8 BULLETIN 531, U. S. DEPARTMENT OF AGRICULTURE. 



at 42° C. (108° F.) Miss Ames also studied the tim^ required for 

 the germination of spores at various temperatures and found that in 

 general the length of time required for germination decreased with 

 rise of temperature, being greatest, 200 hours, at 3° to 4° C, and 

 least, 5^ hours, at 41° C. ; no germination occurred at 42° C. The 

 difference in maximum temperatures as determined by these investi- 

 gators may be due either to their having different strains of the 

 fungus or possibly to their having used different culture media. 

 Miss Ames used Rhizopus from sweet potato grown on string-bean 

 infusion; Hanzawa's temperature tests were made with the fungus 

 growing on potato. 



In the writers' experiments on the temperature relations of Rhizo- 

 pus nigricans the fungus was grown on ripe strawberries and on white 

 corn meal in flasks. The refrigeration plant used by Drs. Brooks and 

 Cooley, of the Bureau of Plant Industry, in their studies of the stor- 

 age rots of apples was used. This gives satisfactory constant tem- 

 peratures at intervals of 5 degrees from 0° to 20° C. In addition, 

 for other low temperatures use was made of an ice thermostat, and 

 for the higher temperatures thermostats heated by gas burners were 

 used. 



Sound berries of the Missionary variety shipped '^^.m Plant City 

 in commercial refrigerators were inoculated with spo s i and mycelium 

 of Rhizopus and placed at temperatures of 0°, 5°, 10.C, *°, and 20° C. 

 At the end of five days berries kept at 0° and 5° sho ui e -o growth of 

 the fungus and were as sound and fresh in appearance and taste as 

 when first placed in the refrigerator. At 10° C. there was no aerial 

 growth of the fungus and only a very tiny decayed spot about the 

 region where inoculation was made. Most of the berry at this tem- 

 perature was still perfect in appearance and taste. Berries at 15° 

 and 20° C. bore abundant fruiting hyphae and were typical "leaks." 

 " Leak " is a term applied to fruit destroyed by Rhizopus because of 

 the collapse of the berries and the leakage of juice from the boxes. 

 Cultures in corn-meal flasks at the same temperatures showed in five 

 days no growth at 0°, 5°, or 10° C, but abundant mycelium with 

 sporangia at 15° and 20°. At 15°, however, there was only about half 

 as much aerial growth as at 20° and about half the sporangia were 

 white and immature. At 20° the surface of the flask was covered with 

 mature black sporangia. Similar flasks kept for five days at 1°, 2°, 4°, 

 G°, 8°, 11°, 14°, and 18° C. showed no growth up to 8°, slight growth 

 with occasional sporangia at 11°, and fairly numerous sporangia 

 at 14° C. 



Barries inoculated as described were kept for two weeks at 0°, 5°, 

 and 10° C. Those kept at 0° and 5° were apparently as sound as 

 when placed in the refrigerator. At 10° the berries were somewhat 

 softened, and there was a slight aerial growth of mycelium near the 



