136 



PROPERTIES OF WOOD. 



Fig. 53. Dead branch enclosed in coniferous 

 wood, causing a loose knot. 



the planks contains the dead knot, which has no fibrous 

 connection with the stem- wood ; the heavier, well-nourished 

 stem-wood then contracts, and the knot becomes loose and 



falls from the plank 

 (Figs. 52 I and 53). It 

 is obvious that such con- 

 ditions reduce greatly the 

 value of the planks. 



Knots that are firmly 

 connected with the wood, 

 dark red in colour and 

 translucent in sunlight, 

 render the wood valuable 

 for certain purposes 

 (wainscotting), especially 

 in larch, Cembran and 

 Scots pine. 



If the branches are re- 

 moved when young, only 

 the central part of the 

 mature stem is knotty ; 

 the resulting knottiness 

 is so much less, the denser 

 the crop when young and 

 the smaller the knots. 



This is the reason why 

 the outer even-fibred wood 

 of old trees is excellent 

 for sawing and cleaving 

 (Fig. 54). The evil of too 

 early thinnings, owing to 

 the consequent mainten- 

 ance of branches which 

 form large knots in the 

 wood is also obvious. 

 Double or multiple heartwood This occurs when a tree 

 has two or more leading shoots, which grow up together and 

 eventually form one stem (Fig. 5(5), or when by multiple- 

 pl;mting,or excess of natural regeneration, two or more 



Fig. 54. Transverse section of a stem, Hie 

 branches of which have been pruned early. 

 The (external wood is faultless. 



