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TIMBER

SOME OF ITS DISEASES

MACMILLAN AND CO., Limited

LONDON . BOMBAY . CALCUTTA
MELBOI RNE

THE MACMILLAN COMPANY

NKW VORK . BOSTON . ( UK m.O
ATLANTA . SA.N FRANCISCO

THE MACMILLAN CO OF CANADA, Ltd.

TORONTO

NATURE SERIES

TIMBER

AND

SOME OF ITS DISEASES

BY

II. MARSHALL WARD, M.A, F.R.S, F.L.S.

LATE FELLOW OF CHRIST'S COLLF.GK, I IMBRIDG1 : PROFESSOR OF BOTANY AT THE
ROYAL INDIAN I E, COUl'tlv's HILL

WITH J!. I USTRATh WS

MACMILLAN AND CO., LIMITED

ST. MARTIN'S STREET, LONDON.
i 9 o g

Richard Ci.ay and Sons, Limited,

bread street htll, e.c., and

bungay, suffolk.

First Edition, 1889.
Reirinted, 1897, 1909.

PREFACE.

THE following attempt at a popular exposition
of a subject almost unknown in this country,
originated in a series of short articles in Nature,
and when the publishers proposed that I should
add to these and cast them into the form of a
book, I assented with the more pleasure because
it afforded an opportunity of calling attention to
several points well worth further investigation.

Had my primary object been to write a treatise
on the whole subject of the diseases of trees,
I should have adopted a somewhat different plan,
and discussed many of the phenomena at greater
length.

Chapter IV. will perhaps be regarded as too
technical for the general reader, but it seemed

vi PREFACE.

better to bring the whole controversy forward,
and make it tell its own story, because, so far as
I am aware, no account of the matter has as yet
been put before the English student, and so many
points of interest turn up by the way.

No author could well approach the subject of
the diseases of timber without consulting the
works of De Bary and R. Ilartig ; nor attempt
to classify woods without referring to the labours
of Nordlingcr and Gamble in addition : to these,
and to the writings of Frank, Sorauer, YVill-
komm, Hesse, and others, I take this opportunity
of acknowledging many obligations.

Cooper's Hill, 1SS9.

CONTENTS.

CHAPTER I.

PAGE
TIMBER, ITS GENERAL CHARACTERS AND STRUCTURE ... I

CHAPTER II.
TIMBER, ITS PROPERTIES AND VARIETIES 20

CHAPTER III.

THE CLASSIFICATION OF TIMBERS 39

CHAPTER IV.

ON THE THEORIES ADVANCED TO EXPLAIN THE ASCENT OF

WATER IN TALL TREES 59

CHAPTER V.

DISEASES OF TIMBER I42

viii CONTENTS.

CHAPTER VI.

PAGE

DISEASES DUE TO AGARIC US MELLEUS AXD POLYPORUS

SULPHUREUS 155

CHAPTER VII.
THE "DRY-ROT" OF TIMBER 1/6

CHAPTER VIII.

THE CORTEX AND BARK OF TREES 199

CHAPTER IX.

THE HEALING OF WOUNDS BY OCCLUSION . 2IO

CHAPTER X.

"CANKER": THE LARCH DISEASE . 227

CHAPTER XL

LEAVES, AND LEAF DISEASES , . . 244

CHAPTER XII.

PINE-BLISTER 256

CHAPTER XIII.
THE " DAMTING OFF " OF SEEDLING TREES 2?I

INDEX 209

TIMBER

SOME OF ITS DISEASES.

CHAPTER I.

TIMBER, ITS GENERAL CHARACTERS AND
STRUCTURE.

On carefully examining the clean-cut end of a
sawn log of timber, it is easy to convince ourselves of
the existence of certain marks upon it which have
reference to its structure. These marks will vary in
intensity and number according to the kind of tree,
the age at which it is felled, and some other circum-
stances, which may be overlooked for the present ;
but in a given case it would be possible to observe
some such mark's as those indicated in Fig. i. In the
£ B

2 TIMBER AND SOME OF ITS DISEASES, [chap.

specimen chosen there is a nearly central spot, the
pith, around which numerous concentric lines — the
"annual rings" — run. Radiating from the pith to-
wards the periphery are cracks, the number, and
length and breadth of which may vary according to
the time the log has been exposed to the weather, and
other circumstances ; these cracks are due to the con-
traction of the wood as it " shrinks," and they coincide
with medullary rays, as lines of weakness. Between
these cracks are to be seen numerous very fine radiat-
ing lines indicating the course of the uninjured
medullary rays, which again will vary in distinctness,
&c, according to the species of timber.

This log of wood, with its annual rings and
medullary rays, is clothed by a sort of jacket, consist-
ing of cork and softer tissues, and termed the cortex,
or, more popularly, the " bark " (an unfortunate word,
which has caused much trouble in its time). The
largest of the cracks is seen to traverse the whole
radius of the face of the wood from centre to circum-
ference, and also to pass through the cortex, which
gapes widely.

The remaining cracks, however, stop short at a line
which marks on the one hand the inner face of the
cortex, and on the other the outer face of the wood :
this line also represents the cambium, a thin sheet of

L] GENERAL CHARACTERS AND STRUCTURE. 3

generative tissue which remains after giving rise to
practically the whole of the wood (a very little in the
centre excepted) and cortex visible in the woodcut.
Since we are not concerned with the cortex and bark
at present, it will be convenient to regard the log as
" barked," and only deal with the wood or timber

Fig. i.— A. log of timber, .showing radial cracks after lying exposed for some time. <i,
a large crack extending from pith to circumference; b, the ci rtex : c, medullaiy
ray ; </, cambium ; c, annua! ring ; f, outer bark, proper. Reduced.

itself, in the condition to which the woodman reduces
it after removing the cortex with certain implements.
If now we split such a log as Fig. 1 along the line
of the big crack, neatly and smoothly, the well-known
" grain " so often observed on planks of wood will
come into view, and it will be noticed that the lines

1; 1

4 TIMBER AND SOME OF ITS DISEASES, [chap.

which mark the " grain " are continuations of the lines
which mark the annual rings, as shown in Fig. 2,

j.'ic;. 2. — Portion of segment of wood fro.n a log such as Fig. i, supposed to be slightly
magnified, a, annual ring ; m, medullary rays ; in', the same in vertical section ;
c, the boundary line between one annual ring and another; sit, autumn wood; s/>,
spring wood ;/, the pith.

which represents on a larger scale a segment such as
could be cut from a log in the way described. It is

I.] GENERAL CHARACTERS AND STRUCTURE. 5

clear from comparison of what has been said, and of
the two figures, that the " annual rings " are simply
the expression in cross-section of cylindrical sheets
laid concentrically one over the other, the outermost
one being that last formed. But on examining the
medullary rays in such a piece of timber as that in
Fig. 2, it will be noticed that they also are the expres-
sion of narrow radial vertical plates which run through
the concentric sheets : the medullary rays are in fact
arranged somewhat like the spokes of a paddle-wheel
of an old type of steamer, only they differ in length,
breadth, and depth, as seen by comparing the three
faces of the figure. It is to be noticed that the
medullary rays consist of a different kind of tissue
from that which they traverse, a fact which can only
be indicated in the figure by the depth of shading. It
is also to be observed that the "annual rings" show
differences in respect to their tissue, as marked by the
darker shading near the boundary lines on the outer
margin of each ring. In order to understand these
points better, it is necessary to look at a piece of our
block of timber somewhat more closely, and with the
aid of some magnifying power. For the sake of
simplicity it will be convenient to select first a piece
of one of the timbers known as " deal " (firs, pines,
&c), and to observe it in the same direction as we

6 TIMBER AND SOME OF ITS DISEASES, [chap.

commenced with, i.e. to examine a so-called transverse
section.

The microscope will show us a figure like that in
the woodcut (Fig. 3). There are to be seen certain
angular openings, which are the cross sections of the
long elements technically called tracheides, shown in
elevation in Fig. 4. It will be noticed that whereas
along some parts of the section these openings are
large, and as broad in one direction as in the other, in
other parts of the section the openings are much
smaller, and considerably elongated in one direction
as compared with the other. The band of small
openings naturally looks more crowded and therefore
darker than the band of larger openings, and it is to
this that the differences in the shading of the annual
rings in Fig. 2 are due. But it is not simply in having
larger lumina or openings that the dark band of
tracheides is distinguished from the lighter one : the
walls of the tracheides are often also relatively thicker,
and obviously a cubic millimetre of such wood will
be denser and contain more solid substance than a
cubic millimetre of wood consisting only of the larger
thin-walled tracheides. It is equally obvious that a
large block of wood in which the proportion of these
thick-walled tracheides with small lumina is greater
(with reference to the bands of thin-walled tracheides)

I.] GENERAL CHARACTERS AND STRUCTURE. 7

will be closer-grained, and heavier, than an equal
volume of the wood where the thin-walled tracheides
with large lumina predominate.

Fig. 3.— Portions of four annual rings from a thin transverse section of the wood of a
Conifer, such as the spruce-fir. M, a medullary ray ; b and c show the entire breadth
of two annual rings ; a, autumn wooi of an annual ring internal to b (and there-
fore older than b) ; d, spring wood of an annual ring external to c (and therefore
younger than c). Bordered pits are seen in section on some of the tracheides.
Magnified about 100 times.

Returning now to the section (Fig. 3), it is to be
observed that the differences in the zones just referred
to enable us to distinguish the so-called "annual

8 TIMBER AND SOME OF ITS DISEASES, [chap.

rings. " The generally accepted explanation of this
is somewhat as follows. In the spring-time and early
summer, the cambium-cells begin to divide, and those
on the inner side of the cylinder of cambium gradually
become converted into tracheides (excepting at a few
points where the cells add to the medullary rays), and
this change occurs at a time when there is (i) very
little pressure exerted on the inner parts of the trunk
by the cortex and corky bark, and (2) only compara-
tively feeble supplies are derived from the activity of
the leaves and roots, in the still cool weather and
short days with little sunlight. In the late summer,
however, when the thickened mass of wood is com-
pressed by the now tightened jacket of elastic bark
which it has distended, and the long, hot bright sunny
days are causing the numerous leaves and roots to
supply abundance of nutriment to the growing cam-
bium cells, it is not surprising that these cells cannot
extend themselves so far in the radial direction {i.e.
in a line towards the centre of the compressed stem),
and that their walls are thickened by richer deposits
of woody material supplied quickly to them.

As the winter approaches, the cambium ceases to
be active, and it then remains dormant for several
months. When its cells are awakened to renewed
growth and division in the following spring, they at

I.] GENERAL CHARACTERS AND STRUCTURE. 9

once begin to form the tracheides with thin walls and
large lumina, because the pressure previously exerted
by the cortical jacket has been reduced by its cracking,
&c. during the winter rest, and it is the sharp contrast
thus displayed between the newly-formed tracheides
with thin walls and large lumina, and the compressed
denser ones cf the previous summer on which they
suddenly abut, that produces the impression of the
" annual ring."

It is now time to attempt to give some clearer ideas
of what this " cambium " is, and how its cells become
developed into tracheides. But first it is necessary to
point out that each tracheide examined singly, is a
long, more or less tubular and prismatic body, with
bluntly tapering ends, and the walls of which have
certain peculiar markings and depressions on them, as
seen in Fig. 4. We cannot here go into the important
signification and functions of these markings and de-
pressions however, since their study will need a
section to themselves. It must suffice for the
present to state that the markings have reference
to the minute structure of the cell-walls, and the
depressions are very beautiful and complicated
pieces of apparatus to facilitate ami direct the
passage of water from the cavity of one tracheide
to that of another, and prevent access of air. Now, the
cambium is a thin cylindrical sheet of cells with very

io TIMBER AND SOME OF ITS DISEASES, [chap.

delicate walls, each cell having the form of a rect-
angular prism with its ends sharpened off like the
cutting edge of a carpenter's chisel : this prism is

Fig. 4. — A small block of wood from a spruce-fir, supposed to lie magnified about 100
times, showing elevation and sectional views of the tracheides of the autumn (to
the right) and spring wnod, and medullary rays («/ n) running radially between
the tracheides. (After Hartig.)

broader in the direction coinciding with the plane of
the sheet of cambium — i.e. in the tangential direction,
with reference to the trunk of the tree — than in the

I.] GENERAL CHARACTERS AND STRUCTURE. 11

direction of the radius of the stem ; and the chisel-
edge must be supposed to run in the direction parallel
to that of a medullary ray, i.e. radially. From the
first, each cambial cell contains protoplasm and a
nucleus, and is capable of being nourished and of
growing and dividing. It is only at or near the tips
of the branches, &c, that these cambium-cells are
growing much in length, however ; and in the parts
we are considering they may be for the most part
regarded as growing only in the radial direction ;
more rarely, and to a slight extent, in the tangential
direction also, as the circumference of the cylinder
enlarges. After a cambial cell has extended the
superficial area of its walls by growth in the radial
direction to a certain amount, a septum or division
wall arises in the longitudinal tangential plane, and
two cells are thus formed in place of one : this process
of division may then be repeated in each cell, and so
the process goes on. This is not the place to lay stress
on certain facts which show that a single layer of cells
probably initiates the division : it suffices to point out
that by the above process of division of the cambial
cells there are formed radial rows of prismatic cells,
as indicated in Fig. 5, where the arrow points along a
radius towards the centre of the stem. It is true such
radial rows of cells are also developed in smaller

12 TIMBER AND SOME OF ITS DISEASES, [chap.

numbers towards the outside of the cambium cylin-
der {i.e. to add to the cortex) but we are now only

Ficj. 5. — Portion of cambium of a fir, showing the development of the young wood
tracheides from the cambium-cells. The arrow points to centre of the stem. The
cambium-cells at length cease to divide, and the walls become thicker (<?), except at
certain areas, where the bordered pits are developed (/' and r). To the right is a
medullary ray. Highly magnified, and the contents of the cambium-cells omitted
for clearness.

concerned with the wood, and therefore only regard
those cells which are developed on the inside {i.e.

l] general CHARACTERS AND STRUCTURE. 13

towards the centre of the stem). After a time the
oldest of these cells {i.e. those nearest the centre of
the stem) cease to divide, and undergo changes of
another kind : the process of division is still going on
in the younger ones, however ; and so the radial rows
are being extended by additions of cells at their outer
ends. Of course, this is normally proceeding along
the whole area of the cylindrical sheet of cambium,
and therefore over the whole surface of the wood of
the stem and roots, with their branches.

Confining our attention for the present to one of the
innermost, oldest cells of the cambium, which has
ceased dividing (aa in Fig. 5), we find that it enlarges
somewhat in the radial direction, and then its hitherto
very thin walls become thicker ; in fact, the protoplasm
in its interior absorbs food-materials, and changes
them into a peculiar substance which it plasters or
builds on to the inner sides of the cell-wall, so to speak,
until the wall is rendered much thicker. This thicken-
ing process is withheld at certain places only —
the thin depressions or " pits " already referred to.
Two chief changes result now: (1) the whole of the
living contents of the young wood-cell gradually
become used up, and eventually disappear without
leaving any trace, their place being occupied by water
and air in most cases ; and (2) the thickening substance

14 TIMBER AND SOME OF ITS DISEASES, [chap.

built on to the inside of the walls undergoes changes
which convert it into true wood-substance — in botanical
language, the walls become lignified. The cells b and
c in Fig. 5 illustrate what is meant.

During all these changes, which occupy several or
even many hours or days, according to circumstances,
it will be observed that the definitive shape of the cell
is gradually completed, and then alters very little :
the prismatic cambium-cell has become a prismatic
tracheide, with thicker, lignified walls, and containing
air and water (with minute quantities of mineral
substances dissolved in it) in place of protoplasm and
nutritive substances. It is not necessary here to speak
of other and more subtle changes which may eventually
cause slight displacements, &c, of these cells.

If I have succeeded in making the chief points in
this somewhat complicated process clear, there will be
little difficulty in explaining what occurs in other
parts of the cambium-cylinder. The cambium-cells
which happen to stand in the same radial row as the
cells of a medullary ray, simply go on being converted
into cells of the medullary ray, instead of into
tracheides ; cells which differ from the tracheides
chiefly in retaining their living contents and nutritive
materials — i.e. substances like starch, proteids, sugars,
&c, which arc used as food by the plant. Again,

L] general characters and STRUCTURE/ 15

those cells of the cambium which are divided off on
the outer side of the cylinder (they are always fewer
in number) are gradually transformed into elements
of the cortex, and many of them finally enter into
the composition of the bark proper.

Now and again, but much more rarely, a radial row
of cambial cells which, from their position, it would
appear should be converted into tracheides of the
wood, alter their destiny, so to speak, and become the
originators of a new medullary ray. But I must pass
over these and some other minor peculiarities, and
refer to the illustrations for further details.

If now, instead of a log of deal, or coniferous wood,
we direct attention to the timber of a dicotyledonous
tree, such as the oak, ash, beech, chestnut, poplar, &c,
the differences in detail will be found to be not very
great in relation to the broad features here under
consideration. Turning again to Fig. 1, it would be
possible to select a cut log of any of these timbers
which presented all the salient characters there exhi-
bited. The " bark " would present external differences
in detail — such as in roughness, colour, thickness, &c.
— but it could still be described, as before, as a more
or less corky jacket around the whole of the wood :
the cut face would show the timber marked by more
or less numerous and prominent "annual rings,"

16 TIMBER AND SOME OF ITS DISEASES. [cHAP.

traversed by smaller or larger medullary rays, radiat-
ing from the central pith, and passing across the
cambium to the cortex. Moreover, cracks would be
apt to form on exposure, as before ; the opening
occurring along the lines of medullary rays — lines of
weakness.

Again, if we cut a segment of the wood, like Fig. 2,
the chief features would present themselves as there
shown, and the lines of demarcation indicating the
annual rings would be found to be due to the sharp
contrast between the spring wood and the autumn or
summer wood, as before.

On closely examining a transvere section of such a
piece of timber, however, we should find differences
which at first sight appear profound, but which on
reflection and comparison turn out to be of more
relative significance, from the present point of view,
than might be expected.

Selecting a given example, that of the beech for
instance, the first difference which strikes us (Fig. 6)
is a number of relatively very large openings on the
transverse section : these are the vessels — pitted
vessels — long tubular structures which are not formed
by the cambium of the conifers. Each vessel may be
regarded as a tube made by the joining of a long
vertical row of tracheides, the lumina of which become

I.] GENERAL CHARACTERS AND STRUCTURE. 17

continuous as they pass out of the cambium stage.
Between these vessels are much more numerous
elements with very small lumina and thick walls : the
latter are the wood-fibres proper, and have to be tech-
nically distinguished from the apparently somewhat
similar wood-tracheides of the pines, firs, &c. Each fibre
is, in effect, a tracheide with much thicker cell-walls
than usual, and devoid of the characteristic " bordered
pits " referred to when speaking of those structures :
it is essentially a tough, strengthening element. Here
and there, scattered in small groups, are certain rows
of shorter cells, which, however, are not very numerous
in the beech : they are called wood-parenchyma (Fig.
6, tup.), and occur particularly in the vicinity of the
vessels. These wood-parenchyma cells are produced
by the cambium-cell becoming divided across into
several superposed short chambers, which retain their
living contents: they resemble the cells of medullary
rays in nearly all respects.

It is beside the purpose here to describe in detail
the histology of the beech-wood, and reference may
be made to the figures for further particulars. It may
suffice to point out that all the elements — cells, fibres,
and vessels — are formed as before by the gradual
development of cambium cells ; and the same is true,

C

18 TIMBER AND SOME OF ITS DISEASES, [chap.

generally, of the medullary rays here that is true of
those of the pines and firs, &c.

Fig. 6. — A piece of wood from a dicotyledonous tree (beech), supposed to be magni-
fied about ioo times. Mr, a medullary ray runn.ng across the transverse section :
the dark band crossed by this ray is the autumn wood («), formed of closely-
crowd-d wood-fibres and tracluides : r\ a lartje. vessel in section: others are seen
aNo— they are smaller and fewer t iwards the autumn wood ; a', wood-fibres, of
which most of the timber is composed ; wp, wood-parenchyma cells.

Attention is to be directed to the fact, which is here
again evident, that the line of demarcation between

l] GENERAL CHARACTERS AND STRUCTURE. 19

any two " annual rings " is due to the sudden apposi-
tion of non-compressed elements upon closely-packed
and apparently compressed elements : the latter were
formed in the late summer, the former in the spring.
Moreover, the spring wood usually contains more
numerous vessels, with larger lumina than the autumn
wood, and for the same reasons as before: in this
particular case, again, the fibres of the autumn wood
are darker in colour. It should be stated, however,
that many dicotyledonous trees show these peculiari-
ties more clearly than the beech : others, again, show
them less clearly.

Now it is obvious that, other things being equal,
the spring wood, with its more numerous and larger
vessels, and its looser tissue generally, will yield more
readily to lateral pressures and strains than the denser
autumn wood ; and the like is true of the pines and
firs — the closely-packed, thick-walled tracheides of
the autumn wood furnish a firmer and more resistant
material than the larger, thinner-walled tracheides of
the spring wood. To this point we shall have to return
presently.

C 2

CHAPTER II.

TIMBER, ITS PROPERTIES AND VARIETIES.

THE enormous variety presented by the hundreds
of different kinds of woods known or used in different
countries depends for the most part on such peculiari-
ties as I have referred to above, together with some
others which have not as yet been touched upon.
Everybody knows something of the multitudinous
uses to which timber is put, and a little reflection will
show that these uses are dependent upon certain
general properties of the timber. Speaking broadly,
the chief properties are its weight, hardness, elasticity,
cohesion, and power of resisting strains, &c, in
various directions, its durability in air and in water,
and so forth ; moreover, special uses demand special
properties of other kinds also, and the colour, close-
ness of texture, capacity for receiving polish, &c,
come into consideration.

CH. II.] ITS PROPERTIES AND VARIETIES. 21

Now, there is no doubt that the structure of the
wood as formed by the cambium is the chief factor in
deciding- these technological characters : it is not the
only factor, but it is the most important one. Conse-
quently no surprise can be felt that those who are
interested in timber have of late years turned their
attention to this subject with a view to ascertain as
much as possible about this structure, and to see
whether it can be controlled or modified, what dangers
it is subject to, and how far a classification of timbers
can be arrived at. The more the subject is studied,
the more interesting and practically important the
matter becomes. The results already obtained (though
the study is as yet only in its infancy) have thrown
light on several burning questions of physiology —
as witness the researches of Sachs, Hartig, Elfving,
and Godlewski, on that old puzzle, to account
for the ascent of water in tall trees. The study is,
moreover, of first importance for the comprehension
of the destruction of timber, due to " dry-rot " and
the parasites which cause diseases in standing trees,
as is shown by the brilliant researches of Prof. R.
Hartig on the destruction of timber by Hymenomy-
cctes ; and again as yielding trustworthy information
as to the value of different kinds of timber in the arts,
and enabling us to recognize foreign or new woods

22 TIMBER AND SOME OF ITS DISEASES, [chap.

of value. In support of this statement it is only
necessary to call attention to the " Manual of Indian
Timbers," prepared for the Indian Government by
Mr. Gamble ; or to refer to the beautiful series of
wood-sections prepared by Nordlingcr.

It is, of course, impossible in a small book like this
to do more than touch upon a few of the more
interesting points in this connection ; but I may
shortly summarize one or two of the more striking of
these peculiarities of timbers, if only to show how
well worth further investigation the matter is.

Many timbers, from both tropical and temperate
climates, exhibit the so-called " annual rings " on the
transverse section ; but this is not the case with all.
Most European timbers, for instance, are clearly
composed of such layers ; but in some cases the
layers (" rings " on the transverse section) are so
narrow and numerous that the unaided eye can
scarcely distinguish them, or the differences between
the spring and autumn wood are so indistinctly
marked that they may appear to be absent, or arc at
least obscure, as in the olive, holly, and orange, for
instance. It is in the tropics, however, that timber
without annual rings is most common, possibly because
the seasons of growth are not sufficiently separated
by periods of rest to cause the formation of sharply-

II.] ITS PROPERTIES AND VARIETIES. 23

marked zones, corresponding to spring and autumn
wood, e.g. some Indian Leguminosae, &c. Zones of
tissue of other kinds (especially wood-parenchyma)
often occur in such timbers, and have to be under-

Fic. 7. — Transverse section of the wo d of Pongamia glabra, Vent , selected to show
a type of timber not uncommon in India. No distin t annual rings appear, but
the wood is traversed by wavy hands of tissue, which may run into one another or
not. The vessels ( " pores" ) are few and scattered, and differ in size ; the medul-
lary lays well marked, but not large. To this type— d, tiering in other details —
belong many species of figs, acacias and other Asiatic Leguminosea;, &c.

stood, since they affect the property of the wood very
differently, e.g. some of the figs.

None of the conifers or dicotyledonous trees,
however, are devoid of medullary rays, and distinctive
characters are based on the breadth and numbers of
these: as examples for contrast may be cited the fine

24 TIMBER AND SOxME OF ITS DISEASES, [chap.

rays of the pines and firs, and the coarse obvious
ones of the oaks.

Again, the prominence or minuteness, or even (Coni-
ferae and a few Magnoliaceae) absence, of vessels in
the secondary wood afford characters for classification.

Fig. 8. — Transverse section of wood of Tamarindus indica. Linn., selected to show
a not uncommon type of Asiatic timber. The annual rings are indistinct, but
occasionally indicated by denser tissue (a\ The vessels are fairly large and few,
and scattered much as in Fig. 7, but there are no such broad bands of cells as
there.

The contrast between the extremely small vessels of
the box and the very large ones of some oaks and
the chestnut, for instance, is too striking to be over-
looked. Then, again, in some timbers the vessels
are distributed more or less equably throughout the

II.]

ITS PROPERTIES AND VARIETIES.

"annual ring," as in the alder, some willows and
poplars, &c. ; whereas in the chestnut and others they
are especially grouped at the inner side of the annual
zone {i.e. in the spring wood), and in some cases these
groupings are such as to form characteristic figures on
the transverse section, as in some oaks, Rhanmus, &c.

F]<;. 9. — Transverse section of the wood of Acer pseudo-platanus, selected to show
a type of timber common in Europe. The annual rings (a) are well-marked and
regular. The vessels are small and numerous, and scattered somewhat equally
over the whole breadth of the ring. The medullary rays are numerous, some
broad, some fine. Many European timbers (beech, hornbeam, lime, &c.) agree
with this type, except in detail.

In the woodcuts (Figs. 7- 10) I have given four
examples illustrating a few of the chief points here
adverted to.

Passing over peculiar appearances due to the
distribution of the wood-parenchyma between the

26

TIMBER AND SOME OF ITS DISEASES, [chap.

vessels, as exemplified by the figs and the maples,
as well as minor but conspicuous features which
enable experts to recognise the timber of certain

Fig. io. — The transverse section of wood of the common elm (JJlmus campestris),
selected as a common type of European timber. The annual rings are very dis-
tinct, owing to the large vessels in the spring wood ; the vessels formed during the
summer and autumn are grouped in bands or zones. The medullary rays are
numerous, but not very broad. The oak, ash. chestnut, and others agree in the
main with this type, d.ffering chiefly in the mode of grouping of the smaller
vessels, and in the breadth of the medullary rays.

trees almost at a glance, I now proceed to indicate a
few other peculiarities which distinguish different
timbers.

II.] ITS PROPERTIES AND VARIETIES. 27

The weight of equal volumes of different woods
differs more than is commonly supposed, and there are
certain details to be considered in employing weight
as a criterion which have not always been sufficiently
kept in mind.

A cubic foot of "seasoned" timber of the Indian
tree Hardzvickia binata weighs about 80 lbs. to 84
lbs., while a cubic foot of Bombax malabaricum may
weigh less than 20 lbs., and all gradations are possible
with various timbers between these or even greater
extremes. If we keep in mind the structure of wood,
it is evident that the weights of equal volumes of
merely seasoned timber will yield only approximate
results. For even if the seasoning, weighing, &c,
are effected in a constant atmosphere, woods which
differ in " porosity" and other properties will differ
in the extent to which they absorb moisture from
damp air or give it up to dry air.

In our climate, timber which is felled in April or
May, generally speaking, contains much more water
than if felled in July and August : it is, in fact, no
uncommon event to find that about half the weight, or
even more, of a piece of recently felled timber is due
to the water it contains. If this water is driven off by
heat, and the piece of wood thoroughly dried, the
latter will be found to weigh so much less, but it

28 TIMBER AND SOME OF ITS DISEASES, [chap.

will gradually increase in weight again as it imbibes
moisture.

Now it happens that the weight of a piece of timber,
compared with that of an equal volume of some
standard substance — in other words, the so-called
specific weight — is of very great importance, because
several other properties of wood stand in relation with
it, e.g. the hardness, durability, value as fuel, tendency
to shrink, &c. Fresh-cut timber in very many cases
contains on an average about 45 to 50 per cent, of its
weight of water, and if " seasoned " in the ordinary
way this is reduced to about 15 to 20 per cent.; but
the fresh timber also contains air, as may easily be
shown by warming one end of a piece of fresh wood at
the fire or in hot water and watching the bubbles driven
out, and the seasoned timber contains less water and
more air in proportion, so that we see how many
sources of error are possible in the usual weighings of
timber. At the same time, many comparative weigh-
ings of equal volumes of well-seasoned timber do yield
results which are of rough practical use.

The fact is that the so-called " specific weight " of
timber, as usually given, is not the specific gravity of
the wood-substance, but of that plus entangled air and
water. It is interesting to note that, although we
associate the property of floating with wood, timber

II.] ITS PROPERTIES AND VARIETIES 29

deprived of its air will sink rapidly, being about half
as heavy again as water, volume for volume.

The point just now, however, is not to discuss these
matters in detail, but rather to indicate that, other
things equal, the density of a piece of timber will be
greater, the more of that closely-packed, thick-walled
autumn wood it contains ; while the timber will be
specifically lighter and contain more air when dry,
the greater the proportion of the looser, thin-walled
spring wood in its "annual rings." In other words,
if we could induce the cambium to form more autumn
wood and less spring wood in each annual ring, we
could improve the quality of the timber ; and, in view
of the statement which has been made, to the effect
that large quantities of timber of poor quality reach
the Continental wood-yards every year, this is ob-
viously an important question, or at any rate may
become one. The remainder of this chapter must be
devoted to this question alone, though it should be
mentioned that several other questions of scientific
and practical importance arc connected with it.

The first point to notice is that the cambium-cells,
like all other living cells which grow and divide, arc
sensitive to the action of the environment. If the
temperature is too high or too low, their activity is
affected and may even be brought to an end ; if the

30 TIMBER AND SOME OF ITS DISEASES, [chap.

supply of oxygen is too small, their life must cease,
since they need oxygen for respiration just as do other
living cells ; if they are deprived of water, they cannot
grow — and if they cease to grow they cannot divide,
and any shortcomings in the matter of water-supply
will have for effect a diminution of activity on the part
of the cambium. The same is true of the supply of
food-substances ; certain mineral salts brought up
from the soil through the roots, and certain organic
substances (especially proteids and carbo-hydrates)
prepared in the leaves, are as necessary to the life of a
cambium-cell as they are to the life of other cells in the
plant. Now, since the manufacture of these organic
substances depends on the exposure of the green leaves
to the light, in an atmosphere containing small
quantities of carbon-dioxide, and since the quantities
manufactured are in direct relation to the area of the
leaf-surface — the size and numbers of the leaves — it is
obvious that the proper nourishment of the cambium
is directly dependent on the development of the crown
of foliage in a tree. Again, since the amount of water
(and mineral salts dissolved in it) will vary with the
larger or smaller area of the rootlets and absorbing
root-hairs (other things equal), this also becomes a
factor directly affecting our problem. Of the inter-
dependencies of other kinds between these various

II.] ITS PROPERTIES AND VARIETIES. 31

factors we cannot here speak, since they would carry
the argument too far for the space at command ; some
of them are obvious, but there are correlations of a
subtle and complex nature also.

First as to temperature. The dormant condition of
the cambium in our European winter is directly
dependent on the low temperature : as the sun's rays
warm the environment, the cambium cells begin to
grow and divide again. The solar heat acts in two
ways : it warms the soil and air, and it warms the
plant. Wood, however, is a bad conductor of heat,
and the trunk of the tree is covered by the thick corky
bark, also an extremely bad conductor, and it would
probably need the greater part of the early summer to
raise the temperature of the cambium sufficiently for
activity in the lower parts of a tree by direct solar
heat : the small twigs, on the contrary, which are
covered by only a thin layer of cortex, and epidermis,
are no doubt thus warmed fairly rapidly, and their
early awakening is to be referred to this cause. The
cambium in the trunk, however, is not raised to the
requisite temperature until the water passing up
through the wood from the roots is sufficiently warm
to transmit some of the heat brought with it from the
soil to the cells of the cambium. This also is a
somewhat slow process, for it takes some time for the

32 TIMBER AND SOME OF ITS DISEASES, [chap.

sun's rays to raise the temperature of the soil while
the days are short and the nights cold. It has been
shown that the cambium in the lower part of the
trunk of a tree may be still dormant three weeks or a
month after it has begun to act in the twigs and
small branches ; and it has also been pointed out
that trees standing in open sunny situations begin to
renew their growth earlier than trees of the same
species growing in shady or crowded plantations,
where the moss and leaf-mould, &c, prevent the sun
from warming the soil and roots so quickly. These
observations have also a direct bearing on the later
renewal of cambial activity in trees growing on
mountains or in high latitudes. Moreover, though I
cannot here open up this interesting subject in detail,
these facts have their connection with the dying off of
temperate trees in the tropics, as well as with the
killing of trees by frost in climates like our own. One
important practical point in this connection may be
adverted to. Growers of conifers are well aware that
certain species cannot be safely grown in this country
(or only in favoured spots) because the sun's rays
rouse them to activity at a time when spring frosts
are still common at night, and their young tissues are
destroyed by the frosts. Prof. R. Hartig has pointed
out a very instructive case. The larch is an Alpine

II.] ITS PROPERTIES AND VARIETIES. 33

plant, growing naturally at elevations where the
temperature of the soil is not high enough to
communicate the necessary stimulus to the cambium
until the end of May or June. Larches growing in
the lowlands, however, are apt to begin their renewed
growth in April, and frosted stems are a common
result, a point which (as the botanist just referred
to also showed) has an important bearing on that
vexed question — the " larch-disease."

The supply of oxygen to the cambium is chiefly
dependent on the supply of water from the roots, and
the aeration of the stem generally. The water begins
to ascend only when the soil is warm enough to
enable the root-hairs to act, and new ones to be
developed, and the supply of mineral salts goes hand
in hand with that of water.

Now comes in the question of the sources of the
organic substances. There is no doubt that the
cambium at first takes its supply of food-materials
from the stores which have been laid by, in the
medullary rays and wood-parenchyma, &c, at the
conclusion of the preceding year ; and it is known
that special arrangements exist in the wood and
cortex to provide for this when the water and oxygen
arrive at the seat of activity.

Assuming that all the conditions referred to are

D

34 TIMBER AND SOME OF ITS DISEASES, [chap.

favourable, the cambium cells become filled with
water in which the necessary substances are dissolved,
and distended (become turgid, or turgescent, as it is
technically called) sufficient for growth. Speaking
generally, and with reference chiefly to the trunk of
the tree, which yields the timber, the distension of the
cells is followed by growth in the direction of a radius
of the stem, and division follows in the vertical plane,
tangential to the stem. Then the processes already
described in connection with Fig. 5 repeat themselves,
and the trunk of the tree grows in thickness.

Now it is obvious that the thickening of the mass of
timber inside the cylinder of cambium must exert
pressure on the cortex and bark — must distend them
elastically, in fact — and some ingenious experiments
have been made by De Vries and others to show that
this pressure has an effect in modifying the radial
diameter of the cells and vessels formed by the
cambium. Several observers have promulgated or
accepted the view that the differences between
so-called spring and autumn wood are due to the
variations in pressure of the cortex on the cambium,
but the view has lately gained ground, based on
experimental evidence, that these differences are
matters of nutrition, and a recent investigator has
declared that the thick-walled elements and small

II.] ITS PROPERTIES AND VARIETIES. 35

sparse vessels characteristic of autumn wood can
be produced, so to speak, at will, by altering the
conditions of nutrition.

It is authoritatively stated that the pines of the cold
northern countries are preferred for ships' masts in
Europe, and that the wood-cutters and turners of
Germany prize especially the timber of firs grown at
high elevations in the Bavarian Alps. Now the most
striking peculiarity of the timbers referred to is the
even quality of the wood throughout : the annual
rings are close, and show less of the sharp contrast
between thin-walled spring wood and thick-walled
autumn wood, and it has been suggested that this is
due to the conditions of their nutrition, and in the
following way. The trees at high elevations have
their cambium lying dormant for a longer period,
and the thickening process does not begin in the
lower parts of the trunk until the days are rapidly
lengthening and the sun's rays gaining more and more
power : the consequence is that the spring is already
drawing to a close when the cambium-cells begin to
grow and divide, and hence they perform their func-
tions vigorously from the first.

One of the most interesting experiments in this
connection came under my observation during the
summer of 1887. There is a plantation of larches at

D 2

36 TIMBER AND SOME OF ITS DISEASES, [chap.

Freising near Munich, with young beeches growing
under the shade of the larches. The latter are
seventy years old, and are excellent trees in every
way. About twenty years ago these larches were
deteriorating seriously, and were subsequently
" under-planted " with beech, as foresters say — i.e.
beech-plants were introduced under the shade of
the larches. The recovery of the latter is remark-
able, and dates from the period when the under-
planting was made.

The explanation is based on the observation that
the fallen beech-leaves keep the soil covered, and
protect it from being warmed too early in the spring
by the heat of the sun's rays. This delays the
spring growth of the larches : their cambium is not
awakened into renewed activity until three weeks or
a month later than was previously the case, and hence
they are not severely tried by the spring frosts, and
the cambium is vigorously and continuously active
from the first.

But this is not all. The timber is much improved :
the annual rings contain a smaller proportion of soft,
light spring wood, and more of the desirable
summer and autumn wood consisting of closely-
packed, thick-walled elements. The explanation of
this is that the spring growth is delayed until the

II.] ITS PROPERTIES AND VARIETIES. 37

weather and soil are warmer, and the young leaves
in full activity ; whence the cambium is better
nourished from the first, and forms better tracheides
throughout its whole active period. Such a result
in itself is sufficient to repay the investigations of the
botanist into the conditions which rule the formation
of timber, but this is by no means the only outcome
of researches such as those carried on so assiduously
by Prof. Hartig in Munich, and by other vegetable
physiologists.

It is easy to understand that the toughness,
elasticity, and such like qualities of a piece of timber,
depend on the character of the tracheides, fibres, &c,
of which it is chiefly composed. Investigations are
showing that the length of such fibres differs in
different parts of the tree. Sanio has already
demonstrated that in the Scotch pine, for instance,
the tracheides differ in length at different heights in
the same trunk, becoming longer as we ascend, and
also are longer in the outer annual rings than in the
inner ones as the tree grows older, up to a certain
period ; and this is in accordance with other state-
ments to the general effect that for many years the
wood improves, and that better wood is found at the
base of the trunk.

