TORTULA. 177 



of Leaves very concave ; nerve gemmiferous above 20. papulosa 



\Nerve not gemmiferous 19 



/Leaf-margin strongly revolute almost to apex ; peristome teeth free. ..12. muralis 



"\Margin plane above, or slightly revolute only 20 



/Peristome teeth free ; hair points shortish 10. Vahliana 



\ Peristome partly tubular ; hair-points long 21 



{Plant very small ; seta short ; capsule elliptic ij. canescens 

 Plant robust ; seta long ; capsule cylindric 16. Icevipila 



A. PTERYGONEURON. 



1. Tortula pusilla Mitt. (Bryum pusillum Hedw. ; Pottia 

 cavifolia Ehrh., Schp. Syn.) (Tab. XXVI. K.). 



Plants very short, densely tufted, bulbiform. Leaves more 

 or less erect and imbricated, small, broadly oblong or obovate, 

 very concave, obtuse or slightly pointed, cucullate at apex, margin 

 slightly incurved ; nerve excurrent in a short mucro or a long 

 hyaline, terete, entire arista, bearing near the summit of the leaf 

 one or two oval sacs, containing chlorophyllose granules, and 

 finally splitting longitudinally so to form 2 or \ lamellae, as in 

 Catharinea, but shorter. Cells in the lower part of the leaf 

 rectangular, rather short (3-5 times as long as broad), with firm 

 walls, the upper smaller, rounded-quadrate, slightly papillose. 

 Seta red, short, 1-2 lines, capsule small, oval or elliptic, dark 

 reddish brown, glossy, somewhat plicate or rugose when empty, 

 gymnostomous ; lid obliquely rostellate, cells in straight rows. 

 Autoicous. 



Var. /3. incana Braithw. (Gymnost. ovatum var. incanum 

 Nees and Hornsch.). In dense hoary tufts. Leaves with very 

 long hair-points ; capsule on a very short seta, hardly exserted, 

 shortly oval. 



Hab. Walls and banks. Locally abundant. The var. /3 rare. Fr. winter and 

 spring. 



A very distinct plant, not to be confounded with any but the next species ; 

 indeed, were it not for its close affinity to that, it would undoubtedly be best placed, 

 as has usually been the case, under Pottia. It is very variable in the length of the 

 hair-point (which is indeed sometimes almost obsolete), and of the seta, and inter- 

 mediate forms may frequently be observed between the type and the var. incana. 



The present species forms larger or smaller low patches or tufts usually producing 

 abundant capsules, which by their deep purplish brown colour and large numbers 

 give a very characteristic tint to the plant ; in the next species the longer seta and 

 paler fruit give a much lighter hue to the patches, and the two are as a rule distinguish- 

 able from one another by this, even at some distance, when the fruit is mature. 



An allied plant, Pharomitrhtm subsessile Schp., should be looked for here; 

 it differs in the denticulate arista, the capsule immersed and almost sessile, the 

 calyptra lobed at the base. It is a frequent species in Germany. 



M 



