586 
Journal of Agricultural Research 
Vol. XXIV, Na 7 
of the soil the following experiment was performed. Layers of oven- 
dried agar were weighed, clipped between filter papers, buried for 24 
hours in cans of soil, the moisture content of which was made up to 
definite percentages, and then removed and weighed. The quantity of 
distilled water absorbed by i gram of oven-dried agar in 24 hours at 
22® to 23® C. was found to be 11.8 grams. This maximum quantity of 
water absorbed under these conditions may be considered the water¬ 
holding capacity of agar. In the same time and at the same temperature 
similar agar placed in samples of a soil containing, respectively, 80 per 
cent, 50 per cent, and 20 per cent of its moisture-holding capacity, 
absorbed, respectively, 55 per cent, 30 per cent, and 10 per cent of its 
water-holding capacity. This shows that agar absorbs water approxi¬ 
mately in proportion to the amount in the soil and may be interpreted 
as indicating fihat the amount of water available to the fungus fluctuates 
with the moisture content of the soil. It would seem that, as far as the 
other factors in the soil are concerned, the conditions to which the spores 
were subjected very closely approximated those occurring in nature, and 
it will so be assumed in the remainder of this paper. 
In the first moisture experiments, the soil temperature was main¬ 
tained between 20® and 24® C., and germination was recorded between 
24 and 27 hours after sowing. Table III gives a summary of the results 
of these experiments. 
From Table III it will be seen that the production of sporidia, or the 
small hyphae which replace the sporidia, seems to be associated with 
conditions favorable to good germination, and occurs less frequently at 
80 per cent soil moisture. 
Table III .—Relation of soil moisture to the spore germination of Ustilago avenae 
incubated at 20^ to 24^ C. in 24 to 27 hours 
30 per cent water-holding 
60 per cent water-holding 
80 per cent water-holding 
Aseof 
capacity. 
capacity. 
capacity. 
spores 
(months). 
Germi¬ 
nation. 
Type of germination. 
Germi¬ 
nation. 
Type of germination. 
Germi¬ 
nation. 
Type of germination. 
Per cL, 
Per ct. 
Per ct. 
21 
Threads,, buds,' 
sporidia. 
21 
Threads. 
4 
Short tubes, 
long tubes, 
•T 
buds. 
II. 
19 
35 
Threads, sporidia. 
Threads, buds; 
sporidia rare. 
19 
28 
.do. 
0 
2 .. 
Threads rare; 
.6 
Tubes just vis¬ 
ible; one long 
buds abundant ; 
Very many 
short tubes. 
with thread. 
a. 
16 
Sporidia abun¬ 
II 
Long tubes. 
5 
Threads. 
dant; threads, 
buds, long 
tubes. 
threads, buds. 
c. 
16 
Very long tubes, 
threads; spo¬ 
10 
Threads. 
c 
Do. 
0 
ridia abundant. 
18 
Threads, spo¬ 
ridia very rare. 
15 
.do. 
7 
Few threads; 
long and short 
5...... 
Aver¬ 
age. 
21 
17 
4 
tubes; buds. 
^ Threads are the infection hyphae which may replace sporidia. Buds, a very early state of infection 
hyphae or sporidia. 