However, it is impossible to pursue these subjects

38 TIMBER AND SOME OF ITS DISEASES, [ch. n.

in all their details : my object is served by showing
how well worthy of the necessary scientific study is
timber even to those who are only concerned with it
in its usual conditions, and within those limits of
variation in structure and function which constitute
health. The importance of the subject in connection
with the modern development of biology along the
grand road of comparative physiology, does not need
insisting upon here. It will be the object of further
chapters to show how it is, if possible, still more
important and interesting to know the structure and
functions of healthy timber, before the practical man
can understand the diseases to which timber is
subject. At the same time it must be clearly borne in
mind that these are but sketches of the subject ; for
it is as true of trees and their diseases as it is of men
and human diseases, if you would be trainers and
doctors you must know thoroughly the structures and
peculiarities of the beings which are to be under your
care.

CHAPTER III.

THE CLASSIFICATION OF TIMBERS.

THE problem of how to arrange the various kinds
of timbers so that they may be easily recognised, has
occupied the attention of many people for a long time,
but it must be confessed that none of the proposed
methods has resulted in a satisfactory classification,
and it may be doubted whether all the difficulties are
likely to be surmounted : nevertheless much may be
done towards system, and the principles employed are
not only interesting in themselves, but are also worth
examination as showing how numerous facts about
timber may be collated, and compared and contrasted.
In any case, while allowing that it is as yet impossible
so to arrange a collection of pieces of timber that all
the kinds can be recognised at a glance, it must be
admitted that the attempt to do so at least aids one
ill determining many kinds of wood by means of their

40 TIMBER AND SOME OF ITS DISEASES, [chap.

peculiar characters : of course more can be done by
taking into consideration other characters in addi-
tion, such as those of the bark, buds, leaves, &c. —
but we then approach the methods employed in the
classification of plants in the natural system of
botanists. The object under consideration is to
arrange small pieces of wood alone, so that, by
characters peculiar to each, the expert (for of course
it needs practice and experience) can recognise
them.

Like all systems of classification, that of timbers
offers every degree of difficulty, and it is easy and
natural to begin with cases which present well-marked
and readily recognisable features. Excluding such
" woods " as those of the tree-ferns, palms, Cycads, and
others which do not properly constitute " timber," I shall
direct attention only to the Conifers and Dicotyledons,
and among these, while regarding especially the true
timber-trees, I propose to give a summary of the chief
features which prove useful in classifying them. This
of course places out of consideration any scheme (such
as those adopted by the late Professor De Bary, and
others) for the classification of fibro-vascular bundles
— the bi-collatcral bundles of Cucurbitacea;, &c. ;
the radial ones of most roots ; closed, as contrasted
with open collateral bundles, &c. — all these matters

III.] THE CLASSIFICATION OF TIMBERS. 41

are foreign to our purpose, and will not help us in
classifying timbers properly so called.

There are, however, a few accessory phenomena
which prove useful occasionally, if pieces of timber
are obtained which include these.

For instance the pith, though of course not belong-
ing to the wood, sometimes presents marked features,
worth noting because it is occasionally included in
the block of timber examined, or can be obtained.
Thus, the pith on transverse section is pentagonal or
rayed in Quercus (oaks) and a few other plants, while
it is chambered in Juglans (walnut) : usually small
and insignificant, it is relatively abundant in Sam-
bit cus (elder) and Ailanthus.

Another of these accessory characters, as we may
term them, is obtained by comparing the inner and
older wood of the tree with the outer, younger wood,
and it should be remarked in passing that much
trouble is sometimes caused by the selection of
timber-specimens which do not show these characters.
Very many woods, as is well known, exhibit marked
peculiarities in their inner or " heart-wood " — the dura-
men of botanists — which is harder, or heavier, or of
some decided colour, and constitutes a true " heart-
wood," as contrasted with the softer, lighter, non-
coloured "sap-wood" {alburnum): in other cases no

42 TIMBER AND SOME OF ITS DISEASES, [chap.

obvious differences are to be noticed, and the tree is
said to have no "heart," but to consist entirely of
"sap-wood. I will not stop to discuss the physio-
logical significance of these cases, but simply quote,
as examples of woods that can be distinguished almost
by their " heart-wood " alone, Ebony, where it is black,
Guaiacum (green), Ccesalpinia Sappan (red), Logwood
(purple), and numerous instances suggest themselves
where the characters of the " heart-wood " are useful.

Yet another accessory feature is the occurrence of
certain peculiar discoloured spots or patches in certain
woods, which are always suggestive and sometimes
distinctive : these are known as " medullary spots " or
" pith flecks," and usually look like small patches of
rust in the substance of the wood. They are not at
all uncommon, and may be seen in the birches, haw-
thorn, species of Pyrus, Salix, &c. : their nature needs
further investigation, but we are only concerned here
with the fact of their occurrence.

In a certain sense we must regard the resin-canals
of some pines, firs, &c, and some Anacardiacea:^ as
useful accessory characters : many Conifers especially
being distinguished by their presence. These resin-
canals have nothing to do with the true vessels of the
wood of Dicotyledons, of which more will be said
presently

in.] THE CLASSIFICATION OF TIMBERS. 43

Turning our attention now to those features which
are more generally characteristic of timbers, it has to
be admitted that their employment is a matter of
considerable difficulty in some cases, though it is
easy enough in others. I will describe some of the
principal varieties as we proceed, and give a few
illustrations in each case.

All Conifers and Dicotyledons which form timber
are provided with medullary rays, and it has been
found possible to make something of the variations
they present in different cases. Thus, the medullary
rays may be few and relatively far apart, as in
Laburnum and Robinia (with 19 or 20 in a breadth of
5 mm.), or numerous and crowded, as in the oak (with
64 in a breadth of 5 mm.). Rhododendron maximum
has as many as 140 in the same area, according to
Nordlinger. Then, they may be very narrow, requir-
ing at least a lens for their observation, as in the
pines, ebony, horse-chestnut, willows, &c. ; or suffi-
ciently broad to be seen at a glance with the unaided
eye, as in the oaks and Casuarhia. All degrees of
breadth from less than CO05 mm. to I mm. occur,
and the attempt has been made to cast them into
six groups, or degrees of fineness, but it seems
impossible to define all these groups : nevertheless
we can speak of fine, medium, and broad rays

44 TIMBER AND SOME OF ITS DISEASES, [chap.

respectively, the common holly giving us a fairly
medium breadth.

In some cases, and markedly so in the oaks, there
are two kinds of medullary rays : large broad obvious
ones, with more numerous finer ones between them.
Such rays may also be distinguished as consisting of
many or one series of cells — pluri-seriate and uni-
seriate medullary rays. In some Conifers a resin-
canal often occurs in the medullary ray : in the beech
the broad rays widen out where they cross the
boundary between the annual rings : in the hornbeam
the so-called broad medullary rays are composed of
several rays running parallel and close together.

The next general character I have to consider is
that afforded by the presence or absence, &c. of the
so-called "annual rings." It may be, and has been
questioned whether zones indicating periodic changes
in increment are ever absent from the timber of trees,
but be this as it may there are certainly cases of
tropical timbers where no such annual-rings, as they
are called, can be distinguished by the unaided eye, or
even with a lens : such timbers are said to be devoid
of " annual rings." I say " so-called annual rings,"
because we are not yet sure that the periodic zones
correspond in all cases with annual increment, though
that is no doubt normally the case with all European

in.] THE CLASSIFICATION OF TIMBERS. 45

trees. Examples of timbers which show no annual
rings on the transverse section are common among
Indian timbers, e.g. iron wood, mango, ebony, &c.
In the vast majority of common timbers, however,
including many tropical forms, the transverse section
always shows more or less concentric zones or rings : in
many cases, as in oak, ash, teak, toon, &c, these are
obviously the " annual rings," but in other cases, as in
the figs, Casuarina, Pongamia, &c. the apparent rings
are found to be of a different character, and due to
concentric or excentric partial or complete zones of
soft tissues, especially wood-parenchyma. I shall term
these " false rings : " a little practice will enable the
student to recognise them in most cases. It may be
noted that in Calophyllum, and many Sapotacecz and
Anonacece, and others, these partial zones are made up
of wavy, pale, bar-like markings between the
medullary rays.

As to the timbers with undoubted rings, two chief
types may be readily distinguished if the student
understands the meaning of the line of demarcation
between the annual rings.

In the one type the vessels in the spring- wood arc
so large or so numerous (or both), as contrasted with
those in the autumn-wood of the same annual ring,
that the boundary between any two rings is par-

46 TIMBER AND SOME OF ITS DISEASES, [chap.

ticularly sharp, owing to the contrast between the
porous and the dense wood, e.g. oak, ash, plum, teak,
&c. In the other of these chief types the line of
demarcation is due to similar differences in the density
of the fibrous and other elements of the wood rather
than to contrast between porous {i.e. very vascular) and
dense wood ; the autumn-wood has very thick walls and
small lumina, the spring-wood thinner walls and
larger lumina, without special reference to the vessels,
which are usually small and nearly evenly dispersed
through the whole. As examples I may refer to the
wood of birch, maple, horse-chestnut, Shorea robusta,
&c. That difficulties in deciding must occur in some
cases is only too evident, and it is well known that in
individual cases departures from the type are produced
by local disturbances — e.g. the formation of two so-
called " annual rings " in one year, and (at least it is
suspected and needs investigation) the suppression of
the demarcation lines by changes due to climatic and
other local influences. Nevertheless the characters
usually work well in practice. It should be remarked
that whereas the course of the annual rings is normally
concentric and regular, it is wavy in some cases, e.g.
barberry, where the crests of the waves project out-
wards at the medullary rays, whereas they project
inwards in Kahnia latifolia, hornbeam, beech, &c.

in.] THE CLASSIFICATION OF TIMBERS. 47

The false zones of soft tissue are often seen to run
into one another, whereas this is not the case with true
rings, however excentric they are.

The next character of general importance is the
presence or absence of vessels — often called " pores "
by technologists — as seen on the transverse section ;
and there are certain peculiarities connected with
them.

The first thing to note is a possible danger of the
tyro mistaking the resin-canals of Conifers for these
vessels of the wood : practical aquaintance with the
irregular outline and very different structure and
distribution of these canals will alone serve the
student here. Vessels (excluding the small spiral
vessels of the proto-xylem which form the so-called
" medullary-sheath," and which do not come into con-
sideration) are found in the wood of all Dicotyledons,
except Drimys and one or two of its allies, while they
are as regularly absent from that of the Conifers ;
consequently it is easy at the outset to distinguish
the woods of these two great groups at a glance, at
least with the aid of a lens. In the Dicotyledons,
however, considerable differences are to be observed
regarding the vessels ; and first, as to their size.

The rule is that the vessels are largest and most
numerous in the spring-wood, diminishing outwards

48 TIMBER AND SOME OF ITS DISEASES, [chap.

(in Kalmia, strange to say, the reverse is the case), as
well seen in oak ; but in some cases the differences are
so slight that we say the vessels are equal all over, e.g.
box, birch, willow, alder, &c. The diameter of the
vessels varies much in different cases, and very large
ones may coexist with very small ones. Neglecting
the wood of some climbers, where the vessels are
easily seen with the unaided eye, and may be
more than half a millimetre in diameter, we find
examples of large vessels in the oak, ash, chest-
nut, walnut, &c, where they are visible without a
lens, and of extremely small ones in box, birch,
willow, maple, horse-chestnut, &c. All sizes between
these extremes are to be met with, and Nordlinger
has tried to arrange them in six groups, but I cannot
recommend this, as it seems impossible to maintain
them. The laburnum and the plane afford examples
of medium-sized vessels.

Characters have been obtained from the mode of
grouping of the vessels, or " pores," on the transverse
section. Thus we have seen how their equal distribu-
tion, or concentration in the spring-wood, as the case
may be, affects the classification as regards annual
rings ; but besides this we find peculiarities of other
kinds which arc characteristic. In the hornbeam, for
instance, there are long, sinuous lines of pores radiat-

III.] THE CLASSIFICATION OF TIMBERS. 49

ing between the medullary rays from centre to
circumference of the stem. In other cases sinuous
bands of small pores are seen running peripherally,
and almost simulating false rings, e.g. the elm.
Beautifully-arranged tongue-like or flame-like groups
of pores are seen in the oaks, chestnut, Rhajunus,
Ulex, &c, and these are very characteristic.

Attempts have been made to carry the examination
of these features further by means of the microscope,
and to distinguish woods where the pores are single
from those where they are apt to be grouped in pairs,
threes and fours, and so on ; but although it is true
that the vessels arc usually single in the box, for
instance, and often in groups of five to twelve or
more in holly and hazel, while less than twenty to
fifty together rarely occur in Rhamnns catharticus,fk.c,
I cannot find that the characters are either sufficiently
constant or sufficiently obvious for practical purposes.

These, then, are the principal general characters
which can be employed in classifying timbers, and we
may now ask whether any others exist that could be
made use of. The reply is that several others could be
used more than they are if we had good records and
scales of comparison. Some of these may be shortly
indicated as follows: The hardness of different tim-
bers may be very different. Thus the Indian Bombax

E

50 TIMBER AND SOME OF ITS DISEASES, [chap.

malabaricum is so soft that a pin may be easily driven
into it, whereas Mesua ferrea is so hard that it turns
the edge of almost any tool ; between these extremes
we find all degrees of hardness, and it is the moderately
hard woods which are so useful for general purposes,
e.g. teak and oak. The dry weight of a timber is
usually not far out of proportion to its hardness, and
characters can sometimes be derived from a sort of
rough scale of weight — the weight of a cubic foot or
metre, or some other unit being chosen for com-
parison. Thus, the wood of ErytJirina suberosa may
weigh as little as 13 lbs. the cubic foot, while that of
Hardzvickia binata may reach 84 to 85 lbs., and all
degrees of heaviness are found in different timbers
between such extremes. At the same time more in-
formation is needed as to the relative weights of equal
volumes of wood, as we have already seen how falla-
cious ordinary rough-and-ready weighings may be,
made, as they usually are, without any guarantee that
each specimen was dried to the same extent : on
the whole, we- may, perhaps, call any timber light
which, when air dry, weighs less than 30 lbs. per
cubic foot, and moderately heavy if it reaches 40
to 50 lbs. ; anything over 60 lbs. is decidedly heavy.
The "closeness" or "porosity" of different timbers
bears an obvious relationship to their hardness and

III.] THE CLASSIFICATION OF TIMBERS. 51

weight in most cases. Woods are also even-grained,
or cross-grained, open, rough, &c, in various degrees.

The colour of a timber is sometimes a useful cha-
racter, and has been already referred to when speaking
of the heart-wood and sap-wood, which usually have
different hues.

There are a few other characteristics afforded by
special kinds of timber which should be noticed,
though they cannot be made use of in a general
classification. I refer particularly to such peculiari-
ties as the odours of sandal-wood, deal, teak, toon,
and the Australian pencil-cedar (Syuoum glandu-
losum), &c. Certain special markings, such as the
satiny lustre of satin-wood ; the white mineral
substances (apatite !) in the vessels of teak ; the
appearance of the polished surface, and a number
of other features which come under the notice of the
timber merchant and technologist must be passed
over here, useful as they are for the recognition of
special timbers on the spot.

A high authority has written, with respect to this
subject, " It is not always easy to give in words an
explanation of the reasons which lead one who is
tolerably conversant with the structure of woods to
pronounce an opinion; there are often characters of
appearance, touch, colour, odour, &C, which afford

E 2

52 TIMBER AND SOME OF ITS DISEASES, [chap.

clues, as well as the arrangement and relative size
of the pores and medullary rays, and the presence or
absence of annual rings ; so that it is really only
experience and habit that can teach us to recognize,
from a mere inspection of a wood, the place which it
ought to occupy in the natural system." But while
we may readily admit the general truth of this re-
mark, it seems a just rejoinder that in so far as the
characters of wood are capable of accurate descrip-
tion, it will become more and more possible to
explain why the expert can recognise a piece of
timber. Definiteness and system are the two things
to aim at.

In order to illustrate the sort of lines along which
a systematic tabulation of the characters of timber
might be looked for, I subjoin a scheme of classifica-
tion of some of the most important European and
Indian timbers, and I may perhaps add my conviction
that if observers will only continue to note peculiari-
ties, and compare them in some such manner as this,
it should be possible to obtain a much more complete
classification than we could bring together now.

For the foresters' purposes in any country, many
extremely valuable characters are to be obtained
incidentally, as it were, to those of the timber proper,
from observing the size of the tree, or shrub, or if

in.] THE CLASSIFICATION OF TIMBERS. 53

it is a climbing plant which yields the wood in
question. Again, the bark and cortex in the young
and older states — its colour, thickness, texture, mode
of stripping, &c. Some trees are evergreen, others
deciduous : some grow in swamps, others on dry
plains or hills ; some are gregarious, and so on.
Moreover, in classifying the trees of a large country,
the facts of geographical distribution of some of them
can often be utilized — for instance, no one need look
for teak on the Himalayan heights, nor for deodar in
the plains of Southern India, and, again, Heritiera
littoralis is a tree of the tidal forests of India and
Burma, and is not likely to be seen by a forest-officer
working away from such districts. Such facts as
these, amplified and accurately generalized, might be
made much use of in drawing up lists, &c, for the
guidance of those at work in geographically different
districts, as it is the timbers as commonly met with
in the yards that need classifying.1

It will be understood that the following table is of
course intended to be, not a complete classification of
timbers, but an illustration how such classification
might be possible, and gradually improved as time
and knowledge progress.

1 Further information on this subject will be found in I.:»lett's
Timber a>ni Timber Trees. Macmillan and Co., 1894.

54 TIMBER AND SOME OF ITS DISEASES, [chap.

I. Conifers.

The wood (except immediately around the pith) contains no
true vessels, though resin-canals occur in many cases in the
autumn wood. Annual rings nearly always sharply marked,
from the denser autumn zone. Medullary rays very fine and
numerous.

A. There are no resin-canals in the wood.

(i) No true " heart" is to be distinguished :

e.g. Silver Fir ; Abies Webbiana.

(2) There is a distinct central " heart-wood " :

e.g. Yew, Juniper, Deodar ; Wellingtonia.

B. Resin-canals are present, at least in the autumn-wood.

(3) No true "heart" is to be distinguished :

e.g. Spruce ; Abies Smithiana.

(4) There is a distinct central " heart-wood " :

e.g. The Pines and the Larch.

II. Dicotyledons.

Always have true vessels (except Drimys and one or two rare
forms), which differ considerably in size, number, and dis-
tribution. The wood is usually complex in structure, the
elements (cells, fibres, tracheides, &c), being variously dis-
posed. Annual rings may be obvious, or indistinct, or even
absent, and marked in various ways. Medullary rays always
present, but differ much in number, size, &c.

A. DICOTYLEDONS with no distinguishable annual rings ; but
there may be also partial zones of tissue (usually wood-
parenchyma) easily distinguished as incomplete bands which

Hi.] THE CLASSIFICATION OF TIMBERS. 55

run into one another, and do not pass round the section
(" false rings ").

N.B.— There are no European timbers in this class ; it
is, on the other hand, very full of Indian and tropical
timbers,
(i) Partial zones are present, running more or less con-
centrically as bands or incomplete rings, passing
into one another here and there, and forming so-
called " false rings."
(i) Medullary rays of two kinds : some very broad and
easily seen without a lens, the majority fine.
This may be termed the type of the Indian
Oaks:

e.g. Quercus lamellosa, Q. incana, and
some other Indian oaks,
(ii) All the medullary rays narrow and of one kind.
The further subdivision of this group depends
on too many characters to be enumerated
in detail here, but the following important
Indian timbers maybe given in illustration :—
a The "false rings" of tissue are particularly
distinct. This may be termed the Fig
type, and its chief characteristic is unmis-
takable when once seen,
(i) No distinct heart-wood is formed, the
timber is moderately hard and dense
(weight about 40 lbs. per cubic foot),
greyish.
e.g. Ficus bengalensis, Pongamia glabra,
Terminalia belerica} &c.
(ii) Heart-wood dark and heavy ; about 60 lbs.
per cubic foot ;
eg. Prosopis spicigcra.
ft The false rings are obscure, and the wood
particularly hard, heavy, and close-grained.
This may be termed the Iron-wo.nl type.

56 TIMBER AND SOME OF ITS DISEASES. [CHAP.

All have a dense red, brown, purple, or
black heart (75 to 85 lbs. the cubic foot) :
e.g. Mesua ferrea, Heritiera littoralis,
Xylia dolabriformis, Hardwickia
btnata, Terminalia tomentosa, Dyos-
pyros Melanoxylon, &c. These are
the chief hard woods of India.
y The following (and others) are less easily
classified, and other characters have to be
used in grouping them :

e.g. Dalbergia Sissoo, D. latifolia, Bassia
latifolia, Melia indica, Acacia
arabica, A. catechu, Lagerstroe7nia
parviflora, Pterocarpus Marsiipium,
&c.
(2) No such partial zones or " false rings " are evident ;
the wood is practically devoid of annual rings
(though microscopic examination of thin sections
may show traces),
(i) Soft wood ; no heart-wood formed ; grey (Bombax
type) :

e.g. Bombax malabaricum, Mango,
(ii) Heart-wood usually present, and the woods denser
and less porous :

eg. Albizzia Lebbek, Schima Wallichii,
Zizyphusjujuba, Tam art xarticu lata,
Adina cordifolia, Dipterocarpus
tuberculatus, &c.

B. Dicotyledons in which the annual rings are always dis-
tinguishable, and usually obvious, though they may be very
narrow. These rings are marked in two chief ways, and a
little practice enables the student to distinguish them easily
in most cases.

(a) The annual rings are particularly clear, because the
vessels in the spring wood are either larger than

in.] THE CLASSIFICATION OF TIMBERS. 57

elsewhere, or they are numerous and crowded,
whereas the vessels in the autumn zone are small
or few and scattered.

(1) The vessels on the inner side of the spring wood in

each annual ring are large and conspicuous.
(Many of our European timbers come here.)
The various types are further distinguished by the
characters of the medullary rays, and the
mode of distribution of the vessels, &c, in
the autumn zone,
(i) Some of the medullary rays are broad, and
easily visible to the naked eye :

e.g. Quercus Robur, &c, the Oak type,
(ii) All the medullary rays are alike, and fine.
(The further subdivision depends on the
arrangement of the autumn vessels, &c.) :
e.g. the Ash, Elm, Chestnut, and the
following Indian timbers : — Teak,
Cedrela Toon a, Melia Asedarach,
Lagerstraemia Regz'ncz, &c.

(2) The vessels on the inner margin of the spring-

wood are not larger than elsewhere, but they
are more numerous and crowded than in the
autumn wood, and hence render this zone
porous in another manner.

e.g. Plum, Elder, Lilac, Buckthorn, &c,
and the following Indian timbers : —
Santalum album, Gmelina arborea,
&c.
(b) The annual rings are distinct, but the line of demarca-
tion is due to the close texture of the elements
composing the autumn wood, and not to con-
spicuous differences in the sizes or distribution
of the vessels, hence the annual zones appear to
be divided by firm thin lines. (Most of our
European timbers come here.) The chief types

58 TIMBER AND SOME OF ITS DISEASES, [ch. ill.

are afforded by the following, and they are dis-
tinguished further by minor details of structure,
colour, density, &c.
(i) The vessels are visible without a lens, and scattered ;

e.g. Walnut, Shorea robusta.
(ii) The vessels are minute, and usually numerous.
The wood (at least the heart-wood) is hard.

e.g. Beech, Birch, Box, Maple, Plane, Horn-
beam, Eugenia J ambolana, Chloroxy-
lon Swie 'tenia, Anogeissus latifolia,
Schleicher a trijuga, ALgle Marme/os,
&c.
The wood is soft,

e.g. Horsechestnut, Willow, Poplar, Alder,
Populus eitphratica, Michelia exce/sa,
Holarrhena antidysenterica, Dillenia
indica, Boswellia thuri/era, &c.

CHAPTER IV.

ON THE THEORIES ADVANCED TO EXPLAIN THE
ASCENT OF WATER IN TALL TREES.

It has often been remarked that no account exists
in any English work, of the recent views as to the
mechanism which lifts water to the top of tall trees,
or of the controversy which has been so eagerly
carried on for some years on this subject, and, con-
sidering the numerous interesting observations and
experiments which have been made in this connection,
some general account of the matter should be of in-
terest both to students and teachers. In view of the
necessity that some botanist should undertake the
task, and that it ought to be done soon because the
phenomena have so many bearings upon matters
now engaging the attention of biologists, I have
attempted it, especially because so many side-lights

60 TIMBER AND SOME OF ITS DISEASES, [chap.

on the structure and functions of timber turn up by
the way during the discussion. It is true, the subject
demands the combined efforts of the physicist and the
botanist for its complete treatment, but it has seemed
possible to give a general account of the whole con-
troversy, without necessarily entering into those side
issues which turn upon the more purely physical and
mathematical points. With respect to the importance
of the subject to the physiologist there is no need to
say more than that it has points of contact and sugges-
tion with almost every department of that vast study.

In and about the year i860, much light had been
thrown on the subject of capillarity, and, for our
purposes, especially by the researches of Jamin,1 who
thought he could show that the ascent of water in
a tree was simply a capillary phenomenon, the
vessels &c. in the stem being the capillary tubes
concerned.

If a capillary glass tube is placed with one end in
water, the surface of the column which rises in the
tube is concave, as is well known, owing to the adhesion
between the glass and the water : the concave surface
may be regarded as a film, which exerts pressure on
the interior of the liquid, but which pressure is smaller
than it would be if the film were plane. Hence the

1 See, for instance, Comptes Rcndus, i860, t. 1. pp. 172, 311, 385.

iv.] VARIOUS THEORIES, &C. 61

pressure on the column exerted by the water outside
is greater than that inside, and the water rises in the
tube till equilibrium is established. For tubes of the
same material this capillary ascension is inversely pro-
portional to the diameter of the tube. If we take a
long capillary tube filled with alternate bubbles of air
and columns of water (such a system is called a chapelet
de Jainin) it will be found that even huge pressures at
one end exhaust their effect before the other end is
reached — each of the columns of water shows less and
less effect. In each partial column, the anterior end
becomes more concave, the hinder end less so ; i.e. we
have two unequally curved films exerting different
pressures on the interior of the column in each case,
the pressure of the hinder (less concave) surface being
larger opposes the external pressure with consider-
able effect. Hence the pressure conveyed by the first
bubble to those in front, is less than that exerted at
the opening of the tube ; the pressure of the second
bubble on the third less still, and so on till the visible
effect has practically disappeared before the other
end of the tube is reached.

It was concluded from Jamin's researches that
a water-column of any height may be held upright
if in a fine tube and broken by a sufficient number
of air bubbles ; and if the tubes are alternately

62 TIMBER AND SOME OF ITS DISEASES, [chap.

thicker and thinner, the chapelct de Jamin is even
more effective.

Jamin has shown, further, that porous bodies such
as gypsum, absorb water with a force equal to a
pressure of several atmospheres : when such bodies are
saturated, they are practically impervious to air, though
easily permeable by water. Hence a block of gypsum
may be fixed to each end of a glass tube, the apparatus
saturated with water and the tube filled, and if the
lower block of gypsum is placed in wet sand and the
upper exposed to the air, the evaporation at the ex-
posed end is compensated by a flow from below.

Jamin thought this explained the ascent of water
in plants, and that the lumina of the vessels, &c, corre-
sponded to the capillaries of his system. Hofmeister
on the contrary thought the experiment confirmed
Meyen's view that the water passes up as imbibed
water — supposing the wood-walls to correspond to
the porous body. We shall see how Sachs has
extended this idea ; but it should be clearly appre-
hended that Sachs's idea of imbibition is a very
different one from the old notion of its dependence
on capillarity. In a capillary system there are pores,
and air may be driven out : the water of imbibition
is inter-molecular (or at most inter-micellar) water.

Such were some of the views which led gradually

iv.] VARIOUS THEORIES, &C. 63

towards the modern ideas of imbibition. Sachs in his
Experimental-PJiysiologie, took both views into ac-
count, and thought that capillarity as well as imbibi-
tion came into play. In 1868 Unger1 concluded that
the water does not ascend in the lumina of the vessels,
&c, but that it passes up as water of imbibition in
the substance of the cell-walls ; and Sachs, in the
fourth edition of his Lehrbuck, definitely threw over
the capillary theory, and assumed that the water
moves either entirely as water of imbibition in the
substance of the walls, or (as Quincke had suggested)
as a thin film of water on the inside of these walls.

Meanwhile observers had begun ranging themselves
more or less into two groups as it were. Boehm 2 in
1864 suggested that the elasticity of the epidermal
cell-walls would come into play, and affect the
pressures on and in the air-bubbles in the cavities of
the elements : and Theod. Hartig 3 had insisted upon
the alternate expansions and contractions of these
air-bubbles as important factors in causing water to
move from cell to cell.

From other points of view Von Hohnel showed '

1 Sitzungsber. </. Akad. J. Wissensch. zu Wien, Ivii. abth. i. 1868.

2 Sitzungsber. </. kaiserl, Akad. der Wiss. zu Wienth. 50 i. (1S64).
:' Bot. Zeitg., 1 86 1, p. 18.

4 Jahrb.fiir Wiss. Bot., 1879, 1). 12, p. 77.

64 TIMBER AND SOME OF ITS DISEASES, [chap.

in 1879 that if a transpiring branch is cut under water,
the air presses the water with considerable rapidity
into the vessels.

So much by way of introduction. I now propose
to start with the position of affairs in 1882, the
year in which Sachs's Vorlesungen uber Pflanzen-
pJiysiologie first appeared.

At this time it was allowed by all that the water which
ascends the stem of the tree passes from the roots to
the leaves in the wood — that it is absorbed by the
root-hairs, traverses the roots to the stem, and passes
up the wood to the leaves, whence it passes off by
transpiration. It was also agreed that the main flow
takes place in the " sap-wood " (alburnum), because
the simple experiment of " ringing " the stem proved
that with most trees the flow is seriously diminished,
or stopped, if the outer wood is removed as well as the
cortex, whereas no harm ensues if the alburnum is
left intact : moreover, observations on hollow trees
showed that the inner parts of the timber are not
necessary to the ascent of the water.

Further points of agreement were found in the
knowledge of the structure of wood — the annual rings,
medullary rays, the differences between duramen and
alburnum, the properties of the cambium, &c. It
was also known that while the secondary wood of

iv.] VARIOUS THEORIES, &c. 65

Conifers has no vessels, but consists almost entirely
of tracheides with bordered pits, the vast majority of
Dicotyledons and Monocotyledons always have vessels
in addition to other elements — tracheides, libriform
fibres, and wood-parenchyma. The proportions of
the latter vary, and one or more kinds may be
absent.

Less unanimity appeared as to the properties and
functions of the elements of the wood, and in fact
the whole controversy at one time turned upon this
question. It had been discovered that, broadly speak-
ing, the vessels contained less water and more air in
the summer than in the winter, and that even in
the tracheides there was usually if not always some
air. Whether the vessels and tracheides were ever
entirely devoid of either air or water was a disputed
point. Much discussion was also still abroad as to
the ultimate structure of the cell-walls of the elements,
but it was common knowledge that, whereas the
wood-parenchyma usually still retains its cellulose
walls, protoplasmic contents, starch, &c. (and the same
with the cells of the medullary rays), the walls of the
vessels, tracheides and fibres are lignified more or less
completely, and soon lose their living contents.

Since most of the other points of importance to
the controversy were either disputed or imperfectly

r

66 TIMBER AND SOME OF ITS DISEASES, [chap.

understood, I shall defer them till such time as they
crop up naturally in the argument.

As to the explanation of the ascent of the water
from the soil to the leaves, two conflicting hypotheses
were in the field — neglecting older views, which either
simply shelved the question by speaking of a process
of suction or diffusion, or tried to explain the
phenomenon as due to root-pressure, or capillarity,
or to the molecular movements in a thin film of
water overspreading the inner surface of the elements.1
The two prominent hypotheses were (i) Sachs's view
that the water travels as water of imbibition in the
molecular interstices of the lignified walls of the
vessels and tracheides, and (2) the view, at the time
most strenuously advocated by Boehm, that the
water ascends in the cavities of the tracheides and
vessels.

YYe will consider Sachs's hypothesis first.2 Taking
his stand on the facts already conceded, Sachs points
out that we have to explain a movement by which a
particle of water must travel at a rate of from fifty to
two hundred centimetres per hour in the wood, and
by which the leaves are supplied so copiously, that

1 For a summary and criticism of older views see Sachs's Text-Book,
second English edition.

'-' See his Lectures on the Physiology of Plants, English edition, p. 225.

rv ] VARIOUS THEORIES, &c. 67

they transpire in one season quantities amounting to
many times the volume of the whole plant.

Taking the wood of Conifers as being the simplest
and most thoroughly studied, and choosing that of
the yew because it is devoid of resin-canals, he
points out that the tracheides are closed cavities —
the membranes of the bordered pits forming a com-
plete septum — and hence a piece of yew wood may
be employed to filter off fine particles. There being
no capillar)- tubes here, we cannot entertain the idea
of a capillary ascent : moreover, even in Dicotyledons,
the sectional areas of the lumina of the vessels are too
large to admit of an ascent by capillarity beyond a
few yards at most.

But now comes a weighty argument. At the time
when transpiration is most active in the summer, and
therefore when most water i-; passing through the
wood, the cavities of the tracheides and vessels are
not full of water, but contain very little, and the
vessels may even (so Sachs asserts) be empty : hence
the wood floats on water, which it would not do
unless considerable air-cavities existed. The presence
of the air can also be proved by warming the wood,
and the phenomenon of " water-logging " depends on
the gradual filling of the cavities by water, which
soaks in and displaces the air.

F 2

68 TIMBER AND SOME OF ITS DISEASES, [chap.

Hence, at the time when most water is ascending
through the wood, the cavities of the elements contain
much air (and no doubt vapour). The determination
of the specific gravity, shows that the substance of the
wood cell-walls is heavier than water in the ratio of
r$6 to 1 ; and of course it was easy to determine how
much water a given piece of wood contained, and it
was found by this method also that the water could
not have been held in the walls : it also showed that
some of the water was in the cavities.

Sachs then, by the ingenious method of finding how
much water is absorbed when a piece of dry wood is
suspended in vapour, determined that the elements
imbibe by means of their lignified cell-walls, to the
extent of half the volume of the latter.

Based on a long series of such investigations,1
Sachs finally came to the conclusion that the lignified
walls of the wood-elements have certain remarkable
molecular properties : that they absorb relatively but
little water, but that this water is wonderfully mobile.
On this assumption he gave to the world his daring
hypothesis, which is that the water in the molecular
interstices of the walls of the tracheides, vessels, &c.
moves upwards to compensate that lost by transpira-

1 See Sachs's Uber die Porositdt des Holzcs, Wurzburg Arbeitcn, ii.
1879.

IV.] VARIOUS THEORIES, &c. 69

tion, because the slightest displacement is sufficient to
disturb the equilibrium of the whole continuous
column of water.

Of course the great advantage claimed for the
hypothesis was that it did away with the difficulty
presented by the height of tall trees. Sachs supposes
the molecules of water to be as it were dissolved in
the substance of the cell-walls, held by molecular
forces in the same way that a particle of salt is
commonly supposed to be suspended between mole-
cules of water in a solution ; and just as any particle
of salt in the ocean, for instance, is free to move in
any direction — to and fro, or up and down — and quite
independently of gravitation, so he thought his mole-
cules of water could be regarded as infinitely mobile
between the particles of the cell-wall. It matters
not whether we regard the cell-wall as composed of
iiiicelhe, or aggregate molecules, or other structural
units, in this connection, as the hypothesis simply
turns on the freedom of movement in spaces beyond
the ken of rough physics.

When we come to experiments offered in support
of this hypothesis, the weak points come out some-
what vividly.

If tin sti n of a hop, flax, &c, be sharply bent on
itself, the cavities of the vessels, &c. arc of course com-

■jo TIMBER AND SOME OF ITS DISEASES. Lchap.

pressed : Sachs assumed that they were closed entirely,
and that the fact that the leaves above still transpired
proved the truth of his assumption — the water moves
in the substance of the cell-walls, because there is here
no other passage open to it. If a branch is cut and
allowed to dry, the power of conducting water is
lost — a dry stick placed in water may become
gradually saturated, but it has lost the power of con-
ducting the water. Sachs explained this as due to some
molecular change in the substance of the cell-walls.
To the same cause he attributes the gradual loss of
conductivity noticed when the cut end of a fresh
branch is immersed for some time in water. Those
familiar with the literature will have noticed that
Sachs did not regard several facts then known, and
bearing more than indirectly on his hypothesis.

For instance, if a shoot is cut and placed with the
cut end in water in one leg of a [J tube, and allowed to
droop, it is often possible to restore the turgid condi-
tion of the upper tissues, by forcing water in under the
pressure of mercury poured into the other leg of the
(J tube.

Again, at the time when transpiration is most active
in the summer, it was found by Von Hohnel that if
a shoot is bent gently down, and cut through under
water, or a coloured solution, or even mercury, the

iv.] VARIOUS THEORIES, &C. 71

liquid rushes up into the vessels under a pressure
which must be regarded as considerable : this is due
to the fact that the air in the tracheides, vessels, &c,
is rarefied, and the pressure just referred to is the
difference between that of the contained air and that
of the external atmosphere. Of course Sachs viewed
all such cases as only going to show that when the
leaves are taking water rapidly from the cell -walls,
the latter supply themselves from whatever surplus
water may exist in the cavities, and, since air cannot
pass through the wet membranes or only to a very
slight extent, the contained air-bubbles expanded, and
so on. Sachs attributes to these air-bubbles, however,
some influence in drawing water into the cavities.1

An old experiment of Theod. Hartig's should be
mentioned here. If a piece of the stem of a Conifer, a
yard or more long and with the ends cut clean across,
is held vertically, and one drop of water is placed on
the upper section, a similar drop appears at the lower
end in a (cxv seconds, enlarging in proportion as the
upper one sinks into the wood : this is regarded by
Sachs as a proof generally of the easy permeability of
wood. I shall have occasion to refer to this experi-
ment of Theod. Hartig's several times in the course of
the discussion, as some important matters turn on its
' Vorlesungen ul>cr Pflanzen-physiologie, p. 122 (Eng. Ed. p. 269).

72 TIMBER AND SOME OF ITS DISEASES, [chap.

explanation. I now pass to the r/sum/ of the alterna-
tive hypothesis, that the water ascends in the cavities
of the tracheides, vessels, &c, and not in the substance
of the cell-walls.

In 1 88 1, Boehm published a paper on the subject,1
which, whatever its shortcomings from the physicist's
point of view, must be quoted in order to show the
direction of thought on the side of those who could
not accept Sachs's assumptions.

Boehm pointed out that the existence of the
"negative pressure" in transpiring plants puts osmosis
out of court as a cause for the ascent of the water in
the wood : he also agrees with those who reject all
capillary hypotheses. He then advances the following
criticisms ; (i) the wood contains more water than
can be contained in the walls ; (2) if cylinders of wood
are cut so that their long axes are parallel to a radius
of the stem, or to a tangent of the same, then the
easy pressure of water in the direction of their longi-
tudinal axes (which is known to occur in cylinders
with their long axes co-incident with the axis of the
stem) is no longer possible. In other words, it takes a
much greater pressure to drive water across the stem,
either tangentially or radially, than it does to drive

r Dt fa cranse du ?novemenl de feau, &c. (Ann. des Sc. Nat. vi. ser.
t. >ii., 1S81.)

