ALBERT R. MANN LIBRARY New York State Colleges of Agriculture and Home Economics Cornell UniversityCornell University Library QK 47.B57 1888 3 1924 001 794 100 31924001794100THE American S®ence Series V FOR SCHOOLS AND COLLEGES. The principal objects of the series are to supply the lack—in some subjects very great—of authoritative books whose principles are, so far as practicable, illustrated by familiar American facts, and also to supply the other lack that the advance of Science perennially creates, of text-books which at least do not contradict the latest generalizations. The books of this series systematically outline the field of Science, as the term is usually employed with reference to general education. The scheme includes an Advanced Course, a Briefer Course, and an Elementary Course. In ordering be careful to state which course is desired—Advanced, Briefer, or Elementary. Physics. By George F. Barker, Professor in the University of Pennsylvania. In Preparation. Chemistry. By Ira Remsen, Professor in the Johns Hopkins University. Briefer Course, 387 pp. Elementary Course, 272 pp. Astronomy. By Simon Newcomb, Professor in the Johns Hopkins University, and Edward S. Holden, Director of the Lick Observatory. Advanced Course, 512 pp. Briefer Course, 352 pp. Biology. By William T. Sedgwick, Pro- fessor in the Massachusetts Insti- tute of Technology, and Edmond B. Wilson, Professor in Bryn Mawr College. Part I,—Introductory, 193 pp. Botany. By C. E. Besset, Professor in the University of Nebraska; formerly in the Iowa Agricultural College. Advanced Course, 611 pp. Briefer Course, 292 pp. Zooloyy. By A. S. Packard, Professor of Zoology and Geology in Brown University. Advanced Course, 722 pp. Briefer Course, 338 pp. Elementary Course, 290 pp. The Unman Body. By H. Newell Martin, Profes- sor in the Johns Hopkins Univer- sity. Advanced Course, 621 + 34 pp. Copies without the Appendix on Reproduction will be sent when specially ordered. Briefer Course, 377 pp. Elementary Course, 261 pp. Political Economy. By Francis A. Walker, Presi- dent Massachusetts Institute of Technology. Advanced Course, 537 pp. Briefer Course, 415 pp. HENRY HOLT & CO., Publishers, NEW YORK.AMERICAN SCIENCE SERIES BOTANY FOR HIGH SCHOOLS AND COLLEGES BY CHARLES E. BESSEY, Ph.D., PROFESSOR OF BOTANY IN THE UNIVERSITY OF NEBRASKA; FORMERLY PROFESSOR OF BOTANY IN THE IOWA AGRICULTURAL COLLEGE; ASSOCIATE EDITOR OF THE “AMERICAN NATURALIST'’ (DEPARTMENT OF BOTANY) FIFTH EDITION, REVISED NEW YORK HENRY HOLT AND COMPANY 1888Copyright, 1880, BY Hemet hoi,t & Co.PREFACE. This book is designed to serve as an Introduction to the Study of Plants. It does not profess to give a complete account of the Vegetable Kingdom, but only such an outline as will best subserve the pur- poses of the work. In its preparation there have been kept in view the wants of the large number, in the schools and out, who wish to obtain, as a branch of a liberal cul- ture, a general knowledge of the structure of plants, with some idea as to their classification into the larger divisions and subdivisions of the Vegetable Kingdom. For this class of students and general xeaders, what is here given will in most cases be amply sufficient to enable any one to understand the greater part of the current biological literature, in so far as it relates to vegetable organisms. For the student who desires to pursue the subject further, or who intends to make botany a special study, this book aims to lead him to become himself an observer and investigator, and thus to obtain at first hand his knowledge of the anatomy and physiology of plants: accordingly the presentation of the matter has been made such as to tit the book for constant use in the Laboratory, the text supplying the outline sketch, which may be tilled up by each student, with the aid of the scalpel and compound microscope. This book is an expansion and considerable modi- fication of the material of several courses of lecturesIV PREFACE. annually delivered to college students. In general plan, Part I. follows pretty nearly that of Sachs’ ad- mirable “Lehrbuch,” and in many instances it has seemed to me that I could not do better than to adopt the particular, treatment which a subject has received at the hands of the distinguished German botanist. This has been rendered possible through the liberality of my publishers, and the courtesy of' Engelmann of Leipzig, the publisher of many of Sachs’ works, by which many of the cuts of the “Lehrbuch” are here reproduced. This book will thus, to a considerable extent, serve as an introduc- tion to that work. Free use has also been made of the recent works of Tie Bary, Hofmeister, Strasbur- ger, Nageli, Schwendener, and others, to whose writ- ings numerous references are made. In Part II. the general disposition of the lower plants is a considerable modification of that proposed by Sachs ; that of the higher plants is made to con- form to the system of classification in vogue in this country and in England, as outlined in Dr. J. D. Hooker’s “Synopsis of the Classes, Sub-classes, Co- horts and Orders,” in the English edition of Le Maout and Decaisne’s “Traite Generale de Botan- ique,” and as given much more fully in Bentham and Hooker’s still unfinished “ Genera Plantarum.” The notes upon the economic values of the more impor- tant plants of each order are based upon my own lec- tures upon Economic Botany. I have also freely used the similar notes in Le Maout and Decaisne’s work, cited above; Balfour’s “Class-Book of Bot- any,” Archer’s “Economic Botany,” Smith’s “Do- mestic Botany,” Laslett’s “Timber and Timber Trees,” etc., etc. Necessarily, there is but little that is really new in a treatise like this. Aside from a more or less important and original arrangement of the matter, so as tofKEFAVE. v secure a more logical presentation of the subject, there are but two considerable innovations, consist- ing (I.) in the recognition (in Chapter VI.) of seven quite well marked kinds of tissue. In this, however, while not adopting De Bary’s classification, I have followed his method of treating the subject, as given in his recent work on the comparative anatomy of plants (“ Vergleichende Anatomie der Vegetations- organe der Phanerogamen und Fame.”) (II.) The second considerable innovation occurs in Part II. ; it consists in raising the Protophyta, Zygosporese, Oos- porem and Carposporese to the dignity of Primary Divisions of the vegetable kingdom, co-ordinate with the Bryo] tliyta, Pteridophyta and Phanerogamia. The usefulness of both of these departures from the common practice has been subjected to the test of the laboratory, and the lecture and class-room, with the most satisfactory results ; and I am led to hope that in the hands of others they may also serve to give a clearer and more accurate notion of the struc- ture of plants. Should they do this they will need no further apology or defense. Of the illustrations, many are entirely new ; many others have been re-drawn, from various sources, with slight modifications, expressly for this work, and all from other sources are specially acknowl- edged in their places. I desire here to acknowledge my indebtedness to Dr. Asa Gray, whom it is an honor to own as my sometime teacher, for kindly aid and counsel in the preparation of the lectures upon which this work is based ; and in the same way I am indebted to Dr. G. L. Goodale, Dr. W, G. Farlow and Professor A. N. Prentiss. For aid in the immediate preparation of the material for the press, acknowledgment is due many of my personal friends : Mr. J. C. Arthur fur- nished the original drawings of the water-pores ofVI PREFACE. Fuchsia, and of various tissues of Echinocystis; Professor H. L. Smith, of Hobart College, New York, contributed the sketch of the classification of the