248 THE RUBBER TREE BOOK 



that at least one would be right, so, in the matter of manuring, 

 a frequent principle upon which the manures are supplied seems 

 to be to put in something of everything and it will surely do. 



Of the substances which may prove deficient and therefore 

 need to be supplemented by manures or treated to be made 

 " available " there are three and three only, except in exceed- 

 ingly rare and extraordinary cases, which require attention. 

 These are nitrogen, phosphorus and potassium, the two latter 

 being generally referred to under the name of their oxides as 

 phosphoric acid and potash. It is true that lime (calcium) 

 is sometimes, nay, frequently, deficient, but in the true sense 

 lime is not so much a manure as an agent which assists in making 

 " available " the stores of the above elements locked up in the 

 soil in a more or less insoluble form. The lime has also the use 

 of keeping down soil acidity and so encourages the beneficial 

 bacteria and gives the roots healthy conditions. 



There are thus three special classes into which manures 

 are generally divided: manures to supply nitrogen, to supply 

 phosphoric acid and to supply potash. In addition, there are 

 the manures which are a general admixture of the foregoing. 

 Now it may be stated that an atom of nitrogen is one of the most 

 active and powerful things in existence. There is a restlessness 

 about an atom of nitrogen which makes it ready to fly off on the 

 slightest pretext from the body with which it was united and 

 to combine with another. The carbon constituents of a tree 

 are the mere framework or skeleton, but the moving, working, 

 vital thing in the protoplasm of the cells which brings about 

 the continuous adjustments necessary to the existence of life 

 is nitrogen. . 



Nearly four-fifths of the atmosphere is composed of nitrogen 

 gas, and every square yard of the globe's surface has pressing 

 upon it nearly seven tons of nitrogen. This is what is called 

 41 free " nitrogen. It is known that flashes of lightning will 

 cause the nitrogen and oxygen of the atmosphere to combine 

 in its path to form nitric oxide and other oxides of nitrogen 

 that are swept down into the soil by rain. The bacteria in the 

 nodules of leguminous plants also are able to fix " free " nitrogen. 

 The quantities, however, extracted in such ways and added to 

 the general stock of " fixed " nitrogen are but small. Were it 

 not for the constant " fixation " of immense quantities of free 



