﻿Evans: The genus Plagiochasma 299 



base, variable in size, the largest about 1.2 X 0.3 mm., about ten 

 cells wide, entire or sometimes with one or two short and irregular 

 teeth, oil-containing cells few and scattered; carpocephalum con- 

 cave at the apex, usually with two short-apiculate and sometimes 

 connivent lobes and maturing two sporophytes: spores yellowish 

 brown, mostly 70-80 n in diameter, minutely verruculose, regularly 

 areolate, the spherical face mostly with twelve to fifteen meshes 

 (nine to twelve marginal), plane faces each with four (or five) 

 meshes; elaters about 225 ^ long and 12 jx in maximum diameter, 

 usually with two distinct spirals, rarely with three. [Fig. 7.] 



The following specimens have been examined : 



MoRELOS: near Cuernavaca, October, 1908, Barnes & Land 

 466; same locality and date, C, G. Pringle 10669 (distributed in 

 Plant. Mex. as P. elongatum). No. 466 may be designated the 

 type. 



A remarkable specimen collected by W. G. Farlow at Orizaba, 

 state of Vera Cruz, and preserved in the Underwood Herbarium, 

 should be noted in this connection. It bears the number 17 and 

 is referred to F. crenulatum (see Underwood, Bot. Gaz. 20: 66. 

 1895). The long and slender appendages of the ventral scales, 

 however, with acuminate apices, would at once exclude it from 

 P. crenulatum and indicate an affinity with P. Landii. Possibly 

 it should be referred to this species, but the epidermal pores are 

 not quite characteristic, and it is impossible to decide from the 

 material examined whether the slight differences which the pores 

 show come within the range of variation to be expected. Appar- 

 ently No. 17 was made up of more than one species; as already 

 noted the specimen in the Farlow herbarium preserved under this 

 number is P. Wrightii. 



In P. Landii the group of species to which P. crenulatum, P. 

 jamaicense and P. Wrightii belong has another member, the rela- 

 tionship being perhaps closest to P. Wrightii. In size and texture 

 the species approaches P. crenulatum but it differs in habit on 

 account of the many apical joints or innovations which it produces. 

 Compared with P. Wrightii the thallus is a trifle larger and firmer. 



Here again the epidermal pores and the ventral scales yield 

 some of the most trustworthy differential characters. The epi- 

 dermal pores tend to be somewhat less complex than in the other 

 members of the group, each radiating series bounding the opening 



