MODERN SCIENCE 
 
 EDITED BY SIB JOHN LUBBOGZ, BART., M.P. 
 
 THE OAK
 
 MODERN SCIENCE. 
 
 Edited by SIB JOHN LUBBOCK, Bart., M.P. 
 
 I. 
 
 THE CAUSE OF AN ICE AGE. 
 
 By SIR ROBERT BALL, LL.D., F.R.S., 
 Royal Astronomer of Ireland. 
 
 II. 
 
 THE HOESE: 
 
 A Study in Natural History. 
 
 By WILLIAM HENRY FLOWER, O.B, 
 
 Director of the British Natural History Muieum. 
 
 HI. 
 THE OAK: 
 
 A Popular Introduction to Forest-Botany. 
 By H. MARSHALL WARD, P.R.S., F.L.S. 
 
 IV. 
 LAWS AND PEOPEETIES OF MATTEE. 
 
 By R. T. (JLAZEBROOK, P.R.S., 
 Fellow of Trinity College, Cambridge. 
 
 London : KEGAN PATJL, TRENCH, TRUBNER & CO. LTD.
 
 THE OAK IN SUMMER (fiosxmassler.)
 
 THE OAK 
 
 A POPULAR INTRODUCTION TO FOREST -BOTANY 
 
 H. MARSHALL WARD, M.A. F.R.S. F.L.S. 
 
 LATE FELLOW OF CHRIST'S COLLEGE, CAMBRIDGE 
 PROFESSOR OF BOTANY AT THE R07AL INDIAN ENGINEERING. COLLEGE, COOPER'S HILL 
 
 LONDON 
 KEGAN PAUL, TKENCH, TEUBNEB, & CO. LTD. 
 
 PATERNOSTER HOUSE, CHARING CROSS ROAD 
 
 1892
 
 (The rights of translation and of reproduction are reserved)
 
 CONTENTS 
 
 CHAPTER PAGB 
 
 I. INTRODUCTION . t . . . . 1 
 
 II. THE ACORN AND ITS GERMINATION THE SEEDLING 10 
 
 III. THE SEEDLING AND YOUNG PLANT . . .24 
 
 IV. THE SEEDLING AND YOUNG PLANT (continued). ITS 
 
 SHOOT-SYSTEM DISTRIBUTION OP THE TISSUES 39 
 V. THE SEEDLING AND YOUNG PLANT (continued}. 
 
 STBUCTTTBE OP THE VASCULAE TISSUES, &c. . . 52 
 VI. THE SEEDLING AND YOUNG PLANT (continued). 
 
 THE BUDS AND LEAVES . . . .72 
 
 VII. THE TEEE ITS ROOT-SYSTEM . . . . 89 
 
 VIII. THE TREE ITS SHOOT-SYSTEM . . .98 
 
 IX. THE TREE (continued). INFLORESCENCE AND 
 
 FLOWERS FEUIT AND SEED . . . . 121 
 
 X. OAK TIMBER ITS STRUCTURE AND TECHNOLOGICAL 
 
 PECULIARITIES . . . . .136 
 
 XI. THE CULTIVATION OP THE OAK, AND THE DISEASES 
 
 AND INJUEIES TO WHICH IT IS SUBJECT . . 147 
 
 XII. RELATIONSHIPS OP THE OAKS THEIR DISTRIBUTION 
 
 IN SPACE AND TIME .... 167 
 
 THE OAK IN SUMMER . . ... . Frontispiece 
 
 THE OAK IN WINTER . , . . To face p. 8 
 
 2090923
 
 THE OAK 
 
 CHAPTER I 
 
 INTRODUCTION 
 
 FAMOUS in poetry and prose alike, the oak must always 
 be for Englishmen a subject of interest, around which 
 historical associations of the most varied character are 
 grouped ; but although what may be termed the senti- 
 mental aspect of the ' British oak ' is not likely to dis- 
 appear even in these days of ironclads and veneering, it 
 must be allowed that the popular admiration for the 
 sturdy tree is to-day a very different feeling from the 
 veneration with which it was regarded in ancient times ; 
 and that, with the calmer and more thoughtful ways of 
 looking at this and other objects of superstition, a cer- 
 tain air of romance seems to have disappeared which 
 to so many would still present a tempting charm. It is 
 not to these latter alone that our few existing ancient 
 oaks are so attractive, however, and a slight acquaint- 
 ance with the oaken roofs and carvings of some of our 
 
 B
 
 2 THE OAK 
 
 historical edifices affords ample proof that the indefin- 
 able charm exercised on us by what has proved so last- 
 ing, is a real one and deep-seated in the Saxon nature. 
 In fact, everything about the oak is suggestive of 
 durability and sturdy hardiness, and, like so many 
 objects of human worship in the earlier days of man's 
 emergence from a savage state, the oak instinctively 
 attracts us. The attraction is no doubt complex, 
 taking its origin in the value of its acorns and timber 
 to our early forefathers, not unaffected by the artistic 
 beauty of the foliage and habit of the tree, and the 
 forest life of our ancestors, to say nothing of the more 
 modern sentiment aroused when ships of war were built 
 almost entirely of heart of oak; for the Aryan race 
 seems to have used and valued both the fruit and the 
 wood from very early times, and both Celt and Saxon 
 preserved the traditional regard for them. Memories of 
 our Anglo-Saxon ancestors are still found ib. the English 
 and German names for the tree and its fruit 3 as seen by 
 comparing the Anglo-Saxon dc or cec, the name of the 
 oak, with the English word, and with the German Eiche 
 on the one hand, and with acorn (Eichel) on the other. 
 In early days, moreover, there were vast oak forests in 
 our island and on the Continent, and, although these 
 have been almost cleared away so far as England is con- 
 cerned, there are still ancient oaks in this country, some 
 of which must date from Saxon times or thereabouts, 
 and the oak is still one of the commonest trees in France, 
 parts of Germany, and some other districts in Europe.
 
 INTKODUCTION 8 
 
 This is nob the place to go further into what may be 
 called the folk-lore of the oak a subject which would 
 supply material for a large volume but it may be re- 
 marked that giant or veteran oaks are still to be found 
 (or were until quite recently) in Gloucestershire, York- 
 shire, and on Dartmoor and other places, and a very 
 fair idea of what an old oak forest must have been like 
 may be gathered from a visit to the New Forest in 
 Hampshire, or even to some parts of Windsor Forest. 
 
 As so often happens in the study of science, we have 
 in the oak a subject for investigation which presents 
 features of intense interest at every turn, and however 
 much the new mode of looking at the tree may at first 
 sight appear to be opposed to the older one, it will be 
 found that the story of the oak as an object of biological 
 study is at least not less fascinating than its folk-lore. 
 With this idea in view, I propose to set before the 
 reader in the following chapters a short account of what 
 is most worth attention in the anatomy and physiology 
 of the oak, as a forest tree which has been so thoroughly 
 investigated that we may confidently accept it as a 
 type. 
 
 In carrying out this idea there are several possible 
 modes of procedure, but perhaps the following will re- 
 commend itself as that best adapted to the requirement? 
 of a popular book, and as a natural way of tracing the 
 various events in the life-history of a plant so complex 
 as is the tree. 
 
 First, the acorn will be described as an object with 
 
 B 2
 
 4 THE OAK 
 
 a certain structure and composition, and capable of 
 behaving in a definite manner when placed in the 
 ground, and under certain circumstances, in virtue of its 
 physiological properties and of the action of the en- 
 vironment upon its structure. The germinated acorn 
 gives rise to the seedling or young oak, and we shall 
 proceed to regard this, again, as a subject for botanical 
 study. It consists of certain definite parts or organs, 
 each with its peculiar structure, tissues, &c., and each 
 capable of behaving in a given manner under proper 
 conditions. The study of the seedling leads naturally 
 to that of the sapling and the tree, and the at first 
 comparatively simple root-system, stem, and leaves, now 
 become complex and large, and each demands careful 
 attention in order that we may trace the steps by which 
 the tree is evolved from the plantlet. A section will there- 
 fore be devoted to the root-system of the tree, its disposi- 
 tion, structure, functions, and accessories ; another sec- 
 tion will be occupied in describing the trunk, branches, 
 buds, and leaves, and their co-relations and functions ; 
 the inflorescence and flowers will demand the space ot 
 another chapter, and then it will be necessary to treat 
 of various matters of importance in separate chapters as 
 follows : The timber must be considered with respect to 
 its composition, structure, uses, and functions ; then 
 the cortex and bark have to be described and their 
 origin and development explained. These subjects 
 naturally lead to that of the growth in thickness of the 
 tree a matter of some complexity, and not to be under-
 
 INTKODUCTION 5 
 
 stood without the foregoing knowledge of structure. 
 Following what has been said concerning the normal 
 structure and life-processes of the tree, we may turn to 
 the investigation of its cultivation and the diseases 
 which attack it, concluding with a necessarily brief 
 chapter on the systematic position of the British oak 
 and its immediate allies, and some remarks on its geo- 
 graphical distribution at the present time. 
 
 Of course, many points which will turn up in the 
 course of the exposition will have to be shortly dealt 
 with, as the object of the book is to touch things with 
 a light hand ; but it is hoped that, this notwithstanding, 
 the reader may obtain a useful glimpse into the domain 
 of modern botanical science and the problems with which 
 forest botany is concerned, and with which every properly 
 trained forester ought to be thoroughly acquainted. 
 
 The oak, as is well known, is a slow-growing, di- 
 cotyledonous tree of peculiar spreading habit, and very 
 intolerant of shade (Plate I.). It may reach a great age 
 certainly a thousand years and still remain sound 
 and capable of putting forth leafy shoots. 
 
 The root-system consists normally of a deep principal 
 or tap root and spreading lateral roots, which become 
 yery thick and woody and retain a remarkably strong 
 hold on the soil when the latter is a suitable deep, 
 tenacious loam with rocks in it. They are intolerant of 
 anything like stagnant water, however, and will succeed 
 better in sandy loam and more open soils than in richer 
 ones improperly drained.
 
 6 THE OAK 
 
 The shoot-system consists of the stem and all that it 
 supports. The stem or trunk is usually irregular when 
 young, but becomes more symmetrical later, and after 
 fifty years or so it normally consists of a nearly straight 
 and cylindrical shaft with a broad base and spreading 
 branches. The main branches come out at a wide angle, 
 and spread irregularly, with a zigzag course, due to the 
 short annual growths of the terminal shoots and the 
 few axillary buds behind, and also to the fact that many 
 of the axillary lateral buds develop more slowly than 
 their parent shoot, and are cut off in the autumn. 
 Another phenomenon which co-operates in producing 
 the very irregular spreading habit of the branches is the 
 almost total suppression of some of the closely-crowded 
 buds ; these may remain dormant for many years, and 
 then, under changed circumstances, put forth accessory 
 shoots. Such shoots are very commonly seen on the 
 stems and main branches of large oaks to which an 
 increased accession of light is given by the thinning out 
 of surrounding trees. 
 
 The short ovoid buds develop into shoots so short 
 that they are commonly referred to as tufts of leaves, 
 though longer summer shoots often arise later. The 
 latter are also called Lammas shoots. The crown of 
 foliage is thus very dense, and the bright green of the 
 leaves in early summer is very characteristic, especially 
 in connection with the horizontal, zigzag spreading 
 of the shoots. 
 
 still young the tree is apt to keep its dead
 
 INTBODUCT10N 7 
 
 leaves on the branches through the winter, or at least 
 until a severe frost followed by a thaw brings them 
 down. The buds, leaves, and flowers are all much 
 attacked by gall-forming insects, many different kinds 
 being found on one and the same tree. 
 
 It is not until the oak is from sixty to a hundred years 
 old that good seeds are obtained from it. Oaks will bear 
 acorns earlier than this, but they are apt to be barren. 
 A curious fact is the tendency to produce large numbers of 
 acorns in a given favourable autumn, and then to bear 
 none, or very few, for three or four years or even longer. 
 The twisted, ' gnarled ' character of old oaks is well 
 known, and the remarkably crooked branches are very 
 conspicuous in advanced age and in winter (Plate II.). 
 The bark is also very rugged in the case of ancient trees, 
 the natural inequalities due to fissures, &c., being often 
 supplemented by the formation of ' burrs.' 
 
 A not inconsiderable tendency to variation is shown 
 by the oak, and foresters distinguish two sub-species and 
 several varieties of what we regard (adopting the opinion 
 of English systematic botanists) as the single species 
 Qiierciis Robur. 
 
 Besides forms with less spreading crowns, the species 
 is frequently broken up into two Q. pedunculate^ with 
 the female flowers in rather more lax spikes, and the 
 acorns on short stalks, the leaves sessile or nearly so, 
 and not hairy when young; and Q. sessiliflora, with 
 more crowded sessile female flowers, and leaves on 
 short petioles and apt to be hairy. Other minute
 
 S THE OAK 
 
 characters have also been described, but it is admitted 
 that the forms vary much, and it is very generally con- 
 ceded that these two geographical race- forms may be 
 united with even less marked varieties into the one 
 species Quercus Robur. 
 
 The amount of timber produced by a sound old oak 
 is very large, although the annual increment is so re- 
 markably small. This increment goes on increasing 
 slightly during the first hundred years or so, and 
 then falls off; but considerable modifications in both 
 the habit of the tree and in the amount of timber pro- 
 duced annually, result from different conditions. Trees 
 grown in closely-planted preserves, for instance, shoot 
 up to great heights, and develop tall, straight trunks 
 with few or no branches, and considerable skill in the 
 forester's art is practised in removing the proper number 
 of trees at the proper time, to let in the light and air 
 necessary to cause the maximum production of straight 
 timber. 
 
 Oaks growing in the open air are much shorter, 
 more branched and spreading, and form the peculiar 
 dense, twisted timber once so valuable for ship-building 
 purposes. Such exposed trees, other things being equal, 
 develop fruit and fertile seeds thirty or forty years sooner 
 than those growing in closed plantations. 
 
 The timber itself is remarkable for combining so 
 many valuable properties. It is not that oak timber is 
 the heaviest, the toughest, the most beautiful, &c., of 
 known woods, but it is because it combines a good
 
 THE OAK IN WINTEB
 
 INTKODUCTION 9 
 
 proportion of weight, toughness, durability, and other 
 qualities that it is so valuable for so many purposes. The 
 richness of the cortex in tannin warranted the growing 
 of young oaks at one time for the bark alone, and the 
 value of the acorns for feeding swine has been immense 
 in some districts.
 
 10 THE OAK 
 
 CHAPTER H 
 
 THE ACORN AND ITS GERMINATION THE SEEDLING 
 
 WHEN the acorns are falling in showers from the oaks 
 in October and November, everybody knows that each 
 of the polished, leather-brown, long, egg-shaped bodies 
 tumbles out from a cup-like, scaly investment which 
 surrounded its lower third at the broader end. Perhaps 
 everybody would not be certain as to whether the 
 detached acorn is a seed or a fruit, so I anticipate the 
 difficulty by stating at the outset that the acorn is 
 the fruit of the oak, and contains the seed within its 
 brown shell, and I propose to commence our studies by 
 examining an acorn, deferring the explanation of some 
 minute details of structure until we come to trace the 
 origin of the fruit and seed in the flower. 
 
 The average size of the fruit is about 15 to 20 mm., 
 or nearly three-quarters of an inch, long, by 8 to 
 10 mm., or nearly one-third of an inch, broad at the 
 middle of its length; the end inserted in the cup or 
 cupide is broad and nearly flat, and marked by a large 
 circular scar (fig. 2, s) denoting the surface of attachment 
 to the cupule. This scar is rough, and exhibits a number
 
 THE ACORN AND ITS GJfiEMINATION 
 
 11 
 
 of small points which have resulted from the breaking 
 of some extremely delicate groups of minute pipes, 
 
 FIG. 1. Sprigs of oak, showing the habit and the arrangement of 
 the acorns, &c., in September. (After Kotschy.) 
 
 called vascular bundles, which placed the acorn in com- 
 munication with the cup and the tree previous to the
 
 12 THE OAK 
 
 ripening of the former. At the more pointed free end 
 of the acorn is a queer little knob, which is hard and 
 dry, and represents the mummified remains of what was 
 the stigma of the flower, and which lost its importance 
 several months previously, after receiving the pollen. 
 
 The outer hard coat of the acorn is a tough, leather- 
 brown, polished skin, with fine longitudinal lines on it, 
 and it forms the outer portion of the true covering of 
 the fruit, called the pericarp (fig. 2, p). On removing it 
 we find a thin, papery membrane inside, adhering partly 
 to the above coat and partly to the seed inside. This 
 thin, shrivelled, papery membrane is the inner part of 
 the pericarp, and the details of structure to be found 
 in these layers may be passed over for the present with 
 the remark that they are no longer living structures, 
 but exist simply as protective coverings for the seed 
 inside. 
 
 The centre of the acorn is occupied more or less 
 entirely by a hard brown body the seed which usually 
 rattles about loosely on shaking the ripe fruit, but 
 which was previously attached definitely at the broad 
 end. A similar series of changes to those which brought 
 about the separation of the acorn from the cup 
 namely, the shrivelling up of the tiny connecting 
 cords, &c. also caused the separation of the seed from 
 the pericarp, and we may regard the former as a dis- 
 tinct body. 
 
 Its shape is nearly the same as that of the acorn in 
 which it looselv fits, and it is usually closely covered with
 
 THE ACORN AND ITS GERMINATION 
 
 13 
 
 a thin, brown, wrinkled, papery membrane, which is its 
 own coat the seed-coat, or testa (fig. 2, ). The extent 
 to which the testa remains adherent to the seed, or to the 
 inner coat of the pericarp, and both together to the 
 harder outer coat of the pericarp, need not be commented 
 upon further than to say that differences in this respect 
 
 FIG. 2. Sections of acorns in three planes at right angles to one 
 another. A, transverse ; u, longitudinal in the plane of the coty- 
 ledons (7) ; c, longitudinal across the plane of the cotyledons ; c, 
 cotyledons ; t, testa ; p, pericarp ; g, scar, and r, radicle ; pi, 
 plumule. The radicle, plumule, and cotyledons together consti- 
 tute the embryo. The embryonic tissue is at r and pi. The dots 
 in A, and the delicate veins in B and c are the vascular bundles. 
 
 are found accordiug to the completeness and ripeness 
 of the acorn. 
 
 Enveloped in its testa and in the pericarp, then, 
 we find the long acorn-shaped seed, which seems at 
 first to be a mere horn-like mass without parts. This 
 is not the case, however, as may easily be observed by 
 cutting the mass across, or, better still, by first soaking 
 it in water for some hours ; it will then be found that
 
 14 THE OAK 
 
 the egg-shaped body consists chiefly of two longitudinal 
 halves, separated by a median plane which runs through 
 the acorn from top to bottom. These two halves, lying 
 face to face so closely that it requires the above manipu- 
 lation to enable us to detect the plane of separation 
 (fig. 2, I), are not completely independent, however ; at a 
 point near the narrower end each of them is attached 
 to the side of a small peg-shaped body, with a conical 
 pointed end turned to wards the narrow end of the acorn. 
 This tiny peg-shaped structure is so small that it may 
 be overlooked unless some little care is exercised, but if 
 the hard masses are completely torn apart it will be 
 carried away with one of them. 
 
 The two large plano-convex structures are called the 
 cotyledons, or seed-leaves (fig. 2, c) and they, together 
 with the small peg-shaped body, constitute the embryo of 
 the oak. The peg-shaped body presents two ends which 
 project slightly between the two cotyledons beyond the 
 points of attachment to them ; the larger of these ends 
 has the shape of a conical bullet, and is directed so that 
 its tip lies in the point of the narrower part of the acorn, 
 the other, and much smaller end, is turned towards the 
 broader extremity of the acorn. The larger, bullet-shaped 
 portion is termed the radicle (fig. 2, r), and will become 
 the primary root of the oak-plant ; the smaller, opposite 
 end is the embryo bud, and is termed the plumule (fig. 2, 
 pZ), and it is destined to develop into the stem and leaves 
 of the oak. If the observer takes the trouble to carefully 
 separate the two large cotyledons, without tearing them
 
 THE ACOltN AND ITS GERMINATION 15 
 
 away from the structures just described, he will find that 
 each is attached by a minute stalk to a sort of ridge just 
 beneath the tiny plumule ; this ridge is sometimes termed 
 the collar. He will also see that the plumule and radicle 
 tit closely into a cavity formed by the two cotyledons, 
 and so do not interfere with the very close fitting of 
 their two flat faces. 
 
 Summing up these essential features of the structure 
 of the ripe acorn and its contents, we find that the 
 fruit contains within its pericarp (which is a more or less 
 complex series of layers of which the outermost is hard) 
 the seed ; that this seed comprises a membranous testa 
 enclosing an embryo ; and that the embryo is composed 
 of two huge cotyledons, a minute radicle, and a still 
 more minute plumule ; and that the tip of the radicle 
 is turned towards the pointed end of the acorn, lying 
 just inside the membranes. 
 
 Leaving the details of structure of the membranes 
 until a later period, when we trace their development 
 from the flower, I must devote some paragraphs to a 
 description of the minute anatomy and the contents of 
 the embryo as found in the ripe acorn, so that the 
 process of germination may be more intelligible. 
 
 Thin sections of any portion of the embryo placed 
 under the microscope show that it consists almost 
 entirely of polygonal chambers or cells, with very thin 
 membranous walls, and densely filled with certain granule- 
 like contents. These polygonal cells have not their own 
 independent walls, but the wall which divides any two of
 
 16 THE OAK 
 
 them belongs as much to one as to the other, and only 
 here and there do we find a minute opening between 
 three or more cells at the corners, and produced by the 
 partial splitting of the thin wall. We may, if we like, 
 regard the whole embryo as a single mass of material 
 cut up into chambers by means of partition walls, which 
 have a tendency to split a little here and there, much as 
 one could split a piece of pasteboard by inserting a 
 paper-knife between the layers composing it ; what we 
 must not do, is to suppose that these cells are so many 
 separate chambers which have been brought into juxta- 
 position. In other words, the cell-wall separating any 
 two of the chambers is in its origin a whole, common to 
 both chambers, and the plane which may be supposed to 
 divide the limits of each is imaginary only. 
 
 I have said that the embryo consists almost entirely 
 of this mass of polygonal, thin- walled cells, and such 
 is called fundamental tissue but here and there, in very 
 much smaller proportion, we shall find other structures. 
 Surrounding the whole of the embryo, and following every 
 dip and projection of its contours, will be found a single 
 layer of cells of a flattened, tabular shape, and fitting 
 close together so as to constitute a delicate membrane 
 or skin over the whole embryo ; this outer layer of the 
 young plant is called the epidermis. 
 
 Whenever the cotyledons, or the radicle, or plumule 
 are cut across transversely to their length, there are 
 visible certain very minute specks, which are the cut 
 surfaces of extremely delicate strands or cords of
 
 THE ACOEN AND ITS GERMINATION 17 
 
 relatively very long and very narrow cells, the minute 
 structure of which we will riot now stay to investigate, but 
 simply mention that these extremely fine cords, running 
 in the main longitudinally through the embryo, are 
 termed ' vascular bundles ' (fig. 2, A). It may be shown 
 that there is one set of them running up the central part 
 of the radicle, starting from just beneath its tip, and that 
 these pass into the two cotyledons, and there branch and 
 run in long strands towards the ends of the latter. 
 
 The three sets of structures which have been referred 
 to are called ' tissues,' and although they are still in a very 
 young and undeveloped condition we may say that the 
 embryo consists essentially of a large amount of thin- 
 walled cell-tissue, of different ages, which is limited by 
 an epidermal tissue and traversed by vascular tissue. 
 At the tips of the radicle and plumule the cell-tissue 
 is in a peculiar and young condition, and is known as 
 embryonic tissue. 
 
 As regards the contents and functions of these 
 tissues, the following remarks may suffice for the pre- 
 sent. The polygonal cells of the fundamental tissue of 
 the cotyledons are crowded with numerous brilliant 
 starch grains, of an oval shape and pearly lustre, and 
 these lie embedded in a sort of matrix consisting chiefly 
 of proteids and tannin, together with small quantities 
 of fatty substances. 
 
 In each cell there is a small quantity of protoplasm 
 and a nucleus, but this latter is only to be detected with 
 difficulty. Certain of the cells contain a dark-brown 
 
 c
 
 18 THE OAK 
 
 pigment, composed of substances of the nature of 
 tannin ; and small quantities of a peculiar kind of sugar, 
 called Quercite, are also found in the cells, together with 
 a bitter substance. 
 
 In the main, the above are stored up in the thin- 
 walled parenchyma cells as reserve materials, intended to 
 supply the growing embryo or seedling with nutritious 
 food ; the starch grains are just so many packets of a 
 food substance containing carbon, hydrogen, and oxygen 
 in certain proportions ; the proteids are similarly a supply 
 of nitrogenous food, and minute but necessary quanti- 
 ties of certain mineral salts are mixed with these. The 
 vascular bundles are practically pipes or conduits which 
 will convey these materials from the cotyledons to the 
 radicle and plumule as soon as germination begins, and 
 I shall say no more of them here, beyond noting that each 
 strand consists chiefly of a few very minute vessels and 
 sieve-tubes. The young epidermis takes no part either 
 in storing or in conducting the food substances ; it is 
 simply a covering tissue, and will go on extending as 
 the seedling develops a larger and larger surface. 
 
 We are now in a position to inquire into what takes 
 place when the acorn is put into the soil and allowed to 
 germinate. In nature it usually lies buried among the 
 decaying leaves on the ground during the winter, and 
 it may even remain for nearly a year without any con- 
 spicuous change ; and in any case it requires a period 
 of rest before the presence of the oxygen of the air and 
 the moisture of the soil are effective in making it ger-
 
 THE ACORN AND ITS GERMINATION 19 
 
 minate a fact which suggests that some profound mole- 
 cular or chemical changes have to be completed in the 
 living substance of the cells before further activity is 
 possible. We have other reasons for believing that 
 this is so, and that, until certain ferments have been 
 prepared in the cells, their protoplasm is unable to make 
 use of the food materials, and consequently unable to 
 initiate the changes necessary for growth. 
 
 Sooner or later, however, and usually as the tempera- 
 ture rises in spring, the embryo in the acorn absorbs 
 water and oxygen, and swells, and the little radicle elon- 
 gates and drives its tip through the ruptured investments 
 at the thin end of the acorn, and at once turns downward, 
 and plunges slowly into the soil (fig. 3). This peculi- 
 arity of turning downwards is so marked that it manifests 
 itself no matter in what position the acorn lies, and it 
 is obviously of advantage to the plant that the radicle 
 should thus emerge first, and turn away from the light, 
 and grow as quickly as possible towards the centre of 
 the earth, because it thus establishes a first hold on the 
 soil, in readiness to absorb water and dissolve mineral 
 substances by the time the leaves open and require 
 them. 
 
