David Pearce Penhallow

“ When a disease involves the entire system, as in peach-yellows or pear-blight, it is often a matter of great difficulty to determine the controlling treatment; but in other cases, where the disorder is strictly of a local character, it may be a simple matter to remedy the trouble. In the case of those peculiar developments of the oak which give us the gall-nuts of commerce, or of similar abnormal developments in the tissues, we have instances of well-defined disease, but it is of a strictly local nature; the disturbance of functional activity does not extend beyond very narrow limits. ”

“ In America hardly a serious thought has yet been given to such considerations, so far as they extend to the protection and preservation of our forests; but it seems probable that the movement to protect our forests from ruthless destruction at the hands of man, which is each year assuming more tangible shape, must ultimately embrace also an effort to have our trees studied according to strict scientific methods, for the purpose of determining their relation to disease and protecting them from injury. ”

“ The peach is naturally a long-lived tree, instances brought to my notice showing that it may live for upward of one hundred or more years, and, if well cared for, it will certainly produce fruit for a long period. At the present time, however, as in the great peach districts of Delaware and New Jersey, we find that, owing to the certainty of disease appearing, or the inherently weak constitution resulting from its previous operation, the period of a profitable life is limited to nine years, at the end of which time the trees are rooted out of the soil as worthless. ”

“ Doubtless the time will come when every man who depends upon the growth of plants for his living will recognize a well-devised system of irrigation, which may be applied to all his orchards and cultivated fields when necessary, as an indispensable part of the machinery which a successful business demands.
The conditions which produce disease in plants, as well as the direct and secondary effects of their operation, are likely to be more or less complicated, and thus render a direct course of diagnosis and treatment correspondingly hard to reach and apply ”

“ In considering the diseases of plants, it is important to bear in mind that we have to deal with subjects which on the one hand are cultivated, and on the other hand not. In forest-trees there has been no modification through cultivation, and disease would not be likely to become complicated from this cause. In cultivated trees, and plants, as in the peach, pear, strawberry, raspberry, etc., a high degree of cultivation has resulted in a corresponding modification upon which the pecuniary value directly depends. ”

“ This analogy, as well as general principles, would show us that the more highly cultivated the varieties of fruits or plants, the more susceptible are they to the influence of environment with the introduction of disease, and this is confirmed, not only by personal observation, but by the experience of practical fruit-growers.
Again, cultivated fruits always tend to revert to the original form when the conditions of their high state of development are withdrawn. ”

“ In instituting pathological comparisons between animals and plants, we have to keep in mind that there are important structural differences and physical peculiarities which may favor the development of disease more in one case than the other. In animals the mass of their structure is composed of highly vitalized and actively growing cells and tissues; while in the higher plants, where the differentiation of structure is carried to a high degree, there is a very considerable portion of the body which has become incapable of further growth, and is virtually dead. ”

“ When the disease is strictly localized, as when produced by injuries, or by the action of parasites proper; when the local disturbance is of sufficiently recent origin to render it improbable that the general system has become involved—then the diagnosis is in most cases a simple matter, and chiefly involves the correct recognition of the cause of the disturbance—i.e., the name and character of the insect or parasite, or the particular means by which the injury was first inflicted. ”

“ It is observed that they are more or less abundant in the rough outer bark and on the surface of most plants; but, though they are present, their growth is limited, and confined to those tissues which are either dead or of very low vitality, while the plant suffers in no wise from their presence. Let the plant be injured or diseased, however, and at once the parasite gains a firmer hold, the tenacity of which will increase continually until remedial measures are applied. Thus, we often find the breakage of a limb to be but the open door by which rot is introduced into the interior tissues. ”

“ Where injuries are inflicted by man, proper attention in caring for the injured part will prevent the introduction of disease. Nature provides means for the healing of injuries produced in this way, and in many cases it is possible for very extensive injuries to be healed without any aid beyond Nature's own efforts. Grape-vines and other vigorously growing plants often exhibit a most remarkable recuperative power. ”

“ In the animal the system is considered diseased when the functions of the body cease to be performed in a normal manner, and the disease is more or less serious, according to whether one or more functions are involved, as well as the degree to which the impairment of a particular function is carried. ”

