. Carnegie Institution of Washington publication. 294 BACTERIA IN RELATION TO PLANT DISEASES. The thermal death-point is 430 C, the lowest yet recorded for any organism infesting plants, and until recently the lowest known. In an experiment made in June, 1896, an exposure of one hour to 410 C. killed all, i. e., no colonies developed on the agar plate poured from the heated bouillon (11 days incubation) whereas the check-plate, i. <?., the plate inoculated from the tube before heating yielded several thousand colonies per square centimeter. Exposure in bouillon for one hour at 400 C. killed
. Carnegie Institution of Washington publication. 294 BACTERIA IN RELATION TO PLANT DISEASES. The thermal death-point is 430 C, the lowest yet recorded for any organism infesting plants, and until recently the lowest known. In an experiment made in June, 1896, an exposure of one hour to 410 C. killed all, i. e., no colonies developed on the agar plate poured from the heated bouillon (11 days incubation) whereas the check-plate, i. <?., the plate inoculated from the tube before heating yielded several thousand colonies per square centimeter. Exposure in bouillon for one hour at 400 C. killed three-fourths or more, as determined by agar poured-plates. Exposure to 400 C. for one-half hour destroyed about half. In many ways B. tracheiphilus is a very sensitive organism, and consequently it is difficult to work with. It is hard to plate out owing to its viscidity. It is very sensitive to heat, to dry air, and to direct sunlight. Freezings are also harmful. It is sensitive also to its own decomposition products, especially acids. It is not a rapid grower nor a very copious one on culture-media and vigorous organisms crowd it out. It does not, however, lose virulence readily by cultivation on artificial media. On most media, transfers must be reasonably frequent to keep it alive. It was alive once on sweet potato after 33 days. It was dead on carrot after ^^ days. In one instance on steamed Irish potato, parts of a culture were alive after 26 days. In another instance a potato culture (which did not gray) was dead at the end of 16 days (see also plant inoculations, pages 275, 283). It has lived, however, in some of the writer's slant agar-cultures for several months and in litmus milk for 3 months; it may be kept alive for several months in peptonized beef-bouillon with addition of cane- sugar, if calcium carbonate is also added so as to neutralize the acid as fast as it is formed. Often from agar-stab-cultures a few months old it is recoverable, if at all, only by pour
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