Page:An introduction to physiological and systematical botany (1st edition).djvu/232

 202 philosopher has not been equally successful. He is recorded as the discoverer of the expiration of plants, but it appears from his work that he merely observed the bubbles of air which cling to leaves, dead as well as living, and indeed to any other body, when immersed in water and exposed to the light of the sun. He found these bubbles disappeared in the evening, and returned again when the sun shone, and he faithfully reports that by their attachment to the surfaces of leaves, the latter were rendered more buoyant, and rose in the water; a sure proof that the air had not previously existed, in the same volume at least, in the substance of those leaves. Accordingly, Bonnet concluded that the latter, in imbibing the surrounding water, left the air which had been contained in the water, and that this liberated air became visible from being warmed and rarefied by the sun. This was as near the truth as Bonnet could come, it not being then known that light has a power of separating air of a peculiar kind, carbonic acid gas, from water. I find no indications in his work of his having had any idea of leaves absorbing air and