CELL-FORMATION. 103 



tinction lies solely in this : that in the first case the whole 

 contents of the extremity of the branch, in the second 

 only a part of them, are converted into a cell.* 



b. With a parietal nucleus. 



Free cell-formation with a visible nucleus I have 

 hitherto only observed with certainty in the embryo- sac 

 of the Phanerogamia. The cell-formation in the pollen- 

 tube is not yet clear to me ; of those cells which form the 

 embryo and the suspensor, I rather imagine that they 

 originate through parietal cell-formation ; of those cells 

 which Schleiden explains as transitory cells, I am still 

 doubtful whether they are actual cells, or not rather mere 

 nuclei. 



When the formation of the endosperm-cells takes place 

 in the embryo-sac, the fluid contains the following struc- 

 tures : 



1. Cells with granular contents, and a perfect nucleus, 

 with evident nucleoli. 



2. Mucilage- granules. 



3. Perfect nuclei, with evident nucleoli. 



4. Minute homogeneous globules of mucilage. 



5. Larger homogeneous globules of mucilage, with a 

 globular cavity. 



6. Larger homogeneous globules of mucilage, with a 

 smaller concentric or excentric ring. 



* In the sporangium which has originated in the above ways, two kinds 

 of cells may be formed, either larger, immoveable, globular spores, with a 

 tough membrane, or smaller oval cellules, with a delicate membrane, which 

 move about actively either already inside the parent-cell or, and especially, 

 after they have been set free. To this end the sporangium grows out into 

 one or more processes (figs. 4, 6, 8), which open at the point and allow the 

 cellules to escape. I formerly believed that even a third kind of cell origi- 

 nated in the sporangium, namely, smaller cells with delicate walls like the 

 moving cellules, but exhibiting no motion, and capable of germination. 

 Whether this third kind actually exists, or whether they are identical with 

 the moving cells, and again, whether these are capable of ^ermination, I 

 must leave open, since the latter has been stated to be the lact by several 

 observers, till further researches have been made. 



