows narrow radial lines -through the wood. These are pith-rays, composed of vertical plates of -living parenchyma cells. These cells, unlike the others in the wood, -are elongated radially, not vertically. The height of the pith-rays -as well as their thickness varies with the species studied. In the -older trunk only the outer portion, a few inches in thickness, remains -light-colored and fresh, and is called sap-wood. The inner wood is -usually darker and harder, and is termed heart-wood. Living parenchyma -cells, in general, are present only in the sap-wood, and in this almost -solely the ascent of sap occurs. Dyestuffs and other substances are -frequently deposited in the walls of the heart-wood.</p> - -<p><span class="pagenum"><a name="Page_382" id="Page_382">[Pg 382]</a></span> -The third region occupying the center of the twig is the pith. This is -composed ordinarily of angular, little elongated, parenchyma cells, -when mature mostly without cell-contents and filled with air. The pith -region in different trees is quite diversified. It may be hollow, -chambered, contain scattered thick-walled cells, have woody partitions, -or rarely be entirely thick-walled.</p> - -<p>The nature of the woody ring is rather perplexing at first; but -its origin is simple. We may conceive that it has developed from a -stem-type like the sunflower, in which the bundles, though separate, -are connected by a continuous cambium ring. In the woody twigs the -numerous bundles are closely packed together, and only separated by -the primary pith-rays extending from the pith to the cortex. Other -secondary pith-rays are produced within each bundle, but they usually -extend only part way from the cortex to the pith. The wood represents -the xylem of the bundle, and the sieve tubes of the bark, the phloem.</p> - -<p><b>744. Growth in thickness.</b>—Although the year’s growth does not -increase in length after the first season has passed, it does increase -in diameter very much. From the size of an ordinary little twig it may -at length become a large tree trunk several feet in thickness. Only a -portion of the first year’s growth is produced by the growing point. -All the rest is a product of the cambium, a cylinder of wood being -added to the exterior of the old wood each season. The cambium, here, -as in the sunflower, lies between the phloem and the xylem, forming a -cylinder entirely around the stem. In spring, when active, it becomes -soft and delicate, thus enabling one to easily strip off the bark from -some trees, such as willow, etc., at that season.</p> - -<p><b>745. Annual rings in woody stems.</b>—The wood produced by the -cambium each season is not homogeneous throughout, but is usually much -denser toward the outer part of the yearly cylinder, wood fibers here -predominating. In the inner portion vessels predominate, giving a much -more porous effect. The transition from one year’s growth to another is -very abrupt, giving rise to the appearance of rings in cross-section. -Since ordinarily in temperate climates but one cylinder of wood is -added each year, the number of rings will indicate the age of the trunk -or branch. This is not absolutely accurate, since in some trees under -certain conditions more than one ring may be produced in a summer. The -porous part of the ring is often termed “spring wood,” and the denser -portion “fall wood,” but since growth from the cambium ceases in most -trees by the middle of July, “summer wood” would be more appropriate -for the latter. It is mainly the alternation of the cylinders of the -spring and summer wood that gives the characteristic grain to lumber. -Pith-rays play an important part in wood graining only in a few woods, -as, for instance, in quartered oak. The reason for the production of -porous spring wood and dense summer wood is still one of the unsolved -problems of botany.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_383" id="Page_383">[Pg 383]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XL" id="CHAPTER_XL">CHAPTER XL.</a><br /> -<span class="h_subtitle">FOLIAGE LEAVES.</span></h3> -</div> - -<h4><a name="XL_1" id="XL_1">I. General Form and Arrangement of Leaves.</a></h4> - -<p><b>746. Influence of foliage leaves on the form of the stem.</b>—The -marked effect which foliage has upon the aspect of the plant or upon -the landscape is evident to all observers. Perhaps it is usual to -look upon the stem as having been developed for the display of the -foliage without taking into account the possibility that the foliage -may have a great influence upon the form or habit of the stem. It is -very evident, however, that the foliage exercises a great influence -on the form of the stem. For example, as trees increase in age and -size, the development of branches on the interior ceases and some of -those already formed die, since the dense foliage on the periphery -of the trees cuts off the necessary light stimulus. The tree, -therefore, possesses fewer branches and a more open interior. In the -forest also, the dense foliage above makes possible the shapely, -clean timber trunks. Note certain trees where by accident, or by -design, the terminal foliage-bearing branches have been removed that -foliage-bearing branches may arise in the interior of the tree system.</p> - -<p>Without foliage leaves the stems of green plants would develop a very -different habit from what they do. This development could take place in -three different directions under the influence of light: (1) The light -stimulus would induce profuse branching, so that there would be many -small branches. (2) The stem would develop fewer branches, but they -would be flattened. (3) Massive trunks with but few or no branches. In -<span class="pagenum"><a name="Page_384" id="Page_384">[Pg 384]</a></span> -fact, all these forms are found in certain green stems which do not -bear leaves. An example of the first is found in asparagus with its -numerous crowded slender branches. But such forms in our climate are -rare, since foliage leaves are more efficient. The second and third -forms are found among cacti, which usually grow in dry regions under -conditions which would be fatal to ordinary thin foliage leaves.</p> - -<p><b>747. Relation of foliage leaves to the stem.</b>—In the study -of the position of the leaves on the stem we observe two important -modes of distribution: (1) the distribution along the individual -stem or branch which bears them, usually classed under the head of -<i>Phyllotaxy</i>; (2) the distribution of the leaves with reference to the -plant as a whole.</p> - -<p><b>748. Phyllotaxy, or arrangement of leaves.</b>—In examining buds on -the winter shoots of woody plants, we cannot fail to be impressed with -some peculiarities in the arrangement of these members on the stem of -the plant.</p> - -<p>In the horse-chestnut, as we have already observed, the leaves are in -pairs, each one of the pair standing opposite its partner, while the -pair just below or above stand across the stem at right angles to the -position of the former pair. In other cases (the common bed-straw) the -leaves are in whorls, that is, several stand at the same level on the -axis, distributed around the stem. By far the larger number of plants -have their leaves arranged alternately. A simple example of alternate -leaves is presented by the elm, where the leaves stand successively on -alternate sides of the stem, so that the distance from one leaf to the -next, as one would measure around the stem, is exactly one half the -distance around the stem. This arrangement is one half, or the angle of -divergence of one leaf from the next is one half. In the case of the -sedges the angle of divergence is less, that is one-third.</p> - -<p>By far the larger number of those plants which have the alternate -arrangement have the leaves set at an angle of divergence represented -by the fraction two fifths. Other angles of divergence have been -discovered, and much stress has been laid on what is termed a law in -the growth of the stem with reference to the position which the leaves -occupy. Singularly by adding together the numerators and denominators -of the last two fractions gives the next higher angle of divergence. -Example:</p> - -<table class="lgfnt150" border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdc bb">1</td> - <td class="tdc"> + </td> - <td class="tdc bb">2</td> - <td class="tdc" rowspan="2"> = </td> - <td class="tdr bb">3</td> - <td class="tdc" rowspan="2">;  </td> - <td class="tdc bb">2</td> - <td class="tdc"> + </td> - <td class="tdc bb">3</td> - <td class="tdc" rowspan="2"> = </td> - <td class="tdc bb">5</td> - <td class="tdc" rowspan="2">;</td> - </tr><tr> - <td class="tdc">3</td> - <td class="tdc"> + </td> - <td class="tdc">5</td> - <td class="tdr">8</td> - <td class="tdc">5</td> - <td class="tdc"> + </td> - <td class="tdc">8</td> - <td class="tdr">13</td> - </tr> - </tbody> -</table> - -<p class="no-indent">and so on. There are, however, numerous exceptions to this -regular arrangement, which have caused some to question the importance of any -theory like that of the “spiral theory” of growth propounded by Goethe -and others of his time. -<span class="pagenum"><a name="Page_385" id="Page_385">[Pg 385]</a></span></p> - -<p><b>749. Adaptation in leaf arrangement.</b>—As a result, however, of -one arrangement or another we see a beautiful adaptation of the plant -parts to environment, or the influence which environment, especially -light, has had on the arrangement of the leaves and branches of the -plant. Access to light and air are of the greatest importance to -green plants, and one cannot fail to be profoundly impressed with the -workings of the natural laws in obedience to which the great variety of -plants have worked out this adaptation in manifold ways.</p> - -<p><b>750. Distribution of leaves with reference to the entire -plant.</b>—In this case, as in the former, we recognize that it is -primarily a light relation. As the plant becomes larger and more -branched the lower and inner leaves disappear. The trees and shrubs -have by far the larger number of leaves on the periphery of the branch -system. A comparison of different kinds of trees in this respect shows, -however, that there is great variation. Trees with dense foliage (elm, -Norway maple, etc.) present numerous leaves on the periphery which -admit but little light to the interior where leaves are very few or -wanting. The sugar maple and red maple do not cast such a dense shade -and there are more leaves in the interior. This is more marked in the -silver maple, and still more so in the locust (Gleditschia tricanthos).</p> - -<p><b>751. Color of foliage leaves.</b>—The great majority of foliage -leaves are green in color. This we have learned (<a href="#CHAPTER_VII">Chapter VII</a>) -is due to the presence of a green pigment, chlorophyll, in the chloroplastids -thickly scattered in the cells of the leaf. We have also learned that -in the great majority of cases, the light stimulus is necessary for -the production of chlorophyll green. There are many foliage leaves -which possess other colors, as red (Rosa rubrifolia), purple (the -purple barberry, hazel, beech, birch, etc.), yellow (the golden oak, -elder, etc.); while many others have more or less deep tints of pink, -red, purple, yellow, when young. All of these leaves, however, possess -chlorophyll in addition to red, yellow, purple or other pigment. -These other pigments are sometimes developed in great quantity in the -cell-sap. They obscure the chlorophyll from view, but do not interfere -seriously with the action of light and the function of chlorophyll, and -perhaps in some cases serve as a screen to protect the protoplast.</p> - -<p><b>752. Autumn colors.</b>—Foliage leaves of many trees display in -the autumn gorgeous colors. These colors are principally shades of -red or yellow, and sometimes purple. The autumn color is more marked -in some trees than in others. In the red maple, the red and scarlet -oak, the sourwood, etc., red predominates, though sometimes yellow -may be present with the red in a single leaf. Sugar maples, poplars, -hickories, etc., are principally yellow in autumn. The sweet gum has a -rich variety of color-red, purple, maroon, yellow; sometimes all these -colors are present on the same tree. -<span class="pagenum"><a name="Page_386" id="Page_386">[Pg 386]</a></span></p> - -<p>The red and purple colors are found suffused in the cell-sap of -certain cells in the leaf much as we have found it in the cells of -the red beet. The yellow color is chiefly due to the disappearance -and degeneration of the chlorophyll while the leaf is in a moribund -state. A similar phenomenon is seen in the yellowing of crops when -the soil becomes too wet, or in the blanching of grass when covered -with a board, or of celery as the earth is ridged up over the leaves -in late summer and autumn. A number of different theories have been -advanced to explain autumn coloring, i.e., the appearance of the -red coloring matter. It has been attributed to the approach of cold -weather, and this has likely led to the erroneous belief on the part -of some that it is caused by frost. It very often precedes frost. Some -have attributed it to the action of the more oblique light rays during -autumn, and still others to the diminishing water-supply with the -approach of cool weather. The question is one which has not met as yet -with a satisfactory solution, and is certainly a very obscure one. It -is likely that the low temperature or the declining activities of the -leaf affect certain organic substances in the leaf and give rise to -the red color, and it is quite certain that in some years the display -is more brilliant than in others. The color is more striking in some -regions than in others and the different soil, as well as climate, has -been supposed to have some influence. The North American forests are -noted for the brilliant display of autumnal color. This is perhaps due -to some extent to the great variety or number of species which display -color. It would seem that there is some specific as well as individual -peculiarities in certain trees. Some individuals, for example, exhibit -brilliant colors every autumn, while others near of the same species -are more subdued.</p> - -<p>It has been shown by experiment that when sunlight passes through -red colors the temperature is slightly increased, and it has been -suggested that this may be of protection to the living substance which -has ceased working and is in danger of injury from cold. There does -not seem to be much ground for this suggestion, however. It certainly -could not protect the protoplasm of the leaf at night when the cold -is more intense, and during the day would only aggravate matters -by supplying an increased amount of heat, since extremes of heat -and cold in alternation are more harmful to plant life than uniform -cold. Especially would this be the case in alpine climates where the -alternation of heat and cold between day and night is extreme, and -brilliancy of the colors of alpine plants is well known. It seems -more reasonable to suppose that the red color acts as a screen, as -the chlorophyll is disappearing, to protect from the injurious action -of light, certain organic substances which are to be transferred back -from the leaf to the stem for winter storage. So in the case of many -stems in the spring or early summer when the young leaves often have -a reddish color, it is likely that it acts as a screen to protect the -<span class="pagenum"><a name="Page_387" id="Page_387">[Pg 387]</a></span> -living substance from the strong light at that season of the year until -the chlorophyll screen, which is weak in young leaves, becomes darker -in color and more effective, when the red color often disappears.</p> - -<p><b>753. Function of foliage leaves.</b>—In general the function of -the foliage leaf as an organ of the plant is fivefold (see Chapters -<a href="#CHAPTER_IV">IV</a>, <a href="#CHAPTER_VII">VII</a>, -<a href="#CHAPTER_VIII">VIII</a>, <a href="#CHAPTER_XI">XI</a>), -(1) that of carbon dioxide assimilation or <i>photosynthesis</i>, (2) that -of transpiration, (3) that of the synthesis of other organic compounds, -(4) that of respiration, and (5) that of assimilation proper, or the -making of new living substance. While none of these functions are -solely carried on in the leaf, it is the chief seat of the first three -of these processes, its form, position, and structure being especially -adapted to the purpose. Assimilation proper, as well as respiration, -probably take place equally in all growing or active parts.</p> - -<p><b>754. Parts of the leaf.</b>—All foliage leaves possess a <i>blade</i> -or <i>lamina</i>, so called because of its <i>expanded</i> and <i>thin</i> character. -The blade is the essential part. Many leaves, however, are provided -with a stalk or <i>petiole</i> by which the blade is held out at a greater -or lesser distance from the stem. Leaves with no petiole are <i>sessile</i>, -the blade is attached by one end directly on the stem. In some cases -the base of the blade is wrapped partly around the stem, or in others -it extends entirely around the stem and is <i>perfoliate</i>. Besides, many -leaves have short appendages, termed <i>stipules</i>, attached usually on -opposite sides of the petiole at its junction with the stem. In some -species of magnolia the stipules are so large that each one envelops -the entire portion of the bud which has not yet opened. Many leaves -possess outgrowths in the form of hairs, scales, etc. (<a href="#Page_392">See leaf -protection</a>.)</p> - -<p><b>755. Simple leaves.</b>—Simple leaves are those in which the -blade is plane along the edge, not divided. The edge may be entire or -indented (serrate) to a slight extent as in the elm. The form of the -simple leaf varies greatly but is usually constant for a given species, -or it may vary in shape in the same species on different parts of the -plant. Some of the terms applied to the outline of the leaf are ovate, -oval, elliptical, lanceolate, linear, needle-like, etc., but it is idle -<span class="pagenum"><a name="Page_388" id="Page_388">[Pg 388]</a></span> -for one to waste time on matters of minute detail in form until it -becomes necessary for those in the future who pursue taxonomic work. It -is evident that a simple leaf, except those of minute size, possesses -advantages over a divided leaf in the amount of surface it exposes to -the light. But in other respects it is at a disadvantage, especially -as it increases in size, since it casts a deeper shade and does not -admit of such a free circulation of air. It will be found, however, in -our study of the relation of leaves to light and air that the balance -between the leaf and its environment is obtained in the relation of the -leaves to each other.</p> - -<p><b>756. Venation of leaves.</b>—A very prominent character of the -leaf is its “venation.” This is indicated by the presence of numerous -“veins,” indicated usually by narrow depressed lines on the upper -surface, and by more or less distinct elevated lines on the under -surface. There are two general types: (1) In the corn, Smilacina, -Solomon’s seal, etc., the veins extend lengthwise of the leaf and -are nearly parallel. Such leaves are said to be <i>parallel-veined</i>. -It is generally, though not always, a character of monocotyledenous -plants. (2) In the elm, rose, hawthorn, maple, oak, etc., the veins -are not all parallel. The larger ones either diverge from the base -of the blade (palmate leaf, maple), or the midvein extends through -the middle line of the leaf, while other prominent ones branch off -from this and extend, nearly parallel, toward the edge of the leaf -(pinnate venation). The smaller intermediate veins which are also -very distinct extend irregularly and branch and anastomose in such a -fashion as to give the figure of a net with very fine meshes. These -are <i>netted-veined</i> leaves. These are characteristic of most of the -dicotyledenous plants. It is evident from what has been said of the -examples cited that there are two types of netted-veined leaves, the -<i>palmate</i> and <i>pinnate</i>. -<span class="pagenum"><a name="Page_389" id="Page_389">[Pg 389]</a></span></p> - -<p class="blockquot"><span class="smcap">Note.</span> As we have -already learned in <a href="#CHAPTER_V">Chapter V</a> the veins contain the vascular -bundles of the leaf. Through them the water and food solutions are distributed -to all parts of the leaf, and the return current of food material -elaborated in the leaf moves back through the bast portion into the -shoot. The veins also possess a small amount of mechanical tissue. This -forms the framework of the leaf and aids in giving rigidity to the -leaf and in holding it in the expanded position. The mechanical tissue -in the framework alone could not support the leaf. Turgescence of the -mesophyll is needed in addition.</p> - -<p><b>757. Cut or lobed leaves.</b>—In many leaves, the indentations -on the margin are few and deep. Such leaves present several lobes -the proportionate size of which is dependent upon the depth of the -indentation or “incision.” Several of the maples, oaks, birches, the -poison-ivy, thistles, the dandelion, etc., have lobed leaves. Where -the indentation reaches to or very near the midrib the leaf is said -to be cut. A study of various leaves will show all gradations from -simple leaves with plane edges to those which are cut or divided, as in -compound leaves, and the lobes are often variously indented.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p> </p> - <img src="images/fig433.jpg" alt="" width="200" height="227" /> - <p class="center">Fig. 433.<br /> Lobed leaves of oak<br /> forming a mosaic.</p> - </div> - <div class="figsub"> - <p> </p> - <img src="images/fig434.jpg" alt="" width="250" height="215" /> - <p class="center">Fig. 434.<br /> Twice compound leaf. Leaflets arranged<br /> - in one plane, but open spaces permit free<br /> - circulation of air through the large leaf.</p> - </div> -</div> - -<p><b>758. Divided, or compound leaves.</b>—The rose, sumac, elder, -hickory, walnut, locust, pea, clover, American creeper, etc., are -examples of divided or compound leaves. The former are pinnately -compound, and the latter are palmately compound. The leaf of the -honey-locust is twice pinnately compound or bipinnate, and some are -<span class="pagenum"><a name="Page_390" id="Page_390">[Pg 390]</a></span> -three times pinnately compound.<a name="FNanchor_44_44" id="FNanchor_44_44"></a><a href="#Footnote_44_44" class="fnanchor">[44]</a> -It is evident that compound leaves are only extreme forms of lobed or -cut leaves and that the form of all bears a definite relation to the -primary venation. There has been a reduction of mesophyll and of the -area of smaller venation.</p> - -<p><b>759.</b> These forms of leaves probably have some definite -significance. It is not quite clear why they should have developed as -they have; though it is possible to explain several important relations -of these forms to their environment. (1) The reduction of the surface -of the leaf, with the retention of the firmer portions, allows freer -movement of the air and affords the leaf greater protection from injury -during violent winds, just as the finely dissected leaves of some -water plants are less liable to injury from movement of the more dense -medium in which they live. It is possible that here we may have an -explanation of one of the factors involved in this reduction of leaf -surface. (2) In trees with compound leaves, like the hickory, walnut, -locust, ailanthus, etc., the midvein, and in the case of the Kentucky -coffee-tree (Gymnocladus) the primary lateral veins also, serve in -place of terminal branches of the stem. By the increase in the outline -of the leaf and the reduction of its surface between the larger veins, -the tree has attained the same leaf development that it would were the -<span class="pagenum"><a name="Page_391" id="Page_391">[Pg 391]</a></span> -larger veins replaced by stems bearing simple leaves. The tree as -it is, however, has the advantage of being able to cast off for the -winter period a layer of what otherwise would have been a portion of -the stem system, to retain which through the winter would use more -energy than with the present reduced stem system, and the stouter -stem is less liable to dry out. In the case of herbaceous plants, in -the case of plants like most of the ferns where the stem is on the -underground rootstock (Pteris), or a very short erect stem, as in the -Christmas fern, the leaf replaces the aerial stem, and the division (or -branching, as it is sometimes styled) of the leaf corresponds to the -branching of the stem. This is more marked in the gigantic exotics like -Cibotium regale, and in the tree ferns which have quite tall trunks, -the massive compound leaves replace branches. In the palms and cycads -are similar examples. Those who choose to observe can doubtless find -many examples close at hand. (3) While divided leaves have probably not -been evolved in response to the light relation, still their relation in -this respect is an important one, since if the leaf with its present -size were entire, it would cast too dense a shade on other leaves below.</p> - -<p><b>760. General structure of the leaf.</b>—The general structure of -the leaf has been already studied (see Chapters <a href="#CHAPTER_IV">IV</a>, -<a href="#CHAPTER_V">V</a>, <a href="#CHAPTER_VII">VII</a>). It is -only necessary to recall the main points. The upper and lower surfaces -of the leaf are provided with a layer of cells usually devoid of -chlorophyll. The mesophyll of the leaf consists usually of a layer of -palisade cells beneath the epidermis, and the remainder consists of -loose parenchyma with large intercellular spaces. Through the mesophyll -course the “veins,” or fibrovascular strands, consisting of the xylem -and phloem portions and serving as conduits for water, salts, and -foodstuffs. In the epidermis are the stomata, each one protected by -the two guard cells. The guard cells as well as the mesophyll contain -chlorophyll. The stomata and the communicating intercellular spaces -furnish the avenues for the ingress and egress of gases, and for the -escape of water vapor.</p> - -<p><b>761. Protection of leaves.</b>—There are many modifications of -the general plan of structure in different leaves, many of them being -adaptations for the protection of the leaf under adverse or trying -conditions. Many leaves are also capable of assuming certain positions -which afford them protection. The discussion of this subject may be presented -under two general heads: Protective modifications; protective positions. -<span class="pagenum"><a name="Page_392" id="Page_392">[Pg 392]</a></span></p> - -<h4><a name="XL_2" id="XL_2">II. Protective Modification of Leaves.</a></h4> - -<p><b>762. General directions in which these modifications have taken -place.</b>—The usual type of foliage leaf selected is that of -deciduous trees or shrubs or of our common herbs. Such a leaf is -usually greatly expanded and thin in order to present as great a -surface as possible in comparison with its mass, since the kind of -work which the leaf has to do can be more effectually carried on when -it possesses this form. This form of leaf is best adapted for work in -regions where there is a medium amount of moisture such as exists in -the temperate zones. But since there are very great variations in the -climatic and soil conditions of these regions, and even greater changes -in desert and arctic regions, the type of leaf described is unsuited -for all. Its own life would be endangered, and it would also endanger -the life of the plant. Modifications have therefore taken place to -meet these conditions, or at least those plants whose leaves have -become modified in those directions which are suited to the surrounding -conditions have been able to persist. Excessive cold or heat, drought, -winds, intense light, rain, etc., are some of the conditions which -endanger leaves. The protective modifications of leaves may be grouped -under four general heads: (1) Structural adaptations; (2) Protective -covering; (3) Reduction of surface; (4) Elimination of the leaf through -the complete assumption of the leaf function by the stem.</p> - -<div class="figcontainer"> - <a id="FIG_435" name="FIG_435"> </a> - <div class="figsub"> - <p> </p> - <img src="images/fig435a.jpg" alt="" width="200" height="224" /> - </div> - <div class="figsub"> - <p> </p> - <img src="images/fig435b.jpg" alt="" width="250" height="221" /> - </div> - <div class="blockquot"> - <p class="center">Fig. 435.</p> - <p>Structure of leaf of Lactuca scariola. Upper one grown in sunlight, - palisade cells on both sides. Lower one grown in shade, no palisade tissue.</p> - </div> -</div> - -<p><b>763.</b> (1) <b>Structural adaptations.</b>—The general structure -of the leaf presents certain features which are protective. The -palisade layer of cells found usually beneath the upper epidermis forms -a compact layer of long cells which not only acts as a light screen -cutting off a certain amount of the light, since too intense light -would be harmful; it also aids in lessening the loss of water from the -upper surface, where radiation is greater. The stomata are usually on -the under side of aerial leaves, and the mechanism which closes them -when the leaf is losing too much water is protective. As a protection -against intense light the number of palisade layers is sometimes -<span class="pagenum"><a name="Page_393" id="Page_393">[Pg 393]</a></span> -increased or the cells of this layer are narrow and long. This is often -beautifully shown when comparing leaves of the same plant grown in -strong light with those grown in the shade. The compass plant (Lactuca -scariola) affords an interesting example. The leaves grown in the light -are usually vertical, so that the light reaches both sides. Such leaves -often have all of the mesophyll organized into palisade cells (<a href="#FIG_435">fig. 435</a>), -while leaves grown in the deep shade may have no palisade cells.</p> - -<p><b>764.</b> (2) <b>Protective covering.</b>—<i>Epidermis and -cuticle.</i>—The walls of the epidermal cells are much thickened in some -plants. Sometimes this thickening occurs in the outer wall, or both -walls may be thickened. Variation in this respect as well as the extent -of the thickening occur in different plants and are often correlated -with the extremes of conditions which they serve to meet. The cuticle, -a waxy exudation from the thick wall of the epidermis of many leaves, -also serves as a protection against too great loss of water, or against -the leaf becoming saturated with water during rains. The cabbage, -carnation, etc., have a well-developed cuticle. The effect of the -cuticle in shedding water can be nicely shown by spraying water on a -cabbage leaf or by immersing it in water. Sunken stomata also retard -the loss of water vapor.</p> - -<p><i>Covers of hair or scales.</i>—In many leaves certain of the cells of the -epidermis grow out into the form of hairs or scales of various forms, -<span class="pagenum"><a name="Page_394" id="Page_394">[Pg 394]</a></span> -and they serve a variety of purposes. When the hairs form a felt-like -covering as in the common mullein, some antennarias, etc., they lessen -the loss of water vapor because the air-currents close to the surface -of the leaf are retarded. Spines (see the thistles, etc.) also afford a -protection against certain animals.</p> - -<p><b>765.</b> (3) <b>Reduction of surface.</b>—Reduction of leaf surface -is brought about in a variety of ways. There are two general modes: -(1st) Reduction of surface along with reduction of mass; (2d) Reduction -of surface inversely as the mass. Examples of the first mode are -seen in the dissected leaves of many aquatic plants. In this finely -dissected condition the mass of the leaf substance is much reduced as -well as the leaf surface, but the leaf is less liable to be injured -by movement of the water. In addition it has already been pointed out -that lobed and divided aerial leaves are much less liable to injury -from violent movements of the air, than if a leaf with the same general -outline were entire. The needle leaves of the conifers are also -examples, and they show as well structural provisions for protection -in the thick, hard cell-walls of the epidermis. To offset the reduced -surface there are numerous crowded leaves. Reduction of surface -inversely as the mass, i.e., the mass of the leaf may not be reduced -at all, or it may be more or less increased. In other words, there is -less leaf surface in proportion to the mass of leaf substance. It is -probable in many cases, example: the crowded, overlapping small scale -leaves of the juniper, arbor-vitæ, cypress, cassiope, pyxidanthera, -etc., that there has been a reduction in the size of the leaf, and at -the same time an increase in thickness. This with the crowding together -of the leaves and their thick cell-walls greatly lessens the radiation -of moisture and heat, thus protecting the leaves both in dry and cold -weather. The succulents, like “live-forever,” have a small amount of -surface in proportion to the mass of the leaf. In the yucca, though the -leaves are often large, they are very thick and expose a comparatively -small amount of surface to the dry air and intense sunlight of the -desert regions. The epidermal covering is also hard and thick. In -<span class="pagenum"><a name="Page_395" id="Page_395">[Pg 395]</a></span> -addition, such leaves, as well as those of many succulents, are so -thick they provide water storage sufficient for the plants, which -radiate so slowly from their surface.</p> - -<div class="figcenter"> - <img src="images/fig436.jpg" alt="" width="500" height="344" /> - <p class="center">Fig. 436.<br /> - A “Phylloclade,” leaves absent, stems<br /> - broadened to function as leaves, on the<br /> - edges numerous flowers are borne.</p> -</div> - -<p><b>766.</b> (4) <b>Elimination of the leaf.</b>—Perhaps the most -striking illustration of the reduction of leaf surface is in those -cases where the leaf is either completely eliminated as in certain -euphorbias, or in certain of the cacti where the leaves are thought -to be reduced to spines. Whether the cactus spine belongs to the -leaf series or not, the leaf as an organ for assimilation and -transpiration has been completely eliminated and the same is true in -the phylloclades. The leaf function has been assumed by the stem. The -stem in this case contains all the chlorophyll; is bulky, and provides -water storage.</p> - -<h4><a name="XL_3" id="XL_3">III. Protective Positions.</a></h4> - -<p><b>767.</b> In many cases the leaves are arranged either in relation -to the stem, or to each other, or to the ground, in such a way as to -give protection from too great radiation of heat or moisture. In the -<span class="pagenum"><a name="Page_396" id="Page_396">[Pg 396]</a></span> -examples already cited the imbricated leaves of cassiope, pyxidanthera, -juniper, etc., come also under this head. In the junipers the leaves -spread out in the summer, while in the winter they are closely -overlapped. An interesting example of protective position is to be seen -in the case of the leaves of the white pine. During quite cold winter -weather the needles are appressed to the stem, and sometimes the trees -present a striking appearance in contrast with the spreading position -of the needles in summer. On windy days in winter, the needles turn -with the wind and become rigid in that position so that they remain in -a horizontal position for some time, often until the wind dies down, -or until milder weather. The following day, should there be a cold -strong wind from the opposite direction, the needles again assume a -leeward direction. In quiet weather appressed to the stem and in the -form of a brush there is less radiation of heat than if they diverged. -In strong winds by turning in the leeward direction the wind is not -driven between the needle bases and scales. Some plants, especially -many of those in arctic and alpine regions, have very short stems and -the leaves are developed near the ground, or the rock. Lying close on -the ground they do not feel the full force of the drying winds, there -is less radiation from them, and the radiation of heat from the ground -protects them. Many plants exhibit movement in response to certain -stimuli which place them in a position for protection. Some of these -examples have been discussed under the head of irritability (see -<a href="#CHAPTER_XIII">Chapter XIII</a>). The night position of leaves and cotyledons -presented by many plants, but especially by many of the Leguminosæ, is brought -about by the removal of the light stimulus at evening. In many leaves, -when the light influence is removed, the influence of growth turns -the leaves downward, or the cotyledons of some plants upward. In this -vertical position of the leaf-blade there is less radiation of heat -during the cool night. The most striking cases of protection movements -are seen in the sensitive plant. As we have seen, the leaves of mimosa -close in a vertical position at midday if the light and heat are too -strong. Excessive transpiration is thus prevented. At night the vertical -<span class="pagenum"><a name="Page_397" id="Page_397">[Pg 397]</a></span> -position prevents excessive radiation of heat. The vertical or profile -position of the leaves of the compass plant already referred to not -only lessens transpiration, but the intense heat and light of the -midday sun is avoided. This profile position is characteristic of -certain plants in the dry regions of Australia, and the topmost leaves -of tropical forests.</p> - -<h4><a name="XL_4" id="XL_4">IV. Relation of Leaves to Light.</a></h4> - -<p><b>768.</b> It is very obvious from our study of the function of the -foliage leaf that its most important relation to environment is that -which brings it in touch with light and air. It is necessary that light -penetrate the leaf tissue that the gases of the air and plant may -readily diffuse and that water vapor may pass out of the leaf. The thin -expanded leaf-blade is the most economical and efficient organ for leaf -work. We have seen that leaves respond to fight stimulus in such a way -as to bring their upper sides usually to face the source of fight, at -right angles to it or nearly so (<i>heliotropism</i>, see <a href="#CHAPTER_XIII">Chapter XIII</a>). -How fully this is brought about depends on the kind of plant, as well as on -other elements of the environment, for as we have seen in our study of -<span class="pagenum"><a name="Page_398" id="Page_398">[Pg 398]</a></span> -leaf protection there is danger to some plants in any region, and to -other plants in certain regions that the intense light and heat may -harm the protoplast, or the chlorophyll, or both.</p> - -<div class="figcenter"> - <img src="images/fig437.jpg" alt="" width="500" height="392" /> - <p class="center space-below2">Fig. 437.<br /> Mosaic form by trailing shoots of<br /> - Panicum variegatum, “ribbon-grass.”</p> -</div> - -<p>The statement that leaves usually face the light at right angles is to -be taken as a generalized one. The source of the strongest illumination -varies on different days and again at different times of the day. -On cloudy days the zenith is the source of strongest illumination. -The horizontal position of a leaf, where there are no intercepting -lateral or superior objects would receive its strongest light rays -perpendicular to its surface. The fact is, however, that leaves on the -same stem, because of taller or shorter adjacent stems, are so situated -that the rays of greatest illuminating power are directed at some angle -between the zenith and horizon. Many leaves, then, which may have -their upper sides facing the general source of strongest illumination, -do not necessarily face the sun, and they are thus protected from -possible injury from intense light and heat because the direct rays of -sunlight are for the most part oblique. This does not apply, of course, -to those leaves which “follow the sun” during the day. Their specific -constitution is such that intense illumination is beneficial.</p> - -<p>The leaf is adjusted as well as may be in different species of varying -constitution, and under different conditions, to a certain balance in -its relation to the factors concerned. The problem then is to interpret -from this point of view the positions and grouping of leaves. Because -of the specific constitution of different plants, and because of a -great variety of conditions in the environment, we see that it is a -more or less complex question.</p> - -<div class="figcenter"> - <img id="FIG_438" src="images/fig438.jpg" alt="" width="400" height="410" /> - <p class="center space-below2">Fig. 438.<br /> - Sunflower with young head<br /> turned toward morning sun.</p> -</div> - -<p><b>769. Day and night positions contrasted.</b>—In many plants the -day and night positions of the leaves are different. At night the -leaves assume a position more or less vertical, known as the <i>profile</i> -position. This is generally regarded as a protective position, since -during the cool of the night the radiation of heat is less than if the -leaf were in a vertical position. In many of these plants, however, the -leaves in assuming the night position become closely appressed which -would also lessen the radiation. This peculiarity of leaves is largely -<span class="pagenum"><a name="Page_399" id="Page_399">[Pg 399]</a></span> -possessed by the members of the family Leguminoseæ (clovers, peas, -beans, etc.), and by the sensitive plants.<a name="FNanchor_45_45" id="FNanchor_45_45"></a><a href="#Footnote_45_45" class="fnanchor">[45]</a> -But it is also shared by some other plants as well (oxalis, for -example). The leaves of these plants are usually provided with a -mechanism which enables them to execute these movements with ease. -There is a cushion (<i>pulvinus</i>) of tissue at the base of the petiole, -and in the case of compound leaves, at the base of the pinnæ and -pinnules which undergoes changes in turgor in its cells. The collapsing -of the cells by loss of water into the intercellular spaces causes the -leaf to droop. When the cells regain their turgor by the absorption -of the water from the intercellular spaces the leaf is raised to the -horizontal, or day position. The light stimulus induces turgor of the -pulvinus, the disappearance of the stimulus is accompanied by a loss of -turgor. It is a remarkable fact that in some sensitive plants, intense -<span class="pagenum"><a name="Page_400" id="Page_400">[Pg 400]</a></span> -light stimuli are alarm signals which result in the same movement as if -the light stimulus were entirely removed. As we know also contact or -pressure stimulus, or jarring produces the same result in “sensitive” -plants like mimosa, some species of rubus, etc. In many plants there is -no well-developed pulvinus, and yet the leaves show similar movements -in assuming the day and night positions. Examples are seen in the -sunflower, and in the cotyledons of many plants. A little observation -will enable any one interested to discover some of these plants.<a name="FNanchor_46_46" id="FNanchor_46_46"></a><a href="#Footnote_46_46" class="fnanchor">[46]</a> -In these cases the night position is due to epinastic growth, and -while this influence is not removed during the day the light stimulus -overcomes it and the leaf is raised to the day position.</p> - -<div class="figcenter"> - <img id="FIG_439" src="images/fig439.jpg" alt="" width="400" height="380" /> - <p class="center space-below2">Fig. 439.<br /> - Same sunflower plant photographed<br /> just at sundown.</p> -</div> - -<p><b>770. Leaves which rotate with the sun.