90 PRINCIPLES OF GARDENING. [CH. II. 



' Magne^a . ... lu all com and many other plants. | 



Phosphate of lime Potatoes, onions, &c. &c. 



Oxide of iron . . In most plants . 



Alumina . . . ] ^ 



^„. rin most plants. 



Silica .... J 



! Stable manure, and for the same reason every 



other manure composed of animal or vegetable I 

 remains, is evidently valuable to plants, by affording 

 them such matters as they are composed of. But 

 this is not the only reason that manures are beneficial : 

 for in that case mere decayed parts of theii" o\\7i 

 species should be the most fertilizing applications. 

 There is no doubt that plants are essentially benefited 

 by such applications ; but why do potatoes, for ex- 

 ample, grow more luxuriantly on ground manured 

 by sprats, than on ground manured vdx\i the dung 

 of horses, and still more superior to the same crop 

 grown on a plot manured with the decayed parts 

 of its own species ? Apparently, but only partly, 

 because the manures mentioned decompose ^\'ith a 

 rapidity exactly proportioned to the order of benefit. 

 Sprats decompose, and their parts become soluble 

 and capable of introsusception, first and most ra- 

 pidly ; then the dimg of animals ; lastly, the vege- 

 table remains. All the less solid animal matters 

 decompose with greater rapidity than vegetable mat- 

 ters: hence the dung of such animals as are car- 



