362 BOTANICAL GAZETTE [NOVEMBER 
With ro per cent sugar, the results confirm the preceding. 
EXPERIMENTS WITH GLUCOSE.—Glucose in strengths of 2.5, 5, 
and 1o per cent was also tried in the same way as described for 
cane sugar. The hyphae grew more vigorously in the glucose and 
reacted better. The results, in general, agree with those given for 
cane sugar. 
MIyYosHI’s TEST BY DIRECT APPLICATION OF THE SUBSTANCES.— 
Among other tests for chemotropism, Mryosur (8) sowed spores 
in a film of 5 per cent gelatin on a glass slide, and when the germ 
tubes were still quite short, he placed a small amount of glucose 
at a given point in the gelatin. Diffusion commenced immediately, 
of course, and spread radially through the gelatin. With Rhizopus, 
he found that although some of the hyphae showed only more 
copious branching and an increase in thickness, others curved 
decidedly toward the center of diffusion. With Penicillium, 
however, no effect could be observed. On experimenting with other 
substances, he concluded that whenever no positive results were 
obtained, the failure was due to too rapid diffusion of the chemical 
substances. 
Since this method was simple, and appeared practical, it was 
tried out extensively by the writer, using agar as well as gelatin 
films, and adding in some cases a small bit of solid glucose, 
in others, of cane sugar. Small pieces of turnip juice agar were 
tried also, these being fitted into corresponding cavities in the 
films. Neither Rhizopus, Penicillium, nor Botrytis gave any 
positive result, beyond the more copious branching and increased 
hyphal thickness mentioned by Miyosui. Even in the case of the 
turnip juice agar, no turning was evident on inspection with the 
microscope. Possibly, as Mriyosui suggests, too rapid diffusion 
is the cause of the failure here. In any case, the mica plate method 
is far more definite and accurate. 
Discussion 
THE STALING SUBSTANCES.—From the foregoing it is clear that 
changes take place in a medium in which the fungus has grown, SO 
that the medium then acts in a negatively chemotropic way toward 
the fungus. Whether these changes are due to the excretion of 
