﻿Evans: The genus Plagiochasma 305 



The spores reproduced (Fig. 8, G, H) were drawn from the 

 specimens collected at Etzatlan, 261, and show very few ridges 

 except those along the edges of the tetrahedron. These ridges 

 do not form a reticulum. On the spherical face a continuous wavy- 

 ridge is present about half way between the periphery and the 

 center, and from one to three additional ridges extend partly or 

 wholly across the enclosed space. On each plane face a single 

 ridge extends across about half way between the base and apex 

 of the triangles. Unfortunately these spore characters, which at 

 first sight appear so striking, are subject to variation. In the 

 spores of the Guadalajara material, 136, a regular reticulum is 

 present in most cases, and the two extreme types of spore-structure 

 are connected by a series of intergradations. The Japanese 

 specimens of P. japonicum show spores with a diameter of about 

 70 n and a well-developed reticulum. In Massalongo's figures, 

 drawn from his variety chinense, the reticulum is clearly shown 

 but the number of meshes represented is greater than in the 

 Japanese material. In the Synopsis Hepaticarum a specimen 

 from Nepal is doubtfully included under F. appendiculatum as 

 " ? /3 depauperata." Gottsche states that this plant is close to 

 P. intermedium and implies that the elaters are of the solid type, 

 while Massalongo cites it as a possible synonym of P. japonicum 

 ^ chinense. Unfortunately the lack of specimens has made the 

 study of this form impossible to the writer. It should be re- 

 membered, however, that Kashyap occasionally finds solid elaters 

 in P. appendiculatum, so that their presence in this doubtful form 

 would not necessarily exclude it from that species. The Synopsis 

 tells us nothing about the epidermis or ventral scales, and Stephani 

 does not mention the plant at all. 



The present paper is based on the study of a large series of 

 specimens, including type material of the following previously 

 published species: P. appendiculatum, P. australe, P. cordatum, 

 P. crenulatum, P. elongatum, Aytonia Evansii, P. eximium, P. 

 jamaicense, P. lanigerum, P. limbattim, Reboulia maderensis, and 

 P. mexicanum. For the privilege of studying this rich material 

 the writer is largely indebted to Dr. M. A. Howe, of the New York 

 Botanical Garden, Dr. W. G. Farlow, of Harvard University, 



