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DISEASE IN PLANTS
DISEASE IN PLANTS
BY
H. MARSHALL WARD, Sc.D., F.R.S.
FELLOW OF SIDNEY SUSSEX COLLEGE, HONORARY FELLOW OF CHRIST'S COLLEGE
AND PROFESSOR OF BOTANY IN THE UNIVERSITY OF CAMBRIDGE
PRESIDENT OF THE BRITISH MYCOLOGICAL SOCIETY, AND FELLOW OF THE
LINNEAN AND ROYAL HORTICULTURAL SOCIETIES; HONORARY FELLOW
OF THE MANCHESTER LITERARY AND PHILOSOPHICAL SOCIETY
AND OF THE BOTANICAL SOCIETY OF EDINBURGH
London
MACMILLAN AND CO., LIMITED
NEW YORK: THE MACMILLAN COMPANY
1901
_All rights Reserved_
GLASGOW: PRINTED AT THE UNIVERSITY PRESS
BY ROBERT MACLEHOSE AND CO.
PREFACE.
It has often been represented to me that the cultivators of plants,
among whom are to be included planters and foresters, as well as
agriculturists and gardeners of every kind, are more particularly
concerned with, and interested in, the maladies themselves of the plants
they grow, than in the life-history of the fungi, insects or other
organisms to which they are due, or in the physiological processes which
are involved; and although it is impossible to really understand any
disease unless we also understand the processes by which it is brought
about, there is room for sympathy with the point of view of the
cultivator. He says, in effect, "I do not want to know all about the
biology of the fungus of wheat-rust, or of the _phylloxera_, nor do I
want to learn what experts can tell me about the action of bacteria in
soil, or the process of starch-formation in the leaves: I have neither
the time nor the means to master these details. What I want is guidance
as to what is wrong with my tomatoes, apple trees, chrysanthemums, fir
trees, turnips, etc., and what I am to do to set things right." Just
so. With the latter part of this cry one must sympathize, much as a
doctor does with the wail of the parent who calls him in to cure his
sick child--we need not stop to classify or compare the motives of the
parent and the cultivator, and perhaps I had done better to select a
breeder of sheep with his flock and a veterinary doctor in the
illustration, but we will let it pass; and as regards the former part of
the cry, I do not know that the plant-doctor can expect the cultivator
to be initiated in the aetiology of the disease any more than the
physician expects the parent to understand the biology of the typhoid
bacillus. That both the cultivator and the parent would be the better
for a real knowledge of the disease in either case must be admitted--nay
insisted on, provided the knowledge _is_ real--but we have to deal with
facts, and it is a fact that the clients of both doctors are impatient
of the details of the case.
Now, of course, I am aware that no short cut or "royal road" to science
exists, and if a man is going to train up trees or other plants, he
ought to know all about them in health and in sickness, in youth and in
old age, and he ought to learn everything about the soil they grow in,
the air that surrounds them, the enemies that beset them, and all the
multifarious relations of these one to another; but when I look at my
boy and reflect how much his nurse, his schoolmaster, his tutor, his
doctor, and his parents _ought_ to know successively and simultaneously
about him in sickness and in health, and about his surroundings, etc., I
begin to wonder whether there is not after all something to be said for
the cultivator's point of view.
Moreover, the cultivator knows a good deal about his plants which I do
not know, and although I should much like to know it, his plea of want
of time rings in my ears and the conviction strikes home that one ought
to try and meet his views, and tell him something about disease as
manifested in plants without insisting on his becoming a professional
mycologist, entomologist, agricultural chemist, and philosopher.
Of course, beyond a certain point, it is his lookout how much the
information is worth, and its educational value--a very different
matter--is sure to suffer from any restrictions imposed on the treatment
of the subject; but if the theme of disease in plants, treated from a
general point of view--I was about to write "treated in a popular
manner," but that is impossible until physiology and mycology are more
widely taught--enables him to understand better the questions he puts to
himself, and, still more, if it stimulates him to enquire further into
the inexhaustible field of science glimpsed at, something may come of
it.
The purpose of these essays is to treat the subject of disease in plants
with special reference to the patient itself, and to describe the
symptoms it exhibits and the course of the malady, with only such
references to the agents which induce or cause disease as are necessary
to an intelligent understanding of the subject, and of the kind of
treatment called for. Consequently I have avoided any unnecessary
classification or elaborate descriptions of parasitic fungi or insects,
histological details of the tissues of plants, chemical and physical
details regarding the soil, and even matters purely physiological as far
as possible. Several admirable works on these subjects are already
available, and must be referred to for further details.
It is, however, quite out of the question to avoid technicalities,
though I have chosen the simpler course wherever it was found feasible,
and have tried to so employ the examples selected that the student who
wishes to go further into the matters dealt with may turn to special
treatises for further information. For one eminently technical section I
ought perhaps to apologise, but the temptation to try and set forth, in
concrete form and suitable for the purposes of this book, some account
of what is known of the most essential and profound factors concerned in
the difficult question of the nature of life and death, health and
disease, was great. Probably my apology should go further, and apply to
what after all must be failure to explore this mystery to the bottom: my
only excuse must be that it may stimulate others to go further.
It was an afterthought to add, in Part I., the considerations on the
factors which influence the plant regarded as a living machine, so to
speak, in order that the student may the better apprehend the point of
view taken of the bearings of the matters discussed in Part II.
With regard to references, it seemed a better plan to give, in the form
of notes after each chapter, the titles of the principal books and
papers on which a student may base a further course of reading, than to
overweight the pages of what is, after all, merely an introductory
sketch to a huge subject, with detailed quotations from the numerous
sources of information made use of. I have freely expressed my own
opinions, but the sources for others are, I hope, as freely given. It
will, however, be understood that I have not aimed at a complete
bibliography, and, particularly, I have only given foreign references
where it seemed that adequate treatment of the subject could not be
found in English.
My sincere thanks are due to Mr. F. Darwin, F.R.S., who has kindly
looked through many of the proofs, and given me the benefit of several
suggestions: and to my wife for the very material aid she has afforded
me in the preparation of the index.
H. MARSHALL WARD.
CAMBRIDGE,
_November, 1900_.
CONTENTS.
_PART I.--SOME FACTORS._
CHAPTER I.
PAGE
THE PLANT AND ITS SURROUNDINGS, 1