588 The Moss Flora of the Marlhorough Grcyicethers. 



a Sarseii Stone might be pardoned if it afforded the bryologist no 

 better sport than its proverbial rolling namesake. In very few 

 instances, indeed, can the mosses be said to flourish, and this only 

 in the case of rigidly saxicolous species. What constitutes the 

 interest of this flora is its specialized character, which corresponds 

 in a remarkable way with the isolated nature of the boulders on 

 which it occurs. Six at least of the species observed, it may be 

 confidently asserted, would not occur elsewhere in the county 

 except on these stones, and this may very likely apply to several 

 others. Grimmia decipiens, for example, occurs in Cornwall and 

 North and South Devon, but nowhere else nearer tlian West Sussex 

 on the east, and Herefordshire on the north. Grimmia leiccophoia 

 has an almost similar distribution, but is still more rare, and occurs 

 only in South, not in North Devon ; while that of G. trichoiihylla 

 and Hcdwigia ciliata is almost precisely analogous. Orthotrichvm 

 riqyestre, again, is only known, I believe, in the South of England 

 from single stations in South Devon, South Wilts (probably equally 

 on Sarsen Stones), and East Sussex. These and most of the other 

 rupestral species noted are almost exclusively silica-loving or 

 calcifuge in their distribution, the only species seen which are at 

 all calcicolous being Anomodon viticulosiis and Fnrhynchium 

 crassinervium, which are indiff'erent, and Tortula intermedia and 

 Grimmia apocarpa, of each of whicli I saw only a single small tuft. 

 The above species then must be considered somewhat as intruders 

 into the flora of the district, where they exist as it were on suffer- 

 ance; much like the Oriental in San Francisco, who is tolerated 

 because he can live under conditions where no one else can subsist, 

 and only as long as he confines himself to his own quarter. How 

 and whence they arrived it is not quite easy to say. It is extremely 

 unlikely that any one of them represents the original flora of the 

 time when the beds were exposed from which the stones themselves 

 were derived. In all probability the spores were in most cases 

 carried by westerly winds from the granite rocks of the Cornish 

 peninsula, in comparatively recent times. For the greater number 

 of the mosses observed, however, which are frequent and widely 

 distributed species, there is no need to seek such an explanation. 



