sprouted in the field and in the cellar, showing that disease is chemical, and involves a change of secretions in the direction of sugar, being equiv alent to a hybernation of longer continuance.

84. In light cases of disease the tuber remains unaffected for weeks; in severe cases it is diseased almost simultaneously with the foliage. In disease from this phase of weather, I think the tuber is much more likely to become soft and ropy than in the other.

85. In contrariety to the phase of disease occasioned by cold wet weather, balls set and grow very freely under this condition, even when the flowerstalk is entirely encircled by mildew. In no state of weather are flowers so large and persistent as on the approach of this form of disease, and during its early progress. Indeed, flowers often continue to expand until the leaves are nearly all dead. The balls, however, if formed during the progress of the disease, and even if nearly full grown at its first develop. ment, usually become diseased, or become brown and unnaturally hard, exactly as is often the case with clusters of grapes under the same weather This fact becomes a very important proof of the pathological identity of the diseases of the potato and grape. In each, the stems, leaves, fruitstems and fruit are similarly marked by mildew, and in each the fruit is affected sometimes by a simple mildew, and at others by a brown hardening. It often happens that the early balls fall a prey to moderate disease, after which, under the influence of better weather, the plant sets and matures other and healthful balls.

86. The two phases of weather whose morbid influence has just been described, usually occur from the middle of July to the middle of August. The last phase (hot, damp intensities,) sometimes marks nearly the whole summer. Thus it was here in 1850, 1851 and 1855.

87. At other times, seasons have a mixed character, cold wet and hot wet intensities alternate with each other, giving a mixed character to the external marks of disease. This mixed form of weather is often felt in the autumn, when a week of warm rains is followed by cold wet weather, greatly injuring late-maturing crops. Thus it was here in the autumn of 1849. In this case much that is called disease, and truly so, is, I apprehend, not disease as technically so called, but water-rot. (See No. 50, above.) In this case I have seen very severe affections of the tuber, when the vines and leaves suffered very little.

88. Two other facts should here be noticed. One, that when disease comes upon the foliage and vines with great violence, often killing both within the course of a week, the tubers seem to escape, even when not halfgrown. The disease on the herbage of the plant seemed to strike with death at the outset, so that morbid matter forming in the plant could not be transmitted to the tuber. So it was in my experience with two plats of potatoes in 1846. (See my essay for 1847, p. 431.)

The other fact is this: disease sometimes is very mild, and continues a long time with but little injury to the herbage of the plant. In such cases the tubers, in the autumn digging, are often found severely affected.

89. The above account of the external marks of disease has been given after no slight experience and is therefore given confidently, yet such is the importance of the whole subject, that with better health, I would

gladly review the whole of it, as, through a series of years, the manifestations of disease might once more occur. The subject, as a whole, is a large one for one man to investigate, and he an invalid and burthened with the constant duties of a profession. I make these remarks for the sake of those who, looking over this field, have come to some different conclusions from myself.

The study of no plant with which I am acquainted involves more than half the labor of that of the potato. This fact arises from its two-fold sympathy noticed in No. 10, above.

90. The question is often asked, does not mildew spread from diseased to healthful plants? I certainly think not. In the cultivation of many thousand seedling plants during the last fifteen years, I have seen hardy and tender sorts growing in alternate rows, in plats side by side, and often in the same hill, yet I have as little expected to have the disease affect the hardy, as that the tubers in the soil should mix into cross varieties. I have often stored sound small potatoes with larger ones that were a little diseased, for the purpose of feeding to stock. So also I have often accumulated a heap in my cellar of hundreds of varieties, a few hills of each; varieties that, for various reasons, I did not wish to continue. They contained many sorts well known to be hardy, and others as well known to be tender. In the course of the winter, the whole were being used for family stores, yet I have never supposed that disease spread from one to the other. In the first case I have taken the small potatoes, when I had neglected to feed them out in season, out of a mass of rottenness made by the decay of the diseased ones, yet they were sound. Just so in years of grape disease, I have had the Black July, Violet, Miller's Burgundy, and Royal Muscadine diseased in various degrees, while hardy American sorts growing in adjoining rows, and often indeed as alternate plants, entirely escaped.

