70 PB ACTIO AL GUIDE TO GABDEN PLANTS 



Plants require at least twelve different kinds of food to develop 

 properly, and to bring their flovs^ers or fruits to perfection. These foods 



are : — 



Oxygen Sulphur Lime 



Carbon Phosphorus Soda 



Hydrogen Potash Magnesia 



Nitrogen Iron Chlorine 



These are present in all cultivated plants in greater or less 

 quantities, besides many other things v^hich are said to be non-essential. 

 As a rule all the foods except Nitrogen, Potash, and Phosphorus are 

 readily obtained from the air, soil, or water by the plants themselves. 

 Lime is often present in sufficient quantities, and is very important for 

 fruit or leguminous crops. Only a small trace of Iron is necessary, yet 

 without its aid the green colouring of leaves cannot be developed. The 

 air supplies Oxygen and Carbon, which are absorbed in a combined state 

 by the leaves of plants and are afterwards split up — the Carbon being 

 retained to build up the frame of the plant, while a large amount of the 

 Oxygen is liberated by the pores of the leaves (see p. 33) . 



All the mineral substances are provided by the roots, but they must 

 first of all be dissolved by water. Salt (chloride of sodium) is generally 

 found in plants which grow naturally near the sea, and where these 

 have been brought under cultivation, dressings of salt may be given to the 

 soil occasionally, as in the case of Asparagus (p. 1145) and Seakale 

 (p. 1121) &c. 



Three important plant foods 



The good growth of plants practically depends upon the presence 

 of Nitrogen, Potash, and Phosphorus in such a state that they can 

 readily enter into the plant and assist the other foods in building it 

 up. The absence of any one of these three foods cannot be made 

 good by an extra supply of the others. The gardener need not 

 often worry himself in regard to the nine other foods mentioned 

 above, with the exception of Lime ; but he should always satisfy 

 himself that his soil is not deficient to any great extent in any of these 

 three foods, the peculiarities and properties of which are referred to 

 below. 



Nitrogen. — Although so abundant in the atmosphere — being four- 

 fifths of the whole — this gas is very shy of uniting with others, or of 

 being absorbed by the leaves of plants like carbonic acid gas. There 



