82 DISTRIBUTION IN CONNECTION 



superior to that of the Scottish highlands. Above 2000 ft. 

 the species are not only fewer, but, with all the advantage 

 of a more southern latitude, they commonly fail much 

 earlier as we ascend the hills. The average heights to 

 which the species mentioned in the preceding lists were 

 observed to attain in the Highlands are, for the first (or 

 those exceeding 3000 ft. in Cumberland), 3900 ft. ; for 

 the second, 3200 ft.; for the third, 2900 ft.; for the 

 fourth, 2400 ft. By average height is meant the mean 

 obtained by dividing the sum of the highest stations ob- 

 served in Scotland by the number of species. 



3. DISTRIBUTION IN CONNECTION WITH LINES OF 

 LATITUDE AND LONGITUDE. 



A correspondence between the extension of plants and 

 the lines of latitude or longitude, viewed as a mere coin- 

 cidence, presents nothing of interest ; but where the 

 former appears to be directly or indirectly dependent on 

 the latter, it is much otherwise. We have seen that 

 many species are found only at certain altitudes on the 

 mountains, or in certain of the regions before described. 

 Consequently, the mere fact of their existence under a 

 given latitude in Britain is chiefly dependent on the 

 extent and elevation of the mountains found there, and 

 does not arise from the latitude or longitude. Were 

 Britain a low plain throughout its whole extent, the dis- 

 tribution of plants, in correspondence with latitude and 

 longitude, would doubtless be very different from that 

 which is now seen under the diversified elevation and 

 configuration of surface. Again, could we remove Britain 

 ten degrees to the South or North, preserving the same 



