nie THE LIBRARY COLLEGE OF AGRICULTURE \ / NEW YORK STATE COLLEGE OF AGRICULTURE, DEPARTMENT OF HORTICULTURE, CORNELL UNIVERSITY, ITHACA, NN. Y. text-book of botany, Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003630591 A TEXT-BOOK OF BOTANY A TEXT-BOOK OF BOTANY BY DR. E. STRASBURGER DR. FRITZ NOLL PROFESSOR IN THE UNIVERSITY PRIVAT DOCENT IN THE UNIVERSITY OF BONN OF BONN DR. H. SCHENCK DR. A. F. W. SCHIMPER PRIVAT DOCENT IN THE UNIVERSITY PROFESSOR IN THE UNIVERSITY OF BONN OF BONN TRANSLATED FROM THE GERMAN BY H. C. PORTER, PD. ASSISTANT INSTRUCTOR OF BOTANY, UNIVERSITY OF PENNSYLVANIA WITH 594 ILLUSTRATIONS, IN PART COLOURED London MACMILLAN AND CoO., Liutrep NEW YORK: THE MACMILLAN COMPANY 1898 TRANSLATORS PREFACE TO THE ENGLISH EDITION IN presenting this translation of the “ Strasburger ” Botany, no words from the translator are needed in commendation of the original. The names of its authors and the distinguished position they occupy in the world of botanical science testify to the high character of the book, while the necessity of issuing a second edition within a year after its first appearance, evidences the speedy recognition of its merits awarded in Germany. Embodying the well-considered con- clusions of a lifetime devoted to botanical work on the part of its chief editor, Strasburger, and the investigations of his able collaborators, Noll, Schenck and Schimper, it will also be found to include all the latest results of botanical study and research. The translation has been undertaken with the consent and approval of both authors and publishers, and is of the second revised German edition. It has been my aim, as translator, to adhere closely to the German, making neither alterations nor omissions. Only in this way it seemed to me possible to ensure a fair repre- sentation of the author’s views, not only on questions of botanical significance, but also on the methods to be pursued in teaching the different branches of Botany. It has also been my effort to avoid any unnecessary introduction of new terms, and I have adopted, as far as consistent with the German, the existing terminology. Wherever possible, in translating technical words of a purely German signification, I have conformed to the usage of previous translations. In seeking for an appropriate translation of the German word ‘ Anlage,” I have reverted to the earlier rendering, rudiment,. which vi BOTANY in its common meaning of “first, unshapen beginning, or “the first or embryotic origin of anvthing,” conveys more accurately than any word yet proposed the true significance of the term Aniage as used in a morphological sense. I have also followed the German custom in using, where consistent with brevity and conciseness, ordinary rather than technical, descriptive word: whose comprehension requires a constant reference, on the part of the student, to a glossary or botanical dictionary. The expression ‘‘ Hochblatter” I have tran:- lated a: bracteal leaves, in conformity with the express statement of the German author, by whom they are also designated a: bractex. In finding satisfactory English equivalents tor German terms lo eretotore untranslated, considerable difficulty has been experienced. It gives me great pleasure to acknowledge the helpful suggestion: and advice received on such points from Professor Mactarlane and Doctor Harshburger, and to expres: my indebtedness to them and to Doctor: Osterhout and Lungershauzer for the kind assistance rendered in other detail: of the work of translation. H. C. PORTER. TSIVERSITY Or PESSSYLVANI4, PHILADELPHIA, Februsry 1496. CONTENTS VAGL ET MODUCTION ‘ : ' ‘ ‘ | PART I GENERAL BOTANY RECTION — MORPHOLOGY WXTUNAL, MOMBPHOLOGY The development of form dn the plank bkingdous F , . 2 LO Helahions of symimebry , F ‘ i ih Diranel) wysbenis ' , ‘ ; : ' V7 Nhe hood i , , ' » 14 She where or isis of diss whol, : : i : » 2s Whe dont r A ‘ : é ‘ . OH The rool, F i é 5 i Fi F AQ Whe onhageny of plaate d : ? ‘ » AS INTMIINAL MOMPHOLOGY Wistology and Anmbonmy) Wie coll, i ' ' . AT Cell fusion ; : F F 4 Winans, ‘ ; ; ; ‘ , , BG “Vinstie syste 1 ‘ ; ' ' , ‘ » 0 Sho prinoey bins ; ' ; : ' : » The iste bation of ble primacy Gisstes ; i i i » 10K Whe necoudiry Gated é ' , , ‘ , 120 The phylogeny of bho Titeraned nities : : ' ' 1h The ontogeny of bho tribe) abe tiire , : ‘ yd Atrnehirad deviabbonn i i 3 » bd SHO'TION Th PIPYSTOLOCY The pliystoal and viliel abbeiba hon of plianba P , » WO TH SV AREery on titi Poa ter Bons, ; , ‘ » Td Weg : : : , : , , 106 Terion of (iain ' , ' : ‘ ' iva Moohaniond Gast Gibarwoni) i i . i . 19 viii BOTANY Nutrition The constituents of the plant ‘body The essential constituents of plant food The process of absorption Water and mineral substances The absorption of carbon (assimilation) The utilisation of the products of assimilation Transfer of the products of assimilation The storage of reserve material Special processes of nutrition RESPIRATION Intramolecular r apietion Heat produced by respiration The movement of gases within the plant Phosphorescence GROWTH . The embryonal development of the organs The phase of elongation The internal development of the oigans Periodicity in development, duration of life, and aontinnity of the embryonic substance THE PHENOMENA OF Movement Movements of naked protoplasm The movements of protoplasm within walled cells Movements producing curvature Hygroscopic curvatures Growth curvatures . Movements due to changes af turgor REPRODUCTION Vegetative neproduction Sexual reproduction Alternation of generations : The dissemination and germination of seeds . PART II, SPECIAL BOTANY SECTION I. CRYPTOGAMS THALLOPHYTA Myxomycetes Schizophyta Diatomeae Peridineae Conjugatae Chlorophyceae Phaeophyceae Rhodophyceae Characeae PAGE 171 171 172 176 178 195 201 202 204 206 216 219 220 221 293 223 224 229 237 237 241 242 244 247 247 248 269 274 277 280 289 291 301 302 305 312 315 315 318 329 334 337 CONTENTS 1x PAGE Hy phomycetes ; 340 Lichenes if . 375 BryoPpHYTA H 381 Hepaticae 385 Musci . ‘ 390 PrERIDOPHYTA . 397 Filicinae ; 400 Equisetinae ‘ ‘ 412 Lycopodinae . 415 SECTION II. PHANEROGAMIA GYMNOSPERMAE . 434 Cycadinae ; . 437 Coniferae P 438 Gnetineae ‘ ‘ : . 443 ANGIOSPERMAE . . : ‘ 444 Monocotyledones : ; . 