Peat. Loam. Functions of the Roots. 5 



in some situations peat. These vary considerably in composition, 

 and the latter contains so large an amount of carbon that it is used 

 profitably as a fuel. The former, when mixed with animal manures, 

 and the latter, when its acidity has been neutralized by lime or al- 

 kalies, become valuable as fertilizers. Both humus and peat ab- 

 sorb water with avidity, and retain it with tenacity. It is partly 

 on this account that vegetable mold, when mixed with other soils, 

 tends to impart fertility by retaining moisture within the reach of 

 vegetation. 



17. The term Loam is attached to a class of soils composed of 

 different earthy materials of dissimilar particles, not easily ductile, 

 readily diffused when thrown into water, and easily penetrated by 

 the roots of trees and other plants. A mixture of humus renders it 

 porous and fertile, and in a forest, this fertility tends constantly to 

 increase, and hence the growth of trees is one of the best means for 

 restoring exhausted soils. 



18. The soil has an influence upon the growth of trees in two 

 ways : it gives them support, and it furnishes them with nourishment. 

 In order to give support, the soil should be permeable by the roots, 

 without being too tenacious to resist their extension, nor too light to 

 hold them. In nursery plantations, the proper qualities may be se- 

 cured by artificial mixture of materials, but except in a very small 

 degree, we can not modify them, and must seek to improve by the 

 choice of species, the conditions as we find them. 



19. As the roots of trees penetrate much deeper into the soil than 

 those of agricultural plants, the welfare of woodlands often depends 

 much upon the depth and character of the sub-soil, as is observed 

 in the "Landes" of south-western France, where a vigorous and 

 profitable growth of trees is obtained upon lands that are almost 

 utterly barren for cultivation in farm crops. In other cases, as in 

 flat limestone districts, the surface soil may be too thin for cultiva- 

 tion, while in the fissures there is sufficient soil for supplying the roots 

 of trees. These roots, when they decay, besides leaving the organic 

 material of which they were composed, also leave open passages 

 penetrating deeply into the soil, and affording opportunities for 

 drainage. These may become filled in with mold from the surface, 

 and thus they in some degree assist in rendering the soil fertile to a 

 greater depth than would be possible from the simple deposit of or- 

 ganic materials upon the surface. 