</b>—During the growth period -the leaves of the sunflower as well as the growing end of the stem -respond readily to the direct sunlight. The response is so complete -that during sunny days the leaves toward the growing end of the stem -are drawn close together in the form of a rosette and the entire -<span class="pagenum"><a name="Page_401" id="Page_401">[Pg 401]</a></span> -rosette as well as the end of the stem are turned so that they face the -sun directly. In the morning under the stimulus of the rising sun the -rosette is formed and faces the east. All through the day, if the sun -continues to shine, the leaves follow it, and at sundown the rosette -faces squarely the western horizon. For a week or more the young -sunflower head will also face the sun directly and follow it all day as -surely as the rosette of leaves. At length, a little while before the -flowers in the head blossom, the head ceases to turn, but the rosette -of leaves and the stem also, to some extent, continue to turn with the -sun. When the leaves become mature they also cease to turn. This is -well shown in all three photographs (figs. <a href="#FIG_438">438</a>-<a href="#FIG_439">439</a>). -The lower leaves on the stem being older have assumed the fixed horizontal -position usually characteristic of the plant with cylindrical habit.</p> - -<div class="figcenter"> - <img src="images/fig440.jpg" alt="" width="400" height="366" /> - <p class="center space-below2">Fig. 440.<br /> - Same plant a little older when the head<br /> - does not turn, but the stem and leaves do.</p> -</div> - -<p>It is not true, as is commonly supposed, that the fully opened -sunflower head turns with the sun. But I have observed young heads -four or five inches in diameter rotate with the sun all day. This is -because the growing end of the stem as well as the young head responds -to the light stimulus. So there is some truth as well as a great deal -<span class="pagenum"><a name="Page_402" id="Page_402">[Pg 402]</a></span> -of fiction in the popular belief that the sunflower head follows the -sun. The young head will follow the sun all day even if all the leaves -are cut off, and the growing stem will also if all the leaves as well -as the flower head are cut away. Young seedlings will also turn even if -the cotyledons and plumule are cut off.</p> - -<p>This phenomenon of the rotation of leaves with the sun is much more -general than one would infer, as may be seen from a little careful -observation of rapidly growing plants on bright sunny days. In Alabama -I have observed beautiful rosettes of <i>Cassia marilandica</i> rotate with -the sun all day. The peculiarity is very striking in the cotton plant, -especially when the rows extend north and south. In the forenoon or -afternoon it is most striking as the entire row shows the leaves tilted -up facing the sun. There are many of our weeds and common flowers of -field and garden which show this rotation of the leaves. Some of these -form rotating rosettes; while in others the leaves rotate independently -as in the sweet clover.</p> - -<p><b>771. Fixed position of old leaves.</b>—In many of the cases cited -in the preceding paragraph, the rotation of the leaf only occurs -on sunny days. During cloudy days the leaves of the sunflower, for -example, are in a nearly horizontal position, or the lower ones may -be somewhat oblique, since the stronger illumination on such a plant -would be the oblique rays rather than the zenith rays. As the leaves -reach maturity also the epinastic growth is equalized by hyponastic -growth so that the growth movements bring the leaf to stand in a nearly -horizontal position, or that position in which it receives the best -illumination. In age, then, many leaves have a fixed position and this -corresponds with the position assumed on cloudy days.</p> - -<p><b>772. Position on horizontal stems.</b>—On horizontal stems the -leaves have a horizontal position, and if such a stem is stood in an -erect position the appearance is very odd. If the leaf arises directly -from the horizontal stem, its petiole will be twisted part way around -in order to bring the face of the leaf uppermost. It is interesting -to observe the different relation of stem, petiole and blade and the -<span class="pagenum"><a name="Page_403" id="Page_403">[Pg 403]</a></span> -amount of twisting as the horizontal stem or vine trails over irregularities -in the surface, or climbs over and through other vegetation.</p> - -<p><b>773. Position of leaflets on divided leaves.</b>—An interesting -comparison can be made with entire, lobed, divided and dissected -leaves. The entire leaf usually lies in one plane, since usually the -problem of adjustment is the same for the entire surface. So the lobes -of a leaf usually lie all in the same plane as they would if the leaf -were entire. We find the same is true usually of the compound leaf. -It forms an incomplete mosaic. Some of the pieces having been removed -allow much of the light to pass through to leaves beneath. Leaves, -especially those of some size rarely lie in a flat plane. Some are more -or less depressed. Some curve downward. Compound leaves often curve -more or less and the leaflets often droop more or less in a graceful -fashion. It is interesting, however, that these far separated leaflets -all lie in the same general plane. This is because the area of the -leaf, if not too large, makes the problem of position with reference -to light much the same as if the leaf were entire. The leaflets or -divisions, though separated, are laminate, and they can work more -efficiently facing the light. But suppose we extend our observation to -the finely dissected capillary leaves of some of the parsley family -(Umbelliferæ), or to the upper leaves of the fennel-leaved thoroughwort -(Eupatorium fœniculaceum) among the aerial plants, and to Myriophyllum -among the aquatic plants. The divisions are thread-like or cylindrical. -One side of the leaflet is just as efficient when presented to the -light as another. As a result the leaflets are not arranged in the same -plane, but stand out in many directions.</p> - -<p>Occasionally one finds a divided or compound leaf in such a position -that one portion, because of being shaded above, receives the stronger -light stimulus from the side, while the other portion is lighted from -above. If this relation continues throughout the growth-period of the -leaf the leaflets of one portion may lie in a different plane from -those of the other portion. In such cases, some of the leaflets are -permanently twisted to bring them into their proper light relation. -<span class="pagenum"><a name="Page_404" id="Page_404">[Pg 404]</a></span></p> - -<h4><a name="XL_5" id="XL_5">V. Leaf Patterns.</a></h4> - -<h5>MOSAICS, OR CLOSE PATTERNS.</h5> - -<div class="figcenter"> - <img id="FIG_441" src="images/fig441.jpg" alt="" width="600" height="411" /> - <div class="blockquot"> - <p class="center">Fig. 441.</p> - <p>Fittonia showing leaves arranged to form compact mosaic. The netted - venation of the leaf is very distinctly shown in this plant. - (Photo by the Author.)</p> - </div> -</div> - -<p><b>774.</b> Where the leaves of a plant, or a portion of a plant, are -approximate and arranged in the form of a pattern, the leaves fitting -together to form a more or less even and continuous surface, such -patterns are sometimes termed “mosaics,” since the relation of leaves -to one another is roughly like the relation of the pieces of a mosaic. -A good illustration of a mosaic is presented by a greenhouse plant -Fittonia (<a href="#FIG_441">fig. 441</a>). The stems are prostrate and the erect -branches quite short, but it may have quite a wide system by the spreading of -the runners; the branches of such a length that the leaves borne near -the tips all fit together forming a broad surface of leaves so closely -fitted together often that the stems cannot be seen. The advantage of -a mosaic over a separate disposition of leaves at somewhat different -levels is that the leaves do not shade one another. Were all the light -rays coming down at right angles to the leaves, there would not be -any shading of the lower ones, but the oblique rays of light would be -cut off from many of the leaves. In the case of a mosaic all the rays -of light play upon all the leaves. Some of the mosaics which can be -observed are as follows: -<span class="pagenum"><a name="Page_405" id="Page_405">[Pg 405]</a></span></p> - -<div class="figcenter"> - <img src="images/fig442.jpg" alt="" width="400" height="450" /> - <p class="center">Fig. 442.<br /> Rosette pattern of leaves.</p> -</div> - -<p><b>775. Rosette pattern.</b>—The rosette pattern is presented by -many plants with “radial” leaves, or leaves which arise in a cluster -near the surface of the ground, and are thus more or less crowded in -their arrangement on the stem. The pretty gloxinia often presents fine -examples of a loose rosette. In the rosette pattern the petioles of -the lower leaves are longer than the upper ones, and the blade is thus -carried out beyond the inner leaves. The leaves being so crowded in -their attachment to the stem lie very nearly in the same plane.</p> - -<p><b>776. Vines and climbers.</b>—Some of the most extensive mosaic -patterns are shown in creeping and climbing vines. A very common -example is that of the ivies trained on the walls of buildings, -covering in some instances many square yards of surface. Where the -vines trail over the ground or clamber over other vegetation, it is -interesting to observe the various patterns, and the distortion of -petioles brought about by turning of the leaves. Of examples found in -greenhouses, the Pellonia is excellent, and the trailing ribbon-grass -often forms loose mosaics.</p> - -<p><b>777. Branch patterns.</b>—These patterns are very common. They -are often formed in the woods on the ends of branches by the leaves -adjusting themselves so as to largely avoid shading each other. <a href="#FIG_443">Figure 443</a> -illustrates one of them from a maple branch. It is interesting to -note the way in which the leaves fit themselves in the pattern, how in -some the petioles have elongated, while others have remained short. Of -course, it should be understood that the pattern is made during the -growth of the leaves. -<span class="pagenum"><a name="Page_406" id="Page_406">[Pg 406]</a></span></p> - -<div class="figcenter"> - <img id="FIG_443" src="images/fig443.jpg" alt="" width="400" height="316" /> - <p class="center">Fig. 443.<br /> Spray of leaves of striped maple,<br /> - showing different lengths of leafstalks.</p> -</div> -<div class="figcenter"> - <img src="images/fig444.jpg" alt="" width="400" height="429" /> - <p class="center">Fig. 444.<br /> Cedar of Lebanon, strong light only<br /> - from one side of tree (Syria).</p> -</div> - -<p><span class="pagenum"><a name="Page_407" id="Page_407">[Pg 407]</a></span> -<b>778. The tree pattern.</b>—Mosaics are often formed by the exterior -foliage on a tree, though they are rarely so regular as some of those -mentioned above. Still it is common to see in some trees with drooping -limbs like the elm, beautiful and large mosaics. The weeping elm -sometimes forms a very close and quite even pattern over the entire -outer surface. In most trees the leaf arrangement is not such as to -form large patterns, but is more or less open. While the conifers do -not form mosaics there are many interesting examples of grouping of -foliage on branch systems into broadly expanded areas, as seen in the -branches of white pine trees, especially in the edge of a wood, or as -seen in the arbor-vitæ.</p> - -<h5>OTHER PATTERNS.</h5> - -<p><b>779. Imbricate pattern of short stems.</b>—This pattern is quite -common, and differs from the rosette in that the leaves are distributed -further apart on the stem so that the central ones are considerably -higher up than in the mosaic. The lower petioles are longer, as in -the rosette, so that the outer lower leaves extend further out. Some -begonias show fine imbricate patterns.</p> - -<div class="figcenter"> - <img src="images/fig445.jpg" alt="" width="400" height="335" /> - <p class="center">Fig. 445.<br /> Imbricate pattern of leaves;<br /> Begonia.</p> -</div> - -<p><b>780. Spiral patterns.</b>—They are very common on stems of the -cylindrical type, which are unbranched, or but little branched. The -sunflower, mullein, chrysanthemum, as it is grown in greenhouses, the -Easter lily, etc., are examples. The spiral arrangement of the leaves -provides that each successive leaf on the stem, as one ascends the -stem, is a little to one side so that it does not cast shade on the leaf -<span class="pagenum"><a name="Page_408" id="Page_408">[Pg 408]</a></span> -just below. In some stems, according to the leaf arrangement (or -phyllotaxy), one would pass several times around in ascending the stem -before a leaf would be found directly above another, which would be -such a distance below that it would not be shaded to an appreciable -extent. Interesting observations can be made on different plants to -work out the relation of distance of leaves on the stem to length of -the upper and lower leaves; the number of vertical rows on the stem -compared to the width of the leaves; and the relation of these facts to -the problem of light supply. Related to the spiral pattern is that of -erect stems with opposite leaves. Here each pair is set at right angles -to the direction of the pair above or below.</p> - -<div class="figcenter"> - <img src="images/fig446.jpg" alt="" width="400" height="383" /> - <div class="blockquot"> - <p class="center">Fig. 446.</p> - <p>Palm showing radiate arrangement of leaves and the petiole of the - leaf functions as stem in lifting leaf to the light.</p> - </div> -</div> - -<p><b>781. Radiate pattern.</b>—This pattern is present in many grasses -and related plants with narrow leaves and short stems. The leaves are -often very crowded at the base, but by radiating in all directions from -<span class="pagenum"><a name="Page_409" id="Page_409">[Pg 409]</a></span> -the horizontal to the vertical, abundant exposure to light is gained -with little shading. The dragon tree screw-pine, and plants grown in -greenhouses also illustrate this type. It is also shown in cycads, -palms, and many ferns, although these have divided leaves.</p> - -<div class="figcenter"> - <img id="FIG_447" src="images/fig447.jpg" alt="" width="400" height="466" /> - <div class="blockquot"> - <p class="center">Fig. 447.</p> - <p>Screw-pine (Pandanus) showing prop roots and - radiate pattern of leaves.</p> - </div> -</div> - -<p><b>782. Compass plants.</b>—These plants with vertical leaf -arrangement, and exposure of both surfaces to the lateral rays of light -have been mentioned in other sections (Lactuca scariola).</p> - -<p><b>783. Open patterns.</b>—Open patterns are presented by divided or -“branched” leaves. Where the leaves are very finely dissected, they may -be clustered in great profusion and yet admit sufficient light for some -depth below. Where the leaflets are broader, the leaves are likely to -be fewer in number and so arranged as to admit light to a great depth -so that successive leaves below on the same or adjacent stems may not -be too much shaded. On such plants, often the leaves lying next the -ground are entire or less divided.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_410" id="Page_410">[Pg 410]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XLI" id="CHAPTER_XLI">CHAPTER XLI.</a><br /> -<span class="h_subtitle">THE ROOT.</span></h3> -</div> - -<h4><a name="XLI_1" id="XLI_1">I. Function of Roots.</a></h4> - -<p><b>784.</b> The most obvious function of the roots of ordinary -plants are two: 1st, To furnish anchorage and partial support, and -2d, absorption of liquid nutriment from the soil. The environmental -relation of such roots, then, in broad terms, is with the soil. It is -very clear that in some plants the root serves both functions, while in -other plants the root may fulfil only one of these requirements.</p> - -<p>The problems which the plant has to solve in working out these -relations are:</p> - -<ul class="index"> -<li class="isub1">(1) Permeation of the soil or substratum.</li> -<li class="isub1">(2) Grappling the substratum.</li> -<li class="isub1">(3) A congenial moisture or water relation.</li> -<li class="isub1">(4) Distribution of roots for the purpose of reaching food-laden soil.</li> -<li class="isub1">(5) Exposure of surface for absorption.</li> -<li class="isub1">(6) The renewal of the delicate structures for absorption.</li> -<li class="isub1">(7) Aid in preparation of food from raw material.</li> -<li class="isub1">(8) The maintenance of the required balance between the environment</li> -<li class="isub3">as a whole and the increasing or changing requirements of the plant.</li> -</ul> - -<p><b>785.</b> (1) <b>Permeation of the soil or substratum.</b>—The -fundamental divergence of character in the environmental relations of -root and stem are manifest as soon as they emerge from the germinating -seed. Under the influence of the same stimulus (<i>gravity</i>) the root -<span class="pagenum"><a name="Page_411" id="Page_411">[Pg 411]</a></span> -shows its geotropic character by growing downward, while the geotropic -character of the stem is shown in its upward growth.</p> - -<p>The medium which the root has to penetrate offers considerable -resistance, and the form of the root as well as its manner of growth is -adapted to overcome this difficulty. The slender, conical, penetrating -root-tip wedges its way between the minute particles of soil or into -the minute crevices of the rock, while the nutation of the root enables -it to search for the points of least resistance. The root-tips having -penetrated the soil, the older portions of the root continue this wedge -action by growth in diameter, though, of course, elongation of the old -parts of the root does not take place. It is the widening growth of the -tapering root that produces the wedge-like action. The crevices of the -rock are sometimes broadened, but the resistance here is so great, the -root is often greatly flattened out.</p> - -<p><b>786.</b> (2) <b>Grappling the substratum.</b>—The mere penetration -of a single root into the soil gives it some hold on the soil and it -offers some resistance to a “pull” since it has wedged its way in -and the contact of soil particles offers resistance. The root hairs -formed on the first entering root growing laterally in great numbers -and applying themselves very closely to the soil particles, increase -greatly the hold of the plant on the soil, as one can readily see by -pulling up a young seedling. Lateral roots are soon formed, and as -these continue to extend and ramify in all directions, the hold is -increased until in the case of some of the larger plants the resistance -their hold would offer would equal many tons. Even in some of the -smaller shrubs and herbs the resistance is considerable, as one can -easily test by pulling with the hand. To obtain some idea of the amount -of resistance the roots of these smaller plants offer, they can be -tested by pulling with the ordinary spring scales.</p> - -<p><b>787.</b> (3) <b>A congenial moisture, or water relation.</b>—In -general, the roots seek those portions of the soil provided with a -modicum of moisture. Usually a suitable moisture condition is present -in those portions of the soil containing the plant food. But if -portions of the soil are too dry and very nearby other portions -<span class="pagenum"><a name="Page_412" id="Page_412">[Pg 412]</a></span> -containing moisture, the roots grow mainly into the moist substratum -(<i>hydrotropism</i>). If the soil is too wet, the roots grow away from it -to soil with less water, or in some cases will grow to and upon the -surface of the soil.</p> - -<p>The roots need <i>aeration</i>, and where the supply of water is too great, -the air is shut out, and we know that corn, wheat, and many other -plants become “sickly” in low and undrained soil in wet seasons. This -can only be said in the case of our ordinary dry land plants, i.e., -those that occupy an intermediate position between <i>water-loving</i> -plants and <i>dry-conditioned</i> plants. This phase of the subject must be -reserved for special treatment. (See <a href="#CHAPTER_XLVI">Chapter XLVI</a>.)</p> - -<p><b>788.</b> (4) <b>Distribution of roots for the purpose of reaching -food-laden soil.</b>—This is one of the essential relations of the -root in the case of the land plant, and probably accounts for the very -extensive ramification of the roots. To some extent it also explains -the different root systems in some plants. The pines, spruces, etc., -usually grow in regions where the soil is very shallow. The root -system does not extend deeply into the soil. It spreads laterally and -extends widely through the shallow surface soil and presents a very -different aspect from the stem system in the air. The root system of -the broad-leaved trees usually extends more deeply into the soil, while -of course, extending laterally to great distances. The hickory, walnut, -etc., especially have strong tap-roots which extend deeply into the -soil, and the root system of such a tree is more comparable in aspect, -if it were entirely uncovered, to the stem system in the air. The -tap-root is more pronounced in some trees than in others. It may be -that in the hickory and walnut the deep tap-root is important in -supplying the tree with water in dry seasons, especially when growing -on dry, gravelly soil which does not retain moisture on the surface -nor hold it within two or three feet of the surface. Experiment has -demonstrated, by pot culture of plants, that where soil rich in plant -food lies adjacent to poor soil, no matter in what part of the pot the -rich soil is, the greatest growth and branching of roots is in the rich soil. -<span class="pagenum"><a name="Page_413" id="Page_413">[Pg 413]</a></span></p> - -<p><b>789.</b> (5) <b>Exposure of root surface for absorption.</b>—The -principal part of root absorption takes place in the young root and -the root hairs growing near the root-tip. The root-tips and root hairs -in their relation to the root systems on which they are borne are -not to be compared morphologically with the leaves and stem system. -But the root-tips and hairs are absorbing organs of the roots while -the main root system supports them, brings them into relation with -the soil and moisture, and conducts food and other substances to and -from them. One of the important relations of the leaf is that of -light, and since the source of light is restricted, i.e., it is not -equally strong from all sides, an expanded and thin leaf-blade is more -effective than an equal expenditure of plant material in the form of -thread-like outgrowths. It is different, however, with the plant food -dissolved in the soil water. It is equally accessible on all sides. A -greater surface for absorption is exposed with the same expenditure of -material by multiplication of the organs and a reduction in their size. -Numerous delicate root hairs present a greater absorbing surface than -if the same amount of material were massed into leaf-like expansions. -There is another important advantage also. Its slender roots and -thread-like root hairs allow greater freedom of circulation of water, -food solutions, and air than if the absorbing organs of the roots were -broadly expanded.</p> - -<p><b>790.</b> (6) <b>The renewal of the delicate structures for -absorption.</b>—The delicate root hairs are easily injured. The thin -cell-walls through which food solutions flow become more or less choked -by the gradual deposit of substances in solution in the water, and -continued growth of the root in diameter forms a firmer epidermis and -cortex through which the solutions taken up by the root hairs would -pass with difficulty. For this reason new root hairs are constantly -being formed on the growing root-tip throughout the growing season, -and in the case of perennial plants, through each season of their growth.</p> - -<p><b>791.</b> (7) <b>Aid in preparation of food from raw -materials.</b>—For most plants the food obtained from the soil is -already in solution in the soil water. But there are certain substances -<span class="pagenum"><a name="Page_414" id="Page_414">[Pg 414]</a></span> -(examples, some of the chemical compounds of potash, phosphoric acid, -etc.) which are insoluble in water. Certain acids excreted by the -roots aid in making these substances soluble (see <a href="#CHAPTER_III">Chapter III</a>). -In a number of plants the roots have become associated with fungus or -bacterial organisms which assist in the manufacture of nitrogenous food -substances, or even in the absorption of ordinary food solution from -the soil, or in making use of the decaying humus of the forest -(see <a href="#CHAPTER_IX">Chapter IX</a>).</p> - -<p><b>792.</b> (8) <b>The maintenance of the required balance between -the environment and the increasing or changing requirements of the -plant.</b>—In this matter the entire plant participates. Mention is -made here only of the general relation which the root sustains to its -own environment and the increased burden placed upon it by the shoot. -The increase in the root system keeps pace with the increasing size of -the stem system. The roots become stronger, their ramifications wider, -and the number of absorbing rootlets more numerous. The observation -is sometimes offered that the correlation between the root system of -a plant, and the form of the stem system and position of the leaves, -is of such a nature that plants with a tap-root system have their -leaves so arranged as to shed the water to the center of the system, -while plants with a fibrous-root system have their leaves so arranged -as to shed the water outward. In support of this attention is called -to the radiate type of the leaf system of the dandelion, beet, etc. -In the second place the imbricate type as manifested in broad-leaved -trees, and in the overlapping branch systems of many pines, etc. One -should note, however, that in the former class the leaves are often -arranged to shed as much water outward as inward. As to the latter -class, there is need of experiment to determine whether these empirical -observations are correct, for the following reasons: 1st, Root and leaf -distribution are governed by other and more important laws, the root -being influenced by the location of food in the soil which usually -forms a very thin stratum while the shoot and leaf is mainly influenced -by light, and root distribution is much wider in a lateral direction -<span class="pagenum"><a name="Page_415" id="Page_415">[Pg 415]</a></span> -than that of the branches. 2d, In light rains the leaf surface holds -back practically all the rain which is then evaporated into the air -and lost to the root systems. 3d, In heavy and long-continued rains -the water breaks through the leaf system to such an extent that roots -under the tree would be as well supplied as those outside, and the -ground outside being saturated anyway, the roots do not need the -small additional water which may have been shed outward. 4th, It is -the habit of plants where left undisturbed (except in rare cases), to -grow in more or less dense formations or societies. Here there is no -opportunity for any appreciable centrifugal distribution of rainfall -and yet the root distribution is practically the same, except that the -root systems of adjacent plants are interlaced.</p> - -<h4><a name="XLI_2" id="XLI_2">II. Kinds of Roots.</a></h4> - -<p><b>793. The root system.</b>—From the foregoing, it will be understood -that the roots of a plant taken together form the <i>root system</i> of that -plant. In soil-roots in general we usually recognize two kinds of root -systems.</p> - -<p><b>794. The fibrous-root system.</b>—Roots which are composed of -numerous slender branching roots resembling “fibers,” are termed -<i>fibrous</i>, or the plant is said to have a <i>fibrous-root system</i>. The -bean, corn, most grasses, and many other plants have fibrous-root systems.</p> - -<p><b>795. The tap-root system.</b>—Plants with a recognizable central -shaft-like root, more or less thickened and considerably stouter -than the lateral roots, are said to have <i>tap</i> roots, or they have a -<i>tap-root system</i>. The dandelion, beet, carrot (see crown tuber) are -examples. The hickory, walnut, and some other trees have very prominent -tap-roots when young. The tap-root is maintained in old age, but the -lateral roots often become finally as large as the tap-root. Besides -tap-roots and fibrous-roots, which include the larger number, several -other kinds of roots are to be enumerated.</p> - -<p><b>796. Aerial roots.</b>—Aerial roots are most abundantly developed -in certain tropical plants, especially in the orchids and aroids. Many -<span class="pagenum"><a name="Page_416" id="Page_416">[Pg 416]</a></span> -examples of these plants are grown in conservatories. The amount of -moisture is so great in these tropical regions that the roots are -abundantly supplied without the soil relation. Certain of the roots -hang free in the air and are provided with a special sheath of spongy -tissue called the <i>velamen</i>, through which moisture is absorbed from -the air. Other roots attach themselves to the trunk or branches of -the tree on which the orchid is growing, and furnish the support to -the <i>epiphyte</i>, as such plants are often called. Among the tangle -of these clinging roots falling leaves are caught. Here they decay -and nourishing roots grow from the clinging roots into this mass -of decaying leaves and supply some of the plant food. Aerial roots -sometimes possess chlorophyll.</p> - -<p>There are a number of plants, however, in temperate regions which -have aerial roots. These are chiefly used to give the stem support as -it climbs on trees or on walls. They are sometimes called clinging -roots. A common example is the climbing poison-ivy (Rhus radicans), the -trumpet creeper, etc. Such aerial roots are called <i>adventitious</i> roots.</p> - -<p><b>797. Bracing roots, or prop roots.</b>—These are developed in a -great variety of plants and serve to brace or prop the plant where -the fibrous-root system is insufficient to support the heavy shoot -system, or the shoot system branches so widely props are needed to hold -up the branches. In the common Indian corn several whorls of bracing -roots arise from the nodes near the ground and extend outward and -downward to the ground, though the upper whorls do not always succeed -in reaching the ground. The screw-pine so common in greenhouses affords -an excellent example of prop roots. The roots are quite large, and long -<span class="pagenum"><a name="Page_417" id="Page_417">[Pg 417]</a></span> -before the root reaches the soil the large root cap is evident. The -banyan tree of India is a classic example of prop roots for supporting -the wide-reaching branches. The mangrove in our own subtropical forests -of Florida is a nearer example.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img src="images/fig448.jpg" alt="" width="250" height="260" /> - <p class="center">Fig. 448.<br /> Bracing roots of Indian corn.</p> - </div> - <div class="figsub"> - <img src="images/fig449.jpg" alt="" width="250" height="244" /> - <p class="center">Fig. 449.<br /> Buttresses of silk-cotton tree,<br /> Nassau.</p> - </div> -</div> - -<p><b>798. Buttresses</b> are formed at the junction of the root and -trunk, and therefore are part root and part stem. Splendid examples -of buttresses are formed on the silk-cotton tree. They are sometimes -formed on the elm and other trees in low swampy ground.</p> - -<p><b>799. Fleshy roots, or root tubers.</b>—These are enlargements of -the root in the form of tubers, as in the sweet potato, the dahlia, -etc. They are storage reservoirs for food. Portions of the roots become -thick and fleshy and contain large quantities of sugar, as in the sweet -potato, or of <i>inulin</i> (a carbohydrate) in the root tubers of the -dahlia and other composites.</p> - -<p><b>800. Water-roots and roots of water plants.</b>—These are roots -which are developed in the water, or in the soil. Water-roots are -<span class="pagenum"><a name="Page_418" id="Page_418">[Pg 418]</a></span> -sometimes formed on land plants where the root comes in contact with a -body of water, or a stream. Water-roots usually possess no root hairs, -or but a few, as can be seen by comparing water-roots with soil-roots, -or by comparing roots of plants grown in water cultures. The greater -body of water in contact with the root and the more delicate epidermis -of the root render less necessary the root hairs. The duck-meats -(Lemna) are good examples of plants having only water-roots. Other -aquatic plants like the potamogetons, etc., have true roots which grow -into the soil and serve to anchor the plant, but they are not developed -as special organs of absorption, since the stem and leaves largely -perform this function.</p> - -<p><b>801. Holdfasts.</b>—These are organs for anchorage which are not -true roots. These are especially well developed in some of the algæ -(Fucus, Laminaria, etc.). They are usually called <i>holdfasts</i>. The -holdfasts of the larger algæ are mainly for anchoring the plant. They -do not function as absorbing organs, and the structure is different -from that of true roots.</p> - -<p><b>802. Haustoria or suckers</b> is a name applied to another kind of -holdfast employed by parasitic plants. In the dodder the haustorium -penetrates the tissue of the <i>host</i> (the plant on which the parasite -grows), and besides furnishing a means of attachment, it serves as an -absorbing organ by means of which the parasite absorbs food from its -host. The parasitic fungi like the powdery mildews which grow on the -surface of their hosts have simple haustoria which serve both as organs -of attachment and absorption, while in the rusts which grow in the -interior of their hosts the haustoria are merely absorbing organs.</p> - -<p><b>803. Rootlets, or rhizoids.</b>—Many of the algæ, liverworts and -mosses have slender, hair-like organs of attachment and absorption. -These plants do not have true roots. Because of the slender form and -small size of these organs, they are called <i>rhizoids</i>, or <i>rootlets</i>. -In form many of them resemble the root hairs of higher plants.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_419" id="Page_419">[Pg 419]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XLII" id="CHAPTER_XLII">CHAPTER XLII.</a><br /> -<span class="h_subtitle">THE FLORAL SHOOT.</span></h3> -</div> - -<h4><a name="XLII_1" id="XLII_1">I. The Parts of the Flower.</a></h4> - -<p>The portion of the stem on which the flowers are borne is the <i>flower</i> -shoot or axis, or taken together with the flowers, it is known as the -<i>Flower Cluster</i>.</p> - -<p><b>804. The flower.</b>—The flower is best understood by an -examination, first of one of the types known as a “complete” flower, -as in the buttercup, the spring-beauty, the blood-root, the apple, the -rose, etc.</p> - -<p>There are two sets of organs or members in the complete flower—(1) the -floral envelope; (2) the essential or necessary members or organs.</p> - -<p>The floral envelope when complete consists of—1st, an outer envelope, -the <i>calyx</i>, made up of several leaf-like structures (<i>sepals</i>), very -often possessing chlorophyll, which envelop all the other parts of the -flower when in bud; 2d, an inner envelope, the <i>corolla</i>, also made up -of several leaf-like parts (<i>petals</i>), usually bright colored and larger -than the sepals. The outer and inner floral envelopes are usually in -whorls (though in close spirals in many of the buttercup family, etc.), -and for reasons discussed elsewhere (<a href="#CHAPTER_XXXIV">Chapter XXXIV</a>) -represent leaves. The essential or necessary members of the flower are also usually -in whorls and likewise represent leaves, but only in rare cases is there -any suggestion, either in their form or color, of a leaf relationship. -These members are in two sets: (1) The outer, or <i>andrœcium</i>, -consisting of a few or many parts (<i>stamens</i>); (2) the inner set, the -<i>gynœcium</i>, consisting of a few or many parts (<i>carpels</i>). -<span class="pagenum"><a name="Page_420" id="Page_420">[Pg 420]</a></span></p> - -<p><b>805. Purpose of the flower.</b>—While the ultimate purpose of -all plants is the production of seed or its equivalent through -which the plant gains distribution and perpetuation, the flower is -the specialized part of the seed plant which utilizes the food and -energies contributed by other members of the plant organization for the -production of seed. In addition to this there are definite functions -performed by the members of the flower, which come under the general -head of plant work, or flower work.</p> - -<p><b>806. The calyx, or the sepals.</b>—These are chiefly protective, -affording protection to the young stamens and carpels in the flower -bud. Where the corolla is absent, sepals are usually present and then -assume the function of the petals. In a few instances the calyx may -possibly ultimately join in the formation of the fruit (examples: the -butternut, walnut, hickory).</p> - -<p><b>807. The corolla, or petals.</b>—The petals are partly protective -in the bud, but their chief function where well developed seems to be -that of attracting insects, which through their visits to the flower -aid in “<i>pollination</i>,” especially “<i>cross pollination</i>.”</p> - -<p><b>808. The stamens.</b>—The stamens (= microsporophylls) are -flower organs for the production of <i>pollen</i>, or <i>pollen-spores</i> (= -microspores). The <i>stalk</i> (not always present) is the <i>filament</i>, the -<i>anther</i> is borne on the filament when the latter is present. The -anther consists of the <i>anther sacs</i> or <i>pollen sacs</i> (microsporangium) -containing the pollen-spores, and the <i>connective</i>, the sterile tissue -lying between and supporting the anther sac. The stamens are usually -separate, but sometimes they are united by their filaments, or by their -anthers. When the pollen is ripe they open by slits or pores and the -pollen is scattered; or in rarer cases the pollen mass (<i>pollinium</i>) is -removed through the agency of insects (<a href="#CHAPTER_XLIII">see Insect pollination, Chap. XLIII</a>).</p> - -<p><b>809. The pistil.</b>—The pistil consists of the “<i>ovary</i>,” the -<i>style</i> (not always present), and the <i>stigma</i>. These are well shown in -a <i>simple pistil</i>, common examples of which are found in the buttercup, -marsh marigold, the pea, bean, etc. The simple pistil is equivalent to -a <i>carpel</i> (= macrosporophyll), while the <i>compound pistil</i> consists of -<span class="pagenum"><a name="Page_421" id="Page_421">[Pg 421]</a></span> -two or several carpels joined, as in the toothwort, trillium, lily, -etc. The <i>ovary</i> is the enlarged part which below is attached to -the receptacle of the flower, and contains within the <i>ovules</i>. The -<i>style</i>, when present, is a slender elongation of the upper end of -the ovary. The <i>stigma</i> is supported on the end of the style when the -latter is present. It is often on a capitate enlargement of the style -or extends down one side, or when the style is absent it is usually -seated directly on the upper end of the ovary. The stigmatic surface is -glutinous or “sticky,” and serves to hold the pollen-spores when they -come in contact with it.</p> - -<p>The <i>ovules</i> are within the ovary and are arranged in different ways -in different plants. The pollen grain (or better pollen-spore = -microspore), after it has been transferred to the stigma, “germinates,” -and the pollen tube grows down through the tissue of the stigma and -style, or courses down the stylar canal until it reaches the ovule. -Here it usually enters the ovule (macrosporangium) at the <i>micropyle</i> -(in some of the ament-bearing plants it enters at the <i>chalaza</i>), and -the sperm cells are emptied into the embryo sac in the interior of the ovule.</p> - -<p><b>810. Fertilization.</b>—One of the sperms unites with the egg -in the embryo sac. This is <i>fertilization</i>, and from the fertilized -egg the young embryo is formed still within the ovule. <i>Double -fertilization</i>,—the other sperm cell sometimes unites with one or both -of the “polar” nuclei which have united to form the “definitive” or -“endosperm” nucleus. As a result of fertilization, the embryo plant is -formed within the ovule, the coats of which enlarge by growth forming -the seed coats, and altogether forming the seed. (See <a href="#CHAPTER_XXXIV">Chapters XXXIV</a>, -<a href="#CHAPTER_XXXV">XXXV</a>, <a href="#CHAPTER_XXXVI">XXXVI</a>.)</p> - -<h4><a name="XLII_2" id="XLII_2">II. Kinds of Flowers.</a></h4> - -<p><b>811. Absence of certain flower parts.</b>—The <i>complete</i> flower -contains all the four series of parts. When any one of the series of -parts is lacking, the flower is said to be <i>incomplete</i>. Where only one -series of the floral envelopes is present the flowers are said to be -<i>apetalous</i> (the petals are absent), examples: elm, buckwheat, etc. -<span class="pagenum"><a name="Page_422" id="Page_422">[Pg 422]</a></span> -Flowers which lack both floral envelopes are <i>naked</i>. When pistils are -absent but stamens are present the flowers are <i>staminate</i>, whether -floral envelopes are present or not; and so when stamens are absent and -pistils present the flower is <i>pistillate</i>. If both stamens and pistils -are absent the flower is said to be <i>sterile</i> or <i>neutral</i> (snowball, -marginal or showy flowers in hydrangea). Flowers with both stamens and -pistils, whether or not they have floral envelopes, are <i>perfect</i> (or -hermaphrodite), so if only one of these sets of <i>essential organs</i> -of the flower is present the flower is <i>imperfect</i>, or <i>diclinous</i>. -Sometimes the imperfect, or diclinous, flowers are on the same plant, -and the plant is said to be <i>monœcious</i> (of one household). When -staminate flowers are on certain individual plants, and the pistillate -flowers of the same species are on other individuals, the plant is -<i>diœcious</i> (or of two households). When some of the flowers of a plant -are diclinous and others are perfect, they are said to be <i>polygamous</i>.</p> - -<p>Many of these variations relating to the presence or absence of flower -parts in one way or another contribute to the well-being of the plant. -Some indicate a division of labor; thus in the neutral flowers of -certain species of hydrangea or viburnum, the showy petals serve to -attract insects which aid in the pollination of the fertile flowers. It -must not be understood, however, that all variations in plants which -results in new or different forms of flowers is for the good of the -species. For example, under cultivation the flowers of viburnum and -hydrangea sometimes are all neutral and showy. While such variations -sometimes contribute to the happiness of man, the plant has lost the -power of developing seed. In diclinous flowers cross pollination is -necessitated.</p> - -<p><b>812. Form of the flower.</b>—The flower as a whole has <i>form</i>. -This is so characteristic that in general all flowers of the different -individuals of a species are of the same shape, though they may vary -in size. In general, flowers of closely related plants of different -species are of the same type as to form, so that often in the shape of -the flower alone we can see the relationship of kind, though the form -of the flower is not the most important nor always the sure index of -<span class="pagenum"><a name="Page_423" id="Page_423">[Pg 423]</a></span> -kinship. Since many flowers resemble certain familiar objects, names -are often used which relate to these objects.</p> - -<p>Flowers are said to be <i>regular</i>, or <i>irregular</i>. In a regular flower -all of the parts of a set or series are of the same shape and size, -while in irregular flowers the parts are of a different shape or size -in some of the sets. The flowers of the pea family (<i>Papilionaceæ</i>), -of the mint family (<i>Labiatæ</i>), of the morning glory, larkspur, -monkshood, etc., are irregular (<a href="#FIG_450">fig. 450</a>). The corolla -usually gives the characteristic form to the flower, and the name is usually -applied to the form of the corolla.</p> - -<div class="figcenter"> - <img id="FIG_450" src="images/fig450.jpg" alt="" width="600" height="232" /> - <div class="blockquot"> - <p class="center">Fig. 450.</p> - <p>Several forms of flowers. Regular flowers. <i>wh</i>, wheel-shaped - corolla; <i>sa</i>, salver-shaped; <i>tub</i>, tubular-shaped. Irregular flowers. - <i>pa</i>, butterfly or papilionaceous; <i>per</i>, personate or masked flower; - <i>lab</i>, gaping or ringent corolla. The two latter are called bilabiate flowers.