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It has been said that the leaves are first affected ; and that the withering of these leaves, as if they had been struck by a blight, is the first sign or warning of the presence of the destroyer. But I am inclined to doubt the correctness of this statement. The first indication of the presence of the disease, is upon the haulm or stalk. This, if carefully examined, will be found to be covered with minute black specks, strikingly resembling in appearance the excrement of the fly, and visible to the naked eye. These specks are a species of fungus, which attacks the plant, in most cases very suddenly, and which, in my estimation, is the chief cause of the rot. As soon as their roots (for they are parasitic) have penetrated through the cuticle of the stalk, the sap, from which they derive their nourishment, becomes vitiated, and the withering of the leaves is the immediate consequence. This withering of the leaves affects the health of the plant, and renders it more susceptible to the attacks of the fungus. Soon the pith of the stalk becomes diseased, and, if examined with a lens, will be found to contain many of these black specks, showing that the fungus is there. Finally, it extends down the stalk to the roots, or parts connecting the stalk with the tubers. These roots are completely hollowed out by the fungus, or in other words, their interior is entirely destroyed, or, eaten up. The skin of the tuber is next attacked, and this becomes discolored. By lifting up the skin carefully, and examining the tuber with a lens, the same black specks will be found, showing that the fungus is there. Last of all, the roots of the fungus penetrate the cells of the tuber, destroy their texture, and, by breaking down their walls, the contents of contiguous cells are brought together, and corruption, or putrifaction ensues. This is the last stage of the disease, or the rot. The above is a brief sketch of the progress of the disease, which I have endeavored to clothe in language comprehensible by
In harvesting a field of potatoes, those who have carefully noticed the appearance of the stalks, have been able to tell what hills were affected by the rot, and what were not; and not only so, but the same observation enabled me to tell what tubers in any particular hill were affected. The stalks of those hills which are affected, are rotten at the bottom, near their connection with the root; that is, their texture is entirely destroyed, and they are in a brittle, decayed state.
Sometimes one stalk only in a hill is in this condition, and the tuber or tubers connected with that stalk, will be found affected with the rot.
After the potatoes are harvested, those on which the black specks above described are found, will decay; but in the process of decay, I have not found that they affected sound tubers, and caused them to rot. The disease cannot be communicated in this way; it must pass through the several stages aforenamed. There may be instances in which tubers slightly affected, or containing merely the germs of the disease, from peculiar causes, will remain sound through the winter, and it may be in this way that the disease is propagated from year to year. But of the correctness of this suggestion, I am not fully satisfied. It needs to be confirmed by observation. Those who are acquainted with the natural history of the Fungus tribe, are aware, that their sporules, or seeds, are exceedingly minute and numerous. Probably millions proceed from a single plant. Besides, these seeds are so light, being but a mere dust, as seen by the naked eye, that they are easily wafted about, and so minute, that they might attack a plant without being perceived, until they had reached their maturity. It is owing to this, that the disease prevails so extensively, and it may be that it has thus been propagated even across the ocean. The wide prevalence of the disease, indeed, will be no matter of surprise to those accustomed to the enlarged views of the diffusion and propagation of plants, which an acquaintance with Botany furnishes.
I have prepared specimens, illustrating the progress of the disease under consideration, which I should be happy to show to any one desiring further information. The fungus which attacks the potato is very small, so much so, that it is probable there are no glasses of sufficient power to render their seeds visible. Yet, that they have seeds, no one can doubt.
The specimens to which I have alluded, show the fungus upon the outside of the stalk; next upon the pith or inside ; next upon the interior of the root ; next upon the skin of the tuber; and, last of all, in the cells of the tubers themselves. I have also prepared specimens, showing the different appearance of the healthy and the diseased plant.
In an article published by Mr. Teschemacher, in the New England Farmer, about two years since, he attributes the disease in the potato to a fungus, and states, that to discover a remedy for the disease, he applied various substances to the fungus, to effect its decomposition; and names salt as the first application. "The action of this was so instantaneous and decided," says he, “that I did not proceed to any other. A portion of the dark substance was placed on a piece of glass on the microscope stand, in a drop of distilled water, and then thoroughly examined: a little salt on the fine point of a penknife was then added; a nearly instantaneous change took place; the dark-colored masses separated, much of them seemed to pass away, and instead appeared numerous dark slate-colored globular bodies, which I easily recognized as the spores or reproducing bodies of the fungus." Having the above article by me at the time I pursued my investigations, I repeated the experiments first tried by him; but not with similar success. The decomposition of the plant was not effected; nor was I able to discover the spores. Three several times I repeated the experiment, but with no different result. I did not try either of the other substances mentioned by him, as time did not permit.
