﻿Evans: The genus PlagiochaSxMA 275 



very rudimentary lid was apparently considered by Leitgeb a 

 sufficient reason for placing Plagiochasma among his Operculatae. 

 Solms-Laubach (29, p. 12) has shown, however, that in Leitgeb's 

 group Astroporae an equally definite lid is developed but that it is 

 easily overlooked on account of the thickenings in the cells of the 

 capsule wall. In spite of this fact the lack of annular thickenings 

 in the capsule wall and the structure of the photosynthetic layer 

 of the thallus would seem sufficient to exclude Plagiochasma from 

 the Astroporae and to place it in the same group as Reboulia, 

 Grimaldia, and Neesiella, whatever this group may be called. 



Stephani (37, p. 776) describes the spores as large, yellowish, 

 tetrahedral, and loosely reticulate on the convex face with high 

 and rough lamellae. The tetrahedral form is of course due to the 

 original arrangement of the spores in the tetrad resulting from the 

 division of the spore mother cell. One face of each spore, the 

 spherical or convex face, represents a fourth of the original surface 

 of the tetrad (see Figs. 4, F; 5, H; 7, H; 8,G). The other three 

 faces, the plane faces, represent the regions of contact with the 

 three other spores of the tetrad (see Figs. 4, G; 8, H). Through- 

 out the genus a broad border is formed where the three plane faces 

 meet the spherical face, and three narrow ridges are developed 

 along the edges of the pyramid formed by the three plane faces. 

 In order to gain a clear idea of the reticulum described by Stephani 

 it is advisable to pass in review a large series of spores and to select 

 for study those which show the spherical face plainly and those in 

 which the apex of the pyramid is turned toward the eye of the 

 spectator. If this is done the meshes of the reticulum will be ob- 

 served in their most diagrammatic position, and it will be seen 

 that the reticulum extends over both spherical and plane faces. 

 A regular reticulum has been observed by the writer in all the 

 the species examined. Sometimes, however, in some or all of the 

 spores in a capsule, the reticulum will be incomplete owing to the 

 partial development of the bounding ridges. Since this condition 

 occurs in species where a normal reticulum is usually developed 

 it can not be used as a distinguishing peculiarity. The spores of 

 Plagiochasma, in fact, in contrast to many genera of the Hepaticae, 

 yield no very helpful differential characters in separating species. 



The elaters in the majority of cases are like those found in other 



