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riDobern Science Series

EDITED BY SIR JOHN LUBBOCK, BART., M.P.

THE OAK

MODERN SCIENCE SERIES.

EdUed by Sir JOHN LUBBOCK, Bart., M. P.

L The Cause of an Ice Age.

By Sir Kobert Ball, LL. D., F. R. S.

n. The Horse:

A Study in Natural History,
By William Henry Flower, C. B.,
Director of the British Natural
History Museum.

m. The Oak;

A Popular Introduction to Forest
Botany.
By H. Marshall Ward, F. R. S.
In press :
rV. The Laws and Properties of Mat-
ter.
By R. T. Glazebrook, F. R. S., Fellow
of Trinity College, Cambridge.

New York : D. Appleton & Co., 1, 3, & 5 Bond St.

Digitized by tine Internet Arciiive

in 2010 witii funding from

University of Britisin Columbia Library

http://www.archive.org/details/oakpopularintroOOward

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The Oak in yuMMER.

THE OAK

A POPrLAR IXTRODUCTIOX
FOREST-BOTANY

TO

BY

H. MARSHALL WARD

M. A., F. R. S., F. L. S.

late fellow of christ's college. cambridge,

professor of botany at the iioyal indian" engineering college,

coopek's hill

NEW YORK

D. APPLETOX AXD COMPAXY

1892

Copyright, 1892,

ct d. appleton and company.
All rights reserved.

EDITOK'S IXTKODUCTIOX.

The works to be comprised in this Series are in-
tended to give on each subject the information which an
intelligent layman might wish to possess. They are not
primarily intended for the young, nor for the specialist,
though even to him they will doubtless be often useful
in supplying references, or suggesting lines of research.

Each book will be complete in itself, care, however,
being taken that while the books do not overlap, they
supplement each other ; and while scientific in treat-
ment, they will be, as far as possible, presented in
simple language, divested of needless technicalities.

The rapid progi-ess of science has made it more and
more difficult, and renders it now quite impossible, to
master the works which appear, almost daily, on various
branches of science, or to keep up with the proceedings
of our numerous Scientific Societies.

A distinguished statesman has recently expressed
the opinion, that we cannot expect in the next fifty
years any advance in science at all comparable to that of
the last half -century. Without wishing to dogmatise, I

vi EDITOR'S INTRODUCTION.

should be disposed to hope that in tlie future the prog-
ress of science will be even more rapid.

In the first place, the number of students is far
greater; in the second, our means of research — the
microscope and telescope, the spectroscope, photography,
and many other ingenious appliances — are being added
to and rendered more effective year by year ; and, above
all, the circle of science is ever widening, so that the
farther we advance the more numerous are the problems
opening out before us.

Xo doubt there are other Scientific Series, but it is
not believed that the present will exactly compete with
any of them. The International Scientific Series and
Nature Series are no doubt useful and excellent, and
some of the volumes contained in them would well
carry out the ideas of the Publishers, but, as a rule, they
are somewhat more technical and go into minuter de-
tails.

The names of the Authors are a sufficient guarantee
that the subjects will be treated in an interesting and
thoroughly scientific manner.

High Elms, Farnboeough:
November, 1891.

CONTENTS.

CHAPTER PAGE

Introduction 1

I. — The Acorn and its Germination — the Seedling . 10
II. — The Seedling and Young Plant , , . .24
III. — The Seedling and Young Plant {continued). Its

Shoot-system — Distribution of the Tissues . 39
IV. — The Seedling and Young Plant (continued).

Structure of the Vascular Tissues, etc. . 52
V. — The Seedling and Young Plant {continued). The

Buds and Leaves 72

VI. — The Tree — its Root-system 89

VII. — The Tree — its Shoot-system 98

VIII. — The Tree {continued). Inflorescence and Flow-
ers— Fruit and Seed 121

IX. — Oak Timber — its Structure and Technological

Peculiarities 136

X. — The Cultivation of the Oak, and the Diseases

AND Injuries to which it is subject . . . 147

XI. — Relationships of the Oaks — their Distribution

in Space and Time 167

THE OAK.

CHAPTER I.

IXTKODUCTIOX.

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 sen-
timental aspect of the " British oak " is not likely to dis-
appear even in these days of iron-clads 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
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.

2 THE OAK.

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, tak-
ing 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 in the English
and German names for the tree and its fruit, as seen by
comparing the Anglo-Saxon dc or mc^ the name of the
oak, with the English word, and with the German Eiclie
on the one hand, and with acorn (EiclieX) 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.

This is not the place to go further into what may be
called the folk-lore of the oak — a subject which would

INTRODUCTION. 3

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 rec-
ommend itself as that best adapted to the requirements
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
a certain structure and composition, and capable of
behaving in a definite manner when placed in the

4 THE OAK.

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, etc., 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 at-
tention 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, aiid 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 of
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 nat-
urally lead to that of the growth in thickness of the
tree — a matter of some complexity, and not to be under-
stood without the foregoing knowledge of structure.
Following what has been said concerning the normal

INTRODUCTIOX. 5

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 notwithstand-
ing, 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 princi-
pal or tap root and spreading lateral roots, which be-
come very 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 intol-
erant of anything like stagnant water, however, and will
succeed better in sandy loam and more open soils than
in richer ones improperly drained.

The shoot-system consists of the stem and all that it

6 THE OAK.

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 com-
-monly 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.

"While still young the tree is apt to keep its dead
leaves on the branches through the winter, or at least

/

Plate II.

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The Oak ix Wixter.

INTRODUCTION. 7

until a severe frost followed by a thaw brings them
down. The buds, leaves, and flowers are all much at-
tacked 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 favorable 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 fis-
sures, etc., 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 Quercus rohur.

Besides forms with less spreading crowns, the spe-
cies is frequently broken up into two — Q. pedunculata^
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 characters

8 THE OAK.

have also been described, but it is admitted that the
forms vary much, and it is very generally conceded 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 produced
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 forest-
er's art is practiced 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 tliat oak timber is
the heaviest, the toughest, the most beautiful, etc., of
known woods, but it is because it combines a good pro-

INTRODUCTION. 9

portion of weight, toughness, durability, and other qual-
ities 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.

CHAPTER II.

THE ACORN AND ITS GERMIXATIOX — THE SEEDLING.

When the acorns are falling in showers from the
oaks in October and Xovember, 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 cupule 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
of small points which have resulted from the breaking

THE ACORN AND ITS GERMINATION.

11

of some extremely delicate groujis of minute pipes,
called vascular bundles, which placed the acorn in com-
munication with the cup and the tree previous to the

\ .pl9^

Fig. 1. — Sprigs of oak, shcsving the habit and the arrangement of the
acorns, etc., in September. (After Kotschy.)

12 THE OAK.

ripening of tlie 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 jjericai-p (Fig. 2,]}). On removing
it we find a thin, papery membrane inside, adhering
partly to the above coat and partly to the seed inside.
This thin, shriveled, 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 usual-
ly 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 — name-
ly, the shriveling up of the tiny connecting cords,
etc. — also caused the separation of the seed from the
pericarp, and we may regard the former as a distinct
body.

Its shape is nearly the same as that of the acorn in
which it loosely fits, and it is usually closely covered

THE ACORX AND ITS GERMINATION.

13

with a thin, browu, wrinkled, papery membrane, which
is its own coat — the seed-coat, or testa (Fig. 2, t). 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

Fig. 2. — Sections of acorns in three planes at right angles to one an-
other. A, transverse ,■ B, longitudinal in the plane of the cotyledons,
(J) ; C, longitudinal across the plane of the cotyledons ; c, cotyledons ;
t, testa ; jo, pericarp ; s, scar, and ;•, radicle ; pi, plumule. The radicle,
plumule, and cotyledons together constitute the embryo. The em-
bryonic tissue is at ;• and pi. The dots in A, and the delicate veins
in E and C, are the vascular bundles.

commented upon further ':han to say that differences in
this respect are found according 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 withoiit 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 the

14 THE OAK.

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 towards 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 be-
yond the points of attachment to them ; the larger of
these ends has the shape of a conical bullet, and is di-
rected 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 phtmule (Fig. 2, pi), and it is destined to
develop into the stem and leaves of the oak. If the ob-
server takes the trouble to carefully separate the two

THE ACORN AND ITS GERillXATIOX. 15

large cotyledons, without tearing them away from the
structures just described, he will find that each is at-
tached 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
fit closely into a cavity formed by the two cotyledons,
and so do not interfere witli the rery 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
inclosing 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 en-
tirely of polygonal chambers or cells, with very thin
membranous walls, and densely filled with certain gran-
ule-like contents. These polygonal cells have not their

16 TUE OAK.

own independent walls, but the wall which divides any
two of 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 pro-
duced 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 par-
tition 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 juxtaposition. In other words, the cell-wall sepa-
rating 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 mem-
brane 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

THE ACORN AND ITS GERMINATION. 17

surfaces of extremely delicate strands or cords of rela-
tively very long and very narrow cells, the minute
structure of which we will not now stay to investigate,
but simply mention that these extremely fine cords,
running in the main longitudinally through the em-
bryo, 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 be-
neath its tij), and that these pass into the two coty-
ledons, and there branch and run in long strands to-
wards 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 limit-
ed by an epidermal tissue and transversed 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 emhryonic tissue.

As regards the contents and functions of these
tissues, the following remarks may suffice for the pres-
ent. The polygonal cells of the fundamental tissue of
the cotyledons are crowded with numerous brilliant
starch grains, of an oval shape and pearly luster, and
these lie imbedded 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

18 THE OAK.

and a nucleus, but this latter is only to be detected with
difficulty. Certain of the cells contain a dark-brown
pigment, composed of substances of the nature of tan-
nin ; and small quantities of a peculiar kind of sugar,
called querciie, are also found in the cells, together with
a bitter substance.

In the main, the above are stored up in the thin-
Avalled parenchyma cells as reserve materials, intended
to supply the growing embryo or seedling with nutri-
tious 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
quantities 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
mav even remain for uearlv a vear without anv con-

THE ACORN AND ITS GERMINATION. 19

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-
minate— a fact which suggests that some profound mo-
lecular or chemical changes have to be completed in the
living substance of the cells before further activity is
possible. \Ve have other reasons for believing that this
is so, and that, until certain ferments have been pre-
pared in the cells, their protojDlasm 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 temper-
ature rises in spring, the embryo in the acorn absorbs
water and oxygen, and swells, and the little radicle
elongates and drives its tip through the ruptured in
vestments at the thin end of the acorn, and at once
turns downward, and plunges slowly into the soil
(Fig. 3). This peculiarity of turning downward is so
marked that it manifests itself no matter in what posi-
tion 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 pos-
sible towards the center 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 inclosed 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

20

THE OAK.

in the cells of the cotyledons, as do all the parts of the
young seedling at this period. In fact, these stores in

Fig. 3. — I. Lonffitudinal section throuffh the posterior half of the em-
bryo, in a plane at right angles to the plane of separation between the
cotyledons (slightly magnified). II. Germinating embryo, with one
cotyledon removed. III. Acorn in an advanced stage of gennination.
a, the scar : s, pericai-p ; sA, testa ; J, plumule ; st, petioles of coty-
ledons, from between which the plumule, J, emerges ; Tie. hypocotyl ;
c, cotyledons ; /, vascular bundles ; w, radicle (primary root") ; «•'. sec-
ondary roots. Root -hairs are seen covering the latter and tlie anterior
part of the primary root in III. (After Sachs.)

