34 



THE PLANT. 



poisonous to plants. "When it exists in the soil it is 

 necessary to use such means of cultivation as shall 

 expose it to the atmosphere and allow it to take up 

 more oxygen and become the peroxide. The black 

 scales which fly from hot iron when struck by the 

 blacksmith's hammer are protoxide of iron. 



The peroxide of iron is a very good absorbent of 

 ammonia, and consequently, as will be hereafter 

 described, adds to the fertility of the soil. 



OXIDE OF MANGANESE, though often found in small 

 quantities in the ashes of cultivated plants, cannot 

 be considered indispensable. 



Having now examined the materials from which 

 the ashes of plants are formed, we are enabled to 

 classify them in a simple manner, so that they may 

 be recollected. They are as follows : 



ALKALIES. 



Potash. 

 Soda. 

 Lime. 

 Magnesia. 



ACIDS. 



Sulphuric acid. 

 Phosphoric " 

 Silicic " 



NEUTRALS. 



Chlorine. 

 Oxide of Iron. 

 " Manganese. 



CHAPTER V. 



GROWTH. 



HAVING examined the materials of which plants are 

 made, it becomes necessary to discover how they are 



