30 



PROPERTIES OF WOOD. 





which appear as long, dark, dull lines. These rays resemble; 

 those of hornbeam-wood, and may attain 10 c.rn. in breadth. 



The sap wood is broad; tin: 

 heartwood, in the grey alder, 

 of almost the same colour as 

 that of the sapwood, in the 

 black alder it is reddish or 

 yellowish-red. 



Owing to the absence of any 

 decided characters that could 

 be reproduced in a drawing, 

 , no plates are given of the 

 4 following woods. They are not, 

 however, difficult to identify 

 if the points brought forward 

 are attended to. 



12. Species of Birch (He tula). 



(European, Asiatic and 

 American.) 



The annual rings are dis- 

 tinct on none of the sections ; a 

 somewhat darker summer- wood 

 marks their position feebly. 

 The fine medullary rays are 

 visible only on a sharply cut radial section. The best charac- 

 teristic of the wood arises from the narrow vessels, which 

 on the transverse section appear as tine points; on the longi- 

 tudinal section, as fine lines ; they are white. When one 

 holds and turns the piece so that the light falls on it over 

 the observer's shoulder, the annual rings then appear as thin, 

 dark lines. 



Most birches have sapwood and heartwood of the same 

 colour, only the wood of the cherry-birch (Bctida lenta) has a 

 brownish heartwood. 



13. tipecics of Lime- trees (Tilia). 



Limewood or linden-wood shows its light yellow annual rings 

 on every section. If the piece of wood is observed as was 



Fig. 10. Type of Alderwood (Alnus). 



