DISPERSION OF PLANTS. 



[From a Correspondent]. 



From a memoir read to the Botanical Society of London on Thursday, the 

 17 th 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 be 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. 



