GUIDE TO TIMBERS OF NIGERIA 75 



more numerous in the outer zone of the ring ; contents, 

 crystals in abundance ; proportion of the wood about one- 

 quarter. 



Vessels visible as perforations, large, diminishing little either 

 in size or numbers ; arrangement oblique (even when the 

 P. (a) is ignored) ; widely isolated, 3-8 per sq. mm. ; simple 

 and in nested or radial groups of 2-4 pores, many pairs ; 

 shape, oval ; contents, various, some white deposit, tyloses 

 and black granules. Proportion of the wood about one- 

 fifth. 



Rays just visible ; of one kind only ; fine, almost too thin 

 to taper ; fairly regular in size and spacing ; very weak and 

 slightly avoiding the pores ; intervals about four times the 

 width of the rays themselves ; proportion of the wood about 

 one-quarter. Crystals present. Number per mm. 7-8. 



Ground-tissue-cells visible with the macroscope. 



Rings apparently defined, but true boundary is indefinite ; 

 there is some difference in density by zones ; contour 

 regular. 



Radial section. Parenchyma (a) visible in vertical lines trace- 

 able over long distances. Vessels often twinned. Rays visible ; 

 colour, buff, nearly the same as that of the P.. (a) ; dull. Rings 

 not traceable. 



Tangential section as the radial, but the P. (#) is very much 

 more prominent as borders and tails to the vessels. Rays just 

 visible with difficulty as a faint hatching on the darker ground ; 

 height, at least twenty cells, and usually more than one cell 

 wide ; not in parallel. 



SAP WOOD " yellowish white ; not wide. The slash is 

 yellowish, with little red spots in it. A white latex exudes 

 when cut " (Unwin, p. 254). 



From specimen No. 2991 colour, oatmeal. The paren- 

 chyma becomes coloured in advance of the other tissues. 

 The sapwood is well and sharply defined from the heart- 

 wood. 



BARK. ic The yellow lenticels, especially on younger speci- 

 mens and also on the red roots, are typical of the tree " (Unwin 

 I.e.). " Bark grey, not deeply fissured ; twigs purple " (Engler 

 1898, p. 52). " Bark thick, exuding a latex of a dirty white 

 colour and very sticky (poisseux) : wrinkled, slightly scaly and 



