66 



CHLOROPHYCEAE 



meristematic. The prostrate system may be (a) loosely branched, 

 (b) richly and compactly branched or {c) a compact disk, but the 

 more developed the basal portion the less elaborate is the aerial 

 and vice versa. Vegetative reproduction is by means of fragmenta- 

 tion, whilst sexual and asexual reproduction are the same as in 

 DraparnaldiUy except that there is only one macrozoospore 



Fig. 46. Stigeoclonium. A, plant of S. teniie. B, basal portion of S. luhricum. 

 C, aerial position of ^S. protensum. D, rhizoids in S. aestivale. E, palmelloid state. 

 (A-C, E, after Oltmanns; D, after Fritsch.) 



produced per cell. In two species, however, a third type of bi- 

 flagellate swarmer is known, and hence reproduction in these 

 species is comparable to that found in Ulothrix (cf. p. 46). These 

 extra swarmers, which are probably the true gametes, are few in 

 number but fusion between them is rare, probably because the 

 plants are dioecious. In general the microswarmers seem to have 

 taken over the function of the sexual biflagellate gametes. The 

 zygote is said to germinate to zoospores, and these then give rise to 



