172 WOODS. 



(86) Guaiacum Wood. 



The heartwood of Guaiacum officinale, Linn. (N.O. Zygophyl- 

 lese). 



Microscopical examination shows that there is but little 

 difference in structure between the sapwood and the heart- 

 wood ; in the latter the fibres are more strongly thickened and 

 lignified. 



The wood exhibits the following structure : 



The medullary rays are closely approximated, one cell wide 

 and contain a yellowish or brownish resin. 



The vessels are numerous, large, mostly isolated, and often 

 filled with resin. They are often wider than the distance 

 between two medullary rays, and the latter therefore diverge to 

 allow room for the vessels. In longitudinal section the walls 

 are seen to bear numerous small pits. 



The wood parenchyma forms narrow lines running transversely 

 to the medullary rays ; some of the cells contain prismatic 

 crystals of calcium oxalate. Both the medullary ray cells and 

 those of the wood parenchyma bear numerous simple rounded 

 pits. 



The wood-fibres are long, tapering, and often oblique in 

 direction. They are very strongly thickened and lignified, and 

 contain yellowish-brown or reddish resin ; the pits are numerous 

 and arranged in a left spiral. 



The diagnostic characters of guaiacum wood are : 



(a) The yellowish, brown, or red resin, with which most 

 of the elements are filled. 



(b) The one-celled medullary rays. 



(c) The vessels with numerous small pits. 



(d) The calcium oxalate crystals. 



