APPENDIX IV 



THE DISTINCTIVE MICROSCOPIC STRUCTURES 01 WOODS 



A GENERAL description of the microscopic structure of wood has been given 

 in Chapter I., and an outline classification of woods based upon this micro- 

 scopic structure has been attempted in Chapter II. The object of the present 

 appendix is to give further details of the distinctive microscopic characters 

 of a series of typical woods, arranged in accordance with that classij&cation 

 and illustrated by plates taken from Mr. J, A. Weale's admirable series of 

 photo-micrographs. These last are uniformly magnified 30 diameters. 



As was explained in Chapter I., the wood of broad-leaved trees (" hard- 

 woods," "porous woods," or " leaf -woods," as they are variously termed, 

 see p. 44) is far more complex in structure than that of Conifers (" soft-woods," 

 *' non-porous woods," or "needle-leaved woods"). Eor convenience, 

 however, the more complex hard-woods will here be dealt with first 

 (Plates I to XL.). 



To realize fully the structure of wood, it is necessary to examine it not only 

 in transverse section— cut, that is, " across the grain," or at right angles to 

 the axis of the stem— but also in longitudinal sections— out, that is, " with 

 the grain," either tangentially, not passing through the centre, or radially— 

 i.e., " quartered," or cut through the centre. At the same time the dis- 

 tinctive characters of woods are seen better in transverse than in longitudinal 



sections. 



For the purposes of the practical examination of transverse microscopic 

 sections of hard-woods, we use for convenience the terms " large pores " 

 and " small pores," signifying mainly tracheae (p. 16) and tracheids respec- 

 tively, the " ground-tissue " of the xylem— generally its hardest portion- 

 being mostly wood-fibres, and the "soft-tissue "—often only relatively soft — 

 being the " wood-parenchyma " (p. 28). This last term we have borrowed 

 from Mr. Gamble. When this soft tissue forms a patch round a large pore we 

 term it an " areola." 



As the structure of Oak— a fairly typical example of complex hard-wood— 

 has been abeady fully illustrated by magnified views of sections in all three 

 directions (Figs. 18 to 24 and 27), we have here taken another hard-wood, a 

 typical Australian representative of the Order Protedcem, cut in all three 

 directions (Plates I. to III.), as our starting-point. 



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