44 



frozen on an icc-sall niixtmc, the jjiotoplasni was com- 

 pletely destroyed and, aftei- t hawinii', it l)roke nj) into 

 crumby coagulated clum])s. If the hairs were })nt, with- 

 out the addition of water, into a thin platinum crucible 

 and the latter lowered into the freezing- mixture, the proto- 

 plasm could be ke})t alixc for 5 minulcs at -14°; after 

 thawing, the ])rotoi)hismic streaming was resumed. At 0° 

 Tra(le.sca)iiia hairs could be kept alive for at least one hour. 



Molisch (1897) who observed, mider the microscope in 

 a cold chamber, the freezing of Tradescantia hair mounted 

 in water, described the cessation of cytoplasmic movement 

 when the temperature reached -2° and the sudden con- 

 gelation of the cell content at al)out -6.5° (temperature 

 of the air within the freezing chest in which the material 

 had been for several hours). After thawing, the nucleus 

 was disorganized and the plasma coagulated. When the 

 hair cells were exposed directly to the air temperature of 

 the chamber, without water as a mounting medium, they 

 withstood 6 hours at - 5° to - 9°. When they were mounted 

 in oil, they did not freeze even at - 9° ; congelation and 

 death occurred only at -15°. In air and in oil the cells 

 could bo subcooled to a much lower temperature than 

 in water, and they stayed alive as long as they were in 

 the subcooled state. The epidermal hairs of Episcia, 

 Ageratum mexicanum and Pelargoniuw had a higher 

 resistance than Tradescantia hairs. 



2. Epidermal Tissue. Molisch (1897) reported that in 

 sections of the epidermis of Tradescantia, mounted in 

 water between slide and cover-slip, and observed under 

 the microscope while exposed in an air chamber to a tem- 

 perature of - 5°, many cells were seen to freeze in sudden 

 flashes. On thawing, after 6 hours exposure, they were 

 dead, as judged by the disorganized, shrunken, and some- 

 times stainal)l(' nuclei, by the coagulated cytoplasm 

 and by the fact that the cell membranes absorbed the 

 anthocyanin present. Some cells did not freeze during 

 that time and at that temi)erature, which would indicate 

 that - 5° is wdthin the range of the lethal temperatures for 

 the epidermal cells. 



