MARCHANTIALES 



263 



affinity with the Marchantiaceae, though showing a similar relation of 



spore-mother-cells and elaters. Since the whole mass is uniform in origin, 



and since the similar mass in Riccia is wholly fertile, it is the natural 



conclusion that certain of the potentially fertile cells have been sterilised 



to form the elaters : or, in other words, remain as somatic cells without 



undergoing chromosome-reduction. The final function of the elaters is to 



assist mechanically in the dispersal of the mature spores ; but it is possible 



that in such a plant as Fegatella (Conocephalus] they may in some 



degree assist in the early nutrition of 



the cells which remain fertile. This 



seems almost certainly to be the case 



in Corsima, and also in those genera 



of more doubtful affinity, viz. Sphaero- 



carpus, Gcothallus, and Riella, where 



the sterile cells are not mechanically 



strengthened by spiral or annular 



thickenings of their walls : they are 



here recognised as " nutritive cells," 



and they undoubtedly aid in the supply 



of nourishment, and perhaps also in 



dispersal of the spores by swelling 



of their mucilaginous remains. The 



obvious importance of these nutritive 



cells, as well as of the elaters, is 



further evidence of the probability that 



a progressive sterilisation, or conversion 



of reproductive into somatic cells, has 



occurred. 



In the Marchantiaceae there is 

 regularly present at the distal end of 



FIG. 123. 



Cynthodium cavernarum, longitudinal section 

 ... of an almost mature sporogonium showing apical 



the CapSUle a Small maSS OI tiSSUe disc. X 200. Above, the apical disc of the same 

 . , . 1*1 sporogonium in median section. X 200. (After 



within the one-layered wall, which Lang.) 



remains sterile, and comes away at 



dehiscence as a cap, or lid. This also originates from the archesporium : 



its development has been clearly shown by Lang in Cyathodium: Fig. 123 



illustrates the apex of a sporogonium, and from comparison of the young 



state it is plain that certain cells of the archesporium are told off as 



sterile from the first. 



From these notes it appears that in the Marchantiaceae, as compared 

 with the Ricciaceae, the evidence is strong for the conclusion that the 

 sporogenous tissue is liable to be reduced at various points by diverting 

 cells, or groups of cells, from their original function as fertile cells : the 

 somatic functions which they then perform have obvious uses, and this 

 gives biological probability to the conclusion. 



