Text-book of the diseases of trees

Universityof Oxford

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William Somerville kbedsc

S IBTHORPIAN PrOFE S SOR

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TEXT-BOOK

DISEASES OF TREES

TEXT-BOOK

OF THE

DISEASES OF TREES

BY

PROFESSOR R. HARTIG

OF THE UNIVERSITY OF MUNICH

TRANSLATED BY

WILLIAM SOMERVILLE, D.CEc, B.Sc, F.R.S.E., F.L.S.

PROFESSOR OF AGRICULTURE AND FORESTRY
DURHAM COLLEGE OF SCIENCE, NEWCASTLE-ON-TYNE

REVISED AND EDITED, WITH A PREFACE, BY

H. MARSHALL WARD, D.Sc, RR.S., RL.S., RR.H.S.

LATE FELLOW OF CHRIST'S COLLEGE, CAMBRIDGE
PROFESSOR OF BOTANY AT THE ROYAL INDIAN ENGINEERING COLLEGE, COOPER's HILL

JHwSllTY OF OXFOkB,

ilontion
M A C M I L L A N AND CO.

AND NEW YORK
1894

The Right of Translation and Reprodtcciion is Reserved

Richard Clay and Sons, Limited,
london and bungay.

PREFACE TO THE ENCzLISH EDITION

[By H. MARSHALL WARD, D.Sc, F.R.S., F.L.S., F.R.H.S.]

The foundation of a science of Mycology by Berkeley, de
Bary, and Tulasne, pursued by Brefeld, Zopf, and others, has
led to a knowledge of the biology of fungi highly creditable
to the industrious observers who have explored this domain of
the vegetable kingdom ; while the gradual building up of the
science of plant-physiology from the days of Knight and Hales,
De Saussure and Boussingault, to those of Sachs and Pfeffer,
has placed us in possession of a vast amount of information
as regards normal life processes in plants. Until much more
recently, however, it cannot be said that we have had a science
of the pathology of plants — i.e. the study of abnormal physio-
logy— of anything like the same importance, in spite of the
splendid and progressive attempts of Berkeley, Frank, and
Sorauer to found one.

In the particular department he has cultivated, Robert Hartig
has succeeded in founding a plant-pathology really worthy
of the name, and I would especially emphasize this, that his
researches are so thoroughly elucidative of pathological pheno-
mena, in that he studies not only the nature of the structural
lesions and of the physiological disturbances consequent on
these, but also the factors of the environment which throw light
on the question. No better illustration of this could be selected

vi PREFACE TO THE ENGLISH EDITION

than his admirable discussion of the complex phenomenon of
"Leaf-casting" on pp. 1 10-117 of the present work ; while his
work on the ZersetzmigserscJieimingen des Holzes is a model of
thoroughness and scientific accuracy and acumen to which all
workers in this branch of botany must look up.

In this country we are awakening rapidly to the necessity
of placing ourselves abreast of the new ideas involved in this
compound study of plant-pathology ; but we are perhaps as yet
by no means so alive to the practical importance of the new
discipline as it might have been inferred (from our national
pride in being practical) we should be.

Animal-pathology is studied with zealous and expensive
enthusiasm — I suppose because, being animals, we are at once
alive to its importance ; but plant-pathology, in the real sense
of the term, scarcely obtains recognition as yet, no doubt owing
to our interest in the culture of trees and agricultural produce
having seemed to be less pressing than coming events are likely
to prove it really to be. From this condition — only apparently
apathy — we are doubtless awakening, and, as is usual, when we
English do awake to new necessities, we at once enthusiasticall}-
set to work to recover lost ground.

Now, in this department, we have to awaken to some startling
new facts, the practical bearings of which have deeply impressed
our Continental cousins for some years past.

One of these new facts is that we may know a very great
deal about the systematic position and the morphology of
parasitic and destructive fungi without knowing much — or,
indeed, necessarily anytJiing — about the diseases and injuries
the}^ induce ; another of these new facts is that pathology —
i.e. the study of disease — cannot be fruitful unless the student
is experimentally acquainted with plant-physiology, and espe-
cially (though by no means only) the physiology of nutrition.

To these statements I would add that we have, as a nation,
to force ourselves even more than we have yet done out of
the groove in which plant-physiology is looked upon as a mere
branch of chemistry and physics. It is no undervaluing of

PREFACE TO THE ENGLISH EDITION vii

the true status of agricultural chemistr}-, or of the study of
the physics and chemistry of soils, &c., to insist upon it that
no one can appreciate even the rudiments of plant-physiology
Avho does not make himself master of the facts of structure
and the essential phenomena of life by experimental investiga-
tion ; nor to point out that, as we come to know more about
the physiology and pathology of plants, we learn that the
chemistr}' of the soil is one of the least important factors we
are concerned with.

These truths have to be faced, and in spite of the at first
sight depressing inference that the study of plant-pathology
— and I suppose the same applies to animal-pathology — de-
mands rigorous and active acquaintance with several other
branches of science. As I have stated in substance elsewhere,
we demand that the surgeon or doctor who attends us shall be
qualified properly to do his work, though we are perhaps not
always alive to the extravagance of our demands on his ability
and training ; and just as we cannot expect him to do his work
in diagnosing the disease or injury, and explaining and com-
bating or removing its cause, unless he is properly qualified,
by the requisite instruction in the physics, chemistry, structure,
and normal working {i.e. physiology) of the healthy body and
in the pathology of the case concerned, so can we as little
expect any one to deal with diseased conditions in plants who
is ignorant of *their structure and physiology, and the patho-
logical conditions of the case concerned. There is, however,
the comforting assurance that the processes in plants, complex
as they are — and we must not err in underrating this — are
simpler than in animals, and must throw useful lights on all
general problems in Biology.

The objection that there are epidemic diseases of plants
which we have as yet failed to prevent or overcome is obviously
no more valid than the cry that we cannot as yet stay the
progress of epidemics of influenza or cholera : the cases are
exactly parallel, and since we do not abandon or depreciate
the study of medicine because medical science is not yet in a

viii PREFACE TO THE ENGLISH EDITION

position always to cope as successfully as we could wish with
human ailments, so we must not undervalue the importance
of the triumphs of the much younger baby science — plant-
pathology.

Probably few people in this country are really aware of the
enormous strides towards lusty and vigorous youth the new
science is now making, and what important contributions to
human progress its study is affording.

Educated and properly trained agriculturists and foresters
have long been familiar with the fact that great advances are
being made in these directions, and perhaps the only fault
that a very severe critic could find with them is that they have
remained a little too long deterred by the failures which have
always to be acknowledged (and met) in a progressive experi-
mental science. That much more general interest in this pro-
gress is now evident, however, is best proved by the various
publications on the treatment of plant-diseases which are
springing up around us ; for even the very sceptical will admit
that, on the one hand, the treatment of diseases depends on
knowledge of them and their origin, and, on the other hand,
that such eminently practical works would not be published
unless they were read.

Foremost among such publications are the reports of the
various experimental stations on the continents of Europe and
America, and it is a matter of the highest credit and con-
gratulation that the Americans are devoting large sums of
money to the experimental study of methods of treatment,
based on knowledge of the diseases treated, at several of their
enthusiastically planned experimental stations. I need only
point to the reports published by the United States Department
of Agriculture (Section of Vegetable Pathology), and to the
ZeitscJirift fur Pflanzen-Krankheiteu emanating under the
auspices of the " Internationalen Phytopathologischen Kommis-
sion," as showing how necessary it is becoming to have special
organs in this branch of science, and to the increasing number
of text-books on the subject of plant-diseases and their treat-

3

PREFACE TO THE ENGLISH EDITION ix

mcnt now being published, as evidence for the justice of the
above statement.

Among these latter, Kirchner's Die Krankheitcn und BescJidd-
igiingen jmserer LandivirtJiscJiaftlicJien Pflanzcn stands high
in the list as a treatise on the diagnosis and treatment of
agricultural and horticultural plant-diseases. Far more of a
classic, however, but dealing more especially with the diseases
of forest trees, is Robert Hartig's beautiful text-book now intro-
duced to the English public. Another encyclopaedic work, Hess's
FortscJmtz, deals more particularly with the " dodges," if I
may use the word, practical foresters are devising to combat
the principal maladies to which forest trees are subject, and
of this work English readers are also promised a translation
at an early date. These more special treatises may be men-
tioned as supplementing — and in part supplanting — the more
academical and general works of Frank and Sorauer previously
referred to.

The great charm of Hartig's book lies as much in the ex-
cellent plan and simple method of exposition of the facts and
principles concerned, as in the astounding richness of infor-
mation it conveys. This is unquestionably owing to Hartig's
prominence as the leading investigator and authority in Ger-
many in this special branch of knowledge — the fungoid diseases
of forest trees.

His pre-eminence as a sturdy and patient inquirer, as an
admirable anatomist and physiologist, and as a bold and
original thinker, is well known to the few who are acquainted
with his special scientific publications, particularly his laborious
memoir on the destruction of timber by fungi. In the present
work I think he shows himself also a master of the art of
teaching the principles as well as the facts of his subject.

Of course there are points of view to be considered in
criticising such a book.

The specialist on the Morphology of the Fungi will probably
complain of the author's classification of these organisms, and
of his somewhat lax use of certain morphological terms ; but

X PREFACE TO THE ENGLISH EDITION

it should be remembered that, in the first place, the student's
attention is not here directed to the fungus itself, as an object
of morphological study, so much as to the action of certain
fungi in inducing specific diseases in trees ; and, in the second
place, it is assumed that the student is already acquainted with
the main facts in the biology of the fungi — including their
morphology — before he attempts this particular branch of
science.

Again, the professed botanist may remark how much is
assumed concerning the structure and physiology of the host-
plants — the trees — whose diseases are here treated of. The reply
is, as before, the student cannot extract all, or nearly all, of
value from such a work as this, unless he is thoroughly
acquainted with the principal facts of the normal anatomy
and physiology of the higher plants.

A third platform of criticism is that of the " practical
forester," who may object that the author gives too little
information as to jhe details of combative or therapeutic
treatment of the special diseases. To this the obvious reply
is that it is not necessarily the duty of the scientific pathologist
to devise the particular mode of attack to be employed in
special cases — these plans of remedial treatment involve the
outlay of money, labour, &c., which vary in different countries
and in different cases, and enough has been done by the in-
vestigator who indicates the factors involved. Special works
must be consulted regarding the details of treatment, though it
seems to me the author, while clearly recognising this, goes even
out of his way to give practical hints as to treatment, and has
in many cases put the principal factors concerned in the treat-
ment so clearly that every thinking practical man can do the
rest himself. No better illustration of the thoroughly practical
nature of his writings could be selected than his recommenda-
tions for the treatment of Dry-rot.

But it is by no means solely on the ground of the information
capable of direct application which the book contains that it
should be judged. I would especially urge the value of this

PREFACE TO THE ENGLISH EDITION xi

study to the student of botany as calculated both to test his
knowledge in other departments of his science and to open
out new lines of thought as he considers the interactions
between one plant and another, and between both and other
factors — living or not — of the environment.

Hartig's ingenious explanation of the spread of the well-
known Larch -disease may or may not be accepted in all its
details, on the evidence given, and dissent from his explanations
of such diseases as " Canker," &c., has been expressed, but I
would maintain — apart from my acceptance of the general truth
of his arguments — that they teach the student very clearly how
to investigate and think out these complicated matters for
himself.

We are still decidedl}' wanting in information concerning
many diseases of trees. Standing elms and other trees are
occasionally found in this country with a species of Hymeno-
mycete growing from the trunks six feet or more above the
ground : are these parasitic or not, and what is their mode of
action .'' How does Polyponis squainosus attack timber .-• What
are the exact biological relations of Polyponis fomentarius,
Fistidina Jiepatica, and a number of other forms found in this
country, to the trees on which they grow .''

These and numerous other questions await solution, by means
of thorough investigations properly conducted in this country,
along such lines as Hartig has laid down in Germany, and it
should be borne in mind that such studies offer stores of facts
likely to be of the utmost interest to investigators in other
branches of Botany. To give one instance only : the study
of the destruction of the walls of the tracheids, and other
elements of which timber is composed, by the h}'phae of fungi,
shows that there is considerable variety in the processes of
piercing, delignifying, corroding, and dissolving them, and it
seems a safe conjecture that valuable information as to the
intimate structure of these walls may be derived from the
examination of the way the fungus unbuilds them, so to
speak.

xii PREFACE TO THE ENGLISH EDITION

Among the Ascomycetes and the Uredineae are numerous
questions already framed for investigation, and I know of no
department of botanical study more fascinating than the scien-
tific hunting for the hetercecious forms of ^cidiomycetes : the
work combines all the excitement of a true hunt with the
intense intellectual pleasure implied in the demand for the
severest critical observation, and skilful and delicate manipula-
tion of the microscopic cultures.

Again, the whole question of wound-rot, opened up on
pp. 236-237, is one which demands long and thorough inves-
tigation ; not only to clear up the many chemical problems
involved, but also to explain the exact behaviour of sapro-
phytic fungi and bacteria, and the part they play in the
phenomena.

My duties as Editor of this work have not seemed to be
such as to demand that I should express my own opinions on
the subjects raised, and I have almost confined myself to merely
noting the occurrence of the principal diseases in this country
(since the original is written for German readers), and to adding
a few explanatory sentences wherever it has seemed useful in the
interests of the lay reader to do so. In some respects Hartig's
book is a popular one — by which I mean it appeals to a wide
circle of readers not professionally engaged in the study of
this branch of science — and it has seemed advisable, therefore,
occasionally to interpolate a short note in explanation of some
of the more technical terms employed. Short notes are apt
to be insufficient in such cases ; but it would so obviously have
been out of place to overload the author's work with long
disquisitions on the matters referred to, that I have been
constrained to risk their being occasionally too brief

Here and there I have ventured, however, to go a step
further, and add a reference which may be useful, and this in
face of my full recognition of the fact that Hartig's book is
an exposition of his own view of his own work rather than
that of others.

In all cases I have been careful to place my remarks, more-

PREFACE TO THE ENGLISH EDITION xiii

over, in footnotes between square brackets, so that the run of
the author's text is uninterrupted. In one case at least I have
expressed dissent from Hartig's views, but here again the
reader has the option of neglecting the footnote, and at any
rate the matter is one of evidence.

H. MARSHALL WARD.

Cooper's Hill, Ifanh 1894.

TABLE OF CONTENTS

INTRODUCTION.

PAGE
I

Development of the Study of Vegetable Pathology . .

The Causes of Disease— Sickliness, Natural and Accidental
Death, Debility of Old Age, Normal and- Abnormal Predis-
position to Disease, Heredity and Disease, the Investigation
of Disease i6

SECTION I. INJURIES INDUCED BY PLANTS.

Phanerogams — Lonicera, Triticum, Melampyrum, Rhinanthus,
Pedicularis, Euphrasia, Lathraea, Orobanche, Monotropa,
Viscum, Loranthus, Arceuthobium, Cuscuta 22

Cryptogams — Pseudo-parasites — Thelephora, Lichens ; Schizomy-
cetes — Bacterium, Bacillus ; Myxomycetes — Plasmodiophora,
Schinzia 35

Fungi — Their Structure and Biology, Mycelium, Hypha, Germ-
tube, Sclerotia, Sporophore, Spore-production, Sexual and
A-sexual Generations, Vital Conditions, Nutritive Adaptation,
Parasites, Saprophytes, Mode of Infection and Distribution,
Epiphytes, Endophytes, Action on the Tissues of the Host-
plant, Prophylactic and Therapeutic Measures, Cfassification . 40

Peronosporeae — Phytophthora, Peronospora, Pythium, Cystopus . 57

Ustilagineae— Tilletia, Ustilago, Urocystis 66

Ascomycetes— Erysiphete — Erysiphe, Oidium ; Tuberaceee — Ela-
phomyces. Tuber, Mycorhiza ; Pyrenomycetes — Trichosphteria,
Herpotrichia, Rosellinia, Dematophora, Cucurbitaria, Sphas-
rella, Stigmatea, Gnonionia, Nectria, Polystigma, Claviceps,
Aglaospora, Plowrightia, Physalospora, Coniothyrium, Gloe-
sporium, Didymosphaeria ; Discomycetes — Rhytisma, Hys-
terium, Peziza, Rhizina, Sclerotinia, Botrytis ; Gymnoascece —
Exoascus 69-

Imperfectly known Ascomycetes— Cercospora, Pestalozzia,
Phoma, Gloesporium, Septogloeum, Septoria, A new Parasite
of Seedlings, Valsa 135

Basidiomycetes — Uredineee — Puccinia, Phragmidium, Gymno-
sporangium, Melampsora, Coleosporium, Cronartium, Peri-
dermium, Chrysomyxa, Isolated /Ecidium-forms 153

Hymenomycetes— Exobasidium, Trametes, Polyporus, Hydnum,
Thelephora, Stereum, Agaricus, Fungi destructive to structural
timber, Dry-rot, Merulius 184.

xvi TABLE OF CONTENTS

SECTION II. WOUNDS.

Healing and Production of New Tissues— Epidermis, Periderm,
Phellogen, Bark, Cortex, Phelloderm, " Wound Cork," Tyloses
Intermediary Tissue, Occlusion of Wounds, "Wound Wood,'
Cinchona Culture, Effects of Pressure, Resin, Wound-rot
Treatment of Wounds, Prev^entitious and Adventitious Buds
Spheroblasts, Dwarf Shoots, Dormant Eyes, Root Suckers . . 225

The various kinds of Wounds — Barking by Game, Mice
Cattle, &c.. Wounds due to Crushing and Collection of Resin
Ring Wounds, Pruning, Shortening Branches, Removing
double Leaders, Coppicing, Injuries to Roots, Propagation by
Cuttings and Grafts, Defoliation by Insects 241

SECTION III. DISEASES DUE TO CONDITIONS OF SOIL.

Soil in relation to Water and Plant Food— Stag-headed or top-
dry condition. Premature Ripening of Cereals, Rupturing of
the Cortex of Trees 270

Circulation of Air in Soil— Root-rot 275

Plant Poisons — Sea-water, Contaminated Water, Carbonic Acid

Gas, Coal Gas 279

SECTION IV. INJURIES DUE TO ATMOSPHERIC IN-
FLUENCES AND FIRE.

Frost, Bark-scorching, Sun-cracks, Deficiency of Light, Hail,

Snow, Wind, Fire, Smoke, Lightning 282

Classified List of Diseases 305

INDEX 317

DISEASES OF TREES

INTRODUCTION

DEVELOPMENT OF THE STUDY OF VEGETABLE PATHOLOGY

During the present century, and especially during the last
few decades, the forests of Germany have been threatened with
dangers of a magnitude formerly unknown. These have been
occasioned by the gradual relinquishment of natural regener-
ation, and by the substitution of pure even-aged woods for
woods consisting of trees of different species and of various
ages, but most of all by the displacement of broad-leaved trees
by pure coniferous woods. It is especially noticeable that
enemies from the animal and vegetable kingdoms find favourable
conditions for rapid development in our modern forests, so
that the complaints of increasing devastation of woods appear
to be by no means unfounded. The foresters of the last cen-
tury had already made themselves familiar with a large number
of the enemies and diseases of trees, as is proved by the
appearance in 1795^ of a work which probably contains the
first compilation of the observations on plant-diseases scattered
throughout the older literature. We may assume from this that a
large number of diseases which have only been properly explained
during the last few years, e.g. the damping off of seedling
beeches, the resinous degeneration of pine-tops, the red-rot of
the spruce, &c., were known to foresters more than a hundred
years ago, though of course the explanation of the causes was

1 Schreger, Erfahrimgs7ndssige Awweisung zur richtige7i Ke7intniss der
Kra7ikhette7t der Wald- iind Garte7ibdit77ie. &c. Leipzig, 1795. 518 pages.

^0

2 DISEASES OF TREES

bound to be defective in accordance with the position of
botanical science at that time.

Some fifty years ago a number of able investigators, of whom
only Saxesen, Th. Hartig, and Ratzeburg need be named here,
applied themselves to the study of insects. The life-history of
forest insects, their harmfulness or usefulness, soon became the
favourite study of many practical foresters, and in a few decades
the joint efforts of numerous workers were rewarded by the
elevation of Forest Entomology to the position of a much-
appreciated subject of scientific instruction, which has become
the common property of all educated foresters.

The case was otherwise with those plant-diseases which
cannot be ascribed to the injuries of animals. Their investi-
gation was delayed until quite recently ; for it was only after
botanical science, by the aid of its chief instrument, the
microscope, had obtained a clear insight into the normal struc-
ture and vital phenomena of plants, and especially after the
study of fungi had been prosecuted in the last few decades by a
series of distinguished investigators, that the examination of the
phenomena of disease in the life of plants could be undertaken
with a prospect of success.

During the period from 1833 to 1841 three text-books of
plant-diseases did indeed appear — namely, those of Fr. Unger,^
Wiegmann,- and Meyen "^ — which bear witness that in attempt-
ing to explain the phenomena of disease in plants the progress
already made in the knowledge of the structure and life of
plants was not left out of account ; but the erroneous views as to
the nature of fungi, and the absolute ignorance of the history
of their development which prevailed, impeded progress towards
a clear understanding of the processes of disease. Independent
investigation was especially interfered with by the mistaken
attempt to apply to the study of the diseases of plants the
scientific results which J. von Liebig in particular had obtained
in the department of agricultural chemistry. After it had

^ Fr. Unger, Die Exantheine der Pflanze7i und eiiiige jnit diesen verwa7tdte
Krankheiten der Gewdchse. Vienna, 1833.

2 Wiegmann, Die Krankheiten und krankhaften Missbildungen der
Gewdchse. Brunswick, 1839.

3 Meyen, PJianzenpathologie. Lehre von dem krankhaften Leben und
Bilden der PJlanzen. Berlin, 1841.

INTRODUCTION 3

been recognized how great is the importance for the welfare of
plants of the quantity and condition of the mineral matter in
the soil, and how an irrational treatment of the soil, such as
scourging tJie ground, in sylviculture, agriculture, and horticulture
can and must lead to exhaustion of one or other of the nutritive
ingredients, which betrays itself in the stunted growth of the
crop, it was supposed to be permissible, though unsupported by
any exact investigations, to proceed a step further, and to regard
acute diseases of crops, so long as they could not be ascribed
to external causes, as the results of the want of one or other of
the nutritive substances of the soil. The fact that unhealthy
symptoms make their appearance quite as often on very fertile
soils as on poor ones led to the assumption that a superfluity
of nourishment may also be the means of causing diseases in
plants.

The works of De Bary^ and Tulasne- first opened the way
for the investigation of plant-diseases ; and with the appearance
of these a new period began, for from that time onwards very
great attention has been devoted to the life-history and action
of parasitic fungi. The view hitherto held that all fungoid
growths appear only as the result of previously existing pro-
cesses of disease, or as indications of the incipient death of the
part of the plant which is attacked, was shown to be erroneous.

Investigation was now directed chiefly to the diseases of
farm and garden crops. Amongst others Jul. Kiihn^ especially
enriched science by a series of most valuable investigations.
Further research gained a surer basis with the appearance of
de Bary's* Morphology and Physiology of the Fungi.

So far the attention of investigators had been almost entirely
directed to agricultural crops, a circumstance which is sufficiently
explained by the fact that but few scientific botanists had the
opportunity presented to them of carrying their researches into

^ De Bar}', Untersiechungen iiber die Brandpilse tend die durch sie veran-
lassten Krankheiten der Pflansen viit Riicksic/it auf das Getreide und andere
NdhrpflcDizen. Berlin, 1853.

- Tulasne, Selectafnngorum carpologia. Paris, 186 1.

^ Julius Kuhn, Die Kranlcheiten der Ciiltia-gewdchse., Hire Ursac/ie?i tend
VerJiiitung. Berlin, 1858.

■* De Bary, Morphologic und Physiologie der Pi/se, (S:c. Leipzig, 1866,
and Vergleichende MorpJiologie und Biologic der Pilze. Leipzig, 1 884.

1! 2

4 DISEASES OF TREES

the forest and of giving their attention to the diseases of trees.
The credit of having first stimulated interest in this direction
undoubtedly belongs to M. Willkomm.i Hallier's attempt to
collate the scattered materials in the form of a text-book^ was
subsequently repeated with happier results by P. Sorauer^ and
Frank/ whose handbooks are useful compilations, in which the
matter diffused through numerous periodicals and works is
collected and systematically arranged. My own investigations
have been published partly in periodicals and partly as
independent works.'^

THE CAUSES OF DISEASE

In the present state of science it is scarcely possible to draw
a sharp line of distinction between those conditions of the
plant known, on the one hand, as healthy, and, on the other, as
diseased. The development of any plant depends upon a series
of external factors of nutrition, and these, such as light, heat,
the kind and proportion of the nutritive materials, and of the
water and oxygen contained in the soil, of the carbonic acid
present in the atmosphere, &c., are available for the plant in
very different quantities. When all these external factors
influence the development of the plant in the most favourable
manner, it is vigorously nourished and flourishes well. But
probably the case is never realised when all these factors of
life act simultaneously and concurrently in the most favour-
able manner possible : on the contrary, one or more is sure
to be deficient or superabundant, and this causes interference
to a greater or less extent with the development of the
plant. We cannot as yet say, however, that such plants are

' M. Willkomm, Die Mikroscopischen Fei?ide des Waldes. Dresden, 1866,
1868.

- E. Hallier, Phytopathologie. Die KrankheiteJi der Cidtu7-geiucichse.
Leipzig, 1868.

^ P. Sorauer, Handbuch der Pfa7izcnkrcmkJieitc?i. Berlin, 1S74. 2nd
Edition, 1886.

* B. Frank, Die Kra)ikheitcn der Pflanzeji. Breslau, 1880.

* R. Hartig, Wichtige Krank/ieiten der Waldbdwne. Berlin, 1874. Die
Zcrsetzungserscheinungen des Holzes der Nadelholzbdwne und der Eiche.
Berlin, 1878. U?itersuchunge?i aus dcm forstbotanischen Institut zu
Micnchen. I. Berlin, 1880. III. Berlin, 1883. Die echte Hausschwamtn,
Mcriilius lacryvtans. Berlin, 1885.

INTRODUCTION 5

unhealth)- ; it is only when the Hfe-processes have sunk to very
small proportions that we speak of a plant as " sickly."

Such sickly plants recover, as a rule, when the deficiency of
light, heat, nutriment, or whatever the cause of the sickliness
may be, is removed. It is the province of physiology to discover
the conditions under which plants thrive best. I do not regard
the investigation of the phenomena of mere sickliness as the task
of pathology. It is only when the sickly condition leads to the
death of some part of the plant that we may speak of actual
disease. Suppose, for instance, that the soil of a wood has
suffered through removal of litter, a diminution of growth will
result, which, however, is not as yet disease ; but if a moribund
condition of the tops of the trees sets in, we are confronted with
the disease known as " top-drying " or " top-drought." This
example shows how gradually the condition of sickliness merges
into that of disease, and how it is only the partial death of the
plant that can be regarded as giving external indication of the
latter.

It is quite as difficult to draw the boundary line between healthy
and diseased, and between normal and abnormal, in the case of
those phenomena which we are accustomed to designate as
monstrosities. In the nature of organisms there is a tendency
towards variation both morphologically and physiologically, and
it is upon this, in fact, that progressive evolution in the organic
world depends.

Variation is, therefore, a normal phenomenon, and depends on
causes which are probably almost always operative in the earliest
stages of the life of the organism before, during, and immediately
after the fertilization of the oosphere.

It is impossible to establish a strict line of demarcation between
normal variation and malformation ; and thus all the phenomena
connected with the latter, which we are not in a position to
explain, have been separated and grouped together to form the
special study of teratology apart from pathology.

In this text-book therefore we shall confine ourselves essen-
tially to describing and explaining those phenomena which bring
about the premature death of the plant, or of any part of it, how-
ever small.

This limitation leads us to the answer to the question whether

6 DISEASES OF TREES

plants all die a natural death, or whether they, at least in part,
succumb to external influences — that is to say, are subject only
to accidental death.

Experience teaches that, at any rate among the more highly
developed plants, each individual dies sooner or later, but that in
the case of perennial plants, particularly trees and shrubs, the
cause of death is always to be found in unfavourable external
influences. In the case of the more lowly organisms, which only
multiply by division and as yet exhibit no sexual reproduction,
one can scarcely speak of a natural death, because each part is
as old as the parent organism by the division, &c., of which it was
formed. Were a natural limit set to the life of a certain species
of plant which can only multiply by dividing, the result would
be that when this limit was reached every part, and therefore
also the offspring which had originated by division, would perish.
It is known, however, that this state of things does not exist.
In the case of those plants which are also reproduced by sexual
processes many different conditions are met with. In the case
of annual plants the vegetative part dies each year, and only the
embryos originating from the fertilized oospheres remain alive.
When, from these, plants capable of bearing seeds have deve-
loped, all that is preserved of them, in their turn, is the forma-
tive product arising from the sexual cells. Thus the vegetative
part of each plant dies owing to internal causes, though these,
in part, depend simply upon exhaustion consequent on the
formation of seed. We see then that natural death of the vege-
tative organs of the plant occurs from internal causes, whereas
the sexual cells only die if they have not been fertilized, or if,
owing to external causes, the product of fertilization has not
given rise to a new plant. Upon the unlimited duration of the
life of this part of the plant — that is to say, of those sexual cells
which do not fall victims to accidental death — depends indeed
continuity in the organic world, in other words, the development
and preservation of the vegetable and animal kingdoms.

In the case of perennial plants it is only certain parts that
succumb to natural death each year. Amongst herbaceous
plants, for instance, it is the parts above ground which thus die
off: in the case of deciduous trees and shrubs, it is the outer
cortical tissues, the leaves, &c.

INTRODUCTION 7

The plant-individual proper, however, only dies in consequence
of unfavourable external influences. As a matter of fact, every
tree is rejuvenated each year by the cambium forming new
tissues at its periphery, and by new shoots and buds. It is a
matter of experience that the duration of the life of all trees is
limited, but it is not proved whether this is to be ascribed to in-
ternal causes, or is the result of the innumerable influences which
act more or less prejudicially on the plant from without. The re-
duction and final cessation of the growth in height of a tree, after
attaining a certain maximum, must be ascribed to interference
with the factors of nutrition, and, in all probability, especially
to the fact that the forces which conduct the water and nutritive
materials to the highest bud of the tree are limited in their
action, and that sooner or later, depending on the specific and
individual nature of the plant, these no longer suffice to provide
for the continuance of growth in height. If we cut a slip from
an old tree, it will pursue the same cycle of development as the
parent tree, thereby proving that by vegetative multiplication
the life of a plant may be indefinitely prolonged. Hitherto no
phenomenon has been discovered from which one may conclude
with certainty that internal natural causes of death are peculiar
to all, or even to any perennial plants. In this connection the
question is at once suggested whether " the feebleness of old
age " is a factor which must be regarded at all in considering the
diseases of plants. In discussing how diseases arise we shall
show that old age, quite as well as youth, may predispose a
plant to some disease or other. In itself, however, the feebleness
of old age is not a natural condition attributable to internal
causes, but is a .state induced by external influences. The older
a tree is, so much the more numerous are the dangers through
which it has had to pass, and so much the greater is the
number of its injuries and wounds through which parasites
and saprophytes can find an entrance into its interior. Again,
the older a tree is, the narrower are its annual rings, and
with so much the more difficulty and tardiness does it suc-
ceed in occluding a wound. Finally, the older a tree is,
the more sluggish are its nutritive processes, because, on the
one hand, the soil in which the roots are fixed has become
denser, thereby impeding the entrance of air, and, on the other

8 DISEASES OF TREES

hand, one or other of the nutritive materials may be partiall}'
exhausted.

With the reduction in the transference of nutrient matters to
the crown of the tree, the latter becomes stunted and partly dies,
and this is followed by diseases which finally kill it altogether.

There are, however, always demonstrable external influences
at work in the matter, so that the question whether the debility
of old age is in itself a natural condition manifesting itself, for
instance, in the enervation of the organization of a cambium
cell, or in the separation of a bud from a tree, must in the mean-
time be answered in the negative. Thus, when we speak of the
natural duration of life of a plant-species, we are to understand
the period of time during which a plant is able to liv^e without
succumbing to the unfavourable external agencies in the soil
and the climate, or to the varied attacks of parasitic and
saprophytic organisms.

The above considerations lead us to the natural classification
of the different kinds of disease which we shall examine in the
following pages, according to the external influences which
induce them.

1. Diseases induced b)^ Phanerogams.

2. Diseases induced by Cr}'ptogams.

3. Wounds.

4. Diseases due to unfavourable conditions of the soil.

5. Diseases due to unfavourable atmospheric conditions.

In the case of most diseases it is demonstrable that the
individuals of a given species of plant, which are subjected to
certain prejudicial influences, do not all succumb to these
influences to an equal extent, but that certain individuals or
varieties prove perfectly or almost perfectly resistant, while
others soon become diseased or die. These observ^ations show
that it is not the environment alone which determines the origin
of a disease, but that, on the contrary, a plant contracts disease
onl}' when subjected to definite pre-existing conditions ; that a
predisposition or tendency to disease must exist, and that there-
fore, to a certain extent, the origin of a disease is determined by
the co-operation of two factors. The first factor is the external
cause of the disease, and this is, as a rule, easy of demonstration.

INTRODUCTION 9

The second factor, however, has its inception in a peculiar
condition of the organization of the plant, which is either present
only at certain times, or is only peculiar to and innate in certain
individuals, or, finally, has been acquired under the influence
of definite external conditions. All these peculiarities in the
organization of the plant may be quite normal in their nature —
that is to say, the organism as such appears to be perfectly
healthy — in which case the predisposition is said to be "normal."
On the other hand, however, the predisposition to disease may
be " abnormal," as is the case when the plant is only predisposed
to one disease because it is already suffering from another.
Abnormal or disease-inducing predisposition may arise, for
example, in the neighbourhood of a wound through which alone
some particular parasite could gain entrance to the plant. The
entire group of infectious wound-diseases may be placed in this
category.

Under normal predisposition, therefore, zve are to tinderstand
every condition, even if only temporary, in the anatomical struc-
ture, in the chemical constitution, or ivt, the vital functions of an
organism, which, though not in itself prejudicial to the individual,
induces a disease zvhen a second, and that an external, factor co-
operates in addition, even though the latter is in itself innocuous
to the plant.

In addition to these cases of normal and abnormal disposition
residing in the organism itself, we may also speak of a pre-
disposition to disease which is due to the locality.

There are a great number of fungi which can only attack a
certain species of tree when plants of another species occur in
the vicinity on which the particular fungus, at certain seasons
of the year, may complete its development. Localities in
which m.any aspens grow impart to the pines a predisposition
for the disease known as "Pine-twist" (caused by Melanipsora
TremulcB pinitorquuni). Rhododendrons abounding in a district
make the spruces liable to " Leaf-blister " (caused by Clny-
somyxa Rhododendri), while barberr\' bushes are associated
with the " rust " of wheat. The mere existence of uninter-
rupted woods, composed of a single species of tree, may give
rise to dangers leading to extensive epidemics. Pure larch
woods away from mountainous regions almost always succumb

lo DISEASES OF TREES

to canker, whereas larches mixed with other trees may remain
unaffected. The cHmatic conditions pecuHar to a given district
may render-it specially liable to outbreaks of certain diseases.
Thus in Alpine districts proximity to lakes and narrow valleys
specially predisposes to certain fungoid diseases, because the
moist air of such places favours the fructification of fungi in
a high degree. In the forest one meets with certain localities,
so-called " frost-beds," which favour the injurious action of
frost. The character of the soil may predispose to definite
diseases, in that, for instance, it specially favours the growth of
underground parasitic fungi, or the conditions may induce the
appearance of "root-rot." In very many cases one can say
forthwith of certain localities that they predispose to definite
diseases, and the latter must occur when some factor or other
of the environment is present, although in other localities the
same factor may be harmless to the vegetable world. Of course
this predisposition which is linked to the locality only forms
a part of the multifarious circumstances favourable to the
occurrence and spread of diseases that are to be ascribed to
the environment of the plant, and it must not be confounded
with the idea of a predisposition to disease in the narrower
sense.

In the first place, the normal predisposition of plants may
consist in phases of development which naturally exist for a time
in every plant. To this class belongs the period of youth of the
plant, and the young condition of its new shoots, leaves,
and roots. These are at first covered only by a delicate
epidermis, which is but slightly if at all cuticularized, and
which can offer no resistance to the attacks of parasitic
fungi ; whereas later on in life, when a cuticle has been formed
on the outer cell-walls, and when periderm and bark have been
formed on the axial organs, the predisposition for many forms
of disease disappears.

On the other hand, later periods of life may also induce
a predisposition to certain diseases. Young conifers which
possess resin-canals are almost perfectly protected from
infection by wood-fungi, at least in so far as these find an
entrance only through wounds caused by the removal of branches,
because each fresh wound is at once covered by a protecting

INTRODUCTION n

substance due to the exudation of turpentine. It is not until
after the development of duramen, which no longer conducts
water, that a predisposition for wood-diseases sets in, because
now, when a branch is broken off, the inner wood no longer
protects itself against attack by pouring out turpentine, for it
is only in the watery alburnum that turpentine and resin are
forcibly pressed out of the resin-canals. In the case of trees
advancing age is also, as a rule, accompanied by a diminution
in the breadth of the successive annual rings, and the result
of this is that wounds are not so quickly occluded as when
they occur on young vigorously growing trees. It is easy to
perceive that, as a consequence, the prejudicial results of injuries
are increased as age advances. In this sense alone can we
speak of the feebleness of old age, and increasing susceptibility
to external dangers in consequence.

The condition of vegetation in regard to the season of the year
has great influence on the power of the plant to resist dangers.
It is well known what low temperatures a plant can stand during
the period of winter rest, whereas in spring, after the beginning
of vegetative activity, and before it ceases in autumn, it is
killed by a few degrees of frost.

The capacity of resisting the attacks of parasitic fungi on
the part of the tissues also differs much according to the
season of the year. Between the living cell of the host-plant
and the cell of the fungus-parasite there is a struggle, in which
(in the case of many parasites infesting the tissues of the cortex
or cambium) the latter can only kill the former if this is in
the condition of vegetative rest — that is to say, not actively
growing, &c. If processes of metabolism are energetically at
work in the cellular tissue of the host-plant itself, it is then
enabled to stave off the attacks of the fungus. The action
of the latter on the cellular tissue of the host — depending
as it does on the secretion of an enzyme * — is only prejudicial
when this tissue is defenceless, as it were, owing to the condition
of inactivity in which it is found. These cortex-fungi grow
only from autumn till spring, and their further development

* [Enzymes are a peculiar class of bodies, often called unorganised or
soluble ferments, capable of producing powerful molecular changes in
organic substances in presence of water. — Ed.]

12 DISEASES OF TREES

is checked with the beginning of vegetative activity in the
host-plant. A similar condition of things is met with in those
fungi which at all seasons luxuriate in the wood of trees, and
even kill its living cells, but which are incapable of penetrating
the living tissues of the cortex till these have succumbed to
drought due to the death of the wood, when they may be
easily occupied. The tissues of the wood and those of the
cortex appear to differ in their power of resisting parasites.

The amount of water in plants, determined by the weather,
also influences the development of endo-parasites. During
periods of much rain, when the plant-tissues contain more
water than during periods of drought, many perennial fungi
flourish with special vigour inside the plant. This is particularly
evident in the case of Melanipsora TroniilcB pinitoi-qiiiun and
Rosellinia qnercina.

In contradistinction to those phenomena of predisposition
which have been already discussed, and which to a certain
extent only appear periodically, there is a second category of
peculiarities which are innate, as it were, only in certain
individuals or varieties, which are thereby specially predisposed
to certain diseases. Variation in the vegetable kingdom ma)'
find expression in morphological, chemical, and physiological
peculiarities, and in each of these directions forms may tend to
occur which are more or less susceptible to one disease or other.
As regards the morphological aspect, it need only be called to
mind that there are varieties of potato which possess a very
delicate skin ; others, a thick periderm ; and it is easy to
explain why the former are far less secure against the attack
of the fungus that causes potato disease than those with a
thick skin.

Amongst the Douglas firs there is a bluish glaucous variety
whose leaves, owing to an abundant waxy covering, are much
better protected against atmospheric drought than the pure
green form. That the latter possesses a predisposition to perish
from drought in a continental climate is to be expected from
the fact that it is natural!}' confined to the west-coast region of
North America.

That individual differences with respect to the chemical com-
position, and especially to the amount of water, occur in plants

INTRODUCTION 13

is undoubted, and it may be safeh' assumed that these differences
also involve differences in behaviour towards prejudicial external
influences. At present, however, we know very little in this
connection, and we can in the meantime only conjecture that
the explanation of the individual differences in the behaviour of
plants towards frost, drought, and even towards the attacks of
fungi will partly be found in such chemical differences.

Even more striking are the cases where differences in the
physiological behaviour of plants serve as disease-inducing con-
ditions. It is well known how certain trees of the same wood
awake from their winter rest and become green at different
times, although in other respects they are perfectly similar. In
a young spruce plantation differences of two or even three weeks
may be easily perceived in the opening of the buds of different
individuals, and this must be accounted for, in most part, by
differences in the heat-requirements of the plants. It is evident
that early unfolding of the leaves implies a disposition for injury
by late frosts, but it may also become the chief stimulus to the
development of fungoid disease. If, for instance, the spruce-leaf-
rust {Chrysomyxd) is, in the spring, at the stage when its spores
are being shed, all those spruces whose buds have not begun
to elongate into shoots w411 remain entirely unaffected by the
fungus, which is only able to force its way into the delicate
leaves of young shoots. A disposition for this disease, therefore,
attaches to the individuals which begin to grow earh'. In
other years it may happen that those individuals which first
begin to grow are so far advanced in development when
Chrysomyxa sheds its spores that the leaves are already too old
to be susceptible to infection. In this case it is perhaps just
the late varieties that contract the disease.

The observation that amongst the individuals of a plant
species there are always some whose requirements as regards
heat are less or more than those of others, and that these are
therefore disposed to suffer from cold to a greater or less extent,
and that, further, demands on the moisture of the air and other
factors of growth vary with the individual, has probably led to
importance being attached to the place of origin of the seeds
which we employ in cultural experiments with exotic species of
plants. We endeavour to obtain seeds from districts where, in

t4 DISEASES OF TREES

the course of time, varieties have spontaneously arisen whose
power of resisting frost, or atmospheric drought, as the case may
be, has become enhanced.

A further group of disease-inducing conditions embraces all
these peculiarities which have only been acquired in the course
of the development of the plant, and which may lead to a disease
if certain external influences be present. If plants are reared in a
moist atmosphere, e.g. in a greenhouse, the epidermal system
develops in response to the moist air which surrounds it, so that
it is only slightly cuticularized. If such plants are placed in a
dry atmosphere — for instance, in the air of a heated room — they
become sickly, because the transpiration of the leaves is unduly
increased.

Trees, especially those with smooth periderm, that are reared
in a very dense wood, and then suddenly isolated in later life,
suffer from scorching of the cortex. Such trees possess a pre-
disposition for scorching which is absent in the case of those
plants of the same species which have been grown, from youth
upwards, in an open or light wood. The disposition to disease
in this case consists in the fact that the external covering is
less strongly developed. Plants grown in the shade also prove
to be unduly susceptible to the direct action of the sun, in
that the chlorophyll in the cells of the upper layers of their
leaves becomes destroyed. Oaks grown in a close beech wood,
and consequently with small crowns, incur a predisposition for
top-drought when they are isolated, whereas, under similar
circumstances, trees with full crowns do not suffer from this
disease.

During the first few years after being transplanted, many
trees show a predisposition to be easily " frosted," which is again
lost with the development of a strong root-system. On shallow
soils evergreens, and especially conifers, are far more susceptible
to injury from coal-smoke than those on deep soils, for the
reason that their root-system, being characterised by superficial
development, is unable to take up water in winter. Desiccation
of the leaves in consequence of action of the sulphurous acid
takes place in their case much more easily than in that of trees
which are able to take up water from greater depths, and this
even in winter.

INTRODUCTION 15

All the disease-inducing conditions which have been dis-
cussed may be designated as normal, because the peculiarities
noted are in themselves quite in accordance with the nature of
the plant-organism, and only become prejudicial when some
other external circumstance co-operates, and which is termed
the cause of the disease.

There still remain to be noticed numerous abnormal disease-
inducing conditions which depend on an unsound state of the
plant. To these belong all those wounds in whose train some
disease or other of the interior of the plant may follow.

When a tree is pruned it thereby incurs an abnormal predis-
position for a series of wound-diseases, infectious or otherwise,
which can be got rid of by the application of timely and appro-
priate— that is to say, antiseptic — dressings. Injury to a root,
e.g. the severance of a rootlet, is in itself damage, but when this
leads to decay spreading from it into the stem, we designate
such an injury as an abnormal disposition to disease.

Insects of various kinds live in the cortex of sound trees,
which they injure, and thus open doors, as it were, to the entrance
of parasitic fungi into the interior, so that the trees are ultimately
killed.

A hailstone strikes the cortex of a tree and injures it. This
creates an abnormal condition, which may lead to an infectious
disease should certain fungi settle on the cortex.

When trees or shrubs are transplanted in any year, and their
development is so much retarded by the operation that the new
shoots have not completed their development when frost appears
— that is to say, when lignification has not been completed —
they possess an abnormal disposition to injury from frost.
Such plants may survive in mild winters, but if intense cold sets
in they may die off completely.

From what has been said it will be clear how endless are
the phenomena which dispose to disease, and also how only one
group of these, "the inherent tendencies," possess the character
of inheritability. The phases of natural development, which
were first discussed, and which are passed through by ever)-
plant, may be left out of account in connection with the ques-
tion of inheritability. Neither acquired predisposing causes nor
those due to an unhealthy state can, however, be transmitted

i6 DISEASES OF TREES

from parents to descendants ; at least nothing is known so far
that indicates such an inheritance. This holds good not only
for the causes but also for the diseases themselves.

A transmission, by inheritance, of diseases to descendants is
unknown in the vegetable kingdom. One may without hesita-
tion make use of the seeds of plants suffering from any con-
ceivable disease for the propagation of new plants. In par-
ticular one may without scruple collect the seed of such trees as
are dwarfed owing to poverty of the soil. Indeed, as a matter
of fact, this is done, for instance, in the case of the Scotch
pine, the cones of which are gathered by preference from those
trees whose proportions are so diminutive, owing to their grow-
ing on barren moors, that the collection of the cones may be
accomplished with ease without climbing the trees. It is only
when a question of individual properties consisting in dwarfed
habit of growth, spiral stems, or other undesirable peculiarities
that are innate in the plant is involved, that the law of in-
heritance comes into consideration, and then propagators of
plants have to exercise the greatest care.

METHOD OF PROCEDURE IN INVESTIGATING THE
DISEASES OF PLANTS

Reference will here shortly be made to the methods of investi-
gation which we have to follow when we wish to determine the
causes of diseases in plants.

In the case of diseases of men or animals the difficulties of
diagnosis are much increased by the fact that in the great
majority of cases the disease of a single organ or part of the
body is followed by secondary phenomena which impede the
discovery of the proper seat of disease. In the bodies of plants,
where the nervous system is absent, a disease as a rule remains
localized, at least at first. The division of labour is not yet so
far differentiated as in the bodies of the more highly organised
animals, where disease of any organ, often even a small one,
involves the whole body sympathetically. A large part of the
body of a plant may be diseased and even killed without the
plant being necessarily perceptibly injured in its general health.
If we have succeeded in observing the disease in its first stage,

INTRODUCTION 17

the further investigation offers comparatively Httlc difficulty. It
is more difficult, as a rule, to determine the true cause of disease
and death in the case of plants already dead, although the skilled
plant-pathologist will seldom fail to recognize with certainty the
true character of a disease.

If we are dealing with injuries caused by animals or plants,
we shall discover and recognize them, or at least their traces,
with most certainty in the preliminary stages of the disease. In
very many cases it is not sufficient, where we are dealing with
injuries due to animals, including insects, that we catch the
creature at work and seek to observe it and its mode of life in
nature, as has hitherto generally been done ; but, and particularly
in the case of insect-injuries, w^e must determine whether the
injured plants did not already possess some predisposition to
disease before they were attacked by the insects, &c. Especially
does this hold good for the great family of the bark beetles,
which often only appear in the train of other prejudicial agencies,
and especially of injuries caused by parasitic fungi. In the case
of parasitic plants, again, it is not to be concluded forthwith from
the presence of a fungus in the dead tissues that death has been
caused by that fungus. True, where we find the mycelia of fungi
vegetating in the apparently Jtualtered living tissues of a plant,
there is practically no room for doubt that we have to deal with
a parasite ; but even in the latter case the attempt must next
be made, by means of suitable infection-experiments, to induce
arbitrarily, and in a somewhat artificial manner, the disease that
we are seeking to investigate.

If spores or gonidia of the suspected fungus are to be had, we
make use of these in carrying out the investigation, after having
first proved that they are capable of germinating. Should no
material capable of germinating be at our disposal, we must, if
possible, undertake artificial cultures in a damp chamber, and
await the ripening of spores, or even the production of sporo-
phores.* According to the character of the disease, infection is
secured by scattering the spores on the leaves, or by placing
them in a wound artificially made in the host-plant. In the

* [Spores may be of several kinds, and the term is used as a general one.
Gonidia are a-sexual spores. Sporophore is a general term to denote any of
the various kinds of spore-bearing structures met with among Fungi.— -Ed.]

i8 DISEASES OF TREES

case of diseases of the cortex it is sufficient to make a fine inci-
sion with the point of a scalpel, to which a drop of water, with
spores suspended in it, is attached ; in the case of diseases of
the wood the latter must be pierced by the wound, which is
then allowed to absorb the drop of water with its contained
spores.

In dealing with diseases of the cortex or wood, infection by
means of mycelium* is the much surer course. Having removed a
small piece of the cortex from that partof a diseased tree where
the mycelium is still young and vigorous — that is to say, from the
boundary between the dead and living tissue, we place it on a
spot in a healthy tree from which a piece of cortex of the same
size and shape has been removed. We may proceed exactly as in
budding roses, but it is generally better if the edges of the piece of
cortex containing the mycelium are brought into intimate contact
with the edges of the cortex surrounding the spot operated upon,
and which, moreover, should be prepared immediately beforehand.

Desiccation should then be prevented by applying grafting-wax
or other dressing. If it is desired to infect the wood of the stem
of a tree with mycelium, a small cylindrical block is removed
(by means of Pressler's growth-borer, an instrument specially
adapted for such work) from the boundary between the sound
and diseased wood, because it is usually only in this region that
the m}'celium contained in the wood is still capable of such
vigorous growth as to be able to extend beyond the surface of the
infecting block. With the same borer an exactly similar hole is
then made in the sound tree selected for infection, the diseased
cylinder being substituted for that which was withdrawn, and
the hole closed externally with grafting-wax.

If, finally, we have to do with parasites which vegetate under-
ground, it suffices, as a rule, to plant a diseased specimen in
immediate proximity to a healthy plant of the same species. In
doing this greater success will probably be secured by bringing
a root of the diseased individual (known to contain mycelium
still living and capable of growth) into immediate contact with
a root of the plant to be infected.

* [The mycelium is the vegetative part of the fungus, and in many cases is
more easily obtained in the requisite quantities than spores are : a rough
equivalent for the word in English is " Spawn " (of mushrooms, &c.) — Ed.]

INTRODUCTION 19

It would be a mistake to attempt to answer the question
whether a fungus is really a parasite or not after the failure of
one or a few attempts at infection. Let us only consider how
numerous are the factors regulating success even in the
sowing or planting of our forest trees, with whose conditions
of life we are to some extent familiar. Of the fungus to be
investigated, however, we, as a rule, know almost nothing ; we
do not know the external conditions of germination, we often
scarcely know whether the spores are really ripe, whether they
are in too damp or too dry a medium, whether sufficient oxygen
is admitted to them, or whether the season of the year is the
right one for sowing — for spores, like the seeds of forest-trees,
require to rest for different periods after ripening, before they will
germinate. What has already been said about the numerous
conditions predisposing plants to disease will show sufficiently
how, even with the best material for infection, experiments ma}-
give only negative results. Since even trained mycologists and
pathologists often succeed only after innumerable abortive
experiments in making themselves acquainted with the con-
ditions under which a plant becomes infected, it will be clear
that it may be regarded as simply an accident when an amateur
succeeds at all with an infection-experiment.

When the infection has succeeded, it is not enough merely to
follow the course of the disease through its various stages — in
doing which, moreover, it is of the utmost importance to compare
cases of disease met with in the forest — but it is also necessary
to discover the external influences which restrict or further the
development of the disease.

This part of the investigation is the most difficult. It

demands, very specially, the power of accurate observation ;

apparently unimportant accessory circumstances must be noticed

and compared ; and, above all things, excursions to the forest

must be made as often as possible. Investigations of the

diseases of our forest trees will seldom lead to any definite

result unless we make careful and extensive observations and

comparisons in the forest itself. At the same time, still less

prospect of success will attend observations of diseases in the

forest if they are not accompanied and supported by exact

scientific investigation.

r o

20 DISEASES OF TREES

If investigation shows that neither animal nor vegetable
organisms are the primary cause of the disease, then the latter
must be due to some influence in the inorganic environment. If
it is suspected that unfavourable properties of the soil are
responsible for the disease, the unhealthy tree should be removed,
and — if possible, at the spot where it stood — a hole should be dug
to the depth reached by the lowest roots. During the opera-
tion attention is to be directed to the consistency of the layers
of soil, and to the quantity of water which they contain, and
especially to their greater or less accessibility to atmospheric
air. In the forest a change in the amount of mineral food, so
great as to induce disease in a previously healthy tree or planta-
tion, would occur only under circumstances that would at once
attract the attention of the skilled observer. For instance, top-
drought may be a consequence of the removal of litter or the
laying bare of the soil ; sickness or death may be occasioned
by the presence of injurious substances derived from factories,
or owing to flooding with sea-water, &c. Chemical investigation
will very seldom be necessary. More frequently the cause is
attributable to atmospheric influences, such as variations of
temperature, moisture, or precipitations, or to lightning, noxious
gases, &c. If it can be determined when the disease first
appeared, the task will often be more quickly mastered by col-
lecting information, and by ascertaining the external conditions,
than by investigating the diseased plant, although the latter
course will, in many cases, lead to the desired end.

As a rule, diseases produced by animals and plants are
characterised by their occurring first of all on single plants or
parts of plants, and then gradually extending from these
centres ; whereas diseases which are due to the influence of soil
or atmosphere generally appear regularly and simultaneously
over large areas, because such influences are seldom bounded
in the forest by narrow limits or confined to the neighbourhood
of single plants.

Mistakes are most likely to occur when a disease is preceded
by an abnormal predisposition, because this alone, and not the
disease rendered possible by it, is apt to be kept in view. It
frequently happens that we meet with different diseases on the
same tree, each of which is at work independently, and when

INTRODUCTION

this is the case we should not at once stop the investigation
when a cause of disease has been discovered. Very often we
encounter, e.g. in the low lands of North Germany, devastated
woods of Scotch pines, in which many trees have been killed by
Trametes radiciperda. More exact investigation, however, often
results in the discovery that in the same wood, in consequence
of insufficient circulation of air in the soil, root-rotting is much
more destructive even than the root-parasite.

Only the most careful research, supported by thorough know-
ledge of the forms of disease, which are so numerous and
varied, can protect us against error.

SECTION I
INJURIES INDUCED BY PLANTS

This is not the place to discuss the many conditions brought
about by the struggle for existence — for space, food-materials,
water, and light — between plants of the same or opposite species.
Any plant may prove injurious to another if it makes the same
or similar claims on the constituents of the soil. When two
plants compete with each other, success does not alone depend
upon the rapid rate of growth of any particular species on a
given situation, but is determined largely by the rate of growth
which characterises iiidividual plants ; and it is this which is
mainly decisive in pure woods. It has long been known that
superior individual growth manifests itself in the earliest stages
of the life of a tree ; in fact, sometimes — for instance, in the
case of the oak — it is recognizable in the size of the fruit. -^
It is therefore of the greatest importance not only to exer-
cise care in the selection of the seed, but also to remove
weak plants when transplanting in the nursery. When
crowded, all plants must struggle with their nearest neigh-
bours ; but I do not consider that it is the province of vegetable
pathology to discuss these conditions : rather do I hold that
I should closely confine myself to the consideration of those
injuries which consist in the direct attack of one plant on
the life and health of another.

1 Th. Hartig established this fact experimentally in the nursery at
Brunswick thirty years ago.

INJURIES INDUCED BY PLANTS

PHANEROGAMS

No sharp boundary can be drawn between parasites and
plants that are only indirectly injurious owing to their proximity,
or to their competition for food-materials, light, and so forth.*
One gradually passes from the latter to plants which, while
not subsisting on the substance of others, still directly attack
them, and induce pathological phenomena.

Allusion may be made, for instance, to Loniccra Periclyme7iiim,\
whose stem, when opportunity offers, winds round young trees
with the result that a few years later the descent of the plastic
materials in the bast is forced to take place in a definite spiral
course. With increasing thickness the tree is soon subjected
to direct pressure by the twining plant, which prevents the direct
vertical descent of the solutions of food-substances coming
from the leaves. It frequently happens that the part of the
stem immediately below that of the honeysuckle is deprived of
nourishment, the result being that the cambium in that region
gradually dies ; whereas the portion above the passively tighten-
ing stem of the honeysuckle on the one hand exhibits very
vigorous growth, and, on the other, experiences abnormal altera-
tion in its younger parts owing to the spiral direction imparted
to all the organs of the vascular bundles.

While there is no doubt that the immediate cause of the
movement of plastic substances in the cortex and bast is the fact
of their being produced in one place and utilised in another, neces-
sitating a transference from the place of origin to the place of con-
sumption, still the assumption that the movement of the plastic
materials in the bast takes place much more easily and quickly
in a vertical than in a lateral direction receives support from
the fact just mentioned, and illustrated in Fig. i, as well as
from many other phenomena. In fact, lateral movement is
so difficult as sometimes to induce complete cessation of the

* [In such cases the plants not vakied are regarded as " weeds " ; but it is
obvious that any plant may act as a weed towards others, and a little reflec-
tion shows that it may act as a weed towards its own species if crowded,
&c.— Ed.] t [Honeysuckle.— Ed.]

24

DISEASES OF TREES

nourishment of the band of cambium situated under the stem
of the honeysuckle.

Tritiaim repeiis* may also be mentioned here, the sharp-pointed
rhizome of which has the power of piercing and growing through

the fleshy roots of other plants which it
may encounter in the soil. This has
been speciall}- observed in beds of oak
seedlings, though it may be remarked
that the piercing of the roots has re-
sulted in no apparent damage to the
oaks.

The passage to the true parasites —
that is to say, to those which subsist
entirely on the plastic materials of
other plants — is formed by a group of
plants in which one cannot at first per-
ceive a parasitic existence, seeing that
they are provided with leaves containing
chloroph}'ll, and take water and inor-
ganic nourishment from the soil with
their roots. While they assimilate plastic
materials for themselves, they also attach
themselves to the roots of other phane-
rogamic plants from which the\- abstract
organic substances by means of an absorb-
ing apparatus (Jiaiistoriiivi) on certain of
their roots. To such plants belong the
RhinantJiecs, a sub- family of the Scro-
pJmlariacece. The cow-wheat {Melampy-
nim arvense), the common }-ellow-rattle
{RJmianthus Crista-galli), and the louse-
wort {Pedicularis) and eye-bright {Eii-
phrasia) furnish well-known examples
of this kind of life. As these plants
are parasitic onl}- on the plants of pastures and meadows, we
cannot here spare time to examine them more closely. The genus
LatJircca, also, which contains the common species Lat/inva
squaviaria, the tooth-wort, has not yet been proved to be wholly
* [" Couch grass " or '• twitch ." — Ed.]

INJURIES INDUCED BY PLANTS 25

parasitic. Its roots arc parti}' attached to the roots of manj-
different plants, including several trees such as beech, hornbeam,
hazel, and alder.

Notwithstanding traces of chloroph)il in the OrobancJiacece,
these must undoubtedl)' be classed as true parasites, which derive
their nourishment exclusively from the host-plants to whose roots
they are attached. Of the numerous species, some occur so
plentifully on cultixated plants as to cause appreciable damage
e.g. Orobanchc raniosa on tobacco and hemp, O. lucoriivi on the
barberry and bramble, O. Hcdcra; on ivy, O. riibens on lucerne,
and O. minor on red clover. The parasitism of the yellow bird's-
nest {Monotropa Hypopitys) is still doubtful, but, as its roots are
found in contact with those of conifers and the beech, it is
extremely probable that though most of its nourishment is got
from the humus a certain amount is also abstracted from these
plants. Besides Monotropa we have the Orchidacccr that are
destitute of chlorophyll, which are all of a saprophytic nature.

Nor can the Loranthacccv be regarded as true parasites,
because for the most part they abstract onl}' water and inorganic
food-materials from trees and shrubs, organic substances being
appropriated to a very limited extent. They possess leaves
containing chlorophyll, and behave towards their host in exactl)-
the same way as a scion does to a stock. In fact they yield up
a portion of the plastic substances which they themselves have
prepared to the host-plant, which employs them for its own growth.
Whether, however, this occurs in the case of all, or even most,
LorantJiacecE is doubtful, but at all events such reciprocal nourish-
ing takes place with Loraiithus eiiropcuus. The manner in which
the different species of this family abstract water and nourishment
by means of their roots from the plants which they inhabit varies
extremely, especiall}- when the exotic species are taken into
account.^

The best-known species is J^iscnni albiu/i, the common mistletoe,
which is distributed throughout the whole of Europe, and Asia to

^ See Solms Laubach in Pringsheim's JaluinicJiern f. tviss. Bot. VI.,
pp. 575 et seq. R. Hartig, Ziir Kennt7riss vo7t Lora7ithus europacus iiud
Visciim album., with, a table, ZeitscJmft fiir Forst- u. Jagd-Wesen . 1876,
pp. 321 et seq. Dr. C. v. Tubeuf, Beitrdge ziir Kenntiiiss der Baiunkrank-
heiteii., pp. 9 — 28. Springer, Berlin, 1888.

26 DISEASES OF TREES

Japan. It is met with on almost all dicotyledons and conifers,
but exibits a preference for certain species, e.g. silver fir, Scotch
pine, poplars, and fruit-trees ; whereas on others, e.g. spruce, oak,
beech, Spanish chestnut, alder, and ash, it has been met with
either very seldom or not at all.^ With regard to the appearance
of this familiar plant, it need only be mentioned that narrow and
broad-leaved varieties occur on different species of trees. The
mistletoe is distributed by thrushes (especially Tiwdiis viscivorus),
which feed upon the berries and carry them off. The birds dis-
engage the sticky seeds from their beaks by rubbing them against
the branches on which they perch, and to which the seeds there-
by become attached. The seeds, which germinate in spring, first
of all develop a kind of sucker, from ^vhose centre a fine root
appears which pierces the tissues of the cortex. This main root
penetrates to the wood of the branch or stem, which, however,
it is too delicate to enter. This then finishes its apical growth
in length, but, on the other hand, owing to the presence of
meristematic tissue behind the apex (such tissue being situated
in the region of the cambium of the host-plant), it is enabled to
elongate at the same rate as the branch increases in thickness,
by the formation of a ring of wood and of bast (" intermediary
growth in length"). Owing to the fact that the wood-ring en-
velops the apex of the root of the mistletoe, the latter appears
to bore deeper into the wood each }'ear, but this is really due to
its being embraced by the stem as it grows in thickness. The
growth in length of this root, as of all the " sinkers " that after-
wards originate in the roots that are met with in the cortex,
very closely resembles the growth in length of a medullary ray
possessing cambium of its own in the cambium mantle that
covers the whole stem, and is thus enabled annually to elongate
both towards the wood and towards the bast. Several lateral roots
next appear on that part of the radicle which is situated in the
cortex, and these proceed to grow both upwards and downwards
in the branch. These " Rhizoids " or " Cortex-roots " push their
pencil-like apices along the }'oung soft bast, without however
coming into contact with or altering the cambium zone. The
organs of the soft bast are dissolved in front of the point, and it

1 Nobbe, " Ueber die Mistel, ihre Verbreitimg, Standorte., tuid forstUche
Eedeiiiiaig" Thorander forstliches Jahrbuch., 1884.

IxNJURlES INDUCED BY PLANTS

ma)- be taken for granted that the products of sohition are absorbed
by the cortex-roots and used for their own growth. From investi-
gations made on the Scotch pine and the silver fir, the annual
growth in length of the cortex-roots is 75 mm. in the former case
and 1 75 cm. in the latter. The growth in thickness would appear
to be somewhat irregular. Once a
year, very seldom twice, often only
each alternate year, a " sinker "
originates on the inner side of the
cortex-root near the apex. This
wedge-like outgrowth is of the
same breadth as the cortex-root,
but varies much in thickness, and
breaks through the cambium zone
until it just reaches the wood of
the host-plant, where it elongates
in the same peculiar manner as
has been already described in the
case of the radicle. If the cortex-
root with its sinkers is exposed, as
is represented in Fig. 2, we may
trace back from the apex of the
root c, and accurately determine
how many years have elapsed since
the various sinkers have originated,
because each year these are em-
braced by a wood-ring. Even in
the most recent descriptions of
the mistletoe we still find, as a
rule, Schacht's illustration repro-
duced, which erroneously represents
young sinkers between older ones
on the same cortex-root. Water
and inorganic nourishment are

absorbed by the whole series of sinkers through their lateral
surfaces, which are in immediate contact with the water-con-
ducting organs of the wood, and are first of all conveyed to
the cortex-root, and through it to the leafy part of the mistletoe.
From the peculiar way in which the sinkers increase in length

Fig. 2. — Roots of Visciini album
in Finns sylvestris. The cortex-
root, which pushes its apex, c,
along the bast tissues, b, puts
forth eight sinkers on the inner
surface, atid buds and shoots on
the outer. The oldest portion
has already been pushed out
nearly to the dead bark. At e
the sinkers ofa cortex-root which
has already been enveloped in
the bark are shown.

28

DISEASES OF TREES

it is evident that the)' elongate not onl}' towards the side next
the wood but also towards the side next the cortex. With
the formation of new phloem-tissues the cortex-roots are con-
stantly being pushed away from the cambium mantle, as may be
seen from Fig. 3. In the case of such trees as the silver fir,

whose stem remains smooth for manj'
decades before the formation of true
bark begins, the cortex-roots may
thus be pushed away from the cam-
bium mantle without their suffering
any appreciable injury. They may
attain to an age of forty years, a
corresponding age being reached by
the sinkers, whose length increases
in proportion to their age. On the
other hand, trees like the Scotch pine,
which form bark early, show only
short sinkers, of a length of 3-4 cm.,
and an age of twelve to fifteen years.
This is to be explained by the fact
that owing to the usually more active
formation of new bast the cortex-
roots are more quickly pushed away
from the cambium mantle. The outer
parts of the cortex are converted
into bark, and as soon as a portion
of cortex containing a cortex-root
is converted into bark, it dries up,
along with that part of the mistletoe
root which it contains, and the con-
nection with the sinker is broken.
This is distinctly brought out in
Fig. 3. The sinker then ceases to
grow, and is covered over sooner
or later by the new wood-rings. Of course the death of a cortex-
root does not take place simultaneously throughout its whole
length. On the contrary, the oldest part — that is to say, the part
situated farthest from the cambium — dies first, whereas those
younger portions which arc still enveloped in living cortex

Fig. 3. — Cross section of a stem
of Abies pectmata containing
Visctiin album, a, dead bark
showing dead cortex-roots ; b,
region of living bast ; c, cam-
bium region ; d, cross section
of a cortex-root showing a
sinker six years old ; e, a
sinker eighteen years old ; the
cortex-root has lately been
enveloped in the bark, while
the apex of the sinker has
withered in the duramen ; at
/" the cortex-root and the por-
tion of the sinker in the bast
have been dead for two years ;
a cortex-root is shown at g
which has been dead for six
years. The boundary line
between the duramen and al-
burnum lies at hh ; at x two
sinkers are shown, those por-
tions situated in the alburnum
being still alive.

INJURIES INDUCED BY PLANTS 29

remain alive. These, however, are in the same position as the
roots of a tree that has been felled — that is to say, they can no
longer conduct nutritive substances to the leafy part of the
mistletoe, which must therefore die when its feeding-roots are all
confined to the bark. Its place is taken by numerous root-
shoots which arise from buds formed on the outer side of
those portions of the cortex-roots which are still alive. The
mistletoe represented in Fig. 2 is just such a root-shoot. These
shoots, which are represented in Fig. 4, form a new root-system

Fig. 4. — Fart of the stem of a silver fir showing a group of mistletoe plants. The
bark has been removed from one side in order to show the position of the corlex-
roots and sinkers.

of their own, and thus it happens that an old stem attacked by
mistletoe contains numerous young and old cortex-roots, as well
as old and young sinkers. In this way the tree comes to bear as
it were a plantation of mistletoes, which is constantly being re-
generated by the production of new root-shoots, and which is
always taking possession of a larger part of the tree. On old
silver firs and Scotch pines it is by no means rare to meet with
such mistletoe plantations a yard long and half a yard broad.
It ought to be mentioned that the living sinkers begin to die at
their apices (Fig. 3) whenever they become enveloped by the

30 DISEASES OF TREES

advancing duramen. Even in the case of the silver fir and spruce
it is only the outer wood which conducts water, and in the bole
this region seldom embraces more than forty to fifty annual
rings, while in the branches it is much narrower.

The damage done by the mistletoe to forest, fruit, park,
and avenue trees is by no means inconsiderable. In the
Reichswald, in the neighbourhood of Nuremberg, I have seen
woods of middle-aged Scotch pines where scarcely a tree had
escaped, and where the foliage of the mistletoes competed for
effect with the natural foliage of the pines. Where practicable,
as in orchards, &c., the infested branches should be entirely
removed before the mistletoe has had time to spread to any
considerable extent. Simply breaking off the plants only
induces the formation of vigorous root-shoots at the same
place.

A few words may here be devoted to the genus Arccuthobiiivi,
of which a species, ArceutJiobimn Oxycedri, occurs in the south
of Europe, and also in Austria, where it forms dense bushes on
Jiiniperns Oxyccdnis ; while in North America quite a number
of species attack forest trees, especially the Abietinea. These
grow in the same wa}- as the European form, or induce the
formation of witches' brooms by the rhizoids which live in the
cortex causing considerable elongation of the infested branch, from
whose cortex numerous shoots i — 2 cm. long break through at
irregular intervals, as happens in the case of ArccutJiobiuni
Douglasii?- In the case of these plants, also, the nutritiv'e sub-
stances are absorbed by simple sinkers consisting of a single row
of cells, or in other cases by vascular sinkers. The injury caused
to forest trees by these plants is very considerable ; still one
need not anticipate that these parasites will find their way into
Europe with the introduction of North American conifers.

More interest attaches to Loranthns curopLVus, a parasite
specially common in Austria, but also found occasionally in
Saxony, the formation of whose roots differs entirely from that
of the LorantJiacccv already described.

LorantJius enropcEus is, for the most part, found on the
common oak, on which account it is known as oak mistletoe,
though it also attacks Casta)iea vcsca ; and in Austria, especially
^ See C. V. Tubeuf, /.(■.

INJURIES INDUCED BY PLANTS

31

in the Wiener Wald, it has proved \-ery destructi\-e in stored
coppice, where b\- kilHng the tops of the oak standards it
prejudicially affects their growth in height. An irregular
swelling of the size of a
man's head (Fig. 5) often
occupies the place of the
leading shoot. The oblong
seeds (Fig. 6,/) of the plant,
which is deciduous, are af-
fixed to branches by thrushes,
as in the case of Visanii.
There they germinate, and in
a few years the base of the
parasite becomes completely
enveloped in a large excre-
scence which forms on the
tree (Fig. 6, r).

The root-s}-stem is to be
distinguished from that of
the Lo7'anthaccce alread}^ de-
scribed by the fact that the few rhizoids which arise on the
radicle always grow downwards — that is to say, in a direction
opposed to that of the ascending water — and b}' these rhizoids

Fig. 5. — A swelling on Quercus Cen-is, a,
bearing an old plant of Loranthiis, />/>.

Fig. 6. — Loranthiis euj-opcsiis on a branch of Qiiernis Cerris. a, a young planL ; /',
a five-year-old plant ; c, an outgrowth of the oak ; d, longitudinal section of a
root of Loranthtts ; x, apex of the root ; e, cross section of a root ; /, a seed.

taking up water and food-materials directly from the wood
without forming sinkers.

The pointed apex of the root (Fig. 7, x) does not grow outside
the cambium zone, but in the voung wood— that is to say, in

DISEASES OF TREES

the part of the branch that is not completely lignified — and
always exactly parallel to the longitudinal course of the xylem
elements. The apex of the root, which is flat upon its inner
side, advances in a definite region of the young wood, at the
same time pressing out, splitting, and dissolving the still
unlignified elements by means of its con-
vex outer surface. This goes on till future
progress in the original direction is pre-
vented by the resistance consequent on
lignification in the outer layers of the new
wood which the roots of the parasite are
unable to split off and dissolve. The root,
whose apex is thus in a cul-de-sac, is forced
to form a new growing-point some distance
behind the apex — namely, at the place where
the convex outer side comes into contact
with the cambium zone (Fig. 7, y). From
this new point growth in length begins
afresh, and is continued in a zone situated
nearer the periphery of the wood. During
the development of an annual ring the root
of LovantJms (which, of course, can only
grow during the period when the cam-

d c b

Fig. 7. — Youngest por-
tion of a root of L.
eiiropceiis. a, cortex

and bast ; /'. cam- bium produces young wood) is generally

bium ; c A, young wood ;

d, the portion of the
wood-ring of the cur-
rent year in which
growth has been com-
pleted ; c, wood-ring
of the previous year ;
z, root of Loraii/hus ;
X, the apex of the root ;
y, the point whe-e a
new root-apex is form-

thrice compelled to shift the direction of
its growth farther out, the result being
that the inner side of the root shows a
corresponding step-like arrangement, which
accords with the advance of the wood, as
is shown in Figs. 6 and 7. The distance
between two steps measures from 5 to 8
^^^' mm., while the annual growth in length

of the root amounts to about 1-5 cm. As the roots grow in a
direction opposed to that pursued by the ascending water, the
latter flows directly from the conducting elements of the wood
into the roots of the Loranthns, at the points of depression.
The root possesses the power of growing vigorously in thick-
ness, whereby it is enabled for a series of years to keep pace
with the increase in thickness of the oak-branch, and thus

INJURIES INDUCED BY PLANTS 33

to protect itself against being overgrown. The root usually
continues to grow in thickness for eight }-ears, though it occa-
sionally ceases to grow in four, when it is enveloped in the adjoin-
ing wood owing to the formation of callus.* Thus, while it still
continues to grow at the point, those portions of a greater age
than eight years lie embedded in the wood, but they remain
capable of performing their functions perfectly and of taking
in food-substances, so long as they are not in the region of the
duramen (heart-wood), where water is no longer in motion. Even
then, however, nutriment may still be furnished to ih.Q Loraiithus.
Here and there processes similar to medullary rays run from
the roots enveloped in the wood to the cortex, and at this point
root-shoots may be formed from adventitious buds, although
this occurs but seldom.