462 Dicotyledones . ‘ s ‘ ‘ ; 490 List oF OFFICINAL PLANTS . ; ‘ 601 List or Poisonous PLANTS ‘ : x 7 603 INDEX es 5 ‘ ‘ 605 ERRATA Page 285, line 5 from foot, for protogymous read protogynous. Page 355, line 2 from foot, for paraphyses read periphyses.: INTRODUCTION It is customary to divide all living organisms into two great kingdoms, animal and vegetable. A sharp boundary line between animal and vegetable life can, however, be drawn only in the case of the more highly developed organisms ; while in those of more simple organisa- tion all distinctions disappear, and it becomes difficult to define the exact limits of Botany and Zoology. This, in fact, could scarcely be otherwise, as all the processes of life, in both the animal and vegetable kingdoms, are dependent on the same substance, protoplasm. The more elementary the organism, the more apparent the general quali- ties of this protoplasm become, and hence the correspondence between the lower organisms is specially striking. With more compli- cated organisation, the specific differences increase, and the character- istics distinguishing animal from vegetable life become more obvious. For the present, it must be confessed, the recognition of an organism, as an animal or a plant, is dependent upon its supposed correspondence with an abstract idea of what a plant or animal should be, based on certain fancied points of agreement between the members of each class. A satisfactory basis for the separation of all living organisms into the categories of animals or plants can only be obtained when it is shown that all organisms distinguished as animals are in reality genetically connected, and that a similar connection exists between all plants. The method by which such evidence may be arrived at has been indicated in the THEoRY or EVOLUTION. From the paleontological study of the imprints of fossil animals and plants, it has been established that in former epochs forms of life differing from those of the present age existed on the earth. It is also generally assumed that all living animals and plants have been derived from previously existing forms. The conclusion is a natural one, that those organisms possess- ing almost exactly similar structures which have been united as species under the same genera are in reality related to one another. Indeed, it is permissible to take a further step, and assume that the B 2 BOTANY union of corresponding genera into one family serves to give expression to a real relationship existing between them. The evolution of a living organism from others previously existing and different in form has been distinguished by HAECKEL as its phylogenetic development or PHyLocENy. Every organism arising from a like organism must, before attaining its mature state, com- plete its own individual development, or, as it has been termed by HAECKEL, its ontogenetic development or ONToGENY. The supposi- tion that the successive steps in the ontogenetic development of an organism correspond to those of its phylogenetic development, and that the ontogeny of an organism is accordingly a more or less complete repetition of its phylogeny, was first asserted by FRITZ MULierR, who based his conclusions on the results of comparative research. The idea of the gradual evolution of higher organisms from lower was familiar to the Greek philosophers, but a scientific basis was first given to this hypothesis in the present century. Through the work of CHARLES DARWIN in particular, the belief in the immutability of species has been overturned. DARWIN is also the author of the so-called THEORY oF SELECTION. In drawing his conclusions, he proceeds from the variability of living organisms, as shown by the fact that the offspring neither exactly resemble their parents nor each other. To establish this theory, he also called attention to the coristant over-production of embryonic germs, by which the destruction of the greater part must inevitably result. If this were not so, and all the embryos produced by a single pair attained their full development, they would alone, in a few generations, completely cover the whole surface of the earth. The actual condition of the floras and faunas is thus maintained by the restricted development of the embryos. On account of insufficient space for all, the different claimants are engaged in an uninterrupted struggle, in which the victory is gained by those that, for any reason, have an advantage. Through this “struggle for existence,” as only those organisms possessing some advantage live and mature, a process of enforced selection between the more fortunate survivors must result. In this manner Darwin arrived at the supposition of a process of NatTurAL SELECTION, and confirmed his position by analogy with known results obtained by experimental cross-breeding and cultivation. Newly-developed peculiarities arising from individual variability must be inherited in order to become permanent characteristics of a later generation. Just as in artificial selection, natural selection, although unconsciously, accomplishes this result. As individual peculiarities may be developed by careful breeding and rendered permanent, so by natural selection those qualities which are advantageous in the struggle for existence become more pronounced and are finally con- firmed by heredity. By the continued operation of natural selection, INTRODUCTION 3 organisms must result which are, in the highest degree, fitted and adapted to their environment. Thus, by the survival of the fittest, through natural selection, that adaptability to the environment is gradually evolved which is such a striking characteristic of organic life. That the transitional forms in this process of phylogenetic de- velopment no longer exist, is accounted for in the theory of natural selection by the assumption that the struggle for existence must necessarily have been most severe between similar organisms. For similar organisms must have similar necessities, and the new and better-equipped forms must ultimately prevail over the original less specialised organisms, which, thus deprived of the essential requisites for their existence, finally disappear. Although the great importance of natural selection in the develop- ment of the organic world has been fully recognised by most naturalists, the objection has been raised that it alone is not a sufficient explanation of all the different processes in the phylogeny of an organism. Attention has been called to such organs as would be incapable of exercising their function until in an advanced stage of development, and so could not originally have been of any advantage in a struggle for existence. How could natural selection tend to develop an organ which would be useless so long as it was still in a rudimentary condition? This objection has led to the supposition of an internal force residing in the substance of the organisms themselves, and controlling their continuous development in certain definite directions. Many naturalists, indeed, have gone so far as to affirm that only less advantageous qualities have been affected by the struggle for existence, while the more advantageous have been uninfluenced by it. The phylogenetic changes in the species have been so gradually accomplished as to have escaped observation, and indirect evidence of their existence is all that can be obtained. If the higher organisms have been evolved from the lower, there must, at one time, have been no sharp distinction between plants and animals. The simplest organisms which now exist are in all proba- bility similar to those which formed the starting-point in the phylo- genetic development of animal and vegetable life; and it is still impossible to draw a sharp distinction between the lower forms of plants and animals. The walls which surround the elementary organs of the plant body, and the green colouring matter formed within them, have been cited as decisive indications of the vegetable character of an organism. Surrounded by firm walls, the living substance becomes more isolated, and, consequently, independence of action in plants, as compared with animals, is diminished. By means of the green colour- ing matter, plants have the power of producing their own nutritive substances from certain constituents of the air and water, and from