BIRCH V. 6702 



BIRCH 



Betula alba Lirm. : synonyms, B. verrucosa Ehrh.; B. nigra Duham. 

 Betulacese. 



A diffuse-porous wood of medium weight and hardness. Colour white, 

 ecru or more rarely brownish. A sapwood tree. 



Transverse section (compare Fig. 2). Boundary just perceptible, a line 

 of contrast in the density of successive rings (sometimes a thin line of 

 flattened cells, under microscope). 



Parenchyma not visible with the lens (except as to the line just 

 mentioned) ; it is dispersed amongst the fibres. 



Vessels just visible, a tendency to arrange themselves in oblique lines, 

 which here and there are quite distinct and run across the whole width 

 of the ring in well-developed rings (they are best seen on a surface which 

 has been wetted, and allowed to dry). The oblique lines frequently make 

 angles one with another. The vessels diminish in size, but very slightlv, 

 from the inner side of the ring outwards. They are isolated widely and 

 in either single or in sub-divided (mother and daughter) groups of two 

 or three vessels. 



Rays just visible, yellow to brown, and of a colour different to that 

 of the fibres: they are almost direct (i.e. not wriggling between the 

 vessels), irregular in spacing, at intervals sometimes equal to the width 

 of a vessel but generally much more. 



Radial section. Boundaries visible, but not prominent. Silver-grain 

 brown, rather inconspicuous except when wet or polished : grain medium 

 coarse. Septa of vessels with grids (scalariform : microscope needed). 



Tangential section. As the radial, but the boundaries are loops with 

 feeble fringes: the surface of the wood, especially where cross-grained, 

 shows vague zigzag in patches. Rays multiseriate. 



Pith flecks abundant in the early rings. Grids of septa of vessels 

 appear in this section as rows of dots or, when torn, like rake-teeth. 



May be confused with: May be distinguished by: 



'Lime (finer grain and paler Coarser grain: vessels in tnms- 



silver-grain : vessels in transverse verse section in well-developed 



section not in oblique lines passing rings in oblique lines making 



across the whole width of the ring; angles: widely isolated. Grids in 



rather crowded. No grids in the the septa. Wood cold to the touch. 

 septa. Wood warm to the touch). 



Willows (light in weight: colour Medium weight: colour ecru to 



pinkish-brown, grain fine, rays brownish: grain rather coarse: 



uniseriate (they seem to meander rays multiseriate, firm and straight, 

 amongst the pores)). 



1 Although the distinguishing characters seem vague on paper yet in a thin 

 transverse section under microscope ( x 20) of Lime and Birch they are very 

 readily recognised (see Figs. 2 and 3). 



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