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PLANT ANATOMY A. FAHN Professor of Botany The Hebrew University, Jerusalem, Israel Translated from the Hebrew by SYBIL BROmO·ALTMAN PERGAMON PRESS .~. ~~~OOK~. OXFORD' NEW YORK £6'\ f'>,-- ~--!.?Y (.;)-.~ ,/ t- ....- """" v~ ~ - ( '\ TORONTO· SYDNEY· BRAUNSCH 00 A r- {) ".1 . ~. CONTENTS PREFACE GENERAL STRUCTURE OF HIGHER PLANTS ....••. 2 THE CELL ••......•..•••...•.•••.....•.....•. 3 MERISTEMS . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mature Tissues 4 PARENCHYMA ............................. 5 COLLENCHYMA ....... . ..................... 6 SCLERENCHYMA ..........•....•.............. vii 7 44 73 80 85 7 XYLEM ••.•.••.• ,.,.. . • • . • . . . . . •. . . . . • . . •. . •. . . . .• 102 I I . 8 PHLOEM •.•••••••....••••••.••.•.•.•••.•...•.••. 118 ! 9 LATICIFERS .•...•..•.....•.•.....••.•.••..••••. 130 10 EPIDERMIS...................................... 137 I • Primary Vegetative Body Of the Plant I I THE STEM ................................... 12 THE LEAF ................................... 13 THE ROOT .......................... Secondary Body of the Plant 14 VASCULAR CAMBIUM •.••..•.••.•...••••.....•• 162 193 240 273 15 SECONDARY XYLEM .•••.....•.••...•.•........ 286 16 SECONDARY PHLOEM •.••..•••••.•.•..••..••... 325 17 PERIDERM ••..•.•••..•.•....••..•..•••. -•••..• 331 18 ANOMALOUS SECONDARY GROWTH .............. 349 Pergamon Press Ltd., Headington Hill Hall, Oxford 011 Press Inc., Maxwell House, Fairview Park, Elmsford, New York 10523 pe(gan1 Pergamon of Canada Ltd., 207 Queen's Quay West, Toronto 1 55 (Amt.) Pty. Ltd. 19a Bounda:y Street, RushcutterslBay, N.S w. 2011 [flo" pen:t.!l pre Australia Vieweg & Sohn GmbH, Burgplatz I, Braunschweig Copyright © J 967 A. FAHN First English Edition 1967 Reprinted with corrections 1969 r-- Reprinted 1972 -___ --, I r~!~iral Ph,l! lti~., Cri)"H1 D~te " ". CAL I CUl-67JOll / N D. .s;- r-:t I Original Hebrew book _published by Hakkibutz Hameuhad Publishing House Ltd. Library of Congress Catalog Card No. 66--24822 Printed in Great Britain by A. Wheaton & Co., Exeter 08 011943 3 PREFACE PLANT anatomy is a basic science and as such is of great importance to students of all the plant sciences. Without a thorough knowledge of this field the physiological processes carried out within the plant and the phylogenetic relationships between the various plant groups cannot be fully under- stood. The detailed study of the elements and tissues of which the plant is constructed enables a better understanding of adaptation to special functions as well as of the adaptation of entire plants to different environ- mental conditions. Without a thorough knowledge of the anatomical and histological structure of plants the results of physiological and ecological oxperiments, for instance, may be incorrectly interpreted. Also, to-day no ~onclusive opinions on evolutionary trends or taxonomic relationships can be suggested on the traditional basis of the study of external morphological characteristics alone; it is now necessary to support such work by the use of the many and varied anatomical and histological characters, which can be observed only from microscopic, and even submicf9scopic, investigation. Anatomy, which draws the attention of the student to the form, varia- bility and structure of the Itissues comprising the plant body, can be said to develop an aesthetic sense. In addition to this, the awareness of the regularity, and repetition, at different levels, of the structural patterns, as well as of the amazing correlation of structure and function, serves to make anatomy a rewarding field of research. A large section of this book deals with the vegetative plant body. The first introductory chapter briefly presents the general structure of the higher plant. This is followed by tbe descriptions of the different types of cells and tissues that are present in the Tracheophyta. Later chapters de- scribe how the vegetative plant body, both primary and secondary, is constructed of these various tissues. The last section deals with the structure of the flower, fruit and seed. In the chapter on the flower I have covered pollination, fertilization and embryo development. In my opinion this is necessary in order that a full and balanced picture of the development and structure of plants and their tissues can be obtained. An effort has been made, when dealing with the structure of the elements, tissues and organs of the plant body, to employ the following ap- proaches-ontogenetic, phylogenetic, physiological and ecological. Atten- tion has also been paid, wherever possible, to such characteristics that are of importance to agriculture and industry. In view of modern research in plant anatomy and biology as a whole, which ha~ hTf"Illnl"d-""" 1: .... 