6 TECHNICAL PROPERTIES OF WOOD. 



as Hardwickia binata; while others, at the extreme end of the scale, 

 like deodar in certain localities and when completely exposed on 

 every slide, remain branched right down to the ground daring their 

 whole life-time. 



(J). A q/lindrical shape. — It is obvious that the general useful- 

 ness of the stem is in direct proportion to its approach to a cylin- 

 drical form. The combined length and upper diameter of a log 

 offer a much safer criterion of value than the mere cubical con- 

 tents, or the combined length and mean diameter. 



Some trees have eccentric or fluted growth. What the causes 

 are, have not yet been fully ascertained. It is certain that the 

 species to which the tree belongs, and the degree of isolation in 

 which it has grown, have a great deal to do with it. The presence 

 of a few large boughs produces an undue width of the concentric 

 rings of wood along the vertical line leading down from each, 

 whereas a tree that has a continuous stem extending up to its 

 summit, and only small but numerous branches distributed all 

 round is placed in the best conditions possible to develop a cylin- 

 drical bole. 



A conical shape is favoured by growth out in the open. The 

 crown coming down half way, if not lower, the inferior portion of 

 the trunk is thoroughly well nourished, and the concentric layers 

 of wood formed there are at least as thick as they are higher up ; 

 the consequence being the maintenance, and, owing to the growth 

 of the main roots, even the more decided formation, of a conical 

 outline. On the other hand, when a tree has been growing con- 

 tinuously in the midst of a leaf-canopy, the crown is high above 

 the ground, and therefore the inferior portion of the bole is less 

 well nourished than the portion above, the consequence being that 

 the concentric layers of wood are thicker above than below, and 

 the shape of the bole, from being originally conical, becomes more 

 cylindrical every year. 



The extent to which the shape of the bole departs from the true 

 cylinder is usually, and with very great convenience, expressed by 

 a factor, which, used as a co-eflBcient with the solid contents of a 

 cylinder having the same circumference as the girth of the tree 

 at breast-height, gives the true contents of the bole. This co-effi- 

 cient, which may be termed the form co-efficient or factor, is 

 obviously the ratio between the true contents and the contents of 

 the ideal cylinder in question. In practice it is obtained by measur- 

 ing a sufficient number of type trees taken from a given class of 

 forest, and representing a given species and a given age or size class. 

 The mean of these measurements is used and the mean co-efficient 