IV.] VARIOUS THEORIES, &C. 73

it in the direction of the long axes of the elements.
(3) Cuttings of willows &c, will, when transpiring,
exert a pull (so to speak) on mercury, to such an extent
as to raise a column sixty mm. in height. (4) Fairly
thick longitudinal sections of fresh branches can be
so arranged under the microscope as to show that air-
bubbles, under feeble pressure, exist in the vessels and
tracheides. Placed in water, the bubbles contract — i.e.
water is forced through the damp walls, which are
impervious to air. It may be mentioned, by the way,
that a rough illustration of the imperviousness of a
wet membrane to air is to be seen in any wash-tub,
where the imprisoned air drives up the wet linen into
rounded hummocks as the laundress pushes various
parts deeper into the water. (5) Boehm rightly lays
stress on the importance of Von Hohnel's discovery1
that the pressure in the vessels in summer may be so
low, that it docs not exceed ten cm. of mercury.
(C) He then points out the bearing of his previous
papers on the whole subject (of which the present
is practically a summary), and his own numerous
observations,2 and among others notes the following.

1 llaberlandt's Wiss. prakt. Unters auf den Gcl>. J. pflanzenbaues,
t. xi., 1877.

2 Of course it is impossible to quote here all that bears on this
auestion. but the chief of these oaners arc in Landw. Versuchs. Stat.

74 TIMBER AND SOME OF ITS DISEASES, [chap.

Theodore Hartig's experiment with the piece of stick
shows (Boehm thought) that the drop of water causes
a long column to move: if, however, the vessels or
tracheides are first injected with mercury, it requires
great pressure to cause movement of the column, and
the experiment fails. Finally, Boehm denies that the
vessels or tracheides are ever totally devoid of liquid
water ; even when the transpiration is most active
there is always some water as well as air present.

Boehm then puts forward his own hypothesis to
explain the .water current in tall trees. The cells of
the transpiring surfaces (such as the leaf epidermis)
have clastic walls, and when they lose water by
evaporation, the pressure of the atmosphere tends to
drive these walls inwards, whereas their elasticity
tends to make them resume their previous shape and
positions. Hence an aspirator action is exerted on
the cells below, the elastic walls acting like valves.
Water is taken from the cells below, and this reduces
the pressure on the imprisoned air-bubbles : this being
so, the air-bubbles in the cavities still lower in the
plant are under slightly greater pressure than those
in the cells just considered, and they will expand

1877, t. xx. pp. 357-389; Jahrb. fur Wiss Bot., 1877, p. 120; Aim.
d. Sc, Nat.t 1878; Warum stcigt <ier Saf/ in doi Ban men? Wien,
1878; Dot. Zeit., 1S79, p. 225.

IV.] VARIOUS THEORIES, &C. 75

and drive water up. In this way a suction-pump-
action was supposed to be transmitted from above
downwards, from leaves to roots, and here the neces-
sary water passes in from the soil, under atmospheric
pressure.

Boehm points out that in any vessel there is a series
of air-bubbles at more or less regular distances, and
separated by capillary columns of water. In fact
the vessel constitutes a veritable cliapelct de Jamin,
where the surface actions are so powerful that even
enormous pressures will not move the column as a
whole, though there is no difficulty in supposing parts
of the capillary columns of water to pass through the
permeable cell-walls if the neighbouring air-bubbles
undergo alterations of pressure.

A point on which Boehm laid some stress, by the
way, is the blocking up of the passages by means of
tyloses, ingrowths of surrounding parenchyma-cells
which push through the bordered pits of the vessels,
and fill their cavities with a spurious tissue. It is (says
Boehm) these tyloses which render the heart-wood
impervious or nearly so, and it is they also which
gradually block up the vessels of cut branchr s.

A few words as to Boehm's views regarding the
origin of the air-bubbles and their reduced pressure.
The air enters in solution at the root-hairs, at the

76 TIMBER AND SOME OF ITS DISEASES, [chap.

pressure of one atmosphere. The aspirator-action of
the cells in the leaves reduces the pressure, and the
bubbles separate and experience relatively enormous
friction. Morever, the oxygen of the air will be
absorbed by the cells, and an equal volume of carbon-
dioxide will be returned : this is soluble in the water,
and is carried in solution to the transpiring surfaces.
Hence is seen a further cause for the reduction of
pressure in the bubbles, and an important aid in the
sucking action : the bubbles at length consist entirely
or almost entirely of nitrogen under a pressure of
considerably less than an atmosphere.

It will be seen that the fatal defect in Boehm's hypo-
thesis is the assumption that water can be raised to
such enormous heights, as it must be in tall trees,
simply by differences of atmospheric pressure, when
we know that the pressure of one atmosphere is
balanced by a column of water a little over thirty feet
in height. However, as the faults in the above views
will come out best in the controversy which follows, I
will not dwell further upon the matter here.

The next important contribution to the subject, in
order of publication, was a paper by Fr. Elfving 1
which appeared in 1882.

Elfving classifies the adherents of the two hypo-
1 Uberdie IVasserlaluttg im Holz, 15ot. Zeit. 1882, October.

iv.] VARIOUS THEORIES, &c. 77

theses as follows. Unger, Pfeffer and Sachs may be
regarded as the exponents of the imbibition theory ;
while Hartig, Naegeli and Schwendener, and Boehm
are the chief adherents to the view that the water
ascends in the cavities or lumina of the vessels and
tracheides — the only general point of agreement
between the botanists last mentioned, however, being
that the lumina constitute the route of the water, for
they differ greatly in details.

Elfving set himself the task of subjecting the two
rival hypotheses to experimental tests. He employed
the wood of the yew, unless otherwise specified.
Having verified Th. Hartig's experiment, he attached
a piece of yew branch, a few centimeters long and
about one centimeter thick, to the end of a piece of
caoutchouc-tubing, and showed that very gentle
blowing and sucking through the tube caused the
alternate expulsion and withdrawal of water, at the
cut face of the alburnum.

He then showed that the yew-wood is readily
permeable to all kinds of fluids, very little pressure
being needed to drive the following in succession
through the same piece, and in the order given —
viz. water, alcohol, benzol, alcohol, water, dilute am-
monia, water, dilute acetic acid, water, alcohol, &c.
Under great pressure he could even drive a solution

7S TIMBER AND SOME OF ITS DISEASES, [chap.

of gum through. He points out that this easy
permeability is not suggestive of imbibition.

If a piece of the yew branch is taken fresh, fastened
to a tube, and the wood of the alburnum exposed
by removing a clean longitudinal slice, then it is
possible to see the air-bubbles in the tracheides ex-
pand and contract under the microscope, if the
observer alternately sucks and blows through the tube.
Similarly, by merely blowing down one leg of a (J
tube containing eosin solution, the dye can be forced
through a piece of yew-branch fastened to the other
leg ; on afterwards splitting the wood, the alburnum
alone is dyed, and the dye is in the cavities of the
tracheides, between the air-bubbles, the substance of
the lignified walls not being stained except at the cut
ends. This and similar experiments proved that the
eosin solution did not traverse the lignified parts at all
— it filtered from tracheide to tracheide through the
unlignified membranes of the bordered pits, the only
part stained.

As is now well known, these bordered pits of the
Conifers occur almost exclusively on the radial walls of
the tracheides, a very few being formed on the outer
tangential wall of the last rows of tracheides formed
in autumn. Elfving argued that if the fluid travels
via the bordered pits, then it ought to be possible

iv.] VARIOUS THEORIES, &c. 79

to make it traverse the wood tangentially, but not
radially.

He therefore had cylinders of sap-wood turned, in
such a way that the long axis was (i) parallel to a
radius of the stem, (2) parallel to a tangent, i.e. in a
plane at right angles to No. I, and compared their
behaviour with (3) cylinders whose axis was parallel
to the axis of the stem. The cylinders were all the
same size, turned fresh, and kept moist : they were
placed on one end of a \J tube, and a solution of eosin
driven through by the pressure of mercury in the
other leg of the tube. The longitudinal cylinders
(3) allowed the eosin to pass with the slightest
pressure so long as they were cut from the alburnum
— the same cylinders cut out of the duramen were
almost impervious.

The tangential cylinders (2) allowed the eosin to
filter through slowly, under a pressure of seventeen cm.
of mercury. But not a drop could be forced through
the radial cylinders (1) under the same pressure.
Even forty cm. of mercury failed to force water
through these cylinders.

This proved that the alburnum transmits water in
the tangential direction, but not in the radial direc-
tion. Even in the tangential direction, however, the
water filters through much more slowly, because, the

8o TIMBER AND SOME OF ITS DISEASES. [chaP.

tracheides being about two mm. long, and only, say,
-V mm. in diameter, the fluid in the longitudinal
cylinder (3) has only five barriers interposed for each
centimeter of length, whereas the tangential cylinder
(2) offers five hundred barriers for each centimeter
of length.

Elfving then showed that if one uses thin plates
(one to two mm. thick) of the wood, the water passes
through as easily in the tangential direction as in the
longitudinal : whereas plates equally thin, but cut
in the plane of a tangent to the stem, will not allow
water to pass even under considerable pressures.
There is no mistaking the significance of the coin-
cidence that the water will pass so long as it meets
bordered pits, but will not pass in directions where it
meets none.

Elfving recognised, however, that the partisans of
the imbibition theory might reply that these experi-
ments only demonstrated that the cell-walls transmit
differently in different directions, and that it was
necessary to test the alleged conductivity of the cell-
walls directly.

He did this by the ingenious method of forcing
cacao-butter — which melts at 300 C, and does not
injure the walls — into the cut end of a piece of wood.
By colouring the cacao-butter with cosin, it was easy

iv.] VARIOUS THEORIES, &C. 81

to sec that a slight pressure forced it into all the
cavities of the alburnum exposed by the section, and
even through the bordered pits, to a height of ten mm.
In this way he blocked up the lumina of the tracheides,
and allowed the cacao-butter to congeal ; he then cut
a clean surface exposing the clean-cut walls of the
tracheides. A pressure of sixty cm. of mercury failed
to force water through, whence Elfving concluded that
apart from any possible molecular movements of
water imbibed in the cell-walls) the rapid currents
of water in the wood take place through the cavities
and not in the substance of the cell-walls.

Elfving then goes on to discuss some other
phenomena, showing that water is held in the vessel
of Aristolochia, for instance, by exactly the same force
as it is held in a capillary tube of like calibre, and that
the tracheides and bordered pits are very impervious
to air.

A piece of wood 3 cm. long allowed water to
pass easily under a pressure of 1 cm. of water,
whereas the pressure of a column of mercury twenty
cm. high failed to drive air through. Now since one
cm. of water exerts a pressure roughly equal to TTTVtr
atmosphere, we have to conclude that the slightest
rise of pressure due to the expanding of an air bubble
in a tracheide, will drive water through.

<;

82 TIMBER AND SOME OF ITS DISEASES, [chap.

Elfving's confirmation of the negative pressure of
the air in wood is interesting. Among other experi-
ments was the following : A transpiring branch was
cut under water, and as rapidly as possible transferred
to eosin, and a fresh cut made under the surface of
the dye : that a strong " suction" still existed was
proved by the taking up of the dye to a height of
2\ cm. in the alburnum. He then shows that cut
branches, transpiring freely, take up eosin, and that
on examining with the microscope, all the evidence
(as before) goes to show that the liquid ascends
through the cavities. It is interesting to note that
in these experiments the medullary rays, the cells
of which communicate with the tracheides by means
of bordered pits, were coloured deep red by the
eosin ; indeed in the upper part the rays had taken
all the colouring matter.

As drying proceeded, the wood lost its conducti-
bility, but to the last Elfving found the coloured fluid
held in the borders of the pits, whence he concluded
that one function of the ring-like border is to retain a
capillary drop, so that however threatening the drought
may be, the pit membrane retains its moist condition
to the last.

The cacao-butter experiments were then applied to
the sclerenchyma strands of the Monocotyledons, which

iv.] VARIOUS THEORIES, &c. 83

Sachs and others assumed to be the conducting
agents here — the result was as before, and I may pass
over the details. The same with Dicotyledons, and
here again it is interesting to note that the injected
cacao-butter penetrated through the vessels, not only
into surrounding elements, but into the starch cells
of the medullary rays. Mere sucking brought the fat
up the vessels and into the tracheides, &c. surrounding
them.

Elfving expressly points out that this remarkable
injection of the xylem-parenchyma and medullary
rays always occurred by merely sucki'.g with the
mouth, though afterwards a pressure of 25 cm. of
mercury failed to drive water through. Elfving's
conclusions are that wood loses its "conductibility "
as soon as the lumina are blocked, and that the rapid
ascent of water under consideration does not take
place in the walls of the elements. Since tracheae in
the widest sense {i.e. vessels and tracheides) are the
only elements which never fail, and are sometimes the
only elements present in the wood, and since they
always contain some water, and are provided with the
easily permeable pits, he concludes that they arc the
conducting elements. The bordered pits are filters,
the ring being a support : the same is true for the rings
of the spiral, the thin parts acting as pit-membranes.

G 2

84 TIMBER AND SOME OF ITS DISEASES, [chap.

The solid thick parts are necessary to prevent crush-
ing, and the thin places are always easily permeable
to water but not to air. As regards the parenchyma
cells of the wood, their protoplasmic contents point to
their having some other duty to perform, but they may
also be employed : so also with the medullary rays.

On the whole Boehm's idea seems to be most in
accord with the facts so far, the easy permeability for
water and the resistance to the passage of air being
the chief factors. Nevertheless, one seems to see that
Elfving was too wide awake to the obvious physical
defects of Boehm's theory to give it his support further
than the foregoing implies. Here, again, however, I
leave further remarks and criticisms to develop
naturally in the course of the controversy.

I may now take together two papers by Robert
Hartig1 which appeared in 1882 and 1883 respectively.
The conflicting views then abroad led him to examine
the question of the distribution of air and water in
wood, and some interesting discoveries were made by
the way. In the first place he found that the
duramen always contains water, though it is incap-

1 " Ueber die Verthcilung der organischen Substanz, des "Wassers
und Luftraumes in den Baunien, und uber die Ursache der "Wasser-
bewcgung in transpirirenden Pflanzen." Unters. aus </. Foist. Bot.
Inst, zu Miinchen ii. and iii.

IV.] VARIOUS THEORIES, &C. 85

able of transmitting it up the stem ; but he also found
that some trees — the birch for instance — never form
any true " heart-wood" (duramen) at all, but consist
throughout of " sap-wood " (alburnum), the inner
layers of which only differ from the outer in being
somewhat less permeable to water.

Hartig also convinced himself that it is the elements
with bordered pits, and especially the tracheides,
which conduct the water.

The absorption of the water at the roots has no
direct relation to the ascent of water in the stem,
being due entirely to the osmotic action of living cells
— especially the root-hairs. Only in cases where the
imprisoned air expands and exerts pressure, or con-
tracts and facilitates the flow of water into a vessel, &c.
need we take any account of the root action. But this
root-action, which is especially favoured by a rise of
temperature in the soil, helps to explain a phenomenon
which has been overlooked, viz. that in the summer, in
spite of the fact that transpiration is then most active,
most of the trees (beech, oak, larch, Scotch pine and
spruce) examined, contained their maximum of total
water : the birch alone was an exception, because its
period of vegetative activity is earlier.

If the tree contains so much water that the air in
the cavities of its tracheides, &c. is at a pressure equal

86 TIMBER AND SOME OF ITS DISEASES, [chap.

to that of one atmosphere and if the roots still con-
tinue to absorb water in greater quantities than the
leaves transpire it (as may actually occur), we have
the phenomenon of " weeping" or " bleeding" : similar
effects are produced when the sun's rays directly raise
the temperature of thin twigs — the expanding air-
bubbles drive water before them, as had already been
shown by Sachs and others. Hartig concludes that the
cause of the ascent of the water in a tree is to be
found in the differences of pressure (density) of the
air-bubbles imprisoned in the tracheides, &c. : the water
is driven from lumen to lumen in the direction of least
pressure.

Taking the simple tracheide system of Conifers, the
elements are in contact on the one hand with the
mesophyll of the leaves, in the venation, and on the
other hand with the parenchyma of the roots ; the
walls in contact are the thinnest of all, and water easily
niters through them, but they need strengthening
lattice work — theraison d'etre for rings, spirals, &c, and
it is interesting to note that this kind of support only
occurs in the proto-xylem, the part which alone comes
into direct contact with the above-named cells. The
trunks of trees, &c, would be impossible, however, if
the secondary wood were not provided with more
support ; hence we find firm, thick-walled organs in it,

iv.] VARIOUS THEORIES, &c. 87

the walls of which are almost impermeable to water.
Elfving's experiments prove that no such easy mobility
of the imbibed water, as Sachs assumes, exists ; and
Hartig confirms the view that the water only moves
through the membranes of the bordered pits.

These delicate closing membranes are very elastic,
and when extended by pressure are particularly thin
and permeable ; the solid ring-border is a support so
arranged that when the delicate membrane is driven
too far it rests on the inner surface of the ring, and
the torus blocks up the pore, the apparatus thus
acting as a safety-valve to prevent undue tension or
rupture of the filter-membrane.

In Dicotyledons water can be more easily forced in
a radial direction than in Conifers, because the
bordered pits are not confined to the radial walls ; but
even in Conifers the last-formed tracheides of each
annual ring have numerous very small bordered
pits on their tangential walls, no doubt to serve as
water-doors to supply the cambium in the spring, as
otherwise it must suffer. Finally, it should be noted
that in the Conifer the long, prismatic tracheides are
arranged in the annual ring in radial rows, those
in each radial row being equal in height : tangentially,
however, the rows stand at unequal heights, so that
anything passing through the bordered pits (on the

88 TIMBER AND SOME OF ITS DISEASES, [chap.

radial walls) from tracheide to tracheide, would go by
steps spirally round the stem as up a spiral stair-case.
It is this last-mentioned position which renders pos-
sible an ascent of the water from lumen to lumen
of the tracheides.

Now, as a mere matter of observation, determined
by finding the quantity of water, &c. in all parts of
the wood at regular heights in the tree, the tracheides
always contain some water and some air, but the
quantities of each differ considerably both according
to the part of the tree and according to the
season. In all cases the walls must be saturated
with imbibed water. In the Dicotyledons, &c. the
liquid water in the lumina of the vessels and tracheides
occupies at least one-third and often two-thirds of the
volume of the lumina : in the Conifers, the tracheides
may have only two-thirds of the lumina occupied by
water, but as much as nine-tenths may occur. The re-
maining portions of lumen are filled with air, and
perhaps the most valuable of Hartig's contributions to
the question was his patient and ingenious determina-
tion of the fact that the actual air-contents of the tra-
cheides, &c, decreases from below upwards : that is to
say, if we suppose the air to be at the same pressure
throughout, the amount of water in the lumina of the
tracheides, &c increases as we ascend the tree.

IV.] VARIOUS THEORIES, &C. 89

No less important was the discovery that the air is
not at equal pressure throughout, but that it is /rss
dense in the upper parts of the tree than in the lower.

Hartig's views, as then expressed, were as follows :
The water, enclosed together with air in a tracheide,
&c, is supported in the tubular cavity by capillarity,
so that its weight cannot make itself felt downwards
through the closing membranes of the bordered pits ;
in true vessels the individual water-columns are
suspended, separated by air-bubbles. When transpira-
tion is active, and the amount of water in the tree
tends to diminish, the air in the upper parts becomes
much more rarefied than that in the lower : for
instance, in the wood of the branches of the crown,
the air may be expanded to five times its original
volume, while that in the lower parts of the stem
expands simultaneously to only twice its volume.

This diminution of pressure as we ascend must
exert a relatively powerful lifting force from tra-
cheide to tracheide, the greater pressure of the air
below driving the water through the membranes of
the bordered-pits.

If the supply of water from below is arrested (as
was done in an old spruce by sawing to the depth of the
non-conducting inner wood) the density of the air
slowly becomes equalized throughout the whole

9o TIMBER AND SOME OF ITS DISEASES, [chap.

system, and all movement of the water ceases — the
leaves and cortex in the upper parts of the tree dry up
and death may ensue. In the case of the spruce
mentioned this occurred when the lumina of the
traclieides contained liquid water to tlie extent of 7$%
of the whole volume.

The more slowly water is being absorbed by the
roots below, as compared with energetic transpiration,
the more the air becomes rarefied, even in the lower
parts of the tree ; and the difference of pressure
between the air above and that below may become so
small that the water ascends only very slowly. On
the other hand, the more energetic the root-action, the
denser the air in the lower tracheides becomes, being
pressed by the water behind. When active transpira-
tion follows upon this state of affairs (as in the early
summer) we have the greatest difference in the
pressures set up — transpiration rarefies the air-bubbles
above, and root-pressure compresses them below —
whence the water ascends rapidly. Moreover this
conduces to a continuance of rapid transpiration, for
leaves transpire more freely when turgid.

On the other hand, the ascent and transpiration of
water act in no appreciable way on the process of
absorption : the osmotic activities at work are
practically independent of such pressures and strains

iv.] VARIOUS THEORIES, &c. 91

as have been considered. And again, the atmo-
spheric pressure outside the plant has no appreciable
effect on the process ; it is controlled and regulated
by alterations in the density of the imprisoned air.

Hartig's methods of observation are worth a short
description here, because they give not only insight
into several peculiarities of wood, but also an idea of
the very different points of view involved.

In the forest, on the spot where the trees
were felled, the pieces of wood to be examined
were chosen and at once weighed, because they
rapidly lose weight after exposure to air. .In choosing
them, the usual plan was to cut up the trunk into
blocks, and to select blocks from the various heights,
about 2 — 3 meters apart, splitting them up as follows :
two opposite wedge-shaped segments were cut out of
the circular block, and each separated into three parts
— the inner part comprising the heart-wood, the outer
part sap-wood, and the middle one both sap-wood
and heart-wood. The pieces thus obtained weighed
from 300 to 700 grams each, and after weighing were
packed and despatched to the laboratory.

Here, the first thing to do was to determine the
volume in the fresh state,1 which was done by reading

' Since the wood does not shrink sensibly until it has lost much water,
it was not necessary to do this in the foriM, but it was done next day.

92 TIMBER AND SOME OF ITS DISEASES, [chap.

the amount of water they displaced. A discussion as
to the sources of error leads to the conclusion that they
do not amount to more than about 0*5 per cent, on the
average. The pieces of wood were then dried for
some weeks. Some interesting observations were
made, confirming the conclusion that so-called air-
dry wood gives various weights according to the
condition of the atmosphere, and therefore of little or
no scientific value.

The drying was then completed in a hot-chamber
at 105 — uo°C, and the dry weight registered: the
loss in weight of course registered the amount of water
contained in the wood.

The next thing was to obtain the volume in the
dry state, in order to estimate the shrinkage ; this was
done, as before, by displacement, several careful
precautions having to be taken.

So far, the following data were to hand :

1. The specific weight (fresh)

Absolute weight (fresh)
Volume (fresh)

2. The specific weight (dry)

Absolute weight (dry)
Volume (dry)

3. The shrinkage

Volume (fresh) - volume (dry)
Volume (fresh)

iv.] VARIOUS THEORIES, &c. 93

4. The weight of the organic wood-substance (+ traces of
ash) per volume (fresh)

Dry weight
Volume (fresh)

5. The amount of water in the volume (fresh)

Weight (fresh) — dry weight
Volume (fresh)

6. The amount of water in 100 units of the fresh weight

Weight (fresh) - weight (dry)
Weight (fresh)

Sachs had already shown in his paper on the
Porosity of Wood, that the specific gravity of the
solid wood-substance is 1*56, a number that was ob-
tained by heating small pieces of wood in solutions of
neutral salts to drive out the air, and then finding
the specific gravity of the solution in which the wood
just begins to sink. Hartig repeated these experi-
ments with birch, beech, oak and pine, both heart-
wood and sapwood, and found that they all remained
for days floating quietly at any level in a solution of
calcium nitrate of specific gravity 1*555, whence we
may regard Sachs' number as confirmed. With this
further datum, we get

7. The percentage volume occupied by the dry wood-wall
per volume ('fresh)

Weight of organic substance per 100 volumes (fresh)
Sp. gr. of wood substance {i.e. 1*56)

94 TIMBER AND SOME OF ITS DISEASES, [chap.

Then, subtracting the dry volume and the water
from the fresh volume, we get

8. The volume occupied by the air-spaces in the wood.

But we have still to determine how much of the
total water is imbibed in the cell-walls, and how much
exists in the liquid state in the cavities of the tra-
cheides, &c. It may be safely assumed that as long
as any liquid water exists in the lumina, the walls will
be saturated. Sachs' method of hanging a piece of
wood, dried at 105° C. in an atmosphere saturated
with moisture, was employed. The temperature was
kept constant, and it was found that in two days the
wood had absorbed water to the extent of half the
quantity it was capable of absorbing, and it then went
on absorbing it more and more slowly, until it took
no more.

Hartig concluded that the capacity for imbibing
stands in intimate relation to the presence or absence
of cells containing substances which swell in water.

For instance, the inner wood ( " heart-wood " ) of
beech continued to imbibe for forty-seven days, and
then had taken up 57 per cent, of its substance-
volume ; while the alburnum of beech, which contains
much starch, continued to imbibe for fifty-seven days,

IV.] VARIOUS THEORIES, &C. 95

and had then taken up water to the extent of 72 per
cent.

Heart of oak took up 75 per cent., oak alburnum
92 per cent, of water. Birch took 66 per cent. Pine
from 45 per cent, to 57 per cent, according to the
quantity of resin, and so on.

It will be remembered that Sachs hung a dried,
and therefore cracked, disc of wood in a damp atmo-
sphere, and regarded the experiment as concluded
when the crack closed : Hartig points out that the
wood goes on imbibing water long after the crack
closes, to make good the shrinkage, hence his higher
numbers.

The next datum is

9. The volume occupied by the saturated woody-walls (+
saturated contents) = dry volume + (dry volume X water
capacity).

And, again,

10. The quantity of liquid water in the lumina of the tra
cheides, &c. = total water - (dry volume X water capacity).

By employing these factors and methods, Hartig
obtained a huge series of numbers for each tree,
tabulating the part of the tree used, the amount of
organic substance, of water and of air, &c. at various

96 TIMBER AND SOME OF ITS DISEASES [chap.

times of the year, which gave him the data for the
generalisation as to the distribution and condition of
the air as we ascend the tree ; from the tables he
constructed curve-diagrams, finally evolving his hypo-
thesis as sketched above.

The next paper of importance is one by Dufour,1
and consists in a deliberate attempt to vindicate
Sachs' imbibition theory against the criticisms to
which it had been subjected.

The author maintains that although various move-
ments of water occur from lumen to lumen of the ele-
ments of the wood, and by filtration through the pits,
these have nothing to do with the transpiration cur-
rent : it is as water of imbibition in the walls that the
rapid flow concerned in transpiration occurs. He
considers that Elfving's experiments in no way over-
throw the theory, because they only prove filtration
under pressure, which is not denied : pressures of this
kind, however, cannot affect the equable distribution
of imbibed molecules in the cell- walls. Sachs had
already insisted that the water is in a peculiar condi-
tion— infinitely mobile, but removed from the influence
of gravitation or of ordinary pressures.

In regard to R. Hartig's criticisms, (i) that the

1 " Ueber den Transpirationstrom in Holzpflanzen." Ari.dcsbot.
in Wiirzburg, 1883.

iv.] VARIOUS THEORIES, &C 97

elements have always some water in their cavities,
and (2) the water contained in the tracheides, &c, of
the splint increases as we ascend the tree, Dufour
simply seeks to show that this does not matter : it is
not urged that the membranes should be in contact
with much or little water, and in fact complete satura-
tion brings about the maximum mobility of the
imbibed water molecules. The water in the cavities
must be looked upon as so much reserve-water, upon
which the membranes can draw : how it comes there is
not explained, but it has nothing to do with the
imbibition-theory.

As a demonstration of the accuracy of Sachs'
views, Dufour again brings forward experiments with
sharply bent shoots, showing that in the majority of
cases the bending of the vascular bundles on them-
selves closes the cavities, and water can no longer
be forced through by such pressures as Elfving and
others used : nevertheless, the plants did not cease to
transpire and conduct water.

Dufour also employed the following method :
Branches were sawn into in such a way that at
two places on opposite sides of the stem, one being
a little higher than the other, the whole of the tissues
were severed as far as the pith : the argument was
that the continuity of all the vessels, tracheides, &c.

II

g8 TIMBER AND SOME OF ITS DISEASES, [chap.

was thus completely severed, although (the two cuts
being at different levels) the continuity of the woody
substance of the cell-walls and their imbibed water
was not broken. In many of the cases Dufour
found he could not drive water through such cut
branches, and yet transpiration was not prevented
and water passed the wounds.

Dufour rejects the view that this could occur by
means of the tracheides, although he is not prepared
to decide how far concurrent movements in the
lumina may affect the matter.

Dufour points out that the " air-pressure theory "
(then being eagerly discussed on all sides) presents
the one insuperable obstacle that it will not account
for the ascent of the water to a greater height than
about 10 meters ; and that it is of no use to invoke
the aid of capillarity, as supporting the columns of
water, for in just so far as it supports them it prevents
their being driven upwards, or moved at all.

In a short paper published in Berlin in 1883,1
R. Hartig offers his hypothesis in an amended form.
In answer to Dufour, Hartig insists that the move-
ment is usually and in the main from lumen to lumen,
but admits the possibility that when transpiration is

1 Die Gasdnuktheoric und die Sachs 'sche Irinbibitionstheoiic. Berlin,
1883.

iv.] VARIOUS THEORIES, &c. 99

so vigorous as to drain all the liquid water from the
cavities, the current may possibly pass as imbibed
water. In those cases where Dufour could not press
water through his sharply bent shoots, the lumina of
the vessels were not quite closed, however nearly they
might have been ; all that occurred was a curtailing of
the supply of water for the time being, whence
continued transpiration rarefied the air above the bend
to such an extent that enough water was squeezed
through to keep the shoot from drooping. In those
cases where Dufour could only drive very little water
beyond the sharp bend, it was because the cells, with
their rarefied air bubbles, retained most of the water
— absorbed it and held it fast.

As to Dufour's criticism that the sum of the air-
pressures in the tree must be less than an atmosphere,
and therefore cannot lift water more than 10 meters
high, that must be conceded ; but the pressure of the
air-bubbles does not perform the lifting of the columns,
its work is rather to distend the elastic closing mem-
branes of the bordered pits, so as to enable water to
filter through them. The lifting is performed chiefly
by capillarity, which raises the column of water
particles in each tracheidc.

One difficulty avowedly arises (but the imbibition
theory does not explain it) — that is, why is it, when

H 2

loo TIMBER AND SOME OF ITS DISEASES, [chap.

the pressure is equal in two tracheides, that the water
does not pass back, through the interstices of the cell-
walls, from the higher to the lower one ? Hartig
assumes that the closing membranes of the bordered
pits only allow water to filter thus easily when
they are distended, by the pressure of the gas-bubbles.
He thus proposes to reject the "air-pressure theory"
altogether, and to substitute for it his " gas-pressure
theory."

Vesque, in 1883, by using branches of Tradescantia,
&c, cut longitudinally, was able1 to see movements
of water and air-bubbles in the vessels and tracheides
exposed and placed under the microscope. On
stopping up the vessels, the leaves still acting, air-
bubbles appeared and grew larger ; on removing the
leaves the movements ceased : any slight bend,
pressure, change of atmospheric moisture, light, &c,
had its effect on the movements.

Similar observations were also made in 1883
by Capus,2 who used begonias, dahlias, &c, and
examined the vessels exposed on sections. The
method was to remove a slice so as to expose the

1 Vesque, " Observations directe du mouvement de l'eau dans les
vaisseaux." Ann. d. Sc. Nat. Ser. vi. t. xv. 1833, No. 1.

- " Sur 1 'observation directe du mouvement de l'eau dans les plantes."
Comptes Rend., 1SS3, t. 97, p. 1087.

iv.] VARIOUS THEORIES, &c. toi

vessels, &c. and then to cut away the opposite side of
the stem down to the pith, thus making the exposed
parts translucent. His results coincide with those of
Vesque.

In the BericJite der deutschcn botaniscJien Gesell-
scliaft for 1883, appeared a criticism by Zimmermann,1
which must not be passed over. He points out that
in spite of the favourable features in the more gener-
ally approved theories, which explain the water-
movements as taking place in the cavities, and not
the walls of the elements, they still sin terribly against
the laws of physics. It is quite right, he says, to insist,
as Boehm and others do, on the importance of the
chapelet de Jamin as a stable column, but the con-
ditions in the plant do not allow of capillarity being
employed as Boehm and Hartig employ it.

For if wc suppose that the intervening membranes
of superposed trachcides composing a column of
water and air-bubbles, present no resistance, then the
column simply resolves itself into a sinuous contin-
uous water column, the axis of which turns aside at
the air-bubbles. Such a column is supported by the
upper meniscus, and can only be as high as accords
with the law of capillarity for the particular tube.

1 " Zur Kritik der Buhm-Hartigschen Theorie der Wasserbeweeung
in der Pflanze." Ber. J. J. hot. ges. B. i. p. 183.

io2 TIMBER AND SOME OF ITS DISEASES, [chap.

Now suppose the interpolated membranes to exert
just sufficient resistance to filtration to balance the
water-column contained in its own cell above it, then,
as Hartig assumes, the movement will depend entirely
on the differences of pressure in the air-bubbles. If
water is removed so as to diminish the pressure of a
bubble in a given tracheide, then the bubble next
below exerts pressure and drives water up, and so on.
Zimmermann comes to the conclusion that on this
assumption also the lifting forces alleged are not
sufficient for the purpose, and that Hartig's theory
also fails to account for the ascent of water up trees
more than thirty feet or so high, for he finds that the
suction action can only be propagated for ten meters
or so along the system.

Attention should be drawn to a second paper by
Zimmermann,1 in which he publishes the results of
his experiments with a number of Jamin's chaplets,
but since the paper deals more particularly with the
purely physical phenomena in the glass tubes, it is
hardly necessary to discuss it here : it may be noticed
that he obtains some curious results with other liquids
than water, however, and there can be no doubt as to
the importance of the cJiapelet de Jamin in the plant.

1 " Ueber die Jamin'ische Kette." Ber. J. Jeut. hot. Gesellsch., 1883.
B. i. p. 384-

IV.] VARIOUS THEORIES, &c. 103

But the most important contribution to the dis-
cussion in 1883, was Westermaier's paper,1 in which
an entirely new departure was made, in that, for the
first time,2 attention was called to the role of the
living parenchymatous cells of the wood and
medullary rays,

Westermaier accepts Zimmermann's criticism as
putting the Boehm-Hartig theory out of court, and
forthwith calls attention to the wood-parenchyma and
medullary rays as integral parts of the tissues
concerned in the ascent of the water. He then puts
the question, Can these living cells raise the water
osmotically ? If so we need no longer be troubled
with the resistance of the membranes, or the heights
of the columns.

Two points are to be noticed : (1) The living cells
of the wood-parenchyma are in communication with
the tracheal system by numerous pits ; and (2) turgid
parenchyma allows water to escape by exfiltration into
dead contiguous elements.

It may perhaps be assumed that cells lower down

1 " Zur Kenntniss der osmotischen Leistungen des lebenden Paren-
chym's." Ber. der deut. bot. Gcscllsch. B. i. 1883, p. 371.

- This is not strictly accurate, as Knight {Phil. Trans. iSor, p. 344)
had suggested the co-operation of medullary rays, but of course Ids
points of view were different.

io4 TIMBER AND SOME OF ITS DISEASES, [chap.

tend to exfiltrate water sooner than those at higher
levels in the tree, and this being so we have to con-
sider not only the absorbing or sucking action of the
parenchyma, but also its exfiltration or forcing action.

Employing the pith of Helianthics, Westermaier
found that in summer the lower parts are filled with
liquid only at the periphery, whereas in the upper
parts of the stem the whole of the pith is full of
sap. A cylinder of this pith more than 50 cm.
long, at first flaccid, became turgescent in twenty-
four hours when exposed to moisture with its end
dipped in water.

In such experiments, it may happen that parts
here and there, above the level of the water in which
the lower end is placed, become turgescent and
stiff, while parts lower down are flaccid — pointing to
a stronger osmotic draught in the turgid cells.

Applying this to the case under discussion, we
must note the numerous points of contact and com-
munication between the tracheal system on the one
hand, and the living, osmotically active cells of the
wood-parenchyma and medullary rays, on the other.
The hypothesis which follows depends, firstly, on
the keeping up of the cJiapclct de Jamin, by supplies
of water from the roots. Secondly it must be
assumed that the individual columns of the chaplet

iv.] VARIOUS THEORIES, &C. 105

are self-supporting — i.e. they must obey the law
of capillarity, and remain suspended in the tube.
That the chaplets exist is a fact of observation,
though we do not know their length.

Now consider the system as simplified in a diagram.
Suppose a vessel, in contact with medullary rays and
wood-parenchyma at different levels. Water rises
in the vessel to a given height, the level of the first
medullary ray, and is held there by the pressure
from below. The parenchyma at that level then
uses this water as a store from which it draws by
endosmose.

At a somewhat higher level, and in contact with
the same vessel, is another medullary ray, the cells
of which are wanting in water : they take water by
endosmose from parenchyma-cells lower down in the
wood, the action reaching to the medullary ray first
considered. This absorbent action goes on till
these cells of the higher medullary ray also are
turgid, and so rich in water that they exfiltrate it
into the neighbouring vessel, where the air is rarefied.
Here — i.e. at a higher level — the expressed water
collects into a small column, grozving in both direc-
tions upwards and downzvards. This will be sup-
ported by capillarity until it reaches a certain length,
and before it exceeds this the action will have

106 TIMBER AND SOME OF ITS DISEASES, [chap.

been repeated with respect to a medullary ray yet
higher up.

We thus have two sets of forces, capillarity and
osmosis, supplementing one another : the capillarity
only supports the columns, the moving force is
endosmose.

Westermaier points to a sentence in Nageli and
Schwendener's book on the microscope, as having
anticipated the probable necessity for distributing
the lifting forces at numerous points ; and he also
claims that his views are supported by their falling
in so well with the facts of anatomy.

In contrast to the " Imbibition-" and the " Gas-
pressure " theories, the above may be named (the
translation is not very happy, I fear) the " climbing "
or " clambering " theory.1

As regards the bearing of this explanation on
Dufour's experiments, the author points out that the
continuity of neither the medullary rays nor the ob-
liquely running wood-parenchyma strands, would be
broken by the bending or sawing.

Westermaier then puts forward the result of some
experiments to measure the hydrostatic pressure and
endosmotic power of such cells as enter into considera-

1 " Klctterbauegting" — perhaps "Step-theory" would meet the re-
quirement of the case ?

iv] VARIOUS THEORIES, SzC. 107

tion here. The principle involved was to oppose
pressure, by means of weights, to the resistance due
to turgidity, and he came to the conclusion that the
hydrostatic pressure concerned may easily reach three
and four atmospheres.

The year 1884 saw the publication of several papers
on our subject, and one of these seems to have practi-
cally closed the discussion except as regards details.
I propose to take first one by Elfving,; because it in-
troduces some excellent criticisms on the foregoing
papers, as well as offering a survey of several physical
principles which had been either neglected or not
properly understood by previous writers.

Elfving first gives a short summary of the older
views, with especial reference to the capillary theory
and the bearing of his own previous experiments, and
then proceeds to point out that the two sets of forces,
capillarity which is effective in the lumina of the tra-
cheides and vessels, and imbibition in the solid sub-
stance of their walls, together with the osmotic forces
concerned in root-pressure, and the expansion and
contraction of the air bubbles, must all be active in
causing the movement of the water up the stem of the
tree.

1 " Ueber den Transpirationsstrom in <lrn Pflanzen." Acta Societatis
Scientiarum Fennica, t. xiv. 1884.

io8 TIMBER AND SOME OF ITS DISEASES, [chap.

