25 



merits from the upper borders of cells below the apex. The 

 first tinpe of division simply increases the length of the 

 filament, the second results in the formation of a nev/ 

 branch. 



There appear to be two methods of cell division. The 

 first occurs most comrnonly in the larger cells, and is al- 

 ways preceded by an acciunulation of cytoplasm, nuclei, and 

 to a less extent of ciiromatophores, which forms a dense, 

 more or less homogeneous irictss in the terminal portion of 

 the apical cell (fig. 37), A thin dome-shaped membrane is 

 now laid dovm, v/ith its convexity to.Tard the apex, cutting 

 a solid accumulation of protoplasm from the tip of the cell 

 (fig, 38) . This membrane is formed simultaneously over its 

 v.hole extent. There is no trace of cleavage in connection 

 with its formation, the protoplasm being in contact \vith 

 it on each side. The nuclei appear to have nothing to do 

 with its formation, nor is its formation visibly associated 

 in ajiy way v/ith nuclear division. The membrane is, howev- 

 er, neyer formed until there is an accvunulation of nuclei 

 and cytoplasm in the tip of the cell. The young cell, at 

 first a solid cap over the tip of the apical cell, grows 

 rapidly, soon acquiring a central vacuole (fig. 39), and 

 forming a tirpica.1 vegetative cell. During the growth of 