</p> - </div> -</div> - -<p>Some of the different forms are wheel-shaped or <i>rotate</i> corolla when -the petals spread out at once like the spokes of a wheel, as in the -potato, tomato, or bittersweet; <i>salver-shaped</i> when the petals spread -out at right angles from the end of a corolla tube, as in the phlox; -<i>bell-shaped</i>, or <i>campanulate</i>, as in the harebell or campanula; -<i>funnel-shaped</i>, as in the morning glory; <i>tubular</i>, when the ends of -the petals spread but little or none from the end of the corolla tube, -as in the turnip flower or in the disk florets of the composites. The -<i>butterfly</i>, or <i>papilionaceous</i> corolla is peculiar as in the pea -or bean. The upper petal is the “banner,” the two lateral ones the -“wings,” and the two lower the “keel.”</p> - -<p>The <i>labiate</i> corolla is characteristic of the mint family where the -<span class="pagenum"><a name="Page_424" id="Page_424">[Pg 424]</a></span> -gamosepalous corolla is unequally divided, so that the two upper lobes -are sharply separated from the three lower forming two “lips.” The -labiate corolla of the toad-flax, or snapdragon is <i>personate</i>, or -<i>masked</i>, because the lower lip arches upward like a palate and closes -the entrance to the corolla tube; that of the dead nettle (<i>Lamium</i>) is -<i>ringent</i> or <i>gaping</i>, because the lips are spread wide apart. In -some plants the labiate corolla is not very marked and differs but slightly -from a regular form.</p> - -<p>The <i>ligulate</i> or <i>strap-shaped</i> corolla is characteristic of -the flowers of the dandelion or chicory, or of the ray flowers of other -composites (<a href="#FIG_451">fig. 451</a>). The lower part of the gamosepalous -corolla is tubular, and the upper part is strap-shaped, as if that part of the -tube were split on one side and spread out flat.</p> - -<p>These forms of the flower should be studied in appropriate examples.</p> - -<p><b>813. Union of flower parts.</b>—In the buttercup flower all the -parts of each series are separate from one another and from other -series of parts. Each one is attached to the <i>receptacle</i> of the -flower, which is a very much shortened portion of the flower axis. -The calyx being composed of separate and distinct parts is said to be -<i>polysepalous</i>, and the corolla is likewise <i>polypetalous</i>. The stamens -are <i>distinct</i>, and the pistils are <i>simple</i>. In many flowers, however, -there is a greater or lesser <i>union</i> of parts.</p> - -<p><b>814. Union of parts of the same series or cycle.</b>—The parts -<i>coalesce</i>, either slightly or to a great extent. Usually they are not -so completely coalesced but what the number of parts of the series can -be determined. Where the sepals are united the calyx is <i>gamosepalous</i>, -when the petals are united the corolla is <i>gamopetalous</i>.</p> - -<p>Union of the sepals or of the corolla is quite common, but union -of the stamens is rare except in a few families where it is quite -characteristic. When the stamens are united by their anthers, they -are <i>syngenœsious</i>. This is the case in most flowers of the composite -family. When all the stamens are united into one group by their -filaments, they are <i>monadelphous</i> (one brotherhood), as in -<span class="pagenum"><a name="Page_425" id="Page_425">[Pg 425]</a></span> -hollyhock, hibiscus, cotton, marsh-mallow, etc. When they are united -by their filaments in two groups, they are <i>diadelphous</i> (two -brotherhoods), as in the pea and most members of the pea family. In -most species of St. John’s wort (Hypericum), the stamens are united in -threes (<i>triadelphous</i>).</p> - -<p><b>815. The carpels are often united.</b>—The pistil is then said to -be <i>compound</i>. Where the pistils are consolidated, usually the adjacent -walls coalesce and thus separate the cavity of each ovary. Each cavity -in the compound pistil is a <i>locule</i>. In some cases the adjacent walls -disappear so that there is one common cavity for the compound pistil -(examples: purslane, chickweeds, pinks, etc.). In a few cases there is a -false partition (example, in the toothwort and other crucifers). The -compound pistil is very often lobed slightly, so that the different -pistils can be discerned. More often the styles or stigmas are -distinct, and thus indicate the number of pistils united.</p> - -<p><b>816. Union of the parts of different series.</b>—While in the -buttercup and many other flowers, all the different parts are inserted -on the torus or receptacle, in other flowers one series of parts may -be joined to another. This is <i>adnation</i> of parts, or the two or more -series are <i>adnate</i>. In the morning glory the stamens are inserted -on the inner face of the corolla tube; the same is true in the mint -family, and there are many other examples. The insertion of parts, -whether free or adnate, is usually spoken of in reference to their -relation to the pistil. Thus, in the buttercup the floral envelopes and -stamens are all free and <i>hypogynous</i>, they are <i>below</i> the pistil. -The pistil in this case is <i>superior</i>. In the cherry, pear, etc., the -petals and stamens are borne on the edge of the more or less elevated -tube of the calyx, and are said to be <i>perigynous</i>, i.e., around the -pistil. In the cranberry, huckleberry, etc., the calyx is for the -most part united with the wall of the ovary with the short calyx -limbs projecting from the upper surface. The petals and stamens are -inserted on the edge of the calyx above the ovary; they are, therefore, -<i>epigynous</i>, and the ovary being under the calyx, as it were, is -<i>inferior</i>. -<span class="pagenum"><a name="Page_426" id="Page_426">[Pg 426]</a></span></p> - -<h4><a name="XLII_3" id="XLII_3">III. Arrangement of Flowers, or Mode of Inflorescence.</a></h4> - -<p><b>817. Flowers are solitary or clustered.</b>—<i>Solitary flowers</i> -are more simple in their arrangement, i.e., it is easier for us to -determine and name their relation to each other and to other parts of -the plant. They are either <i>axillary</i>, i.e., on short lateral shoots -in the axils of ordinary foliage leaves, or they are <i>terminal</i>, i.e., -they are borne on the end of the main axis of an ordinary foliage -shoot. In either case they are so far separated, and the foliage -leaves are so prominent, they do not form recognizable groups or -clusters. The manner of arrangement of flowers on the shoot is called -<i>inflorescence</i>, while the group of flowers so arranged is the -<i>flower cluster</i>.</p> - -<p>Two different modes of inflorescence are usually recognized in -the arrangement of flowers on the stem. (1) The <i>corymbose</i>, or -<i>indeterminate inflorescence</i> (also indefinite inflorescence), in -which the flowers arise from axillary buds, and the terminal bud may -continue to grow. (2) The <i>cymose</i> or <i>determinate inflorescence</i> -(also <i>definite inflorescence</i>) in which the flowers arise from terminal -buds. This arrests the growth of the shoot in length.</p> - -<p>There are several advantages to the plant in the different modes of -inflorescence, chief among which is the massing of the flowers, thus -increasing the chances for effective pollination.</p> - -<p class="center"><b>A. FLOWER CLUSTERS WITH INDETERMINATE<br /> INFLORESCENCE.</b></p> - -<p><b>818. The simplest mode of indeterminate inflorescence</b> is where -the flowers arise in the axils of normal foliage leaves, while the -terminal bud, as in the florist’s smilax, the bellwort, moneywort, -apricot, etc., continues to grow. The flowers are <i>solitary</i> and -<i>axillary</i>. In other cases which are far more numerous, the flowers are -associated into more or less definite clusters in which are a number -of recognizable types. The word type used in this sense, it should be -<span class="pagenum"><a name="Page_427" id="Page_427">[Pg 427]</a></span> -understood, does not refer to an original structure which is the -source of others. It merely refers to a mode of inflorescence which we -attempt to recognize, and about which we group those forms which have -a resemblance to one another. There are many forms of flower clusters -which do not conform to any one of our recognized types, and are very -puzzling. The evolution of the flower clusters has been <i>natural</i>, and -we cannot make them all conform to an <i>artificial</i> classification. -These <i>types</i> are named merely as a matter of convenience in the -expression of our ideas. The types usually recognized are as follows:</p> - -<p><b>819. The raceme.</b>—The flower-shoot is more or less elongated, -and the leaves are reduced to a minute size termed <i>bracts</i>, while the -flowers on lateral axes are solitary in the axils of the bracts. The -reduction in the size of the leaves and the somewhat limited growth -of the shoot in length, makes the flowers more prominent, and brings -them into closer relation than if they were formed in the axils of -the leaves on the ordinary foliage shoot. The choke cherry, currant, -pokeweed, sourwood, etc., are examples of a raceme (fig. 569). In most -plants with the raceme type, while the inflorescence is indeterminate, -and the uppermost flowers (those toward the end of the main shoot) -are younger, still the period of flowering is somewhat restricted -and the raceme stops growing. In a few plants, however, as in the -common “shepherd’s-purse,” the raceme continues to grow throughout the -summer, so that the lower flowers may have ripened their seed while -the terminal portion of the raceme is still growing and producing -new flowers. Compound racemes are formed when by branching of the -flower-shoot there are several racemes in a cluster, as in the false -Solomon’s seal (Smilacina racemosa).</p> - -<p><b>820. The panicle.</b>—The panicle is developed from the raceme type -by the branching of the lateral flower-axes forming a loose open flower -cluster, as in the <i>oat</i>.</p> - -<p><b>821. The thyrsus</b> is a compact panicle of pyramidal form, as in -the lilac, horse-chestnut, etc.</p> - -<p><b>822. The corymb.</b>—The corymb shows likewise an easy transition -<span class="pagenum"><a name="Page_428" id="Page_428">[Pg 428]</a></span> -from the raceme type, by the shortening of the main axis of -inflorescence, and the lengthening of the lower, lateral flower -peduncles so that the flower cluster is more or less flattened on -top. This represents the <i>simple corymb</i>. A <i>compound corymb</i> is one -in which some of the flower peduncles branch again forming secondary -corymbs, as in the mountain-ash. It is like a panicle with the lower -flower stalks elongated.</p> - -<p><b>823. The umbel.</b>—The umbel is developed from the raceme, or -corymb. The main flower-shoot remains very short or undeveloped with -several flowers on long peduncles arising close together around this -shortened axis, in the form of a whorl or cluster. Examples are found -in the milkweed, water pennywort (Hydrocotyle), the oxheart cherry, -etc. A <i>compound</i> umbel is one in which the peduncles are branched, -forming secondary umbels, as in the caraway, parsnip, carrot, etc.</p> - -<p><b>824. The spike.</b>—In the spike the main axis is long, and the -solitary flowers in the axils of the bracts are usually sessile, and -often very much crowded. The plaintain, mullein (<a href="#FIG_422">fig. 422</a>), -etc., are examples. The spike is a raceme, only the flowers are sessile -and crowded. In the grasses the flower cluster is branched, and the -branchlets bearing a few flowers are spikelets.</p> - -<p><b>825. The head.</b>—When the flower axis is very much shortened -and the flowers crowded and sessile or nearly so, forming a globose -or compressed cluster, it is a <i>head</i> or <i>capitulum</i>. The transition -is from a spike by the shortening of the main axis, as in the clover, -button bush (<i>Cephalanthus</i>), etc., or in the shortening of the -peduncles in an umbel, as in the daisy, dandelion, and other composite -flowers. In these the head is surrounded by an involucre, which in -the young head often envelopes the mass of flowers, thus affording -them protection. In some other composites (Lactuca, for example) the -involucre affords protection for a longer period, even while the seeds -are ripening.</p> - -<p><b>826. The spadix.</b>—When the main axis of the flower cluster is -fleshy, the spike or head forms a <i>spadix</i>, as in the Indian turnip, -the skunk-cabbage, the calla, etc. The spadix is usually more or less -enclosed in a <i>spathe</i>, a somewhat strap-shaped leaf.</p> - -<p><b>827. The catkin.</b>—A spike which is usually caducous, i.e., falls -<span class="pagenum"><a name="Page_429" id="Page_429">[Pg 429]</a></span> -away after the maturity of the flower or fruit, is called a catkin, -or an <i>ament</i>. The flower clusters of the alder, willow, (fig. 555), -poplar, and the staminate flower clusters of the oak, hickory, -hazel, birch, etc., are <i>aments</i>. So characteristic is this mode -of inflorescence that the plants are called <i>amentiferous</i>, or -<i>amentaceous</i>.</p> - -<div class="figcenter"> - <img id="FIG_451" src="images/fig451.jpg" alt="" width="400" height="483" /> - <div class="blockquot"> - <p class="center">Fig. 451.</p> - <p>Head of sunflower showing centripetal inflorescence of tubular - flowers. (Photo by the Author.)</p> - </div> -</div> - -<p><b>828. Anthesis of flowers with indeterminate inflorescence.</b>—In -the anthesis of the raceme as well as in other corymbose forms the -lower (or outer) flowers being older, open first. The opening of the -flowers then takes place from below, upward; or from the outside, -inward toward the center of inflorescence. The <i>anthesis</i>, i.e., the -opening of the flowers of corymbose forms is said to be <i>centripetal</i>, -i.e., it progresses from outside, inward. The anthesis of the fuller’s -teazel is peculiar, since it shows both types. There are several -<span class="pagenum"><a name="Page_430" id="Page_430">[Pg 430]</a></span> -distinct advantages to the plant where anthesis extends over a period -of time, as it favors cross pollination, favors the formation of seed -in case conditions should be unfavorable at one period of anthesis, -distributes the drain on the plant for food, etc.</p> - -<div class="figcenter"> - <img src="images/fig452.jpg" alt="" width="600" height="312" /> - <div class="blockquot"> - <p class="center">Fig. 452.</p> - <p class="center">Heads of fuller’s teazel in different stages of flowering.</p> - </div> -</div> - -<p class="center"><b>B. FLOWER CLUSTERS WITH DETERMINATE<br /> INFLORESCENCE.</b></p> - -<p><b>829. The simplest mode of determinate inflorescence</b> is a plant -with a solitary terminal flower, as in the hepatica, the tulip, -etc. The leaves in these two plants are clustered in the form of a -rosette, and the aerial shoot is naked and bears the single flower at -its summit. Such a flower-shoot is a <i>scape</i>. As in the case of the -indeterminate inflorescence, so here the larger number of flower-shoots -are more complex and specialized, resulting in the evolution of flower -clusters or masses. Accompanying the association of flowers into -clusters there has been a reduction in leaf surface on the flower-shoot -so that the flowers predominate in mass and are more conspicuous. Among -the recognized modes of determinate inflorescence, the following are -the chief ones:</p> - -<p><b>830. The cyme.</b>—In the cyme the terminal flower on the main axis -opens first and the remaining flowers are borne on lateral shoots, -<span class="pagenum"><a name="Page_431" id="Page_431">[Pg 431]</a></span> -which arise from the axils of leaves or bracts, below. These lateral -shoots usually branch and elongate so that the terminal flowers on all -the branches reach nearly the same height as the terminal flower on the -main shoot, forming a somewhat flattened or convex top of the flower -cluster. This is illustrated in the basswood flower. The anthesis of -the cyme is <i>centrifugal</i>, i.e., from the inside outward to the margin. -But it is often more or less mixed, since the lateral shoots if they -bear more than one flower are diminutive cymes and the terminal flower -opens before the lateral ones. Where the flower cluster is quite large -and the branching quite extensive, <i>compound cymes</i> are formed, as in -the dogwood, hydrangea, etc.</p> - -<div class="figcenter"> - <img id="FIG_453" src="images/fig453.jpg" alt="" width="600" height="265" /> - <div class="blockquot"> - <p class="center">Fig. 453.</p> - <p>Diagrams of cymose inflorescence. <i>A</i>, dichasium; <i>B</i>, scorpioid - cyme; <i>C</i>, helicoid cyme. (After Strasburger.)</p> - </div> -</div> - -<p><b>831. The helicoid cyme.</b>—Where successive lateral branching -takes place, and always continues on the same side a curved flower -cluster is formed, as in the forget-me-not and most members of the -borage family. This is known as a <i>helicoid cyme</i> (<a href="#FIG_453">fig. 453, <i>C</i></a>). -Each new branch becomes in turn the “false” axis bearing a new branch on the -same side.</p> - -<p><b>832. The scorpioid cyme.</b>—<i>A scorpioid cyme</i> (<a href="#FIG_453">fig. 453, <i>B</i></a>) -is formed where each new branch arises on alternate sides of the “false” axis.</p> - -<p><b>833. The forking cyme</b> is where each “false” axis produces two -branches opposite, so that it represents a false dichotomy (example, -the flower cluster of chickweed). -<span class="pagenum"><a name="Page_432" id="Page_432">[Pg 432]</a></span></p> - -<p><b>834.</b> Some of these flower clusters are peculiar and it is -difficult to see how the helicoid, or scorpioid, cymes are of any -advantage to the plant over a true cyme. The inflorescence of the -plant being determinate, if the flowering is to be extended over a -considerable period a peculiar form would necessarily result. In the -<i>helicoid cyme</i> continued branching takes place on one side, and -the result in the forget-me-not is a continued inflorescence in its -effect like that of a continued raceme (compare shepherd’s-purse). -But we should not expect that all of the complex and specialized -structures from simple and generalized ones are beneficial to the -plant. In many plants we recognize evolution in the direction of -advantageous structures. But since the plant cannot consciously -evolve these structures, we must also recognize that there may be -phases of retrogression in which the structures evolved are not so -beneficial to the plant as the more simple and generalized ones of its -ancestors. Variation and change do not result in advancing the plant -or plant structures merely along the lines which will be beneficial. -The tendency is in all directions. The result in general may be -diagramed by a tree with divergent and wide-reaching branches. Some die -out; others remain subordinate or dormant; while still others droop -downward, showing a retrogression. But in this backward evolution -they do not return to the condition of their ancestors, nor is the -same course retraced. A new downward course is followed just as the -downward-growing branch follows a course of its own, and does not -return in the trunk.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_433" id="Page_433">[Pg 433]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XLIII" id="CHAPTER_XLIII">CHAPTER XLIII.</a><br /> -<span class="h_subtitle">POLLINATION.</span></h3> -</div> - -<p class="center"><b>Origin of heterospory, and the necessity<br /> for pollination.</b></p> - -<p><b>835. Both kinds of sexual organs on the same prothallium.</b>—In -the ferns, as we have seen, the sexual organs are borne on the -prothallium, a small, leaf-like, heart-shaped body growing in moist -situations. In a great many cases both kinds of sexual organs are -borne on the same prothallium. While it is perhaps not uncommon, in -some species, that the egg-cell in an archegonium may be fertilized -by a spermatozoid from an antheridium on the same prothallium, it -happens many times that it is fertilized by a spermatozoid from another -prothallium. This may be accomplished in several ways. In the first -place antheridia are usually found much earlier on the prothallium than -are the archegonia. When these antheridia are ripe, the spermatozoids -escape before the archegonia on the same prothallium are mature.</p> - -<p><b>836. Cross fertilization in monœcious prothallia.</b>—By swimming -about in the water or drops of moisture which are at times present in -these moist situations, these spermatozoids may reach and fertilize -an egg which is ripe in an archegonium borne on another and older -prothallium. In this way what is termed cross fertilization is brought -about nearly as effectually as if the prothallia were diœcious, i.e. if -the antheridia and archegonia were all borne on separate prothallia.</p> - -<p><b>837. Tendency toward diœcious prothallia.</b>—In other cases -some fern prothallia bear chiefly archegonia, while others bear only -antheridia. In these cases cross fertilization is enforced because -of this separation of the sexual organs on different prothallia. -These different prothallia, the male and female, are largely due to a -difference in food supply, as has been clearly proven by experiment.</p> - -<p><b>838. The two kinds of sexual organs on different prothallia.</b>—In -the horsetails (equisetum) the separation of the sexual organs on -different prothallia has become quite constant. Although all the spores -are alike, so far as we can determine, some produce small male plants -<span class="pagenum"><a name="Page_434" id="Page_434">[Pg 434]</a></span> -exclusively, while others produce large female plants, though in some -cases the latter bear also antheridia. It has been found that when the -spores are given but little nutriment they form male prothallia, and -the spores supplied with abundant nutriment form female prothallia.</p> - -<p><b>839. Permanent separation of sexes by different amounts of nutriment -supplied the spores.</b>—This separation of the sexual organs of -different prothallia, which in most of the ferns, and in equisetum, is -dependent on the chance supply of nutriment to the germinating spores, -is made certain when we come to such plants as isoetes and selaginella. -Here certain of the spores receive more nutriment while they are -forming than others. In the large sporangia (macrosporangia) only a few -of the cells of the spore-producing tissue form spores, the remaining -cells being dissolved to nourish the growing macrospores, which are few -in number. In the small sporangia (microsporangia) all the cells of the -spore-producing tissue form spores. Consequently each one has a less -amount of nutriment, and it is very much smaller, a microspore. The -sexual nature of the prothallium in selaginella and isoetes, then, is -predetermined in the spores while they are forming on the sporophyte. -The microspores are to produce male prothallia, while the macrospores -are to produce female prothallia.</p> - -<p><b>840. Heterospory.</b>—This production of two kinds of spores -by isoetes, selaginella, and some of the other fern plants is -<i>heterospory</i>, or such plants are said to be <i>heterosporous</i>. -Heterospory, then, so far as we know from living forms, has originated -in the fern group. In all the higher plants, in the gymnosperms and -angiosperms, it has been perpetuated, the microspores being represented -by the pollen, while the macrospores are represented by the embryo sac; -the male organ of the gymnosperms and angiosperms being the antherid -cell in the pollen or pollen tube, or in some cases perhaps the pollen -grain itself, and the female organ in the angiosperms perhaps reduced -to the egg-cell of the embryo sac.</p> - -<p><b>841. In the pteridophytes water serves as the medium for conveying -the sperm cell to the female organ.</b>—In the ferns and their allies, -as well as in the liverworts and mosses, surface water is a necessary -medium through which the generative or sperm cell of the male organ, -the spermatozoid, may reach the germ cell of the female organ. The -sperm cell is here motile. This is true in a large number of cases -in the algæ, which are mostly aquatic plants, while in other cases -currents of water float the sperm cell to the female organ.</p> - -<p><b>842. In the higher plants a modification of the prothallium is -necessary.</b>—As we pass to the gymnosperms and angiosperms, -however, where the primitive phase (the gametophyte) of the plants -has become dependent solely on the modern phase (the sporophyte) of -the plant, surface water no longer serves as the medium through which -a motile sperm cell reaches the egg-cell to fertilize it. The female -<span class="pagenum"><a name="Page_435" id="Page_435">[Pg 435]</a></span> -prothallium, or macrospore, is, in nearly all cases, permanently -enclosed within the sporangium, so that if there were motile sperm -cells on the outside of the ovary, they could never reach the egg to -fertilize it.</p> - -<p><b>843.</b> But a modification of the microspore, the pollen tube, -enables the sperm cell to reach the egg-cell. The tube grows through -the nucellus, or first through the tissues of the ovary, deriving -nutriment therefrom.</p> - -<p><b>844.</b> But here an important consideration should not escape us. -The pollen grains (microspores) must in nearly all cases first reach -the pistil, in order that in the growth of this tube a channel may be -formed through which the generative cell can make its way to the egg -cell. The pollen passes from the anther locule, then, to the stigma of -the ovary. This process is termed <i>pollination</i>.</p> - -<p class="center"><b>Pollination.</b></p> - -<p><b>845. Self pollination, or close pollination.</b>—Perhaps very few -of the admirers of the pretty blue violet have ever noticed that there -are other flowers than those which appeal to us through the beautiful -colors of the petals. How many have observed that the brightly colored -flowers of the blue violet rarely “set fruit”? Underneath the soil -or débris at the foot of the plant are smaller flowers on shorter, -curved stalks, which do not open. When the anthers dehisce, they are -lying close upon the stigma of the ovary, and the pollen is deposited -directly upon the stigma of the same flower. This method of pollination -is <i>self pollination</i>, or <i>close pollination</i>. These small, closed -flowers of the violet have been termed “<i>cleistogamous</i>,” because they -are pollinated while the flower is closed, and fertilization takes -place as a result.</p> - -<p>But self pollination takes place in the case of some open flowers. -In some cases it takes place by chance, and in other cases by such -movements of the stamens, or of the flower at the time of the -dehiscence of the pollen, that it is quite certainly deposited upon the -stigma of the same flower.</p> - -<p><b>846. Wind pollination.</b>—The pine is an example of -wind-pollinated flowers. Since the pollen floats in the air or -is carried by the “wind,” such flowers are <i>anemophilous</i>. Other -anemophilous flowers are found in other conifers, in grasses, sedges, -many of the ament-bearing trees, and other dicotyledons. Such plants -produce an abundance of pollen and always in the form of “dust,” so -that the particles readily separate and are borne on the wind.</p> - -<p><b>847. Pollination by insects.</b>—A large number of the plants which -we have noted as being anemophilous are monœcious or diœcious, i.e. the -stamens and pistils are borne in separate flowers. The two kinds of -flowers thus formed, the male and the female, are borne either on the -same individual (monœcious) or on different individuals (diœcious). In -<span class="pagenum"><a name="Page_436" id="Page_436">[Pg 436]</a></span> -such cases cross pollination, i.e. the pollination of the pistil of -one flower by pollen from another, is sure to take place, if it is -pollinated at all. Even in monœcious plants cross pollination often -takes place between flowers of different individuals, so that more -widely different stocks are united in the fertilized egg, and the -strain is kept more vigorous than if very close or identical strains -were united.</p> - -<div class="figcenter"> - <img src="images/fig454.jpg" alt="" width="500" height="507" /> - <div class="blockquot"> - <p class="center">Fig. 454.</p> - <p>Viola cucullata; blue flowers above, cleistogamous flowers smaller - and curved below. Section of pistil at right.</p> - </div> -</div> - -<p><b>848.</b> But there are many flowers in which both stamens and -pistils are present, and yet in which cross pollination is accomplished -through the agency of insects.</p> - -<p><b>859. Pollination of the bluet.</b>—In the pretty bluet the stamens -and styles of the flowers are of different length as shown in figures -<a href="#FIG_455">455</a>, <a href="#FIG_456">456</a>. The stamens -of the long-styled flower are at about the same -level as the stigma of the short-styled flower, while the stamens of -<span class="pagenum"><a name="Page_437" id="Page_437">[Pg 437]</a></span> -the latter are on about the same level as the stigma of the former. -What does this interesting relation of the stamens and pistils in the -two different flowers mean? As the butterfly thrusts its “tongue” down -into the tube of the long-styled flower for the nectar, some of the -pollen will be rubbed off and adhere to it. When now the butterfly -visits a short-styled flower this pollen will be in the right position -to be rubbed off onto the stigma of the short style. The positions -of the long stamens and long style are such that a similar cross -pollination will be effected.</p> - -<div class="figcenter"> - <img id="FIG_455" src="images/fig455.jpg" alt="" width="600" height="259" /> - <div class="blockquot"> - <p class="center">Fig. 455.</p> - <p>Dichogamous flower of the bluet (Houstonia cœrulea), the long-styled form.</p> - </div> -</div> -<div class="figcenter"> - <img id="FIG_456" src="images/fig456.jpg" alt="" width="600" height="276" /> - <div class="blockquot"> - <p class="center">Fig. 456.</p> - <p>Dichogamous flower of bluet (Houstonia cœrulea), the short-styled form.</p> - </div> -</div> - -<p><b>850. Pollination of the primrose.</b>—In the primroses, of which -we have examples growing in conservatories, that blossom during the -winter, we have almost identical examples of the beautiful adaptations -for cross pollination by insects found in the bluet. The general shape -<span class="pagenum"><a name="Page_438" id="Page_438">[Pg 438]</a></span> -of the corolla is the same, but the parts of the flower are in -fives, instead of in fours as in the bluet. While the pollen of the -short-styled primulas sometimes must fall on the stigma of the same -flower, Darwin has found that such pollen is not so potent on the -stigma of its own flower as on that of another, an additional provision -which tends to necessitate cross pollination.</p> - -<div class="figcenter"> - <img src="images/fig457.jpg" alt="" width="600" height="257" /> - <p class="center">Fig. 457.<br /> Dichogamous flowers of primula.</p> -</div> - -<p>In the case of some varieties of pear trees, as the Bartlett, it -has been found that the flowers remain largely sterile not only to -their own pollen, or pollen of the flowers on the same tree, but to -all flowers of that variety. However, they become fertile if cross -pollinated from a different variety of pear.</p> - -<p><b>851. Pollination of the skunk’s cabbage.</b>—In many other flowers -cross pollination is brought about through the agency of insects, -where there is a difference in time of the maturing of the stamens and -pistils of the same flower. The skunk’s cabbage (Spathyema fœtida), -though repulsive on account of its fetid odor, is nevertheless a very -interesting plant to study for several reasons. Early in the spring, -before the leaves appear, and in many cases as soon as the frost is out -of the hard ground, the hooked beak of the large fleshy spathe of this -plant pushes its way through the soil.</p> - -<p>If we cut away one side of the spathe as shown in <a href="#FIG_459">fig. 459</a> -we shall have the flowering spadix brought closely to view. In this spadix the -pistil of each crowded flower has pushed its style through between the -plates of armor formed by the converging ends of the sepals, and stands -out alone with the brush-like stigma ready for pollination, while the -stamens of all the flowers of this spadix are yet hidden beneath. The -insects which pass from the spadix of one plant to another will, in -crawling over the projecting stigmas, rub off some of the pollen which -has been caught while visiting a plant where the stamens are scattering -their pollen. In this way cross pollination is brought about. Such -flowers, in which the stigma is prepared for pollination before the -anthers of the same flower are ripe, are <i>proterogynous</i>. -<span class="pagenum"><a name="Page_439" id="Page_439">[Pg 439]</a></span></p> -<p> <span class="pagenum"><a name="Page_440" id="Page_440">[Pg 440]</a></span></p> - -<div class="figcontainer"> - <div class="figsub"> - <p> </p> - <img id="FIG_458" src="images/fig458.jpg" alt="" width="150" height="390" /> - <p class="center">Fig. 458.<br /> Skunk’s cabbage.</p> - </div> - <div class="figsub"> - <p> </p> - <img id="FIG_459" src="images/fig459.jpg" alt="" width="200" height="374" /> - <p class="center">Fig. 459.<br /> Proterogyny in skunk’s cabbage.<br /> - (Photograph by the author.)</p> - </div> - <div class="figsub"> - <img id="FIG_460" src="images/fig460.jpg" alt="" width="200" height="350" /> - <p class="center">Fig. 460.<br /> Skunk’s cabbage;<br /> upper flowers<br /> proterandrous,<br /> - lower ones<br /> proterogynous.</p> - </div> -</div> - -<p> <span class="pagenum"><a name="Page_441" id="Page_441">[Pg 441]</a></span></p> -<p><span class="pagenum"><a name="Page_442" id="Page_442">[Pg 442]</a></span> -<b>852.</b> Now if we observe the spadix of another plant we may see a -condition of things similar to that shown in <a href="#FIG_460">fig. 460</a>. -In the flowers in the upper part of the spadix here the anthers are wedging their -way through between the armor-like plates formed by the sepals, while the -styles of the same flowers are still beneath, and the stigmas are not -ready for pollination. Such flowers are <i>proterandrous</i>, that is, the -anthers are ripe before the stigmas of the same flowers are ready for -pollination. In this spadix the upper flowers are proterandrous, while -the lower ones are proterogynous, so that it might happen here that -the lower flowers would be pollinated by the pollen falling on them -from the stamens of the upper flowers. This would be cross pollination -so far as the flowers are concerned, but not so far as the plants -are concerned. In some individuals, however, we find all the flowers -proterandrous.</p> - -<p><b>853. Spiders have discovered this curious relation of the flowers -and insects.</b>—On several different occasions, while studying -the adaptations of the flowers of the skunk’s cabbage for cross -pollination, I was interested to find that the spiders long ago had -discovered something of the kind, for they spread their nets here to -catch the unwary but useful insects. I have not seen the net spread -over the opening in the spathe, but it is spread over the spadix -within, reaching from tip to tip of either the stigmas, or stamens, or -both. Behind the spadix crouches the spider-trapper. The insect crawls -over the edge of the spadix, and plunges unsuspectingly into the dimly -lighted chamber below, where it becomes entangled in the meshes of the net.</p> - -<p>Flowers in which the ripening of the anthers and maturing of the -stigmas occur at different times are also said to be <i>dichogamous</i>.</p> - -<p><b>854. Pollination of jack-in-the-pulpit.</b>—The jack-in-the-pulpit -(Arisæma triphyllum) has made greater advance in the art of enforcing -cross pollination. The larger number of plants here are, as we have -found, diœcious, the staminate flowers being on the spadix of one -plant, while the pistillate flowers are on the spadix of another. In a -few plants, however, we find both female and male flowers on the same -spadix.</p> - -<p><b>855.</b> The pretty bell-flower (Campanula rotundifolia) is -dichogamous and proterandrous (<a href="#FIG_462">fig. 462</a>). -Many of the composites are also dichogamous.</p> - -<p><b>856. Pollination of orchids.</b>—But some of the most marvellous -adaptations for cross pollination by insects are found in the orchids, -or members of the orchis family. The larger number of the members of -this family grow in the tropics. Many of these in the forests are -supported in lofty trees where they are brought near the sunlight, -and such are called “epiphytes.” A number of species of orchids are -distributed in temperate regions. -<span class="pagenum"><a name="Page_443" id="Page_443">[Pg 443]</a></span></p> - -<div class="figcenter"> - <img src="images/fig461.jpg" alt="" width="400" height="514" /> - <p class="center">Fig. 461.<br /> A group of jacks.</p> -</div> - -<p><b>857. Cypripedium, or lady-slipper.</b>—One species of the -lady-slipper is shown in <a href="#FIG_468">fig. 468</a>. The labellum in this -genus is shaped like a shoe, as one can see by the section of the flower in <a href="#FIG_468">fig. 468</a>. -The stigma is situated at <i>st</i>, while the anther is situated at <i>a</i>, -upon the style. The insect enters about the middle of the boat-shaped -<span class="pagenum"><a name="Page_444" id="Page_444">[Pg 444]</a></span> -labellum. In going out it passes up and out at the end near the flower -stalk. In doing this it passes the stigma first and the anther last, -rubbing against both. The pollen caught on the head of the insect, will -not touch the stigma of the same flower, but will be in position to -come in contact with the stigma of the next flower visited.</p> - -<div class="figcenter"> - <img id="FIG_462" src="images/fig462.jpg" alt="" width="600" height="286" /> - <div class="blockquot"> - <p class="center">Fig. 462.</p> - <p>Proterandry in the bell-flower (campanula). Left figure shows the - syngenœcious stamens surrounding the immature style and stigma. Middle - figure shows the immature stigma being pushed through the tube and - brushing out the pollen; while in the right-hand figure, after the - pollen has disappeared, the lobes of the stigma open out to receive - pollen from another flower.</p> - </div> -</div> - -<p><b>858. Epipactis.</b>—In epipactis, shown in <a href="#FIG_469">fig. 469</a>, -the action is similar to that of the blue iris.</p> - -<div class="figcenter"> - <img src="images/fig463.jpg" alt="" width="600" height="218" /> - <div class="blockquot"> - <p class="center">Fig. 463.</p> - <p>Kalmia latifolia, showing position of anthers before insect visits, - and at the right the scattering of the pollen when disturbed by - insects. Middle figure section of flower.</p> - </div> -</div> - -<p><b>849.</b> In some of the tropical orchids the pollinia are set free -when the insect touches a certain part of the flower, and are thrown -in such a way that the disk of the pollinium strikes the insect’s head -and stands upright. By the time the insect reaches another flower the -<span class="pagenum"><a name="Page_445" id="Page_445">[Pg 445]</a></span> -pollinium has bent downward sufficiently to strike against the stigma -when the insect alights on the labellum. In the mountains of North -Carolina I have seen a beautiful little orchid, in which, if one -touches a certain part of the flower with a lead-pencil or other -suitable object, the pollinium is set free suddenly, turns a complete -somersault in the air, and lands with the disk sticking to the pencil. -Many of the orchids grown in conservatories can be used to demonstrate -some of these peculiar mechanisms.</p> - -<div class="figcenter"> - <img src="images/fig464.jpg" alt="" width="600" height="225" /> - <p class="center">Fig. 464.<br /> Spray of leaves and flowers of cytisus.</p> - -</div> -<div class="figcenter"> - <img src="images/fig465.jpg" alt="" width="600" height="258" /> - <p class="center">Fig. 465.<br /> Flower of cytisus grown in conservatory.<br /> - Same flower scattering pollen.</p> - -</div> - -<p><b>860. Pollination of the canna.</b>—In the study of some of the -marvellous adaptations of flowers for cross pollination one is led to -inquire if, after all, plants are not intelligent beings, instead of -mere automatons which respond to various sorts of stimuli. No plant -has puzzled me so much in this respect as the canna, and any one will -be well repaid for a study of recently opened flowers, even though it -may be necessary to rise early in the morning to unravel the mystery, -before bees or the wind have irritated the labellum. The canna flower -<span class="pagenum"><a name="Page_446" id="Page_446">[Pg 446]</a></span> -is a bewildering maze of petals and petal-like members. The calyx -is green, adherent to the ovary, and the limb divides into three, -lanceolate lobes. The petals are obovate and spreading, while the -stamens have all changed to petal-like members, called <i>staminodia</i>. -Only one still shows its stamen origin, since the anther is seen at one -side, while the filament is expanded laterally and upwards to form the -<i>staminodium</i>.</p> - -<div class="figcenter"> - <img src="images/fig466.jpg" alt="" width="500" height="496" /> - <div class="blockquot"> - <p class="center">Fig. 466.</p> - <p>Spartium, showing the dusting of the pollen through the opening - keels on the under side of an insect. (From Kerner and Oliver.)</p> - </div> -</div> - -<p><b>861.</b> The ovary has three locules, and the three styles are -usually united into a long, thin, strap-shaped style, as seen in the -figure, though in some cases three, nearly distinct, filamentous styles -are present. The end of this strap-shaped style has a peculiar curve on -<span class="pagenum"><a name="Page_447" id="Page_447">[Pg 447]</a></span> -one side, the outline being sometimes like a long narrow letter S. It -is on the end of this style, and along the crest of this curve, that -the stigmatic surface lies, so that the pollen must be deposited on the -stigmatic end or margin in order that fertilization may take place.</p> - -<div class="figcenter"> - <img src="images/fig467.jpg" alt="" width="300" height="421" /> - <p class="center">Fig. 467.<br /> Cypripedium.</p> -</div> -<div class="figcenter"> - <img id="FIG_468" src="images/fig468.jpg" alt="" width="600" height="360" /> - <div class="blockquot"> - <p class="center">Fig. 468.</p> - <p>Section of flower of cypripedium. <i>st</i>, stigma; <i>a</i>, at the left - stamen. The insect enters the labellum at the center, passes under and - against the stigma, and out through the opening <i>b</i>, where it rubs - against the pollen. In passing through another flower this pollen is - rubbed off on the stigma.</p> - </div> -</div> - -<p><b>862.</b> If we open carefully canna flower buds which are nearly -ready to open naturally, by unwrapping the folded petals and -staminodia, we shall see the anther-bearing staminodium is so wrapped -around the flattened style that the anther lies closely pressed against -the face of the style, near the margin <i>opposite that on which the -stigma lies</i>.</p> - -<div class="figcenter"> - <img id="FIG_469" src="images/fig469.jpg" alt="" width="600" height="260" /> - <div class="blockquot"> - <p class="center">Fig. 469.</p> - <p>Epipactis with portion of perianth removed to show details. <i>l</i>, - labellum; <i>st</i>, stigma; <i>r</i>, rostellum; <i>p</i>, pollinium. When the insect - approaches the flower its head strikes the disk of the pollinium and - pulls the pollinium out. At this time the pollinium stands up out of - the way of the stigma. By the time the insect moves to another flower - the pollinia have moved downward so that they are in position to strike - the stigma and leave the pollen. At the right is the head of a bee, - with two pollinia (<i>a</i>) attached.</p> - </div> -</div> - -<p><span class="pagenum"><a name="Page_448" id="Page_448">[Pg 448]</a></span></p> - -<div class="figcenter"> - <img src="images/fig470.jpg" alt="" width="400" height="411" /> - <div class="blockquot"> - <p class="center">Fig. 470.</p> - <p>Canna flowers with the perianth removed to show the depositing of - the pollen on the style by the stamen.</p> - </div> -</div> - -<p><b>863.