198 



Tetrasporineae 



outer layers of the cell-wall are thrown off in a manner comparable with 

 the exuviation of the outer layers of the wall of Nephrocytium ecdysice- 

 pamim. The cells of Ecdysicldamys form a stratum, only one layer of 

 cells in thickness, attached to wet sand-grains, a feature which at once 

 distinguishes the genus from Oocystis. 



Wille ('08) has found that Oocystis submarina may pass through a 

 Tetraedron-st&te, i.e. each cell may form a resting-spore (hypnospore) of 

 a triangular shape which greatly resembles certain species of the genus 

 Tetraedron. These resting-spores form normal 0<>cystis-ce\\s on germination 

 (fig. 122 C and F). Chodat ('95) described the occurrence of zoogonidia in 

 Eremospliazra, but this must be regarded as an error due to contaminated 

 cultures 1 (vide Moore, '01 and G. S. W., '04). In Excentrosphtera Moore 

 observed the formation of numerous gonidia (aplanospores) which were 

 liberated by the bursting open of one end of the mother-cell (fig. 123 C). 



The Ooeystese are mostly found in bogs, but some forms occur in pools and others in 

 the plankton of lakes. Scotiella is a constituent of the snow-flora. 



The genera are : Oocystis Nageli, 1845 ; Nephrocytium Nageli, 1849 ; Ercmosph&ra 

 De Bary, 1858 ; Gl&otitnmm Hansgirg, 1890 ; Excentrosphsera Moore, 1901 ; Scotiella 

 Fritsch, 1912 ; E<;1i/xn-},lamys G. S. West, 1912. Protothecct Kriiger, 1894, is a colourless 

 genus. 



Sub-family MICRACTINIE/E. The Alg.i? belonging to this small group 

 (which has sometimes been called the Phytheliese) are at once distinguished 

 from all other members of the Autosporaceae by the presence of stiff bristles 



Fig. 124. A, Micractinium pusillum Fresen. [ Richteriella botryoides (Schra.) Lemm.], x 520 

 (after Lemmerrnann). B and C, M. pusillum forma quadriseta (Lemm.), x 450. D and E, 

 M. radiatum (Chod.) Wille [ = Golcnkinia radiata Chodat], x about 800 (after Chodat). 

 F, M. pciucispinosum (W. & G. S. West), x 450. 



1 Some of the supposed polymorphic states of Eremosplmra riridis described and figured by 

 Chodat ('95) are merely vegetative cells of Asterococcus superbus (Cienk.) Scherffel. 



