LEAF-SPOT OF ALFALFA AND RED CLOVER. 
17 
transfers of both were made to the cover of the Petri dish contain- 
ing the agar. The spores were discharged simultaneously for 1 to 1^ 
hours. If at the end of this time sufficient spores were present, the 
cover containing the cultures was transferred to another dish and the 
spores placed at the desired temperature. Petri dishes to the number 
of 72, nearly all of them containing spores of the two fungi, were 
incubated in this way. The results are given in Table IY. 
This table shows that the two species germinate with almost ex- 
actly the same degree of vigor at each temperature, except that the 
spores of Pseudopeziza trifolii cease to germinate, or, perhaps more 
exactly, to make growth after the initial stages of germination, at a 
slightly lower temperature than those of P. medicaginis. Although 
the difference here may seem slight — almost within the limit of ex- 
perimental error — it has been found constant and definite in repeated 
tests. The possible significance of this fact in connection with the 
difference in geographic range of the two fungi will be considered 
later. 
EFFECTS OF TEMPERATURE ON SPORE PRODUCTION. 
When cultures of the two fungi are placed at a series of constant 
temperatures they appear to show constant differences in the time 
required for spore production and in the abundance of spore pro- 
duction at each temperature. At the outset it must be stated that 
limitations inherent in the method of starting cultures cause wide 
variation in the behavior of the cultures of each species. This diffi- 
culty is partly overcome by using several cultures and by repeating 
the work. Even then the results must be regarded as being sug- 
gestive rather than accurate. The time required for the production 
of ascopores as obtained in two trials is given in Table Y. Three 
cultures of each fungus were used, and the earliest time at which 
the discharge of ascospores could be demonstrated in any of the three 
cultures was recorded. The three highest and the lowest temperature 
rarely varied more than one degree, and the remaining temperatures 
varied only half a degree. 
Table V. — Time required for the production of ascospores of Pseudopeziza 
medicaginis and Pseudopeziza trifolii at constant temperatures. 
Ascospores of— 
Temperatures (°C.). 
8 
9 
11 
12.5 
13 
14 
15 
16 
18.5 
20 
21.5 
24 
Pseudopeziza trifolii 
Pseudopeziza medicaginis.. 
..days.. 
...do.... 
82 
82 
53 
52 
30 
58 
43 
30 
52 
36 
49 
30 
36 
20 
16 
16 
14 
16 
14 
21 
20 
Table Y shows that below 14° C. the behavior of Pseudopeziza 
medicaginis was erratic, rarely fruiting at all. Only one culture 
89950°— 19 3 
