3 2;2 Theory of Cell-formation [Book n. 



Dumortier had observed the division of cells as early as 1832 \ 

 and Morren had seen it in Closterium in 1836, but had not 

 given the needful details. Finally, von Mohl applied the 

 experience which he had gained from Cladophora to other 

 filamentous Algae, and pointed out the similarity between 

 these processes and the division of Diatoms, which he con- 

 sequently claimed as plants in opposition to Ehrenberg, who 

 considered them to be animals ('Flora,' 1836, p. 492). 



Meyen next, relying on von Mohl's observations on Clado- 

 phora, declared in the second volume of his ' Neues System ' 

 that cell-division was a very common occurrence in Algae, Fila- 

 mentous Fungi and the Characeae, but he neglected any closer 

 investigation of the processes by which the division is intro- 

 duced and completed. His comparison of these cases of cell- 

 formation with the formation of spores, pollen-grains, and endo- 

 sperm-cells is moreover noticeable as the first attempt to distin- 

 guish what is now known as free cell-formation from cell-division ; 

 it was obviously the want of this distinction which long pre- 

 vented clearer views on the whole of this field of observation. 

 The due separation of these two modes of cell-formation was a 

 short step after the observations that had been already made ; 

 and if that step had been taken, Schleiden's theory would have 

 been impossible, and the development of the cell-theory would 

 not have been prejudiced by the mistake, introduced by 

 Schleiden after 1838, of applying the mode of free cell-form- 

 ation, which he believed he had observed in the embryo-sac of 

 Phanerogams, to the multiplication of vegetative cells in grow- 

 ing organs, and regarding it as the only mode of cell-formation. 

 This would have been the more impossible, since von Mohl in 

 the same year gave an excellent description of the development 

 of stomata by division of a young epidermis-cell and the later 

 separation of the dividing wall into two laminae. But von 

 Mohl in the years immediately following was over-cautious in 



1 See Meyen, ' Neues System,' ii. 344. 



