38 OF WOOD IN GENERAL 



seasoned, and unbent, so that eacli fibre may vibrate freely. The 

 notes emitted will vary in pitch directly with the elasticity, and 

 indirectly with the weight of the wood. 



Spruce [Picea excelsa), imported as " Swiss Pine," " Violin- 

 wood," or " Bois de resonnance," is employed for the sounding 

 boards of pianos and the belly of viohns, whilst Maple, a dense 

 wood, is u^ed for the back and ribs of the latter instrument. 



Classification of woods. — Obviously these " rule of thumb " 

 characteristics are generally made use of in practice, not sepa- 

 rately, but together. This will also be the case in the classification 

 which we are about to propose, which refers mainly to the ap- 

 pearance of transverse sections, including both heartwood and 

 sapwood. 



For ready identification and comparison of timbers, considering 

 even the great variety that are used in the arts in various parts 

 of the world, it is obviously necessary to have some system of 

 classification. Botanists group trees, as they do other flowering 

 plants, in accordance with the characters of their flowers, fruit, 

 and leaves, a method which is undoubtedly the best for the 

 purpose of indicating the genetic affinities of the various species. 

 As we have seen, for instance, timber-yielding trees fall naturally 

 into two main groups, conifers and dicotyledonous angiosperms, of 

 which the first is generally distinguished by needle-Hke leaves 

 and seeds borne exposed on the inner surfaces of scales arranged 

 in a cone, whilst the second group has generally broad leaves and 

 the seeds enclosed in a fruit. Tor the practical study of timber, 

 however, we require a scheme of grouping based upon the wood 

 itself ; and, having often to deal with converted timber it is well to 

 be as independent as we can of characters derived from bark, or 

 even from pith. Speaking of this problem in his excellent work, 

 Timber and some of its Diseases, Professor H. Marshall Ward 

 writes : '' It may be doubted whether all the difficulties are likely 

 to be surmounted. ... In any case, while allowing that it is as 

 yet impossible so to arrange a collection of pieces of timber, that 

 all the kinds can be recognized at a glance, it must be admitted 

 that the attempt to do so at least aids one in determining many 

 kinds." 



In describing the many valuable timbers of India, Mr. J. S. 

 Gamble makes use of eight classes of characters : (i) the size of 

 the trees ; (ii) whether they are evergreen or deciduous ; (iii) the 

 bark ; (iv) the wood, its colour, hardness, and grain ; (v) the 

 annual rings ; (vi) the pores or vessels ; (vii) the pith rays ; and 

 {viii) other miscellaneous characters, such as concentric markings 

 or false rings. Of these, the first three are not available to the 



