122 WRITINGS OP JOSEPH HENRY. [1855- 



and thus furnish nourishment to the remaining parts; but 

 changes of this kind would be minute, and the plant, under 

 the influence of heat alone, would in a short time cease to 

 exist. 



Let us next suppose the sun to commence emitting rays 

 of light, in addition to those of heat. These, impinging 

 against the earth, would probably produce some effects of a 

 physical character; but what these effects would be we are 

 unable, at the present time, fully to say. We infer however 

 that the light, not immediately reflected into space, would 

 be annihilated ; but this could not take place without com- 

 municating motion to other matter. It would probably be 

 transformed into waves of heat of feeble intensity. 



Let us now suppose, in addition to heat and light, the 

 chemical rays to be sent forth from the sun. These would 

 also produce various physical changes, the most remarkable 

 of which would be in regard to the plant. 



The carbonic acid of the atmosphere, in contact with the 

 expanding surface of the young leaves, would be absorbed 

 by the water in their pores, and in this condition would be 

 decomposed by the vibrating impulses which constitute the 

 chemical emanation. The atoms of carbon and oxygen, of 

 which the carbonic acid is composed, would be forcibly sepa- 

 rated; the atoms of ox3^gen would be liberated in the form 

 of gas, and the carbon be absorbed to build up, under the 

 directing influence of vitality, the woody structure of the 

 plant. In this condition the pabulum of the plant is prin- 

 cipally furnished by the carbonic acid of the air, while the 

 impulses of the chemical ray furnish the primary power by 

 which the de-composition and the other changes are effected. 

 This is the general form of the process, leaving out of view 

 minute changes, actions, and re-actions, which must take place 

 in the course of organization. 



All the material of which a tree is built up, (with the ex- 

 ception of that comparatively small portion which remains 

 after it has been burnt, and constitutes the ash,) is derived 

 from the atmosphere. That this is so can be proved by 

 growing a plant in perfectly pure flint sand, to which a 



