202 



ALG^E 



more or less imbedded in the thallus, often in special fertile branches ; 

 and its situation is then usually indicated by an external wart-like 

 swelling. In Polyides (Ag.)j the Squamariaceae, and other forms with 

 a perfectly flat frond, the cystocarps are enclosed in nematheces. 



In a considerable number of Florideae the formation of the cystocarp 

 is a more complicated process than that already described, the process 

 of impregnation consisting of two distinct stages (i) the fertilisation 

 of the trichogyne by the pollinoids ; and (2) the fertilisation by the 

 impregnated trichophore-cells of the carpospores, which may be at some 

 considerable distance from the trichophore and trichogyne, even on a 



FIG. 179. Dudresnaya cocclnea Crouan. /, young trichophore. //, young trichogyne ; 

 f, young fertilising tubes. ///, impregnated trichophore with pollinoids on the coiled tncho- 



fyne,^; the fertilising tube,./', impregnating successively the carpogones, VII, VI, and V, 

 V, carpogone before fertilisation ; c, carpogenous cell. VIII, masses of carpospores. 



different branch. This is effected by means of long simple or branched 

 tubes, the fertilising-tubes, or ' ooblastema-filaments ' of Schmitz. The 

 following is the process as it takes place in Dudresnaya (Born.). The 

 trichophore consists of a row of cells which, before fertilisation, put out 

 short branches, which subsequently develop into long tubes. No carpo- 

 gone is found in the immediate neighbourhood of the trichophore ; but 

 at some distance are a number of short segmented filaments, the termi- 

 nal cells of which are considerably larger than all the rest. These cells 

 are carpogones. The fertilising-tubes make their way between the fila- 

 ments or hyphae of which the thallus is composed, come into contact 



