HOW PLANTS GROW. 599 



We also find phosphoric acid, sulphuric acid, and silicic acid. 



The elements chlorine, iron, manganese, and lime, are also 

 found. 



We do not find these things separate, but in combination. 

 We find phosphate of lime, oxide of iron, silicates of potash and 

 soda, carbonate of lime and potash, chloride of soda, or common 

 salt, sulphate of lime and potash, and oxide of manganese. 



Potash is one of the alkalies found in the ashes of plants. 

 This is essential to all plant growth. It must be found in some 

 soluble combination within reach of the roots of plants, if any 

 growth is expected. It exists, to some extent, in all cultivated 

 soil, but in some sandy soils, particularly those near the sea 

 coast, it is deficient. Potash compounds are most abundant in 

 clay soils near the mountains, where granite rocks are found, 

 whose decay and crumbling furnish it to the soil. Rocks con- 

 taining feldspar have a larger percentage of potash than any 

 other. The potash in wood ashes is the most valuable thing 

 they contain, for the farmers use it as a manure. We will say 

 more of this when we come to manures. 



Magnesium is another element found in compounds, in the 

 ashes of plants, and like potash seems essential to their growth. 

 Compounds of magnesium are usually found in plenty in all our 

 cultivated soils. Some kinds of limestone, called magnesian 

 limestone, are very rich in this element. 



Lime, the carbonate of calcium, is very plentiful in the ashes 

 of plants, and is one of the substances absolutely necessary to 

 plant life. Only a small part of the lime, however, that is found 

 in the ashes, has been used as food by the plant. A large part 

 of it exists in plants, just as lime is found on the sides of a 

 kettle in which water containing lime has been boiled, and gets 

 there because abundant in the soil water. Lime* is, however, 

 of great value to the farmer in other ways, which we will explain 

 further on. 



Sodium is another element found in ashes, generally in com- 

 bination with chlorine, making chloride of sodium, or common 

 salt. Its use as a manure will be treated hereafter. 



One of the most valuable ash elements is phosphorus. Phos- 

 phoric acid rapidly unites with lime, and forms phosphate of 

 lime. The bones of animals contain about 65 per cent of phos- 



