SAP-WOOD AND U EAIIT-WOOD. 141 



season, a broad ring of a warmer one. Their width varies also 

 in the same species in different localities : thus, in Finns sylves- 

 tris, grown between 50° and 60° north latitude, in Europe (the 

 space occupied b}- the British Isles), the annual layers are very 

 seldom less than ^ of a miUimeter in thickness ; while in the 

 same tree, grown far north, the thickness is not -^ of a milli- 

 meter.' The width varies also in different parts of the same 

 ring. For instance, in the case of Piniis sylvestris, Bravais and 

 Martins found the two opposite radii in a stem to have the ratio 

 of 9 to 19, the side having the greatest thickness being that 

 which had its foliage best exposed to air and light. The eccen- 

 tric growth of the wood of branches has been often noted ; the 

 longer radii are those on the lower side. 



401. Sap-wood (Alburnum). The new and soft wood con- 

 tains a larger proportion of soluble organic matters, of nitro- 

 genous substances, and, when fresh, of water, than the older, 

 harder wood Ij'ing just within. The " sap " of the tree is found 

 in largest amount in the newer wood. The name alburnum was 

 given to the sap-wood by the earl}^ histologists on account of its 

 white or pale color. Contrasted witli it, but not always very 

 sharplj-, is the harder substance. Heart-wood, or Duramen.^ The 

 latter was given its name because of its greater hardness, or 

 durability. Generally there is some distinction in color between 

 the sap-wood and heart-wood, owing to the presence of peculiar 

 coloring-matters lodged in the texture of the latter.^ 



402. Color of wood. The deep colors which characterize many 

 kinds of wood are contained chiefly in the walls of the cells and 

 ducts. In Hffimatoxylon Campechianum the coloring-matter 

 sometimes occurs also in crystals inside the cells themselves or 

 in clefts of the wood. The wood of Pterocarpus santalinus (Red 

 Sanders-wood) consists of libriform cells intermingled with small 

 groups of very large ducts, both of which contain the rubj- color- 

 ing-matters in large amount. Many Berberidacese, Cladrastis 

 tinctoria, Cercis, etc., have yellow coloring-matters in the wood ; 

 in Guaiacum the color is greenish ; in black walnut, brown ; in 

 ebonj-, nearly black. 



1 Bravais and Martins: Ann. des Sc. nat., ser, 2 tome xix., 1843, p. 129. 



^ The word Duravien is nsed by some writers to denote merely that heart- 

 wood which has become very dense by peculiar infiltrations (Saunersdorfer, in 

 Sitziingsl)er. d. k. Akad. Wien., 1882). 



2 The following figures, giving the proportion of sap-wood to the entire vol- 

 ume oi the trunk, arc from Tredgold (Principles of Carpentry, Section X. , cited 

 by Eankine) : Chestnut, 0.1 ; 0;ik, 0.294 ; Scotch Fir, 0.418. 