Diatomacefe ; Dr. T. F. Allen furnished a synop- sis of the classification of the Characese ; Dr. B. D. Halsted also furnished material and notes upon our native species of Characese ; my colleague, Professor W. H. Wynn, kindly determined some of the more difficult etymologies; to my wife I am deeply in- debted for efficient aid in the laborious tasks of proof-reading and indexing. Should this book serve to interest the student in the study of plants as living things, should it succeed in directing him rather to the plants themselves than to the books which have been written about them, should it contribute somewhat to the general read- er’s knowledge of the structure and relationship of the plants around him, the objects kept in view in its preparation will have been attained. C. E. B. April 12, 1880. PREFACE TO THE FIFTH EDITION. In the preceding editions, which appeared, respectively, in 1881, 1883, and 1885, a considerable number of correc- tions and additions were made. In the present edition that modification of the names of the second, third, and fourth branches of the Vegetable Kingdom (Zygophyta. Oophyta, Carpophyta) heretofore used in the “ Essentials of Botany,” has been adopted, and a number of important paragraphs have been added as foot-notes. C. E. B. University op Nebraska, Lincoln, December 24, 1887.CONTENTS. PART I. GENERAL ANATOMY AND PHYSIOLOGY. CHAPTER I. Protoplasm. ] General Characters—Chemical Composition—Consistence—Power of Imbibing Water—Vacuoles—Physical Activity—Naked Protoplasm—Protoplasm Enclosed in Cell Walls ....... CHAPTER II. The Plant-Cell. General Statement—Ectoplasm and Endoplasm—Bands and Strings of Protoplasm—Nucleus—Size of Cells—Forms of Cells—The Cell the Unit in Plants............................. CHAPTER III. The Cell-Wall. Composition—Growth in Surface—Growth in Thickness—The Markings on Cell Walls—Theories as to the Mode of Thick- ening—Stratification of the Cell Wall—Formation of Chem- ically Different Layers—The Formation of Mucilage—Incom- bustible Substances in the Wall....................... CHAPTER IV. The Formation op New Cells. Cell-Formation by Division: (a) Fission; (6) Internal Cell-Forma- tion—Cell-Formation by Union—Examples.................via CONTENTS. CHAPTER V. The Products of the Cell. PAGE | 1. Chlorophyll—§ 2. Starch, Composition, Form, Molecular Structure—Grauulose and Starch-Cellulose — Formation of Starch Granules in the Chlorophyll-Bodies—Formation of Ordinary Starch Granules—§ 3. Aleurone and Crystalloids— § 4. Crystals in Cells—§ 5. The Cell Sap—§ 6. Oils, Resins, Gums, Acids and Alkaloids......................:.. 50 CHAPTER VI. Tissues. § 1. The Various Aggregations of Cells : (a) Single Cells ; (b) Fam- ilies ; (c) Fusions ; (cl) Tissues ; The Cell-Wall in Tissues— § 2. The Principal Tissues—Parenchyma—Collencliyma— Sclereuchyma—Fibrous Tissue—Laticiferous Tissue — Sieve Tissue—Traclieary Tissue—§ 3. The Primary Meristem. 65 CHAPTER VII. The Tissue Systems. § 1. The Differentiation of Tissues into Systems—§2. The Epi- dermal System of Tissues—Epidermis—Tricliomes—Stomata — § 8. The Fibro-Vascular System of Tissues—General Structure—The Fibro-Vascular Bundles of Pteris, Polypodium, Adiantum, Equisetum, Selaginella, Lycopodium, Zea, Acorus, Ricinus and Ranunculus—Of Xylem and Phloem—Collateral, Concentric, and Radial Bundles — Development of Fibro- Vascular Bundles—§ 4. The Fundamental System—The Tis- sues it Contains—Cork—Lenticels................. 89 CHAPTER VIII. Intercellular Spaces, and Secretion Reservoirs..... 128. CHAPTER IX. The Plant-Body. g 1. Generalized Forms—Thallome—Caulome—Trichome—Root--. Particular Relations of Pliyllome to Caulome—General Modes of Branching of Members—g 2. Stems—The Punctum Veget.a- tionis—Buds—Adventitious Stems—g 3. Of Leaves in General —g 4. The Arrangement of Leaves—g 5. The Internal Struc- ture of Leaves—g 6. The Roots of Plants, Structure, Root-Cap, Growth—Formation of New Roots—Arrangement of Roots... 133CONTENTS. ix. CHAPTER X. The Chemical Constituents of Plants. TAGE § 1. The Water in the Plant—Amount of Water in Plants—Water in the Protoplasm—Water in the Cell Walls—Water in the Intercellular Spaces—Equilibrium of the Water in the Plant— Disturbance of Equilibrium—Evaporation of Water—Amount of Evaporation—The Movement of the Water in the Plant —§ 2. As to Solutions—§ 3. Plant Food—The Most Important Elements—The Compounds Used—How the Food is Obtained —How Transported in the Plant......................... 166. CHAPTER XI. The Chemical Processes in the Plant. £ 1. Assimilation—§ 2. Metastasis—Its General Nature—Trans- formation of Starch—Nutrition of Protoplasm—The Storing of Reserve Material—The Use of Reserve Material—The Nutri- tion of Parasites and Saprophytes—The Formation of Alkaloids —Results of Metastasis................................ 178 CHAPTER XII. The Relations of Plants to External Agents. § 1. Temperature—General Relations—Absorption of Water as Af- fected by Temperature—Evaporation—Assimilation—Metasta- sis-Death from too High a Temperature—Death from too Low a Temperature—§2. Light: General Relations of Light to Assimilation, Light, and Metastasis—£ 3. Heliotropism— £ 4. Geotropism—§ 5. Certain Movements of Plants : General Statement, Spontaneous Movements, Movements Dependent upon External Stimuli, Movements of Nutation, Movements of Torsion........................................ 184 PART II. SPECIAL ANATOMY AND PHYSIOLOGY. CHAPTER XIII. Classification. Principles of a Natural Classification—Critical—A Comparison of several Systems............................................. 202X CONTENTS. CHAPTER XIV. The Protopiiyta. § 1. Myxomycetes—§ 2. Schizomycetes—§ 3. Cyanophyce® CHAPTER XV. The Zygophyta. § 1. Zoospore®—§ 2. Conjugate................ PAGE 206 220 CHAPTER XVI. The Oophyta. § 1. Volvox and its Allies—§ 2. CEdogonie®—§ .3. Cceloblaste®— § 4. Fucace®..................................243 CHAPTER XVII. The Cabpofhyta. § 1. Coleocltete—§ 2. Floride®—§ 3. Ascomycetes—§ 4. Basidio- mycetes—§ 5. Charace®—§ 6. The Classification of Tliallo- phytes........................................... 270 CHAPTER XVIII. The Bryopiiyta. § 1. Hepatic®—g 2. Musci........................ 341 CHAPTER XIX. The Pteridophyta. § 1. Equisetin®—§ 2. Filicin®—§ 3. Lycopodin®....... 361 CHAPTER XX. The Phanerogamia. § 1. General Characters—g 2. Gytnnosperm®—g 3. Angiosperm® —Glossology of Angiospernis—The Tissues of Angiosperms— Classification and Economic Botany of Monocotyledons—Class- ification and Economic Botany of Dicotyledons.389 CHAPTER XXI. Concluding Observations. The Number of Species of Plants—The Affinities of the Groups of Plants—The Distribution of Plants in Time.......................566BOTANY, PART I. GENERAL ANATOMY AND PHYSIOLOGY. CHAPTER I. PKOTOPLASM. 1.—If we examine a thin slice of any growing part of a plant (Fig. 1) under a microscope of a moderately high power (400 to 500 diameters), there may be seen large num- bers of cavities which are more or less filled with an almost transparent semi-fluid substance. In very young parts, as in buds and the tips of roots, this substance entirely fills the cavities, and makes up almost the whole mass, while in older parts it occurs in less quantity, and usually disappears in quite old tissues. This substance is the living portion of the plant, the active, vital thing which gives to it its sensi- bility to heat, cold, and other agents, and the power of mov- ing, of appropriating food, and of increasing its size ; it is, in fact, that ivhich is sensitive, which moves, appropriates food, and increases in size. This sensitive, moving, assimilating, and growing substance is named Protoplasm.