174 



ArORPHOLOGY. 



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

 is illustrated in fig. 185. It measures i5-20f)H or more long, and is pro- 

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

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

 Rhodophycece (Floride;e). In Gracilaria these fruit bodies occur scat- 

 tered over tlic thallus. They are somewhat llask -shaped, are partly sunk 

 in the thallus, and the ..onical 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. Rhabdonia. — This plant is about the same size as the gracilaria, 

 though it possesses more filiform branches. The c}'stocarps form prom- 

 inent elevations, while the carpospores lie in separated grou]>s around the 



FiK. 187. 

 Rhabdi)nia, branched 

 prirti')!! (if friind shuw- 

 ing cystocarps. 



Fig. iSS. 

 Pectiun oi cy3ti)carp ot rliabilonia, showing 

 spores. 



pcripherv of a sterile tissue witliia the cavitv. (See figs. iSy, i88.) Goni- 

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



379. Fertilization of the higher red algae, — The pmcess of fertilization in 

 most of the red alg;e is very complicated, chiellv becausi.' the fertilizrd egg 

 ceil (pTocarp) dues nut devulop the spores directly, as in Xemalion, Le- 



