314 The Scottish Naturalist. 



shores than it is at present), the land rose so much that the bed 

 of the German Ocean became dry land, and afforded a passage 

 for the great mass of our plants and animals. Amongst the first 

 plants to occupy the dry bed of the German Ocean, would be 

 the various species that followed closest on the retreating ice- 

 sheet (viz., the arctic and arctic-alpine) ; but they, at least in 

 the southern part, would soon be crowded out by the plants that 

 followed. 



"We may have some idea of the order in which the species 

 would grow if we study the sequence in which our wild plants 

 occupy any portion of ground recently made bare,- — as, for 

 example, a moor from which the turf has been pared, a drained 

 lake, or a slope uncovered by a landslip on the hills. Perhaps 

 the latter will show us something of what may in part have 

 actually happened at the time of which I treat. Examining 

 such a place, we will notice how, in course of time, one set of 

 plants, and frequently those which are rarest in the immediate 

 vicinity, begin to dot the surface of the unoccupied ground. In 

 a year or two they are joined and jostled, as it were, by others 

 before whom they gradually disappear, and then, perhaps, the 

 second set are joined by others before which some of them, too, 

 vanish. So it is easy to imagine how the arctic and arctic- 

 alpine plants, which seem less fitted than others to live in a 

 crowd, would first occupy the German Ocean plain, gradually 

 cross it and invade Britain, spread over, perhaps, a great part of 

 the country, be pursued and crowded by other plants, and be 

 finally driven up the mountains, where the conditions of life 

 would place them more on an equality with their pursuers (not 

 all of which could live on the mountains), and where they could 

 hold their own." 



Thus it is apparent how powerful an agency climate has been 

 in the distribution and dispersion of our alpine flora. The arctic- 

 alpine flora would be the first to enter our country, likely at 

 several points on the east coast, would gradually spread over the 

 low grounds so long as the snow and ice were on the hills, and 

 would finally ascend the hills when a change of climate from 

 arctic to temperate supervened. For then the temperate or 

 Germanic flora, entering the country with its hosts, would con- 

 test the occupancy of the lowlands with its first immigrants, 

 the arctic-alpines, and as the two could not coexist there, a 

 struggle would commence which, after many fluctuations, would 

 finally result in the latter being driven up the hill before their 



