CHAPTER III. 



MINERALS NECESSARY AND INJURIOUS TO PLANT LIFE HOW 



PLANTS ABSORB THEIR FOOD THE GASES AND THEIR 



VARIOUS TRANSFORMATIONS NITROGEN PHENOMENON 



OF NITRIFICATION IN THE SOIL SOURCES OF NITROGEN 



ITS MANUFACTURE ITS FIXATION ITS ASSIMILA- 

 TION THE NECESSITY FOR ITS ARTIFICIAL APPLICATION 



AS MANURE. 



The presence of a considerable number of mineral substances in 

 the soil is essential to the healthy growth of plants. But, while 

 some of these minerals, such as magnesium, manganese and fluor, 

 take no part in furthering, others are positively fatal to their de- 

 velopment. Thus one per cent, of sulphate of iron will render a 

 soil unproductive, and instances are not wanting where one per 

 cent, of chloride of sodium (common salt), in very dry regions, has 

 killed all vegetation and produced sterility. 



We may therefore consider that the principal essential substances 

 demanded by a healthy and robust plant life, are the following : 



FIRST. Oxygen, hydrogen, carbon and nitrogen, which veg- 

 etables take in and assimilate from the air, through their 

 leaves or respiratory organs . 



SECOND. Phosphorus, potassium and lime, contained in the 

 soil and absorbed by their roots. 



Commencing with the three gases oxygen, hydrogen and carbon- 

 ic acid, we find that they exist in abundance, both in the air and in the 

 soil. A combination of the two first in the form of rain, dew, 

 springs or irrigation, Burnish, with the carbonic acid, the necessary 



