6 BULLETIN 1050, U. S. DEPARTMENT OF AGRICULTURE. 
brown gum, but less plentifully in the light-colored, soft grades than 
in the darker grades. In heavy grades some pores also contain a 
whitish substance. (See fig. I. 7 ) These pores differ from the white 
gum ducts in " Philippine mahogany " in being scattered singly in- 
stead of in tangential rows ; furthermore, the gum ducts in " Philip- 
pine mahogany " are smaller than the sap pores. 
The rays on the radial surface are very distinct. On account of 
the luster of both rays and wood fibers, the rays may appear lighter 
or darker than the surrounding areas, depending on how the light is 
reflected. Actually the rays are only slightly, if any, darker than 
the surrounding fibers, a characteristic which helps to distinguish 
mahogany from crabweod, in which the rays are considerably darker. 
In some pieces of mahogany the rays are in rows or stories extending 
at right angles to the grain — that is, horizontally in the tree — show- 
ing up on the tangential surface as striations, or " ripple " marks, 
across the grain. (See fig. 12.) This condition of the rays being in 
stories is not always found in true mahogany, but is rarely found in 
any of the other species herein described, although it is common in a 
number of other woods not mentioned in this publication. 
The growth rings in true mahogany are defined by light-colored 
concentric lines, in some pieces very close together and in others 
one half inch or more apart, with considerable variation in the same 
piece. 
CRABWOOD. 
(Carapa guiancnsis Aubl.) 
Mahogany Family ( aIeliaclle ) . 
other names. 
This wood is known as " Para mahogany," " Brazilian mahogany," 
" Demerara mahogany," " British Guiana mahogany," and in South 
America as " andiroba." 
WHERE GROWN. 
Crabwood grows in northern South America as far south as the 
Amazon Valley, although the exact limits of its geographical dis- 
tribution are not known. It is a common timber tree of British 
Guiana. 
PHYSICAL PROPERTIES. 
The wood is moderately heavy and hard, and similar to magohany, 
except that such extremes of very light and very heavy grades are not 
found. 
The color is similar to that of true mahogany, except that it is not 
quite so reddish, but rather more of a plain brown. 
7 The text figures will be found grouped at the end of this bulletin. 
