Page:Popular Science Monthly Volume 6.djvu/82

72 of them, contain always more or less green matter, masked. They also possess the property, which the white leaves do not, of absorbing carbonic acid, and exhaling oxygen in a perceptible degree, when exposed to the sun. We lay stress on these phenomena, since it is for want of having understood them that very recent authors describe colored leaves as being usually deprived of the function of assimilation.

If we make the experiment already described with white leaves, we shall find that in the daytime they exhale a perceptible amount of carbonic acid.

Sennebier had observed that the yellow and red stripes of the Amarantus tricolor do not give off oxygen when exposed to the sun, but that the leaves of the Amarantus ruber, on the contrary, possess this property. So, too, leaves naturally green, which change color at the close of their life, entirely cease from absorbing carbonic acid and exhaling oxygen. Corenwinder has shown that faded leaves that are on the point of falling constantly give out carbonic acid. The fact seems to be universal. Here, however, it is not a phenomenon of vitality that appears, but an act of decrepitude, which goes on and increases after the leaf has fallen.

We observe the same phenomena in other plants, some of whose leaves contain no green matter whatever, especially in the striped maple, which is such an ornament of our gardens in summer. In August, 1868, M. Corenwinder gathered off one and the same maple some leaves that were perfectly white, and others that were perfectly green, and analyzed them to determine the amount of nitrogen they respectively contained, with the following results:

Thus we find a much larger amount of nitrogenous elements in the white leaves than in those which contain chlorophyll; on the other hand, the latter are richer in carbonaceous substances. These two observations clearly confirm M. Corenwinder's theory.

Finally, we may conclude, from all the analyses and experiments we have here detailed, that there exist in plants, at every stage of their life, two distinct functions having different centres of action. The one is respiration, which depends upon the nitrogenous organic bodies. The other is assimilation of carbon, which has its seat in special organisms, formed principally, if not exclusively, of ternary elements.

This theory gives a natural explanation of all observations upon the physiology of leaves. M. Corenwinder hopes soon to make an application of it, and will show what it is worth, by explaining, with its aid, the origin of carbon in plants.