The gnarled swelling which forms on an oak-branch attacked
by LoraiitJuis is a very striking object. While the upper part
of the branch ultimately dies, the rugged protuberance increases
in thickness, and envelops the whole of the lower part of the
LorantJms along with its branches. The part of the oak-branch
that bears the swelling also increases in thickness, although it
possesses no leaves of its own, and there can be no doubt that
the products of assimilation of the parasite serve both for its
own nourishment and for that of the host-plant.

As it is not expedient to shoot the thrushes even for the
purpose of preventing the spread of the seeds of Loraut/nis,
we must, in this case also, minimise the evil by cutting off
branches which are infested by the parasite.

Although the Dodders, Cuscutece} which are true parasites
destitute of chlorophyll, are for the most part injurious only
to herbs, they are still met with on woody plants with
sufficient frequency to merit a short description in this
treatise. Their seeds germinate in spring on the ground.
The young plant perishes unless its long thread-like stem

* [Callus is the cushion-like mass of growing tissue which arises at the
edges of a wound and eventually covers over (occludes) the damaged surfaces
—see Part II. under the discussion of wounds, &c.— Ed.]

1 See Sorauer's Handbiich, 2nd Edition, Part II., pp. 32— 48. v. Solms-
Laubach, Ueber den Ban. und die EnHvicklung parasitischer Phanerogamen.
Pringsheim'sycr//;-/^. vol. iv.

D

34 DISEASES OF TREES

finds a suitable host-plant, in which case it twines round the
stem of the latter and sends numerous absorbing roots, or
" Haustoria," into the cortex. Although the root which
originally connected the plant with the ground disappears, the
dodder nourishes itself by extracting nutritive materials from
the host-plant round which it twines by pushing its sucker-roots
as far in as the vascular bundles, in which, by breaking up into
unicellular threads, they often assume a brush-like appearance.
If the plants are small they may soon be killed, but in the case
of larger plants it is only their development that is interfered
with, and, so far, I have not noticed any appreciable damage to
woody plants.

The Ciisaitece are distributed by means of numerous seeds,
which are produced by dense globular inflorescences, situated
at some distance apart on the stem ; and it has lately been
discovered that the plants themselves may survive the winter.
The only protective measure that is practically applicable in the
case of this parasite consists in using seed uncontaminated by
dodder. At the same time, the eradication of the dodder-plants
which arc so common along hedges and fences is also to be
attended to. These are the places where we most frequently
meet with dodder, and there too it will oftenest be found on
various woody plants. Ciisciita eiwopcea* the greater dodder,
is the species most frequently met with. It is parasitic on
almost all trees, as, for instance, Corylits, Salix, Popuhts, Prurms
spiuosa, but especially on Hiiunihis, Urtica, and Galium. As
the lesser dodder, Cusciita Epit/iymnin, is specially liable to
attack clover and lucerne, it is the species most to be feared.
Besides having numerous other host-plants, e.g. Tliyinus, Genista,
Callitna, &c., it has also been met with on Vitis. Cuscuta
Epilinnm is commonest on Limini iisitatissinniin. The other
species are but seldom met with.

*[C Europcea is far less common in this country than is the Lesser
Dodder, C. Epithymum, and C. Epilinnm is not often met with. — Ed.]

INJURIES INDUCED BY PLANTS

35

CRYPTOGAMS
PSEUDO-PARASITES

Among cryptogams, also, we meet with plants which, although
not parasites in the narrower sense of the term, may prove
directly injurious to other plants by the manner of the attack
which they make upon them. A case in point is furnished by
ThelepJiora laciniata} whose thallus '' li\'cs on the humus con-
stituents in the upper
layers of the soil, but
whose sporophores grow
up and embrace young
plants, as is shown in
Fig. 8. Commencing at
the ground, they enve-
lop leaves and branches
so completely as to
smother and kill them.
I have found the fer-
ruginous, sessile, more
or less confluent sporo-
phore, with its lacerate
pileus,"]" commonest on
young spruces, silver firs,
and Weymouth pines,
on which it ascends

to a height of eight inches from the ground. For similar
reasons, though to a much less extent, trees may be injured
by an excessive growth of lichens. A luxuriant growth of
lichens on the stems and branches of trees is a sign that the
air is permanently humid. It is also connected, however, with
the quality of the soil and the rate of growth of the trees, and

' R. Hartig, Untersuchiingen a. d.forstbot. Inst., I. p. 164. Berlin, 1880.

*[Thallus is the term applied to the cellular vegetative body of many
lower plants. — Ed.]

+ [The pileus of a mushroom or similar fungus is the expanded upper part.,
on a portion of whose surface the spores are produced. — Ed.]

D 2

Fig, S. — Thelephora laciniat?

36 DISEASES OF TREES

it is well known that the stems of beeches grown on the best
soils, especially such as are calcareous, bear but few lichens,
whereas on the poorer soils, especially such as are sandy, lichen-
covered stems are very abundant. When a beech grows very
rapidly in thickness, the formation of periderm* must also be
rapid, and, since the dead cork-cells on the outer side of the cor-
tex are soon exfoliated and pushed off, luxuriant development
of lichens is impossible. Where growth in thickness progresses
very slowly, the dead cork-cells adhere to the cortex for a much
longer period, so that lichens are enabled to grow longer and
develop more vigorously. Under such circumstances, too, mois-
ture is longer retained, and this also favours the growth of
lichens. The same remarks apply to trees, such as the spruce,
whose outer layers of periderm are cast off as scales, or whose
moribund layers of cortex are thrown off in later life as plates
of bark. The slower the growth of a tree, the more slowly do the
outer cortical layers die, and so much the more suitable are the
conditions for the growth of lichens. Consequently, although the
presence of lichens is primarily the sign of a permanently humid
atmosphere, or of a slow rate of growth, it cannot be denied
that they do some small amount of damage to trees. During
summer the tree takes in oxygen by means of numerous lenticels,
and this process goes on even in the older parts of the stem.
The presence of oxygen in the interior of the tree is absolutely
necessary for maintaining the processes of metabolic, or chemical
and vital changes. Now, if the passage of oxygen to the lenti-
cels t of the cortex is impeded by a luxuriant growth of lichens
or mosses, we may assume that the tree suffers more or less in
health. This may furnish us with a reason for the death of so
many branches of spruces and larches whose crowns are over-
grown with lichens.

* [Periderm is the corky covering which replaces the dehcate epidermal
layer as the stem grows older. Cortex is the green, living cellular tissue
covered by the periderm, &c. For the connection between "periderm" and
" bark," see later in Part 11. On a two-year-old twig of a tree, about June or
July, we usually find epidermis on this year's growth, and periderm on the
browner, older part. — Ed.]

f [Lenticels are the perforated or pervious corky warts noticed on the
periderm of twigs — c.g.^ they are very evident on twigs of chestnut, elder,
&c.— Ed.]

INJURIES INDUCED BY PLANTS ^

BACTERIA, OR SCHIZOMYCETES

It was not till a few years ago that bacteria were recognized
as plant-infesting parasites, and only in extremely isolated cases
has it been placed beyond doubt that these low organisms are
the primary cause of disease in plants.*

Whereas the processes of decay, and most of the infectious
diseases of man and animals, may be traced to bacteria, the plant-
organism is protected against them by the peculiarity of its
structure, and especially by the absence of circulator}^ channels
for conducting the nutrient fluids which could serve to distribute
any lowly organisms which might happen to be present in the
food. It is only by means of the vessels and intercellular spaces
that they can distribute themselves in any great numbers in the
body of the plant, for in other cases they have to pass through
the cellulose or woody cell-walls, which offer great resistance to
their attack.

In addition to this, the vegetable juices, most of which show
an acid reaction, are unfavourable to their growth. As a matter
of fact, bacteria have hitherto been found only in the tissues
of plants whose cells are parenchymatous in character and
possessed of very delicate walls, as, for instance, bulbs and
tubers. Sorauer ^ applies the collective name bacteriosis
to diseases due to bacteria. These diseases are characterised
by the fact that the succulent parts of the infested plant are
converted into a slimy glutinous pulp, which emits a most
repulsive stench. Owing to the action of those bacteria
which have advanced more rapidly along, and spread out from,
the vessels, the delicate walls of the cells are dissolved, being
employed, along with their protoplasmic and other contents, in
nourishing and fostering the bacteria, whereas the starch is often
left intact.

The yellow "bacteriosis" of the bulbs of hyacinths {Bacterium
HyacintJii) is a common disease. Here the yellow slimy masses

1 Soxdi\\&i\ Ha?idbi/ch. 2nd Edition. Pp. 74— 112.

* [Russell has recently put together the literature on this subject in a
dissertation to the John Hopkins University, Baltimore, 1892. — Ed.]

38 DISEASES OF TREES

of bacteria, called B. HyacintJii by Wakker, occur in the vessels,
and completely decompose the surrounding tissues.

Under normal conditions the bacteria do not attack perfectly
healthy well-developed bulbs. Wounds of some kind are
necessary, which may be easily caused in transplanting the
bulbs, or the bulbs are previously attacked by filamentous fungi,
amongst which a species of HypJiojiiyces almost always accom-
panies the disease. In a damp situation the bacteria enter
the wound and cause it to putrefy.

The wet-rot or "bacteriosis " of the potato, which generally
appears as an accompaniment of the decomposition of tubers
and stalks due to Phytophthora infestans, is also a disease
produced by bacteria.*

The investigations conducted by Vuillemin a few years ago^
have shown that Finns Jiakpensis is subject to a disease induced
by bacteria which may prove fatal to the tree. The first sym-
ptoms are that the stem and branches show small outgrowths
which gradually enlarge till they embrace the whole circum-
ference, when the portion of the tree situated higher up dies and
withers. When, as is usually the case, these swellings occur on
most of the branches, the tree succumbs altogether.

The olive, also, suffers from a disease which is induced by a
species of bacterium {^Bacillus OlecB tiiberailosis)?-

Lately a disease of apple- and pear-trees has been described
by J. Burrill, of Urbana, Illinois, under the name of " blight," the
cause of which, according to this investigator, is to be ascribed
to the invasion of a bacterium. The disease appears to bear
resemblance to the tree-canker produced by Nedria ditissima;
and as, in the case of this fungus, large numbers of small
gonidia resembling bacteria arc produced in the cortex, it remains
to be seen whether this disease has not been erroneously ascribed
to a bacterium.

^ C. R. Seances. November 26th, 1888, and December 31st, 1S88.

" L. Sa.va.rts.ne, Lcs A fa/adies dc r Olivier, Coniptcs Rendus, December 6th
and 20th, 1886.

* [It is extremely probable that in these and other similar cases the
minute bacteria travel into the tissues, down the tubes of the filaments
(hyphse) of the fungus, feeding on the decomposing protoplasmic contents of
the latter. — Ed.]

INJURIES INDUCED BY PLANTS 39

MYXOMYCETES, OR SLIME-FUNGI

Amongst the Myxoniycetes, several — though the number is a
small one — live as parasites, and cause peculiar swellings to form
on the roots of their host-plants. To these belongs Plasinodio-
pliora Brassiccu} which causes '•' club-root "* in cabbages, &c. The
roots and lower parts of the stems of cabbages which are attacked
by this parasite exhibit excrescences which vary in size but are
often as large as one's fist. These soon decay, and the enfeebled
plants frequently fail to give any return. The disease is com-
bated, on the one hand, by burning the stumps of all infested
cabbages, so that the parasite is prevented from spreading in
the soil, and, on the other, by ceasing to cultivate cabbages for
some years on ground where the disease has appeared.

Alder-roots, even when very young, are generally beset with
much-branched tuberous outgrowths, in whose
cells Woronin has discovered a fungus which
he has named Schinzia Alni.

Recently Moller- has referred the plasmo-
dium-like structures which occur in the cellu-
lar tissue of the excrescences of the roots of
alders to a Myxomycete belonging to the yih. 9.— Excrescence

genus Plasvwdiop/iora, which he calls Plasmo- o" ^ ''oot of the

,• , ., ■ ;t., , , . . . , . , . , alder, due to

aiopliora Aim. vVhether this is identical with Schinzia Aim'.

ScJiinsia Alni, or distinct from though oc-
curring simultaneously with it, cannot be decided without
further investigation.

The tubercles on the roots of Leg^nninosa^ and Ela^agiie<^,
in whose parenchymatous cells plasmodium-like structures occur,
also require to be further investigated.

^ Woronin in Pringsheim's _/<?//;'/'., vol. xi. p. 54S.

2 H. Moller, "■ Plasmodiophora Alni:;' Ber. Dciitsch. hot. Cos., 1885, Pt. 3,
p. 102.

* [Often termed " Fingers and Toes " and "Anbury." — Ed.]

t [These tubercles are caused by symbiotic organisms of quite different
nature from Myxomycetes. See Phil. Trans. 1887 and Proc. Roy. Society,
1889.— Ed.]

40 DISEASES OF TREES

FUNGI

THE STRUCTURE AND LIFE-HISTORV OF FUNGI GENERALLY

Every fungus consists of a mycelium and a sporophore.
The former takes in and elaborates the nutrient materials, and
discharges all vegetative functions, whereas the sporophores
produce the organs of reproduction, which may have a sexual or
an a-sexual origin, in the latter case being produced in a vegeta-
tive manner by division and abscission, a process analogous to the
formation of buds in the higher plants. The mycelium has its
first inception in a tubular outgrowth which is produced during
the germination of a fungal cell, and which by absorbing
water, and usually food-materials as well, forms what is called
a fungal filament, germ-tube, or " Hypha." The germ-tube is
characterised by apical growth, and by the formation of lateral
branches, whereby a system of fungal tubes (hyphae) is formed
which is constantly anastomosing, and which has erroneously
been compared to a stream with its tributaries and springs.
This comparison is not apt, because fungal hyphae are almost
uniform in diameter,* there being usually but little growth
in thickness of the oldest part of a system of filamentous
mycelia.

In the case of some species, no partitions form in the fungal
filaments or hyphs, but as a rule transverse septa, \\hich divide
the internal space into chambers, are formed a short distance
behind the apex. Such a hypha is said to be " septate." When
quite young its contents consist of protoplasm, which is usually
colourless, and only at some distance from the apex does a
granular appearance manifest itself, which is generally due to
the formation of fat globules. The cells of the mycelium are
frequently filled with large drops of fat, and this is especially the
case when the mycelium assumes a condition of inactivity, in
which it remains till growth is again resumed. The potato
tuber, by storing up reserve materials (in this case chiefly
starch), which are not utilized in the formation of new

* [Nevertheless, as the author himself points out on the next page, the
hyphas developed later are often progressively finer and finer than those
first produced. This is strikingly obvious in the case of some moulds— ^.^^'.j
Mucor. — Ed.

INJURIES INDUCED BY PLANTS 41

tissues till the following year, behaves in a physiologically
similar manner. The fatty oil is not unfrequently coloured, and
especially in the case of " rusts," whose oil is of a golden yellow
colour, a yellow hue is imparted to the tissues of the leaves and
cortex in which the mycelium grows. Usually drops of cell-sap,
or so-called vacuoles, also appear at an early stage in the proto-
plasm, and these, by forcing most of the protoplasm against the
walls, impart a frothy appearance to the contents.

It is only when nitrogenous food-materials are present in
abundance that the contents of the hyphae are retained for a
long time. This occurs when mycelia vegetate in or amongst
the tissues of the cortex, bast, or leaves, which for the most
part consist of parenchymatous cells. On the other hand,
the contents disappear early when the mycelium vegetates in
tissues containing little nourishment, as is markedly the case in
the wood of trees. When the mycelium of a fungus spreads in the
interior of a tree, it finds abundance of nitrogenous food-materials
in the contents of the cells of the medullary rays and the wood-
parenchyma. It is thereby enabled to produce vigorous hx-phae,
even when traversing the empty lumina of tracheides, wood-
fibres, or vessels. When the hyphae have to pass through
regions of tissue containing no proteids, their apices are supplied
with protoplasm which is sent forward from behind at the
expense of the older parts of the hyphae. The latter are
therefore soon emptied, and become filled with air. Although
the empty mycelial hyphae persist for some time, they ultimately
disappear under the decomposing influence of the fungus itself.
The consequence is that one may frequently fail to find anything
of the fungus itself, although numerous punctures in the walls of
the cells show clearly that the fungus had formerly been present
in that part of the tissues. In proportion as the mycelium
develops in the wood, so does a dearth of proteids for the
production of new fungus-protoplasm set in, and this is
strikingly manifested in the diminished thickness of the new
hyphs;.

The walls of the hyphae, which consist of fungus-cellulose,
are at first very delicate, though in the course of time they
occasionally attain such a thickness that the lumen almost
entirely disappears. In this way it sometimes happens that a

42 DISEASES OF TREES

fungus-body which consists of these thick-walled hyphae
becomes almost as hard as stone.* On the other hand, there are
instances of the entire walls — or only their outer, less frequently
their inner parts — being converted into a mass of slime, and
under certain conditions the walls, when treated with iodine,
become as blue as starch would under similar circumstances.
This occurs, for instance, in the mycelium of Hysteriinn^ and the
apices of the asci of Rosdlinia quercina.

At first the hyphae are almost always colourless, but in later
life the walls very often assume a light or dark brown colour.
In rarer instances other colours are produced, e.g. the blue green
of Pezisa csnighwsa, which causes the so-called green-rot in
the dead wood of the oak, beech, and spruce. Sometimes the
coloration is confined to the outer or to the inner layers of the
cell-wall. The mycelium, which increases acrogenously and pro-
duces lateral branches, generally remains in a filamentous condi-
tion— that is to say, the mycelial filaments remain isolated, or, at
most, coalesce only at the points where they cross each other.

A mycelium which vegetates on the outside of leaves, fruits,
&c., as is the case for instance with the mildews {ErysipJie),
is said to be epiphytic. When it vegetates in the inside of
plants it is called endophytic. In this case it either grows
from cell to cell by piercing the walls (intracellular), or it
advances between the cells (intercellular). In the latter case
it behaves, as a rule, like most epiphytes, sending out short
branches, known as sucker-tubercles or haustoria, into the interior
of the cells, in order to extract the nutrient contents.

When the opportunity is preseated for the filamentous
mycelium to develop vigorously outside the nourishing
substratum — as happens most frequently in the case of the
wood-inhabiting Hyinciiomycetes — it forms a skin-like layer,
Avhich often attains large proportions. In other cases it may fill
cracks or other cavities in the stems of trees. Such layers,
crusts, and masses of fungal growth are best known in the case
of Polyponts sjilphnreus, P. vaporarius, P. borcalis, Hydiunii divcr-
sidens, Prametes Pini, Mernlins lacrytnans, 8zc.

* [Such indurated masses of fungus-mycelium are usually termed Sclerotia,
in reference to their hardness : they commonly serve as storehouses in the
sense indicated on p. 40. — Ed.]

INJURIES INDUCED BY PLANTS 43

Then, again, the mycelium frequently assumes the form of
branching strands, which enable the fungus to traverse strata
containing little if any nutriment. In such a case the strands
are either formed by the loose union of similar hypha^, when
they are called R/iicoctonics, or they are peculiarly constructed of
various kinds of organs. The strands of the dry-rot fungus —
AI. laoyinaus, for instance — possess, first, organs with wide
lumina and perforated transverse walls which resemble vessels ;
secondly, thin sclerenchymatous filaments ; and, thirdly, delicate
hyphas rich in protoplasm, and provided with clamp-cells. In
addition to such strands we have the so-called Rhizomorphs,
which, externally, present a close resemblance to the fibrous
roots of higher plants, while their internal structure displays
peculiarities which depend entirely upon the species of fungus
to which they belong. The best known of these are the
rhizomorphs of Agaricus melkus, which, \\-hen they have room to
develop, assume a round shape. In the cortical tissues of living
trees they spread out in a fan-like manner. Their internal
structure shows characteristic features, by which they ma\' at
once be distinguished from the rhizomorphs of other fungi, e.g.
DematopJiora nccatrix.

Functions similar to those of the tubers and rhizomes
of higher plants are to be ascribed to the so-called sclerotia.
These are peculiarly constructed masses of mycelium, in which
rich stores of nutriment, especially protoplasm and oil, are
deposited. After remaining quiescent, it may be for a long
time, they germinate on the recurrence of favourable conditions,
and produce either a new filamentous mycelium or the
sporophore of the special fungus.

The simplest form of such resting-mycelia is represented
by the cell-groups of Cercospora acerina. Then come the
sclerotia of Rosellinia giiercina, and the well-known sclerotia of
Claviceps purptirea."^

The sporophores which spring from the mycelium bear the
organs of reproduction — that is to say, the spores which give rise
to new individuals. The same species of fungus frequently
produces different kinds of reproductive organs, which develop

* [Rhizomorphs are also, in a sense, extended Sclerotia — see also pp. 40
and 41. — Ed.]

44 DISEASES OF TREES

on or in variously shaped sporophores. The shape of the
sporophore is much more characteristic of the species than the
mycelium, and as the sporophore (which often grows to a large
size) is almost alwaj's outside the nutrient substratum, whereas
the mycelium is hidden in it, the uninitiated often regard the
sporophore as the whole fungus, and pa\- little or no attention
to the mycelium.

When the sporophore consists only of single filaments
springing from the mycelium, it is called a simple or filamentous
sporophore, whereas the compound fungus-body goes by the
name of a compound sporophore. On account of the great
variety in shape and structure exhibited b}' the sporophore, it
would be going beyond our limits were we to consider it more
closely at this time.* Cells which are called spores are separated
off in some way or other in or on the sporophore, and these by
germinating give rise to new individuals. The cells, from which
spores directly originate, are known as sporogenous cells. The
spores are produced either internally, as in the case of the
sporangia of the Phycoviycctes, and the pouches or asci of the
Ascoviycetes, or by apical abscission, in which case the mother-
cell is often called a basidium.

In the case of some groups of fungi, sexual processes have
been proved to exist. "f* The course of development, as in other
plants, has been divided into two sections (generations), of which
the one called the a-sexual generation begins with the germi-
nation of a sexually fertilized cell, and leads to the production
of spores (oospores ; zygospores). The germination of these
spores gives rise to the second generation, which, in form and
development, is essentially different from the a-sexual plant. It
ends with the formation of the male and female sexual
apparatus and sexual cells, and on this account is called the
se.xual generation. Spores which do not mark the close of the
a-sexual generation, but which, like buds, brood-cells, and other

*[The student may be referred to the works of De Bary, Zopf, and Von
Tavel for details. — Ed.]

t [Such a book as this is, of course, not concerned with the morphological
details of this difficult and involved matter, and the student is referred to the
works of Tulasne, De Bary, Zopf, and Brefeld for particulars of the subject.
The outcome of recent researches is to show that sexuality has disappeared
in the case of most fungi. — Ed.]

INJURIES INDUCED BY PLANTS 45

organs of vegetative propagation, produce the same plant-form
as that from which the)' themselves sprung, are called gonidia.
Following the example of De Bar}-, this term may be taken to
replace that of conidia, introduced b\' Fries.

The gonidia serve chiefly for the rapid propagation of
fungi during the growing season, whereas, in general, the
sexual spores serve to carry the species over from one year
to another.

I may here briefly sketch the mode and conditions of life
of the fungi. Just as in the case of phanerogams the ger-
mination of seeds, and the length of time during which they
will retain their vitality, are much influenced by external
factors, so in the case of spores and gonidia the power to
germinate— varj-ing with the different species — appears either
immediate!}' after ripening, or not till after the lapse of a long
period of rest.

On the other hand, in the case, for instance, of the gonidia of
the rust-fungi, the power to germinate is lost a few days after
ripening, whereas the oospores of '<Phytophtliora omnivora may
remain dormant in the ground for at least four years, without
losing their vitalit)'.

The demands as to heat are not so great as in the case of the
higher plants, and thus it is that we see the most luxuriant
fungus-vegetation in autumn, at a time when the growth of trees
has ceased. The optimum temperature for fungi, as for other
plants, varies ver}' much, but in this connection we still await the
results of reliable investigations. In the case of those fungi
which concern us here a temperature over 212° F. (100° C.) is
undoubtedl}' alwa)'S fatal.

One vital condition, of extreme importance for fungi, is a high
degree of humidity of the air or of the substratum in which they
develop. This is due not only to their requiring large quantities
of water, but also, and much more, to the ease with which the
mycelia or young sporophorcs die in a dry medium from the
effects of excessive evaporation. On this account it is very
seldom possible for the mycelium to develop in the open air.
It is for this reason also that in all the rusts and smuts, and even in
the case of a great number of Disconiycctes, the sporophores —
which usuall)' require to scatter their spores outside the plant —

46 DISEASES OF TREES

are formed under the protection of the epidermis of the host-
plant, which is ruptured only after the spores have ripened.

The fact that in summer, in spite of a more favourable
temperature, far fewer so-called " Toad-stools " spring from the
ground than in October, when the atmosphere is relatively much
more humid, shows clearly how dependent on a constant supply
of moisture in the air is the development of sporophores that
expand entirely outside the substratum.* The extensive
distribution which the larch-fungus, Peziza Willkoinmii, has
experienced in the plains of Germany is almost entirely due to
the abundant production of fructifications and spores which have
ripened perfectly in the moist, stagnant air of the dense low-
lying woods ; whereas in the breezy Alps the fructifications
almost always wither before they have had time to mature.

Not only does a moist atmosphere affect the ripening of the
fructifications and the germination of the spores outside the
plant, but it also appears to have great influence on the develop-
ment of the fungus even inside the plant. This assumption is at
least supported by the fact that Caoina pinitorqnmn, which is a
perennial in the shoots of the pine, assumes the proportions of a
plague when the month of June is wet, but causes scarcel}- any
appreciable damage when the weather is dry.

As regards their adaptations for nutrition, fungi ma\- be
arranged in two great divisions. Parasite is the term applied
to those fungi which draw their nourishment from living
organisms ; saprophyte, to those which live on dead bodies. It
is not possible, however, to draw a sharp line of demarcation
between these two categories. To begin with, it may often
be disputed whether an organic body is to be called dead
or living. By far the greater part of the wood of trees is made
up of dead cells, the walls of which alone remain ; and only
a relatively small part, consisting of the parenchymatous cells
of the wood and medullary rays, remains alive and contains
protoplasm. Seeing that many fungi live only on the old
stumps of trees and on trees that have long been felled or
otherwise killed, whereas others destroy growing trees, it would

*[The whole subject needs thorough investigation, however, and it would
be particularly valuable to have more information as to the importance of
sunlight and other factors in this connection. — Ed.]

INJURIES INDUCED BY PLANTS 47

appear to be necessary that we should regard the sound wood of
a growing tree as being aHve, even although only a portion of its
cells may exhibit the phenomena of life.* In man}- cases it is
difficult to decide whether wood — e.g. the duramen in many trees
— was actually living when attacked by the fungus-mycelium,
or whether its parenchymatous cells were then dead. But apart
from those doubtful cases, in which it is difficult to decide at
once whether a fungus is existing as a parasite or as a sapro-
phyte, there are many fungi which occupy a position somewhere
between those which are strictly saprophytic and those which are
strictly parasitic. Numerous fungi are in a position to complete
the whole course of their development as saprophytes, though,
under certain circumstances, they may also live in a purely
parasitic manner. Agariciis vielleiis and the genus Xectria may
serve as examples. Such fungi are designated facultative
parasites. Other fungi, which, as a rule, go through the whole
course of their development as parasites, but which arc capable
of growing as saprophytes, at least during certain stages of their
existence, are designated facultative saprophytes. To this group
belong, for instance, PJiytopJithora ovinivora and Ccrcospora
acerina. We have thus to distinguish four groups : i. Obligate
saprophytes. 2. Facultative parasites. 3. Facultative sapro-
phytes. 4. Pure — that is to sa}', stricth' obligate — parasites^
which can only grow parasitically, e.g. the group Uredinecc.

The spread of an infectious disease may take place in two
distinct ways, either by infection caused b\- the m\'celium, or
by infection caused by the spores, including the gonidia.

Infection by the mycelium is met with in nature most frequentl}-
in the case of those parasites which grow below ground. This is
to be explained by the fact that the varying amount of moisture
in the air admits of the development of the mycelium above-
ground only in exceptional cases, as, for example, in HerpotricJiia
and TricJiospIuvria.

In the case of infection by the mycelium, it is, to a certain ex-
tent, the same individual fungus that spreads from root to root and

* [In many such cases the destructive fungus may be looked upon as a
Saprophyte, when viewed with regard to the immediate seat of its action —
e.g., wood— but as 2l parasite with regard to the tree as a whole, whose life is
destroyed in consequence of the secondary results of the damage. — Ed.]

48 DISEASES OF TREES

from branch to branch. Thus, when a disease spreads in a wood
in this way, it does so with relative slowness, but, in dense woods
at least, it is, as a rule, characterised by the death of all or most
of the trees inside the local area of distribution. The result is
that blanks, varying in size, gradually occur in the wood.

In the case of Trmnetcs radicipcyda,\\\& most dangerous enemy
of spruce and pine plantations, contact of the diseased root
containing the fungus with the sound root of a neighbouring tree
is necessary in order that the latter may be penetrated by the
mycelium which protrudes from between the bark-scales. In the
case of Agaricus inelleus mycelial strands, in the form of rhizo-
morphs, spring from the diseased roots, and proceed to spread
underneath the surface of the ground. The roots of sound
conifers that are encountered are embraced, and an entrance is
effected between the bark-scales : these are forced off b}- means
of the conical apices of the rhizomorphs, which then bore into
the living tissues.

In the case of Rosellinia qiiercina, which destroys the roots of
the oak, the delicate filiform mycelium — which here and there
forms rhizoctones — spreads during moist warm weather from the
diseased plant into the upper layers of the soil, where it attacks
and destroys the roots of neighbouring plants in a manner which
will be described more fully later on. On account of the
mycelium being capable of forming small round sclerotia on oak-
roots, and of assuming a resting condition, the parasite is after-
wards enabled to resume the growth which has been interrupted
by such unfavourable conditions as cold or a temporary lack of
moisture in the soil.

Deinatophora necatrix spreads in a similar manner in vine-
yards.

The distribution of a parasite by spores and gonidia is not, as
in the case of infection by the mycelium, confined to plants in the
immediate neighbourhood, although these are certainly most
exposed to the danger of infection. It may, in fact, happen
that trees at a great distance are infected, while those in the
immediate neighbourhood remain sound. When treating of
special cases we shall have occasion to bring into prominence
how various are the conditions that influence this question, and,
in particular, how animals and men, by spreading the spores, may

INJURIES INDUCED BY PLANTS 49

induce the outbreak of an epidemic. Here a few examples may
be cited in illustration of this point.

PhytophtJiora oiiuiivora produces spores (in this case called
oospores) in the interior of the seedling, as the result of sexual
fertilization. When the plants decay, these spores get into the
ground, where they may rest for a series of years and produce
the disease afresh, should the right kind of seedlings be present.
But, in addition to these oospores, the parasite produces numerous
gonidia on the surface of its leaves. These are capable of
germinating at once, and are blown by the wind, or conveyed by
animals or men, to plants in the neighbourhood, the result being
the formation of new hotbeds of infection.

In the case of Tranietes radicip:rda, which, on the spruce at
least, almost always produces its sporophores in holes in the
ground, new centres of infection are usually established by spores
that have been distributed by mice.

The smut of wheat is generally induced by employing seed to
the outside of which spores of the smut-fungus have adhered^
but it may also be caused by manuring with fold dung if infected
straw has been used as litter.

The conditions become most interesting in the case of heter-
cecious rust-fungi — that is to say, parasitic fungi which complete
the various phases of their development not on the same plant
but on two different species. Here mention need only be made
of the connection between the fungus of the barberry and rust of
wheat, or between /Ecidiiun abietimun and Chrysouiyxa RJiodo-
dendri and Chrysoniyxa Ledi, or, finally, between ^Ecidiuvi
colinnnare and MelaJiipsora Goeppertiana. In the case of these
parasites the occurrence of the disease depends on the presence
of both host-plants : still De Bary has demonstrated that in cases
of necessity Chrysoniyxa Rhododendri may exist without spruces,
and it appears to me to be beyond doubt that Melampsora
Goeppertiana is able to develop without the silver fir. We know
only one or other of the stages of development of a series of
rust-fungi, and it remains to be determined what the other fungus-
forms are with which they stand in relationship.

The method of attack of parasites, also, reveals the most
marked differences. Whereas the epiphytes — whose mycelium
vegetates externally on the epidermis of leaves, fruits, and stems
— send only delicate absorbing organs into the interior of the

E

50 DISEASES OF TREES

epidermis, the endophytes must send either their germ-tubes,
arising from spores germinating externally, or else their mycelia
into the interior of the plant.

According to the mode of attack, we may divide parasites
into two main groups. The first comprises those which have the
power to attack uninjured plants ; the second, those which can
effect an entrance only through a wound. It is those belonging
to the latter group which are accountable for infectious w^ound-
diseases. The former are partly confined to the very early stages
of development of the plant, or of the shoots, leaves, or roots ; in
rarer instances they also force their germ-tube into the stomata
and lenticels of more mature leaves and shoots. It is only when
the mycelial growths are very vigorous, like those of Agariais
vielleiis and Tramctes radiciperda, that they are able, b>' entering
between the bark-scales of the root and forcing them apart, to
bore even into cortical tissues covered with corky layers.

The mode of attack of Rosellinia quercina affords one of the
most interesting examples of this kind. The main root of the
young oak is protected against external attack by a corky mantle
of considerable firmness. The mycelium of Rosellinia is con-
sequently able to get at the interior only by first killing the fine
lateral roots, and as these traverse the corky la}^er the hyphae
form breaches in the protective covering. At the points where
the lateral roots pierce the cork)- mantle the mycelium develops
flesh}- tubercles, which then send one or more processes through
the breach into the interior of the root. It is only some time
afterwards that the destructive filiform mycelium is formed at
the apex of these processes.

Wounds admitting of the entrance of parasites into the interior
of trees arise in many wa}-s. Reference need only be made here
to such agencies as animals, man, hail, wind, snow, &c.

The effects produced b}' parasites on the tissues of the host-
plant can be explained only by assuming that in each species of
fungus a peculiar enzyme (ferment) is produced in its protoplasm,
which by being excreted through the h\'phai is communicated
to the adjoining cells.*

Ver)- often the m}-celium \egetates in living parenchj-matous

* [That such enzymes are really formed and excreted by the protoplasm has
been proved. For instance, Botrytis excretes an enzyme capable of dis-
solving cellulose— see Aitnals of Botany, 1888, "A Lily-disease." — Ed.]

INJURIES INDUCED BY PLANTS 51

tissues without producing any appreciable effect on them.
Especially is this the case when the cells have already attained
the condition of permanent tissue before the mycelium has
appeared in or between them.

The mycelium of Calyptospora has no apparent action on the
permanent tissues of Vaccinuim Vitis-IdcBa ; whereas, in v^xy
)'oung shoots, it causes enlargement of the parenchymatous cells
of the cortex, with the result that very remarkable swellings are
produced on the stem.

One of the most frequent results of the action of fungi is that
a stimulus is given to cell-division. Mention may be made of
the swellings on the stems of silver firs whose cortical tissues are
infested by ^cidhim elatimim, of the swellings on the stems of
junipers owing to Gymnosporanghun, &c. Still more frequently
the infested parts are stimulated to display altogether abnormal
growth. Flowers, fruits, and portions of stem of various species
of plants are transformed in a most peculiar manner by fungi
belonging to the genus Exoascus. It does not necessarily follow,
however, that their vitality is thereby prejudicially interfered
with {e.g. witches' brooms of the hornbeam, &c.)

Changes in the cell-contents are often noticed which are
indirectly induced by fungi. This is the case, for instance
when the mycelium of Hysterium inacvosponini kills the elements
of the bast at the base of spruce-leaves, thereby destroying
their capacity of conducting plastic materials, while the other
parts of the leaves still live and assimilate. The result is that on
account of the newly formed carbo-hydrates not being able to
get away from the leaf, all the cells become packed full of starch.

The tannin which is dissolved in the cell-sap offers excellent
food for the mycelium of Polyponis igniariiis, being absorbed first
of all by the hyphae which penetrate the sound oak-wood, after
which it undergoes metabolic changes in the youngest parts of
the mycelium. The occurrence of mycelia in oak-timber is there-
fore followed by the disappearance of tannin, the smell of which
has long been regarded by practical men as a proof of the sound
condition of the wood. The conversion of a portion of the cell-
contents or of the cell-walls into turpentine under the action of
the hyphae of Peridermiinn Pint is also interesting. Although
it often happens that the starch-grains disappear very soon from

E 2

52 DISEASES OF TREES

amongst the cell-contents, as, for instance, in the case of attack
by Phytophthora omnivora, it also not unfrequently occurs that
starch resists the destructive influence of wood-parasites longer
than the thick lignified walls of the cells in which it is contained.
In fact the manner of decomposition of the starch-grains varies
exceedingly according to the species of fungus that attacks them.
Similarly as regards the cell-walls. The solvent action of living
hyphae is manifested in two distinct ways. Where a hypha
touches a cell-wall it dissolves the particles of calcium oxalate
contained therein, exactly as a root-hair, by means of the
acid solution which it exudes, dissolves the particles of cal-
cium carbonate with which it comes into immediate contact.
This action is confined to the surface of the cell-wall which is
actually in contact with the fungus-filament. But every para-
sitic fungus that lives in the wood of growing trees destroys
the wood in a manner peculiar to itself When one and
the same species of fungus, e.g. Polyponis siilpJmreiis, vegetates
in trees of such different species as oak, willow, and larch, it
changes the wood so peculiarly in a short time that at first
sight it is difficult to distinguish these timbers from each other,
although, in a sound state, they are so strikingly different. This
can be satisfactorily accounted for only by assuming that each
species of fungus exudes an extremely powerful and charac-
teristic ferment, which permeates the walls for long distances, and,
to begin with, frequently dissolves only the incrusting substances,
more especially the lignin.

In the accompanying figure (lo) the upper part of the wall is still
lignified, whereas the lower part consists of pure cellulose. After
the removal of the lignin the middle lamella, which is most ligni-
fied, is the first to disappear, the result being that the various
organs become completely isolated, as happens when sound wood
is treated with potassium chlorate and nitric acid. The hyphee
which pierce the walls with their apices disappear later on, when
they themselves are dissolved by the ferment. In Fig. ii is
shown how the elements of the wood of the oak have been com-
pletely isolated and dissolved by the action of a ferment.

In the case of other wood-parasites the decomposition takes
place in the following manner. By the extraction of the incrust-
ing substances a zone bordering the lumen is first converted into

INJURIES INDUCED BY PLANTS

cellulose, after which decomposition spreads generally through-
out the walls. Thus the walls constantl)' become thinner, till
finally onl\- the corners remain where three tracheids join (Fig.
12). Several wood-parasites, e.^: Polypoms
Schiveinitzii -BiXxA P.sulphureus, induce a form
of decomposition owing to which the walls,
with the exception of the middle lamellae,
shrink so much as to give rise to numerous
cracks which ascend from right to left. By
certain adjustments of the microscope we of
course see simultaneously the correspond-
ing cracks in that half of the wall
which belongs to the neighbouring fibre,
and this makes it appear as though the
cracks crossed each other. The walls,
which are very rich in carbon, assume a
brown colour (Fig. 13). We shall direct
attention in the special division dealing
with this subject to other forms of decom-
position, all of which are characteristic for
some species of fungus. Here it need only
be mentioned that the question whether all
the organic parts of the lignified cell-walls
require to be absorbed by the mycelium
of the fungus before being decomposed
into carbonic acid and water, or whether
to some extent they are directly oxidized
and converted into these substances, can-
not at present be finally decided. As a
large quantity of oxygen must be made
use of during decomposition, its rapidity
depends to a great extent on the facilities
that are afforded for the entrance of air
to the interior of the tree. A certain
amount of air is present in every wood}'

fibre. In dicotyledonous trees the air is conducted to distant parts
by means of the vessels and intercellular spaces, and in resinous
conifers by the resin-ducts ; but in the case of the silver fir
and other conifers destitute of resin-ducts the mode by which

Fig. 10. — Tracheid of
Finns sylvestris, de-
composed by Tranietes
Pini. The primary
cell-wall has been com-
pletely dissolved as far
as a a. In the lower
part the secondary and
tertiary layers consist
only of cellulose, in
which lime - granules
are distinctly visible,
h : filamentous my-
celia, c, penetrate the
walls and make holes
as at d and e.

54

DISEASES OF TREES

the entrance of air to the interior of the tree is ensured has yet
to be explained. The carbonic acid . which is formed can
escape by the same way as the oxygen entered. To what
extent carbonic acid and oxygen when dissolved in water may
traverse the wood remains to be determined.

Fig. II. — Decomposition of oak by Tlie'ephora Ferdix. a, tracheids containing a
few filamentous mycelia,and showing the perforations in the walls which these have
occasioned ; b, wood-parenchyma wiih starch-granules, the latter being in process
of solution, and having to a certain extent disappeared from the neighbourhood
of the cell-walls; <:, vessels containing hyphre ; d, sclerenchymatous fibres show-
ing filamentous mycelia and perforations ; e and /, tracheids which are com-
pletely isolated owing to the dissolution of the primary cell-walls ; the thickened
rings of the bordered pits are also found isolated between the tracheids. On
account of the organs being dismembered the openings into the bordered pits no
longer cross each other ; g, wood-parenchyma, completely dismembered and
almost entirely dissolved ; h, tracheid just before final disappearance ; /, scleren-
chymatous fibre much decomposed ; k, a tracheid whose walls have become
fissured before being dissolved.

In concluding these general considerations, I have still to
discuss the question whether any — and, if so, what — means are
at our disposal for combating the ravages of fungi. I am
convinced that every forester who has received a scientific
education will take a deep interest in obtaining a knowledge of
what tree-diseases are, and how they originate, even though it

INJURIES INDUCED BY PLANTS

55

may not be possible to apply any practical remedies. It is by
no means the first duty of science to call attention to the
practical value of a new discovery ; nor should research be
primarily directed to those fields which promise to yield results

Fig. 12. — Decomjjosition of spruce-timber by Polyporus horealis. a, a tracheid con-
taining a strong mycelial growth and a brownish yellow fluid which has originated
in a medullary ray ; at b and c the mycelium is still brownish in colour and
very vigorous. At d and c the walls have already become much attenuated
and perforated ; here the mycelium has been less abundantly supplied with nutri-
ment and the filaments are very delicate ; at /' the pits are almost completely
destroyed ; at g and h only fragments of the walls remain. The various stages in
the destruction of the bordered pits are to be followed from / to r ; at i the
bordered pit is still intact ; at k the walls of the lenticular space have been largely
dissolved, their inner boundary being marked by a circle ; at / one side of the
bordered pit has been entirely dissolved ; at in and n one sees a series of pits
which have retained a much-attenuated wall on one side only — namely, on that
which is provided with the closing membrane. In making the section a crack
has been formed in this wall. Between o and r both walls of the pits are found
to be wholly or partially dissolved, only at / and q has the thickened portion of
the closing membrane been preserved ; at J the spiral structure of both cell-walls
is distinctly recognizable. These walls when united form the common wall of
the tracheid ; at / hyphce are seen traversing the tracheids horizontally.

capable of immediate conversion into hard cash. The duty
of science is nobler and higher than that. But if, in our
search, we succeed in fathoming the mysteries of nature, and,
at the same time, obtain results of practical value to humanity.

56

DISEASES OF TREES

then it is our duty to direct attention to these. This I have
never neglected to do, and, although I do not under-estimate the
many difficulties which foresters will long have to encounter
in endeavouring to put into practice the
p results of scientific investigation, still I hold

that, as the guardians of the forest, it is their
duty to make themselves acquainted with the
results of scientific investigation, and care-
fully to watch over the health of what is
committed to their charge. Not only must
they do everything that may prevent disease^
but they must also instantly adopt energetic
measures to nip an existing disease in the
bud, and so prevent its further spread.

As every disease must necessarily be treated
differently, this is not the place to enter on
the consideration of specific measures. But
just as human health is better maintained by
the observance of certain general laws, so
there are also general rules for the treatment
of woods, by following which we may pre-
serve the health of the trees.

The best prophylactic measure against the
occurrence and spread of an epidemic is
the formation of mixed woods. Infection,
walls consisting ^^j-j^ y^^^^^^ ^^^ ^^^^^.^ gj-Qund, is least likely

chiefly of lignin. ° ' -'

Fig. 13. — Portion
of a tracheid of
J'iiiiis decomposed
1) y P 0 I y p 0 rii s
Schu'cinitzii. Most
of the cellulose has
been extracted, the

to occur when every tree is isolated by being
surrounded by others of a different species-
On ground which is infested by root-parasites,
or which contains resting-spores whose vitality
is preserved for many years, it may be advis-
able, under certain circumstances, to abandon
the cultivation of some particular species of
tree. One should also try to prevent the
distribution of spores either by men or

animals, and especially so in the sale and purchase of young

trees.

In the case of root-parasites, the therapeutic measures to

be adopted when a disease has broken out consist partly in

In drying, cracks
have been formed,
which however do
not extend to the
primary wall, a b.
These cracks are
seen to cross each
other at the bor-
dered pit (•, and at
the perforations d
and t' ; a simple fis-
sure is shown at f.

INJURIES INDUCED BY PLANTS 57

promptly pulling up or otherwise eradicating the diseased plants,
and partly in isolating the infected area by means of narrow
trenches. As a general and most important measure, it is
advisable at once to remove from the wood all plants attacked
by fungi, so that their spores may not spread infection. Tidiness
is the first hygienic law in sylviculture.

Having noted above the more important points that should be
kept in view in studying the parasitic fungi, I shall now, in
accordance with the plan of this work, pass on to a systematic
examination of the parasites that occur in woody plants.
As regards fungi that are parasitic on farm or garden crops, I
shall shortly refer only to such as are of general practical
importance. For plant-parasites not included in this work I
must refer to the handbooks of Frank or Sorauer.

Following the most recent classification of the fungi, which
distinguishes three groups — namely, PJiycoviycetes (Algal fungi),
Ascoinycetes, and Basidiomycetes — I shall begin with the first
group. This embraces five orders — namely. Zygomycetes,
EiitomophthorecE, Saprolegiacece^ PeronosporecB ChytridiacecE, and
Ustilaginea;*

Of these orders there are only two that need be considered
here.

PERONOSPORE^

The PeronosporecE are true vegetable parasites, whose mycelium
ramifies in the tissues of higher plants, the hyphae being for the
most part intercellular, though occasionally also intracellular.
Special absorbing organs (haustoria) are employed for abstracting
the nutriment from the living cells, which consequently die after
a shorter or longer period. The sporophores which spring from
the mycelium either grow through the stomata or burst through
the epidermis. These in various ways form sporangia, which
produce gonidia, often motile.

Having moved about for some time in a drop of water as
swarm-spores, the gonidia develop a germ-tube, though the
sporangia may also germinate directly without having first
produced swarm-cells in their interior.

* [For details as to the classification of fungi the reader may be referred
to the text-books of De Bary, Zopf, and Von Tavel. — Ed.]

58 DISEASES OF TREES

In the tissues of the host-plant, though occasionally outside
of it, female sexual organs (oogonia) originate on the mycelium,
and during fertilization the male sexual organs, called pol-
linodia or antheridial branches, are brought into contact with
these oogonia. The antheridia send a minute process (the fer-
tilizing-tube) into the interior of the oogonium, which is fer-
tilized by its protoplasm receiving a small portion of the con-
tents of the antheridium. This gives rise to the formation of
the egg-spore (oospore), which is provided with a thick cell-wall.

While the gonidia, being easily detached and carried by
wind or animals, provide for the rapid distribution of the
parasite during summer, the oospores reach the ground in
the dead and decaying parts of plants. There they pass the
winter — indeed, in such a position they may remain alive for a
number of years — after which they either germinate directly, or
first of all produce sporangia with zoogonidia.*

PHYTOPflTHORA OMNIVORA (SYN., PHYTOPHTHORA FAGI,
AND PERONOSPORA SEMPERVIVl).^

The disease caused by this parasite was noticed in forestal
publications over a hundred years ago as " the disease of seedling
beeches," and cannot be unknown to any forester employed in
beech woods. When seedlings are abundant after a rich seed-
year the disease is to be met with over the whole of Germany,
and the more plentifully the wetter the months of May and June.
The fungus also attacks other broad-leafed trees, e.g. Acer,
Fraxinus, Robinia, as also herbaceous plants such as Fagopymm,
Clarkia, Scnipej'vivuin, &c. The parasite is equally widely dis-

' 1 described this parasite in 1875 in the Zeitschrift fiir Forst- uini Jagd-
wesen, pp. 117 — 123, under the name of P. fagi. A detailed account of the
history of its development, and of the disease to which it gives rise, along
with a plate, was contributed by me to the Unteisuchimgen cms dein forst-
hotanischcn InstHut, 1880, pp. 3 — 57. In 1875 — that isto say, simultaneously
with me — Schenk described this fungus under the name of P. sempervivi.
In order to settle the question of priority De Bary selected the name
Phytcphthora omnivora {Beit rage zur Morpli. und Phys. der Pilze, 1881,
p. 22).

* [For an account of the Phycomycetes peculiar to Britain the reader
may be referred to Massee's British Fungi (Reeve & Co., 1891). — Ed.]

INJURIES INDUCED BY PLANTS

59

tributed in the seed-beds of conifers, where it may be met with
on the seedlings of every species.

The disease may attack seedling beeches before they have
reached the surface of the ground, in which case a dark
discoloration spreads from the primary rootlet, and the plants
die off. Or, not till the
cotyledons have unfolded
does the stem above and be-
low them, or at their base,
become dark green and change
colour (Fig. 14, a,b) ; or simi-
lar spots may be recognized on
the cotyledons (Fig. 14, c), or
on the primary leaves (Fig.
14, d). Should the weather
remain long wet, decomposi-
tion quickly spreads over the
w^hole plant, while during dry
weather the plants wither and
assume a reddish brown and
scorched appearance. Young
sycamores, ashes, and robinias
show similar pathological
symptoms, and, in particular,
very black streaks will fre-
quently be found running up
or down the stem from the
base of the cotyledons. Fre-
quently it is only the apex of
the stem and the leaves that
become black, in which case
the plant recovers ; but if, on
the other hand, the lower part

of the stem is attacked, recovery is impossible. Where the seeds
of conifers are sown in rows, it is not unusual for a large number
of the plants to perish before they have appeared above the
surface of the ground. The roots and stem.s usually decay,
and the young plants die or wither without any mechanical
injuries being observable. It is worthy of note that, owing

Fig. 14. — Diseased seedling beech. Stem
below the cotyledons dark green at a ;
cotyledons diseased at b and c ; first
foliar leaves showing blotches as at d.

-60

DISEASES OF TREES

to the death and disappearance of the whole of the seedhngs
at certain places, blanks four inches and more in length may
be formed in the seed-drills.

The infectious character of the disease may be gathered
from the peculiar way in which it is distributed. A diseased

plant soon becomes surrounded
by diseased neighbours, and thus
the epidemic spreads centrifu-
gally in beds that have been sown
broadcast, and in two directions
where the seed has been drilled.
Should a frequented footpath lead
through a beech wood that is being
regenerated b}' seed, all the plants
growing on the path and along
the sides contract the disease and
die in a short time. It has also
been observed that if the disease
has once appeared in seed-beds it
usually recurs in succeeding years
in a much-accentuated form. The
disease is known to be greatl}'
favoured by rainy weather — espe-
cially if accompanied by heat — and
by any kind of shading, whether
produced by standard trees or b)"
artificial covering. The first ap-
pearance of the disease in any year
can only be due to the oospores
of the parasite, which lie dormant
in the soil during winter, and
infect the germinating seedlings in
spring. The mycelium spreads in
the tissues of the seedling, and,
in the case of the beech, both in the stem and in the cotyledons,
the latter being probably attacked as they are being pushed up
through the ground. In the tissues of the cotyledons the mycelium
is almost entirely intercellular (Fig. 15, b), withdrawing the
nourishment from the interior of the cells by means of small

Fig. 15. — Cellular tissue from the
cotyledon of a diseased beech.
The starch-grains have been ab-
stracted from the protoplasm
which has withdrawn from the
cell-walls, a ; the mycelial fila-
ments, which are of varying
thickness, h b, giow intercellu-
larly, and are provided with
minute haustoria ; each fertilized
oogonium contains an oospore, <(■.

INJURIES INDUCED BY PLANTS

6r

roundish haustoria. The consequence is that the starch-
grains soon disappear, and the protoplasm dies and contracts
from the cell-walls (Fig. 15, a). While the fungus continues to
spread in the plant, numerous hyph« break through the epidermis
to become sporangiophores (Fig. 16). The swelling of the ex-
tremity (Fig. 16,/) gives
rise to a lemon-shaped
sporangium, which is pro-
vided with a papilla at the
apex, and a short pedicel
at the base (Fig. 16, g).
After its abscission from
the stalk the latter elon-
gates afresh to produce a
second sporangium (Fig.
16, g,h), and meanwhile
the first generally drops
off (Fig. 16, i). Should
the sporangia come into
contact with water — as, for
instance, a drop of rain
or dew which has lodged
about the cotyledons —
they germinate directly,
putting forth one or more
germ-tubes, which gener-
ally proceed to bore into
the epidermis of the host-
plant. In other cases the
protoplasmic contents of
the sporangium form a
large numberof extremely

minute and very active gonidia (swarm-spores, or zoospores —
Fig. 17, c), which are capable of free movement after the apex
of the sporangium has been dissolved. For some hours these
swim about in a drop of rain with all the activity of infusoria,
until they settle on the epidermis of the host-plant, when they
germ.inate with one or even four tubes (Fig. 17, a, b). Some-
times the zoospores germinate in the interior of the sporangium

Fig. 16. — Epidermis of a diseased cotyledon
of the beech, a, the external wall of an
epidermal cell ; b, the cuticle ; c, a hypha
which has intruded itself between the wall
and the cuticle ; at of it pushes up the latter ;
at e it appears on the surface, and at /' it
forms a sporangiophore. After producing
the first sporangium it branches at g, to
form a second //, while the first drops off
at i ; a stoma is shown at k from which
sporangiophores project.

62

DISEASES OF TREES

when their germ-tubes may either break through the lateral
walls or push out through the open apex of the sporangium
(Fig. 17, c). In either case the germ-tubes creep about for
some time on the epidermis of the host-plant, after which they
force their way into the interior, and especially at those places

where the lateral walls of
the epidermal cells arc
situated (Fig. 17, ^, d).
Less frequently the germ-
tubes reach the interior by
first traversing an epi-
dermal cell (Fig. 17, e).
Under favourable circum-
stances the development
of the parasite may have
progressed so rapidly in
the plant that three or four
days after infection new
sporangiophores may
make their appearance.

The sporangia, and the
swarm-cells that form in
them, serve to spread the
disease during the months
of May, June, and the
earlier part of July. They
either fall directly on to
neighbouring plants, or
are carried by the wind.
Their distribution is great-
ly assisted by animals —
as, for instance, by mice
(in the seed-beds) — and game, but most of all b}' man. The death
of all plants along a path is the result of the sporangia and
swarm-cells adhering to the trousers or coats of passers-by, and
afterwards dropping off farther along the path.

From what has been said, the favouring influence of rain, shade,
&c., is sufficiently evident. In dense seed-beds the hyphae grow
directly from one plant to another, and this offers a simple

I'lG. 17. — The surface of the stem of a seedling
beech. At a d zoospores are seen which
germinate and send their germ-tubes into
the interior at a point where the common
wall of two epidermal cells abuts on the sur-
face ; c, a sporangium whose zoospores have
germinated, d/, in its interior ; at t' a germ-
tube has grown directly into an epidermal
cell ; at ^t; a germ-tube has reappeared on
the surface.

INJURIES INDUCED BY PLANTS 63

explanation for the total destruction of all the plants at certain
parts of the bed.

As the result of the sexual act the oospores originate in the
tissues of the host-plant in the following manner. In the inter-
cellular spaces of the leaf-parench)'ma of the beech, globular
swellings appear at the apex of numerous short hyphal branches,
and become oogonia ; while smaller so-called antheridia originate
in like manner either at the apex of special hyphae, or on the basal
portion of the stalk of the oogonia. In each case a transverse
septum delimits the organ from its stalk (Fig. 15, c c). The
antheridium having very early laid itself against the outer wall
of the oogonium, and the most of the protoplasm of the latter
having become aggregated to form an oosphere, the antheridium
next develops a short process, the fertilizing-tube, which it pushes
into the interior of the female organ as far as the oosphere. A
part of the contents of the antheridium is then transferred to fer-
tilize the oosphere, which is thereby converted into an oospore.

In the roots of conifer seedlings oospores are formed not only
in the cortical parenchyma but also in the interior of the tracheides,
when, in consequence of the restricted space, they frequently
assume an elongated form.

The oospores reach the ground in the decomposing parts of
plants, and there they may remain capable of germinating for at
least four years. Some soil taken from a diseased beech seed-
bed in 1875, having been distributed in water and poured
upon a bed of seedling beeches, caused disease and death of the
germinating plants not only in 1876 but also in 1878, and even
in 1879.

The practical measures at our command for combating the
disease follow from what has been said. In order to guard
against the outbreak of an epidemic, we must avoid sowing seeds
on ground where the disease has once proved destructive, though
we may cultivate transplants on it. The oospores that remain
in the ground will prove destructive only to seedlings. Should
the disease appear in a seed-bed, all contrivances for producing
artificial shading must be removed, as they prevent the rapid
evaporation of water from the surface of the cotyledons. All
dead and visibly diseased plants should be removed. If a
number stand close together, the distribution of the sporangia and

64 DISEASES OF TREES

gonidla may be most quickly prevented b}' heaping on earth. If
the diseased plants occur singly they should be carefully pulled
out and buried in a firmly trodden trench, in order to guard
against the dissemination of the sporangia. In traversing the
bed the spread of this disease ought to be obviated as much as
possible b}- the workman not allowing his boots subsequently to
come into contact with healthy plants. The seed-bed should
also be inspected daily.

PHYTOPHTHORA INFESTANS. THE POTATO DISEASE.

Although the fungus which produces the potato disease had
been introduced from North America before 1845, it is only
since that year that it has assumed the dimensions of a plague in
Europe, where it always causes great loss in wet years. In the
mode of its distribution and in its dependence on wet weather it
very closely resembles P. ovinivofa. A characteristic feature is
the occurrence on the leaves of black blotches, w^hich, con-
stantly increasing in circumference, and finally embracing the
stems, may bring about the premature death of the parts of the
plant above ground. Although the tubers of diseased plants are
generally more or less affected, still this is sometimes the case
only to a small extent, being recognizable merely b)- a few brown
specks on cutting into the tuber. During wet years the tubers
often rot for the most part in the field, those that are less
attacked decaying in the cellar or pit during winter. These
changes (wet- rot) are to a large extent due to the action of
bacteria.*

The mycelium of P. infcstans passes the winter in the tubers,
and when these are planted out it grows into the sprouting shoots
invading the tissues of both stem and leaf On examining the
neighbourhood of the black blotches, one recognizes, even with
the naked eye, a zone which is distinguished by its mouldy
appearance. Here are to be found the numerous sporangiophores,
for the most part projecting from the stomata. They agree
in shape with those of P. omnivora, and bear similar but more
numerous sporangia, which convey the disease to sound plants,
and are even carried by the wind to adjoining fields. There is
* [See footnote on p. 38. — Ed.]

INJURIES INDUCED BY PLANTS 65

no doubt that they are also brushed off and distributed by ani-
mals, as, for instance, by hares. The germination of the sporangia,
or their production of swarm-spores as the case may be, agrees
generally with that of the allied species. The sporangia, how-
ever, reach the ground in large numbers, and are carried down to
the tubers by the rain-water. Should the ground remain wet, in-
fection follows upon the development of the germ-tube. The fact
that varieties of potatoes with thin skins are more easily pene-
trated by the germ-tube of the fungus than those having thick
skins may explain how it is that the latter suffer less from
disease.

The formation of oospores, which I have demonstrated in
the case of P. oninivora, has not )'et been discovered in the
potato fungus, and possibly it may not exist. Seeing that the
mycelium passes the winter in the tubers, the existence of the
fungus does not in this case depend on the formation of oospores.
The occurrence and spread of the disease is most of all in-
fluenced by the humidity of the air and soil, because, in a
moist environment, sporangia are abundantly produced on the
leaves, and the germination of the sporangia and gonidia, both
above and below ground, is greatly favoured.

If dampness prevail during storage in winter, numerous
sporangiophores are produced on the tubers, especially in the
region of the eyes, or where a wound ma}' happen to occur ;
and by means of the sporangia that are formed the disease may
be conveyed to previously sound tubers even at that season of the
\-ear.

PERONOSPORA VITICOLA

A decade or two ago this parasite of the vine was introduced
from America, and in the interval it has rapidly spread through
the vineyards of Europe.

Its American designation of mildew, or grape-vine mildew,
has been changed in France to mildiou. In Germany it is called
the false mildew of the vine {falscher MeJilthmt der Reben).

The disease is characterized by the occurrence of large grey
patches on the under side of the leaves, while on the upper side
the infested spots become yellow or reddish. The diseased
spots dry up, and the leaves are shed prematurely. During

F

66 DISEASES OF TREES

rainy weather the disease spreads rapidly, but dry weather at
once retards further progress. The fungus passes the winter
in the form of oospores, which arc produced in the diseased
leaves. During summer the distribution is effected by sporangia
and zoospores, as in the case of PJiytopJithora. Infection takes
place chiefly on the young shoots and leaves, the epidermis of
which is but slightly cuticularized. The disease proves the more
destructive to vines and grapes the earlier in the season it
appears, and especially so when favoured by wet weather.

It is not improbable that other species belonging to the
genera Peronospora and PytJihuii do injury to young trees. It
is especially desirable that investigations be instituted to prove
whether PytJiiuvi de Baryanuni — which in crowded beds causes
the death of many agricultural plants — is also injurious in the
seed-beds of dicotyledonous and coniferous trees.* The genus
Cystopus also belongs to the Peronosporcz, the best-known species
of which is Cystopus candidiis, which produces the white-rust of
crucifers.

USTILAGINE^ f

Although this order contains only fungi which are parasitic
on herbaceous plants, especially grasses, still the diseases which
they produce are of sufficient importance to require a short
description here.

In the cvery-day language of the farmer, Smut is a term
applied to the most varied phenomena of disease in plants.
In the narrower sense of the word, however, the term is restricted
to those diseases which produce a dark brown mass of spores
in certain parts of plants, especially flowers and fruits, less fre-
quently on leaves, stems, and even roots. In the particular part
of the plant that is occupied by the copious mycelia of the
smut-fungus this spore-powder is formed by the abscission or
abjunction of abundantly developed fungus-filaments, the tissues
of the plant itself being almost completely destroyed.

The mass of spores is either formed on the surface of the

* [An allied form was exceedingly destructive in seed-beds of Cinchona in
Ceylon in 1880-1881.— Ed.]

t [For the British forms of Ustilagines see Massee, op. at., and
Plowright, British UredinecE mid Ustilagineoi (Kegan Paul & Co., 1889). — Ed.]

INJURIES INDUCED BY PLANTS 67

plant or it remains enclosed by the epidermis, in which case
it appears as a black semi-transparent swelling.

The spores of smut may retain their capacity for germination
for several years. On the recurrence of favourable conditions
they usually produce a stout germ-tube called the promycclium
[I'orkeivi), which, after attaining a length equal to two or three
times the diameter of the spore, forms a number of smaller
spores, known as sporidia, at its apex or on its sides.

Frequently the promycelium breaks up directly into a number
of sporidia. In the case of those species which produce \v'horls
of sporidia at the apex of the promycelium, a process of fusion
takes place between adjoining sporidia, and these afterwards
drop off in pairs.

When a germinating smut-spore or sporidium comes into
contact with a suitable young host-plant, it sends its germ-tube
through the epidermis, and thus gets into the tissues of the
stem, where the mycelium grows upwards, chiefly intercellular
without producing any apparent damage. It is only in the parts
of the plant where spores are formed that the tissues are
destroyed.

Those smut-spores which fall to the ground before or during
harvest usually germinate at once, and perish in the absence
of suitable young host-plants.* This being the case, the disease
persists from year to year, for the most part, owing to the employ-
ment of seed to which smut-spores adhere externally. When the
corn is being threshed the detachment of the spores from
smutted plants offers ample opportunity for the contamination
of the seed-grain. Frequently, however, the spores are conveyed
to the field in manure which has been made with smutted
straw.

On account of the germination of the smut-sporcs being
dependent in great measure on moisture in the air and soil,
the occurrence of the disease is favoured in a soil whose
physical condition — either naturally or owing to the liberal
application of farm-yard manure — enables it to retain large
quantities of water.

It follows from what has been said that attention should first

*[Brefeld has shown that the "sporidia" may reproduce by budding
saprophytically during long periods in the manured soil. — Ed.]

F 2

68 DISEASES OF TREES

be directed to preventing the transference of smut-spores to the
field. To secure this, seed which is as clean as possible should
be used. If this cannot be had, the adhering spores should be
killed by steeping the seed-grain for twelve to sixteen hours in
.a one-half per cent, solution of cupric sulphate. Further, the
use of smutted straw for manure should be avoided.

The most important kinds of smut (brand) are : —

The Coal-brand, Stickv-brand, Stink-brand, or Bunt
of wheat ( Tilletia Caries mid T. Icevis) — which besides attacking
wheat is also found on quickens, wall barley, and meadow grass
{^Poa pratensis) — is characterized by the fact that the spore-
powder (which emits a disagreeable smell when fresh) remains
enclosed in the grains till the time of harvest. The bunted
grains being bruised in threshing liberate the spores, which
adhere to the sound grains, and, both being sown, the young
plants become infected.

The Dust-brand [Ustilago) is the most destructive genus,
and also contains the greatest number of species. Ustilago
Carbo attacks not only oats, wheat, and barley, but also a large
number of meadow grasses. It completely destroys the ovary,
and usually the paleae as well, so that brown spore-powder
escapes on to the stalk.

Ustilago destruens, the Millet-brand, destroys the panicles of
the millet while they are still enclosed by the highest leaf-
sheath.

Ustilago Ulaydis, the Maize-brand, produces large swellings,
completely filled with dark brown spore-powder, on the stem,
leaves, and cobs of the maize. Numerous other species occur
on grasses, herbs, and bulbous-rooted plants.

The Stem-brand {Urocystis) is frequently met with, and
especially the brand of rye-stems, Urocystis occulta. It is very
conspicuous, on account of the highest internode of the rye-stem
rupturing longitudinally, and allowing the black spore-powder
to escape.

Other forms often met with are Urocystis J^iolcr, U. Ancnionis,
and U. Cepul<£.

INJURIES INDUCED BY PLANTS 69

ASCOMYCETES. SAC FUNGI

This second group of fungi has obtained its name through the
spores being produced in the interior of sacs (asci). In some
cases the sporocarp results from a sexual process.* The fungi
belonging to this group are very numerous, and are arranged
in four orders — the Erysiphecs, Tiiberacecs, Pyrenomycetes, and
Discoiiiycetes.

THE MILDEW FUNGI, ERYSIPHE^

All the mildew fungi are true parasites. Their mycelium
vegetates on the surface of plants — that is to say, on the
epidermis of leaves, fruits, and stems, and obtains its nourishment
by means of haustoria from the interior of the epidermal cells,
which consequently turn brown and die. The ascocarps which
are developed on the mycelium are usually globular and com-
pletely closed — that is to say, unprovided with an apical or other
opening,-]- and may be recognized with the naked eye as small
dark specks. These hibernate and carry the fungus over to the
following year, while in the course of the summer gonidia are
formed by abscission on numerous simple erect hypha:?. These
are at once capable of germinating, and spread the disease during
the period of growth. On account of the interwoven mycelia and
gonidiophores, when luxuriantly developed, forming a fine grey
meal-like covering on the upper surface of the leaf, the term
" Mildew" has been applied to the disease.

As a preventive measure, the burning in autumn of leaves
infested by the cleistocarps of the fungus has been recommended,
while sprinkling sulphur on the diseased parts after the mildew
has appeared in summer is said to be efficacious. Unfortunately
no scientific investigations regarding the action of the powdered
sulphur on the mycelium of the fungus have as yet been
undertaken.

*[The Sporocarp (in this case termed an Ascocarp) is often a very com-
plex body. The question as to its origin and morphological nature cannot
be discussed here, and the reader is referred to the special works of De Bary,
Brefeld, &c., already quoted. — Ed.]

t [These closed Ascocarps are termed Cleisiocarps, in distinction from
the perforated Perithecia of the Pyrenomycetes and the open Apoihccia of
the Discomycetes. — Ed.]

70 DISEASES OF TREES

The numerous species of mildews have recenth' been arranged
in several genera according to the number of asci in the
cleistocarp, or according to the number of spores in the ascus,
or, finally, according to the structure of the so-called appendiculae,
which are peculiar filiform radiating processes of certain cells
of the wall of the perithccium. Here we need only allude to
a few species.

ErysipJie {Phyllactiiiia) guttata forms the mildew of Fagus,
Carpimis, Cory his, Qiierais, Betula, Almis, Fraxinns, Loniceray
Pynis covimimis, and Cratcrgiis. The cleistocarps are fur-
nished with appendiculae which are straight, unbranched, and
thickened in a bulbous manner at the base, and internally
produce several asci, each containing two spores. In beech woods
this parasite sometimes causes premature withering of the leaves.

ErysipJie bicornis {Uncinnla Accris) very often injures the
leaves and young shoots of Acer. I have encountered this
species most frequently on Acer platanoides and A. campestre.
It covers the whole of the leaf, or forms large greyish white
blotches on one or both sides (the black patches on these leaves
are due to Rhytisma acerimuii). The cleistocarps possess several
asci holding eight spores, and the appendicular are simply forked
at the apex. The gonidia are elliptical in shape. Even so early
as August the leaves of the maple are often completely covered
with these white patches.

ErysipJie Ttdasnei is closely related to the former species,
but occurs only on the upper side of the leaves of the Nor-
way maple. The gonidia are globular. ErysipJie {Uncimild)
adunca produces the mildew of the leaves of willows and
poplars.

ErysipJie {SpJuvrotJieca) pannosa forms the well - known
mildew on the shoots and leaves of the rose. In w^et years
especially it is necessary prompth' to pluck and burn the
diseased leaves.

Oidium Tiickeri, the fungus which causes the disease of the
grape, was observed in England for the first time in 1845, but
has since spread throughout all the vine-growing countries of
Europe. The mycelium grows on the leaves, shoots, and fruit.
When the last is attacked the epidermis dies and loses the
power of expansion, so that as the berry grows the epidermis is

INJURIES INDUCED BY PLANTS 71

ruptured, and the grapes in consequence begin to decaj'. So far
only the gonidia have been discovered, and it remains to be
determined how the fungus survives the winter.

THE TRUFFLES, TUBERACE^

The Truffles are distinguished by having round subterranean
closed fructifications (cleistocarps), in which the asci are produced
on hymenia which clothe the surfaces of contorted passages.
Gonidia and sexual organs are unknown.

Through the investigations of Rees^ it was first established
that the stag truffle, ElapJiomyces granulatiis, develops its
mycelium parasitically on the roots of pines. It is further
known that the edible species of truffle of the genus Tuber are
parasitic on the roots of the oak and beech. Frank has re-
cently devoted much study to the occurrence of fungal growths
on the roots of phanerogamic plants, especially ConifercB and
Cnpulifcnr, and has proved that mycelial growths are ^^^idel)'
distributed on the tender apices of the roots of trees. The outer
surface of young roots may be so closely covered by the
mycelium, which penetrates into and between the cells, as to
form a dense fungal mantle. Owing to luxuriant branching
and growth of the tissues the infested roots to some extent
display abnormal forms, while a sort of symbiotic condition
arises similar to what we find associated with many other plant-
parasites. When the cortical tissue of the roots has been
infested by the fungus for some time, it dies, and should the
fungal filaments penetrate into the internal tissues the roots
themselves die off entirely. Frank has designated these
phenomena by the name MycorJiiza, or fungus-root. It has not
yet been determined how many species of fungi take part in
these phenomena, and, especially, whether fungi belonging to
other groups besides the Tuber acecB form MycorJiisa. Frank
holds the view that these root-fungi, by assisting in nutrition
and by conveying organic plant-food from the soil, play an
important part in the life of trees.*

^ Dr. M. Rees and Dr. K. Fisch, UntcrsiicJiiingeii iiber Ban tmd Lcbot
der Hirschtrii^el^ ""^ ElapJiomyces^^ 1888.

*[The best account of Frank's views for the student is in \i\% Lehrbiich dcr
Botanik, B.I. 1893.— Ed.]

72 DISEASES OF TREES

Whether this view will receive confirmation in the future
remains to be seen, but in the meantime its correctness is open
to grave doubts. In the first place, it has not yet been proved
that trees can take in organic food-substances by their roots ; and,
in the second, it has been established that trees are very well
nourished without the aid of MycorJiiza, and that, besides the
infested roots, there is always a very large proportion of roots
■entirely free from fungoid growth.

PYRENOMYCETES

In the case of Pyrenoinycetes the hymenium bearing the asci
usually lines the inner surface of roundish or flask-shaped
receptacles, called perithecia, which are distinguished from
the cleistocarps of the preceding by having an aperture at the
apex through which the spores escape. The numerous genera
may be divided into two groups, according as the perithecia
stand singly (simplices), or grouped in large numbers on a
common cushion, or sunk in a stroma (compositi).

The following species, being noteworthy parasites, deserve
closer attention.

TRICHOSPH.^RIA PARASITICA ^

This parasite is chiefly met with on the silver fir, though,
according to v. Tubeuf, it also occurs on the common spruce
and hemlock spruce. It is to be found wherever the silver fir
is indigenous. Its colourless perennial mycelium grows on the
under side of the branches, from which it spreads to the under
side of the leaves, knitting them firmly to the branches. On
this account the leaves, instead of falling off on dying, remain
attached to the branches (Fig. i8).

On account of the mycelium being confined to the lower side
of the branch, most of the leaves that are met with on the upper
side survive during the first year at least (Fig. i8, a). The my-
celium encroaches on the new shoots as they are formed, and,

1 R.H3.xt\g, Ein 7ieuer Parasit der IVezssfanuc, " Tridiospharia parasitica:''
AUgem. Forst- tend Jagd-Zeitg.^ January 1884.

INJURIES INDUCED BY PLANTS

73

the young immature leaves at the base of the shoot being killed,
subsequently shrivel up. The leaves on the middle and apex
of the shoot, being
reached somewhat later
by the slowly advanc-
ing m)'celium, retain
their shape.

The cushions which
are formed by the my-
celium on the under side
of the leaves are at first
white, but afterwards turn
brownish (Fig. 19, b b).
They only partially con-
ceal the bluish lines
which are met with on
the under side of the
leaves of the silver fir.
In the course of time
very minute perithecia
are formed on these
cushions (Fig. 20).

The cushion originates
in the following way.
From the hyphae that
cover the leaf (Fig. 21, a)
numerous branches, (^, are
sent out towards the
epidermis, and these
form a fleshy cushion, <r,
consisting of parallel
hyphae closely united
to each other. At the
point, d, where it reaches
the epidermis of the leaf,
each hypha sends a fine

rod-like haustorium into the outer wall, e, of the epidermal
cells, and owing to the secretion of a ferment these cells and
the stomata, f, are killed and become brown. The cells of

Fig. 18. — Branch of the silver fir attacked by
Triihosplueria parasitica, a, healthy leaves ;
h, dead and brown leaves whose bases are at-
tached to the branch by the fungus-filaments.
On account of their not being fully formed when
attacked by the fungus the dead leaves towards
the base of the shoot have shrivelled up.

