THE FILAMENTOUS INDIVIDUAL 57 



with no caps at all. Naturally, it would be a capped cell 

 which would usually produce a gamete. It would, however, 

 be possibe for an uncapped cell to produce a gamete if the 

 cell immediately followed a capped gamete-producer. Fig. 9 

 very diagrammatically illustrates our suggestions. 



The Spirogyra filament is commonly held to represent 

 the gametophyte. " There is no sporophyte and therefore 

 no alternation of generations. The zygospore, instead of 



Fig. 9. — The formation of cell-caps in the light of proximal 

 arrest. The process here is the same as in Fig. 7, with this 

 difference, that when A becomes B, B, distal B will have one 

 cap and proximal b none. Distal b becoming c, c, distal c 

 will then have two caps and proximal c none ; distal c 

 becoming D, d, distal d will have three caps and proximal T> 

 none. In this way the process will go on till the series ends 

 with distal a possessing five caps, and in this cell is produced 

 the gamete, b, when released from arrest, will give rise to 

 an intercalated series, c, s, e, p, o, the last being the game- 

 tangium with four caps. 



giving rise to a purely asexual plant, produces a new 

 gametophyte." (Lowson.) 



But Spirogyra is surely not a " plant " in the strict 

 sense of the term ; its continuity is more apparent than real ; 

 it is a " cell-colony." Its cells are virtually independent 

 although attached in series, and each lives as an Individual 

 although only part of one, and does so in spite of temporary 

 arrest. The filament as a whole cannot therefore be compared 

 to the gametophyte of the proper plant where there is true 

 cell-continuity, for it is nothing more than a series of virtually 



