ULOTA. 



245 



U. curvifolia, a continental species, also growing on rocks, differs in the leaves 

 more twisted when dry, and more strongly papillose, the capsule shorter, and other 

 points. 



U. Hutchinsia is the only British species growing habitually on rocks ; it is 

 widely distributed in this country, but is rarely produced in abundance in the localities 

 where it occurs. The var. rufescens, in addition to its remarkable habitat, has a 

 quite distinct appearance and growth, with a marked difference in the areolation of 

 most, if not all, the leaves. My specimens appear to agree with Mrs. Britton's 

 description of specimens of this plant from fir trees in Virginia in all the essential 

 points, and I have little doubt I am right in referring them to the variety in question, 

 of which, however, I have seen no authentic specimens. How far the differences in 

 structure and habit are directly the result of the different matrix cannot be said, and it 

 is a question of opinion whether the arboreal habitat in a rupestral plant, and vice 

 versa, should be looked upon or not as in itself constituting a separative character. In 

 some genera it would obviously be valueless ; in Ulota, however, and also in 

 Orthotrichum, the habitat is a far more important feature. Macoun goes so far as to 

 say he has never seen 0. species of Ulota which grows on both rocks and trees, and is 

 indeed willing to settle the vexed question of the nomenclature of the present species 

 on that principle alone. But although it is extremely rare to find the habitat changed 

 in a species of Ulota, it is far from being so unusual as the above would indicate ; in 

 addition to the present case of U. Hutchinsia, I have found U. Bruchii and U. crispa 

 growing on rocks, while U. phyllantha is indiscriminate in its choice. 



50. ORTHOTRICHUM Hedw. 



Mosses growing on trees or rocks, comparatively short- 

 stemmed, in close rounded cushions or looser tufts. Leaves 

 appressed and imbricated when dry, rarely twisted or curled, 

 very hygroscopic, not distinctly dilated at base, upper areolation 

 hexagonal or rounded, small, basal rectangular, usually thin- 

 walled, not strongly incrassate nor vermicular. Capsule 

 immersed or emergent on a short seta, rarely exserted on a longer 

 one, elliptic or cylindrical with a tapering neck, smooth, or with 8 

 or 16 striae. Peristome mostly double, outer of 16 teeth more or 

 less bipartite and arranged in 8 pairs or singly, broadly lanceolate, 

 not trabeculate, more or less covered with fine lines or papillae ; 

 inner when present of 8 or 16 narrow processes. Calyptra 

 campanulate , sparsely hairy or naked. Vaginula smooth or hairy 

 with jointed threads, crowned with an ochrea or minute cup-like 

 sheath enclosing the seta. 



A very difficult genus to the systematist, owing in part to the 

 lack of vegetative characters to distinguish most of the species, 

 and in part undoubtedly to the great variability of some of the 

 fruiting characters, and the unquestionable tendency to form 

 connecting varieties between some of the allied species. These 

 difficulties have however been minimised by Venturi in his 

 splendid monograph of the European species in Husnot's 

 Muscologia Gallica, on which the following arrangement is based, 

 at least as regards the primary divisions. 



