14 The Scottish Flora. 



entirely subject to and overshadowed by them. The origin of 

 all these forms can be detected by a close examination of the 

 drvas flora or vaccinium summit flora which occurs on the hilltops. 

 This consists of a thin moss carpet, with scattered plants of 

 vaccinium or grass or sedges. If the moss gets ahead and grows 

 rapidly a wholly wet sphagnum moss will form. If the sedges, 

 which live under half-wet, half-dry conditions, can keep up with 

 the moss growth, a cottongrass moor develops. But if the 

 vaccinium and other plants can keep well ahead of the mosses 

 through insufficient moisture, however caused, then a heather 

 moor results. On the other hand, grass heath will form if no peat 

 to speak of is produced. This happens on very steep slopes if 

 the soil is at all genial or friable, and also on limestone rock, 

 where the water is easily conducted away. If you drain a cotton- 

 grass swamp, it becomes a heather moor; if you burn off the 

 heather, a grass heath will take its place. So it is not difficult 

 to see why the grass heath, heather moor, cottongrass bog, and 

 sphagnum moss have covered the soil. 



But how about the birches and Scotch firs ? Anyone who 

 has visited Lochar Moss or Kirkconnel Moss will bear me out in 

 the fact that both birches and Scots pine will natural!}' grow and 

 spread by self-sown seedlings over the drier — that is heather moor 

 — parts of these mosses. They do not spread over the upland 

 moors and grass heaths because these are regularly burned, and 

 also because sheep will at once eat up any young trees. Birch 

 is one of the shrubs which grows abundantly in the steep-sided 

 linns and corries which occur abundantly in the Moffat district, 

 and reaches at lea.st 2200 feet in that district. Moreover, we are 

 now in a position to say, owing to the splendid work of Clement 

 Reid and Dr Lewis, that a birch forest and again a Scotch pine 

 forest did once flourish even on those desolate, whaup-haunted 

 moorlands of Dumfriesshire and Galloway, where to-day not a 

 shrub higher than three feet is able to exist. Dr Lewis has 

 investigated our own Galloway mosses, and as his researches are 

 already classical, we ought to be familiar with them. 



The first interesting and remarkable fact which is clearly 

 brought out by his researches is that our Merrick (Kells) moss 

 was once a forest of well-grown Scotch pine, with trunks eighteen 

 inches and two feet in diameter. A similar forest occurs everv- 



