116 ON THE FOOD OF PLANTS. 



" the carbon is added to plants from the air, by 

 *' the process of vegetation in sunshine, and 

 " oxygene is added to the atmosphere." He 

 adds, *' This circumstance is proved by a num- 

 ** ber of experiments made by Drs. Priestley, 

 ** Ingenhouz, and Woodhouse, and M. T. de 

 ** Saussure, many of which I have repeated 

 " with similar results. The absorption of car- 

 " bonic acid gr/s, and the production of oxygene^ 

 *' are performed by the leaf And leaves re- 

 " cently separated from the tree, effect the 

 " cliange, when confined in portions of air con- 

 *' taining carbonic acid, and produce oxygene, 

 " even when immersed in water holding carbo- 

 ♦* nic acid in solution." 



From what has been before said, on the nature 

 and properties of the leaves of plants, it is not 

 only pretty clear, that they are not furnished 

 with organs, necessary for the double action, 

 but it is in no respect necessary they should 

 possess this power. Why should a plant be en- 

 dowed with the power of feeding at both ends, 

 any more than animals, and when, like them, it 

 is proved, that the taking in their food at one, 

 is sufficient for all their purposes ? The expe- 

 riment cited, of carbonic acid being absorbed 

 by leaves recently severed from the tree, is no 

 corroboration of Sir Humphry's theory, as it 



