Page:Popular Science Monthly Volume 51.djvu/117

Rh without diminishing its energy. For it to be so, this mass must evidently continually receive new portions of energy, and this can come only either from the surrounding medium or from the reactions that go on in the protoplasm itself. In the former case the agency consists of radiations of different sorts, and is of a purely physico-chemical order; while this can not be in the second case. In fact, the life of protoplasm is manifested by movements which are combined in such a way as to produce an orientation of its parts according to certain structural dispositions succeeding one another in a determined order; phenomena to which ordinary physico-chemical actions never give rise. We are therefore necessarily led to suppose the existence of a special class of reactions of which assimilated matters become capable only after their absorption into this special medium, living and pre-existing protoplasm, into which they penetrate.

Under this relation we might, in a certain way, compare assimilation to what occurs when combustible matter takes fire on being heated in a furnace in which a combustion is already going on, and is kept up by the new matter. So, one might say, it is only after having been previously put into a special condition by their mixture with protoplasm that assimilable substances react among themselves in such a way as to produce a new quantity of living matter. So one may suppose that protoplasm in the condition of latent life, having become inert but retaining the faculty of reviving, resembles those mixtures formed of substances that do not react except under certain conditions of temperature or other influences, and which, so long as those conditions are not fulfilled, continue indefinitely in contact without combining. Such, for example, are explosive mixtures.

The presence of assimilable matter in protoplasm or within its range is not sufficient for the production of the phenomena of assimilation and orientation. Certain conditions of temperature, moisture, and aeration have to be realized. As long as they are not realized, and if nothing occurs to change the composition or structure of the energides, they will remain inert, while they retain the faculty of evolving anew when the circumstances become favorable again.

Such condition of chemical and vital inertia may probably endure for a long time, possibly indefinitely. This, as it seems to me, is at least the only way of accounting for the preservation of seeds during very many years. Cases are in fact known where seeds have germinated after so prolonged a rest that it is impossible to assume that they have lived during the interval even a retarded life. We cite a few examples. M. A. P. de Candolle