Fungous diseases of plants . disease may occur in Japan upon radishes. It has been shown that infection takes place by way of the waterpores of the host. In accordance with this fact, the climatic con-dition favoring the entrance of the organism is sufficient moisturein connection with warm days and cool nights. This would favor Io8 FUNGOUS DISEASES OF PLANTS the suffusion of the plant with water, and even the extrusion ofdroplets from the pores. Cool weather, warm, dry nights, and adry soil offer a check to the disease. Smiths careful study ofwater pore infections has contributed greatly to o
Fungous diseases of plants . disease may occur in Japan upon radishes. It has been shown that infection takes place by way of the waterpores of the host. In accordance with this fact, the climatic con-dition favoring the entrance of the organism is sufficient moisturein connection with warm days and cool nights. This would favor Io8 FUNGOUS DISEASES OF PLANTS the suffusion of the plant with water, and even the extrusion ofdroplets from the pores. Cool weather, warm, dry nights, and adry soil offer a check to the disease. Smiths careful study ofwater pore infections has contributed greatly to our knowledge ofthe method of bacterial attack. Symptoms. The first symptoms in the leaves are manifested ^ at the margins, and consist of yellowing of all the affected partsexcept the veins, which become decidedly brown or black [seeFig. 24]. The leaves appear to have burnt edges. From the mar-gin of the leaf the progress of the disease is inward and downwardthrough the stem. It usually enters the latter through the A B Fig. 23. Black Rot of Cabbage. (Photograph by F. C. Stewart)A, inoculated and diseased plant; B, control, healthy Subsequently the disease passes out again from the infected steminto healthy leaves and up into the center of the head. If leavesdiseased at the edges are pulled off and examined where they jointhe stem, the groups of fibrovascular bundles, or leaf traces, in thepetiole, are seen to be either free from the disease, in the earlystage, or decidedly brown or even deep black from its attacked in this manner fall off prematurely one afteranother, leaving in bad cases a more or less elongated stem cov-ered with leaf scars and crowned with a tuft of small leaves. Ifthe disease has entered the stem only on one side, that side isdwarfed and the head becomes one-sided. When young plants 1 Smith. The Black Rot of the Cabbage, /. c, p. 6. SCHIZOMYCETES. BACTERIA 109 are affected they may be killed. Any affected plants are prey tosaprophy
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