48 



OF WOOD IN GENERAL. 



been possible to carry the discrimination further than genera. 

 Though obvious naked-eye characters have been largely employed, 

 use is also made of those seen only in microscopic sections. For 

 this purpose it is only necessary to take a single shaving, across 

 the grain, with a well sharpened plane, put it at once into methyl 

 blue or some other dye, and then mount it as an ordinary micro- 

 scopic slide. The first character to be observed is the presence 

 or absence of "pores," or the transverse sections of large trachea. 

 If they are absent, which practically means that the wood is 

 coniferous, we next look for conspicuous resin-canals, and for the 



Fio. 29. Transverse section of Linden, a ring-porous wood, showing three 

 annual rings. After Van Tieghein, from The Elements of Botany, by permis- 

 sion of Mr. Francis Darwin and the Syndicate of the Cambridge University 

 Press. 



presence of heart-wood defined by a distinct colour. The out- 

 lines of the annual rings, the hardness, colour, weight, taste and 

 smell of the wood then afford further means of identification ; 

 whilst such microscopic characters as the presence of tracheids 

 in the pith-rays, or of spiral thickening in the tracheids are only 

 requisite as a last resource. Where, on the other hand, the 

 presence of " pores " indicates that the wood is that of a broad- 

 leaved tree, we first note whether there are, or are not, distinct 

 annual rings, or whether " false rings " of wood-parenchyma are 

 present ; then whether the " pores " are so collected in the 

 inner or spring portion of each ring that we should class the 

 timber in question as "ring-porous" (Fig. 29), or whether 



