﻿EvANsj The 



Plagiochasma 



vated material (Fig. i, A, L) the cells tend to be large, the 

 trigones to be small, and the radial thickenings to be very incon- 

 spicuous, but similar conditions are sometimes present in plants 

 growing naturally, so that no very definite conclusions can be 

 drawn with respect to the causes of such variation. 



The older writers laid but little stress on the peculiarities of 

 the ventral scales in distinguishing the species of the Marchan- 

 tiaceae. Perhaps some of the recent writers have over-emphasized 

 the importance of these characters, but in the genus Plagiochasma 

 the scales are often very helpful in the determination of species. 

 They are, however, subject to considerable ' 

 seen especially well in the case of P. rupestre. 

 characteristic form the basal 



and this is 

 In their most 

 of the scale varies from 



