reproduction; evolution 323 



Apophloea in New Zealand waters represent examples of a reduced 

 life cycle, because in these plants the gametophyte generation is 

 wholly suppressed, whereas in other examples it is the sporophyte 

 generation that has been reduced. 



Recently Feldmann (1952) has argued that in all three classes the 

 primitive Ufe cycle is that with alternation of two isomorphic 

 generations. The arguments against this have been put forward in 

 the case of the Chlorophyceae and the thesis has been supported in 

 the case of the Phaeophyceae. In the case of the Rhodophyceae it 

 would seem that if an origin from either the Myxophyceae, uni- 

 cellular organisms or Prasiola is envisaged, the logical, primitive 

 Rhodophycean life cycle would consist of wholly haploid indivi- 

 duals into which sooner or later a sporophyte would be intercalated. 

 Feldmann's proposed primitive life cycle for the Rhodophyceae 

 would appear unnecessarily complex and not fulfilled by any hving 

 representatives. Fundamentally he envisages a steady reduction 

 series throughout the class (Fig. 190). 



The phylogenetic history of the Chlorophyceae and Rhodo- 

 phyceae appears to follow parallel lines if the arguments presented 

 above are accepted. In both, the life cycle with only haploid indivi- 

 duals is the primitive one and a diploid generation is subsequendy 

 interpolated. In the Chlorophyceae the haploid generation even- 

 tually disappears (e.g. Siphonales, Valoniaceae) whereas in the 

 Rhodophyceae it is the newly intercalated sporophytic generation 

 that may become reduced {Phyllophora brodiaei, Ahnfeldtia plicata) 

 as well as the gametophyte generation (e.g. Lomentaria rosea in 

 European waters (cf. p. 248), Hildenbrandtia and Apophloea). The 

 phylogeny of the Phaeophyceae also fits into the general pattern if 

 it is accepted that the primitive condition there is alternation of 

 two isomorphic generations. 







A D ^^ ^ g D 2a 



Fig 190 Evolutionary development of Rhodophycean life cycles 



according to Feldmann. A =- hypothetical original; B, Polysiphoma 



type; C= reduced Liagora type, I = independent carposporphyte ; 



P = parasitic carposporophyte. RD = place of meiosis. 