</b> The walls of the anther locules which lie against the style -become changed to a sticky substance for their entire length, so that -they cling firmly to the surface of the style and also to the mass of -pollen within the locules. The result is that when the flower opens, -and this staminodium unwraps itself from the embrace of the style, -the mass of pollen is left there deposited, while the empty anther is -turned around to one side.</p> - -<p><b>668.</b> Why does the flower deposit its own pollen on the style? -Some have regarded this as the act of pollination, and have concluded, -therefore, that cannas are necessarily self pollinated, and that cross -pollination does not take place. But why is there such evident care to -deposit the pollen on the side of the style away from the stigmatic -margin? If we visit the cannas some morning, when a number of the -flowers have just opened, and the bumblebees are humming around seeking -for nectar, we may be able to unlock the secret.</p> - -<p><b>864.</b> We see that in a recently opened canna flower, the petal -which directly faces the style in front stands upward quite close to -it, so that the flower now is somewhat funnel-shaped. This front petal -is the <i>labellum</i>, and is the landing place for the bumblebee as he -alights on the flower. Here he comes humming along and alights on the -labellum with his head so close to the style that it touches it. But -just the instant that the bee attempts to crowd down in the flower the -labellum suddenly bends downward, as shown in <a href="#FIG_468">fig. 468</a>. -In so doing the head of the bumblebee scrapes against the pollen, bearing some -of it off. Now while the bee is sipping the nectar it is too far below the -stigma to deposit any pollen on the latter. When the bumblebee flies to -another newly opened flower, as it alights, some of the pollen of the -former flower is brushed on the stigma.</p> - -<p><b>865.</b> One can easily demonstrate the sensitiveness of the -labellum of recently opened canna flowers, if the labellum has not -already moved down in response to some stimulus. Take a lead-pencil, or -<span class="pagenum"><a name="Page_449" id="Page_449">[Pg 449]</a></span> -a knife blade, or even the finger, and touch the upper surface of the -labellum by thrusting it between the latter and the style. The labellum -curves quickly downward.</p> - -<p><b>866.</b> Sometimes the bumblebees, after sipping the nectar, will -crawl up over the style in a blundering manner. In this way the flower -may be pollinated with its own pollen, which is equivalent to self -pollination. Undoubtedly self pollination does take place often in -flowers which are adapted, to a greater or less degree, for cross -pollination by insects.</p> - -<div class="figcontainer"> - <p class="center">Fig. 471. </p> - <div class="figsub"> - <img src="images/fig471a.jpg" alt="" width="250" height="312" /> - <p class="center">Pollination of the canna flower by bumblebee.</p> - </div> - <div class="figsub"> - <img src="images/fig471b.jpg" alt="" width="225" height="311" /> - <p class="center">Canna flower.<br /> Pollen on style,<br /> stamen at left.</p> - </div> -</div> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_450" id="Page_450">[Pg 450]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XLIV" id="CHAPTER_XLIV">CHAPTER XLIV.</a><br /> -<span class="h_subtitle">THE FRUIT.</span></h3> -</div> - -<h4><a name="XLIV_1" id="XLIV_1">I. Parts of the Fruit.</a></h4> - -<p><b>867. After the flower comes the fruit.</b>—With the perfection of -the fruit the seed is usually formed. This is the end towards which the -energies of the plant have been directed. While the seed consists only -of the ripened ovule and the contained embryo, the fruit consists of -the ripened ovary in addition, and in many cases with other accessory -parts, as calyx, receptacle, etc., combined with it. The wall of the -ripened ovary is called a <i>pericarp</i>, and the walls of the ovary form -the walls of the fruit.</p> - -<p><b>868. Pericarp, endocarp, exocarp, etc.</b>—This is the part of the -fruit which envelops the seed and may consist of the carpels alone, or -of the carpels and the adherent part of the receptacle, or calyx. In -many fruits the pericarp shows a differentiation into layers, or zones -of tissue, as in the cherry, peach, plum, etc. The outer, which is -here soft and fleshy, is <i>exocarp</i>, while the inner, which is hard, is -the <i>endocarp</i>. An intermediate layer is sometimes recognized and is -called <i>mesocarp</i>. In such cases the skin of the fruit is recognized as -the <i>epicarp</i>. Epicarp and mesocarp are more often taken together as exocarp.</p> - -<p>In general fruits are <i>dry</i> or <i>fleshy</i>. Dry fruits may be grouped -under two heads. Those which open at maturity and scatter the seed are -<i>dehiscent</i>. Those which do not open are <i>indehiscent</i>. -<span class="pagenum"><a name="Page_451" id="Page_451">[Pg 451]</a></span></p> - -<h4><a name="XLIV_2" id="XLIV_2">II. Indehiscent Fruits.</a></h4> - -<p><b>869. The akene.</b>—The thin dry wall of the ovary encloses the -single seed. It usually does not open and free the seed within. Such a -fruit is an <i>akene</i>. An <i>akene</i> is a dry, <i>indehiscent</i> fruit. -All of the crowded but separate pistils in the buttercup flower when ripe make -a head of akenes, which form the fruit of the buttercup. Other examples -of akenes are found in other members of the buttercup family, also in -the composites, etc. The sunflower seed is a good example of an akene.</p> - -<div class="figcontainer"> - <div class="figsub"> - <p> </p> - <img src="images/fig472.jpg" alt="" width="150" height="163" /> - <p class="center">Fig. 472.<br /> Seed, or akene, of buttercup.</p> - </div> - <div class="figsub"> - <img src="images/fig473.jpg" alt="" width="300" height="200" /> - <p class="center">Fig. 473.<br /> Fruit of red oak. An acorn.</p> - </div> -</div> - -<p><b>870. The samara.</b>—The winged fruits of the maple, elm, etc., -are indehiscent fruits. They are sometimes called key fruits.</p> - -<p><b>871. The caryopsis</b> is a dry fruit in which the seed is -consolidated with the wall of the ovary, as in the wheat, corn, and -other grasses.</p> - -<p><b>872. The schizocarp</b> is a dry fruit consisting of several locules -(from a <i>syncarpous gynœcium</i>). At maturity the carpels separate from -each other, but do not themselves dehisce and free the seed, as in the -carrot family, mallow family.</p> - -<p><b>873. The acorn.</b>—The acorn fruit consists of the acorn and -the “cup” at the base in which the acorn sits. The cup is a curious -structure, and is supposed to be composed of an involucre of numerous -small leaves at the base of the pistillate flower, which become -consolidated into a hard cup-shaped body. When the acorn is ripe it -easily separates from the cup, but the hard pericarp forming the -“shell” of the acorn remains closed. Frost may cause it to crack, but -very often the pericarp is split open at the smaller end by wedge-like -pressure exerted by the emerging radicle during germination. -<span class="pagenum"><a name="Page_452" id="Page_452">[Pg 452]</a></span></p> - -<div class="figcenter"> - <img src="images/fig474.jpg" alt="" width="600" height="218" /> - <p class="center">Fig. 474.<br /> Germinating acorn of white oak.</p> -</div> - -<p><b>874. The hazelnut, chestnut, and beechnut.</b>—In these fruits a -crown of leaves (involucre) at the base of the flower grows around -the nut and completely envelops it, forming the husk or burr. When -the fruit is ripe the nut is easily shelled out from the husk. In the -beechnut and chestnut the burr dehisces as it dries and allows the nut -to drop out. But the fruit is not dehiscent, since the pericarp is -still intact and encloses the seed.</p> - -<p><b>875. The hickory-nut, walnut, and butternut.</b>—In these fruits -the “shuck” of the hickory-nut and the “hull” of the walnut and -butternut are different from the involucre of the acorn or hazelnut, -etc. In the hickory-nut the “shuck” probably consists partly of calyx -and partly of involucral bracts consolidated, probably the calyx part -predominating. This part of the fruit splits open as it dries and frees -the “nut,” the pericarp being very hard and indehiscent. In the walnut -and butternut the “hull” is probably of like origin as the “shuck” of -the hickory nut, but it does not split open as it ripens. It remains -fleshy. The walnut and butternut are often called <i>drupes</i> or -<i>stone-fruits</i>, but the fleshy part of the fruit is not of the same origin -as the fleshy part of the true drupes, like the cherry, peach, plum, etc.</p> - -<h4><a name="XLIV_3" id="XLIV_3">III. Dehiscent Fruits.</a></h4> - -<p><b>876. Of the dehiscent fruits</b> several prominent types are -recognized, and in general they are sometimes called <i>pods</i>. There is a -<span class="pagenum"><a name="Page_453" id="Page_453">[Pg 453]</a></span> -single carpel (simple pistil), and the pericarp is dry (gynœcium -<i>apocarpous</i>); or where there are several carpels united the pistil is -compound (gynœcium <i>syncarpous</i>).</p> - -<div class="figcontainer"> - <div class="figsub"> - <p> </p> - <img src="images/fig475.jpg" alt="" width="400" height="141" /> - <p class="center">Fig. 475.<br /> Diagrams illustrating three types<br /> - (in cross-section) of the dehiscence<br /> of dry fruits. <i>Loc</i>, loculicidal;<br /> - <i>Sep</i>, Septicidal, Septifragal.</p> - </div> - <div class="figsub"> - <img src="images/fig476.jpg" alt="" width="150" height="246" /> - <p class="center">Fig. 476.<br /> Fruit of sweet pea; a pod.</p> - </div> -</div> - -<p><b>877. The capsule.</b>—When the capsule is <i>syncarpous</i> it may -dehisce in three different ways: 1st. When the carpels split along -the line of their union with each other longitudinally (<i>septicidal -dehiscence</i>), as in the azalea or rhododendron. 2d. When the carpels -<i>split down the middle line</i> (<i>loculicidal dehiscence</i>), as in the -fruit of the iris, lily, etc. 3d. When the carpels open by pores -(<i>poricidal dehiscence</i>), as in the poppy. Some syncarpous capsules -have but one locule, the partitions between the different locules when -young having disappeared. The “bouncing-bet” is an example, and the -seeds are attached to a central column in four rows corresponding to -the four locules present in the young stage.</p> - -<p><b>878. A follicle</b> is a capsule with a single carpel which splits -open along the ventral or upper suture, as in the larkspur, peony.</p> - -<p><b>879. The legume, or true pod</b>, is a capsule with a single carpel -which splits along both sutures, as the pea, bean, etc. As the pod -ripens and dries, a strong twisting tension is often produced, which -splits the pod suddenly, scattering the seeds.</p> - -<p><b>880. The silique.</b>—In the toothwort, shepherd’s-purse, and -nearly all of the plants in the mustard family the fruit consists of -two united carpels, which separate at maturity, leaving the partition -wall persistent. Such a fruit is a <i>silique</i>; when short it is a -<i>silicle</i>, or <i>pouch</i>.</p> - -<p><b>881. A pyxidium, or pyxis</b>, is a capsule which opens with a lid, -as in the plantain. -<span class="pagenum"><a name="Page_454" id="Page_454">[Pg 454]</a></span></p> - -<h4><a name="XLIV_4" id="XLIV_4">IV. Fleshy and Juicy Fruits.</a></h4> - -<p><b>882. The drupe, or stone-fruit.</b>—In the plum, cherry, peach, -apricot, etc., the outer portion (exocarp) of the pericarp (ovary) -becomes fleshy, while the inner portion (endocarp) becomes hard and -stony, and encloses the seed, or “pit.” Such a fruit is known as a -drupe, or as a stone-fruit. In the almond the fleshy part of the fruit -is removed.</p> - -<div class="figcenter"> - <img src="images/fig477.jpg" alt="" width="500" height="351" /> - <p class="center">Fig. 477.<br /> Drupe, or stone-fruit, of plum.</p> -</div> - -<p><b>883. The raspberry and blackberry.</b>—While these fruits are -known popularly as “berries,” they are not berries in the technical -sense. Each ovary, or pericarp, in the flower forms a single small -fruit, the outer portion being fleshy and the inner stony, just as -in the cherry or plum. It is a <i>drupelet</i> (little drupe). All of the -drupelets together make the “berry,” and as they ripen the separate -drupelets cohere more or less. It is a collection, or aggregation, of -fruits, and consequently they are sometimes called <i>collective fruits</i>, -or <i>aggregate fruits</i>. In the raspberry the fruit separates from the -receptacle, leaving the latter on the stem, while the drupelets of -the blackberry and dewberry adhere to the receptacle and the latter -separates from the stem. -<span class="pagenum"><a name="Page_455" id="Page_455">[Pg 455]</a></span></p> - -<p><b>884. The berry.</b>—In the true berry both exocarp (including -mesocarp) and endocarp are fleshy or juicy. Good examples are found -in cranberries, huckleberries, gooseberries, currants, snowberries, -tomatoes, etc. The calyx and wall of the pistil are adnate, and in -fruit become fleshy so that the seeds are imbedded in the pulpy juice. -The seeds themselves are more or less stony. In the case of berries, -as well as in strawberries, raspberries, and blackberries, the fruits -are eagerly sought by birds and other animals for food. The seeds being -hard are not digested, but are passed with the other animal excrement -and thus gain dispersal.</p> - -<h4><a name="XLIV_5" id="XLIV_5">V. Reinforced, or Accessory, Fruits.</a></h4> - -<p>When the torus (receptacle) is grown to the pericarp in fruit, the -fruit is said to be <i>reinforced</i>. The torus may enclose the pericarps, -or the latter may be seated upon the torus.</p> - -<div class="figcenter"> - <img src="images/fig478.jpg" alt="" width="500" height="417" /> - <p class="center">Fig. 478.<br /> Fruit of raspberry.</p> -</div> - -<p><b>885. In the strawberry</b> the receptacle of the flower becomes -larger and fleshy, while the “seeds,” which are akenes, are sunk in the -<span class="pagenum"><a name="Page_456" id="Page_456">[Pg 456]</a></span> -surface and are hard and stony. The strawberry thus differs from the -raspberry and blackberry, but like them it is not a true berry.</p> - -<p><b>886. The apple, pear, quince, etc.</b>—In the flower the calyx, -corolla, and stamens are perigynous, i.e., they are seated on the -margin of the receptacle, or torus, which is elevated around the -pistils. In fruit the receptacle becomes consolidated with the wall -of the ovary (with the pericarp). The torus thus <i>reinforces</i> the -pericarp. The torus and outer portion of the pericarp become fleshy, -while the inner portion of the pericarp becomes papery and forms the -“core.” The calyx persists on the free end of the fruit. Such a fruit -is called a <i>pome</i>. The receptacle, or torus, of the rose-flower, -closely related to the apple, is instructive when used in comparison. -The rose-fruit is called a “hip.”</p> - -<p><b>887. The pepo.</b>—The fruit of the squash, pumpkin, cucumber, -etc., is called a <i>pepo</i>. The outer part of the fruit is the receptacle -(or torus), which is consolidated with the outer part of the -three-loculed ovary. The calyx, which, with the corolla and stamens, -was epigynous, falls off from the young fruit.</p> - -<h4><a name="XLIV_6" id="XLIV_6">VI. Fruits of Gymnosperms.</a></h4> - -<p>The fruits of the gymnosperms differ from nearly all of the angiosperms -in that the seed formed from the ripened ovule is naked from the first, -i.e., the ovary, or carpel, does not enclose the seed.</p> - -<p><b>888. The cone-fruit</b> is the most prominent fruit of the -gymnosperms, as can be seen in the cones of various species of pine, -spruce, balsam, etc.</p> - -<p><b>889. Fleshy fruits of the gymnosperms.</b>—Some of the fleshy -fruits resemble the stone-fruits and berries of the angiosperms. The -<i>cedar</i> “<i>berries</i>,” for example, are fleshy and contain several seeds. -But the fleshy part of the fruit is formed, not from pericarp, since -there is no pericarp, but from the outer portion of the ovules, while -the inner walls of the ovules form the hard stone surrounding the -<span class="pagenum"><a name="Page_457" id="Page_457">[Pg 457]</a></span> -endosperm and embryo. An examination of the pistillate flower of the -cedar (juniper) shows usually three flask-shaped ovules on the end -of a fertile shoot subtended by as many bracts (carpels?). The young -ovules are free, but as they grow they coalesce, and the outer walls -become fleshy, forming a berry-like fruit with a three-rayed crevice -at the apex marking the number of ovules. The red fleshy fruit of the -yew (taxus) resembles a drupe which is open at the apex. The stony -seed is formed from the single ovule on the fertile shoot, while the -red cup-shaped fleshy part is formed from the outer integument of the -ovule. The so-called “aril” of the young ovule is a rudimentary outer -integument.</p> - -<p>The fruit of the maidenhair tree (ginkgo) is about the size of a plum -and resembles very closely a stone-fruit. But it is merely a ripened -ovule, the outer layer becoming fleshy while the inner layer becomes -stony and forms the pit which encloses the embryo and endosperm. -The so-called “aril,” or “collar,” at the base of the fruit is the -rudimentary carpel, which sometimes is more or less completely expanded -into a true leaf. The fruit of cycas is similar to that of ginkgo, but -there is no collar at the base. In zamia the fruit is more like a cone, -the seeds being formed, however, on the under sides of the scales.</p> - -<h4><a name="XLIV_7" id="XLIV_7">VII. The “Fruit” of Ferns, Mosses, etc.</a></h4> - -<p><b>890. The term “fruit”</b> is often applied in a general or popular -sense to the groups of spore-producing bodies of ferns (<i>fruit dots</i>, -or <i>sori</i>), the spore-capsules of mosses and liverworts, and also to -the fruit-bodies, or spore-bearing parts, of the fungi and algæ.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_458" id="Page_458">[Pg 458]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XLV" id="CHAPTER_XLV">CHAPTER XLV.</a><br /> -<span class="h_subtitle">SEED DISPERSAL.</span></h3> -</div> - -<p><b>891. Means for dissemination of seeds.</b>—During late summer -or autumn a walk in the woods or afield often convinces us of the -perfection and variety of means with which plants are provided for the -dissemination of their seeds, especially when we discover that several -hundred seeds or fruits of different plants are stealing a ride at -our expense and annoyance. The hooks and barbs on various seed-pods -catch into the hairs of passing animals and the seeds may thus be -transported considerable distances. Among the plants familiar to us, -which have such contrivances for unlawfully gaining transportation, -are the beggar-ticks or stick tights, or sometimes called bur-marigold -(bidens), the tick-treefoil (desmodium), or cockle-bur (xanthium), and -burdock (arctium).</p> - -<div class="figcontainer"> - <div class="figsub"> - <p> </p> - <img src="images/fig479.jpg" alt="" width="300" height="313" /> - <p class="center">Fig. 479.<br /> Bur of bidens or bur-marigold,<br /> - showing barbed seeds.</p> - </div> - <div class="figsub"> - <img src="images/fig480.jpg" alt="" width="225" height="305" /> - <p class="center">Fig. 480.<br /> Seed pod of tick-treefoil (desmodium);<br /> - at the right some of the hooks<br /> greatly magnified.</p> - </div> -</div> - -<p><b>892.</b> Other plants like some of the sedges, etc., living on the -margins of streams and of lakes, have seeds which are provided with -floats. The wind or the flowing of the water transports them often to -distant points. -<span class="pagenum"><a name="Page_459" id="Page_459">[Pg 459]</a></span></p> - -<p><b>893.</b> Many plants possess attractive devices, and offer a -substantial reward, as a price for the distribution of their seeds. -Fruits and berries are devoured by birds and other animals; the seeds -within, often passing unharmed, may be carried long distances. Starchy -and albuminous seeds and grains are also devoured, and while many -such seeds are destroyed, others are not injured, and finally are -lodged in suitable places for growth, often remote from the original -locality. Thus animals willingly or unwillingly become agents in the -dissemination of plants over the earth. Man in the development of -commerce is often responsible for the wide distribution of harmful as -well as beneficial species.</p> - -<div class="figcenter"> - <img src="images/fig481.jpg" alt="" width="600" height="354" /> - <p class="center">Fig. 481.<br /> Seeds of geum showing the hooklets<br /> - where the end of the style is kneed.</p> -</div> - -<p><b>894.</b> Other plants are more independent, and mechanisms are -employed for violently ejecting seeds from the pod or fruit. The -unequal tension of the pods of the common vetch (Vicia sativa) when -drying causes the valves to contract unequally, and on a dry summer day -the valves twist and pull in opposite directions until they suddenly -snap apart, and the seeds are thrown forcibly for some distance. In the -impatiens, or touch-me-not as it is better known, when the pods are -ripe, often the least touch, or a pinch, or jar, sets the five valves -free, they coil up suddenly, and the small seeds are thrown for several -yards in all directions. During autumn, on dry days, the pods of the -witch hazel contract unequally, and the valves are suddenly spread -apart, and the seeds are hurled away.</p> - -<p>Other plants have seeds provided with tufts of pappus, or hair-like -masses, or wing-like outgrowths which serve to buoy them up as they are -<span class="pagenum"><a name="Page_460" id="Page_460">[Pg 460]</a></span> -whirled along, often miles away. In late spring or early summer the -pods of the willow burst open, exposing the seeds, each with a tuft of -white hairs making a mass of soft down. As the delicate hairs dry, they -straighten out in a loose spreading tuft, which frees the individual -seeds from the compact mass. Here they are caught by currents of air -and float off singly or in small clouds.</p> - -<div class="figcenter"> - <img src="images/fig482.jpg" alt="" width="600" height="380" /> - <div class="blockquot"> - <p class="center">Fig. 482.</p> - <p>Touch-me-not (Impatiens fulva); side and front view of flower below; - above unopened pod, and opening to scatter the seed.</p> - </div> -</div> - -<p><b>895. The prickly lettuce.</b>—In late summer or early autumn the -seeds of the prickly lettuce (Lactuca scariola) are caught up from the -roadsides by the winds, and carried to fields where they are unbidden -as well as unwelcome guests. This plant is shown in <a href="#FIG_483">fig. 483</a>.</p> - -<p><b>896. The wild lettuce.</b>—A related species, the wild lettuce -(Lactuca canadensis) occurs on roadsides and in the borders of fields, -and is about one meter in height. The heads of small yellow or purple -flowers are arranged in a loose or branching panicle. The flowers are -rather inconspicuous, the rays projecting but little above the apex of -the enveloping involucral bracts, which closely press together, forming -a flowerhead more or less flask-shaped.</p> - -<div class="figcenter"> - <img id="FIG_483" src="images/fig483.jpg" alt="" width="350" height="491" /> - <p class="center">Fig. 483.<br /> Lactuca scariola.</p> -</div> - -<p>At the time of flowering the involucral bracts spread somewhat at the -apex, and the tips of the flowers are a little more prominent. As the -flowers then wither, the bracts press closely together again and the -head is closed. As the seeds ripen the bracts die, and in drying bend -outward and downward, around the flower stem below, or they fall away. -<span class="pagenum"><a name="Page_461" id="Page_461">[Pg 461]</a></span> -The seeds are thus exposed. The dark brown achenes stand over the -surface of the receptacle, each one tipped with the long slender -beak of the ovary. The “pappus,” which is so abundant in many of the -plants belonging to the composite family, forms here a pencil-like -tuft at the tip of this long beak. As the involucral bracts dry and -curve downward, the pappus also dries, and in doing so bends downward -and stands outward, bristling like the spokes of a small wheel. It is -an interesting coincidence that this takes place simultaneously with -the pappus of all the seeds of a head, so that the ends of the pappus -bristles of adjoining seeds meet, forming a many-sided dome of a -delicate and beautiful texture. This causes the beaks of the achenes to -be crowded apart, and with the leverage thus brought to bear upon the -achenes they are pried off the receptacle. They are thus in a position -to be wafted away by the gentlest zephyr, and they go sailing away on -the wind like a miniature parachute. As they come slowly to the ground -the seed is thus carefully lowered first, so that it touches the ground -in a position for the end which contains the root of the embryo to come -in contact with the soil. -<span class="pagenum"><a name="Page_462" id="Page_462">[Pg 462]</a></span></p> - -<p><b>897. The milkweed, or silkweed.</b>—The common milkweed, or -silkweed (Asclepias cornuti), so abundant in rich grounds, is -attractive not only because of the peculiar pendent flower clusters, -but also for the beautiful floats with which it sends its seeds -skyward, during a puff of wind, to finally lodge on the earth.</p> - -<div class="figcenter"> - <img src="images/fig484.jpg" alt="" width="500" height="442" /> - <p class="center">Fig. 484.<br /> Milkweed (Asclepias cornuti);<br /> - dissemination of seed.</p> -</div> - -<p><b>898.</b> The large boat-shaped, tapering pods, in late autumn, are -packed with oval, flattened, brownish seeds, which overlap each other -in rows like shingles on a roof. These make a pretty picture as the pod -in drying splits along the suture on the convex side, and exposes them -to view. The silky tufts of numerous long, delicate white hairs on the -inner end of each seed, in drying, bristle out, and thus lift the seeds -out of their enclosure, where they are caught by the breeze and borne -away often to a great distance, where they will germinate if conditions -become favorable, and take their places as contestants in the battle -for existence.</p> - -<p><b>899. The virgin’s bower.</b>—The virgin’s bower (Clematis -virginiana), too, clambering over fence and shrub, makes a show of -<span class="pagenum"><a name="Page_463" id="Page_463">[Pg 463]</a></span> -having transformed its exquisite white flower clusters into -grayish-white tufts, which scatter in the autumn gusts into hundreds -of arrow-headed, spiral plumes. The achenes have plumose styles, and -the spiral form of the plume gives a curious twist to the falling seed -(<a href="#FIG_485">fig. 485</a>).</p> - -<div class="figcenter"> - <img id="FIG_485" src="images/fig485.jpg" alt="" width="400" height="450" /> - <p class="center">Fig. 485.<br /> Seed distribution of virgin’s bower (clematis).</p> -</div> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_464" id="Page_464">[Pg 464]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XLVI" id="CHAPTER_XLVI">CHAPTER XLVI.</a><br /> -<span class="h_subtitle">VEGETATION IN RELATION TO -ENVIRONMENT.<a name="FNanchor_47_47" id="FNanchor_47_47"></a><a href="#Footnote_47_47" class="fnanchor">[47]</a></span></h3> -</div> - -<p class="center"><b>I. Factors Influencing Vegetation Types.</b></p> - -<p><b>900.</b> All plants are subject to the influence of environment -from the time the seed begins to germinate until the seed is formed -again, or until the plant ceases to live. A suitable amount of warmth -and moisture is necessary that the seed may germinate. Moisture may -be present, but if it is too cold, germination will not take place. -So in all the processes of life there are several conditions of the -environment, or the “outside” of plants, which must be favorable for -successful growth and reproduction. Not only is this true, but the -surroundings of plants to a large extent determine the kind of plants -which can grow in particular localities. It is also evident that the -reaction of environment on plants has in a large measure caused them -to take on certain forms and structures which fit them better to exist -under local conditions. In other cases where plants have varied by -mutation (<a href="#Page_338">p. 338</a>) some of the new forms may be more suited -to the conditions of environment than others and they are more apt to survive. -These conditions of environment acting on the plant are <i>factors</i> which -have an important determining influence on the existence, habitat, -habit, and form of the plant. These factors are sometimes spoken of -as <i>ecological factors</i>, and the study of plants in this relation is -<span class="pagenum"><a name="Page_465" id="Page_465">[Pg 465]</a></span> -sometimes spoken of as ecology,<a name="FNanchor_48_48" id="FNanchor_48_48"></a><a href="#Footnote_48_48" class="fnanchor">[48]</a> -which means a study of plants in their home or a study of the household -relations of plants. These factors are of three sorts: 1st, physical -factors; 2d, climatic factors; 3d, biotic factors.</p> - -<p><b>901. Physical factors.</b>—Some of these factors are water, light, -heat, wind, chemical or physical condition of the soil, etc. <i>Water</i> -is a very important factor for all plants. Even those growing on land -contain a large percentage of water, which we have seen is rapidly lost -by transpiration, and unless water is available for root absorption -the plant soon suffers, and aquatic plants are injured very quickly by -drying when taken from the water. Excess of soil water is injurious to -some plants. <i>Light</i> is important in photosynthesis, in determining -direction of growth as well as in determining the formation of suitable -leaves in most plants, and has an influence in the structure of the -leaf according as the light may be strong, weak, etc. <i>Heat</i> has great -influence on plant growth and on the distribution of plants. The -growth period for most vegetation begins at 6° C. (= 43° F.), or in -the tropics at 10°-12° C., but a much higher temperature is usually -necessary for reproduction. Some arctic algæ, however, fruit at 1.8° C. -The upper limit favorable for plants in general is 45°-50° C., while -the optimum temperature is below this. Very high temperatures are -injurious, and fatal to most plants, but some algæ grow in hot springs -where the temperature reaches 80°-90° C. Some desert plants are able to -endure a temperature of 70° C., while some flowering plants of other -regions are killed at 45° C. Some plants are specifically susceptible -to cold, but most plants which are injured by freezing suffer because -the freezing is a drying process of the protoplasm (<a href="#Page_374">see p. 374</a>). -<i>Wind</i> may serve useful purposes in pollination and in aeration, but severe -winds injure plants by causing too rapid transpiration, by felling -trees, by breaking plant parts, by deforming trees and shrubs, and by -mechanical injuries from “sand-blast.” <i>Ground covers</i> protect plants -in several ways. Snow during the winter checks radiation of heat from -the ground so that it does not freeze to so great a depth, and this is -very important for many trees and shrubs. It also prevents alternate -<span class="pagenum"><a name="Page_466" id="Page_466">[Pg 466]</a></span> -freezing and thawing of the ground, which “heaves” some plants from -the soil. Leaves and other plant remains mulch the soil and check -evaporation of water. The influence of the <i>chemical condition</i> of the -soil is very marked in alkaline areas where the concentration of salt -in the soil permits a very limited range of species. So the physical -and mechanical conditions of the soil influence plants because the -moisture content of the ground is so closely dependent on its physical -condition. Rocky and gravelly soil, other things being equal, is dry. -Clay is more retentive of moisture than sand, and moisture also varies -according to the per cent of humus mixed with it, the humus increasing -the percentage of moisture retained.</p> - -<p><b>902. Climatic factors.</b>—These factors are operative over very -wide areas. There are two climatic factors: rainfall or atmospheric -moisture, and temperature. A very low annual rainfall in warm or -tropical countries causes a desert; an abundance of rain permits the -growth of forests; extreme cold prevents the growth of forests and -gives us the low vegetation of arctic and alpine regions.</p> - -<p><b>903. Biotic factors.</b>—These are animals which act favorably -in pollination, seed distribution, or unfavorably in destroying or -injuring plants, and man himself is one of the great agencies in -checking the growth of some plants while favoring the growth of others. -Plants also react on themselves in a multitude of ways for good or -evil. Some are parasites on others; some in symbiosis (<a href="#Page_85">see p. 85</a>) -aid in providing food; shade plants are protected by those which overtop -them; mushrooms and other fungi disintegrate dead plants to make humus -and finally plant food; certain bacteria by nitrification prepare -nitrates for the higher plants (<a href="#Page_83">see p. 83</a>).</p> - -<p class="center"><b>II. Vegetation Types and Structures.</b></p> - -<p><b>904. Responsive type of vegetation.</b>—In studying vegetation in -relation to environment we are more concerned with the form of the -<span class="pagenum"><a name="Page_467" id="Page_467">[Pg 467]</a></span> -plants which fits them to exist under the local conditions than we are -with the classification of plants according to natural relationships. -Plants may have the same vegetation type, grow side by side, and still -belong to very different floristic types. For example, the cactus, -yucca, three-leaved sumac, the sage-brush, etc., have all the same -general vegetation type and thrive in desert regions. The red oaks, the -elms, many goldenrods, trillium, etc., have the same general vegetation -type, but represent very different floristic types. The latter plants -grow in regions with abundant rainfall throughout the year, where -the growing season is not very short and temperature conditions are -moderate. Some goldenrods grow in very sandy soil which dries out -quickly. These have fleshy or succulent leaves for storing water, -and while they are of the same floristic type as goldenrods growing -in other places, the vegetation type is very different. The types of -vegetation which fit plants for growing in special regions or under -special conditions, they have taken on in response to the influence -of the conditions of their environment. While we find all gradations -between the different types of vegetation, looking at the vegetation -in a broad way, several types are recognized which were proposed by -Warming as follows:</p> - -<p><b>905. Mesophytes.</b>—These are represented by land plants under -temperate or moderate climatic and soil conditions. The normal -land vegetation of our temperate region is composed of mesophytes, -that is, the plants have mesophytic structures during the growing -season. The deciduous forests or thickets of trees and shrubs with -their undergrowth, the meadows, pastures, prairies, weeds, etc., are -examples. In those portions of the tropics where rainfall is great the -vegetation is mesophytic the year around.</p> - -<p><b>906. Xerophytes.</b>—These are plants which are provided with -structures which enable them to live under severe conditions of -dryness, where the air and soil are very dry, as in deserts or -semideserts, or where the soil is very dry or not retentive of -moisture, as in very sandy soil which is above ground water, or in -rocky areas. Since the plants cannot obtain much water from the soil -<span class="pagenum"><a name="Page_468" id="Page_468">[Pg 468]</a></span> -they must be provided with structures which will enable them to -retain the small amount they can absorb from the soil and give it off -slowly. Otherwise they would dry out by evaporation and die. Some -of the structures which enable xerophytic plants to withstand the -conditions of dry climate and soil are lessened leaf surface, increase -in thickness of leaf, increase in thickness of cuticle, deeply sunken -stomates, compact growth, also succulent leaves and stems, and in some -cases loss of the leaf. Evergreens of the north temperate and the -arctic regions are xerophytes.</p> - -<p><b>907. Hydrophytes.</b>—These are plants which grow in fresh water -or in very damp situations. The leaves of aerial hydrophytes are very -thin, have a thin cuticle, and lose water easily, so that if the air -becomes quite dry they are in danger of drying up even though the roots -may be supplied with an abundance of water. The aquatic plants which -are entirely submerged have often thin leaves, or very finely divided -or slender leaves, since these are less liable to be torn by currents -of water. The stems are slender and especially lack strengthening -tissue, since the water buoys them up. Removed from the water they -droop of their own weight, and soon dry up. The stems and leaves have -large intercellular spaces filled with air which aids in aeration and -in the diffusion of gases. Some use the term <i>hygrophytes</i>.</p> - -<p><b>908. Halophytes.</b>—These are salt-loving plants. They grow in -salt water, or in salt marshes where the water is brackish, or in -soil which contains a high per cent of certain salts, for example the -alkaline soils of the West, especially in the so-called “Bad Lands” -of Dakota and Nebraska, and in alkaline soils of the Southwest and -California. These plants are able to withstand a stronger concentration -of salts in the water than other plants. They are also found in soil -about salt springs.</p> - -<p><b>909. Tropophytes.</b><a name="FNanchor_49_49" id="FNanchor_49_49"></a><a href="#Footnote_49_49" class="fnanchor">[49]</a>—Tropophytes -are plants which can live as mesophytes during the growing season, and -then turn to a xerophytic habit in the resting season. Deciduous trees -and shrubs, and perennial herbs of our temperate regions, are in this -<span class="pagenum"><a name="Page_469" id="Page_469">[Pg 469]</a></span> -sense tropophytes, while many are at the same time mesophytes if -they exist in the portions of the temperate region where rainfall is -abundant. In the spring and summer they have broad and comparatively -thin leaves, transpiration goes on rapidly, but there is an abundance -of moisture in the soil, so that root absorption quickly replaces the -loss and the plant does not suffer. In the autumn the trees shed their -leaves, and in this condition with the bare twigs they are able to -stand the drying effect of the cold and winds of the winter because -transpiration is now at a minimum, while root absorption is also at a -minimum because of the cold condition of the soil. Perennial herbs like -trillium, dentaria, the goldenrods, etc., turn to xerophytic habit by -the death of their aerial shoots, while the thick underground shoot -which is also protected by its subterranean habit carries the plant -through the winter.</p> - -<p><b>910.</b> While these different vegetation types are generally -dominant in certain climatic regions or under certain soil conditions, -they are not the exclusive vegetation types of the regions. For -example, in desert or semidesert regions the dominant vegetation -type is made up of xerophytes. But there is a mesophytic flora even -in deserts, which appears during the rainy season where temperature -conditions are favorable for growth. This is sometimes spoken of as the -rainy-season flora. The plants are annuals and by formation of seed can -tide over the dry season. So in the region where mesophytes grow there -are xerophytes, examples being the evergreens like the pines, spruces, -rhododendrons; or succulent plants like the stonecrop, the purslane, -etc. Then among hydrophytes the semiaquatics are really xerophytes. The -roots are in water, and absorption is slow because there are no root -hairs, or but few, and the aerial parts of the plant are xerophytic.</p> - -<p class="center"><b>III. Plant Formations.</b></p> - -<p><b>911.</b> The term plant formation is applied to associations of -plants of the same kind, though there is a great difference in the use -<span class="pagenum"><a name="Page_470" id="Page_470">[Pg 470]</a></span> -of the word by different writers which leads to some confusion.<a name="FNanchor_50_50" id="FNanchor_50_50"></a><a href="#Footnote_50_50" class="fnanchor">[50]</a> -It is sometimes applied to an association of individuals of a species, or -of several species occupying a rather definite area of ground where the -soil conditions are not greatly different (individual formation); by -others it is applied to the plants of a definite physiographic area, as -a swamp, moor, strand, or beach, bank, rock hill, clay hill, ravine, -bluff, etc. (principal formation); and in a broad sense it is applied -to the plants of climatic regions, of those in bodies of water, etc. -(general formations). Space here is too limited to discuss all these -kinds of formations, but the nature of the general formations will be -pointed out. The general formations may be grouped into four divisions:</p> - -<ul class="index"> -<li class="isub3">1st. Climatic formations.</li> -<li class="isub3">2d. Edaphic formations.</li> -<li class="isub3">3d. Aquatic formations.</li> -<li class="isub3">4th. Culture formations.</li> -</ul> - -<p><b>912. Climatic formations.</b>—Climatic influences extend over -wide regions, so that climate controls the general type of vegetation -of a region. In the sense of control there are two climatic factors, -temperature and moisture, especially soil moisture. Temperature exerts -a controlling influence over the vegetation type only where the total -heat during the period of growth and reproduction is very low. This -occurs in polar lands and at high elevations where the climate is -alpine. In the temperate and tropical regions of the globe moisture, -not heat, controls the general vegetation type. These vegetation types -in general are coincident with rainfall distribution, and Schimper -recognizes here three types, which with the arctic-alpine type would -make four climatic formations as follows:</p> - -<p>1st. <i>The woodland formation.</i>—This formation is characterized by -trees and shrubs, and it is what is called a <i>close</i> formation. By this -it is meant that so far as the climate is concerned the conditions are -favorable for the development of trees and shrubs in such abundance -that they become the dominant vegetation type of the region and grow -<span class="pagenum"><a name="Page_471" id="Page_471">[Pg 471]</a></span> -close together. Other plants, as herbs, grasses, etc., occur, but -they grow as subordinate elements of the general vegetation type, and -as undergrowth. The land portion of the globe, therefore, outside of -arctic and alpine regions, where the annual precipitation is 40 to 60 -or more inches, is the area for woodland formation. In some places, -the eastern part of England, for example, the annual precipitation is -25 to 30 inches, but the cool temperature permits a forest growth. It -is true there are places where forests do not grow,—where man cuts -them down, for example. But if cultivated lands in this region were -allowed to go to waste, they would in time grow up to forest again. -So there are swamps where the soil is too wet for trees, or sandy or -rocky areas where there is not a sufficient amount of soil or water to -support forest trees. But here it is the soil conditions, not climatic -conditions, which prevent the development of the forest. But we know -that swamps are being filled in and the ground gradually becoming -higher and drier, and that soil is slowly accumulating in rocky areas, -so that in time if left to natural forces these places would become -forested. So this area of heavy annual rainfall is a <i>potential</i> forest -area. These areas are determined by warm currents of moisture-laden -air from the ocean moving over cooler land areas where the moisture -is precipitated. In general these areas are along the coasts of great -continents and on mountains. Therefore the interior of a continent is -apt to be dry because most of the moisture has been precipitated before -it reaches the interior. Deserts or steppes are therefore usually near -the interior of continents. Some exceptions to this general rule are -found: central South America, which is a region of exceptional rainfall -because the moisture-laden winds here come from the warmest part of the -ocean; the desert region west of the Andes mountains, where the winds -are not favorable; southern California, where the winds come chiefly -from a cooler portion of the Pacific ocean and move over an area of -high temperature, etc.