174 



MORPHOLOGY. 



377. Gracilaria. Gracilaria is one of the marine forms, and one species 

 is illustrated in fig. 185. It measures i$-2ocm or more long, and is pro- 

 fusely branched in a palmate manner. The parts of the thallus are more 

 or less flattened. The fruit is a cystocarp, which is characteristic of the 

 Rhodophyceae (Florideae). In Gracilaria these fruit bodies occur scat- 

 tered over the thallus. They are somewhat flask-shaped, are partly sunk 

 in the thallus, and the Conical end projects strongly above the surface. The 

 carpospores are grouped in radiating threads within the oval cavity of the 

 cystocarp. These cystocarps are developed as a result of fertilization. 

 Other plants bear gonidia in groups of four, the so-called tetraspores. 



378. Bhabdonia. This plant is about the same size as the gracilaria, 

 though it possesses more filiform branches. The cystocarps form prom- 

 inent elevations, while the carpospores lie in separated groups around the 



Fig. 187. 



Rhabdonia, branched 

 portion of frond show- 

 ing cystocarps. 



Fig. it 



Section of cystocarp of rhabdonia, showing 

 spores. 



periphery of a sterile tissue within the cavity. (See figs. 187, 188.) Goni- 

 dia in the form of tetraspores are also developed in Rhabdonia. 



379. Fertilization of the higher red algae. The process of fertilization in 

 most of the red algae is very complicated, chiefly because the fertilized egg 

 cell (procarp) does not develop the spores directly, as in Nemalion, Le- 



