. Carnegie Institution of Washington publication. 84 BACTERIA IN RELATION TO PLANT DISEASES. philic species. Usually even the most resistant spores, if freely exposed, are destroyed by one to two hours exposure to 150° C., of dry heat, or by thirty minutes exposure on each of three consecutive days to streaming steam at 100° C. Some very resistant spores have survived a single steaming or boiling of five or six hours duration (eight hours in one of Tyndall's experiments), and it is not unlikely that some slowly germinating sorts may be able to resist discontinuous steamings for three days. It
. Carnegie Institution of Washington publication. 84 BACTERIA IN RELATION TO PLANT DISEASES. philic species. Usually even the most resistant spores, if freely exposed, are destroyed by one to two hours exposure to 150° C., of dry heat, or by thirty minutes exposure on each of three consecutive days to streaming steam at 100° C. Some very resistant spores have survived a single steaming or boiling of five or six hours duration (eight hours in one of Tyndall's experiments), and it is not unlikely that some slowly germinating sorts may be able to resist discontinuous steamings for three days. It is possible also that there may be some sorts able to germinate and again assume a resistant spore form in less than twenty-four hours although this is not probable. Some spores are destroyed by a short boiling at 100° C., and all spores are quickly destroyed by steam under pressure, i. e., in an autoclave. A. Fig. 70.* temperature of 110° C. for ten or fifteen minutes is sufficient. Exposure of media to higher temperatures and for longer periods should be carefully avoided. It must be remembered, however, in using autoclaves, that all of the air must be replaced by steam before the apparatus is closed, otherwise the temperature to which the medium is exposed will not correspond to that indicated by the pressure gage. The most convenient autoclaves known to the writer are the large sizes of the *Fic. 70.—Earliest stage of fruit spot on green plums, due to Bacterium pruni (Erw. Sm.). The bacteria have entered through the stoma. They disappear farther in, and also a few micra to either side of this stoma, as shown by an examination of the serial sections. Material fixed in strong alco- hol, infiltrated with paraffin, and cut on the microtome in series. Section stained with carbol-fuchsin and drawn directly from the microscope with the aid of a camera Please note that these images are extracted from scanned page images that may have been digitally enhanced for reada
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