Dixon — Mahogany, Recognition of some Different Kinds. 437 



clean," and confers on it a freedom from splitting and warping, In addition 

 a mahogany should have scattered vessels, isolated or in small, mostly radial, 

 groups ; the parenchyma round the vessels should be narrow and incon- 

 spicuous, while the medullary rays are on the average well under 2 mm. in 

 height, and are not more than nine cells thick, except occasionally where the 

 uniform grain of the wood is locally disturbed. 



In other respects the woods classed as mahoganies have very varied 

 properties; e.g., with regard to density, hardness, presence or absence of 

 year-rings, pore-rings, size and contents of vessels, distribution of paren- 

 chyma, structure and size (within the limits above mentioned) of rays, &c. 

 These and other characteristics, however, may be used as diagnostic characters 

 of the different kinds of mahogany. 



Identification of the Different Kinds of Mahogany. 



In a general way the colour of the freshly cut wood may be helpful as 

 a diagnostic. Thus freshly cut Cuban mahogany is rose brown, while 

 St. Domingo is characterized by true brown, approaching the tint of burnt 

 sienna ; but the difficulty of accurately describing small differences in colour, 

 and the colour variations, in samples of the same wood render this property 

 of little use in descriptive distinctions between the several mahoganies. The 

 same criticism applies to the extract. Specific gravity and hardness are also 

 useful; but we must be alive to the fact that considerable variations are 

 often met with in these properties, even in the same woods ; e.g., Cuba 

 mahogany (Swietenia mahagoni) has been found to vary in sp. gr. between 

 073 and 0'84, while the so-called "Spanish," West Indian, and St. Domingo 

 (all probably from Swietenia mahagoni) have been found to have densities 

 ranging from 0'82 to 0'68. The variation is still greater in the woods of 

 S. macrophylla (Honduras, Tabasco mahoganies, and Baywood), in which the 

 density ranges from - 61 down to - 43. Where, however, dislinction is to 

 be made between two specimens of widely different specific gravity the 

 characteristic is useful ; but it is rarely applicable as a distinguishing 

 feature between two samples otherwise generally resembling one another. 



As a general rule microscopic measurements are only satisfactory when 

 large differences characterize different woods ; for small or even considerable 

 differences may be found in different specimens of the same wood, or even 

 in the same piece. Thus the diameter of the large vessels may easily vary 

 30 per cent, or 40 per cent, in any wood, and the limits of the vertical 

 heights of the large medullary rays may be even more extended. Similar 

 variations in other woods are instanced by Bailey (1). There is less varia- 

 tion if we take the maximum diameter attained by the vessels in each sample 



