FLORIDE.E 631 



seaweeds is due to the presence of a pigment known as rkodospermin 

 or phyco-erythrin, soluble in fresh watei', which may be separated in 

 the form of beautiful regular crystals. 



The only mode of propagation which was until recently known 

 to exist in this group of seaweeds is the production and liberation 

 of tetraspores (fig. 472, B), formed by two successive binary 

 subdivisions of the contents of special cells, which sometimes 

 form part of the general substance of the frond, but sometimes 

 congregate in particular parts or are restricted to special branches. 

 If the second binary division takes place in the same direction as 

 the first, the tetraspores are arranged in linear series ; but if its 



JF 



SJ) Q 



FIG. 473. Nemalion multifidum : I, a branch with a carpogone, c, and pollinoids, 

 xj> ; II, III, commencement of the formation of the fructification; IV, V, develop- 

 ment of the spore-cluster ; t denotes the trichogyne, c the carpogone and fructifica- 

 tion. (From Goebel's 'Outline of Classification.' The Clarendon Press.) 



direction is transverse to that of the first, the four spores cluster 

 together. These, when separated by the rupture of their envelope, 

 do not comport themselves as zoospores ; but, being destitute of 

 propulsive organs, are passively dispersed by the motion of the sea 

 itself. Their production, however, taking place by simple cell- 

 division, and not being the result of any form of sexual conjugation, 

 the tetraspores of the Floridece must be regarded, like the 

 zoospores of the Ulvacece, as yonids, analogous rather to the buds 

 than to the seeds of higher plants. It is now known that a true 

 sexual process takes place in this group ; but the sexual organs 

 are not usually found on the plants which produce tetraspores. 

 Antheridial cells are found, sometimes on the general surface of the 

 frond, more commonly at the ends of branches, and occasionally in 

 special conceptacles. Their contents, however, are not motile 