Capillarity and the friction of the air bubbles must
be important, as supporting the columns of water.

Imbibition (in Sachs' sense) will be useful when the
lumina of the elements are nearly deprived of water in
summer.

Osmosis is active in giving a push from behind
especially at certain seasons.

The differences of air-pressure as expressed by the
contractions and expansions of the bubbles, must have
effect in moving small quantities of water from lumen
to lumen.

Elfving then proceeds to show that the " gas-
pressure theory" ofHartig is but a development of the
air-pressure theory of Boehm, though the only point
which remains the same in both is the assumption that
the water moves in the lumina.

Water is always present in the tracheides accord-
ing to Hartig, Boehm, Russow and Elfving ; though
of course this does not itself prove that this water
is any other than a reserve supply, as Dufour alleges
it to be.

The pressure of the atmosphere could have nothing
to do with the matter, because the membranes are
impervious to air : if it could, the hypothesis as it
stands would be absurd ; for a continuous column
could only be ten meters high. There is no com-

iv.] VARIOUS THEORIES, &c. 109

petent vis a tergo in the plant, and the capillaries
are not narrow enough for the heights required.
Boehm, Hartig and others have tried to show that
the water columns are held supported and im-
movable in the lumina, and hence exert no down-
ward pressure which would cause them to fall : Sachs,
and those with him, reply that the capillary forces
which hold these columns so fast as to prevent their
falling, will, with equal obstinacy, prevent their being
moved upwards.

Elfving then examines the well-known and oft-
quoted experiment of Th. Hartig. The vertical
piece of branch — say yew — consists of series of
tracheides each containing water and air, and closed
by pit-membranes which are very permeable to water ;
but this constitutes a cJiapelet de Jamin, the only
peculiarity being the intercalation of the extremely
permeable membranes at more or less regular heights
between the columns of water. In Hartig's experi-
ment then, the vertical rows of tracheides form so
many immovable chapelets de Jamin, but with liquid
communications at the permeable pits : the move-
ment of the water, caused by the weight of a drop
placed above, must therefore be in a sinuous course,
through the lateral pits, and not confined to the one
column. If we take this sinuous course, and examine

no TIMBER AND SOME OF ITS DISEASES, [chap.

it, we find it to consist of parts each bounded above
and below by an air-bubble, and Elfving's contention
in opposition to Zimmermann's, is that the friction
of these bubbles and capillarity completely support
these parts.

Calculation shows that if the tracheides measure
0'02 mm. in diameter, and have the same capillary
ascension as glass (which of course we do not know)
then the capillary ascension would = i '5 meter — a
number amply sufficient for the purpose.

Hence, says Elfving, Ave may safely assume that
each short water-column in the series, between its two
air-bubbles, exerts no pressure downwards — it is a
weightless segment, so to speak — whence the columns
may be maintained at any height likely to come into
dispute. As to the origin of the air-bubble there is
no difficulty. The tracheides, &c. are cells containing
protoplasm and other contents when young, but
when the walls are thickened and the bordered
pits, &c. completed, the living contents disappear,
leaving sap only in the cavities. As water is with-
drawn a tendency to form a vacuum is instituted,
but this is prevented by vapour, the tension of which
increases as the withdrawal of water proceeds. Since
the water absorbed into the plant contains air, how-
ever, the reduction of pressure causes the sap to part

iv.] VARIOUS THEORIES, &C. in

with its air (it cannot retain in solution so much as
it could under a higher pressure) and the air will
continue to pass off from the sap so long as the
pressure is less than an atmosphere. Hence air-
bubbles must be produced when more water is
passing off at the leaves than is entering at the
roots.

The reply that the water held fast by the air-
bubbles proves too much, because it is immovable, is
anticipated by the remark that though each column
is thus fixed as a whole, the individual particles of
water are free to move.

We have already examined Elfving's proofs that
the water travels through the lumina, and may at
once pass to his conclusions. He points out that the
imbibition theory was devised to meet the difficulty
that water is carried up several hundred feet in the
tallest trees, whence the water (i) must be held by
molecular forces, (2) must be easily moved : but the
theory of intra-cellular water above stated quite agrees
with this. Transpiration at the leaves is supplied by
osmotic currents from the extremities of the vascular
bundles to the mesophyll : these osmotic currents are
feeble, but they set the water in movement, via the
vascular bundles of the ribs and petiole. As soon as
the stream encounters an air-bubble, it bends to one

U2 TIMBER AND SOME OF ITS DISEASES, [chap.

side, and since the friction between the wood-wall and
the water, as well as the resistance to nitration, are
almost infinitely small, the water in the columns,
supported in the long chains by the air-bubbles,
moves. If no more water is being transpired than is
absorbed, the air-bubbles themselves do not act in the
process ; but now suppose more water passes off at
the leaf-surfaces than is supplied at the roots. In this
case the air-bubbles must expand (explaining Hartig's
discovery that the air in the upper parts of the tree is
rarer) and a " suction " is started, and propagated
downwards, accelerating the flow above, and extending
its action — which becomes more and more feeble
downwards — till it splits into smaller currents at the
roots.

Hence, according to Elfving, the opponents of the
imbibition theories are right in saying that (i) the
water filters from element to element, and (2) that the
tension of the air-bubbles co-operates ; but they are
wrong in supposing (1) that the pressure of the atmo-
sphere can be effective, or (2) that the tension of the
air-bubbles only makes the pit-membranes permeable.

In Dufour's experiments with sawn branches, he
ignores the effects of cutting in air — the more rapid
the transpiration the more quickly air will pass in and
prevent water under pressure from passing through,

IV.] VARIOUS THEORIES, &C. 113

owing to the impermeability of the wet mem-
branes for air, and the enormous friction of the
air-bubbles.

A paper of some interest at the time was published
by Max Scheit1 early in 1884, in which the author
boldly denied that air-bubbles exist in the vessels, &c.
during the life of the plant, and surmises that they
have entered the sections, &c. at the moment of
cutting. He argues that only two modes of entrance
are possible for the air— (1) through the stomata,
which do not communicate with vessels, and (2) as air
dissolved in the water entering at the roots. Von
Hohnel and Wiesner had proved that air cannot pass
directly into vessels, and we know it will not readily
traverse wet membranes— and since water is always
to be found in the vessels, &c, their walls are never
dry during life.

Scheit argued that any air dissolved in water at the
roots would be used before it reached the places where
it is said to separate out. He gives some conclusive
proofs of the impermeability to air of wet wood:
even 80 to 120 cm. of mercury failed to drive air
through 2 — 3 cm. of wood.

He concluded that only water and aqueous vapour

1 " Die Wasserbewegung im IIolzc." Bot. Zeitung, March, 1884,

p. '77-

1

H4 TIMBER AND SOME OF ITS DISEASES, [chaf.

exist in the cavities of the tracheides, and that the
system which has to be examined, consists of fine
capillary tubes plunged below into cells which absorb
water (root-parenchyma, &c.) and above into cells
which give off water by evaporation (mesophyll of
the leaf), and accompanied on their course by cells
of wood-parenchyma and medullary-rays, the latter
supplying the cortex with water. The whole con-
ducting mechanism moreover is surrounded by the
cambium. The up-taking and giving off of water is
accomplished through the bordered pits, and the
capillary system is, as we have seen, impermeable to
air. It should also be noted that by far the majority
of so-called vessels are really tracheides.

So long as the closing membranes of the bordered
pits are not stretched, the tracheide is a closed system :
pressure on the membrane results in the passage of
water in the direction of the pressure, the membrane
returning to its original position elastically and pre-
venting the back-flow. Hence the water which
traversed the membrane is held in the capillary space
above.

There is, said Scheit, no question of the sum of the
pressures of the columns in superposed tracheides,
because each column is on the one hand held up by
capillarity, and on the other, could only exert pressure

iv.] VARIOUS THEORIES, &c. 115

on the walls of the tracheide containing it. The
diameter of the tracheides (in Pinus = C015 to C02
mm.) shows they could support columns much longer
than they do.

Thus the water in the stem is in long columns, broken
at short intervals by valves, reminding us of a hint
thrown out long ago by De Candolle and Mongolfier.

To get over the difficulty as regards vessels, Scheit
raises doubt as to the continuity of their lumina : in
any case he regards the capillary water in them as of
the nature of a reserve.

The causes of the water-movement are as follows : —
Transpiration tends to exhaust the reservoirs of water ;
the osmotic pressure in the root drives in the closing
membranes of the bordered pits, rendering them per-
meable. The water thus pressed into the vessels, &c.
is at once removed from the action of gravity by
means of capillarity ; and thus the root-pressure has
nothing further to do than press the valves and drive
water in. Th. Hartig's experiment with the vertical
cut branch shows how little pressure is required to do
this, and hence the slightest swaying by the wind may
be a co-operating cause of movement.

Scheit then quotes experiments in which he injected
branches, &c, cut off under the surface of a liquid,
and which completely confirm the negative pressure

I 2

u6 TIMBER AND SOME OE ITS DISEASES, [chap.

discovered by Von Hohnel ; but which he thinks
prove not that air-bubbles under low pressure exist
in the transpiring plant, but the existence of a partial
vacuum or space filled with aqueous vapour.

Dufour's experiments are severely criticised. The
author agrees with Russow that the lumina of the
bent shoots were not completely closed, and asks,
with Hartig, how it could have been expected they
should be, seeing that so many of the elements have
comparatively prominent networks and thickenings
projecting into the lumina. As regards the sawn
branches, the water passes laterally between the two
cuts, traversing the bordered pits.

Scheit also insists that Dufour failed to press water
through his branches, because the air got in, and found
that it was by no means difficult to press liquids
through if the cuts were made under water.

He also offered an improvement on Elfving's ex-
periments, stating that two objections have been made
to them. In the first place Elfving removed his
branches from the tree, and ran the risk of air enter-
ing, and secondly the danger of greasing the cell-walls
by the cacao-butter rendered the method objectionable.
To obviate the latter of these disadvantages Scheit
used gelatine coloured with eosin, and completely
confirmed Elfving's results.

IT.] VARIOUS THEORIES, &C. "7

In Pringsheim's Jahrbiicher for 1884 appeared a
remarkable and brilliant paper by Emil Godlewski,1
which placed the whole subject in an entirely new
position, and seems to have practically closed the
discussion as to principles ; the papers subsequently
published dealing with particular points only.

The paper opens with a critical examination of
the previous theories, especially those of Boehm and
Hartig, and the author collects what is proved by
investigation so far.

Water and air always exist in the lumina of the
tracheides, &c, and the movement takes place in the
lumina : the imbibition theory of Sachs may be regarded
as overthrown by the subsequent researches of Vesque,
Elfving, Russow, Hartig and others.

As to the mechanism of the process, several points
have to be examined. All the botanists except Boehm
agree that osmosis accounts for the absorption of the
water from the soil by the root-hairs, and for move-
ments of water in parenchyma generally: Boehm
refers the phenomena to differences of pressure,
rejecting other causes for the following reasons :

(1) Osmosis acts so slowly.

(2) The epidermis cells, from which transpiration

1 " ZurTheorie der Wasserbewegung in den Pflanzen," Prin&Aeim's

Jahrb.f. IViss. Hot. b. xv. h. 4, 1884, pp. 569-630

n8 TIMBER AND SOME OF ITS DISEASES, [chap.

takes place, contain no chlorophyll-corpuscles, and
therefore cannot produce osmotically active sub-
stances.

(3) If osmosis replaces the transpired water why do
not plants become filled to overflowing when placed
in a damp atmosphere ?

(4) Green plants placed in the dark for some time
ought to use up all their osmotic substances, and
would then droop if placed again in the light, whereas
they do not do so.

(5) If the movements of water in transpiring leaves
is due to osmosis, then so is that in the stem of those
plants which have " parenchymatous wood."

To which Godlewski replies as follows :

(1) Movements due to osmosis are slow, it is true,
but the distances traversed are very minute, and the
fine network of vascular bundles in the leaf is so
arranged that no particle of water need have to
traverse more than two or three cells.

(2) If we had to assume that no osmosis could occur
except at the spots where osmotically active substances
are produced, it would follow that no colourless cells
can become turgesccnt — a conclusion falsified by all
we know of the cells of pith, roots, parasites, &c.
Moreover, Bochm is wrong in ascribing transpira-
tion so expressly to the epidermis cells : it is the

IV.] VARIOUS THEORIES, &c. 119

mesophyll cells which give off so much water, to
the lacunae communicating with the air through
stomata.

(3) The excretion of liquid water is a special case,
and need not be considered here, as it receives full
treatment further on.

(4) This depends on the same assumption as (2),
and falls with it.

(5) Very few woods are, like that of the Papayacece,
composed largely of parenchyma, and we are not
driven to compare such wood forthwith with meso-
phyll.

Boehm comes in for criticism no less severe with
respect to other matters, for his views demand that
the epidermis cells and mesophyll, on the one hand,
and the root-hairs and parenchyma of the root on the
other, must have their contents under less pressure than
the atmosphere — an assumption of course opposed to
all we know of the cell, turgescence, and the properties
of protoplasm and cell-sap. Moreover, to suppose
that the pressure in the epidermis and leaf cells, could
ever be less than that in the tracheal elements surely
ignores the negative pressure which exists in the
wood at times of active transpiration ; besides we
know from actual observations that the cells of
the leaf and root show strong turgescence, at just

120 TIMBER AND SOME OF ITS DISEASES, [chap.

those times when according to Boehm their elastic
walls should be caving in beneath the atmospheric
pressure.

Godlewski agrees that there is much to support
Boehm's view that the ascent of the water takes place
in the lumina of the tracheal elements, since the
negative pressure necessary for his theory actually
exists there, as proved by Von Hohnel's and other
experiments. But however near to ten meters high
the pressure of the atmosphere could raise the water
in a shrub (and we must always remember that the
pressure of the air in the uppermost tracheides will
never fall to o), Boehm's theory is hopeless when
applied to trees.

Moreover, all Boehm's attempts to explain the
support of the water columns (by the resistance of
septa to filtration downwards, and the friction of the
air-bubbles, &c.) break down before the fact that any
resistance to movement downwards will apply to
movement upwards as well.

Finally, Boehm's hypothesis would contradict the
principle of the conservation of energy. For if we
suppose his system — columns of water broken by air-
bubbles and septa, and plunged below in root paren-
chyma and above in mesophyll — to be eleven meters
high, and suppose the root parenchyma to be a

IV.] VARIOUS THEORIES, &C. 121

reservoir of water under the pressure of one atmo-
sphere, and if we then create a vacuum in the
mesophyll, it would not work. The water would at
length sink till its upper level was about ten meters
high, because under no conditions could the atmo-
spheric pressure support a higher column. In fact if
Boehm's system would work it would furnish a case
of "perpetual motion."

Now take Hartig's theory. It may be said to
depend on the following facts. The conducting wood
always contains liquid water as well as water of
imbibition : the alburnum often has more water in the
upper parts than in the lower ; whenever the amount
of water in the tree diminishes, the air-spaces in the
crown enlarge more than those in the stem, especially
below. Hence, the pressure of the air is less in the
upper parts of the tree. Especially striking are
Hartig's results with ringed trees, where some species
began to droop when the upper parts of the stem still
contained 70 per cent, and more of water : in these
cases it cannot be because no water, or too little, was
present, that the tree drooped, and the only alter-
native is that the conditions for driving the water up
were absent. As we have seen, Hartig assumes these
conditions to be the difference of pressure of the air-
bubbles — the ringing lets in air, and the continued

122 TIMBER AND SOME OF ITS DISEASES, [chap.

transpiration co-operates in bringing about equal
pressure all over.

Hartig and others also practically establish the
truth of the view that osmosis is the sole cause of
absorption and root-pressure, for the root's activity
is increased as the temperature of the soil rises
a fact irreconcilable with any notion of pressure
at the roots being the cause.

Hartig, as we have seen, ascribes osmotic activity to
all the parenchymatous and living cells, and claims
for the air-bubbles no other function but that of
moving the water from lumen to lumen : he also
accepts Theodore Hartig's experiment with the
vertical piece of branch, using it to prove how slight a
pressure is needed for movement. The water once
moved through the closing membrane of the pit,
becomes arranged by molecular forces in the new
cavity, rising in it by capillarity.

But, Godlewski points out, the experiment with the
vertical stick has never been properly explained :
each writer in succession has assumed properties for it
which it does not possess, and the various proposed
explanations have again contradicted the principles
of physics.

Suppose a glass tube, one meter long and filled
with water ; both ends closed by membrane perme-

iv.] VARIOUS THEORIES, &c. 123

able to water but not to air. Such a tube held
vertical lets no water flow out, because no air can
enter through the wet membrane above ; but if a drop
of water is placed on the upper membrane, it is at
once absorbed by the water inside, and a corre-
sponding drop appears on the outside of the lower
membrane. But the movement is not due to the
weight of the drop — it is caused by the weight of
the ivJiole column in the tube ; the whole weight being
now greater than the difference of pressures at the
top and bottom of the system.

If the tube is divided up by cross membranes, the
only difference is that the resistance of several
membranes has to be overcome, and a vertically
placed stick of Yew is just such a system, whence
Hartig's conclusion was wrong.

But he was still more in error in regarding the
experiment as proving anything respecting the lifting
of the water — the filtration of the water downwards
is a very different matter from a lift upwards. Thus
supposing we place a piece of Yew branch, one meter
long, vertically into ninety cm. of water : if the pressure
of Hartig's drop sufficed to move the column, then
the pressure of ninety cm. of water ought to drive a
very fountain, which of course it does not.

The real explanation of Theodore Hartig's ex-

124 TIMBER AND SOME OF ITS DISEASES, [chap.

periment is that the drop of water is absorbed to
replace the partial vacuum caused by the down flow
of the whole column, and the phenomenon is opposed
to — and not in accordance with — Hartig's and Boehm's
theories. The drop, as it sinks through the upper-
most membrane causes the concave meniscus in each
upper tracheide to become more raised and convex,
and therefore, for the moment, it cannot support so
much as before.

All that the experiment really proves is that the
sum of the resistances to filtration of all the
membranes is smaller than the pressure of a column
of water as long as the wood used.

After further criticisms, Godlewski decides that
every hypothesis which requires no further forces than
root-pressure, transpiration, and capillarity, must be
cast aside as insufficient ; for root-pressure may sink
to O when transpiration is active ; transpiration at
most cannot produce a vacuum, and hence cannot
lift beyond the pressure of one atmosphere ; and the
capillary machinery is not adapted to raise water more
than a few meters.

Some other factor must be brought into requisition,
and Godlewski, like Westermaier, invokes the aid of
the living cells of the wood parenchyma and medul-
lary rays, wliicli are never absent. These living cells,

IV.] VARIOUS THEORIES, &C. 125

placed at numerous successive levels in the stem, act
alternately as suction and force pumps : they absorb
water forcibly by osmosis, and they drive it out again
(also forcibly) by exfiltration at a higher level.

The chief difficulties which face the hypothesis are
those which recur when we try to explain root-pressure,
and yet it is certain that the living cells of the root-
hairs, and root-epidermis, &c, absorb water from the
soil and force it into the axial vessels.

Now the phenomenon of " root-pressure " can be
got with pieces of older roots, or even bits of stems
put into wet sand ; and Hofmeister, Russow, Kraus
and others have conjectured that the living cells of the
wood must co-operate in producing root-pressure, and
it is difficult to see how it can be otherwise in such
cases as the above.

The next difficulty is to explain how a cell can thus
take up water by endosmose, and then drive it out under
pressure ; for it is impossible to accept Hofmeister
and Sachs's hypothesis that the cells are differently
constructed on two opposite sides. Moreover, the
apparatus designed by Sachs1 to explain root-pressure
will not work — it contradicts the conservation of
energy.

1 This apparatus is represented in Fig. 213, p. 276, of Sachs's Lec-
tures on tlu Physiology of /\'au/s, English edition.

126 TIMBER AND SOME OF ITS DISEASES, [chap.

In root-pressure the water driven up at the cut
stock contains a smaller percentage of soluble sub-
stances than does the sap in the living cells : this
means that energy has been employed in separating
the very dilute solution in the vessels. Moreover,
energy is necessary to overcome the resistance to
filtration of the cell-membranes, and this often under
the pressure of a column of water. Still more will
energy be employed if the cells draw their supply of
water from vessels, and drive water into vessels again
at a higher level.

Hence no mere mechanism of turgescence by
osmosis will account for the phenomena, unless we
can show that the sap in the cells becomes more
concentrated each time, and denser as we ascend the
tree : this is not the case.

We must call in the supply of energy set free by
the respiration of the protoplasm, as well as tur-
gescence, as furnishing the forces which overcome
resistance to filtration, and which separate water again
from the dense sap in the cell. In the turgescence of
a cell we have, first, water being absorbed owing to
the attraction for it exercised by substances in the
sap-vacuole ; this continues until the tension of the
elastic cell wall and the hydrostatic pressure exerted
by the water inside are equal, when the cell is turgid.

iv.] VARIOUS THEORIES, &C. 127

The process may continue until the pressure inside
causes water to filter out through the wall.

But there are two possible ways by which this ex-
filtration of the water under pressure might occur.
(1) By increasing the force which presses the water
out ; or (2) by diminishing the attractive forces which
retain the water, and if we can assume a regular
periodicity of either one of these, we can explain
root-pressure.

As a first possibility, suppose a parenchyma-cell in
contact with the water of the soil on the one side, and
on the other (with the intermediation of other similarly
disposed cells) with a tracheide or vessel. Water is
absorbed, and the cell in question becomes turgid.
Then suppose one or both the following changes to
occur in the cell, due to forces liberated by respiration:
(1) the protoplasm as a whole contracts, and (2) the
particles nearest the vessel undergo some alteration
of position, of such a nature as to permit of filtration.
The consequence would be that after the tension due
to turgescence had reached a certain stage, the proto-
plasm by violent contraction drives the water for-
wards : restitution of the turgid condition would then
follow, and the process be repeated, and so on.

As a second possibility, let us suppose that respira-
tion brings about changes in the substances which

128 TIMBER AND SOME OF ITS DISEASES, [chap.

attract water — i.e. the osmotically active substances —
of such a kind that they suddenly become less power-
ful, and can no longer retain their hold on the water,
which is therefore freed and escapes in the direction
of least resistance. Then the osmotically powerful
substances are restored, attract water, and again lose
their hold, and so on periodically.

Now, as Godlewski points out, it has been shown
by De Vries that every time certain molecular decom-
positions occur in the cell, the attraction for water is
increased ; and it is extremely probable that periodic
changes of the following nature occur in the cell —
first, certain molecular combinations are built up which
have a definite power of attracting water osmotically :
then these molecular complexes undergo explosive de-
compositions under the influence of respiratory oxida-
tion, the larger number of molecules thus formed
having a more powerful osmotic attraction for water.
De Vries seems to have established, in fact, that with
each splitting of a complex compound into simpler
ones, the osmotic power of the cell is increased ; while
with each union of simpler into more complex mole-
cules it is lessened : and, again, with every solution
of a part of the protoplasm, the osmotic power in-
creases ; the reverse occurring each time an excretion
of insoluble substances occurs in the cell-sap.

iv.] VARIOUS THEORIES, &C. 129

Now it is allowed universally that in a living cell
there must be continually recurring splittings of com-
plex to simple bodies, and re-combinations of simple
bodies into complex ones ; oxidations of organic
molecules to carbon dioxide and water ; transforma-
tions of soluble into insoluble substances, and so on.
Whence we have only to assume a certain regularitv
or periodicity of these processes to have all that is
necessary for the hypothesis.

If this is given, we have at the same time an explan-
ation to account for the facts that the sap from a
bleeding stump is more dilute than that in the cells ;
that the root-pressure is so powerful ; that old roots
may be made to exhibit root-pressure.1

If now we take the case of the Conifers, it also
explains in a very simple manner the histological
peculiarities of the wood. On a transverse section
of the stem of a Conifer, any medullary ray-cell,
which is in contact above and below and at both
ends with similar cells, has a radial row of tracheides
on its flanks, and these tracheides have particularly
large and open bordered pits on the sides next the
medullary ray-cell, water passing easily from cell to

1 I would also suggest that it may explain the periodicities observed
in the out-flow from ;i cut stamp.

K

130 TIMBER AND SOME OF ITS DISEASES, [chap.

tracheide, and vice versa, through the large permeable
closing membrane.

At a given time, any of these tracheides contains
air and much water : the cell contains protoplasm and
osmotic substances.

Now suppose the medullary ray-cell to absorb water
osmotically from the tracheides1 along its two sides,
becoming more and more turgid, and the contents
pressing the thin membranes outwards into the
cavities of the tracheides : this does not involve any
change of pressure of the air-bubbles in the tracheides,
for the membrane is pushed in towards the cavity as
water is withdrawn.

The turgesence of the medullary ray-cell at length
attains a maximum. Then follow the changes which
lower the osmotic power of the cell contents, and
some of the water is driven out under pressure —
simply because the cell contents can no longer
retain it. This forcible exfiltration of water will
increase the pressure on the air-bubbles in the
tracheides whence the water came, and so if in any
neighbouring tracheide there is less pressure, part
of the water absorbed from, say eight tracheides, will
escape into that one. Moreover, since the pits are

1 There may Ik- eight tracheides or more flanking any one medullary
ray-ci II.

IV.] VARIOUS THEORIES, &c. 131

on the radial walls only, this neighbouring tracheide
will be in a certain direction only — i.e. either above or
below the level of the medullary ray-cell concerned.

But, it results from R. Hartig's researches that the
air-pressure decreases upwards, whence the momentary
increase of pressure in the tracheide just referred to
will give the water an elastic jog upwards.

Now suppose that renewed decompositions —
molecular splittings, &c, — again occur in the medullary
ray-cell : its osmotic attraction again increases, to
repeat the above phenomena, and so on. If the
pressures in the various tracheides in contact with
the medullary ray-cell differ at any given moment,
of course the movements are different, for the same
moment, in each.

Another point should be noted. When the bulged-
out closing membrane of the pit suddenly flattens as
the cell loses water, it tends to cause a partial va-
cuum in the tracheide concerned ; hence it exerts a
suction-valve action, and water rushes in from the
tracheide below — where the air-pressure is somewhat
greater.

If we remember that each medullary ray consists
of numerous cells, each of which is in contact with
several tracheides ; and that the number of medul-
lary rays is very large, it is clear that these small

K 2

132 TIMBER AND SOME OF ITS DISEASES, [chap.

lifts may amount to a good deal, and account for the
ascent of the water in the tallest trees.

Above all, the hypothesis explains in an intelligible
manner so many hitherto puzzling facts. Thus it
explains why, on cutting through the alburnum of a
Conifer, the young shoots drooped although 6o°/0 of
the cubic contents of the tracheides consisted of water.
The air-pressure in the parts above the cut becomes
equalised, and hence there is no reason for the ascent
of the water, but on the contrary every reason for
its descent, for the suction will act downwards from
tracheide to tracheide, much as in Th. Hartig's
experiment.

Again, the hypothesis affords satisfactory explana-
tions of the details of histological structure — e.g., the
typical bordered pits are so many funnels and filters :
the border is the funnel, the membrane the filter, and
the torus acts the parts of the platinum cone used
to prevent rupture of the filter, the torus fitting tight
into the small hole when the pressure becomes too
great. The position of the pits, again, is explained :
those tracheides which stand on any one radial row
are practically at the same level, whereas those on the
next radial row will be a little higher up or lower down
— hence water is pressed up step by step and spirally
round the stem.

iv.] VARIOUS THEORIES, &c. 133

Less obvious, but important, points are the radial
elongation of the medullary ray-cell, in order to cover
several tracheides — the fine air-canals which run be-
tween the cortical and medullary ray-cells, and thus
lead from the lenticels — the simple pits which enable
the cells of medullary rays to communicate with these
air-channels and with one another, and so on.

Godlewski then passes to the consideration of
YVestermaier's theory of " clambering," pointing out
that however similar they may appear, the two views
differ greatly in detail.

In the first place Westermaier regards the wood-
parenchyma as furnishing the path for the movement,
as well as the moving forces. He also makes no use
of transpiration, and his view would only account for
very slow movements ; moreover the hypothesis would
not apply to the Pines and Firs.

As regards Scheit's views, Godlewski points out
that he stands alone in denying (without proving) that
no air exists in the tracheal elements : as pointed out
over and over again, the water passing in at the roots
has air dissolved in it, and even if all else is used up
there will be nitrogen gas in the bubbles.

In 1885, Kohl published the results of some experi-
ments1 bearing on Dufour's statements. He showed

1 " /ur Wasserleitungsfragc,'* Bot, Zeit. 1SS5, p. 522.

134 TIMBER AND SOME OF ITS DISEASES, [chap.

that when branches are sharply bent, the vessels, if
large and few, are compressed like suddenly bent
caoutchouc tubes, but although the sectional area is
enormously reduced, the lumen of the vessel is not
necessarily closed. Moreover, in the notching experi-
ments, with branches sawn half through, it is quite a
mistake to suppose that the continuity of the water
current is broken ; and by squeezing branches in a
vice it can be shown that the rapidity of the
diminished water-flow may be lessened or increased
as the sectional area of the vessels is reduced or en-
larged— by screwing up or loosening the grip.

Kohl used branches cut under water, as well as
completely rooted plants. He measured the rate of
transpiration in the normal condition, and then
squeezed the stem in the vice : then, taking numer-
ous readings, he compared the time it took to trans-
pire so much water. It was found possible to screw
the vice up tight enough to stop the flow altogether.

Meanwhile a large series of very careful measure-
ments had been and were being made by Fr. Darwin
and W. Phillips of Cambridge,1 of the rate of the
transpiration flow under various conditions. Using

1 " On the Transpiration-stream in Cut Branches," Proc. Camb.
Phil. Soc. vol. v. pt. v., Nov., 1885, pp. 330-367. See also Nature,
May 1, 1884.

iv.J VARIOUS THEORIES, &c. 135

an air-bubble as indicator, the length of time which
it took to traverse a given length of tube measured
the rate of flow of the column of water attached to
the cut branch. These results are quite independent
of Kohl's, and nevertheless bear out the same con-
clusions, but much more exactly and in detail. The
authors show that Dufour (1) was wrong in his
estimate of the great obstruction to transpiration pro-
duced by the double-sawing, and (2) exaggerated
the difficulty of forcing water through doubly-sawn
branches.

A single cut produces far less diminution of the rate
of flow, than the double cuts. Moreover, the obstruc-
tion is greater at first than later on — a recovery of the
rate of flow occurs to some extent as the absorbing
power in the leaves makes itself felt more and more.

I must refer the reader to the original for further
details, merely pointing out that the results arc
distinctly in favour of the theory that the water passes
through the cavities of the vessels and tracheides, and
they are the more valuable because low pressures and
actual transpiration were employed.

An interesting test of the validity of Godlewski's
theory was devised by Janse,1 who set himself to ask —

1 " En experimented bewys voor de theorie van Godlewski omtreut
de bewegung van hct water in de planten," Mttand, bladvoor Natuur-

136 TIMBER AND SOME OF ITS DISEASES, [chap.

Is the water current arrested or slowed when the living
cells of the wood-parenchyma and medullary rays are
killed for a distance up the stem ? If so we have a
strong argument in support of Godlewski's theory.

He accordingly killed all the living cells in a
given stretch of a normal branch by running hot
water round the latter while still attached to the tree
and provided with its foliage.

After killing regions 15 to 20 cm. long by heating
them to 700 C for an hour, it was found that the
leaves above the tortured portion began to droop (in
the case of Fuchsia globosd) next day, and were all
dead and withered in five days. Syringa vulgaris
took longer to die, but the final result was the same.

That this was due to the killing of the cells by the
hot water was concluded from the observation that
control plants remained fresh for a much longer time,
even when the whole of the cortex was removed over
the same stretch of branch.

Hence Janse concluded that the medullary ray-cells
and the wood-parenchyma — living, active cells —

wetek Schappen, 1885, pp. 11-24; £>ot- Zeit, 1885, p. 302. See also
"Die Mitwirkung tier Markstrahlen bei tier Wasserbewegung im
Holze," Pringsheim's Jahrbiicher f. wiss. Bot. 1887, p. 1-69. And
Weber, " Ueber den Einfluss hoherer Teinperaturen auf die Fahig-
keit des Holzes den Transpirationsstrom zu leiten," Ber. d. d. bot.
Gcsellsch. 1885, pp. 345-371.

iv.] VARIOUS THEORIES, &C. 137

are indispensable for the ascent of the water in the
wood.

In 1886 Leo Errera opened up once more the
question of Elfving's experiments,1 and their critics,
and disposed of the latter by using gelatine (as
Scheit had done) to stop up the cavities of the ele-
ments, and by employing the transpiration-current
itself — i.e. using cut branches with their foliage on.
Hence he confuted the objection that Elfving had
only proved the case for filtration under pressures.

Branches were used (1) cut under water, so as to
inject the vessels with water ; (2) cut in air, and the
vessels therefore largely filled with air ; (3) cut under
liquid gelatine, so as to stop up the lumina when the
gelatine congealed. The surfaces were then cut
clean, and the three sets of branches, in water, exposed
to transpiration.

It was found that those blocked with gelatine
drooped at once, but recovered if cut higher up •
whereas the others transpired normally.

Errera also adds a critical note derived from
Sachs's own statements ; the latter says,2 that the
thick walled and dense autumnal wood of each

1 L. Errera, " Kin Transpiration Versuch," Ber. d. Deutsch. Bot.
Geselhch., 1886, p. 16.
- Vorles. iiber p, Physiologie, p. 275.

138 TIMBER AND SOME OF ITS DISEASES, [chap.

annual ring is less capable of conducting water than
the large-celled spring-wood of the same ring ; and
Errera implies that this is hardly what one would
expect if the imbibition theory were true.

Notwithstanding the obvious tendency of the criti-
cisms given in the above, and previous papers, how-
ever, Sachs published a second edition of his Vor-
lesungen in 1887, in which he maintains his original
position, and scarcely notices any of the difficulties
which have been raised since 18S2. The note on p.
225-226 can scarcely be regarded as a reply to what
has been urged by Elfving, Hartig, Westermaier,
Godlewski, and others, and it must be accepted that
the great botanist has nothing further to add in
support of his original hypothesis.1

From the experiments of Strasburger, who has
recently paid especial attention to this subject, and of
others, it now appears that a tree can continue to

1 The reader who is interested in further criticism on details should
consult the following memoirs: Zimmermann, "Zur Godlewskischen
Theorie der Wasserbewegung in der Pflanzen," Ber. d. d. bot. Gesellsch.
1885, pp. 290-292. Hansen, " Ein Beitrag zur Kenntniss des Tran-
spirationsstromes," Arl>. d. bot. Inst. Wiirsburg, 1885, pp. 305-314.
Scheit, " Die Wasserbewegung im Holze," Jenaische Zeitschrift fur
Naturk, 1885, pp. 678-734. Schwendener, " Untersuchimgen ueber
das Saftsteigen," Sitzungsber. <l. I. preuss. Akad. d. Wiss. 1S86, pp.
561-602. Scheit, " Beitrag zur Widerlegung der Imbibitionstheorie,"
Jenaische Zietschr. 1885.

iv] VARIOUS THEORIES, &c. 139

transpire and to raise water to heights far above that
of the barometric column, even though poisonous
substances are dissolved in the water supplied to the
roots. Consequently it is impossible to maintain
Godlewski's hypothesis in the form put forward.
Strasburger's work renders it probable that the
columns of water in the vessels and tracheids of the
sapwood are not broken by air bubbles, but are
continuous filaments of water reaching from root to
crown, at any rate in the newest and most active
wood, or, in Conifers, only incompletely broken by the
septa of the tracheids. In view of these and other dis-
coveries which Strasburger finds it impossible to recon-
cile with Godlewski's theory, we are driven to believe
that, after all, the ascent of water in wood is more
of a physical phenomenon than has been supposed.
This becomes more probable in view of Dixon and
Joly's recent work at this difficult subject, for they make
it appear probable that just such columns of water
as Strasburger maintains exist in the wood can be
raised by the osmotic pull exerted by the cells of the
transpiring leaves, and will not break under the strain,
owing to the power of resisting tensile stress possessed
by liquids. This point of view, introduced for the
first time by Dixon and Joly, and independently
confirmed subsequently by Askenasy, had been
entirely overlooked, partly owing to difficulties in the

140 TIMBER AND SOME OF ITS DISEASES, [chap

investigation of such columns in wood, and partly, no
doubt, owing to the prevalent impression that the
columns in the tree were of the nature of Jamin's chains.

In spite of incompleteness in detail, then, we have
to suppose some such theory as the following.

When a column of water in the vessels is once
formed, it can be maintained so long as no air or
solid particles enter, because a capillary column of
clean water is not easily broken even by pulls
equivalent to the pressure of several atmospheres.
As the leaves evaporate water above, the osmotic
draught of the transpiring cells increases, and they
draw in water from these columns with a force equal
to the pressure of many atmospheres. Great as the
tensile strain on the columns of water is, their tenacity
is such that they do not break, and so the traction is
continued down to the soil.

In course of time air slowly passes in or separates
as the negative pressure increases in the tubes, and this
breaks the older columns, and the wood in which
this occurs is no longer in play, but passes over to
heart-wood : on the other hand, new columns of water,
raised into position by osmotic forces, are built up by
the cambium, and so the supply is kept up, each
column being active so long as no air niters in, or,
more probably, until a certain maximum quantity
finds its way into the strained column.

IV.] VARIOUS THEORIES, &c. 141

According to this, we must look upon the bordered
pits as partly niters to let water pass from one column
to another, and partly as valves which, so long as they
are wet, permit no air to enter, functions they seem
adapted to fulfil.

While it is perhaps still impossible to explain in all
its details the ascent of water in tall trees, then, we
must regard it as most probably depending on long
capillary columns of water being maintained in the
vessels, which are pulled by the osmotic draught in
the cells of the leaves, to replace the water lost by
transpiration ; since we are assured by De Vries and
others who have measured the force of the osmotic
draught, that it amounts to the equivalent of the
pressure of many atmospheres, and by Dixon and Joly
that the columns are capable of withstanding the
strain. This amounts in great measure to a
compromise between the capillary and the osmotic
theories of previous speculators on the subject, and is
not at variance with most of the observed facts. *

Much, however, remains to be done before it can be
fully accepted.

1 Those who wish to go further into these matters should read Mr.
F. Darwin's paper, On the Ascent of Water in Trees, at the Liverpool
Meeting of the British Association, 1896; Annals of Botany, December,
1896, p. 630.

CHAPTER V.

DISEASES OF TIMBER.
Trametes radiciperda.

HAVING now obtained some idea of the principal
points in the structure, functions, and varieties of
normal healthy timber, we may pass to the con-
sideration of some of the diseases which affect it.
The subject seems to fall very naturally into two
convenient divisions, if we agree to treat of (i) those
diseases which make their appearance in the living
trees, and (2) those which are only found to affect
dead timber after it is felled and sawn up. In reality,
however, this mode of dividing the subject is purely
arbitrary, and the two categories of diseases are linked
together by all possible gradations.

Confining our attention for the present to the
diseases of standing timber — i.e. which affect

CH. v.] TRAMETES RADICIPERDA. 143

undoubtedly living trees — it can soon be shown that
they are very numerous and varied in kind ; hence it
will be necessary to make some choice of what can
best be described here. I shall therefore propose for
the present to leave out of account those diseases
which do injury to timber indirectly, such as leaf-
diseases, the diseases of buds, growing roots, and so
forth, as well as those which do harm in anticipation
by injuring or destroying seedlings and young plants.
The present chapter will thus be devoted to some of
the diseases which attack the timber in the trees which
are still standing; and as those caused by fungus
parasites are the most interesting, we will confine
our attention to them.

