NEW AND RARE MOSSES FROM THE \YEST OF SCOTLAND 173 



angle on the nerve, which is excurrent in a sharply pointed 

 acumen of the same structure as in the preceding, breadth 

 at point of attachment to leaf from .04 5 -.06 mm., and 

 length from .12-. 24 mm.; nerve pale, strong, at length 

 reddish, almost convex in front, prominent and smooth 

 behind, latit near base, 'oy-'i mm., tapering and ceasing at 

 base of acumen, margin plane, crenulate and papillose ; 

 basal hyaline cells occupying one-third of leaf, oblong or 

 oblongo-hexagonal in double layer, attached, large, .05 5 -.08 5 

 by .01 -.01 5 mm., becoming narrower towards margin, but 

 nearly as long, ceasing transversely upwardly, but not 

 infrequently a single marginal row of basal cells proceeding 

 farther up than the rest, cells immediately above the basal 

 very dark, with numerous bright points, oblong and detached, 

 .02-.03 by .006-9 mm., the upper cells appearing granular and 

 chlorophyllose at first sight, but rendered very obscure on 

 both sides by crowds of papillae, exactly as in Tortula muralis ; 

 accordingly upper part of pagina is thickened to the extent 

 of .025 mm., or nearly double the thickness near the base or 

 lower third. Such cells can only become clearly defined by 

 making thin cross sections of the leaf, when they are seen to 

 have their long diameter in an antero-posterior direction or 

 across the pagina, and are nearly hyaline, length from 

 .01 5-. 02 mm., the latter dimension in cells near the nerve. 

 Unless such a section is made the contained particles of 

 chlorophyll are apt to be mistaken for cells. The upper 

 third of the pagina of both sides is very generally incurved 

 so as to allow the margins to approach one another, while 

 the nerve and its extension remain in a straight line. On the 

 ground in several places near the sea, Onich, September 1908. 



I have given a detailed description of the minute 

 structure of the leaf, as I strongly suspect that this is a 

 Tortilla. The absence of fruit renders me uncertain. 



As an instance in an opposite direction as regards this 

 acumen, I shall describe another species under the same 

 genus where this acumen is of the same constitution as those 

 already described, but where it is always short and stump- 

 like, and tends to disappear entirely even on leaves of the 

 same stem, when the nerve is seen to cease below the round 

 summit of the leaf 



{To be continued}} 



