232 



RHODOPHYCEAE 



in two opposite and decussate pairs, the first and third appearing 

 before the second and fourth. There is no secondary crop in this 

 species. The carpogonial branches are also formed from hair 



Fig. 154. 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. /a^fz^/a^ww. Z = young tetraspore. F, pro- 

 toplasmic connections of axial thread. G-J, stages in development of carpospores. 

 c/) = carpogonium, a = auxiliary cell, g = gonimoblast, 5f = sterile cells ( x 400, 

 J X 260). K, cystocarp of P. nigrescens with, ripe carpospores ( x 33). L, antheridial 

 branch (X35). 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.) 



rudiments, the support cell cutting off a small section from which 

 lateral sterile cells arise. Later on a fertile pericentral cell is cut 

 off, and this gives rise to the four-celled carpogonial branch, the 

 carpogonium being of interest because there is also a persistent 

 nucleus in the trichogyne. 



