cruickshank's practical planter. 315 



of the substances proper for vegetable nutriment are 

 exhaled from the land in a gaseous state during the 

 dry season of the year. 



" But the principal way in which wood becomes 

 instrumental in enriching land still remains to be no- 

 ticed. When trees attain a certain size, they attract 

 multitudes of birds, which build their nests and seek 

 shelter among the branches. The dung of these ani- 

 mals is the very richest kind of manure which can 

 be applied to land, and possesses, at least, three 

 times the strength of that commonly used in agri- 

 culture. The quantity of it produced during the 

 long series of years which trees require to reach ma- 

 turity is, especially where large colonies of crows take 

 up their abode, very considerable, and must have a 

 powerful influence in improving and fertilizing the 

 soil. 



" I ought not to omit here to mention, among the 

 causes why ground is improved by producing wood 

 — the minuteness into which its particles are divided 

 by the roots and their fibres. On taking up a young 

 tree, or even a gooseberry bush, and shaking the 

 earth from its roots, we find the mould that falls 

 from it as completely reduced to powder, as if it had 

 been passed through a fine sieve. Now, the fact 



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