It has long been known to planters and foresters
that trees become rotten at the core, and even hollow,
at all ages and in all kinds of situations, and that in
many cases the first obvious signs that anything is the
matter with the timber make their appearance when,
after a high gale, a large limb snaps off, and the wood
is found to be decayed internally. Now it is by no
means implied that this rotting at the core — " wet-
rot," " red-rot," &c, arc other names generally applied
to what is really a class of diseases — is always
referable to a single cause ; but it is certain that in
a large number of cases it is due to the ravages of

144 TIMBER AND SOME OF ITS DISEASES, [chap.

fungus parasites. The chief reason for popular
misconceptions regarding these points is want of
accurate knowledge of the structure and functions
of wood on the one hand, and of the nature and
biology of fungi on the other. The words disease,
parasitism, decomposition, &c, convey very little
meaning unless the student has had opportunities
of obtaining some such knowledge of the biology of
plants as can only be got in a modern laboratory :
under this disadvantage the reader may not always
grasp the full significance of what follows, but it will
be at least clear that such fungi demand attention as
serious enemies of our timber.

It will be advantageous to illustrate the remarks I
have to make by a description of one or two of the
contents of what is perhaps one of the most instructive
and remarkable museums in the world — the Museum
of Forest Botany in Munich, which I have lately had
the good fortune to examine under the guidance of
Prof. Robert Hartig, the distinguished botanist to
whose energy the Museum is due, and to whose
brilliant investigations we owe nearly all that has
been discovered of the diseases of trees caused by
the Hymenomycetes. Not only is Prof. Hartig's
collection unique in itself, but the objects are
classical, and illustrate facts which are as yet hardly

v.] TRAMETES RADICIPERDA. 145

known outside the small circle of specialists who
have devoted themselves to such studies as are here
referred to.

One of the most disastrous of the fungi which
attack living trees is Trametes radiciperda (Hartig)
the Polyporus annosus of Fries, and it is especially
destructive to the Conifers. Almost every one is
familiar with some of our common Polyporei,
especially those the fructifications of which project
like irregular brackets of various colours from dead
stumps, or from the stems of moribund trees ; well,
such forms will be found on examination to have
numerous minute pores on the under side or on the
upper side of their cheese-like, corky, or woody
substance, and the spores which reproduce the
fungus are developed on the walls lining these
many pores, to which these fungi owe their name.
Trametes radiciperda is one of those forms which
has its pores on the upper side of the spore-bearing
fructification, and presents the remarkable peculiarity
of developing the latter on the exterior of roots
beneath the surface of the soil (Fig. 11).

This is not the place to discuss the characters of
species and genera, nor to enter in detail into the
structure of fungi, but it is necessary to point out
that in those cases where the casual observer sees

L

1 46 TIMBER AND SOME OF ITS DISEASES, [chap.

Fig. it. — Portion of ro.<t of a spruce-fir, with fructificatir.n of Travietes radiciperda
(after Hartig). Each fructification is a yellowish-white mass of felt-like substance
spread over the root, and with minute pores, in which the spores are produced, on
its outer surface ; the mycelium which has developed it is in the interior of the

v.] TRA METES RADICIPERDA. 147

only the fructification of a Polyporus, or of a toad-
stool, or of a mushroom (projecting from a rotting
stump or from the ground, for instance;, the botanist
knows that this fructification is attached to, and has
taken origin from, a number of fine colourless filaments
woven into a felt-like mass known as the mycelium,
and that this felt-work of mycelium is spreading on
and in the rotten wood, or soil, or whatever else the
fungus grows on, and acts as roots, &c, for the benefit
of the fructification.

Now, the peculiarity of the mycelium of this
Trametes radiciperda is that it spreads in the wood of
the roots and trunks of pines and firs and other
Conifers, and takes its nourishment from the wood-
substance, &c, and it is principally to the researches
of Hartig that we owe our knowledge of how it gets
there and what it does when there. He found that
the spores germinate easily in the moisture around
the roots, and put forth filaments which enter between
the bark-scales, and thus the mycelium establishes
itself in the living tree, between the cortex and the
wood (Fig. 12). It is curious to note that the spores
may be carried from place to place by mice and other
burrowing animals, since this Trametes is apt to
develop its fructification and spores in the burrows,
and the\ arc rubbed off into the fur of the

1. 2

148 TIMBER AND SOME OF ITS DISEASES, [chap.

animals as they pass over and under the spore-
bearing mass.

When the mycelium obtains a hold in the root, it

FlG. 12. — Piece of root of spruce-fir, with the mycelium of Trametes radiciperda
(after Hartig) enlarged about 3 times. The white mycelium spreads in a fan-like
manner over the surface beneath the cortex, as seen in the figure where the latter
has been lifted and removed (a). Here and there the mycelium bursts through
the cortex in the form of white protuberances (i>), to form the fructifications.

soon spreads between the cortex and the wood,
feeding upon, and' of course destroying, the cambium.

v.] TRAMETES RADICIPERDA. 149

Here it spreads in the form of thin flattened bands,
with a silky lustre, making its way up the root to the
base of the stem, whence it goes on spreading further
up into the trunk (Fig. 12).

Even if the mycelium confined its ravages to the
cambial region, it is obvious, from what was described
in Chapters I. and II., that it would be disastrous to
the tree ; but its destructive influence extends much
further than this. In the first place, it can spread to
another root belonging to another tree, if the latter
comes in contact in the moist soil with a root already
infected ; in the second place, the mycelium sends
fine filaments in all directions into the wood itself, and
the destructive action of these filaments — called hyphae
— soon reduces the timber, for several yards up the
trunk, to a rotting, useless mass. After thus destroy-
ing the roots and lower parts of the tree, the mycel-
ium may then begin to break through the dead bark,
and again form the fructifications referred to.

Since, as we shall see, Trametes radiciperda is not
the only fungus which brings about the destruction of
standing timber from the roots upwards, it may be
well to see what characters enable us to distinguish
the disease thus induced, in the absence of the
fructification.

The most obvious external symptoms of the disease

ISO TIMBER AND SOME OF ITS DISEASES, [chap.

in a plantation, &c, are : the leaves turn pale, and
then yellow, and die off; then the lower part of the
stem begins to die, and rots, though the bark higher
up may preserve its normal appearance. If the bark
is removed from one of the diseased roots or stems,
there may be seen the fiat, silky, white bands of
mycelium running in the plane of the cambium, and
here and there protruding tiny Avhite cushions between
the scales of the bark (Fig. 12) ; in advanced stages
the fructifications developed from these cushions may
also be found. The wood inside the diseased root will
be soft and damp, and in a more or less advanced
stage of decomposition.

On examining the timber itself, we again obtain dis-
tinctive characters which enable the expert to detect
the disease at a glance. I had the good fortune some
time ago to spend several pleasant hours in the Munich
Museum examining and comparing the various diseases
of timbers, and it is astonishing how well marked the
symptoms are. In the present case the wood at a
certain stage presents the appearance represented in
the drawing, Fig. 13. The general tone is yellow,
passing into a browner hue. Scattered here and there
in this ground-work of still sounder wood are peculiar
oval or irregular patches of snowy white, and in the
centre of each white natch is a black speck. Nothing

v.]

TRAMETES RADICIPERDA.

surprised me more than the accuracy with which Prof.
Hartig's figures reproduce the characteristic appear-
ance of the original specimens in his classical collection,

?s£

1 i

It V

t

(H '

1

1

i

\ 1

fIG ,j,_ a block of the timber of a spruce-fir, attacked by Trametcs radkifxrda.
The general colour is yellow, and in the yellow matrix of less rotten wood are
soft while patches, each with a black speck in it. These patches are portions
completely disorganized by the action of the mycelium, and the appearance is
very characteristic of this particular disease. (After Hartig.)

and I have tried to copy this in the woodcut, but of
course the want of colour makes itself evident.

It is interesting and important to trace the earlier
changes in the diseased timber. When the filaments

152 TIMBER AND SOME OF ITS DISEASES, [chap.

of the fungus first begin to enter the wood, they grow
upwards more rapidly than across the grain, piercing
the walls of the cells and tracheides by means of a
secretion — a soluble ferment — which they exude.
This ferment softens and dissolves the substance of
the walls, and therefore, of course, destroys the struct-
ure and firmness, &c, of the timber. Supposing the
filaments to enter cells which still contain protoplasm
and starch, and other nutritive substances (such as
occur in the medullary rays, for example), the fila-
ments kill the living contents and feed on them. The
result is that what remains unconsumed acquires a
darker colour, and this makes itself visible in the mass
to the unaided eye as a rosy or purple hue, gradually
spreading through the attacked timber. As the de-
structive action of the fungus proceeds in the wood,
the purple shades are gradually replaced by a yellowish
cast, and a series of minute black dots make their
appearance here and there, then the black dots
gradually surround themselves with the white areas,
and we have the stage shown in Fig. 13.

These white areas are the remains of the elements
of the wood which have already been completely
delignified by the action of the ferment secreted by
the fungus filaments — i.e. the hard woody cell-walls
have become converted into soft and swelling cellulose,

v.]

TRAMETES RADICIPERDA.

153

and the filaments are dissolving and feeding upon the
latter (Fig. 14). In the next stage of the advancing

Fig. 14. — Sectional view of a tracheide of the spruce-fir, attacked by the hyphas (a, 6)
of a Trametcs, highly magnified (after Hartig). The upper part of the tracheide
has its walls still sound, though already pierced by the hyphae ; the lower part (c)
has the walls completely delignified, and converted into cellulose, which swells up
and dissolves. The middle-lamella is also undergoing dissolution. The holes in
the walls have been bored by hyphae. -

destruction of the timber the black dots mostly dis-
appear, and the white areas get larger ; the middle-

154 TIMBER AND SOME OF ITS DISEASES, [ch. v.

lamella between the contiguous elements of the wood
subsequently dissolves, and soft places and cavities
are produced, causing the previously firm timber to
become spongy and soft, and it eventually breaks
up into a rotting mass of vegetable remains.

It will readily be understood that all these pro-
gressive changes are accompanied by a decrease in
the specific gravity of the timber, for the fungus de-
composes the substance much in the same way as it
is decomposed by putrefaction or combustion, i.e. it
causes the burning off of the carbon, hydrogen, and
nitrogen, in the presence of oxygen, to carbon-dioxide,
water, and ammonia, retaining part in its own sub-
stance for the time being, and living at its expense.

CHAPTER VI.

DISEASES DUE TO AGARIC US MELLEUS AND
POL YPOR US SUL PHURE US.

BEFORE proceeding further it will be of advantage
to describe another tree-killing fungus, which has long
been well known to mycologists as one of the com-
monest of our toadstools growing from rotten stumps,
and decaying wood-work such as old water-pipes,
bridges, &c. This is Agaricus melleus (Fig. 1 5), a
tawny yellow toadstool with a ring round its stem,
and its gills running down on the stem and bearing
white spores, and which springs in tufts from the base
of dead and dying trees during September and October.
It is very common in this country, and I have often
found it on beeches and other trees in Surrey, but it
has been regarded as simply springing from the dead
rotten wood, &c, at the base of the tree. As a
matter of fact, however, this toadstool is traced to a

156 TIMBER AND SOME OF ITS DISEASES, [chap.

series of dark shining strings, looking almost like the
purple-black leaf-stalks of the maidenhair fern, and

Fig. 15. — A small group of Agaricus (Armillarid) melleus. The toad-stool is
tawny-yellow, and produces white spores ; the gills are decurrent, and the stem
bears a ring. The fine hair-like appendages on the pileus should be bolder.

these strings branch and meander in the wood of the
tree, and in the soil, and may attain even great

VI.] AGARIC US MELLEUS. 157

lengths — several feet, for instance. The interest of
all this is enhanced when we know that until the last
few years these long black cords were supposed to be
a peculiar form of fungus, and were known as
RhizomorpJia. They are, however, the subterranean
vegetative parts (mycelium) of the Agaric we are
concerned with, and they can be traced without break
of continuity from the base of the toadstool into the
soil and tree (Fig. 16). I have several times followed
these dark mycelial cords into the timber of old
beeches and spruce-fir stumps, but they are also to be
found in oaks, plums, various Conifers, and probably
ma)r occur in most of our timber-trees if opportunity
offers.

The most important point in this connection is that
Agaricus melleus becomes in these cases a true parasite,
producing fatal disease in the attacked timber-trees,
and, as Hartig has conclusively proved, spreading
from one tree to another by means of the rhizomorphs
underground. In the summer of 1887 I had an
opportunity of witnessing, on a large scale, the
damage that can be done to timber by this fungus.
I lundreds of spruce-firs with fine tall stems, growing
on the hill sides of a valley in the Bavarian Alps, were
shown to me as "victims to a kind of rot." In most
cases the trees (which at first sight appeared only

158 TIMBER AND SOME OF ITS DISEASES, [chap.

slightly unhealthy) gave a hollow sound when struck,
and the foresters told me that nearly every tree was
rotten at the core. I had found the mycelium of

Fig. 16. — Sketch of the base of a young tree (s), killed by Agaricvs mellens, whicl,
has attacked the roots, and developed rhizomorphs at r, and fructifications. To
the right the fructifications have been traced by dissection to the rhizomorph
strands which produced them.

Agaricus mellens in the rotting stumps of previously
felled trees all up and down the same valley, but it
was not satisfactory to simple assume that the "rot"

VI. j AGARICUS MELLEUS. 159

was the same in both cases, though the foresters
assured me it was so.

By the kindness of the forest manager I was allowed
to fell one of these trees. It was chosen at hazard,
after the men had struck a large number, to show me
how easily the hollow trees could be detected by
the sound. The tree was felled by sawing close to
the roots : the interior was hollow for several feet up
the stem, and two of the main roots were hollow as
far as we could poke canes, and no doubt further.
The dark-coloured rotting mass around the hollow
was wet and spongy, and consisted of disintegrated
wood held together by a mesh-work of the rhizomorphs.
Further outwards the wood was yellow, with white
patches scattered in the yellow matrix, and, again,
the rhizomorph-strands were seen running in all
directions through the mass.

Not to follow this particular case further — since we
are concerned with the general features of the diseases
of timber — I may pass to the consideration of the
diagnosis of this disease caused by Agarieus mclleus,
as contrasted with that due to Trametes radiciperda.

Of course no botanist would confound the fructifi-
cation of the Trametes with that of the Agaricus ;
but the fructifications of such fungi only appear at
certain seasons, and that of Trametes radiciperda may

160 TIMBER AND SOME OF ITS DISEASES, [chap.

be underground, and it is important to be able to
distinguish such forms in the absence of the fructifi-
cations.

The external symptoms of the disease, where young
trees are concerned, are similar in both cases. In a
plantation at Freising, in Bavaria, I have been shown
young Weymouth pines {P. Strobus) attacked and
killed by Agaricus melleus. The leaves turn pale and
yellow, and the lower part of the stem — the so-called
" collar " — begins to die and rot, the cortex above still
looking healthy. So far the symptoms might be
those due to the destructive action of other forms of
tree-killing fungi.

On uprooting a young pine, killed or badly attacked
by the Agaric, the roots are found to be matted
together with a ball of earth permeated by the resin
which has flowed out : this is very pronounced in the
case of some pines, less so in others. On lifting up
the scales of the bark, there will be found, not the
silky, white, delicate mycelium of the Trametes, but
probably the dark cord-like rhizomorphs : there may
also be fiat white rhizomorphs in the young stages,
but they are easily distinguished. These dark rhizo-
morphs may also be found spreading around into the
soil from the roots, and indeed they look so much
like thin roots that we can at once understand their

vi.] AGARIC US MELLEUS. 161

name — rhizomorph. The presence of the rhizomorphs
and (in the case of the resinous pines) the outflow of
resin and sticking together of soil and roots are good
distinctive features. No less evident are the differences
to be found on examining the diseased timber, as
exemplified by Prof. Hartig's magnificent specimens.
The wood attacked assumes brown and bright yellow
colours, and is marked by sharp brown or nearly black
lines, bounding areas of one colour and separating
them from areas of another colour. In some cases
the yellow colour is quite bright — canary yellow, or
nearly so. The white areas scattered in this yellow
matrix have no black specks in them, and can thus be
distinguished from those due to the Trametes. In
advanced stages the purple-black rhizomorphs will be
found in the soft, spongy wood.

The great danger of Agaricus melleus is its power
of extending itself beneath the soil by means of the
spreading rhizomorphs : these are known to reach
lengths of several feet, and to pass from root to root,
keeping a more or less horizontal course at a depth of
6 or 8 inches or so in the ground. On reaching the
root of another tree, the tips of the branched rhizo-
morph penetrate the living cortex, and grow forward
in the plane of the cambium, sending off smaller
ramifications into the medullar)- rays and (in the case

M

162 TIMBER AND SOME OF ITS DISEASES, [chap.

of the pines, &c.) into the resin passages. The hyphae
of the ultimate twigs enter the tracheides, vessels, &c,
of the wood, and delignify them, with changes of
colour and substance as described. Reference must
be made to Prof. Hartig's publications for the details
which serve to distinguish histologically between timber
attacked by Agaricus melleus and by Trametes or other
fungi. Enough has been said to show that diagnosis
is possible, and indeed, to an expert, not difficult.

It is at least clear from the above sketch that we
can distinguish these two kinds of diseases of timber,
and it will be seen on reflection that this depends on
knowledge of the structure and functions of the
timber and cambium on the one hand, and proper
acquaintance with the biology of the fungi on the
other. It is the victory of the fungus over the timber
in the struggle for existence which brings about the
disease ; and one who is ignorant of these points will
be apt to go astray in any reasoning which con-
cerns the whole question. Any one knowing the facts
and understanding their bearings, on the contrary,
possesses the key to a reasonable treatment of the
timber ; and this is important, because the two
diseases referred to can be eradicated from young
plantations, and the areas of their ravages limited in
older forests.

VI.] AGARICUS MELLEUS. 163

Suppose, for example, a plantation presents the
following case. A tree is found to turn sickly and die,
with the symptoms described, and trees immediately
surrounding it are turning yellow. The first tree is at
once cut down, and its roots and timber examined,
and the diagnosis shows the presence of Agariais
melleus or of Tranictcs radiciperda, as the case may
be. Knowing this, the expert also knows more. If
the timber is being destroyed by the Trametes, he
knows that the ravaging agent can travel from tree to
tree by means of roots in contact, and he at once cuts
a ditch around the diseased area, taking care to include
the recently-infected and neighbouring trees. Then
the diseased timber is cut, because it will get worse
the longer it stands, and the diseased parts burnt. If
Agariais melleus is the destroying agent, a similar
procedure is necessary ; but regard must be had to the
much more extensive wanderings of the rhizomorphs
in the soil, and it may be imperative to cut the moat
round more of the neighbouring trees. Nevertheless,
it has also to be remembered that the rhizomorphs
run not far below the surface. However, my purpose
here is not to treat this subject in detail, but to indi-
cate the lines along which practical application of the
truths of botanical science may be looked for. The
reader who wishes to go further into the subject may

M 2

164 TIMBER AND SOME OF ITS DISEASES, [chap.

consult special works. Of course the spores are a
source of danger, but need be by no means so much so
where knowledge is intelligently applied in removing
young fructifications.

I will now pass on to a few remarks on a class of
disease-producing timber fungi which present certain
peculiarities in their biology. The two fungi which
have been described are true parasites, attacking the
roots of living trees, and causing disease in the timber
by travelling up the cambium, &c, into the stem : the
fungi I am about to refer to are termed wound-
parasites, because they attack the timber and trees at
the surfaces of wounds, such as cut branches, torn
bark, frost-cracks, &c, and spread from thence into
the sound timber. When we are reminded how many
sources of danger are here open in the shape of
wounds, there is no room for wonder that such fungi
as these are so widely spread. Squirrels, rats, cattle,
&c, nibble or rub off bark ; snow and dew break
branches ; insects bore into stems ; wind, hail, &c,
injure young parts of trees ; and in fact small wounds
are formed in such quantities that if the fructifications
of such fungi as those referred to arc permitted to
ripen indiscriminately, the wonder is not that access
to the timber is gained, but rather that a tree of any
considerable age escapes at all.

VI.]

POLYPORUS SULPHUREUS.

165

One of the commonest of these is Polyporus sul-
phureus (Fig. 17), which does great injury to all kinds
of standing timber, especially the oak, poplar, willow,
hazel, pear, larch, and others. It is probably well

-HOi-A'

FlC. 17 — I'olyporus sulphurous : portion of the fungus springing from a piece of bark.
(After Hartig.)

known to most foresters, as its fructification projects
horizontally from the diseased trunks as tiers of
bracket-shaped bodies of a cheese-like consistency ;
bright yellow below, where the numerous minute pores
are, and orange or somewhat vermilion above, giving

1 66 TIMBER AND SOME OF ITS DISEASES, [chap.

the substance a coral-like appearance. I have often
seen it in the neighbourhood of Englefield Green
and Windsor, and it is very common in England
generally.

If the spore of this Polypoms lodges on a wound

-^

Fig. iS. — Piece of timber infested with the mycelium of P. sulphurous : the white
masses of fungus fill up the rings and rays produced by their "rotting" action.
(After Hartig.)

which exposes the cambium and young wood, the
filaments grow into the medullary rays and the vessels,
and soon spread in all directions in the timber,
especially longitudinally, causing the latter to assume

VI.]

POL YPOR US S ULPHURE US.

167

a warm brown colour and to undergo decay. In the
infested timber are to be observed radial and other
crevices rilled with the dense felt-like mycelium formed
by the common growth of the innumerable branched

Fig. 19. — Piece of timber completely destroyed by P. su!f>huretts, the my
which fills up the crevices as a white felt. (After Hartig.)

cerium of

filaments (Figs. 18 and 19). In bad cases it is possible
to strip sheets of this yellowish white felt-work out
of the cracks, and on looking at the timber more
closely (of the oak, for instance) the vessels are found

168 TIMBER AND SOME OF ITS DISEASES, [chap.

to be filled with the fungus filaments, and look like
long white streaks in longitudinal sections of the
wood — showing as white dots in transverse sections.

It is not necessary to dwell on the details of the
histology of the diseased timber : the ultimate fila-
ments of the fungus penetrate the walls of all the
cells and vessels, dissolve and destroy the starch in
the medullary rays, and convert the lignified walls of
the wood elements back again into cellulose. This
evidently occurs by some solvent action, and is due to
a ferment excreted from the fungus filaments, and the
destroyed timber becomes reduced to a brown mass
of powder.

I cannot leave this subject without referring to a
remarkably interesting specimen in the Munich
Museum. This is a block of wood containing an
enormous irregularly spheroidal mass of the white
felted mycelium of this fungus, Polyporus sulphureus.
The mass has been cut clean across, and the section
exposes a number of thin brown ovoid bodies em-
bedded in the closely-woven felt : these bodies are of
the size and shape of acorns, but are simply hollow
shells filled with the same felt-like mycelium as that
in which they arc embedded. They are cut in all
directions, and so appear as circles in some cases.
These bodies are, in fact, the outer shells of so many

vi.] POLYP OR US SULPHUREl'S. 169

acorns, embedded in and hollowed out by the mycelium
of Polyporus sulpJiureus. Hartig's ingenious explana-
tion of their presence speaks for itself. A squirrel
had stored up the acorns in a hollow in the timber,
and had not returned to them — what tragedy inter-
venes must be left to the imagination. The Polyporus
had then invaded the hollow, and the acorns, and had
dissolved and destroyed the cellular and starchy
contents of the latter, leaving only the cuticularized
and corky shells, looking exactly like fossil eggs in
the matrix. I hardly think geology can beat this for
a suggestive story.

The three diseases so far described serve very well
as types of a number of others known to be due to
the invasion of timber and the dissolution of the walls
of its cells, fibres, and vessels by Hymenomycetous
fungi, i.e. by fungi allied to the toadstools and poly-
pores. They all "rot" the timber by destroying its
structure ancT substance, starting from the cambium
and medullary rays.

To mention one or two additional forms, Tranietes
Pint is common on pines, but, unlike its truly parasitic
ally, Tr. radicipcrda, which attacks sound roots, it is
a wound-parasite, and seems able to gain access to
the timber only if the spores germinate on exposed
surfaces. The disease it produces is very like that

170 TIMBER AND SOME OF ITS DISEASES, [chap.

caused by its ally : probably none but an expert could
distinguish between them, though the differences are
clear when the histology is understood.

Polyporus fidvus is remarkable because its hyphse
destroy the middle-lamella, and thus isolate the
tracheides in the timber of firs ; Polyporus borealis
also produces disease in the timber of standing
Conifers ; Polyporus igniarius is one of the commonest
parasites on trees such as the oak, &c, and produces
in them a disease not unlike that due to the last form
mentioned ; Polyporus dryadeus also destroys oaks,
and is again remarkable because its hyphse dissolve
the middle-lamella.

With reference to the two fungi last mentioned it
will be interesting to describe a specimen in the
Museum of Forest Botany in Munich, since it seems
to have a possible bearing on a very important ques-
tion of biology, viz. the action of soluble ferments.

It has already been stated that some of these tree-
killing fungi excrete ferments which attack and dissolve
starch-grains, and it is well known that starch-grains
are stored up in the cells of the medullary rays found
in timber. Now, Polyporus dryadeus and P. igniarius
are such fungi ; their hyphae excrete a ferment which
completely destroys the starch-grains in the cells of
the medullary rays of the oak, a tree very apt to be

vi.] DISEASES DUE TO CERTAIN PARASITES. 171

attacked by these two parasites, though P. igniatius,
at any rate, attacks many other dicotyledonous trees
as well. It occasionally happens that an oak is
attacked by both of these Polyporei, and their mycelia

Fig. 20. — Vertical section through the wall of one of the pores of P. sulphurous,
showing the ordinary hyphae (e), tissue of the fructification (a and i), and the
spore-bearing end ; (d and above). (After Harti? |

become intermingled in the timber : when this is the
case the starcJi-grains remain intact in those cells which
are invaded simultaneously by the hyphcs of both fungi.
I have been shown longitudinal radial sections of

i72 TIMBER AND SOME OF ITS DISEASES, [chap.

oak-timber thus attacked, and the medullary rays
of which appeared as glistening white plates. These
plates consist of nearly pure starch : the hyphse have
destroyed the cell-walls, but left the starch intact. It
is easy to suggest that the two ferments acting to-
gether exert (with respect to the starch), a sort of in-
hibitory action one on the other ; but it is also obvious
that this is not the ultimate explanation, and one
feels that the matter deserves further investigation.

It now becomes a question — What other types of
timber-diseases shall be described ? Of course the
limits of a popular book are too narrow for anything
approaching an exhaustive treatment of such a sub-
ject, and nothing has as yet been said of several other
diseases due to crust-like fungi often found on decaying
stems, or of others due to certain minute fungi which
attack healthy roots. Then there is a class of diseases
which commence in the bark or cortex of trees, and
extend thence into the cambium and timber : some of
these " cankers," as they are often called, are proved
to be due to the ravages of fungi, though there is
another series of apparently similar " cankers " which
are caused by other variations in the environment —
the atmosphere and weather generally.

It would need many chapters to place the reader au
courant with the chief results of what is known of

Vi.] DISEASES DUE TO CERTAIN PARASITES. 173

these diseases, and I must be content here with the
bare statement that these " cankers " are in the main
due to local injury or destruction of the cambium. If
the normal cylindrical sheet of cambium is locally
irritated or destroyed, no one can wonder that the
thickening layers of wood are not continued normally
at the locality in question : the uninjured cells are
also influenced, and abnormal cushions of tissue
formed which vary in different cases. Now, in
" cankers " this is — put shortly — what happens : it may
be, and often is, due to the local action of a parasitic
fungus ; or it may be — and, again, often is — owing to
injuries produced by the weather, in the broad sense,
and saprophytic organisms may subsequently invade
the wounds.

The details as to how the injury thus set up is pro-
pagated to other parts — how the " canker " spreads
into the bark and wood around — are details, and would
require considerable space for their description : the
chief point here is again the destructive action of
mycelia of various fungi, which by means of their
powers of pervading the cells and vessels of the wood,
and of secreting soluble ferments which break down
the structure of the timber, render the latter diseased
and unfit for use. The only too well known larch-
disease is a case in point ; but, since this is a subject

174 TIMBER AND SOME OF ITS DISEASES, [chap.

which needs a chapter to itself, I may pass on to
more general remarks on what we have learnt so far.
It will be noticed that, whereas such fungi as Tra-
metes radiciperda and Agaricus melleus are true para-
sites which can attack the living roots of trees, the
other fungi referred to can only reach the interior of
the timber from the exposed surfaces of wounds. It
has been pointed out along what lines the special
treatment of the former diseases must be followed,
and it only remains to say of the latter : take care of
the cortex and cambium of the tree, and the timber
will take care of itself. It is unquestionably true that
the diseases due to wound-parasites can be avoided
if no open wounds are allowed to exist. Many a fine
oak and beech perishes before its time, or its timber
becomes diseased and a high wind blows the tree down,
because the spores of one of these fungi alight on the
cut or torn surface of a pruned or broken branch. Of
course it is not always possible to carry out the sur-
gical operations, so to speak, which are necessary to
protect a tree which has lost a limb, and in other cases
no doubt those responsible have to discuss whether it
costs more to perform the operations on a large scale
than to risk the timber. With these matters I have
nothing to do here, but the fact remains that by
properly closing over open wounds, and allowing the

vi.] DISEASES DUE TO CERTAIN PARASITES. 175

surrounding cambium to cover them up, as it will
naturally do, the term of life of many a valuable tree
can be prolonged, and its timber not only prevented
from becoming diseased and deteriorating, but actually

increased in value.

In the next chapter I propose to deal with the so-
called "dry-rot" in timber which has been felled
and cut up— a disease which has produced much
distress at various times and in various countries.

CHAPTER VII.

THE " DRY-ROT " OF TIMBER.

It has long been known that timber which has been
felled, sawn up, and stored in wood-yards, is by no
means necessarily beyond danger, but that either in
the stacks, or even after it has been employed in
building construction, it may suffer degeneration of a
rapid character from the disease known generally as
"dry-rot." The object of the present chapter is to
throw some light on the question of dry-rot, by sum-
marizing the chief results of recent botanical inquiries
into the nature and causes of the disease — or, rather,
diseases, for it will be shown that there are several
kinds of so-called " dry-rot. "

The usual signs of the ordinary dry-rot of timber
in buildings, especially deal-timber or fir-wood, are as
follows. The wood becomes darker in colour, dull
yellowish-brown instead of the paler tint of sound

VII.]

THE "DRY-ROT" OF TIMBER.

177

deal ; its specific weight diminishes greatly, and that
this is due to a loss of substance can be easily proved
directly. These changes are accompanied with a
cracking and warping of the wood, due to the shorten-
ing of the elements as their water evaporates and they

Fig. 2i.- Portion of the mycelium of Meruliits lacrymans rem >ved £ro n the sur-
face of a beam of wood. This cake-like mass spreads over the surface of the tim-
ber, to which it is intimately attached by hyphae running in the wood-substance.
Subsequently it develops the spore-bearing areola? near its edges. The shading
indicates differences in colour, as well as irregularities of surface.

part from one another : if the disease affects one side
of a beam or plank, these changes cause a pronounced
warping or bending of the timber, and in bad cases it

N

178 TIMBER AND SOME OF ITS DISEASES, [chap.

looks as if it had been burnt or scorched on the injured
side. If the beam or plank is wet, the diseased parts
are found to be so soft that they can easily be cut with
a knife, almost like cheese ; when dry, however, the
touch of a hard instrument breaks the wood into brittle
fibrous bits, easily crushed between the fingers to a
yellow-brown, snuff-like powder. The timber has by
this time lost its coherence, which, as we have seen,
depends on the firm interlocking and holding together
of the uninjured fibrous elements, and may give way
under even light loads — a fact only too well known to
builders and tenants. The walls of the wood-elements
(tracheides, vessels, fibres, or cells, according to the
kind of timber, and the part affected) are now, in fact,
reduced more or less to powder, and if such badly
diseased timber is placed in water it rapidly absorbs
it and sinks : the wood in this condition also readily
condenses and absorbs moisture from damp air, a fact
which we shall see has an important bearing on the
progress of the disease itself.

If such a piece of badly diseased deal as I have
shortly described is carefully examined, the observer
is easily convinced that fungus filaments (mycelium)
are present in the timber, and the microscope shows
that the finer filaments of the mycelium (hyphce) are
permeating the rotting timber in all directions — run-

vii.] THE "DRY-ROT" OF TIMBER. 179

ning between and in the wood elements, and also on
the surface, and there forming cake-like masses (Fig.
21). In a vast number of cases, longer or shorter,
broader or narrower, cords of greyish-white mycelium
may be seen coursing on the surface and in the cracks :
in course of time there will be observed flat cake-like
masses of this mycelium, the hyphae being woven into
felt-like sheets, and these may be extending themselves
on to neighbouring pieces of timber, or even on the
brick-work or ground on which the timber is resting.
These cord-like strands and cake-like masses of felt,
with their innumerable fine filamentous continuations
in the wood, constitute the vegetative body or mycelium
of a fungus known as Merulius lacrymans. Under
certain circumstances, often realized in cellars and
houses, the cakes of mycelium are observed to develop
the fructification of the fungus illustrated in Fie. 22.
To understand the structure of this fructification we
may contrast it with that of the Polyporusox Trametes
referred to in Chapters V. and VI. ; where in the latter
we find a number of pores leading each into a tubular
cavity lined with the cells which produce the spores,
the Merulius shows a number of shallow depressions
lined by the spore-forming cells. The ridges which
separate these depressed areolae have a more or less
zigzag course, running together, and sometimes the

N 2

iSo TIMBER AND SOME OF ITS DISEASES. [CHAP.

whole presents a likeness to honey-comb ; if the
ridges were higher, and regularly walled in the

Fig. 22. — Mature fructification of Menilius lacrymans. The cake-like mass of
felted mycelium has developed a series of areolae (in the upper part of the figure)
on the walls of which the spores are produced. In the natural position this spore-
bearing layer is turned downwards, and in a moist environment pellucid drops or
" tears " disiil from il. 'I'll'- barren pari 111 the foreground was on a wall, ami the
remainder on the lower side ( f a beam : the fungus was photographed in this
position to show the areolation.

depressed areas, the structure would correspond to
that of a Polyponts in essential points. The spores

VII.] THE "DRY-ROT" OF TIMBER. rSr

are produced in enormous numbers (Fig. 23, A) on this
areolated surface, which is directed downwards, and
is usually golden-brown, but may be dull in colour,
and presents the remarkable phenomenon of exuding
drops of clear water, like tears, whence the name
lacrymans. In well-grown specimens, such as may
sometimes be observed on the roof of a cellar, these
crystal-like tears hang from the areolated surface like
pendants, and give an extraordinarily beautiful ap-
pearance to the whole ; the substance of the glistening
Merulius ma)- then be like shot-velvet gleaming with
bright tints of yellow, orange, and even purple.

It has now been demonstrated by actual experiment
that the spores of the fungus, Merulius lacrymans, will
germinate on the surface of damp timber, and send
their germinal filaments into the tracheides, boring
through the cell-walls (Fig. 23, D), and extending
rapidly in all directions. The fungus mycelium, as
it gains in strength by feeding upon the substance of
these cell-walls, destroys the wood by a process very
similar to that already described (compare Fig. 14).

It appears, however, from the investigations of
Poleck and Hartig, that certain conditions are
absolutely necessary for the development of the
mycelium and its spread in the timber, and there can
be no question that the intelligent application of the

1S2 TIMBER AND SOME OF ITS DISEASES, [chap.

knowledge furnished by the scientific educidation of
the biology of the fungus is the key to successful
treatment of the disease. This is, of course, true of
all the diseases of timber, so far as they can be dealt

,", f.- ; A

Fig. 23. — Illustrating the structure, &c, of Mcrulius, after Hartig and Poleck. A,
transverse section of the spore-bearing mycelium showing layer of spores above.
B, part of the spore-layer more highly magnified : the spores are borne in groups
of four, on peg-like sterigmata, developed from the ends of hyphae, which swell
up into club-shaped basidia. C, germinating spores D, a spore germinating on
a wood-fibre, and sending its perm-tube into the latter (highly magnified).

with at all, but it comes out so distinctly in the
present case that it will be well to examine a little at
length some of the chief conclusions.

Merulius, like all fungi, consists of relatively large

vii.] THE "DRY-RUT" OF TIMBER. 183

quantities of water — 50 to 60 per cent, of its weight at
least — together with much smaller quantities of nitro-
genous and fatty substances and cellulose, and minute
but absolutely essential traces of mineral matters, the
chief of which are potassium and phosphorus. It is
not necessary to dwell at length on the exact quantities
of these matters found by analysis, nor to mention
a few other bodies of which traces exist in such fungi.
The point just now is that all these materials are formed
by the fungus at the expense of the substance of the
wood, and for a long time there was considerable diffi-
culty in understanding how this could come about.

The first difficulty was that although the "dry-rot
fungus " could always be found, and the mycelium
was easily transferred from a piece of diseased wood
to a piece of healthy wood provided they were in a
suitable warm, damp, still atmosphere, no one had as
yet succeeded in causing the spores of the Merulius to
germinate, or in following the earliest stages of the
disease. Up to about the end of the year 1884 it was
known that the spores refused to germinate either in
water or in decoctions of fruit ; and repeated trials
were made, but in vain, to see them actually germinate
on damp wood, until two observers, Poleck and
Hartig, discovered about the same time the necessary
/on. lit ions for germination. It should be noted here

i84 TIMBER AND SOME OF ITS DISEASES, [chap.

that this difficulty in persuading spores to germinate
is by no means an isolated instance : we are still
ignorant of the conditions necessary for the germina-
tion of the spores of many fungi — e.g. the spores of
the mushroom, according to De Bary ; and it is
known that in numerous cases spores need very
peculiar treatment before they will germinate. The
peculiarity in the case of the spores of Merulius
lacrymans was found by Hartig to be the necessity of
the presence of an alkali, such as ammonia ; and it is
found that in cellars, stables, and other outhouses
where ammoniacal or alkaline emanations from the
soil or decomposing organic matter can reach the
timber, there is a particularly favourable circumstance
afforded for the germination of the spores. The other
conditions are provided by a warm, still, damp atmo-
sphere, such as exists in badly ventilated cellars, and
corners, and beneath the flooring of many buildings.

Careful experiments have shown beyond all
question that the "dry-rot fungus" is no exception to
other fungi with respect to moisture : thoroughly dry
timber, so long as it is kept thoroughly dry, is proof
against the disease we are considering. Nay, more,
the fungus is peculiarly susceptible to drought, and
the mycelial threads and even the young fructifica-
tions growing on the surface of a beam of timber in a

vii.] THE "DRY-ROT" OF TIMBER. 1S5

damp close situation may be readily killed in a day or
two by letting in thoroughly dry air : of course, the
mycelium deeper down in the wood is not so easily
and quickly destroyed, since not only is it more
protected, but the mycelial strands are able to trans-
port moisture from a distance. Much misunderstand-
ing prevails as to the meaning of " dry air " and
" dry wood " : as a matter of fact the air usually
contains much moisture, especially in cellars and quiet
corners devoid of draughts, such as Merulius delights
in, and we have already seen how dry timber rapidly
absorbs moisture from such air. Moreover, the
strands of mycelium may extend into damp soil,
foundations, brick-work, &c. ; in such cases they
convey moisture to parts growing in apparently dry
situations.