“ There is thus developed a debilitated condition of the entire system, by means of which the normal functions are impaired, and this in itself constitutes a disease. But the debilitated state permits the operation of other forms of plant-life which would otherwise be unable to develop readily, and also allows certain abnormal physiological and chemical changes to occur, all of which promote secondary features and thus bring about complication. This, it seems tolerably certain, is the case in peach-yellows, and may also prove to be the case in other diseases such as pear-blight. ”

“ Thus it is that within a few years it has become imperative that something be done, looking to the acquisition of facts which will enable us to successfully cope with these disorders, to ward them off or arrest their progress. ”

“ These plants, like the parasites proper, are incapable of providing their own nourishment from the soil and air, and so must depend for their growth upon already-formed organic matter. But this is not all: it is characteristic of their growth that they live upon organic matter which is in an active state of decomposition, and it will thus be easy to see that they are not far removed from being the cause of the decomposition in bodies which have already ceased to live. In their action upon non-vitalized matter, it is quite possible that they are the active promoters of disorganization ”

“ In many cases, as in trees, the permanent structure predominates, and the vitalized tissues are relatively few. Furthermore, through a delicate nervous system which penetrates the most remote parts of the body, the whole animal organism is brought into more or less active sympathy with the diseased portion, even though the disorder be one of a strictly local nature, while the blood as a general medium of circulation tends to distribute the affection and thus bring the entire system into a diseased condition. ”

“ Under the first head we have to deal with those plants, like the mistletoe and dodder, which grow upon others and draw their nourishment directly from them—hence are truly parasitic. Plants of this kind may contain a certain amount of chlorophyl, but usually possess no true roots; hence they are not only incapable of drawing nourishment directly from the soil, but they are also incapable of performing the assimilative functions by which materials for the formation of cellular structure are developed, in more than a limited manner if at all. ”

“ In these examples, therefore, we have illustrations of the inherent tendency of all plants to overcome disease and injury through the operation of vitality.
In soil influences we have to contend with conditions which are not always so easy to control, and, when once they have produced their effect upon the plant, the diseased condition is a somewhat difficult matter to correctly diagnose and treat. Soil influences operate in a variety of ways ”

“ On the other hand, we have more highly organized bodies, which are continually changing their location, and they are thus brought into new relationships, to which they must adapt themselves, and this is liable to complicate the phases of disease already present. ”

“ It was recognized that the important interests involved in forest-growths were liable to be seriously impaired through the operation of disease, and that, even were this not the case, the interests involved could be most fully protected by the development of that knowledge which should secure the best oversight and care of forests in all respects. ”

“ Atmospheric conditions are largely, if not wholly, beyond the control of man. They include, of course, the varying conditions of heat and moisture, and are thus either highly stimulating and favor the excessive growth of weak structure and parasites, on the one hand, or they are depressing and cause a stagnation of vital activity, and thus injure the plants, as through excessive drought; while this, in turn, leads to the development of parasites, which would not otherwise gain a firm hold. ”

“ While these conditions may not actually cause disease, they will certainly promote it when once developed, and we therefore find a certain part of remedial measures to consist in thorough drainage and cultivation. But more than this, we find in special or general exhaustion of the soil a fruitful source of disease. Lands which have been cropped for a long period become at least specially exhausted, and in such case usually in the direction of that food-element most essential to the growth of the plant which has brought about the exhaustion. ”

“ Moreover, such organs often show that this excessive development has obliterated, wholly or in part, those important functions connected with the reproductive processes which they were originally designed to fulfill. These are some of the evidences that all such monstrosities as our modern apples, pears, strawberries—in short, all our cultivated fruits—are in reality abnormal growths which we may designate as hypertrophied structures, and are therefore evidences of disease. ”

“ When local action has been long continued, however, the highly morbid condition of a limited portion of tissue may in time find sympathy in adjoining parts, and so by degrees the whole system become involved in a chronic disorder. ”

“ We can not hope to correctly determine the nature of diseases by seeking new light upon strictly botanical grounds alone—e. g., by assuming that they originate more or less directly in fungoid growths. ”

“ This strong divergence from the original type involves a debility in one or more directions, and is quite parallel with the changes known to occur in more highly civilized communities of men, by reason of which diseases are not only likely to be more prevalent but more complicated. ”