152 



Chlorophycece 



Sub-family I. SACCODERM^E. 



This is a very natural group of Desmids in which the cell-wall 

 is unsegmented and destitute of pores. There is no line of de- 

 marcation between the 

 newer semicell and the 

 older semicell, the cell- 

 wall being absolutely 

 continuous. Division 

 takes place at no fixed 

 part of the cell (except 

 in a few species of 

 Cylindrocystis)a,nd the 

 young semicells are 

 developed obliquely, 

 gradually sliding away 

 from one another as 

 they reach maturity. 



Tribe 1. Gonatozygce. 



This tribe only 

 includes two genera 

 which are considerably 

 removed from other 

 Desmids. The cells 

 are long and cylindri- 

 cal, and are joined by 

 their apices into fragile 

 filaments of variable 

 length. The filaments 

 easily break up, but 

 this in no way inter- 

 feres with the life of 

 the individual cells. 

 Conjugation only takes 

 place between cells 

 which have become 

 free. The cell- wall is 

 layer being hyaline and 



Fig. 53. A and B, Gonatozygon Brebissonii De 

 Bary (x464); A, from Esher Common, Surrey; 

 B, from Strensall, N. Yorks. C E, G. Brebissonii 

 var. lave (Hilse) W. & G. S. West, from Mickle 

 Fell, N. Yorks. (x356). F and G, G. Brebissonii 

 var. minutum W. & G. S. West, from Eiccall 

 Common, E. Yorks. ( x 464). H, zygospore of G. 

 monottenium De Bary ( x 464). I and J, Genicularia 

 Spirot<enia De Bary, from near the Lizard, Cornwall; 

 I, vegetative cell ( x 312) ; J, zygospore ( x 220). 



differentiated into two layers, the inner 