THE ACORN AND ITS GERMINATION. 21

the cotyledons contribute to the support of the baby
plant for many months, and even two years may elapse
before they are entirely exhausted.

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, sf), 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 center of gravitation of the earth and into the
light and air ; and here, again, we have obviously adap-
tations 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

22

THE OAK.

minute bud in its axil. W'lien the primary shoot has
attained a length of about three inches there are usually
two of these small scale-leaves placed nearly opposite
one another close to the tip, and a little longer and nar-
rower 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 throwing
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

Fig. 4 — Gemiinating acorn,

showing the manner of from a point ou the young stem

emergence of the pri- ^|^ip|^ -g ^ |-^^|g J-^igher, and more
marj" shoot, and the first

scales (stipules) on the to one side, than that from which
latter. (After Eossmass- the lowermost One springs ; hence

a line joining the points of inser-
tion of the successive leaves describes an open spiral
round the shoot axis — i. e., the stem — and this of such
a kind that when the spiral comes to the sixth leaf up-

THE ACORN AND ITS GERMINATION. 23

ward it is vertically above the first or oldest leaf from
"vrhich we started, and has passed twice round the stem.

At the end of this first year, which we may term
the period of germination, the young oak-plant or seed-
ling has a primary root some twelve to eighteen inches
long, and with numerous shorter, spreading side root-
lets, 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 b}' a thin colorless cap — the root-cajD — the de-
scription 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.

CHAPTER III.

THE SEEDLING AND YOUNG PLANT.

Before proceeding to describe the further growth
and development of the seedling, it will be well to ex-
amine 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
accurately 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 micro-
scope, on the flat face of the almost colorless section. A
circular area of grayish 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 convenient-
ly 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 covering the tip of the root as a thimble covers the

Fig. 5. — A. Transverse section of yoiinsr root under a lens, showing the
axis cylinder, a ; epidermis or piliferous layer, e ; and the cortex be-
tween. B. The same, more highly magnified : c, cortex ; p, phloem ;
X, xylem ; C. A portion still more highly magnified : ph, phloem ;
jp, pith ; ^«r, pericycle ; sA, sheath (endodermis) ; other letters as
before.

nd of the finger, only we must imagine the extreme tipe
of the finger organically connected with the inside of
the cap to make the analogy suitable (see Fig. 6). The

26 THE OAK.

rest of the section would be mucli 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 pilif-
erous 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 axial
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 tijD of the root to
parts farther 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 conclusion, but it en-
ables 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 be-
hind ; the cells of which it is
comjjosed die and slough off as
the root pushes its way between
the abrading particles of soil.
Obviously this loss of worn-out
tissue must be made good in
some way, and closer examination
shows how this occurs. The ex-
treme tip of the root proper fits
closely into the cap, and evident-
ly 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, more-
over, we make another discovery,
namely, that all the cells are there alihe in shape,
size, and other peculiarities ; and if we could take a

Fig. 6. — Diagrammatic sec-
tion through the end of
the root of the oak. c,
root-cortex ; e, piliferous
layer ; re, root-cap ; m,
the true embryonic tis-
sue fso-called " growing-
point ") ; ph, phloem ; a;,
xvlem.

28 THE OAK.

transverse section exactly at this place we should see
no dilifercntiation into axial cylinder and root-cortex,
etc. ; the small circular mass would consist of cells
all alike, and with very thin walls and full of dense
protoplasm. This undifferentiated formative tissue is
called the embryonic tissue of the root (Fig. 6, in).
A little behind this we see the axis-cylinder and root-
cortex already formed ; still farther away we see the
vascular bundles appearing, first as very thin cords, and
then getting stronger . and stronger as wo recede from
the tip (Fig. G, 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 jjarts 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-cyl-
inder is sharply marked and has well-developed vascular
bundles, 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 groAV-
ing-point, and consisted of embryonic tissue with the
cells all alike. Or we may put it in a different way
thus : the present growing-point consists of embryonic

THE SEEDLING AND YOUNG PLANT. 29

cells all alike ; in a few days some of these cells will
have changed into constituents of the axis-cylinder and
cortex, and subsequently some of them will give rise to
vascular bundles, etc. Xot all, however ; and it is neces-
sary to understand that as the embryonic tissue moves
onward 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 discolored,
being, in fact, converted into a brown, cork -like sub-
stance impervious to moisture, or nearly so ; conse-
quently 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 demarkated off
from the cortex by a single layer of cells shaped like
bricks, and with a sort of black dot on the radial walls ;
this is called the endodermis, and may be regarded as a

30 THE OAK.

sheath limiting wliat belongs to the axis-cylinder (Fig.
5, c, sh). 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 endoder-
mis 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 bun-
dles, 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 fol-
lowing facts about them : In the first place, they are
smaller nearer the pericycle than they are nearer the
center of the axial cylinder, and the comparison of

THE SEEDLING AND YOUNG PLANT. 31

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
caliber 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 inside ;
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.
Consequently these groups of xylem vessels are said to
consist of spiral and pitted vessels, and their chief func-
tion 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.

Returning 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
distinct outlines ; these alternate groups are known as

32 THE OAK.

phloem, and we may shortly examine tlie elements of
which they are composed, as before, by comparing sec-
tions of various kinds.

Here, again, we find the chief structures in the
phloem are also vessels — i. e., long, tubular organs — but
very different 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
lignified Avails of the xylem vessels) ; then, again, they
contain protoplasm and other organized 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 be-
tween the sieve-tubes.

If we shortly summarize 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 cov-
ered by the root-cap, which is organically connected
with the embryonic tissue which forms all these struct-
nres. The axis-cylinder is somewhat complex ; it is
sheathed by the endodermis and the pericyle, the lat-
ter of which gives origin to the new rootlets. Inside
the pericycle are the vascular bundles running up and
down as separate, alternate cords of xylem and phloem ;

THE SEEDLING AND YOUNG PLANT.

33

Fig. 7. — Portion of young growing ends of more advanced root, with nu-
merous rootlets. Some of the latter are much branched into tuft-like
collections, m ; these form the so-called Mycorhiza. Natural size.

34 THE OAK.

the xylem consists of vessels and cells, the former de-
veloped centripetally, while the phloem consists of
sieve-tubes and cells. Any cell-tissue which may lie
in the center 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
behavior in the soil as the young seedling develops fur-
ther, and in the light of the above anatomical facts.

Although the root-system of the young plant is reg-
ularly constituted of a series of lateral rootlets spring-
ing from the primary root, the orderly arrangement is
soon disturbed when the tertiary and other rootlets
begin to develop from the secondary rootlets ; more-
over, 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 bor-
ing into the soil, and, provided the latter is sufficiently
deep and otherwise suitable, the tap-root will go down
a foot or more in the first year. As the roots thick-
en they exhibit considerable plasticity, as is especially
evinced on rocky ground, where the older roots may
often be found in cracks in the rocks, so compressed that
they form mere flattened sheets many times broader
than they are thick (Fig. 8).

TEE SEEDLING AND YOUNG PLANT.

35

It has already been men-
tioned that the tip of the
young primar}' root circum-
nutates, and Darwin also
found that the tip of the
radicle is extremely sen-
sitive to the irritation of
small bodies in contact with
it. It is also positively geo-
tropic, directing itself ver-
tically downward if the par-
tially grown radicle is laid
horizontally ; and it may be
assumed from the behavior
of other plants of the same
kind that the tijD of the
radicle is negatively helio-
tropic — i. e., it turns away
from the source of light.
Whether it is also sensitive
to differences in the degree
of moisture on different
sides (hydrotropic), or to
differences of temperature
( thermotropic ), is not
known, but it may be in-
ferred that such is the
case ; nor do we know
whether it is affected by electric currents in the earth

Fig. 8. — Portion of an older root of
an oak, which had penetrated
while young between two pieces
of hard rock, and had to adapt
its form accordingly as it thick-
ened. (After Dobner.)

36 THE OAK.

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
secondary, tertiary, etc., 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 ex-
terior. 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, cor-
responding to an epidermis — root-hairs are developed at
some little distance behind the root-cap, and these su-
perficial cellular outgrowths also rise in acropetal suc-
cession, the older ones behind dying oS as the younger
ones arise farther forward. If we bear in mind all
that has been shortly stated above, it will be very easy
to figure the behavior of the root-system as it pene-
trates 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 millimetres behind the tip, and these attach
themselves to the 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

THE SEEDLING AND YOUNG PLANT. 37

thin-walled cells full of relatively stiff protoj)lasm with
very little water. Hence the growing-j)oint is a firm
body. The most active growth of the root takes place
at a region several millimetres behind the root-cap, be-
tween 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, etc., of which the latter
is comj)osed. This driving in is aided by the negative
heliotropism, the positive geotropism, the circumnuta-
tion, and other irritabilities of the apical j)ortions of
the root, and it bores its way several centimetres down-
ward. As it lengthens — by the addition of cells pro-
duced by the di\asion of those of the embryonic tissue,
and by their successive elongation — the older parts be-
hind go on i^roducing root-hairs, and thus a vertical
cylinder of soil around the primary root is gradually
laid under contribution for water containing dissolved
salts, etc. 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 devel-
oping 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 grows
out at an obtuse angle from the primary root, and not
vertically downward, and as it does so a similar wave
of root-hairs is developed along it ; thus a series of

38 THE OAK.

nearly horizontal radiating cylinders of soil are placed
under contribution as before. Then the secondary root-
lets emit tertiary rootlets in all directions — these and
the rootlets of a higher order growing without any par-
ticular reference to the direction of gravitation, light,
etc. — and so place successive cylinders of soil in all di-
rections under contribution as before. By this time,
however, the symmetry of the root-system is being dis-
turbed 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 tan-
gled mass of roots now loermeating the soil in all direc-
tions.

These roots supjily 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 absorbing roots, but become merely larger and
larger channels for water, and girder-like supporting
organs.

CHAPTER IV.

THE SEEDLIXG AND TOUXG PLANT {continued).

Its SnooT-SYSTEM — Distribution of the Tissues.

I NOW proceed to describe the chief features of im-
portance 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 ah'eady learned 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 stractures developed from the plumule.

Such sections show that Ave 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 epider-
mis ; and the remainder of the section composes the
third system, often termed the fundamental tissue, and
divided arbitrarily into three regions — the pith, the cor-
tex, 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

Fig. 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 bundles ; M and s, the vascular bundles passing down
from the leaves — M the median bimdles and « 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 Mtlller.)

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 axis-cylinder, nearest the cor-
tex, and the succeeding vessels are formed in centripetal
order from these points. In the young stem the exact

THE SEEDLING AND YOUNG PLANT. 41

converse occurs — the first spiral vessels arise near the
center of the stem, and development proceeds centrifu-
gally 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
communication 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 em-
bryonic tissue, all the cells of which are practically alike
— small, polygonal, thin-walled cells, with large nuclei
and much j)rotoplasm, but Avithout sap-vacuoles ; these
cells are in a state of active division, those in the in-
terior 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 differ-
ences 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 ar-
ranged on the stem. This is of such a nature that each
leaf stands some distance above and to one side of its

42 THE OAK.

next neighbor below, and if a line be drawn from the
insertion of any one leaf through the points of inser-
tion 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 two fifths.

