reproduction; evolution 321 



originated from among unicellular organisms, but there appears to 

 be practically no real source here apart from Porphyridium cruen- 

 tum, which is more probably a reduced than a primitive form. An- 

 other hypothesis is that which considers the Rhodophyceae to have 

 been evolved from the Myxophyceae, the principal argument in 

 support of this view being the resemblance between the pigments, 

 though they are not identical chemically. The principal objection 

 to this theory is the absence of any form of sexual reproduction 

 among the Myxophyceae, whereas even in the Protoflorideae there 

 is evidence of sex organs. A third hypothesis involves an origin of 

 the Protoflorideae from a Chlorophycean ancestral type such as 

 Prasiola, and it is important to note that there is a striking 

 resemblance in morphology and reproduction between Bangia and 

 Prasiola. The production of a red pigment, by a mutation, in an 

 otherwise green alga, would not seem to be insuperable. On the 

 whole this would seem to be as probable a source for the Rhodophy- 

 ceae as any other. There are some who consider that the Proto- and 

 Euflorideae had independent origins but in that case the origin of 

 the latter would be even more shrouded in mystery. 



The Protoflorideae difl'er from the Euflorideae in the usual 

 absence of pit connexions between cells and also in the primitive 

 morphological structure, a far greater variety being found within 

 the Euflorideae. It is, however, possible to treat the Rhodo- 

 phyceae as an evolutionary series in respect of their sexual repro- 

 ductive organs, and in particular of the auxihary cell. 

 True auxiliary cells absent No procarp 



Mostly haplonts Nemalionales 



True auxiliary cells absent 



Haplo-diplonts Gelidiales 



Auxiliary cells present before fertili- Procarp present 



zation. Morphologically simple Cryptonemiales 

 Auxiliary cells present before fertili- 

 zation. Morphologically ad- 

 vanced Gigartinales 

 Auxiliary cells develop after fertiliza- Rhodymeniales 

 tion Ceramiales 



A study of the Hfe cycles (Fig. 189) fully supports the above 

 schema. The primitive condition is represented by Scinaia, Nema- 

 lwn\ Batrachospermum, etc. where only the haploid generation is 

 present. The sporophyte generation is intercalated by delay in the 



iNotiV. helminthoides where the carpospores are diploid (Magne, 1961; see 

 p. 258). 



