TECHNICAL PROPBKTIF.S OF WOOD. 



pores are found in the inner zone, the weight of the wood is, on 

 the contrary, directly proportional to rapidity of growth, since 

 this last bears entirely on the outer zone ; and (c), that in all other 

 woods the rate of growth has no influence on the weight of the 

 wood produced in one and the same soil and locality. These rules 

 have, however, to be accepted with some slight reservations, to be 

 presently explained. 



What has been said in the preceding paragraph is of course true 

 only wh.en the anatomical structure of the specimens of wood com- 

 pared is in every other respect the same. But large difi^erences in 

 weight may be caused by different thicknesses and degrees of solidi- 

 ty of the cell- wall, or in consequence of an abnormally slight or great 

 development of the inner or outer zones. So that a narrow-ringed 

 piece of conifer wood or a broad-ringed piece of oak or teak may 

 nevertheless be lighter respectively than a broader-ringed piece of 

 the same species of conifer or a narrower ringed piece of oak or 

 teak. But it is in the case of woods in which the pores are uni- 

 formly distributed that the thickness and solidity of the cell-walls 

 exercise the most considerable influence on their absolute weight. 



But the relative widths of the interior and exterior zones, the 

 absolute width of the entire concentric ring itself, and the thick- 

 ness and solidity of the cell-walls and fulness of the cells, are them- 

 selves merely effects of which the nature and suitability of the soil 

 and locality, and the degree of closeness of the surrounding leaf- 

 canopy, are the causes. These causes are often so powerful, th.at 

 they may reverse altogether conclusions based on the width of the 

 concentric rings, especially in the case of specimens of wood in 

 which the rings are unusually broad or unusually narrow. In 

 the case of each species, heavy (and also really good) wood is, as a 

 rule, produced in a soil of the proper mineral composition and 

 containing the necessary quantity of moisture, provided that 

 the requisite amount of warmth and light never fails. Where 

 these conditions are wanting, or do not work harmoniously toge- 

 ther for the species in question, especially if light is insufficient, 

 the wood tends to become loose-tissued and light. The great in- 

 fluence of light in determining the weight of the wood is unques- 

 tioned in respect of solitary and canopy-grown trees. In respect 

 of wood coming from different regions, where the power of the 

 sun's rays is difFerent during the season ofvegetation, that influence 

 is proved by the following figures, which have been calculated 

 from data taken from Gamble's Manual of Indian Timbers— data. 

 which, if not scientifically accurate, are nevertheless sufficiently 

 so for our purpose : — 