The previously homogeneous embryonic tissue in
the section now shows certain patches of grayer, closer
tissue, arranged round the center 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 gray 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 inclose a five-angled mass of central tissue (the
pith), the five comers pointing to the angles of the
young stem to which the leaves are attached. At the
comers or ends of the rays just referred to are in some
cases two or three smaller strands.

THE SEEDLING AXD YOCXG PLANT. 43

Xow, the important point to apprehend first is that
these strands at the corners (ii, 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 {m?n, 7ns, and ms in
Fig. 10), pass directly into a given leaf, m wi, 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 in Fig. lU), 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 subse-
quently.

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 intemodes (marked by the horizontal

44

THE OAK.

lines), turning to one side and becoming continuous in
the fifth internode with a strand coming off from an-
other leaf situated at another of the angles at a differ-
ent level. The strands which stand next to this me-
dian one— one on each side {ms)— at first also i)ass

FiCr. 10. — Diairram of the course of the bundles M, «, and «' of Fig. 10, 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) ; I, I
are the lateral bundles s and s' of Fig. 9, A. The small branches fst
go into the stipules. (After Frank.)

vertically down together with it, but at about the
second or third internode below they break up into
smaller strands, which 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 m?n, indeed, running actually in the angle
through five internodes.

THE SEEDLING AND YOUNG PLANT.

45

To right and left in
Fig. 10 are seen two
strands, 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
considering is inserted,
they turn in towards
the leaf, and erentually
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 /, Z-, Z^,
etc., in the diagram,

Fig. 11. — Diagram of the course
of the vascular bundles as
they come down from the
leaves into the stem. The
horizontal dotted lines rep-
resent the levels of sucess-
ive leaves ; the triangular
white area beneath the up-
per letter z is the insertion
of a leaf. Each group of
bundles form a leaf, as mm,
ms, ?«<, etc. (see text), descends into the stem, and joins with the bun-
dles from other leaves after running through several internodes. The
other letters refer to the bundles from other leaves. (After Frank.)

46 TUE OAK.

Fig. 11) receive contributions at successive nodes, and
pass down as stronger and stronger strands through
about seven interuodcs, their lower ends losing them-
selves by joining to others ; and, in fact, the larger bun-
dles 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 Avill
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 ex-
tent 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 outward 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

TDE SEEDLING AND YOUNG PLANT. 47

stem from the insertion of a leaf is spoken of collect-
ively 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 two fifths, there will be twenty-five
bundles in various stages of separation or conjunction
coming down in the five iuternodes between any one
leaf and the leaf 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 downward,
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 center — 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, thev are termed " common bun-

48 THE OAK.

dies." We have seen that a given strand or bundle may
run for part of its course simply side by side with an-
other and separate from it ; at other parts of the course
the bundles may be united with others. In tlie case of
the oak it will be clearly borne in mind that the indi-
vidual 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 symmetrically disposed between the pith and the
cortex, and that the latter (cortex and pith) are in con-
nection through the meshes between the interpectinat-
iug and concomitant vascular bundles. These radial
connections 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

THE SEEDLING AND YOUXG PLANT. 49

those primary medullary rays which happen to have
been cut running between the bundles.

If we now trace the vascular bundles of the leaf-
trace in the other direction — that is, up 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 tij)s 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 flat they are
at the leaf insertion (Fig. 10). Soon after entering 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
inclosing a pith ; moreover, the xylem portions of these
bundles are all turned inward 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 mid-
ribs and chief lateral ribs they interosculate in various
degrees, and give off smaller side branches into the
mesophyll of the leaf (see Chapter VI).

50 THE OAK.

The veins which spring from the chief lateral ribs
run towards one another and anastomose, giving off
smaller veins which form a network in the area in-
cluded by them. In tlie neighborhood 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 center of a mesh and end there. Eound the ex-
treme 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 (cf. 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, z)\
this is the middle strand coming down from the leaf

THE SEEDLING AND YOUNG PLANT. 51

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 stem. Several other small
strands also are formed, as at z, to complete the filling
up the gap, and these may be called completing bun-
dles. These connecting and completing bundles en-
able the young shoot as it develops from the bud to
inclose its own pith in a cylinder of vascular tissue con-
tinuous 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 remoA'e 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 subse-
quently.

CHAPTER V.

THE SEEDLING AND YOUNG PLANT {continued).

Stkucture of the Vascular Tissues, etc.

Before plunging into the intricacies of the vascu-
lar 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 center of the stem, and a phloem porfiou
on the side next the periphery, and these portions are
separated by the cambium layer. The tissue in the
center of the stem, and surrounded by the ring of bun-
dles, 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 pri-
mary medullary 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. Xoav, the cambium
of the individual bundles soon unites across the primary
medullary rays, and thus a complete hollow cylinder of
cambium is formed throughout the stem, and, as we
shall see later, throughout the root also. For the pres-

THE SEEDLING AND YOUXG PLANT. 53

ent it must suffice to notice that the cells of this cam-
bium cylinder go on developing into new xvlem, or
phloem, or medullary rays, according to position and
circiunstances ; 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 vascu-
lar bundles are found to present a definite and symmet-
rical structure, easily distinguished from that of the
fundamental cell-tissue in which they are, so to speak,
imbedded (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 proto-
plasm and nuclei, and in winter become filled to crowd-
ing 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

tannin, and starch in winter. At the rounded angles

of the vascular wedges the cells are smaller than else-
5

54

TUE OAK.

%''

Fig. 12. — Transverse section of youn;^ stem, showinnr primary vaseulur
bundles, etc., highly magnified, a and h. the pitli ; c, primary cortex:
■2, epidermis ; 7i, periderm (cork); {/, collenehyma. Two complete
primary vascular bundles, and parts of two others, are shown, se]ia-
rated by the primary medullary rays, r, spiral vessels fprotoxylem);
/:. bast-fibers (protophlogm) ; n, m, cambium, separating tlie phloCm
from the xylem ; p, wood-parenchyma. Secondary medullary rays
are seen in the bundles, as also are pitted vessels of different sixes.
(Th- Ilartig.)

THE SEEDLING AND YOUNG PLANT, 55

where in the pith, but otherwise their shape, etc., 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.

Imbedded, 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 tracheas, or
vessels with unrollable 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 caliber, and stand in
radial, short rows, single or branched ; those first devel-
oped— 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 sj)iral vessels are always very narrow (Fig.
16, sp). Occasionally some of these vessels have annular
instead of spiral thickenings.

Of colirse, 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 of longi-
tudinal sections also show that these vessels at first sim-
ply consist of longitudinal rows of very narrow, verti-

56 TUE OAK.

cally 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 outward 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 strength-
ened with spiral thickenings, but are thickened and fur-
nished Avith bordered pits, the shape and characters of
which are best seen from the illustrations (Figs. 14-16).
These larger vessels are not always associated with the
radial rows of spiral vessels, but may be scattered be-
tween 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 varia])le (Fig. 16, 2^r).

The large j^itted vessels form groups with parenchyma
and wood-cells scattered between, and are confined chief-
ly to the inner parts, forming radiating series side by
side ; in the outer parts of the bundle are various groups
of smaller vessels — the groups being rounded, or in ra-
dial rows, or curved or oblique rows.

THE SEEDLING AND YOUNG PLANT

58

THE OAK.

THE SEEDLING AND YOUNG PLANT.

59

60 THE OAK.

Successive sections prove that the vessels in the bun-
dle change in number — i. e., there are fewer when pass-
ing from stem to leaf. A vessel may end in an inter-
pectinating, 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 ves-
sels, following on the spiral vessels, we find libriform
fibers, tracheids, wood-parenchyma, and secondary rays
of parenchyma ; the tracheids are esj)ecially in the neigh-
borhood of the vessels (see Fig. 14).

The tracheids are long cells with gradually tapering
ends, and the walls rather thick but by no means obscur-
ing the lumen ; on the walls are numerous, usually elon-
gated, oblique or horizontal bordered pits. These pits
occur whether the next element is a tracheid, a vessel,
or fibers or cells of any kind (Fig. 16, tr).

The length of the tracheids varies, and the diameter
is also variable.

The libriform fibers 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
the true fibers and tracheids ; they occur in those parts
where masses of true fibers abut on the groups consist-

THE SEEDLING AND YOUNG PLANT.

61

f

Fig. 16.— The various chief elements of the -svood of the oak, isolated by-
maceration, and hijrhly magnified. /, a fiber, distinguished by its
thick walls, simple slit-like pits, and no contents ; tv. p, part of a row
of wood-parenchyma cells, with simple pits, and containing starch in
"winter; i?\ a tracheid, distinguished from the fiber especially by its
bordered pits ; p.i\ part of a rather large pitted vessel, made up of
communicating segments, each of which coi-responds to a tracheid,
and has bordered pits on its walls ; sp. part of a spiral vessel.

g2 THE OAK.

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 fibers. 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-parenchma consists of vertical groups of
short cells, each group having the fusiform shape of a
tracheid (Fig. 16, lo.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 bor-
dered 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 tra-
cheids and fibers, and predominates in the more vascular
parts ; after two to four or more fibers in a radial row a
single parenchyma cell may often be seen, but other ar-
rangements occur. In the parts where fewer vessels oc-
cur it is not uncommon to find a series of radial rows of

THE SEEDLING AND YOUNG PLANT. 63

about six to ten fibers 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 hap-
pens, 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, etc., with the cells of
the primary medullary rays. In contact with one an-
other 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 transformed by horizontal divisions, etc., into ver-
tical rows of ray parenchyma, undergo repeated tangen-
tial longitudinal 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 gra-
dations occur. The mother-cells may be very long,
evidently corresponding to two, and they may also di-
vide in the radial longitudinal plane, and the ray be-
come 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 sometimes
cease within the first year's bundle : but the difficulty

64 TUE OAK.

comes in of deciding whether a continuatiou 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,
7i, 7)i). 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 fibers 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 neighbors 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 fibers
with their lumina nearly obliterated ; these are long,
spindle-shaped fibers much like the fibers of the wood.

THE SEEDLIXG AXD YOUXG PLANT. 65

As a rule, the outer and inner side of these bast
grouijs are in contact with vertical rows of nearly cubi-
cal parenchyma cells, strongly thickened on the side next
the bast, and each nearly filled with a crystalline clump
or with an imj^erfectly formed crystal of oxalate of lime.
Similar vertical rows of crystal cells may also occur
within the groups of bast fibers, 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 prosen-
chymatous mother-cells, the conical ends being found in
macerations.

Within the groups of bast fibers are yet other rows,
similarly formed, of parenchyma (Fig. 17, hp)^ 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 fibers 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, hs).

