582 
Journal of Agricultural Research 
Vd. XXIV, No. 7 
In order that Table II be clear to the reader, there are four facts which 
must be borne in mind. First, in many cases the incubators did not hold 
the temperatures within satisfactory limits, so that the upper limit of the 
temperature range was more significant than the average temperature, 
especially when the spores were incubated for a long time. For this 
reason the minimum temperature for spore germination rests between 4® 
and 5° C. In the second place, the age of the spore material influences 
very markedly the percentage of germination and, to a small degree, 
extends the range of temperature within which the spores will germinate. 
This is seen clearly in the germination between 31.7° and 32.7° C. Of 
six observations made after 6 hours, germination occurred when the 
spore material was 2 and 4 months old, but not when it was 5 and 6 
Fig, 2.—Time required for maximum percentage of germination and sporidial formation with Ustilago 
avenae, at temperatures ranging from 4^ to 35° C., in experiment 5. 
months old. Third, the spore material used for experimentation in the 
second year showed a higher percentage of germination, and germination 
at a wider range of temperatures than that used the first year. This 
accounts for the fact that experiments ii to 15, inclusive, conducted 
during the second year, show higher percentages than the earlier experi¬ 
ments. In the fourth place, germination apparently decreased after a 
certain length of time, as some of the figures in the table show. This, of 
course, could not be due to an actual decrease, but was due to the fact 
that the promycelia broke away from some of the spores, leaving them 
indistinguishable from ungerminated spores. The examinations were 
discontinued in most cases when lower percentages were obtained. Where 
the records were made, however, the figures were recorded to show in a 
more decisive way where the maximum germination was attained. 