</p> - -<div class="figcenter"> - <img src="images/fig486.jpg" alt="" width="500" height="360" /> - <div class="blockquot"> - <p class="center">Fig. 486.</p> - <p>Typical prairie scene, a few miles west of - Lincoln, Nebraska. (Bot. Dept., Univ. Nebraska.)</p> - </div> -</div> - -<p>2d. <i>Grassland formation.</i>—Grasses form the dominant vegetation type -where the annual rainfall is approximately 15 to 25 inches. In true -<span class="pagenum"><a name="Page_472" id="Page_472">[Pg 472]</a></span> -grasslands the formation is a close one since -there is still a sufficient amount of moisture to provide for all -the plants which can stand on the ground. Yet there is not -enough moisture to permit the growth of forest as the dominant -type without aid and protection by man. The so-called prairie -regions are examples. Trees and shrubs do occur, but they -cannot compete successfully with the grasses because the climatic -conditions are favorable for the latter and unfavorable for the -former. On the border line between forest and prairie the line -of division is not a clear-cut one because conditions grade from -one to the other. The two formations are somewhat mixed, -like the outposts of contending armies, arms of the forest or -prairie extending out here and there. In the United States the -prairies extend from Illinois to about the 100th meridian, and -beyond this to the foothills of the Rockies and southwest to the -Sonora Nevada desert the region is drier, the rainfall varying -from 10 to 20 inches. This is the area of the Great Plains, -and while grasses of the bunch type are dominant, they make -<span class="pagenum"><a name="Page_473" id="Page_473">[Pg 473]</a></span> -a more or less open formation because the moisture is not sufficient -to supply all the plants which could be crowded on the ground, each -individual tuft needing an area of ground surrounding it on which it -can draw for moisture. Such a formation is an open one, and in this -respect is similar to desert formations.</p> - -<div class="figcenter"> - <img src="images/fig487.jpg" alt="" width="600" height="339" /> - <div class="blockquot"> - <p class="center">Fig. 487.</p> - <p>Winter range in northwestern Nevada, showing open formation; white - sage (Eurotia lanata) in foreground, salt-bush (Atriplex confertifolia) - and bud-sage (Artemisia spinescens) at base of hill, red sage (Kochia - americana) on the higher slope. (After Griffiths, Bull. 38, Bureau - Plant Ind., U. S. Dept. Agr.)</p> - </div> -</div> - -<p>3d. <i>Desert formations.</i>—These occur where the annual rainfall is -still lower, 10 to 4 inches or even less, 2 to 3 inches, while in -one place in Chili it is as low as ½ inch. In the great Sahara desert -it is about 8 inches, while in the Sonora Nevada desert in the -southwestern United States it is 4 to 8 inches. Here the formation is -an open one. In the forest and prairie formations the plants compete -with each other for occupancy of the ground, since climatic conditions -are favorable, so that the struggle against climate is not severe. -But in the desert plants do not compete with each other; since the -climate is so austere, the struggle is against the climate. Hence -plants stand at some distance from each other because the roots need -the moisture from the ground for some distance around them. There is -not enough moisture for all the plants that begin, and those which get -<span class="pagenum"><a name="Page_474" id="Page_474">[Pg 474]</a></span> -the start take the moisture away from the intervening ones, which then -die. Since the struggle is against the adverse conditions of climate -and not a competition between plants to occupy the ground, no one -floristic type dominates as in the case of the grasses and forests of -the grassland and woodland formations, but grassland and woodland types -grow together. So we find grasses, trees, and shrubs growing without -competition in the desert. The dominant vegetation type is xerophytic.</p> - -<div class="figcenter"> - <img src="images/fig488.jpg" alt="" width="600" height="433" /> - <p class="center">Fig. 488.<br /> - Northern limit of tree growth, Alaska.<br /> - (Copyright, 1899, by E. H. Harriman.)</p> -</div> - -<p>4th. <i>Arctic-alpine formation.</i> This formation extends from the limit -of tree growth to the region of perpetual ice and snow. The forest -here comes in competition with climate, with the severe cold of the -long winter night, so that tree growth is limited, and on the border -line with the woodland formation the trees are stunted, bent to one -side by the heavy snows, or the tops are killed by the cold wind. The -arctic zone of plant growth is sometimes spoken of as the “cold waste,” -since conditions here are somewhat similar to those in the desert, the -<span class="pagenum"><a name="Page_475" id="Page_475">[Pg 475]</a></span> -extreme cold exercising a drying effect on vegetation, and the -vegetation type then is largely xerophytic.</p> - -<p><b>913. Edaphic<a name="FNanchor_51_51" id="FNanchor_51_51"></a><a href="#Footnote_51_51" class="fnanchor">[51]</a> formations.</b>—Edaphic -formations may occur in any of the climatic-formation areas. They are -controlled by the condition of soil or ground. The condition of the -soil is unfavorable for the growth of the general vegetation type of -that region, or is more favorable for another vegetation type, so -that soil conditions overcome the climatic conditions. These areas -include swamps, moors, the strand or beach, rocky areas, etc., as well -as oases in the desert, warm oases in the arctic zone, river bottoms -in the prairie and plains region, alkaline areas, etc. The edaphic -formations may be close or open according to the nature of the soil. -The edaphic formations then are infiltrated in the climatic formations, -the different vegetation types fitting together like pieces of mosaic, -which can be seen in some places from a mountain top, or if one could -take a bird’s-eye view of the landscape or from a balloon.</p> - -<p><b>914. Aquatic formations.</b>—These are made up of water plants and -are of two general kinds: fresh-water plant formations in ponds, lakes, -streams; and salt-water plant formations in the ocean and inland salt -seas.</p> - -<p><b>915. Culture formations.</b>—Culture formations are largely -controlled by man, who destroys the climatic or edaphic formation and -by cultivation protects cultivated types, or by allowing land to go to -“waste” permits the growth of weeds, though weeds are often abundant -in the culture areas. In general the culture formations may be grouped -into two subdivisions: 1st, the vegetation of cultivated places; and -2d, the vegetation of waste places, as abandoned fields, roadsides, etc.</p> - -<p class="center"><b>IV. Plant Societies.</b></p> - -<p><b>916. Plant societies</b> are somewhat definite associations of the -vegetation of an area marked by physiographic conditions. A single -<span class="pagenum"><a name="Page_476" id="Page_476">[Pg 476]</a></span> -plant society is nearly if not altogether identical with a “<i>principal -formation</i>,” but is a more popular expression, and besides includes all -the plants growing on the area, while in the use of the term “principal -formation” we have reference mainly to the dominant plants and the most -conspicuous subordinate species.</p> - -<p><b>917. Complex character of plant societies.</b>—In their broadest -analysis all plant societies are complex. Every plant society has one -or several dominant species, the individuals of which, because of -their number and size, give it its peculiar character. The society may -be so nearly pure that it appears to consist of the individuals of a -single species. But even in those cases there are small and conspicuous -plants of other species which occupy spaces between the dominant ones. -Usually there are several or more kinds in the same society. The larger -individuals come into competition for first place in regard to ground -and light, the smaller ones come into competition for the intervening -spaces for shade, and so on down in the scale of size and shade -tolerance. Then climbing plants (lianas) and epiphytes (lichens, algæ, -mosses, ferns, tree orchids, etc.) gain access to light and support by -growing on other larger and stouter members of the society.</p> - -<p>Parasites (dodder, mistletoes, rusts, smuts, mildews, bacteria, etc.) -are present, either actually or potentially, in all societies, and in -their methods of obtaining food sap the life and health of their hosts. -Then come the scavenger members, whose work it is to clean house, as it -were, the great army of saprophytic fungi (molds, mushrooms, etc.), and -bacteria ready to lay hold on dead and dying leaves, branches, trunks, -roots, etc., disintegrate them, and reduce them to humus, where other -fungi change them into a form in which the larger members of the plant -society can utilize them as plant food and thus continue the cycle of -matter through life, death, decay, and into life again. Mycorhiza (see -<a href="#CHAPTER_IX">Chapter IX</a>) or other forms of mutualistic symbiosis occur -which make atmospheric nitrogen available for food, or shorten the path from humus -to available food, or the humus plants feed on the humus directly. -Nor should we leave out of account the myriads of nitrate and nitrite -<span class="pagenum"><a name="Page_477" id="Page_477">[Pg 477]</a></span> -bacteria (see <a href="#CHAPTER_IX">Chapter IX</a>) which make certain substances -in the soil available to the higher members of the society. Most plant societies -are also benefited or profoundly influenced in other ways by animals, -as the flower-visiting insects, birds which feed on injurious insects, -the worms which mellow up the soil and cover dead organic matter so -that it may more thoroughly decay. In short, every plant society is -a great cosmos like the universe itself of which it is a part, where -multitudinous forms, processes, influences, evolutions, degenerations, -and regenerations are at work.</p> - -<p><b>918. Forest Societies.</b><a name="FNanchor_52_52" id="FNanchor_52_52"></a><a href="#Footnote_52_52" class="fnanchor">[52]</a>—Each -different climatic belt or region has its characteristic forest. -For example, the forests of the Hudsonian zone in North America are -different from those of the Canadian zone, and these in turn different -from those in the transition zone (mainly in northern United States). -The forests of the Rocky mountains and of the Pacific coast differ from -those of the Alleghanian, Carolinian (mainly middle United States) -or Austroriparian (southern United States) areas. Finally, tropical -forests are strikingly different from those of other regions. Similar -variations occur in the forests of other regions of the globe. The -character of these forests depends largely on climatic factors. The -character of the forest varies, however, even in the same climatic -area, dependent on soil conditions, or success in seeding and -ground-gaining of the different species in competition, etc.</p> - -<p><b>919. General structure of the forest.</b>—Structurally the forest -possesses three subdivisions: the floor, the canopy, and the interior. -The floor is the surface soil, which holds the rootage of the trees, -with its covering of leaf-mold and carpet of leaves, mosses, or other -low, more or less compact vegetation. The canopy is formed by the -spreading foliage of the tree crowns, which, in a forest of an even -and regular stand, meet and form a continuous mass of foliage through -which some light filters down into the interior. Where the stand is -<span class="pagenum"><a name="Page_478" id="Page_478">[Pg 478]</a></span> -irregular, i.e., the trees of different heights, the canopy is said to -be “compound” or “storied.” Where it is uneven, there are open places -in the canopy which admit more light, in which case the undergrowth -may be different. The interior of the forest lies between the canopy -and the floor. It provides for aeration of the floor and interior -occupants, and also room for the boles or tree trunks (called by -foresters the wood mass of the forest) which support the canopy and -provide the channels for communication and food exchange between the -floor and canopy. The canopy manufactures the carbohydrate food and -assimilates the mineral and proteid substances absorbed by the roots in -the soil; and also gets rid of the surplus water needed for conveying -food materials from the floor to the place where they are elaborated. -It is the seat where energy is created for work, and also the place for -seed production.</p> - -<div class="figcenter"> - <img src="images/fig489.jpg" alt="" width="600" height="480" /> - <p class="center">Fig. 489.<br /> - Mature forest of redwood (Sequoia sempervirens).<br /> - (Bureau of Forestry, U. S. Dept. Agr., Bull. 38.)</p> -</div> - -<p><span class="pagenum"><a name="Page_479" id="Page_479">[Pg 479]</a></span> -<b>920. Longevity of the forest.</b>—The forest is capable of -self-perpetuation, and, except in case of unusual disaster or the -action of man, it should live indefinitely. As the old trees die they -are gradually replaced by younger ones. So while trees may come and -trees may go, the forest goes on forever.</p> - -<p><b>921. Autumn colors.</b>—One of the striking effects produced by -the deciduous forests is that of the autumn coloring of the leaves. -It is more pronounced in the forests of the United States than in -corresponding life zones in the eastern hemisphere because of the -greater number of species. With the disintegration of the chlorophyll -bodies, other colors, which in some cases were masked by the green, -appear. In other cases decomposition products result in the formation -of other colors, as red, scarlet, yellow, brown, purple, maroon, etc., -in different species. These coloring substances to some extent are -believed to protect the nitrogenous substances in the leaf from injury. -The colors absorb the sun’s rays, which otherwise might destroy these -nitrogenous substances before they have passed back through the petiole -of the leaf into the stem, where they may be stored for food. The -gorgeous display of color, then, which the leaves of many trees and -shrubs put on is one of the many useful adaptations of the plants.</p> - -<p><b>922. Importance of the forest in the disposal of rainfall.</b>—The -importance of the forest in disposing of the rainfall is very great. -The great accumulation of humus on the forest floor holds back the -water both by absorption and by checking its flow, so that it does not -immediately flow quickly off the slopes into the drainage system of the -valley. It percolates into the soil. Much of it is held in the humus -and soil. What is not retained thus filters slowly through the soil -and is doled out more gradually into the valley streams and mountain -tributaries, so that the flood period is extended, and its injury -lessened or entirely prevented, because the body of water moving at any -one time is not dangerously high. The winter snow is shaded and in the -spring melts slowly, and the spring freshets are thus lessened. The -<span class="pagenum"><a name="Page_480" id="Page_480">[Pg 480]</a></span> -action of the leaves and humus in retarding the flow of the water -prevents the washing away of the soil; the roots of trees bind the soil -also and assist in holding it.</p> - -<p><b>923. Absence of forest encourages serious floods.</b>—The great -floods of the Mississippi and its tributaries are due to the rapidity -with which heavy rainfall flows from the rolling prairies of the west, -and from the deforested areas west of the Alleghany system. The serious -floods in recent years in some of the South Atlantic States are in -part due to the increasing area of deforestation in the Blue Ridge and -southern Alleghany system.</p> - -<p><b>924. The prairie and plains societies.</b>—These are to be found -in the grassland formation. In the prairies “meadows” are formed in -the lower ground near river courses where there is greater moisture -in soil. The grasses here are principally “sod-formers” which have -creeping underground stems which mat together, forming a dense sod. On -the higher and drier ground the “bunch” grasses, like buffalo-grass, -beard-grass, or broom-sedge, etc., are dominant, and in the drier -regions as one approaches desert conditions the vegetation gradually -takes on more the character of the desert, so that in the plains -sage-brush, the prickly-pear cactus, etc., occur. Besides the dominant -vegetation of the society there are subordinate species, and the -societies are especially marked by a spring and autumn flora of -conspicuous flowering plants which are mixed with the grasses.</p> - -<p><b>925. Desert societies.</b>—These are composed of plants which -possess a form or structure which enables them to exist in a very -dry climate where the air is very dry and the soil contains but -little moisture. The true desert plants are perennial. The growth and -flowering period occurs during the rainy season, or those portions -of the rainy season when the temperature is favorable, and they rest -during the very dry season and cold. Characteristic desert plants are -the cacti with thick succulent green stems or massive trunks, the -leaves being absent or reduced to mere spines which no longer function -in photosynthesis; yuccas with thick, narrow and long leaves with a -firm and thick cuticle; small shrubs or herbs with compact rounded -habit and small thick gray leaves. All of these structures conserve -<span class="pagenum"><a name="Page_481" id="Page_481">[Pg 481]</a></span> -moisture. The mesquite tree is one of the common trees in portions -of the Sonora Nevada desert. Besides the true desert plants, desert -societies have a rainy-season flora consisting of annuals, which can -germinate, vegetate, flower, and seed during the period of rain and -before the ground moisture has largely disappeared, and these pass the -resting period in seed.</p> - -<div class="figcenter"> - <img src="images/fig490.jpg" alt="" width="600" height="438" /> - <div class="blockquot"> - <p class="center">Fig. 490.</p> - <p>Desert vegetation, Arizona, showing large succulent trunks of cactus - with shrubs and stunted trees. Open formation. (Photograph by Tuomey.)</p> - </div> -</div> -<div class="figcenter"> - <img src="images/fig491.jpg" alt="" width="600" height="436" /> - <p class="center">Fig. 491.<br /> Polar tundra with scattered flowers, Alaska.<br /> - (Copyright by E. H. Harriman.)</p> -</div> -<div class="figcenter"> - <img src="images/fig492.jpg" alt="" width="600" height="284" /> - <div class="blockquot"> - <p class="center">Fig. 492.</p> - <p>Perennial rosette plant from alpine flora of the Andes, showing - short stem, rosette of leaves, and large flower. (After Schimper.)</p> - </div> -</div> - -<p><b>926. Arctic-alpine societies.</b>—The most striking of the arctic -plant societies are the “polar tundra,” extensive mats of vegetation -largely made up of mosses, lichens, etc., only partially decayed -because of the great cold of the subsoil, and perhaps also because -of humus acid in the partially decayed vegetation. These tundras -are brightened by numerous flowering plants which are characterized -by short stems, a rosette of leaves near the ground, and by large -bright-colored flowers. Heaths, saxifrages, and dwarf willow abound. -Alpine plant societies are similar to the arctic, although some of the -<span class="pagenum"><a name="Page_482" id="Page_482">[Pg 482]</a></span> -conditions are more severe than in the arctic region. This is -principally due to the fact that during the summer while the plants are -growing they are subject to a high temperature during the day and a -<span class="pagenum"><a name="Page_483" id="Page_483">[Pg 483]</a></span> -very low temperature at night, whereas during the summer in arctic -regions while the plants are growing there is continuous warmth for -growth and continuous light for photosynthesis. Five types of alpine -plants are recognized by some. 1st. <i>Elfin tree.</i> This type has short, -gnarled, often horizontal stems, as seen in pines, birches, and other -trees growing in alpine heights. 2d. <i>The alpine shrubs.</i> In the -highest alpine belts they are dwarfed and creeping, richly branched and -spreading close to the ground, while at lower belts they are more like -lowland shrubs. 3d. <i>The cushion type.</i> The branching is very profuse -and the branches are short and touch each other on all sides, forming -compact masses (examples saxifrages, androsace, mosses, etc.). 4th. -<i>Rosette plants.</i> These are perennial, short stems and very strong -roots, and play an important part in the alpine meadows. 5th. <i>Alpine -grasses.</i> These usually have much shorter leaves than grasses of the -lowlands and consequently form a low sward.</p> - -<p><b>927. Edaphic plant societies.</b>—These are equivalent to edaphic -plant formations, and the vegetation is of course controlled by the -peculiar conditions of the soil. There are a number of different -kinds of edaphic plant societies determined by the character of the -physiographic areas. 1st. <i>Sphagnum moors.</i> These are formed in shallow -basins originally with more or less water. The growth of the sphagnum -moss along with other vegetation and its partial decay in the water -builds up ground rapidly so that in course of time the pond may be -completely filled in. This filling in proceeds from the shore toward -the center, and in the early stages of course there would be a pond -in the center. The partial decay of vegetation creates an excess of -humus acid which retards absorption by the roots. The conditions are -such, then, as require aerial structures for retarding the loss of -water, and plants growing in such moors are usually xerophytes. Some of -the plants are identical with those growing in the arctic tundra. 2d. -<i>Sand</i><a name="FNanchor_53_53" id="FNanchor_53_53"></a><a href="#Footnote_53_53" class="fnanchor">[53]</a> <i>strand of beach.</i> -The quantity of sand with very little or no admixture of humus or plant -<span class="pagenum"><a name="Page_484" id="Page_484">[Pg 484]</a></span> -food makes it difficult for plants to obtain a sufficient amount of -water even where rainfall is abundant. The same may be said of the sand -dunes farther back from the shore. The plants of these areas are then -usually xerophytes. Some of the plants accustomed to growing in such -localities are American sea-rocket, seaside spurge, bugseed, sea-blite, -sea-purslane, the sandcherry, dwarf willow, marram-grass, certain -species of beard-grass, etc. 3d. <i>Rocky shores or areas.</i> Here lichens -and mosses first grow, later to be followed by herbs, grasses, shrubs, -and trees, as decayed plant remains accumulate in the rock crevices. -4th. <i>Shores of ponds, or swamp moors.</i> Here the vegetation often -takes on a zonal arrangement if the ground gradually slopes to the -shore and out into the pond. In <a href="#FIG_493">Fig. 493</a> is shown zonal -distribution of plants. The different kinds of plants are drawn into these zones -by the varying amount of ground water in the soil, or the varying depth -of the water on the margin of the pond as one proceeds from the land -towards the deeper water. On the border lines or tension lines between -the different zones the plants are struggling to occupy here ground -which is suitable for each adjacent individual formation. Other edaphic -societies are those of marl ponds, alkaline areas, oases in deserts, -warm oases in arctic lands, the forested areas along river bottoms in -prairie or plains regions, etc. -<span class="pagenum"><a name="Page_485" id="Page_485">[Pg 485]</a></span></p> - -<div class="figcenter"> - <img id="FIG_493" src="images/fig493.jpg" alt="" width="600" height="311" /> - <div class="blockquot"> - <p class="center">Fig. 493.</p> - <p>Macrophytes in the upper zone of the photic region. Ascophyllum and - Fucus at low tide, Hunter’s Island, New York City. (Photograph by M. A. Howe.)</p> - </div> -</div> -<div class="figcenter"> - <img src="images/fig494.jpg" alt="" width="600" height="358" /> - <p class="center">Fig. 494. <br /> - Zonal distribution of plants, South Shore, Cayuga Lake.</p> -</div> - -<p><span class="pagenum"><a name="Page_486" id="Page_486">[Pg 486]</a></span> -<b>928. Aquatic plant societies.</b>—In general we might distinguish -three kinds, 1st. <i>Fresh-water plant societies</i>, with floating algæ -like spirogyra, œdogonium, etc., the floating duck-meats, riccias; the -plants of the lily type with roots and stems attached to the bottom -and leaves floating on the surface, like the water-lily and certain -pondweeds, and finally the completely submerged ones like certain -pondweeds, the bassweed (Chara), etc. 2d. <i>Marine plant societies</i>, -which are made up mostly of the red and brown algæ or “seaweeds,” -though some green algæ and flowering plants also occur. 3d. <i>The salt -marshes</i> where the water is brackish and there is usually a luxuriant -growth of marsh-grasses.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_487" id="Page_487">[Pg 487]</a></span></p> -<div class="chapter"> -<h3 class="nobreak"><a name="CHAPTER_XLVII" id="CHAPTER_XLVII">CHAPTER XLVII.</a><br /> -<span class="h_subtitle">CLASSIFICATION OF THE ANGIOSPERMS.</span></h3> -</div> - -<p class="center"><b>Relation of Species, Genus, Family, Order, etc.</b></p> - -<p><b>929. Species.</b>—It is not necessary for one to be a botanist in -order to recognize, during a stroll in the woods where the trillium -is flowering, that there are many individual plants very like each -other. They may vary in size, and the parts may differ a little in -form. When the flowers first open they are usually white, and in age -they generally become pinkish. In some individuals they are pinkish -when they first open. Even with these variations, which are trifling -in comparison with the points of close agreement, we recognize the -individuals to be of the <i>same kind</i>, just as we recognize the corn -plants, grown from the seed of an ear of corn, as of the same kind. -Individuals of the same kind, in this sense, form a <i>species</i>. The -white wake-robin, then, is a species.</p> - -<p>But there are other trilliums which differ greatly from this one. The -purple trillium (T. erectum) shown in <a href="#FIG_495">fig. 495</a> is very -different from it. So are a number of others. But the purple trillium -is a species. It is made up of individuals variable, yet very like one -another, more so than any one of them is like the white wake-robin.</p> - -<p><b>930. Genus.</b>—Yet if we study all parts of the plant, the -perennial rootstock, the annual shoot, and the parts of the flower, we -find a great resemblance. In this respect we find that there are -several species which possess the same general characters. In other -<span class="pagenum"><a name="Page_488" id="Page_488">[Pg 488]</a></span> -words, there is a relationship between these different species, a -relationship which includes more than the individuals of one kind. It -includes several kinds. Obviously, then, this is a relationship with -broader limits, and of a higher grade, than that of the individuals -of a species. The grade next higher than species we call <i>genus</i>. -Trillium, then, is a genus. Briefly the characters of the genus -trillium are as follows:</p> - -<div class="figcenter"> - <img id="FIG_495" src="images/fig495.jpg" alt="" width="300" height="422" /> - <p class="center">Fig. 495.<br /> Trillium erectum (purple form),<br /> - two plants from one rootstock.</p> -</div> - -<p><b>931. Genus trillium.</b>—Perianth of six parts: sepals 3, -herbaceous, persistent; petals colored. Stamens 6 (in two whorls), -anthers opening inward. Ovary 3-loculed, 3-6-angled; stigmas 3, -slender, spreading. Herbs with a stout perennial rootstock, with -fleshy, scale-like leaves, from which the low annual shoot arises, -bearing a terminal flower and 3 large netted-veined leaves in a whorl.</p> - -<p class="blockquot"><i>Note.</i>—In speaking of the genus the present usage -is to say trillium, but two words are usually employed in speaking of -the species, as Trillium grandiflorum, T. erectum, etc.</p> - -<p><b>932. Genus erythronium.</b>—The yellow adder-tongue, or dogtooth -violet (Erythronium americanum), shown in <a href="#FIG_496">fig. 496</a>, -is quite different from any species of trillium. It differs more from any of -the species of trillium than they do from each other. The perianth is of six -parts, light yellow, often spotted near the base. Stamens are 6. The ovary is -obovate, tapering at the base, 3-valved, seeds rather numerous, and the -style is elongated. The flower stem, or scape, arises from a scaly bulb -<span class="pagenum"><a name="Page_489" id="Page_489">[Pg 489]</a></span> -deep in the soil, and is sheathed by two elliptical-lanceolate, mottled -leaves. The smaller plants have no flower and but one leaf, while the -bulb is nearer the surface. Each year new bulbs are formed at the end -of runners from a parent bulb. These runners penetrate each year deeper -into the soil. The deeper bulbs bear the flower stems.</p> - -<p><b>933. Genus lilium.</b>—While the lily differs from either the -trillium or erythronium, yet we recognize a relationship when we -compare the perianth of six colored parts, the 6 stamens, and the -3-sided and long 3-loculed ovary.</p> - -<div class="figcenter"> - <img id="FIG_496" src="images/fig496.jpg" alt="" width="450" height="425" /> - <div class="blockquot"> - <p class="center">Fig. 496.</p> - <p>Adder-tongue (erythronium). At left below pistil, and three stamens - opposite three parts of the perianth. Bulb at the right.</p> - </div> -</div> - -<p><b>934. Family Liliaceæ.</b>—The relationship between genera, as -between trillium, erythronium, and lilium, brings us to a still higher -order of relationship, where the limits are broader than in the genus. -Genera which are thus related make up the <i>family</i>. In the case of -these genera the family has been named after the lily, and is the lily -family, or <i>Liliaceæ</i>.</p> - -<p><b>935. Order, class, group.</b>—In like manner the lily family, the -iris family, the amaryllis family, and others which show characters of -close relationship are united into an <i>order</i> which has broader limits -<span class="pagenum"><a name="Page_490" id="Page_490">[Pg 490]</a></span> -than the family. This order is the lily order, or order <i>Liliales</i>. The -various orders unite to make up the <i>class</i>, and the classes unite to -form a <i>group</i>.</p> - -<p><b>936. Variations in usage of the terms class, order, etc.</b>—Thus, -according to the system of classification adopted by some, the -angiosperms form a <i>group</i>. The group angiosperms is then divided into -two <i>classes</i>, the <i>monocotyledones</i> and <i>dicotyledones</i>. (It -should be remembered that all systematists do not agree in assigning the -same grade and limits to the classes, subclasses, etc. For example, -some treat of the angiosperms as a class, and the monocotyledons -and dicotyledons as subclasses; while others would divide the -monocotyledons and dicotyledons into classes, instead of treating each -one as a class or as a subclass. Systematists differ also in usage as -to the termination of the ordinal name; for example, some use the word -<i>Liliales</i> for <i>Liliifloræ</i>, in writing of the order.)</p> - -<div class="figcenter"> - <img id="FIG_497" src="images/fig497.jpg" alt="" width="600" height="269" /> - <div class="blockquot"> - <p class="center">Fig. 497.</p> - <p><i>A.</i> Cross-section of the stem of an oak tree thirty-seven years old, - showing the annual rings. <i>rm</i>, the medullary rays; <i>m</i>, the pith - (medulla).<br /> <i>B.</i> Cross-section of the stem of a palm tree, showing the - scattered bundles.</p> - </div> -</div> - -<p><b>937. Monocotyledones.</b>—In the monocotyledons there is a single -cotyledon on the embryo; the leaves are parallel-veined; the parts -of the flower are usually in threes; endosperm is usually present in -the seed; the vascular bundles are usually closed, and are scattered -irregularly through the stem as shown by a cross-section of the stem -of a palm (<a href="#FIG_497">fig. 497</a>), or by the arrangement of the bundles in the corn -stem (<a href="#FIG_57">fig. 57</a>). Thus a single character is not sufficient to show -<span class="pagenum"><a name="Page_491" id="Page_491">[Pg 491]</a></span> -relationship in the class (nor is it in orders, nor in many of the -lower grades), but one must use the sum of several important characters.</p> - -<p><b>938. Dicotyledones.</b>—In the dicotyledons there are two -cotyledons on the embryo; the venation of the leaves is reticulate; -the endosperm is usually absent in the seed; the parts of the flower -are frequently in fives; the vascular bundles of the stem are -generally open and arranged in rings around the stem, as shown in the -cross-section of the oak (<a href="#FIG_497">fig. 497</a>). There are exceptions -to all the above characters, and the sum of the characters must be considered, -just as in the case of the monocotyledons.</p> - -<p><b>939. Taxonomy.</b>—This grouping of plants into species, genera, -families, etc., according to characters and relationships is -<i>classification</i>, or <i>taxonomy</i>.</p> - -<p>To take Trillium grandiflorum for example, its position in the system, -if all the principal subdivisions should be included in the outline, -would be indicated as follows:</p> - -<ul class="index"> -<li class="isub1">Group, Angiosperms.</li> -<li class="isub2">Class, Monocotyledones.</li> -<li class="isub3">Order, Liliales.</li> -<li class="isub4">Family, Liliaceæ.</li> -<li class="isub5">Genus, Trillium.</li> -<li class="isub6">Species, grandiflorum.</li> -</ul> - -<p>In the same way the position of the toothwort would be indicated as -follows:</p> - -<ul class="index"> -<li class="isub1">Group, Angiosperms.</li> -<li class="isub2">Class, Dicotyledones.</li> -<li class="isub3">Order, Papaverales.</li> -<li class="isub4">Family, Cruciferæ.</li> -<li class="isub5">Genus, Dentaria.</li> -<li class="isub6">Species, diphylla.</li> -</ul> - -<p>But in giving the technical name of the plant only two of these names -are used, the genus and species, so that for the toothwort we say -<i>Dentaria diphylla</i>, and for the white wake-robin we say <i>Trillium -grandiflorum</i>.</p> - -<p><b>940. Kingdom and Subkingdom.</b>—Organic beings form altogether two -<span class="pagenum"><a name="Page_492" id="Page_492">[Pg 492]</a></span> -kingdoms, the Animal Kingdom and the Plant Kingdom. The Plant Kingdom -is then divided into a number of subkingdoms as follows: 1st, -Subkingdom Thallophyta, the thallus plants, including the Algæ and -Fungi; 2d, Subkingdom Bryophyta, the moss-like plants, including the -Liverworts and Mosses; 3d, Subkingdom Pteridophyta, the fern-like -plants, including Ferns, Lycopods, Equisetum, Isoetes, etc.; 4th, -Subkingdom Spermatophyta, the seed plants, including Gymnosperms and -Angiosperms. Subkingdoms are divided into groups of lower order down to -the classes. So there are subclasses, subfamilies or tribes, subgenera, -and even subspecies. But taking the principal taxonomic divisions from -the greater to the lesser rank, the order would be as follows:</p> - -<ul class="index"> -<li class="isub1">Plant Kingdom.</li> -<li class="isub2">Subkingdom, Spermatophyta.</li> -<li class="isub3">Group (not used in a definite sense).</li> -<li class="isub4">Class, Gymnospermæ.</li> -<li class="isub5">Order, Pinales.</li> -<li class="isub6">Family, Pinaceæ.</li> -<li class="isub7">Genus, Pinus.</li> -<li class="isub8">Species, strobus, or, in full,</li> -<li class="isub1">Pinus strobus, the white pine.</li> -</ul> - -<p class="center"><b>Group Angiospermæ.</b></p> - -<p class="center">I. CLASS MONOCOTYLEDONES.</p> - -<p><b>941. Order Pandanales.</b>—Aquatic or marsh plants. The cattail -flags (Typha) and the bur-reeds (Sparganium), each representing a -family. The name of the order is taken from the tropical genus Pandanus -(the screw-pine often grown in greenhouses).</p> - -<p><b>942. Order Naiadales.</b>—Aquatic or marsh herbs. Three families -are mentioned here.</p> - -<p>The pondweed family (Naiadaceæ), named after one genus, Naias. The -largest genus is Potamogeton, the species of which are known as -<span class="pagenum"><a name="Page_493" id="Page_493">[Pg 493]</a></span> -pondweeds. Ruppia occidentalis occurs in saline ponds in Nebraska, and -R. maritima along the seacoast and in saline districts in the interior.</p> - -<p>The water-plantain family (Alismaceæ) includes the water-plantain -(Alisma) and the arrow-leaves (Sagittaria).</p> - -<p>The tape-grass family (Vallisneriaceæ) includes the tape-grass, or -eel-grass (the curious Vallisneria spiralis).</p> - -<p><b>943. Order Graminales.</b>—Two families.</p> - -<p>The grass family (Gramineæ), the grasses and grains.</p> - -<p>The sedge family (Cyperaceæ), the sedges.</p> - -<p><b>944. Order Palmales</b>, with one family, Palmaceæ, includes the -palms, abundant in the tropics and extending into Florida. Cultivated -in greenhouses.</p> - -<p><b>945. Order Arales.</b></p> - -<p>The arum family (Araceæ). Flowers in a fleshy spadix. Examples: Indian -turnip (Arisæma), sweet-flag (Acorus), skunk-cabbage (Spathyema).</p> - -<p>The duckweed family (Lemnaceæ). (Examples: Lemna, Spirodela, Wolffia. -<a href="#PARA_51">See paragraphs 51-53</a>.)</p> - -<p><b>946. Order Xyridales</b>, from the genus Xyris, the yellow-eyed -grass family (Xyridaceæ). Species mostly tropical, but a few in North -America. Other examples are the pipewort family (Eriocaulaceæ, example, -Eriocaulon septangulare), the pineapple family (Bromeliaceæ, example, -the pineapple cultivated in Florida); the Florida moss or hanging moss -(Tillandsia usneoides); the spiderwort family (Commelinaceæ), including -the spiderwort (Tradescantia, several species in North America); the -pickerel-weed family (Pontederiaceæ), including the genus Pontederia in -borders of ponds and streams.</p> - -<p><b>947. Order Liliales.</b>—Some of the families are as follows:</p> - -<p>The rush family (Juncaceæ, example, Juncus), with many species, plants -of usually swamp habit.</p> - -<p>The lily family (Liliaceæ, examples: Lilium, Allium = Onion, -Erythronium, Yucca).</p> - -<p>The iris family (Iridaceæ, examples: Iris, the blue-flag, fleur-de-lis, etc.). -<span class="pagenum"><a name="Page_494" id="Page_494">[Pg 494]</a></span></p> - -<p>The lily-of-the-valley family (Convallariaceæ, examples: -lily-of-the-valley, Trillium, etc.)</p> - -<p>The amaryllis family (Amaryllidaceæ, examples: Narcissus, the daffodil; -Cooperia, in southwestern United States).</p> - -<p><b>948. Order Scitaminales.</b>—This order includes the large showy -cultivated Canna of the canna family.</p> - -<p><b>949. Order Orchidales.</b> Example, the orchid family (Orchidaceæ) -with Cypripedium, Orchis, etc.</p> - -<p class="center">II. CLASS DICOTYLEDONES.</p> - -<p><span class="smcap">Series</span> 1. CHORIPETALÆ. Petals wanting (Apetalæ, or -Archichlamydæ of some authors), or present and distinct from one -another (Polypetalæ, or Metachlamydæ).</p> - -<p><b>950. Order Casuarinales</b>, confined to tropical seacoasts -(example, Casuarina).</p> - -<p><b>951. Order Piperales</b> includes the lizard’s-tail family -(Saururaceæ), Saururus cernuus, lizard’s-tail, in the eastern United -States.</p> - -<p><b>952. Order Salicales.</b>—Shrubs or trees, flowers in aments. -Includes the willows and poplars (Salix and Populus of the willow -family, Salicaceæ).</p> - -<p><b>953. Order Myricales.</b>—Shrubs or small trees. Includes the -sweet-gale (Myrica gale) in wet places in northern United States and -British North America, Myrica cerifera forming thickets on sand dunes -along the Atlantic coast, and the sweet-fern (Comptonia peregrina = C. -asplenifolia) in the eastern United States in dry soil of hillsides.</p> - -<p><b>954. Order Leitneriales.</b>—Shrubs or trees. Includes the -cork-wood, Leitneria floridana (Leitneriaceæ).</p> - -<p><b>955. Order Juglandales.</b>—Trees, staminate flowers in aments. The -walnut family (Juglandaceæ, examples: walnut, butternut, etc. Juglans; -hickory, Hicoria = Carya).</p> - -<p><b>956. Order Fagales.</b>—Trees and shrubs. Flowers in aments, or the -pistillate ones with an involucre which forms a cup in fruit, as in the -acorn of the oak. -<span class="pagenum"><a name="Page_495" id="Page_495">[Pg 495]</a></span></p> - -<p>The birch family (Betulaceæ, examples: Betula, birch; Corylus, -hazelnut; Alnus, alder, etc.).</p> - -<p>The beech family (Fagaceæ = Cupuliferæ, examples: Fagus, beech; -Castanea, chestnut; Quercus, oak).</p> - -<p><b>957. Order Urticales.</b>—Trees, shrubs, or herbs. Examples: the -elm family (Ulmaceæ), the mulberry family (Moraceæ), and the nettle -family (Urticaceæ).</p> - -<p><b>958. Order Santalales</b>, herbs or shrubs, mostly parasitic.</p> - -<p>The mistletoe family (Loranthaceæ), with the American mistletoe -(Phoradendron flavescens), parasitic on deciduous trees in the South -Atlantic, Central, and Gulf States (N. J. to Ind. Ter.).</p> - -<p>The sandalwood family (Santalaceæ, example, the bastard toad-flax, -Comandra umbellata), widely distributed in North America.</p> - -<p><b>959. Order Aristolochiales.</b>—Herbs or vines with heart-shaped or -kidney-shaped leaves. The birthwort family (Aristolochiaceæ, example, -Aristolochia serpentaria, the Virginia snake-root, eastern United -States; wild ginger, or heart-leaf, Asarum canadense, eastern North -America.)</p> - -<p><b>960. Order Polygonales.</b>—Examples: the buckwheat family -(Polygonaceæ), including buckwheat (Fagopyrum), and numerous species -of Polygonum, known as smartweed, water-pepper, tear-thumb, bindweed, -knotweed, prince’s-feather, etc.</p> - -<p><b>961. Order Chenopodiales.</b>—Herbs. There are several families; -one of the largest is the goosefoot family (Chenopodiaceæ). The genus -Chenopodium includes many species, known as goosefoot, lamb’s-quarters, -etc. Here belong also the Russian thistle (Salsola tragus) and the -saltwort (S. kali). The former is sometimes a troublesome weed in the -central and western United States, naturalized from Europe. The latter -occurs along the Atlantic coast on seabeaches. Atriplex occurs in salty -or alkaline soil, also the glasswort (Salicornia herbacea), the bugseed -(Corispermum). The pokeweed family (Phytolaccaceæ), the Amaranth family -(Amaranthaceæ), the purslane family (Portulacaceæ, including the -<span class="pagenum"><a name="Page_496" id="Page_496">[Pg 496]</a></span> -purslane or “pursley,” Portulaca oleracea, and the spring-beauty, -Claytonia virginica), and the pink family (Caryophyllaceæ), belong here.</p> - -<p><b>962. Order Ranales.</b>—Herbs, shrubs, or trees. Examples are:</p> - -<p>The water-lily family (Nymphæaceæ), with the yellow water-lily (Nymphæa -advena = Nuphar advena) and the white water-lily (Castalia odorata = -Nymphæa odorata).</p> - -<p>The magnolia family (Magnoliaceæ), including the magnolias -(Magnolia) and the tulip-tree (Liriodendron). The crowfoot family -(Ranunculaceæ), with the buttercups, hepatica, clematis, etc.</p> - -<p><b>963. Order Papaverales.</b>—Mostly herbs. Examples are:</p> - -<p>The poppy family (Papaveraceæ), including the opium or garden poppy -(Papaver somniferum), the blood-root (Sanguinaria canadensis), the -Dutchman’s-breeches (Bicuculla cucullaria = Dicentra cucullaria), -squirrel’s-corn (Bicuculla canadensis = D. canadensis).</p> - -<p>The mustard family (Cruciferæ), including the toothwort (Dentaria), -shepherd’s-purse (Bursa bursa-pastoris = Capsella bursa-pastoris), the -cabbage, turnip, etc.</p> - -<p><b>964. Order Sarraceniales.</b>—Insectivorous plants.</p> - -<p>The pitcher-plant family (Sarraceniaceæ). Examples: Sarracenia -purpurea, the pitcher-plant, in peat-bogs, northern and eastern North -America.</p> - -<p>The sundew family (Droseraceæ). Examples: Drosera rotundifolia, and -other sundews.</p> - -<p><b>965. Order Rosales.