74

DISEASES OF TREES

Fig. 19. — Lower side of a
leaf of the silver fir at-
tacked by T. parasitica.
At a the colourless my-
celium spreads from the
branch on to the lower
side of the leaf, on which
it forms white cushions,

Fig. 20. — Part of the leaf
of a silver fir, on the left
side of which the cushion
bears a number of small
perithecia.

Fig. 21. — Mycelial cushion of T. parasitica on the under side of the leaf of a silver
fir. The filamentous mycelium a sends down numerous branches at d to form
a cushion c, consisting of parallel hyphre ; where the hyphre reach the surface of
the leaf each sends a rod-like haustorium, c/, into the outer wall of the epidermal
cells, e e ; at dlhe cushion has been somewhat raised from the leaf, so that several
of the haustoria have been pulled out of the epidermis; the epidermal cells yy
have become brown. Although the filamentous mycelium // has penetrated the
chlorophyllous cells of the leaf-parenchyma^^, these do not become brown till
somewhat later ; the mycelial cushion grows into the depressions at the entrance
to the stomata i, where however it is unable to form haustoria ; at these places
it becomes coated with the adhering waxy granules.

INJURIES INDUCED BV PLANTS

75

the interior, ^- which contain chloroph)'ll, do not succumb for
some time to the action of the mycelium, //, which here and
there effects an entrance. The depression at the entrance

to the stomata, being Hned with
wax)' granules, prevents the en-
trance of any haustorium, /. The
dark brown perithecia (Fig. 22)
which ultimately arise on the
cushion are scarcely recognizable
with the naked e}-e. The}^ are

Fig. 22. — Perithecium of T. para-
sitica. The dark brown sphere
shows a round aperture at its
apex, and bristle-like hairs
which jiroject from its upper
half. A portion of the wall
has been removed from the
lower left-hand side in order to
show the pale contents, which
consists of asci and paraphyses.
These are shown more highly
magnified in the lower part of
the figure ; a representing rod-
like bodies which are often pre-
sent ; b, asci with spores, and
r, isolated spores.

Fig. 23. — Herpotrichia nigra on the
spruce ; half natural size.

characterized by having bristle-like hairs distributed over the
upper half In the interior of the perithecia are often to be found
small rod-like organs, a, besides the asci, b, which hold eight
grey spores, usually consisting of four chambers. Should these
spores succeed in obtaining a suitable footing on the branch
of a silver fir, they speedily germinate and produce the disease.
The m}-celium spreads parasiticalh- from the point of infection

76 DISEASES OF TREES

in all directions, so that large branches may be eventually entirely
defoliated. In dense young woods it even spreads from branch
to branch, while fresh centres of disease are produced by the
distribution of the spores.

Seeing that young woods which have been naturally regener-
ated may suffer severely — and especially so where they have been
formed under shelter trees — it is desirable that diseased branches
should be pruned off This treatment has produced good results
where practised on a large scale.

HERPOTRICHIA NIGRA ^

..^X^\/^^^{ C^^ This parasite is met with in the higher mountain ranges, where
it chiefly attacks the spruce, mountain pine, and juniper. In the

jjN^j^j^ijNk^woods of mountain pine, large blanks are met with, which, on a
'^ cursory glance, give one the impression of having been completely

^v.gJL'., charred. In nurseries at high elevations, where the young spruces
are buried under snow during winter and spring, it often happens,

'^^'^^ directly after the snow has melted, that the plants are overgrown

—' and killed by the dark brown mycelium. This is especially notice-

, ^ able when the young trees have been laid prostrate on the ground.

In the spruce woods of the Bavarian Forest one often finds
that the fungus has killed the young seedlings over large areas
either entirely or to the height of twelve or fifteen inches. The
dark brown mycelium envelops the whole branch or plant, knitting
the leaves completely together (Fig. 23).

Instead of forming a definite cushion, the mycelium embraces
the leaves irregularly (Fig. 24, /;), and on these the perithecia
are also produced {a). Dark brown tuber-like bodies are formed
over the stOmata (Fig. 25), while the mycelium also spreads
over the surface of the leaf and sends haustoria into the outer
walls of the epidermal cells, which consequently die and become
brown. The deeper-lying parenchymatous cells are also killed
by the fungus, even before any mycelial threads have gained an
entrance through stomata on other parts of the leaf, and pene-
trated into the interior.

The surface of the dark brown comparatively large perithecia,

^ R. Hartig, Hcrpotrichia m\n-a n. sp. All. Forst- und Jagd-Zeitg.,
January 18S8.

INJURIES INDUCED BY PLANTS ^J^

Fig. 24, is beset with numerous branching h)-pha:, which are
specially abundant on the lower part, near the point of contact
with the mycelium. These black spheroid bodies are frequentl\^
nearly hidden by the mycelium. In the asci the spores arc
arranged in two rows. At first, and apparently also when
mature, thc}^ consist of two chambers, but at last four chambers
are formed. These spores germinate with great readiness.

It is an interesting biological point that the fungus grows, es-
pecially when the temperature is low,
under the snow or during the time it
is melting, because, under such cir-
cumstances, the air is completcl}^
saturated with moisture. The fre-
quenc}' of the disease at high eleva-

FlG. 24. — a and /', two spruce
leaves attacked by H. nigra,
twice natural size. The brown
mycelium forms black tuber-
like bodies in the stomata,
which however are much
smaller than the black peri-
thecia, one of which, magni-
fied fifty times, is shown in
the lower part of the figure.

Fig. 25. — The growth of the mycelium
of H. nigra. I'he filamentous my-
celium a develops a granular mycelium
on the surface of the leaf, and this
covers the stomata with tuber-like
bodies, rod-like haustoria being sent
into the outer walls of the epidermal
cells.

tions has led to the general adoption of the practice of forming
spruce nurseries at low altitudes. It has also been found a
good plan to look over the nurseries immediately after the
melting of the snow, and to raise up all prostrated plants in
order that they may be exposed to the wind. It would also
be a step in the right direction, in planting out trees, to set
them on hillocks and similar elevations, and to avoid placing
them in hollows and other depressions.

78 DISEASES OF TREES

ROSELLINIA QUERCINA ^

The oak-root fungus, Rosellinia qiierciiia, is one of the most
interesthig of parasites, and especially so because its mycelium
displays the same diversity of form as that of Agaricus inelleiis.
The mycelium is one of those parasitic mycelial forms which
were formerly referred to a special genus, RJiisoctonia.

The disease produced by Rosellinia qiiercina appears only to
attack the roots of oaks from one to three years old, but it is
very prevalent, especially in north-west Germany. In oak seed-
beds it gives indications of its presence by the young plants
becoming pale and withered, especially during rainy seasons.
The leaves near the apex of the shoot are the first to wither, but
later on the lower ones go too. If a plant showing the first
.symptoms of the disease be lifted out of the ground, we per-
ceive a few black spheroid bodies of the size of pin-heads situated
on the tap-root, especially at the points where the delicate
lateral rootlets are met with (Fig. 26). It is also observed that,
at certain points, the roots are closely embraced in a web-like
fashion by delicate ramifying strands which resemble so many
threads. These are the Rhizoctonice, which penetrate also into
the adjacent soil, and, as we shall see, spread the disease
underground from root to root. In the neighbourhood of
these black tubers, and wherever the RhisoctonicB have been
closely in contact with the surface of the roots, the cortex
turns brown. The apex of the tap-root is often quite
rotten, but even plants whose roots remain alive to the tip
display the pathological symptoms already described.

Upon older plants that are already dead the RJiizoctonicE are
no longer white, but brown, and there the black spheroid bodies
are often to be recognized in large numbers. Sometimes the
latter are also to be found on the lower part of the stem — that is
to say, on the epicotyledonary axis : they may be most easily
discovered after the plant has been very carefully washed, be-
cause then the lustre of the black tubercles readily betrays their
presence. During damp warm weather all the plants on patches
a yard or so in diameter may become withered and die.

^ R. Hartig, Untersuchiingen aus deni Forstbot. Institute I. pp. 1—32.

INJURIES INDUCED BY PLANTS

79

Where the seed has
been drilled, the disease
spreads from the point
of attack in two direc-
tions ; where sown broad-
cast, it spreads centri-
fugally in all directions.
Should dry weather in-
tervene, or on the ap-
proach of autumn, the
disease ceases to spread,
but on examining the
roots of plants appa-
rently sound situated in
close proximity to those
already dead one will be
able to recognize nume-
rous examples of the
pathological symptoms
which have been already
indicated. If such dis-
eased plants are trans-
planted in the following
year, it will be a question
of weather whether they
die, and possibly trans-
mit the disease to neigh-
bouring trees, or form
a new tap-root, if the
apex was destroyed by
the disease, and, after
remaining stunted for
some years, slowly re-
cover.

If a dead plant be
placed in a damp warm
chamber, or be planted
in July in the middle of
a bed of healthy young

8o

DISEASES OF TREES

seedlings a few months old, a mycelium is very soon developed
from the black tubers — which w^e may call resting-mycelia
(Sclerotia) — which breaks through the bark at different places
and forms a dense whitish-grey mildew-like tissue, and also
spreads rapidly over the surface of the ground (Fig. 27). This
mycelium consists of septate hyphas, which are at first
colourless but afterwards turn brown. These, after a time,

arrange themselves side by
side, grow together laterally
at places, and form the
fine strands called RJiisoctonice,
which consist of numerous in-
dividual hyphse very loosely
united to each other. Should
such a mycelium — whether in
the form of isolated hyphae or
of RhizoctonicB — come into con-
tact with the sound roots of a
neighbouring plant, it embraces
Y/r >)> them in its meshes, and bores

mi-' A''- directly into such of the corti-

cal cells as are still alive.
These are found in the delicate
lateral rootlets and near the
apex of the tap-root. The my-
celium penetrates as far as the
medulla, should such be pre-
sent, and in a short time kills
the root. In the living cortical
parenchyma of the tap-root —
which is only to be found on
the lowest and youngest parts— the cells become plugged up
with a luxuriant growth of pseudo-parenchymatous tissue,
which, owing to the occurrence of numerous oil-globules,
may be recognized as a resting-mycelium. These bodies, which
germinate under favourable conditions, may be designated cham-
bered sclerotia. On account of the formation of a periderm layer
in its cortex, the older parts of the tap-root are protected against
the direct attack of the parasite. The outer cortical cells being

Fig. 27. — Oak root enveloped liy the
mycelium of /v. qiierciiia, a, on which
perithecia have developed at /'.

INJURIES INDUCED BY PLANTS

8i

parti}- shrivelled up and partly cast off, there remains but one
path of entrance into the interior of the root. After the fine
lateral roots that pierce the corky covering have been killed by
the parasite, openings or breaches are left at certain points,
through which the parasite
effects an entrance, and this
it accomplishes in a pecu-
liar manner (Fig. 28). At
such places — frequently both
above and below the base
of the dead root — fine white
mycelial outgrowths are first
formed. These develop into
fleshy tubers, ultimately pos-
sessing a dark brown cover-
ing, which send several fleshy
processes into the tissues of
the oak root (Fig. 28, c, d).

The adjoining cortical tis-
sues are killed and become
brown (Fig. 28, e). Should
dry or cold weather inter-
vene, the host-plant gains
time to form a new layer of
cork in the neighbourhood
of the infecting tubers along
the line that marks the limit
of living tissue. In this way
the plant may be, for the
time, saved. Should the con-
ditions of growth remain
favourable for the fungus,
however, the fleshy pro-
tuberance pushes out a fine

Fig. 28. — Point of infection by R. qtiercina,
magnified twenty times. The delicate
lateral rootlet a, which has been killed by
the filamentous mycelium, displays fleshy
infection-tubercles, b c, at the place
where it has ruptured the periderm
of the tap-root. These tubercles send
processes, d, into the internal tissues.
The adjoining cellular tissue is brown, e,
but free from mycelium. A Rhizoctonia-
strand, f, has been produced by the
upper tubercle, which has consequently
parted with a portion of its nutritive
substance.

filamentous mycelium, which

spreads through all the tissues of the root and kills it.

In the sclerotia the parasite possesses a means of existing
from one year to another, and of resisting the periods of drought
during summer which kill all filamentous mycelia as well as

G

82 DISEASES OF TREES

the sporophores that may be in process of development upon
them.

In summer the mycelium that vegetates on the surface of the
ground produces gonidia on the whorled branches of gonidio-
phores, and these, by being carried on the skins of mice, &c.,
may originate new centres of infection. But besides these, black
spheroid perithecia, about the size of a pin-head, are produced
either on the surface of the diseased oaks themselves or on
the surface of the ground in their neighbourhood (Fig. 27, b).

It is probable that the spores which are formed in the pere-
thecia do not as a rule germinate and reproduce the disease
till the following year.

Generally speaking, it is only in wet years that the parasite
does much damage. It may be combated by digging trenches
round the diseased spots in the seed-bed so as to isolate them.
One should avoid transferring diseased plants from the seed-
bed to the plant-bed.

RJiizoctonia violacea, which kills saffron and lucerne, has not
yet been scientifically examined in its different stages of develop-
ment, and it remains to be determined whether this parasitic
mycelium belongs to a form related to one of the foregoing fungi
or not. Fuckel's statement that this mycelial form belongs to the
fungus ByssotJieciuui circinnans appears so utterly improbable
that it is not worth while to take further notice of it. On the
other hand, I feel called upon to describe here the following
important parasite of the vine.

DEMATOPHORA NECATRIX.* THE VINE-ROOT FUNGUS ^

Amongst the numerous enemies of the vine, the root-fungus,
D. necatrix, occupies a prominent position. The disease which it
induces is known as Wurzelpilz, Weinstockfaule, Pourridie de la
Vigne, Pourriture, Blanc des Racines, Blanquet, Champignon
blanc, Aubernage, Mai nero, and Morbo bianco, and is dis-

•^ R. Hartig, Dematophora necatrix Ji. sp., Untersiichiingen aus deni
Forstbot. Institut zu Miinchen, III., 1883.

*[Viala has published a very thorough investigation of this disease and
the devastations it causes in the south of Fiance, &c. : " Monographie dn
Pourridie des Vigne s et des Arbres fniitiers," 1891.— Ed.]

INJURIES INDUCED BY PLANTS 83

tributed throughout France, Italy, Switzerland, Austria, and
south-west Germany,

Amongst the root-diseases of the vine, that which is caused
by PJiylloxcra vastatrix is generally known. Ver)' similar
pathological symptoms occur on the stems of plants that are
attacked by the vine-root fungus, and confusion often enough
results.

Whether Agariais vielleus also is injurious to the vine — -as has
been maintained — I am not in a position to say, because, so far,
no specimens have been forwarded to me in which the fungus
could actually be identified. On the other hand, it appears as
though, in very wet years and on heavy ground, " root-rot " may
arise as a result of asphyxia — that is to say, owing to deficiency
of air in the soil. On such suffocated vines a fungus, Roesleria
hypog(£a, often occurs, which, it appears to me, is most probably
saprophytic in character.

The parasite that we are here discussing spreads in the vine-
yards from plant to plant by means of its underground mycelium,
so that w^e often hear of great damage being done. Other plants
that are cultivated in the vineyards, such as fruit-trees, potatoes,
beans, beet, and the like, also fall a victim to the fungus. During
my investigations I found that the mycelium could at once kill
young maples, oaks, beeches, pines, spruces, &c.

On plants where the mycelium is vigorously developed, as in the
case of the vine, Fig. 29, and the young maple. Fig. 30, it forms
a luxuriant snow-white mass of a woolly or strand-like texture,
which adheres to the outside of the plants, though it may also
spread in the ground to long distances. Where this mycelium en-
counters the fine fibrous roots of other plants, it kills them, and,
at their base, bores into the interior of the larger roots, Fig. 3 1 a,
spreading afterwards in their interior in the form of peculiar
rhizomorphs. Fig. 32, and killing all the adjoining tissues. In
the soft cortical tissues of the vine-root they retain their strand-
like appearance, and by ramifying laterally and outwards they
envelop the root in a network of strands, Fig. ^^'':).

In structure these rhizomorphs are entirely different from those
oi Agariais melleiis. In Fig. 34 I have represented somewhat
diagrammatically the apex of one of these rhizomorphs, and refer
for details to the description appended to the illustration.

G 2

84

DISEASES OF TREES

n

Fig. 29. — A vine that has been killed by
D. 7iccatrix, and afterwards kept for a
long time in a moist chamber. The fila-
mentous mycelium, a, assumes the char-
acter of white Rhizodonia strands, /',
which anastomose, c c. At rt^and e rhizo-
morphs grow out from the interior.

Fig. 30. — A sycamore infected by
D. necatrix. The portion above
ground is represented some four-
teen days anterior to the rest.
The plant is enveloped in the
white woolly mycelium, a ; on
the subterranean portion Rhizoc-
touiiv consisting of dark my-
celium, b b, are to be seen. Nu-
merous sclerotia, c, project from
the cortex.

INJURIES INDUCED BY PLANTS

85

The branches of the rhizomorph directed outwards break
through the cortex from within and form a new filamentous
myceHum, which penetrates into the soil ; or, in other cases, they
swell up under the cortex to form tuberous sclerotia. Fig. 33 (^,

Fig. 31. — Longitudinal
section of the root of
a vine whose upper
part has been killed
by the rhizomorphs
of D. necatrix as far
as b, and whose lower
portion shows an in-
fection-spot at a.

Fig. 32. — Magnified five
times. Boundar}', a,
of the healthy and dis-
eased parts of the root.
The rhizomorphs send
out lateral branches,
which may occasion-
ally reach the epider-
mis, as at /'.

Fig. t,t,. — A large vine-
root infected by D.
necatrix. A portion of
the cortex has been
carefully removed so as
to show the rhizo-
morphs which begin to
appear at a ; zX b the
mycelial tubers, which
resemble sclerotia, are
formed, and on these
the gonidiophores ulti-
mately develop.

which sometimes break through the cortex and appear in rows
upon the surface, Fig. 35.

On these tubers the gonidiophores are developed in the form
of bristles, at whose apex the gonidia are abscinded, Fig. 36.

It also happens very frequently, however, that these sporophores

86

DISEASES OF TREES

are developed on the filamentous mycelium which clothes the
diseased plant, or foreign substances, in the form of RhisoctonicE
or otherwise

The perithecia of this species have been discovered by Viala.

O C5

t; .S c

i: .- T^ ■z! (u ^ .. Q

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rv t/)>i^3r-.iiiii-ij-.t-.ti *^T?

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rt-:'SSP.S-S.yrt .- c^

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They form only on vines and fruit-trees that have been dead
and decayed for a long period. It is only in soil that has dried
slowly that they are to be found. Associated with bristling ap-
pendages bearing gonidia the perithecia appear partly on sclerotia

INJURIES INDUCED BY PLANTS

87

and parti}' on the mycelium. Between the surface of the ground
and the depth of some two inches they form clusters of small
spheroid bodies round the vine or tree. The sporocarps, which
are very hard, deep brown in colour, approximately spheroid in
shape, and 2 mm. long, are provided with short stalks. They
are completel}- closed,
and enable us to refer
Deviatophora to the
Tiiberacei. The elon-
gated filiform asci,
however, which swell
out on one side like a
lop-sided turnip to en-
close the eight spores,
distinguish this para-
site from all known
Tiiberacei. Deviato-
pJiora necatrix is thus
the sole representative
of a new genus of
Tjtberacei.

The method which I
at first recommended
of starving the para-
site b}- means of iso-
lating trenches, &c.,
having proved too

tedious a process, it remains to be seen whether the impreg-
nation of the poles with creosote can do anything to combat
the disease in the vineyards.

Fig. 35. — Root of a vine
showing numerous scle-
rotia-like tubers, on
which a few bristle-
shaped gonidiophores
have developed.

Fig. 36. — A portion
of Fig. 35 after
the gonidiophores
have been formed ;
magnified five
times.

y

CUCURBITARIA LABURNI ^

This parasite frequently gains an entrance through wounds on
Cytisus Laburnum, destroying the cortex and branches for con-
siderable distances, and even killing the whole plant. Besides
the dark brown spheroid perithecia, which are arranged in groups,

1 Cucurbitai-ia Labiirni, atif Cytisus Laburnum. Freiherr v. Tubeuf.
Cassel, Fischer, 18S6.

f>J».

88 DISEASES- OF TREES

we meet with the most varied forms of gonidia, which are pro-
duced either free on the stroma, or in the interior of cavities in
the stroma, or in pycnida. Owing to the ease with which all
these organs of reproduction germinate, the parasite is frequently
very abundant.

In a similar manner, C. Sorbi appears to attack the bark of
Sorbits Auaiparia.

Here allusion may be made in a few words to the " Disease-
blotches " on the leaves of numerous trees, shrubs, and herbs.
These often occur in great abundance in autumn, the leaves being
covered by numerous sharply defined blotches, which are usually
circular in outline and brown in colour, and frequently surrounded
by a red margin. They are generally due to fungi belonging to
the family Sphczrelloidea, and especially to the genera SpJuErella
and Stigma tea.

The gonidia are formed on the living leaves, but the perithecia
only on the dead parts of plants, and usually not until the spring
after the leaves have fallen.

SpJicBvella FragaricB produces the diseased blotches on the
strawberry.

S . piinctiforniis and .S". viaailiforviis produce brown blotches
on the leaves of the oak, lime, and hazel.

5. Fagi produces blotches on the leaves of the beech, &c.

Stigniatea Mespili induces brownness in the leaves of the pear.

Stigmatea Alni is the cause of blotches on the leaves of the
alder.

Gnomonia belongs to an allied family, Gnonionia erythrostoma,
producing a brown colour in the leaves of the cherr}'. The in-
fected leaves die prematurely, but do not fall off. On these are
developed the perithecia with their unicellular tubular spores. It
is advisable to remove during winter all leaves that may be
hanging on the trees.

A parasite, Valsa Prunastri, frequently proves injurious to the
apricot, cherry, and sloe. The fungus infests the cortex, and
causes the death of the branches. The form producing spermatia
is the first to appear, and ejects its tendril-like masses of sper-
matia ; while later — namely, in the following spring — the peri-
thecia develop in the dead cortex.

INJURIES INDUCED BY PLANTS 89

NECTRIA

The genus Nectria contains a number of parasitic fungi which
produce their perithecia — which are usually red, and grouped in
considerable numbers — on the surface of a pseudo-parenchymatous
wart-like stroma. Before the perithecia make their appearance,
this same stroma serves for the production of numerous gonidia.
The gonidia-bearing stroma was formerly referred to a special
genus called Tnbcrcularia.

The following three species belonging to this genus are faculta-
tive parasites, which, like so many other parasites, can also live
as saprophytes.

NECTRIA CUCURBITULA^

Like all the Nectrias, ^V. Cucurbit2ila is one of those parasites
which, as a rule, can gain access to the interior of a host-plant
only through a pre-existing wound. Here the host-plant is
usually the spruce, in rarer instances the silver fir, Scotch pine,
&c. The means of entrance which the parasite utilizes in the
forest are chiefly the injured spots due to GrapJwlitha pactolana,
Fig. 37, though, less frequently, it also enters through the abra-
sions caused by hail, or the crack at the base of a branch whose
bark in the upper angle has been slightly torn by the depression
due to an accumulation of snow\

The germinating ascospores or gonidia push their germ-
tubes into the tissues of the cortex, and the ramifying mycelium
ultimately develops most luxuriantly in the sieve-tubes of the
soft bast, Fig. 38 b, or in the intercellular spaces between them,
Fig. 1% c. The mycelium is met with in bast tissues that are
apparently perfectly sound and fresh. The brown colour does
not appear in the tissues for some time afterwards. The
fungus would appear to make progress, for the most part, only
when growth is at a stand-still in the cortical tissues. It
generally ceases to advance when the plant and its cambium
awake to renewed activity. From this we must assume that
the power of resistance of the living tissues of the host-plant is

' R. Hartig, Untersuchiingen^ I. p. 88.

9°

DISEASES OF TREES

greater during the season of growth than at other times. As
ma}- be seen from Fig. 'i^'j, the parasite may advance longitu-
dinally more than 2\ inches
during a growing season. Later-
ally the seat of the disease
seldom advances more than
I — \\ inch. The tissues that
have been killed b}' the fungus
become separated from the

Fig. 37.— a spruce attacked by N.
Ciiiiirbitida. At a a wound due to
a hailstone has healed over without
becoming infected ; l>, the gallery
of a larva of GraphcHtha pactolana,
over which a callus has been formed,
but where infection has occurred
two years later : the mycelium has
spread from c to c in the cambium,
and from d to d in the cortex ;
numerous groups of perithecia have
appeared on the dead cortex.

Fig. 38. — Cross section of the
cortex and wood of a spruce
infected a short time previous-
ly ; a, the wood. /' b, the sieve-
tubes containing one or more
mycelial filaments ; c, my-
celium in the intercellular
spaces ; magnified 420 times.

living parts by the formation of a laj-er of cork which prevents
the further progress of the parasite in the following year.

If the cortex that has been killed be exposed to wind and sun,

INJURIES INDUCED BY PLANTS 91

it dries up even so earl}^ as the beginning of summer. When
the part of the tree that is attached is thin, the wood also dries
up, and the top of the tree dies and becomes yellow and
withered. Ver)' frequently one meets with such withered tops
in young spruce woods without being able to find a trace of the
perithecia, which only attain maturity when the cortex in which
the mycelium is hidden is constantly kept moist. When this
occurs — as often happens on the lower parts of the stem, where
the cortex is kept moist by the shade and protection of the
branches — a large number of white and yellow cushion-like
stromata develop on the dead tissues. These, which are about the
size of pin-heads, break through the outer cortical and periderm
layers, or remain hidden amongst the loose bark scales. These
cushion-like stromata first of all produce large numbers of gonidia,
but later on numerous red melon-shaped perithecia are formed,
whose ascospores are usually disseminated in winter or spring,
when they find their way to the injuries caused by G. pactolana,
or to other wounds.

With the disappearance of the moth — as, for instance, in con-
sequence of the severe winter 1879 — 80, in which the caterpillars
were, for the most part, frozen — the injury due to this Ncctvia is
of course also diminished, because it has fewer opportunities for
infection. Spruces which are attacked only by the moth and not
by the fungus hardly ever perish, but after being crippled for a
few years recover completely. Spruces which are attacked by
Nectria only on one side may also recover, because in the course
of time a callus forms over the injured part. The damage, how-
ever, which is done to young spruce woods by the trees dying at
the top is so great that it seems advisable to limit the spread of
the parasite by cutting off and burning all such tree-tops as
are attacked by the fungus.

NECTRIA DITISSIMA^*

It is the dicotyledonous trees that are chiefly attacked by this
fungus, many of the varied forms of disease which are usuall)'

^ R. Hartig, Ufttersicchtmgen, I. p. 209, Plate VI.

* [This fungus is very common in this country, and I have frequently
observed and examined its undoubted connection with the canker of apple
and other trees. — Ed.]

92 DISEASES OF TREES

embraced under the term '" Canker " being due to iV. ditissiiiia.
This canker-fungus appears most frequently upon the beech, oak,
hazel, ash, hornbeam, alder, maple, lime,apple, dogwood, and bird-
cherry. Although as a rule this parasite only gains an entrance
to the cortical tissues of trees through wounds, I have also been
able to infect young leaves by means of gonidia and ascospores.
Abrasions caused by hailstones are probably the commonest kind
of wounds, Fig. 39. Should no infection supervene on such a
wound, a callus forms, and occludes the injured part in a short time,
^^%- 39 '^^- If. however, it is infected by the gonidia or ascopores
oiNectria, death and brownness spread in all directions, but most
rapidly in the direction of the long axis of the stem. Although
in rare instances the mycelium may advance 3 cm. in a year, it
is comparatively seldom that the annual rate of progress in any
direction exceeds one third of that amount. The apparent
deepening of the diseased spot in the course of time is to be ex-
plained from the fact that not only does the contiguous healthy
tissue continue to increase in thickness, but it even displays an
augmented rate of growth. This is satisfactorily enough ex-
plained when we remember that during their movements in the
bast the plastic materials assimilated by the leaves are neces-
sarily confined to the sound side of the stem. As the canker-
spot dries up, their passage is chiefly confined to its margin, which
is consequently very richly nourished, and projects as a well-
marked prominence. Thus in the course of years very striking
malformations are formed.

It also frequently happens that the base of a lateral branch,
whose cortex has been injured in the upper angle, proves the in-
fection-spot from, which death of the tissues annually proceeds.
Fig. 40. In the case of the hazel especially it often happens that
in pulling down the branches to get at the nuts a split is formed
at the point of bifurcation. This then develops into a canker-
spot, which constantly increases in size, as is represented in
Fig. 41.

I believe that I am justified in assuming that under certain
circumstances, with which I am not yet familiar, the mycelium
spreads from the cortex to the wood, in which it progresses up-
wards, and at certain places attacks the tissues of the cortex and
cambium from within. In this way canker-spots may be pro-

INJURIES INDUCED BY PLANTS 93

duced without the part of the tree on which they occur having
been previously injured, Fig. 42. The famihar state of things
where certain trees are covered with canker-spots, while adjoining

trees of the same spe-
cies are tolerably clear
of them, can hardly be
explained in any other
way than by assuming
that the fungus travels

Fig. 39. — Branch of
a beech showing
two hailstone
wounds, of which
the upper one, b,
has been infected
by N'cctria, while
the lower one, a,
has escaped infec-
tion and has been
occluded by a
callus.

Fig. 40. — Hornbeam
infected by N. ditis-
sima, which has en-
tered at the angle
formed by the branch
and the stem ; na-
tural size.

Fig. 41. — Hazel showing the
canker due to N. ditissima,
the spores of which have
germinated in the bifurca-
tion of two branches which
have been somewhat pulled
asunder ; a, b, h, the bound-
ary of the canker-spot,
where red perithecia are
abundant ; c c, the healthy
side of the branch ; half
natural size.

in the wood. This subject, however, requires further inves-
tigation.

As the mycelium spreads in the cortical tissues of trees, it
produces innumerable extremely minute gonidia resembling
bacteria, which apparently assist in no small degree in the

94

DISEASES OF TREES

almost complete decomposition of the tissues of the cortex, with
the exception of the outer periderm layers. Only on those
parts of the cortex which have been killed during the past year
— that is to say, on the periphery of the
canker- spot — do white gonidia-bearing stro-
mata appear. These had already been ob-
served by Willkomm in his investigations
into the canker of the beech, by whom they
were designated Fiisidmm candidiim. On these
the minute deep-red perithecia originate, but
they can only be discovered after careful
search. They are found partly in groups and
partly singly on the dead cortex, and especially
in the fine fissures. Fig. 40. One sometimes
searches for them for a long time in vain upon
the older canker-spots, for the reason that
these have ceased to increase in size at all parts
of their circumference. In Fig. 43 the canker-
spot is increasing in size only in the upper
left-hand corner, and it is only there that the
red perithecia are to be found in abundance.

In the case of the canker of the beech, I
have frequently observed that sooner or later
the mycelium ceases to advance at certain
places, in consequence of which the shape of
the canker-spots becomes exceedingly irregu-
lar. Here and there the canker spreads for a
series of years, but finally the diseased spots
may be entirely covered over by a kind of
callus. See Figs. 43 and 44.

It may also be remarked that the parasite
is distributed throughout the whole of Ger-
many, and that canker of the beech especially
is met with from the Island of Riigen to the
south of Bavaria, being very prevalent, for
instance, in the neighbourhood of Munich.
Young trees from five to ten years old, as well as trees 140 years
of age, may be attacked by the disease, which, however, in the
latter case, is confined to the twigs and branches of the crown.

Fig.

42. — Branch of
a beech showing
numerous canker-
spots, which do
not appear to have
been preceded by
any cortex wounds.

INJURIES INDUCED BY PLANTS 95

Climatic conditions, especially frost, are essentially without
influence on the disease, and the same is true as regards the soil.
Although the damage inflicted by this parasite is by no means

small, still I doubt if, in practice,
anything can successfully be done
to combat it. The injured trees
remain alive as a rule, and at least
yield firewood. Their removal in
the thinnings is certainly advisable,
so long as the ground is not there-
by injuriously exposed. In oak
woods also, whenever thinning and

Fig. 43. — A stem of the beech,
half natural size, showing numer-
ous canker-spots ; these, how-
ever, are increasing in size only
at certain places, and it is only
where increase is taking place
that the red perithecia are to be
found.

Fig. 44. — Cross section taken from the
lower end of the beech stem repre-
sented in Fig. 43 ; natural size.

opening out are undertaken with a view to underplanting, the
cankered trees should be the first to be removed. I cannot advise,
however, that one should go so far as to fell all cankered trees, if
this should mean the formation of large blanks in the wood.

96 • DISEASES OF TREES

Very frequently N. ditissiina is found associated with ApJiida}
LacJinus exsiccator produces large galls in the cambium of the
beech, and when these afterwards burst open they present the
opportunity of infection to the fungus. The mycelium spreads
in the cellular tissues with extraordinary rapidity. The beech
Aphis, too, Chermes fagi, which clothes the stem with a \\h.\\.e
woolly covering, is often associated with the fungus, which, under
these circumstances, quickly kills the cortex, without producing
canker-spots.

NECTRIA CINNABARINA.- *

This Nectria is certainly one of the most widely distributed
of fungi, and finds its way on to almost all dicotyledonous trees
and shrubs when they have been killed by frost. Besides living
saprophytically, it also occurs as a parasite, and that most fre-
quently on the maple, lime, and horse-chestnut. Infection usually
occurs at branch-wounds, though also very frequently at root-
wounds, which cannot be avoided when transplanting either large
or small trees. The mycelium of this fungus, which grows rapidly
upwards in the vessels, penetrates into all the elements of the
wood, decomposing the starch, and leaving a green substance be-
hind. Fig. 45. The consequence is that the wood turns black,
while the cambium and cortical tissues remain sound. The wood
becomes unable to conduct sap, the leaves wither prematurely in
summer or drop off, and the cortex of the youngest shoots
dries up after the wood is completely dead. In autumn or the
following spring the cinnabar-coloured stromata that bear the
gonidia appear grouped together in large numbers on the dead
cortex. On account of their size and colour they are conspicu-
ous even from a distance. The large rough perithecia which are
formed later are much darker red in colour.

It is interesting to note that this fungus cannot injure the

1 Untersuchiingen aiis dem Forstb. Inst, zu Miinchen., I. pp. 151 — 163.

- H. Mayer, Ueber den Parasitismus von Nectria cinnabarina. Un-
lersiich. a. d. Forstb. Institut zu Micnchen, III.

* [This fungus is extremely common on black currant and other trees in
England. It is the species which, in its gonidial form, is so often observed
on pea and bean sticks, dotting them over with scarlet points. ^Ed.]

INJURIES INDUCED BY PLANTS

97

living cambium and cortex. It is, in fact, only able to invade
them when they have been killed either by frost or by the want
of w^ater consequent on the
wood drying up centrifugally
under the influence of the
mycelium of the parasite.

The simplest way to limit
the increase of the parasite
is to cut off and burn twigs
and branches that are bear-
'^^S gonidia and perithecia.
The immediate application of
tar or grafting- wax to wounds
of all kinds is the best safe-
guard ap-ainst infection.

POLYSTIGMA

The various species of
Polystignia induce the forma-
tion of red fleshy blotches
on the leaves of trees belong-
ing to the genus Prnnus.
Polystigma rubrujii^ occurs
on the leaves of the plum
and sloe. On the under side
of the leaves, which in sum-
mer display the large deep-
red fleshy blotches, numerous
small punctures will be found.
These are the orifices of the
spermagonia, which are buried
in the leaf- parenchyma, and
from which hooked colourless

spermatia afterwards appear. The perithecia only occur upon
the leaves between their fall and the following spring. By
sowing the ascospores on young plum-leaves new spermogonia
are obtained in six weeks. The best preventive measure is to

^ Tulasne, Select a Fiaigorum Carpologia^ II. p. 76.

H

Fig. 45. — Wood of maple containing the
mycelium of N. cintmbariiia ; magni-
fied by 1200. The vigorous mycelium,
a a, traverses the elements and dis-
solves the starch-grains, b c, first
attacking the granulose. As the cel-
lulose and the mycelial filaments, ci,
are decomposed, a green solution ap-
pears in the interior of the elements.
The walls are much perforated, as at e e.
(After H. Mayr.)

(-/

98 DISEASES OF TREES

get rid of the infected leaves by raking them together and
burning or burying them.

Poly stigma fiilvum attacks Primus Padiis and Amygdahis.
This parasite is specially destructive to almond-trees, the yellow
patches frequently embracing more than half of the whole leaf-
surface. As the perithecia are formed on the fallen leaves in
the following spring, it is advisable to burn them.

Polystigma ochraceitm is parasitic on the leaves of the wild
cherry.

CLAVICEPS PURPUREA.! ERGOT

Mention may also be made here in a few words of that
disease of cereals which, from the appearance of peculiar
sclerotia or mycelial tubers, is designated ergot.

The well-known black bodies that accompany ergot, and
which occur on many species of Graminece, fall to the ground
when the crop is reaped. There they pass the winter, and
after germinating in the moist soil in the following spring
each sclerotium generally produces a number of long-stalked
spherical sporophores. Sunk over the whole surface of these
reddish spherical bodies are to be seen numerous flask-shaped
perithecia, whose orifices project somewhat above the general
surface. Each ascus holds eight filamentous spores, which reach
the open air by being pushed out through the orifice. Should a
filamentous spore chance to reach and germinate on the flower
of a cereal, the germ-tube forces its way into the ovary, where the
mycelium develops in the tissues and almost completely con-
sumes them. The ovary, which is entirely enveloped in mycelia,
displays on its surface brain-like corrugations, which are the
gonidial stromata. The gonidia, which are very small, oval,
unicellular, and colourless, are imbedded in a sweet mucila-
c-inous fluid which is secreted by the gonidial stromata, and
appears in drops between the parts of the flower, being known
as honey-dew. This gonidial form of the parasite was formerly
designated Sphacelia segetum. Only after the formation of
gonidia is finished does the ergot proper appear, and this it does

Tulasne, Ajdi. des set. nat.^ 3rd sen, vol. xx. p. 56.

INJURIES INDUCED BY PLANTS 99

at the base of the ovary, though completely independent of it.
Morphologically it is essentially distinct from Sphacelia segetum
in having a peculiar pseudo-parenchymatous structure. The
original tissues of Sphaalia segetuui, with possibly some
remnants of the ovary, die completely, and adhere for a short
time to the apex of the ergot.

From what has been said, it will be seen that the disease is
spread partly by the sclerotia that hibernate from year to year,
and partly by the innumerable gonidia which, suspended in the
solution of honey-dew, are carried by various species of insects
to the healthy graminaceous flowers where they germinate and
which they infect.

On account of the sclerotia that reach the fields in the seed
being still capable of germinating in spring, the farmer en-
deavours to prevent the disease by using clean seed-corn.
The ergot should also be gathered before harvest, and this
is accomplished at little cost, because it fetches a good
price. *

AGLAOSPORA TALEOLAi

Amongst the many forms of canker met with on the oak,
some of which still await investigation, the one that is caused
by Aglaospora Taleola is characterised by a number of striking
peculiarities. It would appear to be confined to woods under
the age of forty years, and it is only so long as oaks are without
true bark that they are liable to attack. The disease manifests
itself in the following way. Both on the dominant and the
smaller trees large patches of the smooth cortex die and become
brown, but as this usually occurs only on one side of the stem
the whole of the tree does not succumb. As the cortex often
dies over long distances and on various sides of the tree, patches
of sound cortex are to be met with surrounded on all sides by
dead tissue (Fig. 46, \, a). A year afterwards numerous round
or oval cushion-like stromata appear in the dead cortex. Later
on these break through the periderm in one, two, or three places,
so as to open up external communication with the gonidiophores

' Fflrstlich-natiirwissensch. Zcitschrift, January, 1893.
* [Owing to its use in medicine. — Ed.]

H 2

Fig. 46. — Portions of oaks, thirty-five years old, attacked by A. Taleola ; two thirds
natural size. No. i has been attacked for one to two years, and still shows some
sound patches, as at a a. Numerous stromata are visible on the dead cortex. No. 2
has been suffering from the disease for four years. In the upper portion a canker-
spot will be seen which is still unhealed, while below another is shown which is
nearly closed. No. 3 represents a cross section showing three canker-spots, five,
eight, and ten years old respectively.

INJURIES INDUCED BY PLANTS

lOI

Fig. 47. — Cortex with stromata,
which at a are covered by the
periderm ; at b the periderm has
been removed ; c shows the cross
section of a stroma ; magnified
five times.

and the openings of the perithecia (Fig. 47, a). When the peri-
derm is removed, the stroma appears in the brown cortex as a
dark brown mass of tissue (Fig. 47, /;). If a section be made
of the latter (Fig. 47, r), a black
line will be perceived which sepa-
rates the tissues of the cortex
from those of the fungus. For
each of the openings that appear
at the surface one will generally
recognize three perithecial cham-
bers in the stroma.

If a section is made at right
angles to the stroma so as to
expose the longitudinal view of
the aperture of a perithecium
(Fig. 48), it is seen that the
bounding line consists of dark
brown mycelium {a), which, be-
ginning beneath the surface of the dead periderm, separates
the whole stroma from the cortex, and even traverses the
outermost sclerenchymatous bundle [b). The tissues thus

enclosed consist of de-
composed cortex and
a large quantity of
mycelium. The flask-
shaped perithecia unite
at ^to form a common
neck, the aperture of
which breaks through
the periderm. In the
outer layers of the cor-
tex {c) close beneath
the periderm are the
gonidiophores, which
disperse numerous go-
nidia by abstriction.
The gonidia are sickle-shaped (Fig. 49, a), while the ascospores
that are produced in the perithecia are bicellular and provided
with peculiar filamentous appendages (Fig. 49, b). Three such

Fig. 48. — Cross section of a stroma, a represents
the bounding zone consisting of mycelium; b, the
sclerenchymatous strands of the cortex ; c, the
gonidiophores ; d, the point where several peri-
thecia unite.

I02 DISEASES OF TREES

appendages spring from the middle of the spore, and one from
each end. It is the gonidia and spores that infect the cortex.
It would appear that before infection can occur the periderm
must be slightly injured, and this happens with great frequency
in thick oak woods owing to the rubbing
of the branches of adjoining trees against
each other. Soon after the cortex has been
killed the alburnum becomes brown, and it
frequently happens that absolute decom-
position sets in, in the course of the year.
The sound portions of the tree begin to

Fig. 49.— «, gonidia, form a callus along the edge of the dead
and b, asci oi A. ^ ^

Taleola. part, SO that sooner or later the latter is

again covered over. The dead fibrous cortex
maintains its position for some years, but in the end it is entirely
cast off, so that the dead wood becomes visible (Fig. 46, 2). Of
course the same tree may in the course of years be repeatedly
infected at various points, as the accompanying cross section
(Fig. 46, 3) shows.

This disease is accountable for the death of a great number
of oaks, and renders frequent felling and strong thinning
necessary. The dominant fast-growing trees recover from their
injuries more rapidly than those of slower growth, the con-
sequence being that one is left with a thin wood, consisting for
the most part of the largest trees.

When the disease appears in a young oak wood, it is
advisable at once to fell the infected trees, except where
they belong to the dominant classes. The latter are thus
stimulated to increased growth and enabled to recover from
their wounds, and this result will follow with the greater
certainty if the wood is underplanted with beeches or some
other soil-improving species. The chances of infection are
also thereby reduced, partly owing to the removal of the
diseased trees, and partly because there are afterwards
fewer opportunities for the occurrence of wounds induced
by friction.

Plowrightia morbosa^ (Cucurbitaria morbosa). The

^ W. H. Farlow, "The Black-knot." Bull, of the Bussey Institution.
Bot. Articles., 1876, p. 440.

INJURIES INDUCED BY PLANTS 103

Black-knot of Stone-fruit Trees. Although this disease has
hitherto been met with abundantly only in North America, still
it may find a place here, because experience has taught that
the diseases of cultivated plants may be very easily transported
to us from other parts of the world. It makes its presence
known by the occurrence on the twigs, of plums and cherries, of
hemispherical swellings, which project to about -| of an inch and
are usually congregated in groups.

The surface of the swellings is covered by the gonidia of
the parasite. The ascophores, which ripen in January, are in
the form of round prominent black capsules. The twigs that
are beset with knots should be removed as completely as possible
and burned.

Physalospora Bidwellii is a parasite of the vine which has
been constantly spreading in France since 1885. The disease,
which is known as " Black-rot," is usually confined to the
berries, the young tendrils and stalks of the bunches being
attacked only in exceptional cases. It makes its appearance
a short time before the grapes ripen, when it may be recognized
by the appearance of a small round sooty blotch, which on
enlarging assumes a reddish colour, getting more intense towards
the centre. In a day or two the berry is entirely destroyed, and
three or four days later it assumes a dark colour and becomes
perfectly withered. The skin and succulent tissues become
wrinkled and shrunk and adhere to the seeds, without,
however, showing any wounds. Thus it is not a case of
decomposition but of withering. Gradually but slowly the
disease spreads from bunch to bunch and grape to grape. Its
occurrence would appear to depend on a high temperature and
a humid atmosphere.

The perithecia, pycnidia, and spermogonia of this parasite are
known. The fungus survives from one year to another by
means of stylospores which are contained in the pycnidia, and
also by means of sclerotia.

Coniothyrium diplodiella, a fungus which attacks the vine, is
only known in the form of pycnidia. The disease which it induces
has occurred as an epidemic in Italy, France, and Switzerland.
The fungus for the most part attacks the branches of the raceme
and the stalks of the berries, and these parts frequently become

I04 DISEASES OF TREES

perfectly rotten before the berries themselves are attacked. The
diseased berries soon assume a pale colour, and the yellowish
white appearance is so characteristic as to have suggested for
the disease its popular American name of " White-rot," to
distinguish it from the dark discoloration induced by Black-
rot. So far no effective method of treatment has been
discovered.

Gloeosporium ampelophagum {SpJiacdoina ampelinnni)
produces the " Anthracosis " of the vine. On all parts of the
plant are observed brown blotches which rapidly become black.
These soon turn to depressions surrounded by a ridge. Later
on, when the blotches and surrounding tissues dry up, projecting
portions of the mycelium bearing gonidiophores make their
appearance on the surface as small white spots. Pycnidia are to
be found in the ridge. Anthracosis finds the conditions best
suited to its development in warm situations after prolonged
damp weather.

Didymosphaeria populina attacks the Lombardy poplar, and
produces a disease which is met with in man)' parts of France
and Germany.^

In spring a brown blotch on one side of the young twigs
situated on the lower branches indicates the point to which the
mycelium of the fungus has extended. A little later all that
portion which is situated above the original blotch becomes
black and bends inwards. The buds situated below the diseased
spot produce fresh shoots, which become infected in the following
spring. Branches whose shoots are largely infested wither up
entirely. The lower part of the tree, which suffers most from
the disease, becomes very bushy owing to the abundant
production of suckers, consequent on the stimulus imparted
to the buds by the destruction of the shoots. These sucker-
shoots ultimately succumb to the same fate as their predecessors.
As a consequence of this state of things, all the nourishment
is used up in that part of the tree, with the result that the top of
the infected tree withers before the parasite has ascended so far.
In the month of May the pycnidia begin to break through the
epidermis to admit of the escape of elliptical hyaline st}'lospores,

1 Vuillemin, Compt.Rend.2i\h March, 1889, and Prillieux,zW(/. 27th May,

INJURIES INDUCED BY PLANTS 105

from which one or two much-septated germ-tubes are deve-
loped laterally or terminally. The perithecia, which afterwards
predominate, appear at the same time. As such they remain
through the winter and the following spring. They are
spherical in shape, and measure 0'2 mm. in diameter, and
contain paraphyses and asci, the latter having eight bicellular
spores.

The disease may be combated by lopping off the lower
branches of infected trees.

The gonidium form of this fungus is Fusidadiuni TremiilcUy
which develops on leaves that have been infected in the previous
spring by the ascospores.

DISCOMYCETES *

The essential difference between the Discoinycetcs and
Pyrenoviycetes is that the asci are not formed on the internal
wall of a closed spherical or flask-shaped organ (perithecium),
but on the surface of an open saucer-shaped fructification
(apothecium). Before the ripening of the spores the asci are,
at most, protected by a covering which does not belong to
the fructification itself, but is partly formed out of the epidermal
layers of the host-plant.

The Discomycetes are arranged into several sub-families,
amongst which the P/iacidecs are to be distinguished by the
hymenial layer, originating not on the surface of the fungus-body
but in its interior, where it remains covered, temporarily or
permanently, by the fungal tissues.

Special mention may be made of the genera RJiytisma and
Hysterium, which belong to this group.

RHYTISMA ACERINUM^t

This fungus causes one of the best known of the blotch-
diseases of the Maples. Acer platanoides suffers especially from
this parasite, A. psendoplatanus and A. campestre in a less degree.
On the leaves in July we first of all observe round yellow

^ Cornu, Compt. rend., Ixxxvii. (1878), p. 178.

* [The reader may be referred to Phillips's British Discomycetes (Kegan
Paul & Co., 1887) for an account of our native forms.— ED.]
■]■ [Very common in this country. — Ed.]

io6

DISEASES OF TREES

marks from one to two centimetres in diameter. In August
these begin to turn black (Fig. 50), and the leaves usually fall
somewhat prematurely, so that, by the end of September, the
trees are, for the most part, leafless.

Not till some time during winter or the following spring do
the numerous, somewhat prominent, vermiform apothecia appear
on the black blotches of the rotting leaves. During damp warm
weather these open by a longitudinal fissure. The disease is very
easily produced artificially by laying such black portions of the
leaves of the previous year on young maple-leaves during wet

weather, or in a moist chamber, in
the month of May. The filamentous
spores which escape germinate,
and produce fresh blotches. As
this fungus agrees very closely with
the next genus, Hysterium, both as
regards origin of the perithecia
and the development of the black
stroma, I will not pursue this part
of the subject further here.

The injury, which consists in the
reduced power of assimilation of the
leaves, is not so great as to warrant
the expense of instituting preven-
tive measures. These would con-
sist in raking togetherand removing
the leaves in autumn. In gardens
and parks, where this is done from
other motives — for instance, in the
English Garden in Munich — one never meets with an example of
Rhytisina, whereas along the country roads and forest paths in
the immediate neighbourhood of the city, where the leaves are
left to lie in ditches and hollows, the disease occurs with great
intensity.

RHYTISMA PUNCTATUM

This species of R/iytisma, which closely resembles the pre-
ceding one, is also to be met with on the leaves of Maples.
They are to be distinguished, however, by the appearance of the

Fig. 50. — Part of a leaf of the
Norway maple, showing A'.
acerimun. The black blotches
are surrounded by a pale brown
zone of dead tissue.

INJURIES INDUCED BY PLANTS 107

region of the leaf that is occupied by the mycehum : this in
the former case is a black blotch, and in the latter consists of
black spots on a green ground. In autumn, when the leaves arc
quite yellow, the green colour of the chlorophyll persists in the
blotches for some considerable time.

RHYTISMA SALICINUM

Black blotches similar to those produced by R. acerinmn often
occur on Salix purpurea, nig7'icans, Caprea, aurita, &c. These
are caused by RJiytisma salicinum, but are of relatively minor
importance.

HYSTERIUM (HYPODERMA)

The genus Hysterhim possesses black elliptical to linear
fructifications, which project from the leaves as black, lustrous,
wart-like bodies.

The spores are linear, their walls being externally
mucilaginous and swollen. In the case of the three following
species the germ-tube probably always enters by a stoma. The
mycelium spreads between the cells in the parenchyma of the
leaves of conifers, which consequently become brown and die.
Should the disease attack a leaf near the base at a time when
the upper parts are still healthy and capable of assimilating
under the influence of light, and should the transportation of the
products of assimilation from the leaf be prevented by the death
of the elements of the bast, the plastic substances collect in the
form of starch-granules in such large quantities as to completely
fill up the leaf.

The tissues of the leaves, which are at first pale green, after-
wards become brown, and frequently the fructifications do not
develop in them for more than a year. The ascogenous
fructifications are often preceded by spermogonia, which in the
case of the silver fir (Fig. 53) are arranged on the upper side
of the leaf in two sinuous longitudinal ridges, whereas the
apothecia which produce the ascospores are united on the under
side of the leaf to form a single similar ridge. Both originate
by the mycelium penetrating into and rupturing the epidermal
cells. Ii then develops luxuriantly and forms a lenticular
fungus-body, which afterwards becomes deep brown in colour.

jo8

DISEASES OF TREES

The stroma, which first produces paraphyses and later asci,
originates underneath this mycehal body, which is firmly
attached to the epidermal cells.

The moister the weather, the more rapidly do the spores
ripen. They are disseminated only when a long spell of wet
weather has saturated the dead leaves with water and enabled
the paraphyses and spore-walls to swell by contact with the
water. This swelling leads to the rupturing of the leaf and
the formation of a longitudinal fissure, which immediately

Fig. 51. — Hysteritini niaci-osporum, showing a transverse section through a ripe

ruptured stroma.

recloses on the occurrence of dry weather or when the spores
have escaped (Fig. 51).

HYSTERIUM NERVISEQUIUM^

The distribution of this disease is coterminous with that of
the silver fir, though I have found it really injurious only in the
Erzgebirge, where large woods of silver firs, even of advanced
age, had lost the majority of their leaves. Brownness of the
leaves is always observed for the first time from May to July,
and occurs on the two-year-old leaves which are entering their
third year. A few months after the leaves have turned brown
the spermogonia develop on their upper side, where two sinuously
corrugated black longitudinal ridges make their appearance
(right part of Fig. 53).

^ R. Hartig, Wichtige Krankheiten, pp. 1 14 ei seq.

INJURIES INDUCED BY PLANTS

1 09

Later on the apothecia appear on the under side as a longi-
tudinal ridge on the mid-rib, and ripen in the following April,
when the shoot is three years old. A large proportion of the
leaves, however, fall earlier, the perithecia being produced on

Fig. 52. — The under side of a branch of
silver fir, showing the perithecia united
into a longitudinal ridge.

Fig. 53. — Hysteriuin ner-
viscqiiitim on the leaf
of the silver fir ; the
leaf on the left shows
the apothecium on the
under side, that on the
right the spermogonium
on the upper side.

^

the comparatively few leaves that remain /;/ situ. It may also
be remarked that still older leaves may contract the disease.

HYSTERIUM MACROSPORUM^

This disease of the spruce produces the " spruce-leaf redness,"
which in many years occurs with great severity in woods from
ten to forty years old.

Its presence may be detected by the leaves of the previous
year's shoots turning brown in May, or possibly not till autumn,
and by the invariable occurrence of abundant mycelia in the
leaves even before they become brown. Leaves which change
colour in spring reveal the commencement of the formation of
perithecia in July of the same year, and these ripen next spring
in April and May. At that time they are present on the two-
\ear-old shoots. I observed this rapid process of development
in the humid climate of the Erzgebirge. At Eberswalde, on the
other hand, the leaves on the two-year-old shoots do not become
^ R. Hartig, M'ichtige Krankheiten^^. loi.

no • DISEASES OF TREES

brown till October, and the formation of pcrithecia begins on
the three-year-old leaves in June of the following year, the spores
ripening in the succeeding March and April. The apothecia
appear as long, straight, lustrous-black ridges, for the most part
only on the two under sides of the leaf (Fig. 55). The spores
are about twice as long as those of H. nerviseqiiiuni. It is
desirable that further investigation should be directed to this
and to the immediately preceding disease, because I have not
yet been able to clear up thoroughly many details in the develop-
ment of these parasites. Especially has no explanation so far

Fig. 54. — A spruce-branch, showing
brown leaves on the upper two-year-
old portion, and apothecia on the part
that is three years old.

Fig. 55. — Apothecia
on a spruce- leaf.

been offered regarding the phenornenon of the leaves of the
youngest shoots of many spruces first becoming brown and
then dropping off in autumn, so that these shoots become
almost completely defoliated. Instead of long apothecia-
ridges developing on such leaves, small isolated apothecia-
tubercles similar to those of Hysterhiin Pinastri make their
appearance.

HYSTERIUM PINASTRI*

This is a species of fungus which is everywhere present in
pine woods, and has been identified by Goppert^ as the cause of

' Goppert, Verhandl. d. schlesischen Forstvcreins^ 1S52, p. 67.
* [Common in England. — Ed.]

INJURIES INDUCED BY PLANTS in

the pine-leaf cast. Under the name " Pine-blight" (leaf-cast or
shedding) the most various diseases have been included. These
attack young and old pines, and are characterised by the leaves
becoming brown, and usually also by their being prematurely
shed. The causes of these diseased conditions are very various.
In the first place, frost may actually cause the death of the young-
leaves of pines. On July 23rd, 1878, large pines, especially such
as were growing along the margin of the wood, were so severely
affected by frost in the Turoscheln district that those parts of
the new leaves which had emerged from the sheath died.

As however the leaves of the Scotch pine do not protrude from
the sheath before the beginning of June, late frost can do injury
only in very few cases and in very exceptional localities. In
many seasons one observes — frequently only on one side, espe-
cially the east side, of trees— that all the leaves of the youngest
shoots on trees that are much exposed to the wind become
uniformly brown, except the lowest part, which is enveloped by
the sheath. Whether, in such cases, the injury is always due to
actual frost, or even to severe cooling, I am not in a position to
determine.

In many cases the browning, death, and shedding of the leaves
are the result of drought.^ In cases where the pine seed-beds
have been covered with snow in winter, but which has disappeared
after a few warm sunny days without the ground thawing, it will
be found that the leaves soon become brown, and that the pines
contract " the blight." If one examines the discoloured leaves
after the appearance of the first symptoms of the disease, he fre-
quently fails to find any trace of mycelia. It is also character-
istic that the brownness is equally distributed over the whole
leaf, or spreads back from the apex uniformly to a greater or less
distance. In such a case we have to do with a drying up of the
leaves, which do not receive a sufficient quantity of water from
the frozen ground to compensate for the loss by evaporation
that takes place in the clear dry weather of winter. Although
erroneously ascribed to the action of frost, the cause is the
same, too, in cases where the foliage of Pimts Strobus, the spruce,
and other conifers, as also dicotyledonous evergreens, becomes

^ Ebermayer, Die physikalischcti Eiiin>irkimge7i des Waldes auf Liift und
Boden, 1873.

112 DISEASES OF TREES

withered on the side of the tree which is exposed to wind or sun.
One should certainly not ascribe the withering of spruce-leaves
during winter on the sunny side of the tree to the action of frost,
and there is quite as little reason for relegating to the same
cause the browning of young pines in frozen ground owing to
direct insolation and strong air-currents.

In the height of summer, about the month of July, exactly the
same phenomenon may be observed during dry weather when
pines in a drilled seed-bed on sandy soil are left standing for a
second year. Only those pines remain perfectly healthy which are
situated at the sides of the paths — that is to say, at the edges of
the beds. In spring the one-year-old pines remain quite healthy,
as long as the soil retains a sufficient supply of moisture and
growth has not begun. Afterwards growth proceeds both above
and below ground, though most vigorously in the marginal
plants, whose roots can obtain water and nutriment from the
paths as well as from the bed. Should transpiration of water by
the plants in July be greatly increased partly in consequence of
the air being dry and warm, and partly owing to the formation
of new shoots and leaves ; and, on the other hand, should the
soil have lost its winter moisture, then the pines wither in exactly
the same way as happens in winter when the ground is frozen
and the sky is clear. Only those plants remain green which
stand nearest to the paths, or at least to the edge of the bed.

In the nursery at Eberswalde, after a severe early frost in
October, that portion of the ground of the pine seed-beds which
the sun could not reach was still frost-bound at midday. On
the other hand, the ground which the rays of the sun could affect
was completely thawed and warmed in the course of the fore-
noon. The seed-beds all over were beautifully green, and very
healthy.

A few days later all the pines in the seed-beds which had been
shaded were brown, whereas those which had been exposed to
the sun remained perfectly healthy. I am able to explain this
phenomenon only by the fact that the frozen ground prevented
the absorption of water by the roots, whereas the clear sky and
relatively warm air furthered transpiration by the leaves. In
this case shading had acted prejudicially.

In by far the greater number of cases the pine leaf-cast is

INJURIES INDUCED BY PLANTS 113

parasitic and epidemic in character, and is to be attributed to
Hystcriniii Pinastri. Where " the cast " has become a calamity
which year after year overtakes the seed-beds and young woods,
it may at once be assumed that the disease is present in this
most destructive form.

It may frequently be recognized on young pine-seedlings
even in the first autumn by the primary leaves acquiring
brown blotches, while the other parts often assume a purple-
red colour.

Even at this early stage one always finds the characteristic
mycelium of the parasite in the brown blotches. Frequently it
also happens in the first autumn that a large number of very
small black spermogonia appear on the diseased leaves (Fig. 56,
d, e), the spermatia of which do not seem to be capable of germi-
nating. After wet summers I have found perfectly ripe apo-
thecia on the leaves of young pine-seedlings even in autumn.
As a rule the black apothecia (Fig. 57, -r), which are much larger
than the spermogonia, do not develop till the following year.
Everything depends very much on the weather. On account of
the dry leaves being unable to offer any nourishment to the
fungus, its development, and. that of its sporophore, can proceed
only during wet weather. Dry summers and cold winters do much
to hinder the development and distribution of the fungus, whereas
wet summers and mild muggy winters are specially favour-
able for its growth. During mild winters the blight frequently
spreads rapidly in nurseries and in regenerated forest areas. I
have never observed the apothecia make their appearance during
the first year on the leaves of pines two years old and upwards.
They usually appear only in the third year, and generally after
the leaves have fallen, though they not unfrequently also ripen on
leaves that have remained /// si'tiL As regards the manner of
distribution of the blight-fungus, it may be mentioned that the
ripe apothecia rupture only after long-continued rain. Then the
tissues of the leaf have been thoroughly softened, and a plentiful
Supply of water has been able to reach the apothecia from within.
This causes the asci and spores to swell, a state of things
which is followed by the forcible rupturing of the apothecium-
cover. Long-continued rains, however, do not usually occur
except with west winds. They are less frequent with north or

I

114

DISEASES OF TREES

south winds. This is to be remembered in instituting preventive
measures against the Wight. As a rule the diseased leaves of
one-year-old seedling-pines die off completely in spring, without
however falling off. On the other hand, one finds that all the

diseased leaves of the bifo-
\ \ . i /I .. . liar spurs of two-year-old

pines suddenly become
brown after the advent of
warmer weather in March
or April. This is followed

Fig. -56. — A one-year-old pine in spring whicli
has been attacked by H. /'inastri. a,
healthy green leaves ; It, leaves with a
brown apex and green base ; c, green
leaves showing numerous brown blotches ;
d, leaves whose upper portion has become
brown during the previous winter, and
which now bear the spermogonia of H.
Pitias()-i ; the basal portion of these leaves
has become brown more recently; e, leaves
that are completely dead and covered by
spermogonia.

Fig. 57. — a, a one-year-
old pine-leaf in April
showing brown spots
where infected, but still
remaining green to-
wards the base ; /', a
dead two-year- old pine-
leaf in April with
ripe perithecia, x, and
empty spermogonia, jj'.

by a cast — that is, by defoliation of the dwarf shoots. This
shedding, which frequently follows in a few days, is not to be
regarded as the effect of immediately preceding unfavourable
climatic conditions. It is, in fact, one result of the formation
of cork at the base of the dwarf shoots, which are subsequently

IN7URIES INDUCED BY PLANTS 115

pushed off when t^rowth is resumed. Seedlings affected b)-
the blight usuall}- perish, and can onl}- recover when about
half of the leaves remain green and escape fresh infection. It
is decidedl)- inadvisable to make use of diseased yearling seed-
lings for planting. Neither is it advisable to use diseased
pines two years old and upwards, because they are usuall}-
so weakened by transplanting that thc)^ soon perish. Diseased
plants on a regenerated area ma}-, under favourable circum-
stances, recover from the disease. This, however, never happens
when the mycelium of the fungus has spread from the leaves
into the tissues of the stem itself In particular, if the medulla
of the plant has become brown owing to the presence of the
mycelium, death supervenes, even although the buds look quite
healthy in spring.

Should diseased leaves exist in the crowns of old pines,
infection ma}- be easil}- induced b}- falling leaves. The young
plants are infected either by the dehiscence of the apothecia of
the diseased leaves that fall on them, or b}- the spores that are
conv-e}-ed to them from the diseased leaves in the descending
rain-drops. On this account it is not generall}^ advisable to
form pine seed-beds under the drop of old pine-trees.

Infection, in most cases, accompanies wind and rain which in
blowing over an infected area catches up numerous spores, and
bears them to sound plants. The experience that the disease is
most prevalent on ver}- young plants, and in the case of older
ones onl}- to a height of about two feet from the ground, is to be
explained b}- the fact that onl}- the air-currents that are close to
the ground have the chance of catching up the spores of the
fungus and of depositing them upon plants.

In order to raise health}- plants, it is advisable to form pine
seed-beds in dicot}'ledonous woods, or, at least, at as great a
distance as possible from young woods affected b}- the disease
of leaf-shedding. Nurseries for seedlings and transplanted trees
that have ever shown the disease should onl}- be used for fresh
sowings after all diseased plants in the nurser}- itself, and in its
neighbourhood, have been destro}-ed.

If one is compelled to form seed-beds in unhealth}- districts,
one should select such situations as do not adjoin, at least on
the west side, young diseased woods. If the choice exists, it is

I 2

ii6 DISEASES OF TREES

advisable to form the nursery in such a position at the edge of
the wood that the west winds that impinge upon it shall first
have blown over a wide extent of open country. The seed-beds,
which are not to be made too large, should be enclosed on the
side towards the wood by a perfectly close board fence 6h feet
high. If spruce nurseries are available, containing dense and
high beds of plants running from north to south, the pine seed-
beds may be laid down between the beds of spruce, so that
the latter form a protection against the spores that are borne by
the west wind. Burying pines in deep trenches during winter
often results in complete smothering of the plants owing to the
exclusion of atmospheric oxygen. On the other hand, a light
covering of leaves in winter affords good protection against
contact with the spores.

In protecting the areas under regeneration against fungal
leaf- shed, regeneration by groups, under certain circumstances,
gives the best results. Blanks in close pine woods may be very
successfully restocked even where the disease destroys every-
thing on larger clear-felled areas. This is undoubtedly due in
the first place to the protection afforded against the spore-laden
wind. In arranging the direction of felling one must take all
possible care to prevent the west wind from blowing over large
infected areas before it reaches the part of the wood that is being
regenerated. Very extensive seed-fellings, when they adjoin
each other, further the epidemic distribution of the disease in
any case. Where seed is sown or trees are planted in stripes, it
is a good plan to plough the stripes from north to south, and to
throw the furrow slice on to the west side. If the furrows run from
west to east, the west wind, blowing along them, is sure to carry
the spores from diseased plants to sound ones. Where the
spruce and Douglas fir thrive, these trees may be planted in
stripes running north and south, partly at the edge of the wood,
and partly at fixed distances throughout it, to act as screens and
prevent the disease spreading. This must be done at least ten
years before the final felling of the pine wood.

Areas that are completely overrun by this disease should be
planted with Weymouth pines, or some other disease-resisting
species, according to the character of the soil.

The W'eymouth pine suffers here and there from a leaf-

INJURIES INDUCED BY PLANTS 117

disease which is due to an alUed parasite, Hystenuiii bracliy-
sporuui. I am not j'et able to determine whether Hystcriuin
laricimiui, which has been observed in great abundance
on larches in certain districts of the Alps, is also a true
parasite.

The sub-family of the Pezizecu is to be distinguished by cup-
shaped or saucer-shaped sporophores, which produce the
hymenial layer free on the upper surface.

PEZIZA (helotium) willkommii ^ *

The fungus which induces the larch-blister is the cause of one
of the most destructive and widely distributed diseases of the
larch. It was first described by Willkommr who, however,
made a mistake in its identification, and called it CoTtiaini
amorphiun.

Cortzaun, in fact, bears onl}- a superficial resemblance to
Peziza, and belongs to the Basidioniycetcs. On the strength of a
macroscopic similarity, also, it was next said to be Pesiza
calyciiia, till I recognized that in this fungus we had to do with a
new and still unknown species. The ascophore is at once
distinguishable from that of P. calycina by its very short cup-
stalk. So much by way of explaining the regrettable confusion
of names.

The larch is a forest tree which thrives splendid!}- throughout
the whole of Germany, suffering but little from frost, at least
not more so than other indigenous trees. Originall}', how-
ever, its distribution was confined to high Alpine regions,
because only there could it offer successful resistance to its
enemies. Amongst these enemies are to be classed a number
of insects, notably the Larch moth, ColeopJiom laricclla. This
insect is also found in Alpine regions to a considerable height
(over 4,000 feet), and so widely is it distributed, and so

1 R. Hartig, Ujttersiichimge7i aiis dem Forstb. Inst., I. pp. 63 — 88.

- Willkomm, Mikroskopische Feinde des Waldes, II. pp. 167 et seq.

* [Though often overlooked, this fungus is quite common on the diseased
Larches in EngLand and Scotland, with all the characters and relations to the
"blisters" described by the author. Phillips, op. cit. p. 241, gives it as
LachneUa calycina, and makes no note of its relation to the disease.— Ed.]

ii8 DISEASES OF TREES

numerously represented, that it is at first surprising why it does
hardly any damage there. This is easily explained from the
fact that at high elevations the transition from winter to
spring is very rapid, and the development of the leaf-fascicles
occupies but a short time. On the plains the larch begins to
display green buds even towards the end of March, but their
further development is often retarded for a long time, until,
in the beginning of Ma)% the growth of the leaves pro-
gresses more rapidly. This is the dangerous period for the
larch, because when the caterpillars awake from hiberna-
tion they begin to devour the green buds, and when growth
proceeds slowly these are largely consumed, and the trees
are, for the most part, defoliated. On the other hand, when
the leaf-fascicles develop rapidly, a small proportion of the
foliage suffices to feed the caterpillars. In Alpine regions
the short spring saves the larches from complete or excessive
defoliation, which, especially when often repeated, results in the
crippling and death of the trees. The Larch Aphis also,
C/iennes Laricis, damages the foliage of the larch to no small
extent, though not nearly so much as the moth. The disease
which is induced by P. Willkoinuiii differs entirely from the
crippling which larches experience as a result of the attack of
the moth, aphis, &c. This parasite is indigenous to high Alpine
regions, where it produces the same disease that has resulted in
the destruction of innumerable woods in Germany, Denmark,
and Scotland. In its native habitat, however, it is only under
special conditions of environment that it destroys whole woods.
In order correctly to appreciate this point we must first review
the course of development of the parasite.

The spores — which originate in cup-shaped fructifications to
be afterwards described — soon germinate in the presence of
sufficient moisture, with effect not on an uninjured tree, however,
but only on a wound. Such wounds are very often due to hail-
stones, or to the dwarf-shoots being devoured in spring — as was
mentioned above — or they are formed in the upper angle of
the base of a branch (Fig. 58, U) owing to its depression under
accumulations of snow or hoar-frost. From such wounds the
vigorous, copiously ramifying, septate mycelium spreads in the
soft bast, partly between and partly in the cells advancing in

INJURIES INDUCED BY PLANTS

119

the sieve-tubes, and killing and browning the tissues. The
mycelium also grows into the wood, and even penetrates as far
as the medulla.

That portion of the cortical tissues which has been killed
during the first year dries up and appears as a depression,
especially after growth in thickness has been resumed by the
healthy part of the tree (Fig. 58).

In summer thegrowth of the mycelium ceases, and an unusually

Fig. 58. ^A canker-spot that has been re-
cently formed in the upper portion of
the stem of an eight-year-old larch from
the Tyrol. Infection has occurred above
the branch, b, where a crack has been
formed in the tissues, owing to the branch
having been depressed under a load of
snow. Numerous immature ascophores, c,
have already formed on the dead cortex.

Fig. 59. — Cross section of a well-
grown larch which has been at-
tacked by/'. IVillkommii. Infection
had occurred ten years previously
at the dwarf shoot, a. Each year
the mycelium advances in opposite
directions, in spite of the fact that
a layer of cork, b b, is formed at
the beginning of each growing
season along the boundary of the
living tissue. In the immediately
preceding year a very small quan-
tity of wood had been formed.

broad layer of cork is formed for the protection of the tree
along the boundary between the sound and diseased tissues.
These layers of cork (Fig. 59, b b) which form between the dead
and living tissues induce external rupturing of the cortex
at points along the boundary of the canker-spot (Fig. 60),
the result being that turpentine flows from the interior of
the tree. Year by year the canker-spot enlarges along its
whole periphery, rather more rapidly, however, longitudinally
than horizontally, and it is probably the vital activity of the

I20

DISEASES OF TREES

cortical tissues which in summer causes a temporary inter-
ruption to the progress of the parasite. In autumn the
mycelium again succeeds in entering the Hving bast, either
through the cambium region or by way of the wood, so that,

as a matter of fact, the la}'er of
cork is only of slight service. In
proportion as the passage of the
plastic substances is confined to
one side of the tree, growth of
the wood and bast is stimulated
at that part (Fig. 59). Thus the
conflict between parasite and
host-plant may remain long un-
decided, and in the Tyrol I found
larches still alive with blisters of
a hundred years' standing.

Should the parasite advance re-
latively quickly, and, at the same
time, should the growth of the tree
at the affected part be slow, then
the canker- spot soon embraces
the whole stem or branch (Fig. 59),
and the tree dies above this spot.
By artificial mycelial infection
one may, almost without fail,
produce a blister on any part of
a sound larch.

Soon after the death of the
cortical tissues, the cushion-like
stromata of the parasite originate
in the form of small yellowish
white pustules of the size of a
pin-head (Fig. 58 r. Fig. 60 a). In
the interior of these stromata,
and partly on their surface as
well, vermiform passages or roundish cavities are formed, the walls
of which are covered with innumerable club-shaped sterigmata, at
whose apex extremely minute cells originate. Whether these
organs, w^hich appear to be incapable of germination, are

Fig. 60. — A canker-spot of two
years' standing, close to the collar,
and hidden by the grass. On the
upper portion, which is exposed
to air-currents, the stromata are
abortive ; but in the lower por-
tion, which has been kept moist,
they have developed to form
vigorous ascocarps.

INJURIES INDUCED BY PLANTS 121

abortive gonidia, or arc to be classed with spermatia, remains,
in the meantime, undetermined. In this place it is specialh-
important to emphasise the fact that they are incapable of
assisting in the distribution of the parasite.

The small stromata are very readily affected by a dr)' atmo-
sphere and by air-currents, in which they quickly wither and die.
They develop only when constantly surrounded b}- moist aiiV
Under such circumstances the)' produce the well-known cup-
shaped ascocarg^s (Fig. 60, b b). These possess a hymenium
of a fine red colour. The hymenium consists of innumer-
able asci surrounded by filamentous paraphyses. Eight colour-
less spores arc formed in the interior of each ascus. The fact
that the mycelium penetrates even into the wood, and kills it,
explains why one or a few small blisters may greatly interfere
with the growth of the whole stem. Numerous cup-shaped
ascocarps ultimately make their appearance on the dead cortex,
and these are met with even when blisters are absent.

