Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/273

PHYTOGENESIS. 239 margin of the cytoblast, and quickly becomes so large that the latter at last merely appears as a small body enclosed in one of the side walls. At the same time the young cell frequently exhibits highly irregular protrusions (fig. 1, c), a proof that the expansion by no means proceeds uniformly from one point. During the progressive growth of the cell, and evidently arising from the pressure of the neighboring objects, the form becomes more regular, and then also frequently passes into that of the rhomboidal dodecahedron, so beautifully defined à priori by Kieser. (Compare fig. 1, from b to e, with fig. 8.) The cytoblast is still always found enclosed in the cell-wall, in which situation it passes through the entire vital process of the cell which it has formed, if it be not, as is the case in cells which are destined to higher development, absorbed either in its original place, or after having been cast off as a useless member, and dissolved in the cavity of the cell. So far as I could observe, it is only after its absorption that the formation of secondary deposits commences upon the inner surface of the cell-wall (fig. 9).

As a general rule, it is rarely that the cytoblast accompanies the cell which it formed through its entire vital process; nevertheless, it is,

1. Characteristic of the families of the Orchidæ and Cactæ, that in them a portion of their cellular tissue remains in a lower stage of development during the entire period of life.

2. In various plants it occurs that cellular tissue, which has merely a transitory signification, is not perfectly developed, but retains the cytoblast, and is absorbed together with it at a subsequent period. Yet I have also remarked that the latter in the middle period of its existence lost much of its distinctness and sharpness of outline, which, however, reappeared when absorption commenced; for example, in the nucleus of the ovule of Abies excelsa, Tulipa sylvestris, and Daphne alpina. It is most extraordinary that some physiologists should have felt prepared to deny the fact, that absorption takes place in plants, since even very considerable portions of cellular tissue of the nucleus of the ovule, for instance, become completely fluid again, and are received into the common mass of the sap. It is true this only takes place so long as the cell still consists of the simple original membrane, and is not so far advanced