EUPHYCOPHYTA 7I 



are the more primitive. West (1912) considered that the 

 dwarf males were to be regarded as reduced from normal 

 male filaments, for in one species the male plants are inter- 

 mediate in size. At present there does not appear to be any 

 very convincing evidence in support of either theory. 



* Chaetophorales 



A family in which the fundamental structure is the possession of 

 both a basal and erect system of branched threads, this type of 

 thallus being known as heterotrichous (cf. p. 312). Some authori- 

 ties do not consider this character a sufficient distinction to warrant 

 removal from the Ulotrichales (Fritsch). In some of the genera 

 reduction has taken place and only the basal or erect system is now 

 represented. Sexual reproduction is mostly isogamous but some 

 species are anisogamous and a few oogamous. 



* Chaetophoraceae : Stigeoclonium {stigeo^ sharp-pointed ^c/omwm, 

 branch). {MyxoTiemd). Fig. 37 



Many species are heterotrichous and the plants are frequently 

 enclosed in a broad, watery gelatinous sheath. The chloroplast is 

 band-like and often does not fill the entire cell, especially in the 

 older parts of the thallus. The aerial part bears branches that ter- 

 minate in a colourless hair, the degree and nature of the branching 

 depending upon illumination, nutrition and the rate of water flow. 

 There is no localized area for cell division in the aerial portion, but 

 in the creeping system only the apical cells are meristematic. The 

 prostrate system may be {a) loosely branched, {b) richly and com- 

 pactly branched or {c) a compact disc, but the more developed the 

 basal portion the less elaborate is the aerial and vice versa. Vegeta- 

 tive reproduction is by means of fragmentation, whilst sexual and 

 asexual reproduction are the same as in Draparnaldia (see below), 

 except that there is only one macrozoospore produced per cell. In 

 two species, however, a third type of biflagellate swarmer is known, 

 and hence reproduction in these species is comparable to that 

 found in Ulothrix (cf. p. 51). 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 zoo- 



