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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 UNIVERSI
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PREFACE.
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 a
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CHAPTER I.
CHAPTER I.
The plant the central object of study—soil, climate, atmosphere, etc., are factors of its environment. Agricultural chemistry. The plant a machine. Physiology. If I were asked to sum up the most important result of the numerous advances made during the past decade in agriculture and forestry, I should reply—the clearer and wider recognition of the fact that the plant itself is the centre of the subject, and not the soil, climate, season, or other factors of its environment. Until comparatively r
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CHAPTER II.
CHAPTER II.
The food of plants—"Vital force"—Other errors—Liebig and Boussingault—The botany of agriculture. The synthesis of carbohydrates—The physiology of plant-nutrition. The persistence of misconceptions. The year 1860 may be regarded as a landmark of importance in the history of plant physiology, for it was in that year that Sachs discovered that the bringing together of water and carbon-dioxide, in the green chlorophyll-corpuscles of the plant exposed to sunlight, results in the formation of the grai
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CHAPTER III.
CHAPTER III.
The plant a machine into which energy and material are taken—Carbon assimilation—Feeding—Accumulation and transformations in the plant. The action of light—The chlorophyll-function. The relations of the plant to the environment can only be understood by taking into account the results of modern physiological discoveries. These teach us that the living plant is a highly complex machine, the details of its organisation and structure being much more numerous and much more closely correlated at nume
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CHAPTER IV.
CHAPTER IV.
Quantities of starch formed, and their significance for the plant. The absorption of energy—the conversion of energy in the plant. The plant is a complex machine for concentrating and storing energy and material from without. Sachs measured the increase in dry weight (due to the carbohydrates formed in the chlorophyll-corpuscles) per square meter of leaf-surface, exposed for a definite period, by drying rapidly at 100° C. equal areas of the leaves concerned, and comparing the weights. Of course
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CHAPTER V.
CHAPTER V.
Older views as to root-hairs—Root-hairs and their development—Surface—Variations—Conditions for maximum formation—Minute structure—Adhesion to particles of soil—Functions. On the roots of most plants are to be found delicate, silky-looking, tubular prolongations of some of the superficial cells, known as root-hairs. Malpighi (1687) seems to have been the first to observe them, and he took them for capillary tubes. Grew (1682) seems to have been responsible for the view that the roots act like sp
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CHAPTER VI.
CHAPTER VI.
Excretions from root-hairs—Osmotic phenomena—Turgescence—Plasmolysis—Control of the protoplasm in absorption, etc. Selective absorption. We see then that the root-hairs are the active living instruments in absorbing the water (containing small quantities of dissolved substances) of the soil. If the living root-hairs are so numerous and so active, however, a natural inference is that they must exert some influence on the composition or arrangement of their environment. All the teachings of modern
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CHAPTER VII.
CHAPTER VII.
Soil not a dead matrix—Organic materials—The living organisms of the soil—Their activities—Their numbers and importance. Abandonment of the notion that chemical analysis can explain the problem. It is customary to regard the soil, between the particles of which the root-hairs of plants are distributed, as if it were merely a dead matrix of smaller or larger pieces of rock, such as sand, gravel, stones, etc., and organic remains, such as bits of wood, leaves, bones, etc., with water and air in th
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CHAPTER VIII.
CHAPTER VIII.
The crossing of varieties of wheat, etc.—The essentials of fertilisation—Rimpau's experiments—Hybrids and selected varieties. In the more hopeful view of the case which the new agriculture will have to take, it will recognise the physiological truth that since the living plant is the important and variable machine which constructs the produce looked for, and since that machine will work best in proportion as its needs are properly satisfied; therefore in cases where the needs of a given type of
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CHAPTER IX.
CHAPTER IX.