The remaining younger part of the bast consists
chiefly of delicate, apparently irregular parenchyma
cells with cellulose walls ; this is easily traced to the

Fig. 17.— Transverse section of cortex and phlegm of oak (hiirlily masni-
fied). 1-, the periderm (cork), which has replaced the epidermis; c,
coUeneh yma ; d, cells of cortex containing crystals of oxalate of lime ;
«, schlerenchyma cells. All these belonor to the cortex proper. Be-
low these come tlie phlogm : J, ft, groups of hard bast fibers ; hp,
phloem-parenchyma ; bs, medullary ray ; e, cells containing crystals
of oxalate of lime. (Luerssen.)

THE SEEDLING AND YOUNG PLANT. 67

cambium. The radial rows of tlie 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 ef-
fective in causing displacements. The bast cells devel-
oped earlier, and therefore more distant from the cam-
bium zone, now lie in the perceptibly large periphery,
and thus undergo tangential extension or radial com-
pression, and so undergo changes of form. Besides these
alterations 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 farther out, where great
irregularity 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, in-
terpectinating 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
the above cells are found to be septate and cut up into
parenchyma-like cells — irregular bast-parenchyma. The

(38 TUE OAK.

walls, especially the longitudinal walls, are marked either
with crowded small pits giving a reticulate appearance,
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 fibers of exactly the
same character as those of the primordial groups.

It is obvious that while tlie wood elements remain
fixed in the cylindrical surface where they are developed,
the bast elements formed outside the cambium, being
driven outward in consequence of growth in thickness,
come to lie in a layer of continually increasing radius.
If these last elements were unyielding and lignified there
would be a solid sheath of elements which refused to ex-
tend by mechanical distention, 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-
ness or breadth of the bundles at different points, such
as where other bundles join or leave them. As the leaf-
trace passes into the venation of the leaf the ends be-

THE SEEDLING AND YOUNG PLANT.

69

come thinner (Fig. 21), and the same is found as it tails
off below ; changes in structure also appear in the leaves.

Fig. 18. — Longitudinal radial section of the cortex and phloem of oak.
Eeferences as in Fig. 17. (Luerssen.)

The first noticeable change is the diminution in
the number of wood fibers and the presence of narrow

70 THE OAK.

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 traclieids with reticulated or
spiral thickenings occur, fitting obliquely at tlieir point-
ed ends, and which are shorter and sliorter as we ap-
proach 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 shorten-
ing 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 tlie decreased supply of fluids, etc., on the one
hand, and the smaller weight and strains to be sup-
ported 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 fibers and vessels, until finally only delicate tracheids
are left (Fig. 21), the thickenings of which are at length
not spirals or nets for the most part, but irregular pit-
tings. Moreover, they are nearly isolated. Xeverthe-
less, the inner elements can be distinguished as primary

THE SEEDLING AND YOUNG PLANT. 71

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 nar-
rower. The pith consists of parenchyma, chiefly un-
lignified 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).

CHAPTER VI.

THE SEEDLING AXD YOUXG 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 character-
istically short and broad ovoid bodies, consisting of
numerous overlapping bro^vn scales covered with short,
silky hairs, especially at the margins (Fig. 19). These
scales are really the stipules of arrested leaves, as is
shoAvn by the proper leaf-blades being developed as well
under certain circumstances, such as when nutritive ma-
terials are directed to the young buds. The same mor-
phological fact is also shown by the position of the in-
florescences 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 impor-
tance 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 young shoots — which have by

THE SEEDLING AND YOUNG PLANT. 73

that time ceased to elongate to any considerable extent
farther — they may be seen as small, green, hairy bodies.
During the remainder of the summer the chief changes
going on in these buds is a slow swelling, due to the

Fig. 19. — A. End of a branch of oak showing the characteristic winter
buds. B. A group of buds (slightly magnified): a, bud-scales; d,
leaf-scars. C. The same, in longitudinal section : a, bud-scales (stip-
ules) ; 6, yoirng leaves ; c, vascular bundles ; </, leaf-scars. (Prantl
and Hartig.)

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
conical growing-point, consisting of embryonic tissue,

74 TUE OAK.

occupies the center ; 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) overlapping scales, and be-
tween several pairs of the upper of these the male in-
florescences develop. The female inflorescences 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
following a dry, hot summer, to find the winter buds
beginning to shoot out in August, and not passing into
the prolonged state of dormancy. Such shoots are
known as Lammas shoots. In some districts the oak

THE SEEDLING AND YOUNG PLANT. 75

forms 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 tem-
perature and other conditions improve in the spring, for
instance, the process of cell-division in the growing-
point (and its derivatives, the young leaves, etc.) goes
on rapidly, and the stores of nourishment already there
and in the i)ith and other tissues close at hand are used
up. This originates a series of currents of food materi-
als setting slowly towards these centers of consumption
from other parts of the tree, and very soon the numer-
ous cells developed begin to absorb water with relatively
enormous rapidity and vigor. This brings about two
chief changes — the rapid elongation of the parts of the
cone situated between the points of insertion of suc-
cessive leaves (i. e., the internodes), and the almost si-
multaneous expansion 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 j)art already in existence. The chief
changes which follow consist in the perfection of the
structures — the development and thickening of vascular
tissues, cell-walls, etc.

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

76 THE OAK.

shoot shows a number of small scars in a close spiral.
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 vigor 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 prolonged 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 raceform 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 mid-
rib at an angle of about forty-five degrees to the tip of
each lobe, the points of origin being alternate or nearly
opposite, and the angle referred to subtending forward.
These principal ribs are prominent below, but not at all
so above. Tlie leaf -tissue (mesophyll) between these is
permeated by numerous smaller vascular bundles united

THE SEEDLING AND YOUNG PLANT

77

into an irregular network, but so arranged that they
leave between them nearly equal small areas not trav-
ersed bv bundles.

Fig. 20. — Sprigs of oak, showing the habit and the arrangement of the
acorns, etc., in September. (After Kotschy.)

78

THE OAK.

When young, the leaves are red, gradually becoming
a bright apple-green, and finally — in the autumn — be-
coming russet-brown in color. 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 membrane. As the
leaves approach ma-
turity the lamina be-
comes bright and
hard.

The arrangement of
the leaves is expressed
by the fraction two
fifths, as already de-
scribed, each node giv-
ing off one leaf at an
open angle, the points
of insertion being so arranged tliat 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 arrange-

FiG. 21. — A portion of the ultimate raml-
lications of the vascular bundles, show-
ing tracheids only, isolated from the
leaf by maceration.

THE SEEDLING AXD YOUNG PLANT. 79

ment, however, otlier dispositions are occasionally 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 upward.

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 envel-
ops the whole of the remaining leaf -tissues. Inside 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, imbedded, 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-

80

THE OAK.

tem of the latter lower down. Now the next point to be
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 magnified and
semi-diagrammatic, to show the general arrangement of the prin-
cipal vascular bundles a-s seen cut across : ?m, midrib : e, marginal
veins ; s, lateral branches of midrib. Other smaller veins scattered
oetween. B. A highly magnified vertical section of part of the
above at a place free fi-om vascular bundles : -u, upper epidermis, with
cuticle, c; p, palisade cells; eA, chlorophyll corpuscles, only drawn
in a few cells; m, spongy tissue of mesophyll ; i.s, intercellular pas-
sages communicating with the stoma, st, in the lower epidermis, 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 ab-
sorbed 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, etc.) of the
venation 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 chlorojohyll
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

82 THE OAK.

a minute gap between them, and the gap communicates
with the iutercelkilar air-cavities between the cells of
the spongy mesophyll (Fig. 22, st). If we remove a
piece of this epidermis, and look at it as laid flat (in-
stead 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 realize 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 divarication of the inner concave sides of the curved
guard-cells.

If this is clear, it will be readily understood that
these stomata can regiTlate 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-vapor 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,

THE SEEDLING AND YOUNG PLANT.

83

and phosphates of lime, magnesia, and potash — just as
there are in ordinary well-water. This extremely dilute
solution passes into the root-fibers and up through the

Fig. 23. — A. A small piece of the lower epidermis removed (and highly
magnified) to show the stomata, g ; 7t, 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 chloroiDhyll corpuscles ;
«, orifice of stoma.

vessels, etc., of the vascular bundles of the roots, collect-
ing into the larger and larger channels until it reaches

84 THE OAK.

the stem ; here it passes up the xylem to the branches,
petioles, and leaf-venation — always in the wood — and
is finally distributed to the mesophyll cells, which ab-
sorb 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 tliis
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 eifective
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 evap-
oration is, the more salts the mesophyll cells will ac-
quire in a given time, because, of course, the salts do
not pass away in the evaporated water but are left in

THE SEEDLING AND YOUNG PLANT. So

the cells. It lias been calculated tliat an oak-tree may
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.

Xow 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 colorless protoplasm, which incloses a large
sap-cavity (vacuole) ; in the protoplasm are imbedded a
number of bright-green, rounded chlorophyll corpuscles,
a relatively large nucleus, and a few less conspicuous
granules, etc. 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 colorless 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 chloro-
phyll corpuscle consists of a rounded mass of proto-
plasmic substance of somewhat spongy texture, contain-
ing the peculiar green body, chlorophyll, imbedded in
it as in a matrix. These chlorophyll corpuscles are liv-
ing organs, and they require food materials — water, oxy-

86 THE OAK.

gen, etc. — for the support of their life processes, just as
do the other living parts of the cell — e. g., the colorless
protoplasm and nucleus. They obtain these from the
cell-sap, through the agency of the colorless protoplasm
in which they reside.

In order that they may perform their functions prop-
erly, 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 meso-
phyll of the leaf to be. In fact, the flat, thin, expanded
form of the leaf is a direct adaptation to the end that
these chloroi^hyll corpuscles shall be properly illumi-
nated by the sunlight ; moreover, the large intercellular
passages which communicate by thousands of stomata
with the atmosphere insure their being thoroughly
aerated. In addition to allowing the free access of the
oxygen of the air, moreover, these intercellular passages
admit of the small quantities of carbon dioxide in the
atmosphere also reaching the chlorophyll corpuscles.
Oxygen and carbon dioxide, therefore, are found dis-
solved 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 sun-
light— i. e., energetic vibrations of the ether which per-

THE SEEDLING AND YOUNG PLANT. 87

vades the universe — penetrate into the system. By
means of the energy thus derived from the sun, the
molecules of carbon dioxide and water are broken up in
the meshes of this chlorophyll corpuscle, and experi-
ments prove that the chlorophyll substance plays the
part of the " trap to catch a sunbeam." AVe are not
concerned with the hypothetical explanations offered for
all the details of this remarkable process, but the pres-
ent position of science enables us to say that, be these
what they may, the chlorophyll corpuscle gains energy
from the sun, and brings this energy to bear on the car-
bon dioxide and water in such a Avay that it does work
in tearing asunder their molecules in the substance of
the corpuscle. Then a curious series of results follow.
The carbon, oxygen, and hydrogen undergo new re-ar-
rangements, 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 pas-
sages, and thence through the stomata into the atmos-
phere.

