﻿Evans: The genus Plagiochasma 269 



out with age. The scales are a single cell in thickness except near 

 the base. The cell-structure is sometimes uniform throughout, 

 but the marginal cells are sometimes irregular and project as 

 indistinct teeth bearing slime papillae or their vestiges (Fig. 

 5, D). The cells containing oil-bodies, on account of their small 

 size and lack of pigmentation, form a striking feature of the 

 scales. They are sometimes confined to the basal portion and 

 sometimes occur in the appendages as well. 



With regard to the inflorescence certain species of Plagio- 

 chasma are described as dioicous and others as monoicous, while 

 some are said to be either dioicous or monoicous. Unless the 

 male and female plants grew in separate mats, a dioicous inflores- 

 cence would be difficult to demonstrate beyond doubt on account 

 of the fact that the androecia are often borne on ventral branches, 

 which easily become separated and present the appearance of 

 being distinct plants. It is therefore probable that some of the 

 so-called dioicous species are really monoicous. Stephani (37, 

 p. 777) mentions an interesting case which shows how variable 

 the inflorescence can be and how easily a hasty observation could 

 lead to error. In the thallus he described he found five joints, 

 the first, second, and fourth of which were male, the third and 

 fifth female. Each joint bore ventral branches, the male joints 

 in most cases bearing female branches and the female joints male 

 branches. Among the ventral branches he found further certain 

 ones which bore both male and female inflorescences in succession 

 and others which forked, one fork being male and the other female. 

 SchifTner (28, p. 15) has described material of P. italicum in 

 which the inflorescence was equally variable. In both these cases 

 the inflorescence might properly be described as heteroicous, and 

 this term would probably apply to most monoicous species and to 

 many which are supposed to be dioicous. 



The antheridia, as in most of the other Marchantiaceae, are 

 grouped in definite discoid inflorescences or androecia, slightly 

 raised above the dorsal surface of the thallus and apparently 

 not afTecting its subsequent growth. The androecia vary in out- 

 line from circular to more or less crescentic or cordate, with the 

 convex side turned toward the base of the thallus. These cres- 

 centic androecia, as Leitgeb notes, should not be confused with the 



