112 DISTRIBUTION OF BRITISH FLANTS 



Although liable to some local exceptions, it will be 

 readily recognised that there is a general agreement in the 

 ascending ranges of species, in regard both of elevation 

 and latitude (or latitude and longitude combined). Several 

 apparent exceptions may be explained by the rarity of the 

 particular species in the given country, or to its geo- 

 graphical extension being very limited. Thus we might 

 expect Cotoneaster vulgaris in Lapland and Scotland, 

 since it ascends so high on the Alps and Carpathians. 

 But to the N.W. of these mountains its extension must be 

 limited by other conditions than temperature ; for it fails 

 in Britain and Sweden, where the temperature far exceeds 

 what it bears in Switzerland and Hungary. In Britain, 

 indeed, it has no range properly speaking, only one station 

 being known. Again, in Britain and Switzerland, Vacci- 

 nium Myrtillus ascends so as to become one of the most 

 elevated shrubs ; but, compared with others, it ceases much 

 earlier in Lapland, nor does it extend nearly so far to the 

 N.W. as other shrubs surpassed by it on the mountains of 

 Europe. In such cases, if it may be so expressed, the 

 extension or distribution of the species terminates in the 

 given direction before its range is completed. Opposite 

 exceptions occur in the instance of Betuia nana and An- 

 dromeda polifolia, the ascending ranges of which, com- 

 paratively with other shrubs, are rapidly contracted as we 

 go southward, or in the latitudes of Britain and Switzer- 

 land. 



It might be expected that the countries nearest to Bri- 

 tain, in geographical position and climate, would exhibit 

 the closest resemblance in their floras ; and this accord- 

 ingly is found to be the case. The more distant is any 

 given country, other circumstances alike or allowed for, 

 the less exact is the resemblance in botanical productions. 

 But longitudinal distance operates less rapidly than lati- 

 tudinal ; and in more southern latitudes the addition of 

 non-British species is much greater than it is in countries 