It will be obvious from the foregoing that the gran-
ules of starch represent so much matter (especially car-
bon) obtained from the atmosphere outside the plant,
and so much energy obtained from the sun ; each gran-
ule 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

88 THE OAK.

going into details concerning the nse which the plant
makes of this starch, and it must suffice to say that the
starch serves as the basis of all the constructive materi-
als used by the tree. Thus it is converted into a soluble
form, and combined with nitrogen, phosphorus, sulphur,
etc. (obtained from the earth-salts), to make new proto-
plasmic materials, and it passes down from the leaves to
nourish all the living cells that require it, in the embry-
onic tissue at the apex of the roots, and that at the apex
of the stem and branches, buds, etc., and some of it
passes to nourish the cambium cells, the developing flow-
ers, acorns, etc. ; 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 pro-
portion of salts taken up by the roots being quite incon-
siderable in comparison — we obtain some idea of the
enormous gain of matter and energy from the outside
universe which goes on each summer.

CHAPTEE VII.

THE TKEE — 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 sapling ; 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,
the total area of the leaf -surface exposed to the air and

90 THE OAK.

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 of
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 need-
ed could not be obtained. In the second place, these
larger and larger quantities of water require correspond-
ing increase in the sectional area of the pipes or water
conduits — i. e., the vessels of the wood — through which
they have to pass in order to reach the leaves. This is
insured by the increase in diameter of the stem and
main root and their chief branches, a larger number
of vessels, etc., being added each season. In the third
place, as the leaf-crown enlarges its w^eight increases,
and the surface it exposes to the swaying action of the
wind is correspondingly greater; consequently the ne-
cessity arises for more strength and rigidity in the sup-
porting stem, 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 thickening 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 TREE— ITS ROOT-SYSTEM. QJ

that the substances for making new roots and shoots,
new wood, and new leaves, etc., 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 ob-
tained from the air in the chlorophyll corpuscles, and
consequently a larger yield of plant-forming materials
is possible to meet the demands of the ever-growing
organs.

My present purpose is to describe how the thicken-
ing 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
filiform 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 bai'k.

The first changes which take place Avhen 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 of!
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

92 TUE OAK.

axis-cylinder (see Fig. 5), and especially by means of
tangential walls. The result of this activity is the de-
velopment 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 ; wliile the much more numerous cells formed
on the inner side — i. e., nearest the center 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 groujis, and not radi-
ally outside them (Fig. 24, se.x and se.ph). Moreover,
the youngest vessels are now nearest the cambium,
whence the order of development has become the con-

THE TREE— ITS ROOT-SYSTEM. 93

verse of that of tlie jJi'imary xylem ; there are also no
spiral vessels formed now. In fact, the structure of the
vascular bundles of the root has now changed its char-
acter, and from this point forward 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 in-
creases 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 pri-
mary 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 cylin-
der 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.

94

THE OAK.

Then, inside tliis periderm we shall find the phloem
forming an almost continuous ring (Fig. 24, se.jjJi), and

c.cam.

se.X

Fig. 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, jyr.fh, and outside the primary xylem, pr.x ; and
the larger figure shows the results of its activity in the formation of
secondary phloem, se.ph, inside the primary, and secondary xylem,
se.X, between the primary xylem groups. In both cases, ep., piliferous
layer; c, cortex; P, pith ; sh, endodennis. Within the latter lies the
pericycle, in which the cork cambium, c.cam, is now developed.

consisting chiefly of the sieve-tubes and cells developed
from the cambium cylinder, the small primary phloem

TDE TREE— ITS ROOT-SYSTEM. 95

masses being almost undistinguishably pressed into
{pr.ph).

In the center of the section will be a small speck,
around which the microscopic primary xylem groups
{pr.x) are arranged ; but these, again, are merged be-
tween 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 aro 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 consideration for the present.

Mention must now be made of a remarkable biologi-
cal phenomenon in connection with the roots of the oak.
This is the very common occurrence of young rootlets
clothed by a fungus mycelium ; the mycelium is found

96

THE OAK.

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 cavities of
the cells nor deeper into the tissues. Loose hyphee also

r.c.

Fig. 25. — Longitudinal section of the tip of one of the roots marked m in
Fig. 7, the outer layers of which are infested with fungus hyph8e,y
(mycorhiza) ; r.c, root-cap ; m, embryonic tissue from which all
originates ; P, pith ; sj), spiral vessels of the primary xylem ; c,
cortex.

radiate into the soil around, and often simulate the root-
hairs of other plants, which, in fact, they are said to
replace (Fig. 2o,f). These hyphae are extremely fine

THE TREE— ITS ROOT-SYSTEM. 97

tubes of a cellulose-like substance, filled with the living
protoplasms of the fungus, and possess the remarkable
property of being able to bore their way through or be-
tween the cellulose walls of the roots. The fungus at-
tacks the plant about the second year, and it is not dif-
ficult 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 mycorJiiza, and the view is gain-
ing 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 sub-
stance 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 avail-
able to the root sooner than would otherwise be the case.
The systematic position of these remarkable fungi is not
yet ascertained, but there is some evidence for the view
that the mycelium is that of a truffle, though the ques-
tion is still an open one.

CHAPTER VIII.

THE TREE — ITS SIIOOT-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 vas-
cular 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
cambium C3'linder which was developed, as we saw, in
the primary 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 consider-
ation all we have learned so far. The pith is the same

THE TREE— 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. 2*5. — Photograph of the transverse section of a log of oak. about one
sixth natural size. The cortex and bark are removed, and the outline
is bounded by the cambium. The pith appears as a mere dot in the
center ; the medullary 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 medullary ray as the
section dried. (MuUer.)

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

100 THE OAK.

has also been formed between these outer protective
layers and the cambium.

AVe have now to obtain some ideas as to these curi-
ous processes of increase in thickness of the stems and
branches.

The first thing to insure this is to understand the
constitution and behavior 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 pri-
mary vascular bundle is separated from the phloem of
the same bundle by a thin strand of cambium (Figs. 9
and 12) ; we also saw that the bundles are arranged in a
closed ring round the pith, and are in their turn sur-
rounded by the primary cortex, each being separated
laterally from its neighbors 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 pri-
mary medullary rays, therefore, are merely spokes, as it
were, joining the pith and cortex ; and if we could re-
move, the whole of the vascular bundles and epidermis
from the young stem we should have left a solid cylin-
der of cell (pith) in the center, 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

THE TREE— ITS SHOOT-SYSTEM,

101

is very thin from side to side, and therefore stands out
like a knife, with an upper and a lower edge (Fig. 37).
Now imagine the primary vascular bundles replaced.

Fig. '27. — Tanircntial loiitritudinal section of oak wood, magnified fifty
diameters, and showing the transverse sections of the medullary rays,
cut as they project towards the observer. (Muller.)

The first change is that the cambium in the vascular

bundles becomes continuous across through the medul-
8

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 xyleni — and tlie 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 realize 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 whicli lie on the
inside — i. e., nearest the pith, and therefore al)uttiug on,
lose their cambial nature and the xylem — become con-
verted into elements of the wood ; while a smaller pro-
portion 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 cell
travels outwards ; ever receding radially farther from the
pitli, 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
phloem. Each winter it pauses in this process, and

THE TREE— ITS SHOOT-SYSTEM. 103

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,
etc., 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 tliat 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 jirism 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 pro-
toplasm sufficient food materials, and has accomplished
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 pro-
cesses, 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 sec-
ondary xylem, and the phloem secondary phloem, and
so on, to distinguish them from the primary 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 be-
come 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 outward, 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. Eadial 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 be-
tween as space increases. In the same ring about thir-

THE TREE— ITS SUOOT-SYSTEM,

105

lU^

I

Fig. 28. — The various chief elements of the wood of the oak, isolated by
maceration, and highly magnified: /, a fiber, distinguished by its
thick walls, simple slit-like pits, and no contents ; u'.p, part of a row
of wood-parenchyma cells, with simple pits, and containing starch in
winter; </•, a tracheid, distinguished from the fiber especially by its
bordered pits ; j}:i\ 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 ; sj), part of a spiral vessel.

lOG TUE OAK.

teen rays to the millimetre may be counted on the trans-
verse 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 fibers, tracheids, segments of the
vessels (see Fig. 38).

When a cambium cell passes over into wood-paren-
chyma it first undergoes a few horizontal divisions trans-
verse 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 re-
tain part of their living contents — protoplasm, nucleus,
starch-forming corpuscles, etc. — and indeed present
much resemblance to the cells of the medullary raj^s
themselves.

When the cambial cell becomes transformed into a
libriform fiber it does tliis simply by thickening its walls
at the expense of the living contents, etc., which soon
disappear. The cell undergoes no horizontal divisions,
and probably elongates very slightl3\ 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 diameter increases
and the thickening walls become marked with bordered
pits, quite similar to those of the pine, except that they

THE TREE— ITS SHOOT-SYSTEM. 107

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 ver-
tical 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 en-
tirely obliterated. The markings, thickening, and want
of contents are as in the case of tracheids, the chief dif-
ference 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 diam-
eter 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 suc-
cessive rows of the fibers 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 posi-
tion, 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
— fibers, 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 fibers, etc., 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 un-
aided 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 fibers and tracheids
developed in the autumn have a relatively smaller radial
diameter than those formed earlier, and this, combined
with the fact that those 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 de-
veloped— whence the contrast at the boundary between
the annual rings is intensified. With the diminution in
relative diameter of the tracheids and fibers a correspond-
ing increase in the thickness of their walls is connected
— a phenomenon which again intensifies the contrast
between adjacent annual rings.

THE TREE— ITS SHOOT-SYSTEM. IQQ

But, in addition to these diiferences in diameter with-
in one and the same annual ring, a gradual increment
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 ele-
ments 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 con-
cerned. In the stem of the oak the chief changes in
this connection are :

The fibers 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 (one hundred and thirty
years ?) The tracheids in the same annual rings were
found to average 0-39, 0-43, 0-53, and 0*72 mm. respect-
ively ; and the individual members or segments of the
argar ve353ls averaged 0-25 mm. in the second annual
ring, 0-26 mm. in the fourth, and 0-36 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 in-
crements 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 center of the
stem into the condition known as " heart- wood " (dura-

110 THE OAK.

men) as opposed to " sap-wood " (alburnum) is not at-
tended with any profound anatomical changes ; the chief
alterations are of the nature of infiltration by foreign
chemical substances, and alteration in the physical prop-
erties of the cell-walls and in the contents. These
changes are somewhat sudden, and tlie fact that starch
ceases to be deposited in this altered wood helps to in-
dicate 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 preserv-
ative action of infiltrated bodies.

A remarkable phenomenon which may be noticed
here is the filling up of the older large vessels Av-ith
tyloses. These are thin-walled, bladder-like vesicles
projecting into the cavity of the vessel from the bor-
dered 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 parenchyma-
tous 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
functionless vessel.

THE TREE— ITS SHOOT-SYSTEM.

