466 X. GENERAL REMARKS. 



mountain flora is chiefly made obvious there by the dis- 

 appearance of many of the arctic species of the Scottish 

 hills, and very little so by the appearance of others to 

 replace them ; that is, except in so far as species of the 

 plains ascend high enough to do so. Sedum anglicum, 

 for example, found equally high on the hills of Wales, as 

 several other plants which extend much farther noilh- 

 wards. 



In Britain, comparatively few plants are absolutely 

 rstricted to levels situate much above the coast line, 

 although many of them become more prevalent on the 

 mountains. The opposite of this is not true ; many spe- 

 cies being quite restricted to the low grounds ; and among 

 the ascending species there is a large reduction of num- 

 bers for each thousand feet of vertical height. This 

 reduction may be attributed chiefly to the increasing alti- 

 tude, and consequent deterioration of climate ; but it is 

 also partly attributable to the diminished space or sur- 

 face. It is difficult to analyse the joint result, and appor- 

 tion the share of influence between the two conditions. 

 But the simple fact, that difference of area wiU consider- 

 ably affect the numerical results attained by comparing 

 the floras of different altitudes, has been already shown 

 on page 351, by placing in contrast the numbers of spe- 

 cies ascertained above certain descending levels in the 

 North of England and in the Highlands of Scotland. 



Subject to any necessary correction on account of dif- 

 ferences in the extent of surface, the total floras of the 

 three successive stages adopted in the * summary of dis- 

 tribution ' exhibit these wide numerical differences in the 

 * distributive census,' page 364 : — 



Above 700 yards, .... present 262 species. 

 Between 700 and 200 yards, 687 

 Below 200 yards, 1319 



