178 THE BEAUTIES OF NATURE chap. 



for the association of species is less evident. 

 The Larch and the AroUa (Pinus Cembra) 

 are close companions. They grow together 

 in Siberia ; they do not occur in Scandinavia 

 or Russia, but both reappear in certain Swiss 

 valleys, especially in the cantons of Lucerne 

 and Valais and the Engadine. 



Another very remarkable case which has 

 recently been observed is the relation existing 

 between some of our forest trees and certain 

 Fungi, the species of which have not yet 

 been clearly ascertained. The root tips of the 

 trees are as it were enclosed in a thin sheet 

 of closely woven mycelium. It was at first 

 supposed that the fungus was attacking the 

 roots of the tree, but it is now considered 

 that the tree and the fungus mutually benefit 

 one another. The fungus collects nutriment 

 from the soil, which passes into the tree and 

 up to the leaves; where it is elaborated into 

 sap, the greater part being utilized by the 

 tree, but a portion reabsorbed by the fungus. 

 There is reason to think that, in some cases 

 at any rate, the mycelium is that of the 

 .Truflae. 