 The two cotyledons remain enclosed in the coats of 
 the acorn, and are not lifted up into the air ; the de- 
 veloping root obtains its food materials from the stores 
 in the cells of the cotyledons, as do all the parts of the 
 young seedling at this period. In fact, these stores in 
 the cotyledons contribute to the support of the baby 
 
 c 2
 
 20 THE OAK 
 
 plant for many months, and even two years may elapse 
 before they are entirely exhausted. 
 
 FIG 3 I. Longitudinal section through the posterior half of the 
 embryo, in a plane at right angles to the plane of separation be- 
 tween the cotyledons (slightly magnified). II. Germinating 
 embryo, with one cotyledon removed. III. Acorn in an advanced 
 stage of germination, a, the scar; *, pericarp; sh, testa; &, 
 plumule; **, petioles of cotyledons, from between which the 
 plumule, , emerges ; he, hypocotyl ; c, cotyledons ; /, vascular 
 bundles ; m, radicle (primary root) ; m', secondary roots. Root- 
 hairs are seen covering the latter and the anterior part of the 
 primary root in III. (After Sachs.)
 
 THE ACORN AND ITS GERMINATION 21 
 
 When the elongated radicle, or primary root, has 
 attained a length of two or three inches in the soil, and 
 its tip is steadily plunging with a very slight rocking 
 movement deeper and deeper into the earth, the little 
 plumule emerges from between the very short stalks of 
 the cotyledons (fig. 3, s), which elongate and separate 
 to allow of its exit, and grows erect into the light and 
 air above ground. It will be understood that this plu- 
 mule also is living at the expense of the food stores in 
 the cotyledons, the dissolved substances passing up into 
 it through the tiny vascular bundles and cells, as they 
 have all along been passing down to the growing root 
 through the similar channels in its tissues. 
 
 The plumule or, as we must now call it, primary 
 shoot differs from the root not only in its more tardy 
 growth at first, but also in its habit of growing away 
 from the centre of gravitation of the earth and into 
 the light and air ; and here, again, we have obviously 
 adaptations which are of advantage to the plant, which 
 would soon be top-heavy, moreover, if the shoot were 
 far developed before the root had established a hold- 
 fast in the soil. 
 
 The little oak shoot is for some time apparently 
 devoid of leaves (fig. 4), but a careful examination shows 
 that as it elongates it bears a few small scattered scales, 
 like tiny membranes, each of which has a very minute 
 bud in its axil. When the primary shoot has attained 
 a length of about three inches there are usually two 
 of these small scale-leaves placed nearly opposite one
 
 THE OAK 
 
 another close to the tip, and a little longer and narrower 
 than those lower down on the shoot ; from between these 
 two linear structures the first true green foliage leaf of 
 the oak arises, its short stalk being flanked by them. This 
 first leaf is small, but the tip of 
 the shoot goes on elongating and 
 tnrowing out others and larger 
 ones, until by the end of the 
 summer there are about four to 
 six leaves formed, each with its 
 minute stalk flanked by a pair 
 of tiny linear scales (' stipules,' 
 as they are called) like those 
 referred to above. 
 
 Each of the green leaves 
 arises from a point on the young 
 stem which is a little higher, and 
 more to one side, than that from 
 which the lowermost one springs ; 
 hence a line joining the points 
 of insertion of the successive 
 FIG 4. Germinating leaves describes an open spiral 
 round the shoot axis-i.e. the 
 
 primary shoot, and the s t e m and this of such a kind 
 
 first scales (stipules) on 
 
 the latter. (After Boss- that when the spiral comes to 
 
 the sixth leaf upwards it is ver- 
 
 tically above the first or oldest leaf from which we 
 started, and has passed twice round the stem. 
 
 At the end of this first year, which we may term
 
 THE ACORN AND ITS GERMINATION 23 
 
 the period of germination, the young oak-plant or 
 seedling has a primary root some twelve to eighteen 
 inches long, and with numerous shorter, spreading side 
 rootlets, and a shoot from six to eight inches high, 
 bearing five or six leaves as described, and terminating 
 in a small ovoid bud (figs. 3 and 4). The whole shoot 
 is clothed with numerous very fine soft hairs, and there 
 are also numerous fine root-hairs on the roots, and 
 clinging to the particles of soil. The tip of each root is 
 protected by a thin colourless cap the root-cap the 
 description of which we defer for the present. 
 
 About May, in the second year, each of the young 
 roots is elongating in the soil and putting forth new 
 root-hairs and rootlets, while the older roots are thicken- 
 ing and becoming harder and covered with cork ; and 
 each of the buds in the axils of the last year's leaves 
 begins to shoot out into a branch, bearing new leaves in 
 its turn, while the bud at the end of the shoot elongates 
 and lengthens the primary stem, the older parts of 
 which are also becoming thicker and clothed with cork. 
 And so the seedling develops into an oak-plant, each 
 year becoming larger and more complex, until it reaches 
 the stage of the sapling, and eventually becomes a 
 tree.
 
 24 THE OAK 
 
 CHAPTER III 
 
 THE SEEDLING AND 7OUNG PLANT 
 
 BEFORE proceeding to describe the further growth and 
 development of the seedling, it will be well to examine 
 its structure in this comparatively simple stage, in 
 order to obtain points of view for our studies at a later 
 period. For many reasons it is advantageous to begin 
 with the root-system. If we cut a neat section accu- 
 rately transverse to the long axis of the root, and a few 
 millimetres behind its tip, the following parts may be 
 discerned with the aid of a good lens, or a microscope, 
 on the flat face of the almost colourless section. A cir- 
 cular area of greyish cells occupies the centre this is 
 called the axis cylinder of the young root (fig. 5, A, a). 
 Surrounding this is a wide margin of larger cells, forming 
 a sort of sheathing cylinder to this axial one, and termed 
 the root-cortex. The superficial layer of cells of this root- 
 cortex has been distinguished as a special tissue, like an 
 epidermis, and as it is the layer which alone produces 
 the root-hairs, we may conveniently regard it as worthy 
 of distinction as the piliferous layer (fig. 5, e). 
 
 Similar thin sections a little nearer the tip of the
 
 THE SEEDLING AND YOUNG PLANT 
 
 25 
 
 root would show a more or less loose sheath of cells in 
 addition to and outside this piliferous layer. This is the 
 root-cap, which is a thimble-shaped sheath of looser cells 
 
 per 
 
 FIG. 5. A. Transverse section of young root under a lens, showing 
 the axis-cylinder, a ; epidermis or piliferous layer, e ; and the 
 cortex between. B. The same more highly magnified : c, cortex ; 
 p, phloem ; x, xylem. C. A portion still more highly magnified : 
 j)h, phloem ; p t pith ; per, pericycle ; sh, sheath (endodermis) ; 
 other letters as before. 
 
 covering the tip of the root as a thimble covers the end 
 of the finger, only we must imagine the extreme tip of 
 the finger organically connected with the inside of the 
 cap to make the analogy suitable (see fig. 6). The rest
 
 26 THE OAK 
 
 of the section would be much as before, excepting that 
 the distinction between the axial cylinder and the root- 
 cortex would be less marked. 
 
 Now contrast a section cut a couple of inches or so 
 away from the tip, in the region where the root-hairs 
 are well developed. Here we find the axial cylinder 
 much more strongly marked than before, and the pili- 
 ferous layer is very clearly distinguished by the fact that 
 it gives off the root-hairs, each hair arising from one of 
 its cells. 
 
 A little investigation shows that the axial cylinder 
 is thus strongly marked because certain dark-looking 
 structures have now been formed just inside its boundary 
 i.e. just inside the line which delimits it from the 
 root-cortex. These dark structures are the sections of 
 several fine cords or bundles, called vascular bundles, 
 which can here be traced up and down in the root. As 
 the section shows, these bundles are arranged at approxi- 
 mately equal distances in a cylinder ; they form the 
 vascular system of the root, and they always run along 
 the region just inside the outer boundary of the axis- 
 cylinder (fig. 5, B, p and x). 
 
 If we compare our successive transverse sections, 
 and cut others at various levels along the young root, it 
 will be clear that, as we pass from the tip of the root to 
 parts further behind, certain changes must be going on, 
 which result first in the definite marking out of the axial 
 cylinder, and then in the development of these vascular 
 bundles and of other parts we will not describe in detail.
 
 THE SEEDLING AND YOUNG PLANT 
 
 27 
 
 If, in addition to these successive transverse sections, 
 we examine a carefully prepared longitudinal section, 
 cut so as to pass accurately 
 through the median plane of 
 the root, the comparison not 
 only establishes the above con- 
 clusion, but it enables us to be 
 certain of yet other facts (fig. 6). 
 Such a section shows the root- 
 cap covering the tip as a thimble 
 the end of the finger, and the 
 rim of this root-cap is evidently 
 fraying away behind ; the cells 
 of which it is composed die 
 and slough off as the root 
 pushes its way between the 
 abrading particles of soil. Ob- 
 viously this loss of worn-out 
 tissue must be made good in 
 some way, and closer exami- 
 nation shows how this occurs. 
 
 The extreme tip of the root FIG. 6 Diagrammatic sec- 
 
 proper fit. closely into the cap, 
 
 and evidently adds cells to the 
 
 inside of the latter, and thus 
 
 replaces the old ones which are 
 
 worn away. At this true tip 
 
 of the root, moreover, we make another discovery 
 
 namely, that all the cells are there alike in shape, size, 
 
 cortex ; e, piliferous layer ; 
 re, root- cap ; m, the true 
 embryonic tissue (so- 
 called ' growing-point ' ) ; 
 ph, phloem ; a?, xylem.
 
 28 THE OAK 
 
 and other peculiarities ; and if we could take a trans- 
 verse section exactly at this place we should see no 
 differentiation into axial cylinder and root-cortex, &c. 
 the small circular mass would consist of cells all 
 alike, and with very thin walls and full of dense proto- 
 plasm. This undifferentiated formative tissue is called 
 the embryonic tissue of the root (fig. 6, m). A little 
 behind this we see the axis-cylinder and root-cortex 
 already formed ; still further away we see the vascular 
 bundles appearing, first as very thin cords, and then 
 getting stronger and stronger as we recede from the tip 
 (fig. 6, ph and x) ; and similarly we trace the gradual 
 development of the other parts in acropetal succession 
 i.e. the nearer we go to the apex the younger the parts 
 are. 
 
 Now, there is a conclusion of some importance to be 
 drawn from the putting together of these facts namely, 
 that all the structures found between the embryonic 
 tissue at the tip of the root and the place where the root 
 joins the stem have been gradually formed from the 
 embryonic tissue in acropetal succession. We may 
 picture this by marking a given level on the root, 
 some distance away from the tip, where the axis-cylinder 
 is sharply marked and has well developed vascular bun- 
 dles, the root-cortex is distinct, and the piliferous layer 
 bears root-hairs, and remembering that so many days or 
 weeks ago this very spot was in the then growing-point, 
 and consisted of embryonic tissue with the cells all alike. 
 Or we may put it in a different way thus : the present
 
 THE SEEDLING AND YOUNG PLANT 29 
 
 growing-point consists of embryonic cells all alike ; in 
 a few days some of these cells will have changed into 
 constituents of the axis-cylinder and cortex, and sub- 
 sequently some of them will give rise to vascular bundles, 
 &c. Not all, however, and it is necessary to understand 
 that as the embryonic tissue moves onwards and leaves 
 the structures referred to in its wake, it does so by 
 producing new embryonic cells in front i.e. between the 
 present ones and the root-cap. 
 
 We must now look a little more closely into the 
 structure of the axial cylinder, at a level a little behind 
 the region where the root-hairs are produced on the 
 piliferous layer. 
 
 A thin transverse section in this region shows that 
 the root-hairs have all died away, and the walls of the 
 cells of the piliferous layer are becoming discoloured, 
 being, in fact, converted into a brown, cork-like substance 
 impervious to moisture, or nearly so ; consequently the 
 piliferous layer is no longer absorptive, and it will soon 
 be thrown off, as we shall see. 
 
 The cortex offers little to notice, except that its cells 
 are being passively stretched or compressed by the 
 growth and processes going on in the axial cylinder, and 
 it is this cylinder that attracts our special attention, and 
 several points not noticed before must now be examined 
 in some detail. 
 
 In the first place, the cylinder is demarcated off 
 from the cortex by a single layer of cells shaped like 
 bricks, and with a sort of black dot on the radial walls ;
 
 30 THE OAK 
 
 this is called the endodermis, and may be regarded as 
 a sheath limiting what belongs to the axis-cylinder (fig. 
 5, C, sli). Inside this endodermis are about two rows 
 of thin- walled cells full of protoplasm, and forming a 
 continuous layer beneath the endodermis, This layer is 
 termed the pericycle (fig. 5, C, per), and it is a very 
 important structure, because its cells give rise, by re- 
 peated divisions, to the lateral rootlets, which then 
 grow out and burst their way through the endodermis, 
 cortex, and piliferous layer, and so reach the soil. It is, 
 of course, necessary to bear in mind that the endodermis 
 and pericycle are concentric cylinders superposed on 
 the axis of the root, as it were, and only appear as rings 
 on the transverse section. 
 
 Inside the pericycle are arranged the vascular 
 bundles, and we shall have to devote a few words of ex- 
 planation to these remarkable and somewhat complex 
 structures. 
 
 The section shows that there are about ten alternat- 
 ing groups of tissue constituting these bundles, and 
 again the reader must bear in mind that each group is 
 the transverse section of a long cord running up and 
 down the root. Of these groups five are much more 
 conspicuous than the other five, because they consist 
 chiefly of more or less polygonal openings with firm, 
 dark contours. These are the xylem vessels of the vas- 
 cular bundles (fig. 5, c, x), and we must note the following 
 facts about them : In the first place, they are smaller 
 near the pericycle than they are nearer the centre of
 
 THE SEEDLING AND YOUNG PLANT 31 
 
 the axial cylinder, and the comparison of numerous 
 transverse sections at different levels of the root would 
 prove that the smallest vessels are the first to develop ; 
 whence we learn two facts namely, that the xylem 
 vessels of the young root are developed in centripetal 
 order, and that the later ones have a larger calibre 
 than those formed earlier. 
 
 If longitudinal sections are compared with these 
 transverse ones and I may here observe that it is only 
 by means of numerous such comparisons that these 
 matters have been gradually discovered it is found that 
 each vessel is a long tube, usually containing air and 
 water when complete, the lateral walls of which are 
 curiously and beautifully marked with characteristic 
 thick and thin ornamentation. It must suffice here to 
 say that the small, outer, first-formed vessels are marked 
 with a spiral thickening, reminding one of caoutchouc 
 gas-tubing kept open by means of a spiral wire iaside ; 
 while the larger ones, developed later, usually have 
 numerous small pits on their walls, reminding one of 
 mouths, and the structure of which is very curious. Con- 
 sequently these groups of xylem vessels are said to consist 
 of spiral and pitted vessels, and their chief function is 
 to convey water up the root to the stem (cf. fig. 16). 
 Packed in between these vessels are certain cells known 
 as the wood-cells. 
 
 Eeturning to the transverse section, we saw that 
 between each xylem group described above there is a 
 group of structures differing from the latter in their less
 
 32 THE OAK 
 
 distinct outlines ; these alternate groups are known as 
 phloem, and we may shortly examine the elements of 
 which they are composed, as before, by comparing 
 sections of various kinds. 
 
 Here, again, we find the chief structures in the phloem 
 are also vessels i.e. long, tubular organs but very dif- 
 ferent in detail from the vessels of the xylem. 
 
 In the first place, their walls are thin and soft, and 
 composed of the unaltered cellulose which is so charac- 
 teristic of young cells (instead of being hard like the 
 Hgnified walls of the xylem vessels) ; then, again, they 
 contain protoplasm and other organised cell contents, 
 instead of merely air and water. Finally, they are not 
 so completely tubular as the typical xylem vessels are, 
 because the transverse septa of the constituent cells are 
 not absorbed, but are merely pierced by fine strands of 
 protoplasm, and therefore look like sieves when viewed 
 from above whence the name ' sieve-tubes.' In the 
 phloem also we find cells phloem-cells packed in 
 between the sieve-tubes. 
 
 If we shortly summarise the above we find that the 
 root consists of an axis-cylinder surrounded by a cortex 
 and the piliferous layer. At the tip the whole is 
 covered by the root-cap, which is organically connected 
 with the embryonic tissue which forms all these struc- 
 tures. The axis-cylinder is somewhat complex ; it is 
 sheathed by the endodermis and the pericycle, the 
 latter of which gives origin to the new rootlets. Inside 
 the pericycle are the vascular bundles running up and
 
 THE SEEDLING AND YOUNG PLANT 
 
 33 
 
 FIG. 7. Portion of young growing ends of more advanced 
 root, with numerous rootlets. Some of the latter are much 
 branched into tuft-like collections, m ; these form the 
 so-called Mycorhiza. Natural size.
 
 34 THE OAK 
 
 down as separate, alternate cords of xylem and phloem ; 
 the xylem consists of vessels and cells, the former 
 developed centripetally, while the phloem consists of 
 sieve-tubes and cells. Any cell-tissue which may lie in 
 the centre of the axial cylinder, and surrounded by the 
 vascular bundles, corresponds, in popular language, to 
 pith ; any that runs between the bundles corresponds 
 to medullary rays. 
 
 We now turn to the root as a whole, and examine 
 its behavour in the soil as the young seedling develops 
 further, and in the light of the above anatomical 
 facts. 
 
 Although the root-system of the young plant is 
 regularly constituted of a series of lateral rootlets 
 springing from the primary root, the orderly arrange- 
 ment is soon disturbed when the tertiary and other 
 rootlets begin to develop from the secondary rootlets ; 
 moreover, as the age of the tree increases, the tendency 
 to irregularity is increased owing to the production of 
 rootlets of the higher orders at different places, thus 
 interfering with the acropetal succession of the younger 
 rootlets. 
 
 At first the root-system is especially engaged in 
 boring into the soil, and provided the latter is suffici- 
 ently deep and otherwise suitable, the tap-root will go 
 down a foot or more in the first year. As the roots 
 thicken they exhibit considerable plasticity, as is espe- 
 cially evinced on rocky ground, where the older roots 
 may often be found in cracks in the rocks, so com-
 
 THE SEEDLING AND YOUNG PLANT 
 
 35 
 
 pressed that they form 
 mere flattened sheets 
 many times broader than 
 they are thick (fig. 8). 
 
 It has already been 
 mentioned that the tip of 
 the young primary root 
 circumnutates, and Dar- 
 win also found that the 
 tip of the radicle is ex- 
 tremely sensitive to the 
 irritation of small bodies 
 in contact with it. It is 
 also positively geotropic, 
 directing itself vertically 
 downwards if the partially 
 grown radicle is laid hori- 
 zontally ; and it may be 
 assumed from the be- 
 haviour of other plants of 
 the same kind that the 
 tip of the radicle is nega- 
 tively heliotropic i.e. it 
 turns away from the 
 source of light. Whether 
 it is also sensitive to dif- 
 ferences in the degree of 
 moisture on different sides 
 (hydrotropic), or to differ- 
 
 FIG. 8. Portion of an older root 
 of an oak, which had pene- 
 trated while young between 
 two pieces of hard rock, and 
 had to adapt its form accord- 
 ingly as it thickened. (After 
 Dobner.) 
 
 D 2
 
 86 THE OAK 
 
 ences of temperature (thermotropic), is not known, but 
 it may be inferred that such is the case ; nor do we 
 know whether it is affected by electric currents in the 
 earth. 
 
 The root of the oak, speaking generally, is a typical 
 root in the following respects. It consists, as we have 
 seen, of a primary or tap-root which develops secondary 
 or lateral roots in acropetal succession, and these in their 
 turn produce rootlets of a higher order. These second- 
 ary, tertiary, &c., rootlets arise endogenously, taking 
 origin from the pericycle at the periphery of the strand 
 of vascular bundles which traverse the central axis, and 
 then bursting through the cortex to the exterior. The 
 primary root, as well as the rootlets of all orders, are 
 provided with a root-cap at the tips, and they all agree 
 in being devoid of chlorophyll or stomata. From the 
 outer layer of cells the piliferous layer, corresponding 
 to an epidermis root-hairs are developed at some little 
 distance behind the root-cap, and these superficial cellu- 
 lar outgrowths also arise in acropetal succession, the 
 older ones behind dying off as the younger ones arise 
 further forwards. If we bear in mind all that has been 
 shortly stated above, it will be very easy to figure the 
 behaviour of the root-system as it penetrates the ground, 
 and the following short description of the biology of the 
 root may render the matter clear. When the radicle 
 commences to bore down into the soil it puts forth a 
 large number of root-hairs from the parts a few milli- 
 metres behind the tip, and these attach themselves to the
 
 THE SEEDLING AND YOUNG PLANT 37 
 
 particles of soil and supply points of resistance ; the tip 
 of the radicle is protected by the slippery root-cap, and 
 it must be borne in mind that the embryonic tissue of the 
 growing-point consists of thin-walled cells full of rela- 
 tively stiff protoplasm with very little water. Hence 
 the growing-point is a firm body. The most active 
 growth of the root takes place at a region several milli- 
 metres behind the root-cap, between it and the fixed 
 point above referred to ; hence the apex of the root is 
 really driven into the ground between the particles of 
 rock, &c., of which the latter is composed. This driving 
 in is aided by the negative heliotropism, the positive 
 geotropism, the circumnutation, and other irritabilities 
 of the apical portions of the root, and it bores its way 
 several centimetres downwards. As it lengthens by the 
 addition of cells produced by the division of those of the 
 embryonic tissue, and by their successive elongation 
 the older parts behind go on producing root-hairs, and 
 thus a vertical cylinder of soil around the primary root 
 is gradually laid under contribution for water contain- 
 ing dissolved salts, &c. In those parts of the root which 
 are behind the growing region no further elongation 
 occurs ; hence the tips of the lateral rootlets (which have 
 been developing in the pericycle at the circumference of 
 the axial cylinder of vascular bundles) can now safely 
 break through the cortex and extend themselves in the 
 same manner from the parent root as a fixed base, 
 without danger of being broken off by the elongation 
 of the growing parts. Each of these secondary rootlets
 
 38 THE OAK 
 
 grows out at an obtuse angle from the primary root, 
 and not vertically downwards, and as it does so a 
 similar wave of root-hairs is developed along it ; thus a 
 series of nearly horizontal radiating cylinders of soil 
 are placed under contribution as before. Then the 
 secondary rootlets emit tertiary rootlets in all direc- 
 tions these and the rootlets of a higher order growing 
 without any particular reference to the direction of 
 gravitation, light, &c. and so place successive cylin- 
 ders of soil in all directions under contribution as 
 before. By this time, however, the symmetry of the 
 root-system is being disturbed because some of the 
 rootlets meet with stones or other obstacles, others get 
 dried up or frozen, or gnawed off or otherwise injured, 
 and the varying directions in which new growths start 
 and in which the resistances are least, influence the very 
 various shapes of the tangled mass of roots now per- 
 meating the soil in all directions. 
 
 These roots supply the ever-increasing needs for water 
 of the shoot-system, the leaf-surface of which is becoming 
 larger and larger, and as the greater volume of water 
 from the gathering rootlets has all to enter the stem via 
 the upper part of the main root, we are not surprised to 
 find that the latter thickens, as does the stem ; and so 
 with all the older roots they no longer act as absorb- 
 ing roots, but become merely larger and larger channels 
 for water, and girder-like supporting organs.
 
 89 
 
 CHAPTER IV 
 
 THE SEEDLING AND YOUNG PLANT (conti 
 
 ITS SHOOT-SYSTEM DISTRIBUTION OF THE TISSUES 
 
 I NOW proceed to describe the chief features of import- 
 ance in the structure of the shoot of the young oak- 
 plant, premising that many of the remarks may here be 
 curtailed in view of the facts already learnt in connec- 
 tion with the root. The first object will be to bring 
 out the differences in the shoot as contrasted with the 
 root, and first we may examine the structure by means 
 of transverse sections as before. The shoot consists of 
 all the structures developed from the plumule. 
 
 Such sections show that we have here also various 
 definitely grouped tissues, of which we may conveniently 
 distinguish three systems. A series of vascular bundles 
 grouped in a close ring constitutes one of these systems, 
 another is represented by a single layer of cells at 
 the periphery of the section, and this is called the 
 epidermis, and the remainder of the section composes 
 the third system, often termed the fundamental tissue, 
 and divided arbitrarily into three regions the pith, the 
 cortex, and the primary medullary rays (fig. 9). The
 
 40 
 
 THE OAK 
 
 chief points of difference from the root are that the 
 xylem and phloem of these vascular bundles of the stem 
 do not alternate on the section, as they did in the root, 
 but the phloem of each bundle is on the same radius as 
 the xylem ; and that there is no pericycle, for branches 
 
 FlG. 9. Transverse sections through very young twigs of 
 oak, showing the vascular bundles of the stem (p and X), 
 arranged in a ring round the pith, and joined by the 
 cambium ring the fine line passing through the bun- 
 dles ; M and * the vascular bundles passing down from 
 the leaves, M the median bundles, and s the lateral 
 bundles. The external outline is the epidermis ; the 
 letters P, P stand in the primary cortex ; the letters x, x 
 stand in the pith ; the primary medullary rays separate 
 the bundles. (After Muller). 
 
 are not developed endogenously as rootlets are. Then 
 there are some important differences in the mode of 
 origin of these vascular bundles in space. We saw that 
 in the root the first-formed spiral vessels are developed 
 at the outer parts of the ax is- cylinder, nearest the 
 cortex, and the succeeding vessels are formed in ceutri-
 
 THE SEEDLING AND YOUNG PLANT 41 
 
 petal order from these points. In the young stem the 
 exact converse occurs the first spiral vessels arise near 
 the centre of the stem, and development proceeds cen- 
 trifugally from the first. We may begin our study of 
 the shoot by tracing the course of the vascular bundles, 
 which, it must be remembered, are the channels of com- 
 munication between the water-supply at the roots below 
 and the leaves and young parts of the shoot above. 
 
 If we cut a transverse section of the terminal bud of 
 the oak, as close to the tip as possible, we shall obtain a 
 preparation of the young axis consisting entirely of 
 embryonic tissue, all the cells of which are practically 
 alike small, polygonal, thin-walled cells, with large 
 nuclei and much protoplasm, but without sap-vacuoles ; 
 these cells are in a state of active division, those in the 
 interior dividing successively in all planes. Those which 
 form the peripheral layer, however, are already distin- 
 guished by only dividing in the two planes at right 
 angles to the periphery, and they constitute the primi- 
 tive epidermis. There is no structure corresponding 
 to a root-cap. 
 
