Page:Smithsonian Report (1898).djvu/520

438 be seen from the fact that a totally opposite conclusion may be drawn from applying the premises in field experiment, with the use of certain well-established facts of plant physiology. It has been shown, for example, by the French plant physiologist, Boussingault, that the volume of carbon dioxide taken up by green plants is exactly equal to the volume of oxygen given off in the presence of sunlight. So if, as supposed, all the oxygen of our atmosphere were liberated from carbon dioxide by green plants then would the quantity of carbon dioxide of the earth's atmosphere have been seven hundred times more before the appearance of green plants than at present, while the proportion of oxygen, according to this hypothesis, would have increased from 0 to 21 per cent in volume, while the enormous proportion of carbon-dioxide would have fallen to its present mass, namely 0.03 per cent in volume. If one were to go so one-sidedly into such conclusions as happened in the hypothesis above cited it would be possible, under the assumption of such an enormous decrease of atmospheric carbon dioxide, to under- take beforehand to predict the disappearance of vegetation, indeed to foresee that both organic kingdoms—the plant and the animal world— were so ordained as to maintain continually a reciprocal influence upon each other, and the capacity of adaptation of plants and animals, bordering on the wonderful, would make possible their continuance under external conditions widely different from the present.

But the discovery of Boussingault teaches another thing. Since the quantity of carbon dioxide in the atmosphere is practically constant, namely, an average over the earth of about 0.03 per cent in volume of the atmosphere, and since the succession of elements upon the earth will not be interrupted (i.e., carbon dioxide, through combustion, respiration and putrefaction, is constantly being produced, and also through green plants—whether on this side of the world or at the antipodes—is constantly being reduced to oxygen by the agency of light), this gas can scarcely increase to a greater proportion than 0.03 per cent in volume because so constantly involved in transformation, and even a much higher rate of combustion than is now prevalent would scarcely alter the great surplus of oxygen. An important feature our question has thus far been only, briefly referred to—the extraordinary capacity of organisms of adapting themselves to their environment. If the proportion of carbon dioxide in the atmosphere should notably increase because of the consumption of coal, the plant world would still adapt itself to these changed conditions. This adaptation must, however, be granted to those whose hypothesis leads to such dire consequences as previously depicted; for they must concede that the earlier vegetation of the earth endured a far greater proportion of carbon dioxide than at present, and indeed made use of it. But when the capacity of plants to adapt themselves to the proportion of carbon dioxide in the atmosphere is conceded, then the increased