432 Scientific Proceedings, Royal Dublin Society. 



the only record available is the port of origin, and often this even is not 

 ascertainable. Naturally tliis uncertainty as to species greatly increases the 

 difficulty of constructing any scheme for identification, for it is often hard, or 

 impossible, to determine whether differences in characters are to be interpreted 

 as differences existing between individuals of the same species, or as 

 characteristics of different species. Where it was impossible to ascertain the 

 name of the tree, the commercial or trade name of the timber has been used ; 

 and as much certainty as to specific and individual characteristics has been 

 obtained as possible, by the examination of a number of specimens of the 

 same wood where opportunity allowed. 



As a considerable time must elapse before anything like a complete 

 collection of mahoganies can be examined, and as there appears to be an 

 immediate need for some method of identifying the more common kinds, I 

 have put together descriptions and illustrations of the structure of the 

 mahoganies which up to the present have been available to me, in the hope 

 that they may be useful as a means of identification, and that they may serve 

 as a beginning of an examination of a more extensive list of woods. 



In colour the mahoganies vary from almost white to dark brown, 

 sometimes of tawny, sometimes of rose, and sometimes of ashen grey tinge. 

 They are sometimes dense and sometimes light, having a specific gravity 

 ranging from 087 to 034. In hardness they are variable, and may take a 

 good polish on the end grain or they may be so soft as to be easily marked 

 by the finger-nail. 



With regard to structural differences, we find some mahoganies with 

 almost typical year-rings, others quite without them ; in some the denser 

 region of the growth-zone is produced by the reduction in size and numbers 

 of the vessels (" ring-porous "), in others the greater density is due to the 

 increase in thickness of the wall of the fibrous elements of the wood and the 

 reduction of their lumen. In this latter case the dense tissue is hard and horny, 

 and cuts with a polish, and so in a cross-cut the dense zones, which are polished, 

 contrast very strongly with the less dense and softer tissue which is not 

 polished, and a very marked zonation is produced. This zonation may coincide 

 with a zonation of the vessels in the less dense or soft zone, or it may be 

 apparently independent of the distribution of the vessels. Many mahoganies 

 do not show this form of zonation at all. 



What is true of the larger structures, such as annual rings, pore-rings, and 

 growth-zones, is equally true of the less conspicuous and more minute 

 structures. Thus the size of the pores is very various ; the largest in 

 Lumbayao and Cape Lopez mahoganies may have a diameter of 045 mm. or 

 Q-50 mm. ; while in Turiballi, some Cuban, and other West Indian mahoganies. 



