III.] THE CLASSIFICATION OF TIMBERS. 41 



are foreign to our purpose, and will not help us in 

 classifying timbers properly so called. 



There are, however, a few accessory phenomena 

 which prove useful occasionally, if pieces of timber 

 are obtained which include these. 



For instance the pith, though of course not belong- 

 ing to the wood, sometimes presents marked features, 

 worth noting because it is occasionally included in 

 the block of timber examined, or can be obtained. 

 Thus, the pith on transverse section is pentagonal or 

 rayed in Quercus (oaks) and a few other plants, while 

 it is chambered in Juglans (walnut) : usually small 

 and insignificant, it is relatively abundant in Sam- 

 bucus (elder) and Atlanthis, 



Another of these accessory characters, as we may 

 term them, is obtained by comparing the inner and 

 older wood of the tree with the outer, younger wood, 

 and it should be remarked in passing that much 

 trouble is sometimes caused by the selection of 

 timber-specimens which do not show these characters. 

 Very many woods, as is well known, exhibit marked 

 peculiarities in their inner or " heart-wood " — the dura- 

 men of botanists — which is harder, 01 heavier, or of 

 some decided colour, and constitutes a true " heart- 

 wood," as contrasted with the softer, lighter, non- 

 coloured " sap-wood " {alburnum) : in other cases no 



