ALGAE. VOLVOCINEAE. 35 



Some examples will serve to illustrate the course of life of these plants. 



The genus Chlamydomonas consists of isolated vigorously motile cells, which in the 

 vegetative state multiply by division into two or four. In sexual reproduction the cells 

 divide each into eight motile daughter-cells, provided with four cilia ; these daughter-cells 

 are smaller than their parent-cell, and differ also from one another in size. These cells, 

 according to Rostafinski, conjugate in precisely the same manner as that described by 

 Pringsheim in the case of Pandorina (see below) ; the zygospores thus produced 

 come to rest and grow for some weeks ; if they are then dried and again put into water, 

 they divide repeatedly and form non-motile resting cell-families, identical with the old 

 genus of the Palmellaceae, Pleurococcus 1 . 



FIG. 16. Development of Pandorina Marian. I. a swarming family. //. a similar one divided into sixteen daughter- 

 families. ///. asexual family, the cells of which are issuing from the gelatinous envelope. IV, ^.pairing of the swarm-cells. 

 VI. a zygospore just formed. VII. a fully developed zygospore. VIII. transformation of the contents of a zygospore into 

 a large swarm-cell. IX. the swarm-cell free. X. young fan.ily formed from No. IX. After Pringsheim. 



In Pandorina Morum (Fig. 16) the course of development was first observed in its 

 entirety by Pringsheim, and the first example of the conjugation of swarm-cells was 



1 Goroshankin gives a different account of the process of conjugation in Chlamydomonas fiulvis- 

 culus. In this plant male and female gametes are formed. The male smaller than the female ; eight 

 male gametes are produced in. a vegetative cell, but only 2-4 female. The pointed ends of the 

 gametes meet, the cilia drop off, and a passage is formed at the anterior extremities of the two 

 bodies, through which the protoplasm of the male cell finds its way to that of the female and unites 

 with it to form a zygospore. 



D 2 



