DISEASES.
DIFFICULTIES IN THE OUTSET—WHAT CONSTITUTES DISEASED ACTION—NO ANALOGY TO ANIMAL SICKNESSES—CONGENITAL DEFECTS—DEBILITY. DEFICIENT STRENGTH OF FIBRES—DEFECTIVE FOLIAGE—IMPERFECT AND REDUNDANT BLOSSOMS—THE CIVILIZED AND CULTIVATED PLANT MAY BE ABNORMAL ALTOGETHER—UNSATISFACTORY ACCOUNTS OF DISEASES IN PLANTS—LANKESTER'S CLASSIFICATION CONSIDERED—EFFECTS OF THE EXCESS OR PAUCITY OF MOISTURE, HEAT, AND LIGHT—MODE OF ACTION OF FROST—INJURY RATHER REFERRIBLE TO THE CONDITION OF THE CIRCULATION THAN TO THE DEGREE OF COLD IN MANY HARDY PLANTS—INFLUENCE OF THE SOIL—LIGHT THE GREAT STIMULUS, ITS WITHDRAWAL SUSPENDS HEALTHY ACTION—ITS SUDDEN RESTORATION CAUSES DEATH BY SUN SCALD—INJURY BY SUNSHINE IN WINTER—POISONOUS GASES—MIASMATA—POISONS IN THE SOIL—PARASITIC PLANTS, EPIPHITES, FUNGI, PEAR BLIGHT—VARIOUS THEORIES—WHAT WE KNOW, AND WHAT WE DON'T KNOW—TREATMENT—ROOT PRUNING SUGGESTED—SATISFACTORY RESULTS—MILDEW BLIGHT IN PEACH AND APPLE—TWIG BLIGHT IN APPLE AND QUINCE—THE APPLE BLIGHT—BITTER ROT—CRACKED FRUIT—SCAB—MILDEWS—KIRTLAND'S VIEWS AND SUGGESTED REMEDY—WOUNDS AND INSECTS—NEEDING THE AID OF SURGERY RATHER THAN MEDICINE—DESTRUCTION OF FOLIAGE BY INSECTS IMPAIRS THE HEALTHY CONDITION OF THE PLANT—RESUME—SELECT HEALTHY TREES OF HEALTHY VARIETIES—EMPIRICAL CHARACTER OF TREATMENT USUALLY RECOMMENDED FOR DISEASED TREES—THE BLACK KNOT—THE ROT AND MILDEW OF THE GRAPE.
In opening a discussion upon the nosology of vegetation, it may be expected that one who had spent many years of his life in the investigation of the diseases of the human family, and at the same time was something of a student of comparative anatomy and physiology, tracing analogies between the animal and vegetable kingdoms, should be familiar also with the diseases of plants. Such an anticipation, it is feared, will not, in the present instance, be realized. Indeed, the writer feels very much at a loss how to proceed in discussing this branch of the subject, and hardly knows what departures from undoubted health and vigor should be considered worthy of the title of disease. Nor is it easy to trace the causes of the conditions that are generally viewed in the light of maladies. We find the manifestations both in the tree or plant, and in its several parts, and also in the products which chiefly interest us; the fruits themselves, are often deteriorated by what is called diseased action of different kinds. The analogy to diseases of animals is certainly not very distinct. We do not find anything like fevers, or gout, or rheumatism, in plants, but we may consider some of their conditions somewhat in the light of dropsies, and plethora or hypertrophy on the one hand, and of anæmia or atrophy upon the other; we may consider canker and the death of some parts of a plant analogous to gangrene, and mortification in the animal subject. Then again we find congenital defects in individuals among plants, just as we do among animals. Some are always less vigorous than others, and thus certain varieties seem possessed of a degree of inherent disease that perpetually prevents them from displaying the requisite strength and vigor which we so much desire in our plantations. Certain varieties that, from the size and excellence of their fruits, have attracted the attention of pomologists, are so deficient in health and vigor as to be considered diseased, and are therefore very properly condemned as unworthy a place in our orchards and gardens; others appear simply deficient in the production of some one part, as is illustrated by the inferior strength of the woody fibres of some trees, which break easily under the weight of their own fruit, and thus destroy the symmetry of the tree and diminish its productiveness. Others have defective foliage, which is attended by the imperfect performance of the functions of growth, both in the fruit and in the sustaining woody fibres; others again produce defective blossoms with either a redundancy or deficiency of the parts that are necessary for the production of the seeds needed for the perpetuation of the species. When the parts are deficient, the flowers are called barren or infertile. A redundancy or multiplication of parts is seen in double flowers of our gardens, where they are much prized for their beauty, though considered monstrosities by the botanist, and perhaps properly referred to diseased action by the nosologist.
It is evident, that very often the conditions of a plant and its products, which we most highly prize, and towards which all our efforts in its culture are directed, are really departures from the natural and healthful status; in other words, what we covet, is really a state of diseased and abnormal action. With the other secondary objects of occupying and ornamenting the barren wastes of the earth with plants, and thus supplying food to hosts of insects, and to the higher animals, nature also has primarily in view, the production of perfect seeds for the perpetuation of their species, by the plants that are profusely scattered over the globe. Man, on the contrary, often rejects the true seeds as worthless when compared to their juicy fleshy envelopes that constitute his favorite fruits, or the enlarged and succulent roots, tubers, stalks, and leaves, that characterize his garden vegetables and field crops; while in the grains proper he seeks sustenance in the true seeds, which become the object of his greatest care and ingenuity to enlarge, to increase, and to develop, particularly in regard to their nutritive qualities.
Most writers upon the diseases of plants have given us very indistinct notions upon the subject, and have done very little to enlighten their readers; while they have written voluminously upon the unhealthy and unsatisfactory condition of certain vegetables, and have given us most extensive accounts of the treatment by which they propose to remedy the evils complained of, we gather little of the information needed to enable us to understand the true state of the case, or of the causes of the disease, if it is to be considered such. The reader need not expect that he will be more enlightened by this chapter than he has been by the essays to which reference is here made, but he will be led to a consideration of some of the causes of those departures from health and vigor which are considered diseased action, and in this way he may possibly be put upon the track which will lead him to the avoidance of disastrous results. More than this will not be attempted.
Perhaps the most satisfactory account of diseases of plants is that given by Lankester, in which he divides them according to their causes, as follows:
1st—Those produced by changes in the external conditions of life, such as redundancy or deficiency of the ingredients of soil, of light, of heat, air, and moisture.
2d—Those produced by poisonous agencies, as by injurious gases, miasmata in the air, or by poisons in the soil.
3d—Those arising from the growth of parasitic plants, such as the various Fungi, Dodder, Mistletoe, etc.
4th—Such as are caused by mechanical injuries or wounds, and by the attacks of insects.