824 rniNCiPLEs of gardening. [ch. ix, 



Tliese experiments also determine that plants have 

 but a slight power of generating heat ; for the 

 thermometer, placed mthin their stems, in -sWnter 

 sinks gradually nearly to the temperature of the 

 exterior air ; and in the spring or summer, that instru- 

 ment so placed does not follow implicity the atmo- 

 spheric variations, hut this is not merely hecause 

 wood is a bad conductor of heat. It is evident 

 that a hving plant has the power of preventing the 

 congelation of its juices, and it is impossible to 

 account for this phenomenon without connecting it 

 ydih the plant's vitality ; and I see no reason for 

 concluding that plants, differing from animals, do 

 not, during their respiratory function, convert oxy 

 gen into carbonic acid, set free its latent heat, 

 and thus presen-e their temperature. It is beyond a 

 doubt, that, by this chemical change, some plants at 

 one period of their vegetation generate a considerable; 

 degree of heat. The stamens of Arum cordifolium 

 emit so much heat at the time they shed their pollen, 

 that twelve of them placed by M. Hubert round a 

 thermometer raised the mercury from 79° to 143°. 

 Under similar circumstances, M. Sennebier observ^ed 

 the stamens of the Arum maculatum were nearly 16° 

 hotter than the surrounding air. The flowers of 

 Caladium j;mnaf«/z\Zi<?«, when emitting a strong 

 ammoniacal smell, were obsened by Dr. Schultz to be 

 as hot as 81°, though the atmospheric temperature 



