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width (fig. 5). They are tapered and closed at their ends, polygonal, or 

 rounded and thin walled, with large cavity, lumen 

 or internal space in the spring wood, thick walled 

 and flattened radially with the internal space or 

 lumeD much reduced in the summer wood. (See 

 right-hand portion of fig. 4). This flattening, 

 together with the thicker walls of the cells which 

 reduces the lumen, causes the greater firmness 

 and darker color of the summer wood— there is 

 more material in the same volume. As shown in 

 the figure, the tubes, cells, or "tracheids" are 

 decorated on their walls by circlet- like struc- 

 tures, the " bordered pits," sections of which are 

 seen more magnified at a, b, and c, fig. 4. These 

 pits are in the nature of pores, covered by very 

 thin membranes, and serve as waterways between 

 the cells or tracheids. 



The dark lines on the side of the smaller piece 

 (1, fig. 4) appear when magnified (in 2, fig. 4) as 

 tiers of 8 to 10 rows of cells, which run radially 

 (parallel to the rows of tubes or tracheids) and 

 are seen as bands on the radial face and as rows 

 of pores on the tangential face. These bands or 

 tiers of cell rows are the medullary rays or pith 

 rays, and are common to all our lumber woods. 

 In the pines and other conifers they are quite 

 small, but they can readily be seen, even without 

 a magnifier, if a radial surface of split wood (not 

 smoothed) is examined. The entire radial face 

 will be seen almost covered with these tiny struc- 

 tures, which appear as fine but conspicuous cross 

 lines. As shown in fig. 4 the cells of the med- 

 ullary or pith rays are smaller and very much 

 shorter than the wood fibers or tracheids and 

 their long axis is at right angles to that of the 

 fibers. In pines and spruces the cells of the 

 upper and lower rows of each tier or pith ray 

 have "bordered" pits like those of the wood 

 fibers or tracheids proper, but the cells of the 

 intermediate rows, and of all rows in the rays of 

 cedars, etc., have only •' simple" pits, i. e., pits 

 levoid of the saucer-like "border" or rim. 



In pine, many of the pith rays are larger than 

 the majority, each containing a whitish lme, the 

 horizontal resin duct, which, though much 

 smaller, resembles the vertical ducts seen on the 

 cross section. The larger vertical resin ducts are best observed on 

 3521— No. 10 2 



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