211 



suffering this change, however, the greater portion 

 of its specific caloric is necessarily yielded (166.) 

 by the oxygen gas, and a rise of temperature in con- 

 sequence takes place ; and hence, therefore, we must 

 ascribe the production of temperature which occurs 

 in germination, to the decomposition of the oxyge- 

 nous portion of the air, by the agency of the living 

 seed. 



169. As the same changes are produced on the 

 oxygen gas of the air by the growth of plants (30. 

 et seq.), as by the germination of seeds, the same 

 extrication of its heat may reasonably be expected 

 to follow. The sudden thaw of snow lying on grass, 

 while that on the adjoining gravel continues unthaw- 

 ed ; the fact of the moisture of dead sticks freezing, 

 while growing twigs are not at all affected ; and of 

 herbaceous plants resisting often degrees of cold 

 which freeze large bodies of water, all, says Sir 

 Charles Blagden, seem to shew that vegetables pos- 

 sess a power of generating heat *. Mr Hunter also 

 found the leaves of plants to resist freezing longer 

 than water. A growing fir-shoot, and the leaf of a 

 bean, were laid on a cold mixture of the tempera- 

 ture of 28, and in some minutes they had thawed 

 the surface on which they lay. This did not arise 

 from the greater warmth of the leaves when first ap- 

 plied, for, on removing the fir-shoot to another part, 

 the same effect \yas produced f By applying like- 

 wise thermometers to the internal parts of vegetables, 

 he discovered them to possess a temperature above 



* Philosophical Transactions, 1775, f Ibid. 



02 



