in the background. An exogenous stem may be said to consist of a central pith, seen best during the first years and often thereafter 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 ordinary drying. These thin, shiny, radiating plates of cells lying between the ordinary tissue of the wood give to some sorts of timber its beauty and value. Oak in all its strength would be lacking 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 instanced 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 flecked, as shown in Fig. 7, a sample of the river birch. This wood is
Fig. 7.—Cross Section of River 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