the salts contained in the soil, and are thus able to exist independently ; 4 BOTANY while animals are dependent for their nourishment, and so for their very existence, on plants. Almost all the other differences which distinguish plants from animals may be traced to the structure of plants, characterised by the firm walls of the simple organs, or to the manner of obtaining food. Another characteristic of plants is the un- limited duration of their ontogenetic development, which is continuous, at certain points at least, during their whole life. That none of these criteria are alone sufficient for distinguishing plants from animals is evident from the fact that all the Fungi are devoid of green pigment, and, like animals, are dependent on green plants for their nourish- ment. On the borderland of the two kingdoms, where all other dis- tinctions are wanting, phylogenetic resemblances, according as they may indicate a probable relationship with plants or animals, serve as a guide in determining the position of an organism. While it is thus ditficult to sharply distinguish the two great groups of living organisms from one another, a distinction between them and lifeless bodies is readily recognised. Living organisms are endowed with the quality of IRRITABILITY, in which all lifeless bodies are deficient. External or internal stimuli influence living organisms to an activity, which is manifested in accordance with the requirements and conditions of their internal structure. Even in the smallest known organisms all manifestations of life are occasioned by a similar sensitiveness to external or internal stimuli. The question, however, continually arises whether, in the smallest and simplest organisms at present discernible with the highest magnifying power of the microscope, the ultimate limit of possible life is actually represented. As this limit has always been extended with the increased capabilities of optical instruments, it would seem arbitrary to assert that it would now be impossible to extend it still further. NAGELI accordingly assumed that beyond what is now made visible by the microscope there exists a world of still more and more simple organisms. These he conceived of as showing such a degradation of the vital processes that they finally resemble mere albuminous bodies, which, he supposed, under certain conditions might be produced by purely synthetic processes. In order that a living organism may develop out of such albuminous bodies it must originally have inherent in it the capability of development, that is, the capability of variation and the ability to retain the results of this variability as new qualifications. It must, in addi- tion, have the capability of growth, or of enlarging the mass of its body at the cost of foreign substances, and finally, the power of reproduction, that is, of multiplication by a separation into distinct parts. For the substance itself which serves as a basis for all development, the supposition of an inorganic origin would not be incredible; it would even be possible to imagine that, under certain conditions, this substance is continually in process of formation. On the other INTRODUCTION 5 hand, it must not be forgotten that, so far as is actually known, all living organisms have arisen only from similar organisms. So far as experience has shown, spontaneous generation is unknown. In olden times it was a common supposition that all nature itself was endowed with universal life. According to Aristotle, frogs and snakes sprang from mud and slime. In the same degree that knowledge of the actual development of living organisms was extended, the previously accepted cases of spontaneous generation became more and more restricted, and were finally limited to intestinal worms which could not otherwise, it was thought, be accounted for, and to microscopic organisms the origin of which was also not understood. Now, for such organisms the possibility of a spontaneous generation has been disproved by more modern investigations; the history of the development of intestinal worms is known, and the germs of organic life have been found to exist everywhere. SCHWANN and PasTEuR have been pioneers in this work, and have shown that it is possible to hinder the development of the lower organisms, in places where it is customary to find them, by destroying all existing germs and at the same time preventing the entrance of new ones. It is due to the results obtained by these men in their investigations on spontaneous generation that we are now able to preserve food in a scientific manner. The germs previously existing in the substance to be conserved are destroyed by heat, while, by a proper mode of sealing, the entrance of new germs is rendered impossible, and the decomposition which their presence would occasion is accordingly prevented. All known living organisms have been derived from other living organisms. The attempt to relegate spontaneous generation to an un- known field, and to admit the origin of living from dead substances, has on the other hand derived support from the progress of chemical research. In the early decades of the present century it was customary to draw a distinct line of separation between organic and inorganic chemistry, and to assume that the substances dealt with by organic chemistry could only be produced by the vital action of organisms. The laws governing inorganic chemistry appeared to have no refer- ence to organic chemistry, the formation of organic substance being due to a special force, the “life force.” In 1828 WOHLER obtained urea from ammonium cyanate, and thus for the first time produced an organic compound from an inorganic substance. In 1845 KoLBe completely synthesised trichloracetic acid, and in 1850 BERTHELOT synthesised alcohol and formic acid. By these results the former distinction between organic and inorganic chemistry was destroyed. Organic chemistry has become the chemistry of carbon compounds. Botany, or the science of plants, may be divided into a general and a special part. In the general part, the structure and functions of plants as such will be considered ; in the special part, the particular 6 BOTANY structure and functions of the separate orders of plants will be discussed. The study of the structure of plants is called MorrHoLocy ; that of their functions PHystoLocy. In the general part, morphology and physiology will be treated separately ; in the special part, con- jointly. PART I GENERAL BOTANY SECTION I MORPHOLOGY GENERAL BOTANY SECTION I MORPHOLOGY THE object of vegetable morphology is the scientific study of the forms of plants. It does not attempt to discover the causes of the variation in the forms, but rather has accomplished its purpose when it succeeds in showing how one form may be derived from another. The basis of morphological study is, accordingly, phylogeny (p 2). As phylogenetic development can only be inferred, and cannot be directly followed, the methods of morphology must also be indirect. They are dependent for their successful application upon ontogenetic comparison ; for, in the ontogenetic development (p. 2) of a plant, its phylogeny is, to a certain extent, repeated, so that, by a comparison of transitional forms, it is often possible to discover a connection between