THE PRINCIPAL SPECIES OF WOOD. 15 



Knots are the result of branches. Buds connected with 

 " pith cavities " appear upon the bark and ultimately develop 

 into branches. There are corresponding disturbances between 

 the bark and pith that are known as knots. It is needless to 

 say that such disturbances may be prevented by the early 

 removal of the buds. 



Lumber is now described or purchased upon the basis of 

 some one of the several series of rules that have been prepared 

 with reference to defects, dimensions and the general inspection 

 of lumber. Such standards have been adopted or published by 

 the Hardwood Manufacturers' Association of the United States, 

 the Pacific Coast Lumber Manufacturers' Association, the 

 Yellow Pine Manufacturers' Association and others.* 



Exogenous trees are divided into broad-leaved trees and 

 needle-leaved conifers. The broad, flat leaves of trees such 

 as oaks and chestnuts gave rise to the former term, while the 

 narrow resinous leaves of the pine and hemlock gave rise to 

 the latter. The woods of the former group are usually referred 

 to as hard woods, although some of them are very soft; those 

 of the latter group are referred to as soft woods, although some 

 of them are very hard. Most, but not all, of the broadleai 

 trees are deciduous, that is, they change their foliage every 

 year; and most, but not all, of the needleleaf trees are ever- 

 green, that is, the foliage is persistent. Needleleaf trees are 

 also known as conifers, that is, cone-bearers. 



It is usual to associate the terms broadleaf, deciduous, and 

 hard wood ; and likewise the terms needleleaf, conifer, ever- 

 green, and soft wood. While generally correct, this is, as 

 seen, not always so. A better division is into broadleaf trees 

 or woods, and needleleaf conifers. 



* Copies of these rules may be obtained from the secretaries of the several 

 associations. The principal series have recently been published under one cover 

 as " Forest Service Bulletin No. 71 " Hodson. This Bulletin is called " Rules 

 and Specifications for the Grading of Lumber, Adopted by the Various Lumber 

 Manufacturing Associations of the United States." Also see Trans. American 

 Soc. for Testing Materials. 



