GUIDE TO TIMBERS OF NIGERIA 65 



Parenchyma of two kinds : (a) vasicentric and (b) in fine 

 bars, concentric. 



Parenchyma (a) visible to the unaided eye, narrowly sheath- 

 ing the pores uniting them into radial lines ; lighter in colour 

 than either the rays or the P. (b). 



P. (b) in concentrically arranged bars at right angles from 

 ray to ray, but apparently never passing across a ray. They 

 cut off rectangular areas of the ground tissue, simulating the 

 cells of a ray highly magnified. Colour brown, about the 

 same as that of the rays ; contents, much resin. Number per 

 radial mm. 10-13. 



Vessels visible only from the P. (a) surrounding them, but 

 by this aid they appear as long fine radial strings ; size small, 

 diminishing little if at all outwards ; evenly distributed ; 

 simple at times, but mostly in radial groups connected by 

 P. (a) and also m-and-d groups, which are sometimes difficult 

 to distinguish from the former ; some twinned groups ; isolated 

 but not widely, being very numerous, about 30-36 per sq. mm. ; 

 shape, oval ; contents, some resin and perhaps tyloses. Pro- 

 portion of the wood including P. (a] about one-third. 



Rays not very small and would be visible to the unaided 

 eye (at least "when wet) were it not that they are masked by 

 the radial lines of pores ; doubtfully of two kinds, but there 

 are occasional large rays which are readily visible and which 

 suggest aggregation. Colour, brown ; spacing fairly regular 

 and size also, except as regards the large ones just referred to. 

 Very numerous and closely set, at intervals of about 2-3 times 

 their own breadth. 12-15 per mm. Contents, some resin ; 

 proportion of the wood about one-quarter. 



Ground-tissue-cells visible with the macroscope ; colour, 

 deep, dull amber ; proportion of the wood not more than one- 

 quarter. 



Rings vaguely defined to the unaided eye and less so with 

 lens ; boundary apparently a vague zone of denser tissue ; 

 contour regular. 



Radial section. P. (a) not visible even with the macroscope ; 

 P. (b) with the same magnification appears as excessively fine 

 lines containing resin. Vessels readily visible ; very tortuous ; 

 linings shining ; contents, some dark -coloured globules. Rays 

 very small, visible by reflection, but only where the grain is 



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