REPRODUCTION 



249 



original haploid phase may have produced plants that were more 

 successful and which subsequently eliminated their parents in the 

 struggle for existence. 



C. The original ancestors were filamentous with equal haploid 

 and diploid generations, or perhaps with generations that were 

 slightly unequal, but that both retained the power of producing a 

 ciliated zooid which could develop without fusion, e.g. Nemoderma 

 (fig- 163). 



A further consideration of this problem must now be deferred 

 until the other two groups have been surveyed because a final con- 

 clusion must incorporate phylogenetic considerations. 



SCIMAIA 



LjAg-oka Tetr. 





Phyllophori 



SIPKONIA ETC. 



Ahnfeldtia Plicata 



LOMENTARIA RO-5EA 



Fig. 164. Types of life cycle in the Rhodophyceae and their possible inter- 

 relationships. i?D = position of reduction division in life cycle. 



Fig. 164 is a summary of the principal life cycles that are to be 

 found among the Rhodophyceae. According to Svedelius (1931) 

 the primitive cycle is represented by Scinaia, Nemalion and Batra- 

 chospermum where there is only a haploid generation. Some 

 postponement of meiosis is seen in Liagora tetr asporif era, but the 

 maximum delay is reached in Polysiphonia and most other Rhodo- 

 phyceae where there are two equal generations, the sporophyte 

 reproducing by means of tetraspores, two of which give rise to 



