LEAF-SPOT OF ALFALFA AND RED CLOVER. 
15 
SPORE DISCHARGE. 
The discharge of ascospores has been observed frequently under the 
microscope when apothecia have been crushed in water. The ascus 
slowly becomes longer and of greater diameter, forcing the spores 
forward in a more or less oblique biseriate position. The increase in 
diameter of the ascus of Pseudopeziza medicaginis appears to be 
somewhat greater than in the case of P. trifolii, thus allowing 
the spores to come more nearly into a biseriate position. When 
the limit of resistance of the ascus wall has been reached, the end rup- 
tures, allowing the spores to be expelled in a column. When dis- 
charge takes place under water the spores show no tendency to re- 
main together, but when they are discharged in air they show a ten- 
dency to remain in pairs. This pairing of the spores is probably due 
to the adhesive quality of the spore wall, a quality which is also 
shown by the tenacity with which the spores adhere to the cuticle of 
a leaf. 
It is interesting to note that the tendency to remain in pairs is not 
shown equally by spores of the two species of Pseudopeziza. It is 
somewhat more marked in the case of Pseudopeziza medicaginis. 
This may be due to the fact already cited that the spores of this 
species are brought more clearly into biseriate position before dis- 
charge takes place. In order to determine this difference, spores were 
collected on water agar as though for measurement. The spores in 
each group in selected miscroscopic fields were counted until the 
grouping of 1,000 spores had been determined. The results obtained 
at various times are shown in Table III. 
Table III. — Grouping of ascospores of Pseudopeziza medicaginis and Pseudo- 
peziza trifolii when caught on an agar surface after oeing discharged 
normally from cultures. 
Spores of— 
Spores in group — 
1 
2 
3 
4 
5 
6 
7 
8 
Pseudopeziza medicaginis: 
First lot 
Second lot 
Third lot 
number.. 
do.... 
do.... 
60 
66 
58 
238 
342 
356 
19 
8 
6 
43 
30 
33 
7 
4 
6 
19 
9 
4 
2 
9 
4 
1 
Total 
184 
936 
33 
106 
17 
32 
2 
14 
number.. 
do.... 
do.... 
Pseudopeziza trifoiii: 
First lot 
Second 
Third lot 
133 
272 
242 
215 
189 
185 
39 
48 
54 
28 
22 
19 
16 
7 
10 
11 
4 
9 
2 
5 
2 
6 
3 
4 
Total 
647 
589 
141 
69 
33 
24 
9 
13 
It will thus be seen that while in the case of Pseudopeziza medi- 
caginis each spore group containing an even number of spores is 
greater than the preceding or following group, in the case of P. 
