32 



THE CELL DOCTRINE. 



or less opaque. Single, larger, more sharply defined, 

 granules next become apparent, A, fig. 2, constituting 

 the nucleoli, about which the smaller 

 granules soon collect to form the 

 nuclei or cytoblasts, B. These then 

 grow considerably in the free state, 

 C, but so soon as they have at- 

 tained their full size, a delicate, 

 transparent vesicle rises upon their 

 surface, assuming the relation of the 

 watch crystal to a watch, D, E. 

 Thus is constituted the young cell. 

 The vesicle gradually expands and 

 becomes more consistent, and with 

 the exception of the cytoblast, 

 which always forms a portion of it, 

 the wall now consists of gelatine. 

 The entire cell then increases be- 

 yond the margin of the cytoblast, 

 and quickly becomes so large that 

 the latter at last merely appears as 

 a small body inclosed on one of the 

 side walls. In this manner, we have 

 exogenous free cell formation. With- 

 in these cells, again, as well as in 

 the homogeneous blastema about 

 them, new cytoblasts arise, grow, 

 and form young cells which grow and fill up the mother 

 cells, and finally cause them to disappear. This is 

 endogenous cell formation. According to Schleiden 

 "the entire growth of the plant consists only of a 

 formation of cells within cells." No other method 



E 



Fig. 2. Cellular Tis- 

 sue, from the embryo 

 sac of Chamaedorea 

 Schiedeana, in the act 

 of formation. 



A, Formative sub- 

 stance, gum, mucous 

 granules, nuclei of cy- 

 toblasts (nucleoli). 



B, Cytoblasts. 



C, Single and free cy- 

 toblast more highly 

 magnified. 



D, Cytoblast with 

 cell forming in it. 



E, Same more highly 

 magnified. 



F, Cytoblast isolated 

 after destruction of cell. 



From Schleiden 

 Beitrage zur Phylogen- 

 esis. 



