! 



SIMILAR TO THOSE OF AMMONIA, & c . 223 



many instances been done by the long-continued and indis- 

 criminate use of lime. Hence also the term stimulant applied 

 to lime, as if it only, by some sort of compulsion, urged on the 

 soil or the plant to increased activity. 



In reality, the results of the action of lime resemble those of 

 many other substances which cause the materials of the soil to 

 become available to plants, or the plants to avail themselves 

 more fully of what the soil contains. 



The sulphate and muriate of ammonia, for example, acted in 

 this way in some experiments of Mr Lawes. He sowed wheat 

 during three successive years on the same piece of land, and to 

 the crops of the two last years applied only the salts of ammo- 

 nia, with the following results : 



Manure applied. Produce reaped. 



Grain. Straw. 



1844. Superphosphate of lime, 5 cwt., ) .,~ , , 



Silicate of potash, 220 lb., 16 bush ' 1112 lb ' 



1845. Sulphate and muriate of am- ) 3 



monia, each 11 cwt., . / 31 * "' 



1846. Sulphate of ammonia, . . 27 J ... 2244... 



Now, though the special action of lime is very different from 

 that of the salts of ammonia, yet an increase such as the above, 

 in 1845 and 1846, might have been the consequence of its 

 application to the land. But neither the lime nor the salts of 

 ammonia, if applie'd year by year, would alone suffice to keep 

 up these increased returns. In our crops we take out of the 

 land what neither of these applications restore, and it must, 

 therefore, inevitably be sooner or later exhausted. 



2. Natural differences of composition among limes and 

 limestones. 



Limes and limestones vary in composition often in a very 

 sensible degree. Even when the differences are comparatively 

 small, the large quantities of lime which are usually laid on 

 the land causes a very considerable difference, on the whole, in 

 the nature of the application. 



The natural differences affect chiefly the proportions of sili- 

 ceous or earthy matter, of magnesia, of sulphur, and of phos- 



