CHAPTER V. THE THALLOPHYTA. 



283 



THE CHLOROPHYCEiE. 



This group includes quite a variety of forms, some simple 

 in their structure, others comparatively complex. None of 

 them possess a soluble blue or brown coloring matter in the 

 cells, though the spores of some, when ripe, have portions 

 of their chlorophyll modified into a substance chemically simi- 

 lar to the latter substance, but having a red color. Most of 

 the forms reproduce not only asexually by some mode of 

 ... :: . : ... cell-division, but also sexually, either 



•v>$^§& by conjugation or by the production of 



:-[•';$$;•.%'£■■. oospores. In all of the groups grada- 



'".•-■^0$[--. : :\ tions may be observed between these 



two modes. The sub-class is divided 

 into six orders : the Cceloblastea or 

 Siphonese, the Protocdccacea, the Vol- 

 vocinece, the Confervoidece, the Conjugates 

 and the Characeoe. 



The Coeloblastese. These include 

 both marine and fresh-water forms. 

 One of their most distinctive charac- 

 teristics is the fact that, though often 

 complex in form and attaining a con- 

 siderable size, they are not divided into 

 cells ; each plant, in fact, may be re- 

 garded as a single highly elaborated 

 cell. In a few species no sexual repro- 

 duction is known, in others it takes 

 place by conjugating zoospores, and in 

 still others, by fertilization and the 

 production of oospores. 



Among the simplest forms of the 

 group are the Botrydiums, one of which 

 is represented in Fig. 479. The lower 

 portion forms dichotomously branching 

 root-like bodies or rhizoids, which penetrate the mud and serve 

 for anchorage, while the balloon-shaped upper portion rises into 

 the water above. This is filled with granular protoplasm and 

 contains much chlorophyll. 



Fig. 479. — Botrydium granu- 

 latum, in the act of discharging 

 its zoospores. Magnified about 

 20 diameters. After Wolle. 



