58 THE EVOLUTION OF CONTINUITY 



independent cell-units. It is to these that we must turn, 

 and doing so we recognise that any asexual cell of the filament 

 is a potential gametophyte, through its product. But the 

 cell which divides to produce a gametangium may be regarded 

 as the true gametophyte, and all preceding cell-stages of the 

 cycle as sporophytes in that they divide into or produce 

 " asexual " cells. The production of two cells by a simple 

 act of division may, in fact, be regarded as elementary 

 parthenogenesis, the commonly accepted and limited applica- 

 tion of the term dealing only with the phenomenon when 

 exhibited by a continuously multicellular organism, and 

 not by a single cell. And in the fact that asexual cells must 

 appear as stages on the road to the production of sexual 

 cells or gametes we have the key to " alternation of genera- 

 tions." It is not really an alternation of generations, but 

 of intermediate or " asexual " cycle-stages with terminal or 

 " sexual " forms. 



