PRUNING. 



229 



to resemble the disposition of the branches of a fir 

 tree, only with greater distances between the tiers. 



Fir timber for the use of builders and mast makers 

 cannot be too free from knots, and it is impossible to 

 have it so, unless planted and trained up in the closest 

 order. When so disposed no lower branches can live 

 to distort the longitudinal structure of the bole. The 

 centres of the trunks when cut up for use, only show 

 the bases of the first laterals ; but every concentric 

 layer of wood imposed after these first branches decay 

 is free from knots. (Fig. 55.) 

 Fig. 55. 



u y 



Vertical section of a tree, the lateral branches of which had con- 

 secutively died, or been cut when three years old. 



A single fir requires a large space, and produces 

 the worst timber ; its first branches continue to en- 

 large and extend themselves, sweeping the ground as 

 long as the stem continues to rise ; and though the 

 latter arrives at a great size, its timber is of the most 

 inferior description, being deteriorated by large knots. 

 (Fig-. 56.) 