 Transverse sections a little lower down show dif- 
 ferences of the following nature. In the first place the 
 outline of the section tends to be somewhat pentagonal, 
 the points of origin of the very young leaves being at 
 the angles of the pentagon in accordance with their 
 phyllotaxis i.e. the order in which the leaves are 
 arranged on the stem. This is of such a nature that 
 each leaf stands some distance above and to one side of
 
 42 THE OAK 
 
 its next neighbour below, and if a line be drawn from 
 the insertion of any one leaf through the points of in- 
 sertion of those above, it will describe a spiral, and will 
 eventually come to a leaf standing directly above the 
 leaf started from. In doing this the spiral line will 
 pass twice round the stem, and through the points of 
 insertion of five leaves. This is shortly expressed by -. 
 
 The previously homogeneous embryonic tissue in 
 the section now shows certain patches of greyer, closer 
 tissue, arranged round the centre in a peculiar manner; 
 these are transverse sections of the young vascular 
 bundles strands which at present are distinguished 
 chiefly by the small diameter of their cells, whence the 
 darker grey appearance. 
 
 These strands when young are called procambium 
 strands. Their cells are distinguished from the other 
 embryonic cells around by growing more in length and 
 dividing less frequently across their length, and by 
 growing less in breadth and dividing more often by 
 longitudinal walls. 
 
 On transverse sections a little lower down there may 
 be seen a number of elongated and curved patches of 
 procambium, as shown in fig. 9. On the section it will 
 be noticed that the larger strands are so arranged that 
 they enclose a five-angled mass of central tissue (the 
 pith), the five corners pointing to the angles of the 
 young stem to which the leaves are attached. At the 
 corners or ends of the rays just referred to are in some 
 cases two or three smaller strands.
 
 THE SEEDLING AND YOUNG PLANT 43 
 
 Now, the important point to apprehend first is that 
 these strands at the corners (M, s) are the strands which 
 pass directly into the leaves through the petioles, and 
 it is necessary to be perfectly clear on this subject in 
 order to understand much of what follows. For instance, 
 the three strands marked M in fig. 9, A (mm, ms, and 
 ms in fig. 10), pass directly into a given leaf, mm, in 
 the middle, flanked by ms on either side; but this 
 group is also accompanied on each side by another strand, 
 (marked s, s' in fig. 9, A, and I, I in fig. 10), so that five 
 strands may be regarded as contributing to each corner 
 of the section, the three middle ones running side by 
 side up the midrib of the leaf and then branching out 
 in a manner to be described subsequently. 
 
 It can be shown, moreover, that the larger curved 
 strands, occupying the sides of the pentagon, are simply 
 formed by the union of several of the smaller strands at 
 different levels. 
 
 If, now, successively lower sections are cut of the 
 very young shoot, and compared, or if the shoot is 
 softened and dissected, it is possible to make out the 
 course of these vascular bundle strands lower down ; 
 the course is somewhat complex, but the diagrammatic 
 sketches in fig. 11 will enable the reader to apprehend 
 the chief points. 
 
 In the first place, the middle strand from a leaf, 
 mm, passes vertically down in the angle of the young 
 stem through five internodes (marked by the horizontal 
 lines), turning to one side and becoming continuous in
 
 44 
 
 THE OAK 
 
 the fifth internode with a strand coming off from another 
 leaf situated at another of the angles at a different level. 
 The strands which stand next to this median one one 
 on each side (ms) at first also pass vertically down 
 together with it, but at about the second or third inter- 
 node below they break up into smaller strands, which 
 
 FIG. 10. Diagram of the course of the bundles M, s, and s 1 
 of fig. 9, as they pass out of the stem into the base of 
 the leaf-stalk, mm is the median bundle, and ms, ms its 
 two companions (M in fig. 9, A) ; 1,1 are the lateral 
 bundles s and s' of fig. 9, A. The small branches fst go 
 into the stipules. (After Frank.) 
 
 again join with strands coming from other leaves situated 
 at other nodes and angles. 
 
 If we again compare the figures it will be seen 
 that the three strands just traced come down in the 
 angle of the stem, only turning aside lower down the 
 median strand mm, indeed, running actually in the 
 angle through five internodes. 
 
 To right and left in fig. 10 are seen two strands,
 
 THE SEEDLING AND YOUNG PLANT 
 
 45 
 
 marked I, I, and these 
 run chiefly in what 
 may be called the faces 
 of the five-angled stem ; 
 only, at the node where 
 the leaf we are consi- 
 dering is inserted, they 
 turn in towards the leaf, 
 and eventually they run 
 into the sides of the 
 petiole of the leaf as 
 the so-called ' lateral 
 strands,' or bundles. 
 
 Now, observation 
 shows that these lateral 
 strands (marked I, I 2 , Z 3 , 
 &c., in the diagram, 
 fig. 11) receive contri- 
 butions at successive 
 
 FIG. 11. Diagram of the 
 course of the vascular 
 bundles as they come 
 down from the leaves into 
 the stem. The horizontal 
 dotted lines represent the 
 levels of successive leaves ; 
 the triangular white area 
 beneath the upper letter z 
 is the insertion of a leaf. 
 Each group of bundles 
 from a leaf, as mm, ms, ms, 
 &c. (see text), descends into the stem, and joins with the bundles 
 from other leaves after running through several intemodes. The 
 other letters refer to the bundles from other leaves. (After Frank,)
 
 46 THE OAK 
 
 nodes, and pass down as stronger and stronger strands 
 through about seven internodes, their lower ends losing 
 themselves by joining to others ; and in fact the larger 
 bundles seen on the transverse section (fig. 9) are larger 
 because they consist of so many contingents running 
 parallel, or nearly so, down the stem. 
 
 It results from this that all the vascular bundles in 
 the stem are simply composed of strands which run 
 into the leaves on the one hand, and down the inter- 
 nodes on the other; and, as further comparison will 
 show, all these bundles are continuous in the stem, since 
 the lower ends of the strands are joined on to other 
 strands. 
 
 Moreover, as an examination of the diagrams and 
 figures shows, the main course of these bundles in the 
 stem is approximately parallel they run side by side 
 down from the leaf insertion through two, three, or more 
 internodes, and only bend aside to any great extent 
 when they pass out into a leaf or to join with others. 
 In the section (fig. 9), for instance, all the little 
 bundles at the angles and outside the ring are cut at 
 levels where they have abandoned the larger bundles 
 and are bending outwards through the cortex to the 
 leaves ; lower down we should find them joining to the 
 larger bundles at various levels, and running down with 
 them, just as strands from leaves at higher levels are 
 now conjoined to make up these larger bundles. 
 
 The group of vascular bundles which passes into the 
 stem from the insertion of a leaf is spoken of collec-
 
 THE SEEDLING AND YOUNG PLANT 47 
 
 lively as the ' leaf-trace.' Hence we see the leaf-trace 
 of the oak consists of five bundles one median, two 
 lateral median, and two lateral and since the phyllo- 
 taxis of the oak is f, there will be twenty-five bundles 
 in various stages of separation or conjunction coming 
 down in the five internodes between any one leaf and 
 the leai vertically above it, as well as the parts of 
 bundles from other leaves which are still continuing 
 their course for a short time. 
 
 Now, since the main lengths of the course (in the 
 stem) of these bundles is nearly vertically downwards, 
 with slight swerves to one side or another as the strands 
 join, it is obvious that on the transverse section of the 
 stem the bundles will appear arranged in a series round 
 the centre in fact, they will form on the whole a more 
 or less regular ring of bundles dividing off the pith from 
 the cortical portions of the stem. Even in the very 
 young condition (fig. 9) we see bundles or groups of 
 strands thus surrounding the pith, only the 'ring' 
 which they make is a sinuous one, so that the pith 
 is five-rayed a characteristic point in the oak. At 
 a slightly later stage, as we shall see, this ring of 
 bundles becomes more nearly circular from the gradual 
 filling up of irregularities. 
 
 Before proceeding further it is necessary to make 
 clear one or two other points. Since all the vascular 
 bundles in the oak-stem are bundles which are common 
 to the stem and leaf, they are termed 'common bundles.' 
 We have seen that a given strand or bundle may run
 
 48 THE OAK 
 
 for part of its course simply side by side with another 
 and separate from it \ at other parts of the course the 
 bundles may be united with others. In the case of the 
 oak it will be clearly borne in mind that the individual 
 or separate bundles of the leaf-trace pass into the stem 
 at the node of insertion of the given leaf, and then run 
 down side by side at a practically constant distance from 
 the surface of the epidermis on the one hand, and the 
 longitudinal axis of the pith on the other. At different 
 levels below, at or very near nodes, these bundles turn 
 aside laterally i.e. in the tangential plane, and hence, 
 still keeping their mean distance from the epidermis and 
 pith, join with others. 
 
 This being understood, it is also obvious that on the 
 whole the collection of vascular bundles in a young branch 
 form a nearly cylindrical trellis- work or mesh work sym- 
 metrically disposed between the pith and the cortex, 
 and that the latter (cortex and pith) are in connection 
 through the meshes between the interpectinating and 
 concomitant vascular bundles. These radial connec- 
 tions of the pith and cortex are the primary medullary 
 rays. 
 
 It will now be clear why we observe on transverse 
 sections of the young stem taken across an internode 
 the arrangement shown in fig. 9. The vascular bundles 
 are grouped in a ring round the pith, separating it off 
 from the cortex and its covering the epidermis, and with 
 those primary medullary rays which happen to have 
 been cut running between the bundles.
 
 THE SEEDLING- AND YOl'NG- PLANT 49 
 
 If we now trace the vascular bundles of the leaf- 
 trace in the other direction that is, np into the leaf 
 their course is simple enough, as shown in figs. 10 and 
 11. The five bundles run through the midrib and the 
 stronger lateral ribs to the tips and edges of the leaf, 
 first breaking up into several strands in the petiole and 
 midrib, and then becoming finer and finer as they give 
 off the lateral strands. The median bundle does little 
 more than run directly through the leaf as the midrib, 
 becoming finer and finer as it nears the apex. The 
 two lateral median bundles behave in a somewhat 
 curious way. We have already seen how large and fiat 
 they are at the leaf insertion (fig. 10). Soon after enter- 
 ing the petiole they break up into several strands, two 
 of which converge and take a course along the dorsal 
 side of the midrib, thus nearly completing a cylinder of 
 bundles enclosing a pith ; moreover, the xylem portions 
 of these bundles are all turned inwards towards the pith. 
 
 The lateral bundles, coming obliquely into the leaf 
 insertion, pass up the midrib side by side with the 
 above, and, like them, break up into parallel strands. 
 Before entering the midrib they give off small bundles 
 (fst in fig. 10) to the pair of minute stipules which flank 
 the petiole. As the strands pass along the midribs and 
 chief lateral ribs they interosculate in various degrees, 
 and give off smaller side branches into the rnesophyll 
 of the leaf (see Chapter VI.). 
 
 The veins which spring from the chief lateral ribs 
 run towards one another and anastomose, giving off 
 
 E
 
 50 ME OAK 
 
 smaller veins which form a network in the area included 
 by them. In the neighbourhood of the leaf-margin, 
 however, the smaller veins curve towards one another, 
 and make arches convex towards the margin. In the 
 finer meshes individual minute branches run to the 
 centre of a mesh and end there. Round the extreme 
 edge of the leaf is a single vascular bundle ; this receives 
 small bundles from the above-mentioned arches, and 
 also receives the ends of the midrib and the chief lateral 
 ribs (c/. fig. 1). 
 
 The vascular bundles of the axillary bud, which will 
 eventually, of course, form a system like that already 
 described on their own account, pass down and join the 
 bundles of the parent axis as follows. 
 
 The bundles of each lateral half of the bud (fig. 11, 
 a a) pass down together between the bundles of the leaf- 
 trace of the leaf from whose axil the bud arises, and the 
 next lateral bundles of the stem with which the leaf-trace 
 bundles are conjoined ; the common strand formed by 
 the bundles of each side of the bud then joins with a 
 bundle coming down from another leaf. A few of the 
 strands may also join to the bundles of the leaf-trace 
 itself. 
 
 At the back or top side of the bud i.e. the side next 
 the stem^which bears it a few vascular bundles pass 
 from the bud to the nearest strand (fig. 11, 2) ; this is 
 the middle strand coming down from the leaf vertically 
 above the bud i.e. the sixth leaf up the stem. Knowing 
 this, we of course know how the branch is joined to the
 
 THE SEEDLING- AND YOUNG- PLANT 51 
 
 stem. Several other small strands also are formed, as 
 at z, to complete the filling up of the gap, and these may 
 be called completing bundles. These connecting and 
 completing bundles enable the young shoot as it deve- 
 lops from the bud to enclose its own pith in a cylinder 
 of vascular tissue continuous with that of the parent 
 shoot. 
 
 We thus see that the vascular bundles form a con- 
 nected system in the leaves, buds (i.e. young branches), 
 and stem, and it only remains to add that they are 
 joined below to those of the root-system, with which, 
 in fact, they took origin in the very young embryo. 
 Hence, if we were to remove the whole of the softer 
 tissues of the oak- plant, we should have a model of it 
 left in the form of a more or less open basket-work of 
 vascular bundles. It is necessary to bear this in mind, 
 as some important conclusions follow from it sub- 
 sequently. 
 
 E 2
 
 52 THE OAK 
 
 CHAPTER V 
 
 THE SEEDLING AND YOUNG PLANT (continued) 
 
 STRUCTURE OF THE VASCULAR TISSUES, &c. 
 
 BEFORE plunging into the intricacies of the vascular 
 bundles it will be well to obtain some idea of the 
 general plan of structure which they present on trans- 
 verse section (fig. 9). As already seen, each of the bundles 
 of the ring consists of a xylem portion on the side next 
 the centre of the stem, and a phloem portion on the side 
 next the periphery, and these portions are separated 
 by the cambium layer. The tissue in the centre of the 
 stem, and surrounded by the ring of bundles, is called 
 the pith ; the tissue outside the ring, and between it 
 and the epidermis, is called the cortex ; and the tissue 
 left between the bundles is termed the primary medul- 
 lary rays (fig. 9). 
 
 It will, of course, be remembered that the term 
 ' ring,' as used above, always expresses the fact that a 
 cylinder is here viewed in section. Now, the cambium 
 of the individual bundles soon unites across the primary 
 medullary rays, and thus a complete hollow cylinder of
 
 THE SEEDLING AND YOUNG PLANT 
 
 - m 
 
 53 
 
 FIG. 12. Transverse section of young stem, showingprimary 
 vascular bundles, &c., highly magnified, a and &, the 
 pith ; c, primary cortex ; i, epidermis ; k, periderm (cork); 
 g, collenchyma. Two complete primary vascular bundles, 
 and parts of two others, are shown, separated by the 
 primary medullary rays, r, spiral vessels (protoxylem) ; 
 ft, bast-fibres (protophloem) ; n, m, cambium, separating 
 the phloem from the xylem; p, wood-parenchyma. 
 Secondary medullary rays are seen in the bundles, as 
 also are pitted vessels of different sizes. (Th. Hartig.)
 
 54 THE OAK 
 
 cambium is formed throughout the stem, and, as we 
 shall see later, throughout the root also. For the 
 present it must suffice to notice that the cells of this 
 cambium cylinder go on developing into new xylem, 
 or phloem, or medullary rays, according to position and 
 circumstances ; meanwhile we are only concerned with 
 the vascular bundles of the young shoot. 
 
 On the transverse section through the very young 
 shoot, provided the preparation is thin and examined 
 with a high power of the microscope, the young vascular 
 bundles are found to present a definite and symmetrical 
 structure, easily distinguished from that of the funda- 
 mental cell-tissue in which they are, so to speak, 
 embedded (fig. 12). 
 
 The cells of the medullary rays are seen in one, two, 
 or several rows, each cell having the form of a parallele- 
 piped or ordinary brick the bricks being supposed 
 standing on their narrow sides and with the long axes 
 directed radially. The walls in contact with the vas- 
 cular bundles are thickened, and soon become woody 
 and beset with simple pits ; the cells contain protoplasm 
 and nuclei, and in winter become filled to crowding 
 with starch grains. They also contain tannin. 
 
 The young vascular bundles, in section, project into 
 the pith like wedges with a rounded point giving to 
 the latter the five-rayed shape on the transverse section 
 already referred to (fig. 9). 
 
 The cells of the pith also have their walls thickened 
 and pitted, and also contain protoplasm, nuclei, and
 
 THE SEEDLING AND YOUNG PLANT 55 
 
 tannin, and starch in winter. At the rounded angles 
 of the vascular wedges the cells are smaller than else- 
 where in the pith, but otherwise their shape, &c., are 
 similar; all the pith-cells are vertically twice or three 
 times as long as broad. Thus the shape of the cells is 
 that of short, polygonal prisms, standing on end and 
 closely packed. 
 
 Embedded, as it were, in the smaller pith-cells at the 
 rounded angles of the vascular wedges are the oldest 
 i.e. first-formed vessels, looking like small holes with 
 very firm outlines (fig. 12, r). These are the tracheae, or 
 vessels with unreliable spiral thickenings on their walls. 
 From their shape and peculiarities they are called spiral 
 vessels, and from their position and development they 
 constitute the first-formed elements of the xylem or 
 wood. They are of very narrow calibre, and stand in 
 radial, short rows, single or branched j those first de- 
 veloped i.e. nearest the pith are the narrowest, their 
 diameter being often even less than that of the smallest 
 pith-cells among which they lie. As we pass radially 
 out towards the cortex these vessels get wider and 
 wider, but the true spiral vessels are always very 
 narrow (fig. 16, sp). Occasionally some of these vessels 
 have annular instead of spiral thickenings. 
 
 Of course, their true characters are not elucidated 
 until we compare longitudinal sections of the stem. 
 It is then seen that the spiral thickenings are very 
 closely wound, sometimes to the right, sometimes to 
 the left, and occasionally double. Comparative studies
 
 56 THE OAK 
 
 of longitudinal sections also show that these vessels at 
 first simply consist of longitudinal rows of very narrow, 
 vertically placed, cylindrical cells, standing end to end ; 
 it is because the adjacent ends become resorbed and 
 disappear that the rows of cells at length form long 
 continuous tubes- vessels, or tracheae. 
 
 Turning once more to the transverse section, as 
 the eye follows the bundle radially outwards the 
 lumina of the vessels in the radial rows are found to 
 become wider and wider, until we meet with vessels with 
 diameters many times greater than that of the pith- 
 cells. The walls of these wider vessels, however, are 
 not strengthened with spiral thickenings, but are 
 thickened and furnished with bordered pits, the shape 
 and characters of which are best seen from the illustra- 
 tions (figs. 14-16). These larger vessels are not always 
 associated with the radial rows of spiral vessels, but 
 may be scattered between them. 
 
 The vessels intermediate between the spiral and the 
 pitted ones are thickened sometimes with reticulations. 
 All these larger vessels have septa inclined towards the 
 medullary rays, and perforated with several long*, oval, 
 parallel, horizontal holes : hence the segments are easily 
 macerated and distinguished, and their lengths are found 
 to be variable (fig. 16, p.v). 
 
 The large pitted vessels form groups with paren- 
 chyma and wood-cells scattered between, and are con- 
 fined chiefly to the inner parts, forming radiating series 
 side by side ; in the outer parts of the bundle are
 
 THE SEEDLING AND YOUNG PLANT 
 
 57
 
 58 
 
 THE OAK 
 
 j_ 
 
 S j
 
 THE SEEDLING AND YOUNG PLANT 
 
 59
 
 60 THE OAK 
 
 various groups of smaller vessels the groups being 
 rounded, or in radial rows, or curved or oblique rows. 
 
 Successive sections prove that the vessels in the 
 bundle change in number i.e. there are fewer when 
 passing from stem to leaf. A vessel may end in an 
 interpectinating, pointed, terminal cell ; or it may 
 branch, as it were, dichotomously, owing to fusions with 
 other similar elements ; or such a fusion may occur 
 lower down, the original vessel ending blindly. 
 
 In the vicinity of the reticulated and first pitted 
 vessels, following on the spiral vessels, we find libriforrn 
 fibres, tracheids, wood parenchyma, and secondary 
 rays of parenchyma ; the tracheids are especially in 
 the neighbourhood of the vessels (see fig. 14). 
 
 The tracheids are long cells with gradually taper 
 ends, and the walls rather thick but by no means ob- 
 scuring the lumen ; on the walls are numerous, usually 
 elongated, oblique or horizontal bordered pits. These 
 pits occur whether the next element is a tracheid, a 
 vessel, or fibres or cells of any kind (fig. 16, tr). 
 
 The length of the tracheids varies, and the diameter 
 is also variable. 
 
 The libriform fibres are also long cells, but often 
 more pointed at the ends, and their very thick walls 
 almost obliterate the lumen (fig. 16,/) ; their length is 
 about that of the tracheids. but slit-like, small, simple 
 pits are rare on their walls. In the wood of later years, 
 however, the lengths may be different. 
 
 There are also elements which stand midway between
 
 sp. 
 
 FlG. 16. The various chief elements of the wood of the 
 oak, isolated by maceration, and highly magnified. /, a 
 fibre, distinguished by its thick walls, simple slit-like 
 pits, and no contents ; m.p, part of a row of wood-paren- 
 chyma cells, with simple pits, and containing starch in 
 winter ; tr, a tracheid, distinguished from the fibre 
 especially by its bordered pits ; p.v, part of a rather large 
 pitted vessel, made up of communicating segments, each 
 of which corresponds to a tracheid, and has bordered pits 
 on its walls ; */;, part of a spiral vessel.
 
 62 THE OAK 
 
 the true fibres and tracheids ; they occur in those parts 
 where masses of true fibres abut on the groups consist- 
 ing of vessels and tracheids. They resemble tracheids, 
 but have very few and small, scarcely bordered, oblique, 
 slit-like pits : every stage can be detected between these 
 and true fibres. They must be looked upon as, so to 
 speak, abnormal, because their numbers are small com- 
 pared with the typical elements among which they 
 occur. 
 
 The wood-parenchyma consists of vertical groups of 
 short cells, each group having the fusiform shape of a 
 tracheid (fig. 16, w.p) : hence the upper and lower cell of 
 each group has a pointed end. Each group obviously 
 arises from the transverse divisions of a long, prismatic 
 cell, pointed at both ends a cambium cell. The trans- 
 verse section is round, and somewhat larger than that of 
 a tracheid, and the walls are somewhat thinner. Where 
 they abut on vessels and tracheids their walls have 
 bordered pits, but where they stand in contact with 
 similar groups, or with parenchyma rays, the pits are 
 simple. During periods of rest they are loaded with 
 starch grains. 
 
 The length of the groups i.e. of the fusiform cells 
 cut up into short cells varies ; the shorter ones have 
 only one transverse division. 
 
 The wood-parenchyma is less abundant than the 
 tracheids and fibres, and predominates in the more 
 vascular parts; after two to four or more fibres in a 
 radial row a single parenchyma cell may often be seen,
 
 THE SEEDLING AND YOUNQ PLANT 63 
 
 but other arrangements occur. In the parts where 
 fewer vessels occur it is not uncommon to find a series 
 of radial rows of about six to ten fibres end in a single 
 parenchyma cell, and thus are formed short, tangential 
 rows of wood-parenchyma cells, intercalated, as it were, 
 between the radial rows of other elements (fig. 12, p). 
 It often happens, moreover, that reticulated and pitted 
 vessels are closely surrounded by wood-parenchyma. 
 
 The secondary medullary rays exist as single radial 
 rows of cells, agreeing in form, &c., with the cells 
 of the primary medullary rays. In contact with one 
 another or with wood parenchyma their walls have simple 
 pits, but they have bordered pits where they abut on 
 tracheids or vessels. In winter these cells are filled with 
 starch. On tangential sections (fig. 15) it is easy to 
 see how the vertical groups of cells have the same origin 
 as the groups of wood-parenchyma cells the difference 
 being that the cambial cells which are going to be trans- 
 formed by horizontal divisions, &c., into vertical rows of 
 ray parenchyma, undergo repeated tangential longitudi- 
 nal divisions, and so continued radial rows are formed. 
 The cells of these rays are often much shorter than 
 those of the wood-parenchyma, yet all gradations occur. 
 The mother-cells may be very long, evidently corre- 
 sponding to two, and they may also divide in the radial 
 longitudinal plane, and the ray become biseriate. 
 
 These secondary rays start (on the transverse section) 
 from the first large vessels, or from younger ones, or 
 they may start from other points. The ray may some-
 
 64 THE OAK 
 
 times cease within the first year's bundle ; but the diffi- 
 culty comes in of deciding whether a continuation occurs 
 at a higher or lower level. 
 
 The cells of the cambium, seen in transverse section, 
 are rectangular in shape and arranged in regular radial 
 rows, owing to the regular tangential divisions (fig. 12, 
 n, m). In longitudinal sections they are found to be like 
 the tracheids in shape and size, so that they stand one 
 behind the other at the same level. Regarding the 
 tangential series in rings, however, they are less regular, 
 because the tangential longitudinal divisions of two cells 
 side by side do not lie in the same tangential plane. 
 This regular radial arrangement would be found in the 
 xylem also, and is so to a certain extent, but it is dis- 
 turbed by the differences in diameter which the various 
 elements attain later. The fibres are most apt to pre- 
 serve the regularity, but in many cases growth in 
 length, and the intercalation of oblique septa, disturb it. 
 
 In later years the length of the cambial cells in- 
 creases, and hence the length of the elements in the 
 wood. 
 
 The phloem or bast of the individual bundle is sepa- 
 rated from its neighbours by large rays of parenchyma, 
 the cells of which agree with the secondary bast-paren- 
 chyma rays. As these pass into the cortex they widen, 
 as they do at the pith (fig. 12). 
 
 The oldest portion of the phloem that next the 
 cortex consists of a group of thick- walled bast fibres 
 with their lumina nearly obliterated ; these are long,
 
 THE SEEDLING AND YOUNG PLANT 65 
 
 spindle-shaped fibres much like the fibres of the 
 wood. 
 
 As a rule, the outer and inner side of these bast 
 groups are in contact with vertical rows of nearly cubical 
 parenchyma cells, strongly thickened on the side next 
 the bast, and each nearly filled with a crystalline clump 
 or with an imperfectly formed crystal of oxalate of 
 lime. Similar vertical rows of crystal cells may also 
 occur within the groups of bast fibres, the walls of the 
 cubical cells being more or less thickened and simply 
 pitted. Occasionally a cell here and there retains thin 
 walls. The vertical rows result from cross- divisions of 
 prosenchymatous mother-cells, the conical ends being 
 found in macerations. 
 