Ill

During the whole time of the activity of the cam-
bium ring and the formation of Avood 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
secondar}' phloem (also called secondary cortex) ; the
chief dilfereuces in the process being (1) that much

i

Fig. 29. — A small piece of one annual rincf of old oak wood (maornified
twenty diameters) : a, boundary of the autumn wood of the preced-
ing folder) ring; 5, that between the zone shown and the next
yoimsrest rinsr. In the annual ring shown the spring wood begins
with large vessels, c and (7, some with tyloses, </, in them, and passes
gradually into autumn wood, with smaller vessels, e, ^, and more
traeheids and fibers, fj. Only siuall medullary rays, /, are shown.
(Hartig.)

less phloem tlian xylem is formed ; (2) that the ele-
ments do not become lignified ; and (3) that the dis-
turbances in the arrangement of the elements are more
profound from the continued pressure exerted upon
them between the resistant wood and the elastic peri-
derm and bark, on the one hand, and the increased ex-
tension tangentiallv which it undersfoes as the thicken-

112

THE OAK.

ing mass of wood drives it outwards, on the other. The
other differences chiefly concern tlie individual 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 cor-
tex. 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 ele-
ments of the secondary phloem are as follows :

(1) Bast parenchyma (Fig. 17, Sj?) is developed, like
the wood parenchyma, from cambium cells which un-
dergo a few transverse divisions and then pass over as
longitudinal groups of cells, which retain their living
contents, etc. From these longitudinal groups, accom-
panying the sieve-tubes as parallel series, they are called
companion cells (cambiform cells).

(2) Sieve-tubes (Fig. 18, bp), which may be 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 sieve)

THE TREE— ITS SIIOOT-SYSTEM. 113

through which the protoplasmic and other contents of
the continuous 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 sim-
ple pits) depend almost entirely on the similar develop-
ment. The sieve-pores are very fine, and easily over-
looked.

(3) The bast fibers (Figs. 17 and 18 b), which are
homologous with the libriform fibers of the wood, and
are developed in the same way from single cells of the
cambium. They are short, blunt, very thick-walled
fibers, grouped in strands which appear on the trans-
verse 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 fibers
(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 imbedded in yellowish substance, and
the walls of which are slightly sclerotic. Similar verti-
cal series of cells are found in the soft bast, but they con-
tain 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 of which

114 THE OAK.

are traversed by very numerous pit-canals ; cells contain-
ing crystals also accompany these groups. ,

In consequence of the above arrangements the second-
ary cortex presents a more or less stratified appearance
on the transverse section, the strata consisting chiefly of
alternate tangential layers of hard bast and soft bast
(Fig. 17) ; the elements of the latter also showing a de-
cided tendency to be arranged in layers.

After the first year the young stem or branches cov-
ered with thin periderm are seen to be dotted with len-
ticels or cortical j)ore3. Structures similar in every re-
spect and subserving the same function — viz., the ex-
change of gases Avith the environment — are formed on
the roots as soon as the periderm is developed.

The leuticel 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 leuticel may be de-
scribed as a biconvex projecting swelling of the peri-
derm, 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 leuticel,
and forms periderm in an uninterrupted sheet, to be
ruptured again at the leuticel 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 de-
veloped as such, but they loosen and round off, and their

THE TREE— ITS SHOOT-SYSTEM. 115

cell-walls do not become completely suberizecl 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 len-
ticel 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 suberized 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 protectiug
the tissues beneath through the winter. In the follow-
ing spring new layers of loose, swelling packing-cells

116 TJIE 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 color gradually
passing into a silver-gray as the periderm develops, and
in a few years (when the shoot is from five to twenty
years old, or thereabout) the gradually thickening bark
is shining and turning browner, flecked 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

I

THE TREE— ITS SHOOT-SYSTEM. II7

layer may be called the initial layer. This layer behaves
essentially like the cambium of a fibro-vascular bundle,
except that its daughter-cells become cork and phel-
loderm 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 suberized
— the inner cell remains cajoable 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 side, of the initial layer : those cells which
lie on the inside hecome pheUode?'m (cortical cells), those
on the outside become transformed into ph€Ue7)i (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 center 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-
lying 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, biit 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

THE TREE— ITS SHOOT-SYSTEM.

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120 THE OAK.

trees the pliellogen layers may be formed so far down in
the cortex that they cut out tissues of the secondary cor-
tex— i. e., phloem and bast fibers. It is, of course, this
gradual exfoliation of the cut-out areas of bark that ex-
plains the relative thinness of the bark in very old stems
and branches ; the whole of the primary cortex, and paiost
of that formed from the cambium, have been thrown
ofE as bark Ion? before.

CHAPTER IX.

THE TREE {continued). IXFLORESCEXCE AXD FLO'U'-
ERS — FRUIT AXD SEED.

The oak flo^yers 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 3-ear'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 of the
tree — i. e., f — so far as it goes. It should be borne in
mind that the bud-scales are stijiules.

122

THE OAK.

The mule iufloresccnces hang down from between
the bud-scales as simple catkin-like spikes, each bear-
ing about a dozen llowers. Each mule flower springs

mm.

Fig. 31. — A spriw of oak in May, with the pendent male catkin below,
and the minute spikes of female llower.s 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, inclosing about five
to twelve stamens ; there is no trace of an ovary. The
number of lobes of the perianth varies, as also does the
number of stamens ; the former are covered with short
hairs.

INFLORESCENCE AND FLOWERS— FRUIT AND SEED. 123

Each of the stamens consists of a slender thread
(filament) bearing on its toj) 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 inclosing 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 st3'le into the ovary of
the flower. This process of apjolication 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
from the axils of the foliage leaves. In the commonest
English variety {Q. pedunculata) the spikes are rather
long, obliquely erect, and the flowers are scattered on
the upper end of the rachis of the spike ; in other varie-
ties 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
the male flower. In the flrst place,. the ovary is inferior,
being sunk in and fused into a six-partite perigone, the

124

THE OAK.

teeth of wliich 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 lobes of the stigma are super^sosed on three alter-
nate (outer) lobes of the perigone.

Fig. 32. — A, Flowering twig and inflorescences, male ( i ), and female ( $ ),
semi-diagrammatic. B, Diagram of plan of a .similar but lateral twig.
F. Leaf from axil of which the twig arises : a*, parent stem ; a and P,
bracts. The numbers 1-11 denote pairs of stipules acting as bud-
scales, some with male inflorescences ( i ) springing from between
them ; the continued numbers 12-21 also denote paii-s of stipules, but
these have tlieir accompanying leaves, with or without female inflo-
rescences { 9 ) in the axils. (Eichler.)

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
" cup " in which the " acorn " is inserted (Fig. 34, m).
If the young female flower is carefully bisected longi-

INFLORESCENCE AND FLOWERS— FRUIT AND SEED. 125

tudinally 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 o\n.iles (Fig.
34). These ovules are in-
serted 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 oc-
curs ; then the tissue below the stigma becomes the
three-chambered ovary sunk in the perigone.

The pollination takes place in May-June, and ferti-

FiG. 33. — A group .of female flowers
(slightly magnified). Each has a
spreading stigma above and the
commencing cupule below, and
arises from the axil ot a pointed
bract. (Th. Hartig.)

126

THE OAK.

lization soon afterwards ; in July the young acorns can
be made out peeping from the cupules in which they had
hitherto been inclosed. The acorn reaches its full size
towards the end of September, and ripens and falls in

Fig. 34. — Female flower in .^section. To the left three transverse sections
through the young ovary ; the lower one showing the three placentas,
each with two ovules. To the right, three longitudinal median sec-
tions through the whole flower at successive periods: a. stigma-, h,
carpal ; c, perianth ; d, cavity of ovary with ovules ; w, the eupule.
(Th. Hartig.)

October. When ripe the acorn is, as we have seen, an
ovoid, smooth, olive-brown nut, with the broad end in-
serted into the eupule, and the narrower, somewhat
tapering end projecting free.

INFLORESCEXCE AXD FLOWERS— FRCIT AND SEED. 127

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 centei 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 stij^ules, also
cut across, and rather difficult to identify (Fig 32, 12-20).
Some of the foliage leaves bear female inflorescences in
their axils, as indicated by the sign ? in the figure. Fol-
lowing 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
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

128 TUE OAK.

above diagram will serve to represent the lateral huds
which develop male inflorescences only, or if we suppose
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. AVhen 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 cham-
bers of the ovary (Fig. 34, d). There are two in each
chamber. Each ovule is at first a mere solid lump of
cells (nucelhis), which curves and becomes enveloped in
two thin investing layers, called integuments, as shown
in the figures a-d (in Fig. 35). Inside the solid nucellus,
91, of the ovule there soon arises a small cavity filled with
nucleated protoplasm, and termed the embryo-sac, e, be-
cause the embryo is to be developed in it.

This embrj'O-sac contains, among other structures, a
minute, nucleated, naked mass of protoplasm, called the
oosphore, or egg-cell. The pollen-tube has carried down
in its apex also a nucleated mass of protoplasm, and it
passes this over into the egg-cell in the embryo-sac ; the
union of the nucleus from the pollen-tube with the
nucleus of the egg-cell constitutes the act of fertiliza-

INFLORESCEXCE AND FLOWERS— FRUIT AND SEED. 129

tion, and the fertilized egg-cell is now termed tlie
oospore, and at once begins to grow into tlie embryo.

n B

Fig. .35. — Various stages in the development of the ovule : n, nueellus;
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.)

It would be very interesting to describe at length all
the remarkable details of these processes, and their

130 THE OAK.

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 fertilization 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 fertilized oospore becomes the em-
bryo (Fig. 35, x) ; it grows at the expense of the con-
tents of the embryo-sac, and develops a radicle, a plu-
mule, 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. Wc saw that the ovary con-
sisted of three chambers, each containing two ovules ;
each of these six ovules also had its embryo-sac, contain-
ing an egg-cell, etc., and each of the total of six egg-
cells may be fertilized 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
all the available nourishment to itself. Consequently
the advancing ovary is soon filled by one ovule — the
other five and two of the chambers being pressed to one
side by it.

INFLORESCENCE AND FLOWERS— FRUIT AND SEED. 131

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 em-
bryo-sac in its interior, occupies nearly the whole of its
cavity ; the remains of the two aborted chambers and

Fig. 36. — Sections of acorns in three planes at right angles to one another
A, transverse ; B, longitudinal in the plane of the cotyledons (l) ; C
longitudinal across the plane of the cotyledons ; c, cotyledons ; t,
testa ;/>, pericarp ; s, sear, and r, radicle ; ^?, plumule. The radicle,
plumule, and cotyledons together constitute the embryo. The em-
bryonic tissue is at r and pi. The dots in A, and the delicate veins
in B and C, are the vascular bundles.

the five unsuccessful ovules being traceable as tiny,
shriveled 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 be-
come the coat (testa) of the seed ; and the embryo de-
veloped from the fertilized 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 cupule ; it contains the seed.

132 THE OAK.

The acorn is an egg-shaped, nut-like fruit {glans),
about 18 mm. long and 8-10 mm. broad (Fig. 30) ; the
apex is somewhat pointed with a hard remnant of the
stigma, the base is broader, and marked with the cir-
cular scar Avhich denotes where it was inserted in the
cupule. The trifid character of the stigma can often be
observed even on the ripe fruit, which is smooth (or
with fine longitudinal strife), and olive-brown in color
when rijie. The rij)e acorn may thus be regarded as
consisting of the pericarp (to which the calyx or jjeri-
anth is fused) and the seed.

The pericarp (Fig. 36,^9) 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, com-
prising the chief thickness of the pericarp (Fig. 37). It
is in this tissue that the small vascular bundles supply-
ing the pericarp run, and here and there nests of scleren-
chyma 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 elon-
gated cells in one layer.

