Fig. 90 Petalonia fascia. A, plant ( x |). B, transverse section of 

 thallus with plurilocular sporangia ( x 375). (A, original; B, after 



Setchell and Gardner.) 



because normally the gametophytic generation arises from the pro- 

 ducts of unilocular sporangia. It would therefore seem premature 

 to accept this pecuHar life cycle without further evidence, and at 

 present it would be more in agreement with known life cycles if 

 the plants are simply regarded as being wholly diploid and without 

 a haploid generation. 



In the related genus Scytosiphon it would also seem that only the 

 diploid generation is present and that the reported protonemata 

 are not gametophytic as has been suggested by some workers. 



DiCTYOSiPHONACEAE : Dictyosiphon (dictyo, net; siphon, tube). 

 Fig. 91 



The filamentous plants arise from small lobed discs and have 

 either a few or many branches, the younger ones commonly being 

 clothed with deUcate hairs. In young plants there are the usual 

 apical hairs with a basal meristem. Later the hairs are shed leaving 



163 