* It is a fact of great biological interest that in animals the essential constituent of all living parts is a substance similar to the protoplasm of plants. We cannot distinguish the two by any chemical or physical tests, and can only say that, taken as a whole, the protoplasm of plants * So named by its discoverer, Dr. Hugo Von Mohl, in 1846. It is the Bioplasm of Dr. Lionel Beale and his followers.2 BOTANY. •differs from that of animals in its secretions. And yet these secre- tions are not strictly confined to plants ; cellulose, starch, chlorophyll, and other products of vegetable protoplasm formerly regarded as pe- culiar to plants are now known to occur in undoubted animals. Botanists and zoologists have laboredlong in vain to discover absolute differences between the animal and tbe vegetable kingdoms; between the higher plants and the higher animals there are great and constant differences.- in none of the higher animals, for ex- ample, is chlorophyll produced; but in the lower orders of both kingdoms not one of the differences observed to hold between the higher plants and animals exists. 2.—The exact chemical compo- sition of protoplasm lias not hith- erto been made out, but it is known to be an albuminous, watery substance, combined with a small quantity of ash. It is probably a complex mixture of chemical compounds, and not a single compound. It contains at some time or another all the chem- ical constituents of plants. Oil, granules of starch, and other or- ganic substances are frequently present in it, but they are to be re- garded as products rather than proper constituents of protoplasm. Fig. 1.—A little more than half of -a longitudinal section of the apex of , v i , , , a young root of the Indian corn. (®) ” &ter makes up a considerable The part above s is the body of the part of tbe bulk of ordinary protoplasm, root, that below it is the root-cap ; , . , , , , . v, thick outer wall of the epidermis; smd. is much more abundant in its m young pith-cells;/, voung wood- active than in its dormant conditions, cells ; g, a young vessel; s, a, inner _ . , younger part of root-cap ; a, a, out- lu the protoplasm oi Fuhqo vanans Iach!rr part 0f root-cap'-After (one of the Slime Moulds) just before tbe formation of its spores there is 70 per cent of water ; in dry seeds, on the other hand, the amount is not more than about 8 to 10 per cent. (b) As to its molecular constitution, Strasburger bolds* that proto- plasm is composed of minute solid particles (not, however, of a crystal- -line form), separated from each other by layers of water (see Cell-wall * “ Studien fiber Protoplasma,” 1876.PROTOPLASM. 3 paragraph 37, and Starch, paragraph 69). The thicker the layers of water are, the more watery is the protoplasm, and vice versa. (c) Tests. 1. If a protoplasmic mass is moistened with a solution of iodine, it at once assumes a deep yellow or brown color. 2. If treated with a solution of copper sulphate aud afterward-* with potash, it assumes a dark violet color. Fig. 2.—Parenchyma cells from the central cortical layer of the root of Frttllim ic imperialis, longitudinal sections. A, very young cells lying close above the apex ol the root, still without cell sap or vacuoles. B, cells of the same description about two millimetres above the apex of the root; by the entrance of cell sap the vacuoles a, a, s have been formed. 0. cells of the same description about seven to eight mil- limetres above the apex of the root. In all the figures, h, cell-wall; p. protoplasm ; k. nucleus ; Jck. nucleoli; s, vacuoles ; x y. swelling of the nucleus under the influ- ence of the water in preparing the specimen. X 500.—After Sachs. 3. Treated with a solution of sugar, and afterwards with sulphuric acid, it becomes rose-red. 4. The presence of protoplasm may be demonstrated in a tissue by the application of various staining fluids, as magenta, carmine, etc.4 BOTANY. 5. In a dilute solution of potash protoplasm is dissolved ; if, how- ever, the solution is concentrated, the form of the protoplasm remains unaltered for weeks, but upon the addition of water it at once dissolves. 6. Protoplasm coagulates upon the application of heat (50 degrees Centigrade), or when immersed in alcohol or dilute mineral acids. 3.—In consistence protoplasm is a soft-solid substance, varying from an almost perfect fluidity on the one hand to a considerable degree of hardness and even brittleness on the other. This difference in con- sistence is mainly due to the vary- ing amounts of water imbibed by it, hence the same mass may at different times vary greatly in this regard. Generally there may be seen in protoplasm a large number of minute granules enclosed in a transparent medium (Pig. 2, A) ; in some instances, however, the granules are entirely wanting, or nearly so. By the withdrawal of these granules for a little distance from the surface toward the cen- tre, a mass of granular protoplasm Fisp 3.—Optical section of a re (the endoplasm) may appear to be tractmg branch of a large pianino- surrounded by a hyaline envelope, dium of Fuligo varUms (.JElhalium ., . , . , . r septicum of authors); the narrow the protoplasmic SKin, OY CCtO- inner granular mass of protoplasm TT , 7 • 7 , £ • is seen to be surrounded by a broad plasm (the HautSClllcIlt 01 Pl’ingS- wtuchlnthtj^caecisradiahystmik- heim, and Hauptplasmci of Stras- the body y the6 plaLSSfhs burger) (Pig. 3). It is almost al- fiifo'rarnmnded^by (rh$?n”ei- ways formed when protoplasm is veiope. x 200.—After Hofmeieter. exposed in water or air ; but it, or something very much like it, appears to he generally present, even in closed cells. (a) The fine granules are probably not proper constituents of proto- plasm, but finely divided assimilated food-materials immersed in the proper protoplasm, whicli is itself colorless and transparent. Proto- plasm destitute of granules may he found in the cotyledons of the bean (Plmseolus), In other cases, e.g., in the zygospores of Spirogyra, the granular and coloring matters are so abundant that the hyaline basis can no longer he distinguished.PROTOPLASM. 5 (6) fetrasburger* maintains that the hyaline envelope is not simply a portion of the basis or ground substance of the protoplasm deprived of its granules, but that it is a definite modification of it, and endowed with various properties quite distinct from those of the ground sub- stance. 4. —Active protoplasm possesses the power of imbibing water into its substance, and as a consequence, of increasing its mass. This power varies with the changes in external, and also in internal conditions ; many seeds, for example, which do not swell up (through absorbing water) in cold water, will do so when placed in that of a higher tempera- ture ; but in some seeds it appears that imbibition of water will not take place until after a period of rest. 5. —-When the amount of water imbibed is so great that the protoplasm may be said to be more than saturated with it, the excess is separated within the protoplasmic mass in the form of rounded drops, termed Vacuoles (Vacuoli). In closed cells these may become so large and abundant as to be separated only by thin plates of the protoplasm (Fig. 3, B). As such vacuoles become still larger, the plates are broken through, and eventually we may have but one large vacuole surrounded by a thin layer of protoplasm, which lines the interior of the cell wall (Fig 2, C). In this way some masses of protoplasm assume a bladder-like or vesicular form, so unlike their original form that until very recently their real nature has not been understood.! Frequently when the plates which separate vacuoles break down, instead of breaking entirely away they become pierced with several large openings, leaving strings or bands of protoplasm which extend across the cavity. Occasionally, when vacuoles unite, small masses of the protoplasm which previously separated them become detached as free rounded * “ Studien fiber Protoplasma,” 1876. See also Qr. Jour. Mia. Science, 1877, p. 124 et seq. f Vou Mold gave to this layer the name Primordial Utricle, and it is still frequently used, but the term is objectionable, and Sachs’ name of Protoplasmic Sac is to be preferred. Treatment with glycerine, strong alcohol, or any other substance which removes the water, will cause the protoplasmic sac to contract and be'come visible.6 BOTANY. masses in the large vacuole ; these again may produce vacuoles within themselves, and thus give rise to a peculiar and at first sight perplex- ing structure (Fig. 4). 