plants which are apparently most dissimilar. As, however, the ontogeny of a plant is neither an exact nor invariable repetition of its phylogeny, and as connecting links between extreme forms are often wanting, the results of morphological study are frequently imperfect and incomplete. Such parts or mem- bers of plants which it is reasonable to presume have had a common origin are distinguished as HomoLoGous ; those which, while probably having different origins, yet exercise the same functions, are termed ANALOGOUS. Through the adaptation of different parts to the same function, a similarity in both external form and internal structure often results ; and in this way the correct determination of morphological relationships is rendered extremely difficult. Only homologous parts have the same morphological value. This homology is determined by the facts of phylogeny and origin, and not by any correspondence in function. On account, however, of the intimate relation existing between the form and function, and the modifying influence of the one upon the other, it will be necessary in the morphological 10 BOTANY PARI L study of the different members of plants to take into consideration their physiological signification, as organs. When, for phylogenetic reasons, it seems possible to attribute to a number of different mem- bers a common origin, such a hypothetical original form is termed the fundamental or primitive form (“Grundform”). The various modifica- tions which the primitive form has passed through constitute its META- MORPHOSIS. In this way the theory of the metamorphosis of plants, which was once but an ideal conception, attains its true significance. Slightly differentiated structures, which are found at the beginning of a series of progressively differentiating forms, are termed RUDI- MENTARY ; imperfect structures, which have arisen as the result of the deterioration of some perfect forms, are termed REDUCED. Vegetable morphology includes the study of the external form and the internal structure of plants. The descriptive study of the external form of plants has been incorrectly termed ORGANOGRAPHY, for, by the use of the term “organ,” it would seem to have a physiological signi- fication. Morphology takes no recognition of the parts of a plant as organs, but treats of them merely as members of the plant body. The study of the internal structure of plants is often designated ANATOMY or PHytoromy ; but as it usually includes also the study of the more minute internal structure, it resembles rather histology, in the sense in which that term is used by zoologists, and concerns itself to a much less degree with anatomy, properly speaking. In any case, it is the simplest plan to designate the study of the outer forms EXTERNAL MorpPuHo.oey, and that of the inner structure INTERNAL MoRPHOLOGY. I. EXTERNAL MORPHOLOGY Plants show a great diversity in the form and arrangement of their members ; it is the task of morphology to determine the points of agreement existing between them. To do this, it is necessary to discover a common origin for their similar but variously developed members. The Development of Form in the Plant Kingdom The Thallus.—The simplest form that we can imagine for an organism is that of a sphere, and this is actually the form of some of the lower plants. The green growth often seen on damp walls consists of an aggregation of the small ee bodies of Gloeocapsa polydermatica (Fig. 1), an Alga belonging to the lowest division of the vegetable kingdom. The single plants of the Beer-yeast (Saccharomyces cerevisiae) are ellipsoidal ; but, from their peculiar manner of growth, by budding, they form lateral outgrowths, and thus often appear SECT. I MORPHOLOGY 11 constricted (Fig. 2). Cylindrical and also disc-shaped forms are common to various Algae. The Diatomeae (Fig. 3), in particular, furnish a great variety 2g of spindle, canoe, helmet, a & and fan-like shapes ; but they may all be derived ~* — ¢ from the more simple Fra. 2. — Saccharomyces 7 a a cerevisiae. 1, Cells spherical, discoidal, or without buds ; 2 and cylindrical forms. The — 3, budding cells. (x Bacteria, which, as the 4) cause of contagious diseases and of de- er nae _,.,, composition, have been the object of so 4, Commencement of division; Much recent investigation, also exhibit a B, shortly after division; C,a great diversity of form. A small quantity MEI RERED ene of the white deposit on teeth will furnish examples of spherical, rod-like, fibrous, and spiral bacteria (Fig. 4). In the course of the development of a single species several of m4 Fia. 4.—Bacteria from deposits on teeth. «, Leptothrix bucealis ; a*, the same after treat- ment with iodine; b, Micrococcus ; ¢, Spir- illum dentium after treatment with iodine; d, comma bacilli of the mucous membrane of the mouth. (x 800.) Fic. 3.—Pinnularia viridis. A, Surface view ; B, lateral view. (x 540.) these different forms frequently occur. The next stage in the pro- gressive development of external form in the vegetable kingdom is exhibited by such plants as show a DIFFERENTIATION INTO APEX 12 BOTANY PART I AND BASE. The base serves as a point of attachment, while growth is localised at the apex. In this way a growing point is developed at the apex. As an example of such a form, a young plant of the green Alga, Ulva Lactuca (Fig. 5), may be taken. The development of a more complicated external form is represented by the branched, filamentous, or band-shaped Algae, in which the origin of new formations is more and more restricted to the apex. An ACRO- PETAL order of development, in which the youngest Fic. 5.—Ulva Lactuca, young stage, show- ing apex and _ base. (x 220.) Fia. 6.—Portion of Cladophora glomerata. Fic. 7.—Cladostephus verticillatus. (After (x 48.) PRINGSHEIM, x 30.) lateral members are always nearest the growing apex, is clearly demonstrated by the branched filaments of the common green Alga, Cladophora glomerata (Fig. 6). Still more pronounced is the apical SECT. I MORPHOLOGY 13 growth in the brown sea-weed Cladostephus verticillatus (Fig. 7). The great variety in the form of the larger Fungi and Lichens, by which they are distinguished as club-, umbrella-, salver-, or bowl-shaped, or as bearded or shrub-like, is due to the union or intertwining of apically growing filaments. This manner of develop- ment is limited to Fungi and Lichens. In _ other cases, the more complete segmentation exhibited by the lower plants results from the differentiation of independently branching filaments and bands. As the apex itself may undergo successive modifications through continuous bifurcation, as in the case of Dictyota dichotoma (Fig. 8), it does not always necessarily follow that the for- mation of new members must proceed directly from the ori- ginal apex. The highest de- gree of external differentiation among the lower plants is met with in the group of the red sea-weeds (thodophyceae). Many representatives of this class re- semble the higher plants in the formation and arrangement of their members ; Hydrolupathwm sanguineum (Fig. 9), for ex- ample, as is indicated by its name, has a strong resemblance to a species of /twmex, and affords a remarkable illustration of the analogy of form existing be- tween plants phylogenetically unconnected. On account of a supposed phylogenetic connec- tion between the lower plants, they have been collectively de- Fic. 9.