830 



on three sides, without any adjacent land surface to maintain heat by 

 terrestrial radiation, or to arrest the deposition of moisture from the 

 Atlantic, much of which is precipitated, before it can reach Hamp- 

 shire, upon the peninsular counties of Cornwall and Devon. Hence 

 the amount of direct solar radiation, so active an agent in developing 

 a varied and vigorous vegetation, is oftener and more continuously 

 exerted here than in the north, proving more than equivalent in 

 energy to the power of a diffuse light protracted through days consi- 

 derably exceeding our own in length at the season in question. These 

 conditions of atmospheric dryness and unimpeded solar action, cha- 

 racterize the countries of continental Europe in a still greater degree, 

 and hold good into latitudes higher than those of any part of Britain, 

 enabling plants that are indifferent to the increased rigour of the win- 

 ters, to advance far to the northward of the parallels they can attain 

 in our insular climate, where their progress towards the poles is much 

 sooner arrested by the failure of the conditions above mentioned. To 

 these causes, more than to the very moderate increased heat of the 

 summers, must be attributed the difference we find in the amount of 

 species betwixt the floras of Edinburgh and Copenhagen ; places 

 having almost exactly the same latitude,* but enjoying, the one an 

 ultra-insular, cloudy and equable climate, the other an all but conti- 

 nental, somewhat extreme climate, the greater dryness and sunniness 

 of which gives to the Danish metropolitan flora a much more varied 

 aspect. The same comparative poverty of species, though much less 

 evident, because latitude is not concerned in producing the change, is 

 manifested in the flora of Wales and the west of England over that of 

 the eastern counties, and on crossing St. George's Channel, the total 

 absence or great rarity of plants of common or abundant occurrence 

 on the English side, is a striking feature in the flora of the sister is- 

 land. In each case the cause is the same, diminished solar influence 

 from impeded radiation and increased humidity acting as a bar to the 

 proper hardening of the vegetable fibres. We must all of us have re- 

 marked that those localities are not the richest in species where the 

 vegetation is most luxuriant ; indeed, that the most unpromising spots 

 to the eye, barren, sandy fields and wastes, often yield an ampler har- 

 vest than the merry green wood conceals beneath its leafy bowers. 



* The Edinburgh Catalogue of Plants gives a most unfaithful picture of the real 

 or indigenous, as well as the derived or naturalized flora of that district, embracing, 

 as it does, a multitude of imperfectly established and even planted species, as Staphy- 

 lea, &c. 