 Within the groups of bast fibres are yet other rows, 
 similarly formed, of parenchyma (fig. 17, l>p), the cells of 
 which are longer, however, attaining the length of the 
 wood-parenchyma ; like the latter also their walls are 
 lignified and rather thick, and they contain starch in 
 the winter. Thus we have parenchyma in the bast. 
 Transitions between these two forms of parenchyma 
 cells are also found. 
 
 The cells of the rays between the bast fibres are 
 thickened and pitted ; they are rounded, and not in 
 vertical series as in the rest of the rays, but are scattered 
 in no particular order. Sometimes they are few, and 
 one or all with very thick walls perforated by pit-canals 
 (fig. 17, to). 
 
 The remaining younger part of the bast consists
 
 FIG. 17. Transverse section of cortex and phloem of oak (highly 
 magnified), k, the periderm (cork), which has replaced the epi- 
 dermis ; c, collenchyma ; d, cells of cortex containing crystals of 
 oxalate of lime ; s, schlerenchyma cells. All these belong to the 
 cortex proper. Below these come the phloem : b, b, groups of hard 
 bast fibres ; bp, phloem-parenchyma ; bs, medullary ray ; e, cells 
 containing crystals of oxalate of lime. (Luerssen.)
 
 THE SEEDLING AND YOUNG PLANT 67 
 
 chiefly of delicate, apparently irregular parenchyma 
 cells with cellulose walls ; this is easily traced to the 
 cambium. The radial rows of the latter can be followed 
 for some -distance, the radial diameter of the cells in- 
 creasing, the walls thickening, and the rectangular shape 
 changing. Displacements from the radial arrangement 
 then occur. A few cells assume a nearly circular form 
 (i.e. in transverse section), and the larger ones are effec- 
 tive in causing displacements. The bast-cells developed 
 earlier, and therefore more distant from the cambium 
 zone, now lie in the perceptibly larger periphery, and 
 thus undergo tangential extension or radial compression, 
 and so undergo changes of form. Besides these altera- 
 tions in form and position, the more delicate bast elements 
 increase in numbers by the development of perpendicular 
 division walls; this is quite clear in those parts nearest 
 the cambium, but further out, where great irregu- 
 larity occurs, it is impossible to say which cells have 
 arisen direct from the cambium and which by these 
 later divisions. Still, certain thin septa betray their 
 late origin. 
 
 On tangential sections we see elongated, pointed, 
 interpectinating cells, with secondary rays of parenchyma 
 between, showing that these are formed and continued 
 by the cambium. Each pointed cell has proceeded from 
 a cambium cell, and indeed only differs in its thicker 
 walls and pits. These cells are still simple, or here and 
 there have a transverse septum obliquely across. If the 
 tangential section is in a slightly older portion, most of 
 
 F 2
 
 68 THE OAK 
 
 the above cells are found to be septate and cut up into 
 parenchyma-like cells irregular bast-parenchyma. The 
 walls, especially the longitudinal walls, are marked 
 either with crowded small pits, giving a reticulate ap- 
 pearance, or have sieve-plates ; all intermediate stages 
 occur also. The transverse walls are also pitted with 
 sieve-plates. 
 
 All the cells of the soft bast contain tannin, and 
 small grains which turn brown in iodine (leucoplasts ?). 
 Very little starch is found in them except in winter. 
 Crystals occur in pitted cells here and there (fig. 18, 
 d and e). 
 
 Even in the first year the cambium may produce 
 small groups of thick-walled bast fibres of exactly the 
 same character as those of the primordial groups. 
 
 It is obvious that while the wood elements remain 
 fixed in the cylindrical surface where they are developed, 
 the bast elements formed outside the cambium, being 
 driven outwards in consequence of growth in thickness, 
 come to lie in a layer of continually increasing radius. If 
 these bast elements were unyielding and lignified there 
 would be a solid sheath of elements which refused to 
 extend by mechanical distension, cell division, or growth 
 of cell-walls; this would finally rupture under the 
 pressure from within. This is prevented by the division 
 and growth of the chief phloem elements. 
 
 In the vascular-bundle system of the stem there are 
 no essential differences in structure as we pass from one 
 region to another ; the only variations are in the thick-
 
 THE SEEDLING AND YOUNG PLANT 69 
 
 ness or breadth of the bundles at different points, such 
 as where other bundles join or leave them. As the 
 
 FIG. 18. Longitudinal radial section of the cortex and 
 phloem of oak. References as in fig. 17. (Luerssen.) 
 
 leaf- trace passes into the venation of the leaf the ends 
 become thinner (fig. 21), and the same is found as it tails
 
 70 THE OAK 
 
 off below ; changes in structure also appear in the 
 leaves. 
 
 The first noticeable change is the diminution in the 
 number of wood fibres and the presence of narrow vessels 
 only. As the trace passes through the cortex to the leaf 
 the actual number of both xylem- and phloem-elements 
 diminishes; hence it comes about that the bundles in 
 the leaves consist to a relatively large extent of spiral 
 vessels in the xylem and of sieve-tubes in the phloem. 
 As the bundles leave the midrib and larger veins the 
 true continuous vessels disappear altogether, and only 
 spindle-shaped tracheids with reticulated or spiral 
 thickenings occur, fitting obliquely at their pointed 
 ends, and which are shorter and shorter as we approach 
 the ends of the bundles. 
 
 The phloem also is at length reduced to little more 
 than one or two sieve-tubes, the segments of which are 
 shorter and shorter as we near the end. The shortening 
 of the elements is in evident correlation with the early 
 cessation of growth in length of the parts of the leaf, 
 and the diminution of the number of elements with the 
 decreased supply of fluids, &c., on the one hand, and 
 the smaller weight and strains to be supported on the 
 other. 
 
 We may sum up the changes in structure towards 
 the ends of the vascular bundles thus. The thickening 
 of the walls is less, and the elements become narrower 
 and shorter ; the xylem becomes simplified by the loss 
 of fibres and vessels, until finally only delicate tracheids
 
 THE SEEDLING AND YOUNG PLANT 71 
 
 are left (fig. 21), the thickenings of which are at length 
 not spirals or nets for the most part, but irregular pittings. 
 Moreover, they are nearly isolated. Nevertheless, the 
 inner elements can be distinguished as primary tracheal 
 elements, because, being earlier formed, they partook 
 more in what elongation occurred, and their spirals, for 
 instance, are wider apart. 
 
 In the midrib, in proportion as the structural changes 
 go on, the bundles approach one another, the separating 
 parenchyma becoming narrower and narrower. The 
 pith consists of parenchyma, chiefly unlignified and 
 with simple pits, but as the bundles are approached 
 the cells become longer and lignified ; the rays between 
 the xylem groups are also lignified. 
 
 Towards autumn the cells of the pith and rays fill 
 with starch ; this is nearly, but not quite, all resorbed 
 before the leaf falls. 
 
 The termination of the bundles in the leaf consists 
 only of a few narrow spiral and reticulated cells, which 
 at last become very short and variable in shape, and of 
 a few small sieve elements and cells (see Chapter VI.).
 
 72 THE OAK 
 
 CHAPTER VI 
 
 TEE SEEDLING AND YOUNG PLANT (continued) 
 
 THE BUDS AND LEAVES 
 
 THE. buds of the oak those in the leaf-axils as well as 
 those at the tips of the young shoots are characteris- 
 tically short and broad ovoid bodies, consisting of nume- 
 rous overlapping brown scales covered with short, silky 
 hairs, especially at the margins (fig. 19). These scales are 
 really the stipules of arrested leaves, as is shown by the 
 proper leaf-blades being developed as well under certain 
 circumstances, such as when nutritive materials are 
 directed to the young buds. The same morphological 
 fact is also shown by the position of the inflorescences 
 and young leaves higher up in the bud, for they spring 
 from between the scales, and not from their axils proper 
 (see fig. 32). It is of the highest importance to understand 
 that a bud is simply the young state of a shoot, and that 
 it consists of the growing-point of the shoot enveloped 
 by closely-folded leaf structures. In the oak the buds 
 are already formed before the end of June, and on 
 looking closely into the axils of the leaves on the
 
 THE SEEDLING AND YOUNQ PLANT 
 
 73 
 
 young shoots which have by that time ceased to 
 elongate to any considerable extent further they may 
 be seen as small, green, hairy bodies. During the re- 
 mainder of the summer the chief changes going on in 
 
 FIG. 19. A. End of a branch of oak showing the charac- 
 teristic winter buds. B. A group of buds (slightly mag- 
 nified) ; a, bud-scales ; d, leaf -scars, c. The same, in 
 longitudinal section : a, bud-scales (stipules) ; b, young 
 leaves ; c, vascular bundles ; d, leaf -scars. (Prantl and 
 Hartig.) 
 
 these buds is a slow swelling, due to the gradual storing 
 up of nutritive materials in the pith and growing-point 
 and to the slow division of the cells. 
 
 A vertical section through the bud at the end of the 
 autumn shows the following structures (fig. 19, c). A
 
 74 THE OAK 
 
 conical growing-point, consisting of embryonic tissue, 
 occupies the centre ; around this, arranged in a close 
 spiral, are several young rudiments of foliage leaves, each 
 consisting of meristem, the cells of which are undergoing 
 divisions. The youngest leaf is next the apex of the cone 
 i.e. the order of development is acropetal and each is 
 folded with the upper surfaces of each half in contact; two 
 extremely minute stipules accompany each leaf. Lower 
 down on the cone come the numerous (about thirty) over- 
 lapping scales, and between several pairs of the upper of 
 these the male inflorescences develop. The female in- 
 florescences are developed in the axils of two or three 
 of the above-described true leaves in a terminal bud ; 
 they are not normally formed in the lateral buds of the 
 shoot (see Chapter IX.). 
 
 All the leaves of the shoot may have such buds 
 formed in their axils during the summer, but only some 
 of them develop in the following spring ; it is the buds 
 in the axils of the lower leaves of the shoot which 
 usually come to nothing. 
 
 The normal course of events is that the bud-scales 
 (stipules) become dry, and the protected growing-point, 
 with its rudimentary leaves and flowers, passes into a 
 dormant condition lasting through the winter ; but it is 
 a very common event, especially in a wet autumn follow- 
 ing a dry, hot summer, to find the winter buds begin- 
 ning to shoot out in August, and not passing into the 
 prolonged state of dormancy. Such stoots are known 
 as Lammas shoots. In some districts the oak forms
 
 THE SEEDLING AND YOUNG PLANT 75 
 
 numbers of these Lammas shoots every year, and the 
 tendency to produce them seems to be capable of being 
 inherited. 
 
 The process of sprouting, or putting forth the shoot 
 from the bud, is the same in all the cases. As the 
 temperature and other conditions improve in the spring, 
 for instance, the process of cell-division in the growing- 
 point (and its derivatives, the young leaves, &c.) goes on 
 rapidly, and the stores of nourishment already there and 
 in the pith and other tissues close at hand are used up. 
 This originates a series of currents of food materials set- 
 ting slowly towards these centres of consumption from 
 other parts of the tree, and very soon the numerous cells 
 developed begin to absorb water with relatively enor- 
 mous rapidity and vigour. This brings about two chief 
 changes the rapid elongation of the parts of the cone 
 situated between the points of insertion of successive leaves 
 (i.e. the internodes), and the almost simultaneous expan- 
 sion of the hitherto small and folded leaves. Thus the 
 rapid extension of the shoot is due almost entirely to the 
 energetic absorption of water into cells for the most part 
 already in existence. The chief changes which follow 
 consist in the perfection of the structures the develop- 
 ment and thickening of vascular tissues, cell-walls, &c. 
 
 This process of rapid extension does not occur in the 
 internodes between the bud-scales, or, at any rate, to a 
 slight degree only, just sufficient to enable the shoot to 
 throw the scales off ; hence the base of the outgrown 
 shoot shows a number of small scars in a close spiral.
 
 76 THE OAK 
 
 These scars of the stipular bud-scales, like those of fallen 
 leaves, exhibit the points of rupture of the vascular 
 bundles which ran across from the bundles of the bud- 
 axis. It only remains to point out that the buds vary 
 in size and vigour according to the age and condition 
 of the tree ; the buds on oaks less than fifty years old 
 very rarely have inflorescences developed in them, and 
 I shall defer the consideration of these till we come to 
 the flower. 
 
 The mature leaf of the oak (fig. 20) is obovate in 
 general outline, with rather deep sinuses cutting the 
 margin on each side into about six or eight rounded lobes ; 
 the apex is rounded or blunt, and some variation occurs 
 in the degree of incision between the lobes. The base 
 either tapers slightly into an evident petiole, or it is pro- 
 longed on either side of a very short petiole so as to form 
 small auricles. In the commonest variety the margins 
 and surfaces of the leaf are quite smooth, but the race- 
 form known as Quercus sessiliflora has the young leaves 
 pubescent beneath. 
 
 The venation consists of a midrib running from base 
 to apex, and pinnate lateral ribs running from the 
 midrib at an angle of about 45 to the tip of each lobe, 
 the points of origin being alternate or nearly opposite, 
 and the angle referred to subtending forwards. These 
 principal ribs are prominent below but not at all so 
 above. The leaf-tissue (mesophyll) between these is 
 permeated by numerous smaller vascular bundles 
 united into an irregular network, but so arranged that
 
 THE SEEDLING AND YOUNG PLANT 
 
 77 
 
 they leave between them nearly equal small areas not 
 traversed by bundles. 
 
 FIG. 20. Sprigs of oak, showing the habit and the arrange- 
 ment of the acorns, &c., in September. (After Kotschy.) 
 
 When young the leaves are red, gradually becoming 
 bright apple-green, and finally in the autumn
 
 78 
 
 THE OAK 
 
 becoming russet-brown in colour. Young oaks retain 
 their dead leaves till far into the winter, and even old 
 trees usually have some leaves attached till January. 
 The young leaves secrete small quantities of sweet 
 liquid on the superior face of the lamina, and are much 
 visited by bees and wasps ; this honey must come 
 
 through the mem- 
 brane. As the leaves 
 approach maturity 
 the lamina becomes 
 bright and hard. 
 
 The arrangement 
 of the leaves is ex- 
 pressed by the frac- 
 tion f, as already de- 
 scribed, each node 
 giving off one leaf at 
 an open angle, the 
 points of insertion 
 being so arranged 
 that a line drawn 
 from the insertion of 
 a given lower leaf, 
 and joining it to the 
 
 points of insertion of those above, passes twice round the 
 twig before we arrive at the leaf situated vertically above 
 the one started from, and this upper leaf is the sixth 
 above. Although this is the commonest and normal 
 arrangement, however, other dispositions are occasionally 
 
 FIG. 21. A portion of the ultimate 
 ramifications of the vascular bundles, 
 showing tracheids only, isolated from 
 the leaf by maceration.
 
 THE SEEDLING AND YOUNG PLANT 79 
 
 met with on the same plant. The young leaves are 
 folded in the bud in such a manner that the two halves 
 of the lamina lie one on the other, the upper surfaces 
 being in contact (conduplicate vernation), the margins 
 being therefore turned upwards. 
 
 In order to understand the structure of the leaf, 
 let us look at a section cut neatly across the midrib and 
 lamina, and examined with the microscope. It is found 
 to consist of three principal parts an epidermis above 
 and below, and all round the margins, and therefore 
 over the whole of the leaf ; this epidermis is, in fact, 
 a continuation of that of the young shoot-axis, and 
 envelops the whole of the remaining leaf-tissues. In- 
 side this we have the main mass of the leaf substance 
 called the mesophyll consisting of thin-walled cells 
 arranged in a peculiar manner, and containing (in 
 addition to less obvious structures) large numbers of 
 green chlorophyll corpuscles ; it is the predominance of 
 these corpuscles which causes the leaves to appear 
 uniformly green. Here and there we see vascular 
 bundles, embedded, as it were, in the mesophyll, cut 
 across in various directions, and when it is remembered 
 that these vascular bundles constitute the venation of 
 the leaf this phenomenon is easily explained. 
 
 As we have already seen, the vascular bundles of 
 the venation (fig. 20) are simply the much-branched and 
 thinned-off upper ends of the vascular bundles from the 
 shoot-axis, the lower ends of which join the vascular sys- 
 tem of the latter lower down. Now the next point to be
 
 80 
 
 THE OAK 
 
 clearly apprehended is that these vascular bundles of the 
 leaves have the double duty of supporting the flattened 
 
 FIG. 22. Sections across the leaf of oak. A. Slightly mag- 
 nified and semi-diagrammatic, to show the general 
 arrangement of the principal vascular bundles as seen 
 cut across ; m, midrib ; e, marginal veins ; s, lateral 
 branches of midrib. Other smaller veins scattered be- 
 tween. B. A highly magnified vertical section of part 
 of the above at a place free from vascular bundles : 
 u, upper epidermis, with cuticle, c ; p, palisade cells ; ch, 
 chlorophyll corpuscles, only drawn in a few cells ; m, 
 spongy tissue of mesophyll ; i.s, intercellular passages 
 communicating with the stoma, st, in the lower epider- 
 mis, I. 
 
 mass of leaf-tissue, and of carrying to and from its cells 
 the water from the roots and the organic substances
 
 THE SEEDLING AND YOUNG PLANT 81 
 
 formed in the cells of the leaves. The water, with salts in 
 solution, coming from the soil, after it has been absorbed 
 by the root-hairs, passes up the wood (xylem) of the 
 roots and stem, through the vessels of the petioles and 
 leaf-venation, and is finally distributed to the cells of 
 the mesophyll ; the substances formed in these cells then 
 pass down by the phloem (sieve-tubes, &c.) of the vena- 
 tion and leaf-stalk, and thence are distributed to other 
 parts of the plant. 
 
 Now let us look at the mesophyll which these vascu- 
 lar bundles support and serve as conduits for. It con- 
 sists of two distinct parts (fig. 22). Beneath the upper 
 epidermis, the cells of which are fitted closely together 
 without intercellular spaces and are devoid of chlorophyll 
 corpuscles, there are one or two rows of vertical sausage- 
 shaped cells, closely arranged like the wooden railings 
 of a complete palisade consequently they are termed 
 the palisade cells. The lower moiety of the mesophyll, 
 on the other hand, is composed of irregular cells with 
 large intercellular spaces between them, and this loose, 
 spongy tissue, as it is aptly called, abuts below on the 
 lower epidermis. Both the palisade cells and those of 
 the spongy tissue contain numerous chlorophyll cor- 
 puscles, as said. 
 
 This lower epidermis is worth a few minutes' con- 
 sideration. It, like the upper epidermis, is also com- 
 posed chiefly of closely fitting cells devoid of chlorophyll 
 corpuscles, excepting that here and there we notice pairs 
 of smaller cells containing chlorophyll each pair with a
 
 82 THE OAK 
 
 minute gap between them, and the gap communicates 
 with the intercellular air-cavities between the cells of 
 the spongy mesophyll (fig. 22, si). If we remove a piece 
 of this epidermis, and look at it as laid flat (instead of in 
 section) under the microscope, we find that these pairs 
 of small cells are shaped somewhat like a small mouth, 
 the two curved lips of which are formed by the two cells 
 just mentioned, and the orifice of which is the gap just 
 referred to (fig. 23). These two lips are called the guard- 
 cells, and the whole apparatus is termed a stoma. It is 
 necessary to realise two great facts about these stomata 
 on the under surface of the leaf: firstly, there are several 
 hundreds of thousands of them on an oak-leaf, each 
 square millimetre having from 300 to 350 of them 
 scattered over it ; and, secondly, each one can open or 
 close its little aperture by the approximation or divarica- 
 tion of the inner concave sides of the curved guard-cells. 
 
 If this is clear it will be readily understood that 
 these stomata can regulate the amount of water passing 
 off by evaporation from the walls of the millions of 
 cells of the mesophyll, especially if the further fact is 
 borne in mind that water-vapour scarcely passes at all 
 through the close-fitting epidermis cells themselves. 
 
 We are now in a position to form a sort of picture 
 of the mechanism of the shoot and root in regard to this 
 matter. The root-hairs absorb water from the soil, and 
 in this water there are dissolved small quantities of the 
 soluble salts of the earth chiefly sulphates, nitrates, 
 and phosphates of lime, magnesia, and potash just as
 
 THE SEEDLING AND YOUNG PLANT 
 
 83 
 
 there are in ordinary well-water. This extremely 
 dilute solution passes into the root-fibres and up 
 
 FIG. 23. A. A small piece of the lower epidermis removed 
 (and highly magnified) to show the stomata, <? ; h, minute 
 hairs. The guard-cells contain chlorophyll corpuscles, 
 whereas the ordinary epidermal cells do not. B. A stoma 
 in vertical median section, cut across its longer axis ; a, 
 intercellular space ; g, guard-cell with chlorophyll cor- 
 puscles ; s, orifice of stoma. 
 
 through the vessels, &c., of the vascular bundles of the 
 roots, collecting into the larger and larger channels 
 until it reaches the stem ; here it passes up the xylem 
 
 o 2
 
 84 THE OAK 
 
 to the branches, petioles, and leaf-venationalways in 
 the wood and is finally distributed to the mesophyll 
 cells, which absorb it and evaporate the greater part of 
 the water into the intercellular passages communicating 
 with the outer air through the stomata. 
 
 Two points need notice here. The first is that this 
 absorption and evaporation in the mesophyll constitute 
 a cause of the upward movement of the water in the 
 vascular bundles a movement which is propagated 
 through the whole stem until it makes itself effective 
 even in the roots. The exact mechanism of the move- 
 ment in the stem itself is too complex for discussion 
 here ; but I may sum up the matter by saying that the 
 disappearance of the water at the surfaces of the leaves 
 starts a series of flows in directions of least resistance 
 towards the mesophyll, and as long as the evaporation 
 goes on more water flows into the cells, to replace that 
 lost, from the vessels of the stem, when the water- 
 columns are supported and moved partly by capillarity 
 and by the air bubbles in the cavities, and partly by a 
 peculiar co-operation of the living cells of the medullary 
 rays. The second point referred to above is that the 
 evaporation from the mesophyll cells will be the more 
 rapid in proportion as the air outside is drier and the 
 stomata wide open; and the more energetic this 
 evaporation is, the more salts the mesophyll cells will 
 acquire in a given time, because, of course, the salts do 
 not pass away in the evaporated water but are left in 
 the cells. It has been calculated that an oak-tree may
 
 THE SEEDLING AND YOUNG PLANT 85 
 
 have 700,000 leaves, and that 111,225 kilogrammes of 
 water may pass off from its surface in the five months 
 from June to October, and that 226 times its own 
 weight of water may pass through it in a year. 
 
 Now comes the question What are the salts needed 
 for that so much mechanism should be expended on 
 their accumulation ? To answer this we must look at 
 the mesophyll cells a little more closely. 
 
 Each of these consists of a thin cellulose cell-wall, 
 lined with colourless protoplasm, which encloses a large 
 sap-cavity (vacuole) ; in the protoplasm are embedded 
 a number of bright green, rounded chlorophyll cor- 
 puscles, a relatively large nucleus, and a few less con- 
 spicuous granules, &c. The cell-sap contains various 
 substances dissolved in water. Some of these substances 
 are salts and other materials ready to be made use of; 
 others are, so to speak, waste products or worked-up 
 materials that are going to be got rid of, or sent to 
 places where they will be made use of, respectively. 
 
 In the colourless protoplasm which lines the interior 
 of the cell-wall and surrounds the cell-sap we find a 
 nucleus and the chlorophyll corpuscles, as said, and a few 
 words must be devoted to the latter. Each chlorophyll 
 corpuscle consists of a rounded mass of protoplasmic 
 substance of somewhat spongy texture, containing the 
 peculiar green body, chlorophyll, embedded in it as 
 in a matrix. These chlorophyll corpuscles are living 
 organs, and they require food materials, water, oxygen, 
 &c., for the support of their life processes, just as do the
 
 86 THE OAK 
 
 other living parts of the cell e.g. the colourless proto- 
 plasm and nucleus. They obtain these from the cell-sap, 
 through the agency of the colourless protoplasm in which 
 they reside. 
 
 In order that they may perform their functions 
 properly, however, it is essential that they be exposed 
 to light ; this is effected by their being in cells which 
 are disposed in thin layers, such as we have seen the 
 mesophyll of the leaf to be. In fact, the flat, thin, 
 expanded form of the leaf is a direct adaptation to the 
 end that these chlorophyll corpuscles shall be properly 
 illuminated by the sunlight; moreover, the large in- 
 tercellular passages which communicate by thousands 
 of stomata with the atmosphere ensure their being 
 thoroughly aerated. In addition to allowing the free 
 access of the oxygen of the air, moreover, these inter- 
 cellular passages admit of the small quantities of carbon 
 dioxide in the atmosphere also reaching the chlorophyll 
 corpuscles. Oxygen and carbon dioxide, therefore, are 
 found dissolved with the other materials in the cell- 
 sap which saturates the protoplasm and reaches the 
 chlorophyll corpuscles. 
 
 These facts premised, we are in a position to follow 
 generally the astounding transformations which go on 
 in these millions of chlorophyll corpuscles in the oak- 
 leaf. Carbon dioxide and water exist side by side in 
 the protoplasm of the chlorophyll corpuscle, and rays of 
 sunlight i.e. energetic vibrations of the ether which 
 pervades the universe penetrate into the system. By
 
 THE SEEDLING AND YOUNG PLANT 87 
 
 means of the energy thus derived from the sun, the mole- 
 cules of carbon dioxide and water are broken up in the 
 meshes of this chlorophyll corpuscle, and experiments 
 prove that the chlorophyll substance plays the part of the 
 ' trap to catch a sunbeam.' We are not concerned with 
 the hypothetical explanations offered for all the details 
 of this remarkable process, but the present position of 
 science enables us to say that, be these what they may, 
 the chlorophyll corpuscle gains energy form the sun, and 
 brings this energy to bear on the carbon dioxide and 
 water in such a way that it does work in tearing 
 asunder their molecules in the substance of the cor- 
 puscle. Then a curious series of results follows. The 
 carbon, oxygen, and hydrogen undergo new rearrange- 
 ments, which amount finally to this the substance 
 known as starch, and consisting of carbon, hydrogen, 
 and oxygen, is built up in the form of granules in the 
 chlorophyll corpuscle, and the surplus oxygen escapes 
 into the sap and finds its way to the intercellular 
 passages, and thence through the stomata into the 
 atmosphere. 
 
