CERTAIN SPECIES OF Mucor 309 
color in or on the substratum. This was obtained on bread, on 
rice, and in maltose-peptone-tyrosin solution. It probably rep- 
resents the storing up of excess food material, as a microscopic 
examination showed the color to be due to yellow globules in the 
hyphae; moreover, this color production occurred only in cultures 
with abundant food supply. 
The results of the experiments with carbohydrates plus as- 
paragin, on the one hand, and mineral salts (including ammonium 
nitrate), on the other, which show that the mucors grow much 
better in the first case than in the second, may, it is believed, offer 
some indication as to the reason why complex media (rolled oats, 
bread, rice, cornmeal, etc.) are better than simpler media. 
Fermentation is, apparently, a more widespread process in 
this genus than has hitherto been supposed, knowledge of the 
forms which can produce this phenomenon being limited to some 
twenty species. Wehmer (1907) has given a clear and concise 
summary of the work published on the subject. The writer’s 
results, positive except in one case, have added twelve species to 
the list. | 
Hagem (1910) found that tyrosin was oxidized by several 
species of Mucor and Rhizopus, with the production of a red or 
reddish brown solution. He thinks that this change is brought 
about by the enzyme tyrosinase. In the cases of Mucor strictus, 
M. silvaticus, M. plumbeus the color was pale red, in M. racemosus 
and M. christianiensis, dingy brownish red, but in Rhizopus 
nigricans and R. nodosus the solution was dark red. The writer’s 
experiments showed that the solution was colored dark reddish 
brown, with the formation of a dark brown precipitate, by Mucor 
griseosporus and M. coprophilus. In the case of Mucor proliferus, 
M. spinescens, and M. plumbeus the solution was pale brown and 
a brownish black precipitate was observed. With Glomerula 
repens a brownish tinge to the solution was obtained, while the 
aerial growth was distinctive in that it was pinkish buff (Ridgway). 
The objection might be raised that bread is a variable substance 
and therefore is unsuitable for a standard culture medium. A 
comparison of cultural results obtained, during the past three 
years, with bread obtained from different sources has proven this 
objection negligible. The bread used is the ordinary baker's 
