. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. EFFECT OF DESICCATION. 7^ Organisms believed to be non-sporiferous show great differences, some being killed by an exposure of a few minutes or a few hours, while others remain alive for many weeks. For further information see the special chapters on Bacillus traclie- iphiliis, B. carotovonis, Bad. hyaciiithi, etc. Tests may also be made in air dried over sulfuric acid or calcium chloride. Harding & Prucha have shown recently that Bacteriitni campestre remains alive much longer when dried on cabbage seed than when drie
. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. EFFECT OF DESICCATION. 7^ Organisms believed to be non-sporiferous show great differences, some being killed by an exposure of a few minutes or a few hours, while others remain alive for many weeks. For further information see the special chapters on Bacillus traclie- iphiliis, B. carotovonis, Bad. hyaciiithi, etc. Tests may also be made in air dried over sulfuric acid or calcium chloride. Harding & Prucha have shown recently that Bacteriitni campestre remains alive much longer when dried on cabbage seed than when dried on glass cover-slips. In their experiments this organism was dead on glass at the end of ten days, but alive on seed at the end of thirteen months. EFFECT OF DIRECT SUNLIGHT. The exposures should be made in a thin stratum of nutrient agar, not sowed too thickly (there may be several hundred colonies on the plate, if properly distrib- uted), in thin-bottomed Petri dishes, to an unclouded sun for 5, 10, 15, 30, 45, and 60 minutes, a portion of the bottom of the plate, which is placed uppermost, being covered by some substance impervious to light, such as several folds of Manila paper VL. Fig. 61.* Fig. or of the black paper which comes wrapped around photographic dr}' plates, covered in turn by white paper. Exposures of several hours are not recommended. If the layer of agar is very deep, or if the sowings are too thick, some organisms will screen others and all will not be killed. Ten cubic centimeters is a proper amount of agar to use for a plate having an area of 60 square centimeters. The latitude, altitude, time of year, time of day, and intensity of the light should also be recorded. In the summer- time it is very important that the exposures should be made on blocks of ice or. *FiG. 61.—Gelatin culture of Bacillus amylovorus (Burrill) Trev. in a Petri dish. Exposed in 1896 to direct sunlight for four hours on ice after covering portions of the plate with pasteboar
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