INTRODUCTION ix 



snow -clad peaks preventing any great migration of 

 southern plants northwards, or of northern plants south- 

 wards, such as has occurred, for example, in North 

 America, where there is no such chain of mountains 

 running east and west between the warmer and colder 

 parts of the Continent. But a mixture of southern and 

 of alpine floras does, nevertheless, take place to a certain 

 extent, especially in the valley of that great south-flow- 

 ing river, the Rhone. Here, as, for example, at Visp or 

 Brieg, you may find growing side by side plants which 

 have ascended the river-basin from the Mediterranean, 

 and plants which have descended the mountain-sides 

 from the Alps. 



To the student of geographical botany the absence of 

 certain plants from a given area is not less interesting 

 than the presence of others; and a comparison of the 

 floras of the British Islands and of Switzerland introduces 

 one to many very interesting facts. Of course there is 

 one large element in our flora that is absent from the 

 Swiss the maritime; with the exception of one or two 

 species, like the thrift, which are found here and there 

 on the summits of the loftiest mountains, and one or two 

 others, as the yellow horned poppy, which finds a con- 

 genial home on the sandy shores of Lake Neuchatel. 

 There are also a few Arctic species, such as Primula 

 scotica and Saxifraga nivalis, which occur in our moun- 

 tain districts, but do not get so far south as Central 

 Europe. But the chief element in our flora which would 

 be strange to a Swiss botanist is a Lusitanian one. 

 Owing to the moisture of our climate and the mildness 

 of our winters, many species characteristic of the south- 

 west of Europe extend their range much farther north on 



