. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. 64 BACTERIA IN RELATION TO PLANT DISEASES. passage-ways into the deeper tissues of the plant, and it is probable that bacteria frequently make use of them in canker-diseases and the like, but of this we have, as yet, no clear proof. In case of potato-tubers, the lenticels swell and rupture when the earth is unduly moist or when they are kept in a saturated atmosphere, and an easy entrance is then afforded to all sorts of soil organisms, es- pecially to certain bacteria which induce soft rots. The writer has occasionally se
. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. 64 BACTERIA IN RELATION TO PLANT DISEASES. passage-ways into the deeper tissues of the plant, and it is probable that bacteria frequently make use of them in canker-diseases and the like, but of this we have, as yet, no clear proof. In case of potato-tubers, the lenticels swell and rupture when the earth is unduly moist or when they are kept in a saturated atmosphere, and an easy entrance is then afforded to all sorts of soil organisms, es- pecially to certain bacteria which induce soft rots. The writer has occasionally seen on the potato- tuber a small superficial bacterial rot-spot centered in a single lenticel. Sorauer observed this lenticellate infection many years ago. It was also noted by Reinke and Berthold in 1879, and has been seen by other persons. The writer first observed it in the laboratory in 1886-87, during a winter spent on diseases of the potato, and has seen it in the field in wet autumns. The earliest record of any sort of lenticellate infection appears to be that of Hermann Schacht. In 1856 he stated that scab often begins in the lenticels of the potato-tuber {loc. cit., pp. 24 to 25, and his plate VII, fig. 3), and early the following year Caspary also called attention to the subject (Botanische Zeitung, 1857, column 116). In 1907 Dr. F. C. von Faber described a bacterial scab of beets which begins in the lenticels. This was common in Germany in 1906. Bacteria which have multiplied enormously in the interior of shoots may again reach the surface of the plants through lenticels as in case of the mulberry blight (fig. 3). Extrafloral nectaries.—The stigma. No bacterial diseases are yet known in which infection takes place through extrafloral nectaries or through the stigma, but these are also unprotected places and such channels of infection are likely to be discovered if searched for. PERIOD OF INCUBATION. By this we mean the time between exposure to the cause of the disea
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