1. .. ~- -- vi Contents 19 THE Reproductive Organs I FLOWER .........•....................•. 360 20 THE FRUIT .................................. 439 21 THE SEED ..............•.................... 466 GLOSSARY OF TERMS ......................•...... 't~0 AUTHOR INDEX 495 SUBJECT INDEX viii Preface bility in the definitions of the various elements and tissues is stressed throughout the book. i In many cases I have endeavoured to point out problems which as yet constitute serious gaps in our knowledge, and which await further research. The inclusion of a large number of illustrations has enabled the text to be written in a concise form. The great majority of the micrographs are original and have been made from slides in the collection of.the laboratory of Plant Anatomy at the Hebrew University of Jerusalem. The drawings are in p",rt original or have been taken from previous publications of the author, and the rest have been redrawn and adapted from various books and articles. In the case of the latter the original author is cited in the le-' gend and the reference is given at the end of the relevant chapter or Chap- ter I. In a book of this size and scope it is impossible to deal with all the relevant facts in detail and therefore many references are given in the text. It is hoped that readers will refer to these and other articles, books, etc., in order to broaden their knowledge. For convenience, details of these references are given at the end of each chapter. \ This book was originally written in Hebrew for the use of students study- ing in Israel. Thus many of the examples cited )Ire of plants growing in this and neighbouring regions. / I express my thanks to all those who helped me in the preparation of tlie original'Hebrew book. I am indebted to·my friend S. Stoler for his critical reading of the manuscript and for his valuable suggestions; to Mrs. Ella Werker for her great help in the preparation of the manuscript and for seeing the book through press; to Mrs. Batya Amir for the careful and accurate execution of most of the drawings; to Y. Shehori for his aid in the· preparation of mast of the photographs appearing in tire book; and to Mrs. Irena Fertig for her assistance in reading the pr09fs. My thanks are also extended to all those who have put at my disposal photographs and.drawings, as well as to my colleagues at the Hebrew University who gave me valuable advice at all times. I especially thank my students, throughout the years, who have encouraged me to write this book. In connection with this revised English edition I am indebted to Dr. C. \ R. Metcalfe and Sir George Taylor who suggested and "encouraged me to have my book translated. I greatly appreciate the criticism and advice that Dr. Metcalfe extended after having read the English manuscript. I thank Dr. F. A. L. Clowes who undertook to edit the English. I gratefully acknow- ledge the permission so generously granted to me by the Hakkibutz Hame- uhad Publishing House Limited to translate the original text. I also thank Mrs. Sybil Broido-Altman for undertaking the translation. Once again I thank Mrs. Ella Werker, who assisted in the collation. A.FAHN Jerusalem, April, 1965 CHAPTER I GENERAL STRUCTURE OF HIGHER PLANTS PLANTS that bear seeds are termed spermatophytes. These plants pro- duce spores (newly formed embryo sacs and pollen grains) and therefore they are sporophytes. These plants develop from a zygote which results 3 'v CotyJeEion -Hypocotyl -Root 2 FIG. 1. Schematic drawings of longitudinal sections ofa dicotyledonous plant at various ages. 1. Embryo. 2, Seedling. 3, Mature plant. (Adapted from Troll, 1948.) from the fertilization of an egg cell by a male gamete. At the start the zygote divides into two cells which themselves undergo further divisions to form the embryo. The embryo usually consists of radicle, hypocotyl, cotyledons and olumule (Pi!!. L no n TJ,p. p".,h .. " ...... 0 ............ " ~~ ____ 1_..J 2 Plant Anatomy and dormant within the seed which develops from the entire ovule. IUs not always clear whether the embryo possesses a radicle ~roper or whether it merely has a root apical meristem. It is difficult to make a definite dis- tinction between the radicle and hypocotyl, and therefore the axis of the embryo is called the hypocotyl-root axis. With the germination of the seed the embryo renews its growth. The radicle grows and penetrates deeper into the soil. In some species the hypocotyl elongates and so raises the cotyledons above soil level where they become green (epigeal germination). In other species the hypocotyl does not elongate, .or it elongates only very slightly, and the cotyledons remain below soil level where they eventually rot (hypogeal germination). The