It 



. VII. HEAT OF VEGETABLES. " 153 



atmospheric oxygen, are the source of heat in them ; that 

 among these, combustion of carbon and of hydrogen ought 

 tp be considered as one of the principal, but not the only 

 one ; and that experimental data are yet wanting to discover 

 the exact ratio between the heat produced by an animal, and 

 the heat evolved by chemical actions going on within it, 

 and by those which we are able to produce with our appa- 

 ratus. 



Heat of Vegetables. I shall not leave this subject without 

 telling you, that in vegetables, also, the heat developed by 

 germination is a phenomenon of chemical action, due to the 

 combination of oxygen with the carbon of the germinating 

 seed. We know that in the process of germination, there 

 is an absorption of oxygen, and the evolution of carbonic 

 acid, and that diastase converts starch into dextrine and 

 sugar, which afterwards disappears by producing carbonic 

 acid. It is curious, that in plants, as in animals, there are 

 starch and sugar, which, by burning, disengage the heat 

 necessary to their existence. In a like manner must be ex- 

 plained the heat which accompanies the fecundation of 

 plants. Hence, we find, that in the sugar-cane, the beet- 

 root, and the carrot, the sugar disappears after the flowering 

 and fructification. 



