TRUE MAHOGANY. ig 
the actual quantity of wood laid on during one year, but that of a 
much shorter or longer period. They may be due to drought, to 
defoliation, or to excessive heat or cold which interrupts growth 
activity for a short time. From this region northward the tree 
forms more and more distinct and at the same time much narrower 
annual rings of growth. The growth therefore is very slow, the ves- 
sels or water carriers are small, the wood fibers also are small and 
thick-walled, and as a result the wood is very heavy and hard. 
Mahogany wood is diffuse porous; that is, the pores are distributed 
more or Jess uniformly throughout the wood. They usually occur 
singly, but may occur in radially disposed small groups of from two 
to four. Most of them are filled with tylosis, usually dark brown or 
reddish, but sometimes, as in Cuban and some Central American 
mahogany, white or nearly so. 
The pith rays, from one to four cells wide, are the radially dis- 
posed rows of cells (parenchyma elements) seen with the unaided 
eye as faint lines in a smooth transverse section. They frequently 
have a slightly wavy course and bend around the vessels. In a tan- 
gential section they are often arranged in horizontal rows and are 
known as storied rays. 
MINUTE CHARACTERS OF THE WOOD. 
The quality and often the source of true mahogany may be deter- 
mined by its minute structure. The length of the wood fibers varies 
according to the locality in which the tree grew. This variation m 
the fiber length is shown in Table IV. Microscopically considered, 
the wood of mahogany is made up of pores (or vessels), tracheids, 
wood-parenchyma fibers, wood fibers, and pith-ray cells. The mi- 
nute characters of these elements are as follows: 
Pores* in mahogany are rather large, with an average diameter of 
0.15 milhmeter, and together with accompanying parenchymatous ele- 
ments often occupy the entire width of the wood ray; that is, the 
portion lying between two pith rays. The small pores are located 
near the periphery of the annual ring. These small vessels are com- 
posed of segments which often resemble tracheids in form. These 
segments, which can be seen in longitudinal sections or in macerated 
material, are from one to three times as long as wide (fig. 4, A). 
The openings in the horizontal partition walls of the larger vessels 
are round and simple throughout (fig. 4, A, c), while the openings 
on the smaller vessels are generally oval or elongated and placed 
obliquely. The vessel walls are furnished with numerous lenticular 
bordered pits (fig. 4, A, d), which occur in vertical rows where the 
4+7These elements are known as pores in transverse sections, and as vessels in longi 
tudinal sections. 
