201 



ing its contents, and the trichogyne then disappears. The carpogone 

 now divides by a horizontal wall into two cells ; the upper one of these 

 is functionless, and ultimately disappears ; the lower one contains the 

 impregnated oosphere or carposperm. The carposperm does not, how- 

 ever, in any case possess the power of germinating directly. In the 

 Porphyraceae it breaks up into 

 eight portions, the carpospores, 

 which germinate after moving 

 about with a slow amoeboid mo- 

 tion. In all the other orders 

 the contents of the carpogone 

 undergo, after impregnation, 

 more complicated divisions, and 

 become differentiated into a 

 sterile and a fertile portion, the 

 placenta and the nucleus. The 

 placenta may consist of one or 

 more cells, and frequently occu- 

 pies the larger portion of the 

 carpogone ; or it may be re- 

 duced to very small dimensions. 

 The nucleus is the mass of carpo- 

 spores, and may be made up 

 of a number of secondary nuclei. 

 The mass of carpospores is 

 sometimes, as in Callithamnion, 

 completely exposed except for a 

 gelatinous membrane by which 

 it is surrounded but much 

 more often there is gradually 

 formed round the nucleus after 

 impregnation, not only a layer 

 of mucilage, but also a more or 

 less hard solid layer, the peri- 

 carp; and the whole structure 

 thus constituted is then known 

 as the sporocarp or cystocarp. From this cystocarp the carpospores 

 escape, when ripe, either by the decay of the pericarp ('coccidium' of 

 the older systematists), or through an opening at its apex, the carpostome 

 (' ceramidium ' of older writers). In some genera (Polysiphonia, Lejolisia, 

 Born., Bonnemaisonia, Ag.) the cystocarp is completely exposed, con- 

 spicuous, and sometimes stalked ; but it is usually, as in Gracilaria, 



FIG. 178. Gracilaria. compressa Ag. Branch with 

 cystocarps (natural size). (After Hauck.) 



