CHAPTER II 



GROWTH OF THE PLANT 



As soon as the plumule rises above the surface of the 

 soil it turns green, leaves rapidly form, and the young plant 

 begins to live independently of the food laid up for it in the 

 seed by the parent plant. It now obtains all the material 

 it needs for the manufacture of new tissue from the air 

 through the leaves, and from the soil through the roots. 



I. PLANT FOOD 



12. Definition. — Plant food is material which enables a 

 plant to build new tissue and may still further be defined as 

 substances supplying an element or elements by means of 

 which a plant can carry on its normal functions of growth 

 and reproduction. Some elements thus supplied become a 

 constituent part of the cells. Other elements merely help 

 in this formation of cellular substance. Plant foods may 

 exist in forms readily taken up by the plant, in which case 

 they are called available foods, or in forms not easily taken 

 up by plants, in which case they are called unavailable foods. 

 The latter must go through certain changes before they 

 become available. To be available a plant food must be in 

 a water soluble form. 1 



13. Essential Elements. — For its normal development 

 every crop plant must be supplied with food containing 

 the following ten chemical elements: Carbon, hydrogen, 

 oxygen, phosphorus, potassium, nitrogen, sulphur, calcium, 

 iron, and magnesium. Most, plants contain in addition 

 silicon, sodium, and chlorine. These latter elements have 



1 To the botanist true plant food is material elaborated by the plant and 

 then used in building cellular tissue. It is not material supplied from the 

 outside. These substances might be called plant food materials. But to the 

 agriculturist the definition in the text is the most rational and satisfactory. 



