PRELIMINARY CONSIDERATIONS. 79 



strange to say, the very opposite is the case. Pro- 

 fessor Blytt tells us (p. 19) that "Arctic and Alpine 

 species in the Christiania Botanic Gardens endure the 

 strongest summer heat without injury, while they are 

 often destroyed when not sufficiently covered during 

 winter." The English climate then, one would 

 think, ought to suit these plants, since the winters 

 are not too cold; but we find that at Kew Gardens 

 the large collection of Alpine plants have to be 

 wintered in frames under glass in order to keep 

 them in good health ; and Professor Dyer, the 

 Director of the Gardens, thinks they are mostly 

 intolerant of very low temperatures (compare also 

 pp. 161-164). 



Such being the constitution of Alpine plants, how 

 could they possibly have originated during the Glacial 

 period and wandered from the mountains into the 

 plains, across numbers of formidable barriers, often 

 exposed to icy winds, for thousands of miles? As a 

 matter of fact, Alpine plants have survived in the 

 high North and in the Alps because they are there 

 permanently protected during winter by a covering of 

 snow from very low temperatures, and they are at the 

 same time prevented from drying up. If they are 

 given sufficient moisture and a constant, mild tempera- 

 ture they seem to do very well. Such conditions are 

 afforded them in many parts of the British Islands, and 

 we find indeed the Mountain Avens (Dryas octopetala), 

 one of the most typically Arctic plants, growing wild 

 in profusion on the coast of Galway, in Ireland, at sea- 