 It will be obvious from the foregoing that the 
 granules of starch represent so much matter (especially 
 carbon) obtained from the atmosphere outside the plant, 
 and so much energy obtained from the sun; each 
 granule may therefore be regarded as a packet of stored 
 energy and matter won from the external universe. 
 
 The limits of this little book will not allow of my 
 going into details concerning the use which the plant
 
 88 THE OAK. 
 
 makes of this starch, and it must suffice to say that 
 the starch serves as the basis of all the constructive 
 materials used by the tree. Thus it is converted into 
 a soluble form, and combined with nitrogen, phosphorus, 
 sulphur, &c. (obtained from the earth-salts), to make new 
 protoplasmic materials, and it passes down from the 
 leaves to nourish all the living cells that require it, in 
 the embryonic tissue at the apex of the roots, and that 
 at the apex of the stem and branches, buds, &c., and some 
 of it passes to nourish the cambium cells, the developing 
 flowers, acorns, &c. in short, wherever new organic ma- 
 terial is needed it is supplied from these stores formed 
 by the green leaves waving in the sunshine. If we 
 reflect that the little embryo in the acorn starts its life 
 with only a minute store of starch and proteids in its 
 cotyledon, and that all the tons of organic material 
 (chiefly wood) found in an old oak-tree have been super- 
 added to this by the action of the leaves the small 
 proportion of salts taken up by the roots being quite 
 inconsiderable in comparison we obtain some idea of 
 the enormous gain of matter and energy from the outside 
 universe which goes on each summer.
 
 89 
 
 CHAPTER VII 
 
 THE TREE ITS ROOT-SYSTEM 
 
 WE may now suppose the young oak-plant to be rapidly 
 developing into a tree. Technically the seedling is said 
 to be a plant after the first year, and when it reaches 
 the height of a few feet the young tree is called a sap- 
 ling ; these ideas are by no means well defined, however, 
 and we may regard them as arbitrary terms of little or 
 no scientific value. 
 
 The principal changes which are noticeable as the 
 little tree grows larger are the gradual increase in the 
 length and thickness of the stem, and in the number 
 and spread of the branches put forth year after year. 
 Corresponding with these increments, each spring sees 
 a greater number of leaves than the one before, and it is 
 easy to prove that the roots also become more numerous 
 and complex each season. 
 
 The above simply expresses certain facts of observa- 
 tion, but it is more accurate to link them together as 
 follows. 
 
 In each successive season of growth the young oak 
 develops more leaves than it did before in other words,
 
 90 THE OAK 
 
 the total area of the leaf-surface exposed to the air and 
 sunlight is larger each successive summer than it was 
 the previous one. Several very important consequences 
 follow from this. In the first place, the larger area ot 
 leaf-surface evaporates more water than before, and as 
 this water is derived from the soil the absorbing surface 
 of the roots has to increase, or the larger supplies needed 
 could not be obtained. In the second place, these larger 
 and larger quantities of water require corresponding 
 increase in the sectional area of the pipes or water con- 
 duits i.e. the vessels of the wood through which they 
 have to pass in order to reach the leaves. This is ensured 
 by the increase in diameter of the stem and main root 
 and their chief branches, a larger number of vessels, &c., 
 being added each season. In the third place, as the 
 leaf-crown enlarges its weight increases, and the surface 
 it exposes to the swaying action of the wind is corre- 
 spondingly greater; consequently the necessity a,rises 
 for more strength and rigidity in the supporting stenii 
 and for a larger hold on the soil on the part of the root- 
 system, which has to withstand the lever action of the 
 swaying tree. These needs, again, are met by the thick- 
 ening of the woody parts of the shoot-axis and roots, and 
 by the greater spread and increased number of points of 
 contact in the soil of the latter. 
 
 Correlated with these phenomena we have the in- 
 creased leaf-surface playing the part of an enlarging 
 manufactory, which turns out increased supplies of con- 
 structive materials each summer ; for it is in the leaves
 
 THE TEEE ITS BOOT-SYSTEM 91 
 
 that the substances for making new roots and shoots, 
 new wood, and new leaves, &c., are constructed. It is in 
 the increased area of this leaf laboratory that the larger 
 supplies of salts, dissolved in the larger quantities of 
 water from the soil, are brought into relations with the 
 increased quantities of carbonaceous substance obtained 
 from the air in the chlorophyll corpuscles, and conse- 
 quently a larger yield of plant-forming materials is pos- 
 sible to meet the demands of the ever growing organs. 
 
 My present purpose is to describe how the thickening 
 process occurs in the older roots, for it is evident at a 
 glance that the strong woody roots of a large tree have 
 undergone many changes since they were the thin fili- 
 form rootlets we met with in the young plant (see fig. 7). 
 Not only have they increased in diameter, but they now 
 consist almost entirely of wood, protected by a relatively 
 thin, brown, corky covering, reminding one of certain 
 kinds of bark. 
 
 The first changes which take place when the young, 
 thin roots begin to thicken are first the piliferous layer 
 dies away and the outer cells of the cortex turn brown ; 
 then a cylindrical layer of cork is developed in the peri- 
 cycle, and as this cork is impervious to water it cuts 
 off the cortex from communication with the axis-cylinder, 
 and consequently the cortex gradually shrivels up and 
 is thrown off. 
 
 Meanwhile active divisions have been going on in 
 the cells immediately inside the phloem groups of the 
 axis-cylinder (see fig. 5), and especially by means of
 
 92 THE OAK 
 
 tangential walls. The result of this activity is the 
 development of a cambium layer, as it is called, immedi- 
 ately inside the five phloem groups of the axis-cylinder, 
 and this layer becomes continuous all round the axis- 
 cylinder, but is so arranged that it runs outside the 
 primary xylem groups and inside the primary phloem 
 groups (fig. 24, cam). This cambium layer is a hollow 
 cylindrical layer of thin- walled cells, full of protoplasm, 
 and somewhat longer than they are broad or deep, and 
 these cells have the peculiarity of dividing very rapidly, 
 especially by tangential walls, so that cell multiplication 
 goes on very rapidly, and the layer would soon become 
 very thick if no other changes occurred. As the new 
 cells are formed, however, those on the outer side of the 
 cylinder i.e. those nearest the phloem become for the 
 most part converted into sieve-tubes and cells of the 
 phloem ; while the much more numerous cells formed 
 on the inner side i.e. nearest the centre of the axis- 
 cylinder are chiefly converted into vessels and cells of 
 the xylem. This xylem and phloem developed by the 
 cambium are termed secondary xylem and secondary 
 phloem respectively, and it will be noticed that whereas 
 the secondary phloem is deposited radially on the inner 
 side of the primary phloem, the secondary xylem is 
 placed between the primary xylem groups, and not radially 
 outside them (fig. 24, se.x and se.pK). Moreover, the 
 youngest vessels are now nearest the cambium, whence 
 the order of development has become the converse of that 
 of the primary xylem ; there are also no spiral vessels
 
 THE THEE ITS BOOT-SYSTEM 93 
 
 formed now. In fact, the structure of the vascular 
 bundles of the root has now changed its character, and 
 from this point forwards the root increases in thickness 
 exactly as the stem does, whence I refer the reader to 
 the following chapter for further details. 
 
 The development of the layers of cork which now 
 surround the thickening axis-cylinder go on forming 
 year after year, as the cambium forms more xylem and 
 phloem and so thickens the root ; were this not the case 
 the layer of cork would soon be ruptured as the root 
 increases in diameter. Such rupture, in fact, does occur, 
 but the cork-forming tissue in the pericycle goes on 
 growing and acts as a cork-cambium, and repeatedly 
 develops more cork to make good the layers which are 
 being split and worn off in the soil. 
 
 From what has been said it will be understood that 
 a transverse section of an old root differs entirely in 
 structure from that of a young one, although all the 
 changes in the former can be correlated with the 
 primary structures of the latter. In the first place, 
 such a section shows no piliferous layer or cortex, both 
 having been sloughed off long ago; the protective 
 function of these layers is now assumed by the cork 
 jacket (often called periderm) developed by the cork- 
 cambium cylinder in the pericycle, and even this will 
 not show all the cork that the cambium has developed, 
 because many outer layers will have flaked away, just 
 as the present outer layers are doing. 
 
 Then, inside this periderm we shall find the phloem,
 
 04 
 
 THE OAK 
 
 forming an almost continuous ring (fig. 24, se.pli), and 
 consisting chiefly of the sieve-tubes and cells developed 
 from the cambium cylinder, the small primary phloem 
 
 pr.K 
 
 a. 24. Transverse sections (semi-diagrammatic') of roots 
 of oak, to be compared with fig. 7. The smaller figure, 
 above, shows the cambium ring, cam, now developed as 
 a continuous layer running inside the primary phloem, 
 pr.ph, and outside the primary xylem, pr.x ; and the 
 larger figure shows the results of its activity in the 
 formation of secondary phloem, se^k, inside the primary, 
 and secondary xylem, se.x, between the primary xylem 
 groups. In both cases, ep, piliferous layer; c, cortex; 
 P, pith ; sh, endodermis. Within the latter lies the 
 pericycle, in which the cork cambium, c.cam, is now 
 developed.
 
 THE TEEE ITS HOOT-SYSTEM 95 
 
 masses being almost undistinguishably pressed into 
 these (pr.pJi). 
 
 In the centre of the section will be a small speck, 
 around which the microscopic primary xylem groups 
 (pr.x) are arranged, but these, again, are merged between 
 the relatively huge masses of secondary xylem which 
 makes up by far the major part of the whole (se.x). The 
 thin cambium ring can be distinguished running between 
 the xylem and phloem as a fine line. Certain concentric 
 annular lines may be seen on the section, and each of 
 these marks the position in which the cambium rested 
 during the winter of some previous year. They are the 
 boundaries of concentric zones, termed annual rings, 
 and the thickness of wood which makes up any one 
 annual ring represents the activity of the cambium 
 during that particular year. 
 
 Traversing these annual rings at right angles are 
 fine medullary rays. About five broader ones may be 
 found corresponding to the radii on which the primary 
 xylem groups were formed, but these are not developed 
 by the cambium as the finer ones are. As I shall 
 have to speak of annual rings and secondary medullary 
 rays at greater length when describing the thickening 
 processes in the stem, and as they are formed in the 
 same way in both cases, we may defer their considera- 
 tion for the present. 
 
 Mention must now be made of a remarkable biolo- 
 gical phenomenon in connection with the roots of the 
 oak. This is the very common occurrence of young root-
 
 96 
 
 THE OAK 
 
 lets clothed by a fungus mycelium ; the mycelium is 
 found as a thin sheet of closely- woven hyphae continuous 
 over the whole of the tip, and sending processes in 
 between the cells of the dermatogen, but not into the 
 
 FIG. 25. Longitudinal section of the tip of one of the 
 roots marked ra in fig. 7, the outer layers of which are 
 infested with fungus hyphse, /(mycorhiza) ; r.o, root- 
 cap ; m, embryonic tissue from which all originates ; P, 
 pith ; sp, spiral vessels of the primary xylem ; c, cortex. 
 
 cavities of the cells nor deeper into the tissues. Loose 
 hyphaB also radiate into the soil around, and often simulate 
 the root-hairs of other plants, which, in fact, they are
 
 THE TREE ITS ROOT-SYSTEM 97 
 
 said to replace (fig. 25, /). These hyphas are extremely 
 fine tubes of a cellulose-like substance, filled with the 
 living protoplasm of the fungus, and possess the remark- 
 able property of being able to bore their way through 
 or between the cellulose walls of the roots. The fungus 
 attacks the plant about the second year, and it is not 
 difficult to find true root-hairs on the young root-system 
 when the apices are still free from the fungus mycelium. 
 The parts of the root attacked alter their form slightly ; 
 they grow more slowly in length, and assume a fleshy, 
 coral-like appearance (fig. 7, m). Such a fungus-clothed 
 root is called a mycorhiza, and the view is gaining ground 
 that the symbiosis between the fungus and the root is 
 of advantage to the oak. It has even been suggested 
 that the mycelium performs the functions of root-hairs 
 to the root, absorbing water and nutritive materials from 
 the soil and passing them on to the oak, in return for a 
 certain small proportion of organic substance which the 
 latter can well afford. At any rate, it may be that the 
 fungus hurries the decomposition of vegetable remains 
 in such a way that they become available to the roots 
 sooner than would otherwise be the case. The syste- 
 matic position of these remarkable fungi is not yet as- 
 certained, but there is some evidence for the view that 
 the mycelium is that of a truffle, though the question is 
 still an open one.
 
 THE OAK 
 
 CHAPTER VIII 
 
 THE TREE ITS SHOOT-SYSTEM 
 
 WHEN we cut into an old branch or stem of the oak 
 (fig. 26), it is at once obvious that considerable changes 
 have been produced since it was a twig or young shoot- 
 axis, such as exists in the young plant. Of these changes 
 the two following are the most conspicuous. The pith, 
 instead of being surrounded by a cylinder of small vascu- 
 lar cords, the diameter of which hardly exceeds its own, 
 as was the case in the one-year-old shoot-axis (fig. 9), is 
 now a mere speck in the middle of a huge mass of wood 
 many hundreds of times as broad as itself, and the cam- 
 bium cylinder which was developed, as we saw, in the pri- 
 mary vascular bundles, is now a large (though still thin) 
 layer encircling this huge wood mass. Again, in place of 
 a delicate epidermis surrounding a soft, green, cellular 
 cortex, as we had in the young stem, there is here a hard, 
 brown, rugged bark, splitting off in thick ridges on the 
 outside. 
 
 The two chief series of change may be inferred from 
 comparing the two conditions, and taking into conside- 
 ration all we have learnt so far. The pith is the same
 
 THE TKEE ITS SHOOT-SYSTEM 99 
 
 pith as before, and it is the cambium cylinder which 
 has moved outwards, as it were, putting in all that 
 solid-looking timber as it did so. The epidermis and 
 
 FIG. 26. Photograph of the transverse section of a log of 
 oak, about one-sixth natural size. The cortex and bark 
 are removed, and the out line is bounded by the cambium. 
 The pith appears as a mere dot in the centre ; the medul- 
 lary rays radiate from this, and the annual rings (about 
 forty in number) are arranged concentrically around 
 it. A large crack has formed along the plane of a medul- 
 lary ray as the section dried. (Muller.) 
 
 the cortex of our young stem have disappeared, how- 
 ever, their place being taken by cork and bark. Closer 
 inspection will show that a series of layers of phloem 
 
 H 2
 
 100 THE OAK 
 
 have also been formed between these outer protective 
 layers and the cambium. 
 
 We have now to obtain some ideas as to these curious 
 processes of increase in thickness of the stems and 
 branches. 
 
 The first thing to ensure this is to understand the 
 constitution and behaviour of the cambium cylinder, for 
 it is principally this tissue which brings about the 
 changes we have to study. 
 
 We saw in Chapter IV. that the xylem of each 
 primary vascular bundle is separated from the phloem of 
 the same bundle by a thin strand of cambium (figs. 9 and 
 1 2) ; we also saw that the bundles are arranged in a closed 
 ring round the pith, and are in their turn surrounded by 
 the primary cortex, each being separated laterally from 
 its neighbours by a primary medullary ray. The next 
 point to bear in mind is that these medullary rays (like 
 the pith and cortex) are merely parts of the general cell- 
 tissue, or fundamental tissue, through which the vascular 
 bundles run upwards and downwards with a tangentially 
 sinuous course from the leaves. The primary medullary 
 rays, therefore, are merely spokes, as it were, joining the 
 pith and cortex ; and if we could remove the whole of 
 the vascular bundles and epidermis from the young stem 
 we should have left a solid cylinder of cells (pith) in the 
 centre, a hollow cylinder (cortex) concentric to this, and 
 a space between the two bridged over at numerous places 
 by cellular spokes (medullary rays) radiating from the 
 pith to the cortex. Each spoke is very thin from side
 
 THE TEEE ITS SHOOT-SYSTEM 101 
 
 to side, and therefore stands out like a knife, with an 
 upper and a lower edge (fig. 27). 
 
 Now imagine the primary vascular bundles replaced. 
 
 FIG. 27. Tangential longitudinal section of oak wood, 
 magnified fifty diameters, and showing the transverse sec- 
 tions of the medullary rays, cut as they project towards 
 the observer. (Miiller.) 
 
 The first change is that the cambium in the vascular 
 bundles becomes continuous across through the medul-
 
 102 THE OAK 
 
 lary rays, and so forms a complete thin cylinder, con- 
 centric to the pith from which it is separated by the 
 breadth of the xylem and the cortex, from which it 
 is separated by the breadth of the phloem. 
 
 The cells of this cambium cylinder go on dividing 
 continuously during the whole summer, until the 
 cylinder is, say, ten times as thick as it was before. 
 Now suppose it to rest during the winter and go on 
 again next season, and so on during each successive 
 period of growth. Obviously this would realise one 
 fact in the process we are considering namely, that the 
 stem would grow in thickness year by year, its diameter 
 being increased by twice the thickness of the added 
 cylinder. 
 
 But to make the above supposition accord with the 
 facts, we must further picture to ourselves that when the 
 thickening cylinder has attained a certain thickness, a 
 large proportion of those of its cells which lie on the 
 inside i.e. nearest the pith, and therefore abutting on 
 the xylem lose their cambial nature and become con- 
 verted into elements of the wood ; while a smaller propor- 
 tion of those on the outer side (beneath the phloem) 
 become new phloem elements. In this way it will be 
 seen that the thin cylinder of active cambium cells 
 travels outwards ; ever receding radially further from the 
 pith, and leaving xylem between itself and the primary 
 vascular bundles next the pith, and ever driving outwards 
 the primary phloem and cortex, adding new phloem 
 elements (but in far less proportion) to the inside of the
 
 THE TKEE ITS SHOOT-SYSTEM 103 
 
 phloem. Each winter it pauses in this process, and each 
 spring it renews its activity. Further peculiarities will 
 be noticed as we proceed. 
 
 Now let us see what the cambium cells are, and 
 how they change into new elements of the xylem and 
 phloem, &c., respectively. 
 
 Each cell of the cambium is a thin-walled prism, 
 many times longer than broad or thick, and with its 
 ends brought to an edge like that of a thick chisel, and 
 so arranged that these edges run radially and fit in 
 between those of cambium cells at higher and lower 
 levels. As we have seen, the prism is oblong in trans- 
 verse section. Each of these cells contains protoplasm 
 and a nucleus, surrounding a sap-cavity, and they are 
 nourished like other cells by the substances brought 
 down from the leaves and up from the roots, taking 
 what they need from the sap. 
 
 When a given cambium cell has taken into its 
 protoplasm sufficient food materials, and has accom- 
 plished other life-processes under the action of oxygen, 
 which it absorbs dissolved in the water of the sap, it 
 grows larger, especially in the radial direction, and then 
 it divides into two cells ; then each of these may repeat 
 these processes, and so on. At last the older ones can 
 no longer grow and divide, but become changed into 
 elements of the xylem or phloem, according to their 
 position. All the xylem thus produced by the cambium 
 is called secondary xylem, and the phloem secondary 
 phloem, and so on, to distinguish them from the pri- 
 mary structures found in the early stage.
 
 104 THE OAK 
 
 I now proceed to some further details, which could 
 only be rendered intelligible in the light of the pre- 
 ceding preliminary remarks. 
 
 After the cambium ring is once formed the daughter- 
 cells cut off on the inside of the cambium always 
 become transformed into one or more of the following 
 elements : 
 
 (1) Some cambium cells which lie on the radial con- 
 tinuation of a medullary ray undergo a few horizontal 
 divisions across the long axis, and then simply pass 
 over as constituents of a medullary ray ; as the cam- 
 bium ring moves outwards, in consequence of the re- 
 peated formation of thickening rings, the periphery of 
 the cylinder of course increases, and this allows of more 
 space tangentially. One consequence of this is the 
 occasional and gradual widening of the medullary ray in 
 process of lengthening : this takes place to a small 
 extent only. Another consequence of the increased 
 space is the occasional interpolation of new medullary 
 rays. Radial rows of cambial cells at points which lie 
 between the planes of two gradually diverging medul- 
 lary rays suddenly commence to form new medullary 
 rays. Hence, as the wood mass increases in radial 
 thickness, more and more of these interpolated medul- 
 lary rays appear, cutting up the wood proper into 
 partial sections. In succeeding years the cambium 
 keeps adding to the length of these rays, as it does to 
 that of the older rays, and again forms new ones between 
 as space increases. In the same ring about thirteen
 
 sp. 
 
 p.v. 
 
 FIG. 28. The various chief elements of the wood of the 
 oak, isolated by maceration, and highly magnified. /, a 
 fibre, distinguished by its thick walls, simple slit-like 
 pits, and no contents ; n\j>, part of a row of wood-paren- 
 chyma cells, with simple pits, and containing starch in 
 winter ; tr, a tracheid, distinguished from the fibre 
 especially by its bordered pits ; p.v, part of a rather large 
 pitted vessel, made up of communicating segments, each 
 of which corresponds to a tracheid, and has bordered pits 
 on its walls; sp, part of a spiral vessel.
 
 106 THE OAK 
 
 rays to the millimetre may be counted on the transverse 
 section of the wood. 
 
 (2) The cambium cells situated between the rays 
 except when they suddenly commence to form a new 
 ray, as just described pass over into one or more of 
 the following elements of the wood proper viz. wood 
 parenchyma, libriform fibres, tracheids, segments of 
 the vessels (see fig. 28). 
 
 When a cambium cell passes over into wood paren- 
 chyma it first undergoes a few horizontal divisions 
 transverse to its long axis, and then we have a vertical 
 row of five or six parenchymatous cells, the walls of 
 which do not thicken much, but obtain small simple 
 pits, and retain part of their living contents proto- 
 plasm, nucleus, starch-forming corpuscles, &c. and 
 indeed present much resemblance to the cells of the 
 medullary rays themselves. 
 
 When the cambial cell becomes transformed into a 
 libriform fibre it does this simply by thickening its 
 walls at the expense of the living contents, &c., which 
 soon disappear. The cell undergoes no horizontal divi- 
 sions, and probably elongates very slightly. The 
 thickened walls become pitted with minute simple pits, 
 and are stratified and eventually lignified. 
 
 In the case of the transformation of a cambial 
 cell into a tracheid everything is essentially as 
 described in the last paragraph, except that the dia- 
 meter increases and the thickening walls become 
 marked with bordered pits, quite similar to those of the
 
 THE TEEE ITS SHOOT-SYSTEM 107 
 
 pine, except that they are more numerous, are not 
 confined to the radial walls, and they are not quite 
 circular, but have an oval shape with a slit-like aperture 
 to the border, the long axis of the slit being nearly 
 transverse to the long axis of the tracheid. 
 
 In the conversion of cambium cells into vessels the 
 chief point to note is that the vessel is essentially a 
 vertical row of superposed tracheids each of which 
 has been developed from a cambium cell as just described 
 the oblique separating walls of which become almost 
 entirely obliterated. The markings, thickening, and 
 want of contents are as in the case of tracheids, the 
 chief difference being the more pronounced growth in 
 diameter of the vessel segments, especially those formed 
 in the spring wood. 
 
 It will readily be understood that the growth in 
 diameter of these vessel elements exerts a disturbing 
 effect on the radial arrangement of the other elements 
 of the wood, and the displacements and compression of 
 the latter are considerable and various, so that at length 
 very little trace of the original order is observable. It 
 not unfrequently happens, however, that many succes- 
 sive rows of the fibres or tracheids are formed in the 
 outer parts of the annual ring, and in such cases the 
 original radial series can be detected. 
 
 There are several other points also to be noted in 
 the development of secondary wood. In the first place, 
 the various elements do not maintain an exact vertical 
 position, but may lean over both in the radial and in the
 
 108 THE OAK 
 
 tangential directions. These slight displacements from 
 the vertical are chiefly due to the fact that the elements 
 fibres, tracheids, and vertical groups of wood paren- 
 chyma have not finished their growth in length when 
 they pass over from the cambial condition ; consequently 
 the pointed ends of the elongating fibres, &c., push 
 themselves between the ends of others which lie above 
 and below them, and a slight tilting from the vertical 
 results. This may be sufficient to produce a twisting of 
 the stems and branches which is visible even to the 
 unaided eye. 
 
 Another important point is that the length of the 
 elements, as well as their diameters, vary at different 
 periods in the life of the tree. 
 
 First as to the diameter. The fibres and tracheids 
 developed in the autumn have a relatively smaller 
 radial diameter than those formed earlier, and this, com- 
 bined with the fact that thoso elements which develop 
 in the spring have the relatively largest diameters, 
 alone would suffice to mark the boundary between 
 any two annual rings. But the same holds good for 
 the vessels ; those formed in the spring wood are very 
 large compared with those formed later the latter are 
 also more sparely developed whence the contrast at the 
 boundary between the annual rings is intensified. With 
 the diminution in relative diameter of the tracheids and 
 fibres a corresponding increase in the thickness of their 
 walls is connected a phenomenon which again intensi- 
 fies the contrast between adjacent annual rings.
 
 THE TREE ITS SHOOT-SYSTEM 109 
 
 But, in addition to these differences in diameter 
 within one and the same annual ring, a gradual incre- 
 ment in the average size of certain of the elements (both 
 in length and diameter) occurs as the tree becomes 
 older in other words, the average width and length of 
 the elements increases year by year up to a certain age ; 
 after reaching a definite size they enlarge no more. 
 These changes differ according to the part of the tree 
 concerned. In the stem of the oak the chief changes 
 in this connection are : 
 
 The fibres increase in length as follows, according to 
 Sanio's measurements: While they average 0*42 mm. in 
 length in the first annual ring, they increase to 0'60 mm. 
 in the second, 0'74 mm. in the fourth, and go up to 
 1'22 mm. after a great age (130 years ?). The tracheids 
 in the same annual rings were found to average 0'39, 
 0'43, 0'53, and 0-72 mm. respectively; and the individual 
 members or segments of the larger vessels averaged 
 0'25 mm. in the second annual ring, 0'26 mm. in the 
 fourth, and - 36 mm. in the three outer rings. The 
 mean radial diameter of these vessels also increased : in 
 the third year it was 0'08 mm., and it rose year by year 
 until in the sixth year the definitive width of 0'31 to 
 0-33 mm. was attained. After this the width of these 
 vessels is practically constant. These increments in 
 size appear to take place after the element has passed 
 out of the strictly cambial condition. 
 