plumule, which is situated above the junction of the cotyledons to the hypocotyl, elongates and gives rise to the stem and leaves (Fig. 1, nos. 2, 3) .. That part of the stem to which the leaf is attached is ter~ed the node and that part of the stem between two nodes, the internode. The number of nodes and internodes ihcreases with the continued growth of the stem. At the start of germination all the cells of the embryo divide, but later cell division is restricted to certain areas of the seedling-usually in the apices of the axis. /' ' The morphology of the various organs of the spermatophytes is extrem- ely varied. The nature of the different. organs, such as the stem, leaf, root, flower and fruit, and the differences in their external and internal structure have been variously interpreted (De Bary, 1877; Strasburger, 1891, 1923; Haberlandt, 1918; Goebel, 1928-33; Troll, 1935, 1937,1938, 1939, 195+- 57; Eames and MacDaniels, 1947; Foster, 1950; McLean and Ivimey- 'Cook, 1951, 1956; Esau, 1953; Eames, 1961). The stem (which bears the leaves) together with the leaves forms a single ont9genetic and, apparent- ly, also evolutionary unit, and so these organs together are termed the shoot. The shoot and root, together with their branches, form .an organic con- tinuation of the embryo as their development results form the activity of the apical meristems, which are tissues directly descended from those of the embryo. In those spermatophytes in which the apical meristems of the main shoot remain active throughout the life of the. plant, the shoots developing from the axillary buds remain secondary and the extent of their gro,wth is regulated by the apex of the main shoot. Such branching of the stem is termed monopodia! (Fig. 2, no. 1). The main axis and the successive axial branches do not always have the ability to grow indefinitely. In many plants the shoot apex becomes reproductive or aborts, and then further growth is carried out by lateral buds. Such branching is termed sympodial (Fig. 2, no. 2). In many cases buds and roots may develop from portions of the plant distant from the apical meristems; such organs are termed adventitious General Structure of Higher Plants 3 organs. Examples of such organs are the fibrous roots which are common among the monocotyledons and develop from the hypocotyl or from the basal internodes of the stem,· Adventitious roots sometimes develop from aerial portions or Trom old roots of woody plants. Adventitious shoots are known. to develop on roots and on stems from·places in which no dormant buds are found. The apices of the adventitious shoots and roots contain the same meristematic tissues as the apical meristems of the ordi- ;;ary organs of the primary axis. " J ~ 5-", ..- -4 4--.:- -3 3- '_ -2 2-·, -1 I'::"" -Cotyledons-- 2 FIG. 2. Diagrams of the mode of branching in trees, I, Monopodial branching. 2, Sympodial branching. The numbers indicate the position of the tip at the end of each annual longitudinal incremen!. (Adapted from Troll, 1948.) As the cells formed by the meristem become more distant from the apex, they undergo gradual differentiation (Fig. 3). Near the apex of the shoot and root three meristems of different tissues become observable: (1) protoderm, from which the epidermis, the protective tissue, develops; (2) procambium, from which the primary vascular tissues (primary xylem which serves mainly to transport water and the primary phloem which serves to transport metabolites) develop; (3) ground meristem, from which tissues of the cortex and pith develop. These comprise parenchyma, the basic tissue of the plant, sclerenchyma and colienchyma, the supporting tissues of the plant. The cells of the procambium gradually differentiate into phloem and xylem elements, and so these elements become more numerous as seen in consecutive cross-sections of the stem made at levels further away from the ::Inpv Th ... _1..1 ___ _ 1 _____ "-_ '- 4 Plant Anatomy Primary phloem - lateral root - Root cap FIG. 3. Schematic drawings of a dicotyledonous plant showing the arrangement of the principal tissues. I, Longitudinal section. 