202 



Ghlorophycece 



Wille 1 has placed the genus Trochiscia in the Volvocaceae in 

 close proximity to Chlamydomonas, but a careful consideration of 

 the facts of the case shows this change to be unjustifiable. The 

 ordinary vegetative condition of Trochiscia is a non-motile resting 

 state, zoogonidia rarely being produced ; whereas the normal 

 vegetative condition of Ghla/mydomonas (and indeed, of all the 

 Yolvocacese) is a motile one. 



Genus Pleurococcus Menegh., 1842. [Protococcus Ag., 1824 

 (in part) ; Cystococcus Nag., 1849 ; Chlorococcum Fries, 1825 (in 

 part); Cldorosphcem Klebs, 1883 (in part); Psendoplenrococcus 



Snow, 1899.] The cells 

 are more or less globose, 

 sometimes angular by 

 compression, and they 

 occur frequently in 

 groups of two or four 

 due to imperfect separa- 

 tion after division. As 

 division occurs in three 

 directions a small cubic- 

 al colony is occasionally 

 produced, but this easily 

 dissociates into its indi- 

 vidual cells. The cell- 

 walls are strong and 

 firm. There is one 

 parietal chloroplast in 

 each cell, extremely vari- 

 able in size and form, 

 and with or without a 

 pyrenoid. 



In moist places short filaments of cells are sometimes produced 

 which exhibit a simple type of branching ; they frequently radiate 

 from a few central cells of an angular, more or less parenchymatous 

 form. This condition is readily produced in cultures and can be 

 described as the ' Protoderma-stage.' 



Vegetative multiplication takes place by division and sub- 

 sequent separation of the cells. Reproduction is brought about 



1 Wille, ' Alg. Not. VII,' Nyt Magazin f. Naturvidenskab. 1901, F-istiania, B. 39, 

 H. 1, p. 9. 



Fig. 81, A, Pleurococcus vulgarix Meuegh., 

 from Cirencester, Gloucestershire. B, PI. ru- 

 fescens (Ktitz.) Breb. var. sanyuinens W. & G. S. 

 West, from near Arncliffe, W. Yorks. (All x 520.) 

 rhJ, chloi'oplast; p, protoderma stage; pa, palmel- 

 loid state ; pg, bright red pigment ; pij, pyrenoid. 



