May 19,1923 
Spore Germination of Ustilago A venae 
587 
It was next desired to ascertain whether the same general relation of 
spore germination to varying soil moistures obtains at other tempera¬ 
tures. The low temperatures of 10® to 13° C., and the high temperatures 
of 30^ to 33° were chosen for this study. The duration of the different 
experiments was determined by the length of time required for spore 
germination at those temperatures. Tables IV and V show an agreement 
with Table III, and the three tables make clear that at these different 
temperatures germination is highest at 30 per cent soil moisture, is 
usually less at 60, and falls off very markedly at 80. 
Tabl^ IV.— Relation of soil moisture to the spare germination of Ustilago avenae 
incubated at temperatures of io° to 15° C. in 48 hours 
Age of 
spores 
(months). 
30 per cent water-holding 
capacity. 
Germi¬ 
nation. 
Type of germination. 
60 per cent water-holding 
capacity 
Germi¬ 
nation. 
Type of germination. 
80 per cent water-holding 
capacity. 
Germi¬ 
nation. 
Type of germination. 
9 . 
2. 
5 . 
Aver¬ 
age. 
Per ci. 
24 
Threads, some 
short tubes, 
long tubes, 
buds. 
Sporidia, threads. 
Sporidia rare. 
14 
Per ct. 
26 
II 
Threads very 
long; tubes, 
buds. 
Long tubes.. 
Threads, long 
and short 
tubes. 
Per ct. 
8 
Threads, short 
and long 
tubes. 
Short tubes. 
Threads. 
TABhE V.— Relation of soil moisture to the spore germination of Ustilago avenae 
incubated at temperatures of to 53° C. in 24 hours 
Age of 
spores 
(months). 
30 per cent water-holding 
capacity. 
60 per cent water-holding 
capacity. 
80 per cent water-holding 
capacity. 
Germi¬ 
nation. 
Type of germination. 
Germi¬ 
nation. 
Type of germination. 
Germi¬ 
nation. 
Type of germination. 
Per ct. 
Per ct. 
Per ct. 
10. 
4 
Short tubes, no 
3 
No sporidia or 
0. 06 
Tubes just visi¬ 
sporidia, some 
threads, short 
ble. 
tubes long, 
tubes mostly 
some buds. 
juSt visible. 
2. 
12 
Long tubes with 
4 
Tubes long and 
. 20 
Do. 
few threads. 
just visible. 
5 . 
10 
Long tubes, buds. 
13 
Threads, buds.. .. 
3-0 
Threads, short 
and long 
tubes. 
Aver¬ 
8 
7 
I. 0 
age. 
/ 
These results raise the question of the reason for the decrease of spore 
germination at the higher moisture contents. An increase in water 
might bring about a change in other factors affecting germination. 
These factors may be markedly modified when the puddling point is 
reached. At 80 per cent soil moisture, puddling is easily brought about 
