594 
Journal of Agricultural Research 
Vol. XXIV, No. 7 
An artificial medium was used, therefore, in the study of the effect of 
temperature on spore germination. Arthur and Stuart (j), Brefeld (2), 
Clinton (j), Hitchcock and Norton (4), Maire (5), and Norton (6) germi¬ 
nated the spores in many artificial media. Of these, Pasteur's solution 
was found most favorable for the following experiments. 
The spores from a pustule formed in an anther were suspended in 
a tube of medium, mounted in Van Tieghem cells, and subjected to 13 
different temperatures between 8° and 37° C. in thermo-regulated 
incubators. Duplicate mounts were placed at each temperature and the 
experiment performed 11 times. To determine the cardinal temperatures 
for germination, the percentage of germination was counted; the sporidial 
production, the number of cells in the promycelia, and the cell contents 
were observed; and the length and width of the germ tubes measured. 
Fig. I. —Graph showing percentages of germination of chlamydospores of Ustilago uae at different tempera¬ 
tures. 
The exact minimum for spore germination of Ustilago zeae was not 
determined. Four experiments showed germination at an average 
temperature ranging from 7.9® to 8.4® C., the germ tubes appearing on 
the 12th, 15th, i6th, and 21st days, respectively.’ The temperature 
range of the individual tests was greater than desired. That, together 
with the daily removal of the mounts from the incubators, may have given 
sufficient opportunity for eventual germination. The optimum tempera- 
tiu*e for germination is arbitrarily defined as that at which there is the 
highest percentage of germination within 24 hours together with a pro¬ 
duction of such germ tubes as behave normally, especially with respect 
to sporidial production. The highest percentage of germination within 
24 hours occurred between 26.5° and 34.7° C. as is shown in Table I 
and figure i, which give the average results of all experiments. As 
