434 X. GENERAL REMARKS. 



not an end to be arrived at thereby. It is a certain 

 result of these varied conditions and inequalities of dis- 

 tribution, that on taking any part or section of the earth 

 by itself, any single kingdom or country, any belt of lati- 

 tude or longitude, the areas of the plants are unavoid- 

 ably cut asunder and separated in the most unequal 

 manner and degi-ee. Geographic arrangements and no- 

 menclature thus somewhat arbitrarily multiply and 

 increase the natural inequalities by cutting off fragments, 

 so to say, from the areas of many species, and making 

 them portions of different geographical areas. The area 

 of one species not corresponding with the area of another, 

 by geographic position or extent, each separated country 

 must include unequal portions of the whole geographic 

 areas of its plants. 



Britain appears to have been cut asunder from Europe 

 and much abraded by the encroaching ocean, which may 

 be said to have left in this island only a small portion of 

 the area of Cyperus longus, — a larger portion of the area 

 of Clematis Vitalba, — a still larger portion of the area of 

 Tamus communis, — again, a yet larger portion of the area 

 of Plantago media, — and a much larger portion, equal to 

 the whole island, of the area of Festuca ovina. The 

 restricted distribution of many species in this country, 

 and their consequent low places in the census lists, arises 

 in the manner here set forth ; although, no doubt, other 

 conditions have also to be taken into the account, over 

 and above the mere extent of local area, so cut off from 

 the rest of the geographical area for the same species. 

 Sparseness of distribution, and interruptions to continuity 

 which leave wide interspaces between special localities, 

 are among the conditions which tend to lower the census 

 of species. Even these conditions themselves are often 

 closely connected with the severance of areas, through 



