. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. 26 BACTERIA IN RELATION TO PLANT DISEASES. the contran^, as much as possible should be made out of morphology, particularly that of the living organism, and in this connection the recent efforts of Migula and Fischer are especially deserving of commendation. MOTILITY. If motile, determine kind of motion and rapidity (margin of small hanging drops on thin covers sus- pended over hollow-ground slides).f The cover may be prevented from sliding by touching one edge with a very little vaseline or cedar oil; if too much is used
. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. 26 BACTERIA IN RELATION TO PLANT DISEASES. the contran^, as much as possible should be made out of morphology, particularly that of the living organism, and in this connection the recent efforts of Migula and Fischer are especially deserving of commendation. MOTILITY. If motile, determine kind of motion and rapidity (margin of small hanging drops on thin covers sus- pended over hollow-ground slides).f The cover may be prevented from sliding by touching one edge with a very little vaseline or cedar oil; if too much is used it runs under, mixes with the hanging drop, and spoils the mount, and possibly in the end the objec- tive is ruined, if the student continues to search for a clear field. The beginner is very apt to mistake Brownian movement for self-motility. It sometimes requires very careful observation to be quite certain. Rods which appear to be motionless will sometimes be seen to dart away quite suddenly if watched. In some species young cultures are much more apt to be motile than old ones ; in others motility appears to be an almost constant characteristic. The move- ments of bacteria are sometimes quite characteristic for particular sorts. They may be slow or rapid tumbling motions centering in the shorter axis, or straight or sinuous slow or rapid darting move- ments in the direction of the longer axis, with rotation on this axis. The media of Hiss ('97, Bib- liog., XVI) and of Stoddart ('97, Bibliog., XVI) are sometimes useful for distinguishing macroscopically between motile and non-motile forms. The former spread as a thin layer over the whole surface, the latter pile up in restricted areas around the points of inoculation. The student should not remain con- tent with merely determining motility, but when this has been settled he should turn his attention to Fig. 24.* staining the organs of motion. *Fir,. 24.—Upright Zeiss camera for photomkrographic work. The cup (a) slips over
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