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VEGETABLE CELLS.

of organic matters from the contents; one passes into theother without any definite boundary.

In reference to the formation of membrane, therefore,we may establish the following distinctions: In cell-formation, an universal and momentary production ofnew membrane takes place. In apical growth, an uni-lateral and continuous formation of neio membrane appears.In universal growth, which follows both cell-formationand apical growth, an expansion and thickening of thenewly-formed membrane takes place.

The apical growth may begin in a cell in two ways, inreference to its relations to the life of the cell in timeand space. In the first case, the apical growth beginsat once with the formation of the cell. A portion of thecontents becomes individualized, and secretes membraneover its whole surface, whereby the cell is formed; thisnew formation of membrane continues at one point of thesurface, and the cell goes on growing in this direction.The apical growth is here immediately connected withthe cell-formation. It begins directly after the origin ofthe cell, before the universal growth has commenced.

In the second case, on the contrary, the cell first ex-pands by universal growth. The membrane becomesthickened; the contents are applied upon the internalsurface. Then a portion of homogeneous mucilage is formedat one point of the surface, beneath the membrane, andwith this begins a new apical growth, as I have above de-scribed it. The apical growth, therefore, does not herefollow immediately the cell-formation, but the universalgrowth of the cell. It may occur, either in a cell with-out apical growth, or in a cell with this, as on the lateralpart of a cell-branch growing at the apex, and alwaysappears as a growing-out of a point of the surface.

Through the first kind of apical growth the nascentcell grows longitudinally. By the second kind the cellbranches.

The apical growth is also variable in its duration. It