382 GENERAL BOTANY 



commercial product of these trees, and there is much greater 

 structural variation in the hard woods than in the soft-wooded 

 gymnosperms on account of the ducts and fibers in hard wood. 

 The hard woods are all characterized by the possession of large 

 water ducts, which render the wood more porous and make it 

 less uniform in texture than is the case in spruce and pine. 

 Between the pores, as we have already learned, the wood is com- 

 posed of strong strengthening fibers and living cells, which are 



FIG. 235. Diffuse-porous woods of the sycamore and Lolly 

 Photomicrograph by R. B. Hough 



usually more abundant in the summer wood than in the spring 

 wood (Figs. 47 and 55). The large number of species of hardwood 

 trees and the great variety in the character of the wood make 

 this group of importance in supplying lumber and timbers for 

 almost every commercial purpose. Two varieties of hard wood are 

 recognized in the industries, namely, ring-porous wood and diffuse- 

 porous wood. Ring-porous wood, like that of the sassafras 

 (Fig. 234), has the spring ducts in the early spring wood, while 

 in diffuse-porous woods (Fig. 235) the ducts, or pores, are scat- 

 tered throughout the entire wood ring. In ring-porous woods 

 the annual rings are more distinct than in diffuse-porous woods. 



