CHEMICAL AND PHYSICAL PKOPEKTIES. 703 



needle and one in its curved side. None of these ducts 

 are continued into the cortex, but there is a connection 

 between the vertical ducts of the cortex of different years' 

 shoots, that is formed early owing to the growth in thickness 

 of the verticilary branches ; cork begins to form in ten years. 

 In larches, there is no connection between the ducts in the 

 needles and in the cortex, only the short ducts in the brachy- 

 blasts represent the vertical cortical ducts of the other coni- 

 ferous genera ; the ducts in the hypoderma of the longitudinal 

 shoots die in the first year, when cork is formed ; the bast 

 contains horizontal ducts, as in spruces, pines, and Douglas- 

 firs. 



SECTION II. CHEMICAL AND .PHYSICAL PROPERTIES OF TUR- 

 PKNTINE, OR KESIN. 



Turpentine is a mixture of lixed and etherial carbohydrates ; 

 by its distillation, oil of turpentine is obtained, with the 

 formula Cio Hi 6 . Usually the mixture is spoken of as resin, 

 and oil of turpentine, as turpentine. 



Owing to the evaporation of etherial turpentine and its 

 oxidation, resin usually solidifies into rosin or colophany, 

 which is partly crystalline and partly amorphous. If fresh 

 resin is taken from a tree and dried, the rosin forms a trans- 

 lucid, solid mass. The rosin increases in bulk with the age of 

 a tree, as more and more of the etherial oil becomes oxidised. 

 The following table shows clearly this transformation for 

 spruce and common pine, the figures representing the per- 

 centage of rosin in the resin that exudes : 



Sapwood of spruce . . . 74*87 per cent. 



Resin galls 80*90 ,, 



Sapwood of pine . . . . 69*48 ,, ,, 



Heartwood . ... 75*59 



Sapwood of Weymouth pine . 61*70 ,, ,, 



Heartwood of larch . . . 79*33 ,, 



Bark of silver-fir . . . 62*85 



Sapwood of Pin it-it riy-ida . . 64*15 ,, ,, 



