174 WOODS. 



(87) Jamaica Quassia Wood. 



The wood of Picraena excelsa, Lindl. (N.O. Simarubese). 

 The wood exhibits the following structure : 



It is traversed by medullary rays mostly two or three cells 

 wide, the constituent cells being radially elongated, and having 

 slightly thickened, pitted walls. 



The tissue between the medullary rays is composed of wood- 

 fibres, vessels, and wood parenchyma. 



The wood-fibres have moderately thick walls and, when 

 isolated, are seen to be very long, tapering gradually to a fine 

 point, and bearing scattered, left-spiral, cleft pits. 



The vessels are usually in groups of two or three, and 

 frequently extend from one medullary ray to the next. Their 

 walls are moderately thick, and hear numerous small pits which 

 careful observation will show to be bordered. They often 

 contain an amorphous yellow substance. 



The cells of the wood parenchyma are usually axially elongated. 

 In transverse section they appear square or polygonal with 

 moderately thickened, pitted walls. They often contain large 

 crystals of calcium oxalate usually in superposed cells, each 

 containing a single crystal. This tissue is distributed in 

 irregular concentric rings throughout the wood. 



The wood of Quassia amara, Linn. (Surinam quassia) is 

 similar in structure, but the medullary rays are usually one 

 cell wide, and the calcium oxalate crystals are much less abun- 

 dant. 



The diagnostic characters of powdered Jamaica quassia 

 wood are : 



(a) The medullary rays, two or three cells wide. 



(b) The presence of calcium oxalate. 



(c) The long, moderately thickened fibres. 



(d) The numerous small bordered pits of the vessels. 



