704 PROPERTIES, HARVESTING AND DISPOSAL OF RESIN. 



SECTION III. DISTRIBUTION OF RESIN IN TREES. 



According to Mayr's investigations, normally the root-wood 

 is the richest part of a tree in resin, then in the order given : 

 the base of the stem up to two meters, branchwood, the upper 

 part of the stem in the crown of the tree, the clean bole and 

 the bark. The part of a tree that is most valuable as timber, 

 the bole, is therefore the poorest in resin, the southern half of 

 the bole contains more resin than the northern half; the sap- 

 wood, in spite of general opinion due to the flow from it of 

 liquid turpentine, is always poorer in resin than the heart- 

 wood. In the branches, contrary to the laws of gravitation, 

 the upper side is more resinous than the lower side. The 

 quantity of resin increases with the age of the tree, but 

 decreases again when the tree is over 200 years old or there- 

 abouts, so that the central zones of heartwood contain less 

 resin than its outer zones. All conifers produce more resin 

 in hot than in cold localities ; so that border trees, trees in 

 heavily thinned woods, on southerly aspects, in low latitudes, 

 (altitude being equal), or on sandy soil, produce more resin 

 than under opposite conditions. The ascent and descent of 

 resin in a tree is independent of the specific weight of its 

 parts. 



The following data regarding the amount of resin found in 

 living trees is taken from Mayr's own observations (2*2 Ibs. in 

 a kilo.) : 



