234 



THE CELL 



After a sufficient number of nuclei have developed, a further 

 stage supervenes, when cells are formed (Fig. 124). Between the 

 nuclei, which are arranged at regular distances from one another, 



the protoplasm differen- 

 tiates itself into radial 

 fibrillse. Further it de- 

 velops connecting 

 threads in all directions, 

 which thicken at their 

 centres, and form cell- 

 plates. In the cell-plates 

 the cellulose walls make 

 their appearance in the 

 manner already de- 

 scribed. These swell up 

 easily, and owing to their 

 formation, a portion of 

 the protoplasmic lining 

 becomes encapsuled 

 around each nucleus to 

 form the protoplasm of 

 the cell.. Sometimes 

 two nuclei are enclosed 

 in one cell ; these sub- 

 sequently are either 

 separated from one another by a partition wall, or, as in Corydalis 

 cava, fuse together to form a single cell. 



The sporangium of Saprolegnia is, to commence with, a long 

 cell filled with protoplasm. Later on the nuclei in it increase 

 very much in number through bipartitions, which for the most 

 part occur simultaneously. After a time they distribu te themselves 

 evenly throughout the cell-space. The protoplasm in the neigh- 

 bourhood of each nucleus then differentiates itself into a small 

 mass, which surrounds itself with a firm glistening envelope ; 

 by this means the cell contents split up simultaneously into as 

 many spores as there are small nuclei present in the cell. Later 

 on these are passed to the exterior by the bursting of the mother- 

 cell, the sporangium. 



The formation of swarm-spores in Radiolaria, which has been 

 already mentioned, affords us another peculiar instance of so- 

 called free cell-formation. 



PIG. 124. Reseda odorata. Protoplasmic lining of 

 the embryo-sac at the commencement of free cell- 

 formation, (x 240 ; after Strasburger, Botan. Pralcti- 

 cum, Fig. 192.) 