 The passage of the older wood in the centre of the 
 stem into the condition known as ' heart-wood ' (dura-
 
 110 THE OAK 
 
 men) as opposed to ' sap-wood ' (alburnum) is not 
 attended with any profound anatomical changes ; the 
 chief alterations are of the nature of infiltration by 
 foreign chemical substances, and alteration in the phy- 
 sical properties of the cell-walls and in the contents. 
 These changes are somewhat sudden, and the fact that 
 starch ceases to be deposited in this altered wood helps 
 to indicate that the change is one of degradation the 
 cells of the softer tissues have ceased to be ' alive,' and 
 the ' heart ' commences to undergo degradation. At 
 the same time, although we must regard the ' heart ' as 
 dead, it is very resistant, perhaps owing to the preser- 
 vative action of infiltrated bodies. 
 
 A remarkable phenomenon which may be noticed 
 here is the filling up of the older large vessels with 
 tyloses. These are thin-walled, bladder-like vesicles 
 projecting into the cavity of the vessel from the bordered 
 pits, and are, in fact, due to the protrusion into the cavity 
 of the thin-walled parenchyma cells, which drive the pit 
 membrane in and then swell up. At the planes of 
 contact between various tyloses from opposite points on 
 the wall of the vessel the tyloses are flattened, and the 
 appearance is very like that of a parenchymatous tissue 
 (fig. 29, d). When young the tyloses are found to 
 contain a nucleus, protoplasm, and cell-sap, and they are 
 known to form division membranes and divide like cells 
 of the pith or cortex ; later on they lose their contents 
 and form a sort of packing in the by this time function- 
 less vessel.
 
 THE TREE ITS SHOOT-SYSTEM 111 
 
 During the whole time of the activity of the 
 cambium ring and the formation of wood on its interior, 
 it must not be forgotten that the outer rows of cambial 
 cells are passing over into the tissue known as bast or 
 secondary phloem (also called secondary cortex) ; the 
 chief differences in the process being (1) that much 
 
 FIG. 29. A small piece of one annual ring of old oak wood 
 (magnified twenty diameters), a, boundary of the autumn 
 wood of the preceding (older) ring ; b, that between the 
 zone shown and the next youngest ring. In the annual 
 ring shown the spring wood begins with large vessels, 
 o and d, some with tyloses, d, in them, and passes 
 Gradually into autumn wood, with smaller vessels, e, e, and 
 more tracheids and fibres, g. Only small medullary rays, 
 i, are shown. (Hartig.) 
 
 less phloem than xylem is formed; (2) that the 
 elements do not become lignified ; and (3) that the 
 disturbances in the arrangement of the elements are 
 more profound from the continued pressure exerted 
 upon them between the resistant wood and the elastic 
 periderm and bark, on the one hand, and the increased 
 extension tangentially which it undergoes as the
 
 112 THE OAK 
 
 thickening mass of wood drives it outwards, on the 
 other. The other differences chiefly concern the in- 
 dividual elements now to be described. 
 
 All that was said of the medullary rays in the wood 
 applies also to those in the bast ; the cambium in keep- 
 ing open or originating new medullary rays does so on 
 both sides, and therefore the medullary rays are to be 
 traced radially through the cambium from wood to 
 cortex. The rays in the bast are termed ' bast rays ; ' 
 the broader ones contain isolated groups of sclerotic 
 cells and cells containing crystals. 
 
 The changes which the radial rows of cells on the 
 exterior of the cambium zone undergo to form the 
 elements of the secondary phloem are as follows : 
 
 (1) Bast parenchyma (fig. 17, ~bp) is developed, like 
 the wood parenchyma, from cambium cells which undergo 
 a few transverse divisions and then pass over as longitu- 
 dinal groups of cells, which retain their living contents, 
 &c. From these longitudinal groups, accompanying the 
 sieve-tubes as parallel series, they are called companion 
 cells (cambiform cells). 
 
 (2) Sieve-tubes (fig. 18, bp), which maybe regarded 
 as homologous with the vessels of the wood, and, like 
 those, are constituted of series of segments. Each seg- 
 ment corresponds to a cambium cell, and is obliquely 
 tapering at the end where it fits on to another segment. 
 These dividing septa are not completely broken through, 
 as in the case of the wood-vessels, however, but are 
 pierced by a grating-like series of holes (the sievej
 
 THE TKEE ITS SHOOT-SYSTEM 113 
 
 through which the protoplasmic and other contents of 
 the contiguous segments pass uninterruptedly. Similar 
 sieve-plates occur on the lateral walls of the segments 
 also. The walls are not thickened and not lignified, and 
 thus the morphological similarities between the sieve- 
 tubes of the bast and the vessels of the wood (which only 
 contain air and water, have their septa absorbed, and 
 their walls lignified and covered with bordered and simple 
 pits) depends almost entirely on the similar develop- 
 ment. The sieve-porea are very fine, and easily over- 
 looked. 
 
 (3) The bast fibres (figs. 17andl8,6),whicharehomo- 
 logous with the libriform fibres of the wood, and are deve- 
 loped in the same way from single cells of the cambium. 
 They are short, blunt, very thick-walled fibres, grouped 
 in strands which appear on the transverse section of the 
 bast as tangential bands 2-4 deep, alternating (in the 
 radial direction) with broader bands of sieve-tubes and 
 parenchyma. These bands of fibres (hard bast) are 
 accompanied at their outer and inner boundaries by 
 parenchyma-like cells arranged in vertical rows, each 
 of which contains a large simple crystal of calcium 
 oxalate embedded in yellowish substance, and the walls 
 of which are slightly sclerotic. Similar vertical series 
 of cells are found in the soft bast, but they contain 
 compound (clustered) crystals of the same salt (figs. 17 
 and 18, e). 
 
 The soft bast also contains scattered roundish 
 groups of short sclerenchyma cells, the thickened walls 
 
 I
 
 114 *n OAK 
 
 of which are traversed by very numerous pit-canals ; 
 cells containing crystals also accompany these groups. 
 
 In consequence of the above arrangements the 
 secondary cortex presents a more or less stratified 
 appearance on the transverse section, the strata con- 
 sisting chiefly of alternate tangential layers of hard 
 bast and soft bast (fig. 1 7) ; the elements of the latter also 
 showing a decided tendency to be arranged in layers. 
 
 After the first year the young stem or branches 
 covered with thin periderm are seen to be dotted with 
 lenticels or cortical pores. Structures similar in every 
 respect and subserving the same function- viz. the 
 exchange of gases with the environment are formed on 
 the roots as soon as the periderm is developed. 
 
 The lenticel is a local interruption of the periderm, 
 where the cells are loosened so as to allow air to pass 
 between the loosened cells into the intercellular spaces 
 between the cortical cells. Each lenticel may be de- 
 scribed as a biconvex projecting swelling of the periderm, 
 the swelling being caused by the increased radial 
 diameter of the loosened cells. This is the condition 
 during the spring and summer, but in the winter the 
 cork-cambium is continuous across beneath the lenticel, 
 and forms periderm in an uninterrupted sheet, to be 
 ruptured again at the lenticel during the formation and 
 swelling of the looser cells (complementary or packing 
 cells) in the following spring. These loose packing- 
 cells are at first quite similar to young cork-cells, and 
 are developed as such, but they loosen and round off,
 
 THE THEE ITS SHOOT-SYSTEM 115 
 
 and their cell-walls do not become completely suberised 
 for a long time, but are capable of swelling : in fact, the 
 rounding off depends on the absorption of water by the 
 cellulose walls and contents. The outer parts of the 
 older lenticel openings are thrown off with the bark- 
 scales, but the inner parts remain, and can be found 
 between the scales in older branches, in the fissures. 
 
 The first points of origin of lenticels are usually 
 beneath the stomata, and the lenticels may be regarded 
 as devices for prolonging the passages of the stomata 
 through the thickening periderm year by year. The 
 cortical cells beneath the stoma become meristematic in 
 effect they continue the phellogen below the stoma, only 
 they divide less regularly and in all directions. The 
 daughter-cells thrown off externally swell up and pro- 
 trude, driving the stomatic cells outwards and apart, and 
 emerging between the ruptured guard-cells as the first 
 packing- tissue. The phellogen or cambium of the 
 lenticel forms phelloderm on its interior in continuation 
 of that formed by the rest of the cork-cambium. The 
 protruding packing-cells dry up eventually, and form the 
 powdery substance seen between the gaping lips of 
 older lenticels. In the autumn the cells formed by the 
 meristem below the packing-cells do not separate, but 
 are suberised and closely and radially arranged like the 
 rest of the cork : in fact, they continue the cork layer 
 as a closing layer beneath the lenticel, thus protecting 
 the tissues beneath through the winter. In the follow- 
 ing spring new layers of loose, swelling packing-cells 
 
 i 2
 
 116 THE OAK 
 
 are developed again, and these absorb water and bulge, 
 bursting the closing layer and reopening the lenticel 
 for the season. As the branch ages and its surface in- 
 creases new lenticels are developed between the earlier 
 ones, and, of course, with no reference to stomata. 
 
 The exterior of the very young stem or branch is 
 smooth or slightly pubescent, the green colour gradually 
 passing into a silver-grey as the periderm develops, and 
 in a few years (when the shoot is from five to twenty 
 years old, or thereabouts) the gradually thickening bark 
 is shining and turning browner, necked with lenticels 
 and lichens. Later still the bark is rugged, brown, and 
 fissured, and usually covered with small lichens and 
 fungi. Bark begins to exfoliate at about the thirtieth 
 year. 
 
 The epidermis cracks and peels off when the twigs 
 are a year old, and shreds of the dead membrane may 
 be detected on the outside of the young cork, which 
 begins to form very early during the first year. It is, 
 in fact, owing to the impervious nature of this cork that 
 the epidermis dies, and to the stretching of the cortex 
 as the stem grows in thickness that the dead membrane 
 cracks and peels off (see figs. 17 and 18). 
 
 The first indication of the development of the cork 
 is the conversion of the sub-epidermal layer of cortex- 
 cells into a meristem i.e. the cells become capable of 
 active growth and division. 
 
 Each cell of the layer referred to may be termed an 
 initial cell of the cork-cambium (or phellogen), and the
 
 THE TEEE ITS SHOOT-SYSTEM 117 
 
 layer maybe called the initial layer. This layer behaves 
 essentially like the cambium of a fibro-vascular bundle, 
 except that its daughter-cells become cork and phello- 
 derm instead of phloem and xylem. 
 
 The first event to notice is that each of the initial 
 cells grows radially, and divides by a tangential wall 
 into an inner cell nearest the axis of the branch and an 
 outer cell nearer the epidermis ; the outer cell becomes 
 forthwith a cork-cell i.e. its contents die and mostly 
 disappear, and the cellulose cell-wall becomes suberised 
 the inner cell remains capable of repeating the pro- 
 cess. But this is not the only case. After the division, 
 as before, of the initial cell, it may happen that the inner 
 cell becomes transformed into a collenchymatous cortical 
 cell containing chlorophyll, and it is the outer of the 
 daughter-cells which retains the meristem character 
 and acts again as a phellogen cell, cutting off daughter- 
 cells sometimes on one side and at others on the other. 
 Thus, in the oak, the phellogen gives rise to permanent 
 tissue on both sides of the initial layer : those cells which 
 lie on the inside become phelloderm (cortical cells), those 
 on the outside become transformed into phellem (cork). 
 The three tissues, phelloderm, phellogen, and phellem, 
 are called the periderm. 
 
 It is obvious that the cork-cambium, by thus adding 
 to the cortical parenchyma, is gradually driven radially 
 outwards from the centre of the stem. This means that 
 it obtains room to extend tangentially, and it does this 
 by its cells occasionally dividing by walls perpendicular
 
 118 THE OAK 
 
 to the far more numerous tangential walls. It is also 
 easy to see that the cork-cells must be arranged in 
 radial rows, and this arrangement is very conspicuous 
 (fig. 18). The earlier cork-cells have very thin walls, 
 later ones have the walls thicker. 
 
 After the development of the first layer of cork the 
 stretched epidermis dies, and forms simply a dead mem- 
 brane outside the thin cork. In succeeding years 
 layers of phellogen are formed annually beneath the 
 older ones, and thus the cork layers increase. Moreover, 
 since the successive layers cut out thin, scale-like areas 
 of cortex, trapping them, as it were, between the present 
 and the preceding cork, the thickening corky covering 
 is stratified consists of successive and obliquely over- 
 laying thin sheets of dead cortex and cork proper (fig. 
 30). Again, since the increase in thickness of the stem 
 or branch is continually driving these corky and dead 
 structures outwards, they at length crack, and form the 
 fissured bark found on older parts. Bark is thus seen 
 to be something more than cork, or even periderm, and 
 it is defined to be all the dead tissues cut out by the 
 phellogen. 
 
 It is also to be noticed that the successive phellogen 
 layers of different years are not concentric, but the new 
 ones cut the old ones at acute angles (fig. 30), thus cut- 
 ting out scale-like areas of cortex ; the consequence of 
 this is the formation of the very irregular scales of bark 
 thrown off from the older stems and branches of the oak. 
 It follows from what has been said that in older trees the
 
 THE TREE ITS SHOOT-SYSTEM 
 
 119
 
 120 THE OAK 
 
 phellogen layers may be formed so far down in the cor- 
 tex that they cut out tissues of the secondary cortex 
 i.e. phloem and bast fibres. It is, of course, this gradual 
 exfoliation of the cut-out areas of bark that explains 
 the relative thinness of the bark in very old stems and 
 branches ; the whole of the primary cortex, and most 
 of that formed from the cambium, have been thrown off 
 as bark long before.
 
 121 
 
 CHAPTER IX 
 THE TREE (continued). INFLORESCENCE AND FLOWERS 
 
 FRUIT AND SEED 
 
 THE oak flowers in May in this country, the young 
 inflorescences developing as the leaves unfold. The 
 flowers are unisexual, both male and female appearing 
 on the same branches i.e. the tree is monoecious and 
 even on the same twigs of the current year. The rule 
 is that the apical bud of a last year's twig produces 
 a few male inflorescences from between the axils of the 
 upper scales, and then grows out into a green twig 
 bearing about six to ten normal leaves, the female inflo- 
 rescences arising from the axils of two or three of the 
 upper leaves (figs. 31 and 32). Lateral buds below the 
 terminal bud of the last year's twig usually produce male 
 inflorescences only a phenomenon in accordance with 
 their feeble development generally. Thus the male in- 
 florescences are produced first a common occurrence in 
 forest trees. 
 
 Since the inflorescences arise from the axils of 
 leaves, their arrangement accords with the phyllotaxis
 
 122 THE OAK 
 
 of the tree i.e. - so far as it goes. It should bo 
 borne in mind that the bud-scales are stipules. 
 
 The male inflorescences hang down from between 
 the bud-scales as simple catkin-like spikes, each bear- 
 ing about a dozen flowers. Each male flower springs 
 
 FIG. 31. A sprig of oak in May, with the pendent male 
 catkins below, and the minute spikes of female flowers 
 just showing above. (Th. Hartig.) 
 
 from the axil of a tiny scale-like bract, and consists of 
 a shallow perianth, unequally divided into about five to 
 seven small linear-lanceolate lobes, enclosing about five 
 to twelve stamens ; there is no trace of an ovary. The 
 number of lobes of the perianth varies, as also docs the
 
 INFLOEESCENCE AND FLOWERS FRUIT AND SEED 123 
 
 number of stamens ; the former are covered with short 
 hairs. 
 
 Each of the stamens consists of a slender thread 
 (filament) bearing on its top a four-chambered swollen 
 anther. This contains a yellow dust, the pollen, com- 
 posed of round grains (pollen grains), each with three 
 thinner spots in its otherwise thick wall. Each of these 
 pollen grains consists of a membrane enclosing nucleated 
 protoplasm and food materials. When ripe the wind 
 blows the pollen as it scatters from the dangling stamens, 
 and some of the grains reach the stigmas of the female 
 flowers ; here they germinate, each pollen grain sending 
 a delicate pollen tube down the style into the ovary of 
 the flower. This process of application of the pollen 
 grains to the stigma is termed pollination, and depends 
 on the wind. 
 
 The female inflorescences are also spikes (fig. 32, A), 
 but they bear only one to five flowers, and stand off front 
 the axils of the foliage leaves. In the commonest English 
 variety (Q. pedunculata) the spikes are rather long, ob- 
 liquely erect, and the flowers are scattered on the upper 
 end of the rachis of the spike ; in other varieties the 
 flowers are more clustered in the axils of the leaves. 
 Here, as in one or two other details, minute differences 
 are apparent in different individuals; similar trifling 
 differences are met with in the structure of the male 
 flowers. 
 
 Each female flower springs (like the male) from the 
 axil of a small bract : in other respects it is very unlike
 
 124 
 
 THE OAK 
 
 the male flower. In the first place, the ovary is inferior, 
 being sunk in and fused into a six-partite perigone, the 
 teeth of which project some distance up and surround a 
 trifid stigma (figs. 33 and 34, c). One of the lobes of the 
 perigone will be found opposite to the bract ; the three 
 
 FIG. 32. A. Flowering twig and inflorescences, male ( <?) 
 and female ( ? ), semi-diagrammatic. B. Diagram of plan 
 of a similar but lateral twig. F. Leaf from axil of which 
 the twig arises : x, parent stem ; a and , bracts. The 
 numbers 1-11 denote pairs of stipules acting as bud- 
 scales, some with male inflorescences ( $ ) springing trom 
 between them ; the continued numbers 12-21 also denote 
 pairs of stipules, but these have their accompanying 
 leaves, with or without female inflorescences ( $ ) in the 
 axils. (Eichler.) 
 
 lobes of the stigma are superposed on three alternate 
 (outer) lobes of the perigone. 
 
 There is yet a further covering to the female flower. 
 The somewhat irregular margins of a minute cup-like 
 investment are to be seen arising from beneath and 
 around the perigone : this is the scaly cupula, the future
 
 INFLORESCENCE AND FLOWERS FRUIT AND SEED 125 
 
 ' cup ' in which the ' acorn ' is inserted (fig. 34, m). If 
 the young female flower is carefully bisected longitudi- 
 nally this cupule will be seen to consist of a ring of 
 tissue, arising from beneath the ovary, and with its 
 margin notched into scales. As the ovule enlarges 
 the minute scales become more numerous, new ones 
 arising at the inner margin of the up-growing cupule. 
 
 A transverse section 
 across the female flower 
 at a slightly later period 
 shows that the inferior 
 ovary is divided into 
 three chambers (loculi), 
 each corresponding to 
 one of the lobes of the 
 stigma, and each con- 
 taining two ovules (fig. 
 34). These ovules are 
 inserted at the upper 
 part of the inner angle 
 of the chamber, and 
 thus hang down in 
 
 pairs. A curious point arises here. It seems that at 
 the period when the female flower has just opened, 
 but has not yet received any pollen on its stigma, 
 neither the ovules nor the chambers are as yet formed, 
 and the segments of the perigone spring from the lower 
 portion of the flower, and this condition is not altered 
 until pollination occurs ; then the tissue below the 
 
 FlG. S3. A group of female flowers 
 (slightly magnified). Each has a 
 spreading stigma above and the 
 commencing cupule below, and 
 arises from the axil of a pointed 
 bract. (Th. Hartig.)
 
 126 
 
 THE OAK 
 
 stigma becomes the three-chambered ovary sunk in the 
 perigone. 
 
 The pollination takes place in May-June, and ferti- 
 lisation soon afterwards ; in July the young acorns can 
 
 FIG. 34. Female flower in section. To the left three 
 transverse sections through the young ovary ; the ]ower 
 one showing the three placentas, each with two ovules. 
 To the right, three longitudinal median sections through 
 the whole flower at successive periods, a, stigma ; b, 
 carpel ; c, perianth ; d, cavity of ovary with ovules ; 
 m, the cupule. (Th. Hartlg.) 
 
 be made out peeping from the cupules in which tbey had 
 hitherto been enclosed. The acorn reaches its full size 
 towards the end of September, and ripens and falls in 
 October. When ripe the acorn is, as we have seen, an
 
 INFLORESCENCE AND FLOWERS FRUIT AND SEED 127 
 
 ovoid, smooth, olive-brown nut, with the broad end 
 inserted into the cupule, and the narrower, somewhat 
 tapering end projecting free. 
 
 It will be interesting, in the light of the foregoing 
 remarks, to examine one of the stronger lateral buds 
 of the oak towards the end of April, before it unfolds. 
 A transverse section of such a bud shows the following 
 structures : In the centre is the axis of the young shoot, 
 represented by the small central dot in the diagram (fig. 
 32, B). Surrounding this are about eight to ten green 
 leaves in section, and folded on their midribs in such a 
 way that the two halves of the upper surface are face to 
 face and somewhat crumpled ; some of these are turned 
 so that their edges are directed one way, others with 
 them directed the other. 
 
 Each of these leaves has a pair of small stipules, 
 also cut across, and rather difficult to identify (fig. 32, 
 12-20). Some of the foliage leaves bear female inflo- 
 rescences in their axils, as indicated by the sign 5 in 
 the figure. Following on these stipulate leaves are a 
 number of pairs of larger stipules, devoid of foliage 
 leaves and constituting the bud-scales (fig. 32, 1-11). 
 Some of these bear male inflorescences ( $ ) between them 
 i.e. in the position corresponding to the axil of the leaf. 
 
 It will be understood that in this diagram the parts 
 are all represented on a ground-plan, but that as the 
 bud opens the inner leaves and stipules are on higher 
 levels than the outer scales. In fact, proceeding in the 
 order of the numerals, we pass in an ascending spiral
 
 128 THE OAK 
 
 from the outermost lower pair (1) of scales (stipules) to 
 the innermost upper pair (21) with their leaf. 
 
 If we suppose the female inflorescences removed, the 
 above diagram will serve to represent the lateral buds 
 which develop male inflorescences only, or if we sup- 
 pose the three bracts F, a, and /3 away, it would serve 
 for a terminal bud. 
 
 Each single female flower stands in the axil of a 
 minute scale on the floral axis, as said, and its general 
 structure has been described. When the pollen grains 
 have been dusted on to the trifid stigma, about the end 
 of May or beginning of June, each grain germinates 
 and sends a minute tube down the style, and this pollen- 
 tube soon reaches the cavity of the ovary, and its end 
 becomes applied to one of the ovules. While the 
 pollen-tube is descending the style, the ovules have 
 arisen as minute cellular outgrowths from the angles of 
 the three chambers of the ovary (fig. 34, d). There are 
 two in each chamber. Each ovule is at first a mere 
 solid lump of cells (nucellus), which curves and becomes 
 enveloped in two thin investing layers, called integu- 
 ments, as shown in the figures A-D (fig. 35). Inside 
 the solid nucellus, n, of the ovule there soon arises a 
 small cavity filled with nucleated protoplasm, and termed 
 the embryo-sac, e, because the embryo is to be deve- 
 loped in it. 
 
 This embryo-sac contains, among other structures, 
 a minute, nucleated, naked mass of protoplasm, called 
 the oosphere, or egg-cell. The pollen-tube has carried
 
 INFLORESCENCE AND FLOWERS FRUIT AND SEED 129 
 
 down in its apex also a nucleated mass of protoplasm, 
 and it passes this over into the egg-cell in the embryo- 
 
 FiG. 35. Various stages in the development of the ovule. 
 n, nucellus ; i, i', integuments ; p, point of attachment 
 to placenta ; e, embryo-sac ; r, vascular cord supplying 
 ovule ; m, micropyle ; x, young embryo. (Partly after 
 Th. Hartig.) 
 
 sac ; the union of the nucleus from the pollen-tube 
 with the nucleus of the egg-cell constitutes the act of 
 
 K
 
 130 THE OAK 
 
 fertilisation, and the fertilised egg-cell is now termed 
 the oospore, and at once begins to grow into the 
 embryo. 
 
 It would be very interesting to describe at length 
 all the remarkable details of these processes, and their 
 morphological meaning in the light of modern biology, but 
 the limits and purpose of this little book will not admit 
 of that, and I must content myself with this brief resume. 
 
 During this process of fertilisation the cupule has 
 grown up like a scaly wall round the ovary (fig. 34), and 
 the tip of the latter is seen peeping out from its orifice. 
 
 We are now in a position to understand generally 
 the changes that convert the female flower into the 
 cupped acorn. The fertilised oospore becomes the em- 
 bryo (fig. 35, x); it grows at the expense of the contents 
 of the embryo-sac, and develops a radicle, a plumule, 
 and two relatively large cotyledons, which soon become 
 so big that they occupy the whole space in the sac (fig. 
 36). Moreover, the embryo-sac increases to make more 
 room for this growing embryo. And now comes in a 
 curious point. We saw that the ovary consisted of three 
 chambers, each containing two ovules ; each of these 
 six ovules also had its embryo-sac, containing an egg- 
 cell, &c., and each of the total of six egg-cells may be 
 fertilised by the contents of so many pollen-tubes 
 coming from pollen grains on the stigmas. But the 
 rule is that five of the ovules with their contents 
 perish at an early period, because one strong one takes 
 the lead in development, and starves the rest by taking
 
 INFLORESCENCE AND FLOWERS FKUIT AND SEED 131 
 
 all the available nourishment to itself. Consequently 
 the advancing ovary is soon filled by one avule the 
 other five and two of the chambers being pressed to one 
 side by it. 
 
 In a few weeks the ovary and its cupule have in- 
 creased considerably in size, and the one successful 
 ovule, with the rapidly developing embryo in the 
 
 A , B. C. 
 
 t 
 
 FIG. 36. Sections of acorns in three planes at right angles 
 to one another. A, transverse ; B, longitudinal in the 
 plane of the cotyledons (Z) ; C, longitudinal across the 
 plane of the cotyledons ; c, cotyledons ; t, testa ; p, peri- 
 carp ; *, scar, and r, radicle ; pi, plumule. The radicle, 
 plumule, and cotyledons together constitute the embryo. 
 The embryonic tissue is at r and pi. The dots in A, and 
 the delicate veins in B and c are the vascular bundles. 
 
 embryo-sac in its interior, occupies nearly the whole of 
 its cavity; the remains of the two aborted chambers 
 and the five unsuccessful ovules being traceable as tiny, 
 shrivelled remnants in one corner. The walls of the 
 ovary then gradually change into the polished brown 
 walls (pericarp) of the fruit; the walls of the ovule 
 become the coat (testa) of the seed; and the embryo 
 
 K 2
 
 132 THE OAK 
 
 developed from the fertilised egg-cell fills up the interior 
 of the latter, as described in Chapter II. 
 
 The ripe fruit is the acorn, and we may regard it 
 apart from the cupuie ; it contains the seed. 
 