</b>—Herbs, shrubs or trees. Seventeen families -are given in the eastern United States. Examples:</p> - -<p>The riverweed family (Podostemaceæ), containing the riverweed -(Podostemon).</p> - -<p>The saxifrage family (Saxifragaceæ), containing a number of species. -Example, Saxifraga virginiensis.</p> - -<p>The gooseberry family (Grossulariaceæ), including the wild and the -cultivated gooseberry.</p> - -<p>The witch-hazel family (Hamamelidaceæ), including the witch-hazel -(Hamamelis), in eastern North America, and the sweet gum (Liquidambar -styraciflua). -<span class="pagenum"><a name="Page_497" id="Page_497">[Pg 497]</a></span></p> - -<p>The plane-tree family (Platanaceæ), with the plane-tree, or buttonwood -(Platanus occidentalis), eastern North America. (Other species occur in -western United States.)</p> - -<p>The rose family (Rosaceæ), including roses, spiræas, raspberries, -strawberries, the shrubby cinquefoil (Dasiphora fruticosa), etc.</p> - -<p>The apple family (Pomaceæ), including the apple, mountain-ash, pear, -June-berry (or shadbush, also service-berry), the hawthorns (Cratægus).</p> - -<p>The plum family (Drupaceæ), including the cherries, plums, peaches, etc.</p> - -<p>The pea family (Papilionaceæ), including the pea, bean, clover, vetch, -lupine, etc., a very large family.</p> - -<p><b>966. Order Geraniales.</b>—Herbs, shrubs, or trees. Nine families -in the eastern United States. Examples:</p> - -<p>The geranium family (Geraniaceæ), with the cranesbill (Geranium -maculatum) and others.</p> - -<p>The wood-sorrel family (Oxalidaceæ), with the wood-sorrel (Oxalis -acetosella) and others.</p> - -<p>The flax family (Linaceæ). Example, flax (Linum vulgaris).</p> - -<p>The spurge family (Euphorbiaceæ). Plants with a milky juice, and -curious, degenerate flowers. Examples: the castor-oil plant (Ricinus), -the spurges (many species of Euphorbia).</p> - -<p><b>967. Order Sapindales.</b>—Mostly trees or shrubs. Twelve families -in the eastern United States. Example:</p> - -<p>The sumac family (Anacardiaceæ), containing the sumacs in the genus -Rhus. Examples: the poison-ivy (R. radicans), a climbing vine, in -thickets and along fences, in eastern United States. Sometimes -trained over porches. The poison-oak (R. toxicodendron), a low shrub. -Poison-sumac or poison-alder (R. vernix = R. venenata), sometimes -called “thunderwood,” or dogwood, is a large shrub or small tree, very -poisonous. The smoke-tree (Cotinus cotinoides) belongs to the same -family, and is often planted as an ornamental tree. The maple family -(Aceraceæ), including the maples (Acer). -<span class="pagenum"><a name="Page_498" id="Page_498">[Pg 498]</a></span></p> - -<p>The buckeye family (Hippocastanaceæ), including the horse-chestnut -(Æsculus hippocastanum), much planted as a shade tree along streets. -Also there are several species of buckeye in the same genus.</p> - -<p>The jewelweed family (Balsaminaceæ), including the touch-me-not -(Impatiens biflora and aurea) in moist places. The garden balsam (Imp. -balsamea) also belongs here.</p> - -<p><b>968. Order Rhamnales.</b>—Shrubs, vines, or small trees. There are -two families, the buckthorn (Rhamnaceæ), the grape family (Vitaceæ), -including the grapes (Vitis), the American ivy (Parthenocissus -quinquefolia = Ampelopsis quinquefolia), in woods and thickets, eastern -North America, and much planted as a trailer over porches. The Japanese -ivy (P. tricuspidata = A. veitchii) used as a trailer on the sides of -buildings belongs here.</p> - -<p><b>969. Order Malvales.</b>—Herbs, shrubs, or trees.</p> - -<p>The linden family (Tiliaceæ). Example, the basswood or American linden -(Tilia americana.)</p> - -<p>The mallow family (Malvaceæ), including the hollyhock, the mallows, -rose of Sharon (Hibiscus), etc.</p> - -<p><b>970. Order Parietales</b>, with seven families in the eastern United -States. The St. John’s wort (Hypericum) and the violets each represent -a family. The violets (Violaceæ) are well-known flowers.</p> - -<p><b>971. Order Opuntiales.</b>—These include the cacti (Cactaceæ), -chiefly growing in the dry or desert regions of America.</p> - -<p><b>972. Order Thymeleales</b>, with two families and few species.</p> - -<p><b>973. Order Myrtales.</b>—Land, marsh, or aquatic plants. The most -conspicuous are in the evening primrose family (Onagraceæ), including -the fireweeds, or willow herbs (Epilobium), and the evening primrose -(Onagra biennis = Œnothera biennis).</p> - -<p><b>974. Order Umbellales.</b>—Herbs, shrubs, or trees, flowers in umbels. -<span class="pagenum"><a name="Page_499" id="Page_499">[Pg 499]</a></span></p> - -<p>The ginseng family (Araliaceæ). This includes the spikenards and -sarsaparillas in the genus Aralia, and the ginseng (or “sang”), Panax -quinquefolium.</p> - -<p>The carrot family (Umbelliferæ). This family includes the wild carrot -(Daucus carota), the poison-hemlock (Cicuta), the cultivated carrot and -parsnip, and a large number of other genera and species.</p> - -<p>The dogwood family (Cornaceæ). The flowering dogwood (Cornus florida), -abundant in eastern North America, is an example.</p> - -<p><span class="smcap">Series</span> 2. GAMOPETALÆ (= Sympetalæ or Metachlamydæ). Petals -partly or wholly united, rarely separate or wanting.</p> - -<p><b>975. Order Ericales.</b>—There are six families in eastern United -States. Examples:</p> - -<p>The wintergreen family (Pyrolaceæ), including the shin-leaf (Pyrola -elliptica).</p> - -<p>The Indian-pipe family (Monotropaceæ), with the Indian-pipe (Monotropa -uniflora) and other humus saprophytes. (<a href="#PARA_182">See paragraphs 182-191</a>.)</p> - -<p>The heath family (Ericaceæ). Examples: Labrador tea (Ledum), in bogs -and swamps in northern North America. The azaleas, with several -species widely distributed, are beautiful flowering shrubs, and many -varieties are cultivated. The rhododendrons are larger with larger -flower clusters, also beautiful flowering shrubs. R. maximum in the -Alleghany Mountains and vicinity, from Nova Scotia to Ohio and Georgia. -R. catawbiense, usually at somewhat higher elevations, Virginia to -Georgia. The mountain laurel (Kalmia latifolia) and other species rival -the rhododendrons and azaleas in beauty. The trailing arbutus (Epigæa -repens) in sandy or rocky woods is a well-known small trailing shrub -in eastern North America. The sourwood (Oxydendrum arboreum) is a tree -with white racemes of flowers in August, and scarlet leaves in autumn. -The spring or creeping wintergreen (Gaultheria procumbens) is a small -shrub with aromatic leaves, and bright red spicy berries.</p> - -<p>The huckleberry family (Vaccinaceæ) includes the huckleberries -<span class="pagenum"><a name="Page_500" id="Page_500">[Pg 500]</a></span> -(example, Gaylussacia resinosa, the black or high-bush huckleberry, -eastern United States), the mountain cranberry (Vitis-Idæa vitisidæa -= Vaccinium vitisidæa) in the northern hemisphere; the bilberries and -blueberries (of genus Vaccinium); the cranberries (examples: the large -American cranberry, Oxycoccus macrocarpus and the European cranberry, -Oxycoccus oxycoccus, in cold bogs of northern North America, the latter -also in Europe and Asia).</p> - -<p><b>976. Order Primulales.</b>—Two families here. The primrose family -(Primulaceæ) contains the loosestrifes (Steironema), star-flower -(Trientalis), etc.</p> - -<p><b>977. Order Ebenales.</b>—Of the four families, the ebony family -(Ebenaceæ) contains the well-known persimmon (Diospyros virginiana) and -the storax family (Styracaceæ) with the silverbell, or snowdrop tree -(Mohrodendron carolinum).</p> - -<p><b>978. Order Gentianales.</b>—Herbs, shrubs, vines, or trees. Six -families in the United States.</p> - -<p>The olive family (Oleaceæ) includes the common lilac (Syringa), the ash -trees (Fraxinus), the privet (Ligustrum).</p> - -<p>The gentian family (Gentianaceæ) among other genera includes the -gentians (Gentiana).</p> - -<p>The milkweed family (Asclepiadaceæ) contains plants mostly with a milky -juice. Asclepias with many species is one of the most prominent genera.</p> - -<p><b>979. Order Polemoniales.</b>—Mostly herbs, rarely shrubs and trees. -Fifteen families in the eastern United States.</p> - -<p>The morning glory family (Convolvulaceæ) includes the bindweeds -(Convolvulus), the morning glory (Ipomæa), etc.</p> - -<p>The dodder family (Cuscutaceæ) includes the dodders, or “love-vines.” -There are nearly thirty species in the United States. The stems are -slender and twine around other plants upon which they are parasitic -(<a href="#PARA_179">see paragraph 179</a>).</p> - -<p>The phlox family (Polemoniaceæ). The most prominent genus is Phlox. -Over forty species occur in North America.</p> - -<p>The borage family (Boraginaceæ) includes the heliotrope (Heliotropium), -the hound’s-tongue (Cynoglossum), the forget-me-not (Myosotis), and others. -<span class="pagenum"><a name="Page_501" id="Page_501">[Pg 501]</a></span></p> - -<p>The vervain family (verbenaceæ) contains the verbenas.</p> - -<p>The mint family (Labiatæ) contains the mints (Mentha), skull-cap -(Scutellaria), dead-nettles (Lamium).</p> - -<p>The potato family (Solanaceæ) includes the ground-cherry (Physalis), -the nightshades (Solanum), the tomato (Lycopersicon), tobacco (Nicotiana).</p> - -<p>The figwort family (Scrophulariaceæ) includes the common mullein -(Verbascum), the monkey-flower (Mimulus), the toad-flax (Linaria), -turtle’s-head (Chelone), and many other genera and species.</p> - -<p>The bladderwort family (Lentibulariaceæ) includes the curious bog or -aquatic plants with finely dissected leaves, and with bladders in which -insects are caught (Utricularia).</p> - -<p>The trumpet-creeper family (Bignoniaceæ) includes the trumpet-creeper -(Bignonia), the catalpa tree, and others.</p> - -<p><b>980. Order Plantaginales</b> with one family (Plantaginaceæ) -includes the plantains (Plantago).</p> - -<p><b>981. Order Rubiales</b> with three families is represented by the -madder family (Rubiaceæ) with the bluets (Houstonia), the button-bush -(Cephalanthus), the partridge-berry (Mitchella), the bedstraws -(Galium), etc.</p> - -<p>The honeysuckle family (Caprifoliaceæ) with the elder (Sambucus), the -arrowwoods and cranberry trees (Viburnum), the honeysuckles (Lonicera), -etc.</p> - -<p><b>982. Order Valerianales</b> with two families includes the teasel -family (Dipsacaceæ). Example, Fuller’s teasel (Dipsacus).</p> - -<p><b>983. Order Campanulales</b> with five families, the corolla usually -gamopetalous.</p> - -<p>The gourd family (Cucurbitaceæ) includes the pumpkin, squash, melon, -and a few feral species. Example, the star-cucumber (Sicyos angulatus), -in moist places in eastern and middle United States.</p> - -<p>The bell-flower family (Campanulaceæ) includes the hare-bells or -bell-flowers (Campanula), the lobelias (example, Lobelia cardinalis, -the cardinal-flower), etc. -<span class="pagenum"><a name="Page_502" id="Page_502">[Pg 502]</a></span></p> - -<p>The chicory family (Cichoriaceæ) includes the chicory or succory -(Cichorium intybus, known also as blue-sailors), the oyster-plant or -salsify (Tragopogon porrifolius), the dandelion (Taraxacum taraxacum = -T. densleonis), the lettuce (Lactuca), the hawkweed (Hieraceum), and -others.</p> - -<p>The ragweed family (Ambrosiaceæ) includes the ragweeds (Ambrosia), the -cockle-bur (Xanthium), and others.</p> - -<p>The thistle family (Compositæ) includes the thistle (Carduus), asters -(Aster), goldenrods (Solidago), sunflowers (Helianthus), eupatoriums or -joepye-weeds, thoroughworts (Eupatorium), cone-flowers or black-eyed -Susans (Rudbeckia), tickseed (Coreopsis), bur-marigold or beggar-ticks -or devil’s-bootjack (Bidens), chrysanthemums, etc.</p> - -<hr class="chap" /> -<p><span class="pagenum"><a name="Page_503" id="Page_503">[Pg 503]</a></span></p> -<div class="chapter"><h2 class="nobreak"><a name="INDEX" id="INDEX">INDEX.</a></h2></div> - -<ul class="index"> -<li class="isub1">Absorption, <a href="#Page_13">13</a>, <a href="#Page_22">22-28</a></li> -<li class="isub1">Aceraceæ, <a href="#Page_497">497</a></li> -<li class="isub1">Acorn, <a href="#Page_451">451</a></li> -<li class="isub1">Acorus, <a href="#Page_493">493</a></li> -<li class="isub1">Æcidiomycetes, <a href="#Page_218">218</a></li> -<li class="isub1">Æcidiospore, <a href="#Page_189">189</a></li> -<li class="isub1">Æsculus hippocastanum, <a href="#Page_498">498</a></li> -<li class="isub1">Agaricaceæ, <a href="#Page_199">199</a>, <a href="#Page_219">219</a></li> -<li class="isub1">Agaricus arvensis, <a href="#Page_206">206</a></li> -<li class="isub1">Agaricus campestris, <a href="#Page_200">200-207</a></li> -<li class="isub1">Akene, <a href="#Page_451">451</a></li> -<li class="isub1">Albumen, <a href="#Page_98">98</a></li> -<li class="isub1">Albuminous, <a href="#Page_98">98</a>, <a href="#Page_108">108</a></li> -<li class="isub1">Alder, <a href="#Page_495">495</a></li> -<li class="isub1">Algæ, <a href="#Page_136">136-176</a></li> -<li class="isub1">Algæ, absorption by, <a href="#Page_22">22</a></li> -<li class="isub1">Alismaceæ, <a href="#Page_493">493</a></li> -<li class="isub1">Alpine formation, <a href="#Page_474">474</a></li> -<li class="isub1">Alpine plant societies, <a href="#Page_483">483</a></li> -<li class="isub1">Amanita phalloides, <a href="#Page_207">207</a>, <a href="#Page_208">208</a></li> -<li class="isub1">Amaranth, <a href="#Page_495">495</a></li> -<li class="isub1">Amaryllidaceæ, <a href="#Page_494">494</a></li> -<li class="isub1">Aments, <a href="#Page_429">429</a></li> -<li class="isub1">American mistletoe, <a href="#Page_495">495</a></li> -<li class="isub1">Ampelopsis, <a href="#Page_498">498</a></li> -<li class="isub1">Ancylistales, <a href="#Page_215">215</a></li> -<li class="isub1">Andreales, <a href="#Page_249">249</a></li> -<li class="isub1">Andrœcium, <a href="#Page_319">319</a>, <a href="#Page_419">419</a></li> -<li class="isub1">Anemophilous, <a href="#Page_435">435</a></li> -<li class="isub1">Angiosperms, morphology of, <a href="#Page_318">318-348</a>;</li> -<li class="isub3">classification, <a href="#Page_487">487</a></li> -<li class="isub1">Antheridiophore, <a href="#Page_227">227</a></li> -<li class="isub1">Antheridium, <a href="#Page_144">144</a>, <a href="#Page_149">149</a>, <a href="#Page_155">155</a>, <a href="#Page_176">176</a>, <a href="#Page_223">223</a>, <a href="#Page_228">228</a>,</li> -<li class="isub7"><a href="#Page_240">240</a>, <a href="#Page_245">245</a>, <a href="#Page_246">246</a>, <a href="#Page_266">266</a>, <a href="#Page_287">287</a>, <a href="#Page_433">433</a></li> -<li class="isub1">Anthesis, <a href="#Page_429">429</a></li> -<li class="isub1">Anthoceros, <a href="#Page_240">240</a>, <a href="#Page_241">241</a></li> -<li class="isub1">Anthocerotales, <a href="#Page_242">242</a></li> -<li class="isub1">Anthocerotes, <a href="#Page_242">242</a></li> -<li class="isub1">Apogamy, <a href="#Page_346">346</a></li> -<li class="isub1">Apogeotropic (ap″o-ge″o-trop´ic), <a href="#Page_126">126</a></li> -<li class="isub1">Apogeotropism (ap″o-ge-ot′ro-pism), <a href="#Page_126">126</a></li> -<li class="isub1">Apple, <a href="#Page_456">456</a>, <a href="#Page_497">497</a></li> -<li class="isub1">Apple family, <a href="#Page_497">497</a></li> -<li class="isub1">Aquatic formations, <a href="#Page_475">475</a></li> -<li class="isub1">Aquatic plant societies, <a href="#Page_486">486</a></li> -<li class="isub1">Araceæ, <a href="#Page_493">493</a></li> -<li class="isub1">Archegonia (ar-che-go′ni-a), <a href="#Page_223">223</a>, <a href="#Page_229">229</a>, <a href="#Page_233">233</a>, <a href="#Page_241">241</a>, <a href="#Page_244">244-246</a>,</li> -<li class="isub7"><a href="#Page_267">267</a>, <a href="#Page_288">288</a>, <a href="#Page_291">291</a>, <a href="#Page_307">307</a>, <a href="#Page_308">308</a></li> -<li class="isub1">Archegoniophore, <a href="#Page_229">229</a></li> -<li class="isub1">Archegonium, <a href="#Page_433">433</a></li> -<li class="isub1">Archesporium (ar″che-spo´ri-um), <a href="#Page_235">235</a></li> -<li class="isub1">Archidiales, <a href="#Page_249">249</a></li> -<li class="isub1">Arctic formation, <a href="#Page_481">481</a></li> -<li class="isub1">Aril, <a href="#Page_457">457</a></li> -<li class="isub1">Arisæma, <a href="#Page_493">493</a></li> -<li class="isub1">Arisæma triphyllum, <a href="#Page_442">442</a>, <a href="#Page_443">443</a></li> -<li class="isub1">Aristolochiales, <a href="#Page_495">495</a></li> -<li class="isub1">Arrow leaf, <a href="#Page_492">492</a></li> -<li class="isub1">Arum family, <a href="#Page_493">493</a></li> -<li class="isub1">Asclepias, <a href="#Page_500">500</a></li> -<li class="isub1">Asclepias cornuti, <a href="#Page_462">462</a></li> -<li class="isub1">Ascomycetes (as-co-my-ce′tes), <a href="#Page_195">195-198</a>, <a href="#Page_216">216-218</a></li> -<li class="isub1">Ascus, <a href="#Page_190">190</a>, <a href="#Page_213">213</a></li> -<li class="isub1">Ash of plants, <a href="#Page_79">79</a>, <a href="#Page_80">80</a></li> -<li class="isub1">Ash tree, <a href="#Page_500">500</a></li> -<li class="isub1">Aspidium acrostichoides, <a href="#Page_253">253</a>, <a href="#Page_257">257</a></li> -<li class="isub1">Assimilation, <a href="#Page_67">67</a>, <a href="#Page_109">109</a></li> -<li class="isub1">Aster, <a href="#Page_502">502</a></li> -<li class="isub1">Atriplex, <a href="#Page_495">495</a></li> -<li class="isub1">Auriculariales, <a href="#Page_218">218</a></li> -<li class="isub1">Autotrophic plants, <a href="#Page_85">85</a></li> -<li class="isub1">Azalea, <a href="#Page_499">499</a></li> -<li class="isub1">Azolla, <a href="#Page_296">296</a></li> - -<li class="ifrst">Bacteria, <a href="#Page_164">164</a>, <a href="#Page_165">165</a></li> -<li class="isub1">Bacteria, nitrite and nitrate, <a href="#Page_83">83</a> - <span class="pagenum"><a name="Page_504" id="Page_504">[Pg 504]</a></span></li> -<li class="isub1">Bacteriales, <a href="#Page_164">164</a>, <a href="#Page_165">165</a></li> -<li class="isub1">Bacteroid, <a href="#Page_93">93</a></li> -<li class="isub1">Bangiales, <a href="#Page_175">175</a></li> -<li class="isub1">Basidiomycetes (ba-sid″i-o-my-ce′tes), <a href="#Page_199">199-208</a>, <a href="#Page_218">218</a></li> -<li class="isub1">Basidium, <a href="#Page_201">201</a>, <a href="#Page_213">213</a></li> -<li class="isub1">Bast, <a href="#Page_50">50-52</a></li> -<li class="isub1">Batrachospermum, <a href="#Page_171">171-173</a>, <a href="#Page_175">175</a></li> -<li class="isub1">Bazzania, <a href="#Page_25">25</a></li> -<li class="isub1">Beard-grasses, <a href="#Page_480">480</a></li> -<li class="isub1">Bedstraws, <a href="#Page_501">501</a></li> -<li class="isub1">Beechnut, <a href="#Page_452">452</a></li> -<li class="isub1">Beet, osmose in, <a href="#Page_15">15</a>, <a href="#Page_16">16</a>, <a href="#Page_17">17</a>, <a href="#Page_18">18</a></li> -<li class="isub1">Begonia, <a href="#Page_407">407</a></li> -<li class="isub1">Bellflower, <a href="#Page_501">501</a></li> -<li class="isub1">Berry, <a href="#Page_454">454</a>, <a href="#Page_455">455</a>, <a href="#Page_456">456</a></li> -<li class="isub1">Betulaceæ, <a href="#Page_495">495</a></li> -<li class="isub1">Bicuculla, <a href="#Page_496">496</a></li> -<li class="isub1">Bidens, <a href="#Page_458">458</a></li> -<li class="isub1">Bignonia, <a href="#Page_501">501</a></li> -<li class="isub1">Bilberries, <a href="#Page_500">500</a></li> -<li class="isub1">Biotic factors, <a href="#Page_466">466</a></li> -<li class="isub1">Birch, <a href="#Page_495">495</a></li> -<li class="isub1">Bird’s-nest fungi, <a href="#Page_220">220</a></li> -<li class="isub1">Blackberry, <a href="#Page_454">454</a></li> -<li class="isub1">Black fungi, <a href="#Page_198">198</a></li> -<li class="isub1">Bladderwort, <a href="#Page_501">501</a></li> -<li class="isub1">Blasia, <a href="#Page_164">164</a>, <a href="#Page_236">236</a></li> -<li class="isub1">Bloodroot, <a href="#Page_496">496</a></li> -<li class="isub1">Bluets, <a href="#Page_436">436</a>, <a href="#Page_437">437</a>, <a href="#Page_501">501</a></li> -<li class="isub1">Boletus, <a href="#Page_209">209</a></li> -<li class="isub1">Boletus edulis, <a href="#Page_209">209</a></li> -<li class="isub1">Boraginaceæ, <a href="#Page_500">500</a></li> -<li class="isub1">Botrychium, <a href="#Page_295">295</a></li> -<li class="isub1">Botrydiaceæ, <a href="#Page_162">162</a></li> -<li class="isub1">Botrydium granulatum, <a href="#Page_146">146</a>, <a href="#Page_162">162</a></li> -<li class="isub1">Broom-sedge, <a href="#Page_480">480</a></li> -<li class="isub1">Brown algæ, <a href="#Page_167">167-170</a></li> -<li class="isub1">Bryales, <a href="#Page_349">349</a></li> -<li class="isub1">Buckeye family, <a href="#Page_498">498</a></li> -<li class="isub1">Buckthorn, <a href="#Page_498">498</a></li> -<li class="isub1">Buckwheat, <a href="#Page_495">495</a></li> -<li class="isub1">Buds, winter condition of, <a href="#Page_374">374-377</a></li> -<li class="isub1">Buffalo-grass, <a href="#Page_480">480</a></li> -<li class="isub1">Bug seed, <a href="#Page_495">495</a></li> -<li class="isub1">Bulb, <a href="#Page_372">372</a></li> -<li class="isub1">Bunch-grasses, <a href="#Page_480">480</a></li> -<li class="isub1">Butternut, <a href="#Page_452">452</a>, <a href="#Page_494">494</a></li> -<li class="isub1">Buttonbush, <a href="#Page_501">501</a></li> -<li class="isub1">Buttonwood, <a href="#Page_497">497</a></li> - -<li class="ifrst">Cacti, <a href="#Page_395">395</a>, <a href="#Page_498">498</a></li> -<li class="isub1">Callithamnion, <a href="#Page_173">173</a></li> -<li class="isub1">Calyptrogen, <a href="#Page_361">361</a></li> -<li class="isub1">Cambium, <a href="#Page_50">50</a>, <a href="#Page_52">52</a>, <a href="#Page_358">358</a>, <a href="#Page_363">363</a></li> -<li class="isub1">Campanula rotundifolia, <a href="#Page_442">442</a>, <a href="#Page_444">444</a>, <a href="#Page_510">510</a></li> -<li class="isub1">Campanulales, <a href="#Page_501">501</a></li> -<li class="isub1">Canna, <a href="#Page_445">445-449</a>, <a href="#Page_494">494</a></li> -<li class="isub1">Capsella bursa-pastoris, <a href="#Page_496">496</a></li> -<li class="isub1">Capsule, <a href="#Page_453">453</a></li> -<li class="isub1">Carbohydrate, <a href="#Page_71">71</a>, <a href="#Page_75">75</a>, <a href="#Page_80">80</a>, <a href="#Page_90">90</a></li> -<li class="isub1">Carbon dioxide, <a href="#Page_62">62-67</a>, <a href="#Page_110">110-113</a></li> -<li class="isub1">Cardinal-flower, <a href="#Page_501">501</a></li> -<li class="isub1">Carpogonium, <a href="#Page_172">172</a>, <a href="#Page_176">176</a></li> -<li class="isub1">Carrot family, <a href="#Page_499">499</a></li> -<li class="isub1">Caryophyllaceæ, <a href="#Page_496">496</a></li> -<li class="isub1">Caryopsis, <a href="#Page_451">451</a></li> -<li class="isub1">Cassia marilandica, <a href="#Page_402">402</a></li> -<li class="isub1">Cassiope, <a href="#Page_395">395</a></li> -<li class="isub1">Castalia odorata, <a href="#Page_496">496</a></li> -<li class="isub1">Castor-oil plant, <a href="#Page_497">497</a></li> -<li class="isub1">Catalpa, <a href="#Page_501">501</a></li> -<li class="isub1">Catkin, <a href="#Page_428">428</a></li> -<li class="isub1">Cattail-flag, <a href="#Page_492">492</a></li> -<li class="isub1">Caulidium, <a href="#Page_371">371</a></li> -<li class="isub1">Cedar apples, <a href="#Page_194">194</a></li> -<li class="isub1">Cell, <a href="#Page_3">3</a>;</li> -<li class="isub3">artificial <a href="#Page_20">20</a></li> -<li class="isub1">Cell-sap, <a href="#Page_3">3</a>, <a href="#Page_40">40</a></li> -<li class="isub1">Ceratopteris thalictroides, <a href="#Page_296">296</a></li> -<li class="isub1">Chætophora, <a href="#Page_151">151</a>, <a href="#Page_162">162</a></li> -<li class="isub1">Chætophoraceæ, <a href="#Page_162">162</a></li> -<li class="isub1">Chara, <a href="#Page_176">176</a></li> -<li class="isub1">Charales, <a href="#Page_176">176</a></li> -<li class="isub1">Chemical condition of soil, <a href="#Page_466">466</a></li> -<li class="isub1">Chemosynthetic assimilation, <a href="#Page_109">109</a></li> -<li class="isub1">Chenopodiales, <a href="#Page_495">495</a></li> -<li class="isub1">Chenopods, <a href="#Page_495">495</a></li> -<li class="isub1">Chestnut, <a href="#Page_452">452</a>, <a href="#Page_494">494</a></li> -<li class="isub1">Chicory family, <a href="#Page_502">502</a></li> -<li class="isub1">Chlamydomonas, <a href="#Page_159">159</a>, <a href="#Page_160">160</a></li> -<li class="isub1">Chlamydospores, <a href="#Page_180">180</a></li> -<li class="isub1">Chloral hydrate, <a href="#Page_65">65</a>, <a href="#Page_87">87</a></li> -<li class="isub1">Chlorophyceæ, <a href="#Page_158">158</a></li> -<li class="isub1">Chlorophyll, <a href="#Page_2">2</a>, <a href="#Page_67">67</a>, <a href="#Page_72">72</a></li> -<li class="isub1">Chloroplast, <a href="#Page_68">68</a>, <a href="#Page_69">69</a>, <a href="#Page_71">71</a></li> -<li class="isub1">Christmas fern, <a href="#Page_251">251-253</a></li> -<li class="isub1">Chromoplast, <a href="#Page_71">71</a></li> -<li class="isub1">Chromosomes, <a href="#Page_342">342-345</a></li> -<li class="isub1">Chroococcaceæe, <a href="#Page_163">163</a></li> -<li class="isub1">Chrysanthemum, <a href="#Page_502">502</a></li> -<li class="isub1">Chytridiales, <a href="#Page_215">215</a></li> -<li class="isub1">Cichoriaceæ, <a href="#Page_502">502</a></li> -<li class="isub1">Cichorium intybus, <a href="#Page_502">502</a></li> -<li class="isub1">Clavaria botrytes, <a href="#Page_212">212</a></li> -<li class="isub1">Clavariaceæ, <a href="#Page_210">210</a>, <a href="#Page_219">219</a></li> -<li class="isub1">Claytonia virginica, <a href="#Page_496">496</a> - <span class="pagenum"><a name="Page_505" id="Page_505">[Pg 505]</a></span></li> -<li class="isub1">Cleistogamous, <a href="#Page_435">435</a></li> -<li class="isub1">Clematis virginiana, <a href="#Page_462">462</a>, <a href="#Page_463">463</a>, <a href="#Page_496">496</a></li> -<li class="isub1">Climatic factors, <a href="#Page_466">466</a></li> -<li class="isub1">Climatic formations, <a href="#Page_470">470</a></li> -<li class="isub1">Clostridium pasteurianum, <a href="#Page_93">93</a></li> -<li class="isub1">Clover, <a href="#Page_497">497</a></li> -<li class="isub1">Club mosses, <a href="#Page_284">284</a>, <a href="#Page_289">289</a></li> -<li class="isub1">Coccogonales, <a href="#Page_163">163</a></li> -<li class="isub1">Cocklebur, <a href="#Page_502">502</a></li> -<li class="isub1">Cold wastes, <a href="#Page_474">474</a></li> -<li class="isub1">Coleochætaceæ, <a href="#Page_162">162</a></li> -<li class="isub1">Coleochæte, <a href="#Page_153">153-156</a>, <a href="#Page_226">226</a></li> -<li class="isub1">Collenchyma, <a href="#Page_356">356</a>, <a href="#Page_363">363</a></li> -<li class="isub1">Comandra, <a href="#Page_495">495</a></li> -<li class="isub1">Compass plants, <a href="#Page_409">409</a></li> -<li class="isub1">Compositæ, <a href="#Page_502">502</a></li> -<li class="isub1">Comptonia asplenifolia, <a href="#Page_494">494</a></li> -<li class="isub1">Cone-fruit, <a href="#Page_456">456</a></li> -<li class="isub1">Confervoideæ, <a href="#Page_162">162</a></li> -<li class="isub1">Coniferæ, <a href="#Page_316">316</a></li> -<li class="isub1">Conjugation, <a href="#Page_137">137</a>, <a href="#Page_141">141</a>, <a href="#Page_160">160</a>, <a href="#Page_162">162</a>, <a href="#Page_179">179</a></li> -<li class="isub1">Convallariaceæ, <a href="#Page_494">494</a></li> -<li class="isub1">Cooperia, <a href="#Page_494">494</a></li> -<li class="isub1">Cordyceps, <a href="#Page_218">218</a></li> -<li class="isub1">Coreopsis, <a href="#Page_502">502</a></li> -<li class="isub1">Cork, <a href="#Page_357">357</a>, <a href="#Page_363">363</a></li> -<li class="isub1">Corm, <a href="#Page_373">373</a></li> -<li class="isub1">Cortex, <a href="#Page_50">50</a></li> -<li class="isub1">Corymb, <a href="#Page_427">427</a></li> -<li class="isub1">Cotyledon, <a href="#Page_99">99-101</a></li> -<li class="isub1">Cranberry, <a href="#Page_500">500</a></li> -<li class="isub1">Cratægus, <a href="#Page_497">497</a></li> -<li class="isub1">Crowfoot family, <a href="#Page_496">496</a></li> -<li class="isub1">Cruciferæ, <a href="#Page_496">496</a></li> -<li class="isub1">Cryptonemiales, <a href="#Page_175">175</a></li> -<li class="isub1">Cucurbitaceæ, <a href="#Page_501">501</a></li> -<li class="isub1">Culture formations, <a href="#Page_470">470</a>, <a href="#Page_475">475</a></li> -<li class="isub1">Cultures, water, <a href="#Page_28">28</a>, <a href="#Page_29">29</a></li> -<li class="isub1">Cup fungi, <a href="#Page_199">199</a></li> -<li class="isub1">Cupuliferæ, <a href="#Page_495">495</a></li> -<li class="isub1">Cuscuta, <a href="#Page_83">83</a>, <a href="#Page_500">500</a></li> -<li class="isub1">Cushion type of vegetation, <a href="#Page_483">483</a></li> -<li class="isub1">Cuticle, <a href="#Page_43">43</a></li> -<li class="isub1">Cyanophyceæ, <a href="#Page_163">163</a></li> -<li class="isub1">Cyatheaceæ, <a href="#Page_295">295</a></li> -<li class="isub1">Cycadales, <a href="#Page_316">316</a></li> -<li class="isub1">Cycas, <a href="#Page_311">311</a>, <a href="#Page_312">312</a>, <a href="#Page_457">457</a></li> -<li class="isub1">Cyclosis, <a href="#Page_9">9</a>, <a href="#Page_10">10</a></li> -<li class="isub1">Cyclosporales, <a href="#Page_171">171</a></li> -<li class="isub1">Cyme, <a href="#Page_430">430</a>, <a href="#Page_432">432</a></li> -<li class="isub1">Cyperaceæ, <a href="#Page_493">493</a></li> -<li class="isub1">Cypripedium, <a href="#Page_443">443</a>, <a href="#Page_447">447</a>, <a href="#Page_494">494</a></li> -<li class="isub1">Cystocarp, <a href="#Page_174">174</a></li> -<li class="isub1">Cystopteris bulbifera, <a href="#Page_260">260</a></li> -<li class="isub1">Cystopus, <a href="#Page_215">215</a></li> -<li class="isub1">Cytase, <a href="#Page_92">92</a>, <a href="#Page_108">108</a></li> -<li class="isub1">Cytisus, <a href="#Page_445">445</a></li> -<li class="isub1">Cytoplasm (cy′to-plasm), <a href="#Page_5">5</a></li> - -<li class="ifrst">Dacryomycetales, <a href="#Page_219">219</a></li> -<li class="isub1">Dahlia, <a href="#Page_108">108</a></li> -<li class="isub1">Dandelion, <a href="#Page_502">502</a></li> -<li class="isub1">Dasiphora fruticosa, <a href="#Page_497">497</a></li> -<li class="isub1">Daucus carota, <a href="#Page_499">499</a></li> -<li class="isub1">Dehiscence, <a href="#Page_453">453</a></li> -<li class="isub1">Dentaria, <a href="#Page_322">322-324</a></li> -<li class="isub1">Dentaria diphylla, <a href="#Page_496">496</a></li> -<li class="isub1">Dermatogen, <a href="#Page_359">359</a></li> -<li class="isub1">Desert formation, <a href="#Page_473">473</a></li> -<li class="isub1">Desert societies, <a href="#Page_480">480</a></li> -<li class="isub1">Desmodium, <a href="#Page_458">458</a></li> -<li class="isub1">Desmodium gyrans, <a href="#Page_399">399</a></li> -<li class="isub1">Diadelphous (di″a-del′phous), <a href="#Page_425">425</a></li> -<li class="isub1">Diageotropism (di″a-ge-ot′ro-pism), <a href="#Page_126">126</a></li> -<li class="isub1">Diaheliotropic (di″a-he″li-o-trop′ic), <a href="#Page_127">127</a></li> -<li class="isub1">Diaheliotropism (di″a-he″li-ot′ro-pism), <a href="#Page_127">127</a></li> -<li class="isub1">Diastase, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>, <a href="#Page_108">108</a>, <a href="#Page_116">116</a></li> -<li class="isub1">Diatoms, <a href="#Page_166">166</a></li> -<li class="isub1">Dichogamous (di-chog′a-mous), <a href="#Page_437">437</a>, <a href="#Page_442">442</a></li> -<li class="isub1">Dicentra, <a href="#Page_496">496</a></li> -<li class="isub1">Dicotyledons, <a href="#Page_494">494</a></li> -<li class="isub1">Dictyophora, <a href="#Page_219">219</a></li> -<li class="isub1">Diffusion, <a href="#Page_13">13-20</a></li> -<li class="isub1">Digestion, <a href="#Page_107">107</a>, <a href="#Page_108">108</a>, <a href="#Page_109">109</a></li> -<li class="isub1">Dimorphism of ferns, <a href="#Page_273">273-280</a></li> -<li class="isub1">Diœcious, <a href="#Page_435">435</a></li> -<li class="isub1">Dionæa muscipula, <a href="#Page_133">133</a></li> -<li class="isub1">Dipodascus, <a href="#Page_216">216</a></li> -<li class="isub1">Dipsacus, <a href="#Page_501">501</a></li> -<li class="isub1">Discomycetes, <a href="#Page_217">217</a></li> -<li class="isub1">Dodder, <a href="#Page_83">83</a>, <a href="#Page_84">84</a>, <a href="#Page_500">500</a></li> -<li class="isub1">Dogwood, <a href="#Page_499">499</a></li> -<li class="isub1">Dothidiales, <a href="#Page_218">218</a></li> -<li class="isub1">Downy mildews, <a href="#Page_185">185</a></li> -<li class="isub1">Drosera rotundifolia, <a href="#Page_133">133</a>, <a href="#Page_496">496</a></li> -<li class="isub1">Drupaceæ, <a href="#Page_497">497</a></li> -<li class="isub1">Drupe, <a href="#Page_454">454</a></li> -<li class="isub1">Duckweeds, <a href="#Page_26">26</a>, <a href="#Page_28">28</a></li> -<li class="isub1">Dudresnaya, <a href="#Page_175">175</a></li> -<li class="isub1">Dunes, <a href="#Page_484">484</a></li> - -<li class="ifrst">Ebenales, <a href="#Page_500">500</a> - <span class="pagenum"><a name="Page_506" id="Page_506">[Pg 506]</a></span></li> -<li class="isub1">Ecological factors, <a href="#Page_464">464</a></li> -<li class="isub1">Ecology (sometimes written œcology), <a href="#Page_464">464</a></li> -<li class="isub1">Ectocarpus, <a href="#Page_167">167</a></li> -<li class="isub1">Edaphic formations, <a href="#Page_475">475</a></li> -<li class="isub1">Elaphomyces, <a href="#Page_217">217</a>, <a href="#Page_218">218</a></li> -<li class="isub1">Elder, <a href="#Page_501">501</a></li> -<li class="isub1">Elm family, <a href="#Page_495">495</a></li> -<li class="isub1">Elodea, <a href="#Page_61">61-63</a></li> -<li class="isub1">Embryo of ferns, <a href="#Page_269">269-272</a></li> -<li class="isub1">Embryo sac, <a href="#Page_326">326-328</a></li> -<li class="isub1">Empusa, <a href="#Page_215">215</a></li> -<li class="isub1">Endocarp, <a href="#Page_450">450</a></li> -<li class="isub1">Endomyces, <a href="#Page_216">216</a></li> -<li class="isub1">Endosperm, <a href="#Page_103">103</a>, <a href="#Page_105">105</a>, <a href="#Page_107">107</a>, <a href="#Page_306">306</a>, <a href="#Page_309">309</a>;</li> -<li class="isub3">nucleus, <a href="#Page_327">327</a>, <a href="#Page_329">329-334</a></li> -<li class="isub1">Entomophthorales, <a href="#Page_215">215</a></li> -<li class="isub1">Enzyme, <a href="#Page_92">92</a>, <a href="#Page_98">98</a>, <a href="#Page_116">116</a>, <a href="#Page_117">117</a></li> -<li class="isub1">Epidermal system, <a href="#Page_358">358</a></li> -<li class="isub1">Epidermis, <a href="#Page_358">358</a>, <a href="#Page_359">359</a>, <a href="#Page_363">363</a></li> -<li class="isub1">Epigæa repens, <a href="#Page_499">499</a></li> -<li class="isub1">Epigynous, <a href="#Page_425">425</a></li> -<li class="isub1">Epilobium, <a href="#Page_498">498</a></li> -<li class="isub1">Epinastic (ep-i-nas′tic), <a href="#Page_129">129</a></li> -<li class="isub1">Epinasty (ep′i-nas-ty), <a href="#Page_129">129</a></li> -<li class="isub1">Epipactis, <a href="#Page_444">444</a>, <a href="#Page_447">447</a></li> -<li class="isub1">Epiphegus, <a href="#Page_84">84</a></li> -<li class="isub1">Epiphytes, <a href="#Page_416">416</a></li> -<li class="isub1">Equisetales, <a href="#Page_296">296</a></li> -<li class="isub1">Equisetineæ, <a href="#Page_296">296</a></li> -<li class="isub1">Equisetum, <a href="#Page_280">280-283</a></li> -<li class="isub1">Ericaceæ, <a href="#Page_499">499</a></li> -<li class="isub1">Ericales, <a href="#Page_499">499</a></li> -<li class="isub1">Erythronium, <a href="#Page_493">493</a></li> -<li class="isub1">Etiolated plants (e′ti-o-la″ted), <a href="#Page_68">68</a></li> -<li class="isub1">Euascomycetes, <a href="#Page_217">217</a></li> -<li class="isub1">Eubasidiomycetes, <a href="#Page_219">219</a></li> -<li class="isub1">Eupatorium, <a href="#Page_403">403</a>, <a href="#Page_502">502</a></li> -<li class="isub1">Euphorbiaceæ, <a href="#Page_497">497</a></li> -<li class="isub1">Eurotium oryzæ, <a href="#Page_78">78</a></li> -<li class="isub1">Evening primrose family, <a href="#Page_498">498</a></li> -<li class="isub1">Exalbuminous, <a href="#Page_108">108</a></li> -<li class="isub1">Exoascus, <a href="#Page_217">217</a></li> -<li class="isub1">Exobasidiales, <a href="#Page_219">219</a></li> -<li class="isub1">Exocarp, <a href="#Page_450">450</a></li> - -<li class="ifrst">Fagales, <a href="#Page_494">494</a></li> -<li class="isub1">Fehling’s solution, <a href="#Page_75">75</a>, <a href="#Page_76">76</a></li> -<li class="isub1">Ferment, <a href="#Page_98">98</a>, <a href="#Page_108">108</a>, <a href="#Page_116">116</a></li> -<li class="isub1">Ferns, <a href="#Page_251">251-279</a>, <a href="#Page_292">292</a>, <a href="#Page_457">457</a>;</li> -<li class="isub3">classification of, <a href="#Page_295">295</a></li> -<li class="isub1">Fertilization, <a href="#Page_307">307</a>, <a href="#Page_308">308</a>, <a href="#Page_328">328</a>, <a href="#Page_329">329</a>, <a href="#Page_140">140</a>, <a href="#Page_145">145</a>,</li> -<li class="isub7"><a href="#Page_169">169</a>, <a href="#Page_172">172</a>, <a href="#Page_174">174</a>, <a href="#Page_197">197</a>, <a href="#Page_421">421</a></li> -<li class="isub1">Fibrovascular bundles, <a href="#Page_49">49-54</a></li> -<li class="isub1">Figwort family, <a href="#Page_501">501</a></li> -<li class="isub1">Filicales, <a href="#Page_295">295</a></li> -<li class="isub1">Filicineæ, <a href="#Page_295">295</a></li> -<li class="isub1">Fittonia, <a href="#Page_404">404</a></li> -<li class="isub1">Flagellates, <a href="#Page_83">83</a>, <a href="#Page_165">165</a></li> -<li class="isub1">Flax, <a href="#Page_497">497</a></li> -<li class="isub1">Flower cluster, <a href="#Page_419">419</a></li> -<li class="isub1">Flower, form of, <a href="#Page_422">422</a>;</li> -<li class="isub3">parts of, <a href="#Page_419">419</a>;</li> -<li class="isub3">union of parts, <a href="#Page_424">424</a></li> -<li class="isub1">Flowers, arrangements of, <a href="#Page_426">426</a>;</li> -<li class="isub3">kinds of, <a href="#Page_421">421</a></li> -<li class="isub1">Follicle, <a href="#Page_453">453</a></li> -<li class="isub1">Forest, formations <a href="#Page_471">471</a>;</li> -<li class="isub3">societies, <a href="#Page_477">477</a></li> -<li class="isub1">Forests, relation to rainfall, <a href="#Page_479">479</a></li> -<li class="isub1">Fresh-water societies, <a href="#Page_486">486</a></li> -<li class="isub1">Frond, <a href="#Page_352">352</a></li> -<li class="isub1">Fruit, <a href="#Page_450">450-457</a>;</li> -<li class="isub3">parts of, <a href="#Page_450">450</a></li> -<li class="isub1">Frullania, <a href="#Page_25">25</a>, <a href="#Page_236">236</a></li> -<li class="isub1">Fucus, <a href="#Page_168">168-170</a></li> -<li class="isub1">Fungi, absorption by, <a href="#Page_22">22</a>;</li> -<li class="isub3">classification of, <a href="#Page_213">213-222</a>;</li> -<li class="isub3">nutrition of, <a href="#Page_86">86-90</a>;</li> -<li class="isub3">respiration in, <a href="#Page_115">115</a></li> - -<li class="ifrst">Gametangium (gam″et-an′gi-um), <a href="#Page_140">140</a></li> -<li class="isub1">Gamete (gam′ete), <a href="#Page_138">138</a>, <a href="#Page_139">139</a></li> -<li class="isub1">Gametophore (gam′et-o-phore), <a href="#Page_230">230</a>, <a href="#Page_248">248</a></li> -<li class="isub1">Gametophyte (gam′et-o-phyte), <a href="#Page_225">225</a>, <a href="#Page_226">226</a>, <a href="#Page_244">244</a>, <a href="#Page_245">245</a>, <a href="#Page_250">250</a>, <a href="#Page_262">262</a>, <a href="#Page_270">270</a>,</li> -<li class="isub7"><a href="#Page_283">283</a>, <a href="#Page_292">292</a>, <a href="#Page_294">294</a>, <a href="#Page_305">305</a>, <a href="#Page_314">314</a>, <a href="#Page_317">317</a>,</li> -<li class="isub7"><a href="#Page_336">336-339</a>, <a href="#Page_340">340-348</a>, <a href="#Page_434">434</a></li> -<li class="isub1">Gamopetalous (gam″o-pet′a-lous), <a href="#Page_424">424</a></li> -<li class="isub1">Gamosepalous (gam-o-sep′a-lous), <a href="#Page_424">424</a></li> -<li class="isub1">Gas in plants, <a href="#Page_60">60-64</a></li> -<li class="isub1">Gasteromycetes, <a href="#Page_219">219</a></li> -<li class="isub1">Gemmæ, <a href="#Page_179">179</a>, <a href="#Page_235">235</a></li> -<li class="isub1">General formations, <a href="#Page_470">470</a></li> -<li class="isub1">Gentian, <a href="#Page_500">500</a></li> -<li class="isub1">Geotropism (ge-ot′ro-pism), <a href="#Page_125">125-127</a>, <a href="#Page_410">410</a></li> -<li class="isub1">Geraniaceæ, <a href="#Page_497">497</a></li> -<li class="isub1">Geraniales, <a href="#Page_497">497</a></li> -<li class="isub1">Geranium family, <a href="#Page_497">497</a></li> -<li class="isub1">Germ, <a href="#Page_459">459</a></li> -<li class="isub1">Gigartinales, <a href="#Page_175">175</a></li> -<li class="isub1">Gingko, <a href="#Page_313">313-315</a>, <a href="#Page_457">457</a></li> -<li class="isub1">Gingkoales, <a href="#Page_316">316</a></li> -<li class="isub1">Ginseng, <a href="#Page_499">499</a></li> -<li class="isub1">Glasswort, <a href="#Page_495">495</a></li> -<li class="isub1">Gleicheniaceæ, <a href="#Page_295">295</a> - <span class="pagenum"><a name="Page_507" id="Page_507">[Pg 507]</a></span></li> -<li class="isub1">Glucose, <a href="#Page_108">108</a>. See sugar.