16 
BULLETIN 759, U. S. DEPARTMENT OE AGRICULTURE. 
trifolii there is almost a regular decrease of the number of groups 
from those containing one to those containing eight. Sufficient evi- 
dence has not been collected to determine whether the same clean-cut 
difference in the behavior of the two species appears when the 
spores are discharged from apothecia on living leaves. 
SPOEE GEEMINATION. 
In all the more obvious features of germination, the ascospores of 
the two fungi behave alike. They germinate readily when they have 
been discharged naturally upon a suitable moist surface; but germi- 
nation is infrequent if the spores have been crushed out of the asci 
or if they are submerged in water. A single germ tube emerges from 
any point in the circumference of the spore, except that germination 
from the end has been observed only in the case of a few spores of 
Pseudopeziza trifolii. Under the best conditions that have been 
found, the proportion of germination is usually from 30 to 50 per 
cent. The vigor of germination varies greatly. Many of the spores 
which push out short germ tubes cease growth promptly, while a few 
develop vigorous germ tubes. 
Table IV. — Time required for the germination of ascospores of Pseudopeziza 
medicaginis and Pseudopeziza trifolii and rate of growth of the germ tube 
for three days at constant temperatures. 
[A plus sign indicates that the germ tube could be seen emerging from the spore, but that it did not reach 
a length equal to half the length of the spore. The figures in the body of the table represent the estimated 
length of the germ tube in terms of the length of the spores.] 
Pseudopeziza medicaginis. 
Pseudopeziza trifolii. 
Temperature (°C). 
4 
hours. 
8 
hours. 
12 
hours. 
24 
hours. 
48 
hours. 
72 
hours. 
4 
hours. 
8 
hours. 
12 
hours. 
24 
hours. 
48 
hours. 
72 
hours. 
2.5 to 3 
0.5 
.75 
.75 
1.5 
1.5 
1.5 
2.5 
2.5 
1 
( 2 ) 
1 
1.5 
1.5 
3 
3 
5 
5 
4 
2 
( 2 ) 
2 
2 
2 
4 
4 
+ 
0.75 
.5 
1.5 
1.5 
2 
2.5 
1 
+ 
( 2 ) 
1 
1.5 
1.5 
3 
3.5 
5 
C 1 ) 
2 
6 to 7 
+ 
+ 
0.5 
1 
1 
1 
.5 
+ 
( 2 ) 
+ 
+ 
0.5 
1 
1 
1 
+ 
2 
9 to 10 
+ 
+ 
0.5 
.5 
.5 
+ 
"" + " 
+ 
+ 
+ 
0.5 
.5 
.5 
2 
12 
4 
16 
+ 
+ 
+ 
5 
21 to 22 
24 to 25 
27 to 28 
(i) 
29 
0) 
( 2 ) 
30 
( 2 ) 
( 2 ) 
( 2 ) 
( 2 ) 
( 2 ) 
( 2 ) 
( 2 ) 
Spores disintegrate. 
2 No germination. 
The one significant difference that they show is found in the fact 
that the spores of Pseudopeziza medicaginis will continue to germi- 
nate at a slightly higher temperature than those of P. trifolii. In 
order to test this relation of temperature to germination, spores were 
discharged naturally upon an agar surface with all the precautions 
necessary to secure mature spores previously described in obtaining 
spores for measurement. The agar used in all cases consisted of 2 
per cent of agar-agar in water carefully cleared and filtered. In 
order to insure identical conditions for the two species in each test, 
