72 



CHLOROPHYCEAE 



(b) vertically, when each segment grows out laterally ; in either case it 

 will be noted that hair formation takes place at a very early stage. 



Sexual reproduction is by means of a specialized oogamy, some 

 of the species being dioecious and the remainder monoecious. The 

 female organs, or carpogonia, are borne on short lateral branches and 

 subsequently undergo displacement. Each carpogonium possesses 

 a short neck or trichogyne (the long neck of Coleochaete scutata 

 being an exception) the top of which bursts when the carpogonium 

 is mature. In the disk forms the carpogonia originate as terminal 



Fig. 50. Coleochaete. A, C. ^cwZafa, thallus with hairs ( x 150). B, C. pulvinata 

 with spermocarp ( x 45). C, C. pulvinata with antheridia (a) and young carpo- 

 gonium (c). D, C. pulvinata, almost mature carpogonium. E, C, pulvinata, 

 fertilized carpogonium. F, C. pulvinata, formation of envelope around fertilized 

 carpogonium. G, C. pulvinata, mature spermocarp with carpospores. (A, B, 

 after Smith; C-G, after Fritsch.) 



bodies on the outside of the disk, but as the neighbouring cells 

 continue gro\^1:h they eventually become surrounded and appear to 

 be in the older part of the thallus. The antheridia develop in 

 clusters at the end of branches (C. pulvinata) or from prostrate 

 cells. They finally appear as small outgrowths cut off from a 

 mother cell with stages in their development that are strongly 

 reminiscent of the Rhodophyceae (cf. p. 252). Each antheridium 

 produces one biflagellate colourless antherozoid which has been 

 contrasted with the non-motile rhodophycean spermatium. 



After fertilization the neck of the carpogonium is cut off and the 



