XXVI NOTES ON THE FLORA OF CLYDESDALE. 



he had done he gave abundant promise of more. As it was, his exer- 

 tions, seconded by those of one or two other fellow- workers, had served 

 to call the attention not merely of British botanists to this district, 

 but of several on the Continent of Europe as well as of America. 

 The section of Mosses has, accordingly, been much more thoroughly 

 investigated and determined than the others, and in the following 

 remarks on the peculiarities of plant distribution special reference is 

 made to this class. 



The altitudinal zones are tolerably well marked, but except on 

 Ben Lawers, and to a less extent on Ben Nevis, there can scarcely be 

 said to be a higher zone than the subalpine. On the former we have, 

 indeed, numerous plants belonging to the two highest zones, viz. 

 alpine and supra-alpine, crowded almost indiscriminately. The 

 causes at work likely to have produced such a congeries of plants on 

 one and the same mountain have often engaged the attention of 

 West of Scotland botanists. Many theories have been propounded, 

 to be as often dismissed. One or two circumstances have, however, 

 rivetted my attention, and as they still cling to me in spite of adverse 

 opinions I think it right to state them fairly and candidly. 



In the first place no cryptogamic botanist who has repeatedly 

 ascended any of the more prominent of our western mountains can 

 fail to be impressed with the remarkable fact, that there are special 

 spots on each mountain, and these generally within very restricted 

 limits, where almost all the rarer alpine plants (the word alpine being 

 used in a general sense) may be seen that are likely to be got in each 

 individual case, and that, having once alighted upon such spots, it is 

 almost useless to investigate any others. 



2d. A little experience will further enable the botanist to satisfy 

 himself that such prolific spots are very generally in the form of 

 ravines, or at least hollows, including the sides of such ravines. 



3d. That such hollows have very generally a southern, or more 

 strictly, a south-eastern exposure. 



4th. That these slope upwards in a north-western direction, and 

 terminate in a saddle-back which is almost always of a lower eleva- 

 tion than the rest of the general ridge bounding this hollow on the 

 north. Such hollows are well seen on Ben Lawers, Craig Chailleach, 

 Ben Lomond, Ben Nevis, &c. 



5th. That the parts of the mountain on the other side of this 

 saddle-back, i.e. on its northern aspect, are singularly barren of such 

 alpine rarities. 



Now taking Ben Lawers as our type, it can easily be ascertained 

 by any one even after a cursory survey that the northern shoulder 

 of the mountain, including that of Craig-na-Gour, is worthless as a 

 field of research ; indeed, I cannot recall having ever detected there 

 any moss of any consequence except Dissodon splachnoides, and as 

 this was found well up, near the head of the so-called Corrie of Craig- 

 na-Gour, which, in turn, is protected on its north-western aspect by 