The seed proper fills up the entire cavity inclosed by
the fruit- wall above described. It consists of a relatively
very thin testa, or seed-coat, closely enveloping the large,

INFLORESCEXCE AND FLOWERS— FKUIT AND SEED. I33

Fig. 37. — Transverse sections of the pericarp rm) and seed (VI) of the
oak • E, epidermis ; i, thick layer of sclerenchvma ; under this come
the parenchyma cells, with a few sclerenchyma cells here and there.
T. testa of seed ; G, vascular bundles ; e, the outer layer or epidermis
of the cotyledon ; Co, thin- walled cells of cotyledons (cf. Figs. 35 and
36) filled with starch, etc. (Harz.)
10

134 THE OAK.

straight embryo (Fig. 3G, /). At the broad end thefu-
nicle can be observed attaching the seed to the base of
tlie 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 branca 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 wp by far the greater part
of the space inclosed by the thin testa and pericarp, and
their shape is almost described in saying that. Each is
a colorless, hard, plano-convex body, face to face with
the other by the flat surface (Fig. 3G) ; a transverse sec-
tion of the acorn shows each cotyledon occupjdng 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 tissue, across
which minute vascular bundles run from the embryo
into the cotvledons. If the shell-like investments de-

INFLORESCENCE AND FLOWERS— FRUIT AND SEED. 135

scribed 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 imbedded in a slight dej)ression 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 deli-
cate epidermis inclosing 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 imbedded 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.

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 grayish or yellow brown (fawn color)
to reddish or very dark brown. It darkens on exposure,
and works to a glossy surface if healthy.

Annual rings well marked by the one to four lines of
large vessels in the spring wood, whence radiate outward
tongue-like and branched groups of smaller and smaller
vessels, tracheids, and cells, in a groundwork of darker
fibers. Indistinct peripheral lines of parenchyma are
also visible, especially in the broader annual rings. The
annual rings are slightly undulating, bending outward
between the large medullary rays (Fig. 38).

OAK TlilBER.

13;

Medullary rays of two kinds, a smaller number of
very broad, shining ones, from f to 1 mm., or even a
centimetre or more apart, and very numerous (about

Fig. 38. — Transverse section of wood of oak (ma^nilied live diameters),
showing live annual rin^s, 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, fibers, and wood-parenchyma.
(Muller.)

138 TUE 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 medullary
rays, and the color is chiefly due to pigment in these
wood- and ray-cells. The wood-cells are pitted with ob-
lique, slit-shaped, simple pits.

The vessels have bordered pits, and the septa are per-
forated each by one large circular opening. The smaller
vessels have delicate spirals on their walls as well as bor-
dered pits.

Nordlinger says that pith-flecks occur occasionally.

It is impossible to distinguish between the '.vood of
the varieties pedmiculata 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 sea-
soned wood as about 0-78.

It must be borne in mind, however, that these weights
refer to the wood as a structure — that is, a complex of
vessels and cells, etc., containing air and liquids — and do
not give the specific gravity of the wood substance itself.
The latter may be obtained by driving off all the air and

OAK TIMBER. 139

water from the wood, and is found to be 1'56, compared
with an equal volume of water taken as unity. It is the
varying quantities of this wood substance, 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, etc., 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 j)roportion
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 23 to 39 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 (0-028 to 0*435 per
cent), tlie 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 cylin-
drical stem — the variation is from 0-8 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

140 THE OAK.

how far the difference would hold if sufficiently numer-
ous comparisons were made,

(5) Swelling may be regarded as complementary to
shrinkage. It has been found that if oak wood is
allowed to absorb water until thoroughly saturated it
will increase from 0-13 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 yolume increased from
5-5 to 7'9 per cent, and the weight from GO 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 :r^7th in the former case.
■ The modulus of elasticity is given as 826 to 1,030
kgr., and the breaking limit as 4*G6 to 6*85.

When the pull is in a direction across the length of
the fibers, 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-Gl kgr.

In the case where pressures are applied in the direc-
tion of the length of the fibers the limit of elasticity =
2-09 to 3-22 kgr. ; the modulus of elasticity, 933 to 1,250
kgr. ; and the absolute resistance, 2-58 to 3-64 kgr.

Flexibility.— T\\e 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. ; modu-
lus of elasticity, 612-5 to 785 kgr. ; resistance to torsion,
0-75 to 0-97 kgr.

Eesistance to shearing-stress, in the direction of the
fibers = 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 heavi-
est nor the most supple and toughest of woods, but it
combines in a useful manner the average of these quali-
ties. 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 resist-
ance which the beech offers to the saw, apjjlied trans-

142 TUE OAK.

verse to the fibers, 1, tlieu tliat of freshly felled oak
= 1-09.

(!)) DurahilUy. — 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 be-
comes 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 Kuf us " ; 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. Xever-
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, etc., as we shall see in the next chapter. It
often presents brittle wood, red-rot (foxiness), white-rot,

OAK TIMBER. I43

spottiness 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, etc.

(13) Uses. — Owing to its high price and great spe-
cific 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 mar-
velous 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. pethinculata), it grows rap-
idly, and produces a wood of very tough and horny con-
sistency, which is regarded as the best for naval and
hydraulic work, cartwrights, etc., and wherever 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 color on the fresh section.
It should also have long fibers and a strong, fresh smell.

In close, high forest, on poor soil, and in a rougher
climate, it may take 300 years to reach 0*6 metre diame-
ter, and the wood is then softer and more porous, beau-

lU

THE OAK.

Fig. 39. — Three specimens of oak grown under dill'erent conditions.

OAK TIMBER. 145

tifiilly 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, etc.
Some differences may be put down to the varieties, but
probably Boppe is right in concluding that rate of
growth, etc., due to differences in the soil and climate,
are the determining causes.

The builder employs oak for sills, staircase treads,

Desckiptiox of Fig. 39. — The upper one is from a rapidly-gro-mi
tree, in the open, and at a low altitude ; the wood is very stronsr, hard,
and heavy (density 0-827), because there is a preponderance of fibers 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
in-egularly on poor soil, as shown by the variable rings ; only the parts
with broad rings are good — hence bad wood predominates (density
0-742). (Nanquette-Boppe.)

\

146 THE OAK.

keys, wedges and treenails, 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 six-
teen years if treated with zinc chloride and other pre-
servatives.

On the Continent heavy oak is used in machines, for
axletrees, spokes, stamps of mills, anvil-stocks, hammer- I

handles, etc.

Oak is much used for carving of all kinds, large fur-
niture, paneling, parquetry, for the felloes, spokes, and
axles of wheels, and for other parts of wagons, etc. In
cooperage it is much used for the staves, etc., of casks, J

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.

CHAPTER XL

THE CULTIYATIOX OF THE OAK, AXD THE DISEASES
AXD 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
tree instead of rising up into a tall, straight one. The

148 THE OAK.

forester usually gets over these difficulties by planting
beech, or silver fir, or some otlier species among the oaks,
but in such a way that the oaks are never completely
shaded by the other trees — that is to say, he keeps the
trees at different ages, the beach, hornbeam, silver fir,
spruce, etc., 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 consequently 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 can not 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
to cut back oaks, and allow them to sj^rout into what is
known as coppice — that is to say, numerous buds which

THE CULTIVATIOX OF THE OAK. 149

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 follow-
ing 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 Avater to the subsoil ; consequently many soils, other-
wise 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 ex-
cept the larch, birch, and one or two others, and rapidly
suffers if shaded or unduly crowded. Further, as com-
pared 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
it grows. In return for this, however, it yields the

best of all temperate timbers.
11

150 THE OAK.

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, etc.),
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 croTSTis 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 realized 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
forester also has to aim at getting as much timber as
possible on the gi-ound in a given time, and in the case

THE CCLTIVATIOX OF THE OAK. 151

of a tree like the oak liis 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
maximum of light and air. Consequently a modifica-
tion 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 croj^s of good seeds only recur every five (or
perhaps three) years or so, the yield in the intervals be-
ing 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 phos-
phorus 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 exhausting that it requires
three to five years to re-store sufficient of these sub-
stances for another " seed-year." The season or weather
is also concerned in the matter.

Of course there are very many other details to be

152 THE OAK.

considered in the technical cultivation of the oak, but
enough has been said to give the reader a general ac-
count of the i^rocedure, 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, etc. ;
others are due to the attacks of living organisms, both
vegetable and animal — from the Aveeds 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 in-
vade 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 enor-
mous. Other destructive agents during these early phases
of the life of the oak are cattle and deer, which not only
tread down the shoots but also nibble them off, and
mice, squirrels, etc., do their share of injury, as also do

THE CULTIVATION OF THE OAK. I53

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. Cynips 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
playing the same inimical i^art, in fact, that grass and
weeds, etc., 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.

Much mischief is effected by the attacks of insects

154

TUE OAK.

of various kinds. The caterpillars of certain moths
(especially Cnethocampa and Tortrix), for instance, eat
off the loaves in June, and then form large masses of
mingled debris, skins, etc., as they pass into the pupa
stage in July. The denudation of the leaves brought

Fio. 40. — Toi'trix riridana, the (rrccn oak-moth, the Larvae of which eat
off the youug 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 devel-
oped.

THE CULTIVATION OF TEE 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, etc., which nibble roots and
buds and destroy the acorns, etc. ; and a few birds ; and
certain beetles, which bore into the wood.

Among the pests belonging to the vegetable kingdom
the following may be selected from a large number :
The honeysuckle occasionally twists tightly round the
young stem, and in course of time so compresses 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 horizontally round
the stem.

As a rare event the mistletoe is found on the oak.
A much commoner parasite of the same family is Loran-
tlius europmus, which does considerable damage to oaks
in some parts of Europe. The sticky seeds are carried
into the trees by thrushes. Here they germinate, 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 hypertrophy of the tis-
sues, to which abnormal quantities of food materials
now flow (Fig. 41) ; and frequently bringing about the
death of the u^oper parts of the branches owing to the

156

THE OAK.

paucity of water at tliose parts, the parasite taking much
of that whicli reaches the injured place, and tlie impov-
erished Avood allowing less to pass thau it would normally
have done.

Among the fungi there are several enemies to the
oak-tree. The leaves are attacked by Fhi/Uactinia, one

Fkj. 41. — Loranthns eiirnp(viis. A. Lower part of stem attaeliod toLranch
of oak, both denuded of cortex. B. Longitudinal section tliroufrh 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 Lnj-ariflnis ; a a, dead remains
of old haustorial strands; 5 ^, young Loranflnis plants developed as
buds from the older ones. The asterisks mark .still younger speci-
mens. (Ilartig.)

