Desmidiacece 



141 



It frequently happens that conjugation takes place immediately 

 after vegetative division and before the young semicells have 

 arrived at maturity 1 , and for any trace of sexuality to exist under 

 such conditions, one must imagine that the physiological change 



Fig. 52. A C, Staurastrum Dickiei Ealfs; three stages in the conjugation, from 

 the New Forest, Hants. (x356). D and E, Penium didymocarpum Lund.; 

 D, conjugation of four individuals just produced by division; E, completed 

 conjugation showing the double zygospore; from near Balallan, Lewis, Outer 

 Hebrides (x464). F, Closterium lineatum Ehrenb., showing the double zygo- 

 spore, from near Glenties, Donegal, Ireland ( x 100). z, zygospore. 



from the vegetative to the reproductive cell occurs immediately 

 antecedent to conjugation. Conjugation between adjacent cells of 

 filamentous species (i.e. lateral conjugation) has been observed in 



1 Archer in Quart. Journ. Micr. Sci. ii, p. 251 ; W. & G. S. West in Journ. 

 Eoy. Micr. Soc. 1896, p. 151. 