In muggy situations the larches soon become diseased, and die
in a few years without any large blisters making their appear-
ance. The cup-shaped ascocarps of the parasite appear upon the
cortex. It looks as though the large quantity of water present in
larches whose transpiration is interfered with greatly favours the
development and spread of the fungus in the wood, and that the
disease consequently spreads throughout the whole plant.

The foregoing descriptive sketch of the results of my investiga-
tions may suffice to explain the recognized facts connected with
the occurrence and distribution of the disease.

The larch-blister has been indigenous to high Alpine regions
from time immemorial. It occurs, however, with marked in-
tensity only in damp muggy valleys in immediate proximity to
lakes {e.g. the Achensee in the Tyrol, &c.), though on plateaus
it may also destroy a small tree here and there. Owing to the
prevalence of air-currents, freely exposed ascocarps never ripen
on plateaus and valley-slopes. The ascocarps ripen only on
those blisters which are situated at the foot of the stem close to
the ground, or on blistered branches that are in contact with the
earth. This is owing to the surrounding high grass sheltering the
young ascocarps against air-currents, and so keeping them moist.

In the early decades of this century, when the larch was planted

122 DISEASES OF TREES

in various parts of Germany, the enemy was left behind in its
native habitat, and the trees flourished to perfection. Prob-
ably every old forester knows some groups of larches of the
most stately growth which date back to that period. In conse-
quence of these satisfactory results, the larch was generally
planted throughout the whole of Germany. Most excellent
results were obtained, even where the inferior quality of the soil
held out but a poor prospect of success.

But after woods of all sizes had been established from the foot
of the Alps to the coasts of the North Sea and Baltic, the fungus
spread downwards from the Alps, to find everywhere the most
favourable conditions for its development. These consisted of
dense young pure woods, groups that had been formed in re-
planting up old beech woods, moist stagnant air, wounds caused
by the moth, &c. Commerce also assisted to intensify the evil,
diseased larches being sent out from the nurseries and trans-
ported from district to district.

Under these conditions the fructifications of the fungus
attained to luxuriant development and ripened their spores on
the blisters, while the spores found ample opportunity of germin-
ating, and of infecting the trees in the close pure woods. To-day
but few of the many promising young woods remain. The
larches have maintained their ground best in those woods
where a few were introduced as advance-growth. The air
circulating in the freely developed crowns has not only kept
the disease in check, but has also prevented the spores from
ripening on diseased specimens.

Supposing that we have to do with a diseased larch wood, it
is first necessary to determine whether the damage is entirely
due to the moth or whether it is a case of fungoid blister.

Often enough both will appear in company. If it is simply
a case of stunting in consequence of the attack of the moth,
pruning away the branches till only the vigorous upper part
of the crown remains may be permanently beneficial. The
upper branches will grow vigorously, and may form a good,
permanently healthy crown, especially as the moth is most
destructive on the lower branches.

If it is a case of fungoid injury, pruning may assist somewhat
only if the bole as a whole, and especially the part in the crown,

INJURIES INDUCED BY PLANTS 123

is sound If a tree is in vigorous growth, the smaller blisters
low down on the stem, although they increase in size, will induce
death only at an advanced age.

Blisters on the branches are, in themselves, of less importance.
They merely contribute to the danger of the further spread of
the disease by means of spores.

As regards the future cultivation on plains and at moderate
elevations of this so essentially valuable tree, the following points
may be noted in the light of what has been said. It should only
be grown singly — that is to say, it should form but a small part
of a mixture, and it ought, if possible, to be planted somewhat
in advance of the other trees. It should never be planted in
pure woods, and should always occupy an open situation. Where
diseased woods are present in the immediate neighbourhood,
it is better to abandon the idea of cultivating this tree. The
greatest caution is to be exercised in procuring young trees
from outside sources, and plants showing any signs of disease in
the seed or plant beds must at once be removed and burned.

RHIZINA UNDULATA* FR. THE ROOT-FUNGUS ^

On the light sandy soils of Germany, France, &c., especially
in pine and other coniferous woods, one not unfrequently meets
with numerous ascophores o{ R.iindulata growing on the ground.
These bear a considerable resemblance to a morel (Fig. 61).
In diameter they vary from two thirds of an inch to two inches.
The broad ascophore (Fig. 61, a) is undulating and chestnut
brown on the upper surface, diverse in shape, of a velvety lustre,
and glutinous in wet weather. The under side (Fig. 61, h), which is
destitute of a stalk, is pale yellow and woolly, and is frequently
united to the subterranean mycelium by means of numerous loose
mycelial strands (Fig. 62). If a section be made of the ascophore,
it will be found that towards the upper surface the hymenium
(Fig. 63) is composedofasci,each containing eight spores, amongst
which filamentous septate paraphyses, clavate towards the apex,
will be made out (Fig. 63, a). Besides these there are present
numerous non-septate secreting-tubes {b), which project a little
above the surface of the hymenium. These are filled with a

I R. \{?LX\:\'g, Naturioisscnschaft : Zcttschriff, Awgwit 1892.

* [This occurs on heaths, &c., in England.— ED.]

124

DISEASES OF TREES

brown secretion which pours over the surface as a slimy glutinous
substance, swarming with bacteria. The bacteria also find their
way between the paraphyses, so that it is scarcely possible to
get a culture of spores that is free from them. It is these, too,
which induce the rapid decay and solution of the entire ascophorc.
The spores (Fig. 64, a) are spindle-shaped and pointed at both
ends, and the wall of the spore is thickened at both of the ex-
tremities. Before germinating, each
spore generally contains two large
drops of oil.

Ascophores of Rhiai)ia were
sent to me ten years ago from
Silesia, with the remark that in a
young pine wood where many of
the plants had died the fructifica-
tions of this fungus appeared on
the surface of the ground in the
neighbourhood of the dead trees.

Fig. 61. — a, the upper side, and, /',
the under side of a sporophore
of J\. undulata; t: is a small fun-
gus-body.

Fig. 62. — Section of a sporophore.

My request that a few dead trees should be forwarded for in-
vestigation was not complied with, so that it was only two years
ago, on receipt of material from Herr von Bliicher, forester in
Schwerin, that I found myself in a position to make a more
intimate acquaintance with the parasite and its life-history.

In the beginning of August 1890, Herr von Bliicher and Herr
von der Liihe sent me numerous ascophores of the parasite, as
well as diseased and dead conifers, along with information re-
garding the occurrence of the disease at Schildfeld, near Bennin,
in Mecklenburg-Schwerin, The diseased and dead plants were

INJURIES INDUCED BY PLANTS

125

specimens four to ten years old of Abies pectinata, Tsnga Mer-

tcnsiana, Pseudotsuga Douglasii, Picea Sitkcvnsis, Pinus Strobus,

and Larix curopcca.

The part of the wood that was attacked extended to about

2I acres. In the whiter of 1889-90 the wood which then existed
— namely, a thin stocking of pines, larches,
and spruces about fifty years old — was
stubbed, and in the spring of 1890 the
area was replanted chiefly with three- to
four-year-old plants, which were inserted
partly in pits and partly in notches.

In the month of June disease had
appeared among the plants. The leaves

]L

Fig. 63. — H ymenium ,
consisting of a,
paraphyses ; b, se-
creting-tubes ; c,
asci, which contain
eight spores each.

Fig. 64. — a, spores of Rhizina ; l>, ditto,
twenty-four hours after sowing ; c,
ditto, twenty-four hours later ; (/, the
spore c more highly magnified.

rapidly died and fell off, and the fungus appeared to be gra-
dually spreading over the area. The ascophores were found
almost exclusively at a distance of about ten inches from the
plants, but on the surface of what had been the pit. But
between the plants also, on the bare ground covered with raw
humus, numerous ascophores were met with. The soil was
sandv in character, covered with raw humus and bilberry-bushes.

126

DISEASES OF TREES

The above report refers onl}- to conifers attacked b}' the
parasite. Professor Crie of Rennes was good enough to send me
more than once the roots of diseased plants of Castanea t'esca.
On one of these I found RJiizina iindidata luxuriantly developed.
On removing a diseased or dead plant from the ground, one
will find that a large quantity of sandy soil is firmly held
amongst the roots by means of numerous fungus-filaments, but

that no outpouring of resin what-
ever is visible (Fig. 65).

On the roots being isolated

fi and carefully examined, it will

be found that peculiar m}'celial

Fig. 65. — The roots of a silver fir
which has been killed by Rhizina.

Fig. 66. — Mycelial growths resembling
Rhizoctonia, which are met with on
the roots of plants infested by
Rhizina, magnified by 3. Mycelial
strands protruding from the cut sur-
face in moist air. Natural size.

bodies resembling Rhizoctonia project from the cortex. At a
distance of two to three fifths of an inch these begin to ramify,
and ultimately divide into filamentous mycelia (Fig. 66). If
one cuts off a root and makes a culture in a moist chamber, it
will be found that such mycelial bodies will form in large numbers
on the cortex, or on the cut surface of the wood. These ramify
in the usual way and end in a fine point (Figs. 66 and 6j).
and are always brilliantly white in colour.

A microscopic investigation will reveal the cause of this
colour, which is due to drops of ethereal oil adhering in great
numbers to the external filaments, or to the apices of the fine

INJURIES INDUCED BY PLANTS

127

hair-like filaments which stand more or less at right angles to
the m)-celial strands (Figs. 68 and 69).

These short simple or compound hairs produce a large drop
of ethereal oil at the apex, which finall)- rup-
tures the elastic cell-wall at the end of the hair,
and flows out. The hair thus comes to have
a funnel-like aperture at its apex (Fig. 69, e).

I am not aware of attention having pre-
vioush' been called to the formation of
ethereal oil in the form of drops by fungi.
The oil is immediately dissolved by alcohol.
As the mycelial filaments in the periphery
of the strands contain numerous small oil-
drops, it would appear that this ethereal oil
is also exuded from the lateral walls of the
hyphas, although it is quite possible that this
has gradually found its way thither from the
apex of the hairs. When the filamentous
m}xelia that envelop the soil-particles are
examined, it will be found that most of the thin threads possess
numerous clamp cells, and are somewhat brown in colour.

Fig. 67.— Mycelial
strands of Rhiziua
which have been
cultivated in moist
air. They are part-
ly separated from
the wood.

Fig. 6S. — A mycelial strand
bearing; hairs.

Fig. 69. — a, a mycelial filament with an oil-
drop attached ; b, ditto, with an oil-drop at
the apex ; c, a hair with a large oil-drop ;
d, a bifurcated hair from whose apices the
oil-drops have become detached ; c, apex
of a hair viewed from above.

Although I have much diffidence in maintaining that this
feature, which otherwise is peculiar to the Hyvieuouiycetes, is

128 DISEASES OF TREES

characteristic of this parasite, still I cannot doubt that these
filaments with clamp cells belong to it. However, I will not
maintain this as an absolute fact, especially as clamps do not
occur either in the interior of plants or in the mycelia pro-
duced by germinating spores of RJiizina.

My first cultures were undertaken on August 19th, 1890, with
fresh spores, which I sowed partly on a gelatine extract of
fruit and partly on humus sandy soil. These produced no
result.

On repeating the culture with numerous spores on Septem-
ber 1 8th, only a single one germinated. On the other hand,
germination was general in twenty-four hours in a seeding on
gelatine extract of fruit which was undertaken on November
18th. These germinating spores are shown in Fig. 64, b. The
extraordinarily thick germ-tube proceeded from the lateral
wall of the spore, and from the first its diameter was as
great as that of the spore itself. After only forty-eight
hours the germinating spore had reached the stage which is
represented, slightly magnified, in Fig. 64, c.

The stout much-branching mycelium is septate, and resembles
in every respect that which is found penetrating the healthy
cortex of slightly or much-diseased plants. Under such circum-
stances it grows between the cells of the parenchymatous
tissues, while in the soft bast its progress is partly intercellular
and partly intracellular, the sieve-tubes being frequently packed
full of a dense filamentous mycelium. In the process of time
the mycelium kills the tissues of the cortex and soft bast, whose
elements become brown and completely dismembered, or, in other
words, isolated. The development is so luxuriant that it forms,
in certain places, a pseudo-parenchymatous fungus-tissue, consist-
ing of vesicular swollen cells. This however is speedily destroyed
as soon as the tissues between the wood and periderm become
almost completely decayed. In this process of decay very
minute organisms resembling Micrococcus play an important
part. When employing a high power, the whole field of view
sometimes swarms with these minute cells, whose diameter does
not exceed i to i"5 micromillimeters. These originate (Fig. 70)
on very small stalks resembling sterigmata, which project some
from the lateral walls and some from the apices of the fila-

INJURIES INDUCED BY PLANTS

129

mentous mycelia. Subsequentl}' they appear to increase by
budding.

It is very desirable that foresters, especially in sandy districts,
should direct their attention to the occurrence and biology of
this parasite.

The term "Soil Canker" has been used for twenty years to
designate all those diseases in young and old woods where no
indications above ground can be referred to as a cause. Such
diseases have their seat below the surface, and gradually
spreading from the first point of
attack they occasion blanks and
gaps in woods and nurseries.
During the last twenty years I
have described a whole series
of parasitic fungi which induce
such diseases. These include
Agaricus inelleus, Trametes ra-
diciperda, Polypoms vaporarius,
Rosellinia guerciua, DcviatopJiora
necatrix, and PJiytopJitJiora oui-
nivora (in the narrow sense).
To these must now be added
RJiizina nndulata.

The various species of Vac-
cinecE are attacked by parasites
of the genus Sclerotinia.^ The
gonidiophores appear in spring
on young leaves and stems, which
consequently become brown, in

the form of a mould-like covering which emits an almond-
like perfume. The insects that are thereby attracted con-
vey the gonidia to the stigmata of the flowers of the
Vaccinea;. A sclerotium is formed in the berries, which be-
come brown, dry, and " mummified " and drop off, and from
them there develop in the following spring one or two
long-stalked chestnut brown cup- like ascocarps. The ejected
ascospores infect the young shoots, and again produce the
gonidium-bearing form.

1 Woronin, Uebcr die ScIc7-otienkra7ikheit der Vaccimeribecrcn, 1888.

K

Fig. 70. — Mycelium ol KJiizina from
the cortex of the silver fir. a, a
filament of average thickness ;
b, very thin filaments ; c, gonidia
resembling Micnxoccus. Magni-
fied 1500 times.

I30

DISEASES OF TREES

Sclerotinia Vaccinii is parasitic on Vacciniiun Vitis Idcsa ;

S. Oxycocci, on V. Oxycoccos ; S. baccanini, on V. Myrtilliis ;

S. niegalospora, on V. idiginosnui.

Of still greater importance, from an agricultural point of

view, is Peziza ciborioides {Sclero-
tinia Trifolionim), the clover-can-
ker, or the sclerotium disease of the
clover. This parasite is interesting
from the fact that on clover-plants
infested by the mycelium sclerotia
from O'l — I cm. in size are formed,
and these produce ascocarps in the
following year in July or August.

A similar course of development
is found in Peziza Sclerotionivi
{Sclerotinia Libertiana), which pro-
duces the sclerotium disease of the
beetroot and carrot.

The best known is Peziza
Fuckeliatia, through its gonidium-
bearing form Botrytis cinej'ea* the
vine-mould, which finds its way on
to various plants in forcing-houses
and conservatories, producing a
loose grey mycelial covering and
killing the twigs.

For some years a species, Botrytis
Douglasii} has proved injurious to
the Douglas fir, which is now gener-
ally cultivated in Germany. In
seed- and plant-beds especially,
where infection by lateral contact
is such an easy matter, one often
notices that the young incompletely

developed shoots die and become brown. The shoots of the

Fig. 71.— Branch of the Douglas
fir, the youngest shoot of which
has been killed by B. Donglasii.
The apex of the shoot of the
previous year has also been
killed.

1 Botrytis Douglasii n. sp., C. Freiherr v. Tubeuf, Bcitriige zur Kenntniss
der Baumkrankheite7i. Berlin, Springer, 1888.

* [Several forms of Botrytis are common and destructive parasites in our
green-houses and gardens. — Ed.]

INJURIES INDUCED BY PLANTS 131,

previous year may also die back for a certain distance
(Fig. 71).

One afterwards observes, both on the leaves and on the
twigs, small black sclerotia not larger than a pin-head. In
a moist chamber these germinate and produce the gonidiophores
of Botrytis. The gonidia germinate easily, and infect the tender
shoot of the Douglas fir. Tubeuf's researches show that silver
firs, spruces, and larches were also infected by this fungus,
and it remains to be determined whether diseases in the forest
may not also be induced by it.

GYMNOASCE^ 1

In the case of the parasites that belong to this sub-family
of the Discoinycetes, there is no proper fructification. The
hymenium is a flat layer which occupies the surface of the
plant, and consists of free tubes which develop among the
epidermal cells, or between the epidermis and cuticle.

All the species induce characteristic hypertrophy of the
part of the plant that is attacked.

EXOASCUS PRUNI-*
This is a widely distributed parasite, which is familiar enough
by causing the formation of the so-called " Mock," " Pocket,"
" Starved," &c., plums. Its mycelium persists from year to
year in the soft bast of the branches of Priums doniestica,
P. spinosa, and P. Padus, in which it grows intercellularly,
gaining access to and contorting the young leafy shoots. The
same is true in the case of the flowers, where malformation of
the ovary is recognisable even in the beginning of May.
Proceeding from the soft bast the mycelium spreads through
the fleshy parenchyma of the fruit, where, on the one hand,
it prevents the formation of the stone and seed, and, on the
other, induces elongation and the well-known deformation of the

1 Sadebeck, U7tte7'siichungen iibcr die Pilzgattieng ^'- ExoasciisP Hamburg,
1884.*

- De Bary, Beitriige ziir JMorphologte dcr Pilze, I. p. 33.

* [Common in this country. Sadebeck has just pubUshed an exhaustive
monograph on the whole group of parasitic ExoascccB (Hamburg, 1893),
revising the classification, and clearing up many doubtful points.— Ed.]

K 2

132 DISEASES OF TREES

fruit. Numerous mycelial branches penetrate between the
epidermis and cuticle, where, by the formation of transverse
branches, they form short chambers. In this way an almost
uninterrupted layer of fungal mycelium is formed under the
cuticle. Each fungus-cell next grows outwards to produce a
short cylindrical ascus, and the cuticle after being detached
from the epidermis is ruptured, and the ascogenous layer
becomes completely exposed.

Each ascus becomes separated from the basal part, or "stalk,"
by a transverse septum ; and, by free cell-formation, six to eight
roundish spores are formed in its interior, to be afterwards
ejected through the ruptured apex. The spores either germi-
nate forthwith, or multiply by budding, and form a kind of yeast.

The pocket-plums decay owing to the concurrence of numerous
saprophytic fungus-forms.

Exoascus deformans is closely related to the foregoing species,
but lives partly in the leaves and shoots of Persica vulgaris and
Amygdalus comnmnis, and partly in the leaves and shoots of
Primus avuun, P. Cerasus, P. Chanicccerasiis, and P. domestica.
On these trees, according to the investigations of Rathay,^ it
causes the so-called witches' brooms. Whether the Exoascus
that occurs on cherries is really a new species {^Exoascus Wies-
neri), as Rathay assumes, or whether the distinctions that have
been noted are not perhaps due to differences in the host-plants,
must remain doubtful until infection-experiments have been
carried out. Peculiar crumpling is induced in the leaves, similar
to that which is sometimes caused by Aphides. The branches
that have been taken possession of by the fungus anastomose
freely, and usually exhibit decided negative geotropism, while
the basal portion is often hypertrophied. These constitute
the thunder-brooms and witches' brooms. Towards the base,
the branches of these witches' brooms are often double the
thickness of the branches from which they spring. Towards
the apex, on the other hand, they become normal. A possible
explanation of these phenomena is that, as the mycelium grows
more slowly than the young shoot, it finds immature tissue only

1 Rathay, Ueber die Hexenbesen der Kirschbdume und iiber Exoascus
Wiesneri, Rath., im Sitzber. d. Wien. Akad. d. Wzssensch., vol. Ixxxiii., March
l88i.

INJURIES INDUCED BY PLANTS

133

at its base, which, under the influence of the parasite, enlarges or
increases abnormally. On the other hand, the mycelium arrives
too late at the apex of the shoot to be able to exert a similar
influence there.

Exoascus InsititiiS produces witches' brooms on Pritnus in-
sititia.

Exoascus bnllatiis induces bladder-like swellings, which after-
w^ards become mealy underneath, on the leaves of pear-trees.
In the case of the hawthorn it produces formations like witches'
brooms, which bear leaves of a reddish colour.

Exoascus ahiitorqiius {Asconiyces Tosqui)ietii) often appears im
great abundance both on the
leaves of Alnus glutinosa and
on the scales of the female
catkins of that tree and of
Alnus iiicana. Not only does
it cause the leaves to become
crumpled and corrugated, but
also to increase in size in
every way. On the cones of
the alders it produces pocket-
like outgrowths, which, when
fresh, are of a brilliant red
colour, and remind one some-
what of the pockets of plums
(Fig. 72).

Exoascus flavus {Sadebeckii)
causes the formation of yellow blotches, in this case also on the
leaves of A. ghitmosa and A. incana.

Exoascus epipJiyllus, which infests the leaves of Alnus incana
and A. glutinosa, is only with difficulty to be distinguished from
the former species by its broader stalk-cells. It induces sinuous
crumplings of the leaves, the outgrowths usually appearing on
the upper side.

Exoascus borcalis produces witches' brooms on Alnus incana.
These are very numerous near Munich and at other places in
Bavaria. It is probably identical with E. cpipJiyllus.

Exoascus turgidus {Taphrina betulina) very often produces
witches' brooms on the birch.

Fig. 72. — Malformation of the fruit of
Alnus imanu induced by Exoascus.

134

DISEASES OF TREES

Fig. 73. — A leaf of /'. niora
affected by Exoasais Pof-iili.

f IG. 74. — Malformation
of the fruit of P.
trennila, due to E.
Popiili.

Fig. 75. — -A witches' broom of the hornbeam induced by Exoasctis Carpini.
Half natural size.

INJURIES INDUCED BY PLANTS 135

Exoasciis Betithe {Ascojiiyces BetiilcE) produces bladder-like
outgrowths on the upper side of the leaves of the birch.

Exoascus carnca produces globular bladder-likc swellings on
the leaves of the birch.

Exoascus aureus* {Tap/iriua aurea, T. Populi) produces golden
yellow outgrowths on the leaves of Populus nigra (Fig. 73)
and pocket-like outgrowths on the ovary of P. treimda and
P. alba (Fig. 74).

Exoascus Carpiiii produces witches' brooms on the hornbeam

(Fig- 75)-

Exoascus ccerulcscens {^Ascomyces ccBruksceiis) produces bladder-
like swellings on oak-leaves.

Exoascus Ulmi produces outgrowths on the upper side of elm-
leaves.

IMPERFECTLY KNOWN ASCOMYCETES t

The number of those fungus-forms with all of whose stages
of development we are not yet acquainted is an extremely
large one. In particular a large number of fungi are known
to us with whose gonidia — whether on sporiferous hyphae or in
closed organs (pycnidia, spermogonia) — we are familiar, but of
whose ascophores we are ignorant, so that we are unable
systematically to classify them.

A few of the more important species that occur parasitically
on trees, especially on forest trees, may be referred to here.

Cercospora acerina.i The Maple-Seedling Fungus

In rainy years a disease is sometimes conspicuously prevalent,
both on maple seedlings in the nursery and on those which have
sprung up naturally. It is to be recognized by the cotyledons
and first leaves, and also by the shoot axis, becoming black
and decomposed, or, if less severe, merely by black blotches

1 R. Hartig, Ufitcrsuchujij^efi, I. p. 58.

*[I have found this species deforming the ovaries of poplars in Surrey.—
Ed.]

t [No group of fungi offers more opportunities to the investigator anxious
to add to our knowledge of pathogenic forms than the numerous " imperfect "
ascomycetes so common on our trees, &c. — Ed.]

136 DISEASES OF TREES

appearing on the leaves. Even with the naked eye one may
often recognize a grey covering on the diseased leaves.

On more thorough investigation we perceive a luxuriant
mycelial growth in the tissues of the diseased parts, from which
innumerable short gonidiophores grow outwards. These pro-
duce tufts of long curved multicellular gonidia, which germinate
in moist air even in a few hours, and push their germ-tube
directly into the epidermis of the maple-leaves, which conse-
quently become brown.

The mycelium, which is intercellular, swells up to form
large brown mycelial resting-cells and cell-plexuses, which
contain oil-drops. These persist during the winter, and carry the
disease over to the following year. The fungus is also able to
live saprophytically on humus in the soil.

PESTALOZZIA HARTIGII^

The disease induced by this fungus, which has often been met
with all over Germany, appears most frequently in seed- and
plant-beds which are stocked with spruces and silver firs. I
described it in the AUgevieine Forst- unci Jagd-Zeitung, 1883,
where I advanced the view that it was due to the formation
of ice and the consequent crushing of the cambium. As I
expressly stated, the truth of the hypothesis which I there
advanced had still to be determined. Von Tubeuf has now
proved that here, as in so many cases, we have to do with a
parasitic disease. In summer one notices in nurseries of the
spruce and silver fir that a number of plants first become pale
and then die. If the plants are pulled up, it is seen that the
cortex on the parts immediately over the ground is withered,
but that, farther up, the stem is swollen as a natural consequence
of continued growth (Fig. "](>).

When the wood dries up or dies at the point where death of the
cortex first took place, the plant must perish. On the rind, at the
place where contraction is visible, one finds the mycelium of the
fungus, and numerous gonidial cushions which develop partly in

1 C. V. Tubeuf, Beitriige zur Ktnntniss dcr Baui/ikrank/ictte?i, pp. 40 — 51,
Plate V. Berlin, Springer. 1888.

Fig. 77. — Gonidiophoie of P. Hartigii.
(After Tubeuf.)

Fig. 78. — A branch of silver fir infected by
Fig. 76.— a young spruce which has been infected P. abietitta. Numerous black tubercles

close to the ground by P. Hartigii.

are visible on the dead cortex.

138 DISEASES OF TREES

spheroidal p)xnidia, and partly on flat stromata which arc
disposed in the tissue of the cortex.

The characteristic gonidia (Fig. jj), which are situated on
short or long stalks, are at first hyaline, thin, oval, and uni-
cellular, but afterwards become four-celled owing to repeated
transverse division. The two middle cells are large and dark,
the small stalk-cell and the terminal cell remain colourless. The
latter pushes out a branched filament which, however, must not
be confounded with a germ-tube. It is only one or other of the
three lower cells that germinates, most frequently the lower of
the two brown middle cells.

On account of the general distribution of this disease, and the
consequent loss incurred, it would appear advisable carefully to
root out and burn all diseased and dead plants that may be
found in nurseries.

Similar pathological symptoms have also been observed on
young beeches, ashes, and maples. I should be glad to receive
such plants, in order to prove whether parasites are the cause of
disease, and, if so, to determine the species.

PHOMA ABIETINA N.SP. THE FUNGUS OF THE CORTEX
OF THE SILVER FIR

A disease which has not hitherto been described, but which is
extremely common on young and old trees in the Bavarian
Forest, is due to a parasite which may temporarily be called
PJioina abietina. The disease may be recognized by both small
and large branches of the silver fir becoming pale and withered ;
in fact, I have occasionally observed diseased spots two inches
in diameter on the cortex of silver firs as thick as one's arm.
As a rule the disease appears only on branches or on the main
axis of the younger classes of silver firs, and attracts atten-
tion by the cortex dying right round the branch, as is shown
in Fig. "j"^.

Numerous small black pycnidia break through the epidermis
and appear on the dead cortex, either as small roundish bodies
or as many-chambered, irregularly shaped, black sclerotium-like
tubercles (Fig. 79, a). Numerous unicellular, colourless, abruptl\-

INJURIES INDUCED BY PLANTS

139

Fig. 79.-

pycnidium

spindle-shaped gonidia (Fig. 79, b), which at once germinate in
water, develop on the h}-menial layer that lines the walls of the
cavities of these organs.

Although I have watched the disease every year since 1885,
and have sought for the ascophores, I have hitherto been unable
to find them. I may, however, remark that in almost all my
cultures on silver fir branches a luxuriant growth of the
ascocarps of Peziza calycina has appeared upon the cortex on
both sides of the diseased part. This fact, however, is not
sufficient proof of a connection between
these two fungus-forms. Attempts to
produce the one form from the other
by cultural experiments have so far
proved abortive.

The pycnidia ejaculate the gonidia
probably for the most part during wet
weather in summer and autumn.

It does not appear necessary that
mechanical injury of the cortex should
precede the entrance of the parasite —
at all events, I have never been able
to observe such. On old trees a large

proportion of the twigs and branches are often brown, a state of
things that struck me at once on my first visit to the Bavarian
Forest. In the Black Forest also, and at several places in the
Bavarian Alps, the disease is to be met with. In the case of
the thicker branches nutrition through the wood may still be
continued for several years after the cortex has died. For this
reason growth in thickness above the dead part is distinctly
visible, and causes the cortex to rupture at the boundary of the
living and dead parts. When the wood covered by the dead
cortex dies and dries up, the passage of water ceases, and the
branch dies above the seat of the disease.

Should the fungus attack one side of the branch only, the
dead cortex is exfoliated, and the formation of callus commences
along the healthy margin.

of p. abictiim which has
ruptured the periderm ;
magnified twenty times.
/', gonidia magnified 420
times.

I40 DISEASES OF TREES

GLCEOSPORIUM NERVISEQUIUM.^ THE PLANE-TREE

FUNGUS

Plane-trees i^Platamis) suffer very frequently from a disease
which is characterised by the leaves acquiring brown blotches
and dying. From the middle of May onwards one observes
that death sets in at certain places, and continues along the
nerves of the leaf. Small black spots may then be observed
appearing on the dead parts, which are the gonidial cushions of
Gloeosporiuin nerviseqiLUivi.

Unfortunately we still know very little regarding the develop-
ment of this fungus, for even trials at infection have not yet
succeeded.

THE FUNGUS OF THE BLACK (AUSTRL\N) PINE ^

For a number of years a disease of the black (Austrian) pine
has been observed in the south of Norway and throughout the
whole of Germany. This disease has constantly been on the
increase, but has not yet been thoroughly investigated. It is
now a considerable number of years since Dr. C. v. Fischbach
sent me 'diseased branches, and an opportunity for observing
the disease was afforded in the forest division of Freising, near
Munich, but the investigation yielded no satisfactory results.
This disease may find mention here, especially since Dr. Brunc-
horst's description is now available.

The most vigorously growing Austrian pines show a pale-
ness in the leaves of the previous year's shoots, whose buds,
instead of shooting out, die off. The disease spreads from the
tissues of the shoots, having its inception in the cortical tissues.
Here infection is very often brought about, as it appears to me,
through the agency of a small plant-mite, which bores through
the epidermis into the cortical tissues of the shoot to a depth
of I — 2 mm. Infection may, however, also take place easily
enough at the base of the leaves, where the epidermis is thin.

1 Dr. Fr. v. Tavel, Bot. Zeit., iS86, No. 49.

- Dr. C. V. Fischbach, Eiiic ncue Kraitkhcit der Schwarskiefer. Central-
blatt fiir das gesammt Forstivesen, 1887, p. 435. Dr. Brunchorst, Ueber eifie
jicicc verheerende Krankheit der Schwarsfohrc. Bergen, 1888.

INJURIES INDUCED BY PLANTS 141

Black pycnidia, with gonidia similar to those of Fusidium,
develop at the base of the dying leaves, and on the wounds that
result from the separation of the leaf-fascicles.

Dr. l^runchorst has not yet been able to observe perithecia,
nor has he hitherto succeeded with infection-experiments. Not
only has the death of single pines been noticed, but in many
cases, especially in Norway, the destruction of large woods has
been recorded.

It is strongly to be insisted upon that whenever this disease
appears in young woods of the Austrian pine, all diseased shoots
should be cut off and burned.

SEPTOGLCEUM HARTIGIANUM SACC ^

In the neighbourhood of Munich the branches of the English
tnaple {Acei- caiiipestre) suffer from a disease which kills them
off before the young shoots develop in spring. In the middle
and lower parts of the crown especially, it frequently happens
that more than half of the previous year's shoots perish. On
these it will be found that the periderm has been ruptured
by oblong cushion-like fungus-bodies.

The disease almost always confines itself to the youngest
shoots, the two-year-old shoots being infected only in very
exceptional cases. Infection takes place in May and the
beginning of June, when the young shoots are still tender and
unprovided with periderm. When the spores of the parasite
(Fig. 80, 6) come into contact with a young shoot, they germinate
within a few hours. The spore represented in the figure had lain
in water for five hours only, at the end of which time it showed
large germ-tubes at both ends. The mycelium bores into the
cortex, and takes possession of the shoot for a distance of 2 — 4
inches, but does not kill it in the same year. Even when the
leaves are shed in autumn there are no external symptoms of
disease. In spring, the buds of the diseased shoots swell up,
as a rule, but soon wither. At that time the mycelium is to be
found growing vigorously, not only in the diseased cortex, but
also in the medullary rays and the vessels of the wood. It
grows both intercellular and intracellular, and pushes numerous

1 R. Hartig, Forstl. N'aturwiss., Zeitschrift, August 1892.

142

DISEASES OF TREES

short stout lateral branches, which resemble haustoria, into the
interior of the parenchymatous cells.

Colourless stromata of a fleshy, pseudo-parenchymatous
structure (Fig. 80, j) form in the cortex beneath the periderm.
In cross section these measure 0'3 — 0'6 mm., while longitudinally
their length varies between i and 4 mm. In the month of May
the periderm ruptures longitudinally, and reveals the sporogenous

Fig. 80. — Septoglceum Hartigianum.

.ayer as a greyish green cushion, surrounded by the edges of the
elevated periderm (Fig. 80, 2). The surface of the colourless
fleshy stroma (Fig. 80, ^) is formed of cylindrical sterigmata,
which frequently enlarge somewhat towards the base. These
sterigmata measure 30 — 35 micromillimeters in length and
6 — 7-5 micromillimeters in breadth. The gonidia, which are
formed at the apex of the sterigmata, measure, when ripe,
from 24 — -36 micromillimeters in length and 10 — 12 micromilli-
meters in breadth. In shape they are irregularly oblong-oval,
and truncated at both ends (Fig 80, 5).

INJURIES INDUCED BY PLANTS 143

In the great majority of cases the gonidia appear to be doubly
septate, ahhough occasionally one meets with singly septate
examples, and even unicellular gonidia are not unknown. They
are of a pale brown colour, and germinate in a few hours,
pushing out a thick germ-tube from both ends (Fig. 80, 6).

The parasite is distributed in May and the beginning of June
by means of the gonidia, which are washed by the rain from
the higher diseased shoots on to the young shoots of the lower
part of the crown. In other cases the wind may carry them on
to distant maples.

This destructive parasite of our gardens and parks can only
be combated by removing the diseased shoots from the crown in
the beginning of May.

SEPTORIA PARASITICA, THE SPRUCE-SHOOT DISEASE ^

Both in young spruce woods and in the seed- and plant-beds
of the nursery a disease, which on a cursory examination may
easily be mistaken for damage by frost, very frequently attacks
the young shoots.

In the month of May, when the young shoots are still succu-
lent and delicate, the disease generally manifests itself (see
Fig. 81, a) by the leaves at the base, or it may be the middle, of
the shoot becoming brown and soon dropping oft". At first the
apex of the shoot remains quite green, but on lateral branches
it droops downwards. The disease advances rapidly towards
the apex of the shoot, and the base of the young leaves appears
dark green (Fig. 81, d). When held up to the light, it will be seen
that the internal tissues of the leaf are dead and shrivelled, and
possess a reticulated appearance. Finally the leaves all drop
off", or a few dead ones may adhere to the apex of the shoot, as
indicated in Fig. 82, a. The axis of the shoot shrinks more or
less according as death had overtaken it in an early or late stage
of development. Very frequently the shoot becomes diseased
and begins to shrink at the point where its base is enveloped by
the scales of the previous year's terminal bud, and this often
occurs in the case of shoots that are tolerably well developed.
The base of the shoot shrinks, and its internal tissues are so dis-

1 R. Hartig, Zeitsclirift fiir Forst- und Jagdivesen, November 1890, p. 668.

144

DISEASES OF TREES

organized by the fungus which causes the disease — as we shall
see presently — that the shoot bends sharply over at that point
under its own weight, as though it had been fractured at the
base. Very frequently death spreads back from the base of the
youngest shoot to the apex of the shoot of the previous year
(Fig. 8 1, r), in which case the young lateral shoots that are
situated there also succumb (Fig. 82, a).

As already indicated, this may, in May or early in June, be

mistaken for damage due
to frost, although the latter
is generally confined to cer-
tain localities, appears sud-
denly on a great number
of shoots, and is character-
ised by all the affected
leaves dying simultaneous-
ly. The disease at present
under discussion has no re-
lation whatever to frost.
Shoots that have succumb-
ed to this disease also bear
a certain resemblance in
many cases to those dam-
aged by Chermes abietis ;
the galls which the latter
induces at the base of the
shoots being often so small
as not to be visible on the
upper side, and in both
cases there is a deflexion of
the shoot downwards.
In the course of the summer the dead shoots display spore-
receptacles (pycnidia) in greater or less abundance in the form
of very minute black tubercles. These are so small as just to be
visible to the naked eye, and are very often to be found only
amongst the bud-scales at the base of the dead shoot. In other
cases they are also to be met with higher up ; in fact, they are
often specially abundant on the shrunken shoot-apex (Fig. 82, a)-
They either rupture the epidermis of the shoot or occur on the

Fig. 81. — (T, a young diseased spruce branch,
the apex of which is still green and fresh.
h, a leaf attacked by disease towards the
base, twice natural size, c, apex of a
two-year-old shoot, into which the disease
has spread backwards from the younger
shoot. The brown discoloration of the
cortex and pith is indicated by shading.

INJURIES INDUCED BY PLANTS

HS

leaf-scar on the long pulvinus, where they present a bud-like
appearance (Fig. 82, b). It also frequently happens that black
pycnidia develop on the few dead leaves that have adhered
to the shoot (Fig. 82, a).. a

These pycnidia, which are
uni- or multicellular, pro-
duce numerous small go-
nidia (stylospores) at the
apex of subulate sterig-
mata which spring from
the inner wall. These
stylospores, which are bi-
cellular, colourless, spindle-
shaped, and some 13 — 15
micromillimeters in size
(Fig. 82, r), appear as white
tendrils on the pycnidia in
the month of May, at which
time they produce the dis-
ease, if borne by the wind or
rain to the still tender and
non-cuticularized shoots of
the spruce.

On May 6th, when growth
was active, I infected young
spruces by taking a drop
of water, in which stylo-
spores were suspended, and
placing it by means of for-
ceps amongst the leaves in
the middle of a shoot and
partly amongst the bud-
scales at its base. Infection
succeeded in every case,
and eight days later death
appeared amongst leaves at
the infected points, and
soon spread in all direc-
tions. On the 13th of May,

Fig

82. — a, a spruce-leader of which the
youngest shoot, the apex of the older
shoot, and the two lateral branches have
been killed. /', pycnidia projecting from
the cortex and leaf-scars, magnified five
times, c, formation of spores in the inte-
rior of a pycnidium, magnified by 400. d,
spores germinating in water. e, spores
germinating in nutritive gelatine.

L

146 DISEASES OF TREES

a drop of water containing spores was placed amongst the
scales at the base of a shoot some three inches long, on
a twenty-year-old spruce. About twelve days later the shoot
was so much diseased as to droop in the manner shown in
Fig. 81, a.

Spores sown in water on May 6th showed the first symptoms
of germination in eighteen hours (Fig. 82, d). When sown in
nutritive gelatine the spores and germ-tubes were rather more
vigorous (Fig. 82, e), an extremely luxuriant mycelium with
spherical and clavate segments being developed both on a
microscope-slide and in a test-tube. Twelve days after
sowing, pycnidia with ripe stylospores developed on this
mycelium.

The culture, which was continued till August 12th, produced a
dense mycelial growth, with pycnidia but no perithecia, so that
at that time I abandoned the hope of obtaining the latter. An
investigation of the diseased shoots showed that the stout vigor-
ous mycelium developed between the cells in the green leaves,
and immediately induced death in adjacent cells. In the shoot
axis it penetrated all the tissues, growing as both intra- and
intercellular filaments in the pith and cortex, while in the wood
it was specially abundant in the annular and spiral vessels. The
development of the parasite is confined to the short period
between the beginning of May and the early part of June.
Whether the pycnidia will form early or late in summer appears
to depend on the humidity of the air, or, in other words, on the
occurrence of dry or wet weather. As already stated, they may
ripen in fourteen days, provided the conditions are favourable,
as m the case of artificial cultures.

Until we obtain the perithecia we must rest satisfied with a
provisional name for this new parasite. The character of the
pycnidia and spores leads us to place this fungus in the genus
Septoria, but as there is already a Septoria Pini I have named
this fungus Septoria parasitica. Finally, it may be mentioned
that in the spring of 1 890 I found this parasite on Picea Menziesii,
and this makes it probable that it also occurs on other species
of spruce.

INJURIES INDUCED BY PLANTS 147

A NEW PARASITE OF SEEDLINGS 1

Seed-beds of the pine and spruce are frequently subject to
disease in the months of May and June, so that, even where
seed has germinated satisfactorily, the plants are more or less
decimated, and the otherwise well-stocked drills show blanks as
large as one's hand. During wet weather the young plants die
and rapidly decay. At first only single plants are attacked, but
soon the disease spreads more or less rapidly along the whole
drill. If the weather is dry the diseased plants wither, their
yellow colour attracting attention even from a distance. During
summer, say from the middle of June, the disease ceases, and
the dead plants disappear, to leave only the blanks, which are
usually ascribed to the ravages of cockchafer grubs, crickets,
surface caterpillars, &c. I have shown that in most cases these
pathological phenomena are due to PhytoptJioj-a omnivora, which
spreads not only by ^onidia but also by its mycelium, which
traverses underground from root to root, and thus explains the
rapid spread of the disease.

In 1889 I received a number of diseased pine seedlings from
Herr Mantel, forester in Grossostheim, with the information that
for some years a disease agreeing with the symptoms just
described had appeared immediately after the germination of the
seed in his pine seed-beds on sandy land. Some plants which
he sent to the forest school of Aschaffenburg were examined,
when it was found that, instead of P. omnivora being the cause
of the damage, it was some other unknown disease.

An investigation of this new disease showed that it was
induced by a different parasite. The mycelium of the parasitic
fungus which caused the damage attacked not only the seed-
lings of the pine but also those of the spruce, alder, birch,
&c. In the seed-bed the plants were attacked either at the
roots (Fig. 83, a) or at the hypocotyl {b), close beneath the
surface of the ground. In very dense seed-beds and during wet
weather the mycelium also spreads above ground, and infects the
cotyledons and the highest part of the stem (Fig. 83, c). At
the point where it comes into contact with the epidermis of

^ Forstlich Naturwissensch. Zeitsch., November 1892.

L 2

DISEASES OF TREES

the seedling the filamentous septate mycelium, which becomes
somewhat brown with age, produces tortuous lateral hyphae,
which ramify abundantly, apply themselves closely to the epi-
dermis (Fig. 84, a), and exercise a solvent action on the delicate
non-cuticularized epidermis. If one lifts up the hyphae it will
be seen that the epidermis has been dissolved at the points

of contact. Without doubt mycelial
filaments also bore directly from these
points right into the plant.

The stomata form a means both
of ingress and egress for the hyphae.
Such a stoma is depicted in Fig. 85,
which shows that the sides of the
depression leading to the stoma, and
the external walls of the epidermal
cells, are dissolved at the points where
the hyphae are or have been in close

Fig. 83. — Diseased pine seedlings.

a, a specimen with dead roots ;

b, ditto with a dead stem ;

c, ditto with dead leaves and
buds.

Fig. 84. — A filamentous mj'celium whose
lateral hyphpe, a, come into close con-
tact with the epidermis ; b, a mycelium
which has developed in a nutrient
solution.

contact. These places appear granulated because the ash con-
stituents of the cell-wall are either left wholly intact or are but
partially dissolved. I have proved that under the action of the
ferments exuded by wood-destroying parasites the cell-walls also
display granulation during the last stages of decomposition, and
for the same reasons as those just given. When a diseased
plant is investigated on the first symptoms of attack, a vigorous
growth of mycelium will be found in all the tissues. Although
the green cells do not part with their chlorophyll till some time
after death, they easily lose connection with each other, and the

INJURIES INDUCED BY PLANTS

149

stem or root becomes limp. At this stage of the disease the
interior of the plant is nearly full of a luxuriant mycelial growth.
In a short time large numbers of bacteria appear in the tissues
and induce complete decomposition, the mycelium of the para-
site sharing the common fate. In plants that still appear sound
towards the top, the stem or roots frequently retain only the
epidermis and the xylem of the vascular bundles. I have
infected vigorous pine and spruce seedlings, which were taken
from dense seed-drills and planted in flower-pots, by laying
one or more diseased plants amongst them. When a bell-
glass was placed over the flower-pot all the plants were
diseased or dead in four days.
The mycelium enveloped the whole
plant, and the disease began, for
the most part in the upper portion
(Fig. 83, c). On the other hand, if
the flower-pot was left in a room
uncovered, infection was induced
only by the mycelium growing in
or on the surface of the soil and
attacking the roots or the lower
portion of the stem (Fig. 83, a, b).
All the plants succumbed in eight
days, with the single exception
of one seedling which remained
healthy. No results followed trials
at infection which I conducted in
the end of June on vigorous seed-
lings. As has already been proved in the case of other parasites*
it is only when the epidermis is unprovided with a cuticle that it
can be dissolved by the mycelium. It is known thz-t P . onuiivora
also is only destructive in May and June.

Innumerable gonidia develop in dense bunches on the
luxuriantly branching mycelium, and especially in the stomata
of the diseased plants. I have represented such a mycelial
branch with gonidia in Fig. 86. When ripe they are more or
less falcate, pointed at both ends, and generally consist of six
cells. In germinating they usually produce two germ-tubes at
or near the apices, as is shown in the lower part of Fig. 86-

Fig. 85.- — Epidermis of a pine
seedling showing a stoma.
Solution has taken place
wherever the filaments have
been in contact.

ISO

DISEASES OF TREES

The shape of the gonidia makes it probable that the parasite is
a species of Nectria. A few days after being sown in a gelatine
extract of fruit they produce a luxuriantly branching mycelium,
whose hyphae are much septated and anastomose irregularly
(Fig. 84, ^). This mycelium produces either similar gonidia, or
such as are somewhat smaller, less bent, and possessed of fewer
cells.

On being transferred to black bread the mycelium grew so
vigorously that the large glass jar in which the culture was
conducted was completely filled with a white growth. In the
flower-pots also, in which the infected conifer seedlings were
growing, the mycelium developed so luxuriantly in the soil as
to find its way out at the hole in the bottom and to form a dense

mass between the pot and the table.
This proves conclusively that the
fungus, like most species of Nectria,
can also exist as a saprophyte, and
as such may live in the soil.

Unfortunately I have not been

successful in reproducing the peri-

thecium form of the fungus. On

a slide numerous spheroid bodies

which were the first stages of peri-

thecia or pycnidia formed in the mycelium, but they always

failed to mature. On this account I am unfortunately still

unable to refer the fungus to a species.

As regards measures that may be instituted with the view of
preventing the spread of the disease, attention should in the first
place be directed to the diminution of surplus moisture. If
such are present, we should also remove all objects such as latticed
frames, branches, &c., that have been laid down to shelter the
plants. As it is certain that the fungus remains in the ground
from one year to another, one must take care, in laying down
new seed-beds, to avoid situations where the disease was
prevalent in the previous year. If this cannot be done, one
should interstratify the upper nine inches of soil with brush-
wood, dry turf, or some such material, and roast it, or at least
raise its temperature to such a pitch that any spores present in
it may be killed. Herr Mantel related to me how he had heated

Fig. 86. — Immature, ripe, and
germinating gonidia.

INJURIES INDUCED BY PLANTS 151

the soil of certain beds by burning dry wood in parallel trenches
a foot deep and about a foot apart. The fire was kept up for
two days, so that the soil was practically roasted to the depth of
more than a foot. Seed was afterwards sown on these beds as
on the others. On the beds so treated the plants remained
sound for two years, but in the third year the old symptoms
reappeared. It is most likely that the fungus again invaded the
ground by means of gonidia carried from adjoining beds. It
would appear desirable, should circumstances make it advisable,
that the above plan should be experimentally tested. One
would thus discover whether infested seed-beds may continue
to be utilized without incurring much expenditure, or whether
it is better to change the ground.

VALSA (MONOSTICHA) OXYSTOMA^

In Alpine districts a disease is very prevalent on Alnus
viridis, which, superficially examined, reminds one strongly of
the ravages of the larvae of CryptorhyncJms lapathi. Numerous
stems and branches contract the disease and die. It is chiefly
in August that the leafy branches become infected. The
withering of the cortex attracts attention to the presence of the
fungus, and directly afterwards small black tubercles appear
on the dead tissues. The stage of the development of these
pustules depends upon the length of time that has elapsed since
the branch died. Thus, although the presence of the fungus may
be detected on branches that are still living, it is met with in its
highest development only on such as are perfectly dead. The
progress of the disease down the tree is indicated by a sharp line
between the diseased wood, which is brown, and that which is
still sound. As the disease advances, other lateral branches
become affected. An exceedingly vigorous and very tough
mycelium is easily discoverable in the moribund wood, and
especially in the vessels. The lenticular tubercles consist of
black pseudo-parenchyma situated beneath the periderm.
Owing to their rupturing the periderm at the highest point

1 \'.T\ihe\xi,Forstltch-Jtatur'wis. Z^//Jt7w7//, October 1892.

152

DISEASES OF TREES

of their concave surface, a small roundish aperture is formed.
Numerous perithecia, with very small tubes and hyaline spores,
form in the dead cortex underneath the lower surface of the

oq'

Fig. 87. — The upper left-hand figure represents a portion of a branch of Almis viridis.
The periderm has been ruptured at four places by the stroma of Valsa oxystotna,
on which the necks of the perithecia are visible. To the right are seen the asci
and spores. The upper right-hand figure represents a piece of a smaller branch
whose periderm has also been ruptured by the stromata, but on which the peri-
thecia have not yet developed. The central figure shows the microscopic section
of one of the stromata of the upper left-hand figure, and the lowest figure a similar
section taken from the branch shown in the upper right-hand corner.

lenticular tubercles. The perithecia push a long stout flask-
shaped neck through the lenticular stroma. On account of the
black necks finally protruding to some extent from the stroma,
each tubercle shows a considerable number of them.

INJURIES INDUCED BY PLANTS 153

BASIDIOMYCETES

The Basidiomycetes constitute the third group of fungi. In
their case ah spores originate by abscission.

UREDINE^.* RUST-FUNGI

The rust-fungi are true parasites, and develop their mycehum,
which is usually intercellular, in the tissues of the leaves and
cortex (and also, though less frequently, in the wood, e.g. Cole-
osporiuin SenecioJiis) of phanerogams, and abstract their nutri-
ment by means of haustoria from the interior of the cells.
Their course of development is characterised by most species
producing sporocarps, which are usually cup-like in shape. The
bottom of these so-called secidia is lined by a hymenium
consisting of numerous, usually club-shaped, basidia, each of
which at its apex abjoints a series of spores which are usually
reddish yellow in colour. These are united to each other by so-
called intermediate cells, which are dissolved before the forma-
tion of the spores is completed. The basidia that are situated
at the periphery of the hymenium, instead of forming spores,
grow together to form an envelope called the peridium, which
opens at the apex or by a longitudinal fissure. The peridium
may, however, be entirely absent.

Before the formation of aecidia, spermogonia with spermatia
usually originate, the latter probably playing the part of male
sexual cells.-|- It is probable that the aecidium is the result of a
preceding sexual act, and is therefore a true sporocarp, like the
perithecium and apothecium of Ascomycetes. However, there
are also rust-fungi in which the aecidium is entirely absent
{CJirysomyxa Abietis).

* [The British species have been worked up into a monograph by Plowright
{BriL Uredinecc and Ustilaginece, Kegan Paul, 1889), who has also devoted
attention to the experimental investigation of some of the heteroecious
forms. — Ed.]

t [Researches into the morphology and physiology of these and other
organs of the Uredine£e by no means support this conclusion. Brefeld's
statements, as well as those of De Bary, much as they differ in detail, point
to the opposite view — that there is no probability of sexuality in this group.
The curious and interesting homologies are well put forth by Von Tavel.—
Ed.]

154 DISEASES OF TREES

Besides the secidium, a kind of gonidium is almost always
formed, which, being designed to carry the fungus over from one
year to another, has great capacity for retaining its power of
germinating. This is known as a resting-spore or teleutospore,
and, instead of directly forming a mycelial filament, it first pro-
duces a promycelium, on which a number of small cells, called
sporidia, develop, and it is these which produce the disease by
infecting new host-plants. The teleutospores are unable to
produce infection, because they are usually in such intimate
contact with the substance of the host-plant that their distribu-
tion by the air is almost entirely precluded. The mycelium that
is developed from the sporidia again produces spermogonia, and
— after fertilization — sporocarps (aecidia). Thus an alternation
of generations between the two forms of aecidia and teleutospores
is presented, which, however, in the case of many rust-fungi, is
further complicated by the fact that a form bearing teleutospores
is not directly produced by the germinating aecidiospores, but
that numerous generations of gonidia of another kind — namely,
uredospores — often originate. These at once germinate, without
forming a promycelium, and reproduce the form bearing uredo-
spores. During summer they serve for the rapid distribution of
the fungus, till the teleutospores are produced by the mycelium,
as usually happens in autumn. The cycle of development of
many rust-fungi is interesting, from the fact that not only the
uredo form but also the aecidium form may possess a facultative
character ; that is to say, these forms may develop only under
certain favourable circumstances, and in the absence of such
conditions they may be entirely omitted without the existence
of the parasite being thereby imperilled.

The generation which forms the aecidia, and that which pro-
duces the teleutospores, are either to be found on the same plant
(autoecious parasites), or, with the alternation of generation,
there also occurs a change of the species of host-plant (heter-
oecious parasites). In the case of the hetercecious rust-fungi the
discovery of the related forms which belong to one and the same
species of fungus naturally presents great difficulties. This is
sufficient to explain why we are not at present acquainted with
the aecidia of many teleuto forms, and, on the other hand, do not
yet know to which teleuto forms many aecidium forms belong.

INJURIES INDUCED BY PLANTS 155

On this account it will be necessary, as in the case of the
Ascomycetes, to append a list of imperfectly known rust-fungi,
to which, depending on the development form, the provisional
names of Aicidimn, C<2oma, and Uredo are given.

The rust-fungi are divided into several families, of which we
are here interested only in the PuccinicB and MelampsorecE. The
former are characterised by the teleutospores being situated
singly, or several together on a stalk ; whereas, in the case of
the latter, the teleutospores are united to each other in large
numbers to form a firm palisade-like layer.

PUCCINI^

The genus Piiccinia, which is rich in species, is characterised
by the teleutospores containing two cells and remaining attached
to the basidia, which at the same time serve as the stalk. They
appear as small brown or black brown heaps of a round or
oblong shape.

Piiccinia graminis * is the commonest kind of rust amongst
cereals, occurring everywhere, not only on our various kinds of
grain but also on many grasses. The teleutospores, which are
disposed in narrow ridges, hibernate on the common grasses,
though, if they have been produced on the lower parts of the
stems of cereals, they may also be left on the stubble fields. In
spring, when the sporidia that originate on the promycelia gain
a footing on the young leaves of the barberry, Berberis viilgaris,
they produce the barberry fungus, ^ciditun Berberidis. The
aecidium form — whose spores germinate on cereals and other
species of grasses, and produce the wheat-rust, Uredo linearis —
is distinguished from the black ridges of teleutospores of
Piiccinia graini?iis, which occur later, by the reddish brown
colour.

This destructive cereal rust may be most effectively combated
by rooting out the barberry. This measure must not, however,
be confined within narrow limits, because the spores of the bar-
berry-fungus can be widely distributed by wind.

*[This, the common rust of wheat and other grasses, is of classical
interest, since it was this species in which De Bary first estabUshed the
remarkable phenomenon of hetercecism. — Ed.]

156: DISEASES OF TREES

Piiccinia stricEforviis {strainifiis) produces a cereal rust on rye,
wheat, and barley. It closely resembles the foregoing disease,
from which it differs, however, by the ridges being smaller
and less elongated, and by the very short-stalked club-shaped
teleutospores remaining hidden by the epidermis. Theaecidium
form is ^cidhun asperifolii, which develops on the leaves of
AncJmsa officinalis, Borago, EcJiiuni, &c.

Piiccinia coronata produces a rust on cereals, especially oats.
Its teleutospores are provided at the shoulder with a girdle of
punctiform thickenings of the spore membrane. The aecidium
form y^cidiiim Rhanini is well known by the peculiar rich golden
yellow swellings which it produces on the leaves, flowers, and
stalks of Rhamnus catJiartica and R. frangula in which it
develops.

Of the large number of species of Puccinia, the only other one
that need here be noticed is Piiccinia Asparagi, which completes
its course of developmen t on the asparagus alone. The asparagus
rust, which may seriously devastate asparagus-beds, is best com-
bated by burning the halms in autumn, and by the timely
removal of the shoots that are first diseased.

THRAGMIDIUM

The species of this genus are distinguished from the species
of Piiccinia by the teleutospores being stalked and consisting
of a number of cells. The groups of teleutospores which
develop on the under side of the leaves are preceded by uredo-
spores, whose orange red powder often covers the under side of the
leaves in large quantity. The course of development of the
various species has not yet been sufficiently studied.*

PJiragniidiiun incrassatinn, the rust of the bramble, induces the
formation of red blotches on the leaves of Rnbus fniticosiis and
R. ccesiiis, and the organs consequently die prematurely.

Phraginidiinn Rnbi Idcei produces similar pathological sym-
ptoms on the leaves of Rubiis Idceiis.

Phragviidinvi siibcorticiun produces the rust of the rose.

*[A11 occur in this country. — Ed.]

INJURIES INDUCED BY PLANTS 157

GYMNOSPORANGIUM

The species of this genus with which we are acquainted arc
perennial in the cortical tissues of various species of Jimiperus.
They induce local increase in growth, which takes the form of
peculiar swellings on the branches and parts of the stem that are
attacked.* Each autumn the teleutospores are developed under
the outer cortical layers, and in spring and early summer they
break through the cortex in large numbers and appear as fructifi-
cations which are conical or sausage-shaped, yellow or brown, and
mucilaginous or cartilaginous in texture. These fructifications
consist of the very long filamentous basidia whose outer wall
has been converted into mucilage, and of the two-celled resting-
spores which they bear at their apex. The formation of the
promycelium and sporidia takes place in the mucilaginous mass,
which in the end is completely dissolved by rain-water. The
sporidia gain a footing on the leaves of various pomaceous trees,
where they produce the aecidium form of the genus RcEstclia.

It appears to me desirable that the forms which are already
known and described should be subjected to further examination,
because the few test trials that I have undertaken have at once
led to results which are at variance with what has been accepted.
I append here a short description of the three recognised species,
without, however, being able to vouch for its accuracy on the
strength of my own investigations.-|-

GYMNOSPORANGIUM CONICUM (JUNIPERUM)

Teleutospore layers on Jiinipenis connminis. They are hemi-
spherical or conical, golden yellow, later swelling up to very
large, variously shaped (spherical, pear-shaped, ovate, &c.) bodies.
Spores spindle-shaped, some brown with a thick endosporium,
75 microm. long and 27 microm. broad ; others yellow, with a

1 Oersted, Bot. Zeit., 1865, p. 291 and elsewhere.

* [These are often called Cedar-apples in America. See Farlow, Mem.
Boston Soc. of Nat. Hist., 1880. — Ed.]

f [A good deal of work has been done on the various and very confusing
species of late years, most of which occur in this country. See Plowright,
/.^,and Von Tubeuf {Cent. f. Bakt., 1891, and Zeitschr. f. PJlansenkrankh.,
B. II. p. no). Also Farlow, t.c, &c. — Ed.]

IS? DISEASES OF TREES

thinner endosporium, about 66 microm. long and 17 microm.
broad. The aecidium form has been observed as Rcestelia
corniita on Sorbiis Aiicuparia, S. tonninalis, Aronia, and other
pomaceous plants. The secidia are situated on orange yellow
or red swollen blotches, which are united in various numbers
into round or oblong groups. The peridium, which has the
shape of a very long-necked bottle, is yellowish, or yellowish
brown, twisted like a horn, up to 8 mm. long, open at the
shoulder, serrulated, and either not or only ultimately slightly
and irregularly lacerated.

GYMNOSPORANGIUM CLAVARI^FORME

Teleutospore-layers on Jiiniperus commiinis. They are
cylindrical, tongue- shaped or band-like, often bifurcated,
twisted, and bent, somewhat cartilaginous in texture, yellow.
and up to 12 mm. long. Spores spindle-shaped, contracted at
the middle, bright golden brown, 70 — 120 microm. long, and
14 — 20 microm. thick. The aecidium form, RcBstelia lacerata,
is met with on species of CratcBgus, and occurs abundantly
in smaller or larger groups on orange yellow swollen blotches
— -though frequently covering large areas, especially on fruit —
and is usually accompanied by contortions and other deforma-
tions. Peridia, flask-shaped when young, later cylindrical cup-
shaped, dirty white, rupturing longitudinally to various depths
into numerous erect or somewhat outwardly inclined lobes.

GYMNOSPORANGIUM SABINE (SYN. G. FUSCUM)

Teleutospore-layers on Juniperus Sabina, J. virginiana, J .
pJicenicea^ J. Oxycednis, and Finns halepensis. When fresh they
are abruptly conical or cylindrical, often slightly compressed
laterally and expanding somewhat towards the top, sometimes
pectinate, red brown, 8 — 10 mm. long. Spores broadly
elliptical, either not contracted at the middle or contraction
scarcely observable, chestnut brown, 38 — 50 microm. long, and
23 — 26 microm. thick. The aecidium form, called RcBstelia cancel-
lata, is found on Pyrus communis^ P. Michauxii, and P. tomentosa.
In shape the secidia are like very short-necked bottles, about
2 — 2\ mm. high, and several are situated together on orange

INJURIES INDUCED BY PLANTS 159

yellow, roundish or irregular, cushion-like swollen blotche?.
Pseudo-peridium yellowish white, closed at the shoulder,
ruptured on the side by numerous longitudinal fissures, which
extend to the surface of the leaf. These longitudinal fissures
are bridged over by short transverse rodlets, whence the whole
peridium appears grated. In this connection I may remark that
I have repeatedly observed the pear-rust in great abundance
in places where no examples of the above-mentioned host-
plants of the teleuto form were to be found within a wide
radius.

GYMNOSPORANGIUM TREMELLOIDES

To the three above-mentioned species a fourth falls to be
added, whose aecidium form is very abundantly met with in
the Bavarian Alps on Sorbiis Aria and 6". CJiamcBinespilus, and
which as ^cidium pejicillatum has already been described as an
independent form (Fig. 88).

In equal abundance one meets in the same region with a
teleuto form on Jmiipenis coniiminis which does not agree with
any of the above-named species, but whose connection with the
aecidium form on Sorbiis Aria has been proved by infection-
experiments in the garden of the Munich institute of forest
botany.

The teleutospore-layers appear in May on Juniperiis com-
inunis, as hemispherical orange yellow to yellowish brown masses,
which, as in the case of Nostoc coimminis, are mucilage-like
in texture and capable of swelling (Fig. 89, a a). They
easily drop off when the branches are shaken, and then pale
yellow smooth scars remain, which are often i cm. in diameter
(Fig. 89, b b). The spores are all about the same size, being
approximately 40— 45 microm. long and 20 — 25 microm. broad.
The two short abruptly conical cells, whose height is about
equal to their greatest diameter, are provided with smoky-
grey walls. Some of them coalesce all along their base, others
are to a certain extent separated owing to contraction — in fact,
it not unfrequently happens that the two parts of a teleutospore
become completely disunited. Most of the cells possess three
germ-pores, which, when situated near the transverse septum,
frequently alternate with those of the second cell (Fig. 90).

i6o

DISEASES OF TREES

The secidia appear on Sofbus Ai-ia, S. Chamcsmespilus, Pyrus
Malus, and Sorbiis tormmalis (?).

The cushion-like stroma, on which the aecidia are often
arranged in circles, is very thick, and luxuriantly developed.
The pseudo-peridia are somewhat cup-shaped, and are split
up as far as the base into a large number of filaments i mm.
in length, which bend out somewhat. The aperture of the

Fig.
G.

88.— /Ecidia of

trenielloides on

leaf of Sordiis

Aj-ia.

Fig. 89. — G. trenielloides on
J. communis, a a, teleu-
tospore-layers ; b b, scars
which are left after the
mucilaginous mass has
dropped off.

Fig. 90. — Teleutospores of
G. trenielloides. a, basi-
dium ; b, spore that has
not yet germinated ; c, a
similar spore, showing
contraction along the
centre ; d, ditto with the
cells separated ; e, a
germinated teleutospore
with promycelium and
sporidium ; /, basal view
of a teleutospore showing
three germ-pores, the
one from which the germ-
tube is issuing being
closed by a lamella.

jEcidium is distinct, and is black in colour owing to the dark
spores. Material sent by Herr Nawaschin, of Moscow, shows
that this species also occurs in Russia, where the teleuto form
develops not only in the cortex but also on the leaves of
Junipcnis communis, forming an oblong cushion-like stroma
which extends over about half of the leaf. In that country the
aecidia occur on the leaves of the apple-tree.

INJURIES INDUCED BY PLANTS

i6i

MELAMPSORA (CALVPTOSPORA) GOEPPERTTANA ^

The fungus which attacks the
cowberry, and its aecidium form,
yEcidiiun coluniuarc, which pro-
duces the columnar rust of the
silver fir, are indigenous wher-
ever silver firs abound. The
first-mentioned form, indeed, is
also met with in districts from
which the silver fir is absent, and
this furnishes a proof that the
oscidium form possesses only a
facultative character.

Specimens of Vacciniinn Vitis
Idi^a that are attacked by the
parasite are at once distinguishable
from healthy plants by their man-
ner and habit of growth. Whereas
the latter rise but a short distance
above the ground, individuals that
are infested by the fungus grow
quite erect, display an unusually
vigorous height-growth, and de-
velop two shoots even in the same
year. The diseased plants, singly or
in groups, tower above the healthy
plants, whose height they exceed
in some cases by a foot. At the
same time they exhibit a striking
appearance, the greater part of the
stem being swollen to the thickness
of a quill, while only the upper
part of each shoot retains its normal
dimensions (Fig. 91). At first the
thickened spongy part of the stem
is of a white or beautifully rosy
red colour, which soon, however,
changes into brown, and later be-
^ Hartig, Lehrbuch der Baumkrankkeiien, ist edition, pp. 56 et seq., Table II

M

Fig. 91. — A plant of \'. Vitis Idaa
which lias been infected by M.
Goeppertiana. a, the infected
stem containing the mycelium.
The new shoots /', in the year
succeeding that in which the plant
was infected, undergo abnor-
mal thickening under the in-
fluence of the mycelium ; the
apex alone retaining normal
dimensions. c, the youngest
shoot ; d, a dead portion.

[62

DISEASES OF TREES

comes almost black. The lower leaves of each shoot are dwarfed,
while the upper ones develop normally. If one infects a healthy
cowberry plant with the aecidiospores of the columnar rust of the
silver fir — which will be described presently — the stem remains
unaltered during the first year, although the mycelium spreads
in the tissues of the cortex. Next year, however, the young
shoots are affected in the manner just described. The my-
celium grows into the young shoots, where, by the exuda-
tion of a ferment, it
p^p^-_,_^ stimulates growth in
all the cortical cells.
This effect, however,
can onlybe produced
so long as the cells
of the new shoots are
still young. But on
account of the slow
upward growth of
the mycelium in the
shoot, it only reaches
the apex at a time
when the cells of
the cortex are com-
pletely matured, and
w^hen, consequently,
it is no longer able
to stimulate to in-
creased growth.

Fig. 92. — Cortical parenchyma and epidermal cells
from the stem of V. Vids Idcea. The mycelium
grows in the intercellular spaces, and pushes short
branches, which swell at the apex, against the outer
wall of the cells. A delicate prolongation at the
apex of these branches penetrates the cell-wall, after
which a sac-like haustorium develops in the interior
of the cell. Underneath the epidermal cells the
hypha; enlarge in a clavate manner, a a. Haus-
toria, /', and teleutospore-mother-cells, c c, develop
in the epidermal cells. Magnified 420 times.

The mycelium,
however, pushes up
as far as the topmost bud, which may be stimulated to shoot
out even in the same year as that in which it is formed. The
mycelium, which is perennial, is intercellular, and abstracts
nutriment from the parenchymatous cells by means of haustoria
(Fig. 92). It ultimately reaches the epidermis, underneath which
it swells up in a clavate manner (Fig. 92, a a).

Haustoria {b) are also pushed into the epidermal cells, which
may at once be distinguished, by their shape, from the young
spore-mother-cells {c c), which are also developed there.

INJURIES INDUCED BY PLANTS

163

From four to eight, usually six, such mother-cells are produced
in each epidermal cell. These increase in size till they occupy
the whole space, and then divide each into four teleutospores,
which are arranged side by side in a palisade fashion (Fig. 93,(7).
During wet weather in May of the following year, each teleuto-
spore germinates /// situ to
produce a promycelium {li),
on which the sporidia deve-
lop on short sterigmata (r).
Should these reach the silver
fir they penetrate the young
leaves by means of a germ-
tube, and four weeks later
the mycelium produces two
rows of secidia on the un-
der side of each leaf, which
are characterised by an ex-
tremely long peridium (Fig.
94). The peridia burst open
in various ways at the apex,
and allow the ?ecidiospores to
escape (Fig. 95). These are
characterised by the unusual
length of the intermediate
cells, which separate the in-
dividual spores from each
other. The jecidiospores ger-
minate when they reach the
epidermis of Vacciniiivi Vitis
IdcEa, and produce either a
tube which remains of uni-
form thickness, though it
sometimes branches, or a
germ-tube which enlarges in

a sac-like fashion towards the extremity. Infection is accom-
plished by means of a fine hypha which springs from the germ-
tube.

The infected leaves remain green for a considerable period,
and only fall off in the course of the summer. Even in

Fig. 93. — Epidermis and cortex of Jl
Vids Idira containing ripe teleuto-
spores of M. Goeppcrtiana, some of
which are germinating. The mother-
cells, each of which forms four teleuto-
spores, are usually found six together
in an epidermal cell, a. A germinat-
ing teleutospore produces a promy-
celium, /', on which, after the formation
of three transverse septa, four sporidia,
(■, usually develop on short sterigmata.
jNIagnified 420 times.

M 2

i64

DISEASES OF TREES

August I have found green leaves beset with the withered
aecidia.

Serious damage is done only when the young silver firs are
situated amongst badly infested cowberr}'-bushes, and when the
greater part of the leaves contract the disease. The aecidium
form possesses a facultative character — that is to say, it may be
absent without endangering the existence of the parasite whose

Fig. 94. — a, the branch of a silver
fir on the under side of whose
leaves two rows of the aecidia
ofyi/. Goeppe7iiana {ALcidiuin
cohtinnarc) have developed ; b,
the nscidia magnified.

Fig. 95. — An recidium of yl/. Goeppei--
tiana, a, in the tissues of a leaf of
the silver fir ; /', the strings of
cecidiospores with intermediate
cells ; c, germinating cecidiospoi-es.

sporidia are capable of germinating on, and of directly infecting
cowberry- plants.

Where damage is to be apprehended from the columnar rust
of the silver fir during the regeneration of a wood, one may reduce
the chances of an outbreak by rooting out diseased cowberry-
plants. On account of their striking appearance, these arc not
difficult to find.

MELAMTSORA TREMUL/E *

Under the name Melampsora popidiua, the Poplar-rust, are
denoted the fungus-forms belonging to this genus which are
met with on various species of poplars, and which await more
thorough and exact investigation.

Forms are met with on Popiihis tremnla whose cushion-like
* [Occurs in England, and reqtiires investigation. — Ed.]

INJURIES INDUCED BY PLANTS

165

stromata are distinguished by their smaller size from those which
occur on P. balsaniifera {JSI. Balsamifera Thinn.), and it would
also appear that the form M. populina Jacq. which is often
met with in luxuriant development on P. nigra is distinct from
the first two. Owing to the development and increase of the
uredospores in the course of the summer, the foliage may
appear quite golden yellow in August, and poplars sometimes
suffer so severely from this
rust that even in September
the trees may be entirely
leafless.

The teleutospore- layers
are primarily concealed by
the epidermis of the leaf, but
ultimately appear above the
surface as smooth brownish-
yellow cushions, which after-
wards become dark brown
(Fig. 96) ; while the yellow
uredo-layers, after rupturing
the epidermis, may be recog-
nised as loose clusters of
spores.

It would appear desirable
that these various forms of
poplar-rust should be made

the subject of more exact investigation, seeing that their jecidium
forms have not yet been determined with certainty.

I have, so far, investigated only the Melampsora that affects
Popnlns tremnla. Even as early as 1874^ I drew attention to
the fact that, with scarcely an exception, aspens present
in young Scotch pine woods are infested by Caoiiia piiiitor-
qniivi, and that some connection might possibly exist between
Ccvouia and some fungus that occurs on the aspen.

I indicated that such a connection was doubtful in the
case of Melmnpsora Treimdce, because this fungus occurs in
districts where Cczoma pinitorqiiiim is unknown. In the in-
terval, however, Rostrup proved experimentally the connection
^ Wichtige Krankheiteii dcr Waldbiittmc, p. 91.

Fig. 96. — Aspen-leaf showing the teleuto-
spore-layers of M. Tremuhr.

i66 DISEASES OF TREES

between these two fungi, and this I was able afterwards to
confirm. At the same time I proved that M. TreimilcE produces
Cceorna Lands on the larch.

Then .Rostrup also obtained Caonia Merairialis by infection
with M.,.rTr£;mii Ice. Rathay believes that he has also obtained
y^cidiuin Ciematitis on Clematis v it alba by infection with spores
oiM.populina. .

As regards CcEoma piiiitorqitmn apd C. Laricis, I obtained the
aecidia of both by infection with sporidia from the same aspen-leaf,
and, further, I have infected Pimis with teleutospores of Melamp-
sora which I had raised by sowing CcBoma Laricis on the aspen.

Thus, although it appears to me that the identity of these
two species of Ccconia has been conclusively proved, still it
would be desirable to have this confirmed. Even more pressing,
however, is the solution of the. problem whether CcEonia Mer-
airialis also originates in the same species of Melainpsora, or
whether various species occur on the aspen to which these
aecidium forms belong. Further, it is necessary to discover
whether the species present on P. nigra, P. alba, and P. bal-
saniifera are identical with those on the aspen ; and, finally, it
remains to be determined whether the cccidium forms possess a
facultative character, as appears to me most probable. I have
described below the two diseases produced on conifers by M.
T renin I a;.

