CELL-FORMATION. 109 



is mostly somewhat more dense than the substance of the 

 nucleus ; sometimes it is brighter than the latter. 



The mucilage surrounding the nucleus now continually 

 increases in quantity; the nucleus is always distinctly 

 visible, situated at the periphery (fig. 8,/). There are, 

 however, isolated exceptional cases here, where the nucleus 

 is free, and more or less removed from the circumference. 



The mucilage then becomes evidently granular, and a 

 distinct membrane is to be made out upon its surface 

 (fig. 8,y). The latter frequently becomes visible even when 

 the contents are still homogeneous. In this stage, as in 

 the preceding, the nucleus is mostly less dense than the 

 surrounding mucilage, and therefore appears like a clearer 

 space. The cell is now visibly formed. Whether the 

 membrane first originates at the time it becomes visible, 

 or had originated at a still earlier period, can scarcely be 

 ascertained by observation. The latter appears to me 

 probable. 



According to Schleiden, the cell-membrane originates 

 immediately on the surface of the nucleus ; it absorbs 

 watery fluid by endosmose, and expands ; the nucleus re- 

 mains attached on one side of the cell ; the cell is a fine, 

 transparent vesicle ; its contents a watery fluid, and ap- 

 pear merely as a hollow space between the nucleus and 

 the granular mucilage of the embryo-sac, which is pushed 

 backward by its expansion.* Schleiden adds, that the 

 cells become wholly dissolved in a few minutes in distilled 

 water, so that only the nuclei remain. I confess that I 

 have never seen such very clear and transparent cells. 

 In most cases I find the contents of the cells more dense 

 and darker than those of the nucleus ; rarely clearer, but 

 even then always either homogeneously mucilaginous or 

 finely granular. In like manner, I did indeed see various 

 effects on the young cells and their contents produced by 

 the action of water, but never a solution. 



* Miiller's Archiv, 1838. [Schleiden has changed this opinion in the 

 latest edition of his ' Principles of Botany' 1849). See Appendix to Dr. 

 Lankester's Translation. A. H.] 