2, 3 and 4, Cross-sections at varioUS levels. (Adapted from Esau, 1953.) General Structure of Higher Plants 5 circumference inwards. In the root the direction of differentiation of the primary xylem is also centripetal, while in the stem these elements increase from the centre toward the circumference. Therefore in .lhe stem the primary phloem and xylem approach one another during their development. In monocotyledons and in a few herbaceous dicotyledons all the cells"of the procambium differentiate into elements of the conductive tissues. In most dicotyledons and gymnosperms, one layer of procambial cells . between the primary xylem and primary phloem forms a new meristematic tissue called the vascular cambium. The vascular cambium produces secondary phloem towards the circumference, and secondary xylem towards the centre of the axis, as a result of cell division in a plane parallel to the circumference. The volume of the secondary tissues, especially of the xylem, continually increases and thus the thkk stem and,root of the shrub or tree is developed. In such a case the functions of the tissues produced by the apical meristems are restricted to the ends of the shoots and Toots only . . With the increase in width of the axis of the plant, as a result of the increase .and· development of the secondary vascular tissues, the epidermis and cortex peel off, and then the function of protection against external damage • is taken over by a secondary protective tissue-the periderm. In the periderm a second,uy meristematic tissue, the phellogen, is present. The phellogen produces the phe/lem (several layers of dead cork cells) towards the exterior and inwards, in the majority of cases, it produces the phelloderm, which consists of one to five laye}s of living cells. The complex of plant tissues developing from the primary meristems, which are usually found in the apices of the roots and shoots, is termed the primary plan! body, and those tissues developing from the vascular cambium and phellogen constitute the secondary plant body. Leaves develop from the apical meristem. They consist of an epidermis, mesophyll and veins-strands of vascular tissue surrounded by parenchyma or by parenchyma and supporting tissues. In addition to the tissues mentioned above, other tissues; such as latid- fers, are found in the spermatophytes. Idioblasts, i.e. specialized ceils, as well as some of the specialized tissues may develop from the basic tissues within the plant body. References BOUREAU, E. 1954, 1956, 1957. Anatomie Vegetate, VQIs. 1, 2, 3, Presses Univer- sitaires de France, Paris. CARLQUIST, S., 1962. Comparative Plant Anatomy, Holt, Reinhart and Winston, New York. De BARY, A. 1877. Vergleichende Anatomie der Vegetationsorgane. W. Engelmann, Leipzig. EAMF<:' 4 T 10£1 .,,----, , Plant Anatomy EAMES, A. 1. and MACDANIELS, L. H. 1947. An Introduction to Plant Anatomy. '2nd ed. McGraw~Hill. New York-London. t ESAU, K. 1953. Plant Anatomy. John Wiley, New York. FOSTER, A. S. 1950. Practical Plant Anatomy. D. Van Nostrand, New York-London., GOEBEL, K. 1928-33. Organographie der Pflanzen, Vols. 1-3.' G. Fischer. Jena. HABERLANDT, G.1918.Physi%gischePjlanzenanatomie. 5thed. W. Engelmann, Leipzig. McLEAN, R. C. and IVIMEY-Com" W. R. 1~51. 1956. Textbook o/Theqretical Botany, 1 and 2. Longmans. London. PALLADIN, W. I. 1914. Pjianzenanatomie. B. G. Teubner, Leipzig and Berlin. StRASBuRGER, E. 1891. Ober den Bau und die Verrichtungen der Leitungshahnen in den PJlanzen. Histo!ogische Dei/riige. Vol. 3. G. Fischer, Jena. STltASBURGER, E. 1923. -Das botanische Praklikum. 7th ed. G. Fischer, Jena. TROLL, W. 1935, 1937. 1938, 1939. Verglelchende Morph%gle der Mheren Pflanzen. Gebr. Borntraeger, Berlin. TROLL, W. 1948. Allgemeine Botanjk. F. Enke, Stuttgart. TROLL, W. 1954-7. Praktische £infiihrung in die Pf/anzenmorphologie. Vols. 1, 2. G. Fischer, Jena. CHAPTER 2 THE CELL THE basic. units of which organisms are constructed are the cells. The term cellula was first used by Robert Hooke in 1665 .. Hooke gave this term to the small cavities surrounded by walls that he saw in cork; later he observed cells in other plant tissues and saw that they contained "juice" (Matzke, 1943). Still later the protoplasm-the substance within the cell-was discovered." In 1880 Hanstein coined the term protoplast to indicate the unit of protoplasm found in a single cell. He also suggested that the term protoplast should be used instead of the term cell, but his suggestion is not gener- ally,accepted and cell is the accepted term. In plants the term cell includes 'the protoplast together with the wall. The cell wall. was, for a long time, regarded as a non-living excretion of the living cell matter, but recently more and more evidence has been found that organic unity exists bhween the protoplast and the wall, especially in young cells, and that the two together form a single biological unit. In 1831 Robert Brown discovered the nucleus in an epidermal cell of an .s-."cJ.h.ld 0\ttft. lcr 18# H(J)sa H7Jl' l~l(h'hl db'tiago.