63 



- 13° for varying leiigtlis of time. After three hours of 

 freezing, 95 per cent of the cells were killed in the sub- 

 merged mycelia of a 24-hour-old culture, and after 12 

 hours all the cells were killed. Death was determined by 

 the inability to grow, which was observed to correspond 

 with the inability to plasmolyse. In a 48-hour-old cul- 

 ture, 90 per cent of the cells were destroyed after 4^ hours 

 and all were dead after 24 hours. So, the older cultures 

 had a higher resistance. When the submerged mycelia of 

 a 48-hour-old culture were kept subcooled at - 13° for 8 

 hours, only a few cells were killed ; after 24 hours of sub- 

 cooling many of the cells were dead, but a few older cells 

 still survived. The air liyphae showed no visible signs of 

 injury after 4^ hours at - 11°, while, after 7^ hours at 

 - 13°, disorganization occurred in the basal cells of the 

 hyphae, and after 24 hours all the air hyphae were dead. 

 According to Lindner, the duration of the exposure is an 

 important factor in causing death. 



Molisch (1897) observed that Phycomyces nitens grow- 

 ing on bread and exposed over night to a temperature 

 which reached - 9°, presented the next day filaments which 

 were turgescent and growing. Hyphae of the same spe- 

 cies, mounted without water between slide and coverslip 

 and observed under the microscope during an exposure of 

 8 hours to - 10° to - 12°, showed no stiffening of the cellu- 

 lar fluids. When the temperature was lowered to - 17°, 

 ice crystals separated from the protoplasm, disaggregat- 

 ing the latter. 



Rumbold {Naturw. Ztschr. f. Forst. u. Landw., 6, 110, 

 1908) found that the mycelia of Coniophora and of 3Ie- 

 ruleiis, in gelatine cultures, did not survive being hard 

 frozen at - 6° for 12 hours, while the gemmae of Coni- 

 ophora were not killed when kept over night in the open 

 at about - 20°, even though their aqueous medium was 

 hard frozen. 



Bartetzko (1910) subjected germinating spores, with 

 mycelia 70 to 200 micra long, of Aspergillus, Penicillium, 

 Botrytis and Phycomyces to low temperatures in liquid 



