OphiocytiacesB 



409 





chromatophores in each cell, fewest in Centritractus and most in Botrydiopsis 

 and Polyohloris, The chromatophores are sometimes discoidal, but at other 

 times cushion-like. The cells are uninucleate. 



Multiplication takes place by cell-division in three directions in Chlorobotrys 

 and Polychloris, and in the former it is the usual method of propagation, 

 motile cells being unknown. In this genus the families of 4, 8 or 16 cells 

 are often very symmetrical, but beyond this number they become irregular. 

 During division the contiguous walls of the daughter-cells are at first much 

 flattened, but afterwards they gradually become more convex. In Pseudo- 

 tetraedron and Chlorobotrys 'cysts' 

 occur, which on germination produce 

 one or two individuals. In Botrydiopsis 

 a number of spherical aplanospores 

 are sometimes formed in each mother- 

 cell (fig. 259 B). It is only in Botry- 

 diopsisandPolychloris that zoogonidia 

 occur, a large number being formed 

 in each cell (fig. 259 C). These 

 zoogonidia possess two or many 

 chromatophores and in Botrydiopsis 

 it has been shown that they possess 

 two unequal cilia. In Botrydiopsis 

 the aplanospores may at once become zoogonidangia, or, after a period of 

 rest, they may become gametangia. The gametes have only one chromato- 

 phore and a pair of almost equal cilia. 



The genera are: Botrydiopsis Borzi, 1889; Polychloris Borzi, 1892; Chlorobotrys Bohlin, 

 1901 ; Centritractus Lemmermann, 1900 ; Pseudotetraedron Pascher, 1913. 



Chlorobotrys mostly occurs in Sphagnum-bogs. The other genera are usually found in 

 small ponds and ditches, although Centritractus has been observed in the plankton. 



It is possible that Pelagocystis Lohmann, 1903 [ = Clementsia Murray, 1905] should be 

 placed in this family. It is an Alga of the marine plankton occurring as small colonies, 

 which are enveloped in a rounded mass of mucus. The cells are mostly arranged in pairs, 

 or in fours, and each group shows a more or less distinct lamellation of the mucus 

 immediately surrounding it. The cell-wall is firm, and there is apparently only one 

 parietal chrornatophore and an abundance of oil as a food-reserve. Division of the cells 

 takes place in three directions and the larger colonies dissociate into smaller ones. The 

 general disposition of the cells in the colony is very similar to that in Chlorobotrys although 



B 



Fig. 260. Chlorobotrys regular is (West) 

 Bohlin. Three colonies, x 450. 



the colonies attain a larger size. 



Family Ophiocytiacese. 



The Algre of this family are either free-floating or attached and they 

 differ from all other members of the Heterococcales in the greatly elongated 

 cells. The principal genus is Ophiocytium, in which the cells are generally 