A large series of comparative experiments, made
especially by Hartig, have fully established the
correctness of the conclusion that damp foundations,
walls, &c, encourage the spread of dry-rot, quite
independently of the quality of the timber. This is
important, because it has long been supposed that
timber felled in summer was more prone to dry-rot
than timber felled in winter : such, however, is not
shown to be the case, for under the same conditions
both summer- and winter-wood suffer alike, and

186 TIMBER AND SOME OF ITS DISEASES, [chap.

decrease in weight to the same extent during the
progress of the disease. There is an excellent
opportunity for further research here however, since
one observer maintains that in one case at any rate
{Pinus sylvestris) the timber felled at the end of
April suffered from the disease, whereas that felled
in winter resisted the attacks of the fungus : internal
evidence in the published account supports the
suspicion that some error occurred here. The
wood which succumbed was found to contain much
larger quantities of potassium and phosphorus (two
important ingredients for the fungus), and Poleck
suggests that this difference in chemical constitution
explains the ease with which his April specimens
were infected.

It appears probable from later researches and
criticism that Poleck did not choose the same parts of
the two stems selected for his experiments, for (in the
case of Pinus sylvestris) the heart-wood is attacked
much less energetically than the sap-wood — a circum-
stance which certainly may explain the questionable
results if the chemist paid no attention to it, but
analyzed the sap-wood of one and the heart-wood of
the other piece of timber, as he seems to have done.

The best knowledge to hand seems to be that no
difference is observable in the susceptibility to dry-rot

VII.] THE " DRY-ROT" OF TIMBER. 187

of winter-wood and summer-wood of the same timber ;
i.e. Merulius lacrymans will attack both equally, if
other conditions are the same.

But air-dry and thoroughly seasoned timber is much
less easily attacked than damp fresh cut wood of the
same kind, both being exposed to the same con-
ditions.

Moreover, different timbers are attacked and
destroyed in different degrees. The heart-wood of
the pine is more resistant than any spruce timber.
Experimental observations are wanted on the com-
parative resistance of oak, beech, and other timbers,
and indeed the whole of this part of the question is
well worth further investigation.

When the spore has germinated, and the fungus
hyphse have begun to grow and branch in the moist
timber, they proceed at once to destroy and feed upon
the contents of the medullary rays ; the cells
composing these contain starch and saccharine
matters, nitrogenous substances, and inorganic
elements, such as potassium, phosphorus, calcium,
&c. Unless there is any very new and young wood
present, this is the only considerable source of proteid
substances that the fungus has : no doubt a little may
be obtained from the resin-passages, but only the
younger ones. In accordance with this a curious fact

188 TIMBER AND SOME OF ITS DISEASES, [chap.

was discovered by Hartig : the older parts of the hyphse
pass their protoplasmic contents on to the younger
growing portions, and so economize the nitrogenous
substances. Other food-substances are not so sparse ;
the lignified walls inclose water and air, and contain
mineral salts, and such organic substances as coniferin,
tannin, &c, and some of these are absorbed and
employed by the fungus. Coniferin especially appears
to be destroyed by the hyphae.

The structure of the walls of the tracheides and
cells of the wood is completely destroyed as the
fungus hyphae extract the minerals, cellulose, and
other substances from them. The minerals are
absorbed at points of contact between the hyphae and
the walls, reminding us of the action of roots on a
marble plate : the coniferin and other organic
substances are no doubt first rendered soluble by a
ferment, and then absorbed by the hyphae. This
excretion of ferment has nothing to do with the
excretion of water in the liquid state, which gives the
fungus its specific name : the " tears " themselves have
no solvent action on wood.

It will be evident from what has been stated that
the practical application of botanical knowledge is
here not only possible, but much easier than is the
case in dealing with many other diseases.

VII.] THE "DRY-ROT" OF TIMBER. 189

It must first be borne in mind that this fungus
spreads, like so many others, by means of both spores
and mycelium : it is easy to see strands of mycelium
passing from badly-diseased planks or beams, &c,
across intervening brick-work or soil, and on to
sound timber, which it then infects. The spores are
developed in countless myriads from the fructifications
described, and they are extremely minute and light :
it has been proved that they can be carried from
house to house on the clothes and tools, &c, ol
workmen, who in their ignorance of the facts are
perfectly careless about laying their coats, implements,
&c, on piles of the diseased timber intended for
removal. Again, in replacing beams, &c, attacked
with dry-rot, with sound timber, the utmost ignorance
and carelessness are shown : broken pieces of the
diseased timber are left about, whether with spores on
or not ; and I have myself seen quite lately sound
planks laid close upon and nailed to planks attacked
with the " rot." Hartig proved that the spores can
be carried from the wood of one building to that of
another by means of the saws of workmen.

But perhaps the most reckless of all practices is the
usage of partially diseased timber for other con-
structive purposes, and stacking it meanwhile in a
yard or outbuilding in the neighbourhood of fresh-cut,

190 TIMBER AND SOME OF ITS DISEASES, [chap.

unseasoned timber. It is obvious that the diseased
timber should be removed as quickly as possible, and
burnt at once : if used as firewood in the ordinary
way, it is at the risk of those concerned. Of course
the great danger consists in the presence of many
ripe spores, and their being scattered on timber which
is under proper conditions for their germination and
the spread of the mycelium.

It is clearly an act worthy only of a madman to
use fresh " green " timber for building purposes ; but
it seems certain that much improperly dried and by
no means " seasoned " timber is employed in some
modern houses. Such wood is peculiarly exposed to
the attacks of any spores or mycelium that may be
near.

But even when the beams, door-posts, window-
sashes, &c, in a house are made of properly dried
and seasoned deal, the danger is not averted if they
are supported on damp walls or floors. For the sake
of illustration I will take an extreme case, though I
have no doubt it has been realized at various times.
Beams of thoroughly seasoned deal arc cut with a
saw which has previously been used for cutting up
diseased timber, and a few spores of Merulius are
rubbed off from the saw, and left sticking to one end
of the cut beam : this end is then laid on or in a

vii.] THE "DRY-ROT" OF TIMBER. 191

brick wall, or foundation, which has only stood long
enough to partially dry. If there is no current of
dry air established through this part, nothing is more
probable than that the spores will germinate, and the
mycelium spread, and in the course of time — it may
be months afterwards — a mysterious outbreak of
dry-rot ensues. There can be no question that the
ends of beams in new houses are peculiarly exposed
to the attacks of dry-rot in this way.

The great safeguard — beyond taking care that no
spores or mycelium are present from the first — is to
arrange that all the brick- work, floors, &c, be
thoroughly dry before the timber is put in contact
with them ; or to interpose some impervious substance
— a less trustworthy method. Then it is necessary
to aerate and ventilate the timber ; for dry timber
kept dry is proof against " dry-rot."

The ventilation must be real and thorough however,
for it has been by no means an uncommon experience
to find window-sashes, door-posts, &c, in damp
buildings, with the insides scooped out by dry-rot,
and the aerated outer shells of the timber quite sound :
this is undoubtedly often due to the paint on the outer
surfaces preventing a thorough drying of the deeper
parts of the wood.

Of course the question arises, and is loudly urged,

192 TIMBER AND SOME OF ITS DISEASES, [chap.

Is there no medium which will act as an antiseptic,
and kill the mycelium in the timber in the earlier
stages of the disease ? The answer is, that mineral
poisons will at once kill the mycelium on contact, and
that creosote, &c, will do the same ; but who will take
the trouble to thoroughly impregnate timber in
buildings such as harbour dry-rot ? And it is simply
useless to merely paint these specifics on the surface
of the timber : they soak in a little way, and kill the
mycelium on the outside, but that is all, and the
deadly rot goes on destroying the inner parts of the
timber just as surely.

There is one practical suggestion in this connection,
however ; in cases where properly seasoned timber is
used, the beams laid in the brick walls might have
their ends creosoted, and if thoroughly done this
would probably be efficacious during the dangerous
period while the walls finished drying. I believe this
idea has been carried out lately by Prof. Hartig, who
told me of it. The same observer was also kind
enough to show me some of his experiments with dry-
rot and antiseptics : he dug up and examined in my
presence glass jars containing each two pieces of
deal — one piece sound, and the other diseased. The
sound pieces had been treated with various anti-
septics, and then tied face to face with the diseased

vii.] THE " DRY-ROT" OF TIMBER. 193

pieces, and buried in the jar for many months or even
two years.

However, I must now leave this part of the subject,
referring the reader to special publications for further
information, and pass on to a sketch of what is known
of other kinds of " dry-rot." It is a remarkable fact,
and well known, that Alendius lacrymaiis is a domestic
fungus, peculiar to dwelling-houses and other build-
ings, and not found in the forest. We may avoid the
discussion as to whether or no it has ever been found
wild : one case, it is true, is on record on good authority,
but the striking peculiarity about it is that, like some
other organisms, this fungus has become intimately
associated with mankind and human dwellings, &c.

The case is very different with the next disease-
producing fungus I propose to consider. It frequently
happens that timber which has been stacked for some
time in the wood-yards shows red or brown streaks,
where the substance of the timber is softer, and in fact
may be " rotten " : after passing through the saw-mill
these streaks of bad wood seriously impair the value
of the planks, beams, &c, cut from the logs.

Prof. Hartig, who has devoted much time to the in-
vestigation of the various forms of " dry-rot, " has
shown that this particular kind of red or brown streak-
ing is due to the ravages of J^olyporus vaporarius. The

O

i94 TIMBER AND SOME OF ITS DISEASES, [chap.

mycelium of this fungus destroys the structure of the
wood in a manner so similar to that of the Merulius
that the sawyers and others do not readily distinguish

FlG. 24. — A piece of pine-wood attacked by the mycelium of Polyporus vaporarius.
The timber has warped and cracked under the action of the fungus, becoming of
a warm brown colour at the same time ; in the crevices the white strands of felt-like
mycelium have then increased, and on splitting the diseased timber they are fjund
creeping and applying themselves to all the surfaces. Except that the colour is
snowy white, instead cf gray, this mycelium may easily be mistaken for that of
Merulius. The fructification which it develops is, however, very different.
(After R. Hartig.)

between the two. The mycelium of Polyporus
vaporarius forms thick ribbons and strands, but
they are snowy white, and not gray like those of

VII.] THE "DRY-ROT" OF TIMBER. 195

Merulius lacrymans : the structure, &c., of the
fructification are also different. I have shown in Fig.
24 a piece of wood undergoing destruction from the
action of the mycelium of this Polypoms, and it will
be seen how the diseased timber cracks just as under
the influence of Merulius.

Now Polyporus vapvrarius is common in the forests,
and it has been found that its spores may lodge in
cracks in the barked logs of timber lying on the
ground — cracks such as those in Fig. 1, p. 3). In
the particular forests of which the following story
is told, the felling is accomplished in May (because
the trunks can then be readily barked, and also
because such work cannot be carried on there in the
winter), and the logs remain exposed to the sun and
rain, and vicissitudes of weather generally, for some
time. Now it is easy to see that rain may easily wash
spores into such cracks as those referred to, and
the fungus obtains its hold of the timber in this
way.

The next stage is sending the timber down to the
timber-yards, and this is accomplished, in the districts
referred to, by floating the logs down the river. Once
in the river, the wood swells, and the cracks close up ;
but the fungus spores arc already deeply imprisoned
in the cracks, and have no doubt by this time

O 2

196 TIMBER AND SOME OF ITS DISEASES, [chap.

emitted their germinal hyphse, and commenced to
form the mycelium. This may or may not be the
case : the important point is simply that the fungus is
already there. Having arrived at the timber-wharves
the logs are stacked for sawing in heaps as big as
houses : after a time the sawing up begins. It usually
happens that the uppermost logs when cut up show
little or no signs of rot ; lower down, however, red and
brown streaks appear in the planks, and when the
lowermost logs are reached, perhaps after some weeks
or months, deep channels of powdery, rotten wood are
found, running up inside the logs in such a way that
their transverse sections often form triangular or
Y-shaped figures, with the apex of the triangle or V
turned towards the periphery of the log.

The explanation is simple. The uppermost logs
on the stack have dried sufficiently to arrest the
progress of the mycelium, and therefore of the
disease : the lower logs, however, kept damp and
warm by those above, have offered every chance to
the formation and spread of the mycelium deep
down in the cracks of the timber. I was much im-
pressed with this ingenious explanation, first given
to me by Prof. Hartig, and illustrated by actual
specimens. It will be noticed how fully it explains
the curious shape of the rotten courses because the

VII.]

THE "DRY-ROT" OF TIMBER.

197

depths of the cracks are first diseased, and the
mycelium spreads thence.

Obviously some protection would be afforded if the
bark could be retained on the felled logs, or if they
could be at once covered and kept covered after bark-

FlG. 25. — Part of a longitudinal radial section through a piece of wood infected with
t'olyporus igniarius. After Hartig (highly iragnified).

ing ; and, again, something towards protection might
be done by carting instead of floating the timber, when
possible. At the same time, this is not a reliable
mode of avoiding the disease by itself; and even the
dry top logs in the saw-yard arc not safe. Suppose
the following case. The top logs of the stack arc

193 TIMBER AND SOME OF ITS DISEASES. [CH.VIL

quite dry, and are cut into beams and used in building ;
but they have spores or young mycelium trapped in
the cracks at various places. If, from contact
with damp brick-work or other sources of moisture,
these dormant spores or mycelia are enabled to spread
subsequently, we may have " dry-rot " in the building ;
but this " dry-rot " is due to Polyporus vaporarius and
not to the well-known Merulius lacrymans.

There can probably be no question of the advantage
of creosoting the ends of such rafters, beams, &c. ;
since the creosote will act long enough to enable the
timber to dry, if it is ever to dry at all. But the
mycelium of Polyporus vaporarius makes its way into
the still standing timber of pines and firs ; for it is a
wound-parasite, and its mycelium can obtain a hold
at places which have been injured by the bites of
animals, &c: it thus happens that this form of " dry-
rot " is an extremely dangerous and insidious one,
and I have little doubt that it costs our English timber-
merchants something, as well as Continental ones.
Nor are the above the only kinds of " dry-rot " we
know. A disease of pine-wood is caused by Polyporus
mollis, which is very similar to the last in many
respects, and the suspicion may well gain ground
that this important subject has by no means been
exhausted yet.

CHAPTER VIII.

THE CORTEX AND BARK OF TREES.

If we turn our attention for a moment to the
illustrations in the first chapter, it will be remembered
that our typical log of timber was clothed in a sort of
jacket termed the cortex, the outer parts of which
constitute what is generally known as the bark. This
cortical covering is separated from the wood proper by
the cambium, and I pointed out (pp. 11 and 12) that
the cells produced by divisions on the outside of the
cambium cylinder are employed to add to the cortex.

Now this cortical jacket is a very complicated
structure, since it not only consists of numerous
elements, differing in different trees, but it also under-
goes some very curious changes as the plant grows up
into a tree. It is beyond the purpose of this book to
enter in detail into these anatomical matters, however ;
and I must refer the reader to special text-books for

2oo TIMBER AND SOME OF ITS DISEASES, [chap.

them, simply contenting myself here with general
truths which will serve to render clearer certain state-
ments which are to follow.

It is possible to make two generalizations, which
apply not only to the illustration (Fig 26) here selected
but also to most of our timber-trees. In the first
place, the cortical jacket, taken as a whole, consists
not of rigid lignified elements such as the tracheides
and fibres of the wood, but of thin-walled, soft, elastic
elements of various kinds, which are easily compressed
or displaced, and for the most part easily killed or
injured — I say for the most part easily injured, because,
as we shall see immediately, a reservation must be
made in favour of the outermost tissues, or cork and
bark proper, which are by no means so easily destroyed,
and act as a protection to the rest.

The second generalization is, that since the cambium
adds new elements to the cortex on the inside of the
latter, and since the cambium cylinder as a whole is
travelling radially outwards — i.e. further from the
pith — each year, as follows from its mode of adding
the new annual rings of rigid wood on to the exterior
of the older ones, it is clear that the cortical jacket
as a whole must suffer distension from within, and
tend to become too small for the enlarging cylinder of
rigid wood and growing cambium combined. Indeed,

VIII.] THE CORTEX AND BARK OF TREES. 201

it is not difficult to see that, unless certain provisions
are made for keeping up the continuity of the cortical
tissues, they must give way under the pressure from
within. As we shall see, such a catastrophe is in part
prevented by a very peculiar and efficient process.

Before we can understand this, however, we must
take a glance at the structural characters of the whole
of this jacket (Fig. 26). While the branch or stem is
still young, it may be conveniently considered as con-
sisting of three chief parts.

(1) On the outside is a thin layer of flat, tabular
cork-cells (Fig. 26, Co), which increase in number by
the activity of certain layers of cells along a plane
parallel to the surface of the stem or branch. These
ceWs(CCa) behave very much like the proper cambium,
but the cells divided off from them do not undergo
the profound changes suffered by those which are to
become elements of the wood and inner cortex. The
cells formed on the outside of the line C.Ca in fact
simply become cork-cells ; while those formed on the
inside of the line C.Ca become living cells {CI) very like
those I am now going to describe.

(2) Inside this cork-forming layer is a mass of soft,
thin-walled, "juicy " cells, pat which are all living, and
most of which contain granules of chlorophyll, and
thus give the green colour to the young cortex — a

202 TIMBER AND SOME OF ITS DISEASES, [chap.

colour which becomes toned down to various shades
of olive, gray, brown, &c, as the layers of cork increase
with the age of the part. It is because the corky
layers are becoming thicker that the twig passes from
green to gray or brown as it grows older. Now these
green living cells of the cortex are very important for
our purpose, because, since they contain much food-
material and soft juicy contents of just the kind to
nourish a parasitic fungus, we shall find that, whenever
they are exposed by injury, &c, they constitute an
important place of weakness — nay, more, various fungi
are adapted in most peculiar ways to get at them.
Since these cells are for the most part living, and
capable of dividing, also, we have to consider the
part they play in increasing the extent of the cortex.
(3) The third of the partly natural, partly arbitrary
portions into which we are dividing the cortical jacket
is found between the green, succulent cells {pa) of the
cortex proper (which we have just been considering),
and the proper cambium, Ca, and it may be regarded
as entirely formed directly from the cambium-cells.
These latter, developed in smaller numbers on the out-
side, towards the cortex, than on the inside, towards
the wood, undergo somewhat similar changes in shape
to those which go to add to the wood, but they show
the important differences that their walls remain un-

I i .. 26.— Cambium and cortex of oak, at the end of the first year. We have(i)cork-
cclls (X), furmed from the cork-cambium (C.Ca): the cells developed on the
inside of the latter (Ch are termed collenchyma. and add to the cortex. (2) The
cortex proper, c insisting of parenchymal elk(/a), s une of which c mtain crystals.
(1) The inner or secondary cortex (termed phloem or bast), developed chiefly by
the activity of the cambium (Ca) : this phloem consists of hard basl fibres (/;/•),
1 cells (c), and is added to internally by the cambium (Ca) each
year. It is also traversed by medullary-rays {Mr), which are continuations of
those in the wood. The dotted line (tfO in the cortical parenchyma indicates
where the new cork-cambium will be developed.

204 TIMBER AND SOME OF ITS DISEASES, [chap.

lignified, and for the most part very thin and yielding,
and retain their living contents. For the rest, we
may neglect details and refer to the illustration for
further particulars. The tissue in question is marked
by S, c, hb in the figure, and is called phloem or bast.

A word or two as to the functions of the cortex,
though the subject properly demands much longer
discussion. It may be looked upon as especially the
part through which the valuable substances formed in
the leaves are passing in various directions to be used
where they are wanted. When we reflect that these
substances are the foods from which everything in the
tree — new cambium, new roots, buds, flowers, and
fruit &c. — are to be constructed, it becomes clear that
if any enemy settles in the cortex and robs it of
these substances, it reduces not only the general
powers of the tree, but also — and this is the point
which especially interests us now — its timber-produc-
ing capacity. In the same way, anything which cuts
or injures the continuity of the cortical layers results
in diverting the nutritive substances into other
channels. A very large class of phenomena can be
explained if these points are understood, which would
be mysterious, or at least obscure, otherwise.

Having now sketched the condition of this cortical
jacket when the branch or stem is still young, it will

VIII.] THE CORTEX AND BARK OF TREES. 205

be easy to understand broadly what occurs as it
thickens with age.

In the first place, it is clear that the continuous
sheet of cork (Co) must first be distended, and finally
ruptured, by the increasing pressure exerted from
within : it is true, this layer is very elastic and exten-
sible, and impervious to water or nearly so — in fact it
is a thin layer or skin, with properties like those of a
bottle cork — but even it must give way as the cylinder
goes on expanding, and it cracks and peels off. This
would expose the delicate tissues below, if it were not
for the fact that another layer of cork has by this time
begun to form below the one which is ruptured : a
cork-forming layer arises along the line <£, and busily
produces another sheet of this protective tissue in a
plane more or less parallel with the one which is
becoming cracked. This new cork-forming tissue
behaves as before : the outer cells become cork, the
inner ones add to the green succulent parenchyma-
cells (pa). As years go on, and this layer in its turn
splits and peels, others are formed further inwards ;
and if it is remembered that a layer of cork is
particularly impervious to water and air, it is easy to
understand that each successive sheet of cork cuts off
all the tissues on its exterior from participation in the
life processes of the plant, and they therefore die:

206 TIMBER AND SOME OF ITS DISEASES, [chap.

consequently we have a gradually increasing bark
proper, formed of the accumulated cork-layers and
other dead tissues.

A great number of interesting points, important in
their proper connections, must be passed over here.
Some of these refer to the anatomy of the various
"barks" — the word " bark" being commonly used in
commerce to mean the whole of the cortical jacket —
the places of origin of the cork-layer, and the way in
which the true bark peels off: those further interested
here may compare the plane, the birch, the Scotch
pine, and the elm, for instance, with the oak. Other
facts have reference to the chemical and other sub-
stances found in the cells of the cortex, and which
make " barks " of value commercially. I need only
quote the alkaloids in Cinchona, the fibres in the
Malvaceae, the tannin in the oaks, the colouring-matter
in Garcinia (gamboge), the gutta-percha from Ison-
andra, the ethereal oil of cinnamon, as a few examples
in this connection, since our immediate subject does
not admit of a detailed treatment of these extremely
interesting matters.

The above brief account may suffice to give a general
idea of what the cortical jacket covering our timber
is, and how it comes about that in the normal case the
thickening of the cylinder is rendered possible without

viii.] THE CORTEX AND BARK OF TREES. 207

exposing the cambium and other delicate tissues : it
may also serve to show why bark is so various in
composition and other characters. But it is also clear
that this jacket of coherent bark, bound together by
the elastic sheets of cork, must in its turn exert con-
siderable pressure as it reacts on the softer, living,
succulent parts of the cortex, trapped as they are
between the rigid wood cylinder and the bark proper ;
and it is easy to convince ourselves that such is the
case. By simply cutting a longitudinal slit through
the cortex, down to near the cambium, but taking care
not to injure the latter, the following results may be
obtained. First, the bark gapes, the raw edges of the
wound separating and exposing the tissues below ;
next, in course of time the raw edges are seen to
be healed over with cork — produced by the conversion
of the outer living cells of the cortex into cork-cells.
As time passes, provided no external interference
occurs, the now rounded and somewhat swollen cork-
covered edges of the wound will be found closing up
again ; and sooner or later, depending chiefly on the
extent of the wound and the vigour of the tree, the
growing lips of the wound will come together and
unite completely.

lint examination will show that although such a slit-
wound is so easily healed over, it has had an effect on

2o8 TIMBER AND SOME OF ITS DISEASES, [chap.

the wood. Supposing it has required three years to
heal over, it will be found that the new annual rings of
wood are a little thicker just below the slit ; this is
simply because the slit had relieved the pressure on
the cambium. The converse has also been proved to
be true — i.e. by increasing the pressure on the cambium
by means of iron bands, the annual rings below the
bands are thinner and denser than elsewhere.

But we have also seen that the cambium is not the
only living tissue below the bark : the cortical paren-
chyma {pa), and the cells (V) of the inner cortex
(technically the phloem) are all living and capable of
growth and division, as was described above. The
release from pressure affects them also ; in fact, the
" callus," or cushion of tissue which starts from the
lips of the wound and closes it over, simply consists
of the rapidly growing and dividing cells of this cortex,
i.e. the release from pressure enables them to more
than catch up the enlarging layer of cortex around
the wound.

An elegant and simple instance of this accelerated
growth of the cortex and cambium when released from
the pressure of other tissues is exhibited in the healing
over of the cut ends of a branch, a subject to be dealt
with in the next chapter ; and the whole practice of
propagation by slips or cuttings, the renewal of the

vin.] THE CORTEX AND BARK OF TREES. 209

" bark " of Cinchonas, and other economic processes,
depend on these matters.

In anticipation of some points to be explained only
if these phenomena are understood, I may simply re-
mark here that, obviously, if some parasite attacks the
growing lips of the " callus " as it is trying to cover
up the wound, or if the cambium is injured below, the
pathological disturbances thus introduced will modify
the result : the importance of this will appear when
we come to examine certain disturbances which de-
pend upon the attacks of Fungi which settle on these
wounds before they are properly healed over. In con-
cluding this brief sketch of a large subject, it may be
noted that, generally speaking, what has been stated
of branches, &c, is also true of roots ; and it is easy
to see how the nibbling or gnawing of small animals,
the pecking of birds, abrasions, and numerous other
things, arc so many causes of such wounds in the
forest.

CHAPTER IX.

THE HEALING OF WOUNDS BY OCCLUSION.

IF we pass through a forest of oaks, beeches, pines,
and other trees, it requires but a glance here and there
to see that various natural processes are at work to
reduce the number of branches as the trees become
older. Every tree bears more buds than develop into
twigs and branches, for not only do some of the buds at
a very early date divert the food-supplies from others,
and thus starve them off, but they are also exposed to
the attacks of insects, squirrels, &c, and to dangers
arising from inclement weather, and from being struck
by falling trees and branches, &c, and many are thus
destroyed. Such causes alone will account in part for
the irregularity of a tree, especially a Conifer, in which
the buds may have been developed so regularly that
if all came to maturity the tree would be symmetrical.
I^ut that this is not the whole of the case, can be

ch. ix.] HEALING OF WOUNDS BY OCCLUSION, an

easily seen, and is of course well known to every
gardener and forester.

If we remove a small branch of several years' growth
from an oak, for instance, it will be noticed that on
the twigs last formed there is a bud at the axil of
every leaf; but on examining the parts developed two
or three years previously it is easy to convince our-
selves of the existence of certain small scars, above
the nearly obliterated leaf-scars, and to see that if a
small twig projected from each of these scars the
symmetry of the branching might be completed. Now
it is certain that buds or twigs were formed at these
places, and we know from careful observations that
they have been naturally thrown off by a process
analogous to the shedding of the leaves ; in other
words the oak sheds some of its young branches
naturally every year. And many other trees do the
same ; for instance, the black poplar, the Scotch pine,
Dammara, &c. ; in some trees, indeed, and notably in
the so-called swamp cypress (Taxodium distichuni)
of North America, the habit is so pronounced that it
sheds most of its young branches every year.

But apart from these less obvious causes for the
suppression of branches, we notice in the forest that
the majority of the trees have lost their lower branches
at <i much later date, and that in many cases the

P 2

212 TIMBER AND SOME OF ITS DISEASES. [chm\

remains of the proximal parts of the dead branches
are sticking out from the trunk like unsightly wooden
horns. Some of these branches may have been broken
off by the fall of neighbouring trees or large limbs ;
others may have been broken by the weight of snow

Fig. 27. — Portion of a tree from which a branch has been cut off close to the stem.
C, the cambium of the branch ; B, its cortex.

accumulating during the winter ; others again, may
have been broken by hand, or by heavy wind ; and
yet others have died off, in the first place because the
overbearing shade of the surrounding trees cut off the
access of light to their leaves, and secondly because
the flow of nutritive materials to them ceased, being
diverted into more profitable channels by the flourish-

ix.] HEALING OF WOUNDS BY OCCLUSION. 213

ing, growing parts of the crown of leaves exposed to
sunlight and air above.

The point I wish to insist upon here is that in these
cases of branch-breaking, however brought about,
open wounds are left exposed to all the vicissitudes of
the forest atmosphere ; if we compare the remnant of
such a broken branch and the scar left after the
natural shedding of a branch or leaf, the latter will
be found covered with an impervious layer of cork, a
tissue which keeps out clamp, fungus-spores, &c,
effectually.

It is, in fact — as a matter of observation and experi-
ment— these open wounds which expose the standing
timber to so many dangers from the attacks of
parasitic fungi ; and it will be instructive to look a
little more closely into the matter as bearing on the
question of the removal of large branches from trees.

If a fairly large branch of a tree, such as the oak, is
cut off close to the trunk, a surface of wood is exposed,
surrounded by a thin ring of cambium and bark (as
in Figs. 27 and 28). We have already seen what the
functions of the cambium arc, and it will be observed
that the cut edge of the cambium (C) is suddenly
placed under different conditions from the usual ones ;
the chief change, and the only one we need notice at
present, is that the cambium in the neighbourhood of

2U TIMBER AND SOME OF ITS DISEASES, [chap.

the cut surface is relieved from the compressing
influence of the cortex and bark, and owing to this
release of pressure it begins to grow out at the edges
into a cushion or "callus," as shown in Figs. 29 and 30.
A very similar " callus" is formed in the operation of

t'iG. 28.— The same in longitudinal section. P, the pith of stem and branch ; on
either side of thi-; are the twelve annual z nes of wo d produced during the years
1867-78, as marked. The cambium, C, separates these from the cortex, B.

multiplying plants by "cuttings," so well known to all :
the cambium at the cut surface of the " slip" or
" cutting" is relieved from the pressure of the cortex,
and begins to grow out more rapidly in the directions
of less pressure, and forms the callus

IX.] HEALING OF WOUNDS BY OCCLUSION. 215

Now this callus (Fig. 29, Cat) is in all cases some-
thing more than mere cambium — or rather, as the
cambium extends by cell-divisions from the cut edge
of the wound, its outer parts develop into cortex, and

Fig. 29. — The same piece of stem four years later. The cushion-like development,
Cal, resulting from the overgrowth of the cambium and cortical tissues of the cut
branch, has extended some distance from the edges, and is covering in the exposed
wood. £ is the dead outer corky i issue, incapable of growth, and partially
cracked under the pressures exerted by the thickening of the stem. The latter is
?omewhat swollen transversely, owing to the release of pressure in this region,
enabling the cambium to devel >p a lit t le more actively here ; the quicker growth
of the occluding cushion in the horizontal direction is due to the same cause.

its inner parts into wood, as in the normal case. The
consequence is that we have in the callus, slowly
creeping out from the margins of the wound, new

216 TIMBER AND SOME OF ITS DISEASES, [chap

layers of wood and cortex with cambium between
them (Fig. 30) ; and it will be noticed that each year
the layer of wood extends a little further over the sur-

FlG. 30. — The same in longitudinal section; P. B, and C as before. The four new
layers of wood formed during 1879-82 are artificially separated frim the preced-
ing by a stronger line. On the left side of the figure it will be noticed that the
cambium (and therefore the wood developed from it) projected a little further
over the cut end of the branch each year, carrying the cortical layers (Cor) with
it. At + , in both figures, there is necessarily a depression in which rain-water,
&c, is apt to lodge, and this is a particularly dangerous place, since fungus-
spores may here settle and develop.

face of the wood of the wound, and towards the
centre of the cut branch ; and in course of time,

IX.] HEALING OF WOUNDS BY OCCLUSION. 217

provided the wound is not too large, and the tree is
full of vigour, the margins of the callus will meet near
the middle, and what was the exposed cut surface
of the branch will be buried beneath layers of new

Fig. 31. — The same piece of stem six years later still ; the surface of the cut branch
has now been covered in for some time, and only a boss-like projection marks
where the previous cut surface was. This projection is protecied by cork layers,
like ordinary outer cortex, the old outer cortex cracking more and more as the
stem expands.

wood and cortex, between which lies the cambium
now once more continuous over the whole trunk of the
tree (Figs. 31 and 32).

It is not here to the purpose to enter into the very

218 TIMBER AND SOME OF ITS DISEASES, [chap.

interesting histological questions connected with this
callus-formation, or with the mechanical relations of

J- CO «S)

Fig. 32. — The same in longitudinal section : lettering as before Six new layers of
wood have been developed, and the cut end of the branch was completely
occluded before the last three were formed — i.e. at the end of 1885. After thai
the cambium became once more continuous round the whole stem, and, beyond a
slight protuberance over the occluded wound and the ragged edges of the dead
corky outer layers, B, there are no signs of a breach.

the various parts one to another. It is sufficient for
our present object to point out that this process of
covering up, or occlusion, as I propose to term it,

IX.] HEALING OF WOUNDS BY OCCLUSION. 219

requires some time for its completion. For the
sake of illustration, I have numbered the various
phases in the diagram, with the years during which
the annual rings have been successively formed ; and
it will be seen at a glance that in the case selected, it
required seven years to cover up the surface of the
cut branch (cf. Figs. 27-32). During these seven
years more or less of the cut surface was exposed
(Fig. 30) for some time to all the exigencies of the
forest, and it will easily be understood that abundant
opportunities were afforded during this interval for the
spores of fungi to fall on the naked wood, and for
moisture to condense and penetrate into the interior ;
moreover, in the ledge formed at + in Figs. 29 and 30,
by the lower part of the callus, as it slowly creeps up,
there will always be water in wet weather; and a sodden
condition of the wood at this part is thus insured. All
this is, of course, peculiarly adapted for the germina-
tion of spores ; and since the water will soak out
nutritive materials, nothing could be more favourable
for the growth and development of the mycelium of a
fungus. These circumstances, favourable as they are
for the fungi, arc usually rendered even more so in
practice, because the sawyers often allow such a
branch to fall, and tear and crush the cambium and
cortex at the lower edge of the wound. These and

220 TIMBER AND SOME OF ITS DISEASES, [chap.

other details must be passed over, however, and our
attention be confined to the fact that there are ample
chances for the spores of parasitic and other fungi to
fall on a surface admirably suited for their develop-
ment. The further fact must be insisted upon that
numerous fungus-spores do fall and develop upon
these wounds, and that by the time the exposed sur-
face is covered in (as in Fig. 31) the timber is frequently
already rotten, usually for some distance down into
its substance. In the event of fungi, such as have
been described above — parasites and wound-parasites
— gaining a hold on such wounds, the ravages of the
mycelium will continue after the occlusion is complete,
and I have seen scores of trees apparently sound and
whole when viewed from the exterior, the interior of
which is a mere mass of rottenness : when a heavy gale
at length blows them down, such trees are found to
be mere hollow shells, the ravages of the mycelium
having extended from the point of entry into every
part of the older timber.

In a state of nature the processes above referred to
do not go on so smoothly and easily as just described,
and it will be profitable to glance at such a case as
the following.

A fairly strong branch dies off, from any cause
whatever — e.g. from being overshadowed by other

IX.] HEALING OF WOUNDS BY OCCLUSION. 221

trees. All its tissues dry up, and its cortex, cambium,
&c, are rapidly destroyed by saprophytic fungi, and
in a short time we find only a hard, dry, branched
stick projecting from the tree. At the extreme base,

Fig. 33 — Base of a strong branch which had perished naturally twenty-four years
previously to the stage figured. The branch decayed, and the base was gradually
occluded by the thickening layers of the stem : the fall of the rottiDg branch did
not occur till six years ago, however, and can be determined from the layers at e
andy, which then began to turn inwards over the stump. Meanwhile, the base
had become hollow and full of rotten wood, g. It is interesting to note how slight
the growth is on the lower side of the branch base, i, as compared with that at A
above : the line numbered 24 refers to the annual zones in each case. As seen at
b and d, the roiting of the wood passes backwards, and may invade the previously
healthy wood for some distance (After llartig.)

where it joins the tree, the tissues do not at once
perish, but for a length of from half an inch to an
inch or so the base is still nourished by the trunk.
After a time, the wind, or a falling branch, or the

222 TIMBER AND SOME OF ITS DISEASES, [chap.

weight of accumulated snow, &c, breaks off the dead
branch, leaving the projecting basal portion : if the
branch broke off quite close to the stem, the wound
would, or at least might, soon be occluded ; but, as it
is, the projecting piece not only takes longer to close
in, but it tends to rot very badly (Fig. 33), and at the
best forms a bad " knot " or hole in the timber when
sawn up. Of course what has already been stated of
cut branches applies here : the wounds are always
sources of danger so long as they are exposed.

It is beyond the scope of this chapter to set forth
the pros and cons as to the advisability of adopting
any proposed treatment on a large scale : the simple
question of cost will always have to be decided by
those concerned. But whether it is practicable or not
on a large scale, there is no question as to the desira-
bility of adopting such treatment as the following to
preserve valuable trees and timber from the ravages
of these wound-parasites. Branches which break off
should be cut close down to the stem, if possible in
winter, and the clean cut made so that no tearing or
crushing of the cambium and cortex occur ; the sur-
face should then be painted with a thorough coating
of tar, and the wound left to be occluded. If
the cutting is accomplished in spring or summer,
trouble will be caused by the tar not sticking to the

IX.] HEALING OF WOUNDS BY OCCLUSION. 223

damp surface. Although this is not an absolute safe-
guard against the attacks of fungi — simply because
the germinal tubes from spores can find their way
through small cracks at the margin of the wound, &c.
— still it reduces the danger to a minimum, and it is
certain that valuable old trees have been preserved in
this way.

Before passing to treat of the chief diseases known
to start from such wounds as the above, it should be
remarked that it is not inevitable that the exposed
surface becomes attacked by fungi capable of entering
the timber. It happens not unfrequently that a good
closure is effected over the cut base of a small branch
in a few years, and that the timber of the base is
sound everywhere but at the surface : this happy
result may sometimes be attained in pines and other
Conifers, for instance, by the exudation of resin or its
infiltration into the wood ; but in rarer cases it occurs
even in non-resinous trees, and recent investigations
go to show that the wood formed in these healing pro-
cesses possesses the properties of true heart-wood.
At the same time there is always danger, as stated,
and we will now proceed to give a brief account of the
chief classes of diseases to which such wounds render
the tree liable.

The first and most common action is the decay

224 TIMBER AND SOME OF ITS DISEASES, [chap.

which sets in on the exposure of the wood surface to
the alternate wetting and drying in contact with the
atmosphere : it is known that wood oxidizes under
such circumstances, and we may be sure that wounds
are no exception to this rule. The surface of the
wood gradually turns brown, and the structure of the
timber is destroyed as the process extends.

The difficulty always arises in Nature, however,
that mould-fungi and bacteria of various kinds soon
co-operate with and hurry these processes, and it is
impossible to say how much of the decay is due to
merely physical and chemical actions, and how much
to the fermentative action of these organisms. We
ought not to shut our eyes to this rich field for investi-
gation, although for the present purpose it suffices to
recognize that the combined action of the wet, the
oxygen of the air, and the fermenting action of the
moulds and bacteria, &c, soon converts the outer
parts of the wood into a mixture of acid substances
resembling the humus of black leaf-mould.