6.—The most remarkable peculiarity of living protoplasm is its physical activity. When the proper conditions are pres- ent, a living mass of protoplasm is apparently never at rest, but, on the contrary, continually altering its shape and changing the position of its constit- uent parts. The move- ments are all of the same general nature; each one maybe regard- ed as the aggregate re- sult of the chemical and physical changes taking place in the substance of the protoplasm. We may study the ac- tivity of protoplasm under two conditions, which will give us the two cases. (1.) The Activity of Naked Pro- Fig. 4.— Forms of the protoplasm contained in toplasm, and (2.) The cells. A and B, of Indian Com tZea main); A, A £ -js , cells from the first leal’-shrarh of a germinating Activity 01 1 rotoplasni plant, showing the frothy condition of the proto- ^r,nir.Qn)q * n Poll wall plasm, the many vacuoles separated by thin tnciObeCL 111 a v^eil-wail. plates. B, cells from the first internode of the 17 rn|~ft a n-HTri+Tr rtf germinating pi nt; the protoplasm is broken up ' * J--Llv /xoiiviiy 01 into many rounded masses, in each of which there N aked Protoplasm, is a vacuole, b ; these are the so-called “ sa, contracted protoplasm. After Sachs. ^ Slime Moulds, present the best examples of the activity of naked vegetable protoplasm. In their plasmodia (as the masses of naked proto- plasm are called), many kinds of movements may be observed, the commonest of which is streaming. In plasmodia com- posed of thin (i.e., watery) protoplasm, streams or currents of the latter may be seen running in various directions1 PROTOPLASM MO VEMKA'TS. . 7 (Fig. 5). The streams arc made clearly risible by the motion of the grannies which are carried along by the moving hya- line portion of the protoplasm. After running in one Fig. 5.—A email mass of the naked protoplasm (plasmodium) of Didymium ser pula ; the arrows show the direction of the currents, x 30.—After Hofmeister. direction for some minutes (about five) the current stops, and then it usually sets in an exactly opposite direction for about the same length of time, and carries back the previ- ously moved protoplasm.8 BOTANY. i The formation of the new current may he explained as follows: Let A..........B he a stream in which the movement is from A to B; clearly ihere will be an aggregation of protoplasm about B. When the current in the direction A B stops, the new one, in the reverse direction, B A, begins at A, by the movement toward it of the particles nearest to it; next the particles further off move toward A ; after this, those still further off, and so on. The current extends back- ward. So, too, when a stream begins de now, it is propagated back, ward from the point of beginning. , AS * 8.—Mass-Movement (Amoeba-Movement). In the flowing back and forth in the streams the movement may be greater in one direction than in the other; this causes a slow motion of the whole plasmodium in the direction of the greatest movement. When this takes place in the case of streams which begin in the mar- gin of the plasmodium, protuberances of vari- ous shapes arise; these may be extended into branches (pseudopo- dia), which may again be branched one or Fig. 6.—Outline of a plasmodium of Didymium times. By tile spjmla forming pseudopodla The heavy black anastomosing of these line indicates the outline at the beginning ol the ° observation ; the pseudopodium a-b formed in 8 brandies a COmpl&X seconds, c-d in 30, and c-e in 55 seconds. X 10. . . —After Hofmeister. moving and changing network is formed. (See Fig. 140, page 208) There is pos- sibly to he separated from the above-described mass-move- ment that more or less rapid change of external contour which has, from its resemblance to the motions of the Amoeba, been denominated the Amoeba-movement (Fig. 6). It is best observed in the so-called “Amoeba-form ” stage of the swarm-spores of the Mvxomycetes.PROTOPLASM MOVEMENTS. 9 While in thinner protoplasm the streaming and mass- movements are always horizontal, or, at least, parallel with the surface upon which the plasmodium rests, in the case of tougher protoplasm they may give rise to branches which have an upward direction, as in the formation of sporangia. 9.—Effect of External Influences. The movements of the protoplasm of the Myxomyeetes, and probably to a greater or less extent of all plants, are suspended by certain external influences. Violent jarring, pressure, a thrust as with the point of a pin or pencil, electrical discharges, sudden changes of the temperature, and sudden changes in the concentration of the surrounding fluid, stop the move- ments, and cause the plasmodium to contract into one or more spheroidal masses. When these influences cease, if they have not been so violent as to destroy the organization of the protoplasm, it returns after a greater or less length of time to its original form, and the movements are resumed. (а) The effect of mechanical disturbances (jarring, pressure, and thrust) may be best studied in the tougher or least fluid plasmodia (e.g., of Stemonitis fused). (б) The effect of electrical discharges may be studied by placing a small plasmodium (e.g., Didymium serpula) upon a glass plate provided with platinum points which are in connection with the poles of an induction apparatus. When a discharge takes place through a narrow branch (pseudopodium) it contracts so violently as to be broken up into a row of little spheres ; if it takes place through the mass of the plas- modium it becomes more or less spherical by its contraction. In any case, if the shock has not been too severe,the protoplasm after awhile returns to its normal shape again.* (c) The plasmodium of Didymium serpula, when removed from a tem- * Kuhne performed the following curious experiment. Taking a portion of the plasmodium of Didymium serpula., in its resting state, he mixed it with water so as to make a pulpy or pasty mass. With this he filled a piece of the intestine of a water-beetle, and tying the ends, laid it across the electrodes of an induction apparatus. The pre- paration was kept in a film of water in a damp chamber for twenty-four hours, at the end of which time it was considerably distended. He now allowed the electrical current to pass through it, when it contracted itself “like a colossal muscle-fibre.’' Upon extending it by pulling at the ends, and then sending through it a stronger electrical current, it contracted itself one third of its length.10 BOTANY. perature of 30° C. to one of 30° C. (68° to 80° Fahr.l. withdraws its pseud- opodia and ceases its activity in tlie space of five minutes. In an hour after the restoration of the normal temperature (20° C.) the movements begin again. If the temperature is raised to 35° C. (95° Fahr.) the organization of the plasmudium is destroyed. The plasmodium of Euligo varians, tionimf. (JEthalium septwum, Fr.), when placed in a chamber surrounded by ice, contracts into a rouuded form and ceases all motion ; upon gradually raising the tem- perature again the normal state is resumed. (d) In glycerine, a concentrated solution of sugar, a five percent solu- tion of potassium nitrate, or a five percent solution of sodium chloride, a plasmodium contracts, and becomes rounded and motionless. A sudden decrease in the concentration of the solution by which a plasmodium is surrounded also results in a stoppage of its movements. A plasmo- dium of Didymium serpula, when placed in a one per cent solution of potassium nitrate, and allowed time to regain its activity, suddenly rounds itself up and stops its movements when the preparation is washed out with distilled water; after the lapse of a few minutes (ten to twelve) the activity begins to show itself again, and in half an hour the normal state is restored. 