—Hydrolupathum sanguineum. (4 nat. size.) Signated THALLOPHYTES, while the body of the individual organisms, having neither true leaves nor stem, is referred to asa THALLUS. In contrast to the thallus, the body of the higher plants, Fic. 8.—Dictyota dichotoma, (3 nat. size.) 14 BOTANY PART I with its segmentation into stem and leaves, is frequently termed a coRMuS, and the plants themselves CorMopHYTES. To the Cormo- phytes belong all plants from the Mosses upwards. 3 Transition from the Thallus to the Cormus.—The lowest division of the Bryophytes, the Liverworts (Hepaticae), although in many cases Fic. 10.—Riccia fluitans. (Nat. size.) Fic. 11.—Blasia pusilla. s, Sporogonium ; r, Thizoids. (x2.) possessing thalloid bodies without any segmentation into members, contain also forms with the same differentiation into stem and leaves as the higher plants. As between these two extremes there may be found transi- tional forms, this class of plants, accord- ingly, affords valuable assistance in the phylogenetic study of the development of higher plants. A few examples will best illustrate these stages of differentiation exhibited by the Hepaticae. The bifur- cately branching thallus of Riccia fluitans (Fig. 10) is flat and ribbon-like, and in its general appearance resembles the thallus of the previously mentioned brown Alga, Dictyota dichotoma (Fig. 8). A more advanced development is shown by Blasia pusilla (Fig. 11), which has incisions in the sides of its ribbon-like body. The lobes thus formed by the lateral incisions, oe a as is shown by comparison with other Tec ee more highly differentiated Hepaticae, and also by the study of their development, are properly to be regarded as rudimental leaves. Finally, in Plagio- chila asplenioides (Fig. 12), with alternating ovate leaves and elongated fibrous stems, the segmentation into stem and leaf is complete. The Cormus.—With the segmentation into stem and leaf, the SECT. I MORPHOLOGY 15 distinctive differentiation of the Cormophyte is completed. This, in all probability, has occurred twice in the phylogenetic development of the vegetable kingdom ; once in the Bryophytes, and a second time in the evolution of the Pteridophytes, presumably from ancestral forms resembling the Liverworts. All Bryophytes are attached to the surface on which they grow, by means of root-like hairs or RHIZOIDS (Fig. 11, 7). It is in the next higher group of plants, which, as Vascular Cryptogams, are united in one class, that true roots, in a morphological sense, first make their appearance. They are for the most part cylindrical bodies with apical growing points. Disregarding the distinctions perceptible in its internal structure, a root may always be distinguished from a stem by the ROOT-CAP or CALYPTRA sheathing its apex, and also by the absence of leaves. The Metamorphosis of the Primitive Forms.—After the completion of its differentiation into stem and leaf, and the appearance of roots, there occur only such modifications of the primitive form of the plant body of a Cormophyte as are embraced under its metamorphosis (p. 9), occasionally including a more or less complete fusion of parts originally separate and distinct. The relationships between homologous members, which are often very striking, did not escape the notice of earlier observers. They suggested comparisons, although no real phylogenetic basis for such comparisons existed. Thus, an ideal conception of the form of external members was developed, and finally reached its highest elaboration in Gorrun’s Theory of Metamorphosis ; and its abstract scientific conclusion in the writings of ALEXANDER Braun. As the great variety exhibited in the external appearance of the lower plants precluded any possibility of assigning to them hypothetical primitive forms, the whole terminology of the external morphology of plants has been derived from conceptions applicable only to the Cormophytes. Even to-day, the same terms used in reference to the Cormophytes are applied to parts of the Thallophytes, which are evidently cnly analogous. In this sense it is customary to distinguish between stem and leaf in such Algae as Hydrolapathwm (Fig. 9). Such a use of terms is only permissible where reference is made to the manner of segmentation, with the intention of emphasising the analogy with the somewhat similar members of the Cormophytes. The question whether, in the different groups of the Cormophytes, all the members designated by the same names are really homologous, cannot properly be discussed here. It would seem almost impossible to derive from the Bryophytes all the forms of cormophytic segmentation shown by the Pteridophytes. However this may be, from the Pteridophytes upwards, the segmentation of the members appears to have had a similar origin, and the similarity of terminology is based, therefore, upon an actual homology of the parts. Relations of Symmetry Every section through an organ or member of a plant, made in the direction of its longitudinal axis, is distinguished as a longitudinal 16 ‘BOTANY PART 1 section ; those at right angles to it being termed cross or transverse sections. Such parts of plants as may be divided by each of three or more longitudinal planes into like halves are termed either PoLysyM- Fic. 13.—Diagram showing the so-called de- Fic. 14.—Diagram showing two-ranked cussate arrangement of leaves. alternate arrangement of leaves. METRICAL, RADIAL, or ACTINOMORPHIC. The degree of symmetry peculiar to any leafy shoot will be more Ss apparent from a diagram, that is if the leaves which it bears be projected on a plane at right angles to its axis. The radial symmetry of a shoot with opposite leaves is clearly shown in the adjoining diagram (Fig. 13). A shoot with its leaves arranged alternately in two rows shows quite different relations of sym- metry. The diagram of such a shoot (Fig. 14) can only be divided into similar halves by two planes. When such a condition exists, a member or plant is said to be BISYMMETRICAL. When, however, a division into two similar halves is only possible in one plane, the degree of sym- metry is indicated by the terms sym- METRICAL, MONOSYMMETRICAL, or ZYGO- MORPHIC. When the halves are equal, but have a different structure and are spoken of as ventral and dorsal sides, the body Fio. 15, Diagram of a foliage-leaf, is termed DORSIVENTRAL. Ordinary foli- A, Surface view; B, transverse sy : : see Ulun) a ulane of EAHIGLiN: age-leaves exhibit this dorsiventral struc- ture, and their upper and lower surfaces are not only different in appearance but they also react differently to external influences. In the accompanying figure (Fig. 15) such a SECT. I MORPHOLOGY 17 monosymmetrical, dorsiventral foliage leaf is diagrammatically repre- sented. From the surface view (4) and from the cross-section (JB), in which the distinction between the dorsal and ventral sides is in- dicated by shading, it is obvious that but one plane of symmetry (s) can be drawn. As the zoologists often term this degree of symmetry BILATERAL, the same term is frequently employed with reference to plants. Branch Systems Thallophytes as well as Cormophytes exhibit systems of