DISPERSION OF PLANTS. 
[From a Correspondent]. 
From a memoir read to the Botanical Society of London on Thursday, the 
17th of November, on Local Botany, it appears that two-thirds of the British spe¬ 
cies grow within about twenty-five miles of the metropolis; also that five-sixths 
of the British genera and nine-tenths of the British natural orders are found 
within these bounds; that the greater part of the British plants are to he found 
in the continental floras of Europe ; that upwards of 300 grow in the United 
States of America; that the flora of a part of Hindostan, by Wight and Arnott, 
containing about 2800 species, comprises not more than 30 British species ; and 
among the 6000 plants of tropical America there is not one dicotyledonous species, 
and only a very few monocotyledonous species. It appears that the genera com¬ 
mon to this country and the Indian flora above cited are 120, being four times 
the amount of common species ; and that the genera common to England and the 
equinoctial flora of America are 270. The author farther states that one-half 
the British species, and above two-thirds of the British genera, grow in any parish 
of moderate extent; also that he collected, classified, and described 670 vascular 
species growing on Hampstead Heath and in the woods and fields adjoining; that 
latterly he has gathered about 900 species of the same kind (vascular) within 
twelve miles of Croydon, and has reason to believe that many more exist in that 
district. 
Dr. Murray, an acute observer and excellent botanist, author of a valuable 
work on the wild plants of the north and east of Scotland, entitled The Northern 
Flora , some years ago published in Jameson’s Philosophical Journal , a paper, 
in which he states that “ a great proportion of Scottish plants are found in the 
Valley of Alford;” and, again, that “ the mass of Scottish species grow in the 
environs of Paris.” It farther appears that the extent of Great Britain, from the 
Channel Islands to the extremity of the Mainland in Shetland, is equal to the 
extent of that part of continental Europe from the Gulf of Venice to the 
north end of the Peninsula of Jutland; but the number of species in these parts 
of Europe is more than double the number found in Great Britain and Ireland, 
although the average temperature of this country is about equal to that of Mid 
Europe ; and, with the exception of Switzerland and part of Hungary, the range 
of elevation is greater : from which it would seem that the comparative deficiency 
of species here is, in some degree at least, to be attributed to our insular 
situation. 
