404 



Heterococcales 



In the Heterococcales it would appear that there is nothing corresponding to the family 

 Volvocacese of the Protococcales. The only forms predominantly motile, such as Chloramceba 

 and Vacuolaria, are distinctly Flagellate in character, being naked and amoeboid, and 

 cannot rightly be placed in the Heterococcales. Pascher ('13 B) tabulates his 'Hetero- 

 chloriadales ' as more or less equivalent to his ' Volvocales,' but this is not in agreement 

 with known facts and the two genera included in his new group, namely, Chloramceba and 

 Stipitococcus, have not much in common with each other. 



The families Chlorosaccacese and Chlorotheciacese are respectively almost 

 exactly equivalent to the "Palmellacese and the Planosporaceoe among the 

 Isokontse. In Ophiocytium is seen the probable starting-point of the principal 

 filamentous type, and the striking similarity between the structure of the 

 cell-wall in this genus and in Tribonema (consult fig. 262) is particularly 

 significant. 



Multiplication occurs in various families by cell-division and by the 

 breaking up of the larger colonies. Reproduction occurs in many cases by 

 zoogonidia and sometimes, as in Ophiocytium, aplanospores are chiefly formed. 



Family Chlorosaccaceae. 



This is the most primitive family of the unicellular and colonial 



Heterokontse, occupying much the same 

 position as the Palmellacese among the 

 Tetrasporine Protococcales. The non-motile 

 condition is the dominant one, and in 

 Cfilorosaccus and Racovitziella the cells are 

 embedded in a copious mucus. Cell-division 

 takes place abundantly in this state. In 

 Stipitococcus (fig. 255) and Peroniella the 

 cells are attached by delicate stalks to the 

 filaments of larger Algae, and in many cases 

 the length of the stalk is determined by the 

 thickness of the mucous investment of the 

 host. It seems probable that in both genera 

 the stalk is the modified longer cilium. In 

 Miscliococcus the cells are globular and are 



united to form small branched colonies by thick tubular stalks of mucilage in 

 the distal ends of which the cells are embedded (fig. 256). Each cell 

 possesses from one to four chromatophores. Reproduction is by zoogonidia, 

 which in Chlorosaccus and Mischococcus have each a pair of chromatophores. 

 The unequal cilia are attached at the anterior extremity. Aplanospores are 

 known to be formed in Peroniella. 



D 



Fig. 255. Stipitococcus urceolatus W. & 

 G. S. West. A C, epiphytic on a 

 filament of Mougeotia ; D, epiphytic 

 011 Sphserozosma excavatum. A and 

 D, x500; B and C, x 780. 



