The American Agriculturist Volume 6 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1847 Excerpt: ...and even from America. Guided by these specimens, he has traced the progress of the disease from its very commencement, both in the leaves and stalk and in the tuber. All of his conclusions seem reasonable and not improbable. The disease in the tuber always commences by the appearance of a brown matter in the cells which contain the starch. Each of these cells includes a little bag filled with grains of starch, and a liquid, having in solution albuminous substances, dextrine, and a little sugar; by the decomposition of these substances is produced the brown color which, in a more advanced stage of the disease, becomes black. On chemical examination, these colored substances have all the properties of humus and ulmin, two bodies which, under the form of humic and ulmic acids, occupy a prominent position in the organic part of the soil. As the disease advances, the walls of the cells are destroyed, and finally large cavities are formed where the potato is exposed to drying influences. At, or sometimes before, this stage of the malady, parasitic fungi begin to appear, generated within the cells. Of these plants, Professor Harting has figured and described no less than nine varieties. It has been said that these are the cause of the malady; but the most powerful microscopes show nothing of them until an advanced stage of disease, and sometimes not even then; instances are not unfrequent when the whole tuber is destroyed without their appearance. A nother very conclusive reason against the fungus theory, is the fact that infection is with difficulty, if at all, transmitted by these plants. When they were placed in contact with a freshly cut surface of a healthy tuber, and allowed so to remain for a month, in no instance was the same species reproduced in one cas...