10.—Ciliary Movement. The swimming of swarm-spores, spermatozoids, and many other naked protoplasmic bodies, is due to the rapid vibratory motion of extremely small whip- like extensions of the hyaline portion of the protoplasm. Examples of ciliary movement are very common. In some swarm- spores, as in those of Vaucheria, the whole surface is covered with short cilia ; in others, as in CEdogonium, the cilia lorm a crown about the hya- line anterior extremity ; those of Pandorina and Cladopliora, and the spermatozoids of Bryophytes and Pieridophytes, have two or more cilia ; while the swarm-spores of Myxnmycetes have but one. The rapidity of the swimming motion produced by cilia is consider- able, as shown by measurements made by Holmeister* in the case of swarm-spores, viz. : Fuligo varians (JEtlialium septicum)... .7 to .9 mm. per second. Lycogola epidendrnm................ .33 min. “ “ CEdogonium vesicatum..................15 to .20 mm. “ “ Yauclieria sp.........................10 to .14 mm. “ “ 11 .—The Activity of Protoplasm Enclosed in a Cell-wall. The movements of protoplasm in closed cells differ but little from those in naked ones ; the differences are such as are due to the fact that in the latter case the protoplasm is Lelire von der Pflanzenzelle,” p. 30.PROTOPLASM MOVEMENTS. 11 free to move in any direction, while in the former its move- ments are greatly restricted by the surrounding walls. In closed cells there are two general kinds of movements—one a streaming, the other a mass movement—comparable to the streaming and Amoeba movements of the naked cells or pro- toplasmic masses. No movement takes place, however (at any rate to no great extent), until the vacuoles are quite large. 12—The streaming movements occur in the protoplasmic strings, bands, and plates which cross or separate the vacu- oles, and in the lining layer of protoplasm which invests the inner surface of the cell-wall. The motion, in many cases, shows the same alternation as in the Myxomycetes, the direc- tion of the streaming usually being reversed after the lapse of a few minutes. The mass-movement in closed cells is not as clearly sepa- rated from the streaming as in naked cells. It usually con- sists in a sliding or gliding of the protoplasm upon the inner surface of the cell-wall, in much the same way as the naked plasmodium of one of the Myxomycetes moves upon the sur- face of its support. The limited space in which its move- ment must take place in closed cells, and its disposition over the whole inner surface of the wall, compel the protoplasm to move in opposite directions upon opposite sides of the cell. There is thus a kind of rotation of the protoplasm when the movement of all its parts is uniform. (a) Tlie streaming movements may be studied in the stamen-hairs of Tradescantia Virginica, the stinging hairs of the nettle (Urtica), the hairs of Cucurbita, Ecbalium, and Solatium tuberosum, the styles of Zea mais, the easily separated cells of the ripe fruit of Symphoricar- pus racemosus, the young pollen grains of (Emthera, and the paren- chyma of succulent monocotyledons—e.g., in the flower peduncles and the filaments of Tradescantia. The parenchyma cells of the leaves of many trees and of the prothallia of ferns and Equisetums show a net- work of hyaline strings in which a streaming may with difficulty be seen. Among the lower plants good examples may be found in the hyphae of some Saprolegniae, and in the cells of Spirogyra, Closterium, Denti- cella, and Ooscinodiscus. (b) In many cases (e.g., in the unfertilized embryo-sac of many Phanerogams, in the young endosperm cells, and in the spore-mother- cells of Anthoceros lavis)—where the strings and bands resemble those in the cases cited above—no movement of the protoplasm is visible,12 BOTANY. doubtless because of tlie mechanical injury of the cells in making1 the preparation, and the disturbing influence of the water in which it is mounted. (c) In the stamen-hairs of 2'radescantia Virginica the protoplasm Fig. 7.—An optical section of a cell of one of the stamen-hairs of Ti'adescantia Virginica, after treatment with a solution of sugar. The protoplasmic 6ac has partly collapsed, on account of the withdrawal of some of the interior water by the sugar solution. At the bottom of the cell is the large nucleus ; in the strings and bands of protoplasm there are streamings of the protoplasm, shown by the arrows.— After Hofmeistcr. forms a rather thick layer over the inner surface of the cell-wall, and in some part of this layer the nucleus lies imbedded. From the nucleus and from various parts of the protoplasmic layer there pass to the opposite side of the cell thicker or thinner bands and strings, always.PROTOPLASM MOVEMENTS. 13 however, more or leas parallel with the longer axis of the cell (Fig. 7). In a string there may be one, two, or three currents ; when there are two they are in opposite directions ; when there are three the central one takes one direction and the two outer ones the other. The strings are not stationary in the cell, but, on the contrary, they change their position with a consideiable rapidity, and in a prepara, tion soon pass out of the focus of the microscope.* By this change of place two strings may come together and fuse into one, or a string may pass to the side of the cell and become obliterated by fusing with the protoplasmic sac. New strings may be formed by a process exactly opposite to the one just described. A stream in the substance of the lining protoplasm forms a ridge projecting into the vacuole ; this ridge gradually becomes higher, and finally breaks away from the protoplas- mic sac, retaining its connection only at the ends. After a stream has been running in a certain direction for from ten to fifteen minutes, the motion suddenly becomes slower and soon stops entirely for from a few seconds to several minutes, and then begins to move in the opposite direction. The new movement begins and spreads as in the Myxomy- cetes (see paragraph 7). (d ) In the hairs of Cucurbita Pepo the arrangement of the protoplasm is much as in Tradescantia. The strings and bands are, however, broader, and frequently contain several currents, and the nucleus, instead of being imbedded in the lining layer of protoplasm, is in a centrally placed mass. There is a more rapid change in the form and position of the bands and strings than in Tradescantia, but the streaming motion is, on the contrary, considerably slower. The reversal of the streaming currents takes place in from seven to twenty minutes. (e) In most cases the streams lie in the lining protoplasmic layer of the cell, or form low ridges upon its inner surface. This is the case in the hairs of the style of Campanula, in liyphte (of fungi), and in the suspensor and young embryo of Funkia ccerulea. In long cells, the movement being parallel with the longer axis, there may be, as in the pollen tube of Zostera marina, currents passing up one side and down the other, f * This fact must be borne in mind in studying the movements of pro- toplasm in these cells, otherwise grave mistakes may be made. One string may move out of focus, and another, with a contrary current, may move into it, and thus a reversal of the current in the first string may erroneously be supposed to have taken place. f To study the movements of protoplasm in pollen tubes it is usual y necessary only to make a thin longitudinal slice of the stigma, and to mount and cover it in the usual way, using no water, however. After placing it under the microscope the preparation should be carefully crushed, when some of the pollen tubes may be distinctly seen. Their movements frequently continue for some hours in such preparations.14 BOTANY. (/) The passage from the condition in the last examples (the so. called circulation of protoplasm) is an easy one to the cases where the whole mass of protoplasm moves along the cell-wall as a broad stream, passing up one side and down the other (the so-called rotation of pro- toplasm). Common and well-known examples of this kind of mass-move- ment occur in Ohara, Naias, and Vattisneria. It may also (on the authority of Meyen) be studied in the root-lrairs of many land plants— e.g., of Imprrtiens Balmmina, Vida faba, Ipomcea purpurea, Cucumis, Cucurbita, Ranunculus sceleratus, and Marchantia polymorpha. Note.