First Form on Pinus sylvestris rt'//// Caeoma pinitorquum. The
Pine Shoot Twist Disease. Melampsora Tremulse pinitorquum

This disease is distributed throughout the whole of Ger-
many, being most prevalent in the north, where it has proved
exceedingly destructive, especially from 1870 to 1873. It may
attack young pine seedlings even at the stage when they are
just appearing above ground. In such a case longish pale
yellow sporogenous layers rupture the epidermis and appear
upon the surface of the stems or leaves. The disease is most
frequently observed in pine woods from one to ten years old,
infection being brought about by the teleutospores of M.
Tremnla; which develop on aspen- leaves that are lying about on
the ground. The disease ma}- be recognized by the fact that in
the beginning of June, sometimes even in the end of May, at the

INJURIES INDUCED BY PLANTS

167

season when the apex of the green leaf-fascicles on the young
shoots is projecting somewhat from the leaf-sheath, pale yellow
patches f to li inch long and )- to f inch broad appear upon the
green cortical tissues of the shoots (Fig. 97), and on these, with
the help of a pocket lens, numerous small rather deeper yellow
tubercles, the spermogonia, may be made out. These are
formed partly in the epidermal cells, and partly between them
and the cuticle, the latter being raised up to cover the spermo-
gonium (Fig. 98). The CtroinaAd-y^r originates in the second
or third row of cortical cells, and is formed by the inter-
cellular mycelium growing outwards from the interior of the
stem to produce a sporophore in that
region. The secidiospores are afterwards
distributed by abscission from the apex
of basidia in the usual way. While the
formation of this internal sporogenous

Fig. 97. — Apex cf a young
pine-shoot showing the
sporogenous layers of
C.piniiorquinn through
the ruptured cortex.
Natural size.

Fig. 98. — Transverse section of a sporogenous layer
of C. pinitorquuiii before the cortex has ruptured.
Two tubercular spermogonia are visible in the
epidermis. i

layer is proceeding, the surface of the part of the cortex affected
is constantly assuming a deeper golden }'ellow colour, while,
at the same time, it forms a cushion-like elevation which
results in the development of a longitudinal fissure (Fig. 97) in
the external layers of the cortex through which the spores are
shed. The tissues of the cortex beneath the sporophore after-
wards die as far in as the wood, and a callus is formed, under
favourable circumstances, in about a year.

During the development of the spores, and for some time
afterwards, the young shoot continues to elongate normally,
except at the seat of the disease. The result is that the diseased

1 68

DISEASES OF TREES

shoot bends over a little at the place occupied by the spore-layers.
In many cases, however, the ultimate contortions, which have
earned for the parasite the designation Pine Twister, C.
pinitorqimm, are due to the weight of the young shoot, whose
apex, in the case of lateral branches that are considerably
damaged on one side, is bound to be depressed. Later on the
apex again grows up, and thus S-shaped contortions arise. If
the weather is normal, a few such sporophores are formed

Fig. 99. — Apex of a pine which has been attacked by C. pinitorquitm. The leading
shoot has been killed almost to the base. The branches of the whorl, as well as
the main shoot-axis, show diseased spots and contortions which have existed for
a considerable time.

annually on the young shoots, while in very dry weather the
sporogenous layers wither up as soon as formed, and no external
damage is visible. Should May and the beginning of June be
very wet, the sporophores develop so abundantly and luxuriantly
that the shoots, with the exception of the base, die off and dry
up completely (Fig. 99). A badly diseased young Scotch pine
wood appears in the end of June as if a late frost had killed and
contorted all the young shoots. Next year the dormant eyes

INJURIES INDUCED BY PLANTS

169

of the leaf-fascicles that survive at the base of the shoot develop
into shoots, and these afterwards become diseased like the rest.
The fact that a pine that is once attacked by the fungus suffers
from the disease year after year during successive decades
justifies the assumption that the mycelium of the fungus is
perennial in the shoots. From the part of a pine wood that is
first attacked — the focus of the disease — the disease continues to
spread each year in a centrifugal manner. The point is to be
emphasized that very young woods — those from one to three
years old — suffer most from the disease. Pines that become
diseased at a later period are sometimes so badly crippled as to
hold out but faint hope of a healthy wood, but as a rule a dry
spring occurs sooner or later which retards the development of
the fungus, and so, a few years' mitigation of the disease being
granted, the plants gradually recover, although they again suffer
in unfavourable seasons. About the thirteenth year the disease
spontaneously disappears. Clearing out the aspens from the
young pine woods is the surest method of combating the disease

Second Form on Larix europaea wit/i Caeoma Laricis.i Melampsora

Tremulae Laricis

The larch-Ieaf-rust is distributed throughout the whole of
Germany, and is frequently so common that a large part of the
foliage is destroyed by the fungus.
It is often overlooked on account
of the damage bearing a certain re-
semblance to that due to Chernies
Laricis. In the month of May
numerous spermogonia first of all
appear on the leaves, amongst
which the 6"<^^;//rt- layers break
through the epidermis of the leaf
in the form of long or short yellow
cushions.

After the spores have been shed
the leaves wither and fall off. Felling the aspens in the neigh-*"
bourhood of larch woods protects the latter against the disease.

1 Wichtige Krankheite?i der Waldbdume, 1 874, p. 93, and Allgemeine Forst-
joid Jagd-Zcitung 1885, p. 326.

Yic. 100. — Larch-leaves attacked by
CtCiV/tii Laricis.

I JO

DISEASES OF TREES

MELAMPSORA SALICINA.^ THE WILLOW-RUST

Several species of Melanipsora occur on the various willows,
and these, until a short time ago, were grouped under the
common collective name of M. salicina. By means of the form
of the teleutospores and urcdospores, Thiimen was the first to
distinguish a number of species, which ought to be thoroughly
investigated for the sake of verification.
Rostrup - has, in the interval, succeeded
in obtaining the scidia of two species,
which will now be more particularly
described.

MELAMPSORA HARTIGII
The uredospores appear sometimes as
early as the end of May or the begin-
ning of June, in small reddish yellow
clusters on the lower surface, more
rarely on the upper surface, of the
leaves of Salix pruinosa, S. daphiioidcs,
S. viniinalis, and other willows. The
disease spreads rapidly, partly owing to
the internal growth of the mycelium,
which penetrates the cortex of the
shoots by way of the leaf-petioles, and
partly by means of the uredospores
which are carried by the wind. These
germinate very quickly, and produce
numerous new uredo-clusters, generalh'
on the eighth day after they have been
sown on a sound leaf. Leaves that are
attacked soon become marked with black blotches, and drop off.
Before the leaves fall off or die numerous teleutospore-layers,
about the size of a pin-head, develop beneath the epidermis of
the leaf (Fig. loi). These occur more especially in late summer

^ Von Thiimen, Mittheilungen aus dem forstlichen Versiichswesen Oester-
reichs, ii. p. 41 et seq. Hartig, Wichtige Krankheiteii der Waldbiiume^
pp. \\() et seq.

2 Rostrup, Fortsatte Undersogeher over Snyltesvampes Angreb par
Skoi'traeerne Kjobcnliaven., 18S3.

Fig. ioi. — M. Hartigii on
Salix p7-uhiosa. a, a living
leaf with sporophores ; /',
a leaf which has been
killed at places ; c, sporo-
phores on the stem close
to the base of the leaf

INJURIES INDUCED BY PLANTS 171

and in autumn. These small cushion-like bodies, which are at
first pale brown and later very dark brown in colour, pass the
winter in the tissues of the decaying leaves that are l}'ing on the
ground, and produce promycelia and sporidia in spring. These
sporidia are carried by the wind to the leaves of the young willow-
shoots, and induce the disease afresh. They produce Ccuoma
Ribesii on the leaves of Ribcs alpimiui, R. Grossularia, R. rnbnun,
and R. nigriini. This aecidium form appears, however, to pos-
sess merely a facultative character, for we annually meet with
numerous instances of the disease, especially in autumn, even in
places where no examples of Ribes are to be met with for long
distances.

Hitherto I have met with serious infestations of the fungus
only on Salix prtiinosa (syn. caspica, acntifolid), numerous osier-
beds being entirely destroyed by repeated premature defoliation.
The best preventive measures consist in raking together and
burying or burning the fallen fungus-infested leaves from
autumn till spring, and in careful attention to the osier-beds
during summer. As soon as the rust appears sporadically it is
advisable to cut off and bury, the infested shoots. In place of
the glabrous-leaved Salix pniinosa, which suffers most from the
fungus, the cultivation of the hybrid J?, pruinosa x daphnoides
is to be recommended, the latter being pubescent, and thus better
protected against infection.

MELAMPSORA CAPREARUM

This willow-rust is very common on Salix Caprea, S. cinerea,
S. aiirita, S. longifolia, S. repens, and vS. reticulata. It produces
the cEcidia of Cceoina Evonyini on Evonynms.

Then we also meet with Melajupsora epitca on vS. alba,
S. incana, S. piopiirea, S. nigiicans, and 5". retiisa ; and J/.
mixta on S. triaiidra, S. hastata, and 6". silesiaca.

M. betulina occurs on various species of Betula.

M. Caipini „ „ Carpinus Bctiilus.

M. Sorbi ,, „ Sorbus Aiiaiparia ?a-\A S.torminalis.

M. Arice „ ,, Sorlnis Aria.

M. Padi ,, „ Primus Padus.

M. Vaccina „ ,, Species of Vacciuiuni.*

♦[Several of these are recorded for this country, and are much in need of
thorough investigation. — Ed.]

172

DISEASES OF TREES

COLEOSPORIUM SENECIONIS
The genus Coleosporiiim is distinguished from the preceding
one by the teleutospores being formed out of several super-
imposed cells, each of which produces a unicellular promycelium
with a single sporidium.

According to the investigations of Wolf and Klebahn, three
species of this genus produce aecidia on the leaves of the pine.
These include not only C. Senecionis, which occurs on various
species of Senecio (according to Wolf), but also C. Euphrasies
and C. Tnssilaginis (according to Klebahn). The aecidium forms
are known under the names of Peridermium Pini acicola or
Peridennunn oblongisporinm, the pine-Icaf-rust.^

In the months of April and May the cxcidia may be observed
on the one- and two-year-old leaves chiefly of younger pines,
occasionally also of old trees. The sper-
mogonia are found scattered amongst the
reddish yellow vesicles (Fig. 102), which
are only a few millimetres in size. The
former become brown with age, and thus
look from the outside like small black
blotches. The mycelium develops in the
interior of the leaf, where it passes the
winter, and in the following year it may
again produce aecidia without killing the
leaf Seeing that the leaves which are
infested by the aecidia do not die pre-
maturely, or at least not to any great ex-
tent, the injury done by this form of the
fungus is insignificant. Discoloured spots are merely formed
upon the leaves.

Several species of Cronartiiiui produce aecidia and spermo-
gonia in the cortical tissues of pines. These have hitherto been
grouped under the name Perideriniuin Pini corticola* The
disease, which occurs both in young and old woods, is very
prejudicial to the health of the trees. How infection takes place
— whether it must always be preceded by an abrasion of the
cortical tissue, such as is induced by insects, woodpeckers, hail-
' R. Hartig, Wichtige Krankheifen der IValdbaiinie, 1874.
* [This disease occurs every year on pines in this country. — Ed.]

Fig. 102. — The secidia
and spermogonia of
Perideriiiiiiin Pini
acicola on the leaves
of a pine.

INJURIES INDUCED BY PLANTS

173

stones, &c. — remains for the present undetermined. Parts of
the stem older than 20 — 25 years appear to be incapable of
receiving infection. The mycelium of the fungus spreads by
intercellular growth amongst the cells of the cortex and of the
bast, from which it proceeds, by way of the medullary rays, into
the wood to the depth of about four inches.

Wherever the mycelium obtains access, the starch-grains and
other cell-contents disappear, their place being taken by drops
of oil of turpentine, which form on the inside of the walls, or
saturate the wall-substance itself. The cells are, of course,
killed, death however being unaccompanied by browning of the
tissues. The whole stem, to a depth of some three or four inches,
is completel}- saturated with resin, a section of wood, as much as
one to two inches in thickness, being more or less translucent.
As the mycelium penetrates the resin-ducts as well, killing the
surrounding tissues, there is no doubt that a portion of the
turpentine finds its way down from parts of the stem situated
at a higher elevation. The
assumption that direct con-
version to turpentine of the
cell-contents and of the wall-
substance of the parench}'-
matous cells also takes place
is, however, justified by the
complete resinous saturation,
and by a frequent volumin-
ous outpouring of turpentine
from the cortex, which de-
taches itself from the tree
after death.

Each year the mycelium
spreads from the diseased
part into adjoining tissues,
the rate of progress being usually somewhat more rapid longi-
tudinally than horizontally. In proportion as the mycelium
spreads, so is the passage of the plastic materials confined to
the sound side of the tree, in consequence of which the cam-
bium in that region is stimulated to such a degree of activity as
to produce exceptionally broad annual rings. Fig. 103 exhibits
the cross section of a stem which, when fifteen )-ears old, was

Fig. 10

Transverse section from the
upper part of the stem of a pine which,
seventy years previously, had been in-
fected at a by P. Pini corticola. The
crown of the tree died in the year im-
mediately preceding that in which the
section was removed, and at that time
the only portion of alburnum that was
not saturated with resin or attacked by
the fungus was the portion marked b.
The portion of the wood saturated with
resin is shaded in the figure. One tenth
natural size.

174

DISEASES OF TREES

infected at a, but which, with the part of the crown situated
above the point of infection, only succumbed in its eighty-fifth
year. The top of a diseased tree is specially liable to die during
a dry warm summer, when the wood, having for the most part
undergone resinous degeneration, is unable to allow sufficient
water to pass to compensate
for the rapid evaporation from
the crown.

For the most part ascidia
are formed only in that re-
gion of the cortex which has
become diseased during the
preceding year. They break

Fig. 104. — Portion of the stem of a
young pine showing the vesicular
CEcidia of P. Pint corticola break-
ing through the cortex. At three
places which are darker shaded
spermogonia are situated beneath
the periderm. Natural size.

Fig. 105. — A pine-branch which has been
infested by P. Pini corticola for several
years. The branches on the left side,
which were the first to be attacked, are
already dead. From these the mycelium
has spread backwards on to the main
branch and the other lateral branches.
One fifth natural size.

through the outer dead cortical layers in the months of May and
June as hemispherical, oblong, sausage-shaped, yellowish white
vesicles filled with reddish yellow powdery spores (Fig. 104).
Amongst these one recognizes with difficulty the flat spermo-
gonia which are about the size of a pea. These consist of
innumerable fine sterigmata which are situated between the
deepest periderm-layer and the living cortex, being arranged at
right angles to the former. The small spermatia are abjointed
from the apex of these sterigmata.

Branches and twigs of the crowns of the older classes of trees

INJURIES INDUCED BY PLANTS 175

often die in a few years, after which the parasite frequently
spreads downwards from the base of the branch to the main
axis of the stem (Fig. 105). Even should the latter die the tree
will still remain alive, provided there are branches and twigs well
provided with leaves beneath the canker-spot. These branches
constitute a kind of new leader, and the dead crown forms
the " resin-top " or " resin-leader " (" bird-resin "), which was
regarded by Ratzeburg as the result of injury caused by the
Pine Beauty Moth, and designated as " spear-top."

The disease has also been described by this observer as
'' moth-wither," or, in other words, as the result of the attack of
Phycis abictdla ( Tinea sylvestrella, Ratz).

Three species of pine-blister-rust are to be distinguished in
the cortex of trees, viz. : —

(i) PeridermiiLin Strobi, which occurs only in the cortex of
PiiiiLS Strobus. The aecidium form is Cronaytium ritbicila.

(2) Peridcniiiuin Conuii, which occurs in the cortex of Piniis
sylvestris, has for its aecidium form Cyonartinni asdepiadeuin on
A sdepiiis Vincctoxicum.

(3) Peridermium Pini. This is probably the most destructive
species, and it is to be regretted that so far the plants have
not been determined on which the teleutospores are produced.
Until we discover the teleuto form preventive measures must be
confined to felling pines that arc attacked.

CIIRY.SOMVXA
The genus Chrysomyxa is closely related to the preceding one,
in that here also each teleutospore consists of a row of cells, the
terminal one of which produces a multicellular promycelium
with four sterigmata and sporidia. The sporophore consists of
a dense orange yellow cushion-like body of varying shape. The
urcdo and aecidium layers are similar to those of the genus
Coleosporiuin.

CHRYSOMYXA ABIETIS,! THE SPRUCE-LEAF-RUST
This is a disease of the spruce which is met with through-
out the whole of Germany, with the exception of the higher
Alpine regions. It occurs on old as well as on young spruces,

^ Reess, Bat. Zeit., \2,6s, Nos. 51 and 52, and \\-\\\komm^ D/c mzk?-os-
kopischen Fcinde des Waldos, 1868, pp. 134 — 166.

^' O-^^Ji^.^::^ u,^c0jJ ^ tVt.74.^>^

176

DISEASES OF TREES

and is frequently so prevalent on the youngest shoots as to kill
a large proportion of the leaves, which subsequently drop off.

The fungus is autcEcious, the uredo and jecidium layers being
entirely absent. Its teleutospore-layers alone are developed on
the spruce-leaves. In the month of May the sporidia germinate
on the delicate leaves of the young shoots, inside which they
produce the mycelium, which contains numerous drops of yellow
oil. By the end of June the part of the leaf that is infested may
be recognized by its pale yellow colour. The diseased portion
may occupy the base, middle, or apex of the leaf As autumn
approaches it constantly becomes deeper lemon yellow in
colour, while the rest of the leaf remains green. In autumn
formation of the teleutospore-layers begins on both the
under sides of the leaf These take the form
of oblong, somewhat prominent cushions,
which are at once to be recognized by their
more golden yellow colour. In this condi-
tion the fungus hibernates on the tree, and
in the following spring the teleutospore-layer
still further develops (Fig. 106), until finally
the epidermis ruptures longitudinally and ex-
poses a golden yellow stroma. The pnDmy-
celia with their sporidia next develop from
the cells of the teleutospores, as is shown
in the case of C. Rhododendri in Fig. 107,
and as this occurs in the month of May, at a
time when the young shoots of the spruce arc
forming, the sporidia have the opportunity
of germinating directly on the young leaves.
It is probable that spruces wdiich arc very backward in growth
at the time when the spores ripen escape infection, and this
explains why many individuals of a wood remain entirely free
from the fungus while others are very badly attacked. Such
cases have frequently inspired non-professional minds with the
belief that the fungoid disease is dependent upon a pre-
disposition to disease on the part of particular spruces. After
the sporidia drop off the teleutospore-layers wither, while the
leaves themselves soon afterwards die and fall from Uhe tree.
As a rule the tree suffers but little from the loss of leaves.

Fig. 106. — A spruce-
leaf attacked by
C. Abietis, the
golden yellow
spore-layers of
which have not
yet ruptured the
epidermis.

INJURIES INDUCED BY PLANTS 177

because a sufficient supply of foliage is always left on the older
parts of the branches as well as on the youngest shoots. As the
meteorological conditions are not always equally favourable for
the germination of the sporidia, and as the teleutospores may
germinate at a time when most of the spruces are either too far,
or not far enough, advanced in development to be infected by
the sporidia, it very seldom happens that the disease maintains
its intensity throughout a long series of years. With the
exception of a spruce wood in the Saxon Erzgebirge, I have
never come across very serious damage due to Chrysomyxa
Abietis. Certain years occur, and not uncommonly, when the
disease is very scarce, and when the spruces are in a position to
clothe themselves with a full stock of leaves. On this account
I am not able to agree w^th Willkomm, Frank, &c., in their
recommendations regarding measures for combating the fungus,
because felling the diseased trees, and such like measures, would
have worse consequences than the disease itself.

It may be not uninteresting to note that in the severe winter
1879-80 it was noticed that in many districts the diseased leaves
dried up so that the development of the fungus was prevented.
And, further, it not unfrcquently happens that Hysterhun macro-
sporum is encountered along with Chrysomyxa, the result being
that the development of the leaves is interfered with, and they
acquire black blotches. ^2»^CU^. 1 1

CHRYSOMYXA RHODODENDRI ^ ^tJ fL

The Rust of the Rhododendron is of special interest in that it / j. f
is heteroecious, developing its teleutospore- and uredo-layers in »
clusters in the form of small roundish and oblong cushions ' *M4aa*»<
on the leaves of rhododendrons, while the aecidia [ALcidmni 4m»*-*-'*'
abietimim, the Spruce-Blister-Rust) develop on the leaves of the Ou/u/t^
young shoots of th^ spruce. -VfcxJ* /^•*

The occurrence of the disease on spruces is consequently ^
dependent on the presence of rhododendrons,- although, ofC^^^V-**'
course, the spread of the sporidia, by means of wind and rain, >sc«sr /*
from high elevations into the valleys or otherwise is not im- ^I 1
possible. De Bary, to whom we are indebted for our know- rf^

1 De Bary, i5^/. Z«V., 1879. ^ ^^

- In the Alps R. hirsutuin and R. ferruginium are the common species. ^ -^ Liy

N

178

DISEASES OF TREES

ledge of the biology of this parasite, has, however, proved that
the aecidium form may be dispensed with. Where spruces arc
absent the sporidia germinate directly on the leaves of the
rhododendron to produce the uredo layers, and these serve
to maintain and spread the fungus during summer, until, in
autumn, teleutospore-layers are again formed on the leaves of
the youngest rhododendron shoots. These hibernate, and in the
following spring the germination of the teleutospores results in
the rupturing of the leaf-epidermis (Fig. 107).

At first the development of the parasite in the spruce-leaf
resembles that of Cluysoniyxa Abietis, but even in July and

Fig. 107. — Teleutospore-Iayer of C. Rhodo-
dendri on R. lii^sntum. The development
of the promycelia has caused the epidermis
of the leaf to rupture.

Fig. 108. — Spernio-
gonia and secidia
of C. Rhododetidri
on a spruce-leaf \

CH'

August numerous small spots, the spermogonia,/!, are to be
observed on the yellow parts of the leaves. Shortly afterwards
one sees the yellow vesicles of the aecidia breaking through the
epidermis, and these bear a close resemblance to those produced
by the pine-blister-rust on the leaves of pines (Fig. 108), In
August and September, when the peridia burst at the apex, the
secidiospores are liberated in such numbers that if a diseased
spruce is shaken the air is filled with a dense cloud of spores.
In the course of the same year the diseased leaves die and drop
off. This distinguishes the parasite at once from Chrysomyxa
Abietis, which, in an immature state, hibernates on the tree. On
lateral branches it is usually only the leaves that are situated on the
upper side that are diseased. The leaves on the under side, being
preserved against infection by those above, escape the disease.

INJURIES INDUCED BY PLANTS 17^

CHRYSOMYXA LEDI 1

This parasite induces the same pathological symptoms in the
spruce as the preceding one, but it differs in producing its teleu-
tosporcs and uredospores on the leaves of Ledum palustre*
Letters received from Russia mention that the fungus occurs in
extraordinary abundance in that country, and I have also recently
had it forwarded from the district of Konigsberg. It has also
frequently been observed in other parts of Germany, with the
exception of the south, but of course only where Ledum occurs
in the immediate neighbourhood.

In the case of the parasites about to be described, the aecidium
forms alone are as yet known, so that the investigation of the
course of development of what are probably all heteroecious
forms of fungi is work for the future.

ISOLATED yECIDIUM FORMS

From amongst the aecidium forms of whose teleutospore-forms
we are so far ignorant, attention will here be directed only to
those species which occur on forest trees.

^CIDIUM (PERIDERMIUM) ELATINUM ^ f

This fungus is parasitic on the silver fir, where it produces the
so-called witches' brooms and canker-knobs which may be seen
an)-whcre in Germany where woods of silver firs occur.^ As I
have always noticed small wounds on one- or two-year-old
witches' brooms close to their base — near the point, namely, where
they have developed from a bud — it may in the meantime be
assumed that infection occurs at such wounds. The mycelium
of the fungus, which stimulates growth in a very marked manner,
is perennial in the cortical and bast tissues of the stem, and even
penetrates the cambium and the wood. Should infection occur

1 De Bary, Bot. Zeif., 1879. 2 /^/^^ 1867.

[3 Very common also in many parts of Britain, Ci^. the south-west of
Scotland. — Tratts.']

*[An Ericaceous plant found on moors, &c., in N.E. Europe. — Ed. ]

t [The cankers occur in various Silver Firs grown in English gardens,
though they often seem devoid of the Witches' Brooms and secidia. I have
seen both, however, on Abies Pinsapo and other species. — Ed.]

N 2

I So

DISEASES OF TREES

at a part of a stem or branch where there are no buds capable of
developing, the stimulated growth of the cambium induces the
formation of a knob-like swelling at that place, which is due
both to the increased formation of wood and to the more vigorous
development of the cortex (Fig. 109). With the spread of the
mycelium the swellings or canker-spots increase in size, and if
present on the stem of
a vigorous tree they may
attain to large dimen-
sions. At such places
the tissues of the cortex
and bast soon become
fissured (Fig. no), and
dry up here and there
as far in as the wood, so
that in course of time a

Fig. 109. — Swelling on the silver
fir, but without the formation
of a witches' broom. Natural

P'lG. no. — Longitudinal section of a silver fir
showing a swelling,one third natural size, which
had originated by infection thirty-one years
previously, when the stem was four years old.
On the right side the cortex, which has been
dead for three years, has withered and dropped
off. At the infected part the growth of the
cortex and wood has been stimulated.

door is opened for the entrance of wood-parasites. One of the
commonest of these is Polyporus Hartigii, which produces a kind
of white rot. A species oi Agar i ens also — namely, A. adiposus—
frequently appears as a wood-destroying parasite. In consequence
of the decomposition of the wood, storms and snow often break
the trees. One not unfrequently finds swellings which have

INJURIES INDUCED BY PLANTS

i8i

originated without any connection with witches' brooms (Fig.
109), and on such swelHngs no formation of spores ever occurs.

More frequently infection occurs on or in the immediate
neighbourhood of a bud. When the bud proceeds to grow it
forms a young witches' broom — ^that is to say, a shoot whose
cortex is stimulated to growth by the advancing mycelium, and
whose young leaves are so affected by the parasite that they
remain small, are somewhat round in cross-section, and show

Fig. III. — Branch of a silver fir, with a witches' broom two years old, a:. The
mycelium in advancing through the tissues of the branch has so stimulated a
dormant eye that it has developed into a shoot a year later, b. The portion of
the branch that has been invaded by the mycelium is much swollen.

scarcely any chlorophyll. They remain yellowish, and in the
beginning of August two rows of aecidia appear on their under
side, which open and shed their spores in the end of the
month (Fig. in). Soon afterwards the leaves die and fall off.
The witches' broom is consequently deciduous. Each year
the mycelium advances into the new shoots, to produce the
phenomena already described. The twigs of branches which
show this peculiar symbiosis * anastomose abundantly, and for
the most part incline upwards, so that they appear amongst
the ordinary branches of the silver fir like perfectly independent

* [Symbiosis signifies the fact that two organisms are living together— a
dual existence.]

DISEASES OF TREES

organisms, somewhat after the manner of the mistletoe. The
myceHum also spreads slowly backwards in the cortical and
bast tissues, so that a swelling or canker-spot, such as I have

already described, is formed on
the stem or branch to which the
witches' broom is attached (Fig.
112). This swelling increases
independently, even after the
witches' broom, as such, is dead,
an event which is sometimes de-
layed for twenty years or more.
In young woods all trees that
show cancerous swellings on their
boles should be removed in the
thinnings, even in cases where
they belong to the larger class
of trees.

Fig. 113. — i^cidia Fig. 114. — Theouter

Fig. 1X2. — The appearance of a witches'
broom, seven years old, in winter,
when, being deciduous, of course it is
leafless. Above the point from which
the witches' broom springs the fir
branch has almost ceased to exist.

of ^. strobiliiiiini
on the upper side
of a scale of a
spruce-cone.

side of the scale
of a spruce-cone,
showing two pale
patches which had
previously been oc-
cupied by the seci-
dia of A. conoriim
Picece.

yEClDIUM STROBILINUM ^
This aicidium form develops its mycelium in the green living
carpellary scales of the spruce. It destroys the organs of the
flower, and produces dark hemispherical brown aecidia, which are
densely crowded, for the most part on the inner side of the
scales, though to some extent also on the outer side. These
aecidia usually rupture transversely (Fig. 113). When such
cones fall to the ground they arc easily recognized by the fact

^ Reess, Die Rostpilsforuien der dei/tsc/ien Coniferen.

INJURIES INDUCED BY PLANTS

183

that they open even in damp weather, whereas sound cones
remain tightly closed. This cone-disease occurs throughout the
whole of North Germany, reaching as far south as the spurs
of the Alps.

.tCIDIUM CONORUM PICE.E
This cone-infesting fungus differs from the former by the fact
that only two large aecidia are situated on the outer side of
each scale of the spruce-cone. After the pale peridia have
ruptured and the spores have been scattered, pale spots are left
on the scales (Fig. 1 14).

.■ECIDIUM CORUSCANSi
When this rust-fungus, which is common on spruces in
Sweden and Finland, attacks a young shoot, the whole of the

Fig. 115. — A spruce-branch, one shoot of which, a, has developed normally, while
two shoots, d, have been attacked by A. coniscans. All the leaves of the
diseased shoots are short and fleshy, and bear secidia on all their four sides. The
lower sides, c, and the upper sides, d, of a diseased leaf showing the cecidia,
the peridia of which are still present at c, but have mostly disappeared at (/.

leaves are affected. They become occupied by a peridium, which
ruptures in places or along the whole length of the leaf, and
displays the golden yellow aecidia underneath. Such leaves
make the shoot look like a fleshy cone (Fig. 115). These " cones "
are eaten in Sweden under the name " Mjolkomlor."

^ Reess, Die Rostpilzformen dcr dcutschcn Coiiifereti^ p. 100.

1 84

DISEASES OF TREES

C.EOMA ABIETIS rECTINAT.li i

This disease closely resembles the vesicular or columnar
rust, y^cidinm cohininare {Melanipsora Goep-
pertiajid), from which it is distinguished by
the presence of numerous spermogonia, and
by the absence of a peridium. It occurs
on the lower side of the leaves of the
silver fir, usually in the form of linear
sporogenous layers, which are situated on
both sides of the mid-rib (P'ig. Ii6). It is
very abundant in the Bavarian Alps and
in the woods near Passau, and is probably
to be met with wherever the silver fir is
indigenous.
The damage which it causes takes the form of the diseased

leaves falling off in the first year, but the injury is comparatively

unimportant.

Fig. ii6. — A fir-leaf
showing C. Abieiis
pectinatiF.

HYMENOMYCETES (CAP-FUNGI *)

Most of i\\c: HfJiieiioniycetcs are saprophytes, and develop their
mycelium in soil that is rich in humus, or in the interior of the
dead parts of plants, and especially in dead wood ; while the
sporophore, which is often of large proportions, appears on
the surface of the ground or on the outside of the plant, Onl)-
relatively few of the Hymenomycetes are undoubtedly parasitic
in character, and, in the case of many, more exact investigation
must determine whether they are to be classed as parasites
or saprophytes. The peculiarity in the production of the spores
consists in their being simultaneously formed in fours at the
apex of basidia, and that these basidia constitute a more or less
dense layer (hymenium), which may occupy a part or the whole
surface of the hymenophore.

^ Reess, Die Rostpilzforinen der dcKtschcn Coni/eren, p. 115.

* [These include the " Mushrooms" and " Toadstools "' in the wider sense:
we are still in want of a good English general term for them, and the trans-
lation of the German Htit-pilze does not really meet this need. — Ed.]

INJURIES INDUCED BY PLANTS

185

EXOBASIDIUM

The genus Exobasidiiim induces the formation of character-
istic galls on the leaves, flowers, and stems of various ligneous
plants. The basidia originate on the mycelium, which is chiefly
intercellular, and force their way outwards between the cells
of the epidermis, on the surface of which they form a hymenial
layer. No special sporophore, in the narrower sense of the term,
is produced.

EXOBASIDIUM VACCINII 1

This parasite produces swellings on the leaves, flowers, and
stems of Vaccinhim Vitis Idcva, V. Myrtillus, and V. riliginosuin.
These are partly of a beautiful white colour and partly of a
bright rosy hue, and arc to be distinguished from the swellings due
to Melampsora Goeppertiana hy their being dusted over with the

Fig. 117. — A shoot of V. J'ltis Idtca,
with the hymenium of E. Vaccinii
on the leaves, a a, and in the stem.

Fig. 118. — "Alpine-rose apple" on
Rhododendron h irsntti?n.

white spores, whereas, in the case of the latter, the lustrous
epidermis hides the sporogenous layer ; and further by their
occurring more frequently on the under surface of the leaves or
on the racemose inflorescence than on the stem (Fig. 117). A
microscopic examination at once reveals the fact that the long
somewhat bent spores are situated on four delicate stcrigmata at
the apex of the clavate basidia.

This fungus, which was formerly described as a separate

^ Woronin, I'erhandliingcn dcr 7iatiirf. GesellscJiaft zic Freibtiri:;, 1S67, I\'.

i86 DISEASES OF TREES

species under the name Exobasidiiivi RJiododendri, produces the
familiar " Alpine-rose apples " (Fig. Ii8) on the leaves of the
Alpine rhododendrons. These bear a strong resemblance to
many of the galls on oak-leaves which are caused by various
species of Cynips, and are to be met with in all Alpine districts
where rhododendrons occur.

TRAMETES RADICIPERDA ^ *

T. radiciperda is undoubtedly the most dangerous of all the
parasites met with in coniferous woods, not only because it
produces the worst kind of red-rot, but also on account of its
being the most common cause of gaps in both young and old
plantations. I have had the opportunity of observing it on
various species of pines, especially P. sylvestris and P. Strobjis,
and also on other conifers, notably Picea excelsa, Abies pectinata,
^.wd, Jiiniperiis comniunis. It is true that I have also occasionally
met with its sporophores on the roots of old stools of Betiiia,
and on beeches that have been damaged by mice, still I doubt if
it occurs on dicotyledons as a parasite.

Not unfrequently the disease appears in plantations which are
not more than five to ten years old, though it also occurs in
woods of a hundred years' standing. Here and there indi-
vidual trees showing luxuriant growth suddenly become pale,
and die. We shall afterwards see that identical pathological
symptoms are displayed by trees infected by Agariais inclleus.
In the neighbourhood of a tree that has been killed — no matter
whether it is left standing or has been felled — other trees soon
die, and so in the course of years the death-circle constantly
extends outwards. Large gaps and openings are thus formed in
woods which were previously quite close. At first one generally

' R. Hartig, Zersetzungserschei)iu7igen des Holzes,'^'^. 14 et set/., Tables
I. — IV. Under the name Polyporus annosus, Fr., a number of different
species of fungi have been described, Tramefcs radiciperda amongst the
others. This mode of description has, however, been accepted as sufficiently
accurate even in the second edition of Fries's Systetna, which appeared some
years after I had described T. radiciperda. The name T. radiciperda is thus
entitled to priority, and is also to be preferred, as it prevents any confusion.

* [Brefeld, Unters. aus dcm Gesammigeb. der Mykol. VIII., re-names this
Heterobasidion annosum, and describes its second kind of spores — conidia.- -
ED.]

INJURIES INDUCED BY PLANTS

1S7

observes only one or a very limited number of diseased spots in
a wood, but when these have been allowed to extend for some
\'cars one notices new seats of disease establishing themselves all
over the wood.

When the dead trees are examined about the roots, one finds
the sporophores, with their snow-white hymenial surface, appear-

FiG. 119.- — The sporophores of T.
radiciperda on the roots of a
spruce. Natural size.

FiCt. 120. — The mycelium of T.
radiciperda on the root of a
spruce. The outer bark-scales
have been removed from the
lower portion so as to show
the felted mycelium, a a, while
in the upper portion only
cushion-like mycelial masses,
h, project from between the
scales. Twice natural size.

ing between the bark-scales as very small yellowish-white cushion-
like structures (Fig. 119). These coalesce with similar adjoining
cushions, and in exceptional cases attain to a diameter of twelve
to sixteen inches. In the case of pines the sporophores are
usually to be found on the stool close under the surface of the
ground, though sometimes also on the deeper roots, while in the
case of the spruce they are almost always to be found only on
the roots. Between the bark- scales one finds the ramifying
felted mycelium, which is distinguished from that of Agariais
inellens by its extremely delicate te.xture (Fig. 120). It scarcely

i8S DISEASES OF TREES

attains to the thickness of the finest tissue paper, and only where
it penetrates between the bark scales does it swell up to form
yellowish-white bodies varying in size from a pin-head to a pea.
Decomposition (red-rot) spreads from the roots up into the
interior of the stem to a considerable distance. It is only in
the case of the Scotch pine that the rot does not ascend into
the stem from the stool.

Shortly described, the biology of the parasite is as follows.
The spores, which are formed in the hymenial layer of the
subterranean sporophore, do not as a rule spread from the place
where they originate, unless they are brushed off by a passing
object. As sporophores are especially liable to be formed on
diseased roots at the point where they abut on mouse-holes,
it appears to be a likely supposition that the mice, or other
burrowing animals, carry away the spores on their fur, possibly
for long distances, and afterwards rub them off on healthy roots.
The spores soon germinate in warm humid air, and the m}--
celium, entering between the bark-scales, will probably reach
the living cortex at some point or other. From this time its
course of development is in two directions. It forces its way
into the wood, in which it very rapidly travels up the stem. The
contents of the parenchymatous cells are killed and turned
brown by the action of the ferment that is exuded by the
mycelium, while a violet colour in the wood is the visible
symptom of this stage of the decomposition. With the
disappearance of the protoplasmic contents of the cells the violet
colour is replaced by pale brownish yellow, except for a few
dark blotches which persist. The latter afterwards become sur-
rounded by a white zone, and simultaneously the wood gradually
becomes lighter and more spongy. Ultimately numerous holes
are formed, the tissues become dismembered, sodden, and pale
brownish yellow, but never dark brown.

The hyphae of the fungus travel upwards in the lumina of
the elements of the wood, and easily pierce the walls of the cells.
As they send off lateral branches they also invade the cells of
the medullary rays, as well as adjoining tracheides. As already
mentioned, the first perceptible change in the wood occurs in the
contents of the living cells, which become brown and partly
disappear. This is succeeded by the conversion of the lignified

INJURIES INDUCED BY PLANTS 189

cell-wall into cellulose, a change which begins on the side next
the lumen, and advances outwards. The cellulose is soon
completely dissolved, and at last the delicate skeleton of the
middle lamellae also disappears. At certain points this process
proceeds with great rapidity. Here and there, for instance, one
finds that the tracheides, in immediate proximity to the medullary
rays, are filled with a brown fluid, which has probably originated
in the latter, and which discolours and nourishes the mycelium
to such an extent that a brown " mycelial nest " is formed. So
energetic is the action of the ferment in the neighbour-
hood of these bodies that the encrusting substances entirely
disappear from the adjoining tracheides, which, to the dis-
tance of several millimeters, are completely transformed into
cellulose, and thus become colourless — in other words, white.
Almost immediately after being converted into cellulose the
middle lamella disappears entirely, and the individual elements
of the wood thus become isolated, so that, when disturbed by a
needle, they fall apart like the strands of asbestos. Gradually
they are dissolved, and holes, which are constantly increasing in
size, are formed in the crumbly wood.

While the mycelium thus decomposes the wood, sometimes to
a height exceeding eight yards, the parasite advances much
more slowly in the cortex, where its presence is betrayed b}- three
distinct phenomena. From the point of infection the mycelium
spreads both towards the root-apices and towards the stem. It
kills the cortex, and consequently the root, and when, after some
years, it has reached the stem, it spreads from the stool on to
roots that have hitherto remained sound. As soon as these are
also attacked by the disease, the tree dies.

A second function of the mycelium that grows in the cortex
consists in the formation of sporophores, which appear here and
there between the bark-scales of the roots or stool. These lead
to the production of fresh seats of disease in the plantation, as
has been already described.

A third function is concerned with the spread of the disease
subterraneously owing to infection by the mycelium. Where a
diseased root comes into contact with the sound root of an
adjoining tree (Fig. 121), or where the two are positively grown
(grafted) together — as may very frequently be observed in a dense

I go

DISEASES OF TREES

wood — the mycelium, which appears as a small cushion between
the scales, grows into the cortex of the neighbouring tree. It is
easy to induce infection artificially by taking a piece of cortex
containing a portion of living m}xelium still capable of growth,
and binding it firmly to the cortex of the root of another tree.

Owing to the mycelium spreading subterraneously from tree
to tree, these well-known gaps, which increase in size each year
by the death of the marginal trees, appear in woods. At one
time no reason whatever could be assigned for the peculiar
behaviour of these gaps. On account of the decomposition of
the wood proceeding rapidly and advancing far up the stem, and

as it is succeeded by the
death of the tree, the dis-
ease is to be classed with
the most dangerous forms
of " red-rot." It is very
abundant in the pine
forests of North Germany,*
and quite as much so in
the spruce woods, especi-
ally where these are situated
in hilly districts. There is this difference to be noted, however,
that when pines are killed by the parasite it is usually only their
roots that are affected and rotten, the stem, with the exception
of the stool, showing no signs of decomposition. The wood of
the stool is generally strongly impregnated with resin, and I
believe I am right in concluding that it is the abundant resinous
contents of the pine, which are especially prominent in the lowxr
part of the stem, that form a barrier to the upward growth of the
mycelium of the fungus. In the case of the spruce, on the other
hand, and of the Weymouth pine, w^iich is poor in resin, decom-
position of the wood spreads high into the stem.

It appears to be necessary to keep a watchful eye upon
coniferous woods at all stages of their growth, so that diseased or
dead trees may be instantly removed. In the case of the older
woods, one may isolate the diseased spots by surrounding them
with narrow trenches, and by severing all roots that may be
encountered. In order to attain this end we must, of course,
* [It is also by no means uncommon in this country. — Ed.]

Fig. 121. — The thinner root has been killed by
T. radicipcrda, and the stronger one has
been infected at the point of contact. The
disease has spread as far as the dark shading.
One eighth natural size.

INJURIES INDUCED BY PLANTS 191

form the trenches at such a distance from the diseased gaps as
to warrant the assumption that all trees already infected are
included in the isolated area. As a rule it suffices to include the
trees nearest to the margin of the gap. If the workman notices
that a dead root crosses the trench, then it will be necessary
at that point to divert the course of the trench farther into
the wood, otherwise the labour will be in vain. Although this
operation is a certain preventive when it is properly performed,
its careful supervision is so difficult when conducted on a large
scale that I am doubtful if a general adoption of the practice is
to be recommended in commercial sylviculture. The objection
that the sporophores develop in the trenches does not appear
tenable, because it is a simple matter to examine the trenches
once a year and to remove such sporophores.* When the fungus
appears at many points in a wood, even the most careful isolat-
ing is of no avail. The gaps should either be filled up with
dicotyledonous trees, or if, for any reason, this is deemed im-
practicable and conifers must be employed, then the young trees
must be carefully watched so that infected plants may be rooted
out and the disease be promptly checked.

TRAMETES PINI 1

This parasite is exceedingly abundant in the pine woods of
North Germany.-f- In South Germany, where it is less common,
it is met with chiefly in spruce woods. It also occurs in the
spruce woods of the Harz, the Thuringian Forest, and Schleswig,
as well as in the larch and silver fir woods of the Riesengebirge.

It produces a so-called bark-shake, ring-shake, or heart-
shake, which nearly always commences at a branch, and there-
fore usually in the crown of a tree,

The brown woody sporophores, which attain an age of fift}'
years, vary in shape between an incrustation and a bracket. In
the case of pines and larches they occur only on the part of a
stem where a branch has fallen off (Fig. 122), while in spruces

^ R. Hartig, Wichtige Kratik]ieiteti def Waldbdunie, p. 43. Zcrsetztings-
erschei7iungen des Holzes, p. 32, Tables V. and VII.

*[If Brefeld's account of the conidial fructification is correct, this maybe
a more difficult matter than appears. — Ed.]

"t" [Also occurs in this country. — Ed.]

192

DISEASES OF TREES

and silver firs they may spring directly from the bark as
well.

The spores which are annually produced in these sporophores
are scattered by the wind, and should they gain a footing on a
fresh branch-wound which is not protected by a covering of
resin they push their germ-tube into the stem, and the mycelium

Fig. 122. — Part of the stem of a pine bearing the sporophore of T. Piiii. a, healthy
alburnum ; b, wood saturated with resin in the neighbourhood of the sporo-
phore ; c, decomposed wood ; d, the canals in which the spores are produced ;
e, older canals which have become filled up by fungus-tissue ; /", the upper
surface marked by zones. One half natural size.

spreads partly upwards and partly downwards. The younger
class of trees enjoy immunity from infection, because in their
case wounds are very quickly protected by an exudation of
turpentine. From the time when the heart-wood becomes
comparatively dry, turpentine ceases to exude from the central
part of a branch-wound, and this consequently becomes liable to
attack from the spores of the fungus. This accounts for the

INJURIES INDUCED BY PLANTS

193

disease not usuall}- appearing upon trees younger than fift}'
years.

The mycehum shows a preference for growing longitudinally in
the stem, while its distribution horizontally is most pronounced
in some particular annual ring. On this
account decay often takes the form of ring-
shake — that is to sa}-, it is most pronounced
in peripheral zones which encircle a part or
the whole of the stem. At first the wood
becomes somewhat deeper red brown in
colour, and then white blotches or holes
appear here and there. In the case of
the pine especiall}^ these are largely con-
fined to the spring wood of some par-
ticular annual ring, in which the}' enlarge
parallel to the longitudinal axis of the
stem, the result being that the resinous
zone of autumn wood ma}- persist alone
for a long time, until it also is destro}-ed
b}' decomposition.

A resinous zone is formed along the
boundary between the alburnum and the
decomposed wood, and this interferes with
the outward progress of the mycelium of
the fungus. In those specimens which I
have examined, this zone is absent onl}' in
the comparatively non-resinous silver fir
and in spruce-branches, and thus, in their
case, the fungus is able to reach and pene-
trate the cortex with ease. The action of
the ferment of the parasite produces white
spots, similar to those that have been de-
scribed in the case of T. radicipcrda. The
lignin is extracted from the cell-walls, and
pure cellulose is left. The middle lamella

is completely dissolved as soon as the lignin disappears, and
thus the tracheids become isolated before being finally dissolved
(Fig. \2i,a a to /;). The lamella which is nearest to and bounds
the lumen persists the longest, and before it is dissolved the

O

Fig. 123. — A tracheid
of P. sylvestris which
has been decomposed
by T. Pini. The prim-
ary eel I -wall has been
completely dissolved as
far as a a. In the lower
portion of the figure the
secondary and tertiary
walls consist of cellu-
lose alone, in which
granules of lime are
distinctly recognizable,
/' ; filaments penetrate
the walls and leave
holes behind, d, c.

194 DISEASES OF TREES

ash-constituents of the wall impart to it a finely gi-anulatcd
appearance.

The fungus is only in a position to produce sporophores when
it has developed luxuriantly in the interior of the tree. In that
case the mycelium pushes its way outwards at a place where the
base of a dead branch opens a passage through the alburnum.
At such a place the sporophores are produced, and should these
be forcibly removed a number of new ones are, as a rule, formed
in a short time.

It is thus seen that nothing is gained by removing the
sporophores, but trees infested by the fungus should always be
removed in the thinnings and other fellings. We thus remove
the danger of infection, and utilize the trees before they are
rendered entirely valueless by the advancing decomposition. It
frequently happens that, although fungi are visible on the upper
region of the tree, the disease has not extended down to the
lower and valuable part of the stem, so that, after cutting off the
upper portion, some good useful timber is available. If one
waits till the final felling before removing the fungus-infested
trees, all that one gets is very worthless rotten wood. Of course
a stop must also be put to pilferers breaking or sawing off
green branches, as this practice increases the probabilities of
infection. Old branches that have died naturally cannot be
attacked by the fungus.

This disease is most prevalent in the neighbourhood of towns
and villages, where the pilfering of branches is common, and in
woods that are much exposed to the wind, and where, conse-
quently, branches arc frequently broken off.

rOLYPORUS HARTIGII (ALL.)
When I first described this parasite of the silver fir and spruce,
I made the remark, " Whether this is a new species distinct from
Polyponis fiilvJis can only be decided by a careful study of the
allied species of this genus. In the meantime it may pass
under the name of P.fiilvus."^ Since then it has been recog-
nized as an undoubtedly new species, and has been introduced
into the literature of the subject by Herr Allaschen under the
name P. Hartigii.

1 R. Hartig, Die Zc}-set::u/!gserschcininio-e?i dcs Hohcs, p. 40.

INJURIES INDUCED BY PLANTS 195

This fungus producesa kind of white-rot in silver firs and spruces,
and is very frequently encountered in association with ALcidmm
elatiiunn. Apparently infection is most liable to occur naturally
on those parts of the cancerous swellings where the cortex has
ruptured and exposed the wood. The mycelium, which is at
first very vigorous, is yellowish in colour, and produces numerous
short lateral branches, which are twisted in a worm-like manner,
and are apt to fill up the cavities of the bordered pits of the
tracheids. This vigorous mycelium gives off a few exceedingly
delicate lateral hyphae, which bore through the walls, in which
they form very minute holes. Only in the later stages of de-
composition is the disappearance of the middle lamella effected,
after which the inner walls are also dissolved, having first been
greatly attenuated and then temporarily isolated. At this stage
the mycelium is of extraordinary fineness. The wood of the
silver fir appears yellowish, clear oblong patches being observable
if carefully looked for on a smooth surface. The vigorous
yellow hyphze induce the formation of narrow dark lines at the
boundary of the sound wood.

As the silver fir cannot form a strongly resinous zone, it is
unable to prevent the progress of the mycelium into the
youngest layers of wood. The mycelium consequently grows
outwards with ease into the cortex, and, having advanced far
enough, it produces the sporophores on the surface. These are
at first hemispherical, but in the course of years they become
more and more bracket-like in shape. Externally they are
yellowish brown on the hymenial surface, but elsewhere they are
ashy grey, almost smooth, display no zones, and are beset with
exceedingly minute punctures or pits. The interior, which is
tawny and lustrous, shows distinct zones, except in the region of
the pore-canals, which increase in length each year at their
lower extremity.

As it is found that silver firs with cancerous swellings sooner
or later break at the diseased spot owing to snow or storms,
it has become the custom in many districts — for instance,
in the Black Forest in Wiirtemberg — to fell all cankered trees
during the thinnings, even when such trees belong to the larger
class. In this way the spread of Polyponis Hartigii can best be
prevented.

O 2

196 DISEASES OF TREES

rOLVPORUS BOREALIS^*

This fungus produces an exceedingly characteristic form of
white-rot in the spruce. In the Salzburg and Bavarian Alps,
and in the spruce woods near Munich, it is the commonest form
of decomposition in the spruce, and I have also noticed it in the
Harz. Infection takes place, and the sporophores are produced,
above ground. On account of their white colour the sporo-
phores are conspicuous even at a distance. They are annual,
more or less bracket-shaped, and frequently superimposed the
one above the other and grown together. They are verj-
watery, somewhat sodden on the upper surface, and destitute
of zones.

The colour of the wood is but little altered by the decompo-
sition. It becomes brownish yellow, and horizontally disposed
holes filled with mycelium appear in vertical rows in the spring
wood. These holes, which stand i to ih mm. apart, impart to
the wood an appearance which reminds one of the finest graphic
granite. The wood constantly becomes lighter and more friable,
but the peculiar appearance is retained till the end of the final
stage of decomposition.

Should the wood be exposed, without chying, when decom-
position is beginning, the mycelium will grow outwards to form
a white skin, the m}xe]ial strands of which are chiefly disposed
in a horizontal direction.

Growth and decomposition are in several ways characteristic.
The hyphit, which in the first stage of decomposition are yellow
and stout (Fig. 124, a, b), are replaced by more delicate fila-
mentous mycelia as decomposition proceeds, until at last the
hyphse which are formed can onl}' be seen b)^ the aid of a very
powerful microscope. The mycelium has a marked tendency to
grow to some extent in a horizontal direction, at right angles to
the long axis of the elements (Fig. 124, t), the chief result being
the formation of the above-mentioned horizontal holes in the
wood. Why these are formed only at definite distances from
each other I have not been able to determine. Dissolution of the

^ R. Hartig, Zcrsetzungsei'scheimingen, pp. 54 et seq.
* [This is quoted as a British species. — Ed.]

INJURIES INDUCED BY PLANTS

197

cell-wall begins at the lumen and proceeds outwards, being pre-
ceded by the conversion of certain layers of lignin into cellulose.

Fig. 124.^ — Decomposition of spruce timber by /'. horealis. a, a vigorous mycelium
in a tracheid containing a brownish yellow solution which has originated in the
medullary rays. In b and c the mycelia are still brown in colour and very
vigorous. At d and e the walls are much attenuated and perforated, and the
mycelia, not being so well nourished, are very delicate. At /" the pits are almost
entirely destroyed. At g and h only traces of the walls remain. The destruction
of the bordered pits is to be followed from i to r. At i the bordered pit is still
intact, at /■ one \\all of the lenticular chamber has been largely destroyed, its
inner boundary being marked by a circle. At / one side of the bordered pit
has entirely disappeared. A series of pits is shown from ui to n, in each of
which only a single delicate wall has been preserved — namely, that which is pro-
vided with the closing membrane. In preparing the section a crack has formed
in this wall. From 0 to r pits are shown where both of the walls have been
partially or completely dissolved, and only at p and q does one perceive the
thickened portion of the closing membrane. At s one can plainly see the spiral
structure of both cell-walls, which when united form the common wall between
two tracheids. At t mycelia are to be seen traversing the tracheids horizon-
tally.

The thin middle lamella persists longest, being converted into
cellulose and dissolved only after the internal portion of the wall
has entirely disappeared.

198 DISEASES OF TREES

rOLYl'ORUS VATORARIUS^ *

The decomposition produced b}- this and the following parasite,
P. ScJnveinitzii, bears a very strong resemblance to that caused
by the dry-rot fungus Memlius lacrymans.

P. vaporaj'ius is exceedingly common on spruces and pines,
both roots and wounds above ground being attacked. It very
frequently effects an entrance through a wound due to the
barking of red deer. The wood becomes reddish brown, dr}-,
and fissured, and as time goes on the resemblance to half-
charred timber becomes more and more apparent. When rubbed
between the fingers it crumbles into yellow dust. The m}--
celium is specially liable to develop in cracks, or between
the dead wood and the bark, in the form of snow-white
much-branched woolly felted strands, similar to many of the
mycelial growths of Meniliits lacryvians. Although I have
made no direct observations on the point, still I think it prob-
able that the mycelial strands which grow on dead roots and
stools may convey the disease subterraneously to adjoining trees.
The sporophores, which are pure white, form incrustations,
but never brackets. These originate on decayed wood or
dead bark, or on luxuriant mycelial growths or strands. This
fungus very frequently appears on the timber of buildings
where, on account of its luxuriant mycelial growths, which
have sometimes a fasciated, sometimes a strand-like appear-
ance, it is usually confounded with Mernliiis lacrynians, whose
mycelial growths, however, always assume an ashy grey colour
shortly after being formed. As regards its importance as an
agent in inducing decay in buildings, I may refer to the remarks
which I shall have to offer when discussing M. lacrynians.

POLYPORUS SCHWEINITZII f

In describing this parasite in Zerset::nngserscJieiunngen dcs
Holzes'^ I have called it Polyporus luollis. This mistake was

^ R. Hartig, Zosctziingsci-schciniiugcn, pp. 45 ct scq., and Table VI I L
- P. 49-

*[\'ery common on dead wood, and I have found it on the decayed wood
of a green-house. — Ed.]
t [Quoted as British.— Ed.]

INJURIES INDUCED BY PLANTS

199

due to my having access onl}- to old dr}'
rendered the correct identification difficu
Professor Magnus has correctl)- identified
the fungus as P. ScJnveinit::ii. It appears
on the Scotch pine, the Weymouth pine,
and the larch.

The decomposition which it produces
very closely resembles that due to the
preceding species, but in the present case
the white branching mycelial strands are
absent, the mycelium at most growing
out of the fissures as a fine chalky in-
crustation. The smell of the wood, which
is very characteristic and intense, reminds
one of the smell of turpentine, without
however being perfect!}^ identical.

The sporophorcs, which appear on the
dead wood or project from the bark-fissures
of living trees, take the form of reddish
brown cushions, which afterwards assume
a somewhat bracket-like shape. The porous
layer, which is yellowish green when }-oung,
assumes a deep red colour if ever so slightly
abraded.

As decomposition advances the tracheids
exhibit spiral cracks and fissures (Fig. 125).
Apparently these cracks are due to the
shrinkage of the wall-substance,which always
remains fairly dr}-. It is owing to these
cracks that the wood is so easil}- pul-
verised.

P. vaporarins also induces cracks and
fissures in the cell-walls, but, instead of
extending completely round the cell-lumen,
these are small, and are arranged in large
rows.

■ sporophorcs, which
It. In the interval

Fic'r. 125. — Tracheid o
Finns destroyed by /'.
Schweinitzii, The eel
lulose has been largely
extracted, the walls
consisting chiefly of
lignin. Cracks occur
in the secondary wall
when dry, while the
primary wall, a h, re-
mains intact. The
spiral structure of the
secondary wall is the
cause of the fissures
in the walls of adjoin-
ing cells crossing at the
bordered pits, c, and at
the punctures, d , e.
Where pits and punc-
tures are absent the
fissures ai'e simple, f.

numbers in vertical

200 DISEASES OF TREES

POLYPORUS SULPHUREUSi*

This is one of the most widely distributed parasites of the oak,
Robinia, alder, tree-willows, poplars, walnut, and pear. It also
occurs as a parasite on the common larch. Infection takes place
through a branch-wound, and the mycelium spreads rapidly in
the wood, causing it to become red brown and dry. The wood
reveals numerous cracks, into which the mycelium grows, to form
laro-e sheets of felted hyphae. In the case of dicot}-ledonous
trees the vessels become filled, in the early stages of decom-
position, with a dense fungoid growth, so that, on a transverse
section, they appear as white spots, and, on a longitudinal section,
as white lines. The walls of the elements of the wood become
brown and very rich in carbon, and shrink greatly, but on being
treated with dilute caustic potash they swell up and become
almost completely dissolved. The spiral cracks, which always
ascend from right to left in the interior of the fibres, never
extend into the middle lamella.

Whenever old snags, or any kind of wound, admit of the
mycelium reaching the surface, a group of sporophores is annually
formed. These are succulent, of a pale sulphur-yellow colour
beneath, and pale reddish yellow on their upper surface, and by
their size and strikingly luminous colour they readily attract
attention. The pileus is internally of a white colour and cheesy
consistenc)'. The pores reveal a hymenial layer with clavate
basidia. The mycelium of this fungus very frequently develops
numerous round gonidia in the wood itself, and during my early
investigations on this parasite I regarded these as belonging to
a different species of fungus. It very frequently happens that
before diseased trees are overthrown by storms, their tissues, on
one side or other, die as far out as the bark, and the latter,
withering, drops off and allows the red-brown decayed wood to
fall out from the inside of the tree. Thus it is not impossible that
the gonidia may be carried into the air along with the dust of the
decayed wood, and so assist in the distribution of the parasite.

1 R. Hartig, Zersetzungserscheimmgen^ pp. no et seq. De Seynes,
Rccherches pour servir a Vhistoh'e naturelle dcs vegctaux inferieia's, 1888.

* [Verj' common in this country. I have frequently collected it in Windsor
Park and elsewhere. — Ed.]

INJURIES INDUCED BY PLANTS 201

POLVrORUS IGNIARIUSi*

This is the parasite most frequently met with on the majority
of dicotyledonous trees. My investigations on its destructive
effects on wood have been conducted for the most part on the
oak.

Infection may occur on branches or on bark-wounds, and the
myceHum spreads rapidly in the wood. At first the wood
assumes a deep brown colour, and this is succeeded by yellowish
white decomposition, which is the commonest kind of white-
rot in the oak. The yellowish white wood constantly becomes
lighter and softer, and resembles in its properties the cellulose
that is used in paper-making. The h}'phae, which are at first
very strong and afterwards extremely delicate, completely fill
up the elements, and induce a form of decomposition which is
characterised by the inner layers of the walls being converted
into cellulose and dissolved, before the middle lamella, which
persists for a long time as a delicate skeleton, undergoes similar
changes. It will thus be seen that the process of decomposition
bears a close resemblance to that described under P. borealis.
The sporophores, which usually spring directly from bark that
is infested by the mycelium, are at first hemispherical, but
afterwards become more or less hoof-shaped. Although they are
familiar enough, it may be mentioned that they differ from
those of P. Hartigii, which they resemble in external appearance,
by exhibiting concentric zones, and frequently cracks as well, on
their upper surface, while internally the layers of pores are also
interrupted by the zones.

POLYPORUS DRYADEUS-f

This fungus of the oak produces a form of decomposition
in which oblong yellowish or white blotches occur, surrounded
by firm wood which displays the original colour of the duramen.

^ R. Hartig, Zersetzungserschcinitngcn, pp. \\\ ct jit^'., and Tables XV.
and XVI.

^ Ibid., pp. 124 et scq.^ and Table XVII.

*[One of the commonest fungi in Windsor Park and neighbourhood,
especially on old Beeches. — Ed.]

t [Common in Britain. — Ed.]

202 diseasp:s of trees

The white blotches consist of elements which have been con-
verted into cellulose, and which have become isolated by the
solution of the middle lamella. The yellowish parts, on the
other hand, reveal a form of decomposition of the cells which
is exceedingly like that due to P. igniarhis, and which is cha-
racterised by the middle lamella persisting the longest. The
white patches are the first to be dissolved, and thus holes, sur-
rounded by very hard sides, are formed. When freel}- exposed
to the air the wood assumes a cinnamon brown colour, and is
replaced by a mass of firm brown hyphae.

The large hoof-shaped annual sporophores arc of a cinnamon
brown colour, and appear on the bark or on the spots previously
occupied by branches. They possess so little durability that
one but seldom meets with a perfect specimen.

Should P. dryadeits and P. igniariiis simultaneously attack an
oak, and should their hyphae come into contact, a peculiar kind
of decomposition occurs along the line where the hyphae of the
two species meet. The wood becomes yellowish white, the
decomposition being similar in appearance to that which is
induced by P. igniarhis alone. All the longer medullary rays^
however, are represented by snow-white bands, which, on being
investigated, are often found to consist of nothing but unaltered
starch-grains, while the cell-walls have been almost entirely
dissolved, or have been converted into cellulose.

HYDNUM DIVERSIUENS i *

A parasite is frequently met with on oaks and beeches whose
yellowish white sporophore takes the form of an incrustation or
bracket, and which is distinguished by the hymenium being
disposed on downward-directed spines of unequal length. The
hymenium, which is at first simple, periodically increases in
thickness by the hyphae growing through the last layer to form
a new hymenium. In the lower portion of the spines especially
this process is repeated five to eight times, the result being that
the spines increase greatly in thickness, and the hymenium
displays five to eight layers.

In this case also the decomposition, which spreads from

^ R. Hartig, Zersetziingscrscheintingcn^ pp. 97 ct seq., and Table XII.
*[This is also British. — Ed.]

INJURIES INDUCED BY PLANTS 203

infected wounds on the stem, takes the form of a white-rot.
The colour is )-ellowish ashy grey, alternating with stripes of a
pale brown colour, which generally persist longest in the
medullary rays. In the later stages of decomposition snow-white
masses of felted mycelium occur where a zone of spring wood
is much deca}'ed.

The peculiarity of the action of the ferment consists in the
inner layers of the cell-walls swelling up into a gelatinous mass,
without being converted into cellulose, before they are completely
dissolved ; the middle lamella being the last to disappear.

THELEPHORA PERDIX^*

A form of disease which is very common in the oak throughout
the whole of German}- is known as " partridge wood," on account
of the peculiar discoloration w'hich it induces in the wood, and
which reminds one of the white-speckled feathers met with on
certain parts of the body of the partridge. At first the diseased
wood assumes a deep red brown colour, and then white blotches
on a dark ground make their appearance which stand in a certain
relationship to the large medullary rays. These blotches after-
wards become transformed into sharply defined cavities with a
white lining. As the cavities, which are separated from each
other by firm brown wood partitions, increase in size, the wood
looks as though it had been attacked by ants, and, as a matter
of fact, the symptoms are often mistaken for the work of these
creatures. It is to be noted that each ca\'it}- usuall}- remains
distinct until the stage of complete decomposition is reached.
In the wood of the oak the mycelium first induces the contents
of the parenchymatous organs to become brown. Graduall}-
proceeding inwards, the starch-grains fail to give a blue reaction
with iodine, colourless granules persisting for some time in the
central cells of the medullary ra}-s, until the}' also are at last
destroyed (Fig. 126).

Where the white blotches make their appearance, as also in
the partitions of the white cavities, all the organs are converted
into cellulose, and the middle lamellae being dissolved the

^ R. Hartig, Zcrsctzungscrschcimingcii^ pp. 103 et seq.

*[I do not know this as British, but a specimen of diseased wood sent
from India was marked in exactly the way Hartig describes. — Ed.]

204 DISEASES OF TREES

individual elements of the wood become isolated (Fig. 126, e — /i).
It is remarkable that the process of decomposition in the
neighbourhood of the cavities undergoes a change when these
have become enlarged. The latter no longer appear white but
greyish yellow, and reveal abundant felted mycelia, which pierce
the walls at numerous places. Instead of a conversion into

Fig. 126. — Decomposition of oak induced by T. Peniix. a, tracheids containing
some filamentous mycelia, and showing a few perforations on their walls ; b,
wood-parenchyma containing starch which is partly undergoing solution, the
outer granules being the first to disappear ; (", vessels containing hyphse of the
fungus ; d, sclerenchymatous fibres containing fungus-filaments, and showing
perforations in the walls ; c and /, tracheids which are completely isolated by
the solution of the primary wall. The thickened rings of the bordered pits are
also seen to be isolated between the tracheids. As the elements are isolated, the
cracks no longer cross at the bordered pits, g, cells of wood-parenchyma which
are completely isolated and almost completely dissolved ; h, a tracheid just
before final solution ; ?', sclerenchymatous fibre much decomposed ; k, a
tracheid whose wall has been dismembered by cracks before being dissolved.

cellulose resulting, the wood-substance is dissolved, partly by the
enlargement of the perforations and partly by the centrifugal
attenuation of the cell-walls.

The sporophores of the parasite occur as incrustations in
fissures or other cavities in the diseased wood, or on the outside
of dead branches. The incrustations, which vary in thickness
from rrV to J inch, are brownish yellow in colour, and consist of

INJURIES INDUCED BY PLANTS 205

a layer of hjq^haj disposed at right angles to the surface. The
hyphas end in somewhat club-shaped basidia, which are covered
b}' peculiar hair-like outgrowths. Only a certain number of the
basidia produce spores (four in each case), those which remain
sterile producing a new hymenium in a succeeding period of
growth, and in doing so they anastomose here and there b}*
lateral budding. On a transverse section a sporophore, depending
on its age, shows more or less distinct strata, of which only the
youngest possesses a pale colour, the others being of a deep
brown hue. When dead the whole of the sporophore appears
dark brown.

STEREUM IIIRSUTUM ^ *

A ver}' striking and characteristic form of decomposition in
the oak is produced by S. hirsutiun. In practice such wood is
called " yellow piped " or " white piped." Usually a brown
colour first makes its appearance in certain concentric zones,
which to begin with are confined to one side but afterwards
encircle the whole of the stem, and later on a longitudinal
section will show detached snow-white or yellow stripes which
appear as white spots on a cross section (" fly wood "). When
the oxygen of the air has free access, as in the alburnum,
branch- snags, &c., the whole of the w^ood is frequently converted
into a uniform yellow mass. It scarcely seems to admit of
doubt that this fungus also plays an important part as a sapro-
ph}-te, and finds its way on to branches that are dying naturally.
In the white stripes the mycelium converts the wood into cellu-
lose, and when the middle lamella disappears the elements
become isolated. In the yellow parts of the wood, on the other
hand, the solvent action proceeds from the lumen outwards, as
in the case of P. igiiiarins, and this is not preceded by a con-
version into cellulose. The sporophores, which usually develop
on the bark, appear first as a crust, but afterwards their upper
edge — which is brown, faintly zoned, and covered with stiff hairs
— projects in a distinctly horizontal direction.

' R. Hartig, Zersctziingserscheittiin^^en, pp. 129 ct scq.^ Tabic XVIII.
*[\'ery common in England. — Ed.]

2o6 DISEASES OF TREES

POLYPORUS FOMENTARIUS*
The familiar tinder-fungus, which occurs on beeches and oaks,
produces a form of white-rot, and its mycelium has a tendency
to form luxuriant patch-like or skin-like growths in fissures of
the decayed wood. So far it has not been made the subject of
thorough investigation.

POLYPORUS BETULINUSif

Occasionally P. beiuliiuis is to be found abundantly developed
on the birch. Its hirsute sporophore, which is white beneath and
brownish grey above, is at first globular, but afterwards takes
the form of an inverted bracket with a convex upper surface.
The decomposition induced by the parasite is a form of
red-rot.

POLYPORUS L/EVIGATUS-

This parasite produces a form of white-rot in the birch. Its
sporophore appears on the surface of the bark as a dark brown
porous incrustation.

Numerous other species of Polyponis doubtless occur as
parasites on the wood of trees, but these, so far, have not
been subjected to investigation.

The following fungi are also worthy of mention. Dcudalca
quercina\ is met with everywhere on old oak-stumps, where
it forms large bracket-like sporophores which bear the hymenium
partly in pores and partly on lamellae. During decomposition
the oak-wood assumes a grey brown colour. Having found the
fungus vigorously developed on branch-wounds of the older
classes of oaks, I suspect that it is also a parasite.

Fistulhia hcpatica., the Beef-steak Fungus, produces a deep
red brown decomposition in the wood of the oak.

All the above-mentioned wood-parasites, which obtain an
entrance through wounds above ground, can only be combated
in one or other of the following ways. First, great care must be

1 D. H. Mayr, Hot. Centnilblatt, 1885. ^ Ibid.

* [Common in Britain.— Ed.]

t [1 have frequently collected this in this (Cooper's Hill) part of England.
—Ed.]

J [Both this and the next occur in Surrey and elsewhere in Britain. — Ed.]

1

INJURIES INDUCED BY PLANTS 207

taken to do nothing that will cause the formation of wounds
in trees, of which more will be said in the section on wounds ;
and, secondly, where wounds are intentionally produced on trees,
as in pruning, the necessary prophylactic measures must be at
once put in force, and in particular an antiseptic dressing in
the form of a covering of tar should be provided.

At the same time woods should be kept tidy and free from
decaying wood, which may bear the sporophores of parasites,
but this must not be taken to mean that all old oaks that
are already decayed are to be felled without regard to other
considerations. For the sake of effect the forester should allow
old trees and picturesque bits of timber to stand where deemed
desirable in the neighbourhood of frequented paths, even
although the benefits of so doing may not be at once manifest
in the shape of hard cash.

AGARICUS MELLEUS.^ * THE HONEY AGARIC

This fungus belongs to the most widely distributed and
destructive of parasites. It lives parasitically on alTEuropean
conifers, besides destroying those that have been introduced
from Japan, America, &c., and I have even recognized it in the
fossil wood of Ciipressinoxylon. Amongst dicotyledonous trees it
appears to occur as a parasite on Pninits avium and P. doiiiestica,
while as a saprophyte it is to be met with everywhere, not only
on the dead roots and stools of all dicotyledonous and coniferous
trees, but also on the structural timber of bridges, conduits, mines,
&c. It has frequently been asserted that it also occurs as a
parasite of the vine, but I have had no opportunity to convince
myself of the correctness of this view. Those rhizomorphs
whose occurrence I have hitherto observed on the vine belonged
to Deniatophora necatrix.

The disease often manifests itself on plants only three to five
years old, though it also destroys spruces, pines, &c., a century
old. One recognizes it by removing the bark at the collar

^ R. Hartig, Wichtige KrankJieitcii dcr Waldbaumc, 1874, pp. 12 et seg.,
Tables I. and II. R. Hartig, ZcrsctziingscrscJtcinuugcii^ pp. 59 ct seq.^ Table
XI., Figs. 1-5.

* [This is one of the commonest of British fungi, and its rhizomorphs and
sporophores are well known. — Ed.]

2oS

DISEASES OF TREES

and on the roots, when a firm snow-white myccHum (Fig. i2y,cc)
is observed, which, in the case of the older class of trees, some-
times ascends under the bark while the tree is still alive to the
height of ten feet or more. Brownish black lustrous strands,

2-V to yV inch in thickness, which occa-
sionally anastomose, are observed in
greater or less abundance adhering to
the roots. These are met with in con-
junction with the sheets of white my-
celium under the cortex, though some-
times they merely embrace the roots
externally.

A great deal of turpentine and resin
frequently adheres to the outside of the
stronger roots, and this, mixing with the
particles of soil, forms a firm mass round
the collar (Fig. 128). The diseased trees
speedily succumb, and are seldom to be
recognized more than a }'ear before their
death by their pale colour or stunted
shoots. If we carefully dig up a plant
that appears to be perfectl}' healthy, in
the immediate neighbourhood of one
that is manifestly diseased or dead, we
will as a rule discover on the roots one
or more places of infection where a black
rhizomorph strand has bored into the
cortex (Fig. 127, a). When the cortex is
carefully removed the strand will be ob-
served expanding from the place of
entrance into a snow-white bod}' (Fig.
127, b), which spreads in the cortical
tissues and causes browning and death,
as far as it reaches (Fig. 127, c c). The
mycelium that grows in the living cortex
is characterised b}- its fasciated and skin-like appearance. It
very easily resumes the round strand-like form, which may
cither grow to the outside of the roots or proceed to develop
between the wood and cortex. When, owing to the death of

Fig. 127. — The living root
of a spruce, showing two
spots, a, h, where the
rhizomorph has entered
.ind infected the cortex.
The cortex has been re-
moved from the larger
root, d to d, in order to
show the mycelium, c c,
which has gained an en-
trance at h.

INJURIES INDUCED BY PLANTS

209

the tree, the shrinkage of the cortex affords space for the de-
velopment of these strands, they anastomose abundantly, hke so
many twigs, and envelop the wood of the stem in a reticulate
fashion. The rhizomorphs that spring from the roots progress
underneath the surface of the ground, at a depth seldom exceed-
ing four inches, and bore into any sound roots of conifers that
they may encounter, and thus the disease is spread from tree
to tree (Fig. 127). In autumn, from the end of August till

Fig. 128. — A young pine which has been killed by
A. tnelleiis. Numerous sporophores are seen which
have broken through the cortex at the surface of
the ground. Branching rhizomorph- strands are
present on the roots.

Fig. 129. — A sporophore
of A. nielleus which has
developed on a rhizo-
morph, a lateral branch
of which has produced
only abortive sporo-
phores.

