THE METABOLISM OF PLANTS. 283 



temperature of 1 27 I32C. Hoffman found that the dry spores 

 of Uredo destruens and segetum (Ustilago Carbo] can survive 

 being heated for an hour to 128 C, whereas if they are moist 

 they are killed in the case of Uredo destruens at 70 73 C., 

 and in the case of Uredo segetum at 58-5 62C. by an ex- 

 posure of two hours. 



Schindler made the following determinations with spores 

 of Tilletia Caries : 



1. Dry heat (2 hours) 



Heated. Unheated. 



at 50 C. germination began in 4 4 days. 



55 65 6 



C Q 







95 5) 8 



100 no germination. 



2. Moist heat (2 hours) 



at 30 C. germination began in 4 4 days. 



?) 35 55 4 5> 



?J 4^ 55 5 JJ 



i) 45 5? > 5 



50 no germination. 



Cohn has found that the spores of Bacillus subtilis survive 

 prolonged boiling. This is due, as in the case of seeds men- 

 tioned above, to the fact that water penetrates them with 

 difficulty. 



We have to enquire, finally, into the cause of death conse- 

 quent on exposure to high temperatures. It might be imagined 

 that, since a rise of temperature promotes the activity of the 

 metabolic processes, a high temperature would make them 

 excessively active and that the cell would die in consequence 

 of living, as it were, too fast. But such an explanation is 

 inadmissible, for, as we have seen, a rise of temperature above 

 the optimum-point has a depressing effect upon the activity 

 of the metabolic processes. Many physiologists are inclined 

 to believe that the fatal effect of a high temperature is due to 

 the coagulation of the coagulable proteids in the cell, but this 

 connexion cannot be regarded as established. It is doubtless 

 upon the living protoplasm of the cell that the temperature 