</li> -<li class="isub1">Gnetales, <a href="#Page_316">316</a></li> -<li class="isub1">Gonidia, <a href="#Page_118">118</a>, <a href="#Page_143">143</a>, <a href="#Page_172">172</a>, <a href="#Page_174">174</a>, <a href="#Page_178">178-184</a></li> -<li class="isub1">Gonidiangium (go″nid-an′gi-um), <a href="#Page_178">178</a></li> -<li class="isub1">Gonidium, <a href="#Page_213">213</a></li> -<li class="isub1">Gooseberry, <a href="#Page_496">496</a></li> -<li class="isub1">Goosefoot family, <a href="#Page_495">495</a></li> -<li class="isub1">Gracilaria, <a href="#Page_173">173</a>, <a href="#Page_174">174</a>, <a href="#Page_175">175</a></li> -<li class="isub1">Graminales, <a href="#Page_492">492</a></li> -<li class="isub1">Gramineæ, <a href="#Page_492">492</a></li> -<li class="isub1">Grape, <a href="#Page_498">498</a></li> -<li class="isub1">Grass family, <a href="#Page_492">492</a></li> -<li class="isub1">Grassland formation, <a href="#Page_471">471</a></li> -<li class="isub1">Green algæ, <a href="#Page_158">158</a></li> -<li class="isub1">Growth, <a href="#Page_118">118-124</a>, <a href="#Page_380">380</a></li> -<li class="isub1">Gulfweed, <a href="#Page_170">170</a></li> -<li class="isub1">Gymnosperms, <a href="#Page_311">311</a>, <a href="#Page_456">456</a></li> -<li class="isub1">Gymnosporangium, <a href="#Page_194">194</a></li> -<li class="isub1">Gynœcium, <a href="#Page_320">320</a>, <a href="#Page_419">419</a>, <a href="#Page_451">451</a>, <a href="#Page_452">452</a></li> -<li class="isub1">Gyrocephalus, <a href="#Page_219">219</a></li> - -<li class="ifrst">Halophytes, <a href="#Page_468">468</a></li> -<li class="isub1">Harpochytrium, <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Haustorium, <a href="#Page_87">87</a>, <a href="#Page_88">88</a></li> -<li class="isub1">Hawkweed, <a href="#Page_502">502</a></li> -<li class="isub1">Hawthorn, <a href="#Page_497">497</a></li> -<li class="isub1">Hazelnut, <a href="#Page_452">452</a>, <a href="#Page_495">495</a></li> -<li class="isub1">Head, <a href="#Page_428">428</a></li> -<li class="isub1">Heart-leaf, <a href="#Page_495">495</a></li> -<li class="isub1">Heath family, <a href="#Page_499">499</a></li> -<li class="isub1">Heliotrope, <a href="#Page_500">500</a></li> -<li class="isub1">Heliotropism (he-li-ot′ro-pism), <a href="#Page_127">127-131</a>, <a href="#Page_133">133</a>, <a href="#Page_397">397</a></li> -<li class="isub1">Helvellales, <a href="#Page_217">217</a></li> -<li class="isub1">Hemiascomycetes, <a href="#Page_216">216</a></li> -<li class="isub1">Hemibasidiomycetes, <a href="#Page_218">218</a></li> -<li class="isub1">Hepaticæ, <a href="#Page_242">242</a></li> -<li class="isub1">Heterospory (het″er-os′po-ry), <a href="#Page_434">434</a></li> -<li class="isub1">Heterothallic, <a href="#Page_180">180</a></li> -<li class="isub1">Heterotrophic plants, <a href="#Page_85">85</a></li> -<li class="isub1">Hickory, <a href="#Page_494">494</a></li> -<li class="isub1">Hickory-nut, <a href="#Page_452">452</a></li> -<li class="isub1">Hilum, <a href="#Page_101">101</a>, <a href="#Page_102">102</a></li> -<li class="isub1">Hippocastanaceæ, <a href="#Page_498">498</a></li> -<li class="isub1">Holdfasts, <a href="#Page_418">418</a></li> -<li class="isub1">Hollyhock, <a href="#Page_498">498</a></li> -<li class="isub1">Homothallic, <a href="#Page_180">180</a></li> -<li class="isub1">Honeysuckle, <a href="#Page_501">501</a></li> -<li class="isub1">Hormogonales, <a href="#Page_163">163</a></li> -<li class="isub1">Horse-chestnut, <a href="#Page_498">498</a></li> -<li class="isub1">Horsetails, <a href="#Page_280">280-283</a></li> -<li class="isub1">Houstonia cœrulea, <a href="#Page_437">437</a></li> -<li class="isub1">Huckleberry, <a href="#Page_499">499</a></li> -<li class="isub1">Humus saprophytes, <a href="#Page_85">85</a>, <a href="#Page_91">91</a></li> -<li class="isub1">Hybridization, <a href="#Page_338">338</a></li> -<li class="isub1">Hydnaceæ, <a href="#Page_210">210</a>, <a href="#Page_219">219</a></li> -<li class="isub1">Hydnum coralloides, <a href="#Page_210">210</a></li> -<li class="isub1">Hydnum repandum, <a href="#Page_211">211</a></li> -<li class="isub1">Hydrocarbon, <a href="#Page_75">75</a></li> -<li class="isub1">Hydrodictyaceæ, <a href="#Page_161">161</a></li> -<li class="isub1">Hydrophytes, <a href="#Page_468">468</a></li> -<li class="isub1">Hydropterales, <a href="#Page_295">295</a></li> -<li class="isub1">Hydrotropism (hy-drot′ro′pism), <a href="#Page_133">133</a>, <a href="#Page_134">134</a>, <a href="#Page_412">412</a></li> -<li class="isub1">Hygrophytes, <a href="#Page_468">468</a></li> -<li class="isub1">Hymeniales, <a href="#Page_219">219</a></li> -<li class="isub1">Hymenogastrales, <a href="#Page_219">219</a></li> -<li class="isub1">Hymenomycetes, <a href="#Page_219">219</a></li> -<li class="isub1">Hymenomycetineæ, <a href="#Page_219">219</a></li> -<li class="isub1">Hymenophyllaceæ, <a href="#Page_295">295</a></li> -<li class="isub1">Hypericum, <a href="#Page_498">498</a></li> -<li class="isub1">Hypocotyl (hy′po-co″tyl), <a href="#Page_101">101</a></li> -<li class="isub1">Hypocreales, <a href="#Page_217">217</a></li> -<li class="isub1">Hypogenous, <a href="#Page_425">425</a></li> -<li class="isub1">Hyponastic (hy-po-nas′tic), <a href="#Page_129">129</a></li> -<li class="isub1">Hyponasty (hy′po-nas-ty), <a href="#Page_129">129</a></li> -<li class="isub1">Hysteriales, <a href="#Page_217">217</a></li> - -<li class="ifrst">Impatiens, <a href="#Page_498">498</a></li> -<li class="isub1">Impatiens fulva, <a href="#Page_460">460</a></li> -<li class="isub1">Indian-pipe, <a href="#Page_499">499</a></li> -<li class="isub1">Indian turnip, <a href="#Page_493">493</a></li> -<li class="isub1">Indusium, <a href="#Page_252">252</a></li> -<li class="isub1">Inflorescence, <a href="#Page_426">426</a></li> -<li class="isub1">Insectivorous plants, <a href="#Page_133">133</a>, <a href="#Page_496">496</a></li> -<li class="isub1">Integument, <a href="#Page_304">304</a></li> -<li class="isub1">Intramolecular respiration, <a href="#Page_113">113</a>, <a href="#Page_114">114</a></li> -<li class="isub1">Inulase, <a href="#Page_108">108</a></li> -<li class="isub1">Inulin, <a href="#Page_108">108</a>, <a href="#Page_417">417</a></li> -<li class="isub1">Iodine, <a href="#Page_65">65</a></li> -<li class="isub1">Ipomœa, <a href="#Page_500">500</a></li> -<li class="isub1">Iridaceæ, <a href="#Page_493">493</a></li> -<li class="isub1">Iris, <a href="#Page_493">493</a></li> -<li class="isub1">Irritability, <a href="#Page_125">125-135</a></li> -<li class="isub1">Isoetales, <a href="#Page_296">296</a></li> -<li class="isub1">Isoetes, <a href="#Page_289">289-291</a>, <a href="#Page_292">292</a></li> -<li class="isub1">Isoetineæ, <a href="#Page_296">296</a></li> -<li class="isub1">Ivy, <a href="#Page_498">498</a></li> - -<li class="ifrst">Jack-in-the-pulpit, <a href="#Page_373">373</a></li> -<li class="isub1">Jewelweed, <a href="#Page_498">498</a></li> -<li class="isub1">Juglandales, <a href="#Page_494">494</a></li> -<li class="isub1">June-berry, <a href="#Page_497">497</a></li> -<li class="isub1">Jungermanniales, <a href="#Page_242">242</a></li> - -<li class="ifrst">Kalmia latifolia, <a href="#Page_444">444</a> - <span class="pagenum"><a name="Page_508" id="Page_508">[Pg 508]</a></span></li> -<li class="isub1">Karyokinesis, <a href="#Page_341">341-344</a></li> -<li class="isub1">Kelps, <a href="#Page_168">168</a></li> -<li class="isub1">Kingdom, <a href="#Page_492">492</a></li> - -<li class="ifrst">Labiatæ, <a href="#Page_423">423</a>, <a href="#Page_501">501</a></li> -<li class="isub1">Laboulbeniales, <a href="#Page_218">218</a></li> -<li class="isub1">Labrador tea, <a href="#Page_499">499</a></li> -<li class="isub1">Lactuca canadensis, <a href="#Page_460">460</a></li> -<li class="isub1">Lactuca scariola, <a href="#Page_409">409</a>, <a href="#Page_460">460</a>, <a href="#Page_461">461</a></li> -<li class="isub1">Lagenidium, <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Laminaria, <a href="#Page_168">168</a>, <a href="#Page_169">169</a></li> -<li class="isub1">Lamium, <a href="#Page_424">424</a>, <a href="#Page_501">501</a></li> -<li class="isub1">Larch, <a href="#Page_367">367</a></li> -<li class="isub1">Laurel, <a href="#Page_499">499</a></li> -<li class="isub1">Leaf patterns, <a href="#Page_404">404</a></li> -<li class="isub1">Leathesia difformis, <a href="#Page_168">168</a></li> -<li class="isub1">Leaves, form and arrangement, <a href="#Page_383">383-391</a>;</li> -<li class="isub3">function of, <a href="#Page_387">387</a>;</li> -<li class="isub3">protective modifications of, <a href="#Page_392">392</a>;</li> -<li class="isub3">protective positions, <a href="#Page_395">395</a>;</li> -<li class="isub3">reduction of surface, <a href="#Page_394">394</a>;</li> -<li class="isub3">relation to light, <a href="#Page_397">397</a>;</li> -<li class="isub3">structure of, <a href="#Page_40">40-43</a>, <a href="#Page_131">131</a>, <a href="#Page_391">391</a>, <a href="#Page_393">393</a></li> -<li class="isub1">Legumes, <a href="#Page_92">92</a>, <a href="#Page_93">93</a>, <a href="#Page_453">453</a></li> -<li class="isub1">Leguminosæ (= Papilionaceæ), <a href="#Page_396">396</a>, <a href="#Page_399">399</a></li> -<li class="isub1">Leitneria floridana, <a href="#Page_494">494</a></li> -<li class="isub1">Leitneriales, <a href="#Page_494">494</a></li> -<li class="isub1">Lemanea, <a href="#Page_171">171</a>, <a href="#Page_173">173</a>, <a href="#Page_175">175</a>, <a href="#Page_492">492</a></li> -<li class="isub1">Lemna, <a href="#Page_418">418</a></li> -<li class="isub1">Lemna trisulca, <a href="#Page_26">26</a>, <a href="#Page_27">27</a></li> -<li class="isub1">Lenticel, <a href="#Page_357">357</a>, <a href="#Page_358">358</a></li> -<li class="isub1">Lepiota naucina, <a href="#Page_208">208</a></li> -<li class="isub1">Lettuce, <a href="#Page_502">502</a></li> -<li class="isub1">Leucoplast, <a href="#Page_71">71</a></li> -<li class="isub1">Lichens, <a href="#Page_86">86</a>, <a href="#Page_93">93-95</a>, <a href="#Page_220">220</a>, <a href="#Page_221">221</a></li> -<li class="isub1">Light, <a href="#Page_465">465</a></li> -<li class="isub1">Liliaceæ, <a href="#Page_490">490</a>, <a href="#Page_493">493</a></li> -<li class="isub1">Liliales, <a href="#Page_490">490</a>, <a href="#Page_493">493</a></li> -<li class="isub1">Lilium, <a href="#Page_489">489-493</a></li> -<li class="isub1">Linaria vulgaris, <a href="#Page_501">501</a></li> -<li class="isub1">Linden, <a href="#Page_498">498</a></li> -<li class="isub1">Linum vulgaris, <a href="#Page_497">497</a></li> -<li class="isub1">Lipase, <a href="#Page_108">108</a></li> -<li class="isub1">Liquidambar, <a href="#Page_496">496</a></li> -<li class="isub1">Liriodendron, <a href="#Page_496">496</a></li> -<li class="isub1">Live-forever, <a href="#Page_394">394</a></li> -<li class="isub1">Liverworts, <a href="#Page_222">222-239</a>;</li> -<li class="isub3">absorption by, <a href="#Page_23">23-25</a>;</li> -<li class="isub3">classification of, <a href="#Page_242">242</a></li> -<li class="isub1">Lobelia, <a href="#Page_501">501</a></li> -<li class="isub1">Lupinus perennis, <a href="#Page_353">353</a></li> -<li class="isub1">Lycoperdales, <a href="#Page_220">220</a></li> -<li class="isub1">Lycopodiaceæ, <a href="#Page_296">296</a></li> -<li class="isub1">Lycopodiales, <a href="#Page_296">296</a></li> -<li class="isub1">Lycopodiineæ, <a href="#Page_296">296</a></li> -<li class="isub1">Lycopodium, <a href="#Page_284">284-286</a></li> - -<li class="ifrst">Macrosporangium, <a href="#Page_94">94</a>, <a href="#Page_302">302</a>, <a href="#Page_304">304</a>, <a href="#Page_311">311</a>, <a href="#Page_312">312</a>, <a href="#Page_321">321</a></li> -<li class="isub1">Macrospore, <a href="#Page_287">287</a>, <a href="#Page_290">290</a>, <a href="#Page_326">326-328</a>, <a href="#Page_434">434</a></li> -<li class="isub1">Magnolia, <a href="#Page_496">496</a></li> -<li class="isub1">Mallow family, <a href="#Page_498">498</a></li> -<li class="isub1">Malvales, <a href="#Page_498">498</a></li> -<li class="isub1">Maple family, <a href="#Page_497">497</a></li> -<li class="isub1">Marchantia, <a href="#Page_24">24</a>, <a href="#Page_226">226-236</a></li> -<li class="isub1">Marchantiales, <a href="#Page_242">242</a></li> -<li class="isub1">Marine plant societies, <a href="#Page_486">486</a></li> -<li class="isub1">Marratiales, <a href="#Page_295">295</a></li> -<li class="isub1">Marsilia, <a href="#Page_370">370</a></li> -<li class="isub1">Marsiliaceæ, <a href="#Page_296">296</a></li> -<li class="isub1">Matoniaceæ, <a href="#Page_295">295</a></li> -<li class="isub1">Medicago denticulata, <a href="#Page_92">92</a></li> -<li class="isub1">Medulla, <a href="#Page_50">50</a></li> -<li class="isub1">Members of the flower, <a href="#Page_335">335</a></li> -<li class="isub1">Members of the plant, <a href="#Page_349">349-353</a></li> -<li class="isub1">Meristem, <a href="#Page_359">359</a></li> -<li class="isub1">Mesocarp, <a href="#Page_450">450</a></li> -<li class="isub1">Mesophytes, <a href="#Page_467">467</a></li> -<li class="isub1">Microsporangia, <a href="#Page_294">294</a>, <a href="#Page_299">299</a></li> -<li class="isub1">Microspore, <a href="#Page_287">287</a>, <a href="#Page_290">290</a>, <a href="#Page_299">299</a>, <a href="#Page_312">312</a>, <a href="#Page_435">435</a></li> -<li class="isub1">Microsporophylls, <a href="#Page_299">299</a>, <a href="#Page_320">320</a>, <a href="#Page_420">420</a></li> -<li class="isub1">Milkweed family, <a href="#Page_500">500</a></li> -<li class="isub1">Mimosa, <a href="#Page_132">132</a>, <a href="#Page_396">396</a></li> -<li class="isub1">Mimulus, <a href="#Page_501">501</a></li> -<li class="isub1">Mint family, <a href="#Page_501">501</a></li> -<li class="isub1">Mistletoe, <a href="#Page_84">84</a>, <a href="#Page_495">495</a></li> -<li class="isub1">Mitchella, <a href="#Page_501">501</a></li> -<li class="isub1">Mixotrophic plants, <a href="#Page_85">85</a></li> -<li class="isub1">Mnium, <a href="#Page_243">243-246</a></li> -<li class="isub1">Molds, nutrition of, <a href="#Page_86">86-90</a></li> -<li class="isub1">Molds, water, <a href="#Page_181">181</a></li> -<li class="isub1">Monadelphous, <a href="#Page_424">424</a></li> -<li class="isub1">Monoblepharidales, <a href="#Page_215">215</a></li> -<li class="isub1">Monoblepharis, <a href="#Page_215">215</a></li> -<li class="isub1">Monocotyledons, <a href="#Page_490">490</a>, <a href="#Page_492">492</a></li> -<li class="isub1">Monœcious, <a href="#Page_435">435</a></li> -<li class="isub1">Monotropa uniflora, <a href="#Page_499">499</a></li> -<li class="isub1">Morchella, <a href="#Page_198">198</a>, <a href="#Page_199">199</a></li> -<li class="isub1">Morel, <a href="#Page_198">198</a>, <a href="#Page_199">199</a></li> -<li class="isub1">Morning-glories, <a href="#Page_500">500</a></li> -<li class="isub1">Mosaics, <a href="#Page_405">405</a></li> -<li class="isub1">Mosses, <a href="#Page_243">243-248</a>, <a href="#Page_457">457</a>;</li> -<li class="isub3">absorption by, <a href="#Page_25">25</a>;</li> -<li class="isub3">classification of, <a href="#Page_248">248</a></li> -<li class="isub1">Mucor, <a href="#Page_6">6</a>, <a href="#Page_7">7</a>, <a href="#Page_15">15</a>, <a href="#Page_118">118</a>, <a href="#Page_119">119</a>, <a href="#Page_177">177-180</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Mucorales, <a href="#Page_215">215</a></li> -<li class="isub1">Mulberry, <a href="#Page_495">495</a></li> -<li class="isub1">Mullein, <a href="#Page_366">366</a>, <a href="#Page_394">394</a>, <a href="#Page_501">501</a></li> -<li class="isub1">Mushrooms, <a href="#Page_199">199-208</a> - <span class="pagenum"><a name="Page_509" id="Page_509">[Pg 509]</a></span></li> -<li class="isub1">Mustard family, <a href="#Page_496">496</a></li> -<li class="isub1">Mutation, <a href="#Page_338">338</a></li> -<li class="isub1">Mutualism, <a href="#Page_95">95</a></li> -<li class="isub1">Mycelium, <a href="#Page_6">6</a>, <a href="#Page_86">86-90</a></li> -<li class="isub1">Mycetozoa, <a href="#Page_213">213</a>, <a href="#Page_214">214</a></li> -<li class="isub1">Mycorhiza, <a href="#Page_86">86</a>, <a href="#Page_91">91</a>, <a href="#Page_92">92</a>, <a href="#Page_217">217</a></li> -<li class="isub1">Myosotis, <a href="#Page_500">500</a></li> -<li class="isub1">Myrica cerifera, <a href="#Page_494">494</a></li> -<li class="isub1">Myrica gale, <a href="#Page_494">494</a></li> -<li class="isub1">Myricales, <a href="#Page_494">494</a></li> -<li class="isub1">Myriophyllum, <a href="#Page_403">403</a></li> -<li class="isub1">Myrtales, <a href="#Page_498">498</a></li> -<li class="isub1">Myxobacteriales, <a href="#Page_165">165</a></li> -<li class="isub1">Myxomycetes, <a href="#Page_83">83</a>, <a href="#Page_213">213</a>, <a href="#Page_214">214</a></li> - -<li class="ifrst">Naiadaceæ, <a href="#Page_492">492</a></li> -<li class="isub1">Naiadales, <a href="#Page_492">492</a></li> -<li class="isub1">Naias, <a href="#Page_492">492</a></li> -<li class="isub1">Nemalion, <a href="#Page_171">171</a>, <a href="#Page_172">172</a>, <a href="#Page_175">175</a></li> -<li class="isub1">Nemalionales, <a href="#Page_175">175</a></li> -<li class="isub1">Nettle, <a href="#Page_495">495</a></li> -<li class="isub1">Nicotiana, <a href="#Page_501">501</a></li> -<li class="isub1">Nidulariales, <a href="#Page_220">220</a></li> -<li class="isub1">Nitella, <a href="#Page_8">8</a>, <a href="#Page_9">9</a>, <a href="#Page_176">176</a></li> -<li class="isub1">Nitrobacter, <a href="#Page_83">83</a></li> -<li class="isub1">Nitrogen, <a href="#Page_92">92</a>, <a href="#Page_93">93</a></li> -<li class="isub1">Nitromonas, <a href="#Page_83">83</a></li> -<li class="isub1">Nostocaceæ, <a href="#Page_164">164</a></li> -<li class="isub1">Nucellus, <a href="#Page_304">304</a></li> -<li class="isub1">Nucleus, <a href="#Page_3">3</a>, <a href="#Page_4">4</a>;</li> -<li class="isub3">morphology of, <a href="#Page_340">340-345</a></li> -<li class="isub1">Nuphar advena, <a href="#Page_496">496</a></li> -<li class="isub1">Nutation, <a href="#Page_123">123</a>, <a href="#Page_124">124</a></li> -<li class="isub1">Nymphæa odorata, <a href="#Page_496">496</a></li> - -<li class="ifrst">Oak, <a href="#Page_495">495</a></li> -<li class="isub1">Oak family, <a href="#Page_495">495</a></li> -<li class="isub1">Œdogoniaceæ, <a href="#Page_162">162</a></li> -<li class="isub1">Œdogonium, <a href="#Page_147">147-151</a>, <a href="#Page_350">350</a></li> -<li class="isub1">Œnothera biennis, <a href="#Page_498">498</a></li> -<li class="isub1">Œnothera gigas, <a href="#Page_338">338</a></li> -<li class="isub1">Œnothera lamarkiana, <a href="#Page_338">338</a></li> -<li class="isub1">Olpidium, <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Onagar biennis, <a href="#Page_498">498</a></li> -<li class="isub1">Onagraceæ, <a href="#Page_498">498</a></li> -<li class="isub1">Onoclea sensibilis, <a href="#Page_254">254</a>, <a href="#Page_273">273-278</a></li> -<li class="isub1">Oogonium, <a href="#Page_144">144</a>, <a href="#Page_150">150</a>, <a href="#Page_155">155</a></li> -<li class="isub1">Oomycetes, <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Ophioglossales, <a href="#Page_295">295</a></li> -<li class="isub1">Ophioglossum, <a href="#Page_295">295</a></li> -<li class="isub1">Opuntiales, <a href="#Page_498">498</a></li> -<li class="isub1">Orchidaceæ, <a href="#Page_494">494</a></li> -<li class="isub1">Orchidales, <a href="#Page_494">494</a></li> -<li class="isub1">Orchids, <a href="#Page_442">442</a></li> -<li class="isub1">Oscillatoriaceæ, <a href="#Page_163">163</a></li> -<li class="isub1">Osmosis, <a href="#Page_13">13-20</a></li> -<li class="isub1">Osmundaceæ, <a href="#Page_295">295</a></li> -<li class="isub1">Ostrich fern, <a href="#Page_279">279</a></li> -<li class="isub1">Ovule, <a href="#Page_302">302</a>, <a href="#Page_321">321</a>, <a href="#Page_334">334</a>, <a href="#Page_421">421</a></li> -<li class="isub1">Oxalis, <a href="#Page_497">497</a></li> -<li class="isub1">Oxycoccus, <a href="#Page_500">500</a></li> -<li class="isub1">Oxydendrum arboreum, <a href="#Page_501">501</a></li> -<li class="isub1">Oxygen, <a href="#Page_63">63</a>, <a href="#Page_110">110-113</a></li> - -<li class="ifrst">Palisade cells, <a href="#Page_41">41</a>, <a href="#Page_43">43</a></li> -<li class="isub1">Palmaceæ, <a href="#Page_493">493</a></li> -<li class="isub1">Palmales, <a href="#Page_493">493</a></li> -<li class="isub1">Palms, <a href="#Page_408">408</a></li> -<li class="isub1">Pandanales, <a href="#Page_492">492</a></li> -<li class="isub1">Pandanus, <a href="#Page_492">492</a></li> -<li class="isub1">Pandorina, <a href="#Page_160">160</a>, <a href="#Page_350">350</a></li> -<li class="isub1">Panicle, <a href="#Page_427">427</a></li> -<li class="isub1">Papaverales, <a href="#Page_496">496</a></li> -<li class="isub1">Papilionaceæ, <a href="#Page_423">423</a>, <a href="#Page_497">497</a></li> -<li class="isub1">Parasites, <a href="#Page_83">83</a>, <a href="#Page_84">84</a>, <a href="#Page_86">86</a></li> -<li class="isub1">Parasitic fungi, nutrition of, <a href="#Page_86">86-90</a></li> -<li class="isub1">Parenchyma, <a href="#Page_50">50</a>, <a href="#Page_356">356</a>, <a href="#Page_363">363</a></li> -<li class="isub1">Parietales, <a href="#Page_498">498</a></li> -<li class="isub1">Parkeriaceæ, <a href="#Page_296">296</a></li> -<li class="isub1">Parmelia, <a href="#Page_96">96</a></li> -<li class="isub1">Parthenogenesis, <a href="#Page_184">184</a></li> -<li class="isub1">Partridge-berry, <a href="#Page_501">501</a></li> -<li class="isub1">Pea, <a href="#Page_497">497</a></li> -<li class="isub1">Pea family, <a href="#Page_497">497</a></li> -<li class="isub1">Pear, <a href="#Page_456">456</a></li> -<li class="isub1">Pediastrum, <a href="#Page_161">161</a></li> -<li class="isub1">Pellia, <a href="#Page_164">164</a></li> -<li class="isub1">Pellonia, <a href="#Page_405">405</a></li> -<li class="isub1">Peltigera, <a href="#Page_94">94</a>, <a href="#Page_95">95</a></li> -<li class="isub1">Pepo, <a href="#Page_456">456</a></li> -<li class="isub1">Pericycle, <a href="#Page_360">360</a></li> -<li class="isub1">Peridineæ, <a href="#Page_166">166</a></li> -<li class="isub1">Perigynous, <a href="#Page_425">425</a></li> -<li class="isub1">Perisperm, <a href="#Page_331">331</a>, <a href="#Page_332">332</a></li> -<li class="isub1">Perisporiales, <a href="#Page_217">217</a></li> -<li class="isub1">Peronospora, <a href="#Page_183">183</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Peronosporales, <a href="#Page_215">215</a></li> -<li class="isub1">Persimmon, <a href="#Page_500">500</a></li> -<li class="isub1">Pezizales, <a href="#Page_217">217</a></li> -<li class="isub1">Phacidiales, <a href="#Page_217">217</a></li> -<li class="isub1">Phæophyceæ, <a href="#Page_167">167</a></li> -<li class="isub1">Phæosporales, <a href="#Page_171">171</a></li> -<li class="isub1">Phallales, <a href="#Page_219">219</a></li> -<li class="isub1">Phloem, <a href="#Page_50">50-52</a>, <a href="#Page_360">360</a>, <a href="#Page_361">361</a>, <a href="#Page_363">363</a></li> -<li class="isub1">Phlox family, <a href="#Page_500">500</a></li> -<li class="isub1">Phoradendron flavescens, <a href="#Page_495">495</a></li> -<li class="isub1">Photosynthesis, <a href="#Page_67">67</a>, <a href="#Page_68">68</a>, <a href="#Page_70">70</a>, <a href="#Page_117">117</a> - <span class="pagenum"><a name="Page_510" id="Page_510">[Pg 510]</a></span></li> -<li class="isub1">Phycomycetes (Phy″co-my-ce′tes), <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Phyllidium, <a href="#Page_371">371</a></li> -<li class="isub1">Phylloclades, <a href="#Page_373">373</a>, <a href="#Page_395">395</a></li> -<li class="isub1">Phyllotaxy, <a href="#Page_375">375</a>, <a href="#Page_384">384</a></li> -<li class="isub1">Physical condition of soil, <a href="#Page_465">465</a></li> -<li class="isub1">Physical factors, <a href="#Page_465">465</a></li> -<li class="isub1">Phytolaccaceæ, <a href="#Page_495">495</a></li> -<li class="isub1">Phytomyxa leguminosarum, <a href="#Page_92">92</a></li> -<li class="isub1">Phytophthora, <a href="#Page_182">182</a>, <a href="#Page_184">184</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Pickerel-weed, <a href="#Page_493">493</a></li> -<li class="isub1">Pilularia, <a href="#Page_296">296</a></li> -<li class="isub1">Pinales, <a href="#Page_216">216</a></li> -<li class="isub1">Pine, white, <a href="#Page_297">297-310</a></li> -<li class="isub1">Piperales, <a href="#Page_494">494</a></li> -<li class="isub1">Pitcher-plant, <a href="#Page_496">496</a></li> -<li class="isub1">Pith, <a href="#Page_50">50</a></li> -<li class="isub1">Plant food, sources of, <a href="#Page_81">81</a></li> -<li class="isub1">Plant formations, <a href="#Page_496">496</a></li> -<li class="isub1">Plant substance, analysis of, <a href="#Page_79">79</a>, <a href="#Page_80">80</a></li> -<li class="isub1">Plantaginales, <a href="#Page_501">501</a></li> -<li class="isub1">Plantago, <a href="#Page_501">501</a></li> -<li class="isub1">Plasmolysis (plas-mol′y-sis), <a href="#Page_19">19</a></li> -<li class="isub1">Plasmopara, <a href="#Page_183">183</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Plectascales, <a href="#Page_217">217</a></li> -<li class="isub1">Plectobasidiales, <a href="#Page_220">220</a></li> -<li class="isub1">Pleurococcaceæ, <a href="#Page_161">161</a></li> -<li class="isub1">Pleurococcus, <a href="#Page_161">161</a></li> -<li class="isub1">Plum family, <a href="#Page_497">497</a></li> -<li class="isub1">Plumule, <a href="#Page_99">99</a></li> -<li class="isub1">Podostemon, <a href="#Page_496">496</a></li> -<li class="isub1">Poison-hemlock, <a href="#Page_499">499</a></li> -<li class="isub1">Poison-ivy, <a href="#Page_497">497</a></li> -<li class="isub1">Poison-oak, <a href="#Page_497">497</a></li> -<li class="isub1">Poisonous mushrooms, <a href="#Page_207">207</a>, <a href="#Page_208">208</a></li> -<li class="isub1">Poison-sumac, <a href="#Page_497">497</a></li> -<li class="isub1">Pokeweed, <a href="#Page_495">495</a></li> -<li class="isub1">Polemoneales, <a href="#Page_500">500</a></li> -<li class="isub1">Pollen grain, <a href="#Page_299">299</a>, <a href="#Page_305">305</a></li> -<li class="isub1">Pollination, <a href="#Page_303">303</a>, <a href="#Page_304">304</a>, <a href="#Page_420">420</a>, <a href="#Page_430">430</a>, <a href="#Page_433">433-449</a></li> -<li class="isub1">Pollinium, <a href="#Page_420">420</a></li> -<li class="isub1">Polygonales, <a href="#Page_495">495</a></li> -<li class="isub1">Polygonum, <a href="#Page_495">495</a></li> -<li class="isub1">Polypodiaceæ, <a href="#Page_296">296</a></li> -<li class="isub1">Polyporaceæ, <a href="#Page_209">209</a>, <a href="#Page_219">219</a></li> -<li class="isub1">Polyporus, <a href="#Page_209">209</a>, <a href="#Page_210">210</a></li> -<li class="isub1">Polyporus mollis, <a href="#Page_92">92</a></li> -<li class="isub1">Polyporus sulphureus, <a href="#Page_209">209</a></li> -<li class="isub1">Pomaceæ, <a href="#Page_497">497</a></li> -<li class="isub1">Pondweeds, <a href="#Page_492">492</a></li> -<li class="isub1">Poppy, <a href="#Page_496">496</a></li> -<li class="isub1">Porella, <a href="#Page_237">237</a></li> -<li class="isub1">Portulaca, <a href="#Page_495">495</a></li> -<li class="isub1">Potamogeton, <a href="#Page_492">492</a></li> -<li class="isub1">Potato, <a href="#Page_501">501</a></li> -<li class="isub1">Powdery mildews, <a href="#Page_195">195-198</a>, <a href="#Page_217">217</a></li> -<li class="isub1">Primrose, <a href="#Page_498">498</a>, <a href="#Page_500">500</a></li> -<li class="isub1">Primula, <a href="#Page_438">438</a></li> -<li class="isub1">Primulales, <a href="#Page_500">500</a></li> -<li class="isub1">Procarp, <a href="#Page_172">172</a>, <a href="#Page_174">174</a>, <a href="#Page_175">175</a></li> -<li class="isub1">Progeotropism (pro″ge-ot′ro-pism), <a href="#Page_126">126</a></li> -<li class="isub1">Promycelium (pro″my-ce′li-um), <a href="#Page_192">192</a></li> -<li class="isub1">Proterandrous, <a href="#Page_441">441</a>, <a href="#Page_442">442</a></li> -<li class="isub1">Proterandry, <a href="#Page_444">444</a></li> -<li class="isub1">Proterogenous, <a href="#Page_441">441</a>, <a href="#Page_442">442</a></li> -<li class="isub1">Proterogeny, <a href="#Page_440">440</a></li> -<li class="isub1">Prothallium, <a href="#Page_265">265</a>, <a href="#Page_287">287</a>, <a href="#Page_288">288</a>, <a href="#Page_291">291</a>, <a href="#Page_292">292</a>, <a href="#Page_304">304</a>, <a href="#Page_305">305</a>,</li> -<li class="isub7"><a href="#Page_311">311</a>, <a href="#Page_325">325</a>, <a href="#Page_328">328</a>, <a href="#Page_335">335</a>, <a href="#Page_433">433</a>, <a href="#Page_434">434</a></li> -<li class="isub1">Protoascales, <a href="#Page_216">216</a></li> -<li class="isub1">Protoascomycetes, <a href="#Page_216">216</a></li> -<li class="isub1">Protobasidiomycetes, <a href="#Page_218">218</a></li> -<li class="isub1">Protococcoideæ, <a href="#Page_158">158</a>, <a href="#Page_162">162</a></li> -<li class="isub1">Protodiscales, <a href="#Page_217">217</a></li> -<li class="isub1">Protomyces, <a href="#Page_216">216</a></li> -<li class="isub1">Protonema (pro″to-ne′ma), <a href="#Page_248">248</a>, <a href="#Page_264">264</a></li> -<li class="isub1">Protoplasm, <a href="#Page_1">1-12</a>, <a href="#Page_42">42-43</a>, <a href="#Page_342">342</a>;</li> -<li class="isub3">movement of, <a href="#Page_7">7-11</a></li> -<li class="isub1">Psilotaceæ, <a href="#Page_296">296</a></li> -<li class="isub1">Pteridophytes, <a href="#Page_295">295</a>, <a href="#Page_434">434</a></li> -<li class="isub1">Pteris cretica, <a href="#Page_346">346</a></li> -<li class="isub1">Puccinia, <a href="#Page_187">187</a></li> -<li class="isub1">Puff-balls, <a href="#Page_220">220</a></li> -<li class="isub1">Pumpkin, <a href="#Page_501">501</a></li> -<li class="isub1">Purslane, <a href="#Page_495">495</a></li> -<li class="isub1">Pyrenoid, <a href="#Page_2">2</a>, <a href="#Page_3">3</a></li> -<li class="isub1">Pyrenomycetes, <a href="#Page_217">217</a></li> -<li class="isub1">Pyrola, <a href="#Page_499">499</a></li> -<li class="isub1">Pyxidium, <a href="#Page_453">453</a></li> - -<li class="ifrst">Quercus, <a href="#Page_495">495</a></li> -<li class="isub1">Quillworts, <a href="#Page_289">289-291</a></li> -<li class="isub1">Quince, <a href="#Page_456">456</a></li> - -<li class="ifrst">Raceme, <a href="#Page_427">427</a></li> -<li class="isub1">Radicle, <a href="#Page_99">99</a></li> -<li class="isub1">Ragweed, <a href="#Page_502">502</a></li> -<li class="isub1">Rainy-season flora, <a href="#Page_481">481</a></li> -<li class="isub1">Ranales, <a href="#Page_496">496</a></li> -<li class="isub1">Ranunculaceæ, <a href="#Page_496">496</a></li> -<li class="isub1">Raspberry, <a href="#Page_454">454</a>, <a href="#Page_455">455</a></li> -<li class="isub1">Red algæ, <a href="#Page_171">171</a>, <a href="#Page_174">174</a>;</li> -<li class="isub3">uses of, <a href="#Page_175">175</a></li> -<li class="isub1">Reproduction, <a href="#Page_137">137</a>, <a href="#Page_143">143</a>, <a href="#Page_149">149</a>, <a href="#Page_154">154</a>, <a href="#Page_155">155</a>, <a href="#Page_179">179</a>, <a href="#Page_185">185</a>, <a href="#Page_186">186</a></li> -<li class="isub1">Respiration, <a href="#Page_110">110-116</a>, <a href="#Page_117">117</a></li> -<li class="isub1">Rhamnales, <a href="#Page_498">498</a> - <span class="pagenum"><a name="Page_511" id="Page_511">[Pg 511]</a></span></li> -<li class="isub1">Rhizoids, <a href="#Page_24">24-26</a></li> -<li class="isub1">Rhizome, <a href="#Page_354">354</a></li> -<li class="isub1">Rhizomorph (rhi′zo-morph), <a href="#Page_89">89</a></li> -<li class="isub1">Rhizophidium, <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Rhizopus, <a href="#Page_177">177-180</a>, <a href="#Page_215">215</a></li> -<li class="isub1">Rhododendron, <a href="#Page_499">499</a></li> -<li class="isub1">Rhodomeniales, <a href="#Page_175">175</a></li> -<li class="isub1">Rhodophyceæ, <a href="#Page_171">171</a></li> -<li class="isub1">Rhus radicans, <a href="#Page_416">416</a>, <a href="#Page_497">497</a></li> -<li class="isub1">Riccia, <a href="#Page_23">23</a>, <a href="#Page_164">164</a>, <a href="#Page_222">222-226</a></li> -<li class="isub1">Ricinus, <a href="#Page_497">497</a></li> -<li class="isub1">Riverweed, <a href="#Page_496">496</a></li> -<li class="isub1">Root, function of, <a href="#Page_410">410-418</a></li> -<li class="isub1">Root hairs, absorption by, <a href="#Page_19">19</a>, <a href="#Page_30">30</a>, <a href="#Page_32">32</a></li> -<li class="isub1">Root hairs, action on soil, <a href="#Page_82">82</a></li> -<li class="isub1">Root pressure, <a href="#Page_33">33</a>, <a href="#Page_34">34</a>, <a href="#Page_45">45</a></li> -<li class="isub1">Root, structure of, <a href="#Page_30">30</a>, <a href="#Page_361">361</a>, <a href="#Page_362">362</a></li> -<li class="isub1">Root-tubercles, <a href="#Page_92">92</a></li> -<li class="isub1">Roots, kinds of, <a href="#Page_415">415</a></li> -<li class="isub1">Rosaceæ, <a href="#Page_497">497</a></li> -<li class="isub1">Rosales, <a href="#Page_496">496</a></li> -<li class="isub1">Rose family, <a href="#Page_497">497</a></li> -<li class="isub1">Rosette, <a href="#Page_405">405</a></li> -<li class="isub1">Rosette plants, <a href="#Page_483">483</a></li> -<li class="isub1">Rubiales, <a href="#Page_501">501</a></li> -<li class="isub1">Rudbeckia, <a href="#Page_502">502</a></li> -<li class="isub1">Rusts, <a href="#Page_187">187-194</a></li> - -<li class="ifrst">Salicaceæ, <a href="#Page_494">494</a></li> -<li class="isub1">Salix, <a href="#Page_494">494</a></li> -<li class="isub1">Salsify, <a href="#Page_502">502</a></li> -<li class="isub1">Salviniaceæ, <a href="#Page_296">296</a></li> -<li class="isub1">Samara, <a href="#Page_451">451</a></li> -<li class="isub1">Sandalwood, <a href="#Page_495">495</a></li> -<li class="isub1">Sanguinaria, <a href="#Page_496">496</a></li> -<li class="isub1">Santalales, <a href="#Page_495">495</a></li> -<li class="isub1">Sap, rise of, <a href="#Page_53">53</a>, <a href="#Page_54">54</a></li> -<li class="isub1">Sapindales, <a href="#Page_497">497</a></li> -<li class="isub1">Saprolegnia, <a href="#Page_181">181-184</a></li> -<li class="isub1">Saprolegniales, <a href="#Page_215">215</a></li> -<li class="isub1">Saprophytes, <a href="#Page_83">83-85</a></li> -<li class="isub1">Sargassum, <a href="#Page_170">170</a></li> -<li class="isub1">Sarraceniales, <a href="#Page_496">496</a></li> -<li class="isub1">Sarsaparilla, <a href="#Page_499">499</a></li> -<li class="isub1">Saxifrage, <a href="#Page_496">496</a></li> -<li class="isub1">Schizæaceæ, <a href="#Page_295">295</a></li> -<li class="isub1">Schizocarp, <a href="#Page_451">451</a></li> -<li class="isub1">Schizomycetes, <a href="#Page_164">164</a></li> -<li class="isub1">Schizophyceæ, <a href="#Page_163">163</a></li> -<li class="isub1">Sclerenchyma, <a href="#Page_356">356-357</a>, <a href="#Page_361">361</a>, <a href="#Page_363">363</a></li> -<li class="isub1">Scouring rush, <a href="#Page_282">282</a></li> -<li class="isub1">Screw-pine, <a href="#Page_409">409</a>, <a href="#Page_492">492</a></li> -<li class="isub1">Scrophulariaceæ, <a href="#Page_501">501</a></li> -<li class="isub1">Sedge family, <a href="#Page_492">492</a></li> -<li class="isub1">Seed, dispersal of, <a href="#Page_458">458-463</a></li> -<li class="isub1">Seed plants, <a href="#Page_338">338</a></li> -<li class="isub1">Seed, structure of, <a href="#Page_98">98</a>, <a href="#Page_102">102</a></li> -<li class="isub1">Seedlings, <a href="#Page_97">97-107</a></li> -<li class="isub1">Seeds, <a href="#Page_330">330-334</a></li> -<li class="isub1">Selaginella, <a href="#Page_286">286-288</a>, <a href="#Page_292">292</a></li> -<li class="isub1">Selaginellaceæ, <a href="#Page_296">296</a></li> -<li class="isub1">Sensitive fern, <a href="#Page_273">273</a></li> -<li class="isub1">Sensitive plants, <a href="#Page_132">132</a>, <a href="#Page_396">396</a>, <a href="#Page_399">399</a></li> -<li class="isub1">Sexual organs, <a href="#Page_144">144</a>, <a href="#Page_147">147</a></li> -<li class="isub1">Shadbush, <a href="#Page_497">497</a></li> -<li class="isub1">Shepherd’s-purse, <a href="#Page_496">496</a></li> -<li class="isub1">Shoot, floral, <a href="#Page_419">419</a>, <a href="#Page_432">432</a></li> -<li class="isub1">Shoots, <a href="#Page_353">353-355</a>;</li> -<li class="isub3">types of, <a href="#Page_361">361-373</a>;</li> -<li class="isub3">winter condition of, <a href="#Page_374">374-377</a></li> -<li class="isub1">Sieve tissue, <a href="#Page_358">358</a>, <a href="#Page_363">363</a></li> -<li class="isub1">Sieve tubes, <a href="#Page_52">52</a>, <a href="#Page_53">53</a></li> -<li class="isub1">Silique, <a href="#Page_453">453</a></li> -<li class="isub1">Silk-cotton tree, <a href="#Page_417">417</a></li> -<li class="isub1">Silver bell, <a href="#Page_500">500</a></li> -<li class="isub1">Siphoneæ, <a href="#Page_146">146</a>, <a href="#Page_162">162</a></li> -<li class="isub1">Skunk’s cabbage, <a href="#Page_439">439-442</a></li> -<li class="isub1">Slime molds, <a href="#Page_83">83</a></li> -<li class="isub1">Smoke-tree, <a href="#Page_497">497</a></li> -<li class="isub1">Societies, <a href="#Page_475">475</a></li> -<li class="isub1">Solanum, <a href="#Page_501">501</a></li> -<li class="isub1">Solidago, <a href="#Page_502">502</a></li> -<li class="isub1">Sourwood, <a href="#Page_499">499</a></li> -<li class="isub1">Spadix, <a href="#Page_428">428</a></li> -<li class="isub1">Spartium, <a href="#Page_446">446</a></li> -<li class="isub1">Spathyema fœtida, <a href="#Page_438">438</a>, <a href="#Page_493">493</a></li> -<li class="isub1">Spermagonia, <a href="#Page_190">190</a></li> -<li class="isub1">Spermatophytes, <a href="#Page_338">338</a></li> -<li class="isub1">Sphacelaria, <a href="#Page_168">168</a></li> -<li class="isub1">Sphærella lacustris, <a href="#Page_158">158</a>, <a href="#Page_159">159</a></li> -<li class="isub1">Sphærella nivalis, <a href="#Page_158">158</a>, <a href="#Page_350">350</a></li> -<li class="isub1">Sphæriales, <a href="#Page_218">218</a></li> -<li class="isub1">Sphagnales, <a href="#Page_248">248</a></li> -<li class="isub1">Sphagnum, <a href="#Page_164">164</a></li> -<li class="isub1">Spiderwort, <a href="#Page_11">11</a>, <a href="#Page_493">493</a></li> -<li class="isub1">Spike, <a href="#Page_428">428</a></li> -<li class="isub1">Spirodela polyrhiza, <a href="#Page_27">27</a></li> -<li class="isub1">Spirogyra, <a href="#Page_1">1-5</a>, <a href="#Page_13">13</a>, <a href="#Page_14">14</a>, <a href="#Page_60">60</a>, <a href="#Page_72">72</a>, <a href="#Page_136">136-140</a>, <a href="#Page_350">350</a></li> -<li class="isub1">Sporangia, <a href="#Page_178">178-182</a></li> -<li class="isub1">Sporangium, <a href="#Page_253">253-258</a>, <a href="#Page_281">281</a>, <a href="#Page_290">290</a></li> -<li class="isub1">Spores, <a href="#Page_225">225</a>, <a href="#Page_256">256-258</a>, <a href="#Page_263">263</a>, <a href="#Page_264">264</a>, <a href="#Page_281">281</a></li> -<li class="isub1">Sporocarp, <a href="#Page_173">173</a></li> -<li class="isub1">Sporogonium (spo″ro-go′ni-um), <a href="#Page_224">224</a>, <a href="#Page_231">231</a>, <a href="#Page_233">233</a>, <a href="#Page_234">234</a>, <a href="#Page_237">237</a>, <a href="#Page_238">238</a>,</li> -<li class="isub7"><a href="#Page_239">239</a>, <a href="#Page_241">241</a>, <a href="#Page_246">246</a>, <a href="#Page_247">247</a>, <a href="#Page_248">248</a> - <span class="pagenum"><a name="Page_512" id="Page_512">[Pg 512]</a></span></li> -<li class="isub1">Sporophyll, <a href="#Page_274">274</a>, <a href="#Page_281">281</a>, <a href="#Page_292">292</a></li> -<li class="isub1">Sporophyte (spo′ro-phyte), <a href="#Page_225">225</a>, <a href="#Page_226">226</a>, <a href="#Page_232">232</a>, <a href="#Page_234">234</a>, <a href="#Page_237">237-239</a>, <a href="#Page_241">241</a>, <a href="#Page_242">242</a>,</li> -<li class="isub7"><a href="#Page_250">250</a>, <a href="#Page_261">261</a>, <a href="#Page_268">268</a>, <a href="#Page_270">270</a>, <a href="#Page_283">283</a>, <a href="#Page_292">292</a>, <a href="#Page_294">294</a>, <a href="#Page_314">314</a>,</li> -<li class="isub7"><a href="#Page_315">315</a>, <a href="#Page_317">317</a>, <a href="#Page_336">336-339</a>, <a href="#Page_340">340-348</a> <a href="#Page_434">434</a></li> -<li class="isub1">Spurge family, <a href="#Page_497">497</a></li> -<li class="isub1">Squash, <a href="#Page_501">501</a></li> -<li class="isub1">Staminodium, <a href="#Page_446">446</a></li> -<li class="isub1">Starch, formation of, <a href="#Page_68">68</a>, <a href="#Page_70">70-74</a>;</li> -<li class="isub3">changed to sugar, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>;</li> -<li class="isub3">translocation of, <a href="#Page_73">73</a>;</li> -<li class="isub3">digestion of, <a href="#Page_75">75</a></li> -<li class="isub1">Stems, types of, <a href="#Page_365">365-373</a></li> -<li class="isub1">Stems, woody, structure of, <a href="#Page_381">381-382</a></li> -<li class="isub1">Stoma (pl. stomata) (sto′ma-ta), <a href="#Page_42">42-44</a>, <a href="#Page_46">46</a></li> -<li class="isub1">Strawberry, <a href="#Page_455">455</a>, <a href="#Page_497">497</a></li> -<li class="isub1">Sugar, test for, <a href="#Page_75">75</a>, <a href="#Page_76">76</a></li> -<li class="isub1">Sumac, <a href="#Page_497">497</a></li> -<li class="isub1">Sundew, <a href="#Page_133">133</a>, <a href="#Page_496">496</a></li> -<li class="isub1">Sunflower, <a href="#Page_399">399-401</a>, <a href="#Page_502">502</a></li> -<li class="isub1">Sweet gum, <a href="#Page_496">496</a></li> -<li class="isub1">Symbiosis, <a href="#Page_85">85</a>, <a href="#Page_86">86</a>, <a href="#Page_92">92-95</a></li> -<li class="isub1">Synergids (syn´er-gids), <a href="#Page_327">327</a>, <a href="#Page_330">330</a></li> -<li class="isub1">Syngenœsious, <a href="#Page_424">424</a></li> -<li class="isub1">Synthetic assimilation, <a href="#Page_67">67</a></li> - -<li class="ifrst">Tape-grass, <a href="#Page_493">493</a></li> -<li class="isub1">Taraxacum densleonis, <a href="#Page_502">502</a></li> -<li class="isub1">Teasel, <a href="#Page_501">501</a></li> -<li class="isub1">Telegraph-plant, <a href="#Page_399">399</a></li> -<li class="isub1">Teleutospore, <a href="#Page_188">188</a></li> -<li class="isub1">Temperature, <a href="#Page_134">134</a>, <a href="#Page_135">135</a>, <a href="#Page_465">465</a></li> -<li class="isub1">Tetrasporaceæ, <a href="#Page_161">161</a></li> -<li class="isub1">Tetraspores, <a href="#Page_173">173</a>, <a href="#Page_174">174</a></li> -<li class="isub1">Thallophytes, <a href="#Page_352">352</a></li> -<li class="isub1">Thallus, <a href="#Page_352">352</a></li> -<li class="isub1">Thelephoraceæ, <a href="#Page_219">219</a></li> -<li class="isub1">Thistle family, <a href="#Page_502">502</a></li> -<li class="isub1">Thunderwood, <a href="#Page_497">497</a></li> -<li class="isub1">Thyrsus, <a href="#Page_427">427</a></li> -<li class="isub1">Tilia, <a href="#Page_498">498</a></li> -<li class="isub1">Tillandsia, <a href="#Page_493">493</a></li> -<li class="isub1">Tissue, tensions of, <a href="#Page_57">57-59</a></li> -<li class="isub1">Tissues, classification of, <a href="#Page_363">363</a>, <a href="#Page_364">364</a>;</li> -<li class="isub3">kinds of, <a href="#Page_356">356-359</a>;</li> -<li class="isub3">organization of, <a href="#Page_356">356-362</a></li> -<li class="isub1">Toad-flax, <a href="#Page_501">501</a></li> -<li class="isub1">Tomato, <a href="#Page_501">501</a></li> -<li class="isub1">Tradescantia, <a href="#Page_493">493</a></li> -<li class="isub1">Tragopogon, <a href="#Page_502">502</a></li> -<li class="isub1">Trailing arbutus, <a href="#Page_499">499</a></li> -<li class="isub1">Trametes pini, <a href="#Page_90">90</a></li> -<li class="isub1">Transpiration, <a href="#Page_35">35-46</a></li> -<li class="isub1">Tremellales, <a href="#Page_218">218</a>, <a href="#Page_219">219</a></li> -<li class="isub1">Triadelphous, <a href="#Page_425">425</a></li> -<li class="isub1">Trillium, <a href="#Page_318">318-322</a>, <a href="#Page_494">494</a></li> -<li class="isub1">Trumpet-creeper, <a href="#Page_501">501</a></li> -<li class="isub1">Tuberales, <a href="#Page_217">217</a></li> -<li class="isub1">Tubers, <a href="#Page_373">373</a></li> -<li class="isub1">Tundra, <a href="#Page_481">481</a></li> -<li class="isub1">Turgescence, <a href="#Page_14">14</a>, <a href="#Page_15">15</a></li> -<li class="isub1">Turgor, <a href="#Page_20">20</a>;</li> -<li class="isub3">restoration of, <a href="#Page_56">56</a>, <a href="#Page_57">57</a></li> -<li class="isub1">Typha, <a href="#Page_493">493</a></li> - -<li class="ifrst">Ulmaceæ, <a href="#Page_495">495</a></li> -<li class="isub1">Ulmus americana, <a href="#Page_495">495</a></li> -<li class="isub1">Ulothrix, <a href="#Page_162">162</a></li> -<li class="isub1">Ulotrichaceæ, <a href="#Page_162">162</a></li> -<li class="isub1">Ulvaceæ, <a href="#Page_162">162</a></li> -<li class="isub1">Umbel, <a href="#Page_428">428</a></li> -<li class="isub1">Umbellales, <a href="#Page_498">498</a></li> -<li class="isub1">Uredinales, <a href="#Page_218">218</a></li> -<li class="isub1">Uredineæ, <a href="#Page_187">187-194</a>, <a href="#Page_218">218</a></li> -<li class="isub1">Uredospore, <a href="#Page_189">189</a></li> -<li class="isub1">Uromyces caryophyllinus, <a href="#Page_87">87</a></li> -<li class="isub1">Urticales, <a href="#Page_495">495</a></li> -<li class="isub1">Ustilaginales, <a href="#Page_218">218</a></li> -<li class="isub1">Ustilagineæ, <a href="#Page_218">218</a></li> -<li class="isub1">Utricularia, <a href="#Page_501">501</a></li> - -<li class="ifrst">Vaccinium, <a href="#Page_499">499</a></li> -<li class="isub1">Vacuoles, <a href="#Page_7">7</a>, <a href="#Page_8">8</a></li> -<li class="isub1">Valerianales, <a href="#Page_501">501</a></li> -<li class="isub1">Vallisneria spiralis, <a href="#Page_493">493</a></li> -<li class="isub1">Variation, <a href="#Page_338">338</a></li> -<li class="isub1">Vascular tissue, <a href="#Page_358">358</a>, <a href="#Page_363">363</a></li> -<li class="isub1">Vaucheria, <a href="#Page_142">142-146</a></li> -<li class="isub1">Vaucheriaceæ, <a href="#Page_162">162</a></li> -<li class="isub1">Vegetation types, <a href="#Page_464">464</a></li> -<li class="isub1">Venus fly-trap, <a href="#Page_133">133</a></li> -<li class="isub1">Verbascum, <a href="#Page_501">501</a></li> -<li class="isub1">Verbena, <a href="#Page_501">501</a></li> -<li class="isub1">Vessels, <a href="#Page_52">52</a>, <a href="#Page_53">53</a></li> -<li class="isub1">Vetch, <a href="#Page_92">92</a>, <a href="#Page_497">497</a></li> -<li class="isub1">Viburnum, <a href="#Page_501">501</a></li> -<li class="isub1">Vicia sativa, <a href="#Page_459">459</a></li> -<li class="isub1">Viola cucullata, <a href="#Page_436">436</a></li> -<li class="isub1">Violaceæ, <a href="#Page_498">498</a></li> -<li class="isub1">Virgin’s bower, <a href="#Page_462">462</a>, <a href="#Page_463">463</a></li> -<li class="isub1">Viscum album, <a href="#Page_84">84</a></li> -<li class="isub1">Vitaceæ, <a href="#Page_498">498</a></li> -<li class="isub1">Volvocaceæ, <a href="#Page_158">158</a></li> - -<li class="ifrst">Walnut, <a href="#Page_452">452</a>, <a href="#Page_494">494</a></li> -<li class="isub1">Water, <a href="#Page_465">465</a>;</li> -<li class="isub3">flow of, in plants, <a href="#Page_53">53</a>, <a href="#Page_54">54</a></li> -<li class="isub1">Water-lilies, <a href="#Page_496">496</a></li> -<li class="isub1">Water-plantain, <a href="#Page_493">493</a></li> -<li class="isub1">White pine, <a href="#Page_396">396</a> - <span class="pagenum"><a name="Page_513" id="Page_513">[Pg 513]</a></span></li> -<li class="isub1">Wild carrot, <a href="#Page_499">499</a></li> -<li class="isub1">Willow family, <a href="#Page_494">494</a></li> -<li class="isub1">Wind, <a href="#Page_471">471</a></li> -<li class="isub1">Wintergreen, <a href="#Page_499">499</a>;</li> -<li class="isub3">leaf of, <a href="#Page_43">43</a></li> -<li class="isub1">Witch-hazel, <a href="#Page_496">496</a></li> -<li class="isub1">Wolffia, <a href="#Page_28">28</a></li> -<li class="isub1">Woodland formation, <a href="#Page_470">470</a></li> - -<li class="ifrst">Xerophytes, <a href="#Page_467">467</a></li> -<li class="isub1">Xylem, <a href="#Page_50">50</a>, <a href="#Page_52">52</a>, <a href="#Page_360">360</a>, <a href="#Page_361">361</a>, <a href="#Page_363">363</a></li> -<li class="isub1">Xylogen, <a href="#Page_92">92</a></li> -<li class="isub1">Xyridales, <a href="#Page_493">493</a></li> - -<li class="ifrst">Yeast, <a href="#Page_216">216</a>;</li> -<li class="isub3">fermentation of, <a href="#Page_115">115</a>, <a href="#Page_116">116</a></li> -<li class="isub1">Yucca, <a href="#Page_480">480</a>, <a href="#Page_493">493</a></li> - -<li class="ifrst">Zamia, <a href="#Page_313">313</a>, <a href="#Page_316">316</a>, <a href="#Page_457">457</a></li> -<li class="isub1">Zoogonidia, <a href="#Page_143">143</a>, <a href="#Page_149">149</a>, <a href="#Page_178">178-184</a></li> -<li class="isub1">Zoospore, <a href="#Page_149">149</a>, <a href="#Page_154">154</a></li> -<li class="isub1">Zygomycetes, <a href="#Page_215">215</a></li> -<li class="isub1">Zygospore, <a href="#Page_2">2</a>, <a href="#Page_138">138-140</a>, <a href="#Page_157">157</a>, <a href="#Page_160">160</a>, <a href="#Page_179">179</a>, <a href="#Page_180">180</a></li> -<li class="isub1">Zygote (zy′gote), <a href="#Page_138">138</a>, <a href="#Page_179">179</a></li> -</ul> - -<hr class="full" /> -<div class="chapter"> -<p class="f150 u"><b>TWO NOTABLE NATURE BOOKS.