18 



INTRODUCTOUY REMARKS. 



But we must recollect, that when trees are planted 

 in single hedge-rows, they but very imperfectly ex- 

 clude the rays of the sun, and cannot prevent eva- 

 poration — that their leaves, instead of lying where 

 they fall, are scattered in all directions — and that 

 they allure few or no birds, either to build their 

 nests or take up their nightly habitation among their 

 branches. Besides, the sterility of land near hedge- 

 rows proceeds not wholly from its exhaustion, but 

 partly from the drip and shade of the trees, partly 

 from the soil being rendered boss or hollow by the 

 roots, and partly from the latter making it impossi- 

 ble to plough so deep as would be necessary 



* 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 Jihres. 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 seems undoubted, that land is 

 much increased in fertility, by being brought to this state. 

 TuLL, the inventor of drill husbandry, ascribed so much to 

 pulverization, as to assert, that it answered of itself every pur- 

 pose of manure. This was undoubtedly carrying a favourite 

 idea to an extravagant length ; but the common practice of agri- 

 culture clearly shows, that the fruitfulness of the soil is pro- 

 moted, in no ordinary degree, by the comminution of its parts. 



