THE PRINCIPAL SPECIES OF WOOD. 



INTRODUCTION. 



A KNOWLEDGE of the properties of the substances employed 

 in construction causes confidence and permits smaller margins 

 beyond calculated requirements than would otherwise be 

 possible. 



Wood is one of the primary materials of construction; the 

 others are stone and iron. These principal substances possess 

 distinguishing peculiarities, and each one includes a series of 

 individuals that are also distinguished from one another by 

 reason of minor characteristics. Iron thus includes the steels 

 and cast irons, while stone includes brick, concrete and other 

 artificial products, as well as sandstones and granites that cccur 

 in nature. Wood differs from the other primary structural 

 substances. It is the only one that is organic. 



Information relating to the general properties of wood is as 

 desirable as information relating to properties of steel, stone or 

 cement. Engineers use more wood than any other set of 

 men, yet general facts aside from those relating to strength 

 are often associated with the province of the botanist or 

 forester. 



Wood is the solid part of trees, the part that, when other- 

 wise suitable, is used in construction. It consists of a ground- 

 work of starch-like substance known as cellulose* permeated 

 by materials collectively known as lignin; there are also secre- 



* Flax is almost pure cellulose. 