October, the large familiar sporophores (Fig. 129) may be
observed developing on the rhizomorphs which grow in-
dependently in the ground, or projecting from the cortex,
especially the collar (Fig. 128), of trees that have been killed by
the parasite. For further details I may refer to what I have
published in the works already alluded to. The white spores of
this Hymenomycete, which are spread either by the wind or by
being brushed off by passing objects, develop first of all a
filamentous mycelium, and from this the m)xelium form
designated Rhizoinorpha is produced, as is easily proved by

P

2IO DISEASES OF TREES

sowing the spores in a decoction of plums. The pathological
symptoms can onl\- be explained in the light of the peculiar
organization of the mycelial growth that lives in the cortical
tissues. The apex of the rhizomorphs (Fig. 130) consists of
delicate pseudo-parench}-ma, which, elongating by the division
and growth of the cells, produces delicate hyphae on the inside
at a certain distance from the point, whereby a felted tissue,
called the medulla, is produced in the interior. The outer parts
of the pseudo-parenchyma (Fig. 130, c), on the other hand,
coalesce to form the so-called rind (Fig. 131, d), which when
young gives off numerous delicate hyphae, and these, taking
advantage of the medullar}- rays, penetrate the wood, and
especially the resin-ducts, should such be present. In the wood
the growth is upwards. This filamentous mycelium, which
progresses much more rapidh' in the interior of the wood
than the rhizomorphs which grow in the cortex, completely
destroys the parenchyma that exists in the neighbourhood of
the resin-ducts, and to all appearance this is accompanied
by a partial conversion of the cell-contents and the cell-walls
into turpentine (Fig. 131). The turpentine sinks down under
its own weight, and in the collar, where the cortex is
withered, having been killed by the rhizomorphs, it streams
outwards, pouring partly in between the wood and the cortex,
and partly into the surrounding soil at places where the cortex
has ruptured owing to dr}'ing. On this account the disease was
formerly called " Resin-flux " or " Resin-glut." In the upper
parts of the stem, where the cambium and cortex are still sound,
the turpentine also flows lateralh', b}- means of the ducts of the
medullary rays, from the injured canals towards the cambium and
cortex. In the latter this accumulation induces the formation of
large resin-blisters. Wlien, during the summer, the cambium is
forming a new ring, the plethora of resin has the effect of causing
the production of numerous resin-canals, which are unusually
large and abnormally constructed, and these impart to the wood-
ring formed during the }'ear of sickness a very striking and
characteristic appearance.

The mycelium gradualh- spreads from the cells of the
medullary rays and from the resin-ducts into the vascular
elements of the wood, where it produces a form of deca}- which

INJURIES INDUCED BY PLANTS 211

may be termed a variety of white-rot. During the progress of
the decomposition from the surface of the stem inwards a
certain stage is reached, which is highly favourable to the

Fig. 130. — Longitudinal section
through the apex of a rhizomoiph
from the outer hyphsc of which
numerous hair-Hke filaments, a a,
spring. In the interior the central
cells enlarge greatly, /', at a short
distance from the apex, while the
cells of the hyphse situated to-
wards the periphery, c, remain
smaller, to form the pseudo-paren-
chyma of the "rind" ; d d indi-
cates the boundary of the mucila-
ginous layer which envelops the
strand.

Fig. 131. — Transverse section through the
cortex and wood of a pine-root which has
been killed by a rhizomorph. a, the dead
tissues of the bast ; b, the dead cam-
bium ; c, the medulla of the rhizomorph ;
d d, the pseudo-parenchyma of the rind
of the rhizomorph ; e e, filamentous
hyphae which have grown from the
rhizomorph into the wood ; /, dead im-
mature wood-cells ; g, a resin-duct which
has been completely destroyed, the paren-
chymatous cells which surround it being
also dissolved.

development of the m}xelium. While previously it was simply
filiform and furnished with numerous lateral hyphoe, it now
develops large bladder-like swellings, and at the same time the
hyphse change into a kind of large-meshed parenchyma, which,
like the tyloses in the vessels of many dicot)^lcdonous trees,

P 2

212 DISEASES OF TREES

completely fills up the lumina of the tracheides. On account
of the mycelium assuming a brown colour when in this con-
dition, it makes the portion of diseased wood which it infests
appear to the naked eye like a black line. As this kind of
mycelium soon dies off and is dissolved, being replaced by a
delicate filamentous mycelium, it seldom happens that the zone
which it occupies exceeds the breadth of 3 — 4 tracheids. The
walls of the elements of the wood afterwards display a cellulose
reaction, and speedily dissolve from the lumen outwards.

On account of the trees drying up, after the rhizomorphs have
spread from the point of infection on the roots into the stem, and
again from the stem into the hitherto sound roots, decomposition of
the stem usually ceases before the mycelium has advanced from the
alburnum into the duramen. It is only in the stool and roots
that decay rapidly spreads throughout the whole of the wood.

The practical preventive measures to be enforced in the
case of this parasite are the same as those which I have
already recommended for Trainetes 7'adiciperda (see pp. 190-91).

THE DESTRUCTION OF STRUCTURAL TIMBER BY FUNGI

Although, strictly speaking, the diseases of felled timber
should not be discussed in a te.Kt-book of the diseases of trees,
still an abbreviated summary of the results of my investigations
on this subject may not be altogether out of place.^

As regards the management of squared and round timber
before it is utilised — that is to say, in the forest and during
transport — one should in the first place take all reasonable
precautions to see that, after felling, only sound wood is retained
as structural timber. Of course it is always possible that now
and again a log or beam will be retained that turns out to be
diseased during subsequent manipulation. This may be due to
the fact that a parasite which has entered through a branch-
wound has not spread up or down to one of the sectional
surfaces, so that it is impossible to recognize the destructive
effects of the fungus when the timber is despatched. It is often

' Der iichte Hausschwamui {Merulhes lacry7nans) (Berlin, Springer, 1885),
and Die Rothsireifigkeit des Bate- und Blochholzes und die Trockeitfdule.
Allg. Forst- und Jagd-Zeit., November 1887.

INJURIES INDUCED BY PLANTS 213

the case, however, that the diseased portion of a tree which is
easil}- recognized — as, for instance, OM'ing to brownness, &c. — is
cut off till the saw-cut appears to the naked eye to be perfectly
sound. The apparently sound portion of the tree is afterwards
disposed of, say as a log. Now, it may easily happen that the
parasite has already penetrated into the portion of the tree that
was regarded as free from attack, and consequently an infected
piece of timber is sold as sound. Should such wood retain a
portion of its moisture for a considerable period, the parasite
will continue to grow^ until it destroys not only the wood that
contained the filamentous mycelium at the time the tree was
felled, but frequently also very considerable portions of the
timber that was primarily sound.

Polyponis vaporarhis, which occurs on spruces and pines even
when alive, and which I have described at page 198, is the
commonest and most destructive of these fungi. Frequently
when investigating the destructive effects of " dry-rot " I have
found the cause to be not Meniliits lacryi)ians but P. vaporariiis,
whose mycelium forms snow-white sheets on beams and deals,
and produces stiff strands several yards in length. Should
timber which is infested by this parasite be applied to structural
purposes, and should it not dry quickly enough, the fungus
develops more or less luxuriantly, and in a short time com-
pletely destroys all the wood-work. This fungus is apt to be
speciall)- prevalent in cellars, and in the wooden floors of the
ground flat of houses that are unprovided with cellars.

Perfectly sound timber may, however, also be infected during
the time it is lying in the forest. The danger is greatest in
the case of peeled timber that is in immediate contact with
the ground. Various wood-fungi, and amongst them Merulhis
lacrymans, may induce disease in felled timber when it is stored
for a considerable time on the ground in the forest. At the time
of issuing my publication on Merulius lacrymans, I stated that
it was doubtful whether this fungus occurs in the forest at the
present da}'. Since that time I have received genuine speci-
mens of J/, lacrymans, from Herr W. Krieger, Konigstein,
Saxony. Peeled timber that is exposed to air-currents by being
piled upon supports is much better protected, because the
surface la^-ers soon dry, and render the entrance of the fungus

214 DISEASES OF TREES

impossible. In the case of peeled stems that are freely exposed,
drought in a few weeks induces the formation of cracks in the
alburnum. These occur about an inch apart, and penetrate to a
depth of an inch or more. The rain-water enters these cracks,
carrying with it any spores that it may contain. After pro-
longed rain the wood swells owing to the absorption of water,
and the cracks close. During wet years, or long storage of
the timber, decomposition may begin even in the forest, the
spores that have entered by the cracks germinating and causing
the wood to become brown along both sides of the fissure.

As a rule, however, spores that enter cracks in the alburnum
do not germinate in the forest, because when the rain ceases the
superficial layers of the wood quickly dry again, so that even if the
cracks should have closed they subsequently reopen. Should such
wood be removed from the forest to the building or saw-mill in
a dry condition, it remains sound, even although the spores in
the cracks retain their power of germinating for a long time-
If, on the other hand, the wood is floated, so that it has the
opportunity to become again fully saturated with water, a very
undesirable pathological symptom makes its appearance, which
is known to saw-millers, timber-merchants, &c., as " the red
stripe," and represents the first stage of what is popularly called
„ dry-rot."

It is a familiar fact that there is no essential difference as
regards durability, or resistance to the attack of M. lacryuians
and other wood-fungi, between coniferous timber that is felled in
summer and that which is felled in winter. The attempt that
has been made to show that the destructive effects of M.
lacrymans are modified by the varying chemical composition
(as regards potash, phosphoric acid, &c.) of wood felled in
summer and in winter must be described as total failure^. On
the other hand, it is an undoubted fact that wood which is felled
in summer suffers far more from dry-rot than that which is felled
in winter. This apparent contradiction is easily explained.
Winter-felling takes place in the lowlands and in the less
elevated mountains. In these districts the timber is chiefly
removed from the forest by land, after it has lain for a longer or
shorter period with or without its bark. Such timber is either
free from spores, or, should it contain spores that have entered

INJURIES INDUCED BY PLANTS 215

by cracks formed in the alburnum during drying, it afterwards
remains dry, and therefore sound, because the spores are unable
to germinate in the dry wood. On all the higher mountains, on
the other hand, felling takes place in summer. The wood is at
once peeled and piled on supports, and in winter it is conveyed
on the snow to the streams, to be sent off in rafts in spring.
The timber is dried in the first summer — that is to say, directly
after being felled and peeled — when cracks form through which
the spores of fungi enter. During floating the logs become
saturated with water, and the cracks close. When the wet logs
arrive at the saw-mills they are piled up in thousands, to be
sawn up in the course of the summer. The logs that are sawn
up in May are, as a rule, perfectly sound, but from June onwards
the number of " red-stripeci " specimens constantly increases,
until in autumn it frequently happens that more than 50 per
cent, of the logs are so decayed as to furnish but few serviceable
boards. This is easily explained, if one considers that the
saturated logs are prevented from drying owing to the way
they are piled up on one another, and that the high summer
temperature is suitable for the germination of the spores present
in the cracks, and favours the destructive development of the
fungi.

The owners of saw-mills in the Bavarian Forest calculate that
they lose 33 per cent, of their total timber by logs becoming
red-striped. For some years I conducted extensive investiga-
tions not only at Zwiesel in the Bavarian Forest, but also at
Marquardstein and Freising, partly to determine the cause of
timber becoming red-striped, and partly with the object of dis-
covering a means of preventing the mischief. This is not the
place to go into the details of these arduous investigations.
I have shortly described the causes of the phenomenon above.
As regards the prevention of the disease, it was found to be
possible to obtain perfectly sound logs by protecting them
against rain by a covering of boards or spruce-bark. Unfor-
tunately this only induces another evil — namely, the excessive
cracking of the timber, which means a very serious shortage in
good boards. The rejected red-striped boards are used in
houses for underflooring and for false floors. As it very often
happens that the wood has not been sufficiently dried to kill the

2i6 DISEASES OF TREES

enclosed fungus-mjxelium, the latter continues to grow in the
presence of moisture, and the wood is still further destroyed.

Squared timber that has been floated suffers quite as much
from red-stripe as that which comes straight from the saw-mill.
As nowadays it hardly ever happens that perfectly dry timber
is employed for structural purposes, there is great danger of the
so-called " dry-rot " appearing in a destructive form.

The greatest danger attaches to the ends of joists that are
built into a wall. If the latter contains water, it is transmitted
to the wood, so that joists which may have been fairly dry are
again rendered so wet as to enable any fungus-mycelium con-
tained in the cracks of the wood to develop and destroy timber
that was perfectly sound when placed in the building. Should
the ends of the joists have originally shown any appearance of
red-stripe, the danger of total decay is of course increased. One
ought therefore to endeavour, as far as possible, to avoid using
red-striped joists, or at least their use should be confined to the
highest story of a building, where the walls being thinner dry
faster. Under any circumstances, however, one should never
neglect to apply several coats of creosote (common coal-tar oil)
or some special carbolic preparation to the ends of the joists for
a distance of three feet, before they are built into the wall. Tar
cannot be recommended, because it does not penetrate far into
the wood, and it forms a covering which prevents the joists
from drying.

The other parts of the joists are not so much exposed to
danger. Even when they are red-striped they usually dry so
soon in properly constructed buildings as not to suffer further
damage from any fungus that they ma}' contain, though of course
their strength is reduced in proportion to the extent of the
disease.

The name " dr}--rot " is unhappily chosen, in so far that it is
characterized as occurring only in wet or damp wood, in which
the fungi can find sufficient moisture for growth. Merulhis
laciyviaiis, on the other hand, may destroy perfectly dry wood
by imbibing and conducting the water requisite for growth from
other parts of the building, and either parting with it to the
woodwork or letting it escape in the form of drops or " tears."
The disease has, in fact, acquired the name " dr}'-rot " because it

I

INJURIES INDUCED BY PLANTS 217

is usuall\- only noticed in a building- when it, and consequently
the woodwork also, has become practically dry.

Frequently, however, dry-rot appears in new buildings to such
an extent that not only the joists but also the boards of the
false and true floors decay. When this is the case the cause
is usually to be found in gross negligence on the part of the
contractor. Most frequently the mistake is committed of placing
wet deadening material (" pugging ") on the false floor and
covering it over too soon, either with the boards of the sub-floor
or of the true floor. I have thoroughly discussed the subject of
deadening ma-terial in my work on M. lacryiiians. It must be
as dry as possible, and free from humus or an)'thing that will
condense moisture. Clean gravel or coarse dry sand suits best.
Anj'thing of the nature of coal-dust should on no account be
used.

It is a great mistake to cover the floor too soon with oil
paint or with parquet, because this prevents the evaporation of
any moisture that may have been originally present in the
boards, or that may have been imparted to them by the packing
material. The water that is contained in the packing material
and in the woodwork cannot afterwards escape upwards. All
that is possible is an extremely slow evaporation downwards —
that is to say, through the ceiling of the room beneath. Between
the false ceiling and the matchboard ceiling the air becomes
saturated with moisture, and this space offers conditions which
are extremely favourable for the growth of fungi. The flooring
boards, being saturated with moisture derived from the packing
material, decompose under the action of the spores which are
brought from the forest in the cracks of the wood. In two years'
time, when the building has become perfectly dry, the moisture
in the boards also disappears. The withdrawal of water induces
very great shrinkage in the already decomposed w^ood of the
lower side of the boards, while the upper side, being exposed to
the air or protected by paint or varnish, is not similarly affected.
The result is that the upper side of each board becomes convex
in the middle, and the nails are easily wrenched out of the
partiall}- rotten joists. Open joints are thus formed, which may
be large enough to admit of the entrance of one's finger. -^

The repairs thus rendered necessar}' are very expensive, and

2i8 DISEASES OF TREES

give rise to vexatious litigation between the architect, builder,
carpenter, and timber-merchant. Nor are the distinctions be-
tween this form of dry-rot and that induced by Mentlius
laaynians sufficiently appreciated as a rule, although the ravages
of the latter may be easil)' recognized since the publication of
my work on the subject.

As a rule the term " dry-rot " is applied to those forms of
decomposition in structural timber where the fungus that does
the damage is invisible to the naked eye. This want of
conspicuousness is accounted for by the fact that such fungi,
instead of covering the wood or of filling up cracks in the timber
or spaces between the woodwork and the walls with mycelial
growths, distribute their fine hyphae in the substance of the wood
itself. But in a series of fungi which destroy structural timber a
luxuriant mycelial growth is produced outside of the wood, and
it is to these that the term " House Fungus" is generally applied.
These fungi vary exceedingly as regards appearance and life-
history. Of them the most important and destructive is Menilhis
lacryinans. Then we have also Polyporus vaporarius, which has
already been described, and a number of other fungi which I am
at present busily engaged in investigating.

Space may also be found here for a few remarks on the
soundness and quality of timber furnished by conifers that have
been entirely defoliated by caterpillars, and especially by
Liparis inonacJia and Gastropacha pini. When spruces or pines
have been completely defoliated during spring or summer, the
leafless branches as well as the top of the tree die in the course
of the following autumn, winter, or spring, while the more
valuable parts of the stem remain perfectly sound till the middle
of the succeeding summer. As a rule it is not till the beginning
of July that the inner cortex, especially on the south-west side of
the ti'ee, begins to show brown patches and die. During the
devastations committed by the nun moth in recent years, the older
classes of spruces were almost all dead by autumn — that is to say,
the cortex was brown. Underneath the dead cortex the wood
of the alburnum became discoloured, and rapidly decomposed
under the influence of numerous fungi. The timber of all those
trees which were felled and immediately barked before the
beginning of July of the year in which the havoc was committed

INJURIES INDUCED BY PLANTS 219

was found to be of exceptionally high qualit)', and showed
no blemishes. This was the case even after the barked trees
had been piled for a whole year before being removed from the
forest. Owing to the stores of carbo-hydrates having been
nearly all used up by the cambium in the formation of the wood-
ring during the summer of the first year, such timber offered less
suitable conditions for the growth of fungi than the wood of
trees that had not been defoliated. It was only after the
cortex had died, or had been perforated by wood and bark
beetles, that fungi could gain an entrance, when the high
temperature and abundance of moisture offered favourable
conditions for their growth. The low repute in which timber
furnished by trees destroyed by insects is held is entirely due
to the fact that such trees are often left standing in the forest
till the cortex is dead. Trees that have been stripped of their
leaves should therefore be felled and barked not later than the
beginning of July of the year succeeding the defoliation.

I now return to the consideration of the true dry-rot fungus,
Meriilhis lacryinmis.

Although this plant has been encountered at least once on the
old stool of a conifer in the open forest, it is usually associated
with man. It is probable, however, that it has hitherto escaped
notice in plantations, and that it is more generally distributed
than is usually supposed. Although it lives chiefly on coniferous
timber, it also grows on oak, and the oaken boards of parquet
floors are liable to be infected.

The filamentous mycelium which is invisible to the naked eye
grows inside the wood, from which it abstracts the proteids
necessary for its growth. At the same time it dissolves
the coniferin and cellulose of the cell-walls, and leaves behind
a brown residue consisting of lignin, tannin, and oxalate of lime.
So long as sufficient moisture is present these substances
enable the wood to retain its original volume, but whenever
water is withdrawn the wood becomes traversed by numerous
fissures running at right angles to each other, and frequently
breaks up into regular cubes.

As the wood decomposes it becomes brown in colour, a result
which is probably due to the higher oxidation of the tannin.
Although soft when damp, the wood bears some resemblance to

220 DISEASES OF TREES

charcoal when di'}-, and may be rubbed down between the fingers
into an impalpable yellow powder. An important property which
it possesses is its great sponge-like power of absorbing water.
This is chiefly due to the fact that, owing to the cell-walls having
been perforated by the filamentous mycelia, the air is enabled to
escape in front of the water which enters by capillarity. Thus
it happens that when a house is attacked by M. lacryvians
the woodwork is able to absorb water with great ease, and to
transport it to considerable distances. Thus the capillarit}' of
the diseased wood makes it possible for liquid water to be
conveyed from the ground floor of a house to the upper stories,
which it may render damp by evaporation. So far wood that is
decomposed by M. lacrynians resembles that which is attacked
by what is popularly called dry-rot.

il/. lacrymans is, however, capable of growing out of the wood
in which it feeds, if onl}- the surrounding air remains sufficiently
humid to prevent the advancing m}'celial filaments drying
up. Where, therefore, the air is stagnant and humid, the
mycelium grows out of the wood, at first taking the form of a
snow-white loose woolly growth, which spreads over the wood
and covers its surface. These white fungus-growths also spread
on to other objects from which they can obtain no nutriment,
provided they are situated in the neighbourhood of the wood-
work. Thus they creep up the walls, and spread over the
damp ground, flag-stones, &c. Later on stouter branching
strands of the same colour occur amongst the masses of floccose
fungoid hyphae. These may attain to the thickness of the
finger, and are of immense importance in the life-histor}' of
M. lacrynians.

Before proceeding to describe these stout strands, I may
mention that the woolly mass of mycelia attains more consistency
as it gets older, and forms a lustrous silk}- ash-coloured sheet which
may be detached from the substratum. The ash}- grey colour
of this mycelium enables us to distinguish it from that of
P. vaporariiis, already described, which always remains white.
/ The mycelial strands of M. /aery mans consist of(i) firm fibres,

which make them to a certain extent untearable, (2) filaments rich
in protoplasm, which in humid air may send out buds in all
directions, and (3) organs resembling vessels with large lumina,

INJURIES INDUCED BY PLANTS 22J

which contain a plentiful supply of proteid substances. Not
only water but also large quantities of nutritive substances are
apparently conveyed in these vessel-like organs from the nutrient
substratum — that is to say, the woodwork — to the more remote
portions of the growing mycelium. Now, as these strands attain
to a length of many yards, and by taking advantage of depres-
sions in walls mount from the cellar to the ground floor, and
from there to the upper stories, it is easily seen that the fungus
may occur in parts of a building in which there is absolutely no
woodwork, without having encountered any nourishment — that
is to say, wood — on its way. Of course those strands do not
advance as such. It is the delicate filamentous mycelium which,
supplied with water and nourishment from the strands behind,
and taking advantage of every crack and cranny, growls through
walls, soil, &c. The chink in a wall which was entered at first
by a delicate floccose mycelium later on contains a thick strand,
which, however, has gradually developed from the former.
Should the mycelium during its progress again gain access to
woodwork, it destroys the latter, the delicate filaments entering
and abstracting the nourishment, and thus gaining strength for
more vigorous development. It is characteristic of AI. lacry-
Dians that it is able to destroy even dry woodwork. This is
rendered possible by the strands conducting enough water from
other damp parts of the building to soak the dry wood, and
thus make it suitable for attack. In muggy rooms, when wood
is not available to absorb the water, the fungus parts with it
in the form of drops or " tears," which has gained for it the
name of the " weeping " house-fungus {lacrymans).

If sufficient space be available, and as a rule in the presence
of more or less light, though this is not absolutely necessary, the
familiar sporophores are formed. Though they vary in form,
these are usually of a flat saucer-like shape. The fungus-mass,
which is at first white and loose, assumes a reddish colour in
places, and displays vermiform folds, which soon become so
covered with rusty spores that the whole surface is coloured
deep-brown. The brown spores, which are so small that about
sixty-five thousand millions can be contained in a cubic inch of
space, display a germ-aperture in the thick wall at one end,
which is closed however by a clear lustrous plug.

222 DISEASES OF TREES

The spores of M. lacrynians can germinate only when this
plug has been dissolved or has disappeared in some way, and
this seems to occur only under the action of some alkali. I
succeeded with germination experiments only when I had added
some ammonia or salts of potash or soda to the infusion in
which the spores were placed. These salts are not to be
regarded as nutritive in their effects, but merely as rendering
possible the removal of the spore-pellicle that covers the germ-
aperture. Every seed and every spore contains a certain quan-
tit}' of nourishment which has been derived from the parent
plant, and which is instantly available for use. Only when this
has been used up during germination is further development
dependent upon a supply of nourishment from the environment.
I will not contest the possibility that now and then a spore
of J/, lacrymans may germinate directly on wood, which
of course contains minute traces of alkalis, still I have only
succeeded in inducing spores to germinate on wood by adding a
little alkali. This explains why injuries from M. lacrymans are
specially apt to occur in places where urine, humus, wood ashes,
coal-dust, and such like are present.

Wood is the natural food of M. lacrymans, and in this respect
there is no difference between summer-felled and winter-felled
timber. The causes of the frequent complaints regarding
summer-felled wood have already been discussed.

Soil that is very rich in humus also offers nourishment to M.
lacrymans, though only in small quantity. It is probable,
although not certain, that when the mycelium is growing in
contact with walls it dissolves and consumes minute quantities
of lime, but in any case these are so small that no direct
damage can be ascribed to this cause.

When alive or still fresh, M. lacrymans has a very pleasant
odour and delicate flavour, though this is succeeded by a some-
what astringent taste. When sporophores, especially large ones,
decompose, they disseminate a highly repugnant and very
characteristic smell. There is no doubt that the gases generated
by the decaying fungus are highly injurious to the health of
human beings inhabiting rooms exposed to them. In addition
to this, large quantities of water are evaporated from the fungus,
and thus rooms are kept damp.

INJURIES INDUCED BY PLANTS 223

Even under the most favourable circumstances, M. lacryinans
can only appear after infection by spores or pieces of mycelia,
and on this account it is important to determine how the spores
or mycelia are distributed and carried about.

I have already mentioned above that, under certain circum-
stances, the spores may be brought with the timber from the
forest. Such cases, however, must be extremely rare, at least
under the conditions of forest conservanc}' that obtain in
Germany, where large quantities of timber are seldom
stored in the forest to admit of the development of M.
lacrymaiis, which has hitherto been observed but once in such
a situation. That timber may be infected and attacked by
AT. laaynians during long storage in the forest naturally follows
from what has been said. But as a rule infection occurs only in
the towns, either in the wood-yards of carpenters, cabinet-makers,
&c., or in houses. It happens often enough in wood-yards that
the timber of old houses, which is still useful for certain
purposes, is stored beside sound wood, so that the rain washes
any loose spores and bits of mycelium on to the sound wood.
Workmen, especially carpenters — who, let us say, have been
executing repairs in a structure affected by ]\I. lacrymans —
easily introduce the "spores into new buildings, by proceeding
from the one to the other without changing or cleaning their
clothes, boots, or tools.

For M. lacrymans to appear it is not merel}' necessary that
spores or mycelia should be present, but the conditions necessary
for their development must also be favourable. The spores
germinate onl}- in the presence of alkalis. This explains the
disastrous consequences of emplo}'ing humus-substances or
wood or coal ashes as packing materials, or allowing the work-
men to pollute the building with urine. The further growth
and vigorous development of the fungus are, however, most
encouraged by the use of damp materials, e.g. damp wood,
damp packing, damp stones, &c., because moisture is neces-
sary for the gro\\-th of M. lacrymans as well as ever}- other
plant.

This is no more the place to go into further details regarding
preventive measures to be taken in building a house than it is
to describe the measures to be instituted when J/, lacrymans

224 DISEASES OF TREES

appears in a structure. In the book which I have quoted I have
thoroughly discussed all these matters.

Amongst the saprophytic wood-fungi, Peziza centginosa
excites a general interest. Although belonging to the Dis-
coinycetes, it may be mentioned in this place, as it is to it
that the so-called " green-rot " of wood is due. When much-
decayed wood, of the oak and beech especially, less frequently
of the spruce and birch, lies constantly soaked on the ground
of the forest for a long time, it frequently assumes an intense
verdigris-green colour. This is due to the wood being occupied
by the mycelium of the above-named fungus, which, along with
the saucer-shaped sporophore, is vividly green in colour. The
green pigment, which may be extracted, is also present in the
walls of the elements of the wood.

On account of its indestructibility the green colouring matter
finds employment in the arts, and recently experiments have
been instituted to produce green-rot in wood on a large scale by
artificial propagation.

The so-called " blueness " of coniferous wood is due to a
Pyrenomycete, Ceratostoma piliferiini {^Sph(zria diyina), whose
brown mycelium enters the stem by the medullary rays, and very
rapidly reaches the pith. It is specially common in pine woods
on unhealthy trees, such as those which have suffered from
caterpillars, or it may appear in a heap of damp fagots.
Probably on account of deficiency of moisture it rather avoids
the duramen, whereas the alburnum is often quickly occupied by
the mycelium, and destroyed.

SECTION II

WOUNDS

Numerous wounds are produced annually in plants which are
the result of normal biological processes. Thus leaves are shed
in autumn, certain twigs are naturally cast off {e.g. in poplars
and oaks), and the outer layers of the cortex die. The plant
makes preparation some time in advance for all such wounds
as occur naturally, so that at the moment when the wound is
formed the process of healing may be regarded as completed.
This preparation consists in a periderm being formed in the
tissues along the plane which the surface of the wound
ultimately occupies. In its origin and structure this periderm
entirely agrees with the periderm of uninjured shoots, or with
the peridermal covering that gradually forms on wounds which
have resulted from an accident. In many cases a protective
covering of gum is first spread over the wound, and later on the
formation of a periderm is gradually accomplished. Only such
wounds as are due to external mechanical causes, which have
exposed the internal living tissues to the prejudicial influences
of the environment, come into the category of pathological
phenomena.

HEALING AND PRODUCTION OF NEW TISSUES IN GENERAL

In order to understand the processes of healing and the
production of new tissues, we must first cast a glance at the
different kinds of tissues and their capacity to produce new
growths.

On the young parts of plants the protective covering is
represented solely by the epidermis, which usually consists of
a single cell-layer. But before this has entirely lost its power

226 DISEASES OF TREES

of expanding, and has been ruptured by the growth in thickness
of the stem, a new protective covering is formed beneath it,
which protects the inner hving cortical tissues against drought.
This periderm — on whose structure and characteristics it would
be out of place here to enlarge — is formed from a layer of
phellogen (cork-cambium), which results from the tangential
division either of the epidermal cells w^iile still alive, or of a
layer of cortical cells which is situated at a greater or less
distance beneath the epidermis. The radially arranged cells,
which are being constantly formed by division, die and become
converted into cork, and thus a protecting envelope, more or less
thick, is formed on the outside of the living tissues. By division
of the phellogen-layer the envelope is constantly being renewed
on its inner surface, whereas the oldest cork-cells on the outside
are being lost by the exfoliation or detachment of compact
layers of cork-cells. In the case of most trees bark is formed
sooner or later, owing to the older layers of the cortex and bast
losing their power of expansion.* When this occurs new cork-
layers form in the interior of the cortex, and these separate the
inner layers from the outer layers of cortex, immediately before
the latter die, dry up, and rupture.

It is evident that an injury to the dead periderm or bark
is unaccompanied by any prejudicial results. The only way in
which it can affect the growth of the tree is that by diminishing
the pressure it stimulates the cambium to increased activity.
Where the dead bark has been mostly removed in a broad
zone from pines, for the purpose of laying on a ring of tar
with the object of intercepting caterpillars, the trees during suc-
ceeding years grow distinctly faster at the barked region than
either above or below. In the event of the layer of living
phellogen being injured, a new zone of phellogen and cork,
which is continuous with the cork layer along the edge of
the wound, is formed from the uninjured cells which are situated
deeper in the cortex or phelloderm.

The cortical parenchyma (Fig. 132, b c) which lies beneath the

*[" Bark " is, therefore, all the dead tissue situated outside the phellogen:
it may be represented by the corky layer of the periderm only, or may include
this and dead tissues of the cortex, which the periderm has cut out as well.
—Ed.]

WOUNDS

>27

periderm possesses sufficient power of cell-division to enable it
to keep pace with the increasing thickness of the stem. In the
case of a wound, however, its reproductive capacity is confined
to the development of a periderm close beneath the surface
of the exposed tissues. This layer of cork, which is also formed
along the boundary between the sound and dead tissues when
plant-parasites induce diseases of the cortex, is called "Wound

Fig. 132. — The formation of callus on the edge of a wound on an oak-branch, a
periderm ; b, collenchyma ; c, outer cortex ; d, primary bundles of hard bast
e, cortical parenchyma ; f, soft bast ; g, cambium ; h, wood ; /, " wound-cork '
formed by the outer cortex ; k, callus.

Cork" (Fig. 132, i). Its formation does not depend on the
season of the }^ear, for even in winter, should the weather be
favourable, it is formed soon after the occurrence of a wound.

Only that portion of the cortical parenchyma which is situated
nearest to the cambium, or the soft bast, or in other cases merel}'
the deepest-h'ing and }-oungest organs of the soft bast, take part
in the reproductive processes that are about to be discussed.

As wood consists for the most part of empty elements— viz.
fibres, tracheids, and vessels — it possesses only a very limited re-
productive capacity. The cells of the wood that retain vitalit}-
consist of the parench)^ma of the medullary ra)'s and the wood-

Q 2

228

DISEASES OF TREES

parenchyma, but these are so surrounded by the elements
above mentioned that they are scarcely able to exercise even
the limited reproductive capacity which they do possess. This
capacity is exhibited in but two forms — first, in the production
of tyloses or " filling cells " in the vessels of the wood whenever
these are injured, and, secondly, in the development of so-called
" intermediary '' tissue (" cementing tissue ") during the process
of engrafting.^ When the cut surfaces of the scion and stock are
bound together in a sufficiently fresh condition, any empty space
which may exist between the two portions of wood becomes
filled with parenchymatous tissue, which
originates in the above-mentioned paren-
chymatous cells of the wood itself.

Wood that is exposed by a wound has
the power of producing cortex and wood
only if the cortex is removed during the
season when the cambium is active, and
the cambium layer or the young wood
is protected against drought. In such a
case the regeneration of the covering
layers is effected. The region of the
cambium, with its delicate cells and
abundant protoplasm, consists, during the
period from May to August, of initial
cells, mother-cells that have been formed
from these by division, and young em-
bryonic cellular tissue (young bast and
young wood) which is still capable of
growth. When exposed to the air this region dries up very
easily, and only during rainy weather, or when the air is saturated
with moisture, does this tissue survive, and, by the transverse
division of the elongated elements of the cambium, become
converted into a healing tissue consisting of parenchymatous
iso-diametric cells.

Owing to energetic cell-division this gives rise in a few days

to an investing layer (Fig. 133), which, under the influence of

light, assumes a green colour. Frequently the cambium that

covers the surface of a wound withers, with the exception of the

^ Gcippert, Ueber iimere Vorgimge bei detii Veredcln, Cassel, 1874.

Fig. 133. — Surface of a
beech-stem from which
the cortex has been re-
moved, and on which
an investing layer has
been partially formed.
Natural size.

WOUNDS

229

cambium of the medullar}- raj-s, so that the clothing of the surface
of the wound is almost exclusively undertaken by the latter,
giving the impression that the medullary ra}'s have grown out of
the wood. The healing tissue, which is originally homogeneous,
soon shows a certain amount of differentiation. The elements
which abut upon the old wood change into wood-cells, while
towards the outside a new bast region forms amongst the layers
of cells that are assuming the form of parenchymatous cortical

77 m 7 ''■'«'

Fig. 134. — Cross-section of the stem of an oak which, two years before being felled,
had ruptured at several places in the cortex in consequence of much-augmented
growth. X and ;', two places where the cortex had ruptured ; a \.o b, new in-
vesting layers formed by occlusion with their cortex, d ; c, callus ; e to e,
lower surface of the loosened cortex, the cambium of which has also produced
new growth.

tissue. A portion of tissue between the wood and bast preserves
the character of meristematic cambium, while a new epidermis
forms on the surface of the cortex.

In the accompanying woodcut (Fig. 134), which represents the
cross-section of an oak whose bark became separated from
the stem two years before felling, the portion of the surface
of the wound situated between b and b has dried up. Beneath
the shelter of the loosened cortex, e e, on both sides of the wound
new healing tissues {a b) have been formed on the wood, and
these have alread\' attained an age of two )-ears (1876-77).

230 DISEASES OF TREES

Should the loosened cortex be supplied with nourishment by
remaining in organic union with the tree, new tissue may of
course also be formed on its under surface, to which some
cambium will also have adhered. In such a case the process of
cell-division proceeds normally in the cambium, after it has been
converted as explained above into short-celled cambium. It is
in this way that the new tissues have been formed during the
two years which have succeeded the loosening of the flaps of
bark, e e (Fig. 134).

The wood which is formed on the surface of the exposed wood
of the stem and on the inner surface of the detached bast is
distinguished from ordinary wood by its abnormal structure,
and especially by the shortness of its cells and the absence or
scarcity of vessels. H. de Vries/ who was the first to direct
attention to this abnormality, designated such wood with the
name " Wound-Wood."

The formation of new cortex in the manner above de-
scribed has been made use of on a large scale in the cultiva-
tion of cinchona bark under Maclvor's system. Strips of
cortex several yards long are separated from the wood along
the cambium zone, alternate strips of the same breadth being
left in situ. The whole is then covered with moss. The
system can only be practised during the rainy season. The fresh
growth contains twice as much quinine as the original bark.*

When the cambium on the portion of a stem that has been
deprived of its cortex dries up before it can produce an invest-
ing layer, or should cambium be entirely absent from the sur-
face of a wound, as, for instance, in the case of branch-wounds,
&c., the only regenerative process that is possible is the
formation of callus from the edge of the wound.

Under the so-called Javanese method the cortex is removed,
with the exception of a thin layer which contains the cambium
and youngest bast. In a short time a layer of periderm forms
beneath the surface, and prevents the loss of moisture. By this
method, which may be practised at all seasons, the tree does not
require to be bound round with moss.

1 Hugo de Vries, Ueber Wundholz , Flora, 1876.

* [This system of "niossing" has been much in vogue among the planters
in Ceylon. — Ed.]

WOUNDS 231

The process by which callus is formed begins in the soft bast,
and in the embryonic tissue along the edge of the wound —
namely, the cambium (Fig. 132, £-). It is a purely mechanical
process, and results from the bark-pressure on these tissues
being reduced. The annual growth in thickness of the stem
produces distension of the cortex and bast, which, however,
is balanced for the most part by the living cells of these tissues
dividing and growing, and so keeping pace with the increase in
the periphery of the stem, while the dead external portions
become fissured longitudinally. Nevertheless there is always
a cer:ain amount of tension in the cortical mantle, whereby a
considerable pressure is exerted on the cambium. Should this
pressure on the cambium be locally reduced by a wound
reaching to the wood, the processes of cell-division and
growth are accelerated not only along the edges of the wound
but also at greater distances. In Fig. 132 this is visible as far as
^. Wherever the pressure has been reduced (in Fig. 1 34 this
may be perceived at a distance of some inches from the points
a a), the normal cambium changes into " wound-cambium "
with short cells, which produces a luxuriant growth of " wound-
wood," destitute of vessels and without distinct medullary rays.
The process of cell-division proceeds most energeticall}- in the
direction of the surface of the wound, where of course there is
absolutely no counter-pressure, and one may perceive the
cushion-like callus appearing between the wood and the cortex
Either in the year in which it originated, or not till later, the
wound-wood assumes a normal character, whereas the cortex of
the callus remains thinner and more expansive for a series of
years, and exerts less pressure than old cortex or bark. The
increased rate of growth is consequently not confined to the
first year, but is often maintained till the various callus-cushions
which advance from the edges of the wound come into contact
and coalesce.

This coalescence is retarded, if not rendered absolutely
impossible, in the case of trees which at an early stage clothe
the callus with dead bark.

Should the cortex of callus-growths that have come
into contact be thin, living, and free from dead bark, it is
squeezed out during further growth, so that cambium abuts upon

232 DISEASES OF TREES

cambium, and complete coalescence results.* Thick bark may
retard this coalescence for many decades, as, for instance, in the
case of the pine (Fig. 138).

When one considers that the pressure exerted by the bark
in consequence of the peripheral enlargement of the stem acts
for the most part horizontally, like the pressure of a barrel-
hoop upon the staves, it is evident that the formation of callus
must proceed much more vigorously in the case of a longi-
tudinal incision in the cortex than when the incision is a
transverse one. This sufficiently explains why callus is most
vigorously produced along the lateral margins of branch-wounds.

Should an injury produce little or no reduction in the bark-
pressure, as in the case of bruises caused, for instance, by one
tree knocking against another during felling, the formation of
callus is either absolutely prevented or proceeds with great
slowness. The dead cortex, which, without becoming detached
from the uninjured portion, retains its position on the bruised
and lifeless spot, does not admit of a reduction of pressure along
the edge of the wound, and consequently no formation of callus
takes place.

Finally, it may be mentioned that the shape of the wound
may be recognized on the surface of the tree for many decades,
the boundary between the old and new cortex being usually
visible for a long time.

It need hardly be mentioned that coalescence of the wood
exposed by a wound, with the wood of the callus that is
subsequently formed over it, is impossible, and especially so as
the external wood-layers of the wound have previously died,
dried up, and become decomposed to a greater or less depth.

This leads us to the consideration of the changes that occur
in wood which is exposed by a wound. In the case of those
conifers which are furnished with resin-ducts, the surface of the
wound is more or less perfectly protected, owing to the outer
layers of wood becoming impregnated with resin.

The resin-ducts, into which resin mixed with turpentine
is shed from the surrounding parenchymatous cells which

* [I have proposed to call all such cases of covering over of wounded sur-
faces by the agency of a callus, "occlusion": the wound is said to be
" occluded.'' — Ed.]

WOUNDS

2S3

produce it (resiniferous cells), are disposed in the wood both
vertically and horizontally — that is, radiall}-. I was the first to
show that the latter,
which are known as
medullar}'-ray canals,
communicate freely at
certain points with the
vertical canals. This
is owing to the fact
that at those places
where the two sets of
canals come into con-
tact the parenchyma-
tous epithelial cells,
instead of remaining
coherent to each other,
become widely sepa-
rated (Fig. 135, 4

By means of these
intercellular spaces
the resin of the ver-
tical canals can with
ease gain access to
ihe radial canals, and
should the latter be
opened by a wound
on the outside of the
tree the resin is en-
abled to flow freel)'
out to the surface.
This explains the
abundant outpouring
which takes place
when conifers are par-
tially barked in order
to procure the resin.

Under the oxidising influence of the air the resin that oozes from
the wounded surface soon forms a hard incrustation ; and of
course the partial volatilization of the turpentine also contri-

FlG. 135. — Manner of communication between a ver-
tical resin-duct, a, and a duct in a medullary ray,
/', in the Norway spruce. The epithelial cells of
both canals are for the most part empty and
furnished with very thick walls ; the walls be-
tween adjoining epithelial cells being abundantly
pitted, ci. Only a small ]iroportion of these cells
retain thin walls, protoplasm, and a nucleus, and
seive for the preparation of turpentine, dd. At
the point where the back of the vertical canal
facing the reader, a, comes into contact with the
horizontal canal behind, /', the epithelial cells of
both canals are provided with very delicate walls,
and are separated by large intercellular spaces,
e e, the latter providing the means for the passage
of the turpentine from the one canal to the other.

234 DISEASES OF TREES

butes to the induration of the exposed mixture of resin and
turpentine.

If a conifer be felled or a branch removed, either during
summer or winter, one very soon perceives an exudation of resin
from the alburnum (" sap-wood ") of the cut surface. But in
the case of the pine, spruce, and larch no resin exudes from the
older parts of the wood, although these parts are frequently
more resinous than the alburnum. I believe that this state of
things may be easily explained by the fact that not only are
the cell-walls of the alburnum completely saturated with water,
but the lumina of the tracheids are more than half full of water.
In spite of its volatility the turpentine contained in the resin-
ducts is unable to distribute itself throughout the wet wood,
and in the case of a wound is forced out of the canals. When
the wood, with advancing age, loses its power of conducting
water, and so becomes drier — no matter whether this is accom-
panied by the formation of duramen (" heart-wood ") or not —
there is nothing to prevent the turpentine spreading throughout
the wood. Not only does it spread into the cell-walls and
impregnate them with resin, but it is also deposited in the form
of drops on the walls in the lumina of the tracheids, and in
fact the lumina are not unfrequently^-completely filled with tur-
pentine or resin. In this way old pine-wood is frequently so
saturated with resin that sections as thick as one's finger become
partially transparent. Should a .section be made of old wood
that can no longer conduct water, there will be no exudation
of turpentine, for the reason that it has become a part of the
walls of the tracheids, or has been deposited in their lumina.

This also explains why the alburnum becomes completely
impregnated with resin when, in consequence of a wound, its
outer layers are exposed and dry up. The water that is lost
by evaporation is at once replaced by turpentine, which is
conveyed in abundance from other parts by means of the resin-
canals. The resinous impregnation of these outer layers forms
a protection against further injury from the environment.

The resinous saturation of the old stools of conifers, and the
distribution of the turpentine in trees whose wood is being
decomposed by parasitic fungi, are very peculiar. The
turpentine moves from the decomposed parts to the boundary

WOUNDS 235

between the sound and diseased wood. One is inclined
to assume that when the cell-walls arc destroyed by the
m}xelium of the fungus the turpentine in the interstices of the
micellee is again liberated and becomes volatile, and so
penetrates such cell-walls as are either wholly or for the most
part free from decomposition. As a matter of fact, those parts
of the wood which are the last to be attacked by the parasite
become completely saturated with resin, whereas mere traces of
resin are to be found in the decomposed portions. Thus, when
the alburnum has been destroyed, the duramen of old pine-stools
is very resinous. So far there is no proof to support the view
that the cell-walls are converted into resin during the decom-
position of the wood.

When wounds due to pruning, barking, &c., expose the wood
of a dicotyledonous tree, the tree protects itself against the
unfavourable influences of the environment in two ways. In
the first place, the vessels become completely plugged up
by tyloses,* which both prevents the entrance of rain-water
and the evaporation of any water that may be present in
these organs. In the second place, gums are formed in abun-
dance in the neighbourhood of the wounded surface, and these
fill up and close the lumina of the organs, especially the vessels,
thereby protecting them to a certain extent against the
prejudicial influences of the environment. It is probably to
the direct action of the oxygen of the air that the brownness
of the wood under the surface of the wound is due, tannin and
its allies especially assuming a brown colour in the higher
stages of oxidation.

The foregoing protective agencies are, however, insufficient to
afford absolute security to the exposed wood against decompo-
sition and decay. On this account wound-diseases are much
more liable to occur in dicotyledonous trees than in the resinous
conifers.

In the previous section attention has already been directed to
wound-diseases due to parasites, and I shall again refer to this
subject when dealing with the pruning of trees. But besides

* [Tyloses are ingrowths of the cells surrounding a vessel, which push
their way through the bordered pits into the cavity, and may there divide and
grow further. — Ed.]

236 DISEASES OF TREES

the forms of decay in wounds which are induced b}' parasites,
there are other forms of decomposition in wood in which parasitic
fungi take no part. It is rather to the saprophytic fungi, in
conjunction with atmospheric influences, that a variety of forms
of decay in wood are to be ascribed. In the meantime I propose
to apply the collective term " Wound-rot " to those various
forms of decay which have not yet been explained.^

The many forms of decomposition which are embraced under
this term have not yet been subjected to scientific investigation.
Should a large portion of the stem become functionless and die,
saprophytic fungi belonging to the Hymenoniycetes or Ascomycetes
induce decomposition, especially when their growth is stimulated
by the unrestricted entrance of rain-water. This state of things
exists in the case of snags destitute of buds, the stools of felled
trees, trees that have lost large patches of bark by game,
sun-scorching, &c., and which soon die to a considerable depth
owing to the effects of drought. When water and air find
easy access to a wound, as in the case of root-wounds, and
branch-wounds that have not been tarred, decomposition spreads
fairly rapidly in the direction followed by the water in the
elements, although this wound-rot certainly does not progress
nearly so rapidly as that which is due to parasitic fungi. The
so-called false duramen of the beech always proceeds from a
wound, and not onl}' arc all the vessels filled with tyloses, but
the tannin is also so changed as to produce brownness in
the heart-wood. Saprophytic fungi slowly advance from the
wounds, and produce decomposition in the false duramen. The
sooner a wound is closed, either artificially or naturally, the
better for the tree. When air and water are excluded, wound-
rot advances so slowly as only to reach a depth of half an inch
in a century, as is shown by the occluded branch-wound of an
oak in my collection.

The treatment of wounds follows from what has been said.
Two objects have to be kept in view — first, the process of
healing, and, secondly, protection against wound-diseases, both
infectious and non-infectious.

The most perfect form of healing — namely, the re-clothing of
the wound with a new cortex — can only be looked for when the
1 Zersef::i/ngsersrheininii;^en. &c., p. 63.

WOUNDS 237

injur}' is due to the separation of the cortex during the season
of cambium-activity, and provided the cambium can be preserved
against drought by the immediate appHcation of a bandage,
which, however, must not come into contact with the cambium.
The only practicable means consists in binding moist oil-cloth,
straw ropes, moss, or such like round the stem.

Should there be no prospect of a new cortex forming, every-
thing should be done to favour the production of a callus. All
dead and crushed portions of cortex which may press in-
juriously on the edge of the wound should be removed with a
sharp knife, only those portions of cortex which remain uninjured
on the surface of the wound, and which are nourished through a
connection with the edge, should be carefully retained. From
these a callus is formed quite as quickly as from the edge of
the wound proper.

In order further to guard against wound-diseases, all loose
portions of cortex along the edge of the wound should be
removed, as moisture lingers for a long time between them and
the wood, and is absorbed by the latter. The moisture itself
hastens decay in the wound, and moreover it induces condi-
tions that are favourable for the germination of the spores of
infectious fungi, which thus gain an entrance into the interior
of the tree.

In the case of those conifers which arc supplied with resin-
ducts, wounds need be protected only when a thick branch which
possesses duramen is cut or broken off, or when the cortex
has become detached by pruning or the barking of game during
summer. The spruce is most exposed to wounds of this
character.

The wounds of dicotyledonous trees require protection at all
seasons. In order to form a waterproof covering over the wound,
grafting-wax is used by gardeners and coal-tar by foresters.
I have never observed any injurious effect of the tar on the
tissues, as has been repeatedly asserted by practical men ; in
fact, I can affirm that it is only the ruptured organs and their
walls that are penetrated and impregnated by the tar. Cells in
the immediate neighbourhood of vessels, and libriform fibres that
were filled with tar, remained healthy and perfectly sound after a
number of years.

238 DISEASES OF TREES

" Preventitious " buds are also to be reckoned amongst the
regenerative phenomena that follow on injuries to trees, and
which compensate for portions that have been lost. Only a
limited number of the axillary buds of a shoot develop in the
following year to form new shoots. The majorit}' of these buds,
and especially such as are situated in the axils of the bud-scales
and of the undersized leaves towards the base of the shoot,
remain imperfectly developed, and do not, as a rule, shoot out in
the following year. It is these which constitute the dormant
eyes, or " Preventitious Buds " of Theodore Hartig, so called
because they are present on any given portion of stem from the
first year of its existence. Only under certain circumstances do
these burst forth into new shoots, e.g. epicormic * branches and
the like. Preventitious buds is a term emplo}'ed in contradistinc-
tion to adventitious buds, the latter indicating nciv buds that are
formed under certain conditions. j-

These axillary buds may remain alive for a hundred years and
more, especially in the case of trees with a smooth rind, such as
the beech, &c.

It is only as regards apical growth that the preventitious buds
(Fig. 136, a) are inactive, for they display a peculiar form of
growth in length, which Theodore Hartig has called " Inter-
mediary Growth." Each year the delicate vascular bundles, which
extend from the medulla to the buds (Fig. 136, b), increase in
length to the same extent as the portion of the stem on which
the buds are situated increases in thickness. Such growth is
perfectly analogous to the growth of the sucker-roots of Visaiin
album, or to the growth in length of medullary rays. The bud-
axis that is embraced by the stem possesses its own cambium, \
at the point where it crosses the cambium of the stem.

The cambium of the axis of the bud, which divides at the
same rate as the common cambium of the stem, annually pro-
duces two portions of tissue — namely, a larger one on the inside

* [Shoots which develop in this way on the trunk are known as Epicormic
shoots. Such shoots are very common on old Elms, &c. — Ed.]

f [" Adventitious," because they arise in places where they would not
normally be expected. — Ed.]

X [Embryonic tissue, which adds new tissues to those already existing in the
suppressed bud. — Ed.]

WOUNDS

239

whose length corresponds to the breadth of the wood-ring, and
a smaller one on the outside equal in length to the thickness of
the new bast. A cambium region persists between these two
portions till the dormant e}'e dies, when the bud-axis, which
is disposed at right angles to the main stem, ceases to grow
and is overgrown and enve-
loped by the advancing wood-
rings.

Numerous bud-axes tra-
verse the wood of dicotyledo-
nous trees, exactly as is the
case with medullar)- rays.
Should these be stimulated
to form shoots (Fig. 136, r),
the latter produce their own
growth of wood, and both
they and their medulla form
an acute angle with the main
axis of the stem.

In the case of some trees,
more particularly the beech,
a certain proportion of the
dormant eyes develop in a
peculiar manner after the ces-
sation of intermediary growth.
Concentric growth in thick-
ness of that portion of the
wood of the bud-axis which
is situated in the cortex and
bast gives rise to the familiar
wood-balls, or " spheroblasts "
(Fig. 137), which project from
the surface of the stem and

Fig. 136. — Longitudinal section of a
beech-stem, twelve years old. At a
two dormant axillary buds are shown
whose vascular bundles, h, stand at
right angles to the main axis. A third
dormant eye, c, had burst forth to
form a shoot two years previously.
A dwarf shoot, d, has been formed
by the unfolding of a bud when the
main shoot was a year old ; c, a shoot
that has been dead for four years.
Natural size.

frequenth' exceed the size of

rifle bullets. As they have no connection with the wood of

the stem, they may be detached by a slight pressure.*

In the case of our conifers, almost all axillary buds are in the

* [These " Spheroblasts " are very common on the old Beeches in Windsor
Park. Burnham Beeches, and elsewhere. — Ed.]

240

DISEASES OF TREES

habit of developing into dwarf shoots,* and consequently dormant
eyes are very scarce on these trees. In the case of old pines
only one or two buds remain dormant in each whorl, and in rare
cases a dormant bud may be perceived to burst forth at the base
of a shoot where the dwarf shoots (foliar spurs) are absent.
Should a pine be so injured, by the repeated attacks of cater-
pillars, that not only all the foliar spurs with their dormant
buds but also the youngest shoots with their whorls of buds
wither, the only buds that the tree retains are the dormant
whorl-buds of the older shoots. These elongate to form the
so-called " Rosette Shoots," which however
are unable to preserve the life of the tree.
The rosette shoots either bear simple lance-
olate leaves alone, or along with these a few
foliar spurs.

In the case of the larch only about 10 per
cent, of the leaves of the one-year-old shoots
have buds in their axils, all of which develop
to normal or dwarf shoots (leaf-fascicles). A
lost leader can be replaced only by the
vigorous development of one of these dwarf
shoots.

The spruce and silver fir are also but
sparingly supplied with axillary buds, some
of which, however, remain dormant until
special circumstances stimulate them to shoot
out. These dormant buds are frequently to
be found in a whorl at the base of the annual shoot.

The conditions under which dormant eyes may be stimulated
to form vigorous shoots vary, but all agree in this, that the buds
receive an accession of nutriment. As examples of stimulating
conditions I may mention pruning, coppicing, light-thinning,
defoliation by insects, late frost, &c.

Adventitious buds are, generally speaking, comparatively
scarce. Their first inception is not in the axil of a leaf but at other
points of the stem, roots, or leaves, where they originate in after
years, and are therefore supplementary to the axillary buds.

* [e.^^. The pairs of leaves 0:1 a Scotch or Austrian Pine arise each on such
a dwarf shoot or "foliar spur." — Ed.]

Fig. 137. — Globular
shoot ("sphero-
blast ") of a beech
which has been
formed from a
dormant eye after
the latter had be-
come disconnect-
ed from its vas-
cular bundles.

WOUNDS 241

It but rarely happens that adventitious buds originate above-
ground on uninjured portions of a plant, whereas endogenously
developed buds occur regularly on the roots of many species of
trees (root-suckers). On the other hand, their occurrence on the
callus or investing layer of a wound is a frequent phenomenon
(Fig. 151). There they originate close beneath the surface in
the meristematic parenchymatous tissue, where they form their
ring of vascular bundles, which internally are in intimate union
with the wood of the callus.

Adventitious roots, which may occur endogenously both on
the uninjured cortex and on wound-tissues, have a precisely
similar origin.

THE VARIOUS KINDS OF WOUNDS ^

Of the endless variety of wounds, we need select for discussion
only a few of the more generally interesting.

BARKING BY GAME

Barking (peeling) by red deer is usually confined to conifers,
though dicotyledonous trees, for example the beech, are also
similarly attacked less frequently. Fallow deer, on the other
hand, abrade most if not all of our forest trees, though certain
trees, e.^: the ash, are specially liable to attack. Roe deer,
hares, and rabbits also bark trees under certain circumstances.
Roe deer cause a special form of injury by rubbing off the bark
of young trees with their newly formed horns.

During winter, game bark trees for want of food, the starchy
cortex of smooth-stemmed trees being nibbled to satisfy hunger.
In summer, when trees are easily peeled, the more characteristic
feature of the injury consists in the separation of large flaps of
cortex, and this is frequently done to a considerable height.
Views differ as to the motive of peeling during summer. It ap-
pears to me most probable that the game regard the rich store of
sugar in the cortex as a toothsome morsel. Some believe that
the animals find an important aid to digestion in the tannin of the
cortex. Game are also said to peel trees for the sake of the lime
contained in the bark. Excellent results attended the feeding

1 R. Hartig, Zersetziingerschciniini^en, pp. 67 ct seq.

R

242 DISEASES OF TREES

of red deer in the forest district of Ramsau with a substance
containing bone meal, as well as with a special powder (Hofeld's)
consisting chiefly of phosphate of lime and oak-galls. It was
reported that the trees were not afterwards barked. Others
again believe that summer peeling is merely the continuance
of a mode of obtaining food which necessity taught the animals
during winter, and that game thus get into the habit of barking
during summer even when other food is present in abundance.

On account of their periderm remaining smooth for a long time
up to the height of four or five feet, bark being formed only
comparatively late in life, the spruce and silver fir are longest
exposed to the danger of barking. In the case of these trees,
therefore, it often happens that barking is repeated after an interval
of several years (Fig. 139), and stems are not unfrequently to
be met with which show evidences of having been barked at
various ages as often as five times.

As the Scotch pine and larch, especially the former, produce
rough bark early in life, they are exposed to the danger of
barking only for a short period. It is only that portion of the
stem of the Scotch pine which is from three to five years old
that is barked. The portions that are younger are protected by
the leaves, and those that are older by the thick bark.

The damage which results from barking varies with the spe-
cies of tree, time of year, and dimensions of the wound. The
resinous pine suffers but little, unless the stem is completely
barked round. The exposed w^ood dries and becomes so
abundantly impregnated with turpentine and resin that further
decomposition is prevented, and evaporation of water from the
internal layers is retarded. The wounds, however, close with
great difficulty, because the coalescence of the callus-cushions
is interfered with by the early formation of rough bark

(Fig. 138).

The spruce, on the other hand, suffers much more from
barking, partly because it is not usually attacked till a later
period of growth, when much larger wounds are formed, and
partly — and more particularly — because the wounded surface is
not impregnated with resin to the same extent as in the case of
the pine. Less damage is done by barking during winter than
during summer, not onl}' because in the former case the wounds

WOUNDS

J43

are usuall}- smaller, but also because the wounds have the
opportunit}' to become impregnated with resin before the
season when a higher temperature favours the formation of
wound-rot, or the germination of the spores of parasitic fungi.

Should parasites gain an entrance, decomposition spreads
rapidly in all directions, and results in the destruction of the
tree.. In other cases the wound-rot merely induces the inner
layers of wood to become brown, without, however, attacking the
wood that is formed in succeeding years. Should the wound
remain long open, wound-rot may assume very serious propor-

FiG. 138. — Transverse section
of a pine-stem showing a
wound caused by the peeling
of red deer over which a
caUus has formed, but which,
after twenty-four years, is
not yet quite closed. One
third natural size.

Fig. 139. — Transverse section of a spruce-stem
showing three wounds due to the barking of
game. One half natural size.

tions. As a rule it ascends in the stem only to the height of a
few yards, so that, when this is the form of " Red-rot," the
timber is sound after the removal of a few short lengths. As
the spot where the bark has been removed offers the least resist-
ance, it is evident that should the tree be loaded with snow it
will break most easily at that point.

BARKING BY MICE

The wood-mouse {Mtis sylvaticus) and the field-mouse {Arvicola
ai'valis'^) especially injure young dicotyledonous trees by gnaw-

1 A. arvalis is not a native of Britain, but other species of the same
genus do considerable damage to trees in this country. — Tr-ans.

R 2

244 DISEASES OF TREES

ing the cortex during winter. Young beech woods especially
frequently suffer very severely. If one allows the injured plants
to remain standing, most of them will develop in spring appa-
rently in a perfectly normal manner, because the sap is conducted
up through the wood as before. In the course of the summer
the exposed wood generally dries up, the outer layers being the
first to be affected, and wound-rot also makes its appearance.
Should the cortex have been removed right round the stem
above the collar, the plant loses the power of conducting water
at the injured part, and withers. If one delays cutting over the
plant till this has occurred, it seldom happens that any stool-
shoots are produced. If, on the other hand, one examines the
young plantation before the leaves appear, and cuts over all
injured plants close to the ground, vigorous shoots will be pro-
duced, at the expense of the store of reserve materials present
in the roots, and in a short time the young wood will be almost
as promising as before. The more vigorous plants may remain
alive for several years, and adventitious roots may even be formed
above the wound, as is represented in Fig. 140.

BARKING DUE TO THE DRAGGING AND CARTING OF TIMBER,
THE GRAZING OF CATTLE, &C.

Abrasions of the bark which are caused during the process
of removing timber from the wood, especially on declivities,
are amongst the commonest form of wounds to which shallow
roots and the lower parts of stems are subjected. During the
dragging of timber, and especially when water is in active
movement in the tissues, large portions of cortex are detached
from the base of growing trees. Where cattle are grazed or
folded, and where roads occur in a wood, the shallow roots are
subjected to all sorts of injuries, and from these, in the case of
the spruce, the wound-rot ascends in the stem, attaining to a
height proportionate to the amount of moisture that enters the
wound from the soil. On this account wounds that are covered
by moss or humus are much more dangerous than those which
are perfectly exposed.

The majority of the brown patches of red-rot that are observ-
able on the cut surface of the stool of the spruce, and which

WOUNDS

245

disappear when one or two short lengths of the tree are
removed, ma\' be traced to such wounds on the root or collar

(F"ig. 141 \ Should the mycelium of
Agaricus melleus gain an entrance into
such root-wounds, decomposition pro-
ceeds much more rapidly, and the
lower part of the stem may become
perfectly rotten.

When wood-ants {^Formica Jiercu-
Icaiia, or F. ligniperda) take possession
of these wounds, they frequently form

Fig. 140. — A beech which has
been severely barked by mice
above the collar. On the left
side a stripe of cortex has
been left. Numerous adven-
titious roots are seen breaking
through the uninjured cortex
above the wound. Natural
size.

Fig. 141. — The stool of a spruce that had formed
two stems. One of the stems, a, had been
removed in the thinnings, and from it decom-
position subsequently spread downwards into
the sound stem, b. At c c wounds have been
formed in the cortex during the dragging of
timber, and at e wound-rot has spread upwards
from a damaged root into the stem. One tenth
natural size.

galleries which extend far up into the sound part of the stem,
and rapid decomposition succeeds their excavations.

Intentionally or unintentionally, man is accountable for the
most varied forms of bark-wounds. Take, for example, the

246 DISEASES OF TREES

carving of figures or letters. Should these be formed in the
cortex the wound will be of the same shape as the figure,
and the latter may be recognized for many decades, even
after callus has been formed, owing to the difference in the
appearance of the old and new cortex. If, on the other hand,
the cortex is first removed from a considerable surface of wood,
and the figures are carved in the wood itself, they disappear
when the wound closes. All that can afterwards be perceived
is the boundary between the old cortex and the place from which
the cortex had been removed.*

When it is intended to remove a ring of dead bark from the
Scotch pine for the purpose of la}'ing on a band of tar, the living
bast, and even the wood, are frequently unintentionally cut into
as well. Even after the tar has been laid on, turpentine and resin
continue to exude from the wound and form a white covering on
the black tar. This has given rise to the erroneous impression
that the tar partially dissolves the cortical tissues and causes
wounds in the bast.

Precisely similar wounds result from the removal of bark from
old pines for the purpose of obtaining fuel for laundries, as
occasionally happens in the neighbourhood of towns. When
climbing irons are used for scaling trees wounds are also
extensively formed, and especially so during the harvesting
of cones, and the cutting down of spruce-branches for litter.

WOUNDS DUE TO CRUSHING

During the felling of timber in a close wood, it often happens
that a falling tree, or one of its branches, strikes an adjoining
tree, stripping off and crushing the cortex. During pruning the
top rung of the ladder crushes the cortex of the branch against
which it is laid. In dealing with insect ravages it was formerly
a common practice to shake the trees by beating them violently
with the back of an axe so as to frighten the caterpillars and
make them drop off. In consequence of crushing due to these

* [Such cut letters, &c., are often found deep down in the wood many years
later, the successive annual rings formed by the occluding callus having
covered them completely over. The burying of wire, nails, chains, &c., deep
in the wood is due to similar occlusion by a callus which gradually forms
wood over the edges of these objects. — Ed.]

WOUNDS 247

causes the cortex dies, and growth ceases at the injured spot.
But more than that, the dead cortex remains for a long time in
union with that which is Hving and uninjured, and no formation
of callus can take place, because growth is stimulated along the
edge of the wound only when the bark-pressure is reduced.
The formation of wound-rot is encouraged by water collecting
behind the dead cortex, which becomes locally fissured owing to
shrinkage consequent on drying, and finally rots away, but only
after the lapse of many years.

WOUNDS CAUSED DURING THE COLLECTION OF RESIN

Turpentine and resin are procured from conifers in various
ways. In the case of the silver fir, it is only the turpentine
that is gathered. This collects in vesicles in the cortex, which
sometimes attain to the size of a pigeon's egg (Strasburg
Turpentine).

In the case of the larch, large holes are bored into the stem,
and these being afterwards plugged up collect the " Venetian
Turpentine " which flows down from the vertical resin-ducts of the
wood. In the case of the black Austrian pine, the cortex is
removed from the stem in fairly broad stripes, the turpentine
that exudes freely from the canals of the medullary rays being
collected in a receptacle that is cut in the stem below the
wound, while the resin is scraped from the wound after it has
solidified. On account of the exposed wood soon becoming
impregnated with resin, and the canals of the medullary rays
becoming choked up with the same substance, it is necessary
from time to time to remove fresh portions of cortex at higher
points on the stem.

In the case of the spruce, vertical strips of cortex, one to two
inches in breadth and extending from the base of the stem to a
height of about six feet, are detached from the tree. When the
tree is small the resin is taken from one side only, but as it gets
thicker four sides may be utilized (Fig. 142). When the flow of
resin ceases, the callus that has been formed along both sides of
the wound since the last time of stripping is removed, and thus
a new set of resin-ducts is opened, from which resin continues
to flow.

248

DISEASES OF TREES

In the course of }'ears the exposed wood dries up, and decay
begins to make its appearance, being greatly favoured b}' the
larvse of Sirex, which bore from the surface of the wound deep
into the wood, and thus enable rain-water to reach the interior of
the tree. Decomposition frequentl}' spreads from the wound
high up the tree, and does so much damage that in woods where
resin is collected the yield of timber ma}' be reduced from seventy

Fig. 142. — Transverse section of the stem of a spruce which has been tapped for
resin on four sides for ten to fifteen years. The only wood that is capable of
conducting water is those portions of alburnum, a, which are marked off by lines
between the four gutters. The wood, /', beneath the two upper gutters is much
decomposed, whereas the wood, c, beneath the other gutters has remained sound.
Numerous galleries, £, formed by Sirex are seen proceeding from the upper
gutters. One fifth natural size.

to twenty or thirty per cent, of the gross output. It has
not been proved that trees that are tapped suffer in growth,
nor is it to be expected that such will be the case, seeing that
trees cannot utilize turpentine for growth. Tapping, however
greatly reduces the value of timber, because the quality to
a large extent depends on the amount of resin which it
contains.

WOUNDS 2+9

RING-WOUNDS

These are often caused b}- game and mice, though they maj-
also be due to human agenc}', as, for instance, in a mixed wood,
where it is desirable to protect a valuable species against its
more vigorous neighbours. Their effects upon the tree are not
always alike. It is known that, if even a narrow band of cortex
be removed completely round the stem, the cambium below
the girdled portion ceases to be nourished, and there, as a
consequence, growth in thickness comes to a stand-still. As the
tree even where ringed retains its power of conducting the
ascending sap, it remains alive as a rule for some years. What
the conditions are that limit the duration of life of the portion
above the ring-wound has not }'et been full}' made out.^ In June
1 87 1 I selected fifteen equal-sized Scotch pines 120 years old
which were standing close together, and from these I completely
removed the cortex to the height of some six feet. While
certain of the trees died in 1872, several were still perfectl}-
healthy in 1877. As this shows that it is not the desiccation ot
the exposed portion of the stem from the surface inwards that is
the sole cause of death, investigation should be directed to the
question whether the cessation of growth beneath the ring-
wound ma\' not prejudicialh' affect the absorption of water b\-
the roots.

Those cases where ringed trees remain alive for a long period
may possibly be explained b}' root-engrafting, the roots of the
girdled stem being thus nourished b}' neighbouring trees.

PRUNING'^

Although the pruning of trees is a subject that has often
been treated in forestry literature, still the views regarding its
admissibility are so diverse that a somewhat full discussion of
the operation may not be out of place here.

The natural pruning of trees is accomplished by shade, which
causes the branches to become functionless, and ultimatel}' to

^ This is not the place to discuss bicoUateral fibro-vascular bundles,
where the plastic materials may descend in the bast organs near the pith^
- R. Hartig, ZerseiziingscrscJicinitngcn, pp. 68 ct scq.

2SO DISEASES OF TREES

die. The dying twigs and branches are more or less quickly
decomposed by saprophytic fungi.

The rate of decomposition and the period when the branches
will drop off are most of all regulated by the condition of the
wood. Branches of dicotyledons which consist only of alburnum
drop off much sooner than branches which contain duramen.
On account of the shaded branches of young Scotch pines
consisting of soft broad-ringed wood, these trees clean them-
selves much sooner than the spruce and silver fir, the wood
of whose branches is tough, firm, and durable. The thicker,
more resinous, and narrower-ringed branches on the upper part of
the stem of the Scotch pine, on the other hand, retain their
position for a long time, and are more or less embraced or over-
grown at their bases by the growth of the stem. This embracing
of dead branches is the general rule in the case of the silver fir
and spruce, and as they have no organic connection with the
adjoining wood-layers they drop out of boards as loose knots
when the wood shrinks in drying.

The embracing of dead branches would be a much commoner
occurrence, were it not for the fact that the base does not die,
and in the case of the thicker branches it often remains alive for
a distance of about two inches (Fig. 143). The base of the
branch, being nourished from the stem, remains alive, and is
capable of growing in thickness. When, after some }'ears, the
increase in thickness of the bole of the tree has become equal to
the length of the living basal part of the branch, the dead part
of the branch will have become so much decayed as to drop
off under the action of wind, snow, &c. (Fig. 144). After the
wound has healed over only a small dark brown blotch remains
in the interior of the tree to indicate the limits of the enclosed
stump.

It is in the manner just described that the tree protects itself
against the dead stumps of branches being overgrown. It is
only the larger branches that frequently do not drop off until a
portion of the dead base has been embraced by the stem. In
the case of conifers this portion is saturated with resin, and in
the case of dicotyledons it is more or less decomposed. After-
wards, when the branch has become completely rotten and has
dropped off, a hole remains behind which is only partially filled

WOUNDS 251

by the occluding callus, and which of course greatly reduces the
value of the tree for technical purposes (Fig. 145).

Thus it is always a good plan, in the case of every variety of
tree, to remove as early as possible all the larger dead branches
that have succumbed to the natural shading processes. I do not

Fig. 143. — An oak-branch which
has succumbed to the natural
process of shading, its base, /',
however, still receiving nourish-
ment from the main stem.

FiCt. 144. — The snag of an oak-branch which
has dropped off after being killed by the
natural process of shading. The basal por-
tion, h, of the branch which remained alive,
and originally projected from the stem, has
been grown over. After a callus has formed,
the dark brown zone, c, between the living,
/', and the much -decomposed wood, a, re-
mains unchanged in the interior of the tree,
as is shown in the case of a small branch at
d. The axis of the stem of a latent bud is
shown at e.

propose to enter into the technique of the operation, merely
remarking that it is evident that the expense should be incurred
only in the case of such trees as promise to yield high-class
timber. With this limitation there is no doubt that as forestry
advances the pruning of dead branches will become general.

252

DISEASES OF TREES

The contention that such pruning is too costly is justified only
when it can be proved that the difference in value between a log
free from knots and one where they are abundant is not equal to
the cost of pruning phis interest on the outlay.

When we come to consider the removal of green branches —
that is to say, branches or twigs that are living and provided with
leaves— we find that, except in a few exceptional cases which
will be presently discussed, a loss of growth attends the oper-
ation. This is the case no matter whether the separation

from the stem be effected
b}' the hand of man or
b}' such natural agents
as storms, accumulations
of snow, &c. If one re-
duces the number of the
organs of assimilation
(the foliage leaves), the
products of assimilation
generally suffer to a like
extent. As I have proved
conclusively,^ it is only
in the case of trees that
are growing in a per-
fect!}^ open situation,
whose stems are branch-
ed to the ground, and
which have a very large
mass of foliage, that
limited pruning may be performed without diminishing the
amount of growth. In the case of such trees there is a greater
extent of foliage than is necessary to effect the metabolic
processes in the plant-food that is taken in by the roots. Of
course the amount of growth depends essentially upon the
quantity of such food. Under such circumstances a reduction
in the extent of the foliage merely results in more active
assimilation in the leaves that remain.

In the great majority of cases the practical operation of
pruning is followed by more or less considerable reduction in
^ Das Holz der Rothbiichc. Berlin, Springer, 1888.

Fig. 145. — The dead and rotten stump of an oak-
branch over which an occluding caHus has
formed. Two thirds natural size.

WOUNDS 253

growth. This becomes evident in the lower region of the stem,
where in fact, if pruning is carried far enough, growth ma}- cease
altogether, as I have also proved to be the case with trees that
are very much overcrowded.

One must always bear in mind that as pruning generally
interferes with growth there must be important reasons for
performing the operation if the loss of growth is to be com-
pensated for. Amongst these may be mentioned, on the one
hand, the improvement of the form of the stem and the
production of a clean bole, and, on the other, the admission of
light to underwood.

If, for the purpose of obtaining smooth stems, pruning is
carried further than the mere removal of a few branches, one
must remember that in such a case there is not only reduction
of growth, but that there are also indirect dangers consequent on
such pruning. The first of these dangers is connected with the
retardation of the healing of the wounds. It is evident that
the formation of callus over a branch-wound depends to a large
extent on the supply of plastic substances with which the
cambium along the edge of the wound or the callus-cushion is
provided. Very severe pruning will seriously interfere with the
formation of callus, and consequently with the occlusion of
wounds. This leads us to consider whether the pruning of the
stem to the desired height should not be accomplished in two
operations, separated by an interval of several }'ears. If one first
of all removes the branches from the lower half of the portion of
the stem that it is desired to clear, the diminution of the products
of assimilation does not interfere to such an extent with the
formation of callus, and the wounds may be covered over in
a few years. The more vigorous development of the crown
compensates to a certain extent for the branches removed by
pruning, so that when the operation is repeated the new wounds
close sooner than would have been the case had the whole
operation been performed at one time.

By dividing the operation in this way there is also much less
chance of an excessively large number of epicormic shoots being
produced. Such shoots originate partly in the adventitious
buds of the callus along the edge of the wound, and partly in
dormant eyes. In the latter case, it is chiefly the buds that are

254 DISEASES OF TREES

situated on the basal portion of the severed branch that is
embraced by the stem which produce the shoots.

