28 TECHNICAL PROPERTIES OF WOOD. 



weight of green wood is in question here, there can be no doubt 

 that, as the amount of water in wood differs at different seasons, 

 to this extent its weight varies. Thus broad-leaved wood con- 

 tains least water in winter, conifers least during spring, allow- 

 ance being made for the irregularities in this respect of certain 

 species. The season of felling has, however, no effect on the 

 specific gravity of dry wood. 



(b) Resin.* — In the case of conifers and of many broad-leaved 

 trees of hot countries, resin replaces water in filling-up the lumina 

 of the woody elements. Highly-resinous wood is always consider- 

 ably heavier than similar wood poor in resin. R. Hartig states that 

 the wood of European conifers t differs in this respect : thus 

 the spruce only produces resin in the younger zones of the 

 sapwood, and it is therefore evenly distributed throughout the 

 stem ; the Scotch pine also produces resin in mature wood, 

 and its heartwood thus becomes highly resinous. The larch 

 appears to resemble the spruce, and owing to the fluid nature 

 of larch-resin in old trees it tends to accumulate at the base of 

 the tree. In all conifers, however, the specific gravity of the 

 wood increases and diminishes with the quantity of resin it 

 contains. 



(c) Other Substances contained in Woody Tissue. — It would 

 appear that the different relative quantities of reserve 

 nutritive material (starch, proteins, &c.) which are contained 

 in wood at different seasons might affect its specific weight,^ 

 and Th. Hartig believed that in summer a reduction of 

 5 to 8 per cent, should be made on this account, but E. Hartig 

 has rendered this more than doubtful by his observations on the 

 amount of reserve-material in the wood of oak and beech during 

 summer and winter. These substances, as well as inorganic 

 salts, are chiefly found in bark and sapwood ; their influence 



* [By resin, the crude material is lueant wliicli is found in trees and from 

 wliicli oil of turpentine is distilled, rosin or colophany hauif!; left as a residual 

 liroduct— Tr..] 



t [As regards exotic trees, the more southern trees are generally most resinous ; 

 thus /-•/?*)/» a;(A</v(/(.'* (Jliohaux) in America, Rud Finus Mcrkitsii in India, yield 

 liighly resinous coniferous wood, and I'imis Piwistcr (Solander) in S.W. France, 

 is more resinous than the Scotch pine. — Th.] 



t [In India, various woods contain deposits in their heartwood which consider- 

 ably increase the weigiit of the latter. 



Thus in the heartwood of ehoiiy, the lumina of the woody tissue are filled with 

 substances which raise its weight, as conipiireil with the sapwood, in the ratio 

 of 5 : 8.— Til.] 



