Page:Popular Science Monthly Volume 17.djvu/784

764 be quite possible. But it is also possible that the difference may be a physical one. To produce the colloid state from the crystalloid is by no means beyond the power of science. We qualify our previous statement, then, only so far as to say that when the chemist produces a body in the colloidal form, having the identical constitution of protoplasm, there is every reason to believe that it will have the properties of protoplasm.

The important question now arises whether, since the protoplasm of animals is identical with that of vegetables, and the latter is the food of the former, any protoplasm whatever is vitalized by the animal as such. That this identity exists would seem satisfactorily established. Though the protoplasm of vegetables is inclosed within a cellulose bag, it is only a closely imprisoned rhizopod. In the Nitella, it shows all its characteristic irritability, and from Vaucheria it escapes to exhibit all its amoeboid movements. Spores swim about by cilia or flagella, and the cell-division of the one kingdom is the same as that of the other. In plants, however, protoplasm seems to be associated with chlorophyl, whose function was for a long time supposed to be to decompose carbon dioxide under the influence of sunlight. But Draper in 1843 showed that this decomposition took place before the chlorophyl was formed. Recent researches have shown that the function of chlorophyl is wholly protective. The assimilative power of the protoplasm reaches its maximum in the orange and yellow rays. Now, Bert has shown that the absorption band in the chlorophyl spectrum is in the exact position of this maximum. Hence, Gautier believes that this substance acts as a regulator of plant respiration, the greater or less amount of luminous energy thus absorbed and transformed being utilized by the protoplasm and stored up. Growth and cell-division, however, are independent of orange light and hence of chlorophyl. In the higher plants these functions are performed by a separate and deep-lying set of cells. But, in the lower, the same cell discharges both functions, assimilation going on in it during the day, and growth chiefly at night. Sachs had already proved that the maximum growth of plants takes place just before daylight, and the minimum in the afternoon. This retarding action of sunlight upon growth is as curious as it is unexpected. It now appears that in orange light plants assimilate—absorb carbon dioxide and evolve oxygen—but do not grow—are not heliotropic; while in blue light they are strongly heliotropic, but do not give off oxygen. Chlorophyl, however, is not confined to vegetables; infusoria, hydras, and certain planarian worms are green from the presence of this substance, and Geddes has shown that such animals placed in the sunlight give off a gas which is more than half oxygen. These cells, moreover, contain starch-granules.

A still more striking evidence of this intimate relationship has been developed by Darwin, in his researches upon insectivorous plants. Not only do these plants possess a mechanism for capturing