1 6 MANURES FOR FRUIT TREES 



In addition to iron, potassium plays an impor- 

 tant part in the physiology or nutrition of chloro- 

 phyll ; without potassium, the chlorophyll has less 

 vitaUty, and is incapable of forming starch. 



Plant Respiration. — Plants require small quan- 

 tities of oxygen to oxidise carbonaceous and other 

 matters, and therefore they evolve small quantities 

 of carbon dioxide. This was first proved by Ingen- 

 Houss in 1779. 



Transpiration. — By means of the leaves and 

 other parts, plants exude or transpire their excess 

 of water. The aqueous vapour escaping from the 

 stomata is formed in the intercellular spaces. 



Nitrogen Absorption. — Supplies of nitrogen are 

 absorbed in the form of nitrates, nitrites and 

 ammoniacal salts ^ by the roots of plants; and 

 Jamieson has recently discovered organs in plants 

 that absorb atmospheric nitrogen. 



Nitrogen is an important element in the growth 

 and development of trees and other plants {see 

 chapter iii). 



Supplies of nitrogen are essential for all plants,^ 



' A. B. Grifiaths, Ohemical News, vol. 64, p. 147 ; A Treatise on 

 Manures (3rd edition), pp. 399 and 438. 



2 Sir William Crookes, in his book, The Wheat Prohlem, states : 

 "that under present conditions of heedless culture, a scarcity of 

 wheat is within appreciable distance ; that wheat-growing land all 

 over the world is becoming exhausted, and that at some future 

 time— not far distant— no available wheat land will be left. But 



