240 The Farm Woodlot 



they should be crowded into a slow and eyen growth by 

 close planting and light thinnings. The timber of a sound 

 mature tree is more durable than that of an immature or 

 overmature specimen. There is more solid wood substance 

 in it. If a tree is too old, the center of the heartwood is 

 not very durable. 



Intense coloration of heartwood is another indication 

 of the durability of timber. As a rule the trees with dark 

 heartwoods are durable. This is a rough criterion. In 

 the same species the darker specimen is always the more 

 durable. This coloring is due to the formation of tannin 

 and vanillin in the heartwood. Both these are distasteful 

 to bacteria and fungi. Colorless heartwoods lacking these 

 substances have nearly the same properties as sapwood and 

 are little more durable than they. 



Besides this lack of protective materials in its make-up, 

 the sapwood is at great disadvantage in resisting rot. 

 The cell walls are not thoroughly lignified and the wood 

 is consequently soft and of low specific gravity. There is 

 more moisture in sapwood than in the heartwood, and the 

 greater porosity of the sapwood makes it easier for it to 

 alternately dry out and absorb moisture. The drying of 

 the sap leaves a sugary residue in the cells which seems very 

 attractive to the spores of the bacteria and fungi. It is 

 the combination of these causes that makes the sapwood 

 of the cedar, — whose heart is one of the most durable 

 woods we have, — • rot in a year or two ; it contains more 

 ready food and served in more attractive form for its 

 enemies. 



The season of cutting is popularly supposed to be a very 

 important factor in the durability of timber, and there has 



