16 BULLETIN 474, U. S. DEPARTMENT OF AGRICULTURE. 
tains large dimensions, some trees measuring + to 6 feet in diameter 
just above the enormous root swelling (Pl. III), 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. 3) 
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; Swéetenia macro- 
phylla 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, tracheids, 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 