Now as the rain soaks into this, it dissolves and
carries down into the wood below certain bodies which
are poisonous in their action on the living parts of the
timber, and a great deal of damage may be caused by
this means alone. But this is not all : as soon as the
decaying surface of the wound provides these mixtures

ix.] HEALING OF WOUNDS BY OCCLUSION. 225

of decomposed organic matter, it becomes a suitable
soil for the development of fungi which are not
parasitic — i.e. which cannot live on and in the normal
and living parts of the tree— but which can and do
thrive on partially decomposed wood. The spores of
such fungi are particularly abundant, and many of the
holes found in trees are due to their action. The
hyphse follow up the poisonous action of the juices
referred to above, living on the dead tissues ; and it
will be intelligible that the drainage from the pro-
ducts aids the poisonous action as it soaks into the
trunk. It is quite a common event to see a short
stump, projecting from the trunk of a beech, for
instance, the edges of the stump neatly rounded over
by the action of a callus which was unable to close up
in the middle, and to find that the hollow extends
from the stump into the heart of the trunk for several
feet or even yards. The hollow is lined by the
decayed humus-like remains of the timber, caused
by the action of such saprophytes as I have referred
to. Similar phenomena occur in wounded or broken
roots, and need not be described at length after
what has been stated.

But, in addition to such decay as this, it is found
that if the spores of true wound-parasites alight on
the damp surface of the cut or broken branch, their

(2

226 TIMBER AND SOME OF ITS DISEASES, [ch. IX.

mycelium can extend comparatively rapidly into the
still healthy and living tissues, bringing about the
destructive influences described in previous chapters,
and then it matters not whether the wound closes
over quickly or slowly — the tree is doomed.

CHAPTER X.

"canker": the larch disease.

There is a large and important class of diseases
of standing timber which start from the cortex and
cambium so obviously that foresters and horticulturists,
struck with the external symptoms, almost invariably
term them " diseases of the bark " ; and since most of
them lead to the production of malformations and
excrescences, often with outflowing of resinous and
other fluids, a sort of rough superficial analogy to
certain animal diseases has been supposed, and such
terms as " canker," " cancer," and so forth, have been
applied to them.

Confining our attention to the most common and
typical cases, the following general statements may be
made about these diseases. They usually result from
imperfect healing of small wounds, the exposed cortex
and cambium being attacked by some parasitic or

Q 2

228 TIMBER AND SOME OF ITS DISEASES, [chap.

semi-parasitic fungus, as it tries to heal over the wound.
The local disturbances in growth kept up by the
mycelium feeding on the contents of the cells of these

Cam.

Fig. 34. — Piece of tree stem affected with "canker." The injury commenced after
the two inner zones of wood (1 and 2) had been developed : it extended further in
successive periods of growth, as shown by the receding zones 3, 4, 5, and 6, until
all the cambium and cortex was destroyed except the pieces D to D. Cam, cam-
bium ; Cnr, living cortex ; D D, dead tissues. At each period of growth the
attempt has been made to heal over the Wuund, as shown by the successively
receding lips.

tissues lead to the irregular growths and hypertrophies
referred to ; the wounds are kept open and " sore," or

x.] "CANKER": THE LARCH DISEASE. 229

even extended, and there is hardly any limit to the
possibilities of damage to the timber thus exposed to
a multitude of dangers.

In Fig. 34 is represented a portion of a tree stem
affected with " canker " : the transverse section shows
the periods of growth numbered 1 to 6 from within
outwards. When the stem was younger, and the
cambium had already developed the zones marked 1
and 2, the cortex suffered some injury near the base
of the dead twig, below the figure I. This injury was
aggravated by the ravages of fungus mycelium, which
penetrated to the cambium and destroyed it over a
small area : in consequence of this, the next periodic
zone of wood (marked 3) is of course incomplete over
the damaged area, and the cortex and cambium strive
to heal over the wound by lip-like callus at the
margins. The accomplishment of the healing is pre-
vented, however, by the mycelium, which is continually
destroying fresh cells and extending the area of in-
jury : consequently the next zone of wood (4 in the
figure) extends even a shorter distance round the stem
than this one, and so on with 5 and 6, the cambium
being now restricted to less than half the circumference
of the stem — i.e. from D to D, and the same with the
living cortex. Of course the injured area extends
upwards and downwards also, as shown by the lips of

-so TIMBER AND SOME OF ITS DISEASES, [chap.

the healing tissue. As soon as the injury extends all
round, the stem dies — it is, in fact, ringed. It is also
interesting to note that the zones 4 and 5 (and the
same would be true of 6 when completed) are thicker
than they would have been normally : this is partly
due to release from pressure, and partly to a con-
centrated supply of nutritive materials, due to the
stimulating action of the fungus.

Much confusion still exists between the various
kinds of " canker " : some of them undoubtedly are
due to frost or to the intense heat of direct insola-
tion ; these are, as a rule, capable of treatment
more or less simple, and can be healed up. Others,
again, can only be freed from the irritating agents
(which, by the by, may be insects as well as
fungi) by costly and troublesome methods.

I shall only select one case for illustration, as it
is typical, and only too well known. As examples
of others belonging to the same broad category,
I may mention the " canker " of apple-trees,
beeches, oaks, hazels, maples, hornbeams, alders,
and limes, and many others ; and simply pass the
remark that whatever the differences in detail in the
special cases, the general phenomena and processes
of reasoning are the same in all.

Perhaps no timber disease has caused so much

x.] "CANKER": THE LARCH DISEASE. 231

consternation and difference of opinion as the
" larch-disease," and even now there is far too
little agreement among foresters either as to what
they really mean by this term, or as to what causes
the malady. The larch, like other timber-trees, is
subject to the attacks of various kinds of fungi
and insects, in its timber, roots, and leaves ; but
the well-known larch-disease, which has been
spreading itself over Europe during the present
century, and which has caused such costly
devastation in plantations, is one of the group of
cancerous diseases the outward and visible signs
of which are manifested in the cortex and young
wood.

The appearance presented by a diseased larch-
stem is shown in Fig. 35. In the earlier stages
of the malady the stem shows dead, slightly
sunken patches, #, of various sizes on the cortex,
and the wood beneath is found to cease growing :
it is a fact to be noted that the dead base of a
dricd-up branch is commonly found in the middle
of the patch. The diseased cortex is found to
stick to the wood below, instead of peeling off
easily with a knife. At the margins of the
flattened patch, just where the dead cortex joins
the normal living parts, there may frequently be

232 TIMBER AND SOME OF ITS DISEASES, [chap.

seen a number of small cup-like fungus fructifications
(Fig. 35, b), each of which is white or grey on the
outside, and lined with orange-yellow. These are
the fruit-bodies of a discomycetous fungus called
Pcziza Willkommii (Htg.), and which has at various
times, and by various observers, received at least
four other names, which we may neglect.

In the spring or early summer, the leaves of
the tree are found to turn yellow and wither on
several of the twigs or branches, and a flow of
resin is seen at the dead patch of cortex. If the
case is a bad one, the whole branch or young tree
above the diseased place may die and dry up. At
the margins of the patch, the edges of the sounder
cortex appear to be raised.

As the disease progresses in succeeding years,
the merely flattened dead patch becomes a sunken
blistered hole from which resin flows : this sinking
in of the destroyed tissues is due to the up-growth
of the margins of the patch, and it is noticed that
the up-growing margin recedes further and further
from the centre of the patch. If this goes on, the
patch at length extends all round the stem or
branch, and the death of all that lies above is
then soon brought about, for since the young wood
and cambium beneath the dead cortex are also

x.] "CANKER": THE LARCH DISEASE. 233

destroyed, the general effect is eventually to " ring "

the tree.

To understand these symptoms better, it is
necessary to examine the diseased patch more
closely in its various stages. The microscope shows
that the dead and dying cortex, cambium, and

lie,. 35 - Porti n of stem of a young larch affected wnh the larclvd.sease as mdicated
by the dead "cancerous" patch of cracked cortex, a : at and near the marg jns of
the patch are the small cup-like fructifications of Peziza Willkommti (Htg ), which
spring from mycelium in the dead and dying cortex and cambium beneath. (After

1

young wood in a small patch, contain the mycelium
of the fungus which gives rise to the cup-like
fructifications— Peziza 1 1 Hllkommii— above referred
to (Fig. 35) ; and it has been proved that, if the
spores of this Peziza are introduced into the cortex

234 TIMBER AND SOME OF ITS DISEASES, [chap.

of a healthy living larch, the mycelium to which
they give rise kills the cells of the cortex and
cambium, penetrates into the young wood, and
causes the development of a patch which every one
would recognize as that of the larch-disease. It
is thus shown that the fungus is the immediate
cause of the patch in which it is found.

The next fact which has been established is that
the fungus can only infect the cortex through some
wound or injury — such as a crack or puncture —
and cannot penetrate the sound bark, &c. Once
inside, however, the mycelium extends upwards,
downwards, sideways, and inwards, killing and
destroying all the tissues, and so inducing the out-
flow of resin which is so characteristic of the
disease. The much-branched, septate, colourless
hyphae can penetrate even as far as the pith, and
the destroyed tissues turn brown and dry up.

After destroying a piece of the tissues in the
spring, the growth of the mycelium stops in the
summer, the dead cortex dries up and sticks to the
wood, and the living cortex at the margins of
the patch commence to form a thick layer of cork
between its living cells and the diseased area.

It is this cork-formation which gives the appear-
ance of a raised rim around the dead patch. It

x.] "CANKER": THE LARCH DISEASE. 235

has long been known that the patches dry up and
cease to spread in the dry season. It should be
pointed out that it is one of the most general
properties of living parenchymatous tissue to form
cork-cells at the boundaries of an injury : if a slice
is removed from a potato, for instance, the cut
surface will be found in a few days with several
layers of cork-cells beneath it, and the same
occurs at the cut surface of a slip, or a pruned
branch, — the " callus " of tissue formed is covered
with a layer of cork.

If it is remembered that the cambium and
young wood are destroyed beneath the patch, it
will be at once clear that in succeeding periods of
growth the annual rings of wood will be deficient
beneath the patch.

Next year, the cambium in the healthy parts of
the stem begins to form another ring ; but the
fungus mycelium awakens to renewed activity at the
same time, and spreads a little further upwards, down-
wards, and sideways, its hyph?e avoiding the cork-
layer and traversing the young wood and cambium
below. During this second spring, therefore, a
still larger patch of dead tissue — cortex, cambium,
and young wood — is formed, and the cork-layer,
developed as usual at the edges of the wound,

236 TIMBER AND SOME OF ITS DISEASES, [chap.

describes a larger boundary. Moreover, since the
cambium around the, as yet, undiseased parts has
added a further annual ring — which of course stops
at the boundaries of the diseased patch — the
centre of the patch is yet more depressed (cf.

Fig. 34)-

And so matters go on, year after year, the local
injury to the timber increasing, and ultimately
seriously affecting, or even bringing to an end, the
life of the tree.

At the margins of the diseased patches, as said,
the fungus at length sends out its fructifications.
These appear at first as very minute cushions of
mycelium, from which the cup-like bodies with
an orange-coloured lining arise : the structure of
this fructification is best seen from the illustration
(Fig. 36, A). The orange-red lining (h) is really
composed of innumerable minute tubular sacs, each
of which is termed an ascus, and contains eight
small spores : as seen in the figure (Fig. 36, B),
these asci stand upright like the pile of velvet lining
the cup. They are formed in enormous numbers,
and go on ripening and scattering the spores,
which they do forcibly, day after day. There are
many interesting details connected with the develop-
ment and structure of these fructifications and

X.]

"CANKER": THE LARCH DISEASE.

237

spores ; but we may pass over these particulars
here, the chief point for the moment being that

Fig. 36. — A, vertical section (magnified) through the dead cortex of a larch, infected
with the mycelium (d) of Peziza Willkommii (Htg.), which is developing its
fructifications {a and P). The mycelium fills up the gaps in the cortex, d, with a
white felt-work, a is a boss-like cushion of this felt-work bursting forth to become
a cup-like fructification ; F, the mature Peziza fructification (in section) ; c. its
stalk ; r, the margins of the cup ; h, the layer of spore-sacs (asci). H, four of the
a^ci from h, very highly magnified, a, hair-like barren filaments between the
saci ; c, a fully-developed ascus, containing the eight spores ; <i, an asms emptied
ofsp res (they have escaped through the hole at the apex); /», a young ascus in
« hich the ■•pores are not yet formed : to the left below is a small one still younger.
(Afier Hanig and Willkomm.)

very large numbers of the minute spores are formed,
and scattered by the wind, rain, animals, &c. More-

238 TIMBER AND SOME OF ITS DISEASES, [chap.

over, as already stated, it has been shown by
experiments that the spores will infect the stem
of the larch if they are introduced into a wound ;
but it is important to notice that the fungus cannot
penetrate the sound cortex.

It now remains for us to see if, in the natural
course of events, infection of the larch can take
place to any great extent ; for, unless this is the
case, we cannot reconcile the above peculiarities of
the fungus with the prevalence of the disease.

It must be borne in mind that the larch is an
Alpine tree, growing naturally at an elevation of
from about 3000 to 6000 feet above sea level, and
even more. In its native heights, both the larch-
disease and Peziza Willkommii occur associated as
we have described them, but the malady does not
become epidemic, as it has done in the valleys and
plains of Europe.

Several insect-enemies of the larch are known,
some of which feed on the buds, and others on the
leaves, &c. : it is not impossible that insect-wounds
may serve occasionally as points of entry for the
fungus.

But attention should be directed to the remark
made when describing the symptoms of the disease —
namely, that a dead branch often springs from near

X.] "CANKER": THE LARCH DISEASE. 239

the centre of the patch. Now it is a well-known fact
in the hill-forests of Switzerland, Germany, Austria,
&c, that heavy falls of snow often load the branches
until they bend down to the ground, and the bark in
the upper angle where the branch joins the stem
is ruptured ; similar cracks are also caused by the
bending down of the branches under the weight of
water condensed from mists, &c. If a spore alighted
near such a place, the rain would wash it into the
crevice, and it would germinate in the moisture
always apt to accumulate there. This certainly
accounts very completely for the situation of the
dead branch, which of course would at once suffer
from the mycelium. Another way in which such
wounds as would give access to the parasite might
arise, is from the blows of hailstones on the still
young and tender cortex.

But probably the most common source of the
crevices or wounds by which the fungus gains an
entry is frost ; and to understand this we must
say a few words as to what is known of the larch
at home in its native Alps.

It is well known, since Ilartig drew attention
to the fact, that in the high regions of the Alps
the trees begin to put forth their shoots very late :
the larch in the lowlands of Germany and the British

240 TIMBER AND SOME OF ITS DISEASES, [chap.

Isles often begins to shoot at the end of March
or beginning of April, whereas in the mountains it
may be devoid of leaves in May. This is because
the transition from winter to spring is very sudden
on high slopes, whereas in the lowlands and valleys
it may be very gradual. The consequence is that
in the Alps, when the buds once begin to open
they do this rapidly and vigorously, and the tender
leaves and shoots are quickly formed and soon
harden beyond the reach of those late spring frosts
which do so much damage in our country : in the
lowlands, on the contrary, the leaves slowly develop
at a time when late frosts are very apt to recur
at night, and they are for several weeks exposed to
this danger ; and if a sharp frost does come, the
chances are that not only will the first output of
tender leaves be killed off, but the whole shoot
suffers, and frost-wounds are formed in the young
cortex.

Another point comes into consideration also.
In warm damp valleys the whole tree is apt to be
more watery, and it is well known that the soft
tissues, like the cortex, suffer more from frost when
filled with watery sap, than do harder, drier, more
matured ones. It has been shown, according to
Soraucr, that dead patches, exactly like those which

X.] "CANKER": THE LARCH DISEASE. 241

characterize the larch-disease in its early stages, can
be artificially produced by exposing the stem to
temperatures below zero, so as to freeze the water
in the cells.

Given the above conditions for producing frost-
wounds, then, and the presence of spores of Peziza
Willkommii, there is no difficulty in explaining the
well-known phenomena of the larch-disease.

But Hartig has brought to light some other facts
of great importance in considering this admittedly
complex question. We have already stated that
the Peziza does occur at the margins of the wounds
in trees growing in the Alps where the larch is
native. In these higher regions, however, the air
is usually relatively dry during periods of active
growth, and the young fructifications of the fungus
are particularly sensitive to drought ; consequently
even when many scattered trees are affected, the
cups developed at the edges of the .wounds are apt
cither to dry up altogether, or to produce relatively
few spores, and these spores have fewer chances of
germinating. In fact, the fungus enjoys at best a
sporadic existence, chiefly at the bases of trees where
the herbage ensures a certain degree of dampness.

When the larch was brought down to the plains
and valleys, however, and planted in all directions

R

242 TIMBER AND SOME OF ITS DISEASES, [chap.

over large areas, the Peziza was also brought with
it ; but it will be clear from the foregoing discussion
that the climatic conditions were now proportionally-
raised in favour of the fungus, and lowered to the
disadvantage of the larch. Plantations in damp
valleys, or in the neighbourhood of the sea, or of
large lakes, were especially calculated to suffer from
frost, and the damp air favoured the propagation
of the fungus, and the disease tended to become
epidemic. The enormous traffic in larch plants also
shows how man too did his share in spreading the
epidemic ; and in fact the whole story of the larch-
disease is of peculiar interest biologically, as illus-
trating the risks we run every day in trusting to
the chapter of accidents to see us safely through any
planting undertaking, no matter how great the stake
at issue, or how ruthless the interference with those
complex biological and physical conditions which
always play such an important part in keeping the
balance in the struggle for existence between all
organisms living together.

Let us now very shortly see what are the chief
lessons taught us by the bitter and costly experience
which the larch-disease brought to foresters. It is
evident that the larch should not be planted at all
in low-lying situations exposed to late frosts ; and

X.] ''CANKER": THE LARCH DISEASE. 243

even in more favoured valleys experience points to
the advantage of mixing it with other trees : large
areas of pure larch are planted at enormous risk
in the lowlands.

As to the treatment of trees already diseased, it
is possible (when it is worth while) to remove diseased
branches from trees of which the trunk and crown
are healthy, but it hardly needs mention that such
diseased branches must be burnt at once. As regards
trees with the stems diseased — in those cases where
the patches are large, and much resin is flowing from
the wounds, experience points to the advisability
of cutting them down. In those cases where the
tree is already very large, and the diseased wound
but small, it may be expedient to let them alone :
theoretically they ought to go, or at any rate the
diseased tissues be excised and burnt : but it seems
to be proved that such a tree may go on forming
timber for many years before the wound will spread
far enough to reduce the annual increment below
the limits of profit, and we all know the view a
practical forester will take of such a case. At the
same time, it is the duty of the man of science to
point out that even such a tree is a source of danger
to its neighbours.

R 2

CHAPTER XI.

LEAVES, AND LEAF DISEASES.

If the leaves are stripped from a timber-tree early
in the summer, or during their young conditions in the
spring, the layer of wood produced in the current
year — and probably even that formed next year — will
be poor and thin. This is simply a fact of observa-
tion, and does not depend on what agent deprives
the tree of its leaves. Those oaks which suffered so
greatly from the ravages of certain tiny caterpillars
during the summer of 1887 — many of them having
all their leaves eaten away before July — will have
recorded the disaster by a thin annual ring of wood :
it is true the more vigorous trees produced (at the
expense of what stores of food materials remained
over) a second crop of leaves in August, and so no
doubt the zone of wood will prove to be a thin
double one, but it was at the expense of the next
year's buds.

CH. xi.] LEAVES, AND LEAF-DISEASES. 245

Now there are very many foes which injure the
leaves of our timber trees, and I wish to show, as
clearly as possible in a short chapter, how it comes
about that injury to the leaves means injury to the
timber. The sum total of the matter is that the
substances which are to be sent down to the cambium,
and converted through its agency into wood, are
produced in the cells of the leaves : consequently,
from our point of view, when an insect or a fungus
consumes the substance of the leaves, it consumes
timber in prospective. Similarly, when the leaves are
removed from a tree by any agent whatever, the latter
is robbed in advance of timber. A leaf, generally
speaking, is an extended, flattened appendage of a
branch, covered by a continuation of the epidermis
of the branch, and containing a continuation of its
other tissues — the vascular bundles of the branch
being continued as the venation, and the cellular
cortex reappearing as the green soft tissue of the leaf.
The epidermis of the leaf is so pieced at hundreds of
thousands of nearly equi-distant points, that gases
can enter into or escape from all its tissues : at these
points are the so-called stomata, each stoma being a
little apparatus which can open and close according
to circumstances.

These openings lead into excavations or passages

246 TIMBER AND SOME OF ITS DISEASES, [chap.

between the loose cells of the softer leaf-tissue, and if
we supposed a very minute creeping organism to
enter one of the stomata, it would find itself in a
labyrinth of inter-cellular passages : supposing it able
to traverse these, it could pass from any part of the
leaf to any other between the cells ; or it could
emerge again from the leaf at thousands of places —
other stomata. In traversing the whole of the
labyrinth, however, it would pass over many millions
of times its own length. Moreover it would find these
intercellular passages filled with a varying atmosphere
of diffusing gases — oxygen, nitrogen, the vapour of
water, and carbon-dioxide being the chief. It would
also find the cell-walls which bound the passages
damp, with water continuous with the water in the
cells. If we suppose our hypothetical traveller
threading the mazes of these passages at night,
and able to perceive or test the changes which go on,
it would find relatively little oxygen and relatively
much carbon-dioxide in the damp atmosphere in the
passages ; whereas in the daylight, if the sun was
shining brightly on the leaves, it would find the atmo-
sphere rarer, and relatively little carbon-dioxide
present, but an abundance of oxygen. These gases
and vapour would be slowly moving in and out at the
stomata by diffusion, the evaporation of the watery

XL] LEAVES, AND LEAF-DISEASES. 247

vapour especially being quicker on a dry, hot, sunny
day.

Inside the cells between which these tortuous
passages run, are contained structures which have
much to do with these changes. Each of the cells I
am considering contains a lining of protoplasm, in
which a nucleus, and a number of small protoplasmic
granules, coloured green, and called chlorophyll-
corpuscles, are embedded : all these are bathed in a
watery cell-sap.

Now, putting together in a general manner some of
the chief facts which we know about this apparatus, it
may be said that the liquid sap inside the cells gives
off water to replace that which escapes through the
damp cell-walls, and evaporates into the above-named
passages and out through the stomata, or at the sur-
face. This evaporation of the water is in itself the
cause of a flow of more water from behind, and this
flow takes place from the vascular bundles forming the
so-called venation of the leaf, coming directly from
the wood of the stem. The course of this water, then,
is from the soil, through the roots, up the young wood
and into the venation of the leaf, and thence it is
drawn into the cells wc are considering. But this
water is not pure water : it contains in solution small
quantities of salts of lime, potash, magnesia, nitric,

248 TIMBER AND SOME OF ITS DISEASES, [chap.

sulphuric, and phosphoric acids, as well as a little
common salt, and traces of one or two other things.
It is, in fact, of the nature of ordinary drinking water,
which always contains minute quantities of such
salts : like drinking water, it also contains gases
(oxygen, nitrogen, carbon-dioxide) dissolved in it

It follows from what has been said that the cell-sap
tends to accumulate small increasing quantities of
these salts, &c, as the water passes away by evapora-
tion. But we must remember that the living contents
— the protoplasm, nucleus, and the green chlorophyll-
corpuscles — use up many of these salts for their life-
purposes, and other portions pass into the cell-walls.

It will thus be seen that the green chlorophyll-
corpuscles are bathed by a fluid cell-sap, the dissolved
gaseous and mineral contents of which are continually
changing, even apart from the alterations which the
life-processes of the living contents of the cell them-
selves entail. We may say that the chlorophyll-
corpuscles find at their disposal in the cell-sap, with
which they are more or less in direct contact, traces of
salts, oxygen, carbon-dioxide, and of course water,
consisting of hydrogen and oxygen.

Now we have the best possible reasons for knowing
that some such changes as the following occur in these
chlorophyll-corpuscles, provided they are exposed to

XL] LEAVES, AND LEAF-DISEASES. 249

sunlight : they take up carbon-dioxide and water, and
traces of minerals, and by means of a molecular
mechanism which is as yet unexplained in detail, they
perform the astonishing feat — for it represents an
astonishing transformation when regarded chemically
and physically — of tearing asunder, by the aid of the
light, the carbon, hydrogen, and oxygen of the carbon-
dioxide and water, and rearranging these elements in
part so as to form a much more complex body —
starch, or an allied compound, oxygen being at the
same time set free.

It is of course not part of my present task to trace
these physiological processes in detail, or to bring for-
ward the experimental evidence on which our know-
ledge of them is based. It must suffice to state that
these compounds, starch and allied substances, do not
remain in the chlorophyll-corpuscles, but become
dissolved and carried away through certain channels
in the phloem of the vascular bundles of the venation,
and thence pass to wherever they are to be employed
as food. The chemical form in which these substances
pass from one cell to another in solution is chiefly
that of grape-sugar, and it is a comparatively easy
observation to make that the cells so often referred to
contain such sugar in their sap.

We are only concerned at present with the fate of

250 TIMBER AND SOME OF ITS DISEASES, [chap.

a portion — but a very large portion — of this starch
and sugar : we can trace them down the vascular
bundles of the venation, through the leaf-stalk, into
the cortex, and eventually to the cambium-cells ; and
it is necessary to be quite clear on the following
points : (i) the cambium-cells, like all other living cells
which contain no chlorophyll, need to be supplied
with such foods as sugar, starch, &c, or they starve
and perish ; (2) since these foods are prepared, as we
have seen, in the leaves, and in the leaves only, it is
obvious that the vigour and well-being of the cam-
bium depend on the functional activity of the leaves.

We have already seen how the cambium-cells give
rise to the young wood, and thus it will be clear how
the formation of timber is dependent on the functional
activity of the leaves. Moreover, it ought to be
mentioned, by the way at least, that it is not only the
cambium which depends upon the leaves for its
supplies — all the roots, young buds, flowers, and fruits,
&c.,as well as the cortex and cork-forming tissues, are
competitors for the food supply. Now it is clear that
if we starve the buds there will be fewer leaves
developed in the following year, and so next year's
cambium will again suffer, and so on.

I have by no means traced all the details of even
the first ramifications of the complex network of

XL] LEAVES, AND LEAF-DISEASES. 251

correlations implied by this competition of the various
organs and tissues for the food supplies from the
leaves ; but probably the following proposition will be
generally clear: — If the leaves are stripped, the
cambium suffers starvation to a greater or less extent,
depending on the intensity of its competition with
other tissues, &c. ; of course a starved cambium will
form less wood, and, it may be added, the timber will
be poorer.

Again, even if the leaves are not stripped quickly
from the tree, but the effect of some external agent is
to shorten their period of activity ; or to occupy
space, on or in them, and so diminish the amount of
leaf-surface exposed to the light and air ; or to block
up their stomata, the points of egress and ingress for
gases and water ; or to steal the contents of the cells
— contents which should normally be passed on for
the growth, &c, of other parts of the tree — in all or
any of these ways injury to the timber may accrue
from the action of the agent in question. Now there
are numbers of parasitic fungi which do all these
things, and when they obtain a hold on pure planta-
tions or forests, they may do immense injury before
their presence is detected by any one not familiar with
their appearance and life-histories.

The great difficulty to the practical forester who

252 TIMBER AND SOME OF ITS DISEASES, [chap.

attempts to deal with these " leaf diseases " is at least
twofold ; for not only are the leaves so numerous and
so out of reach that he can scarcely entertain the idea
of doing anything directly to them, but (and this is
by no means so clearly apprehended as it should be)
they stay on the tree but a short time as a rule, and
when they fall are a continual source of re-infection,
because the spores of the fungi are developed on
them. It is a curious fact that those fungi which are
known to affect the leaves of forest-trees nearly all
belong to two highly-developed groups —the Uredineas
and the Ascomycetes — and the remarkable biological
adaptations which these parasites exhibit for attack-
ing or entering the leaves, passing through periods
of danger, and so on, are nearly as various (and one
might almost say ingenious) as they are numerous.
Some of them, such as the Erysiphecs or mildews on
beeches, oaks, birches, ashes, &c., only form small ex-
ternal patches on the leaves, and do little if any harm
where the leaf-crown is large and active ; others, such
as many of the very numerous SpJiceriacece and their
allies, which form small dark-coloured flecks and spots
on leaves, may also be looked upon as taking only a
slight tax from the leaves. Even in these cases, how-
ever, when the diseases become epidemic in certain
wet seasons, considerable damage may accrue, because

XL] LEAVES, AND LEAF-DISEASES. 253

two chief causes (and many minor ones) are co-
operating to favour the fungus in the struggle for
existence : in the first place, a continuously wet
summer means loss of sunlight and diminished trans-
piration, &c, to the leaves, and so they form smaller
quantities of food materials ; and secondly, the damp
in the atmosphere and leaves favours the fungi pro-
portionally more than the leaves, and so they destroy
and occupy larger areas of leaf surface.

It should be mentioned here, by the way, that all
leaves of all trees are apt to have fungi on them in a
wet summer, but many of these arc only spreading
their mycelia in all directions over the epidermis, in
preparation, as it were, for the fall of the leaf: they
are saprophytes which feed on the dead fallen leaves,
but cannot enter into them while they are yet alive.
In some cases, however, this preparation for the fall is
strikingly suggestive of adaptation towards becoming
parasites. I will quote one instance only in illustration
of this. On the leaves of certain trees in Ceylon,
there was always to be found in the rainy season the
much-branched mycelium of a minute SpJiicria : this
formed enormous numbers of branches, which, on the
older leaves, were found to stop short over the stomata,
and to form eventually a four-celled spore-like body
just blocking up each stoma on which it rested. So

254 TIMBER AND SOME OF ITS DISEASES, [chap.

long as the leaf remained living on the tree, nothing
further occurred ; but wherever a part of the leaf died,
or when the leaf fell moribund on the ground, these
spore-like bodies at once began to send hyphae into
the dying tissue, and thus obtained an early place in
the struggle for existence among the saprophytes
which finished the destruction of the cells and tissues
of the leaf.

There is another group of fungi, the Capiwdiece,
which form sooty black patches on the leaves, and
which are very apt to increase to a dangerous extent
on leaves in damp shady situations ; these have no
connection with the well-known black patches of
Rhytisma from which the leaves of our maples are
rarely free. This last fungus is a true parasite, its
mycelium penetrates into the leaf tissues, and forms
large black patches, in and near which the cells of the
leaf either live for the benefit of the fungus alone,
or entirely succumb to its ravages : after the leaf has
fallen, the fungus forms its spores. Nevertheless,
although we have gone a step further in destructive -
ness, foresters deny that much harm is done to the
trees — no doubt because the foliage of the maples is
so very abundant. Willows, pines, and firs suffer from
allied forms of fungi.

But it is among the group of the Uredinece, or rusts,

XI.] LEAVES, AND LEAF-DISEASES. 255

that we find the most extraordinary cases of para-
sitism, and since some of these exhibit the most
highly developed and complex adaptations known to
us, I propose to select one of them as the type of these
so-called "leaf diseases." This form is Coleosporium
Senecionis {Peridermium Pini), rendered classical by
the reseaches of several excellent botanists.

It is true, Coleosporhim Senecionis is not in some
respects the most dangerous of these fungi — or, rather,
it has not hitherto been found to be so — but in view
of the acknowledged fact that foresters have not as
yet been able to devise practical measures against the
ravages of these numerous rust-fungi, and since we
arc still very ignorant of the details of the biology of
most of them, it seems advisable to choose for illustra-
tion a form which shows in a distinct manner the
complexities of the subject, so that those interested
may sec in what directions botanists may look for
new results. That the story of this fungus is both
complicated and of great biological interest will be
sufficiently evident from the mere recital of what we
know concerning it.

CHAPTER XII.

PINE-BLISTER.

In the months of April and May, the younger
needle-like leaves of the Scotch pine are occasionally
seen to have assumed a yellow tinge, and on closer
examination this change in colour, from green to
yellow, is seen to be due to the development of
what look like small orange-coloured vesicles or
blisters standing off from the surface of the
epidermis, and which have in fact burst through
from the interior of the leaf (Fig. 37). Between
these larger orange-yellow blisters the lens shows
certain smaller brownish or almost black specks.
Each of the vesicular swellings is a form of fungus-
fructification known as an yEcidiuui, and each of
the smaller specks is a fungus-structure called a
Spcrmogoniuui, and both of these bodies are

CH. XII.]

PINE-BLISTER.

257

developed from a mycelium in the tissues of the
leaf. I must employ these technical terms, but
will explain them more in detail shortly : the

Fig. 37. — To the left is a pair of leaves of the Scotch pine, with the blister-like
JEcidia. a, of Peridermium Pini (var. acicola) projecting from their tissues :
these blisters are orange-yellow in colour, and contain spores, as sh jwn in Fig. 38.
Between the Misters are the minute s/>crinogonia, b. To the right is a small
branch, lulled at a a a by Peridermium Pini (var. corticola), the blister-like
yellow sEciciia of the fungus being very conspicuous. (Reduced, after Hartig. )

point to be attended to for the moment is that
this fungus in the leaf has long been known
under the name of Peridermium Pini (var. acicola,

S

258 TIMBER AND SOME OF ITS DISEASES, [chap.

i.e. the variety which lives upon the needle-like
leaves).

On the younger branches of the Scotch pine,
the Weymouth pine, the Austrian pine, and some
others, there may also be seen in May and June
similar but larger bladder-like orange vesicles

Fig. 38. — Blisters (/Ecidia) of PericUrmium Pini (var. corticold) on a branch of the
Scotch pine : some of the sEcidia have already burst at the apex and scattered
their spores, b, b ; the others are still intact. (Natural size, after Hess.)

{/Ecidid) bursting through the cortex (Figs. 37 and
38); and here, again, careful examination shows the
darker smaller spermogonia in patches between
the tzcidia. These also arise from a fungus-
mycelium in the tissues of the cortex, whence the
fungus was named Peridennium Pini (var.

XII.]

PINE-BLISTER.

259

corticold). It is thus seen that the fungus Peri-
dermium Pini was regarded as a parasite of pines,
and that it possessed at least two varieties, one in-
habiting the leaves and the other the cortex : the
" varieties " were so considered, because certain
differences were found in the minute structure of the

FlG. 39 — Vertical section through a very young /Ecidium of Peridermium Pini
(var. acicola), with part of the subjacent tissue of the leaf, h, the mycelium of the
parasitic fungus running between the cells of the leaf : immediately beneath the
epidermis of the leaf, the ends of the hyphae give rise to the vertical rows of
spores (6). the outermost of which (/>) remain barren, and form the membrane of
the blister-like body. The epidermis is already ruptured at / by the pressure of
the young /Ecidium, (After R. Hartig : highly magnified.)

cecidict and spermogonia. The disease is popularly
denoted " Pine-blister."

If we cut thin vertical sections through a leaf and
one of the .smallest blisters or cecidia, and examine
the latter with the microscope, it will be found to
consist of a mass of spores arranged in vertical
rows, each row springing from a branch of the

S 2

260 TIMBER AND SOME OF ITS DISEASES, [chap.

mycelium : the outermost of these spores — i.e.
those which form a compact layer close beneath
the epidermis — remain barren, and serve as a kind
of membrane covering the rest (Fig. 39, /). It is
this membrane which protrudes like a blister from
the tissues. The hyphae of the fungus are seen
running in all directions between the cells of the
leaf-tissue, and as they rise up and form the
vertical chains of spores, the pressure gradually
forces up the epidermis of the leaf, bursts it, and
the mass of orange-yellow powdery spores protrude
to the exterior, enveloped in the aforesaid membrane
of contiguous barren spores. If we examine older
cecidia (Fig. 38, V) it will be found that this mem-
brane at length bursts also, and the spores escape.

Similar sections across a spermogonium exhibit a
structure which differs slightly from the above. Here
also the hyphae in the leaf turn upwards, and send
delicate branches in a converging crowd beneath the
epidermis ; the latter gives way beneath the pressure,
and the free tips of the hyphae constrict off extremely
minute spore-like bodies. These minute bodies are
termed Spermatid, and I shall say no more about them
after remarking that they are quite barren, and that
similar sterile bodies are known to occur in very many
of the fungi belonging to this and other groups.

XII.] PINE-BLISTER. 261

Sections through the czcidia and spermogonia on
the cortex present structures so similar, except in
minute details which could only be explained by
lengthy descriptions and many illustrations, that I
shall not dwell upon them ; simply reminding the
reader that the resemblances are so striking that
systematic mycologists have long referred them to a
mere variety of the same fungus.

Now as to the kind and amount of damage caused
by the ravages of these two forms of fungus.

In the leaves, the mycelium is found running
between the cells (Fig. 39, h), and absorbing or
destroying their contents : since the leaves do not
fall the first season, and the mycelium remains living
in their tissues well into the second year, it is
generally accepted that it does little harm. At the
same time, it is evident that, if very many leaves are
being thus taxed by the fungus, they cannot be
supplying the tree with food materials in such
quantities as if the leaves were intact. However,
the fungus is remarkable in this respect — that it lives
and grows for a year or two in the leaves, and does
not (as so many of its allies do) kill them after a few
weeks. It is also stated that only young pines are
badly attacked by this form : it is rare to find cccidia
on trees more than twenty years or so old.

262 TIMBER AND SOME OF ITS DISEASES, [chap.

Much more disastrous results can be traced directly
to the action of the mycelium in the cortex. The
hyphse grow and branch between the green cells of
the true cortex, as well as in the bast-tissues beneath,
and even make their way into the medullary rays
and resin-canals in the woods, though not very deep.
Short branches of the hyphae pierce the cells, and
consume their starch and other contents, causing a
large outflow of resin, which soaks into the wood or
exudes from the bark. It is probable that this
effusion of turpentine into the tissues of the wood
cambium, and cortex, has much to do with the drying
up of the parts above the attacked portion of the
stem : the tissues shrivel up and die, the turpentine in
the canals slowly sinking down into the injured
region. The drying up would of course occur in any
case if the conducting portions are steeped in turpen-
tine, which prevents the conduction of water from
below.

The mycelium lives for years in the cortex, and may
be found killing the young tissues just formed from
the cambium during the early summer: of course the
annual ring of wood, &c, is here impoverished. If
the mycelium is confined to one side of the stem,
a flat or depressed spreading wound arises ; if this
extends all round, the parts above must die.

xii.] PINE-BLISTER. 263

When fairly thick stems or branches have the
mycelium on one side only, the cambium is injured
locally, and the thickening is of course partial. The
annual rings are formed as usual on the opposite side
of the stem, where the cambium is still intact, or they
are even thicker than usual, because the cambium
there diverts to itself more than the normal share of
food-substances: where the mycelium exists, however,
the cambium is destroyed, and no thickening layer is
formed. From this cause arise cancerous mal-
formations which are very common in pine-woods
(Fig. 40).

Putting everything together, it is not difficult to
explain the symptoms of the disease. The struggle
between the mycelium on the one hand, which tries to
extend all round in the cortex, and the tree itself, on
the other, as it tries to repair the mischief, will end
in the triumph of the fungus as soon as its ravages
extend so far as to cut off the water-supply to the
parts above : this will occur as soon as the mycelium
extends all round the cortex, or even sooner if the
effusion of turpentine hastens the blocking up of
the channels. This may take many years to accom-
plish.

So far, and taking into account the enormous
spread of this disastrous disease, the most obvious

264 TIMBER AND SOME OF ITS DISEASES, [chap.

measures seem to be, to cut down the diseased trees
— of course this should be done in the winter, or at
least before the spores come — and use the timber as
best may be ; but we must first see whether such a
suggestion needs modifying, after learning more
about the fungus and its habits. It appears clear,
at- any rate, however, that every diseased tree removed
means a source of aecidiospores the less.

