17 



section it is quadrangular in Teak, nearly circular in Corylus 

 Colurna, the shape of a cross in Bauhinia Vahlii, usually 

 oblong in Birches and pentagonal in Oaks. 



The remainder of the stem lying between the pith and the Heart- an d 

 bark is occupied by the wood proper and, unless our stem is Sap ~ Wood> 

 too young, we shall find that the central portion of this woody 

 cylinder is dark-coloured and is surrounded by a belt of paler 

 wood. The former is the heart-wood or duramen and the latter 

 the sap-wood or alburnum. In some trees, eg. the Silver Fir, 

 there is no heart- wood, but when this is present its colour and 

 size in comparison with those of the sap-wood are important 

 characters. In Teak the heart-wood, when fresh, is dark golden 

 yellow and the sap-wood is white. 



In the wood, arranged around the pith, we find numerous Alinual 

 lines which divide the wood into concentric layers ; the latter Rmgs ' 

 are the annual rings, so-called because each of them usually 

 represents the amount of wood formed in one year and 

 hence by counting these rings the age of the stem may be 

 calculated. These rings are due to a difference in the density 

 of adjacent concentric layers of wood, the wood formed on the 

 outer side of each ring being denser than that on the inner 

 side of the next ring which adjoins it. In several species no 

 annual rings are found, e.g. the Mango ; in others there are 

 so-called false rings, i.e. bands of tissue which do not pass 

 uninterruptedly around the stem and which often run into 

 one another. These may be seen in Pongamia glabra and 

 Quercus semecarpifolia. 



Through the wood, passing from the centre outwards, Medullary 

 towards the circumference of the stem, are radiating lines called Rays> 

 the medullary rays. The presence or absence, width and other 

 characters, of these rays are important points in the identi- 

 fication of different woods. If we split a piece of the Teak 

 stem radially we find the medullary rays appearing on the 

 surface of the radial section as shining plates, giving an orna- 

 mental appearance to the wood and constituting the so-called 

 silver-grain. Looking again at the cross section of our stem we 

 find a number of minute pores which are larger and more Pores - 

 numerous in the inner part of each annual ring than in the 

 outer part. The size of these pores and the way in which they 

 are distributed throughout the wood are important characters 

 for the identification of trees from their wood. 



The hardness and weight of wood are also well-known 

 characters for distinguishing trees. With Teak, for example, 

 we may compare the much softer, lighter wood of Erythrina 