—In the study of the structures treated of in Chapters I to Y inclusive, the student will do well to consult a recent laboratory man- ual—“Botanical Micro-Chemistry,” by V. A. Poulsen (William Tre- lease, 1884).CHAPTER II. THE PLANT-CELL. 13. —In some cases plant protoplasm has no definite or constant form. This- is its permanent condition in some of the lowest plants—e.g., the Myxomycetes. In most other lower plants, and in all the higher ones, it has this condition only temporarily, if at all. In the great majority of cases, however, the protoplasm of which a plant is composed has a definite, and, within certain limits, a constant form. It usu- ally appears in more or less rounded or cubical masses of minute size, and which may or may not be surrounded by a cell-wall. In this condition it constitutes the Plant-Cell. The undifferentiated protoplasm of the Myxomycetes reminds us of the lower Monera among animals. In Bathybius and Protamoeba the naked protoplasm of which they are composed has no constant form. In Protomyxa we have a few simple transformations which are in every respect comparable to those of the Myxomycetes.* In higher animals the protoplasm exists in minute and definitely marked masses, termed cells, or corpuscles, and these have been shown to be the exact homo- logues of the cells of plants. 14. —While in young cells provided with a wall the pro- toplasm fills the whole cavity, as in A, Eig. 2 (p. 3), in older ones it never does so, and generally these contain only a very small portion of it, as a thin layer covering the inner surface of the cell-wall (B and C, Fig. 2). Close examina- tion shows that this protoplasmic sac consists of (1) a firmer hyaline layer, the ectoplasm, which is in contact with the * See further on this subject in paragraph 222, Chapter XI. For a short account of these interesting animal forms mentioned above, the student is referred to Dr. Packard’s “ Zoology for Students and Gen- eral Readers,” (p. 18 et neq.) in the series of which the present work forms a part, and his “ Life-Histories of Animals,” where are also given numerous references to fuller accounts.16 BOTANY. cell-wall ; and (2) within this a less dense granular one, the endoplasm ; the two layers are, however, not separated from each other by any sharp line of demarkation.* When the endoplasm attains a considerable thickness it becomes dif- ferentiated into an external denser layer and an internal less dense one. Often one of these layers may he found to be in motion while the other is at rest.f 15. —There may almost always be seen in plant-cells bands or strings of protoplasm which lie in or between the vacu- oles (Fig. 2, B). They are at first thickish plates which separate vacuoles, but afterward they become narrower as the vacuoles enlarge, and at last they disappear entirely. In these bands and strings, as previously stated (paragraph 12), streaming movements are frequently to be seen. 16. —Each of the protoplasm masses constituting the cells of most plants usually has a portion of its interior substance differentiated into a firmer rounded body, the nucleus Its normal position is in the centre of the cell; but it may be displaced and pushed aside by the vacuoles, so that in an optical section of the cell it may often appear to be in the margin. The nucleus is to be regarded simply as a modified part of the protoplasm of the cell, and not as something dis- tinct from it. It may dissolve, and its substance pass into that of the remainder of the cell; afterward a nucleus may form again ; and this may occur a number of times. Com- monly in each nucleus one or more small rounded granules may be seen; these are called the nucleoli. The nucleus may form a skin (hautschicht) about itself, and vacuoli may be present in its interior. 17. —Cells are of very varying sizes. They differ in dif- ferent plants, and also in the different parts of the same plant. ' In but few cases, however, are they of great size, by far the larger number being microscopic. The most striking; * These two layers were first described by Pringsheiin in his “ Theorie der Pflanzenzelle,” 1854. t Cf. Strasburger, “ Studien fiber Protoplasma,” 1876 ; and Qr. Jr, 1lie. Science, 1877, pp. 124-132.THE PLANT-CELL. 17 examples of large cells are found in the Thallophytes ; Nitella, dor example, has cells 50 mm. (2 inches) long, and 1 mm. {.04 inch) thick. According to Von Mold, the bast-cells of a species of palm (Astrocaryum) are from 3.6 to 5.6 mm. (.13 to .21 inch) in length. For ordinary plants the average size of the cells may be given as from .1 to .02 mm. (.004 to .0008 inch). From this average size the dimensions of cells decrease to exceedingly small magnitudes. In the Yeast Plant (Saccharomyces cerevisice) the cells are about .008 mm. (.0003 inch) in diameter. The cells of Bacterium tenno are from .0021 to .0028 mm. long and from .0028 to .0005 mm. broad (.0001- 00008 by .00008- 00002 inch). The following table, taken from Hofmeister’s “ Lelire von der Piian- aenzelle,” is useful as showing how the dimensions of similar cells vary in different plants : Table of Dimensions of Various Kinds of Cells of Woody Plants. (In decimals of a millimetre.) • Robinia Pseudaca- cia (five year - old branch). FaGUS 6YLVATICA (49-yr.-old trunk). 3 P . ss ■'C- p _ M ~ ~ «fj p CT3 U 3*0 tf-O •• pa* ;►> & Viburnum Lantana (fonr-yr.-old branch). 1 Cinchona Calisaya. (branch 2 cm. | thick). g X3 zo 5 g 3 >> m bfl z z 2 p '-a ■Cambium-cells, average length .201 .413 .528 .339 .786 1.511 Vessel-like wood-cells, average length .308 .712 1.179 1.819 2.020 Bast-like wood-cells, average length .301 .513 .‘615 Vessel-cells of the wood, average length — .205 .404 Latticed cells of young secondary bark, aver- .212 .520 age length Bast-cells of young secondary bark, average 1.292 .403 1.152 length .798 2.183 Cells of medullary ray in the cambium ring, .321 .437 .178 .838 .466 maximum length in tangential section .049 Do., do., maximum width in tangential sec- .011 tion .041 .076 .017 .056 .014 Cells of medullary ray in the young wood, .519 .285 .567 .630 average length in tangential section .376 .095 Do., do., average width in tangential section. 043 .077 .019 .037 .075 .019 Cells of medullary ray in the young secon- dary bark, average length in tangential .912 468 .504 .744 .172 section .342 .Do., do., average width in tangential sec- .066 031 .076 .075 .026 tion .057 18 BOTANY. 