LIAGORA TETRASPORIFERA 



'4 



'o^'.D 



PHYLLOPHORA BRODIAEI ^ 



ASPARAGOPSIS 



I 



J 



MOST FLORIDEAE 



( 



AHNFELDTIA PLICATA 



LOMENTARIA ROSEA 



Fig. 189 Types of life cycle in the Rhodophyceae and their pos- 

 sible inter-relationships. RD = position of reduction division in 



life cycle. 



reduction division, as in the Chlorophyceae, the interpolation stage 

 being represented at present by species such as Liagora tetraspori- 

 fera (see p. 231). Finally there is the regular alternation of the type 

 found in most Euflorideae, e.g. Polysiphonia. Early variants of this 

 type are found in the Nemalionales (Galaxaura and Asparagopsis) 

 where there is a distinct alternation of unhke generations; in 

 the former they are also cytologically different but not so in 

 the latter (cf. p. 230). Subsequent developments, which must be 

 interpreted as retrogressive, can be seen in Phyllophora memhrani- 

 folia, where the tetraspores are grouped into nemathecia on the 

 diploid plant; in P. brodiaei, where the diploid phase has disap- 

 peared and the nemathecia can be regarded as growing parasitically 

 in the haploid thallus; and finally in Ahnfeldtia where meiosis no 

 longer takes place and instead the nemathecia contain monospores. 

 Hildenbrandtia and Lomentaria rosea in European waters and 



322 