branching, resulting either from the formation of new growing points by the bifurcation of a previously existing growing point, or from the develop- ment of new growing points in addition to those already present. In this way there are produced two systems of branching, the DICHOTO- MOUS and the MONOPODIAL. By the uniform development of a continu- ously bifureating stem, a typical dichotomous system of branching is produced, such as is shown in Dictyota dichotoma (Fig. 8). In a typically developed example of the monopodial system there may always be distinguished a main axis, the MONOPODIUM, which gives rise to lateral branches from which, in turn, other lateral branches are developed. A good example of this form of branching is afforded by a Fir-tree. Where one of the two branches is regularly developed at the expense of the other, the dichotomous system assumes an appearance quite different from its typical form. The more vigorous branches may then, apparently, form a main axis, from which the weaker branches seem to spring, just as if they were lateral branches. This mode of branching is illustrated by the Selaginellae (Fig. 351). Such an apparent main axis is termed, in accordance with its origin, a SYM- Popium. On the other hand, in the monopodial system two or even several lateral branches may develop more strongly than the main axis, and so simulate true DICHOTOMY or POLY- Tomy. Such monopodial forms of branching are referred to as FALSE DICHOTOMY or FALSE POLYTOMY, as the case may be. A good example of false dichotomy may be seen in the SP vitin Oeeea a Pata Mistletoe (Viscum album, Fig. 16). ""* “Gaceaicnotomy. (hnat.sve) If, however, a lateral branch so ex- ceeds the main axis in development that it seems ultimately to become a prolongation of the axis itself, a sympodium is again formed. This is exactly what occurs in the Lime and Beech; in both of these trees the terminal buds of each year’s growth die, and the prolonga- Cc 18 BOTANY PART I tion of the stem, in the following spring, is continued by a strong lateral bud, so that in a short time its sympodial origin is no longer recognisable. In most rhizomes, on the other hand, the sympodial nature of the axis can be easily distinguished ; as, for example, in the rhizome of Polygonatum multiflorum (Fig. 21), in which, every year, the terminal bud gives rise to an aerial shoot, while an axillary bud pro- vides for the continuance of the axis of the rhizome. In the flower- producing shoots or inflorescences of Phanerogams the different systems of branching assume very numerous forms. These will be more fully-described in their proper place. To such inflorescences belong the ventrally coiled dorsiventral shoots, which produce new shoots from their convex dorsal surfaces, instead of in their leaf-axils. The Shoot The Development of the Shoot.—Under the term shoot a stem and its leaves are collectively included. A stem possesses an apical mode of growth (Fig. 17), and its unprotected growing point is described as naked, in contrast to that of the root with its sheathing root- cap. The apex of the shoot gener- ally terminates in a conical pro- tuberance, designated the VEGE- TATIVE CONE. As it is always too small to be visible to the unaided eye, it is best seen in magnified median longitudinal sections. So long as the apex of the shoot is still internally un- differentiated, it continues in em- bryonic, condition, and it is from the still embryonal vegetative cone that the leaves take their origin. They first appear in acropetal succession as small, Fic. 17.—Apex of a shoot of a phanerogamic conical protuberances, and attain plant. v, Vegetative cone; f, leaf rudiment; : g, rudiment of an axillary bud. (x 10.) a larger size the further removed they are from the apex of the stem. As the leaves usually grow more rapidly than the stem which produces them, they envelop the more rudimentary leaves, and over- arching the vegetative cone, form, in this manner, a BUD. Buds are therefore merely undeveloped shoots. If they are to remain for a long time undeveloped, as for example is the case with winter buds, they are protected in a special manner during their period of rest. SECT, I MORPHOLOGY 19 The Origin of New Shoots.—The formation of new growing points by the bifurcation of older points of growth, in a manner similar to that already described for Dictyota dichotoma (Fig. 8), occurs also, in almost typical form, in the lower thalloid Hepaticae (Miccia fluitans, Fig. 10). Among the Cormophytes this method of producing new shoots is of less frequent occurrence, and is then mainly limited to the Pteridophytes, for one division of which, the Lycopodiuceae, it is characteristic. In this case, whenever a shoot is in process of bifurcation, two new vegetative cones are formed by the division of the growing point (Fig. 18). In most of the Lycopodiaceae the new shoots thus formed develop unequally ; the weaker Fic. 18.—Longitudinal section of a becomes pushed to one side and ultimately _ bifurcating shoot (p) of Lyco- appears as a lateral branch (Fig. 19). podium alpinum, showing me ‘ . a & equal development of the rudi- Although a relationship as regards posi- jnentary shoots, p', p”; b, leaf tion is generally apparent between the rudiments; ¢, cortex; /, vascular origin of leaves and the lateral shoots, in aa (Alter MEG ELMAIER, the system of branching resulting from such : a bifurcation of the vegetative cone this connection does not exist. In the more highly developed Bryophytes, particularly in the true Mosses, new shoots arise obliquely below the still rudimentary leaves at some distance from the growing point. In the Phanerogams new shoots generally arise in the axils of the leaves. In the accompanying illustration of a longi- tudinal section of a phanerogamic shoot (Fig. 17) the rudiment of a shoot (g) is just appear- Fic. 19.—Bifureating shoot ing in the axil of the third uppermost leaf ; in (p) of Lycopodium inun- the axils of the next older leaves the conical datum, showing unequal a development of the rudi- protuberances of the embryonic leaves are mentary shoots, »’, p”; already beginning to appear on the still rudi- b, leaf rudiments. (After : Hearvasnan S40) mentary shoot. These rudimentary shoots may either continue to develop, or they may remain for a time in an embryonic condition, as buds. Shoots thus pro- duced in the axils of leaves are termed AXILLARY SHOOTS. The leaf in the axil of which a shoot develops is called its SUBTENDING LEAF. An axillary shoot is usually situated in a line with the middle of its subtending leaf, although it sometimes becomes pushed to one side. As a rule, only one shoot develops in the axil of a leaf, yet there are instances where it is followed by additional or ACCESSORY SHOOTS, which either stand over one another (serial buds), as in Lonicera, Gleditschia, Gymnocladus, or side by side (collateral buds), as in many Liltaceae. 