Page:Popular Science Monthly Volume 5.djvu/481

Rh show is probably already a compound of many removes from the beginning.

The law of compounding is not at all mysterious. If the first force of reproduction, the genesis of individuals, exhibits itself in the form of an evolution—a budding forth, a repetition of the form and structure of the parent cell—the law of compounding first presents itself as an arrestation of the law of gemmation. The old cell fails in force to throw off the new one; or, by another law, equally in force, adhesion takes place between the contiguous surfaces of the old and the new, and the extrusion to complete independence cannot be effected. This is the simple rule extending up through all the shining ranks and files of life. In the higher forms this law presents itself in the form of involution; but in lower creatures it is but an adhesion—an anchylosis. In all it is a failure of a perfect evolution—a failure perfectly to develop and reproduce a separate cell.

Now that we have the laws, let us see if we comprehend their application in Nature's workings. Really we might go to mathematics, and take from geometry, not only illustrations, but the very definitions of biology. Geometry, first and simplest of the sciences, begins its definitions with a point; from a point it proceeds to a line; from a line to a surface; from a surface to a solid. In biology, beginning with a cell, which is the physiological point or unit; the next development is to an axis, a line of cells, the type of all baculate structures. This baculus revolved upon itself, phyllate structure—a biological surface, the type of all organisms having one depth of cells. The next step is to the biological solid. This is made by an involution, a folding down of the surface upon itself, constituting a creature of two laminæ—two tiers of cells.

Passing on to another class, typically displayed for instance in hepaticæ, we find that another involution has taken place. This time the phyllum of two tiers of cells is folded upon itself, constituting one normally of four layers. Here first occur those curious openings into the centre of the structure known as stomata, rendered necessary, of course, from the fact that two of the strata are internal, and but for these contrivances would be cut off from that direct contact with atmospheric air which is necessary to the life of external living creatures. The next and the last evolution which takes place in the ascending development of plants is the folding upon itself of this leaf of four thicknesses of cells, so as to make a sheet consisting essentially of eight thicknesses of cells—the type of all the so-called higher plants. In this respect exogens and endogens do not differ; their only real difference being the atrophy and suppression of one cotyledon of the former to constitute the latter. In exogens there may be, in addition to these, various subordinate adhesions, but no further involutions of the whole creature. These may be called topical, as affecting only portions of the compound structure; and among endogens, from the