SAP-WOOD AND HEART-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 by the British Isles), the annual layers are veiy 

 seldom less than -\ of a millimeter in thickness ; while in the 

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

 meter. 1 The width varies also in different parts of the same 

 ring. For instance, in the case of Finns 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 



* s <^7 ^j 



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 lying 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 early histologists on account of its 

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

 sharply, is the harder substance. Heart-wood, or Duramen. 2 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. 3 



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

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



ft/ 



ducts. In Hrematoxylon Campechiannin the coloring-matter 

 sometimes occurs also in crystals inside the cells themselves or 



V 



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

 Sanders-wood) consists of libriform cells intermingled with small 

 groups of veiy large ducts, both of which contain the ruby color- 

 ing-matters in large amount. Many Berberidaceae, Cladrastis 



>^-/ ^_ ' f 



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



*/ C7 



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

 ebony, nearly black. 



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



2 The word Duramen is used by some writers to denote merely that heart- 

 \v(u)d which has become very dense by peculiar infiltrations (Saunersdorfer, in 

 Sitzungsber. d. k. Akad. Wien., 1882). 



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

 ume ot the trunk, are from Tredgold (Principles of Carpentry, Section X., cited 

 by Rankine) : Chestnut, 0.1 ; Oak, 0.294 ; Scotch Fir, 0.418. 