 The acorn is an egg-shaped, nut-like fruit (glans\ 
 about 18 mm. long and 8-10 mm. broad (fig. 36) ; 
 the apex is somewhat pointed with a hard remnant of 
 the stigma, the base is broader, and marked with the 
 circular scar which denotes where it was inserted in the 
 cupuie. The trifid character of the stigma can often be 
 observed even on the ripe fruit, which is smooth (or 
 with fine longitudinal striae) and olive-brown in colour 
 when ripe. The ripe acorn may thus be regarded as 
 consisting of the pericarp (to which the calyx or peri- 
 anth is fused) and the seed. 
 
 The pericarp (fig. 36, p) is a thin, hard shell, com- 
 prised of four layers: (1) An epidermis of small, 
 cuboidal cells with their external walls much thickened 
 (fig. 37, E). (2) Four or five series of very thick-walled 
 and pitted sclerenchyma cells (fig. 37, 1). (3) Then 
 follow numerous rows of thin-walled parenchyma cells, 
 comprising the chief thickness of the pericarp (fig. 37). 
 It is in this tissue that the small vascular bundles 
 supplying the pericarp run, and here and there nests 
 of sclerenchyma cells are scattered. The parenchyma 
 cells may contain minute starch grains, in addition to 
 the remains of chlorophyll corpuscles, even when ripe ; 
 they also contain tannin, and, here and there, crystals 
 of calcium oxalate. (4) The internal epidermis consists 
 of elongated cells in one layer.
 
 INFLOKESCENCE AND FLO WEES FKUIT AND SEED 133 
 
 HT 
 
 FIG. 37. Transverse sections of the pericarp (in.) and 
 seed (vi.) of the oak. E, epidermis ; i, thick layer of 
 sclerenchyma. Under this come the parenchyma cells, 
 with a few sclerenchyma cells Lere and there. T, testa 
 of seed ; G, vascular bundles ; e, the outer layer or epi- 
 dermis of the cotyledon ; Co, thin-walled cells of cotyle- 
 dons (cf. figs. 35 and 36) filled with starch, &c. 
 (Harz.)
 
 134 THE OAK 
 
 The seed proper fills up the entire cavity en- 
 closed by the fruit-wall above described. It consists 
 of a relatively very thin testa, or seed-coat, closely 
 enveloping the large, straight embryo (fig. 36, f). At 
 the broad end the funicle can be observed attaching the 
 seed to the base of the acorn ; it is inserted laterally, 
 and traces of the aborted ovules may sometimes be 
 found at the point of insertion. The vessels from the 
 funiculus braucn at the chalaza and ramify in the testa. 
 
 The testa is a shining, pale-brown or yellowish skin, 
 consisting only of a few rows of cuboidal, thin-walled 
 parenchyma cells, the outer rows of which may be the 
 integuments, and the innermost possibly belong to the 
 remains of the nucellus ; or the latter may be repre- 
 sented by the outer portion of the thin membrane which 
 includes all that remains of the embryo-sac. A few 
 feeble vascular bundles run through the testa (fig. 37, G). 
 
 The testa is closely applied to the surface of the 
 two stout cotyledons. These fill up by far the greater 
 part of the space enclosed by the thin testa and pericarp, 
 and their shape is almost described in saying that. 
 Each is a colourless, hard, plano-convex body, face to 
 face with the other by the flab surface (fig. 36) ; a trans- 
 verse section of the acorn shows each cotyledon occupy- 
 ing half the circle. At the more pointed end of the 
 acorn these two cotyledons will be found to be joined 
 to the very small embryo (plumule and radicle) by what 
 will on germination lengthen into very short stalks 
 (petioles), but which are at present mere bridges of
 
 INFLORESCENCE AND FLOWERS FKUIT AND SEED 135 
 
 tissue, across which minute vascular bundles run from 
 the embryo into the cotyledons. If the shell-like invest- 
 ments described above are removed from the embryo, it 
 is then possible to gently separate the cotyledons and 
 see the minute plumule and radicle to which they are 
 joined (fig. 36) ; on removing one cotyledon the plumule 
 will be seen embedded in a slight depression at the base. 
 At this point there is a little room to spare, not quite 
 filled up by the radicle and plumule; a minute remnant 
 of endosperm may occasionally be found here, not having 
 been entirely absorbed by the developing embryo. 
 
 The cotyledons and embryo are composed of a 
 delicate epidermis enclosing the whole (fig. 37, e), and 
 very thin-walled cells forming the main mass of tissue 
 in which the vascular bundles run. These bundles are 
 scattered in the thickness of the cotyledons, ready to 
 convey fluids to and fro on germination, and- already 
 contain lignified vessels in the xylem and sieve-tubes in 
 the phloem. 
 
 The iso-diametric, closely-packed cells of the cotyle- 
 dons are filled with reserve materials, consisting of 
 large quantities of starch grains embedded in proteids 
 and tannin. Here and there are scattered cells filled 
 with brown pigments and containing tannin; some 
 cells also contain oil-drops. Traces of sugar (quercite), 
 certain bitter principles, acids, and mineral substances 
 also occur in the tissues.
 
 136 TILE OAK 
 
 CHAPTER X 
 
 OAK TIMBER ITS STRUCTURE AND TECHNOLOGICAL 
 PECULIARITIES 
 
 IT is now time to look at the timber of the oak as a 
 material, and to examine its technical properties from 
 the various points of view of those who employ such 
 material. Oak timber may be described as follows : 
 
 (1) Appearance and Structure. Pith pentangular, 
 1 to 4 mm. diameter, whitish at first, and then browner, 
 formed of small, thick-walled cells. 
 
 Sap-wood narrow and yellowish-white ; heart- wood 
 varies in shades of greyish or yellow brown (fawn colour) 
 to reddish or very dark brown. It darkens on expo- 
 sure, and works to glossy surface if healthy. 
 
 Annual rings well marked by the one to four lines 
 of large vessels in the spring wood, whence radiate out- 
 wards tongue-like and branched groups of smaller and 
 smaller vessels, tracheids, and cells, in a groundwork of 
 darker fibres. Indistinct peripheral lines of parenchyma 
 are also visible, especially in the broader annual rings. 
 The annual rings are slightly undulating, bending out- 
 wards between the large medullary rays (fig. 38).
 
 OAK TIMBEE 
 
 137 
 
 Medullary rays of two kinds, a smaller number of 
 very broad, shining ones, from ^ to 1 mm., or even a 
 centimetre or more apart, and very numerous (about 
 
 FIG. 38. Transverse section of wood of oak (magnified five 
 diameters), showing five annual rings, as denoted by the 
 large vessels of the spring wood ; the vessels become 
 smaller in the summer and autumn wood, and are arranged 
 in tongue-like groups. Nine broad medullary rays are 
 shown, the rest are very narrow (cf. fig. 27). The rest 
 of the section is filled with tracheids, fibres, and wood- 
 parenchyma. (Miiller.)
 
 138 THE OAK 
 
 twelve per mm.) fine ones between them, which undu- 
 late between the vessels. In slowly-grown, close wood 
 there is no vestige of radial arrangement left. 
 
 In the tangential section the small medullary rays 
 are seen to consist each of a vertical row of a few cells, 
 the large ones having numerous cells (see fig. 27). 
 
 Wood-parenchyma cells broader than small medul- 
 lary rays, and the colour is chiefly due to pigment in 
 these wood- and ray-cells. The wood-cells are pitted 
 with oblique, slit-shaped, simple pits. 
 
 The vessels have bordered pits, and the septa are 
 perforated each by one large circular opening. The 
 smaller vessels have delicate spirals on their walls as 
 well as bordered pits. 
 
 Nordlinger says that pith-flecks occur occasionally. 
 
 It is impossible to distinguish between the wood of 
 the varieties pedunculata and sessiliflora. 
 
 (2) Its density varies considerably. Taking the 
 weight of a given volume of water as unity, the weight 
 of an equal volume of oak timber may weigh from 0-633 
 when air-dry to 1-280 when fresh cut. We may take 
 the average density of green i.e. newly-felled oak, 
 with all its sap present, as about 1-075, and that of the 
 seasoned wood as about - 78. 
 
 It must be borne in mind, however, that these 
 weights refer to the wood as a structure that is, a com- 
 plex of vessels and cells, &c., containing air and liquids 
 and do not give the specific gravity of the wood sub- 
 stance itself. The latter may be obtained by driving
 
 OAK TIMBER 139 
 
 off all the air and water from the wood, and is found to 
 be l - 56, compared with an equal volume of water taken 
 as unity. It is the varying quantities of this wood sub- 
 stance, and of air and water in the cavities, which make 
 the density of different pieces of oak vary so much. 
 
 (3) The proportion of sap contained in the cavities of 
 the vessels, cells, &c., of course differs at different times. 
 In the spring, just as the buds are opening, the quantity 
 of water increases more and more up to about July, when 
 the maximum is attained ; the proportion of water to 
 solids then sinks until October, when the leaves fall ; 
 it increases again up to Christmas-tide, and then sinks 
 to the minimum in the coldest part of the winter. The 
 proportion of water to the total weight of the felled 
 wood may vary from 22 to 3 9 per cent. 
 
 (4) Obviously the loss of water on drying causes 
 shrinkage of the wood, and although oak shrinks very 
 little in the direction of its length (O028 to 0*435 per 
 cent.), the effect is very marked in other directions. In 
 the radial direction i.e. in the direction of the medul- 
 lary rays it may shrink from 1 to 7'5 per cent, of its 
 measurement when first felled ; and in the direction 
 vertical to this i.e. parallel to a tangent to the cylindrical 
 stem the variation is from O8 to 10' 6 per cent. Of 
 course, green oak shrinks much more than seasoned and 
 older wood, the process of seasoning being, in point of 
 fact, the period of chief shrinkage. It is said that wood 
 from the variety sessiliflora shrinks more than that of 
 the variety pedunculata, but it may be doubted how far
 
 140 THE OAB. 
 
 the difference would hold if sufficiently numerous com- 
 parisons were made. 
 
 (5) Swelling may be regarded as complementary to 
 shrinkage. It has been found that it oak wood is 
 allowed to absorb water until thoroughly saturated it 
 will increase from O13 to 0'4 per cent, in length, and 
 be distended radially from 2-66 to 3 '9 per cent., or tan- 
 gentially 5'59 to 7'55 per cent., according to age and 
 condition, young wood swelling more than old. It has 
 also been found that the total volume increased from 5'5 
 to 7'9 per cent., and the weight from 60 to 91 per cent., 
 on complete saturation. 
 
 (6) Elasticity and Tenacity. Oak is very elastic, 
 and easily bent if steamed, and it does not readily 
 splinter. When pulled in a direction parallel to the 
 length of the structure the absolute tenacity = 2-23 to 
 14'51 kgr. i.e. it took a pull equal to this weight per 
 1 sq. mm. of section to pull the wood asunder. 
 
 The limit of elasticity corresponds to a load of 2 -72 
 to 3'5 kgr., according to various authorities, the speci- 
 men lengthening ^g-<j-th in the former case. 
 
 The modulus of" elasticity is given as 826 to 1,030 
 kgr., and the breaking limit as 4'66 to 6-85. 
 
 When the pull is in a direction across the length of 
 the fibres, the results differ according as the load is 
 applied so as to act radially or tangentially. 
 
 When acting radially the modulus of elasticity is 
 given as 188*7 kgr., and the breaking limit as 0'582 kgr. 
 
 When acting parallel to a tangent the modulus of
 
 OAK TIMBER 141 
 
 elasticity = 129'8 kgr., and the breaking limit 0-406 
 kgr. 
 
 The absolute tenacity in the transverse direction is 
 given as 0-44 to 0-61 kgr. 
 
 In the case where pressures are applied in the direc- 
 tion of the length of the fibres the limit of elasticity = 
 2-09 to 2-22 kgr. ; the modulus of elasticity, 933 to 1,250 
 kgr. ; and the absolute resistance, 2*58 to 3'64 kgr. 
 
 Flexibility. The limit of elasticity = 1-77 to 2'71 
 kgr. ; modulus of elasticity, 620 to 735 kgr. ; resistance 
 to bending, 4-53 to 6-18 kgr. 
 
 Torsion. Oak warps considerably unless carefully 
 seasoned. Limit of elasticity = 0*4 to 0'54 kgr. ; 
 modulus of elasticity, 612*5 to 785 kgr. ; resistance to 
 torsion, 0'75 to 0'97 kgr. 
 
 Resistance to shearing-stress, in the direction of the 
 fibres = 0-61 to 0'97 kgr. ; perpendicular to them, 1-9 
 to 3-49 kgr. 
 
 (7) Resistance to Splitting. Oak is easily split into 
 tolerably smooth and even staves, and is much employed 
 for this purpose. 
 
 (8) Hardness. Oak is neither the hardest and 
 heaviest, nor the most supple and toughest of woods, but 
 it combines in a useful manner the average of these 
 qualities. Good oak is hard, firm, and compact, and 
 with a glossy surface, and varies much ; young oak is 
 often tougher, more cross-grained, and harder to work 
 than older wood. According to Gayer, if we call the 
 resistance which the beech offers to the saw, applied
 
 142 THE OAK 
 
 transverse to the fibres, 1, then that of freshly-felled 
 oak =1-09. 
 
 (9) Durability. A mild climate and open situation 
 produces the most durable oak, and it is extraordinarily 
 durable under water, in the earth, or exposed to wind 
 and weather, or under shelter; in the latter case it 
 becomes more and more brittle as years roll by. 
 
 The alburnum becomes rotten usually in a few years 
 if exposed, and is the prey of insects if under cover. 
 The heart, if sound, may last for centuries under cover 
 and well ventilated, and even in earth or water will 
 endure for several generations. There are, for instance, 
 in the museum at Kew, a portion of a pile from old 
 London Bridge which was taken up in 1827 after hav- 
 ing been in use for about 650 years, and a piece of a 
 beam from the Tower of London of which it is stated 
 that it was ' probably coeval with the building of the 
 Tower by William Rufus ; ' and many other specimens 
 of very old oak are known. 
 
 (10) Burning Properties. The calorific power of 
 oak wood is high, in accordance with its density, but it 
 splutters and crackles and blackens too much. Never- 
 theless, it produces a valuable charcoal. Hartig says 
 that if we call the cooking-power of a given volume of 
 beech 1, that of an equal volume of oak =0'92 to 0'96. 
 
 (11) Peculiarities. Oak timber is apt to suffer from 
 various diseases, and from frost-cracks and star-shakes, 
 cup-shakes, &c., as we shall see in the next chapter. It 
 often presents brittle wood, red-rot (foxiness), white-rot,
 
 OAK TIMBER 143 
 
 epottiness of various kinds, and is sometimes twisted. 
 At the roots it is very often affected with burrs. It con- 
 tains gallic acid, and so corrodes iron nails, clamps, &c. 
 
 (12) Uses. Owing to its high price and great specific 
 weight oak has suffered in competition with spruce, 
 larch, and pine so far as building is concerned ; but its 
 uses are very various and widespread, nevertheless, and 
 it is invaluable to the engineer and builder wherever 
 strength and durability are aimed at. 
 
 As already said, its great value depends on its 
 marvellous combinations of several average properties ; 
 and considerable variations in the density, durability, 
 ease of working, and beauty when worked, and so forth, 
 are met with according to the situation and climate in 
 which the oak grows. Generally speaking, it is found 
 that when the oak grows isolated in plains, in rich soil 
 and a mild climate (habitat of Q. pedunculata), it 
 grows rapidly, and produces a wood of very tough and 
 horny consistency, which is regarded as the best for 
 naval and hydraulic work, cartwrights, &c., and wher- 
 ever strength, tenacity, and solidity are required in 
 high degree (fig. 39, top). The best should have broad 
 and equal rings, but not broader than 7 to 8 mm., with 
 narrow vascular zone and the smallest possible vessels, 
 and with a pale, rather than dark, and even colour on 
 the fresh section. It should also have long fibres and 
 a strong, fresh smell. 
 
 In close, high forest, on poor soil, and in a rougher 
 climate, it may take 300 years to reach - 6 metre diameter,
 
 FIG. 39. Three specimens of oak grown under different conditions. 
 
 The upper one is from a rapidly-grown tree, in the open, and at a low altitude ; 
 the wood is very strong, hard, and heavy (density 0-827), because there is a pre- 
 ponderance of fibres in the broad rings. The middle specimen comes from a tree 
 growing slowly in a forest at a considerable altitude ; the narrow rings have too 
 large a proportion of vessels, whence the wood is soft (density 0'691), porous, and 
 weak. The lower section is from a tree which has grown very irregularly on poor 
 soil, as shown by the variable rings ; only the parts with broad rings are good- 
 hence bad wood predominates (density 0742). (Nanquette-Boppe.)
 
 OAK TIMBER 145 
 
 and the wood is then softer and more porous, beautifully 
 speckled, and shrinking little (fig. 39, middle). Such 
 wood is excellent for sculpture and carving, and is very 
 pretty ; it is also well adapted for cooperage. 
 
 In deep soil of moderate quality, in hilly country, 
 and growing as coppice under standards, we have a wood 
 of irregular growth and not very valuable, but useful 
 in an all-round way for sawing and splitting (fig. 39, 
 bottom). 
 
 Speaking generally, it is found that, other things 
 being equal, the most resistant, closest, and toughest 
 timber comes from isolated trees growing in the open ; 
 straight and long timber, less marked for the above 
 qualities, comes, on the contrary, from trees grown in 
 close, high forest. This is the conclusion arrived at by 
 the naval authorities in France and England, and may 
 be accepted as according with the facts of structure, &c. 
 Some differences may be put down to the varieties, 
 but probably Boppe is right in concluding that rate of 
 growth, &c. due to differences in the soil and climate 
 are the determining causes. 
 
 The builder employs oak for sills, staircase treads, 
 keys, wedges and trenails, gate-posts and doors, and 
 superior joinery. 
 
 Railway-sleepers are best made of young oak, as 
 it is denser, and the Austrians say such sleepers last 
 from seven to ten years if not treated, and for as long 
 as sixteen years if treated with zinc chloride and other 
 preservatives. 
 
 L
 
 146 THE OAK 
 
 On the Continent heavy oak is used in machines, for 
 axletrees, spokes, stamps of mills, anvil-stocks, hammer 
 handles, &c. 
 
 Oak is much used for carving of all kinds, large 
 furniture, panelling, parquetry, for the felloes, spokes, 
 and axles of wheels, and for other parts of waggons, &c. 
 In cooperage it is much used for the staves, &c., of casks, 
 measures, sieves. 
 
 Split oak makes excellent palings and shingles, and 
 oak vine-props are only second to those of chestnut. 
 Walking-sticks are also made of oak, and even water- 
 pipes have been used, but they taint the water.
 
 147 
 
 CHAPTER XI 
 
 THE CULTIVATION OF THE OAK, AND THE DISEASES AND 
 INJURIES TO WHICH IT IS SUBJECT 
 
 THE oak has been cultivated in all kinds of ways, but 
 by far the best timber is produced in what is called ' high 
 forest ' that is, the young trees all start at the same age 
 and planted much closer together than they will be later 
 on, their number being lessened period after period by 
 successive removals until there is left a forest of large 
 trees at equal distances. As it takes from 140 to 200 
 years to bring such a crop of timber to maturity, we may 
 easily understand that such are rarely met with except 
 as State forests, and the governments of various countries 
 keep them going at various ages : one set of plantations 
 will be ten, another twenty, a third thirty years old, for 
 instance, when a given set is ready to be finally cut over 
 for heavy timber. 
 
 There are many difficulties, however, in cultivating 
 pure oak woods, and the custom of mixing other trees 
 is a common one, for the young oaks need much light ; 
 and yet, if each plant has the space given it necessary to 
 allow of this light, it grows into a short and spreading 
 
 L 2
 
 148 THE OAK 
 
 tree instead of rising up into a tall, straight one. The 
 forester usually gets over these difficulties by planting 
 beech, or silver fir or some other species among the 
 oaks, but in such a way that the oaks are never com- 
 pletely shaded by the other trees that is to say, he 
 keeps the trees at different ages, the beech, hornbeam, 
 silver fir, spruce, &c., only being allowed to just close 
 in the forest, leaving the leaf-crowns of the oaks to 
 be fully exposed to the light above. The oak grows 
 faster than the beech or spruce, for instance, while 
 young, and so keeps its head easily above the others 
 for a time. Very often the oak is cultivated pure at 
 first, and then, when the oaks are becoming too crowded 
 and he has to thin them, the forester puts in the 
 silver fir or beech, which prevents the light coming 
 in to the lower parts of the young oak-trees, and con- 
 sequently prevents the development of lower branches, 
 which would give the spreading, squat habit he wishes 
 to prevent. For without light the leaves of the 
 lower twigs of course cannot make the materials to 
 strengthen and thicken the latter into branches, and 
 so they die off, and the trunk remains a straight, clean 
 cylinder. 
 
 Although oaks are often raised from seed, a number 
 of veteran trees being allowed to stand for many years 
 in order to scatter the acorns, yet in by far the greater 
 number of cases the plants are put in artificially, the 
 long tap-roots being first cut in order to make them 
 throw out lateral rootlets. It is also a common practice
 
 THE CULTIVATION OF THE OAK 149 
 
 to cut back oaks, and allow them to sprout into what is 
 known as coppice that is to say, numerous buds which 
 would not have developed at all are impelled to grow 
 up into twigs and branches (stool-shoots) from the lower 
 parts of the cut tree. It was very usual at one time to 
 grow oak in this way for the sake of the bark, which 
 was employed in tanning, the trees being cut back again 
 and again, and renewing the coppice growth after each 
 cutting. 
 
 There are various other modes of growing oak in 
 forests, but, whatever the system employed, the following 
 facts have to be borne in mind and provided for. The 
 oak is a tree that requires a soil of great depth, and 
 sufficiently open to allow of the free penetration of air 
 and water to the subsoil; consequently many soils, 
 otherwise rich enough, are unsuited for the culture of 
 this tree. Again, young seedlings and plants are apt 
 to suffer from frost unless they are protected by suitable 
 mixtures of other plants ; but such mixtures must be 
 chosen properly, for this tree demands light and space 
 to a degree greater than most other European trees 
 except the larch, birch, and one or two others, and 
 rapidly suffers if shaded or unduly crowded. Further, 
 as compared with other European trees the oak is a tree 
 of the plains, and requires a relatively high temperature. 
 These requirements also accord with its adaptation to 
 deep, rich, well-drained soil, and, taking it all round, we 
 have to regard the oak as a tree which makes consider- 
 able demands on the locality (soil and climate) where
 
 150 THE OAK 
 
 it grows. In return for this, however, it yields the 
 best of all temperate timbers. 
 
 As we have seen, the forester has to exercise con- 
 siderable forethought the outcome of long experience 
 in growing oak so as to obtain long, clean stems. The 
 natural habit of the tree is to form a short, thick bole 
 and a widely spreading crown, the main branches of 
 which come off not far from the ground. To compel 
 the stem to elongate into a long pole he has to plant 
 other trees with it (as we have seen, beech, spruce, &c.), 
 which, while they keep the light off the lower parts of 
 the oaks, do not overtop them. This makes the trees 
 long and spindly at first, as they run up their leaf- 
 crowns higher and higher, and it is part of the forester's 
 art to select the exact time when he may cut away some 
 of the nurse trees and let in just enough, and not too 
 much, light and air, so that the crowns of the oaks shall 
 fill out more and thicken the stems. For it must never 
 be forgotten that the timber is laid on from substance 
 prepared in the leaves. 
 
 The natural shape, so to put it, of an oak-tree is 
 that of a wide-spreading, short-stemmed mushroom, and 
 such a shape is realised in the open ; the forester com- 
 pels it to lengthen its stem as much as possible before 
 he lets it extend its crown. Hence he aims at length 
 first, and then lets the tree put on timber in the mass. 
 He does this, of course, by taking advantage of the tree's 
 peculiarities, and one of these is that it grows very 
 rapidly when young. It will be obvious that the skilled
 
 THE CULTIVATION OF THE OAK 151 
 
 forester also has to aim at getting as much timber as 
 possible on the ground in a given time, and in the case 
 of a tree like the oak his calculations have to be well 
 made beforehand, for the tree may have to stand for 
 from 120 to 200 years before it is cut. Left alone it 
 may live for 1,000 years, but the proportion of good 
 timber in trees after a certain age rapidly diminishes 
 a fact that has also to be reckoned with. 
 
 It is quite different, however, when trees are re- 
 quired for seed purposes. The oak hardly bears fruit 
 at all before it is fifty to sixty years old, and seventy to 
 eighty years is a better age for the purpose ; but, as 
 with other trees, to produce really good seed the oaks 
 must be isolated, or nearly so, so that they get the maxi- 
 mum of light and air. Consequently a modification of 
 procedure has to be made when seed-trees are required. 
 
 When the fruiting period has once been reached 
 the tree goes on producing acorns every year ; but it is 
 noticed that heavy crops of good seeds only recur every 
 five (or perhaps three) years or so, the yield in the 
 intervals being inconsiderable. This is in accordance 
 with Hartig's discovery that in the beech, for instance, 
 the tree goes on storing up nitrogenous materials and 
 salts of phosphorus and potassium during the first 
 seventy or eighty years of its life, and then suddenly 
 yields these stores to the seeds ; the drain is so exhaust- 
 ing that it requires three to five years to re-store suffi- 
 cient of these substances for another ' seed-year.' The 
 season or weather is also concerned in the matter.
 
 152 THE OAK 
 
 Of course there are very many other details to be 
 considered in the technical cultivation of the oak, but 
 enough has been said to give the reader a general 
 account of the procedure, and I now pass to the subject 
 of the dangers and diseases which threaten the tree at 
 various periods in its development, and the timber 
 afterwards. 
 
 The diseases and injuries to which the oak is subject 
 are very numerous and various, although, compared 
 with some other indigenous trees, it suffers remarkably 
 little from the different dangers which await it at all 
 stages in the course of its long life from the seedling 
 to the aged tree. Some of these are referable to the 
 exigencies of the non-living environments the climate, 
 soil, &c. ; others are due to the attacks of living or- 
 ganisms, both vegetable and animal from the weeds 
 which smother the young seedlings by keeping the 
 light from them, to man himself, who injures the trees 
 in various ways. The earliest struggles of the young 
 seedling are with the weeds, slugs, and insects of 
 various kinds that invade the territory on which the 
 acorn has germinated, and of course the baby plant 
 has also to contend against any inclemencies of climate 
 or unsuitableness of soil that it may meet with. Owing 
 to such vicissitudes very many of the seedlings never 
 obtain the dimensions of a plant at all, and in some 
 seasons the mortality is enormous. Other destructive 
 agents during these early phases of the life of the 
 oak are cattle and deer, which not only tread down
 
 THE CULTIVATION OF THE OAK 153 
 
 the shoots but also nibble them off, and mice, squirrels, 
 &c., do their share of injury, as also do wood-pigeons 
 and other birds. In the North of Europe the young 
 plants suffer terribly from the ravages of a fungus 
 named Rosellinia, the mycelium of which sends its 
 branches into the roots and kills them, consequently 
 entailing the death of the plant. The larvae of various 
 insects also damage the roots and bring about injuries 
 which may prove fatal. Gynips corticalis produces galls 
 on the lower parts of the stems. 
 