91. I am well aware that the extreme advocates of the doctrine that the fungus or mildew is the sole and originating cause of potato disease, claim that this fungus may be communicated from diseased to sound tubers, when they are placed in close proximity. Be it so, as a matter of experiment. The same result was long ago claimed for wheat, where it was said that a whole field of healthful plants could be gradually innoculated with rust, merely by bringing a handful of diseased grain, and shaking it over the standing healthful crop. Whatever may have resulted from such experiments, this is not the way, I apprehend, in which disease is propagated naturally in the field.

92. My experience in the spread of disease has been this:

(a) Suppose a whole field to have been planted with seed of a fairly healthful variety, and that the summer proves favorable to disease; then the rich spots of soil, the low sheltered hollows, the damp places, and those where the plants have been unwisely crowded will show disease on the vines, and it may be on the tubers, at the autumnal digging, while the rest of the field will escape.

(b) Let another field be planted with seed less hardy than the foregoing, and then, in a season of disease, its first manifestations will be in places as above, from which it will spread in a milder form to the whole plat.

(c) Supposing the seed and the season eminently favorable to disease,

and the soil, in dryness, texture, richness and slope to be very uniform, then the disease will begin simultaneously all over the field, and proceed to the worst results should the bad weather continue; or cease entirely should dry cold weather come before much injury has been done to the foliage.

93. It was early asserted that the rust or mildew, which is a fungus plant, one growing upon another without rooting in the soil, was a new plant in Europe and North America at the beginning of the potato disease, and not before known to botanists. This opinion went largely to sustain the theory, that it was the exclusive cause of disease. The advocates of this theory further guess, for it is nothing more, that prevailing winds blew the dust or spores, as the seed is called, from the continent of South America, to some of the adjacent islands east, and that thence it was gradually carried from point to point, until it reached the coast of Western Europe. They suppose, also, that in some similar way it was brought into the United States. Others would suggest that it was carried in a latent state, in imported tubers.

94. Now of the truth of the first of these positions I utterly doubt. It is now admitted that the potato disease was in Europe long before it first excited public attention and alarm about 1843. But during those early years of the existence of the disease botanists did not happen to notice and analyze this fungal plant. If this plant be indigenous in South America, and be naturally developed there upon it, why may it not have been imported in some way into Europe and this country in the original reception of the potato from South America? Nay, more, why may we not suppose that as the particular fungus or rust that affects wheat, plum trees, cucumber vines, &c., seems to spring up spontaneously in fitting circumstances of disease, all these enemies of vegetation, or certainly many of them, are able to be sustained on other plants, though taking most naturally to those which have now been mentioned.

The cultivator who shall sow wheat, set plum trees, and plant cucumbers, in the centre of an almost boundless forest may expect disease on each of them under fitting circumstances, showing that the enemy of his several crops was already in possession of the soil, though not developed before on the plants just named.

95. If the preceding account of disease (22-69), be at all in harmony with facts, then this theory of the principal agency of this fungus in the production of disease is impossible, or certainly in the highest degree improbable. The supposition that this fungus has this principal agency goes on the assumption that the potato, aside from this danger, has a natural immortality, without the ordinary pathological liabilities of other plants. Other plants may suffer from bad seed, bad weather, and bad culture, until they fall a prey to disease, and many of them, sometimes whole varieties, gradually become fully exterminated. But upon the theory which I am now opposing, the potato has no ordinary subjection to pathological laws. I do not suppose that any advocate of the fungal theory would deliberately take this ground, but sure I am, that the mode of reasoning adopted by more than one of its advocates both early and late in

the discussion, must drive them legitimately to this most absurd conclusion.

96. If the train of reasoning and the recital of facts which I have exhibited in the preceding pages, be at all true, the fungus, instead of being the cause of disease is but the external proof of the previously morbid condition of the interior of the plant. Fungus on the potato and on other plants holds the same position in vegetable pathology that cancer, and erysipelas have in animal pathology, that is, they are not diseases approaching the body from without, but developments of a morbid condition within. Hence the conclusion is reached similarly in both cases that the cure cannot be accomplished, certainly not permanently by external applications but by a renovation of the system. The present influence of cancer may be veiled by excision, but it is not cured by that alone. Potato disease, in a given case, may be entirely checked by a change of weather. So a grape vine may receive great benefit from the present application of sulphur to the mildew on its leaves but such temporary benefit to either the potato or the grape will not save either from liability to disease in future years. Such exemption, can only be procured by renewal, in a wise mode of culture, from the proper seed.

