THE CELL DOCTRINE. SJ 



completely dissolved in distilled water, leaving only 

 the cytoblasts behind. The vesicle gradually ex- 

 pands and becomes more consistent, and with the 

 exception of the eytoblast, which always forms a 

 portion of it, the wall now consists of gelatin. The 

 entire cell then increases beyond the margin of the 

 eytoblast, and quickly becomes so large that the 

 latter at least merely appears as a small body inclosed 

 in one of the side-walls in such a manner that the wall 

 of the cell splits into two laminse, one of which passes 

 exterior and the other interior to the eytoblast. That 

 upon the inner sideis generally the more delicate, and 

 in most instances only gelatinous, and is also absorbed 

 simultaneously with the eytoblast. Within these cells, 

 again, new cytoblasts arise, grow, and form young 

 cells, which grow and fill up the mother cells, and 

 finally cause the latter to disappear., This is endogen- 

 ous ceU formation, while the formation of cells external 

 to other cells constitutes exogenous cell formation. 

 But according to Schleiden -" the entire growth of the 

 plant consists only of a formation of cells within 

 cells."* No other method of formation of new cells 

 seems to have been conceived by him. For although 

 the multiplication of cells, by fissiparous division of 

 previously existing cells, had been demonstrated by 

 Mirbel,t and confirmed by Von Mohl,:^ ^^^ ^^^ ^^g- 



• ? 



* Loo. citat., p. 257. 



f Mirbel, Kecherches sur la Marchantia, 1833. Schleiden, how- 

 ever, says distinctly (op. cit. p. 232), "JVTirbel does not make any 

 allusion to the process of cell formation." 



I Von Mohl, Bntwicklung und Bau der Sporen der Kryptogam. 

 Gew., Flor., 1833. 



4 



