EUPHYCOPHYTA 



249 



Bostrychia, Plumaria). The order is the most highly evolved in the 

 Rhodophyceae and is the only one in which the auxiliary cell is cut 

 oflf after fertilization and as a direct consequence of the process. 



* Rhodomelaceae : Polysiphonia {poly, many; siphonia, siphons). 

 Fig. 141 



The thallus in this genus generally arises from decimibent basal 

 filaments that are attached to the substrate by means of small 



Fig. 141 Polysiphonia violacea. A, plant of P. nigrescens ( x ^). 

 B, life cycle. C, apex and cells cut off from central cells. D, thallus 

 construction in longitudinal section. E, transverse section of thallus, 

 P. fastigiata. f= young tetraspore. F, protoplasmic connections 

 of axial thread. G-J, stages in development of carpospores. cp = 

 carpogonium, a = auxiliary cell, ^ = gonimoblast, 5f= sterile cells 

 ( X 400), (J X 260). K, cystocarp of P. nigrescens with ripe carpospores 

 ( X 33). L, antheridial branch ( x 35). M, a-f, stages in development 

 of antheridia. N, P. nigrescens, tetraspores ( x 33). (A, K, N, after 

 Newton; B, after Svedelius; C, F, schematic; D, E, after Oltmanns; 

 G-J, after Kylin; L, after Grubb; M, after Tilden.) 



