THE PLANT. 31 



acid, this substance has the power of combining with 

 any of the alkalies. Its most important compound 

 is formed with lime. 



Phosphate of lime forms about 65 per cent, of the 

 dry weight of the bones of all animals, and it is all 

 derived from the soil through the medium of plants. 

 As plants are intended as food for animals, nature 

 lias provided that they shall not attain their perfec- 

 tion without taking up a supply of phosphate of 

 lime as well as of their other earthy ingredients ; 

 consequently, there are many soils which will not 

 produce good crops, simply because they are deficient 

 in phosphate of lime. It is one of the most impor- 

 tant ingredients of manures, and its value is depen- 

 dent on certain conditions which will be hereafter 

 explained. 



Another use of phosphoric acid in the plant is to 

 supply it with the small amount of phosphorus, 

 which seems to be required in the formation of the 

 seed. 



SULPHURIC ACID. 



Sulphuric acid is important to vegetation, and its 

 addition to the soil often renders it more fertile. It 

 is composed of, sulphur and oxygen, and is made for 

 manufacturing purposes, by burning sulphur. "With 

 lime it forms sulphate of Unie, which is gypsum or 

 "plaster." In this form it is often found in na- 

 ture, and is most extensively used in agriculture. 

 The methods for supplying sulphuric acid will be 

 described hereafter. It gives to the plant a small 



