1922] 



ROSEN — A BACTERIAL DISEASE OF FOXTAIL 381 



none at 40 ° . Growth appeared first and was heaviest at 30-35 ° , 

 which may be regarded as the optimum zone. The minimum 

 zone has not been determined but it is probably around ° , while 

 the maximum is around 40 ° . Death occurred at 41 to 43 ° . It 

 is thus seen that the optimum, a rather high temperature, is 

 quite close to the maximum which in turn is close to the thermal 

 death point. 



Effect of drying. — Bacterial smears on sterile cover glasses were 

 kept dry for 1 hour, 5 hours, 48 hours, and 3 days, at 25° C. 

 When these glasses were dropped into broth growth occurred in all 

 except the one kept dry for 3 days. One would conclude then 

 from this experiment that the foxtail organism is sensitive to 

 desiccation. The following data indicate that such a conclusion 



is quite false. Diseased material collected July 30, 1921, and kept 

 in a dry condition in the laboratory at about 25 ° C. until March 

 24, 1922, a period of about 7 months, was surface sterilized in 

 the ordinary manner, macerated in sterile water, and sprayed 

 on oat seedlings, giving abundant infections, while a check pot 

 sprayed with sterile water showed none. The experiment was 

 duplicated with the same results. 



The writer is convinced that the effect of drying cannot be 

 measured merely by smears on glass, and taken by themselves 



such tests are aDt to lead 



The reason 



for this is apparent, bacteria within infected host tissue being 

 of course more or less closely associated with cellular matter. 

 The action of plant colloids in taking up and holding water has 

 been carefully investigated (see MacDougal, Carnegie Inst. 

 Publ. 297) so that the colloids in association with bacteria must 

 be considered in any water relationships. It thus appears that 

 the foxtail organism is resistant to drying. 



Effect of freezing. — Using 48-hour broth cultures, 0.2 cc. was 

 inoculated in tubes containing 10 cc. of broth. Two tubes were 

 placed into a freezing, brine-ice mixture, and 2 into an incubator 

 at 35 ° C. After 2 hours the 2 tubes, which had remained in the 

 form of solid frozen masses for more than \Vi hours, were re- 

 moved from the freezing mixture, thawed out, and poured plates 

 made from calculated dilutions. Check tubes kept in the incu- 

 bator for the same length of time were treated in the same way. 

 Using equal amounts of inoculum no noticeable difference in the 

 number of colonies which developed was obtained. The experi- 