18. —Every free mass of protoplasm tends to assume a spherical form. The free cells of the unicellular water plants are generally more or less rounded, as are also the floating spores of most aquatic Thallophytes. In plants composed of masses of cells their mutual pressure gives them an angular outline. Where the pressure is slight the cells depart but little from the spherical shape, but as it becomes greater they assume more and more the form of bodies bounded by planes. If the diameters of the individual cells are equal and the development of the mass of cells has been uniform in every direction, we may have regular cubes, or twelve-sided bodies, i.e., dodecahedra. It is rarely the case, however, that the cells have a perfectly regular form. Even when their diameters are approximately equal, they are generally so much distorted that they are best described as irregular polyhedra. 19. —It much more frequently happens that cells grow more in some directions than in others, and thus give rise to elongated and many irregular forms. In many of the Thallophytes the long filaments composing the plants are made up of elongated cylindrical cells placed end to end ; while in others the cells are repeatedly and irregularly branched. In higher plants many elongated cells occur, but here, by pressure, they generally become prismatic in cross-section. (a) Many forms of cells have been enumerated, but they may all be arranged under tbe two principal kinds 'indicated above, viz., the short, and tbe elongated. As will be more fully shown hereafter, the various kinds of short cells constitute what is called Parenchyma; hence tbe cells themselves are termed Parenchymatous Cells, or Paren- chyma cells. Similarly, certain kinds of the elongated cells constitute Prosenchyma, and hence such are termed Prosenchymatous cells, or Prosencliyma cells. While it is impossible to draw an exact line be- tween parenchymatous and prosenchymatous forms, yet the terms are valuable, and are in constant use to indicate the general form. (b) Duchartre* has made an excellent classification of the prin- * In his Elements de Botanique,” second edition, a large and valuable work, which the student may profitably consult.THE PLANT-CELL. 19 cipal forms of cells, which is given below in a slightly modified form: Cell short (Par enchyma-- tous). f Cell globular or I ovoid, in section | round or oval .... Spheroidal. ! Cell polyhedral. Polyhedral Outline smooth, Cell a parallelo- or without promi--J pipedon, in section nences. rectangular....... Cuboidal. Cell tabular, with an elongated rectangular sec- tion.............. Tabular. f Cell ramose, (having short and irregular projec- tions............. Ramose. Cell star-shap- I ed, having long I projections which [are more regular.. Stellate. Cell elongated. Cell cylindrical, with its ends at right angles to its axis, or but little inclined............................. Cylindrical. Cell prismatic, with its ends at right angles to its axis, or but little - inclined............................. Prismatic. Cell fusiform [cylindrical or pris- matic], with its ends oblique and pointed.............................. Fusiform (Prosenchyma- tous). 20. —When one or more sides of a cell are not in contact with other cells, as is the case with those cells which com- pose the surface of plants, the free sides are generally con- vex, and they often become more or less prolonged, sometimes in a curious way. The velvety appearance of the petals of many plants is due to such prolongations of the free sides of the surface cells (Pig. 8). Of a somewhat similar nature are the tubular extensions of the surface cells of young roots— the root-hairs. And here we may also place the curious star- shaped cells which project into the intercellular spaces in the interior of the stem of the water lily (Fig. 9), and those which compose the pith of certain rushes (Pig. 9J). 21. —In the unicellular plants each cell is an independent20 BOTANY. •organism ; reproduces it absorbs nourishment, assimilates, grows, and its kind. In the higher plants, although this independence is not so evident, it still exists in a considerable degree. Here each cell is an individual in a commu- nity ; but it still has a life-history of its own, a formation (genesis), growth, ma- turity, and death. It is the unit in the plant. Upon its changes in size, form, and structure depend the volume, shape, Fig. 8.—a small piece of and structural characters of the plant the epidermis of the petal 1 or a pansy (viola tricolor), and all its parts. It is thus the Morplio- shovviug prolongations ol . , TT T, , . ± the free (upper) sides of the logical Unit Ot the plant. GhartreMas'_ After Du' 22.—As the whole structure of the plant is an aggregation of cells, so the functions of the whole, or of any part of a plant are but the sum or result- Fie. a Fig. 9.—A cross-section through the petiole of Nuphar adverta ; s, «, 6tar-shaped cells projecting into the intercellular spaces i, i ; g, a reduced flbro-vascnlar bundle. Magnified.—After Sachs. Fig. %. — Stellate cells from the pith of Juncus effusus, magnified.—After Du- chartre. ant of the physiological activities of its individual cells. The cell is thus also the Physiological Unit of the plant.CHAPTER III. THE CELL-WALL. 23.—In all but the lowest plants the protoplasm of every cell surrounds itself sooner or later with a covering or wall of cellulose. The substance of the cell-wall is a secretion from the protoplasm. Cellulose, as such, does not exist in the protoplasm ; it is formed on the surface when the wall is made. On its first appearance the wall is an extremely thin membrane, hut by subsequent additions it may acquire vary- ing degrees of thickness. The cell-wall forms a complete covering for the protoplasm ; there are at first no openings in it, at least none that are visible; later in the life of the cell pores are formed iti the wall in some cases, while quite frequently in dead cell-walls there are large perforations of various sizes and shapes. (a) Cellulose is related chemically to starch and sugar. Its composi- tion is C12 H21> O,o. It is tough and elastic. It is but slightly soluble in dilute acids and alkalies, and not at all iu water and alcohol. In water, however, it swells up from imbibing some of the liquid, but it shrinks again in bulk when dried. (b) Tests.—1. If cellulose is treated with dilute sulphuric acid, and shortly afterward with a weak solution of iodine, it is colored blue. 2. Treated with gchultz’s Solution it assumes a blue color. (c) In the Mvxomycetes, if the large mass of protoplasm composing a plant is somewhat dried, it separates itself into smaller masses, which surround themselves with a cell-wall. Upon applying sulphuric acid and iodine, the characteristic blue color of cellulose appears, showing that the wall is a true wall of cellulose. If, however, any such dried mass of protoplasm is subjected to the proper conditions of moisture and temperature, the cell-wall is dissolved and absorbed into the proto- plasmic mass. Tests applied now utterly fail to show the presence of cellulose. These observations prove the truth of the statement that cellulose is a secretion, and that it is not contained, as cellulose, in the protoplasm.22 BOTANY. 24.—After the formation of tlie cell-wall it generally grows, and increases its surface and thickness. Usually the surface-growth at first preponderates, afterward that in thickness. Neither the one nor the other is uniform over all points of the cell-wall, hence each cell during its growth may also change its form. As the growth of the cell-wall is directly dependent upon the protoplasm, it is clear that it can continue only as long as the protoplasm is in contact with its inner surface. In the growth of the cell-wall the new cellulose secreted by the protoplasm is deposited between the molecules of the membrane already formed. When the new molecules are de- posited between the previously formed ones only in the plane of the cell-wall, surface-growth takes place ; but when the planes of de- position of the new molecules lie at right angles to the plane of the cell-wall, increase in thickness is the result; when the molecules are deposited in both planes, the wall increases both in surface and thick- be Fig. 10.