268 On the Planthig of Forest-Trees. 



such trees require for their nourishment, amon2:st which potash 

 is the most influentiah This is strikingly etinced by the re- 

 markable circumstance, that when forests of pines in North 

 America are destroyed by fire, oaks and other deciduous plants 

 spontaneously succeed them, owing to the presence of potash, 

 which had been accumulating for ages by the growth of the pines, 

 and is thus abundantly furnished by their ashes to the plants 

 which require it. Whatever alkaline or earthy substances are 

 constantly found in the ashes of particular trees, these are neces- 

 sary to their existence^, and the presence of them in the soil must 

 have a principal share in effecting the distribution of such trees ; 

 they grow very slowly where such substances are insufficient, and 

 refuse to grow at all where they are entirely absent.* To such 

 minute, and generally unnoticed, causes, are to be attributed the 

 predominance of particular trees in certain localities, and that 

 beautiful and ever varyin": changfe of tint and foliasfe which 

 diversifies the aspect of forests, and constitutes the principal attrac- 

 tion in the enchanting scenery of nature. 



In this country, which is singularly favoured in regard to soils, 

 we have every variety which geology presents, from the most 

 recent to the oldest formations, and have therefore a greater range 

 of natural adaptation than can, perhaps, be found in any other 

 part of the world of equal dimensions ; and to this cause, united 

 with the mildness and humidity of the climate, is owing the 

 lively verdure and attractive variety for which British scenery is so 

 remarkable. With these advantages, there are few forest-trees of 

 the temperate zones which might not be naturalized in this 

 country, and many of the most valuable, which were unknown to 

 our ancestors, have long since been extensively cultivated, while 

 there is little doubt that some valuable additions may yet be made 

 from the western continent. 



I now proceed to enumerate the principal and most valuable 

 trees which constitute the British Sylva, with a brief character of 

 each, and with some notice of its geological or natural distribu- 

 tion, as a guide to the selection of those soils and sites to which 

 it is best adapted. In doing this I shall omit many species that 

 are not commonly planted, the insertion of which would be in- 

 compatible with the limited nature, and useless to the principal 

 object, of this paper. 



The common oak (Quercus robur pcdunculata) is, from its size, 

 and the strength and durability of its timber, the most valuable 

 tree of the British forests. It flowers in April and May, and 

 bears its fruit upon long foot-stalks, a peculiarity which dis- 



* See Liebig's 'Chemistry of Agriculture and Physiology,' a book which 

 should be in the possession of every landed proprietor and every intelligent 

 agriculturist. 



