ABNORMAL TISSUES. 



the occurrence of the wound and then resume their former 

 direction. 



Stems are very rare in which the fibres run in the same 

 plane as the pith, so that their course is straight. A spiral 

 torsion of the fibres, that is more or less pronounced, is the 

 rule. Twisted wood, or rather torse wood, for twisting 

 implies an external force acting on the wood, may be left- 

 inclined, or right-inclined, i.e., its direction may follow the 

 apparent diurnal motion of the sun, or the reverse. This is 

 without economic interest, for wood the fibres of which encircle 

 the stem within thirty feet is useless for sawing or cleaving 

 whether the fibres bend to the right or left; it may, how- 

 ever, still be used for posts, and Mathey says, for railway - 

 sleepers. 



As some wood is perfectly vertical, the theory set up by 

 Braun and Goppert, that torsion is the result of the length- 

 ening of the fibres as the tree becomes older, must be 

 abandoned. The fact, that, in torse wood the transverse 

 division of the mother cambium cells is usually in one 

 direction only, <v/. to the right, whilst when straight-grained 

 wood is formed, these divisions arc alternately to the right 

 and left (Hartig), is the effect only of an unknown cause. 



Pines are more subject to torsion than spruces or silver-firs, 

 Scots pine fibres always turning to the right in such cases 

 (Mathey). Neumeister states that all horse-chestnuts (but no 

 birches) have torse fibre. Torsion is common also in sweet- 

 chestnut wood. There are certain localities, e.g. stony soil 

 and sunny aspects, where torse wood is very common and 

 there the price of timber is remarkably low.* Straight- 

 grained wood is recognisable on standing trees by the vertical 

 lines of the bark- cracks and as felled and peeled trees become 

 dry the direction of the fibres is shown by the fine longitudinal 

 cracks in the wood (Fig. 57, a and b). 



Wavy texture forms what is known economically as curl- 

 wood. It diminishes the utility of wood less than torsion. 



* [Such a locality is cited by Fernandez, op. cit., at Kanikhet, in the Hima- 

 layas, where he says that all the Pimis longifulia trees have torse fibre. Mathey 

 cites Marchiennes and St. Ainand, as forests where it is hereditary with oaks. 

 Mates that there is a Scots pine wood near Trier, where .si per cent, of 

 the trees are torse. Tr.J 



F.U. K 