97. As a proof how natural disease is to the potato pathologically considered, let me, in addition to the general argument detailed in Nos. 21-62 above, cite a number of striking facts. They all relate to the behavior of seedlings the year of their origination.

1st. In 1849, among others, I raised a family of about eighty sorts derived from the common Western Red. They were transplanted unwisely, too late, and in the use of fresh unfermented manure. They took root very slowly and grew too late. On digging, many of the sorts were of eatable size, but nearly all such were diseased. The influence of the manure had caused too rapid and large a growth, particularly in the plants producing these large tubers. It would be difficult to tell whence the mildew came unless impelled by natural pathological laws, so far were they removed from other potato crops.

2d. In 1852 I originated four thousand two hundred and ten sorts, which is considerably more than one fourth of all I have ever originated. They were in eleven different families, about one half of which were from the balls of South American varieties imported in 1848 and 1851. Nearly all these families of South American origin were ruinously late, as their parents before them had been, though often the seedlings were an improvement on the parent in time of maturity.

These seedlings as a body were far removed from older varieties of potatoes, except some that were very hardy. The year as a whole was finer for potato culture than any experienced in all this region since that time, or, indeed, for many years before. Yet these five or six late families were badly diseased both in foliage and tuber, the latter when dug in October being propably not half grown in many cases. All I can say of them is that they were diseased, not by contact with, or close neighborhood to, feeble roots, but in obedience to pathological law. In other words the disease arose out of a feeble parentage aggravated by growth amid unfa

vorable weather occurring at a period of the year (October) when every variety of valuable potato is ripe and usually harvested.

3d. In 1863, having a few plants more than I had room for in the field, I left them in the seed bed, thinning them out very much. They were however left standing quite too thick. The situation of the bed was low and sheltered from wind, and the soil was rich. There were no plats of potatoes growing within probably twenty rods of them, and they were shut out by a close growing nursery of apple trees. The season was one of the worst we have ever had for potato culture. These plants, forty-two in all, of three different families were all badly diseased.

Here again I see no origin for disease but from pathological causes. These causes were, feeble parentage in the case of two of the families, and bad season, rich moist soil, crowded condition, and seclusion from air in all of them. It would be easy for me to recite facts of this kind in great numbers from the culture of other years.

98. There is another most striking fact in the cultivation of seedlings the year of their origination. It is this, that other things being equal, such as weather, soil, culture, &c., their health is always worse than in subsequent years. This fact I noticed in a short article published in 1854, giving directions how to originate seedlings.

The reasons of this fact are few and obvious:

a. The plants mature usually a little later than in subsequent years. Hence they encounter uncongenial autumnal weather.

b. The plant is less favorably situated in the soil than that produced by an ordinary tuber when planted. That is, the young plant is necessarily set near the top of the ground, instead of being planted from four to six inches deep. Hence, during the whole season of growth it heats and chills too readily amid the changes of the weather. We have an exactly parallel case in the behavior of young apple and plum trees in rows of the nursery. They too, the first two or three years of their growth from the seed, present a much less healthy state of leaf and young shoots than in late years. The reason obviously is, that in these years of early growth, the roots are spread too near the surface of the soil where they dry, heat and chill too readily. In later years, their roots strike deeper and maintain a more equable condition of moisture and temperature, and are proportionately more healthful.

99. In closing this branch of my subject, it seems proper to advert to a few leading facts in relation to fungal plants generally.

I will begin with a brief description of fungal plants. There is a large class of plants called Cryptogamous, because having no flowers, or very imperfect ones-their mode of producing seed being unknown. Indeed their seeds are usually a fine dust, and bear little semblance to ordinary seeds. This family of plants includes six classes of some botanists, such as ferns, mosses, liverworts, sea weeds, and some other water plants, lichens, or those moss like patches found on stones, and fungi. This last comprehends mushrooms, toadstools, mould, smut and mildew. Fungi rarely grow out of the ordinary soil, but are found on decaying matter, as dying trees, old logs and stumps, manure heaps, cheese, milk, bread, and meat long left in a damp atmosphere, or clothes in the same position.