SUNSHINE THROUGH THE WOODS, 321 



in the background. An exogenous stem may be said to consist 

 of a central pith, seen best during the first years and often there- 

 after disappearing, and an outer ring of pithlike substance, the 

 inner bark, and a series of plates connecting the two, also of the 

 nature of pith. These thin plates separate incompletely the wood 

 into wedges, and on account of them it often splits more easily 

 in radial lines than in others, and may crack along them in ordi- 

 nary drying. These thin, shiny, radiating plates of cells lying 

 between the ordinary tissue of the wood give to some sorts of tim- 

 ber its beauty and value. Oak in all its strength would be lack- 

 ing in much of its peculiar attractiveness were the silver grains 

 absent. Fig. 6 shows a radial, longitudinal section of the pin oak 

 with a few of these plates in view. They are usually small in 

 area and appear in the finished article of furniture as shining, 

 smooth patches, no two of the same size or shape. The beauty of 

 this system of radiating plates is often enhanced by a curling and 

 twisting, due to small knots scattered through the wood, as in- 

 stanced in some sorts of maple, as the so-called "bird's-eye," a 

 most attractive wood for finishing. 



The birch is a good illustration of the wood being necked, 

 as shown in Fig. 7, a sample of the river birch. This wood is 



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FIG. 7. CROSS SECTION OF RIVEB BIRCH. 



peculiar in the absence of any conspicuous medullary rays, and of 

 prominent vascular areas in the annual rings, and therefore with 

 the exception of the pithy patches, the wood is quite uniform 

 throughout ; but the coloration characteristics of the heart may 

 appear upon one side of the center like a radiating fan, thus 

 showing that the change of color is far from constant, and does 

 not depend upon the wood having reached a certain fixed age. 

 Many other sections of wood might be shown, and each in its 



