Conchocelis 

 phase 



Fig. 124 Diagram of life cycle of Porphyra umhilicalis. 



eciousj but in either case the male thaUi or portions of the thalli 

 are commonly paler in colour than the female. Each antheridial 

 mother cell gives rise to 64 or 128 antheridial cells, each of which 

 produces one spermatium. The fertihzed (?) carpogonium divides 

 into four or eight cells that represent primitive carpospores; in this 

 plant these are haploid (though in most Rhodophyceae they are 

 diploid) because meiosis occurs at germination of the zygote. 

 FertiHzation has never actually been observed although there is 

 strong evidence which suggests that it does take place. The carpo- 

 spores germinate and in the case of P. umhilicalis produce a pros- 

 trate, creeping filament (usually in shells) that has been identified 

 with the algal species Conchocelis rosea. In the case of P, tenera of 

 Japan, penetration of shells takes place within three days. This 

 dwarf phase bears sporangia that produce monospores,^ and these 

 on germination are thought to give rise to a new adult plant, though 

 some workers consider that they only redupUcate the Conchocelis 

 phase. New adult plants of P. umhilicalis and P. perforata are said 

 to arise from spores {conchospores) liberated from short swollen 

 branches (fertile cell rows) or to arise as vegetative buds. At present 

 there is no evidence that this dwarf phase is diploid. Production of 

 the phase is apparently not universal because in New Zealand 

 plants from the north produce the Conchocelis phase but similar 

 plants from the south do not. It is clear that further work on the 

 Ufe history of species of Porphyra may well produce interesting 

 results. Japanese workers consistently report monospores from the 

 Conchocelis phase of P. tenera^ whereas in the case of P. umhilicalis 

 only conchospores and buds are reported. In the American 

 Smithora naiadum the carpospores give rise to a prostrate cushion 



1 These only mature under short day conditions, the spores being liberated 

 from late September to mid December. 



226 



