16 TKCHNICAL PROPERTIES OF WOOD. 



(b) Trees with incomplete heartwood, in which there is no 

 distinction in colour between the sapwood and Iicartwood, but tiie 

 latter contains little or no water and takes no share hi the vital 

 processes of the tree : — 



Spruce, silver-fir, beech. 



(c) Alburnum trees, without ascertained ilistinction between 

 heartwood and sapwood : — 



i. Hardwoods. 

 Box, holly, ash, hornbeam, sycamore, maples, plane, birch. 



ii. Softivoods. 

 Aspen, lime, alder, horse-chestnut. — Tit.] 



Among trees with heartwood, oaks contain more water in 

 their heartwood than in their sapwood, whilst pines and larch 

 have a nearly dry heartwood. As a rule, old trees grown on 

 rich soils have more heartwood than young trees from poor 

 localities. 



Up to the present time, no very complete account of the 

 nature of the formation of heartwood is available. Kobcrt 

 Hartig has however written most lucidly on this question for 

 the chief European trees. He holds,, in opposition to an old 

 theory, that the colouring of the heartwood is not a commence- 

 ment of decay, nor a chemical change in the walls of the tissue- 

 elements, but a deposition of tannin, gums, oleo-resius, 

 naineral matter, &c., in their lumina or walls ; hence there is an 

 increase in substance and weight in heartwood, as compared 

 with sapwood. In the case of some woods with imperfect 

 heartwood (alburnum woods), however, the central parts of the 

 tree, as it becomes older, lose weight owing to a loss of starch, 

 or remain unaffected. 



The so-called false heartwood (red central zones of beech, kc.) 

 is caused by a commencement of decay, or by the conveyance of 

 soluble products of decomposition from other parts of the tree. 

 The heartwood of old trees is in many species heavier, harder 

 a,nd more durable than their sapwood, which is frequently trimmed 

 off the logs on account of its want of durability. The larger 

 the heartwood in oaks, pines, larch, &c., the more valuable 

 the wood. 



As the breadth of the annual zones of wood often causes a 



