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54 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
late spring planting favored the host, while late fall and early 
spring planting increased infection. 
Among the rusts a similar relation between spore germina- 
tion and infection occurs. Howell (’90), working on the clover 
rust (Uromyces Trifolii), showed that infection would take 
place only at comparatively low temperatures, the reason 
given being that it was only at the low temperatures that spore 
germination occurred; the maximum temperature for both 
uredo- and aecidiospores was in the neighborhood of 25°С. 
Marshall Ward (’01) in his notable experiments with the 
brome rust (Puccinia dispersa) showed that the optimum tem- 
perature for germination for this form was also at 18°C. 
Eriksson (’95), in making experiments with rusts, and es- 
pecially with the germination of spores of different forms, 
found that chilling the spores in the case of Aecidium Ber- 
beridis, Peridermium Strobi, Uredo glumarum, and 17. coro- 
nata accelerated germination when they were brought 
back to higher temperatures, Johnson (719), working with 
uredospores of Puccinia graminis, P. rubigo-vera, and P. 
coronata, showed that their optimum temperatures for 
germination were 12-17°C.; hence epidemics of grain 
rusts usually spread at periods of subnormal temperatures. 
From these observations it is easily seen that the rusts have 
developed the parasitic habit to a very special degree, adapt- 
ing the temperatures when there is likely to be dew as those 
at whieh spore germination will take place, and thus aiding 
themselves in their attack on the host. 
Balls (208) has shown in some very careful work on the 
temperature relation of the Rhizoctonia causing ‘‘sore shin” 
of cotton that this fungus attacks the cotton plant at 20°C., 
but not at 83°C. Не checked his work with observations on 
pure eultures of the organism, and found that at high tem- 
peratures the fungus secreted, or excreted, an inhibiting sub- 
stance into the culture fluid which was injurious to the fungus. 
Whether this same toxie substance prevented that attack on 
the host is questionable. 
As to the wood-destroying fungi, Falek (’07) found that 
Merulius silvester, M. domesticus, M. sclerotiorum, Polyporus 
