THE METABOLISM OF PLANTS. 



279 



2. Leaves : 



3. Cryptogams (entire plant in water) : 



Funaria hygrometrica 43 '4 C. 



Marchantia polymorpha 46*4 



Oedogonium sp. 44'2 



Spirogyra sp. 44-2 



Oscillatoria (various species) 45*1 



According to Mayer and others the fatal temperature for moist Yeast 

 is about 53 C. ; but the temperature is not the same for all species of 

 Saccharomyces, and it varies with the nature of the liquid in which the 

 Yeast is warmed. Schiitzenberger states that dry Yeast may be heated 

 to nearly iooC. without losing its vitality. Cohn has found that Bacteria, 

 in his normal solution, are killed when the liquid is heated up to or above 

 60 C. for an hour, and that an exposure of 14 hours to a temperature of 

 45 C. or of 3 hours to a temperature of 50 C. proves fatal. Kiihne 

 found that the plasmodium of jElhalium septicum were killed by an 

 exposure of two minutes to a temperature of 40 C. 



Some plants exhibit a remarkable tolerance of high tem- 

 peratures. De Candolle mentions that Oscillatorias grow in 

 hot-springs such as those of Plombieres, at 51 C., of Dax, at 

 49 C., of Carlsbad, at 50 C. Cohn found Leptothrix lamellosa 

 growing in the hot-springs of Carlsbad at temperatures of 

 from 54 C. 44 C. In these cases there seems to be a certain 

 adaptation of the organisms to the conditions of their envi- 

 ronment. 



The most striking illustration of the fact that when 

 organs contain a relatively small proportion of water they are 

 better able to endure exposure to high temperatures than 

 when they contain a relatively large proportion of water, is 