Fig. 40. — Section across an old pine-stem in the cancerous region injured by Pcrider-
mium Pini (var. corticold). As shown by the figures, the stem was fifteen years
old when the ravages of the fungus began to affect the cambium near a. The
mycelium, spreading in the cortex and cambium on all sides, gradually restricted
the action of the latter more and more : at thirty years old, the still sound
cambium only extended half-way round the stem — no wood being developed on
the opposite side. By the time the tree was eighty years old, only the small area
of cambium indicated by the thin line marked 80 was still alive ; and soon after-
wards the stem was completely "ringed," and dead, all the tissues being suffused
with resin. (After Hartig.)

Probably every one knows the common groundsel
(Senecio vulgaris) which abounds all over Britain and
the Continent, and no doubt many of my readers are
acquainted with other species of the same genus to
which the groundsel belongs, and especially with the
ragwort {Senecio Jacobaza). It has long been known

xil] PINE-BLISTER. 265

that the leaves of these plants, and of several allied
species, are attacked by a fungus, the mycelium of
which spreads in the leaf-passages, and gives rise to
powdery masses of orange-yellow spores, arranged in
vertical rows beneath the stomata : these powdery
masses of spores burst forth through the epidermis,
but are not clothed by any covering, such as the
(zcidia of Peridermium Pini, for instance. These
groups of yellow spores burst forth in irregular
powdery patches, scattered over the under sides of
the leaves in July and August : towards the end of
the summer a slightly different form of spore, but
similarly arranged, springs from the same mycelium
on the same patches. From the differences in their
form, time of appearance, and (as we shall see)
functions, these two kinds of spores have received
different names. Those first produced have numerous
papillae on them, and were called Uredosporcs, from
their analogies with the uredospore of the rust of
wheat ; the second kind of spore is smooth, and is
called the Tclcittospores, also from analogies with the
spores produced in the late summer by the wheat-rust.
The fungus which produces these uredosporcs and
teleutospores was named, and has been long dis-
tinguished as, Colcosporium Senecionis (Pcrs.). We
are not immediately interested in the damage done

266 TIMBER AND SOME OF ITS DISEASES, [chap.

by this parasite to the weeds which it infests, and at
any rate we are not called upon to deplore its
destructive action on these garden pests : it is
sufficient to point out that the influence of the
mycelium is to shorten the lives of the leaves, and to
rob the plant of food material in the way referred to
generally in the last chapter.

What we are here more directly interested in is the
following. A few years ago Wolff showed that if the
spores from the JEcidia of Peridermium Pini
(var. acicold) are sown on the leaf of Senecio, the
germinal hyphae which grow out from the spores e7iter
the stomata of the Senecio leaf, and there develop into
the fungus called Coleosporium Senecionis. In other
words, the fungus growing in the leaves of the pine,
and that parasitic on the leaves of the groundsel and
its allies, are one and the same : it spends part of its
life on the tree and the other part on the herb.

If I left the matter stated only in this bald manner
it is probable that few of my readers would believe
the wonder. But, as a matter of fact, this pheno-
menon, on the one hand, is by no means a solitary
instance, for we know many of these fungi which
require two host-plants in order to complete their
life-history ; and, on the other hand, several observers
of the highest rank have repeated Wolff's experiment

xii.] PINE-BLISTER. 267

and found his results correct. Hartig, for instance, to
whose indefatigable and ingenious researches we owe
most that is known of the disease caused by the
Peridermium, has confirmed Wolff's results ; and in

Fig. 41. — A spore of Periderminm Pint germinating. It puts forth the long,
branched germinal hypha: on the damp surface of a leaf of Senecio, and one of
the branches enters a stoma, and forms a mycelium in the leaf : after some time,
the mycelium gives rise to the uredospores and teleutosporcs of Colcospoiium
Senecionis. (After Tulasne : highly magnified.)

this country Mr. Plowright has successfully repeated
the culture.

It was to the brilliant researches of the late Prof.
De Bary that we owe the first recognition of this

268 TIMBER AND SOME OF ITS DISEASES. Ichap.

remarkable phenomenon of hetercecism — i.e. the
inhabiting more than one host — of the fungi. De
Bary proved that the old idea of the farmer, that the
rust is very apt to appear on wheat growing in the
neighbourhood of barberry-bushes, was no fable ; but,
on the contrary, that the yellow JEcidium on the
barberry is a phrase in the life-history of fungus
causing the wheat-rust. Many other cases are now
known, e.g. the JEcidium abictinum, on the spruce
firs in the Alps, passes the other part of its life on the
Rhododendrons of the same region. Another well-
known example is that of the fungus Gymno-
sporangium, which injures the wood of junipers :
Oersted first proved that the other part of its life is
spent on the leaves of certain Rosaceae, and his
discovery has been repeatedly confirmed. I have
myself observed the following confirmation of this.
The stems of the junipers so common in the
neighbourhood of Silverdale (near Morecambe Bay)
used to be distorted with Gymnosporanginm, and
covered with the teleutospores of this fungus every
spring: in July all the hawthorn hedges in the
neighbourhood had their leaves covered with the
iEcidium form (formerly called Rcestclid), and it was
quite easy to show that the fungus on the hawthorn
leaves was produced by sowing the Gymnosporangium

XII.] PINE-BLISTER. 269

spores on them. Many other well-established cases
of similar hetercecism could be quoted.

But we must return to the Peridermium Pini. It
will be remembered that I expressed myself somewhat
cautiously regarding the Peridermium on the bark
(var. corticold). It appears from further investigations
into the life-history of this form, that it is not a mere
variety of the other, but a totally different species.

Recent researches have shown that Peridermium
Pini (var. corticold) is totally distinct from the form
on Pinus Strobus, and that several species are in-
cluded under the former name ; while the astounding
discovery has been made that the latter species,
Peridermium Strobus, develops a totally different
fungus — Cronartium ribicolum — on the leaves of
Currants and Gooseberries.

It will be seen from the foregoing that in the study
of the biological relationships between any one plant
which we happen to value because it produces timber,
and any other which grows in the neighbourhood, there
may be (and there often is) a scries of problems
fraught with interest so deep scientifically, and so
important economically, that one would suppose no
efforts would be spared to investigate them : no
doubt it will be seen as time progresses that what
occasionally looks like apathy with regard to these

270 TIMBER AND SOME OF ITS DISEASES, [ch.xii

matters is in reality only apparent indifference due to
want of information.

Returning once more to the particular case in
question, it is obvious that our new knowledge points
to the desirability of keeping the seed-beds and
nurseries especially clean from groundsel and weeds
of that description : on the one hand, such weeds
are noxious in themselves, and on the other they
harbour the Coleosporium form of the fungus Perider-
mium under the best conditions for infection. It
may be added that it is known that the fungus can
go on being reproduced by the uredospores on the
groundsel-plants which live through the winter.

CHAPTER XIII.

THE " DAMPING OFF " OF SEEDLING TREES :
PliytopJithora omnivora.

It may possibly be objected that the subject of the
present chapter cannot properly be brought under the
title of this book, since the disease to be discussed is
not a disease of timber in esse but only of timber in
posse ; nevertheless, while acknowledging the validity
of the objection, I submit that in view of the fact that
the malady to be described effects such important
damage to the young plants of several of our timber-
trees, and that it is a type of a somewhat large class
of diseases, the slight inconsistency in the wording of
the general title may be overlooked.

It has long been known to forest nurserymen that,
when the seedling beeches first appear above the
ground, large numbers of them die off in a peculiar
manner — they are frequently said to "damp off" or

272 TIMBER AND SOME OF ITS DISEASES, [ch. XIII.

to " rot off." A large class of diseases of this kind is
only too familiar, in its effects, to cultivators in all
parts of the world. Every gardener probably knows
how crowded seedlings suffer, especially if kept a trifle
too damp or too shaded, and I have a distinct recollec-
tion of the havoc caused by the "damping off" of
young and valuable Cinchona seedlings in Ceylon.

In the vast majority of the cases examined, the
" damping off" of seedlings is due to the ravages of
fungi belonging to several genera of the same family
as ""he one {PJtytophtJiora infestans) which causes
the dreaded potato disease — i.e. to the family of
the Peronosporese — and since the particular species
(Phytofihthora omnivord) which causes the wholesale
destruction of the seedlings of the beech is widely
distributed, and brings disaster to many other plants ;
and since, moreover, it has been thoroughly examined
by various observers, including De Bary, Hartig,
Cohn, and others, I propose to describe it as a type
of the similar forms scattered all over the world.

It should be premised that, when speaking of this
disease, it is not intended to include those cases of
literal damping off caused by stagnant water in ill-
drained seed-beds, or those cases where insufficient
light causes the long-drawn, pale seedlings to perish
from want of those nutrient substances which it can

Xlii.] "DAMPING OFF" OF SEEDLING-TREES. 273

only obtain, after a certain stage of germination, by-
means of the normal activity of its own green coty-
ledons or leaves, properly exposed to light, air, &c.
At the same time, it is not to be forgotten that, as
conditions which favour the spread of the disease to
be described, the above factors and others of equal
moment have to be taken into account : which is in-
deed merely part of a more general statement, viz.
that, to understand the cause and progress of a disease,
we must learn all we can about the conditions to which
the organisms are exposed, as well as the structure,
&c, of the organisms themselves.

First, a few words as to the general symptoms of
the disease in question. In the seed-beds, it is often
first noticeable in that patches of seedlings here and
there begin to fall over, as if they had been bitten or
cut where the young stem and root join, at the surface
of the ground : on pulling up one of the injured seed-
lings, the "collar," or region common to stem and
root, will be found to be blackened, and either rotten
or shrivelled, according to the dampness or dryness of
the surface of the soil. Sometimes the whole of the
young root will be rotting off before the first true
leaves have emerged from between the cotyledons ; in
other cases, the "collar" only is rotten, or shrivelled,
and the weight of the parts above ground causes them

T

274 TIMBER AND SOME OF ITS DISEASES, [chap.

to fall prostrate on the surface of the soil ; in yet
others, the lower parts of the stem of the older seed-
ling may be blackened, and dark flecks appear on
the cotyledons and young leaves, which may also
turn brown and shrivel up (Fig. 42).

If the weather is moist — e.g. during a rainy May or
June — the disease may be observed spreading rapidly
from a given centre or centres, in ever-widening circles.
It has also been noticed that if a moving body passes
across a diseased patch into the neighbouring healthy
seedlings, the disease in a few hours is observed
spreading in its track. It has also been found that if
seeds are again sown in the following season in a
seed-bed which had previously contained many of
the above diseased seedlings, the new seedlings will
inevitably be killed by this "damping off." As we
shall see shortly, this is because the resting spores of
the fungus remain dormant in the soil after the death
of the seedlings.

In other words, the disease is infectious, and spreads
centrifugally from one diseased seedling to another,
or from one crop to another : if the weather is moist
and warm — " muggy," as it is often termed — such as
often occurs in the cloudy days of a wet May or June,
the spread of the disease may be so rapid that every
plant in the bed is infected in the course of two or

xui.] "DAMPING OFF" OF SEEDLING-TREES. 275

three days, and the whole sowing reduced to a putrid
mass ; in drier seasons and soils, the spread of the
infection may be slower, and only a patch here and

Fig. 42.— A young beech-seedling attacked by Phytophthora. omnivora : the mori-
bund tissues in the brown and blai 1 n the young stem, cotyledons, and
ure :i prey to the fungus, the mycelium of which is spreading from the
different centres. The horizontal line denotes the surface of the soil.

T 2

276 TIMBER AND SOME OF ITS DISEASES, [chap.

there die off, the diseased parts shrivelling up rather
than rotting.

If a diseased beech seedling is lifted, and thin
sections of the injured spots placed under the micro-
scope, it will be found that numerous slender colourless
fungus-filaments are running between the cells of the
tissues, branching and twisting in all directions. Each
of these fungus-filaments is termed a hypha, and it
consists of a sort of fine cylindrical pipe with very
thin membranous walls, and filled with watery proto-
plasm. These hyphae possess the power of boring
their way in and between the cell-walls of the young
beech seedling, and of absorbing from the latter
certain of the contents of the cells. This is accom-
plished by the hyphae putting forth a number of
minute absorbing organs, like suckers, into the cells
of the seedling, and these take up substances from
the latter : this exhaustion process leads to the death
of the cells, and it is easy to see how the destruction
of the seedling results when thousands of these hyphae
are at work.

At the outer parts of the diseased spots on the
cotyledons or leaves of the seedling, the above-named
hyphae are seen to pass to the epidermis, and make
their way to the exterior : this they do either by pass-
ing out through the openings of the stomata, or by

xiii.] "DAMPING OFF" OF SEEDLING-TREES. 277

simply boring through the cell-walls (Fig. 43). This
process of boring through the cell-walls is due to the
action of a solvent substance excreted by the growing

Fig. 43. — Portion of a cotyledon of the beech, infested u ith PhytojthtUora omnivora :
the piece is shown partly in vertical section. The mycelium, spreading between
the cells, puts f .rth atrial hyphje, which bore between the cells of the epidermis.
/>, and d, or emerge from the stomata, a, and form conidia at their apices : the
various stages of development are shown. On other hyphae. between the cells of
'he interior, the oospores are f rmed in oogonia, e and./! (Highly magnified.)

tip of the hypha : the protoplasm secretes a ferment,
winch passes out, and enables the tip to corrode or
dissolve away the substance of the cell-walls. It is

27S TIMBER AND SOME OF ITS DISEASES [chap.

also characteristic of these hyphae that they make
their way in the substance of the cell-walls, in what
is known as the " middle lamella " : in this, and in
what follows, they present many points of resem-
blance to the potato-disease fungus, which is closely
allied to Phytophthora omnivora.

The hyphae which project from the epidermis into
the damp air proceed to develop certain spores,
known as the coiiidia, which are capable of at once
germinating and spreading the disease. These coni-
dia are essentially nothing but the swollen ends of
branches of these free hyphae : the ends swell up and
large quantities of protoplasm pass into them, and
when they have attained a certain size, the pear-
shaped bodies fall off, or are blown or knocked off.

Now the points to be emphasized here are, not so
much the details of the spore-formation, as the facts
that (I) many thousands of these spores 1 may be formed
in the course of a day or two in warm, damp weather ;
and (2) any spore which is carried by wind, rain, or a
passing object to a healthy seedling may infect it (in
the way to be described) within a few hours, because
the spore is capable of beginning to germinate at once
in a drop of rain or dew. A little reflection will show

1 I here use the popular term for them : they are more properly
called Conidia,

xiii.] "DAMPING OFF" OF SEEDLING-TREES. 279

that this explains how it is that the disease is spread
in patches from centres, and also why the spread is so
rapid in close, damp weather.

When a conidium germinates in a drop of dew for
instance, the normal process is as follows. The proto-
plasm in the interior of the pear-shaped conidium

Fig 44 —Portion of epidermis of a beech-seedling, on which the conidia of the
' Phvtofihthora have fallen and burst, a and d, emitiing the motile zoospores, l>,
which soon come to rest and germinate, c, by putting forth a minute gcrmina
hvnha c e which penetrates between the cells of the epidermis, e and /, and
fo-mstne mycelium in the tissues beneath. At rf a zoospore has germinated,
without escaping from the conidium. (Highly magnified : partly after De Bary
and Hartig.)

becomes divided up into about twenty or thirty little
rounded naked masses, each of which is capable of
very rapid swimming movements ; then the apex of

28o TIMBER AND SOME OF ITS DISEASES, [chap.

the conidium bursts, and lets these minute motile
zoospores, as they are called, escape (Fig. 44, a).

Each zoospore then swims about for from half an
hour to several hours in the film of water on the sur-
face of the epidermis, and at length comes to rest
somewhere. Let us suppose this to be on a cotyledon,
or on the stem or root. In a short time, perhaps
half an hour, the little zoospore begins to grow out
at one point — or even at more than one — and the
protuberance which grows out singly bores its way
directly through the cell-wall of the seedling, and
forms a cylindrical hypha inside (Fig. 44, b, c, e, J ) :
this hypha then branches, and soon proceeds to
destroy the cells and tissues of this seedling. The
whole process of germination, and the entrance of
the fungus into the tissues, up to the time when it
in its turn puts out spore-bearing hyphae again, only
occupies about four days during the moist warm
weather in May, June, and early in July.

We are now in a position to make a few remarks
which will enable practical people to draw helpful
conclusions from what has1 been stated. Let us
suppose a seed-bed several feet long and about three
feet wide, and containing some thousands of young
beech seedlings : then suppose that — by any means
whatever — a single conidium of PliytopJitlwra omnivora

Xin ] "DAMPING OFF" OF SEEDLING-TREES. 281

is carried on to a cotyledon of one of the seedlings.
Let us further assume that this occurs one warm
evening in May or June. During the night, as the
air cools, the cotyledon will be covered with a film or
drops of water, and the conidium will germinate and
allow, say, thirty zoospores to escape. Now, the
average size of a conidium is about 1/400 of an inch
long by about 1/700 of an inch broad, and we may
take the zoospore as about 1/2000 of an inch in
diameter ; thus it is easy to see that the film of
moisture on the cotyledon is to a zoospore like a
pond or a lake to a minnow, and the tiny zoospores,
after flitting about in all directions, come to rest at
so many distant points on the cotyledon — or some of
them may have travelled abroad along the moist stem,
or along a contiguous leaf, &c. Before daylight, each
of these thirty zoospores may have put forth a
filament (Fig. 44, e,f) which bores between the cells
of the cotyledon, and begins to grow and branch in
the tissues, destroying those cell-contents which it does
not directly absorb, and so producing the discoloured
disease-patches referred to. Supposing the weather
to remain damp and warm, some of the hyphae may
begin to emerge again from the diseased and dying
seedling on the fourth day after infection— or at any
rate within the week— and this may go on hour after

282 TIMBER AND SOME OF ITS DISEASES, [chap.

hour and day after day for several weeks, each hypha
producing two or more conidia within a few hours of
its emergence ; hence hundreds of thousands of conidia
may be formed in the course of a few days, and if
we reflect how light the conidia are, and how their
zoospores can flit about to considerable distances, it
is not surprising that many of them are shed on to

Fig. 45. — An. oogonium and antheridium of Phytophtkoraomnruora. The oogonium
is the larger rounded body, borne on a branch of the mycelium : it contains an
oosphere, in process of being fertilized by the protoplasm of the antheridium (the
smaller body applied to the side of the oogonium). The antheridium has pierced
the wall of the oog' nium, by means of a fertilizing tube, through which 1 he contents
pass into the oosphere, converting the latter into an oospore. (Very highly
magnified ; after De Bary.)

the surrounding seedlings, to repeat the story. If we
further bear in mind that not only every puff of wind,
but every drop of rain, every beetle, or fly, or mouse,
&c, which shakes the diseased seedling may either
shake conidia on to the next nearest seedlings or even
carry them further, it is clearly intelligible how the
infection is brought about, and spreads through the

Xili.] "DAMPING OFF" OF SEEDLING-TREES. 283

seed-bed, gathering strength, as it were, hour by
hour.

But, although we have explained the rapid infection
from plant to plant, it still remains to see how it is
that if we sow the seeds in this bed next year, the
seedlings are almost certain to be generally and badly
attacked with the disease at a very early stage.

When the fungus-mycelium in the cotyledons and
other parts of the diseased seedlings has become fully
developed, and has given off thousands of the conidia
above described, many of the branches in the dying
tissues commence to form another kind of spore
altogether, and known as an oospore, or egg-like
spore. This spore differs from the conidium in size,
shape, and position, as well as in its mode of develop-
ment and further behaviour, and if it were not that
several observers have seen its formation on the same
hyphse as those which give rise to the conidia, it might
be doubted by a beginner whether it really belongs to
our fungus at all. As it is absolutely certain, however,
that the oospore on germination gives rise to the
fungus we are considering, the reader may rest
satisfied on that point.

The spore in question is formed in a swelling of the
free end of a branch of the hypha as follows (Fig. 45).
The protoplasm in the rounded end of the hypha

284 TIMBER AND SOME OF ITS DISEASES, [chap.

Decomes collected into a ball (the egg-cell or oosphere)
and then a smaller branch with a distinct origin applies
itself to the outside of this rounded swelling and
pierces its wall by means of a narrow tube : protoplasm
from the smaller branch (antkeridium) is then poured
through the tube into the " egg-cell," which thus
becomes a fertilized " egg-spore " or oospore. This
oospore then acquires a very hard coating, and possesses
the remarkable peculiarity that it may be kept in a
dormant state for months and even a year or more
before it need germinate : for this reason it is often
called a resting spore. It has been found that about
700,000 oospores may be formed in one cotyledon, and
a handful of the infected soil has sufficed to kill 8000
seedlings.

Now, when we know this, and reflect that thousands
of these oospores are formed in the rotting seedlings
and are washed into the soil of the seed-bed by the
rain, it is intelligible why this seed-bed is infected.
If seeds are sown there the next spring, the young
seedlings are attacked as soon as they come up.
These oospores are, in fact, produced in order that the
fungus shall not die out as soon as it has exhausted
the current year's supply of seedlings ; whereas the
conidia, which soon lose their power of germinating^
are the means by which the parasite rapidly extends

Xiii.] "DAMPING OFF" OF SEEDLING-TREES. 285

itself when the conditions are most favourable for its
development and well-being.

It has already been mentioned that other plants
besides the beech are destroyed by the ravages of this
fungus. Not only has it been found to grow on her-
baceous plants, such as Sempervivum, Clarkia, and
many others, but it habitually attacks the seedlings
of many timber trees, such as, for instance, those of
the spruce and silver firs, the Scotch pine, the Austrian
and Weymouth pines, the larch, the maples, and par-
ticularly those of the beech.

It is obvious that this makes the question of com-
bating this disease a difficult one, and the matter is by
no means simplified when we learn that the fungus
can live for a long time in the soil as a saprophyte,
and apart from the seedlings. In view of all the facts,
let us see, however, if anything can be devised of the
nature of precautionary measures. It must at least
be conceded that we gain a good deal by knowing so
much as we do of the habits of this foe.

In the first place, it will occur to everybody never
to use the same seed-bed twice ; but it may be added
that this precaution need not be taken as applying to
anything but seeds and seedlings. Young plants,
after the first or second year, are not attacked by the
fungus — or rather are attacked in vain, if at all —

286 TIMBER AND SOME OF ITS DISEASES, [chap.

and so the old beds may be employed for planting
purposes. In the event of a patch of diseased seed-
lings being found in the seed-bed, as in our illustration
quoted above, the procedure is as follows : cover the
whole patch with soil as quietly and quickly as possible,
for obviously this will be safer than lifting and shaking
the spore-laden plantlets. If, however, the sharp eye
of an intelligent gardener or forester detects one or
two isolated seedlings showing the early stages of the
disease, it is possible to remove the single specimens
and burn them, care being taken that the fingers, &c,
do not rub off spores on to other seedlings.

In the last event, the beds must be looked to every
day to see that the disease is not spreading. All
undue shading must be removed, and light and air
allowed free play during part of the day at least ; by
such precautions, carefully practised in view of the
above facts and their consequences, it is quite feasible
to eradicate the disease in cases where ignorant or
stupid mismanagement would result in the loss of
valuable plants and time. In the case of other seed-
lings also, much may be done by intelligently applying
our knowledge of the disease and its cause. It is not
our purpose at present to deal with the diseases of
garden plants, &c, but it may be remarked in passing
that in the large majority of cases the "damping off"

xiii.] "DAMPING OFF" OF SEEDLING-TREES. 287

of seedlings is due to the triumphant development of
fungi belonging to the same genus as the one we have
been considering, or else to the closely allied genus
Pythium. In illustration of this I will mention one
case only.

It is always possible to obtain well-grown specimens
of the fungus Pythium by sowing cress seed fairly thick
and keeping the soil well ivatered and sheltered. Now
what does this mean ? Nobody imagines that the
fungus arises spontaneously, or is produced in any
miraculous manner ; and in fact we need not speculate
on the matter, for the fact is that by keeping the crowded
cress seedlings moist and warm we favour the develop-
ment of the Pythium (spores of which are always there)
in somewhat greater proportion than we do the
development of the cress. In other words, when the
cress is growing normally and happily under proper
conditions, it is not because the Pythium is absent,
but because (under the particular conditions which
favour the normal development of healthy cress) it
grows and develops spores relatively so slowly that the
young cress seedlings have time to grow up out of its
reach. The recognition of this struggle for existence on
the part of seedlings is of the utmost importance to
all who are concerned with the raising of plants.

INDEX.

A.

Abies [see Fir), 54

Acacia, 23, 56

Acer (see Maple), 25

Adina, 56

.Ecidium, 256 — 26S

AZgle, 58

Agaricus melleus, 155 — 174

Ailanthus, 41

Air and air-bubbles in wood, 2S,

63-139
Air canals, 133
Air-pressure theory of Ilartig,

84, 98, 100, ic8
Allrizzia, 56
Alburnum {see Sapwood), 41,

64, 77—8i, 85, 94. ii9. 132
Alder, 25, 48, 58, 230
Anacardiaceae, 42
Annual rin^s, 2, 4, S, 15, 19,

22, 25, 29, 35, 44. 54- 5°-

13S, 20S, 214, 219, 229, 235,

244, 262
yissits, 58
Anoncu <■,,-, 45
Antheridium, 2Sj
Apple, 230
Aristohchia, 81

Ascent of water in the tree, 59 —

141. 247
Ascomycetes, 252
Ash, 15, 45, 48, 57, 252
Assimilation, 249
Austrian Pine, 25S. 285
Autumn wood, 7, S, 16, 19, 22,

29, 34, 36, 45, 54, 57, *37

B.

Bacteria, 224

Barberry, 46, 26S

Bark, 2, 15, 31, 34, 165, 172,

199—209, 213, 227, 239
Bassia, 56

[see Phloem), 203, 204
h, 15, 16, 18, 36, 44, 4''-

58, 85, 93, 94, 155, 157, 174,

1S7, 210, 230, 252, 271— 2.S5
'a, 100
Birch, 42, 46, 4S, 5S, S5, 93, 95,

206, 252
Bleeding, S6
Boehm's theory "f ascent of

water, 66, 72 — 76, 1 19
BombaX) 27, 49, 56

U

290

INDEX.

Bordered pits, 12, 65, 67, 78,
81, 82, 87, 100, 114, 129, 132

Boswellia, 58

Box, 2i, 48, 49, 5S

Breaking of branches, 164, 212,
222, 239

Brown streaks in wood, 193, 196

Buckthorn, 57

Ccesalpinia, 42

Callus, 208, 214 — 225, 229, 235

Calophyllum, 45

Cambium, 2, 8, 9, 11, 13, 16,

31— 34, 36, 87, 148, 161, 172,

199—209, 212 — 226, 227 —

236, 250, 262 — 264
Canker, 172, 227, 229 — 243, 263
Capillarity, 60—63, 67, 75, 101,

105 — no, 114, 122, 124
CapnodieeB, 254
Capus's experiments, 100
Carbon dioxide, 246 — 249
c'asuarina, 43, 45
Cedrela, 57
Cell-sap, 247
Cellulose, 152, 153, 16S
Chaplet de Jamin, 60 — 62, 75>

101 — 105, 109
Chestnut, 15, ix, 48, 49, 57
Chlorophyll-corpuscles, nS,20i,

247, 249
Chloroxylon, 5S
Cinchona, 206, 209, 272
Cinnamon, 206
" Clambering theory," 106
Clarkia, 285
Classification of woods, 21, 39,

52, 54—58
Climbers, 4S
Coleosporium Senccionis, 255 —

270
Colour of wood, 51
Conductivity of wood, 70, 80 —

83, 97, 138
Conidiuin, 277— 2S3

Coniferous wood, 7, 10, 12, 15,

23, 54, 129, 132
Conifeis, 40—47, 54, 65, 67, 71,

7S, 86— S8, 129, 145, 147, 157,

I70, 2IO, 223

Cork, 200 — 207, 213 — 218, 234

Cork-cambium, 201 — 205

Cortex, 2, 12, 15, 16, 34, 133,
147, 161, 174, 199—209,
212 — 222, 227 — 240, 258 —
266

Cotyledon, 273 — 284

Cress, 287

Cucurbitacere, 40

Cuttings, 20S, 214

Cycads, 40

D.

Dahlia, 100

Dalbergia, 56

Dammara, 211

" Damping off," 27 1 — 287

Darwin, F., on transpiration,

134
Deal, 5, 51, 176, 17S, 190, 192
Decay of timber, 223 — 225
Density of wood, 29
Deodar, 53, 54
Development of wood, 9, 30
Dicotyledonous wood, 15, iS,

23>'65
Dicotvledons, 40, 43, 47, 54, 83,

87,'SS
Dillenia, 58
Diospyros, 56
DipLrocarpus, 56
" Diseases of bark," 227
Drii/iys, 47, 54
Drooping, 70
Dry-roi, 176— 19S
Dry-rot Fungus, 184
Dry weight of wood, 92
Dufour's observations on ascent

of water, 96
Durability of wood, 20, 28
Duramen, 41, 64, 79, 84

INDEX.

291

E.

Ebony, 42, 43, 45
Elasticity of wood, 20, 37
Elder, 41, 57

Elfving's experiments on ascent
of water, 76—80, 107, 116,

137
Elm, 26, 49, 57, 206
Errera's experiments on ascent

of water, 137
Erysiphese, 252
Erythrina, 50
Eugenia, 58

European woods, 22, 44, 57
Exfiltration of water, 103 — 105,

125—130

F.

False rings, 23, 45, 47, 54~ 56
Ferment, 152, 168—173, i^S,

277
Fermentation, 224
Fibres, 17, 37, 54, 65, 17S
Ficus, 55

Fig (see Ficus), 23, 26, 45, 55
Fir (see Abies), 5, 12, 17, 18,

24, 42, 133, 147, 170, 176,

198, 254
Frost, 32, 36, 164, 230, 239—

242
Fuchsia, 136

G.

Gamboge, 206
Garcinia, 206
Gases in leaves, 246
Gas-pressure theory of ascent of

water, IOO, 106, 108, 138
General characters of wood, 1 —

'9 .
Gmelina, 57

Godlewski's theory of ascent of

water, 1 17 — 133, 139— 141

Grain of wood, 3, 51
Guaiacum, 42
Gutta-percha, 206
Gymnosporaiigium, 268

H.

Hardness of wood, 20, 2S, 49
HardwicJda, 27, 50, 56
Hartig's theory and observations

on ascent of water, 84, 1 1 7,

121, 131, 138
Hawthorn, 42, 26S
Hazel, 49, 165, 230
Healing of wounds, 207 — 209,

210 — 226, 229
Heart-wood (see Duramen) 41,

54—58, 75, 85, 94, 1S6
Helianthus, 104
Heritiera, 5 J. 56
Hetercecism, 268
Holarrhena, 58
Holly, 22, 43, 49
Hornbeam, 44, 46, 4S, 5S, 230
Horse-chestnut, 43, 46, 48, 58
Hymenomycetous fungi, 169
Hypha, 149, 153, 178, 1S7, 254,

276—283

Imbibition, 62, 6S, 94, 9S, 107,

112
Imbibition theory of ascent of

water, 62, 66, 77, 96, III,

"7, 13S

Impermeability of wood for air,

Sr, S4, 108, 113
Indian woods, 23, 45, 55 —

57
Infection, 149, 1S3, 189, 195,

234, 238, 242, 252, 269, 273

—275, 278—284
Intercellular passages, 246
Iron wood, 45, 55
Isonaudra, 206

29-

INDEX.

J-

Jamin's chaplet, 60 — 62, 75,

102
Jan-e's experiments on ascent of

water, 135
Juglans, 41
Juniper, 54, 263

K.

Kalmia, 46, 4S

Kohl's experiments on ascent of
water, 133

Laburnum, 43, 4S

Lagerstra'inza, 56, 57

Larch, 32, 33, 35, 54, S5, 165,

231—243, 2S5
Larch-disease, 33, 173, 227,

229—243
Leaf-disease, 244 — 255
Leaves, 86, III, 114. 11S, 244 —

255. 259—261,265, 269, 275
Le^uminosere, 23
Lilac, 57
Lime, 230
Logwood, 42

M.

Mesua, 50, 56

JMichclia, 5S

Middle lamella, 153, 170, 27S

Mildew, 252

Monocotyledons, 65, S2

Mould fungi, 224

Mycelium, 147 — 150, 157, 167,
177, 1S2, 190, 194, 228, 233,
253. 257—266, 277, 2S2

N.

Negative pressure, 71, 72, 82,
"5

O.

Oak, 15, 24, 25, 41, 43—45,
4S— 50, 55, 57, 85, 93, 95,
157. 165, 167, 170—17^
174, 1S7, 206, 210, 211, 230,

244,_252

Occlusion of wounds, 210 — 225

Olive, 22

Oogonia, 277, 2S2

Oosphei-e, 2S2, 2S4

Oospores, 277, 2S2

Orange, 22

Osmosi-, 72, S5, 90, 103 — 10S,

117— 131
Oxidation of wood, 224
Oxygen respiration, 30, 33, 76,

126, 12S, 246

Magnoliacere, 24

Malvaceae, 206

Mango, 45, 56

Maple, 26, 46, 48, 5S, 230, 254,
2S5

Medullary rays, 2, 5, 10, 14, iS,
33, 43, 54—57, 65, 82-84,
103—106, 114, 124—153, 136

Medullary sheath, 47

Medullary spots, 42

Melia, 56, 57

Mcrulius lac ry mans, 177 — 19S

Palms, 40
Papayacece, 119

Parasitic fungi, 142 — 175, 202,
213, 220, 227—243. 251—255,
259—270, 272-2S7

Tear, 165

Peridermium Pini, 255 — 270

Periodicity of osmotic pheno-
mena, <S:c. , 127 — 130, 139 —
ui

INDEX.

go"

rcrmeability of wood for water,

71—73. 77— Sl' 87
Peronospirex, 272
Pcziza Willkommii, 232—242
Phytophthora infestans, 272
Phytophthora omnivora, 271 —

282
Piue, 5, 17. lS> 24 35. 37. 42,

43. 54- 85, 93. 95. J-33, »47.

160—162, 169, 187, I9\

210, 223, 254, 259, 261, 264,

266
Pine-blister, 256—270
Pinus sylvrstris (see Scotch

Pine), 186
Pith, 2, 16, 41, 104
Pith-flecks, 42
Phloem, 203, 204, 2o3
Plane, 48, 5$, 206
Plum, 57, 157
Polyporei, 145. I7I
Polypoms, 147, 169. l~9
Polyporus annosus, 145
Polypoms borealis, 1 70
Polyporus dryadetis, 1 70
Polyporus futous, 170
Polyporus igniarius, 170, 197
Polyporus mollis, 198
Polyporus sulphurtus, 155, 165

— !"I c

Polyporus vaporanus, 193 — 19b
Pongamia, 23, 45, 55
Poplar, 15, 25, 58, 165, 211
Populus. 58

" Tores" of wood, 47— 49
Porous wood, 46, 47, 50
Pol ■ i-disease, 272, 278
Pressures on cortex, &c, 34, 214,

230
Properties of wood, 20
Prosjpis, 55
Proto-xylem, 47, S6

Pyru . \-

ium, 2S7

O.
Quae us (sec Oak), 41, 55, 57

R.

Kate of movement of water, 66
Red streaks in wood, 193, 1*96
Reserve materials, 33
Resin-canals. 42, 44, API, 54, 67..

162, 1S7, 262
Respiration. 30, 33, 76, 126,

127, 139, 140, 246
Resting-spores, 274, 2S4
Rhamnus, 25, 49
Rhizomorpha, 157, 160, 163
Rhododendron, 43, 268
Rhytisma, 254
Robinia, 43
Rixstelia, 2 68
Root-hairs, 85, 1 17, 125
Root-pressure, 90, lcj, 115, 122

—131. Hi

Rot in ti nber, 143, 157, 169,

220, 225
Rust of wheat, 265, 26S
Rust fungi, 255

S.

Sachs's imbibition theory of as-
cent of water, 64 — 6S, 117, 138

Salix [see Willow), 42

Sambucus, 41

Sandal-wood, 51

San/alum, 57

Sapotacere. 45

Saprophytic fungi, 173, 221,
253- 285

Sap-wood (see Alburnum), 41 . 5 1 ,
64, 85, 91, 93. lS6

Satin-wood, 51

Scheit's observations on ascent
of water, 113, 133

Schleichera, 5S

Schima, 56

Scotch Pine, 206, 211, 256, 25;.
2^S, 285

Seasoned timber, 27, 1S7, 190
192

Secondary wood, S6

294

INDEX.

Seedlings, 271, 287

Sempervivum, 285

SeneciOf 264, 266, 269

Shedding of branches, 211

Shorea, 4.6, 58

Silver Fir (see Abies), 54, 285

Specific weight of wood, 2S, 6S,

91, 94, 154, 177
Spermogonium, 256 — 261
Sphcrria, 253
Sphceriacese, 252
Spores, 145, 147, 155, 171, 1S0,

184, 189, 195, 220, 236, 241,

253, 259, 265, 278, 283
Spring wood, 7, 8, 16, 19, 22,

25> 29, 34, 36, 45—48, 57,

138
Spruce, 7, 10, 54, S5, S9, 146,

148, 151, 153, 157, 187, 268,

285
"Step theory of ascent of

water, 106
Stomata, 113, 119, 245, 251,

265, 277
Structure of wood, 1, 21, 64,

129, 132, 139
Swamp-Cypress, 211
Synoum, 51
Syringa, 136

T.

Tamarindus, 24

Tamarix, 56

Taxodinm distichiim, 211

Teak, 45, 50, 51, 53, 57

Teleutospores, 265, 267, 26S

Temperature, action on cam-
bium, 29, 31

Tcrminalia, 55, 56

Theodore Hartig's experiment,
71, 74, 77, IC9, 115, 122

Theories of ascent of water, 59 —
141

Toon, 45, 51

Tracheides, 6, 8, 9, 14, 16, iS,
37, 65, 67, 73, 78, 80-83,

S5 — 90, 100, 109, 114, 129 —

132, 139, 153
Tradescantia, 100
Trametes, 153, 161, 179
Tra,77ietes pini, 169
Tratnetes radiciperda, 142 — 154,

159, 163, 169, 174
Transpiration, 67, 70, 74, S2,

89, 98, 122, 135, 137, 247
Tree-ferns, 40
Turgescence, 104, 107, 118, 126,

130
Tyloses, 75

U.

Ulex, 49
Ulmus, 26
Uredinece, 252, 254
Uredospores, 265, 267, 270
Uses of timber, 20

V.

Vapour in leaves, 246
Venation, 86, 245, 247, 249
Vesque's experiments on ascent

of water, 100
Vessels, 16, 18, 24, 45 — 49, 54 —

58, 65, 71, 74, S9, 105, 114,

126, 134, 166, 16S

W.

Walnut, 41, 48, 5S
Warping, 177 »

Water in wood, 28, 65—68,

84 — 97, 105, no, 130
Water of imbibition, 62, 121,

140
Weeping, 86

INDEX.

295

Weight of wood, 20, 27, 50
Wellingtonia, 54
Westermaier's theory of ascent

of water, 103—107, 133
Wet-rot, 143 . _

Weymouth Pine, 25S, 2i>0
Willow, 25, 43. 48. 58» 73. l65>

254
Wood-parenchyma, 17, 25, 4;><

54, 65, 103, 114. 133
Wood-substance, 14, I52. 245
Wound- parasites, 164, i74> I9S>»

222, 225
Wounds, 164, J 74. 210—226,

228, 241, 262

Xylia, 56

Yew, 54, 67, 77, 78. I09, I23

Zimmermann
water, 10 1
Zizyphus, 56
Zoospores, 279— 2S

on ascent of

THE END.

HARD CLAY AND SONS, LIMITED, LONDON AND BUNGA1

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46 m

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OCT t$

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