The disease called in Germany the Potato scab or wart, and which Dr. Wallworth ascribes to a species of subterranean fungus, which he calls Erysibe subterranea, cannot be the same, I think, as the Potato rot, for this is not caused by a subterranean fungus, but by one which attacks the stalk of the plant, as I have already stated. Mr. Teschemacher, in a subsequent article in the New England Farmer, appears to be of the same opinion, and the remarks which I have offered upon this disease will be found, in the main, to agree with his.
A writer in Silliman's Journal of Science and Arts, for September, 1845, states that it “cannot be said with certainty that the disease first appears as a fungus upon the leaves; and that “there are well authenticated instances where the potato tops have remained green and flourishing, while the tubers were much diseased.” In this statement, I am inclined to think there is an unintentional mistake, which has arisen from want of accuracy in the observations. There may be well authenticated instances of diseased tubers in VOL. XIII.--NO. I.
hills where a part of the tops were green and flourishing; but I think if all the tops had been closely examined, some one would have been found affected, and that one communicating with the very tubers which were rotten. I am fully convinced, that the disease is caused by the fungus in question, and that it first attacks the stalk.
In the remarks of Professor Playfair, in his Lectures delivered before the Royal Agricultural Society, in London, reports of which were published about a year since, he attributes the disease to the destruction of the cellular walls of the tuber, and in this he follows Liebig, the scientific German chemist. But this destruction of the cells, it appears to me, is not the primary cause of the disease, but an effect, as I have already stated, of the penetration of those cells by the roots of the fungus. Most of the phenomena described by both the above gentlemen, may be discovered attending the disease; but its true cause lies behind those phenomena. That there is any constitutional weakness affecting the cellular tissue of the potato, I am inclined to doubt. We have had peculiar seasons, both here, and in Europe, for the past three years; seasons which have been highly favorable to the generation and propagation of Fungi, and they have been remarkably abundant every where. It is these fungi that have attacked the potato, and produced the disease. I believe its prevalence to be owing, or attributable, to the peculiar state of the atmosphere; and that no specific, or infallible remedy for the disease, has been yet discovered. It may disappear in a few years. A change in the atmosphere may render the reproducing spores of the fungus inert for a time sufficient to destroy them, and this may check the disease. I indulge in no apprehensions for the future. A merciful Providence watches over us all, and in his goodness we may safely trust.
West Scituate, Mass., Dec. 1846.
Art. IV. Zinc Labels for Trees. By J. Owen, Cambridge.
In the last number of your Magazine, you have described a kind of label for trees, which comes near enough to a
method practised by me, for several years, to induce me to think that you alluded to a conversation I had with you on the subject a short time since. I have now written out my method, and accompanied it with some explanations. If you think the genuine reading of any importance, you are at liberty to give it a corner in your next number. A great objection to the use of unpainted zinc, marked with a lead pencil, one of the modes adopted by your correspondent, is the indistinctness of the writing, the color of the zinc and of the pencil mark being nearly the same.
Loudon, in his great work on Gardening, has enumerated many kinds of tallies used in England, no one of which combines, to so great a degree, those essential advantages, durability, convenience and economy, as the painted zinc. Even for mercantile purposes, I think this will prove the most convenient mode to nurserymen, and be highly useful to purchasers, most of whom, with the loss of the common wooden labels, soon lose the names of their fruit trees, about which they remain indifferent, till at length the different varieties begin to bear. Then curiosity is excited to identify the kinds. The greatest confusion follows. Serious mistakes are made and perpetuated. A large and dear experience is necessary, before the amateur can separate the wheat from the chaff, distinguish the genuine from the spurious, and at last arrive at even a tolerable degree of certainty in the nomenclature of fruits.
I send you a few tallies, as specimens of the various methods I have used, at different times, while seeking for something better than the “good old way."
Cambridge, Nov. 21, 1846.
METHOD OF MAKING THE LABELS.*—Have ready a sheet of zinc, which must be perfectly clean. Take the purest white lead, ground in oil; thin it with spirits of turpentine, in place of oil; add mastic varnish (copal turns the paint yellow,) sufficient to make the composition adhere well to the zinc and give it hardness, but not in excess, which
* Any tinman will furnish strips of clean zinc, cut them into pieces of two square inches, after being painted, and punch them, at the rate of 25 cents per hundred. This would be cheaper than to use whole sheets.