20 BOTANY PART I Although in the vegetative regions, iz. the regions in which merely vegetative organs are produced, the rudiments of the new shoots of phanerogamic plants make their appearance much later than those of the leaves, in the generative or flower-producing regions the forma- tion of the shoots follows directly upon that of their subtending leaves, or it may even precede them. In this last case the subtending leaves are usually either poorly developed or completely suppressed, as in the inflorescence of the Cruciferae, in which a series of phylogenetic changes has probably led to this result. Shoots developing in definite succession from the growing points of other shoots are designated NORMAL, in contrast to ADVENTITIOUS SHOOTS, which are produced irregularly from the older portions of a plant. Such adventitious shoots show no definite arrangement, and frequently spring from old stems, also from the roots of herbaceous plants (Brassica oleracea, Anemone sylvestris, Convolvulus arvensis, Rumex Acetosella), or of bushes (Rubus, Rosa, Corylus), or of trees (Populus, Ulmus, Robinia), or they may develop even from leaves, particularly from the fronds of Ferns. An injury to a plant will frequently induce the formation of adventitious shoots, and for this reason gardeners often make use of pieces of stems, rhizomes, or even leaves as cuttings from which to produce new plants. A leaf of a Begonia merely placed upon damp soil will soon give rise adventitiously to new plants. Leaves and also normal shoots, which make their appearance as outgrowths from the portions of the parent shoot still in embryonic condition, have an external or EXOGENOUS origin. Adventitious shoots, on the other hand, which arise from the older parts of stems or roots, are almost always ENDOGENOUS. They must penetrate the outer portions of their parent shoot before becoming visible. Adventi- tious shoots formed on leaves, however, arise, like normal shoots, exogenously. The further Development of the Shoot.—All normal shoots are dependent for their origination upon the embryonic substance of the growing point of the parent shoot ; even when they make their appearance at some distance from the growing apex (Fig. 17), embryonic substance has been reserved at that point for their forma- tion. The growing points of adventitious shoots are also, for the most part, produced from tissue which has retained its embryonic condi- tion in the older portions of the plant. In some cases, however, they arise from newly-developed growing points, and afford evidence of the power inherent in plants to return to an embryonic state and produce new growing points. The processes of development which result in the production of new segments at the apex of a shoot are followed by an increase in size and by the further growth of the segments. This growth is usually introduced by the vigorous elonga- tion of the segments, by means of which their rapid unfolding from SECT. I MORPHOLOGY 21 the bud is brought about. The region of strongest growth in a shoot is always at some distance from its growing point. The growth in length and consequent elongation of the shoot is in some cases so slight that the leaves remain close together, and leave no free spaces on the stem, thus forming so called DWARF SHOOTS. As examples of such dwarf shoots may be mentioned the thickly-clustered needles or fascicled leaves of the Larch, the rosettes formed by the fleshy leaves of the Houseleek (Sempervivum), and also the flowers of Phanerogams with their thickly-crowded floral leaves. In the ordinary or ELONGATED SHOOTS, such as are formed in the spring by most deciduous trees, the portions of the stem between the insertions of the leaves become elongated by the stretching of the shoot. The stem of a shoot, as contrasted with the leaves, is often spoken of as the axis ; while the portions of the stem axis between the insertions of the leaves are termed the INTERNODES, and the parts of the axis from which the leaves arise the NoDES. When the base of the leaves encircles the stem, or when several leaves take their origin at the same node, the nodes become strongly marked (Labiatue). In some cases the growth in length of a shoot continues for a longer time at certain intermediate points by means of INTERCALARY GRowtTH. Such points of intercalary growth are generally situated at the base of the internodes, as in the case of the Grasses. A displace- ment from the position originally occupied by the members of a shoot frequently results from intercalary growth. A bud may thus, for example, become pushed out of the axil of its subtending leaf, and so apparently have its origin much higher on the stem ; or a subtending leaf, in the course of { its growth, may carry its axillary bud along | with it, so that the shoot which afterwards develops seems to spring directly from its sub- tending leaf; or, finally, the subtending leaf may become attached to its axillary shoot, and growing out with it, may thus appear to spring from it (Fig. 20). Resting Buds.—As a means of protection, buds may become invested, in winter, with scale-like leaves or BUD-SCALES, which are rendered still more effective as protective struc- tures by hairy outgrowths and excretions of resin and gum, and also by the occurrence of ; at Fic. 20.—Samolus Valerandi, air-spaces. Not infrequently the subtending Q,cy axinary shoot leaf takes part in the protection of its axillary bearing its subtending bud, and the base of the leaf-stalk, after the ee in leaf itself has fallen, remains on the shoot and Stats forms a cap-like covering for the winter bud. The buds of tropical plants, which have to withstand a dry period, are similarly protected ; 22 BOTANY PART I but where the rainfall is evenly distributed throughout the year buds develop no such means of protection. Many of the deciduous trees in Temperate regions are inclined to unfold their winter buds in the same vegetative period in which they are produced. This tendency is particularly marked in the Oak, and results in the development of a MIDSUMMER GROWTH. All the buds of a plant do not develop; there are numerous deciduous trees— such as the Willow, in which the terminal buds of the year’s growth regularly die. Sometimes buds, usually the first-formed buds of each year’s shoot, seem able to remain dormant during many years without losing their vitality ; these are termed DORMANT BuDS. In the case of the Oak or Beech such latent buds can endure for hundreds of years ; in the meantime, by the elongation of their connection with the stem, they continue on its surface. Often it is these, rather than adventitious buds, which give rise to the new growths formed on older parts of stems. It may sometimes happen that the latent buds lose their connection with the woody parts of their parent stem, but nevertheless grow in thickness, and develop their own wood ; they then form remarkable spherical growths within the bark, which may attain the size of a hen’s egg and can be easily separated from the surrounding bark. Such globular shoots are frequently found in Beech and Olive trees. The Metamorphosis of the Shoot.—The BULBILS and GEMMA, which become separated from their parent plant and serve as a means of reproduction, are special forms of modified buds. They are always well supplied with nutritive substances, and are of a corresponding size. Many plants owe their specific name to the fact that they produce such bulbils, as, for example, Lilium bulbiferum and Dentaria bulbifera. Shoots that live underground undergo characteristic modifications, and are then termed ROOT-STOCKS or RHIZOMES. By means of such sub- terranean shoots many perennial plants are enabled to persist through the winter. A rhizome develops only modified leaves in the form of larger or smaller, sometimes scarcely visible, scales. By the presence of such scale leaves and by its naked vegetative cone, as well as by its internal structure, a rhizome may be distinguished from a root. Rhizomes usually produce numerous roots; but when this is not the case, the rhizome itself functions as a root. Rhi- Fic. 21.