When a spruce is pruned, numerous shoots spring apparently
from the cortex of the main stem. These are chiefly due to
the vigorous development of small weak dwarf shoots, which
originated at the base of the branches in their first year, and
which have become occluded during the increasing thickness
of the stem. I have not been able to prove that true adventitious
buds are formed in the case of this tree.

If in pruning green branches one leaves the stump of a
branch (snag) without any foliage, the same state of things
occurs as when branches are suppressed naturally. The
snag dies, except for an inch or two at the base, and the
formation of callus is either rendered impossible or is so much
interfered with and delayed that the dead stump has time to
become completely rotten. If the bark is removed from the
snag, the conditions are rendered more favourable for the forma-
tion of callus, and a covering will more easily grow over the
snag from the base than is possible when the dead and dry
cortex remains in situ on the stump. In Fig. 146 I have
represented the progress of the formation of callus on a thick
snag, where for clearness the bark has been mostly removed.
The bark of the dead snag presses firmly on the wood, and the
formation of the new growth («, U), which already covers more
than half the stump, has been rendered possible only by its
pushing in like a wedge and separating the dead cortex from the
dead wood, so that the thin and primarily non-vascular edge of
the living tissues has been enabled to grow into the space that
has thus been formed. The familiar curled growths on the
stumps of branches are formed when the new tissues advance
unequally, as is most frequently the case when they are growing
over an irregularly fractured surface (Fig. 146, x x, in the upper
part).

As a dead snag interferes with occlusion, the general rule in
pruning is to cut as close as possible and to make the cut
parallel to the stem. If this is attended to, a callus is formed in
the way already described, its formation proceeding most rapidly
from the lateral edges of the wound. For obvious reasons the
bark is there most easily raised, much more easily, in fact, than

WOUNDS

255

along the upper and lower edges. The upper edge, however,
is greatly favoured as compared with the lower edge, because
the plastic substances during their passage down the stem are
conveyed directly to the former, whereas the latter lies out of the
stream as it were, and is but sparingly supplied with nutriment
(Fig. 147).

There is, however, a much more important reason for the

Fig. 146. — A fractured oak-branch. The wound is being gradually occluded by a
callus which is slowly advancing beneath and pushing off the thick cortex. At
a the new gi'owth shows curls, while at b it pushes its thin non-vascular edge
forward regularly over the dead wood. The dead wood is represented at c.
One fourth natural size.

slow formation of callus on the lower part of a wound. In
that region the cortex is, as a rule, loosened from the wood
during the operation of pruning. At the time when the
cambium is active, it is quite impossible to prevent the cortex-
being loosened, the friction of the saw being sufficient to
account for it. But the main cause is to be traced to the fact
that, in order to prevent the cortex being torn off, a cut is first
of all made underneath, and during the sinking of the branch
the lower edge of the wound is subjected to severe pressure.

!56

DISEASES OF TREES

The cortex of the lower edge of the wound forms a pivot
round which the sinking branch turns, and, although the effects
may not be immediately visible, still the crushing and tearing
at that point kills the cambium for an inch or two back from
the edge of the wound. Of course, in such a case, the new
growth — namely, the callus — is not formed at the edge of the
wound, but at a considerable distance from it, where it is covered
by the cortex (Fig. 148). The result is that the cortex, which was
originally in intimate contact with the wood, becomes detached,

Fig. 147. — A branch-wound on
an oak which has been half
occluded by a callus.

Fig. 148. — The lower edge
of a branch-wound one
year after being formed.
The cortex, a, that has
been crushed during the
sinking of the branch,
dies as far as /', at which
point the formation of
callus, c, begins, and the
cortex is gradually separ-
ated from the wood.
Natural size.

SO that a cavity is formed beneath the wound between the wood
and the dead tissues. This cavity acts like a gutter to catch the
rain-water that flows over the surface of the wound, as well as
all the organisms that it may contain. This forms a specially
suitable place for the germination of the spores of parasitic
fungi, and it is from here that water containing the soluble
products of decomposition finds its way by means of the
medullary rays into the interior of the wood. This cavity is
a gutter in every sense of the term, and at the same time the
point of attack for fungi. Even although the surface of the
wound may have been coated with tar immediately after
pruning, this spot remains unprotected, and indeed it is only

WOUNDS 257

formed after the cortex has been separated from the wood by
the advancing callus. It is in fact the Achilles heel of the
branch-wound. In pruning, the main object must be to prevent
its formation, but this is possible only if pruning be confined
to autumn and winter, when growth is at a stand-still, and when
the cortex is least liable to be detached from the wood. If
one also takes the precaution to support the branch during
sawing, and at the moment of separation to push it clear of the
wound, danger is reduced to the minimum.

The rate at which a wound is occluded depends entirely upon
the vigour of the tree and the size of the wound. A callus
forms on young trees, with their relatively broad annual rings,
faster than upon old trees, and the faster too the higher on
the stem the wound is situated, because with few exceptions
the breadth of the rings increases as we ascend. It is equally
apparent that occlusion will be accomplished sooner where the
situation is good than where bad. In the case of dicoty-
ledonous trees, especially the oak, to which my investigations
have hitherto been confined, branches of a greater diameter than
4 — 5 inches should not be removed.

The effects of pruning as regards the health of the tree
depend chiefly upon the period of the year in which the opera-
tion is performed. So far as my observations go, it is always
highly dangerous to prune the spruce during summer, as
rapidly advancing wound-rot is an almost invariable con-
sequence. It may be mentioned, however, that in all the cases
which I examined, the cortex had been injured during the
process of pruning. This may be avoided by pruning during
autumn or winter, and as the cut surface becomes immedi-
ately covered with a resinous exudation the wound is almost
certainly safe from rot. It is only in the case of the older
branches, where the heart-wood emits no turpentine, that parasitic
infection is liable to occur. It thus appears to me that conifers
may be pruned in autumn and winter, if the wounds caused by
the removal of the larger branches be coated with tar, but
since in the case of these trees the branches are generally small
this will seldom be necessary.

When the wounded surface of a dicotyledonous tree has not
been tarred, one first observes a brown colour penetrating to a

S

2;8

DISEASES OPV TREES

depth of an inch or two, and this is succeeded in a few years by
wound-rot, which, however, ceases to make progress when the
wound closes (Fig. 149). If pruning has been done in summer,
it will be found that beneath the wound brownness appears
in the youngest annual ring, and often spreads down the stem
for four or five yards. If one omits to apply a coat of tar, the
danger of infection by parasitic fungi is naturally increased.
These, however, penetrate even into tarred wounds should they

Fig. 149. — Oak pruned in July.
Rot has spread from and be-
neath the untarred surface of
the wound far into the stem.
One third natural size.

Fig. 150. — The occluded branch-
wound of an oak which has been
infected by Hydniim diversidens.
One half natural size.

be formed in spring or summer, because at that time the germ-
tubes are able to enter beneath the lower edge of the wound
(Fig. 150).

Tarring produces satisfactory results only when pruning has
been done in late autumn or in winter, because it is only then
that the tar is absorbed by the surface of the wound. It would
appear that the absorption of the tar is due partly to the
diminished amount of water in the wood during autumn, and

WOUNDS 259

parti}' to the consequent negative pressure of the air in the
tree.

When pruning is undertaken in spring or summer,, the tar
altogether fails to enter the wood, and the thin superficial layer
does not prevent the cut surface from drying later, and forming
fissures into which water and fungi may gain an entrance. And
then, again, the separation of the crushed cortex from the
lower edge of the wound frustrates the object of tarring.

From what has been said, it follows that dicotyledonous trees
may be best pruned in the months of October, November, and
December — perhaps also in January and February — and that a
good coat of coal-tar should at once be applied to the wounds.

Hitherto pruning has usually been undertaken in summer, and
this explains wh}' the operation has caused such enormous
damage to trees, especially the oak. It is, however, desirable
from every point of view that the subject be further investi-
gated with scientific accuracy. Several species of trees should
be taken in hand, because the trials which I conducted were
confined to the oak, and even in their case sufficient time has
not yet elapsed to make it possible to furnish conclusive
answers to all the questions that have just been raised.^

SHORTf:NING OF BKAXCHES

The shortening of the branches of plants from three to ten
or twelve feet in height differs from pruning proper only as
regards the size of the branches. Most of what has been said
in connection with pruning may be applied here. It therefore
follows that all shortening of branches is an evil which can only
be excused when important objects are to be gained. The
dressing of the younger classes of plants is most admissible at
the time of transplanting, when the number of the roots has been
considerably reduced. In the early part of the season when
foliage is scarce, and when transpiration of water proceeds but
slowly, the quantity of roots may suffice ; whereas in summer
the diminished mass of roots may be unable to provide sufficient

1 It is very desirable that observations be Gontinued on some 240 pruning
experiments that I carried out in 1S75 in the woods attached to the Forest
School of Ebersvvalde.

' S 2

26o DISEASES OF TREES

nourishment for the undiminished crown, which consequently
withers. The danger is avoided, and the plant gets over the
loss in a short time, if equilibrium between the roots and the
foliage is restored at the very first by shortening the longer
branches.

A second reason for shortening the branches is the im-
provement of the shape of the plants, whether in the nursery or
in the wood. I do not intend in this place to enter upon the
technique of the subject, but will merely say that so far as the
growth of the plant is concerned the usual time — namely, summer
— is the least suitable. If we dress a plant in spring or autumn
we remove, in the main, only the branches, the reserve
materials being left in the storehouses of the stem. But if
summer be selected for the operation, the reserve materials of
the stem, being partially utilized in the production of shoots
and leaves, are lost. If one waits till autumn, the leaves of
the branches to be removed will have assimilated materials for
the following year, and these will have been partly deposited in
the main stem. It appears desirable to institute investigations
in this direction, and the question whether wounds are least
attacked by parasitic fungi, such as Nectria, during summer or
during autumn and spring should also receive careful attention.
This question has special force with respect to Acer, Tilia, and
Aesc2iliis, seeing that these genera suffer most from Nectria
cinnabarina, and in their case even small wounds should be
protected by grafting-wax.

The practice of leaving snags destitute of buds on the main
stem is justly condemned, for the reason that if growth is rapid
they are partly embraced or completely enveloped when dead and
withered. On the other hand, it is a mistake to suppose that
decay spreads in the wood from such snags in after years, for I
have never been able to observe such a state of things even in
oaks that had been pollarded or coppiced in youth.

As the wounds are small and are usually soon occluded by a
callus, the application of tar is scarcely necessary, except in the
case of the above-named trees, which are specially liable to suffer
from Nectria cinnabarina. The technical properties of timber
are not interfered with by the small brown wounds in the body
of the stem, for it must be borne in mind that numerous wounds

WOUNDS 261

of a similar character are also formed when branches drop from
trees naturall^^

As has been already stated, it sometimes happens that
parasitic fungi, especially species of Nectria, enter through
branch-wounds and produce cancerous diseases, which afterwards
spread in the stem.

REMOVING DOUBLE LEADERS FROM THE SPRUCE

When the spruce is grown in open lines in the nursery, it
tends to develop a double leader when about three or four years
old, so that instead of a single stem we find two. If one of the
two stems is not removed till the first thinning, the base dies and
decays exactly like the snag of a branch (Fig. 141), and becomes
enveloped more or less by the other stem. The wound-rot spreads
easily from the stump to the other stem, in which it may ascend
to the height of four feet.

In order to avoid this injury, one of the shoots should be
removed in early life, as is easily done by means of a knife with
a long handle and a bent blade. In rare cases the technical
properties of the timber are reduced by a double leader again
forming in later life. Such an occurrence, however, happens
but seldom, and probably only when the tree occupies a very
open situation.

Less damage is done by removing, during the first thinning, a
stem that has grown into another at the collar, as sometimes
happens in a very dense wood. Such cases of natural grafting
occur most frequently in woods that have been formed by
planting the young trees in bunches. Seeing that the stems are
separated by their cortex up to the twentieth or thirtieth year,
when the first thinning takes place, the coalescence is usually
only apparent, and the removal of one stem scarcely injures the
survivor.

COPPICING

When trees are cut over close to the ground, various
phenomena of regeneration which vary with species and age
make their appearance. Amongst conifers the Scotch pine
produces stool-shoots from dormant eyes only when very young.

262 DISEASES OF TREES

In the case of that tree the axillan- buds of the primar)- leaves
preserve their vitaht}' until the formation of bark begins, usuall)-
about the fifth year, when the)' perish, and with them the power
of producing stool-shoots is lost.

Those American pines which have three leaves in the sheath,
for instance P. rigida, retain the power of producing stool-shoots
till a late age. This is owing to dwarf shoots being developed
partly in the whorls, and partly on the main axis midwa}'
bet\\'een the whorls. These dwarf shoots grow each }-ear to an
extent corresponding to the growth in thickness of the stem, and
produce but few leaf-fascicles. It is these that give rise to an
abundant growth of stool-shoots. On account of the absence of
dormant eyes that are capable of producing shoots, the regene-
rative power of the stools of conifers is a very limited one, if
we except those cases that have been quoted. The formation of
adventitious buds in the callus of wounds is also ver}- exceptional,
and it is only in the case of the silver fir that I have occasionally
observed new buds and shoots produced from the callus of the
stool. On the other hand, it frequentl}' happens that the stools
of conifers — more especiall}- those of the silver fir, spruce, and
larch, very rarely those of the Scotch pine — live for several
decades, and form callus more or less energetically along the
edge of the cut surface, so that in certain cases the whole of the
transverse section ma)- be occluded. It is probable that the
formation of callus on the stool is generally due to the natural
grafting of the roots of the tree that has been felled (the
nourished stem) with those of an adjoining tree (the nourishing
stem). There is, however, no getting over the case quoted by
Th. Hartig, where a larch-stool showed a growth of callus
notwithstanding the fact that the tree had stood in a large gap
in a wood, so that the possibilit)' of nutriment being transferred
from a neighbouring tree was absolutely precluded. This case
can only be explained by supposing that in the course of years
the reserve materials stored up in the roots and stool were
dissolved and applied to 'the nourishment of the cambium.

If the cortex and cambium have not been destroyed for some
distance back, by the drying up and decay of the wood, the
stools of dicotyledons develop a callus and numerous buds
during the year succeeding that in which the tree was felled.

WOUNDS

263

These adventitious buds frequently produce vigorous stool-shoots
(Fig. 151), which, however, fail to become self-rooted, and suffer
from the advancing decomposition of the parent stool. The
stool-shoots that are formed from dormant e}'es are much more
serviceable, and also more abundant. As it is very desirable
that these should become self-rooted, so that the new plants
ma}- be unaffected by the health of the parent stool, it is an
advantage to have them as low down on the stool as possible.
For this reason coppice poles are cut as low as possible, and
in order to destroy all shoots that have
formed too high up on the stools, and thus
encourage the formation of deeper shoots, it
is a common practice in oak coppice to char
the stools by burning any ground vegetation.

As the dormant eyes preserve their
vitality for only a limited period, no shoots
need be expected from old stools. The stools
of the older class of birches produce abun-
dant shoots, which however usually succumb
after a year or two. The reason for this
is that the extremely hard bark does not
yield to the growth in thickness of the
shoots whose base it envelops. The result
is that when, on account of the base of
the shoots being nipped by the bark, the
supply of water fails to keep pace with the

accelerated transpiration, the shoots formed early in the' }'ear
succumb about midsummer.

When young dicotyledonous trees that have become stunted
in growth are cut over close to the ground, the young shoots
often grow so satisfactorily and persistently that the plan is
frequently practised with good results as a cultural measure.
Although this matter has not yet been made the subject of
scientific investigation, it seems probable that after the tree has
been cut over the reserve materials present in the roots and
stool are utilized in stimulating root-growth, so that when the
roots have penetrated to a deeper, fresher, and richer layer of the
soil the plant continues to grow satisfactorily. Stunted oaks
that are situated on ground that is covered by weeds or heather

Fig. 151. — Shoots that
have formed from
adventitious buds on
the one-year-old cal-
lus of a beech-stool.
Natural size.

264 DISEASES OF TREES

are often induced to throw out strong shoots, and to show
vigorous and persistent growth, by setting fire to the whole
wood.

INJURIES TO THE ROOTS

These are partly due to animals, e.g. mice, but are mostly
caused during cultural operations, and are always prejudicial to
the plants. The greatest care must therefore be exercised to
preserve the roots during lifting, transport, and planting.

Pruning the roots is always an evil, and is admissible only in
two cases. The first occurs when roots are crushed, nipped, or
broken off during the process of lifting. A clean cut imme-
diately above the damaged part encourages the formation of a
callus from which adventitious roots are produced, and also
prevents or reduces the chances of decay in the roots. The
second case where shortening the roots is admissible occurs
where it would be too expensive to preserve the whole root-
system during the operations of lifting and planting. It may be
mentioned that many plants suffer less from their roots being
shortened than from their being doubled back during planting.
In order to induce the formation of a dense mass of roots by the
production of numerous roots in the neighbourhood of the collar,
repeated shortening of the roots may be necessary where the
attainment of extra large plants is the object in view.

The practice, which is unfortunately still so common, of
aimlessly cutting back the roots is in the highest degree
reprehensible.

Other forms of root-injury are occasioned by removing litter
from woods, tearing up roots, the attack of cockchafer grubs,
mice, &c.

CUTTINGS

The growth and future success of parts entirely destitute
of roots, e.g. slips, pole-cuttings, &c., depends essentially upon
the greatest possible restriction of evaporation from the plants
until they have produced an abundant supply of roots. For
this reason one at first suppresses the development of leaves
by almost entirely burying the cutting, so that only the highest
bud is able to produce a shoot ; or, in other cases, and more

WOUNDS 265

especially in Horticulture, the rootless cuttings are placed in
a chamber where the air is saturated with moisture.

Cuttings of the Caspian willow, that appear to have rooted
perfectly, frequently die off on sandy soil in the height of
summer, or in the autumn of the first year. The reason for this
is that in the earK' part of the season adventitious I'oots appear
both upon the cortex and the callus of the cutting, and when
the upper layers of the loose sandy soil dry up the greater
portion of the roots on the cortex, most of which are dis-
posed horizontally, die off. When this is the case, it often
happens in the height of summer that the roots which have
originated in the callus of the wound, and which always
penetrate the soil obliquely, are unable to supply sufficient
water to satisfy the wants of the leafy shoots, which con-
sequently wither. On this account the soil of osier-beds should
be worked to as great a depth as practicable, so as to encourage
the roots to go deep.

GRAFTING

A technical discussion of the various operations connected
with the transference of a living shoot or bud from one
plant to another would be entirely out of place here. It is
sufficient that we should shortly consider the internal changes ^
that are associated with the process. If we except grafting by
approach, where two adjoining plants are so united to each
other at one or more places that similar wounds in the cortex
of both plants are brought into and retained in intimate con-
tact till complete coalescence has taken place, we find that all
grafting operations agree as regards the main principles. A
portion of a plant provided with buds but destitute df roots, the
so-called scion, or only a portion of cortex furnished with a bud
(the shield and eye), is united to a rooted plant, called the wild
plant or stock, in such a way that when coalescence takes place
water and food-materials will be transferred from the stock to
the scion, as well as plastic materials from the scion to the
stock.

The operation succeeds, as a rule, only when, on the one

^ Goppert, I line re Ziistdnde der Biiiinie nacJi iiusseni Verletzinigcn.
Breslau, 1873.

266 DISEASES OF TREES

hand, the cambium of the stock is active, so that immechate
coalescence may take place between the callus-tissues produced
by its cambium and by the cambium region of the scion, and
when, on the other hand, the scion or bud is at the same time
inactive. The coalescence, in fact, demands a certain time.
Should the scion become active before coalescence has been
effected, or should its buds even be swollen at the time of the
operation, it withers in consequence of transpiration from the
young leaves before it can obtain a sufficient supply of water
from the stock. On this account the scions are prepared as early
as February, and are preserved in such a manner that by
repressing the tendency to growth as far as possible they will still
be inactive at the time when the stock has burst into leaf. As
is well known, budding is usually undertaken in summer, after
the new axillary buds have been formed, the buds being united to
the stock at a time when cell-division is still active in its cambium.

The scion and stock are united in such a way that their
cambium layers are brought into as intimate contact as pos-
sible, care being also taken that no considerable interspaces
are left between the cut surfaces of the wood. According to
Goppert's investigations, coalescence is due to two distinct
processes, for not only does union occur between the cambial
layers, or the callus-tissues that are produced from them, but also
between the cut surfaces of the wood. The cells of the paren-
chyma, both of the medullary rays and of the wood, are stimu-
lated to divide, and so form a connecting or intermediary tissue,
which completely fills up the space between the two cut surfaces.

If the operation has succeeded and the scion has grown, the
latter is in future supplied with the raw food-materials that are
absorbed from the soil by the roots of the stock. On the other
hand, the plastic materials that are elaborated in the scion
nourish the cambium both of the scion and the stock. Of
course the new elements that are produced by the cambium
cells of the scion are the characteristic elements of the scion, and
similarly with regard to the elements produced by the cambium
of the stock. The plastic materials produced in the scion afford
assimilable nourishment to both scion and stock, just as cow's
milk may serve as nourishment not onl}- to a calf but also to a
child. But the latter does not on that account assume the pecu-

WOUNDS

267

liarities of a cow, nor docs the stock assume the pccuUaritics of
the scion, although it is nourished b)- the metabolic products of
the latter. If the cambium cells of the stock naturally divide
more actively than those of the scion, the former will increase in
thickness more rapidly than the latter, and vice versa. The line
which marks externally the point of union between the fast-
growing and slow-growing portions of the stem has been called
by Goppert the "External line of demarcation," and is often
recognizable by distinctions in the cortex and bark. Internally
there is of course also
a corresponding line of
demarcation, along which
the wood of the stock
and scion unite, and
which may often be re-
cognized by a difference
in the colour of the wood
(Fig. 152).

Many cases are known
where it must be ad-
mitted that the scion
exerts an influence on
the stock. It has been
observed, for instance,
that when a scion with
variegated leaves has
been used, variegated
leaves have sometimes
been produced on the

shoots that have afterwards formed on the green-leafed stock.
Such a case forces us to the conclusion that the plastic materials
produced in the variegated leaves of the scion possess peculiar
properties which act upon the cambium cells of the stock in
such a way as to induce variegation in the leaves of the new
shoots. It is not my intention now to discuss the still more
potent influences which the scion has been known to exert in
certain cases on the stock, merel}- remarking that hybrid forms
have been obtained b}' grafting different varieties of potatoes on
each other.

Fig. 152. — Transverse section through the region
where Sorhits Aria has been grafted on
S. Aiiaiparia. The boundary line, a a, be-
tween the slow-growing S. Aria and the fast-
growing S. Auciiparia is known as the in-
ternal line of demarcation. One fourth natural
size.

268 DISEASES OF TREES

DEFOLIATION OF TREES BY INSECTS^

The effects on dicotyledonous trees of defoliation by insects
depend on the season when it occurs. When the }^oung shoots
as well as the leaves are destroyed in spring, fresh shoots are soon
produced by the dormant eyes of the older branches, or by the
buds that may have escaped at the base of the young shoots.
Should defoliation occur in June or July, the trees reclothe
themselves during August with leaves which spring from the
buds of the defoliated shoot itself When defoliation takes
place still later, fresh leaves are either not produced at all or
only very sparingly. In the following year it usually happens
that the effects of the defoliation are entirely obliterated. The
wood-ring formed during the year of defoliation is narrow, and
the growth of the succeeding year is usually also below the
normal. The effects on the larch are similar to those met with
in dicotyledons. In mixed woods of beeches and conifers,
the former often suffer very severely from bark-scorching after
the conifers have been stripped of their leaves.

As compared with dicotyledons, evergreen conifers usually
suffer very severely from defoliation, but in their case also much
depends on the season of the year when the damage is done.
Should this occur in spring, before the new shoots have been
formed, or in autumn, after the wood-ring has been nearly
or entirely completed, the life of the tree is not endangered.
The new shoots, being prevented from deriving any nourishment
from the leaves of the older branches, do not indeed develop so
vigorously as those of trees that have not been defoliated, still a
sufficient quantity of foliage is produced to enable such a tree to
regain its normal condition in a few years. Fatal results, on the
other hand, attend total defoliation at, or shortly after, the time
when the new shoots are formed — that is to say, in May and
June. On account of their tender condition, the young shoots
are either totally destroyed or a portion persists long enough for
the buds to develop. In any case there is a reserve supply of
dormant buds, which the defoliation may stimulate to further

^ R. W.zx\\^^ Das ErJo'iDiken iiiid Absterbeii der Fichte iiach der E7itnade-
lung durch die Nonne. Forst. naturiuiss. ZeitscJirift. Nos. i, 2, 3, 7, jo.
1892.

WOUNDS 269

development, and some of which ma}- even produce short shoots.
The trees are, however, unable to reclothe themselves with a
permanent supply of leaves, for the following reasons. During
the year in which defoliation takes place, all, or nearly all, the
reserve supplies of plant-food that are stored up in the tree are
made use of by the cambium in the formation of a wood-ring.
No growth takes place in the following year. The reserve
supplies in the young shoots also are quickly consumed by the
cambium, so that the buds are prevented from forming shoots.
In the course of the autumn and winter, especially during
long-continued winter drought, all, or nearly all, the twigs and
branches of the crown die for want of water. The bole of
the tree maintains its vitality till the middle of summer — that is
to say, for a full year after defoliation. During that period,
however, no growth takes place. Then the inner cortex begins
to become brown, and the bole dies. This is largely due to
the high temperature of the tree, which is induced by the lack of
shade in a wood that has been entirely defoliated by the ravages
of insects. Especially is this the case with spruces, whose bark
is but ill-adapted for mitigating the action of direct insolation.

Should the defoliation not have been complete, the wood
may slowly recover. This is most likely to occur when a
mild wet winter follows the season in which the ravages were
committed. New shoots are formed on those branches which
have retained a large proportion of their leaves, and which have
therefore been in a position to produce reserve materials
even while the insects were at work, and to store them up
for use during the succeeding season. The thin-barked spruce,
however, is apt to succumb to bark-scorching, consequent on
direct insolation. Trees which are to a certain extent protected
against the action of the sun by the foliage of their neighbours
may gradually recover, even after having lost a great deal
of their foliage, but not after complete defoliation.

SECTION III
DISEASES DUE TO CONDITIONS OF SOIL

Since science has recognized that the occurrence of all
infectious diseases is perfectly independent of the chemical
composition of the soil, that section of plant-pathology which
deals with diseases induced by peculiarities of soil has been
greatly restricted in extent.

SOIL IN RELATION TO WATER AND PLANT-FOOD.

The supply of water and food-materials in the soil has a great
influence on the rate of growth of a plant, although it is only
in rare instances that it produces disease, in the restricted sense
of the term explained at page 5.

One such form of disease is the condition where the tree is
said to become " stag-headed " or *' top-dry," * and which is usually
to be traced to considerable diminution of the supplies of water
or food-materials in the soil, and this prevents sufficient nourish-
ment being continued to plants that have grown up under more
favourable conditions.

In beech woods this disease is specially liable to occur, in
consequence of the removal of litter, and often appears as early
as the pole-wood stage. The reduction in soil-fertility first
makes itself noticeable in a general diminution of the rate of
growth, though frequently also in the withering of the upper
portion of the crowns, while the lower portion remains green.

In alder woods top-drought follows excessive draining.
When oaks that have grown up in a dense wood of beeches,

*[i.e., the topmost branches become completely leafless, and die off, and
remain as dry sticks, like antlers projecting above the foliage. — Ed.]

DISEASES DUE TO SOIL-INFLUENCE 271

and that have but poorl}- developed crowns in consequence, arc
isolated by the removal of the beeches, they clothe their stems
abundantly with epicormic branches. For some years these as
well as the crowns thrive perfectly satisfactorily. In the process
of time, however — and especially on the lighter classes of soil
which are subject to rapid drought or are liable to produce weeds
— ^a portion of the topmost branches of the crowns die, and the
oaks become stag-headed. If the ground is protected in time, by
under-planting, the top branches either do not die or the disease
soon fails to make any progress, and the stag-headed condition
ma}' entirely disappear owing to the dry branches dropping off.

It is difficult to demonstrate the causes of these phenomena
experimentally, but the following explanation may be accepted
as sufficiently accounting for the disease. Directly the oaks are
isolated the amount of soluble food-materials in the soil is
augmented, owing to the accelerated decomposition of the humus
that covers the ground, and, at the same time, the leaves of the
crown, being more exposed to direct sunlight, are enabled to
assimilate more rapidly. These two causes combine to produce
considerable increase of the plastic substances, and consequently
an increase in growth, and the dormant axillar}' buds are also
enabled to develop into shoots.

The first impulse to activit}' is probabl}- communicated to the
dormant eyes by the increase in the products of metabolism,
while their further development into shoots is rendered possible
by the intensified action of the light. When the crowns and
branches have grown vigorously for a few }'ears, the stock of
humus becomes exhausted, while the soil dries up in summer to
considerable depths, owing to the upper layers being deprived of
their protective covering. The result is that the processes by
which plant-food is rendered available are interfered with, and the
stock of soluble food-materials in the soil is reduced. Such a
state of things is commonly expressed by saying that the ground
has " become wild."

The }'ears when plant-food is abundant are followed by a
period of famine. Owing to the reduced supply of water and
nutriment, the upper part of the crowns is starved, the lower
branches appropriating the whole of the water and plant-food.

Provided the crowns have not been too severely crippled, they

272 DISEASES OF TREES

may recover under the influence of an increased supply of food-
materials, consequent on the improv^ement of the soil by under-
planting. Trees that were possessed of well-developed crowns
before the wood was light-thinned produce but few, if any,
epicormic branches, nor do they become stag-headed. The
reason for this is that, owing to vigorous development, the
crowns are able to make use of the excess of nutriment that
is produced during the years immediately following the light-
thinning. No epicormic shoots are produced, so that there are
none to interfere with the nourishment of the crowns during the
years of famine. No doubt the general health of the crowns
suffers, but at all events their upper branches do not die.

It follows from what has been said that if top-drought is to be
avoided there must be no temporary reduction of soil-fertility.
The discovery of the means by which the soil may be protected
and its fertility conserved falls within the province of sylviculture.

In the case of agricultural plants we are familiar with a
number of pathological phenomena which are primarily due to
the effects of drought on the soil. Here I will only mention
the " going off " of cereals — namely, the withering of the straw
before the grain has formed — and the premature ripening of grain,
where the plants wither after the seeds have formed, but before
all the nutritive materials have been stored up in the grain.

Under exceptional circumstances it may also happen that the
growth of plants is interfered with by excess of nutriment. I
would, however, again utter a word of warning against hastily
ascribing sickly appearances to the soil, in the absence of
scientific evidence. A sudden increase in the supply of plant-food,
and the consequent important augmentation of the plastic sub-
stances, may, under certain circumstances, cause the outer tissues
to rupture, and this occurs when their extension has been unable to
keep pace with the growth of the internal tissues. It occasionally
happens, when some cultural operation has suddenly induced
considerable increase of growth in trees, that the bark, especially
on the main stem, is ruptured on all sides owing to the powerful
internal pressure that is set up. When hornbeams ^ that were
mixed with beeches in a wood were suddenly isolated in the
seed-felling, their annual sectional growth at breast-height
1 Untersitchungen aiis dent Forstbot. Inst., \q\. 1 1 1, pp. 141 — 144.

DISEASES DUE TO SOIL-INFLUENCE

73

increased in a few years from O'l 86 sq. in. to 2-124 sq. in.,
and even more. This caused such high tension in the outer
periderm that longitudinal rupturing was finally induced at
numerous points. Owing
to subsequent shrinkage the
fissures extended to the wood
(Fig. 153, (?:), and it some-
times happened that the
whole of the cortical tissues
became detached from the

wood along the cambium region for some distance on each side
of the fissure (Fig. 153,1!^). The consequence was that the whole
of the cortex warped like a board that has been dried on one
side. Most of the numerous wounds healed very quickly in

Fig. 153. — Diagrammatic representation of
two ways in which the cortex may rupture
when the rate of growth is suddenly
increased.

Fig. 154. — Transverse section of the stem of a hornbeam whose cortex had been
ruptured in 1876 owing to sudden acceleration in the rate of growth, a, a fissure
in the cortex which does not extend to the wood ; b, an occluded fissure ; (-, a
fissure which has not yet been completely occluded. The figures correspond to
the annual rings, these being very narrow in the years 1861 — 1871. One half
natural size.

about a year, though some not till later (Fig. 1 54), but for a
long time the cortex of such hornbeams exhibited an unusual
appearance (Fig. 155)-

I have frequently observed the cortex of oaks ^ to be similarly

1 Op. elf., vol. i. pp. 145—150.

274

DISEASES OF TREES

ruptured, when trees that have grown for a long time in a wood,
overcrowded owing to neglect in thinning, have been suddenly
isolated, or when trees that have been reared in restricted light
have been suddenly exposed by the removal of the standards.

The augmented supply af
food-materials in the soil,
and the intensified action
of the light, resulted in
such an acceleration of
growth that fissures of
various sizes were formed
all over the stem. Fig.
156 represents the trans-
verse section of such an
oak a hundred years
old, and exhibits the
interesting manner in
\\hich new tissues are
produced as a result of
the formation of the fis-
sures. These wounds are
injurious, not only be-
cause the resulting cica-
trization and formation
of callus interferes with
the splitting of the wood,
but also because they
offer a means of ingress
to parasitic wood--de-

FiG. 155.— Hornbeam whose cortex has been Stroying fungi. They

ruptured, a, a crack which does not extend almo'^1- alwavs he

to the wood ; fi, a fissure reaching to the wood, ^^Y almost al\\ ays DC

but which has been occluded by the formation avoided by Strongly thin-

of callus (see Fig. 154, d); c, a crack which . , . .

extends to the wood only in the upper portion. ^rig tne plantation SOmC

One half natural size. years before it is in-

tended to " lighten " it.

It being taken for granted that roots rot and the whole plant
dies when excess of stagnant water in the soil prevents the
entrance of air to the roots, and, further, that the same cause
induces the formation of injurious humic acids, increases the

DISEASES DUE TO SOIL-INFLUENCE

■'-■T:>

danger of frost in the case of man>' plants, and conduces to
seedlings being thrown out by frost, &c., the subject need
not be further discussed.

IJ'6

Fig. 156.— Transverse section of an oak which in consequence of much accelerated
growth has ruptured in two places, x and j', two years before being felled At
the three places marked a b the cambium has occluded the surface of the wood
with new tissues, which are possessed of an independent cortex, d d. The loose
flaps of cortex have TiX e e formed new wood on their inner surface. This has
formed a kind of callus-cushion at c, which constitutes the edge of the wound.
The wood-nng formed underneath the cortex in 1876, the year in which the
cortex was ruptured, is a sort of double ring, and consists of two parts,/ and ^^
both of which contain a porous zone and a zone where vessels are comparativeW
scarce. The porous zone of the inner of these two pr.rts, namely/ was formed
m the spring before rupturing had taken place.

CIRCULATION OF AIR IN SOIL i

The metabolic processes in the roots demand an abundant
supply of oxygen. The roots die owing to asphyxia if
they are excluded from a constant supply of this element.
Oxygen is necessary not only for growth but also for the
formation and solution of reserve materials, processes which
are specially active in roots. The air in the soil is impoverished
to an extent corresponding to the amount of oxygen thus
abstracted. Under normal conditions the loss is abundantly
compensated for, partly by the variations of temperature in the

^ R. Hartig, Zersetziaigserschcinungen, pp. 75 ^/ seq.

T 2

276 DISEASES OF TREES

superficial layers of the soil, partly by the processes of diffusion,
and partly by the entrance of water containing dissolved oxygen.
The greater the daily and annual variations of temperature in the
upper layers of the soil, and the greater the depth at which they
operate, so much the more thorough is the interchange of gases,
or, as it is sometimes called, the " respiration " of the soil. As
is well known, the temperature of the soil depends, in a great
measure, on its specific heat. The lower the specific heat, so
much the more quickly is the soil heated or cooled. Water and
humus possess a high specific heat, and the more of these sub-
stances a soil contains the greater will be the quantity of heat
required in order to raise its temperature. A forest soil that is
unprotected by umbrage, that is easily dried owing to exposure,
and that has lost the greater part of its humus, is much more
easily warmed than a soil that is protected by a dense wood,
is constantly moist, and contains abundance of humus.

It is further evident that a forest soil which is exposed to
direct insolation is much more easily warmed, though it also cools
much more easily owing to radiation of heat, than one where
the crowns of the trees and a covering of leaves and humus
afford a double protection.

So far as the diffusion of air in the soil is concerned, we know
that it only occurs to a considerable extent in porous soil
which is not over-wet. In the case of dense, firm wet soil the
mixing of gases proceeds with extreme slowness. It may
happen, under certain circumstances, that the interchange of
gases in the soil is so limited as to induce asphyxia and deca}'
in the roots of plants. I have applied the term "Root-Rot" to
cases where the roots die by asphyxia, in contradistinction to
infectious root-diseases.

ROOT-ROT 1

This disease is specially destructive in the young Scotch pine
woods of the north of Germany. It seldom appears before the
twentieth year, usually not till the thirtieth, and is characterized
by the trees appearing unhealthy for a short time and then
falling over while still perfectly green, after snow or a strong
gale has supplied an external impulse. The tap-root will be
^ Op. cit., pp. 74 ct scq.

DISEASES DUE TO SOIL-INFLUENCE 277

found to be wet and rotten almost back to the stool, while on the
other hand all or most of the shallow lateral roots remain per-
fectly sound. Only in rare cases is the withering of the tree due
to saturation of the stool with resin, consequent on the decay of
the tap-root. Root-rot is to be distinguished from the ravages
of Tranietes radicipcrda — both being frequently met together
in pine woods — by the tap-root rotting and the lateral roots
remaining sound, whereas in the case of the parasite the tree
is killed, though not thrown, owing to the lateral roots being
attacked.

The disease is also to be met with in spruce woods growing
on decidedly shallow soils that contain stagnant water. Under
such circumstances, however, it is less destructive, because the
shallower root-system of the spruce makes the tree more
independent of the decay of the few roots that penetrate deep
into the soil.

In the case of pine woods, root-rot appears only on soils
where, at a short distance from the surface (usually about \\ ft.), a
stratum is encountered which offers no obstacle to the entrance
of the tap-root when the trees are young, but which is of such a
texture as to prevent the free circulation of air after the wood
has become close. This stratum, which usually consists of
argillaceous loam or of very fine-grained quartz (alluvial loam),
is so difficult to work with the spade as to necessitate the use of
the pick. As such conditions of soil are also unsuitable for
agricultural purposes, we very frequently find such strata where
farming has been replaced by forestry. For this reason the
subsequent disease of the pines has been erroneously ascribed
to the previous tillage operations. At first young pine woods
thrive admirably on such soils. The tap-roots penetrate to the
deeper layers of the soil, to which at first the circulation of air
also extends. It is only when the branches begin to interlace
and to form a dense umbrageous canopy which protects the
soil summer and winter, and when a thick layer of leaves and
humus forms on the ground, that the circulation of air in the
soil is interfered with. Insolation becomes impossible, and both
heating and cooling are rendered alike difficult. As the soil
remains constantly moist, while the air is largely excluded from
soil that is argillaceous and very impervious, or consists of dense

278 DISEASES OF TREES

sand, the processes of diffusion proceed but slowly. Although it
may not be for some decades, this interference with the air-
circulation may ultimately induce asphyxiation of the deeper
roots, by preventing their obtaining a sufficient supply of
oxygen.

Root- rot never occurs in dicotyledonous trees, and only with
extreme rarity in pines that are mixed with dicotyledons.
Possibly this may be explained by the fact that during half of
the year the soil is subjected to the minimum of umbrageous
shelter, and consequently there is more air-circulation than in a
wood composed entirely of conifers.

This brings us to the immediate consideration of the best
means of prevention. These must always be directed towards
securing better aeration of the soil. The circumstances of any
particular case must determine which of the following courses
is to be taken : cultivating mixed woods of dicotyledons
and conifers, or, should this be impracticable, the pine may
be replaced by the shallow-rooted spruce ; the removal of
excessively large accumulations of leaves in hollows ; or the
abstraction from the soil of stagnant water by drainage.

The death of the deeper roots on trees that have been
too deeply planted may to a certain extent be described as a
variety of root-rot. The heavier the soil, so much the more
dangerous is it to plant deeply. It is best that such a tree
should succumb at once, but in most cases it lingers through
several decades without being able to produce new roots to
replace those that have rotted off. Only a few trees, such as
willows, poplars, and especially shrubs, develop a plentiful supply
of adventitious roots immediately beneath the surface of the
ground, by means of which a new root system is formed, as in
the case of cuttings which are absolutely destitute of roots.

Similar conditions are induced when the roots of older trees
are covered with a thick layer of earth, as often occurs during
the operations attending road-making, mining, &c. In such cases
less damage is done if the air can get at the roots from the side,
as usually happens when trees grow on sloping ground, but if
the entrance of air to the roots is rendered a matter of great
difficulty the trees either die off entirely, or at all events their
growth is seriously impaired. I found close beneath the surface

DISEASES DUE TO SOIL-INFLUENCE 279

of the earth-heap that adventitious roots were being abundantl}'
produced from the uninjured cortex of smooth-barked trees, such
as the beech and hornbeam, even when the stems were eight
inches in diameter.

Where it has been deemed desirable to preserve valuable trees,
excellent results are said to have been got by ringing the stems
a short distance beneath the surface of the ground, or at least
by removing the bark in patches as far in as the wood. From
the callus that formed at these places numerous roots were
produced, which by ramifying close beneath the new surface of
the heaped-up soil preserved the life of the tree.

It is scarcely necessary to mention that failure in the natural
regeneration of beech woods is often to be traced to the
insufficient aeration of soil that is covered with a thick layer
of humus. Small seeds especially, that are buried too deepl}\
frequently fail to produce plants on account of the supply of air
being insufficient to replace the carbonic acid gas that is pro-
duced during germination. The familiar fact that unsatisfactory
results are almost always got when the germination of alder-
and birch-seeds is tested in a room, although these seeds ger-
minate splendidly when they are sown outside, is probably due
to the circumstance that it is only outside that the air in the
neighbourhood of the seeds is constantly being changed, owing
to the daily variations in the temperature of the soil. In the
room the temperature is uniform and the air is comparatively
still, so that the carbonic acid gas which is given off during
germination cannot be removed quickly enough from the
neighbourhood of the seed. Death occurs in heaps of germinat-
ing seeds for similar reasons.

Analogous to the root-rot that has already been described
is also the decay of the roots of plants that are culti-
vated in glazed pots, which render the free circulation of air
impossible.

POISONOUS SUBSTANCES

In the narrower sense of the term poisons are taken to mean
only such substances as are directly injurious to plant-cells and
effect their destruction. Such substances may be naturally pre-
sent in the soil, but are more often imported into it. As a rule.

28o DISEASES OF TREES

the meaning is extended to include innocuous soluble substances
— -which may even be valuable constituents of plant-food — when
the solutions in which they are present in the soil are in a too
concentrated form. The endosmotic process by which the roots
take in water can go on only if the cell-sap of the roots is
so much more concentrated than the solutions in the soil that
it can absorb water >rom the environment. On this account
any strong solution of food-materials in the soil will prove
injurious, and may even attract water from the roots. The
result is that the plants wither. . Such a state of things may
be frequently observed when very soluble mineral manures are
applied in excessively large quantities. Other soluble salts which
are innocuous in themselves may also cause plants to wither.

When spring tides have inundated woods situated behind
dunes, the water, being unable to return, has slowly percolated
into the soil, and the chloride of sodium which sea-water
contains has frequently proved extremely injurious.^ The pine,
alder, oak, and beech succumbed altogether and were found to
suffer most, while the birch was least affected. In July 1874,
along with Herr Schiitze, the chemist at Eberswalde, I insti-
tuted investigations on the action of common salt, using solu-
tions of the strength of the water of the Baltic (27 per cent.)
and of the North Sea (3'47 per cent.) The Scotch pine, spruce,
false acacia, and beech were selected for experiment, beds of
seedlings and transplanted trees being sprayed with the salt
water, each square yard receiving 2-57 gallons at a time. One-
and three-year-old spruces succumbed both to the weak and
the strong solutions, while six-year-old plants were only killed
by the stronger solution, though they became partially brown
under the action of the other. When spruces some six feet
high each received fully three gallons of the stronger solution,
some were killed, while others showed only a temporary brown-
ness and ultimately recovered. False acacias one year old were
also killed by the weaker solution, while, strange to say, in the
case of thirty-year-old beeches it was only the points of the
leaves that died, some time after the solution had been applied.

^ Schiitze, " Untersuchung von Boden und Holz aus Bestiinden, welche
durch Sturmfluthen der Ostsee beschadigt sind," Zeitschrift fur Forst-
und Jagdwesen, 1876, p. 380.

DISEASES DUE TO SOIL-INFLUENCE 281

In this experiment the Scotch pine proved least sensitive, a
result which was possibly due to its deeper roots.

The injurious effects of urine oh plants are generally well
known, and may be sufficiently explained from its saline
contents.

Many acids and leys act as true poisons, and are sometimes
conveyed to the soil in large quantities in the impure water that
flows from factories. As experience proves, they are highly
injurious, but this is not the place to discuss the many poisons
that may occur in such contaminated water.

A certain amount of interest also attaches to the injurious
influences exerted on vegetation by continuous exhalations of
carbonic acid gas from the soil. At the baths of Cudowa in
Silesia many springs of water containing carbonic acid are
distributed throughout the park. At such places one finds
only grass, shrubs being unable to grow. This is probably due
to the soil being so permeated by free carbonic acid that the
respiratory processes of the roots are rendered impossible. Grass,
however, is enabled to grow because the circulation of air close
beneath the surface of the ground is sufficient to maintain the
roots alive.

It has been proved that the roots of trees are injured by
coal gas when it escapes from pipes into the soil in large
quantity. The unhealthy condition or death of trees that line
the streets of towns is, however, not altogether to be attributed to
this form of injury. The cause is rather to be found in the close
paving of the streets and footpaths, which precludes the entrance
of water and even air, so that the tree-roots suffer both from
want of moisture and of air.

It may be shortly mentioned here that coal gas also interferes
considerably with the cultivation of flowers in rooms. This is the
case even when but little gas is burned, for small quantities are
always escaping from the pipes. Camellias, azaleas, and ivy are
very sensitive to gas, the least sensitive plants being palms and
DraccEua*

* [In many cases, at least, these injuries are due to the sulphurous anhy-
dride of which traces are frequently present. — Ed.]

SECTION IV

INJURIES DUE TO ATMOSPHERIC
INFLUENCES AND FIRE

THE ACTION OF FROST

The action of frost on plants, whether fatal or otherwise, can
be understood only when one has gained a clear idea of the
sources of heat of which plants can avail themselves.

The metabolic processes which make the more highly
developed animals independent to a greater or less degree of the
influences of external heat constitute a factor in the vegetable
kingdom which may be neglected, in comparison with the effects
exerted on plants by the heat of the surrounding media. In
the case of the older classes of trees, especially those which are
covered by thick bark, the temperature of the lower and inner
portions of the tree is chiefly determined by that of the soil.
The temperature of the surrounding air has, however, most
influence on branches and twigs.

At the time of active growth, and in fact whenever trans-
piration of water is proceeding energetically, the temperature
of the interior of a plant is brought into conformity with
that which prevails in the soil by means of the water that
is absorbed by the roots. This has been placed beyond
the shadow of a doubt by the following experiment. Two
trees alike in all respects and equally exposed to the sun
were selected, of which one was deprived of its branches. It
was then found that the temperature of the tree that had been
left intact was 1 8° F. lower than that of the tree which had been
pruned. When the former was also pruned, and the ascent of

INJURIES DUE TO ATMOSPHERIC INFLUENCES 283

water consequcntl}' stopped, the temperature at once rose 18° F.
When the soil is frozen so that no water can enter by the
roots, the tree receives heat from the soil only by the process
of direct conduction. This, however, is always of sufficient im-
portance to explain why the temperature of the interior of
a tree, even during prolonged cold, rises as we descend ; and
also why a deep soil, in which the roots descend to long dis-
tances, has a more favourable thermic effect on trees than a
shallow soil. This also explains why a natural or artificial
covering on the soil is so useful in enabling fruit and ornamental
trees to resist the winter's cold. The reason also why certain
trees that are easily frosted when young are apparently less
sensitive to cold in later life — or become " hardened," as it
is called — is to be traced to the greater amount of heat which
the roots receive when they have penetrated to greater depths.

The extraordinary rapidity with which shrubs and trees
become green in spring after a heavy shower of warm rain is
also due to the rise in temperature of the soil. Finally, the
early appearance of leaves on the smaller classes of trees in a
wood, as compared with the larger trees, is due to the fact that
the soil-strata in which the roots of the former are chiefly
distributed experience a rise in temperature at a time when the
cold of winter still prevails in the deeper strata, and it is from
the latter that the stronger and more vigorously developed roots
derive their heat.

It is the temperature of the surrounding air that chiefly
determines the temperature of twigs and branches, as well
as of all the more delicate parts of plants generally. Heat
penetrates with extreme slowness into the interior of those
portions of a stem which are covered with a very thick periderm
or a layer of bark. It is only when insolation is uninterrupted
that the side of a tree which is exposed to the sun's rays may
become heated to such a pitch as to induce such pathological
phenomena as "Bark-scorching" and "Sun-cracks." As op-
posed to the heat which plants receive, we have the loss of heat
which they experience. Owing to the evaporation of water, heat
is directly abstracted from the tissues where this process is active-
The process of assimilation is also connected with loss of heat.

The rate of cooling is, however, most influenced by radia-

284 DISEASES OF TREES

tion of heat. This proceeds most energetically in the more
divided up parts of plants, where the surface is large in
proportion to the mass of the organ. The depression of tem-
perature consequent on radiation of heat not only explains the
phenomena of hoar-frost, dew, &c., but is also in most cases
accountable for late frosts which not unfrequently occur during
still clear weather, even when the temperature of the air is
above the freezing-point. From what has been said it is
sufficiently evident that the readings got from thermometers
inserted in holes of different trees are the result of the joint
action of various heat-producing and cold-inducing factors. The
determination of the internal temperature of trees at the Forestal
Meteorological Research Stations has absolutely no scientific
value, and represents a waste of time on the part of the observer
that is quite unjustifiable.

When the temperature of any portion of a plant sinks below
the minimum necessary for the production and continuance of
the chemical processes of metabolism — that is to say, for the
calling into action of the vital forces — a period of rest ensues,
which continues until the necessary thermal conditions are again
restored in the tissues. Should the temperature sink considerably
below 32° P., the plant is frosted ; in other words, a portion of the
water of imbibition in the cell-walls and a portion of the water
of the cell-sap separates in the form of ice crystals, while a
more concentrated solution with a lower freezing-point remains
behind in the liquid form.

In the wood of a tree, where for the most part intercellular
spaces are absent, the water of the cell-walls can only separate
out to form ice crystals in the lumina of the cells, while the
walls themselves become drier but do not freeze. As the lumina
of the wood-cells contain abundance of air besides water, there
is ample space to admit of the expansion which the water
undergoes in changing into ice. The lower the temperature
sinks, so much the more water leaves the walls, and so much
the drier do they become. This explains why trees shrink in
exactly the same way during intense cold as felled timber does
on drying. The volume of the cell-walls is reduced proportion-
ally to the water that is withdrawn, and the stem ruptures
longitudinally and displays frost-cracks or frost-fissures. These

INJURIES DUE TO ATMOSPHERIC INFLUENCES 285

are most abundant on the north-east side of trees, because intense
cold usually occurs with a north-east wind. As a rule, frost-
cracks are formed only when a great reduction of temperature
occurs suddenly, and when the interior of the tree is therefore
relatively warm, so that excessive shrinkage is confined to the
outer layers of the wood.

It is a familiar fact that, when such frost-cracks have closed up
with the restoration of a higher temperature, they become oc-
cluded by the callus that forms along their edges. The reduced
pressure of the bark
causes the forma-
tion of new tissues
along both sides of
the crack, and these
project from the
surface as a " frost-
rib." On account
of the thin callus-
layers being easily
ruptured, it requires
but a few degrees
of frost in succeed-
ing years to re-
open the crack.
Repeated opening
and closing of the
wound sometimes
induces the forma-
tion of strikingly

prominent frost-ribs. Should several mild winters occur in
succession, a frost-crack may close up entireh', as is seen in

Fig- 157-

In the interior of old oaks I have sometimes noticed numerous
radial and peripheral cracks which did not extend to the outside
of the stem, nor had they reached the surface even at the time
when they were formed. At present it is uncertain whether
these cracks are also to be attributed to the action of frost, and
no satisfactory explanation has been given as to the circum-
stances under which they originated.

Fig. 157. — An oak-stem showing a frost-crack which has
been produced in the winter before the wood-ring,
a, was formed. Originally the crack extended from
n to d. For nine years in succession the crack has
been annually reopened, so that the frost- rib, a to b,
has been formed, and this has ruptured laterally
at c. During the last five years the crack has re-
mained closed. One half natural size.

286 DISEASES OF TREES

When the tissues of the leaves and cortex, and in fact when
any parenchymatous tissues are frosted, pure water is withdrawn
into the adjoining intercellular spaces, but the cells themselves
do not generally freeze. The result is that the cells lose their
turgidity, and at the same time begin to droop. This explains
the familiar phenomenon of lilies, hyacinths, &c., which have been
caught by late frost, being prostrated on the ground, until the
ice melts and the cells reabsorb the water into their interior
and again become turgid, when the plants resume an erect
position.

Cells which contain a concentrated solution part with water
only under the influence of very intense cold, and I have often
found that the cortex and bast of trees showed no signs of ice
when the wood was hard frozen.

As a rule, when living plant-tissues that contain much water are
frosted — and this applies especially to young leaves and shoots
that are affected by late frost — large masses of ice are formed in
certain regions, and notably underneath the epidermis of leaves
and shoots, and in the medulla. The tissues, however, remain
entirely free of ice, merely shrinking in proportion to the
quantity of water that is lost. These masses of ice consist of
parallel prismatic crystals, which are arranged at right angles
to the tissues from which the water has been abstracted. The
cortical parenchyma of the shoot usually contains numerous
intercellular spaces, especially along the line that marks the
limits of the collenchymatous tissues of the outer cortex.
Owing to the formation of a sheet of ice in this region, a
separation of the cortical tissues may take place, which however
may occasion but little damage to the plant. I have noticed
after a late frost that the epidermis on the under side of the
leaves of the sycamore was pushed out into numerous vesicular
swellings, but it was only after the lapse of several weeks that
this forcible separation exercised any prejudicial influence on the
health of the leaves.

On account of its numerous large intercellular spaces, it is
evident that the spongy parenchyma of the under part of the
leaf offers specially favourable conditions for the formation of ice.
In the case of the false acacia and other trees that are still green
when the first frost occurs in autumn, a sheet of ice forms in the

INJURIES DUE TO ATMOSPHERIC INFLUENCES 2S7

layer of cells that has previously been formed across the petiole
of the leaf. Simultaneously with the formation of the ice the
connection of the leaf with the tree is severed, the result being
that on the following morning there is a general fall of leaves.

When a thaw occurs in the frosted parts of a plant, the tissues
usually regain the condition which characterized them before the
frost appeared. As the water is set free by the melting of the
ice it is slowly absorbed by the cell-walls and the cell-contents.
In many cases, however, it is found that the parts have been
killed. Instead of the chemical processes that are revived under
the action of a recurrence of heat inducing normal metabolism,
they initiate chemical decomposition. The views are divided
as to the time when frost proves fatal. While Goppert con-
cludes that death occurs during the continuance of the frost,
Sachs is of the opinion that the tissues die only after they
have thawed, and that a fatal issue depends very much on
the manner and rate of thawing. The two views may to
a certain extent be reconciled, for it is possible that during
winter death occurs during the continuance of the frost, whereas
in the case of a late spring frost it appears at the moment
of thawing.

The death of a plant under the action of frost during winter
bears a close resemblance to the effects of drought on the
tissues. No matter whether the deficiency of water in the
tissues is due to the action of frost, or to evaporation being in
excess of the absorption of water by the roots, the cells must die
if the deficiency exceeds a certain limit. A change is induced
in the molecular constitution of the protoplasm, the main
feature of which is that the protoplasm is rendered incapable
of retaining any considerable quantity of water. This change is
probably connected with the dissociation of molecular groups
in the protoplasm in consequence of the abstraction of water.
In a living condition the micellse * of the protoplasm are
surrounded by water, the water and the micellae being held
together by that kind of molecular attraction whose action in an
organic substance is spoken of as the force of imbibition. It

*[The hypothetical structural units of an organized body have been
termed, among other names, micellse : each micella is supposed to have its
own molecular structure also, much as a crystal has. — Ed.]

288 DISEASES OF TREES

may be assumed, although it cannot be demonstrated, that the
arrangement or grouping of the ultimate particles of the
protoplasm suffers a change during excessive abstraction of
water, and that, when the supply of water is again restored, they
are unable to regain their original position. Should the critical
limit of drought not be overstepped, the cell passes from the
condition of plasmolysis * into that of turgescence ; but, on the
other hand, a cell withers and is unable to regain its normal
vital condition if the limit of drought has been exceeded. The
same holds true when the loss of water is induced by frost. A
cell is able to bear a certain amount of cold with impunity, the
molecular derangement that causes the death of the plant — that
is to say, the changes in the normal properties of the protoplasm
— occurring only when the loss of water due to the action of frost
or drought has exceeded a definite limit.

In order to illustrate the molecular derangement of the
protoplasm, reference may be made to the familiar changes
that occur in starch-paste under the action of frost. When
that substance freezes it parts with more or less of its water,
and the comparatively dry residue suffers a molecular change
which prevents its reabsorbing as much water as it originally
possessed. When the thaw occurs, the clear water remains
outside the disorganized ■ paste, which consequently loses its
glutinous character.

In the condition of vegetative inactivity our perennial plants
are capable of withstanding our coldest winters without perishing
from frost. In other words, our winters are never so cold that
our forest trees succumb to a molecular disorganization of the
protoplasm of the cells. On the other hand, trees that have
been introduced from warmer countries — and these include most
of our fruit trees — perish from frost during unusually severe
winters. The winter 1879-80 furnished a lamentable instance
of this fact. Exotic plants exhibit every degree of hardiness,
down to the point which is reached even in our mildest winters,
and which precludes the possibility of their passing the winter
out of doors. Apart from specific peculiarities, we also find

* [Plasmolysis is a condition of collapse of the living contents of the cell,
so that water escapes : the cell cannot grow until it is again distended with
water (turgescent). — Ed.]

INJURIES DUE TO ATMOSPHERIC INFLUENCES 2S9

individual differences, and it is this fact that makes it possible
for us to acclimatize plants. As the capacity to resist frost
varies amongst individuals of the same species, just like any
other physiological or morphological pcculiarit}% it becomes
possible to acclimatize a tender plant by propagating hardy
varieties. It is also probable that hardier varieties are produced
in the struggle for existence that takes place along the line
which limits the natural geographical distribution of a plant,
where the increasing severity of the climate bars the way to
a further advance. From this it follows that in attempting to
introduce a certain species it must be advantageous to procure
the seeds from such frontier regions.

Indigenous shrubs and forest trees suffer from winter frost
only under very exceptional circumstances. The roots of young
trees, more especially oaks up to four years old, may be killed if
severe and long-continued frost finds the lighter classes of soil
unprotected by snow or any other covering. The periderm on
roots is thinner than that on stems, and consequently the former
are less protected and moreover growth is active for a longer
period in roots, where it frequently continues till the middle of
winter, so that when frost occurs the tissues arc not in the inert
condition which assists them to resist cold. Such plants burst
their buds in spring, but wither up whenever transpiration
from the delicate young shoots has exhausted the stock of
water.

Shoots that have not completed their growth, especially the
Lammas shoots of the oak, suffer from winter frost. This is a
matter, however, that belongs to the seconci division of our
subject, which treats of the phenomena induced by frost in
plants that are affected while in a state of vegetative activity.

Even our indigenous trees, more especially evergreen di-
cotyledons and conifers, may succumb during winter owing to
their supplies of water being abstracted not by cold but by
transpiration.^ The absorption of water by the roots ceases
when the ground is frozen to a depth that is reached by the
roots of young plants. No harm is done if the trees are
protected above-ground against evaporation, by snow or any
other covering. They die, however, if they are exposed for
^ R. Hartig, Untersuchtmgen, I. p. 133.

U

290 DISEASES OF TREES

months to the action of air and sun, as was the case, for instance,
in the winter of 1879-80. In this case drought alone was
accountable for death. Even in the course of the winter 1879-80
the leaves of middle-aged spruces and silver firs became brown
and died where the foliage was exposed to the direct rays
of the sun, and where constant air-currents encouraged trans-
piration, as, for instance, on the southern edges of woods, on
railway embankments, or on spruce hedges, &c. It was said
that in Alpine regions which were much exposed to the south
wind even old woods of silver firs succumbed entirely to the
influence of the frost. In my opinion these phenomena can
only be explained by the circumstance that repeated thawing and
accelerated transpiration are induced in the leaves by the direct
action of the sun during the bright wintry weather that usually
prevails in these parts, or by the warm south winds, as the
case may be, and that the leaves wither because they are unable
to obtain any water from the stems which have been frozen
under the influence of long-continued and severe cold. Man}-
of the phenomena accompan}-ing the defoliation of pines, as well
as the death of the branches of old pines, may also be explained
in this wa}'. The injurious effects of repeated thawing and
freezing, long-continued frost, or strong drying winds are to be
explained by the scarcity of water that results from the inter-
rupted or at least reduced passsage of water.

The limits of forest growth in northern latitudes and in
mountainous regions are determined not so much by the low
temperature as by the action of drought on those parts of the
tree that project from the snow during the long period of
vegetative inactivity. On this account, too, we find that the
limits of tree-growth are reached at a considerably lower
elevation on south and west slopes, where the action of the sun,
augmented as it is by reflection from the snow, is stronger than
on north and east slopes.

We are still awaiting a satisfactory explanation of the
familiar fact that trees, especially exotic conifers, are more easily
killed by frost in a wet situation than in a dry one, and that in
general the more succulent parts of plants are more liable to suc-
cumb to frost than those portions which are comparatively dry.

When trees have suffered from frost during winter the

INJURIES DUE TO ATMOSPHERIC INFLUENCES 291

injurious effects manifest themselves in a variet)' of wa}'s which
have not hitherto been sufficiently investigated. After ver\'
severe and long-continued winter cold, the cortex, bast, and
cambium, and the wood-parenchyma as well, die and become
brown. The trees either fail to produce leaves in the following
season, or if they do bear leaves, flowers, and even fruit the\'
wither up entirely in the course of the summer or autumn. As
the wood does not lose its power of conducting water all at once,
trees that are injured by frost may be able to produce leaves.
The power, however, disappears as decomposition spreads from
the parenchymatous cells to the conducting organs, or as the
wood dries up from without inwards. Sometimes the cortex
and bast are only killed in patches, and when this is the case a
callus may gradually form over the damaged parts.

It sometimes happens, especially in the case of exotic conifers,
occasionally also in dicotyledons, that the cortex, bast, cambium,
and frequently also the youngest annual wood-rings exhibit
immunity from frost ; the wood-parenchyma, especially that in
the neighbourhood of the medulla, being alone destroyed. In
such a case conifers usually die suddenly from drought in the
beginning of Ma}- ; whereas dicotyledons, whose cambium
becomes active during the bursting of the buds, frequently
remain alive. This result is due to the fact that the cambium
having remained unaffected, forms a new wood-ring before the
old frosted wood has lost its power of conducting sap ; or else
the youngest annual rings escape the frost and suffice for the
transference of the sap. Although the shoots and leaves are but
poorly nourished for some years after the occurrence of the frost,
such trees ultimately recover. Under such circumstances it
often proves an excellent plan to prune severely, so as to bring
evaporation into proportion with the diminished quantity of
water that finds a passage through the wood. In very dr}'
years, however, many trees ultimately succumb to the after-
effects of the frost.

When frost affects plants during the season of growth — and
this is the case with late and early frosts — a fatal issue no longer
depends on the hardiness of the plant, but upon the manner of
thawing. When in a state of vegetative inactivity, our indigenous
trees can withstand the most severe cold of winter with

U 2

292 DISEASES OF TREES

impunity, whereas if the leaves have appeared they suffer from
a few degrees of frost. In this case the view is undoubtedly
correct that death from frost only occurs with the thaw. When
plant-tissue is frozen during active growth, it exhibits the
conditions that have already been described. Should the plant
thaw very gradually, the water is absorbed by the walls and
contents of the cells at the same rate as it is formed from the
ice-crystals by the gradual accession of heat, so that when the
cells have attained the temperature at which chemical processes
are possible the normal conditions of imbibition have also
been again restored, and the metabolic processes which were
temporarily suspended are resumed under the influence of the
higher temperature. The case is different, however, when the
frosted parts of plants are rapidly thawed, as occurs, for instance,
when they are brought into a warm room, or are touched by the
warm hand, or are suddenly warmed by the sun. The rapid
accession of heat induces the ice in the intercellular spaces to
thaw rapidly, and the ice-water, being but slowly absorbed by
the cell-walls and protoplasm, flows into the intercellular spaces,
and drives out the air, with the result that leaves which are
suddenly thawed become translucent. The normal conditions of
imbibition have not been restored when the chemical processes
start afresh under the influence of the rise in temperature.
Instead of these processes assuming the normal features of
metabolism, they lead to chemical decomposition in the com-
paratively dry and withered tissues ; in other words, they induce
death from frost. It is therefore emphatically to be recom-
mended that plants affected by late frost should be protected
against a too rapid thaw.

It often happens, even in the case of our indigenous trees,
e.g: the oak, that after a cold wet summer the vigorous Lammas
shoots have not ceased growing when the first early frost
appears. Exotic trees, whose vital processes demand more heat
for their normal maintenance than our climate has to offer, find
themselves every year in an unprepared condition on the advent
of winter. The youngest organs of the annual shoots have not
completed their development (and especially is this the case
when growth in height continues till the latter part of summer,
as happens with Ailanthus, Sic), the youngest elements of the

INJURIES DUE TO AT^IOSPHERIC INFLUENCES

293

wood-ring arc still in an cmbr\-onic condition and with their
walls unlignified, and the plastic substances have not yet been
converted into reser^•e materials. Such trees display the same
sensitiveness to winter frost that our indigenous trees do to
late spring frost. After a rapid thaw the interrupted chemical
processes induce decomposition.

Numerous pathological phenomena in plants have been
crroneousi}- attributed to frost, and in particular so-called tree-
canker has frequent!}' been ascribed to this cause.* Most of the
forms of canker are infectious diseases, and it is only in a few
extrcmel}' frost}' localities that I have had
the opportunity of noticing cancerous spots
which were undoubted!}' due to frost. These
were met with on a great variet}" of dicot}'-
ledonous trees, and in order to distinguish
this form of disease from the work of can-
ker-inducing fungi I have designated it
" Frost-canker." ^

Frost-canker always occurs at the base
of a lateral branch that has been killed
b}' severe late frost. The first symptoms
are found in the callus which surrounds
the base of the dead branch. Should the
locality (frost-hollow) be \-isited b}' late
frosts during a series of }-ears, the callus,
which has not had time to protect itself
b}- a dense firm periderm, is killed in the
month of May by frosts which occur after

the tissues have resumed the state of vegetative activity. The
tissues often die to the distance of half an inch or more from
the base of the branch (Fig. 158). Subsequenth' a new callus
forms under the dead and rapidly decomposing cortex. Should
the plant be unaffected by late frosts for several successive years,
these canker-spots ma}' heal up complete!}'. But, on the other
hand, should such frosts recur, the canker-spot increases in size
with each unfavourable year. The fact that frost-canker makes

' R. Hartig, Untef^siichi/ngen, I. p. 135, Table VII.

* [See Sorauer, PJianzenkrankheiten^ B.I. 1SS6, for the arguments in
favour of this view. — Ed.]

Fig. 158. — The branch
of a beech showing
frost-canker in the
vicinity of the base of
a shoot that has been
killed by frost. The
wood is brown intern-
ally. Natural size.

294 DISEASES OF TREES

progress only in a frosty year distinguishes it from fungoid
canker, which spreads every year. It is further to be noted that
the late frost also kills the wood at the exposed region as far in
as the medulla. The products that result from the decomposi-
tion of the contents of the dead cells distribute themselves more
or less both up and down the stem, whereas in the case of
fungoid canker the exposed wood usually becomes brown only
on the surface.

In the case of many trees, especially exotic dicotyledons, the
small fissures in the cortex which are induced by cold prove the
primary cause of canker.

BARK-SCORCHING, SUN-CRACKS, AND DEFICIENCY OF

LIGHT

In science and in practice two entirely different phenomena
are referred to under the first of these terms. The more
frequent phenomenon, which I shall specially designate bark-
scorching, is caused during the months of July or August by the
action of unusually strong sunshine on the bark of smooth-
stemmed trees which have been suddenly exposed after growing
up in a close wood.

The trees that suffer most from bark-scorching are the beech,
hornbeam, spruce, Weymouth pine, and silver fir.* The
commonest causes of exposure are the formation of roads,
railways, or rides, or the retention of certain trees for the
production of seeds, or as standards.

The injury to the bark by drying up and exfoliation occurs
almost always on the south-west side, the reason being that this
is the side on which the sun's rays impinge at the time of the
maximum daily temperature.

The extensive clear-felling of spruce woods that had been
entirely or largely defoliated in Upper Bavaria by the nun
moth afforded an opportunity for some careful observations on
the temperature of isolated trees. On August i8, the warmest
day of 1892, when the thermometer registered 96"8° F. in the

* [These injuries occur not unfrequently even in our climate. It should be
noted that the word "bark" is here vised in a somewhat loose sense : true
bark is dead, and it is the living tissues below which suffer. — Ed.]

INJURIES DUE TO ATMOSPHERIC INFLUENCES 295

shade, and I04'9°F. on a felled area that was not exposed to
the wind, it was found that on the south-west side of eighty-
year-old spruces fully exposed to the sun the temperature was
131° F. between the wood and the bark. Four weeks later the
whole of the south-west side of most of the trees had died.
The high temperature may possibly be explained by the fact
that the trees had small crowns, and that consequently but little
water found its way up the younger wood-rings. B}- com-
paring the temperature of the cambium of beeches, spruces, and
pines of the same age and thickness, the influence of the cortex
and bark in modif)'ing the temperature of trees fully exposed
to the sun was determined. On September 30, at 10 A.M., when
the temperature of the air was 6g-8° F., the temperature on the
south-east side of the thin-barked beech was 98'6° F., of the thin-
barked spruce 82'4° F., and of the thick-barked pine 68° F. This
would appear to indicate that in trees with thin periderm or
bark the branches on isolated individuals come well down the
stem, so as to afford protection against the sun, a state of things
that one does not find to the same extent in trees with thick
bark.

On standards in a young wood bark-scorching first appears,
and is most severe, near the surface of the ground. There are
two reasons for this. First, the rays reflected from the ground
increase the temperature ; and, secondly, the air-currents that
assist so materiall}' in cooling those parts of a tree which are
exposed to the sun are interfered with by the young trees.

Even the parenchymatous tissues of the injured parts of the
stem succumb to drought, and the alternate desiccation and
saturation with external moisture induces rapid decomposi-
tion, which of course speedily affects the internal portions of
the stem. Should parasitic tree-fungi effect an entrance, the
tree may be rapidly killed, but otherwise the decomposition
retains the simple character of wound-rot.

I investigated and described a disease which I found in a
wood of Weymouth pines about forty years old.^ This disease
both agrees with and differs from bark-scorching, and may be
designated " bark-drought." The extraordinary drought of 1876
had reduced the supplies of water in the trees of a wood growing
1 Uiitcrsiichiingcn^ III. pp. 145 — 149.

296 DISEASES OF TREES

on dry ground intermixed with a silicious moor-pan, to such an
extent that the cortical and other Hving tissues beneath the
bark exposed to the drying winds became completely withered.
This occurred on the south and west sides of the trees, and
especially at a height of from three to six feet, although
portions both above and below these heights were also affected.
The Weymouth pine is found naturally in marshy situations,
and, adapting itself to the natural habitat of the tree, its
cortex is but poorly protected by periderm and bark. It
is thus easy to understand that on a dry soil and in a hot
dry year the wood is unable to furnish the cambium and
cortical tissues with sufficient moisture. It follows therefore
that this species of tree should not be cultivated on excessively
dry ground, especially where water cannot be expected to ascend
from the subsoil.

Of quite another character is the pathological phenomenon
appropriately called " sun-crack," which is sometimes met with in
late winter or spring in the beech, hornbeam, Acer, and oak.^ In
spring, fissures varying in length form in the cortex, which
separates from the wood for an inch or more on both sides of
the wound. In the case of the beech, with its thin cortex, the
rind * not only becomes detached but also dies. Owing to the
vigorous formation of callus, such a sun-crack frequently heals
up after a few years, whereas in the case of bark-scorching it is
very seldom that healing occurs. Fig. 159 represents, in one half
the natural size, the cross section of the upper part of an oak
taken from the south side of the stem. The tree, which was
about 170 years old, and was taken from a light pole-wood of
beeches on a fairly steep north slope, showed that numerous
sun-cracks had been formed all over the stem, at various periods
of its existence.

The cold ground, which in spring was hardly affected by the
sun even at midday, must have kept down the temperature
of the wood of the oak to a low point, even when the stem
was intensely heated by the sun's rays. It is probable that
the cortex had become so warm at certain places under the

^ Lhitersuchimgen, I. p. 141.

* [The word " rind " is here used in a general sense to denote all the tissues
outside the cambium. — Ed.]

INJURIES DUE TO ATMOSPHERIC INFLUENCES 297

influence of the sun's rays that it expanded violentl)', and so
became detached from the wood. The question, however, has
not yet been settled by experiment, and unfortunately it is
scarcely possible in this wa\- to determine the factors that
combine to produce sun-cracks.

As a further result of dryness of the air and of excessivel)-
strong sun, the premature withering and fall of leaves may here
be mentioned. In 1876 Ihad the opportunity of observing this
in an intensified form in all the beech woods on south and \\-est

Fig. 159. — Transverse section of an oak-stem showing numerous sun-cracks. ( )ne

half natural size.

slopes in the northern Harz. The beech pole-woods were
almost entireh' defoliated in the end of August — that is to
sa}', nearl}' two months before the normal time of the fall of
the leaf. As this state of things was manifest even on fairly
fresh ground, it must be attributed to an abnormal rate of
transpiration from the leaves during the hot di')' summer, to
compensate for which water could not be convej-ed quickl}-
enough from the ground.

When plants have been kept in a humid atmosphere, as, for
instance, in a forcing-house, a conservatory, or under the shade
of a close wood, the shoots, but especiall}' the leaves that are

298 DISEASES OF TREES

produced under such circumstances, are peculiar in possessing
an epidermis which is comparatively non-tuberous.* On this
account it is ill-adapted to prevent the excessive transpiration
which is encouraged by air-currents and a dry atmosphere, and
such plants wither or lose a portion of their leaves prematurely.

