PROPERTIES OF TIMBER 



127 



The mechanical properties of timbers depend largely on the 

 proportion of fibres, on the number and size of the vessels, and 

 on the thickness of the fibre walls. Thus, so-called close-grained 

 woods (e.g. Box, Holly, etc.) are characterised by having abun- 

 dant fibres and small vessels, whilst the coarse or open grain 

 of wood (seen in the Lime, Horse Chestnut, etc.) is due to the 



FIG. 61. Tyloses in a vessel of the Vegetable Marrow (Cucurbita) as seen 

 in transverse section. On the right the connection with the wood- 

 parenchyma is shown. 



large number of wide vessels and often to the thin character of 

 the fibres as well. The " soft woods " of commerce are mostly 

 obtained from Conifers whose wood is solely composed of long 

 narrow tracheids (cf. pp. 340, 341), having thinner walls than the 

 fibres of hard-wood trees. 



The employment of timber for commercial purposes is deter- 

 mined by such qualities as closeness of grain, ease of working, 

 elasticity, toughness, durability, colour, figure, etc. Thus, the 



