Naturalization of Plants. 203 



tli at in all this group of islands, the easterly winds are more fre- 

 quent, more durable, and I think more severe. 



I must therefore leave this question of the cause of the bene- 

 ficial influence of this peculiar climate as to the plants which it 

 encourages, to future inquiry and other hands ; yet not without 

 remarking that this is not a very sunny climate, either as to light 

 or heat. I believe that in a great many matters appertaining to 

 vegetation, whether in horticulture or agriculture, the question of 

 light is often of much more importance than that of heat, how- 

 ever much it has been overlooked by agricultural as well as 

 philosophical writers. It is of most material importance as to the 

 perfection of flowers, whether in vigour, colour, or odour ; and 

 not less so, as is very well known, as to the ripening of fruits. 

 Nor does it appear to me less so as to ordinary agriculture, 

 whether as it relates to the perfection of certain herbaceous 

 plants, or the ripening of grain. I think this is peculiarly visi- 

 ble in certain parts of Scotland, where the most serious differ- 

 ences in this respect occur ; where no other circumstance of 

 difference than that of the annual quantity of light can be dis- 

 covered, and when indeed the condition as to temperature, and 

 soil both, is highly in favour of those climates where the produce 

 is worst. This is remarkably true in comparing the eastern and 

 western sides of Scotland generally, and in noting the singular 

 limitation of the region of wheat thus produced ; and, unless I 

 mistake, a difference in the vigour, and especially in the vigour 

 of flowering, in clover, not to be accounted for by differences in 

 the soil, method of cultivation, or quantity of manure. And while 

 the power of producing wheat, or what, for the present purpose, 

 is analogous in principle, the early ripening, as well as the 

 superior quality of barley, diminishes in proceeding westward on a 

 parallel of latitude, till we arrive at the cloudy region, it re- 

 appears on passing this again to the westward ; insomuch, indeed, 

 that much more northern latitudes, if the lands are insular and 

 flat, are superior in these respects to the southern ones, while 

 there are no differences as to soil, cultivation, or aught else, 

 capable of explaining the facts. It is not a difference in rain 



