This section is from the book "The Gardener's Monthly And Horticulturist V18", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
In accordance with your request, I send you the following:
There are three diseases, apparently, afflicting the potato. First, the potatoes may be gathered apparently sound, but after being housed a short time, many of them and often the entire crop, are found soft and in a condition of decay.
Secondly, many tubers are nearly or entirely filled with hard concretions, while only a small part is seemingly healthy, but the entire potato remains dry.
The third diseased state - if it be really distinct from the other conditions - I have more carefully examined. The potato presents many irregular excavations on the surface, extending often deeply into it. These excavations on carefulest examinations present no trace of insect ravages. The sides and entire circumference of each pit are bounded by shrunken, irregular cells destitute of starch granules. On making very thin sections entirely across these excavations and properly treating the sections, a careful microscopical examination reveals the following facts: In many of the empty cells next the boundary of the excavation are beaded filaments of a fungus, two or more round cells, with the terminal one often presenting a point. Mycelial filaments obscurely septate creep all among these cells, and extend back into and among the more normal cells, in which the starch is still in a natural state. On many of these mycelial threads in the still full cells are oval or round bodies, about the one eight hundredth of an inch in diameter, each containing one or more distinct nuclei.
The cells containing these bodies - which, probably are resting spores or oogonia - are generally destitute of starch, though a few grains often remain, but are altered in structure, being rough and broken into fragments. It is apparent, that no insect could produce ravages similar to these, I am, therefore, convinced that a fungus is the cause of this form of disease, and that the plant is Peronospora, and that the resting spores are placed where they are in order to get nutrition through their resting stage in order to perpetuate the fungus in the coming season when the new crop shall be planted in the spring.
[At a recent meeting of the Academy of Natural Sciences, Philadelphia, Dr. J. Gibbons Hunt announced the discovery of what he believed to be the resting spores of the potato fungus in potato tubers. These resting spores had never been seen till last spring, when they were discovered in England by Mr. Worthington G. Smith, and found to be the cause of what was supposed to be a new potato disease. It was, however, but a new phase of the same old species of Peronospora, the peculiar season having favored the development of these resting spores, and hence leading to their discovery.
We believe, however, that Mr. Smith's discovery extends no further than the open ground; and that Dr. Hunt's finding them on the tubers and actively at work, is new and important. His remarks will, no doubt, be given in full in the Academy's proceedings; in the meantime, at our request, Dr. Hunt has kindly given the above abstract to us. Ed. G. M.]