History. References in the Bible—Greeks and Romans—Shakespeare—Rouen law—Superstitions—Malpighi and Grew—Hales—Unger—Berkeley—De Bary, etc. Physiology and Biology—Diagnosis—Etiology—Therapeutics. Study of causes. Phytopathology, from Greek words which signify to treat of diseases of plants, comprises what is known of the symptoms, course, and causes of the diseases which threaten the lives of plants, or bring about injuries and abnormalities of structure. As a distinct and systematised branch of
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CHAPTER X.
CHAPTER X.
Variation—Disease—Comparison to a top. Health—Extinction of species—Natural demise. Examples of complex interactions in health—Interference, and tendencies to ill-health. When we come to enquire into the causes of disease, it appears at first an obvious and easy plan to subdivide them into groups of factors which interfere with the normal physiology of the plant. Scientific experience shows, however, that the easy and the obvious are here, as elsewhere in nature, only apparent, for disease, like
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CHAPTER XI.
CHAPTER XI.
A. External causes—I. Non-living environment: soil, atmosphere, temperature—II. Living environment: plants, animals—Complex interactions—Predisposing causes—No one factor works alone—Tangled problems of natural selection involved. B. So-called internal causes. It is customary to classify the causes of disease in plants into two principal groups—(1) those due to the action of the non-living environment—soil, atmosphere, physical conditions such as temperature, light, etc.; and (2) those brought a
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CHAPTER XII.
CHAPTER XII.
Causes due to animals—Vertebrata—Wounds, etc.—Invertebrata—Insects, etc.—Plants as causes of disease—Phanerogams, weeds, etc.—Cryptogams, fungi—Epidemics, etc. Passing now to those causes of disease which are connected with the living environment, we may obviously divide them into two groups of agents, animals and plants. Among animals, the various vertebrata, including man, are especially responsible for the larger kinds of wounds and wholesale destructive processes due to breakage, stripping o
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CHAPTER XIII.
CHAPTER XIII.
General and local disease—General death owing to cutting-off supplies, etc.—Disease of organs—Tissue-diseases, e.g. timber—Root-diseases—Leaf-diseases, etc.—Diseases of Respiratory, Assimilatory, and other organs—Physiological and Parasitic diseases—Pathology of the cell—Cuts—Cork—Callus—Irritation—Stimulation by protoplasm—Hypertrophy. On going more deeply into the nature of those changes in plants which we term pathological or diseased, it seems evident that we must at the outset distinguish b
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CHAPTER XIV.
CHAPTER XIV.
Actions of poisons in small doses—Results of killing a few cells—Malformation—Enzymes—Secretions and excretions—Acids, poisons, etc.—Chemotactic phenomena—Parasitism—Epiphytes and endophytes—Symbiosis—Galls. Physiological research has shown that the respiratory activity of cells may be increased by small doses of poisons, and even that growth may be accelerated by them— e.g. chloroform, ether—and, still more remarkable, that fermentative activity may be enhanced by minute doses of such powerful
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CHAPTER XV.
CHAPTER XV.
Dissemination of fungi by the aid of snails, rabbits, bees, and insects—Man—Distribution in soil, on clothes, through the post, etc.—Worms, wind—Puffing of spores—Creeping of mycelia—Lurking parasites—Spread of insects and other animals—Losses due to epidemics. The dissemination of plant diseases is a subject which has been far too much neglected, but our knowledge of it is slowly increasing. The spores of fungi such as Rusts and Erysipheae are often carried from plant to plant by snails; those
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CHAPTER XVI.
CHAPTER XVI.
Illustrations afforded by the potato disease—The larch disease—The phylloxera of the vine. When we come to enquire into what circumstances bring about those severe and apparently sudden attacks on our crops, orchards, gardens, and forests by hosts of some particular parasite, bringing about all the dreaded features of an epidemic disease, we soon discover the existence of a series of complex problems of intertwined relationships between one organism and another, and between both and the non-livi
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CHAPTER XVII.
CHAPTER XVII.
