274 M. N. Pringsheim on the Pairing of Zoospores. 



less than sixteen cells, especially with eight cells, are oftener 

 prodnced. Moreover the dissolution of the membrane of the 

 mother cell proceeds more slowly than in the case of neuter 

 plants, one result of which is that the young sexual plants 

 vary much in the extent of their growth, and continue united 

 in groups of different sizes for a long time after their forma- 

 tion, according as a greater or less number of them have hap- 

 pened to become free from the gelatinous mass in which they 

 were imbedded. 



As the individual gTOups are at first motionless, and the 

 mother plant loses its cilia during the formation of the young 

 ones, the entire group is at first entirely quiescent. But 

 afterwards the young sexual plants, like the neuter ones, pro- 

 duce upon each of their cells two cilia, which commence their 

 motion as soon as the enveloping mucus admits of it ; and 

 thus ultimately the entire group assumes a state of active 

 rotation. During the rotation of the groups the same process 

 of expansion and dissolution takes place in the membrane of 

 the sexual plants as occurred in the mother plant ; but the 

 contents of the cells of the sexual plants do not undergo divi- 

 sion, but combine to form a single zoospore, which becomes 

 free by the rapid dissolution of the membranes. 



In their general structure these zoospores differ in no way 

 from other zoospores. At their colourless apex they exhibit, 

 like other zoospores, a red body placed on one side of the apex, 

 and two long vibrating cilia, by which they move in the 

 manner common to zoospores. 



The individual zoospores exhibit no marked differences, 

 except that (like the sexual plants from which they spring) 

 they vary in size within tolerably wide limits, but not in a 

 manner to indicate the existence of two different sorts. 



Amongst the groups of isolated zoospores of different sizes, 

 some are at last seen to approach one another in pairs. They 

 come into contact at their anterior hyaline apex, coalesce with 

 one another, and assume a shape resembling a figure of 8*. 

 The constriction which marks their original separation dis- 

 appears by degrees ; and the paired zoospores form at last a 

 single large green globe, showing at the circumference no 

 trace of their original separation. It may be seen, however, 

 that the globe is larger than the individual neighbouring zoo- 

 spores, that it has a strikingly enlarged colourless mouth-spot, 

 with two red bodies on the right and left, and that it is fur- 

 nished with four vibrating cilia originating in pairs near the 



* [The German expression is " biscuit-artige Gestalt," but this, if trans- 

 lated literally, would convey no idea to an English reader. — Tr.] 



