330 V. SUMMARY OF DISTRIBUTION. 



blanks, that greater differences are traceable between the floras of these 

 latitudinal divisions, than was the case with those for longitude ; also, 

 that the blanks are least numerous in South Britain, most numerous iu 

 North Britain. The general flora, or total number of species, is thus 

 shown to decrease in a northerly direction. Some small amount of this 

 apparent decrease may be attributable to a less complete knowledge of 

 the flora of North Britain ; some of it also to the rejection of several 

 species from that flora, which are admitted as being truly wild iu South 

 Britain, and are regarded as having been introduced thence into North 

 Biitain. But the decrease of numbers is mostly real; arising from the 

 fact that many English species either do not extend into Scotland, or 

 else occur there only in its most southerly provinces, the Lowlands, 

 which constitute part of Middle Britain. The plants marked only by 

 the single letter with two blanks preceding it '- - n' are chiefly those 

 of the higher mountains, which fail to reappear on the hills of England 

 and Wales. There are, however, some few plants so marked which are 

 not mountain species ; for example, the Primula scotica, Goodyera repens, 

 and others hitherto recorded only from pLices of slight elevation. To- 

 gether, these boieal and alpine species are not sufficiently numerous to 

 counterbalance the absence of many southerly species; and thus the 

 move northern flora is reduced in its total number of species. 



3. Allitvde. — In the third column a ternary division of the surface is 

 made which has not before been adverted to. The letters ' c a u ' sig- 

 nify three stages of elevation, ' coast-level, ascending, upper.' These 

 <livisions may be explained thus : — 



c. Below 200 yards of altitude. 



a. Between 200 and 700 yards. 



u. Above 700 yards of altitude. 

 While nearly all the species descend below 200 yards in some part of 

 Britain, it is apparent from the list that a very large portion of them fail 

 to reach the upper stage, that above 700 yards. Not unlikely, some of 

 the plants may eventually be ascertained to ascend into a higher stage 

 than is noted in the table ; more especially several of those distinguished 

 by the single letter ' s - - ' in the list. The heights have been examined 

 chiefly in the provinces of Humber, Lakes, East and West Lowlands ; 

 with some few additional observations made in North Wales and North 

 Highlands. It is quite likely that various species of the lower stage 

 only, as they yet appear to be by the list, may truly ascend above 200 

 yards in some of the six most southerly provinces, if not so high in 



