CERTAIN SPECIES OF MUCOR 257 
ammonium nitrate or asparagin. Rolled oats and wheat starch 
were both used with water in the proportion of I : 2 parts water 
by weight; corn meal was used with equal parts of water. Bread 
was used in the same manner as previously mentioned. Rice 
was used with three parts of water. Only the pulp and juice of 
the grapefruit were used. In the case of prunes, about one fourth 
of a prune was moistened with 5 c.c. of water. The results are 
given in TABLE III. 
From this table we see that the best growth occurs on rolled 
oats, and that of the six best media, five are complex substances, 
while the sixth—glucose-asparagin agar—contains an available 
carbohydrate and an organic nitrogen compound. A comparison 
of the results obtained with glucose-asparagin agar and glucose- 
nitrate agar shows that the former is a more favorable medium. 
This is due to the form of the nitrogen offered the plant, and this 
nitrogen source is probably one of the important reasons why 
complex media are more suitable for these forms. Mannit with 
asparagin is better than sucrose with asparagin, but sucrose with 
nitrate is a better combination than mannit with nitrate. This 
is in accord with Jost’s (1907) statement that the quality of the 
nitrogenous material has an influence on the nutritive value of 
any particular carbon compound. The growth on grapefruit 
was fair, while that on prunes was poor. This last result was, in 
all probability, due to the fact that the medium contained too 
high a percentage of sugar. This hypothesis is borne out by 
the fact that in practically all cases in which growth occurred, 
only a sterile mycelium developed. It should be mentioned in 
connection with the use of rice that, in order to determine whether 
there would be any difference in results with rice from different 
places, an experiment was set up with fifty-three numbers of 
mucors, using rice from different sources, purchased in Detroit 
and in Ann Arbor. The results showed no appreciable difference. 
It seemed advisable, from the results obtained in the first 
two series of experiments, to select certain media and test them 
with a larger number of forms. Consequently a series of cultures 
was made with rice, bread, and grapefruit, including a large number 
of mucors. The height of the cultures is given in TABLE IV. 
An interesting feature of the cultures on rice was the frequent 