 When the plant has passed into the condition of a 
 sapling its dangers are for the most part of quite other 
 nature, the injurious fungi especially being different. 
 The chief diseases of the roots now arise from their 
 spreading into unsuitable soil, the drainage of which 
 may be incomplete, and thus bring about a sodden, 
 acid, ill-aerated condition. The want of oxygen and the 
 low temperature combine to kill the root-hairs and 
 young rootlets, and the leaves above part with their 
 water faster than it can be supplied from below, and 
 they turn yellow and die off, the branches dry up, and 
 the tree dies. 
 
 Other dangers arise from the persistent overshadow- 
 ing of other trees, which slowly kill the young oaks by 
 depriving their leaves of light ; the offending trees play- 
 ing the same inimical part, in fact, that grass and weeds, 
 &c., play towards the small seedlings. Or the roots may 
 be too thickly set in the soil if the trees are too crowded, 
 and each suffers from over-competition with others.
 
 154 THE OAK 
 
 Much mischief is effected by the attacks of insects 
 of various kinds. The caterpillars of certain moths 
 (especially Cnettiocampa and Tortrix), for instance, eat 
 off the leaves in June, and then form large masses of 
 mingled debris, skins, &c., as they pass into the pupa 
 stage in July. The denudation of the leaves brought 
 
 FIG. 40. Tortrix mridama, the green oak-moth, the larvre 
 of which eat off the young leaves. (Altum.) 
 
 about by such caterpillars is apt to be very exhaustive 
 to the trees, for although they put forth new foliage in 
 July and August, it must not be forgotten that these new 
 leaves are constructed from materials which should have 
 gone to the general stores in the tree, and from which 
 new wood, for instance, would have been developed.
 
 THE CULTIVATION OF THE OAK 155 
 
 Of other animals which injure oaks I may mention 
 the various cattle, which bite off or rub the bark and 
 buds ; hares, squirrels, mice, &c., which nibble roots and 
 buds and destroy the acorns, &c. ; and a few birds ; and 
 certain beetles, which bore into the wood. 
 
 Among the pests belonging to the vegetable king- 
 dom the following may be selected from a large 
 number. The honeysuckle occasionally twists tightly 
 round the young stem, and in course of time so com- 
 presses the cortex that the formative materials from the 
 leaf-crown have to pass in a spiral course between the 
 coils of the strangling plant, and the tightly-squeezed 
 parts may be starved as the tree thickens, and even the 
 death of the cambium may follow, especially if one or 
 two of the honeysuckle coils come to lie nearly horizon- 
 tally round the stem. 
 
 As a rare event the mistletoe is found on the oak. 
 A much commoner parasite of the same family is 
 Loranthus europceus, which does considerable damage to 
 oaks in some parts of Europe. The sticky seeds are 
 carried into the trees by thrushes. Here they germi- 
 nate, and send their roots, or haustorial strands, into 
 the cortex of a branch as far as the cambium, where 
 they spread and feed on the contents of the young 
 wood- and cambium-cells, causing malformations of the 
 injured branch at the spot attacked owing to the hyper- 
 trophy of the tissues, to which abnormal quantities of 
 food materials now flow (fig. 41) ; and frequently 
 bringing about the death of the upper parts of the
 
 156 
 
 THE OAK 
 
 branches owing to the paucity of water at those parts, 
 the parasite taking much of that which reaches the 
 injured place, and the impoverished wood allowing less 
 to pass than it would normally have done. 
 
 Among the fungi there are several enemies to the 
 oak-tree. The leaves are attacked by Phyllactinia, one 
 
 FIG. 41. Loranthus europcBus. A. Lower part of stem 
 attached to branch of oak, both denuded of cortex. B. 
 Longitudinal section through one of the haustorial strands, 
 showing its progress, year by year, as the branch thickens. 
 C. Transverse section, through a branch which has long 
 been badly infested with the Loranthus ; a a, dead re- 
 mains of old haustorial strands ; b b, young Loranthus 
 plants developed as buds from the older ones. The 
 asterisks mark still younger specimens. (Hartig.) 
 
 of the mildews, which forms white networks, like spiders' 
 webs, on their surfaces. Numerous small ascomycetous 
 fungi are found on the dying and dead leaves, but these 
 do not directly injure the living tree. 
 
 Other fungi are found in the cortex, and one of the 
 most interesting of these is a red Nectria, the spores of
 
 THE CULTIVATION OF THE OAK 157 
 
 which germinate on the bark, but cannot infect the tree 
 unless there is a wound in the neighbourhood. How- 
 ever, owing to the numerous small cracks and ruptures 
 due to the injuries caused by insects, hail, frost, &c., 
 the mycelium easily gains access to the cortex and cam- 
 bium, and feeds on the contents of the cambium cells, 
 which it destroys. The consequence of the irritations 
 set up is the formation of canker-like knots on the 
 branches, and the injury may be great enough to destroy 
 smaller ones, and occasionally even a large one. 
 
 Unquestionably the most important of the diseases 
 to which the older oak-trees are subject are those which 
 result in the destruction of the timber. 
 
 There are about six or eight of the fungi known popu- 
 larly as toadstools technically as Hymenomycetes which 
 are able to injure and even destroy the timber of stand- 
 ing oaks, and while each of these pests does the damage 
 in its own peculiar way, they show considerable simi- 
 larity in general behaviour. In the first place, these 
 fungi are unable to penetrate the bark of sound trees, 
 and their hyphee always gain access to the timber by 
 means of actual wounds and exposed surfaces of wood, 
 such as the cracks caused by frost or by the bending 
 down of heavy branches under the weight of a load of 
 snow, or the ruptured ends of broken branches blown 
 off by strong gales or struck by falling trees, or places 
 where animals have removed the bark, where cart-wheels 
 have abraded the larger roots, and so on. Once inside, 
 the hypha3 of these fungi pierce the vessels, cells, &c., of
 
 158 
 
 THE OAK 
 
 the wood by excreting soluble ferments which dissolve 
 the substance of their walls, and feed on the products of 
 solution. Hence they damage the timber in two ways 
 they riddle it through and through by myriads of 
 minute apertures, and thus ruin its structure, and they 
 
 FIG. 42. Piece of oak destroyed by Thelephora Perdix, 
 showing the characteristic markings due to the action 
 of the fungus. (R. Hartig.) 
 
 reduce its substance by dissolving it and converting it 
 to their own uses. The wood, therefore, loses in strength 
 and in weight, and becomes ' rotten.' There are differ- 
 ences in detail as to the mode of destroying the elements 
 of the wood, but the final result is much the same, in all
 
 THE CULTIVATION OF THE OAK 
 
 159 
 
 cases some of the fungi destroy the vessels, fibres, 
 fee., by dissolving their walls from inside, while others 
 destroy the part common to contiguous cells, &c., and 
 thus first isolate the elements and then complete the 
 destruction. A series of very interesting researches by 
 
 FIG. 43. Oak timber destroyed by the fungus Hydnwni 
 diversidens. a shows the medullary rays on the tan- 
 gential section; b, a mass of felted mycelium. (B. 
 Hartig.) 
 
 Hartig has demonstrated that the presence of these 
 timber-destroying fungi can be detected from the mark- 
 ings and discolorations they produce in the wood ; those 
 due to Hydnum diversidens, Thelephora Perdix, Poly- 
 porus sulphur eus } P. igniarius, P. dryadeus, and Stereum
 
 160 
 
 THE OAK 
 
 hirsutum being all different, and in some cases so charac- 
 teristic that the merest glance suffices to diagnose the 
 disease (cf. figs. 42 to 45). 
 
 There is yet another disease of oak timber to be 
 noticed, and one which causes great havoc in buildings 
 
 FlG. 44. Oak damaged by Polyporus igniarius, a very 
 common timber fungus. (B. Hartig.) 
 
 where the ventilation is bad and the air damp. This is 
 the too well known dry-rot, due to the destructive 
 action of the fungus Merulius lacrymans, a hymenomy- 
 cete allied to the preceding, but differing from them in 
 not attacking the standing timber. The spores of this 
 fungus are able to infect oak planks, beams, &c. ; and
 
 THE CULTIVATION OF THE OAK 
 
 161 
 
 the mycelium rapidly spreads on and in the wood, 
 destroying the cell-walls, and causing the wood to shrink 
 and crack and warp, and finally to fall to pieces. 
 Thorough ventilation is fatal to the fungus and stops 
 the rot. 
 
 A series of enemies to the oak-tree not yet referred 
 
 FIG. 45. Oak wood destroyed by I'olyporus dryadeus, 
 showing the very characteristic markings, like insect 
 tunnels in a deep red-brown matrix. (R. Hartig.) 
 
 to are various gall-insects, so called because they pierce 
 the young leaves or buds, &c., and lay their eggs in the 
 wound ; the irritation set up suffices to induce a flow of 
 food materials to the stimulated spot, and the overfed
 
 FIG. 46. Piece of oak-bark with fructification of Polyyorus 
 sulphureus. 
 
 FIG. 47. Piece of oak attacked by Polyporus sulphureus, the 
 yellowish- white mycelium of which Ls seen at c and d. (R. Hartig.)
 
 J 
 
 FIG. 48. Transverse section of oak timber destroyed by 
 Polyporus sulphureut. (K. Hartig.) 
 
 FIG. 49. Highly magnified longitudinal radial section of 
 a piece of oak destroyed by a timber fungus, showing 
 the ravages of the hyphae in the various tissues. (R. 
 Hartig.) 
 
 M 2
 
 164 THE OAK 
 
 cells multiply and form the gall. This is a mere out- 
 line sketch of the matter, however, for the differences in 
 behaviour are enormous. Each insect causes the forma- 
 
 FlG. 50. Portion of the spore-bearing hymenium of Merulius 
 lacrymans, the fungus of ' dry rot.' 
 
 tion of a specific kind of gall, differing in shape, size, 
 colour, and other characters from those caused by other 
 gall-insects. There are many kinds, and only a few can 
 be mentioned here. Each species of oak may have its
 
 THE CULTIVATION OF THE OAK 
 
 165 
 
 own galls also, those on the American oaks differing 
 from those on the European species, bat some are common 
 
 FIG. 51. An oak-ieaf with several kinds of Cynips galls 
 on it. a, gall produced by Cynipsscutellaris; b, C. divisa; 
 c, Neuroterus Reawnmril; e, Biorhiza renum; f, Neuro- 
 terus ostreus. (Frank.) 
 
 to more than one species. The insects which produce 
 the commonest English oak-galls are nearly all members 
 of the Cynipidece, a group of hymenoptera which lay
 
 166 THE OAK 
 
 their eggs in the young tissues of various plants, espe- 
 cially oaks and roses. 
 
 Some of the resulting galls are discoid, such as the 
 'oak-spangles' of our woods ; others, again, are spherical, 
 such as the common leaf-galls so well known in England, 
 and the so-called oak-apple ; then there are the ' arti- 
 choke galls,' produced by the partial metamorphosis of 
 the buds of the oak in which the cynips has laid its 
 egg, and many others.
 
 167 
 
 CHAPTER XII 
 
 RELATIONSHIPS OF THE OAKS THEIR DISTRIBUTION 
 IN SPACE AND TIME 
 
 THE oak is a member of a very large and ancient group 
 of dicotyledonous flowering plants, embracing the 
 beeches, chestnuts, hazel-nuts, &c., and many other 
 forest trees of the Northern Hemisphere. 
 
 The number of species of oaks (Quercus) is very 
 large, probably more than 300, of which the majority 
 belong to North America, Europe, China, Japan, and 
 other parts of Asia. There are none in Africa south of 
 the Mediterranean region, nor in South America or 
 Australasia. Some remarkable species are found in the 
 Himalayas, and many in the Malayan Archipelago. 
 
 The various species of the genus Quercus axe 
 arranged into groups according to differences in the 
 form and arrangement of the scales of the cupule, the 
 characters of the leaves, and certain peculiarities in the 
 acorns. Many oaks, especially those of warm countries, 
 for instance, are ' evergreen,' with hard, leathery leaves, 
 quite unlike the leaves of our common British oak.
 
 168 THE OAK 
 
 The latter is denominated botanically as Quercus 
 Robur, but certain varietal forms of it have been distin- 
 guished, of which the commonest in this country are 
 Q. pedunculata, a variety with the female flowers on long 
 peduncles, and Q. sessiliflora, with the female flowers on 
 short peduncles ; but although numerous attempts have 
 been made to define these forms, and while small differ 
 ences in the petioles, lobing of the leaves, and the wood, 
 &c., have been insisted upon at various times by ob- 
 servers, it appears that the two varieties graduate into 
 one another by intermediate forms. In England the 
 variety pedunculata is the commonest over the country 
 generally, but in the hilly districts of North Wales and 
 the North of England the variety sessiliflora is said to 
 prevail. Similarly, on the Continent the latter variety 
 is found at higher elevations than the former, though its 
 area of occurrence is more restricted. This pronounced 
 variability of the oak was commented upon by the late 
 Charles Darwin, who points out in the ' Origin of Species,' 
 that more than a dozen species have been made by a 
 certain author out of what other botanists regard as mere 
 varieties of the common oak. 
 
 De Candolle, who made a special study of this group, 
 found the variations so enormous that, although he 
 made something like 300 species, he concluded that 
 the majority of these were merely provisional ; and he 
 concluded, as others have done, that we have in the 
 numerous varieties of the species this old genus Quercus, 
 series of incipient species. If the connecting forms
 
 RELATIONSHIPS OF THE OAKS 169 
 
 were to die out, leaving certain varieties more isolated 
 than they are at present, systematists would elevate the 
 latter to the rank of species. 
 
 It is interesting to observe that twenty-eight varie- 
 ties of the common English oak (Q. Robur) have been 
 described, and that the majority of these can be grouped 
 around the three forms pedunculata, sessiliflora, and 
 pubescens, the latter being a somewhat hairy variety 
 found on the Continent. No doubt we have here, again, 
 a case where the three varieties mentioned would be 
 accorded specific rank if the connecting forms died out, 
 as some of them appear to be doing. 
 
 I have already stated that the oaks are a very 
 ancient family, and their great variability is in accord- 
 ance with this. It probably implies that the genus has 
 had time during its migrations over the Northern Hemi- 
 sphere to vary immensely, and that some of the varie- 
 ties have become adapted to given situations, others to 
 others. On the whole, the oak family must be regarded 
 as a northern type which has sent extensions south- 
 ward. 
 
 Now let us glance at their geological history. Some- 
 thing like 200 forms of fossil oaks have been described 
 from remains, chiefly of leaves and wood, found in 
 various parts of the world. Some of the European fossil 
 forms remind us of species now found only in hot 
 countries near the tropics, others are peculiar, and some 
 are very doubtful. 
 
 The earliest remains of oaks come from the Greta-
 
 170 THE OAK 
 
 ceous strata, being coeval with the first undoubted dico- 
 tyledons that have been found. Many have been found 
 in the Tertiary also, and we have to conclude that the 
 oaks were probably already a well-developed group of 
 plants before the higher mammalia existed i.e. so far 
 as we can judge from the fragmentary records of the 
 rocks. It seems that even the present species of oaks 
 were already in existence in Tertiary times, and possibly 
 some of their varieties also. 
 
 From the evidence of their fossil remains, together 
 with the facts of their present distribution, it is at least 
 exceedingly probable that the European oaks, including 
 our English oak, came into existence somewhere in the 
 East, and that, after spreading from Asia towards the 
 West, they are now slowly retreating before competing 
 forms e.g. the beech. Meanwhile the English oak 
 (Q. Robur) has been giving rise to several varieties, of 
 which three at least (viz. pedunculata, sessiliflora, and 
 pubescens) have become sufficiently marked to be re- 
 garded as species by those who do not consider the con- 
 necting forms. 
 
 It is not improbable that this migration of the 
 European oaks from Asia was completed before the 
 islands of Sicily, Sardinia, Corsica, and Britain were 
 separated from the mainland of the Continent. More- 
 over, our English oak is not distantly related to certain 
 species of Eastern Asia and of Western North America, 
 and it has been surmised that all these related forms 
 sprang from a common ancestor not unlike our English
 
 RELATIONSHIPS OF THE OAKS 171 
 
 oak of to-day. Again, fossil leaves from Italy, found in 
 diluvial deposits, are so like those of certain Californian 
 oaks now existing that a common origin is also suggested, 
 and similar leaves have been discovered in Tertiary de- 
 posits in North-west America. If all the evidence is 
 put together we may conclude with Asa Gray that ' the 
 probable genealogy of Q. Rolur, traceable in Europe up 
 to the commencement of the present epoch, looks east- 
 ward and far into the past on far distant shores.' 
 
 Many of the oaks yield products which are made use 
 of in the arts, apart from their timber, the most valuable 
 of which comes from our European oak, the white oaks 
 of North America, and one or two Himalayan species. 
 In several countries oaks are grown for the sake of the 
 bark, cups, &c., as a tanning material, and these even 
 form important articles of export. Quercitron, a yellow 
 dye and tanning material, is obtained from Q. tindoria 
 in North America. 
 
 Cork, as used for bottling and other purposes, is 
 obtained in Spain, the South of France, and in Algiers, 
 from the thick periderm of Q. 8ul>er. 
 
 Q. infectoria yields the chief galls of commerce,. 
 They are caused by the punctures of Cynips gallce tinc- 
 tvricB, and are used for making ink and for dyeing. In 
 these and similar galls the value depends on the pre- 
 sence of relatively large quantities of tannic and gallic 
 acids which they contain.
 
 INDEX 
 
 ACO 
 ACCESSORY shoots, 6 
 
 Acorn, 4, 7, 10-23, 130 ; figs. 1-3 
 Age of oak, 151 
 Alburnum, 110, 136 
 Annual rings, 95, 108, 136 
 Axis-cylinder, 24, 28, 32, 91 ; 
 fig. 5 
 
 BABK, 98 111, 118-120; fig. 30 
 
 Bast. See Phloem 
 
 Beech, 148, 151 
 
 Biology of roots, 36 
 
 Bud, 50, 72-76, 127; figs. 19, 32 
 
 Burning of oak, 142 
 
 Burrs, 7 
 
 CAMBIUM, 40, 62,64, 92,98, 100, 
 
 103, 1 11 ; figs. 9, 24 
 Cattle, 155 
 Cells, 15, 136 
 Chlorophyll, 79, 85 
 Cnethouavipa, 154 
 Common bundles, 47 
 Coppice, 1 49 
 
 Cork, 93, 116; figs. 17,18 
 Cortex, 62, !'8 ; figs. 17, 18 
 
 Cotyledons, 14, 130, 134 : figs. 2, 
 
 3,37 
 Course of vascular bundles, 42- 
 
 51, 68-71 ; figs. 10, 11 
 Cultivation of oak, 147-152 
 Cupule, 10, 124, 130 
 Cynips, 153, 162 ; fig. 48 
 
 DENSITY of oak, ] 38 
 Diseases of oak, 152-163 
 Drainage, 153 
 Dry-rot. See Aferulius 
 Durability of oak, 142 
 Duramen, 109, 136 
 
 ELASTICITY of oak, 140 
 
 Embryo, 14 
 
 Embryonic tissue, 17, 28, 41, 96 ; 
 
 ligs. 2, 6, 25 
 
 Embryo-sac, 128 ; fig. 35 
 Endodermis, 30. 32 ; fig. 5 
 Epidermis, 16, 39, 41, 52 
 
 FEETILISATION, 130 
 Fibres, 60, 106, 108, 113, 136; 
 fig. 16
 
 174 
 
 THE OAK 
 
 FLE 
 
 Flexibility of oak, 141 
 
 Flowers of oak, 121 ; figs. 31, 
 
 32 
 
 Folk-lore, 2, 3 
 Fruit of oak, 10, 131 
 Fundamental tissue, 16, 39 
 Fungi, 96, 153, 156-163 ; figs. 25, 
 
 42-47 
 
 GALL-INSECTS, 161 ; fig. 48 
 General description of oak, 5 
 Germination, 10-23 
 Growing-point, 37, 74, 96 ; figs. 6, 
 
 19 
 Growth in thickness 68, 91, 100- 
 
 103 
 
 HABIT of oak, 150 
 
 Hardness of oak, 141 
 
 Heart-wood. See Duramen 
 
 High forest. 147 
 
 Honeysuckle, 155 
 
 Hornbeam, 148 
 
 Hydnum diversidens, 159 ; fig. 
 
 43 
 
 Hymenomycetes, 157 
 Hyphae, 97, 157 ; fig. 25 
 Hypocotyl, fig. 3 
 
 INFLORESCENCE of oak, 121 ; figs. 
 
 31,32 
 Injuries to which oak is subject, 
 
 152-163 
 Insects, 154 
 
 LAMMAS shoots, 6, 74 
 
 Leaf, 21, 76-88 ; figs. 20, 21, 22 
 
 Leaf-trace, 47, 49, 69 
 
 Lenticels, 114 
 
 Lorcmthus europceus, 155 ; fig. 41 
 
 MEDULLARY rays, 34, 39, 48, 52, 
 64, 63, 95, 100, 104, 136 ; figs. 
 9, 12, 27, 38 
 
 Merulius lacrymans, 1 60 ; figs. 
 
 46,47 
 Mesophyll, 76, 79, 81, 85 ; fig. 
 
 22 
 
 Mistletoe, 155 
 Mixed woods, 148 
 Mycorhiza, 96 ; figs. 7, 25 
 
 NECTKIA, 156 
 
 OAK-APPLE, 163 
 Oak-moth. See Tortrix 
 Ovary, 124, 130 ; figs. 33, 34 
 Overcrowding, 153 
 Ovules, 125, 128 ; figs. 34, 35 
 
 PARENCHYMA, 18 
 Peculiarities of oak, 142 
 Pericarp, 12, 131 ; figs. 2, 3, 37 
 Pericycle, 30, 32 ; fig. 5 
 Periderm, 93, 111, 117 
 Perigone, 124 
 Phellem. See Cork 
 Phelloderm, 117 
 Phellogen, 116 
 Phloem, 32, 40, 52-71, 92, 99, 
 
 103, 111 ; figs. 5, 6, 9, 17, 18, 
 
 24 
 
 Phyllactinia, 156 
 Phyliotaxis, 42, 47, 78, 122 
 Physiology of roots, 35 
 
 of leaf, 83-87, 91 
 
 of stem, 90 
 
 Piliferous layer, 24, 32, 91 ; figs. 
 
 5,6 
 Pith, 39, 52, 55, 98, 130 ; figs. 5, 
 
 12, 99 
 
 Plasticity of roots, 35 
 Plumule, 14, 21, 130; figs. 2, 3 
 Pollen, 123, 128 
 Pollination, 123, 126 
 Polyporus dryadeus, 159 ; fig. 45 
 
 igniarius, 159 ; fig. 44 
 
 sulphivreus, 159 
 Primary root, 14, 22 ; fig. 3
 
 INDEX 
 
 175 
 
 PKI 
 
 Primary shoot, 21, 39 ; fig. 4 
 Procambium, 42 
 Properties of oak, 136-146 
 Proleids, 17, 18 
 Protoplasm, 17 
 Pure oak woods, 147 
 
 QUALITIES of oak, 144 ; fig. 39 
 
 Quercite, 18 
 
 yuercus pedunculate, 7, 123, 138 
 
 JRobur, 7, 8 
 
 sessiliftora, 7, 76, 138 
 
 RADICLE, 14, 130; figs. 2, 3 
 Requirements of oak, 149 
 Hocking of root, 20, 35 
 Root-cap, 23, 25, 32 ; fig. 6 
 Root-cortex, 24, 28, 32, 91 ; figs. 
 
 5,6 
 Root-hairs, 23, 28, 36, 82, 97 ; 
 
 fig. 3 
 
 Root-system, 33, 91-97 
 Rosellinia, 153 
 
 SAPLING, 4, 89 
 Sap-wood. See Alburnum 
 Scale-leaves, 21 
 Secondary roots, 34 ; fig. 3 
 Seed of oak, 10, 12, 132 ; figs. 36, 
 
 37 
 
 Seed-coat. See Testa 
 Seed-leaves. See Cotyledons 
 Seed-trees, 149, 151 
 Seedling, 4, 19-24, 89 ; fig. 3 
 Sheath, fig. 5 
 Shoot-axis, 22, 39, 75, 98; figs. 9, 
 
 26 
 
 Shoot-system, 6, 39, 98-120 
 Shrinkage of oak, 139 
 Sieve-tubes, 32, 112 
 Silver fir, 148 
 Splitting of oak, 141 
 Spruce, 148 
 Stamen, 123 
 
 Starch-grains, 17, 18, 87 
 Sterevm hirsutum, 159 
 
 XYL 
 
 Stigma, 12, 123 
 
 Stipules, 22, 74, 122, 127; figs. 
 
 4, 19, 32 
 
 Stomata, 82 ; fig. 23 
 Stores of food materials, 20, 88 
 Structure of oak, 136 
 of root, 24 ; fig. 5 
 Swelling of oak, 140 
 
 TANNIN, 9, 17, 68, 135 
 Technology of oak, 136-146 
 Tenacity of oak, 140 
 Testa, 13, 131 ; figs. 2, 3 
 Thelephora Perdix, 159 ; fig. 42 
 Timber, 8, 136-146; figs. 26, i>6, 
 
 39 
 
 Tissues, 17, 39 
 Torsion of oak, 141 
 Tortrix viridana, 154 ; fig. 40 
 Tracheids, 60, 106, 108. 136 ; fi. 
 
 16 
 
 Tree-killing fungi, 157 
 Ty loses, 110; fig. 29 
 
 USES of oak, 143 
 
 VASCULAR bundles, 11, 17, 18, 
 
 26, 41-51, 100; figs. 2, 3, 9, 
 
 10-12 
 
 svstem, 51-71 
 Venation of leaf, 49, 70, 76, 79 ; 
 
 fig. 21 
 Vessels, 30, 31, 40, 55-62, 90, 
 
 106, 108, 136; figs. 12-16,38 
 
 WATER in oak, 139 
 Winter state, 7 
 Wood. See Xylem 
 Wood-cells, 31, 62, 106 ; fig. 16 
 
 XYLEM, 30, 40, 52-71, 92, 100, 
 103, 111 ; figs. 5, 6, 9, 13-15 
 24
 
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