—Rhizome of Polygonatum multifiorum. «, Bud of zomes often attain a con- next year’s aerial growth; 0, scar of this year’s, and siderable thickness and c, d, e, scars of three preceding years’ aerial growth; wv, store up nutritive material roots. (} nat. size.) for the formation ak -geeial shoots. In the accompanying illustration (Fig. 21) is shown the root-stock of the so-called Solomon’s Seal (Polygonatum nulti- florum). At d and c are seen the scars of the aerial shoots of the SECT. I MORPHOLOGY 23 two preceding years; and at b may be seen the base of the stem growing at the time the rhizome was taken from the ground, while at a is shown the bud of the next year’s aerial growth. The rhizome of Coralliorrhiza innata, a saprophytic Orchid, affords a good example of a root-stock functioning as a root (Fig. 22). BuLss, also, belong to the class of metamorphosed shoots. They represent a shortened shoot with a flattened, discoid stem (Fig. 23, zk), the fleshy thickened scale Fic. 22.—Rhizome of Coralliorrhiza innata, Fic. 23. — Longitudinal section of tulip a, Floral shoot; b, rudiments of new bulb, Tulips Gesneriana. zk, Modified rhizome branches. (After ScHAcHT, stem; zs, scale leaves; v, terminal nat. size.) bud; k, rudiment of a young bulb; w, roots. (Nat. size.) leaves (zs) of which are filled with reserve food material. The aerial growth of a bulb develops from its axis, while new bulbs are formed from buds (k) in the axils of the scale leaves. Another form of underground shoot, allied to bulbs and connected with them by transitional forms, is distinguished as a TUBER. The axis of a typical tuber, in contrast to that of a bulb, is fleshy and swollen, functioning as a reservoir of reserve material, while the leaves are thin and scaly. Of such tubers those of the Meadow Saffron (Colchicum autumnale) or of Crocus sativus are good examples. In the Meadow Saffron new tubers arise from axillary buds near the base of the modified shoot, but in the Crocus from buds near the apex. In consequence of this, in the one case the new tubers appear to grow out of the side, and in the other to spring from the top of the old tubers. The tubers of the Potato 24 BOTANY PART I (Fig. 24) or of the Jerusalem Artichoke (Helianthus tuberosus) are also subterranean shoots with swollen axes and reduced leaves. They are formed from the ends of branched, underground shoots or runners (STOLONS) and thus develop at a little distance from the parent plant. The so-called eyes on the outside of a potato, from which the next year’s growth arises, are in reality axillary buds, but the scales which represent their subtending leaves can only be distinguished on very young tubers. The parent plant dies after the formation of the tubers, and the reserve food stored in the tubers nourishes the young plants which afterwards develop from the eyes. As, in their uncultivated Fic. 24.—Part of a growing Potato plant, Solanum tuberosum. The whole plant has been de- veloped from the dark-coloured tuber in the centre. (From Nature, copied from one of Bai.on’s illustrations, 4 nat. size.) state, the tubers of the Potato plant remain in the ground and give rise to a large number of new plants, it is of great advantage to the new generation that the tubers are produced at the ends of runners, and are thus separated from one another. Similar advantages accrue from surface runners, such as are produced on Strawberry plants. Surface runners also bear scale-like leaves with axillary buds, while roots are developed from the nodes. The new plantlets, which arise from the axillary buds, ultimately form independent plants by the death of the intervening portions of the runners. Still more marked is the modification experienced by shoots which only develop reduced leaves, but the axes of which become flat and leaf-like, and assume the functions of leaves. Such leaf-like shoots are called CLADODES or PHYLLOCLADES. Instructive examples of such forma- SECT. I MORPHOLOGY 25 tions are furnished by Muscus aculeatus (Fig. 25), a small shrub whose stems bear in the axils of their scale-like leaves (/) broad, sharp-pointed cladodes (cl), which have altogether the appearance of leaves. The flowers arise from the upper surface of these cladodes, in the axils of scale leaves. In like manner the stems of the Opuntias (Fig. 26) are considerably fattened, while the leaves are reduced to small thorny protuberances. In this case the juicy flat shoots perform not only the functions of assimilatory organs, but also serve as water-reservoirs in time of drought. It is possible that all the leaves of a plant may become more or less completely reduced, without any marked change Fic. 25,—Twig of Ruscus aculeatus. f, Leat ; Fie. 26.—Opuntia monacantha Haw., showing flower cl, cladode ; bl, flower. (Nat. size.) and fruit. (After Scuumany, } nat. size.) occurring in the appearance of the stems, except that they then take on a green colour; this, for example, is the case in the Scotch Broom (Spartium scoparium), which develops only a few quickly-falling leaves at the end of its long, naked twigs; or, as in many species of rushes (Juncus, Scirpus), whose erect, slender, wand-like stems are entirely leafless and at the same time unbranched. As a rule, however, all leafless green Phanerogams will be found to have swollen stems, as in the variously shaped Huphorbiae and Cacti. A great reduction in the leaves, and also in the stems, often occurs in phanerogamic parasites, in consequence of their parasitic mode of life. The leaves of the Dodder (Cuscuta, Fig. 185, 6) are only represented by very small, yellowish scales, and the stem is similarly yellow instead of green. The green colour would, in fact, 26 BOTANY PART I be superfluous, as the Dodder does not. produce its own nourishment, but derives it from its host plant. Cuscuta Trifolii, one of the most fre- quent of these parasites, is often the cause of the large yellow areas frequently observable in the midst of clover fields. In certain tropl- cal parasites belonging to the families Rafflesi- aceae and Balanophoraceae, the process of re- duction has advanced so far that the flowers alone are left to represent the whole plant. Rafflesia Arnoldi, a plant growing in Sumatra, is a remarkable example of this ; its flowers, although they are a metre wide, the largest flowers in existence, spring directly from the roots of another plant (species of Cissus). A peculiar form of metamorphosis is ex- hibited by some climbing plants through the transformation of certain of their shoots into TENDRILS. Such tendrils assist the parent plant in climbing, either by twining about a support or otherwise holding fast to it. The twining bifurcated tendrils of the Grape-vine, for example, are modified shoots, and so are also the more profusely branched, hold-fast tendrils of