222 TORTULACEjE. 



Very variable in height, length of leaves, etc., the smaller forms, and notably the 

 var. fragilifolium, closely approaching Tr. nitidum, but differing in the more slenderly 

 pointed leaves, usually more laxly incurved when dry, and of softer texture. I have 

 however gathered a plant on Snowdon with exactly the dark small dense rigid 

 cushions of Tr. nitidum, but in this case with the nerve hardly at all glossy at back. 

 It is probable that the above variety and var. rigida Boulay are not more than dwarf 

 and somewhat starved forms induced by their habitat, which is usually on exposed 

 mountain rocks. The leaves in this species are always more or less fragile, but they 

 are of a much softer, less rigid texture than in Tr. fragile, and it may be noted that 

 in our present plant it is usually the lamina that is torn, often leaving the nerve 

 denuded (though the apex of the leaf, especially in var. fragilifolium, is often broken 

 off), while in Tr. fragile the nerve itself is extremely brittle, and the rigid leaves are 

 usually found snapped in half at or above the middle. 



The robust stems, and longly linear or even subulate leaves, spreading and 

 flexuose when moist, with very tapering points will generally serve to distinguish this 

 species from all the foregoing ones ; Tr. hibemicum being known by its more slender 

 stems with laxer leaves expanded at the base. 



The fruit is rare, and sparingly produced, ripening in summer ; but unless 

 gathered just at maturity it is very difficult to get good specimens showing the 

 peristome. 



I have seen no specimens of the var. (3, the description of which I have taken 

 from Braithw. Br. M. Fl. 



9. Trichostomum fragile Dixon (Didymodon fragilis 



Drumm. ; Barbula fragilis B. & S., Schp. Syn. ; Mollia fragilis 



Lindb., Braithw. Br. M. Fl.) (Tab. XXXII. D.). 



In shorter dense tufts, bright or yellow green, resembling 

 small plants of Tr. tortuosum. Leaves erecto-patent, straight or 

 very slightly flexuose, scarcely undulate ; when dry the mature 

 leaves are usually slightly arcuate, rigidly spirally twisted, or 

 rarely more strongly curled, but almost always more firm and less 

 crisped than in the last, very glossy and shining at the back ; 

 either gradually tapering as in that species or more usually with 

 the apex prolonged into a capillaceous trigonous subula, composed 

 chiefly of the nerve and nearly smooth or strongly papillose, very 

 fragile and broken off in all but the young leaves. Nerve broad, 

 whitish. Areolation as in the last, but usually rather more 

 obscure. Capsule and peristome almost or exactly as in that 

 species. 



Hab. Mountain rocks and sand-hills. Very rare, and sterile. 



In its typical form this plant is at once known from the other species of the genus 

 by its rigid, brittle leaves only slightly twisted and indeed sometimes almost straight 

 and erect when dry, very narrow above and brilliantly shining at the back ; when 

 moist the straighter more rigid leaves distinguish it from Tr. tortuosum, and the 

 elongate, subulate points from all other species. I have however received specimens 

 from two or three localities in Labrador showing a distinct approach to Tr. 

 tortuosum ; the leaves on some of the plants, and even the lower leaves on some 

 stems in which the upper ones are quite typical, being strongly contorted when dry, 

 crisped and undulate at the margin, and when moist slightly flexuose and undulate ; 

 hardly indeed to be recognised from the var. fragilifolium of Tr, tortuosum except by 

 the leaves somewhat firmer, the very shining nerve, and the presence (usually), of 



