AGRONOMY 37 



due to the action of the bacteria present in the 

 soil. Plants will not grow in sterile soil — that is 

 to say, soil devoid of bacteria. The " infiniment 

 petits " are potent factors in the growth of fruit 

 and other trees. 



Humus. — The term humus is applied to those 

 constituents of the soil which have been derived 

 chiefly from the decay of vegetable and animal 

 matter. In the processes of decay the organic 

 matter is converted largely into acids of the 

 humic series, and the nitrogenous principles of 

 the plant become changed from a proteid to a 

 more inert form, in which it is more readily pre- 

 served. In this inert form the soil bacteria exercise 

 their activity in preparing it for the plant. Recent 

 investigations, however, tend to prove that in some 

 instances, humus itself may serve as food for 

 plants without undergoing entire decomposition. 



Although, as the immortal Liebig proved, the 

 vast preponderance of the food of trees, shrubs, 

 and other plants is of a mineral nature, it 

 would not be safe, in the face of recent researches, 

 to deny to the plant the ability to absorb, to a 

 certain extent, organic compounds. 



Humus performs a number of different functions 

 in the soil which are of the highest importance 

 in the growth of fruit trees. It influences the 



