ADAPTATION OF TREES TO SOILS. 21 



must adapt his trees to each. In planting slopes he 

 will choose his trees not only with regard to the soil, 

 but with regard to the aspect ; also with regard to 

 exposure to prevailing winds. The object, too, he 

 will consider in his selection of trees, whether that 

 object is ornament, commerce, shelter, or for preven- 

 tion of floods. He must bear in mind that he has 

 little control over the soil, so that he cannot undo 

 by future action an error committed in the present. 

 The control which he possesses over the soil will be 

 mechanical only i.e., by the change of condition 

 brought about by drainage, by retention of water 

 through planting, by the retardation of the drift of 

 soil on hill-sides, and so forth. Chemical changes 

 will, of course, arise through these natural and artificial 

 agencies, but not by direct application of chemical 

 dressings. True, to some extent, direct application 

 of manures may be made in cases of planting special 

 trees for ornamental purposes, on land naturally unfit ; 

 but on a large scale this cannot be done. 