—Diagrams to illustrate the intercalary growth of CEdoso- neSS. nium. A, internal ring of cellu- lose secreted at f; B, showing 25.— Surface-growth may the wav in which, by the liom n- . . .. J „ tai splitting of ihe ring, the ceil is terminal or intercalary. in the ior- •elongated ; z, the new portion of ,, 1 , the wall formed i>y the splitting mer case the growth is greatest at ^,'^,eth?nso-cai”eVcap?lbrmeVby some point on the surface, decreas- 1^erdi88b^re»i^epiwth.- ing in intensity on all sides. The Modified from Sachs. growing point thus comes to pro- ject as a point or knob, or it becomes the end of a cylindri- cal sac. If several points of growth occur in a cell it may become star-shaped, and by a continuation of the process repeatedly branched. The typical form of intercalary growth takes place in definite belts which surround the cell, as is seen in (Edogonium (Fig. 10). The growth of the whole of the side wall of a cylindrical ceil, as in Spirogyra, is also a form of intercalary growth.THE CELL-WALL. 23 26. —Growth in thickness of the wall produces changes in the cell of even greater importance than growth in sur- face. While surface-growth has but little to do with the ■determination of the functions of the cell, the thickening of its wall generally results in a change in function, or an entire suspension of all physiological activities. Cells with extremely thin walls are most active; only ■such can take part m growth. ■(See Chap. XI.) Nutrition and assimilation are confined to cells whose walls have but slight thick- ness. Cells with moderately thick walls may be used as storehouses “S for food ; starch, for example, is x m~ Atter DucharIre- frequently found in such cells. But as the walls attain great thickness the protoplasm loses all activity save that neces- sary to the secretion of cellulose. 27. —The thickening generally produces certain markings ■or sculpturings in the shape of projecting points, ridges, bands, etc., which on the one band are on the outside of the wall, while on the other they are on the inside. In some pollen grains and spores we have the best examples of external markings. Here, in some cases, certain isolated points in the cell-wall become strongly thickened, giv- ing -ise io sPines or prickles (Fig. 11). bus. The almost spherical jn other cases the thickening is in cer- substance of the cell-wall . ° is fur' ished with ridge- tain bands, which may rise into high like thickenings united __ ° into a network. Each of walls, as in Fig. 12. External markings these bears thickeuiDgs, , , . ■, « wh / y a toe, older wood-cell-* (tracheides); being formed by the bottom of t\ t", V", bordered piis, increasing in ,, . ,. age; $t, large pits where c lla of the the pit, and the inner by the medullary rays lie next 10 the wood- f , ... J cells. X 3S5.-After Sachs. opening at its top. The bordered pits of pines, firs, and other Conifer* may be readily examined by making a longitudinal radial section. They are nut found in abundance on the tangential surfaces of the cells. The real structure of the bordered pitsof theConiferee was not under- stood until quite recently.* Von Mohl, apparently not noticing the * Schacht, in 1859 (Botanische Zeitung, pp. 238,239), and in a memoir in 1860 (“ De Maculis in Plantarum Vasis Cellulisque Lignosis”), gave the first correct explanation of the structure of bordered pits.26 BOTANY. tliin partition, thought that the lenticular cavity was formed by the- separation of the walls of the two contiguous cells at that place, and con- sequently that they were intercellular. This in- terpretation is still given in some hooks.* 31. — While the bordered pits of the Conifer* are never crowded together, in the cells of some plants they are so numerous as to lie closely side by side (Fig. 17). In such ease the first thick- ening of the'wall pre- sents itself as a net- work of ridges en- closing elliptical thin places. As the thick- ening advances £he ridges increase in height, but at first not in breadth ; later they increase in breadth at the top and overarch the thin areas, much as in the Fig. 16.—Bordered pits of Firms sylvestris. A, bordered pits of the transverse section of mature wood ; m, central layer rinnifaYco Tn of the common wad; /, a mature pit cut through the ^OniieroB. in iniS middle ; t\ the same, but in a thicker part of the sec- Vmwpvpv flip tion, the part of the cavity of tne pit seen in perspec- iiuvvevei, tntJ tive ; t"y a pit cut through below its openings ; B, rvnprnnrr af thp frm nf transverse section through the cambium ; c, cambium ; 0Pynill& h, very young wood-cells; ty t, very young bordered fV»p nit ia ari ploncrnf- pits, seen in section ; C, diagram of sectional and lat- . P1L dn eiOI18dt eral views of a young bordered pit; D, diagram of ed slit instead of a sectional and lateral views of a mature bordered pit; . Ey section of a mature pit, seen in perspective; F. Circle (Pig* 17, -d, section of a younger pit seen in perspective. A and , ~ ° , . b x 800.—After Sachs. and G, c). Ihe thin plate separating opposite bordered pits of this kind breaks- * See I.e .Muout and Decaisne’s" Traite Generate de Butanique,” 1868 ^English edition, 1872] ; Griffith and Heufrey’s “ Micrographic Die-THICKENINGS OF THE WALL. 27 away as in the previous case, and so free communication between adjacent cells or vessels is established. Fig. 18. Fig. 17.—Bordered pits of the thick root of Dahlia varinMlix. A, front view of a piece of the wall of a vessel, seen from without; B, transverse section of the same (horizontal, ana at right angles to the paper); C, longitudinal section of A (vertical, and at right angles to the paper) ; q, septum ; a, the original thin thickening-ridge ; b, the expanded part of the rh ckeiung masses, formed later and overarching the pit; the fissure through which the cavity of the pit communicates with the cell cavity ; at '), and many modifications and irregularities occur—e.g., in the figure at v"’" is the form known as the reticulated. 34.—In all the foregoing cases the marking of the wall has been general; there are some cases, however, where it is localized. A good example of this is in the formation of the pits of sieve-cells (Fig. 20). The horizontal walls, and also areas upon the longitudinal ones, become thickened reticulately, leaving rather large thin areas, as shown in Fig. 20, q, q. After a while the thin areas become absorbed,THICKENINGS OF THE WALL. 29 allowing the protoplasm of contiguous cells to become struc- turally united. The sieve-like appearance of these modified portions of tire wall give to the cells their name of sieve-cells. 35.—The collen- chyma cells which are frequently found beneath the epider- mis of the succulent parts of h i g h e r plants afford an- other instance of localized thicken- ing. Here only the angles of the cells become thickened, leaving broad por- tions of the wall un- modified (Fig. 21). (а) Examples of tlie uniform thickening of the cell-wall may he obtained for study by making thin sections of the hard parts of many nuts and seeds (Figs. 58 to 61); in many of these more or less complex channels may be found. Bordered pits are best studied in longitudinal sections of the young wood of the pines, firs, Fig. 20.—Young sieve tujjes of Cucurbita pepo The and tlio crowded drawing made from specimens whirh, hr having lain a etc., ana me cro aea jong time m absolute alcohol, have allowed the produc- pits in the stems of tion of extremely clear sections ; q, transverse view of , , -p, sieve-like septa; si, sieve plate ou side wall; at, thin- most other mianero-, ner part8 of the longitudinal wall; l, the same seen in