Preventible diseases—The principles of therapeutics—Powders and their application—Spraying with liquids—Nature of chemicals employed—Employment of epidemics and natural checks—The struggle for existence. It may be said that in no connection is the proverb "Prevention is better than cure" more applicable than with this subject, and undoubtedly the best utilitarian argument that can be used in favour of a thorough study of the causes of disease is that only by understanding these causes is there a
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CHAPTER XVIII.
CHAPTER XVIII.
Predisposition and immunity—Pathological conditions vary—Hardy varieties—"Disease-proof" varieties—Disease dodging—Thick skins—Indian wheats, etc. Cell-contents vary—Citrus, Cinchona, Almonds, etc. Double ideals in selection—Cultivation of pest and host-plant—Variations of fungi—Bacteria—Specialised races—Difficulties—Experiment only will solve the problems. The numerous and often expensive failures in the application of any prophylactic treatment, have proved an acute stimulus to the research f
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CHAPTER XIX.
CHAPTER XIX.
Discolorations—Pallor—Etiolation—Laying of Wheat—Chlorosis—Yellowing—Albinism—Variegation—Uprooting, Exposure and Wilting of seedlings. Everybody knows in a general way when the geraniums in the window pots are drooping from want of water, or when the young Wheat is sickly, or the Pear-trees "blighted," and we have now to see how far we can systematise the knowledge that has been gained in course of time regarding the signs which sick plants exhibit. Pallor. —Under this heading, which includes a
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CHAPTER XX.
CHAPTER XX.
Spotted leaves—The colours of spots—White, yellow, brown, and black spots on leaves—Parti-coloured spots—The browning, etc., of leaves. Discoloured spots or patches on the herbaceous parts of plants, especially leaves, furnish the prominent symptoms in a large class of diseases, due to many different causes, and although we cannot maintain this group of symptoms sharply apart from the last, as seen from the considerations on albinism , it is often well marked and of great diagnostic value. By fa
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CHAPTER XXI.
CHAPTER XXI.
The nature of wounds and of healing processes—Knife wounds—Simple cuts—Stripping—Cuttings—Branch-stumps and pruning—Stool-stumps—Ringing—Bruises. Wounds. —All the parts of plants are exposed to the danger of wounds, from mechanical causes such as wind, falling stones or trees, hail, etc., or from the bites of animals such as rabbits, worms, and insects, and although such injuries are rarely in themselves dangerous, they open the way to other agencies—water, fungi, etc., which may work great havo
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CHAPTER XXII.
CHAPTER XXII.
Burrows and excavations. Bark-boring—Wood-boring—Wood fungi—Leaf-miners—Pith flecks—Erosions. Skeleton leaves—Irregular erosions—Shot holes. Frost cracks—Strangulations—Spiral grooving. Natural wounds are produced in a variety of ways during the life of the plant, and, generally speaking, are easily healed over by the normal process if the area destroyed is not too large, and the parts remaining uninjured are sufficiently provided with foliage, or with supplies of food-materials stored up in the
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CHAPTER XXIII.
CHAPTER XXIII.
Herbaceous excrescences, or galls—Erineum—Intumescences—Corky warts, etc.—Pustules—Frost-blisters—Galls and Cecidia—Root nodules. Excrescences , or out-growths of more or less abnormal character from the general surface of diseased organs, are very common symptoms, and widely recognised. They are due to hypertrophy of the tissues while the cells are young and capable of growth, and may be induced by a variety of causes, among which the stimulus of insect-punctures and of the presence of insect e
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CHAPTER XXIV.
CHAPTER XXIV.
Cankers—Burrs—Sphaeroblasts, and other excrescences of woody tissues—Witches' Brooms. Cankers are irregular excrescences due to the perennial struggle between tissues attempting to heal up a wound, and some organism or other agent which keeps the lesion open. A canker always originates in a wound affecting the cambium, and usually in a small wound such as an insect puncture or frost nip; if undisturbed the dead parts would heal over by cork and callus, but if recurring frost-cracks break open th
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CHAPTER XXV.