A sudden accession of light in too large quantity has also a
prejudicial influence on the health of plants, and especially
on the leaves of trees, whether dicotyledons or conifers.
Under normal conditions the chlorophyll-corpuscles protect
themselves against the action of too bright light, which would
destroy their green colouring matter, by so arranging themselves
in the cells of the leaf that their narrow edge only is exposed to
the intense illumination. The leaves of plants that have been
reared in shade become yellow or brown when suddenly exposed
to the action of direct sunlight. In such a case, however, it is
always difficult to determine how much of the damage is to be
ascribed to the accelerated transpiration induced by the intense
sunlight, and to the consequent withering of the cells.

On the other hand, it is a familiar fact that pathological
phenomena may also be induced by deficiency of light. A plant
that has grown up in unrestricted light possesses a certain stock
of the products of metabolism which have not, so far, been
utilized in the construction of cells. These may take the form
of reserve materials which have been stored up in the plant, or
of active plastic substances which are distributed throughout the
leaves and organs of the stem. By means of these substances a
plant is able to grow for a certain time even without light, until,
in fact, the substances have been utilized and the supply has
been exhausted. Shoots and leaves that have been produced
in the dark are, however, abnormally constructed. They are
spindly, and " drawn," and display the phenomenon of so-called
etiolation. As chlorophyll can normally be produced only under
the action of light, and as the supply of nutritive substances is
insufficient, the shoots and leaves are yellowish and not properly
developed. Seeing that light cannot exert its retarding influence,
the shoots become abnormally elongated. Such drawn shoots,

* [There are other anatomical differences also in the cellular tissues of
such shade leaves, as Stahl has shown, which are calculated to make them
less resistant. — Ed.

INJURIES DUE TO ATMOSPHERIC INFLUENCES 299

being unprovided with a properly developed epidermis, wither or
easil}' succumb to other influences when the plants are again
fully exposed to the light, and are incapable of developing into
normal shoots.

The laying of cereals is the result of the shading of the lower
internodes in consequence of thick seeding or heavy manuring.
The restriction of light that results from drilling seed thickly
stimulates spruces, pines, and other plants to make increased
height-growth, but this is secured at the expense of the lateral
shoots and the health of the plants.

MECHANICAL INJURIES

Reference may here be made in a few words to such
mechanical injuries as are due to atmospheric precipitations
and violent gales, and especially as these often lead to other
diseases.

Flowers and leaves are damaged by heavy hail, which ma}-
also severely injure the cortex of trees, especially when the rind
is smooth. At the places where the hailstones strike, the rind
is crushed, or, it may be, knocked off altogether. Although as a
rule a callus very soon forms over such wounds, still it not
unfrequently happens that the injured portion of the stem dies.
In young spruce woods in the neighbourhood of Munich I found
that the leading shoots which were affected b)- hailstones died —
a result doubtless due to the excessive evaporation from the
wood, which in many cases was stripped of its cortex on one side
of the shoot to the distance of about an inch.

It very frequently happens that the wounds caused by
hailstones form an entrance for parasitic fungi. The spores of
Ncctria ditissinia are specially apt to germinate on such places,
and to produce canker in the beech (Fig. 39, page 93). Larches,
too, are often similarly infected by Peziza Willkovnnii.

There is not much to be said about the damage that is induced
by snow-crushing. For obvious reasons, this occurs almost
exclusively in woods of evergreen conifers, where it takes the
form either of the breaking off of the tops and branches, or of
the fracturing of young poles. It may be worth noting, however,
that wounds are very often formed at the base of branches
which are bent down by a load of snow. .Should the ground be

300 DISEASES OF TREES

covered with snow, and should the apex of such a branch become
frozen into the upper layers, it may readily happen that during
the gradual melting and shrinking of the snow the branch is
forcibl}' detached from the stem altogether. Such wounds
frequenth' form the means of entrance for the above-named
parasitic fungi.

Gales ma}' fracture stems or tear trees up by the roots, but
such injuries fall rather within the limits of a treatise on
s}'lviculture or forest management than of pathology.

INJURIES DUE TO FIRE, COAL SMOKE, AND LIGHTNING

Attention ma)- here be directed to the fact that the destructive
effects of the passage of fire over the ground of a wood depend
not onl}- upon the intensity and duration of the conflagration,
but also upon the species and age of the trees, or, in other words,
upon the amount of protection afforded by the cortex and bark.
As is known, the lower portions of the bark of old pines may be
perfccth' black and charred without the cambium being killed.
This is due to the low conductivity of the bark for heat.* If ro
brownness is to be observed in the younger layers of the bast,
it is evident that the fire can have done no damage. On the
other hand, trees with thin bark are very sensitive to fire, and by
making a few incisions in the cortex one may determine whether
it has been killed or not. Although trees whose lower cortex is
damaged ma}' produce fresh leaves, one must not be deceived
b}' such a state of things. Trees that are no thicker than one's
arm become green in spring when the lower cortex is charred
or withered right round. A similar state of things occurs with
beech-saplings that have been barked by mice, but in both cases
the trees ultimately wither up entirel}^ During the growing
season the starch that is stored up in the stem at a lower level
than the dead cortex is utilized by the cambium — which is no
longer nourished from above — in the formation of the wood-ring
so that when the trees die in the course of the summer the
stools, being destitute of reserve supplies, are unable to produce

* [In cases where the cambium is scorched for some distance, but not
entirely, round the stem, the remnant of living cambium may slowly creep
round and form callus over the injured side : years afterwards, on felling ,
such parts of the stem present " ring-shakes."' — Ed.]

INJURIES DUE TO ATMOSPHERIC INFLUE.XCES 301

fresh shoots. Shoots arc produced much better from the stools
of trees that have been entirely consumed, or that have been cut
over close to the ground directh' after the injury occurred. In
such a case the whole of the plastic materials stored up in the
subterranean parts of the tree are at the disposal of the new-
shoots. If the injured stem is sufficiently young to hold out the
prospect of stool-reproduction at all, it can only do harm to
delay cutting it over.

SULPHUROUS ACID IN COAL SMOKE AND THE SMOKE FROM

IRON-WORKS 1

In the neighbourhood of extensive blast furnaces or similar
centres of industry, where large quantities of coal are consumed,
it has alwa}-s been noticed that vegetation suffers from the
smoke. To such an extent is this the case that in industrial
towns like Essen scarcely any vegetation exists. In the direction
of the prevailing winds very serious damage is not unfre-
quently caused even for a distance of two miles from the fur-
naces. The views at one time held that the damage was due to
metallic poisons (arsenic, zinc, lead) present in such smoke, or
to the soot deposited on the leaves, hav'e proved to be incorrect-
The investigations of Stockhardt - and Schroder ^ have shown
that the damage is due entirely to the sulphurous acid present
in the smoke. It has been determined by experiment that the
sulphurous acid being absorbed by the surface of the leaves
induces local death and brownness in the tissues. The tissues
prove most resistant in the neighbourhood of the larger ribs.
Although the leaves of conifers absorb less sulphurous acid than
those of dicotyledonous trees, still, on account of their being
longer exposed to the prejudicial influences, they generally
suffer more than the foliage of deciduous trees.* If one examines

^ Hasenclever, Ucbcr die Bcschiidigung dcr Vegetation dureh satire Case.
Berlin, 1879.

- Stockhardt, Tharander forstl. JaJirbiicli^ 1871, p. 218.

■'■ ScYixodeY, La?idwirthsc/iaftL Versuehsstationen, 1872 and 1873.

* [I have investigated many such cases, and find the Larch sutlers greatly-
The cases are complex, and it is by no means clear that the action of the
acid-gases is merely local on the leaves ; there is evidence to show that the
damage is largely due to the gases passing through the stomata and into the
lacunae of the living leaves. — Ed.]

302 DISEASES OF TREES

spruces that are still living, though full)' exposed in the
neighbourhood of blast furnaces, it will be found that it is only
on the }'oungest shoots that the leaves are still green. The
farther one moves from the seat of the mischief, so do the
annual crops of leaves that still maintain their position on the
spruce-shoots increase. It is thus evident that the duration of
the leaves depends in large measure on the intensity of the
action of the smoke. Amongst dicotyledonous trees the beech
is the most sensitive, after which come the oak and the
sycamore, while the elm, ash, and mountain ash, and, amongst
conifers, the black pine are some of the most resistant. In
towns where it is only in winter that large quantities of coal
are used as fuel, the conifers alone suffer. In summer the air
is almost free from sulphurous acid, and it is only on the
approach of cold weather that the deleterious influences begin
to make themselves manifest. At this time the deciduous trees
have shed their leaves, so that it is only the conifers that are
affected. The sulphurous and sulphuric acids that collect in
large quantities in snow that has covered foliage for some time
prove injurious to the trees.

The ease with which sulphurous acid is oxidized to hydrated
sulphuric acid not only explains how this plant-poison is
constantly being removed from the atmosphere, but also
indicates how we may remove sulphurous acid from the smoke
of blast furnaces and factories generally. To some extent this
has already been put into practice. By leading the sulphur
gases through moistened hydrated lime 90 per cent, is rendered
innocuous. Another plan is to conduct the gas through a long
pipe in which a stream of water flows in the opposite direction.
By this process a conversion into hydrated sulphuric acid is
effected.

According to recent observations the chlorine and soda fumes
that are produced in certain factories also prove injurious to
vegetation.

THE EFFECTS OF LIGHTNING

Up to the present the way in which lightning affects the
health of trees remains unexplained.

When lightning strikes a wood, its effects may be confined to

INJURIES DUE TO ATMOSPHERIC INFLUENCES 303

a single tree, or the}' ma}' be noticeable on a whole group of
trees. As regards the former case, we find that all trees are
subject to be struck b}' lightning, but that some are more liable
to suffer than others. Oaks and the Lombard}' poplar would
appear to be struck most frequently, though the Scotch pine is
also very often affected ; whereas the beech enjoys comparative
immunit}' from such injur}'. Even in trees of the same species
the form of damage varies exceedingly. As a rule the injury is
confined to the separation from the wood of a strip of cortex
about an inch in breadth. This lightning score, w^hich begins
in the crown, is frequentl}' interrupted over considerable portions
of the stem. It may leave one side of the tree and appear on
another, again to return to the original side at a different level.
In stems with straight fibres it runs straight, but in trees
showing spiral growth it follows a similar course. At the
bottom of the tree it disappears between two roots close to the
surface of the ground ; or it runs for some distance along the
under side of a strong lateral root, and then suddenly disappears.
B}' this treatment the health of the tree is in no wise affected.
The narrow strip of wood is either wholly uninjured or else
reveals a small crack down the centre. Externally it shows but
little brownness, and in a few years it becomes entirely covered
over b}' a callus.

In other cases trees (pines) that are struck b}' lightning
reveal externally the same form of injury, but in a few days
the entire cortex — with the exception of that on the collar,
the roots, and the upper part of the crown — dies and becomes
brown. Such trees generall}' wither up after an interval varying
from a few months to a }'ear or so, although the}- may remain
alive for four or five years, to die at the end of that period. In
some cases the electric current barks the tree and leaves the
stem almost naked, or it splits the stem longitudinally into
several parts, dismembering it almost entirely, and scattering
large splinters to a distance of one hundred yards. In certain
cases all that is left in the ground is a short stump.

It is onl}'' when the tree is perfectly dry, or possesses dr}'
branches or at least dr}' rotten wood, that the lightning sets it
on fire. Combustion does not follow in a fresh living tree.

So far no explanation is forthcoming to account for the death

304 DISEASES OF TREES

of the trees over considerable areas that have been affected by
hghtning, a state of things that I have several times observed
both in young and old pine woods. ^ In such cases it was
remarkable that death, instead of affecting the whole area
simultaneously, spread centrifugally and radially from a given
point, and frequently continued to carry off the trees for five
years or more. An investigation of the trees showed that only
one or a few examples revealed traces of lightning, but that
between the crown and the collar of such trees, and many others
in their vicinity, the cortex was dead. In an old pine wood the
dead bark hung loose from the boles, while the crowns retained
perfectly green foliage. In a younger wood about thirty years
of age I found three stems showing traces of lightning along
the margin of the devastated area which had been steadily
extending for five years previously. The first of these had died
within the past year, the second still possessed a green crown
although its cortex and bast had died between the heights of
one and a half and eight feet, while the third, in spite of the
lightning having detached a broad strip of cortex, was perfectly
healthy in all parts. I confess that in face of these observations
I am unable to offer an explanation of the action of the
lightning. The fact that trees struck by lightning sometimes
remain alive for five years is to be explained in the same way
as the frequent survival for several decades of pines that have
been girdled. The water and plant-food move upwards in
the wood, and the crown, utilizing the products of metabolism,
remains healthy, and forms new organs. Death occurs only
when the exposed wood of the bole has graduall}- dried up
to such an extent that water is unable to pass upwards in
sufficient quantity. That a tree scored by lightning may
remain perfectly healthy, while a neighbouring tree not so marked
may die, may possibly be explained by supposing that in the
former case the electric current was confined within narrow
limits, whereas in the latter it was distributed over the whole
surface, or throughout the entire cortex, of the stem.

^ R. Hartig, Zcitschrift fii)- Forsf- i/nd Jagdwcsc?z, 1876, pp. 330 cl scq.

THE DISEASES DESCRIBED IN THIS
VOLUME CLASSIFIED ACCORDING TO
THE PLANT, AND PART OF THE PLANT,
ATTACKED

The number placed after the name of a disease refers to the page in
the text-book where a description will be found.

Abies

1. The seedlings droop and die : PhytophtJiora oi/mivora, 58.

2. Young plants in the nursery become yellow or die, the stems
contracting suddenly close to the surface of the ground : Pestalozzia
Hartigii^ 136.

3. Young plants are enveloped by a brown fungus : Thelephora
iactniata, 35.

4. The leaves bear numerous columnar Kcidia on their under
surface : Melampsora Goeppertiana, 161.

5. The leaves display long sporogenous layers on their unde''
surface. These rupture and emit yellow spores : Ccro/na Abietis
pectifiatce, 184.

6. The leaves, whicn are deformed, are pale yellow, and bear
aecidia. The branches form witches' brooms : yEciditun elatitmin^ 179.

7. The leaves are yellowish brown, while, on the under side, the
mid-rib bears a black longitudinal ridge : Hysterimn nervisequium, 108.

8. The leaves are yellow, and remain attached to the branch by
being enveloped in white mycelial filaments : Trichosphcei-ia parasifico,
72.

9. The branch or stem shows a spheroidal swelling : Aicidiuni
elatmum, 179.

10. The branches bear mistletoe, or the stem shows perforations :
Viscuvi, 25.

X

3o6 CLASSIFIED LIST OF DISEASES

11. The cortex dies right round the branch or stem, and bears
black tubercles : Phoma abietina, 138.

12. The stem bears irregular or bracket-shaped sporophores which
show very fine pores : Polyporus Hartigii, 1 94.

13. The stem bears sporophores with large pores: Irametes Fitii,
191.

14. The stem bears tawny yellow cap-shaped sporophores, which
.spring from rhizomorphs : Agaricus melleus, 207.

15. The roots bear white sporophores : Trametes radidpej-da, 186.

16. The roots are attacked by rhizomorphs : Agaricus melleus, 207.

Acer

1. The seedlings show black blotches on the leaves or stem, and
may decay : Cercospora acerina, 135 ; Phytophthora omnivora, 58.

2. The leaves show white blotches : Erysiphe bicornis, 70 ; E.
Tulasfiei^ 70.

3. The leaves show black blotches : Rhytisma acerinum, 105.

4. In autumn the leaves show persistent green blotches, which
ultimately bear black spots : R. piaictatitui, 1 06.

5. The branches wither, while a transverse section of the wood
shows dark green blotches : Nectria cinnabarina, 96.

6. The branch or stem dies, while the cortex bears cinnabar-coloured
fungus bodies : JV. cinnabarina^ 96.

7. The stems of young plants contract suddenly above the roots :
Pestalozzia Harligii? 136.

8. The branches show canker-spots : Frost-canker, 293.

9. The branches bear mistletoe : Viscuvi, 25.

Acer platanoides

The branches die in spring, and show oblong fungus-bodies :
Septogloeuni Hartigiamim^ 141.

^sculus

The branches die, and bear cinnabar-coloured fungus-bodies on the
cortex : Nectria cinnabarina, 96.

Alnus

1. The leaves show yellow vesicular swellings : Exoascus flavus, 133.

2. The leaves show greyish white downy corrugations : E. epiphyllus,

133-

3. The cones show pocket-like outgrowths : E. alfiitorqims, 133.

4. The branches show canker-spots : Nectria ditissima, 91,

5. The wood shows red-rot : Polyporus sulphureus, 200.

6. The roots show fleshy outgrowths : Schinzia Ahii, 39.

CLASSIFIED LIST OF DISEASES 307

Alnus glutinosa

The leaves show vesicular corrugations : E. ainiforquus, 133.

Alnus incana

The branches bear witches' brooms : E. borealis, 133.

Alnus viridis

The branches wither, and black tubercles appear on the dead
cortex : Valsa oxy stoma, 151.

Berberis

The leaves show golden yellow blotches : Piurinia gramhiis, 155.

Betula

1. The leaves show small yellow fungus-bodies : Melampsora
hetnlina, 171.

2. The leaves show vesicular swellings : Exoascus carnea, E. Betuke^

3. The branches bear witches' brooms : Exoascus turgidus, 133.

4. The stem bears large bracket-shaped sporophores : Polyporus
befuli7ius, 206.

5. The stem bears brown crust-like sporophores : Polyporus Icevigatus,
206.

Brassica

The roots bear fleshy outgrowths : PlasmodiopJiora Brassicce, 39.

Carpinus

1. The leaves bear small golden yellow fungus-bodies : Melampsora
Carpini, 171.

2. The branches bear witches' brooms : Exoascus Carphii, 135.

3. Branches or stem show canker-spots : JSlectria dilissima, 91
Frost-canker, 293.

Castanea

The branches show prominent swellings, and bear a " mistletoe " :
Lorant/ms, 30.

Corylus

r. The leaves show small brown blotches : SphcErella, 88,

2, The leaves show white dusty blotches : Erysiphe guttata, 70.

3. The branches show canker-spots : Nectria ditissima, 91.

Crataegus

1. The leaves bear golden yellow swellings, which produce secidia :
Gyinnospora7igium clavariceforme, 158.

2. The leaves show white dusty blotches : Erysiphe guttata, 70.

3. The branches bear witches' brooms: Exoascus bullatus, 133.

X 2

3o8 CLASSIFIED LIST OF DISEASES

Cynanchum

The leaves show small yellow fungus-bodies : Crojiarthon asckpia-
deujH, 175.

Fagus

1. The seedlings show dark patches on the leaves and stem, and
decay or wither : Phytophthora onifiivora, 58.

2. The stem of young plants contracts suddenly close to the surface
of the ground, and the tree withers : Pestalozzia Hartigii, 136.

3. Young plants in the nursery are enveloped by a brown fungus :
Thelephora laciniaia, 35.

4. The leaves show white blotches : Erysiphe guttata., 70.

5. The leaves show brown blotches : Sphcerella Fagi, 88.

6. The cortex shows canker-spots : Nectria difissi??ia, 9 1 ; Frost-
canker, 293.

7. The cortex is covered with a white woolly substance : Chermes
fagi, 96.

8. The cortex shows pustular swellings : ilnd.

9. The cortex of branches is ruptured longitudinally : Lachmis
exsiccator, 96.

10. The cortex of the stem withers on the south side : Bark-
scorching or Sun-crack, 294.

11. The stem bears large bracket-like sporophores : Polyporus
fonientarms, 206.

12. The wood shows a verdigris-green colour: Peziza (srugijiosa,
224.

Fraxinus

The cortex shows canker-spots : Nectria ditissi/na, 91.

Gentiana

Gentiana asclepiadea shows yellow fungus-bodies : Cronarthim
asclepiadeuDi, 175.

Gleditschia
The branches bear mistletoe : Viscian, 25.

Gramineae

1. Culm and leaves show fungus-bodies, which are first yellow and
later brown : Pucci?iia graminis, 155.

2. The spikelets are covered with a sweetish secretion or produce
black fungus-bodies : Claviceps purpurea, 98.

3. The spikelets produce dark brown powder : Ustilago Carbo, 68.

Hyacintlius

The bulb becomes soft and slimy, and emits a repulsive s^iiell :
Bacterium, 37.

CLASSIFIED LIST OF DISEASES 309

Juglans

1. The branches bear mistletoe : Viscu/n, 25.

2. The stem bears sulphur-yellow sporophores. The wood shows
red-rot : Polyporus sulphureiis, 200.

Juniperus communis

1. Leaves and branches enveloped in dark brown mycelia : Herpo-
trichia fiigni, 76.

2. Branches show swellings which, in spring, produce abundant
yellow or brownish spores : Gymnospora?igiu)n cofiicum, 1573 G.davarice-
forme, 158; G.tremelloides^ 159.

3. Roots bear white sporophores : Tramefes radiciperda, 186.

Juniperus Oxyeedrus

Branches bear a " mistletoe " : Arceuthobium Oxycedri, 30.

Juniperus Sabinse

Branches show swellings which, in spring, produce abundant yellow
spores: Gyunwsporangium Sabince^ 158,

Laburnum

The cortex and branches die : Cucurbitaria Labtirni, 87.

Larix

1. The seedlings droop and wither : Phytophthora omnivora, 58.

2. The young trees die, and reveal mycelia on their roots : Rhizina
undulata, 123.

3. The leaves show yellow fungus-bodies : Melampsora Tremul(B,
164.

4. The leaves become brown, and show black fungus bodies :
Hysterium laricitiian, 117.

5. The cortex shows canker-spots : Peziza Willkominii^ 117.

6. The cortex, on its inner side, shows white mycelial sheets :
Agaricus me ileus, 207.

7. The cortex bears brown crust-like sporophores : Trametes Pint,
191.

8. The cortex bears large sulphur-yellow sporophores : Polyporus
sup/mreus, 200.

9. The cortex bears cap-like tawny yellow sporophores : Agaricus
melieus, 207.

10. The roots are dead, and show rhizomorphs : ibid.

11. The wood shows red-rot : Poiyporus ScJiweijiitzii, 198.

12. The wood is decayed, and marked by white blotches : Trauietes
Pifii, 191.

13. The wood shows red-rot and luxuriant white fungus-growths :
Poiyphorus suiphureus, 200.

3IO CLASSIFIED LIST OF DISEASES

Ledum

The leaves are marked by brown blotches, and show small yellow
fungus-bodies: Chrysomyxa Ledi. 179.

Medicago, see Trifolium

Picea

1. The seedlings droop soon after appearing : Phytophthora o/?inivora,
58 ; Nedria cuairbiiuia, 89.

2. Plants in the nursery become yellow and die, the stem being con-
tracted close above the surface of the ground : Pestalozzia Hartigii, 136.

3. Young plants, or the branches of older trees, are enveloped in
dark brown mycelia : Herpotrichia nigfa, 76.

4. Young plants are enveloped in the sporophore of a fungus :
Thelephora laciniata, 35.

5. Young and old trees die, their roots showing mycelia : RJiizimx
undulata, 123.

6. The leaves and branches wither in winter and spring : Frost,
291.

7. The leaves bear golden yellow vesicles : ChrysoJiiyxa Rhododendri,
177 ; C. Ledi, 179.

8. The leaves become yellow, and show golden yellow longitudinal
ridges on their under surface : Chrysoinyxa Abietis, 175

9. All the leaves of a young shoot are abnormally short, and rupture
on their four sides : yEcidium coriiscans, 183.

10. The leaves become red, and later yellowish brown. They either
show longitudinal black ridges, or fall prematurely : Hysterium macro-
sporutn, 109.

11. The branches die in May or June : Septoria parasitica, 143.

12. The scales of the cones show numerous round brown swellings
on their upper surface : Aicidiiim strobiIi7ium, 182.

13. The scales of the cone show two large tecidia on their lower
surface: ^cidijim amorum Piccce, 183.

14. The cortex shows dead patches beset with groups of red fungus-
bodies : Nedria Cucurbitula, 89.

15. The cortex in the lower part of the stem shows resinous exuda-
tion: Trametes radidperda, 186.

16. The cortex shows white mycelial sheets on its inner surface :
Agaricus melleus, 207.

17. The cortex shows evidences of injury by sun : Bark-scorching,
294.

18. The root is dead, and bears small yellowish white fungus-bodies,
or large white sporophores : Trametes radidperda, 186.

CLASSIFIED LIST OF DISEASES 311

1 9. The root shows red-rot and white mycelia : Folyporus vaporarius^
198.

20. The root is dead, and shows black mycelial strands which form
white enlargements between the cortex and wood : Agaricus melkus,
207.

21. Branch-wounds bear brown sporophores : Tra metes Phii^ 191 r
Polyporus Hartigii, 194.

22. Wounds bear large white sporophores : Polyporus borealis, 196.

23. The wood shows white-rot : Polyporus Hartigii, i()s^.

24. The wood shows white-rot. The pure white patches have usually
a black spot in the centre : Trametes radiciperda^ 186,

25. The wood shows white-rot, and contains numerous cavities :
Trametes Pi?ii, 191.

26. The wood shows white-rot, and crumbles down into very small
cubes : Polyporus borealis, 196.

27. The wood shows red-rot : Polyporus vaporarius, 198.

28. The wood shows dark brown blotches or cavities : Wound-rot,
236, 243.

29. The wood shows green-rot: Peziza aruginosa, 224.

Pinus Cembra

The roots show numerous Mycorhizce, 71.

Pinus montana

The branches with their leaves are enveloped and killed by dark
brown mycelia : Herpotrichia nigra, 77. See also the diseases, i, 6, 8^
10, 13, 16, 17, under Pinus sylvestris.

Pinus Strobus

1. The leaves die, and display black fungus-bodies : Hysterium
brachysporum, 117.

2. The cortex shows resinous exudation and golden yellow vesicles :
Peridermiuni Strobi, 175. See also diseases i, 4, 10, 13, 14, 16, 17,
under Pinus sylvestris.

Finns sylvestris

1. The seedlings droop and die: Phytophtho7-a omnivora, 58:
Nectria Cucurbitula, 89.

2. Seedlings and older plants show brown blotches, which afterwards
bear small black tubercles : Hysterium Pinastri, no.

3. Seedlings and older plants are entirely yellow and finally brown
or the discoloration spreads gradually back from the apex of the shoots
"Bhght," III.

312 CLASSIFIED LIST OF DISEASES

4. Young plants in their lower parts are enveloped in the brown
sporophores of a fungus : Thekphora laciniata, 35.

5. The leaves become suddenly brown in summer : " Frost-bhght,"
I II.

6. The leaves show^ golden yellow^ vesicles : Coleosporiiim Se?iedo?us,
C. Eiiphrasice, C. Ttissilagi?iis, 172,

7. The young shoots in the end of May show golden yellow spots
■on the cortex. These afterwards rupture, and the shoots either die or
become contorted : Melampsora Tremulce, 164.

8. The cortex shows golden yellow A^esicles filled with spores :
Teriderinhim Pmi, 172 ; CroJiartmm asclepiadeian, 175.

9. The cortex gradually dies, and shows resinous exudation :
ibid.

10. The cortex dies, and shows large white sheets of mycelium on its
inner surface : Agariais melleus^ 207.

11. Branch-wounds bear brown bracket-Uke sporophores: Trametes
Fini, 191.

12. Wounds bear large reddish brown cushion-like sporophores:
Poly poms Schweinitzii, 198.

13. The cortex close to the ground bears cap-like yellow sporophores :
Agariais vielleus, 207.

14. The cortex close to the ground bears white cushion-like sporo-
phores : Trametes radidperda, 186.

15. The cortex or wood close to the ground bears white porous
crust-like sporophores : Polyporus vaporarius, 198.

16. The roots are dead, and bear yellowish white cushion-like sporo-
phores : Trametes radiciperda^ 186.

17. The roots are dead, and show resinous exudation. Between the
wood and cortex white mycelial sheets and black mycelial strands are
found : Agaricus 7JieUeus, 207.

18. The roots are dead, and show white floccose mycelial strands :
Polyporus vaporarius., 198.

19. The roots show mycelial growths : Elaphomyces, 71.

20. The leading shoot or the branches die above a black mark from
which resin flows: Crojiartium asdepiadeum, 175; Peridermiuju Pi?ii,
172.

21. The wood shows white-rot, with numerous small round or oval
holes: Trametes Piiii^ \Q)\.

22. The wood shows red-rot, without much smell. Floccose mycelial
growths and strands are found : Polyporus vaporarius., 198.

23. The wood shows red-rot, and emits a very strong smell of turpen-
tine. Thin white mycelial incrustations are found in the cracks :
Polyporus Sdiweinitzii, 198.

CLASSIFIED LIST OF DISEASES 313

24. The wood shows holes, the branches bear mistletoe : Visciim, 25.

25. The wood (alburnum) shows a dark blue colour : Ceratostoma
pilifej'um^ 224.

26. Old and young trees die, the roots showing mycelia : Rhizina
jmdiilata., 123.

Platanus
The leaves and young shoots die, or the former become brown along
the ribs : Glaosporium ner-viseqiimm^ 140.

Populus

1. The leaves show small yellow blotches, which afterwards become
dark brown : Melampsora, 164.

2. The leaves show yellow vesicular swellings : Exoascus aureus,

135-

3. The branches bear mistletoe : Viscum, 25.

4. The flowers exhibit golden yellow much-enlarged ovaries :
Exoascus mireiis, 135.

Populus pyramidalis
The branch and twigs die : Didyinosphceria popiilijia, 104.

Prunus Cerasus

1. The leaves are crumpled, and frequently also blood-red in colour :
Exoascus IVtesnen, 132.

2. The leaves become prematurely yellow and die, and remain
attached to the tree during winter : Gnomonia erythrostoma, 88.

3. The branches form witches' brooms : Exoascus Wiesneri, 132.

4. The cortex bears brown sporophores : Polyporus igniarius, 201.

Prunus domestica

1. The flowers show yellowish red fleshy blotches : Poly stigma
rubrum, 97.

2. The fruit forms "pockets" : Exoascus Pruui, 131.

3. The branches form witches' brooms : Exoascus defortiians, 132.

4. The branches show black tuberous swellings : Plowrightia mor-
bosa, 102.

Prunus instititia
The branches form witches' brooms : Exoascus InstititicE, 133.

Prunus Padus

1. The fruit forms "pockets": Exoascus Pruni, 131.

2. The cortex shows canker-spots: Nectria ditissima, 91.

Prunus spinosa

1. The leaves show yellowish red fleshy blotches: Polystigvia
rubrum, 97.

2, The fruit forms "pockets " : Exoascus Prufii, 131,

314 CLASSIFIED LIST OF DISEASES

Pseudotsuga

I The young shoots die, and become brown : Botrytis Donglasii^ 130.
2. The branches bear a "mistletoe," and show witches' brooms:
Arceuihobhim Dotiglasii^ 30.

Pyrus communis

1. The leaves show yellow swellings, which produce ^cidia :
Gymnosporanghim SabincB, 158.

2. The leaves show vesicular swellings : Exoascus bullafus, 129.

3. The stem bears brown cushion-like or bracket-shaped sporo-
phores : Poly poms ignariits, 201.

4. The branches bear mistletoe : Visciun, 25.

Pyrus Malus

1. The leaves bear yellow swellings, which produce ascidia : Gyimio-
spora?2gh(m tremelloides, 159.

2. The branches show canker-spots: Nectria ditissi?iia, 91; Frost-
canker, 293.

3. The stem bears brown cushion-like or bracket-shaped sporo-
phores : Poly poms ig7iarius^ 201.

4. The branches bear mistletoe : Viscum, 25.

ftuercus

1. One- and two-year-old plants wither, and show mycelial strands
and black tubercles on their roots : Rosellinia querchia^ 78.

2. The leaves show vesicular swellings : Exoascus ccerulescetis, 135.

3. The leaves show round brown blotches : Sphcerella, 88.

4. The cortex shows canker-spots: Nectria ditissi?)ia, 91; Frost-
canker, 293.

5. The cortex of young oaks dies over large areas of the stem, and,
should the trees have survived, a callus forms along the margin of the
wound : Aglaospora Taleola, 99.

6. The wood is dry, and shows red-rot : Polypoms sulp/inreus, 200 ;
FistuHna /lepatica, 206 ; Dc^dalea quercbia^ 206.

7. The wood shows white-rot: Polypoms ignarius, 201; Hydman
diversidens, 202.

8. The wood shows red-rot with white stripes : Stereuvi hirsuiian,
205.

9. The wood shows red-rot with white blotches and cavities :
Thelepho7-a Perdix, 203.

10. The wood shows irregular oblong patches of red-, white-, and
yellow- rot : Polypoms dryadeiis, 201.

11. The branches bear a deciduous "mistletoe" and prominent
swellings : Loraiithus europceiis, 30.

CLASSIFIED LIST OF DISEASES 315

Rhamuus

The leaves and shoots show golden yellow swellings : Puccinia
coro7iata^ 156.

Rhododendron

1. The leaves bear large galls : Exobasidhim Vaccinii, 185.

2. The leaves show brown blotches : Chrysomyxa Rhododendri^ 177.

Eibes

The leaves show yellow swellings : Melampsora Hartigii, 170.

Eobinia

The wood shows red-rot. Sulphur-yellow sporophores appear upon
the cortex : Polyporiis sulp/iureus, 200.

Salix

1. The leaves show small yellow fungus-bodies, which become
brown in autumn: Melampsora sa/ichia, 170.

2. The leaves show large black thickened blotches : Rhytisma
salicmian, 107.

3. The leaves show white dusty blotches : Erysiphe adiinca, 70.

4. The wood shows red-rot, and sulphur-yellow sporophores appear
upon the surface of the stem : Polyporiis sulpliureiis, 200.

Senecio

Leaves and stem show reddish yellow fungus-bodies : Cokospormm
Sefiedonis, 172.

Solanum

1. Leaves and stem show black blotches : Phytophthora mfestans, 64.

2. The tubers show disease : P. infestans^ 64 ; Bacterium, 38.

Sorbus Aria

The leaves show fungus-bodies, which produce secidia : Gymnospor-
angium tretnelloides, 159.

Sorbus aucuparia

1. The leaves show large golden yellow blotches, which produce
secidia: Gymnosporangium coniaan, 157.

2. The leaves show small yellow fungus-bodies : Melampsora Sorln,

171-

3. The cortex shows dead patches, which bear small fungus-bodies :

Ciicurbitaria Sorbi, 88.

4. The branches bear mistletoe: Viscum, 25.

Sorbus torminalis

The leaves show yellow blotches, which bear cecidia : Gymjiosporan-
gium coniaan, 157.

3i6 CLASSIFIED LIST OF DISEASES

Tilia

1, The twigs and branches die, and produce cinnabar-coloured
fungus-bodies : Nedria ciiutabarma, 96.

2. The cortex shows canker-spots : Nedria ditissima, 91.

Trifolium and Lucerne

1. Roots attacked by violet Rhizodonice, 82.

2. Close to the root-collar white mycelia and black resting-mycelia
may be detected : Peziza ciboriodes, 130.

Tsuga

The leaves and shoots enveloped in white mycelia, the former
dying: Trichosphceria parasitica, 72.

Ulmus

The leaves show vesicular blotches : Exoasctis U/mi, 135.

Vaccinium Myrtillus

1. The young shoots die and the berries shrivel up : Sderotinia
baccarum, 130.

2. The leaves show small brown blotches : MeIa?npsora Vacdnii,
171.

Vaccinium Vitis-idaea

1. The stem becomes much elongated, and attains the thickness of
a goose-quill : Melampsora Goeppertiaiia, 161.

2. Leaves, flowers, and stem are swollen, and dusted with white
spores: Exobasidium Vacd?iii, 185.

3. Leaves, fruit, and young shoots become brown : Sderotinia
Vacdnii, 130.

Vitis

1. Leaves, stem, and berries show mildew : Oidiuvi Tuckeri, 70.

2. The leaves show yellow blotches above and white blotches
below : Peronospora viticola, 65.

3. The berries wither : Physalospora Bidwellii, 103.

4. The berries are pale in colour, and their stalks decay : Coiiiothy-
riii/ii diplodiella, 103.

5. The roots are killed by Rhizoctonice and Rhizomorphs : Demato-
phora 7iecatrix, 82.

6. All parts of the plant show brown or black blotches : Gloeosporiuvi
ainpelophagum, 104.

Zea
Leaves, flowers, and stem show black vesicles filled with spores :
Ustilago Maydis, 68.

INDEX

INDEX

Abies pectinata, see Fir, Silver
Abnormal predisposition to disease,

9 . . .

Acclimatization of exotics, 2S8

Acer, Dematophora necatrix on, 82

Erysiphe bicornis on, 70

Nectria cinnabarina on, 96
ditissima on, 92

Rhytisma acerinum on, 105
punctata on, 106

campestre, Septoglceum Hartigi-
anum on, 141

platanoides, Mildew on, 70

Seedlings, Disease of, 58
Acorns, Influence of size of, on growth

22
^cidium abietinum, 49, 177

asperifolii, 156

Berberidis, 155

Clematitis, 166

columnare, 49, 161, 184

conorum Piceee, 183

coruscans, 183

elatinum, 51, 179, 195

pencillatum, 1 59

Rhamni, i 56

strobilinum, 182
Agaricus adiposus, 180

melleus, 47, 48, 50, 83, 186, 187,
207, 245
Rhizomorphs of, 43
Age in relation to disease, 7,8, 11
Aglaospora Taleola, 99
Air in soil. Circulation of, 275

wood, 53
Alder, see also Alnus

Nectria ditissima on, 92

New parasite of, 147

Polyporus on, 200

Stigmatea on, 88

Witches' brooms on, 133
Alder-roots, Disease of, 39
Algal fungi, 57
Almond, see Amygdalus

Alnus, see also Alder

Erysiphe guttata on, 70
glutinosa, Exoascus alnitorquus

on, 133
E. epiphyllus on, 133
flavus on, 133
incana, Exoascus alnitorquus on,

133

E. borealis on, 133
epiphyllus on, 133
flavus on, 133
viridis, Valsa oxystoma on, 151
Alpine Rose Apples, 186
Alternation of generations, 154
Amygdalus, Polystigma fulvum on, 98
communis, Exoascus deformans
on, 132
Annuals, Death of, 6
Antheridia of Peronosporeas, 58
Anthracosis of Vine, 104
Anthusa officinalis, /Ecidium asperi-
folii on, 156
Ants, 203, 245
Aphidas on beech, 96
Apothecium of Discomycetes, 105
Apple, see also Pyrus
Apple-trees, Nectria ditissima on, 92
Probable bacterial disease of,
38
Apricot, Valsa on, 88
Arceuthobium Douglasii, 30

Oxycedri, 30
Arona, Rccstelia cornuta on, 1 58
Arsenic in smoke, 301
Arvicola, Barking by, 243
Asci, 69
Asclepius Vincetoxicum, Cronartium

on, 175
Ascomyces Betulae, 135
Ccerulescens, 135
Tosquinetii, 133
Ascomycetes, 57, 69, 153, 155
Imperfectly known, 135
Spore-formation in, 44

320

INDEX

A-sexual generation, 44
Ash, Erysiphe guttata on, 70
Nectria ditissima on, 92
Seedlings, Disease of, 58
Asparagus, Puccinia on, 1 56
Aspens and Pine Twist, Connection

between, 9
Atmospheric influences, Injuries due

to, 282
Autoecious parasites, 154, 176

BaciUus Olea tubeixulosis, 38
Bacteria, 37
Bacteriosis, 37
Bacterium Hyacinthi, 37
Barberry, Parasite of the, 25, 155

in relation to wheat-rust, 9, 49,

155
Bark, 226
" Bark-drought," 295

Scorching by sun, 268, 269, 283,
294
Barking by Cattle, &c., 244

Game, 241
Barley, Puccinia striteformis on, 156

Ustilago Carbo on, 68
Bary's, de, Work, Value of, 3
Basidia, Abscission of spores by, 44
Basidiomycetes, 57, 153
Beans, Dematophora necatrix on, 83
Beech, Dematophora necatrix on, 83

Erysiphe guttata on, 70

Green-rot of, 42

Hydnum diversidens on, 202

Nectria ditissima on, 92

Peziza aeruginosa on, 224

Polyporus fomentarius on, 206

Spha^rella on, 88

Trametes radiciperda on, 186

Tuber on, 71

Wood-balls, or Spheroblasts, on,

239

Seedlings, Disease of, 58
Beef-steak fungus, 206
Beet, Dematophora necatrix on, 83

Peziza Sclerotiorum on, 130
Beetles in wood and bark, 219
Betula, Erysiphe guttata on, "]"]

Exoascus on, 133

Melampsora on, 171

New parasite of, 147

Peziza aeruginosa on, 224

Polyporus on, 206

Trametes radiciperda on, 186
Birch, see Betula
Bird Cherry, see Prunus Padus

"resin," 175

Bird's Nest, Yellow, see Monotropa

Hypopitys
Black knot, 103

Rot of Vine, 103
Blanc de racines, 82
Blanquet, 82
Blight of apple- and pear-trees, 38

pines, III
Blister of larch, 117

pine, 172
Blotches, Disease, 88
Borago, yEcidium asperifolii on, 1 56
Botrytis cinerea, 130

Douglasii, 130
Bramble, Parasite of the, 25

rust, 156
Brands, 68
Brood-cell, 44

Brownness of conifer leaves, 1 1 1
Buckwheat, see Fagopyrum
Buds, Adventitious, 238

Preventitious, 238
Bunt, 68
Byssothecium circinnans, 82

Cabbages, Club-root of, 39
Casoma Abietis pectinat^e, 184
Evonymi, 171
Laricis, 166, 169
Mercurialis, 166
pinitorquum, 166

in regard to moisture, 46
Ribesii, 171
Calluna, Dodder on, 34
Callus, Formation of, 226, 229

on the stools of conifers, 262
Calyptospora without effect on old
tissues, 51

Goeppertiana, 161
" Cambium, Wound-," 231
Canker due to frost, 293

Nectria ditissima, 92
soil, 129
on larch, 117
pine, 172
silver fir, 179
Cap fungi, 1 84
Carbonic Acid gas. Injurious effects

of, 281
Carpinus, see Hornbeam
Carrot, Peziza Sclerotiorum on, 130
Castanea vesca, Loranthus europa>us
on, 30

Rhizina undulata on, 126
Caterpillars, Surface, 147
Ceratostoma piliferum, 224

INDEX

Cercospora acerina, 135

a facultative parasite, 47
Resting-mycelium of, 43
Cereals, Puccinia coronata on, 156

Rust of, 155
Champignon blanc, 82
Chermes abietis, 144
Fagi, 96

Laricis, 118, 169
Cherry, Black-knot of, 103
Gnomon i a on, 88
Valsa on, 88
Bird, see Primus Padus
Wild, see Prunus avium
Chestnut, Horse, Nectria cinnabarina
on, 96

Spanish, see Castanea vesc^
Chlorine, Effects of, on vegetation,

302
Chrysomyxa, 175

abietis, 13, 153, 175, 177
Ledi, 49, 179
Rhododendri, 9, 49, 177
Chytridiaceae, 57

Cinchona bark, Cultivation of, 230
Clarkia seedlings. Disease of, 58
Claviceps purpurea, 98

Sclerotia of, 43
Clematis vitalba, Ca;oma on, 166
Climatic predisposition to disease,

10
Clover, Dodder on, 34

Peziza ciborioides on, 130
Red, Orobanche minor on, 25
Club-root, 39
Coal-brand, 68

Smoke, 300
Cockchafer grubs, 147, 264
Coleophora laricella, 117
Coleosporium Euphrasia^, 172
Senecionis, 153, 172
Tussilaginis, 172
Conidium, 45

Conifers, Agaricus melleus on, 207
Hysterimii on, 107
Mycelium on the roots of, 71
Polyporus Hartigii on, 194

vaporarius on, 198
Rhizina undulata on, 123
Seedlings, Disease of, 58
Withering of the leaves of, 112
Coniothyrium diplodiella, 103
Coppicing, 261
Cork, 226

" Woimd," 227
Cortex, 225
Roots. 26

Corticum amorphum, 117
Corylus, see Hazel
Cow-wheat, see Melamp^rum
Cowberry, see Vaccinium
Cracks, Frost, 284

Sun, 283, 294, 297
Crataegus, Erysiphe guttata on, 70

Exoascus bullatus on, 133

RjEstelia lacerata on, 1 58

Witches' brooms on, 133
Crickets, 147
Cronartium, 172

asclepiadeum, 175 * f '

rfbic/la, 175 -• ' *

Crucifers, white-rust of, 66
Cryptogams, 35
Cryptorhynchus lapathi, 151
Cucurbitaria Laburni, 89

morbosa, 102

Sorbi, 88
Cupressinoxylon, Agaricus on, 207
Cupuliferje, Mycelium on roots of, 71
Cuscuta Epilinum, 34

Epithymum, 34

eiu'opaea, 34
Cuscutea;, 33, 34
Cynips, 186
Cystopus candidus, 66
Cvtisus Laburnum, Cucurbitaria on,
'^1

Deedalea quercina, 206

Damping off of seedlings known to

early writers, i
Deadening material, 217
Death due to external causes, 7
frost, 2S7
internal causes, 6
of animals, 6

plants, cause of, 6
Natural and accidental, 6
Natural, discussed, 6
Debility of old age as a factor of

disease, 7, 8, 11
Deer, Fallow, Barking by, 241
Red, „ ' 241

Roe, „ 241 •

Defoliation by insects, 268
Demarcation, Line of, between scion

and stock, 267
Dematophora necatrix, 43, 82

an example of mycelial infection,
48
Development dependent on variation,

5
Didymosphaeria populina, 104

Y

INDEX

^

Discomycetes, 69, 105

Protection of sporophores of,
against drought, 45
Disease-blotches, 88
Disease, Causes of, 4, 20

determined by two factors, 8, 9

Investigation of, 16

and sickliness distinguished, 5
Diseases classified, 8

due to soil, 270
Dodder, see Cuscuta
Dogwood, Nectria ditissima on, 92
Dormant eyes, 239
Draining, Effects of excessive, on

alders, 270
Drawn shoots, 298
Drought, Effects of, on cereals, 272

Leaves of conifers injured by, 1 1 1

of Bark, 294
Dry-rot, 214

fungus, 219

see also Alerulius lacrymans
Duramen, 33, 44
Dust-brand, 68

Echium, ^cidium asperifolii on, 156

Egg-spores of Peronosporese, 58

Elsagncce, Tubercles on the roots of, 39

Elaphomyces granulatus, 71

Elm, Exoascus on, 135

Endophyte defined, 42

Endophytes, Mode of attack of, 50

Engrafting, 228

Entomology, Forest, an old study, 2

Entomophthoreee, 57

Enzyme, 1 1, 50

Epicormic branches, 238, 253, 271

Epidermis, 225

Epiphyte defined, 42

Epiphytes, Mode of attack of, 50

Ergot, see Claviceps purpurea

Erysiphe, see also Mildew

Epiphytic character of, 42

adunca, 70

bicornis, 70

guttata, 70

pannosa, 70

Tuiasnei, 70
Erysiphe^, 69, 70
Etiolation, 298

Euphrasia, a partial parasite, 24
Even-aged woods specially liable to

disease, i
Evonymus, C^eoma on, 171
Exoascus, 131

alnitorquus, 133

aureus, 135

Exoascus Betulce, 135

borealis, 133

buUatus, 133

carnea, 135

Carpini, 135

CcCrulescens, 135 »•

deformans, 132

epiphyllus, 133

flavus, 133

Instititias, 133

Primi, 131

Sadebeckii, 133

turgidus, 133

Ulmi, 135

Wiesneri. 132
Exobasidium \^accinii, 185
Exotics, Acclimatization of, 288
Experiments in infection, 17, iS, 19,

20
Eye-bright, a partial parasite, 24

Factories, Refuse of, 281
Facultative parasites, 47

saprophytes. 47
Fagopyrum seedlings, Disease of, 58
Fagus, see Beech
Felling in summer and winter, 214
Ferments exuded by parasites, 50
Figures carved in bark, 246
Filaments, Truncated, of Erysiphe, 69
Fir, Douglas, as a protection against
pine-blight, 116

Botrytis on, 130
in relation to drought, 12
Rhizina undulata on, 125
Scotch, see Pinus sylvestris
Silver, ^-Ecidium columnare on,
161

elatinum on, 179
Ca^oma on, 1 84
Columnar rust of, 161, 184
Hysterium macrosporum on, 109

nervisequium on, 108
Nectria Cucurbitula on, 89
Pestalozzia Hartigii on, 136
Phoma abietina on, 138
Rhizina undulata on, 125
Trichospha.ria parasitica on, 72
in connection with adventitious
buds, 262
Fire, Effects of. 300
Fistulina hepatica. 206
Flower-pots, Failure of plants in glazed.

279
Fly wood, 205
Frank's work, 4
Fraxinus, see Ash

INDEX

Frost, Action of, 282
Causes of, 284
Death due to, 287
Leaves of conifers injured by, 112
Shedding of leaves owing to, 286
Transplanting favours injury by,

I4« 15
Frost-beds, 10

canker, 293
cracks, 284
"Rib," 285
Fruit - trees, Dematophora necatrix

on, 82
Fungi, 40

Biology of, 45
Classification of, 57
Heat requirements of, 46
Importance of moisture for, 46
may attack uninjured plants, 50
enter only through a wound, 50
Fungus, Beef-steak, 206

House, see Merulius lacrymans
Fusicladium Tremulas, 105
Fusidium, 141

candidum, 94

Gales, Damage due to, 299
Galium, Dodder on, 34
Game, Barking by, 241, 249
Gas, Coal, Effects of, 28 1
Gastropacha pini, 218
Genista, Dodder on, 34
Germ -pore, 159

tube, 40
Germination of seed, 279
Glceosporium ampelophagum, 104

nervisequium, 140
Gnomonia erythrostoma, 88
Gonidia of Peronospore^e, 57
Gonidium defined, 45
Grafting, 265

Wax as a dressing for wounds, 260
Gramineae, Ergot on, 98

Rust of, 155
Grape, see Vine

Disease, 70
Grapholitha pactolana, 89
Grasses, see Graminea;
Green-rot, 42, 224
Growth-borer, Pressler's, 18

in height, how limited, 7
Gymnoasce£E, 131
Gymnosporangium, 51, 157

clavariteforme, 158

conicum (Juniperum), 157

Sabin^e (fuscum), 158

tremelloides, 1 59

Hail, Effects of, 299
may predispose to disease, 15, 118,
299
Hallier's early work, 4
Hardening of trees, 283
Hares, Barking by, 241

in regard to potato disease, 65
Hartig's, R., chief works, 4
Haustoria of fungi, 42

PeronosporejE, 57
on the roots of Phanerogams,
24, 34
Hawthorn, see Crataegus
Hazel, Dodder on, 34

Erysiphe guttata on, 70

Nectria ditissima on, 92

Sphasrella on, 88
Healing in general, 225
Heat-requirements of fungi, 46
Height-growth, how limited, 7
Helotium Willkommii, 117
Hemp, Parasite of, 25
Heredity in relation to disease, 15, 16
Herpotrichia, an example of mycelial
infection, 47

nigra, 76
Hetercecious fungi, 49, 154, 176
Honey Agaric, 207

Dew, 98
Honeysuckle, see Lonicera
Hop, see Humulus
Hornbeam, Exoascus on, 135

Melampsora on, 171

Nectria ditissima on, 92
Hornbeams, Fissures in the cortex of,

272
Host, Watery condition of, favourable
to parasites, 13

Active growth of, unfavourable to
parasites, il
House-fungus, see Merulius lacrymans
Humulus, Dodder on, 34
Hyacinths, Hyphomyces on, 38

Bacteriosis of, 37
Hydnum diversidens, 202, 258
Mycelial growths of, 42
Hymenomycetes, 184

Klycelial growths of, 42
Hypha;, see also Mycelium

action on calcium oxalate, 52

Characteristic action of, 52

Septate, 40
Hyphomyces on hyacinths, 38
Hypoderma, 107
Hysterium, 107

Effects of iodine on, 42

resemblance to Rhytisma, 106

Y 2

324

INDEX

Hysterium brachysporum, 117
laricinum, 1 17
macrosporum, 51, 109, 177
nervisequium, loS
Pinastri, 1 10

Immersion in water, Effects of, on

timber, 214, 215
Individual predisposition to disease, 12
resistance to disease, S
rate of growth, 22
Infection, Animal agency in, 48
experiments, 17 — 20, 120
by mycelium, 47, 120
spores, 48, 49
Injuries due to fire, 300

Phanerogams, 23
plants, 22

precipitations and gales, 299
Mechanical, 299
Insects, Effects of defoliation by, 218,
268

may predispose to disease,! 5,1 17
Intercellular growth of endophytes, 42
Intermediary growth, 26, 238

tissue, 228, 266
Intracellular growth of endophytes, 42
Ivy, Orobanche on, 25

Juniperus, Gymnosporangium on, 157
Sabina; on, 158
Herpotrichia nigra on, 76
communis, Gymnosporangium
clavariaeforme on, 158
conicum on, 157
tremelloides on, 1 59
Oxycedrus, Arceuthobium on, 30

Knots, 250

Kiihn's contributions to plant-path-
ology, 3

Laburnum, see Cytisus Laburnum
Lachnus exsiccator, 96
Larch, Cteoma on, 166, 169

Hysterium on, 117

Polyporus on, 199, 200

Rhizina undulata on, 125

Aphis, 118

Blister, 117

Disease, 117

in relation to moisture, 46
pure woods, 122
Larix europjea, see Larch
Lathrjea, a partial parasite, 24
Lead in smoke, 301
Leaders, Double, Removal of, 261
Leaf-Cast, 113

Leaves, Natural shedding of, 225
Premature withering of, 297
Shedding of, owing to frost, 2S6
Ledum palustre, Chrysomyxa on, 179
Leguminosie, Tubercles on roots of, 39
Letters carved in bark, 246
Lichens on trees, 35
Liebig's discoveries erroneously ap-
plied, 2
Life, Prolongation of, by slips, 7
Light, Effects of excessive, 298

restricted, 294, 298
" Lightening " woods. Effects of, 274
Lightning, Effects of, 302
Lime, Nectria cinnabarina on, 96
ditissima on, 92
Sphccrella on, 88
Limits of this treatise, 5
Linum usitatissimum. Dodder on, 34
Liparis monacha, 218
Litter, Consequences of removing,

from a wood, 5, 270
Local predisposition to disease, 9
Lonicera Periclymenum, Damage done
by, 23, 24

Erysiphe guttata on, 70
Loranthacea;, Partial parasitism of, 25
Loranthus europasus, 25, 30, 31
Louse Wort, Partial parasitism of, 23
Lucerne, Dodder on, 34

Orobanche rubens on, 25
Rhizoctonia violacea on, 82

Maize, Ustilago on, 68

Mai nero, 82

Malformation, Difficulty of defining a, 5

Malformations induced by fungi, 51

Maple, see Acer

Maple, Norway, see Acer platanoides

Meadow grasses, Ustilago Carbo on, 68

Medullary rays contain living cells, 46

Melampsora Arias, 171

betulina, 171

Caprearum, 171

Carpini, 171

epitea, 171

Goeppertiana, 49, 161, 184

Hartigii, 170

mixta, 171

Padi, 171

populina, 165

salicina, 170

Sorbi, 171

Tremula:, 164
Laricis, 169
pinitorquum, 9, 12, 166

Vaccinii, 171

INDEX

'■S

Melampyrum arvense, a partial para-
site, 24.
Merulius lacrymans, 19S, 216, 219

Mycelial growths of, 42
Mice, Barking by, 243, 249, 300

injuring roots, 264
Micella, 287
Micrococcus, 12S
Mildew, see also Erysiphe

Epiphytic character of, 42

of Vine, 65
Millet-brand, 68
Mistletoe, Common. 25—30

Oak, 30
Mites, on Black Austrian pine, 140
Mixed woods in relation to disease,

56
Mock plums, 131
Moisture in relation to fungus-growth,

46
Monosticha oxystoma, 151
Monotropa Hypopitys, Doubtful para-
sitism of, 25
Monstrosity, Difficulty of defining a, 5
Morbo bianco, 82
Moth, Pine Beauty, 175

Nun, 218, 294
Moth-wither, 175
Mus sylvaticus, Barking by. 243
Mycelial nest, 1S9
Mycelium, see also Hyphas

of fungi, 40

Cell-sap in the, 40

Oil or fat in the, 40

Resting, 43

Strandlike, 43
Mycorhiza, 71
Myxomycetes, 39

Nectria, 89, 150, 260

Facultative parasitism of, 47

cinnabarina, 96

Cucurbitula, 89

ditissima, 91, 299

the possible cause of "blight,''
38
Normal predisposition to disease, 9
Norway maple, see Acer platanoides
Nostoc communis, 1 59

Oak, see also Ouercus

Aglaospora Taleola on, 99
Daedalea on, 206
Dematophora necatrix on, 82
Erysiphe guttata on, 70
Exoascus cajrulescens on, 135

Oak, Green-rot on, 42

Hydnum diversidens on, ?02
Nectria ditissima on, 91
Peziza aeruginosa on, 224
Polyporus dryadeus on. 201

fomentarius on, 206

igniarius on, 201

sulphureus on, 200
Rosellinia on, 78
Sphasrella on, 88
Stereum hirsutum on, 205
Thelephora Perdix on, 203
Tuber on, 71
Oaks, Predisposition of, to top-drought,

14

Rupturing of the cortex of, 273
Oats, Puccinia coronata on, 156

Ustilago Carbo on, 68
Obligative parasites, 47
Occlusion of wounds, 229
Oidium Tuckeri, 70
Olive, Bacterial disease of, 38
Oogonia of Peronosporeae, 58
Oospores, Vitality of, 45

of Peronosporea;, 58
Orchidacea.-, Parasitism of, 25
Organisms, Low, in relation to death, 6
OrobanchacecC, true parasites, 25
Orobanche, Parasitism of species of,

25
Outgrowths on Alder-roots, 39

Paraphyses, 108

Parasite, Definition of the term, 46

Difficulty of defining a, 23
Parasites, Facultative, 46

Obligative, 46

Partial, 24

Pseudo, amongst cryptogams, 35
Parenchymatous cells scarce in wood,

46
Partridge wood, 203
Pathology, Vegetable, Development of,

I
Pear, see also Pyrus

Erysiphe guttata on, 70

Polyporus sulphureus on, 200

Probable bacterial disease of, 38

Exoascus bullatus on, 133

Stigmatea on, 88
Pedicularis, a partial parasite, 24
Perennials, Partial death of, eachvear,

6
Periderm, 225
Peridermium Cornui, 175

elatinum, 179

oblongisporium, 172

326

INDEX

Peridermium Pini, 172, 175

in regard to turpentine, 51
acicola, 172
corticola, 172
Strobi, 175
Peridium of Uredineaa, 153
Perithecium of Pyrenomycetes, 72
Peronospora Sempervivi, 58

viticola, 65
Peronosporese, 57
Persica vulgaris, Exoascus deformans

on, 132
Pestalozzia Hartigii, 136
Peziza aeruginosa, 42, 224
calycina, 117, 139
ciborioides, 130
Fuckeliana, 130
Sclerotiorum, 130
Willkommii, 117, 299

in regard to moisture, 46
Pezizje, 1 17
Phacidea;, 105

Phanerogams, Injuries due to, 23
Phelloderm, 226
Phellogen, 226
Phoma abietina, 138
Phragmidium incrassatum, 1 56
Rubi Idfea, 156
subcorticum, 156
Phycis abietella, 175
Phycomycetes, 57

Formation of spores by, 44
Phyllactinia, 70
Phylloxera vestatrix, 83
Physalopsora Bidwellii, 103
Phytophthora Fagi, 58
infestans, 36, 64
omnivora, 58

a facultative saprophyte, 47
its action on starch, 52
its manner of spreading, 49
vitality of oospores of, 45
Picea, see also Spruce.

Menziesii, Septoria parasitica on,

146
Sitkaensis, Rhizina undulata on,
125
Pileus, 35

Pine, Dematophora necatrix on, 82
Elaphomyces granulatus on, 71
Hysterium pinastri on, no
Nectria Cucurbitula on, 89
New parasite of, 147
Rosette shoots of, 240
Black Austrian, Disease of, 140
-Mountain, Herpotrichia nigra on,
76

Pine, Scotch, see Pinus sylvestris
Weymouth, see Pinus Strobus
Beauty moth, 175
leaf blight, 1 1 1
twist, 166

in regard to aspens, 9
moisture, 46
Pinus halepensis. Bacterial disease of,

Gymnosporangium Sabins on,

rigida in regard to stool-shoots,

262
Strobus, Bark-drought of, 295
Hysterium brachysporum on,

Peridermium on, 175
Polyporus Schweinitzii on, 198
Restocking diseased areas with,

116
Rhizina undulata on, 125
Withering of the leaves of,
II t
sylvestris, see also Pine

Peridermium Cornui on, 175
Polyporus Schweinitzii on,
198
Plant-food in soil, 270
Planting, Deep, 278
Plants, Importance of rejecting weak,
22

Injuries due to, 20
Plasmodiophora Alni, 39

BrassicK, 39
Plasmolysis, 288
Platanus, Glceosporium nervisequium

on, 140
Plowrightia morbosa, 102
Plum, see also Prunus
Black-knot of, 103
Plums, ]\Iock, Pocket, or Starved,

131
Poa pratensis. Bunt on, 68
Pocket plums, 131
Poisons, Plant, 279, 301
Polyporei, Preventive measures

against, 206
' Polyporus betulinus, 206 •
borealis, 42, 55, 196
dryadeus, 201 <
^' fomentarius, 206
fulvus, 194 .,
Hartigii, 180, 194
v> igniarius, 51, 201 >,
l^evigatus, 206
mollis, 198
Schweinitzii, 53, 56, 198

INDEX

327

^ Polyporus sulphureus, 42, 52, 53,
200 y

vaporarius, 42, 19S, 199, 213
Polystignia fulvum, 98
ochraceum, 98
rubrum, 97
Poplar, see also Populus

Lombardy,Didymosphi'eria 011,104
Populus, Dodder on, 34

Erysiphe adunca on, 70
alba, Exoascus aureus on, 135
nigra, „ „ 135

tremula, „ „ 135

Potato disease, 64

Potatoes, Dematophora necatrix on,
82

Engrafting, 267
Reserve materials in, 40
Resistance of, to disease, 12
Pourridie de la Vigne, 82
Pourriture, 82
Predisposition to disease, 8
Abnormal, 9, i 5
Climatic, 10
Individual, 12, 13
Induced by hail, 15

conditions of growth, 14
insects, i 5
soil, 10
Local, 9
Normal, 9
Seasonal, 11
Temporary, 10
to frost, 14
Pressler's growth-borer, 18
Preventitious buds, 238
Preventive measures against parasites,

54
Progress, Organic, depends on varia-
tion, 5
Promycelium of smut-spores, 66
Pruning, 249

of roots, 264
Prunus, Polystignia rubrum on, 97
avium, Agaricus on, 207
Exoascus deformans on, 132
Polystignia ochraceimi, 98
Cerasus, E. deformans on, 132
Chamaecerasus, ., 132

domestica, Agaricus on, 207
Exoascus deformans on, 132
Pruni on, 131
instititia, Exoascus on, 133
Padus, „ Pruni on, 131

Melampsora on, 171
Nectria ditissima on, 91
Polystigma fulvum on, 98

Prunus spinosa. Dodder on, 34
Exoascus Pruni on, 131
Polystigma rubrum on, 98
Valsa on, 88

Pseudo-parasites amongst cryptogams,

35
Pseudotsuga Douglasii, see Fir,

Douglas
Puccinia Asparagi, i 56

coronata, 156

graminis, 155

straminis, 1 56

striieformis, 156
"Pugging," 217
Pure woods specially liable to disease,

I, II
Pycnidium of Cucurbitaria, 88
Pyrenomycetes, 69, 72
Pyrus, see also Apple and Pear

R^estelia cancellata on, 158
Pythium de Baryanum, 66

(^uercus, see also Oak

Cerris, Loranthus on, 31
Quickens, see Triticum repens
()uinine, 230

Rabbits, Barking by, 241
Red-rot of birch, 206

spruce known to early writers,
I
Trametes radiciperda, a cause
of, 186
"stripe," 215
Rejuvenescence, Annual, of trees, 7
Remedial measures against parasites,

Reserve materials m regard to prun-
ing, 260
Resin-ducts, 232

tlux, 210

glut, 210

leader, 175

top, 175
Resinous degeneration, Early mention

of, I

saturation of wood, -234
Resistance to disease. Individual, 7
Resting-myceliuni, 43
Rhaninus, ^Ecidium on, 156
Rhinantheje as partial parasites,

Rhinanthus Crista-galli, a partial para-
site, 24
Rhizina undulata, 123
Rhizoctonia violacea, 82

328

INDEX

Rhizoctoniae, 43, 48, 78
Rhizoids, 26
Rhizomorphs, 43, 48
Rhododendron, Chrysomyxa on. 177
Rhododendrons and spruce-leaf blister,

9

Rhytisma acerinum, 70, 105

punctatum, 106

salicinum, 107
Ribes, Caeoma on, 171
Robinia, Polyporus sulphureus on, 200

seedlings, Disease of, 58
Roesleria hypog^ea, 83
Rsestelia cancellata, 158

cornuta, 1 58

lacerata, 158
Root-fungus of conifers, 123

rot of vine, 82

suckers, 241
Roots, adventitious, 240, 264, 279

Eftects of heaping earth on, 278

Injuries to, 264

Natural engrafting of, 262
Rose, ]\Iildew of, 70

Rust of, ■ 1 56
Rosellina quercina, 78

an example of mycelial infection,

48
Effect of iodine on, 42
in relation to water, 1 2
Mode of attack of, 50
Sclerotia of, 43
Rosette shoots on the pine, 240
Rot, Dry, 214

Green, 42, 224

Red, I, 186, 244

Root, 276

White, 195

Wound, 236, 244, 247, 257, 262,

295
Rubus cassius, Phragmidium incrassa-
tum on, 1 56

fruticosus, Phragmidium incrassa-

tum on, 1 56
IdfEus, Phragmidium incrassatum

on, 156
Rust, Spruce-leaf blister, 175
of Asparagus, i 56

Crucifers, White, 66

Larch, 169

Pine, 172

Poplar, 164

Rhododendron, 177

Rose, 156

Spruce, 175

^^'heat, 48, 155

Colour of, 40

Rust, Protection against drought of, 45

Fungi, 153
Rye, Puccinia striaeformis on, 1 56

Brand, 68
Sac Fungi, 69

Saffron, Rhizoctonia violacea on, 82
Salix, see also Willow

aurita, Rhytisma salicinum on, 107

Caprea, ,, ,, 107

nigricans, „ „ 107

purpurea, „ ,, 107

Saprolegiacea;, 57
Saprophyte, the term defined, 46
Saprophytes, Facultative, 47
Schinzia Alni, 39
Schizomycetes, 37
Sclerotia, 43, 48
Sclerotinia, 129,130

baccarum, 130

Libertiana, 130

megalospora, 130

Oxycocci, 130

Vaccinii, 130
Scorching of bark by fire, 300

sun, 300
Scrophulariaccce as partial parasites, 24
Sea-water, Effect of, on trees, 20, 280
Seed from stunted pines, 16

Germination of, 44

Importance of care in selecting,
13, 22
Seeding, Effects of thick, 299
Seedling beech disease. Early mention
of, 58

conifers. Effects of drought on, 112

Parasitic disease of, 147

pines, Caeoma on, 166
Sempervivum seedlings. Disease of,

5S .
Senecio, Coleosporium on, 172
Septoglffium Hartigianum, 141
Septoria parasitica, 143
Sexual generation, 44

processes in fungi, 44
Shake — Bark, Ring, or Heart, 191
Shedding of pine-leaves, 1 1 1
Shoots, Stool, 261, 262
Shortening of branches, 259
Shrinkage of wood due to frost, 284
Sickliness and disease distinguished, 5
Sinkers of Mistletoe, 26
Sirex, 248
Slime Fungi, 39
Slips, 264

may prolong life, 7
Sloe, see Prunus spinosa
Smoke, Damage due to, 300

INDEX

329

Smoke, Special liability to injury from,
14

Smut, Formation of spores of, 66
Popular use of the term, 66
of Wheat, how spread, 49, 67

Smuts, Protection of. against drought,

45

Snags of branches. 254, 260

Snow, Damage due to, 299

Soda-fumes, Effects of, 300

Soil-canker, 129

in relation to disease, 10, 270

Solutions in soil, Effects of strong,
279

Soot, Effects of, 300

Sorauer's work. 4

Sorbus, ^cidium pencillatum on, i 59
IMelampsora on, 171
Rjestelia cornuta on, 15S
Aucuparia. Cucurbitaria on, 88

Spear-top, 175

Sfthacelia segetum, 99

Sphaceloma ampelinum, 104

Sph^erella, Leaf-blotches due to, 88
Fagi, 88
Fragaria?, 88
maculiformis, 88
punctiformis, 88

Sphaeria dryina, 224

Sphasrotheca pannosa, 70

Spheroblasts on the beech, 239

Sporangia of Peronosporea;, 57

Spore-mother-cells, 162

Spores, how formed, 43
Germination of, 45
Infection by, 48

Sporidia, 154
of smut, 67

Sporocarp of Basidiomycetes, 153

Sporophore of Fungi, 43
PeronosporccC, 57
Pezizffi, 117

Spruce, see also Picea

yEcidium abietinum on, 177

coruscans on, 183

Chrysomyxa abietis on, 175

Ledi on, 179
Dematophora necatri.x; on, 82
Green-rot on, 42, 224
Herpotrichia nigra on, 76
Hysterium macrosporum on, 109
Nectria Cucurbitula on, 89
Parasitic disease of, 147
Pestalozzia Hartigii on, 136
Peziza aeruginosa on, 224
Polyporus borealis on, 196
Trichospheeria parasitica on, 72

Spruce, Withering of leaves of, in

cones, /Ecidium strobilinum on,
182

conorum Piceaeon, 183

leaf blister, 9, 13, 175
redness, 109
rust, 175
Spruces as a protection against pine-
blight, 116
Stag-headed condition, 270
Starved plums, 131
Stem-brand. 68
Stereum hirsutum, 205
Sterigmata, 142
Sticky-brand, 68
Stigmatea, Leaf-blister due to, 88

Alni, 88

Mespili, 88
Stink-brand, 68

Stone-fruit trees. Black-knot of, 103
Strawberrry, Sphaerella on, 88
Stumps of branches, 254, 260
Sucker-tubercles of fungi, 42
Sulphurous acid in smoke, 301
Sun, injurious effects on conifers, 112

cracks, 283, 294, 296
Swarm-spores of Peronosporea;, 57
Swellings induced by fungi, 50
Sycamore, see Acer
Symbiosis, 71, 181

Tannin as food for fungi, 50
Taphrina aurea, 135

betulina, 133

Populi, 135
Tar-girdles, Effect of, on j^ines, 246
Tarring wounds, 258
Teleutospore, 154
Temperature of trees, 283
Teratology defined, 5
Thelephora laciniata, 35

Perdix, 54, 203
Thinning woods, Effects of, 271
Thrushes as distributors of mistletoe,

26, 30
Thunder brooms, see Witches' brooms
Thymus, Dodder on, 35
Tidiness, Importance of, 57
Tilletia Caries, 68

laevis, 68
Timber, Coniferous, Blue colour of, 224

Structural, Attack of fungi on, 212
Merulius lacrymans in, 219
Tinder-fungus, 206
Tinea sylvestrella, 175
Toad-stools, 46
Tobacco, Parasite of, 25

INDEX

Tooth Wort, a partial parasite, 24
Top-drouglit or Top-drying, 5, 14, 20,

270
Town trees. Unhealthy condition of,

281
Trametes Pini, 191

Action of ferment of, 53
Mycelial growths of, 42
radiciperda, 186, 277

an example of mycelial infec-
tion, 48
associated with root-rot, 21
may pierce suberose tissues, 50
may spread by spores, 49
Transplantation in regard to frost, 14,

15
Trenches as a preventive measure, 57
Trichosphteria, an example of mycelial
infection, 47

parasitica, 72
Triticum repens, Bunt on, 68

Damage due to, 24
Tsuga Mertensiana, Rhizina undulata

on, 125
Tuber, 71
Tuberacei, 69, 71
Tubercularia, 89
Tulasne's work, 3
Turgescence, 288
Turpentine, Strasburg, 247

Venetian, 247
Twigs, Shedding of, 225
Twitch, see Triticum repens
Tyloses, 228, 235, 236

Uncinula Aceris, 70

adunca, ']o
Uredine^e, 153

as obligative parasites, 46
Uredo linearis, 155
Uredospores, 154
Urine, Effects of, on plants, 281
Urocystis Anemonis, 68

Cepulee, 68

occulta, 68

Violas, 68
Urtica, Dodder on, 34
Ustilaginete, 57, 66
Ustilago Carbo, 68

destruens, 68

Maydis, 68

Vaccinium, Exobasidium on, 185
Melampsora on, 171, 185
Myrtillis, Sclerotinia baccarum

on, 130
Oxycoccus, Sclerotinia on, 130

uliginosum, Sclerotinia megalo-
spora on, 130
Vaccinium Vitis Idaea, Effects of
Calyptospora on, 51
Melampsora Goeppertiana on,
161
Valsa oxystoma, 151

Prunastri, 88
Variation in relation to development, 5
Possible directions of, 12
probably initiated in the oosphere,

5

Vine, see also Grape

Botrytis cinerea on, 130
Coniothyrium diplodiella, 103
Dematophora necatrix on, 82
Dodder on, 34
Glceosporium on, 104
Physalopsora Bidwellii on, 103
Mildew, 65

Viscum album, 25

Walnut, Polyporus sulphureus on, 200
Water, Contaminated, Effects of, 281

Salt, Effects of, 280

Stagnant, Effects of, 276

in soil, 270
Weinstockfaule, 82
Wet-rot of potato, 64
Wheat, Bunt of, 68

Puccinia striasformis on, 156

Ustilago Carbo on, 68

rust in relation to barberrv, 9,

155
\\ hite piped wood, 205
rot of birch, 206
conifers, 21 1
fir and spruce, 195, 196
oak and beech, 203, 205
vine, 104
Willkomm's pioneer work, 4
Willow, see also Salix
Dodder on, 34
Melampsora on, 171
Mildew of, 70

Polyporus sulphureus on, 200
Caspian, Behaviour of, on sandy
soil, 265
Wind injuring leaves of conifers, 1 1 1
Witches' brooms, 51
on alder, 133
birch, 135
hawthorn, 133
Prunus, 131
silver fir, 179
Wood, Distinction between dead and
living, 46

IxNDEX

Wood, " Wound," 230, 231
balls on the beech, 239
Works, Early, on plant-diseases, 2,

3, 4
Wound-rot, 236, 244, 247, 257, 262,

295
\\ ounds, 225

Agencies that produce, 50

Effects of, on wood, 232

General treatment of, 237

Natural, 225

Ring, 249

Varieties of, 241

Wounds, due to crushing, 246

resin-collecting, 247
predispose to disease, 1 5
Wurzelpilz, 82

Yellow-piped wood, 205
Rattle, see Rhinanthus

Zea, see Maize
Zinc in smoke, 301
Zoogonidia of Peronosporea?, 58
Zygomycetes, 57
Zygospores, 42

THE END

RICHARD CLAY AND SONS, LUIITED, LONDON AND BUNGAY.

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