MACROSCOPIC STRUCTURE. 31 



recommended above for birch, the whitish vessels are either 

 invisible, or are seen here 1 and there ; the medullary rays are 

 somewhat more distinct. The sap wood is broad, the heart- 

 wood slightly brown. JJirchwood is always heavier than 

 limewood. [Lime is also the name for species of Citrus. Tr.] 



14. Species of Pear, Apple and 



(Including the genera Pirns and Sorbus, represented by 

 numerous species in Asia, America and Europe.) 



Decided characteristics are wanting. The medullary rays 

 may be distinguished on good sections. Owing to the 

 uniformity of the spring-wood and summer-wood, no valuable 

 information is obtainable from an inspection of any of the 

 sections. The superior hardness and specific gravity of their 

 wood, when compared with limewood, is a useful test. 



The sapwood is broad ; the heart-wood in applewood, reddish- 

 brown, and browner in pearwood, in the wood of species of 

 Sorbus, of a lighter yellow or brown. 



15. Species of 1'optilus tind S<tli.r. 



The soft, light wood of poplars and willows most closely 

 n .-cinblus that of conifers, but may always be distinguished 

 from the latter by its numerous very line vessels; it is distin- 

 guishable also from birch wood, which is heavier, by the 

 whitish gleam of the pores (obhrrved as in birchwood with a 

 favourable incidence of light) ; from limewood, by the absence 

 of bright annual rings. 



The sapwood is very broad, in poplarwood of the same 

 colour as the heartwood, but abnormal colouring owing to 

 decay is frequent. Various species of willow possess variously 

 tinted heartwood. 



16. N/KTR'.s of Horse -Chestnut (Aesculus). 

 (Europe, Asia and America.) 



On none of the sections is there any decided characteristic, 

 owing to the almost homogeneous pale-yellow wood ; the wood 

 can therefore without difficulty be distinguished from that of 



