THE AGENTS WHICH AFrECT PLANTS. 



17 



hand. A great deal of Vv'heeiing or carting is thus saved. 

 Secondly, they frequently have the ammonia which they 

 contain so fixed by acids as to occasion a prodigious saving 

 of this most effective element, and to avoid altogether 

 the disagreeable and noxious odours common to the 

 older manures. Thkdly, they are sometimes made to 

 contain or combine the element or elements on which 

 particular crops almost entirely feed ; the researches of 

 chemistry having laid bare, to some extent, the consti- 

 tuents of many plants, and their consequent requirements. 

 These are all properties of the highest interest and the 

 greatest value. 



But there remains another view of the case, which it 

 will not be wise to neglect. Artificial manures seldom 

 act mechanically on the soil. They do not improve its 

 texture. Nor does their influence often last long. It is 

 trtinsient, and extends but to one or two crops. They 

 cause, moreover, little or no additions to the soil. The 

 available parts for cultivation do not acquire any extra 

 substance or depth by their use. They are likewise too 

 stimulating for some cro^^s, especially permanent ones, 

 and occasion extravagant growth, without corresponding- 

 fertility. On all these points, therefore, the commoner 

 manures must be deemed yet in advance of those more 

 recently devised. 



On the whole, it will be well to adopt such new manures 

 as have been ascertained to be good, (though there are 

 numbers that are perfectly worthless,) as a general rule, 

 for temporary crops ; with the occasional use of the 

 more solid kinds, and the selection of these last alone for 

 fruit trees and more lasting crops. 



From the excrements of various animals, mixed with 

 partially decayed vegetable matter, such as straw, the best 

 possible manure may be obtained. Sheep dung and that 

 from_ birds are among the most powerful, and may be 

 applied simply, without any admixture. Horse, cow, and 

 other manure will be improved by mixing them with 

 vegetable substances, and fermenting and turning them 

 several times before using. The addition of a little lime 

 will render them more thoroughly and more immediately 

 efficacious. They should be covered up with earth while 



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