210 



Chlorophycew 



8=1+7; colony of 16 = 1 + 5 + 10 ; colony of 32 = 1 + 5 + 10 + 16; 

 but this arrangement is not always observed. 



Multiplication occurs in some species by the formation of 

 autocolonies which arise by the division of the contents of a single 

 coenocyte. Hypnospores are also frequently formed (fig. 85 E h). 



Fig. 85. A, Pediastrum integrum Nag., from Ben Lawers, Perthshire ( x 475). 

 B, P. tricornutum Borge, from Glen Tummel, Perthshire ( x 475). C and D, 

 P. tetras (Ehrenb.) Ealfs, from Pilmoor, N. Yorks. (x475). E, P. duplex 

 M'eyen, from Lough Fea, Londonderry, Ireland; hypnospores (h) ( x 475). 

 F H, P. Boryanum (Turp.) Menegh.; G, showing escape of zoogbnidia ; 

 H, young colony formed by apposition of quiescent zoogonidia ; F, from 

 Frizinghall, W. Yorks., x 475 ; G and H, x 220 (after Kerner). I, two marginal 

 cells of P. glanduliferum Benn., from Bisley Common, Surrey. J L, zoogo- 

 nidia and gametes of P. Boryanum (after Askenasy); J, zoogonidia and K, 

 gamete (x500); L, conjugation of gametes to form zygospores (z) (gametes 

 x 730, zygospores x 220). 



Reproduction takes place by the successive division of the 

 contents of a coenocyte to form a number of zoogonidia, which are 

 suddenly liberated into an external vesicle through a slit in the 

 wall of the mother-ccenocyte. The zoogonidia swarm in this 

 vesicle and at length become quiescent, arranging themselves in 

 one plane as a new coenobium. Biciliated gametes have been 

 observed by Askenasy 1 , which are much smaller than the zoogonidia 



1 Askenasy, 'Entwickl. von Pediastrum,' Ber. Deutsch. Bot. Gesellsch. vi, 1888. 