·l~hed (;e{~\.X'U' tire f'l'(lt<J- plasm and the cell sap, and in 1862 Kiilliker introduced the term cytoplasm. From the end of the nineteenth century and during the twentieth century research on the cell has developed so rapidly and with such enormous strides that cytology has become a science of its own. It is customary to divide the protoplast constituents into two groups: (a) protoplasmic components and (b) non-protoplasmic components. To the first group belongs the cytoplasm, the "living" protoplasmic substance of the cell in which the specialized protoplasmic organelles, such as the nucleus and plastids, are located (Fig. 4, no. 6). The nucleus carries the information of heredity and so is of paramount importance to all the processes in the cell. The plastids usually contain pigments, but sometimes they are devoid of pigments and then they may store starch granules, lipid droplets and protein crystals. Other protoplasmic organelles are the mito- chondria, which are minute bodies concerned in the respiratory processes and the ribosomes, still smaller organelles, which are the sites of protein synthesis. To the second group belong the vacuoles, which are nOllofotonl::1o;;:mi,.. inclu~i(\n<:l (,.. ... ~ .. _.J ~ ~. • 8 . Plant Anatomy include reserve materials such as starch grains, oil droplets, and aleurone grains, and other products of metabolism such as various crystals. , Usually the cell contains a single nucleus, but in some lower plants the. presence of a nucleus with a distinc.t and permanent structure. is doubtful. Pr'oplaslid Endopla smic reticulum FIG. 4. 1, Three-dimensional diagram of a plant cell from which a porlion has been removed to reveal a large central vacuole and the cytoplasm, which contains the nucleus, lining the cell waU. 2, As above, but of a cell in which 'the nucleus is located more or less centrally and in which the cytoplasm surrounding the nucleus is connected to the peripheral cytoplasm by cytoplasmic strands. 3, An adaxial epidermal cell from the calyx of Tropaeolum majus containing chromoplasts. 4, Chromoplasts in a carrot root cell. 5, Leucoplasls in a young endosperm cell of Zea. 6, Diagram of a meristematic plant cell. (No.3, adapted from Strasburger, J923 ; nos. 4 and 5, adapted from Eames and MacDaniels, 1947;' no. 6, adapted from Sitte, 1961.) In some cells of the higher plants, such as the sieve elements of the phloem which are adapted for translocation, the nucleus is absent from the mature cell. However, there are also cells which have numerous nuclei. A .multi- The Cell 9 nucleated cell can comprise an entire organism as in some fungi and algae, or multi-nucleated cells may be a transitory stage in the development of a tissue as, for example, in the endosperm of many plants and sometimes in fibres. The accepted view in many cases is that each nucleus together with the protoplasm surrounding it' forms a walHess cell so that the entire multi-nucleate body comprises a group of protoplasmic units. Such a structure is called a coenocyte. The coenocyte aroused much interest in phylogenetic and ontogenetic studies. Two theories exist which deal with the relation of the entire organism and the single cell. According to the cell theory, which was developed about the middle of the nineteenth century, the organism consists, both phylogenetically and ontogenetically, of a complex of an enormous number of cells each of which plays a role in determining the nature of the organism. The theory contradicting the above is the organisrnal theory. This theory gives less importance to the individual cells and mainly stresses the unity of the protoplasmic mass of the entire organism. According to this theory the. organism as a unit, to a large extent, determines the nature of the cells. _. These two theories are important and, for the following reasons, atten- .,!ion_was.paid to both of them in histological and cytological research of . plants. ,Many aspects of ontogeny, such as the processes of cell division, _the.· origin· of vessels and articulated laticifers, the development of idioblasts, etc., were investigated in the light of the cell theory. However, the specialization of the different cells and tissues in the plant and the sites of appearance of the various types of cells and tissues can be explained only on the basis of the organismal theory which regards the organism as an unit. Tlie protoplast PROTOPLASMIC COMPONENTS The cytoplasm The cytoplasm comprises part of the protoplast. Physically it is a vis- cous substance which is more or less transparent in visible light. Chemi- cally the structure of the cytoplasm is very complex even though the major component (85-90 %l is water. Of the most important components of the cytoplasm are the proteins. Many of the physical properties of the cytoplasm can be explained by the fact that most of the inorganic and organic substances in it are present in colloidal solutions. However, these substances may occur in other states such as solutions and crystals. Until recently the cytoplasm was considered to be structureless, but with the aid of thf' plp.rtr<" .... ...... : ...... ~~---- ~--, .