STRUCTURE OF BROAD-LEAVED WOODS. 



19 



those of the spring wood in oak being the most conspicuous (see fig. 7); 

 so that in an oak table the darker, shaded parts are the spring wood, 

 the lighter, unicolored parts the summer wood. 



On closer examination of the smoothed cross section of oak, the 

 spring wood part of the ring is found to be formed, in great part, of 

 pores : large, round, or oval openings made by the cut through long 



Fig. 8 A Cross section of oak magnified about 5 times. 



vessels. These are separated by a grayish and quite porous tissue 

 (see fig. 8 A), which continues here and there in the form of radial, often 

 branched, patches (not the pith rays) into and through the summer 

 wood to the spring wood of the next ring. The large vessels of the 

 spring wood, occupying 6 to 10 per cent of the volume of a log in very 

 good oak, and 25 per cent or more in 

 inferior and narrow-ringed lumber, are a 

 very important feature, siuce it is evi- 

 dent that the greater their share in the 

 volume, the lighter and weaker the wood. 

 They are smallest near the pith, and grow 

 wider outward; they are wider in the 

 stem than limb and seem to be of in defi- 

 nite length, forming open channels in 

 some cases probably as long as the tree 

 itself. 



Scattered through the radiating gray 

 patches of porous wood are vessels simi- 

 lar to those of the spring wood, but 

 decidedly smaller. These vessels are fig. 8 b.— Portion of the firm bodies of 

 usually fewer and larger near the spring fibers wi * h . *T° cells ° f ' a 8ma11 pith 



, ., , act ray mr Highly magnified. 



wood, and smaller and more numerous 



in the outer portions of the ring. Their number and size can be util- 

 ized to distinguish the oaks classed as white oaks from those classed as 

 black and red oaks; they are fewer and larger in red oaks, smaller but 

 much more numerous in white oaks. The summer wood, except for 

 these radial grayish patches, is dark colored and firm. This firm por- 

 tion, divided into bodies or strands by these patches of porous wood 



