THE FOREST. 15 



aged trees, they may all become weak and sickly because of 

 hindering one another. On the other hand, this crowding 

 of trees forces them to take on an upward growth and kills 

 out the lower branches. Trees growing under such condi- 

 tions make long timber free from knots, which is therefore 

 most valuable. 



SOIL CONDITIONS. 



Water Supply. Water is the most important element in 

 soils for tree-growth, and the greatest attention must be 

 given to its conservation and distribution through the soil. 

 Trees do not grow to best advantage in very wet or in very 

 dry soil, although some can live and almost thrive under 

 such unfavorable conditions. There is very little land, 

 except in the arid region, but that will support some form 

 of tree-growth. The soil best adapted to all kinds of trees 

 is one that is moderately but evenly moist, porous, deep, 

 and well drained; yet with a subsoil compact enough to 

 transmit the subsoil water from below upwards without its 

 being so solid that it cannot be easily penetrated by the 

 roots. It does not matter about its being stony if it has 

 these qualities. On land that is very wet, as the muskegs 

 of Northern Minnesota, which are covered with Tamarack 

 and Spruce, the trees never get to be of large size. In the 

 case of one Spruce grown on such land, 73 years was occu- 

 pied in growing a tree IJ inches in diameter, and a Tama- 

 rack under similar conditions formed a diameter of only 

 ly'o inches in 48 years. We also find that growth is 

 extremely slow on very dry land. On very open porous 

 land the water sinks quickly out of reach of the roots, and 

 where the soil is too compact it cannot be penetrated by 

 the water or by the roots, so that on such soils trees gener- 

 ally suffer for moisture a part of the year. 



Relation Between Trees and Soils. The growth of trees 

 and the kinds growing on land are good though not infalli- 



