CHAPTER III 



pant STonb 



^^THE essential conditions of plant growth arc ; 

 1|L I, plant food ; 2, vitality ; 3, moisture ; 4, heat ; 



In studying the principles of plant growth, it 

 is important to understand what plants contain, and 

 what are the sources from which they derive food. 

 Plants are chiefly derived from air and from water. 

 The greater part of a fresh or living plant is water. 

 Young grass, for example, contains about seventy-five 

 per cent of water and the more succulent vegetables 

 contain a still larger proportion. This water comes 

 from the soil : i e, it is taken into the plant through 

 the roots. All the carbonaceous matters in a plant 

 are formed from carbonic acid, which is taken into the 

 plant through the leaves. Oxygen, which next to 

 carbon is the predominant constituent of the dry matter 

 in plants, comes largely from the air, though much 

 oxygen comes to the plant in the form of water. 

 Hydrogen also is derived from water. From the soil, 

 plants take in that small proportion of inorganic mat- 

 ter, usually ranging between one and five per cent, 

 which is left as ashes when the plant is burned. 

 Although the proportion is small, the constituents of 

 the ash are as necessary for plant growth as are those 

 constituents which come from the air. It is from the 

 soil also, through their roots, that all farm crops, unless 

 it be legumes, take in the nitrogenous compounds 

 which are needed for their growth. 



Briefly, the elements of plant food obtained from 

 the air and from water are : carbon, hydrogen, oxygen.. 



