II.] ITS PROPERTIES AND VARIETIES. 37 



weather and soil are warmer, and the young leaves 

 in full activity ; whence the cambium is better 

 nourished from the first, and forms better tracheides 

 throughout its whole active period. Such a result 

 in itself is sufficient to repay the investigations of the 

 botanist into the conditions which rule the formation 

 of timber, but this is by no means the only outcome 

 of researches such as those carried on so assiduously 

 by Prof. Hartig in Munich, and by other vegetable 

 physiologists. 



It is easy to understand that the toughness, 

 elasticity, and such like qualities of a piece of timber, 

 depend on the character of the tracheides, fibres, &c., 

 of which it is chiefly composed. Investigations are 

 showing that the length of such fibres differs in 

 different parts of the tree. Sanio has already 

 demonstrated that in the Scotch pine, for instance, 

 the tracheides differ in length at different heights in 

 the same trunk, becoming longer as we ascend, and 

 also are longer in the outer annual rings than in the 

 inner ones as the tree grows older, up to a certain 

 period ; and this is in accordance with other state- 

 ments to the general effect that for many years the 

 wood improves, and that better wood is found at the 

 base of the trunk. 



However, it is impossible to pursue these subjects 



