A Dry Rot of the Irish Potato Tuber 
39 
celled spore is formed, the sterigma grows rapidly and shoves 
the spore off. If sufficient food is present, the spore germinates 
at once either into a hypha or into a several-septate spore. 
Under the most favorable conditions, however, the spore germi- 
nates at once into a hypha. When the food supply gives out, 
the one-septate condition is the most prevalent and, as mentioned 
above, many of these spores show only one viable end. At times 
the spores germinate directly into other conidia (PI. XXVII, figs. 
23 and 24). Very often the conidia fuse and then we have an 
appearance like that presented by the basidiospores of Tilletia, 
joined up and producing other conidia (PL XXVII, fig. 10). 
Fusions in the mycelium are often found. 
INFLUENCE OP TEMPERATURE. 
As mentioned above, temperature has a decided influence on 
the septation of the mycelium. The fungus grows best at 
temperatures ranging from 22° to 27° C. Temperatures above 
this retard the growth, and when the organism is subjected to 
temperatures ranging from 40° to 55° C, no growth sets in. At 
1° C, —22° C, and —3.9° C. no growth takes place, but when the 
fungus which was kept at 1° C. for a period of three weeks is 
brought into a temperature of 3.3° C, growth begins,, and when 
the cultures were kept at —22° C. and —3.9° C. for two 
weeks and then gradually brought up to the temperature of 
3.3° C, no growth was noted. When these were put into a 
temperature of 30° C, growth set in at once. The fungus which 
had been kept at the lowest temperature made the fastest growth 
when it was removed to higher temperature. A temperature rang- 
ing from 8° to 10° C. is only slightly inhibitive to growth and 
when potatoes infected with the organism are stored at this 
temperature the most rapid decay takes place provided the air 
is quite moist. 
