48 FERTILIZERS 



lack of nitrogen is shown by yellow trees and 

 small growth, or lack of vigor. Nitrogen will not 

 give its best effect unless phosphoric acid and potash 

 are present. 



EFFECT OF PHOSPHORIC ACID. 



70. Phosphoric acid helps a plant to assimilate 

 other plant foods. It is also essential to the final 

 maturity of the plant or its seed production, and 

 hastens this maturity, if abundant and available at 

 blossoming time. Although the navel orange con- 

 tains no seed, phosphoric acid is as essential as 

 though it did. What usually thus goes into seed is 

 needed elsewhere in the development of the fruit. 



If maturity is hastened by the presence of an 

 abundance of available phosphoric acid at the time 

 of blossom, the early ripening of the orange can be 

 likewise effected, though plant food effects are 

 directly dependent upon culture and water. 



Phosphoric acid will not give its best effect unless 

 there is some nitrogen present. Plants well supplied 

 with phosphorus, vegetate faster and are earlier. 

 If an over abundance of nitrogen is making fruit 

 rough or "puffy," phosphoric acid will help to 

 correct this. Its tendency is to make thin-skinned, 

 smooth fruit. 



EFFECT OF POTASH. 



71. Potash is necessary to the full development of 

 the wood of the tree. If potash is wanting, the 

 wood not only will not mature, but is subject to 

 frost and disease ; neither can immature wood carry 

 much fruit. Potash aids in the formation and trans- 

 fer of starch, first to the leaves and from there to 

 the flesh of the fruit, which would be imperfect other- 