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 Nedria, the spores of

THE CULTIVATION OF THE OAK. 157

which germinate on the bark, but can not infect the tree
unless there is a wound in the neighborhood. How-
ever, owing to the numerous small cracks and ru^Dtures
due to the injuries caused by insects, hail, frost, etc., the
mycelium easily gains access to the cortex and cambium,
and feeds on the contents of the cambium-cells, which
it destroys. The consequence of the irritations set uj) 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
popularly as toadstools — technically as Hymenomycetes
— which are able to injure and even destroy the timber
of standing oaks, and while each of these pests does the
damage in its own peculiar way, they show considerable
similarity in general behavior. In the first place, these
fungi are unable to penetrate the bark of sound trees,
and their hyphfe 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
hyphge of these fungi pierce the vessels, cells, etc., of the

158

THE OAK.

wood by excreting soluble ferments which dissolve the
substance of their -walls, and feed on the products of
solution. Hence they damage tbe timber in two ways
— they riddle it through and through by myriads of
minute apertures, and thus ruin its structure, and they

Fio. 42.— Piece of oak dostroyccl by Thelephora Perdi.i\ slinwiiiir 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 tlie fungi destroy the vessels, fibers, etc.,
by dissolving their walls from inside, while others de-
stroy the part common to contiguous cells, etc., and
thus first isolate the elements and then complete the
destruction. A series of very interesting researches by

l;i

Fig. 43. — Oak timber destroyed by tlie fiinirus Jlijihi um diversidens :
a shows the medulhiry rays on the tangential section ; i, a mass of
felted mycelium. (E. Hartig.)

Hartig has demonstrated that the presence of these tim-
ber-destroying fungi can be detected from the markings
and discolorations they produce in the wood ; those due
to Hychium diversidens, Thelepliora Perdix, Pohjporus
sulplmreus, P. igniarins, P. dryadevs, and Stereum

160

THE OAK.

hirsutum being all different, and in some cases so char-
acteristic 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

Fig. 44. — Oak damaged b_y Polyporus igniarius, a very common timber
fmigus. (E. 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 Mendius lacrymayis, a hymenomycete
allied to the preceding, but differing from them in not
attacking the standing timber. The spores of this

THE CULTIVATIOX OF THE OAK.

161

fungus are able to infect oak planks, beams, etc. ; and
the mycelium rapidl\- spreads on and in the wood, de-
stroying the cell-walls, and causing the wood to shrink
and crack and warp, and finally to fall to pieces. Thor-
ough ventilation is fatal to the fungus and stops the rot.

Fig. 45. — Oak wood destroyed by Pohjporus dryadexi8, showing the very
characteristic markings, like insect tunnels in a deep red brown ma-
trix. (E. Hartig.)

A series of enemies to the oak-tree not yet referred
to are various gall-insects, so called because they pierce
the young leaves or buds, etc., 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. 40.— Piece of oak-bark witli fructiiication of Polyporus 8ul2>hureu8.

C «^

Fig. 47. — Piece of oak attacked by Pohjporuft foilpliureus. th e yellowish
•white niyceliuiu of which is seen at c and d. (R. Hartig.)

Fig. 48. — Transverse section of oak-timber tk-stroyed by Polyjporus sul-
phureus. (K. ilartig.)

Fig. 49.— Highly magnified longitudinal radial section of a piece of oak
destroyed by a timber fungus, showing the ravages of the hj'phai in
the various tissues. (K. Hartig.)

104

TUE OAK.

cells multiply and form the gall. This is a mere out-
line sketch of tlie matter, however, for the differences in
behavior are enormous. Each insect causes the forma-

FiG. 50. — Portion of the spore-bearing hymeniura of Merulius lacrymans,

the fundus of " dry rot."

tion of a specific kind of gall, differing in shape, size,
color, 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

I

THE CULTIVATION OF THE OAK.

165

owu galls also, those on the American oaks differing
from those on the European species, but some are com-
mon to more than one species. The insects which pro-

FiG. 51. — An oak-leaf with several kiuds of Cynips galls on it: «, gall
produced by Cynips scutellaris ; S, C. divisa ; c, Neuroterus Beau-
murii ; e, BiorMza renum ; f^ Neuroterus ostreus. (Frank.)

duce the commonest English oak-galls are nearly all
members of the Cynipidem, a group of hymenoptera
which lay their eggs in the young tissues of various
plants, especially oaks and roses.

12

1(56 TUE OAK.

Some of the resulting galls are discoid, such as the
" oak-sj^angles " of our woods ; others, again, are spheri-
cal, such as the common leaf -galls so well known in Eng-
land, and the so-called oak-apple; then there are the
"artichoke galls," produced by the partial metamor-
phosis of the buds of the oak in which the Cynips has
laid its egg, and many others.

CHAPTER XII.

EELATIOXSHIPS OF THE OAKS — THEIE DISTKIBUTIOiir
IX SPACE AXD TIME.

The oak is a member of a very large and ancient
group of dicotyledonous flowering plants, embracing the
beeches, chestnuts, hazel-nuts, etc., 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 orA ustral-
asia. Some remarkable species are found in the Hima-
layas, and many in the Malayan Archipelago.

The various species of the genus Quercus are ar-
ranged into groups according to differences in the form
and arrangement of the scales of the cupule, the charac-
ters of the leaves, and certain peculiarities in the acorns.
Many oaks, especially those of warm countries, for in.
stance, are " evergreen," with hard, leathery leaves, quite
unlike the leaves of our common British oak.

The latter is denominated botanically as Quercus

l(Jji THE OAK.

Rohiir, 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. sessilijlora, 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 w^ood,
etc., 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
vaxiety j^edicnculata is the commonest over the country
generally, but in the hilly districts of Xorth Wales and
the north of England the variety sessilijlora 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 decided that the ma-
jority of these were merely provisional ; and he conclud-
ed, as others have done, that we have, in the numerous
varieties of the species of this old genus Quercus, series
of incipient species. If the connecting forms were to
die out, leaving certain varieties more isolated than they

RELATIONSHIPS OF THE OAKS. 169

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. Rohur) have been
described, and that the majority of these can be grouped
around the three forms pedunculata^ sessiliflora, and
puhescens, the latter being a somewhat hairy variety
found on the Continent. No doubt Ave 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 accordance with
this. It probably implies that the genus has had time
during its migrations over the Northern Hemisphere to
vary immensely, and that some of the varieties have be-
come adapted to given situations, others to others. On
the whole, the oak family must be regarded as a north-
ern type which has sent extensions southward.

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 vari-
ous parts of the world. Some of the European fossil
forms remind us of species now found only in hot coun-
tries near the tropics, others are peculiar, and some are
very doubtful.

The earliest remains of oaks come from the Creta-
ceous strata, being coeval with the first undoubted dico-
tvledons that have been found. Many have been found

170 THE OAK.

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
puhesceyis) 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 Euro-
pean oaks from Asia was completed before the islands
of Sicily, Sardinia, Corsica, and Britain were separated
from the mainland of the Continent. Moreover, 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 oak
of to-day. Again, fossil leaves from Italy, found in
diluvial deposits, are so like those of certain Californian

RELATIONSHIPS OF THE OAKS. I7I

oaks now existing that a common origin is also sug-
gested, and similar leaves have been discovered in Ter-
tiary deposits in Xorthwest America. If all the evi-
dence is put together, we may conclude with Asa Gray
that " the probable genealogy of Q. Eobur, traceable in
Europe up to the commencement of the present epoch,
looks eastward 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 valu-
able 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, etc., as a tanning material, and
these even form important articles of export. Quer-
citron, a yellow dye and tanning material, is obtained
from Q. tinctoria in Xorth 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. Siiher.

Q. infectoria pelds the chief galls of commerce.
They are caused by the punctures of Cynips galloB tinc-
torim, and are used for making ink and for dyeing. In
these and similar galls the value depends on the pres-
ence of relatively large quantities of tannic and gallic
acids which they contain.

IIs^DEX.

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-cyUnder, 24, 28, 32, 91;
fig. 5.

Bark, 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, 52, 64, 92, 98, 100,

103, 111; figs. 9, 24.
Cattle, 155.
Cells, 15, 136.
Chlorophyll, 79, 85.
Cnethocampa, 154.
Common bundles, 47.
Coppice, 149.

Cork, 93, 116; figs. 17, 18.
Cortex, 52, 98; 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, 138.
Diseases of oak, 152-163.
Drainage, 153.
Dry-rot. See Jferulius.
Durability of oak, 142.
Duramen, 109, 136.

Elasticity of oak, 140.

Embryo, 14.

Embryonic tissue, 17, 28, 41, 96;

figs. 2, 6, 25.
Embryo-sac, 128 ; fig. 35.
Endodermis, 30, 32 ; fig. 5.
Epidermis, 16, 39, 41, 52.

Fertilization, 130.

Fibers, 60, 106, 108, 113, 136;

fig. 16.
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.

174

INDEX.

Habit of oak, 150.

Hardness of oak, 141.

Heart-wood. See Duramen.

High forest, 147.

Honeysuckle, 155.

Hornbeam, 148.

Hydnum diver.sidens, 159; fig. 43.

Hymenomycetcs, 157.

Hyphcfi, 97, 157 ; fig. 25.

Hypocotyl, fig. 3,

Inflorescence of oak, 121 ; figs. 31,
32.

Injuries to wliich the oak is sub-
ject, 152-163.

Insects, 154.

Lammas shoots, 6, 74.

Leaf, 21, 76-88; figs. 20, 21, 22.

Leaf-trace, 47, 49, 69.

Lenticels, 114.

Loranthus europceux, 155; fig. 41.

Medullary rays, 34, 39, 48, 52, 54,
63, 95, 100, 104, 136; figs. 9,
12, 27, 38.

Menilius lacrymans, 160 ; figs. 46,
47.

Mesophyll, 76, 79, 81, 85 ; fig. 22.

Mistletoe, 155.

Mixed woods, 148.

Mycorhiza, 96 ; figs. 7, 25.

Nectria, 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, 62-71, 92, 99,

103, 111; figs. 5, 6, 9, 17, 18,

24.
Phyllactinia, 156.
Phyllotaxis, 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, 136 ; figs. 5,

12, 99.
Plasticity of roots, 35.
Plumule, 14, 21, 130 ; figs. 2, 3.
Pollen, 123, 128.
Pollination, 123, 126.
PoJyporus dryadetis, 159 ; fig. 45.

igniarius, 159 ; fig. 44.

sulphuretis, 169.

Primary root, 14, 22 ; fig. 3.
Primary shoot, 21, 39 ; fig. 4.
Procambium, 42.
Properties of oak, 136-146.
Proteids, 17, 18.
Protoplasm, 17.
Pure oak woods, 147.

Qualities of oak, 144 ; fig. 39.

Quercite, 18.

Qiiernts peduncufata, 7, 123, 138.

Hobur, 7, 8.

sessilifora, 7, 76, 138.

INDEX.

175

Radicle, 14, 130; figs. 2,3.
Requirements of oak, 149.
Rocking 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, 38, 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.
Stcreicm hirsutum, 159.
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. 6.

Swelling of oak, 140,

Tannin, 9, 17, 68, 135.
Technology of oak, 136-146.
Tenacity of oak, 140.
Testa, 13, 131 ; figs. 2, 3,
Thdcphora Ferdix, 159 ; fig. 42,
Timber, 8, 136-146 ; figs, 26, 38,

39.
Tissues, 17, 39.
Torsion of oak, 141.
Tortriz viridana, 154 ; fig. 40.
Tracheids, 60, 106, 108, 136 ; fig.

16,
Tree-killing fungi, 157,
Tyloses, 110; fig, 29.

Uses of oak, 143.

Vascular bundles, 11, 17, 18, 26,
41-51, 100 ; figs, 2, 3, 9, 10-12.

system, 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,
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