IX. ALTITUDE. 461 



we travel over several hundreds of miles horizontally. In 

 another single day, by ascending Loch-na-gar or other of 

 the lofty hills in Aberdeenshire, we may further change 

 our flora, by the walk of a few miles in length, more than 

 we did by the railway run of half as many hundreds. 

 Starting from an elevated inland base, this rapid change 

 is made by an ascent of about three thousand feet in ver- 

 tical height ; during which a change of climate is expe- 

 rienced, which is more than equivalent to the climatal 

 difference between Middlesex and Aberdeenshire, at or 

 near the coast-leveh 



As before alluded to, it is currently known that the 

 changes traceable in the flora and general vegetation, 

 while ascending mountains, much resemble those changes 

 which would be obsei'ved on the plains or other low 

 grounds, by travelling the necessary distance in a polar 

 direction. Though rather close, the similarity is not by 

 any means so close and uniform as it is represented to be 

 by various botanical writers, whose ideas of science are 

 confined to reading books at home, and then re -concocting 

 their contents into other books. For instance, the upper 

 limits of plants on mountains, those both of individual 

 species and of groups, are not seldom found higher than 

 might have been anticipated from their polar extension ; 

 and occasionally they are less high. 



Further, the floral identity is often far less than it is 

 usually represented to be by the retailers of book know- 

 ledge. The highest flora of intertropical countries, at 

 levels bordering closely on the snow-line, is not at all 

 identical with the arctic flora by its species, nor yet ex- 

 clusively so by its genera, or even by its orders. So like- 

 wise, the vipper mountain and alpine floras of North Africa 

 and its adjacent islands include comparatively few boreal 

 or arctic species. These countries have their own moun- 



