16 FOREST PLAXTING. 



by mixing sandy loam with them, especially when the 

 latter contains marl, because such a mixture furnishes 

 rich plant-food for the tree roots. But even coarse sand 

 added to peaty soil would be a great improvement, because 

 sand contains always a large part of silica combined with 

 kali, which, either by the influence of the carbonic acid 

 of the air, or of the humic acid in the soil, are disin- 

 tegrated and converted into carbonate of lime, this being 

 soluble in water, and in this shape available to the roots. 



Moreover, this treatment acts beneficially upon the me- 

 chanical condition of the loose soil, which by the weight 

 of the coarse sand is compressed, and yet remains porous 

 enough to let the air joercolate in the ground. Fine sand 

 should not be used, because it never contains kali ; in 

 coarse sand kali always is found, and for this reason it 

 deserves the preference. 



Eaising the soil by throwing earth over the surface of the 

 borders (beds) is especially helpful in the regions of large 

 rivers, where otherwise drainage is impossible. 



The extent of the drainage, as well as the increase of 

 the elevation of the borders, depends upon how much or- 

 dinary moisture shall be retained in the eoil, and especially 

 how high the water table in the subsoil shall rise. Upon 

 common soil trees grow best when the ground water does 

 not rise higher than 3 or 4 feet below the surface, because 

 under such circumstances the superfluous water can run 

 off, and at the same time the water evaporated on the sur- 

 face soil can be easily replaced from the ground water 

 through the capillary attraction. But the spongy peat 

 soils, bogs, ferns, etc., attract, owing to their increased 

 capillary functions, water too easily, and, therefore, must 

 have a lower water-line than common soil. 



We shall consider this question more fully, when fur- 

 ther treating upon the drainage of swamps, bogs and 

 peaty fens. 



