16 BULLETIN 474, U. S. DEPARTMENT OF AGRICULTURE. 



tains large dimensions, some trees measuring 1 to 6 feet in diameter 

 just above the enormous root swelling (PI. Ill), with a height of 

 from 80 to 100 feet. Exceptional trees are known to have reached 

 a diameter of 12 feet. Trunks are frequently clear of branches for 

 from 40 to 50 feet, above which is a broad oval-shaped crown. The 

 pinnately compound leaves are made up of oval lance-shaped leaflets 

 (fig. 2, a), which are light green in color, smooth and shining above, 

 and slightly brownish on the under surface. The small whitish or 

 purplish flowers (fig. 2, b and c) are borne during July and August, 

 and by October or November the large dark-brown seed pods (fig. B) 

 are ripe. The latter are from 1 to 2 inches in diameter and from 3 to 

 6 inches long. The trees of these two species can be readily distin- 

 guished. Swietenia mahagoni has rather small leaves, an open 

 crown, and the pods are seldom over 3 inches long ; Swietenia macro- 

 fhylla has larger leaves, a dense crown, and the fruit pods are from 

 3 to 6 inches long. 



The commercial distinctions made in mahogany from different 

 regions have a basis in the gross and minute structure of the wood. 

 Regions of like climatic and soil conditions as a rule produce ma- 

 hogany of similar or nearly similar structural characteristics and 

 qualities. In the matter of weight and hardness, however, there are 

 occasional exceptions to this general rule. As already pointed out, 

 Florida mahogany is almost invariably harder and heavier than 

 that from Cuba or Mexico. Individual trees from Cuba or Mexico, 

 however, may yield very much harder and heavier wood than the 

 average grades from Florida. Weight and hardness therefore are 

 not invariable means of distinguishing mahogany from different 

 regions. The chief constant difference in the mahogany of the 

 various regions lies in the presence or absence of the annual rings 

 of growth, in their width, and in the character of the pith rays. 



True annual rings are not formed regularly in the wood of 

 mahogany farther south than British Honduras, owing to the fact 

 that growth continues practically throughout the year. Mahogany 

 wood produced north of British Honduras commonly shows in trans- 

 verse sections more or less distinct annual rings of growth. These 

 rings are made prominent, not as in ring-porous hardwoods of the 

 Temperate Zone, by rows of large pores in that part of the ring formed 

 in the beginning of the growing season, but by an abrupt reduction 

 of the radial diameter of the outer rows of wood fibers formed at 

 the end of the growing season, as well as by several rows of large 

 wood fibers, tracheitis, and wood-parenchyma fibers formed in the 

 next succeeding layer. This narrow line of demarcation can be seen 

 readily with the unaided eye on a smooth transverse section. How- 

 ever, marks resembling the limits of annual growth do not indicate 



