36 MANURES FOR FRUIT TREES 



Schloesing states tliat the nitrification of am- 

 moniacal salts is not for all plants a necessary pre- 

 liminary to the absorption of nitrogen by the plant. 



Mineral Matter. — The mineral matter present 

 in a soil is of the utmost importance to provide 

 proper nourishment of trees. The roots appear to 

 possess a selective power. Some trees are richer 

 in potash than other trees, and others again are 

 richer in phosphates. The various composition of 

 the ashes of trees proves the selective power of 

 their roots. Highly insoluble matter such as 

 silica, for instance, passes into solution under the 

 influence of the secretions and vital forces of the 

 rootlets. It is not improbable, however, in view of 

 the knowledge we already possess of independent 

 soil bacteria, that there may be a class of such 

 organisms especially active in the disintegration of 

 mineral particles, and the preparation of them for 

 plant absorption. 



It may therefore be assumed that the agencies 

 at work in the conversion of the insoluble soil 

 constituents into soluble compounds are (1) the 

 plant secretions, (2) the vital activity of the rootlet 

 itself, and (3) the decomposing influence of soil 

 bacteria. The conversion of the insoluble mineral 

 particles of a soil into soluble compounds, and 

 thereby preparing them for plant-absorption, is 