CHAPTER XXV.
Tumescence—Rankness—Bursting of fruits, etc.—Root rot—Rot of fruits—Bulb diseases—Flux—Honey-dew—Slime flux—Resinosis—Gummosis—Manna. I put together in one artificial class a varied group of diseases, the principal symptom of which is the escape of fluids from the tissues, under circumstances which betray an abnormal state of affairs, often obvious, but sometimes only to be inferred. In many of these cases bacteria abound in the putrefying mass, and some evidence exists for connecting these micr
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CHAPTER XXVI.
CHAPTER XXVI.
Patches—Frost-patches—Bruising due to hail, shot, etc.—Fire—Sun-burn or scorching—Sun-cracks. Dying-back—Frost—Fungi—Wound fungi—Defoliation by insects—Defoliation by hand—Staghead. Necrosis. —This is a general term for cases where the tissues gradually turn brown or black in patches which die and dry up, the dead area sometimes spreading slowly and invading the usually sharply demarcated healthy tissues around. It is a common phenomenon on the more slender stems or branches of trees, especially
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CHAPTER XXVII.
CHAPTER XXVII.
Monstrosities—Teratology—Atrophy of organs—Shanking of grapes—Barren fruit trees—Dwarfing—Distortions and malformations—Fasciations—Flattened roots—Torsions—Curling and puckering—Leaf rolling—So-called "spontaneous" teratological changes. Monstrosities. —In a wide sense this term is applicable to many cases here treated under other headings, and signifies any departure from the normal standard of size, form, arrangement, or number of parts, and so forth, due to arrest of growth, excessive growth
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CHAPTER XXVIII.
CHAPTER XXVIII.
Proliferations—Vivipary—Prolepsis—Lammas shoots—Dormant buds—Epicormic shoots—Adventitious buds—Apospory and apogamy. Proliferation consists in the unexpected and abnormal on-growing or budding out of parts—stems, tubers, flowers, fruits, etc.—which in the ordinary course of events would have ceased to grow further or to bear buds or leaf-tufts directly. Thus we do not expect a Strawberry—the swollen floral axis—to bear a tuft of leaves terminally above the achenes, but it occasionally does so,
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CHAPTER XXIX.
CHAPTER XXIX.
Grafting—Comparison with cuttings—Effects of environment—Relations between scion and stock—Variation in grafts—Grafting and parasitism—Infection—Pollination—Grafts-hybrids—Predisposition of Natural grafts—Root-fusions. Grafting is a process which consists in bringing the cambium of a shoot of one plant into direct union with that of another, and is practised in various ways, the commonest of which is as follows: One plant—the stock —rooted in the ground, is cut off a short distance above the sur
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CHAPTER XXX.
CHAPTER XXX.
Protoplasm—Hypothesis as to its structure and behaviour—Assimilation—Growth—Respiration—Metabolism—Action of the environment—Nuclear protoplasm—Pollination—Grafting—Parasitism—Graft-hybrids—Life—Death—Variation—Disease. We have seen that all the essential phenomena of disease concern only the living substance—the protoplasm—of the plant, and that however complex the symptoms of disease may be, the occurrence of discolorations, lesions, hypertrophies, and so forth are all secondary matters subsid
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MACMILLAN AND CO.'S WORKS ON BOTANY.
MACMILLAN AND CO.'S WORKS ON BOTANY.
BY THE SAME AUTHOR. Crown 8vo. Price 6s. Timber and Some of its Diseases. By H. Marshall Ward , D.Sc., F.R.S., F.L.S., Fellow of Sidney Sussex College, and Professor of Botany in the University of Cambridge. Illustrated. MANCHESTER EXAMINER. —"The subject as a whole is one which is little understood in England, and Professor Marshall Ward's work cannot fail to be useful. The student will be much helped by the numerous illustrations." GARDENER'S CHRONICLE. —"This is a book whose appearance we hai
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