</b></p> -<p class="f150"><b>FERNS</b></p> -</div> -<p class="neg-indent">A Manual for the Northeastern States. By C. -E. WATERS, Ph.D. (Johns Hopkins). With Analytical Keys Based on -the Stalks. <i>With over 200 illustrations</i> from original drawings -and photographs. 362 pp. Square<br /> 8vo. Boxed. $3.00 <i>net</i>. (By mail, $3.34.)</p> - -<p>A popular, but thoroughly scientific book, including all the ferns -in the region covered by Britton’s Manual. Much information is also -given concerning reproduction and classification, fern photography, etc.</p> - -<p>PROF. L. M. UNDERWOOD, OF COLUMBIA:</p> -<p class="blockquot">“It is really more scientific than one would -expect from a work of a somewhat popular nature. -The photographs are very fine, very carefully -selected and will add much to the text. I do not -see how they could be much finer.”</p> - -<p>THE PLANT WORLD:</p> -<p class="blockquot">“This book is likely to prove the leading popular -work on ferns. The majority of the illustrations are from original -photographs; in respect to this feature, it can be confidently -asserted that <i>no finer examples of fern photography have ever -been produced</i>.... May be expected to prove of permanent scientific -value, as well as to satisfy a want which existing treatises have but -imperfectly filled.”</p> - -<p class="f150 space-above2"><b>MUSHROOMS</b></p> - -<p class="neg-indent">Edible, Poisonous Mushrooms, etc. By Prof. GEO. F. ATKINSON, -of Cornell.</p> - -<p>With recipes for cooking by Mrs. S. T. RORER, and the chemistry and -toxicology of mushrooms, by J. F. CLARK. With 230 illustrations from -photographs, including fifteen colored plates. 320pp.<br /> 8vo. $3.00 <i>net</i> -(by mail, $3.23).</p> - -<p>Among the additions in this second edition are ten new plates, -chapters on the “Uses of Mushrooms,” and on the “Cultivation of -Mushrooms,” illustrated by several flash-light photographs.</p> - -<p>EDUCATIONAL REVIEW:</p> -<p class="blockquot">“It would be difficult to conceive of a more -attractive and useful book, nor one that is destined to exert a -greater influence in the study of an important class of plants that -have been overlooked and avoided simply because of ignorance of their -qualities, and the want of a suitable book of low price. In addition to -its general attractiveness and the beauty of its illustrations, it is -written in a style well calculated to win the merest tyro or the most -accomplished student of the fungi.... These clear photographs and the -plain descriptions make the book especially valuable for the amateur -fungus hunter in picking out the edible from the poisonous species of -the most common kinds.”</p> - -<p>THE PLANT WORLD:</p> -<p class="blockquot">“This is, without doubt, the most important and -valuable work of its kind that has appeared in this country in recent -years.... No student, either amateur or professional, can afford to be -without it.”</p> -<hr class="chap" /> - -<p class="f150"><b>HENRY HOLT AND COMPANY,</b></p> -<p class="center">NEW YORK. (xii, ’03). CHICAGO.</p> -<hr class="full" /> - -<div class="chapter"><p class="f120"><b>BRITTON’S MANUAL OF THE FLORA OF<br /> -THE NORTHERN STATES AND CANADA.</b></p></div> - -<p class="center">By Director <span class="smcap">N. L. Britton</span> -of the New York Botanical Garden.<br /> -1080 pp. 8vo. $2.25, net.</p> - -<div class="blockquot"> -<p>A comprehensive manual of over a thousand pages, containing about -4,500 descriptions, probably one-third more than any other. It is -designed to meet modern requirements and outline modern conceptions of -the science. It is based on <i>An Illustrated Flora</i>, prepared by Prof. -Britton in co-operation with Judge Addison Brown. The text has been -revised and brought up to date, and much of novelty has been added. All -illustrations are omitted, but specific reference has been made to all -of the 4,162 figures in the <i>Illustrated Flora</i>.</p> - -<p>“It is the most complete and reliable work that ever appeared in -the form of a flora of this region, and for the first time we have -a manual in which the plant descriptions are drawn from the plants -themselves, and do not represent compiled descriptions made by the -early writers.”—Prof. D. M. Underwood of Columbia.</p> - -<p>“This work will at once take its place as the standard manual of -the region that it covers. It is far superior to any other work of its -class ever published in America.”—Prof. Conway MacMillan of University -of Minnesota.</p> - -<p>“This book must at once find its way into the schools and -colleges, to which it may be commended for the students in systematic -botany.”—Prof. Chas. E. Bessey in “Science.”</p> - -<p>“It is nothing if it is not compact; it is nothing if it is not up -to date; it is nothing if it is not the work of a master. What more can -be said, save that the more it is used the greater the appreciation by -the plant-lovers in the region which it covers.”—Prof. Byron D. Halsted -of Rutgers College.</p> - -<p>“The work is well done; and as it is the only volume which gives in -a way suitable for students the present state of the science, it cannot -fail to take its place as a standard work.”—Prof. George Macloskie of -Princeton.</p> - -<p>“I regard the book as one that we cannot do without and one that -will henceforth take its place as a necessary means of determination of -the plant species within its range.”—Prof. V. M. Spalding of University -of Michigan.</p> - -<p>“An exceedingly valuable contribution to our botanical -literature.... It is convenient to handle, and the low price will help -to give it a large circulation.”—Prof. T. J. Burrill of the University -of Illinois.</p> -</div> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl" rowspan="2"><span class="lgfnt200">HENRY HOLT & CO.</span></td> - <td class="tdl_ws1"><b>29 West 23d Street, New York</b></td> - </tr><tr> - <td class="tdl_ws1"><b>378 Wabash Avenue, Chicago</b></td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">viii</span>, ’05</td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<div class="chapter"> -<p class="f120">CHAMPLIN’S YOUNG FOLKS’</p> -<p class="f150">Cyclopædia of Natural History</p> -</div> - -<p class="center">By <span class="smcap">J. D. Champlin</span> and - <span class="smcap">F. A. Lucas</span></p> - -<p class="center">With over 800 illustrations. 725 pp. $2.50</p> - -<div class="blockquot"> -<p>A whole “nature library” about animals prepared by experts. -Scientific facts are presented in simple language, and are enlivened by -anecdotes, personal experiences, and references to history, art, and -literature.</p> - -<p>The illustrations are not only superior as animal pictures, but are -genuinely illustrative, since they show the creature in its natural -surroundings and characteristic action.</p> - -<p>Extinct animals are fully treated, because these strange forms are -fascinating to children, and because they illustrate the derivation of -such familiar living animals as birds, horses, and dogs.</p> - -<p>“A full menagerie of all sorts of animals, with a multitude of -pictures.... A wonderful exhibition, and the story of each individual -is interesting and calculated to stimulate the youthful mind in -research.... 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The range -of the volume is very wide, for besides those items of classical -knowledge which constitute the average school encyclopædia, we have -brief descriptions given of modern books, poems, inventions, pictures, -and persons about which the lad of the period should be acquainted.... -The pictures in the volume are varied and truly illustrative. Old -pictures and sculpture are presented in the usual line of drawings, but -modern scenes and buildings are pictured through excellent half-tone -reproductions of photographs.”—<i>N. Y. Times Saturday Review.</i></p> - -<p class="f120 space-above1">Earlier Volumes of Champlin’s Young Folks’ Cyclopædia.</p> -<p class="center">With numerous illustrations. 8vo. $2.50 each.</p> - -<p class="f120">COMMON THINGS.<span class="ws3">PERSONS and PLACES.</span><br /> -GAMES and SPORTS.</p> - -<p class="center space-below1">⁂ <i>12-page circular, with sample pages of Champlin’s Young -Folks’ Cyclopædias and his other books, free.</i></p> -</div> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl" rowspan="2"><span class="lgfnt200">HENRY HOLT & CO.</span></td> - <td class="tdl_ws1"><b>29 West 23d Street, New York</b></td> - </tr><tr> - <td class="tdl_ws1"><b>378 Wabash Avenue, Chicago</b></td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">viii</span>, ’06</td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<div class="chapter"> -<p class="f150">AMERICAN SCIENCE SERIES</p> -</div> -<hr class="r5" /> - -<p class="center"><i>All prices are</i> NET <i>unless marked</i> RETAIL. <i>Details of the books -will be found in Henry Holt & Co.’s Educational Catalogue, free on application.</i></p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl" colspan="2"><b>Physics.</b> By Prof. <span class="smcap">George F. 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Tufts</span>, Chicago University.</td> - </tr><tr> - <td class="tdl_ws1" colspan="2"><span class="ws3">(<i>In preparation.</i>)</span></td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>Political Economy.</b> By the late President <span class="smcap">Francis A. Walker</span>,</td> - </tr><tr> - <td class="tdl_ws1" colspan="2"><span class="ws3">Mass. Institute of Technology.</span></td> - </tr><tr> - <td class="tdl_ws1"><i>Advanced Course.</i> 537 pp. 8vo.</td> - <td class="tdr">2.00</td> - </tr><tr> - <td class="tdl_ws1">The same. <i>Briefer Course.</i> 415 pp. 12mo.</td> - <td class="tdr">1.20</td> - </tr><tr> - <td class="tdl_ws1">The same. <i>Elementary Course.</i> 423 pp. 12mo.</td> - <td class="tdr">1.00</td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>Finance.</b> By Prof. <span class="smcap">Henry Carter Adams</span>, University of Michigan.</td> - </tr><tr> - <td class="tdl_ws1"><i>Advanced Course.</i> 573 pp. 8vo.</td> - <td class="tdr">3.50</td> - </tr> - </tbody> -</table> -<p> </p> -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl" rowspan="2"><span class="lgfnt200">HENRY HOLT & CO.</span></td> - <td class="tdl_ws1"><b>29 West 23d Street, New York</b></td> - </tr><tr> - <td class="tdl_ws1"><b>378 Wabash Avenue, Chicago</b></td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">viii</span>, ’02</td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<div class="chapter"> -<p class="f200"><b>CHEMISTRY</b></p> -</div> -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl" colspan="2"><b>Cairns’s Quantitative Chemical Analysis</b></td> - </tr><tr> - <td class="tdl_ws1">Revised and enlarged by Dr. <span class="smcap">E. Waller</span>. 417 pp. 8vo.</td> - <td class="tdr">$2.00, <i>net</i>.</td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>Cohen’s Physical Chemistry for Biologists</b></td> - </tr><tr> - <td class="tdl_ws1">Translated by Dr. <span class="smcap">Martin Fischer</span>, Chicago University. 343 pp. 12mo,</td> - <td class="tdr">$1.75, <i>net</i>.</td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>Congdon’s Qualitative Analysis</b></td> - </tr><tr> - <td class="tdl_ws1">By Prof. <span class="smcap">Ernest A. Congdon</span>, Drexel Institute. 64 pp. <i>Interleaved.</i> 8vo.</td> - <td class="tdr">60c., <i>net</i>.</td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>Nicholson and Avery’s Exercises in Chemistry</b></td> - </tr><tr> - <td class="tdl_ws1"><p>With Outlines for the Study of Chemistry. To accompany any elementary - text. By Prof. <span class="smcap">H. H. Nicholson</span>, University - of Nebraska, and Prof. <span class="smcap">Samuel Avery</span>, - University of Idaho. 413 pp. 12mo. 60c., <i>net</i>.</p></td> - <td class="tdr"> </td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>Noyes’s (A. A.) General Principles of Physical Science</b></td> - </tr><tr> - <td class="tdl_ws1"><p>An Introduction to the Study of the Principles of Chemistry. By - Prof. <span class="smcap">A. A. Noyes</span>, Mass. Institute of - Technology. 160 pp. 8vo. $1.50, <i>net</i>.</p></td> - <td class="tdr"> </td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>Noyes’s (W. A.) Organic Chemistry</b></td> - </tr><tr> - <td class="tdl_ws1"><p>By Prof. <span class="smcap">Wm. A. Noyes</span>, Rose Polytechnic - Institute. 534 pp. 12mo. $1.50, <i>net</i>.</p></td> - <td class="tdr"> </td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>Qualitative Analysis (Elementary)</b></td> - </tr><tr> - <td class="tdl_ws1"><span class="ws3">x + 91 pp. 8vo. 80c., <i>net</i>.</span></td> - <td class="tdr"> </td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>Remsen’s Chemistries</b></td> - </tr><tr> - <td class="tdl_ws1" colspan="2">By Pres. <span class="smcap">Ira Remsen</span>, Johns Hopkins. (<i>American Science Series.</i>)</td> - </tr><tr> - <td class="tdl_ws3"><b>Inorganic Chemistry</b> (<i>Advanced</i>). <span class="smcap">xxii</span> + 853 pp. 8vo.</td> - <td class="tdr">$2.80, <i>net</i>.</td> - </tr><tr> - <td class="tdl_ws3"><b>College Chemistry</b> <span class="smcap">xx</span> + 689 pp. 8vo.</td> - <td class="tdr">$2.00, <i>net</i>.</td> - </tr><tr> - <td class="tdl_ws3"><b>Introduction to Chemistry</b> (<i>Briefer</i>). <span class="smcap">xix</span> + 435 pp. 12mo.</td> - <td class="tdr">$1.12, <i>net</i>.</td> - </tr><tr> - <td class="tdl_ws3"><p>This book is used in hundreds of schools and colleges in this - country. It has passed through several editions in England, and has - been translated into German (being the elementary text-book in the - University of Leipsic), French, and Italian.</p></td> - <td class="tdr"> </td> - </tr><tr> - <td class="tdl_ws3"><b>Remsen and Randall’s Experiments</b> (<i>for the “Introduction”</i>).</td> - <td class="tdr">50c., <i>net</i>.</td> - </tr><tr> - <td class="tdl_ws3"><b>Elements of Chemistry</b> (<i>Elementary</i>). <span class="smcap">x</span> + 272 pp. 12mo.</td> - <td class="tdr">80c., <i>net</i>.</td> - </tr><tr> - <td class="tdl_ws3"><b>Laboratory Manual</b> (<i>for the “Elements”</i>).</td> - <td class="tdr">40c., <i>net</i>.</td> - </tr><tr> - <td class="tdl_space-above1"><b>Torrey’s Elementary Chemistry</b> By <span class="smcap">Joseph Torrey</span>, Jr., Harvard. 437 pp. 12mo.</td> - <td class="tdr">$1.25, <i>net</i>.</td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>White’s Qualitative Analysis</b></td> - </tr><tr> - <td class="tdl_ws1">By Prof. <span class="smcap">John White</span>, Univ. of Nebraska. 96 pp. 8vo.</td> - <td class="tdr">80c., <i>net</i>.</td> - </tr><tr> - <td class="tdl_space-above1" colspan="2"><b>Woodhull and Van Arsdale’s Chemical Experiments</b></td> - </tr><tr> - <td class="tdl_ws1">By Prof. <span class="smcap">John F. Woodhull</span> and <span class="smcap">M. B. Van Arsdale</span>,</td> - <td class="tdr"> </td> - </tr><tr> - <td class="tdl_ws3">Teachers’ College, New York City. 136 pp. 12mo.</td> - <td class="tdr">60c., <i>net</i>.</td> - </tr><tr> - <td class="tdl_ws3">Extremely simple experiments in the chemistry of daily life.</td> - <td class="tdr"></td> - </tr> - </tbody> -</table> -<p> </p> -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl" rowspan="2"><span class="lgfnt200">HENRY HOLT & CO.</span></td> - <td class="tdl_ws1"><b>29 West 23d Street, New York</b></td> - </tr><tr> - <td class="tdl_ws1"><b>378 Wabash Avenue, Chicago</b></td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">viii</span>, ’05</td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<div class="chapter"> -<p class="f150 space-above1">CHAMBERLIN & SALISBURY’S</p> -<p class="f200"><b>GEOLOGY</b></p> -</div> - -<div class="blockquot"> -<p class="neg-indent">By <span class="smcap">Thomas C. Chamberlin</span> and <span class="smcap">Rollin D. Salisbury</span>, -Professors in the University of Chicago. -(<i>American Science Series.</i>) 2 vols. 8vo.</p> - -<p><i>Vol. I. Geological Processes and their Results.</i> <span class="smcap">xix</span> + 654 pp. $4.00.</p> -<p><i>Vol. II. Earth History.</i> [<i>In preparation.</i>]</p> - -<p>This is a notable scientific work by two of the highest authorities -on the subject in the United States, and yet written in a style so -simple that it can be clearly understood by the intelligent reader who -has had little previous training in the subject.</p> - -<p><b>Chas. D. Walcott</b>, <i>Director of U. S. Geological Survey</i>:—I -am impressed with the admirable plan of the work and with the thorough -manner in which geological principles and processes and their results -have been presented. The text is written in an entertaining style -and is supplemented by admirable illustrations, so that the student -cannot fail to obtain a clear idea of the nature and work of geological -agencies, of the present status of the science, and of the spirit which -actuates the working geologist.</p> - -<p><b>Henry S. Williams</b>, <i>Professor in Yale University</i>.—I -believe it is the best treatise on this part of the subject which we -have seen in America.</p> - -<p><b>R. S. Woodward</b>, <i>Professor in Columbia University</i>:—It is -admirable for its science, admirable for its literary perfection, and -admirable for its unequalled illustrations.</p> - -<p><b>T. C. Hopkins</b>, <i>Professor in Syracuse University</i>:—It gives -us the most advanced thought on all the great questions of dynamical -and structural geology to be found in geological literature.</p> - -<p><b>H. Foster Bain</b>, <i>U. S. Geological Survey</i>:—The book is -pre-eminently a teaching book and I have no doubt that it will at once -become the standard American text-book on geology.</p> - -<p><b>William N. Rice</b>, <i>Professor in Wesleyan University</i>:—The -book is full of new ideas. It is one of the indispensable books for the -library of every working geologist and every one who wishes to be an -up-to-date teacher of geology.</p> - -<p><b>T. A. Jaggar, Jr.</b>, <i>Assistant Professor in Harvard -University</i>:—The book appears to be an excellent statement of modern -American geology, with abundant new illustrative material, based upon -the most recent work of government and other surveys. It is especially -satisfactory to have in hand a geological volume which does not attempt -to cover the whole field. Modern geology is much too large a subject to -be condensed into a single volume.</p> -</div> - -<p> </p> -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl" rowspan="2"><span class="lgfnt200">HENRY HOLT & CO.</span></td> - <td class="tdl_ws1"><b>29 West 23d Street, New York</b></td> - </tr><tr> - <td class="tdl_ws1"><b>378 Wabash Avenue, Chicago</b></td> - </tr><tr> - <td class="tdl" colspan="2"><span class="smcap">viii</span>, ’05</td> - </tr> - </tbody> -</table> - -<hr class="chap" /> -<div class="chapter"> -<p class="f150"><b>THE METRIC SYSTEM.</b></p> -</div> -<div class="figcenter"> - <img src="images/ruler.jpg" alt="" width="600" height="99" /> - <p class="center">10-centimeter rule.<br /> - The upper edge is in millimeters, the lower in - centimeters and half centimeters.</p> -</div> -<hr class="r5" /> -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <thead><tr> - <th class="tdc"><span class="smcap">Units.</span></th> - <th class="tdc" colspan="2"><span class="smcap">The most commonly used divisions and multiples.</span></th> - </tr> - </thead> - <tbody><tr> - <td class="tdc" colspan="3"> </td> - </tr><tr> - <td class="tdl" rowspan="6"><span class="smcap">The Meter</span>,<br /> for <span class="smcap">Length</span></td> - <td class="tdc" rowspan="6"><img src="images/cbl-6.jpg" alt="" width="37" height="132" /></td> - <td class="tdl"><i>Centimeter</i> (cm), 1/100 meter;</td> - </tr><tr> - <td class="tdl"><i>Millimeter</i> (mm), 1/1000 meter;</td> - </tr><tr> - <td class="tdl"><i>Micron</i> (μ), 1/1000 millimeter.</td> - </tr><tr> - <td class="tdl_ws3">The micron is the unit in micrometry.</td> - </tr><tr> - <td class="tdl"><i>Kilometer</i>, 1000 meters;</td> - </tr><tr> - <td class="tdl_ws3">used in measuring roads and other long distances.</td> - </tr><tr> - <td class="tdl" rowspan="3"><span class="smcap">The Gram</span>,<br /> for <span class="smcap">Weight</span></td> - <td class="tdc" rowspan="3"><img src="images/cbl-3.jpg" alt="" width="16" height="57" /></td> - <td class="tdl"><i>Milligram</i> (mg), 1/1000 gram.</td> - </tr><tr> - <td class="tdl"><i>Kilogram</i>, 1000 grams,</td> - </tr><tr> - <td class="tdl_ws3">used for ordinary masses, like groceries, etc.</td> - </tr><tr> - <td class="tdl" rowspan="3"><span class="smcap">The Liter</span>,<br /> for <span class="smcap">Capacity</span></td> - <td class="tdc" rowspan="3"><img src="images/cbl-3.jpg" alt="" width="16" height="57" /></td> - <td class="tdl"><i>Cubic Centimeter</i> (cc), 1/1000 liter.</td> - </tr><tr> - <td class="tdl">This is more common than the correct form,</td> - </tr><tr> - <td class="tdl_ws1">Milliliter.</td> - </tr><tr> - <td class="tdl" colspan="3"><i>Divisions</i> of the <i>units</i> are indicated by Latin prefixes:</td> - </tr><tr> - <td class="tdl_ws1" colspan="3"><i>deci</i>, 1/10; <i>centi</i>, 1/100; <i>milli</i>, 1/1000.</td> - </tr><tr> - <td class="tdl" colspan="3"><i>Multiples</i> are designated by Greek prefixes:</td> - </tr><tr> - <td class="tdl_ws1" colspan="3"><i>deka</i>, 10 times; <i>hecto</i>, 100 times; <i>kilo</i>, 1000 times; <i>myria</i>, 10,000 times.</td> - </tr> - </tbody> -</table> - -<p class="f150 space-above1"><b>TABLE OF METRIC AND ENGLISH MEASURES.</b></p> - -<table border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl"><span class="smcap">Meter</span></td> - <td class="tdl_ws1" colspan="2">= 100 centimeters, 1000 millimeters, 1,000,000 microns, 39.3704 inches.</td> - </tr><tr> - <td class="tdl">Millimeter (mm)</td> - <td class="tdl_ws1" colspan="2">= 1000 microns, 1/10 millimeter, 1/1000 meter, 1/25 inch, approximately.</td> - </tr><tr> - <td class="tdl"><span class="smcap">Micron</span> (μ)</td> - <td class="tdl_ws1" rowspan="3" colspan="2">= 1/1000 mm, 1/1000000 meter (0.000039 inch), 1/25000 inch, approximately.</td> - </tr><tr> - <td class="tdl_ws1">(unit of measure in</td> - </tr><tr> - <td class="tdl_ws1"> micrometry)</td> - </tr><tr> - <td class="tdl">Inch (in.)</td> - <td class="tdl_ws1" colspan="2">= 25.399772 mm (25.4 mm, approx.).</td> - </tr><tr> - <td class="tdl"><span class="smcap">Liter</span></td> - <td class="tdl_ws1" colspan="2">= 1000 milliliters or 1000 cubic centimeters, 1 quart (approx.).</td> - </tr><tr> - <td class="tdl">Cubic centimeter (cc or cctm)</td> - <td class="tdl_ws1" colspan="2">= 1/1000 liter.</td> - </tr><tr> - <td class="tdl">Fluid ounce (8 fluidrachms)</td> - <td class="tdl_ws1" colspan="2">= 29.578 cc (30 cc, approx.).</td> - </tr><tr> - <td class="tdl"><span class="smcap">Gram</span></td> - <td class="tdl_ws1" colspan="2">= 15.432 grains.</td> - </tr><tr> - <td class="tdl bb"><span class="smcap">Kilogram</span> (kilo)</td> - <td class="tdl_ws1 bb" colspan="2">= 2.204 avoirdupois pounds (2⅕ pounds, approx.).</td> - </tr><tr> - <td class="tdl">Ounce Avoirdupois</td> - <td class="tdl_ws1 br" rowspan="2">= 28.349 grams</td> - <td class="tdl" rowspan="2"> (30 grams, approx.).</td> - </tr><tr> - <td class="tdl_ws3">(437½ grains)</td> - </tr><tr> - <td class="tdl">Ounce Troy or Apothecaries’</td> - <td class="tdl_ws1 br" rowspan="2">= 31.103 grams</td> - </tr><tr> - <td class="tdl_ws3">(480 grains)</td> - </tr><tr> - <td class="tdc bt" colspan="3"> </td> - </tr> - </tbody> -</table> - -<p class="f150 space-above1"><b>TEMPERATURE.</b></p> -<div class="blockquot"> -<p>To change Centigrade to Fahrenheit: (C. × ⁹/₅) + 32 = F. -For example, to find the equivalent of 10° Centigrade,</p> -<p class="center">C. = 10°, (10° × ⁹/₅) + 32 = 50° F.</p> - -<p>To change Fahrenheit to Centigrade: (F. - 32°) × ⁵/₉ = C. -For example, to reduce 50° Fahrenheit to Centigrade,</p> -<p class="center">F. = 50°, and (50° - 32°) × ⁵/₉ = 10° C.;</p> - -<p class="no-indent">or - 40° Fahrenheit to Centigrade,</p> -<p class="center">F. = - 40°, (- 40° - 32°) = - 72°,</p> -<p class="no-indent">whence - 72° × ⁵/₉; = - 40° C.</p> - -<p class="author">—<i>From “The Microscope” (by S. H. Gage) by permission.</i></p> -</div> -<hr class="full" /> - -<div class="footnotes"> -<p class="f150"><b>Footnotes:</b></p> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> -For apparatus, reagents, collection and preservation of material, etc., -see Appendix.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> -If spirogyra is forming fruit some of the threads will be lying -parallel in pairs, and connected with short tubes. In some of the cells -there will be found rounded or oval bodies known as <i>zygospores</i>. These -may be seen in <a href="#FIG_86">fig. 86</a>, and will be described in another -part of the book.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> -The most suitable preparations of mucor for study are made by growing -the plant in a nutrient substance which largely consists of gelatine, -or, better, agar-agar, a gelatinous preparation of certain seaweeds. -This, after the plant is sown in it, should be poured into sterilised -shallow glass plates, called Petrie dishes.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> -We should note that the coloring matter of the beet resides in the -cell-sap. It is in these colored cells that we can best see the -movement take place, since the red color serves to differentiate well -the moving mass from the cell wall. The protoplasmic membrane at -several points usually clings tenaciously so that at several places the -membrane is arched strongly away from the cell wall as shown in <a href="#FIG_24">fig. 24</a>. -While water is removed from the cell-sap, we note that the coloring -matter does not escape through the protoplasmic membrane.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> -See <a href="#CHAPTER_XXXVIII">Chapter 38</a> for organization of members of the plant body.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> -Demonstrations may be made with prepared sections of leaves,</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> -This ring and the bundles separate the stem into two regions, an outer -one composed of large cells with thin walls, known as the cortical -cells, or collectively the <i>cortex</i>. The inner portion, corresponding -to what is called the pith, is made up of the same kind of cells and is -called the <i>medulla</i>, or <i>pith</i>. When the cells of the cortex, as well -as of the pith, remain thin walled the tissue is called parenchyma. -Parenchyma belongs to the group of tissues called fundamental.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a> -In the formation of starch during photosynthesis the separated -molecules from the carbon dioxide and water unite in such a way that -carbon, hydrogen, and oxygen are united into a molecule of starch. This -result is usually represented by the following equation: CO₂ + H₂O = -CH₂O + O₂. Then by polymerization 6(CH₂O) = C₆H₁₂O₆ = grape sugar. -Then C₆H₁₂O₆-H₂O = C₆H₁₀O₅ = starch. It is believed, however, that the -process is much more complicated than this, that several different -compounds are formed before starch finally appears, and that the -formula for starch is much higher numerically than is represented by -C₆H₁₀O₅.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> -Paragraphs 156-160 were prepared by Dr. E. J. Durand.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a> -Make up three stock solutions as follows:</p> - -<table border="0" cellspacing="0" summary="Stock Solutions" cellpadding="0" > - <tbody><tr> - <td class="tdc" colspan="3">(1)</td> - </tr><tr> - <td class="tdl">Copper sulphate  </td> - <td class="tdr">9</td> - <td class="tdr"> grams</td> - </tr><tr> - <td class="tdl">Water</td> - <td class="tdr">250</td> - <td class="tdl"> cc.</td> - </tr><tr> - <td class="tdc" colspan="3">(2)</td> - </tr><tr> - <td class="tdl">Caustic potash</td> - <td class="tdr">30</td> - <td class="tdr"> grams</td> - </tr><tr> - <td class="tdl">Water</td> - <td class="tdr">250</td> - <td class="tdl"> cc.</td> - </tr><tr> - <td class="tdc" colspan="3">(3)</td> - </tr><tr> - <td class="tdl">Rochelle salts</td> - <td class="tdr">49</td> - <td class="tdr"> grams</td> - </tr><tr> - <td class="tdl">Water</td> - <td class="tdr">250</td> - <td class="tdl"> cc.</td> - </tr> - </tbody> -</table> - -<p>For Fehling’s solution take one volume of each of (1), (2), and (3), -and to the mixture add two volumes of water.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11]</span></a> -This solution of taka diastase should be made up cold. If -it is heated to 60° C. or over it is destroyed.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12"><span class="label">[12]</span></a> -Calcium is not essential for the growth of the fungi.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a> -For example, silicon is used by some plants in strengthening supporting -tissues. Buckwheat thrives better when supplied with a chloride.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span class="label">[14]</span></a> -Evidence points to the belief that certain cells of the host form -substances which attract, chemitropically, the fungus threads, and that -in these cells the fungus threads are more abundant than in others. -Furthermore in the vicinity of the nucleus of the host seems to be the -place where these activities are more marked.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_15_15" id="Footnote_15_15"></a><a href="#FNanchor_15_15"><span class="label">[15]</span></a> -In lieu of Arisæma make a practical study of the pea. See paragraph 216<i>a</i>.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_16_16" id="Footnote_16_16"></a><a href="#FNanchor_16_16"><span class="label">[16]</span></a> -Dissolve a half gram of osmic acid in 50 <i>cc.</i> of water -and keep tightly corked when not using.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_17_17" id="Footnote_17_17"></a><a href="#FNanchor_17_17"><span class="label">[17]</span></a> -In Engler & Prantl’s Pflanzenfamilien, Wille uses the term class -for these principal subdivisions of the algæ. Systematists are not yet -agreed upon a uniform use of the terms.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_18_18" id="Footnote_18_18"></a><a href="#FNanchor_18_18"><span class="label">[18]</span></a> -See Bot. Gaz., 17, 389, 1892.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_19_19" id="Footnote_19_19"></a><a href="#FNanchor_19_19"><span class="label">[19]</span></a> -<b>Class Myxomycetes</b>, or <b>Mycetozoa</b>.—To this -class belong the “slime molds,” low organisms consisting of masses of -naked protoplasm which flows among decaying leaves and in decaying -wood, coming to the surface to fruit. The fruit in many cases resembles -miniature puff-balls, and these plants were formerly classed with -the puff-balls. The spores germinate by forming swarm spores which -unite to form a small plasmodium, which in turn grows to form a large -plasmodium or protoplasmic mass. It is doubtful if they are any more -plant than animal organisms. Examples: Trichia, Arcyria, Stemonitis, -Physarum, Ceratiomyxa, etc., on rotten wood; Plasmodiophora brassicæ -is a parasite causing club foot of cabbage, radishes, etc. It lives -within the roots, causing large knots and swellings on the same.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_20_20" id="Footnote_20_20"></a><a href="#FNanchor_20_20"><span class="label">[20]</span></a> -As suborder in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_21_21" id="Footnote_21_21"></a><a href="#FNanchor_21_21"><span class="label">[21]</span></a> -As suborder in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_22_22" id="Footnote_22_22"></a><a href="#FNanchor_22_22"><span class="label">[22]</span></a> -As suborder in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_23_23" id="Footnote_23_23"></a><a href="#FNanchor_23_23"><span class="label">[23]</span></a> -The Uredinales and Auriculariales in Engler and Prantl are -placed in order, Auriculariineæ.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_24_24" id="Footnote_24_24"></a><a href="#FNanchor_24_24"><span class="label">[24]</span></a> - The Uredinales and Auriculariales in Engler and Prantl are -placed in order, Auriculariineæ.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_25_25" id="Footnote_25_25"></a><a href="#FNanchor_25_25"><span class="label">[25]</span></a> -May be used as an alternate study for marchantia.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_26_26" id="Footnote_26_26"></a><a href="#FNanchor_26_26"><span class="label">[26]</span></a> - As subclass in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_27_27" id="Footnote_27_27"></a><a href="#FNanchor_27_27"><span class="label">[27]</span></a> -As subclass in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_28_28" id="Footnote_28_28"></a><a href="#FNanchor_28_28"><span class="label">[28]</span></a> -As subclass in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_29_29" id="Footnote_29_29"></a><a href="#FNanchor_29_29"><span class="label">[29]</span></a> -Called the calyptra.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_30_30" id="Footnote_30_30"></a><a href="#FNanchor_30_30"><span class="label">[30]</span></a> -As subclass in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_31_31" id="Footnote_31_31"></a><a href="#FNanchor_31_31"><span class="label">[31]</span></a> -As subclass in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_32_32" id="Footnote_32_32"></a><a href="#FNanchor_32_32"><span class="label">[32]</span></a> -As subclass in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_33_33" id="Footnote_33_33"></a><a href="#FNanchor_33_33"><span class="label">[33]</span></a> -As subclass in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_34_34" id="Footnote_34_34"></a><a href="#FNanchor_34_34"><span class="label">[34]</span></a> -As class Filicales in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_35_35" id="Footnote_35_35"></a><a href="#FNanchor_35_35"><span class="label">[35]</span></a> -As class Equisetales in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_36_36" id="Footnote_36_36"></a><a href="#FNanchor_36_36"><span class="label">[36]</span></a> -As class Lycopodiales in Engler and Prantl.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_37_37" id="Footnote_37_37"></a><a href="#FNanchor_37_37"><span class="label">[37]</span></a> -<b>Suggestions to the teacher.</b>—In the study of the flowering plants -in the secondary school and in elementary courses three general topics -are suggested. 1st, the study of the form and members of the plant and -their arrangement, as in Chapters XXXVIII-XLV. 2d, the study of a few -plants representative of the more important families, in order that the -members of the plant, as studied under the first topic, may be seen in -correlation with the plant as a whole in a number of different types. -3d, the study of plants in their relation to environment, as in <a href="#CHAPTER_XLVI">Chapter -XLVI</a>. The first and second topics can be conducted consecutively in the -classroom and laboratory. The third topic can be studied at opportune -times during the progress of topics 1 and 2. For example, while -studying topic 1 excursions can be made to study winter conditions of -buds, shoots, etc., if in winter period, or the relations of leaves, -etc., to environment, if in the growing period. While studying topic 2 -excursions can be made to study flower relations, and also vegetation -relations to environment (see Chapters XLVI-LVII of the author’s -“College Text-book of Botany”). It is believed that a study of these -three general topics is of much more value to the beginning student -than the ordinary plant analysis and determination of species.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_38_38" id="Footnote_38_38"></a><a href="#FNanchor_38_38"><span class="label">[38]</span></a> -It is interesting to note that in some foliage shoots the stem is -entirely subterranean. See discussion of the bracken fern and sensitive -fern in <a href="#CHAPTER_XXXIX">Chapter XXXIX</a>.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_39_39" id="Footnote_39_39"></a><a href="#FNanchor_39_39"><span class="label">[39]</span></a> -Some fibers occur also very frequently in the Fundamental System, -forming bundle-sheaths, or strands of mechanical tissue in the cortex.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_40_40" id="Footnote_40_40"></a><a href="#FNanchor_40_40"><span class="label">[40]</span></a> -Besides these specialized shoots for the storage of food, -food substances are stored in ordinary shoots. For example, in the -trunks of many trees starch is stored. With the approach of cold -weather the starch is converted into oil, in the spring it is converted -into starch again, and later as the buds begin to grow the starch -is converted into glucose to be used for food. In many other trees, -on the other hand, the starch changes to sugar on the approach of -winter.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_41_41" id="Footnote_41_41"></a><a href="#FNanchor_41_41"><span class="label">[41]</span></a> -This topic was prepared by Dr. K. M. Wiegand.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_42_42" id="Footnote_42_42"></a><a href="#FNanchor_42_42"><span class="label">[42]</span></a> -See discussion of Tropophytes in <a href="#CHAPTER_XLVI">Chapter XLVI</a>.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_43_43" id="Footnote_43_43"></a><a href="#FNanchor_43_43"><span class="label">[43]</span></a> -<a href="#CHAPTER_V">Chapter V</a>, and Organization of Tissues in -<a href="#CHAPTER_XXXVIII">Chapter XXXVIII</a>.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_44_44" id="Footnote_44_44"></a><a href="#FNanchor_44_44"><span class="label">[44]</span></a> -Some of the different terms used to express the kinds of -compound leaves are as follows:</p> - -<p><i>Unifoliate</i> (for a single leaflet, as in orange and lemon where -the compound leaf is greatly reduced and consists of one pinna -attached to the petiole by a joint). <i>Bifoliate</i> for one with two -leaflets; <i>trifoliate</i> for one with three leaflets, as in the clover; -<i>plurifoliate</i> for many leaflets. <i>Odd pinnate</i> for a pinnate leaf with -one or more pairs of leaflets and one odd leaflet at the end.</p> - -<p>So leaves are <i>palmately bifoliate</i>, etc., <i>pinnately bifoliate</i>, etc. -<i>Decompound</i> leaves are those where they are more than twice compound, -as <i>ternately decompound</i> in the common meadow rue (Thalictrum).</p> - -<p><i>Perfoliate</i> leaves are seen in the bellwort (Uvularia), <i>connate -perfoliate</i>, as in some of the honeysuckles where the bases of opposite -leaves are joined together around the stem. <i>Equitant</i> leaves are found -in the iris, where the leaves fit over one another at the base like a -saddle.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_45_45" id="Footnote_45_45"></a><a href="#FNanchor_45_45"><span class="label">[45]</span></a> -The most remarkable case is that of the “telegraph” plant (Desmodium -gyrans). Aside from the day and night positions which the leaves -assume, there is a pair of small lateral leaflets to each leaf which -constantly execute a jerky motion, and swing around in a circle like -the second hand of a watch.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_46_46" id="Footnote_46_46"></a><a href="#FNanchor_46_46"><span class="label">[46]</span></a> -Seedlings are usually very sensitive to light and are good -objects to study.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_47_47" id="Footnote_47_47"></a><a href="#FNanchor_47_47"><span class="label">[47]</span></a> -For a fuller discussion of this subject by the author see Chapters -XLVI-LVII of his “College Text-book of Botany” (Henry Holt & Co.).</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_48_48" id="Footnote_48_48"></a><a href="#FNanchor_48_48"><span class="label">[48]</span></a> -<b>οῖκος</b> = house, and <b>λόγος</b> = discourse.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_49_49" id="Footnote_49_49"></a><a href="#FNanchor_49_49"><span class="label">[49]</span></a> -Term used by Schimper.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_50_50" id="Footnote_50_50"></a><a href="#FNanchor_50_50"><span class="label">[50]</span></a> -See the author’s “College Text-book of Botany.” Chapter XLIX.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_51_51" id="Footnote_51_51"></a><a href="#FNanchor_51_51"><span class="label">[51]</span></a> -<b>ἔδαφος</b> = ground.</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_52_52" id="Footnote_52_52"></a><a href="#FNanchor_52_52"><span class="label">[52]</span></a> -For a full discussion of forest societies see Chapter L in -the author’s “College Text-book of Botany.”</p></div> - -<div class="footnote"><p class="no-indent"> -<a name="Footnote_53_53" id="Footnote_53_53"></a><a href="#FNanchor_53_53"><span class="label">[53]</span></a> -See Chapter LIV of the author’s “College Text-book of Botany.”</p></div> -</div> - -<div class="transnote bbox epubonly space-above2"> -<p class="f120 space-above1">Transcriber’s Notes:</p> -<hr class="r5" /> -<p>The cover image was created by the transcriber, and is in the public domain.</p> -<p>The illustrations have been moved so that they do not break up - paragraphs and so that they are next to the text they illustrate.</p> -<p>Typographical errors have been silently corrected.</p> -</div> -<div style='display:block; margin-top:4em'>*** END OF THE PROJECT GUTENBERG EBOOK ELEMENTARY BOTANY ***</div> -<div style='text-align:left'> - -<div style='display:block; margin:1em 0'> -Updated editions will replace the previous one—the old editions will -be renamed. -</div> - -<div style='display:block; margin:1em 0'> -Creating the works from print editions not protected by U.S. copyright -law 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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