﻿Evans: The gexus Plagiochasma 301 



often bears vestiges of slime-papillae. The basal portion is un- 

 usually deeply pigmented, and the pale scattered cells contain- 

 ing oil-bodies stand in sharp contrast to the others. The appen- 

 dages of the scales, sometimes borne singly and sometimes in 

 pairs, are narrowly triangular or subulate in outline and gradually 

 taper to acuminate points, although the extreme apex is often 

 tipped with two cells bearing the vestiges of a slime-papilla 

 between them. There is no sharp line of demarcation between 

 the basal portion and the appendages and the latter are not 

 constricted at the base. For the most part the margins are entire 

 but occasionally an indistinct tooth is present. The appendages 

 are very different from the broad and strongly constricted append- 

 ages of P. crenulatiim and P. jamaicense. They resemble more 

 closely the narrow appendages exceptionally found in P. Wrightii. 

 The latter species, however, is sure to show appendages of the 

 usual type on some or most of the scales. 



6. Plagiochasma intermedium Lindenb. & Gottsche 

 Plagiochasma intermedium Lindenb. & Gottsche; G. L. & N. Syn. 



Hep. 513. 1846. 

 Rupinia intermedia Trevis. Mem. R. 1st. Lomb. III. 4: 437. 



1877. 

 Aytonia intermedia Underw. Bot. Gaz. 20: 66. 1895. 



Thallus pale green above but not glaucous, with a narrow 

 purple border, plane or broadly canaliculate, strap-shaped, 

 occasionally forking but more usually innovating at the apex, 

 sometimes with ventral adventive branches, margins undulate- 

 crenate, i cm. or more long, mostly 3-5 mm. wide, thickness of 

 thallus about one seventh the width ; epidermis composed of thin- 

 walled cells with small but usually distinct trigones and a thin, 

 smooth cuticle, the cells averaging about 25 n in diameter; pores 

 distinctly elevated, large, surrounded by about eight (six to ten) 

 radiating series of cells, with two to four cells in each series, radial 

 walls strongly thickened; aeriferous layer about two thirds the 

 thickness of the thallus, of a loose structure, the air spaces often 

 three or four times as wide as the green cells; ventral scales 

 lunulate, purple, sinuous to crenulate along the margin, some of 

 the marginal cells often contorted, cells containing oil-bodies few 

 and scattered, the scales gradually contracted into two appendages, 

 less often into only one, the appendages slightly or not at all 

 constricted at the base, lanceolate to ovate, entire, usually acute 



