456 ATTENTIONS TO GIVE TO THE SOIL. 



ters absorbed by the trees from the entire thickness of soil pene- 

 trated by their roots. Moreover the decomposition of these disjecta, 

 and the loose condition of the soil brought about by their decom- 

 position and that of the innumerable dead root fibres and hairs in its 

 interior, help it to fix no inconsiderable quantity of carbonic acid 

 and nitrogen from the air. 



Nevertheless, as we have seen before, the decomposition of the 

 vegetable disjecta may be so slow that it may produce an acid 

 humus if too much moisture be present, or the undecomposed 

 portion may form so thick a layer as to prevent any natural repro- 

 duction from taking place. These drawbacks do not, however, often 

 exist, and we have explained in various places what measures to 

 adopt in order to overcome them when they do exist. Briefly 

 speaking, these measures are either the removal of a portion of the 

 undecomposed layer, or mixing it up with the mineral soil below, 

 or driving cattle or pigs over the area, or the free admission of 

 air throughout the decomposing or incompletely decomposed mass 

 by turning it up and by opening out the leaf-canopy above, if this 

 be too thick. 



General. 



From the preceding remarks it will be seen that all the factors 

 which jointly compose the productiveness of a forest soil are in- 

 creased and maintained by one and the same measures, viz., the 

 maintenance of an unbroken leaf-canopy and the preservation and 

 proper decomposition of the decayed and decaying leaves, &c., lit- 

 tering the ground. 



