SOILS AND MANURES. 355 



The turnips will flourish in the pea-field, because there is 

 plenty of potash there; and the pease will flourish in 

 the turnip-field, because the turnips have not used up the 

 lime. 



495. Manures. You have seen in 486 what analogy 

 there is between the stomach of the animal and the root 

 of the plant. Let us follow out this analogy a little far- 

 ther. If we give an abundance of proper food to the ani- 

 mal it grows well, but with scanty and improper food it 

 becomes lean and languishing. So it is with the plant. 

 If its root be supplied in the soil with a proper amount of 

 those substances which are fitted for its nutrition, it grows 

 vigorously, and its leaves, flowers, and fruit are abundant. 

 The object of manures is to supply to the soil whatever of 

 these substances are deficient. In doing this we must have 

 regard to the kinds of food which different kinds of plants 

 need. There are certain substances the presence of which 

 in the soil is required by all plants in order to secure vig- 

 orous growth. But then in regard to many substances the 

 wants of plants are very different. A potash-plant, for ex- 

 ample, must have a soil that has considerable potash in it ; 

 while a lime-plant must have one that contains considera- 

 ble lime. If lime or potash be deficient where it is wanted, 

 it must be supplied in the form of manure. And the same 

 can be said of other substances. 



The term manure is applied to any substance which acts 

 as a fertilizer. Sometimes such substances act indirectly 

 by producing some mechanical effect upon the soil, or by 

 modifying the action of other substances, instead of afford- 

 ing a direct supply of nutriment, as is generally done by 

 manures. 



496. Chemical Knowledge Requisite. In order to apply 

 manures appropriately we must know something of the 

 chemical characters of the soils, of the plants, and of the 



