200 



Tetrasporineae 



1894 *; Pilidiocystis Bohlin, 1897; Chodatella Lemmermann, 1898; Bohlinia Lemmer- 

 mann, 1899] ; Franceia Lemmermann, 1898. 



Sub-family TETRAEDRE.E. This small group is chiefly represented by 



Fig. 126. A, Tetraedron minimum (A. Br.) Hansg. B, T. caudatum (Corda) Hansg. C, 

 T. regulare Kiitz. D, T. enorme (Ealfs) Hansg. E G, T. horridum W. & G. S. West. 

 auts, autospores. All x 450. 



the genus Tetraedron 



Fig. 127. A and B, Chio- 

 naster nivalis (Bohlin) 

 Wille; A, vegetative 

 cell showing nucleus 

 (n); B, cell with aplano- 

 spore. x 450 (after 

 Wille). C, Mycotetrae- 

 dron cellare Hansg. 

 x 1500 (after Hansgirg). 



in which the cells are free-floating without any mucous 

 investment. They are compressed and angular, with 

 a definite number of angles; or they are tetrahedral, 

 octahedral, or polyhedral (fig. 126). The angles of the 

 cells may be rounded, emarginate, or furnished with 

 spines. Each cell contains a massive parietal chloro- 

 plast, usually with a distinct pyrenoid. Reproduction 

 occurs by the formation of 4 or 8 autospores which are 

 miniature adults when set free by the rupture of the 

 mother-cell-wall (fig. 126 4/and B c). 



The fact that Tetraedron-like states of other mem- 

 bers of the Protococcales are known (as in Pediastrum, 

 Hydrodictyon and Oocystis) in no way interferes with 

 the validity of this genus. Most of the forms occur in 

 stagnant waters, and a few are frequent constituents 

 of the freshwater plankton. In Cerasterias the angles 

 of the cells are so greatly produced that the in- 

 dividuals are stellate in general appearance. 



The genera are : Tetraedron Kiitzing, 1845 [incliis. Polyedrium Nageli, 1849 ; Stauro- 

 phanum Turner, 1893 ; Folyedropsis Schmidle, 1898; Dichotomum W. & G. S. West, 1896 

 (in part)] ; Cerasterias Reinsch, 1867 [inclus. Astrodadium Tschourina, 1909] ; Thamnias- 

 trum Reinsch, 1888. 



There are two interesting colourless members of this sub-family : Mycotetraedron 

 Hansgirg, 1890 (fig. 127 C} and Chionaster Wille, 1903 (tig. 127 A and B}. 



1 Chodat (1895) states ' nomen ineptum ob affine Tetracera Dilleniacearum.' 



