Prof. Henry on the Conservation of Force. 87 
starch and nitrogenous materials, in which the germs of plants - 
are imbedded, have two functions to fulfill—the one to supply 
the pabulum of the new plant, and the other to furnish the 
power by which the transformation is effected, the latter being 
as essential as the former. In the erection of a house, the appli- 
cation of mechanical power is required as much as a supply of 
ponderable materials. 
To return to our first supposition. We have said (and the 
assertion is in accordance with accurate observation) that the 
plant would cease to increase in weight under the mere influence 
of heat, however long continued, after the tuber was exhausted. 
Some slight changes might, indeed, take place; a small portion 
of pabulum might be absorbed from the earth; or one part of 
the plant might commence to decay, and thus furnish nourish- 
ment 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 charac- 
ter; but what these effects would be we are unable, at the pres- 
ent 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 communicating motion to other 
matter. It would probably be transformed into waves of heat 
of feeble intensity. 
of the plant is principally furnished by the carbonic acid of the 
air, while the impulses of the chemical ray furnish the primary 
power by which the decomposition and the other changes are 
effected.” This is the general form of the process, leaving out of 
view minute changes, actions and reactions, which must take 
place in the course of organization. : 
Inthe decomposition of the carbonic acid by the chemical ray, 
a definite amount of power is expended, and this remains, as it 
