DR, M. J. SCHLEIDEN ON PIIYT0GENESI9. 301 



We find an annual thickening of the axile formations, the de- 

 velopment of the woody stem. 



Let us now see which of the three possibiUties of the forma- 

 tion of new cells, in each of the cases just enumerated, is actu- 

 ally realized. I have shown how the new cells are developed in 

 the embryonal sac, and consequently in a large ceU. A similar 

 process is evident in the embryonal end of the pollen tube, 

 consequently in a highly elongated cell ; and I shaU now proceed 

 to dehneate the further development of the embryo. After the 

 first cells, generally few in number, have formed, they rapidly 

 expand so much that they fill the pollen tube, which is then very 

 soon no longer recognisable as the old enveloping membrane. 

 But at the same time sevex'al cytoblasts again originate in the 

 interior of each of these cells, and produce new cells, on the 

 rapid expansion of which, the mother-cells also cease to be ap- 

 parent and are reabsorbed. The same process is repeated indefi- 

 nitely. But since the newly originated cells have continually less 

 room to expand, and therefore constantly become smaller, the 

 previous transparency is soon destroyed by the cytoblasts which 

 are constantly being produced anew in the interior, and by 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 con- 

 tinues the same, since no new force comes into action, which 

 might determine us to admit a sudden variation of the vital ac- 

 tion, more especially as we very soon meet with the same indi- 

 cation of the vegetative power again. 



The seed, meanwhile, 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 Ave are here very soon convinced 

 of the negative, — that an origin of new cells on the surface of 

 already existing organs does not take place. The sm-face is 

 always smooth, and generally provided in a very early state with 

 a kind of epidermis, the outer layer being more transparent and 

 almost as clear as water; and never do we find even an indication 

 of a newly formed cell on the surface. 



But if the embryo is the image of the whole plant, and this 

 latter does not present anything that is not a repetition of its 

 organs, if we have found in the embryo that its growth only 

 consists in the formation of cells within cells, we may expect to 



