Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/287

PHYTOGENENSIS. 253 cell. A similar process occurs in the embryonal end of the pollen-tube, consequently in a highly elongated cell; I shall now proceed to describe the further development of the embryo. After the first cells, generally few in number, are formed, they rapidly expand to such an extent that they fill the pollen-tube, which soon ceases to be perceptible as the original enveloping membrane; but at the same time several cytoblasts originate in the interior of each of these cells, and generate new cells, on the rapid expansion of which the parent-cells also cease to be visible and become absorbed. The same process is repeated indefinitely. But since the newly-generated cells have continually less room to expand, and therefore constantly become smaller, the previous transparency is soon lost in consequence of the continual production of new cytoblasts in the interior, and the tissue becoming more and more compressed; and from this stage to the perfect completion of the embryo we are conducted by the clearly logical inference that the process thus introduced continues the same, since no new force comes into operation which could induce us to assume a sudden variation of the vital action, more especially as we soon meet with the same manifestation of the vegetative power again.

Meanwhile the seed germinates, and the embryo becomes a plant; and then indeed the question may arise,—Does the process of life continue the same thenceforward in the internodes and foliaceous organs? Now we are here very quickly convinced of the negative, that is, that a formation of new cells on the surface of the existing organs does not take place. The surface is always smooth, and generally covered in a very early state with a kind of epidermis, the outer layer being more transparent and almost as clear as water; and we never find even an indication of a newly-formed cell upon the surface.

But if the embryo be the type of the entire plant, and the latter do not present anything which is not a repetition of its organs, if we have found the growth of the embryo to consist only in the formation of cells within cells, we may then expect to find the same result also in the process of the growth of the whole plant. It is especially a foliaceous organ, the anther, which has hitherto been studied and followed in its development by many celebrated men (particularly well by Mirbel);and here it is quite decided that the increase of cells takes