154 GRIMMIACE/E. 



varying acuteness of the leaves, and the form, size, and texture of the capsule. There 

 appears to be little or no correlation between these characters, and it is therefore 

 unsafe to found even varieties on them. Thus forms with obtuse, muticous leaves 

 occur correlated with the most widely different form of capsule and varying degrees of 

 robustness and of branching, and I do not feel able to follow Braithwaite in making a 

 species, nor indeed even a variety of the obtuse-leaved form. Moreover, it is not at 

 all uncommon to find plants with the greater number of the leaves obtuse and 

 muticous, with here and there one with a short hyaline point. 



The var. gracilescens is with equal difficulty separated from the var. alopecurum, 

 but I have taken it as embracing the slender forms with more or less dichotomous, not 

 fasciculately branched stems, the leaves closely imbricated when dry, more frequently 

 muticous and hairless, and the capsule smaller and paler. In some of its forms it 

 shows a distinct approach to R. sudeticum. It is to be found abundantly all over the 

 summit of Snowdon and several of the neighbouring mountains in large, deep tufts, 

 almost black, with tall, erect, densely crowded, almost unbranched slender stems, 

 nearly always barren. 



Some forms have the upper margins distinctly thickened, which, with the shorter, 

 almost quadrate apical areolation, distinguishes the species from R. ramulosum, and 

 also, in its muticous form, from R. fasciculare. It is more difficult to separate from 

 R. sudeticum, although in its typical form widely different ; in the var. gracilescens 

 the characteristic branching tends to disappear, the capsule becomes smaller, thinner 

 and paler, and in short a very close approach is made to R. sudeticum. 



R. heterostichum in its mode of growth is sometimes not unlike a Grimmia, such 

 as G. trichophylla or G. decipiens ; the broad base of the wide hyaline points is some- 

 times sufficient to distinguish them in the field, with the wider, less elongated leaves ; 

 in the absence of these marks, and of the typical Rhacomitrium branching, recourse 

 must be had to the microscope. 



* Rhacomitrium sudeticum B.&S. (Trichostomum sudeticum 



Funck. ; Grimmia microcarpa Lindb., Braithw. Br. M. Fl. ; 



R. microcarpon Brid. in part.) (Tab. XXIV. B.). 



Resembling slender forms of R. heterostichum var. 

 gracilescens, in wide lax patches with ascending branches, dull or 

 yellowish-green above. Leaves small, narrowly acuminate, 

 margin incrassate above, nerve distinct ; hair-point short but 

 usually distinct, narrow, denticulate. Areolation frequently a 

 little wider and less sinuose at mid-base, but not constantly so ; 

 above roundish-quadrate. Seta short, pale, flexuose or curved, 

 calyptra slightly papillose at apex. Capsule small, elliptic, pale 

 brown, thin-walled ; peristome teeth irregularly divided. 



Hab. Shaded alpine rocks. Not common. Fr. early summer. 



Although this is almost universally considered a separate species, I have little 

 hesitation in uniting it with R. heterostichum. I can find no constant difference in the 

 areolation of the two, nor in the other characters of the leaves. The slender habit 

 and the branching are no doubt striking features, but R. heterostichum var. 

 gracilescens is often every whit as slender, while it has, as noted above, every form of 

 ramification ; in the form and texture of the capsule R. heterostichum is equally 

 variable, and I have forms which, on the basis of the fruit alone, would certainly be 

 called R. sudeticum. The var. validius Jur. , moreover, of R. sudeticum, appears to 

 be in every way a transition to R. heterostichum. 



