GRAIN OF WOOD. 21 



are too small to be distinguished. Studied with the microscope, 

 each vessel is found to be a vertical row of a great number of short, 

 wide tubes, joined end to end (fig. 9, c). The porous spring wood and 

 radial gray tracts are partly composed of smaller vessels, but chiefly 

 of tracheids like those of pine, and of shorter cells, the a wood paren- 

 chyma," resembling the cells of the medullary rays. These latter, as 

 well as the fine concentric lines mentioned as occurring in the summer 

 wood, are composed entirely of short, tube-like parenchyma cells with 

 square or oblique ends (fig. 9, a and b). The wood fibers proper, which 

 form the dark, firm bodies referred to, are very fine, threadlike cells 

 one twenty-fifth to one-tenth inch long, with a wall commonly so thick 

 that scarcely any empty internal space or lumen remains (figs. 9, e, 

 and 8, B). 



If instead of oak a piece of poplar or basswood (fig. 10) had been 

 used in this study, the structure would have been found to be quite 

 different. The same kinds of cell-elements, vessels, etc., are, to be 



Fig.IO.— Cross section of basswood (magnified), v, vessels; mr, pith rays 



sure, present, but their combination and arrangement is different, and 

 thus from the great variety of possible combinations results the great 

 variety of structure and, in consequence, of the qualities which distin 

 guish the wood of broad-leaved trees. The sharp distinction of sap 

 wood and heartwood is wanting; the rings are not so clearly defined, 

 the vessels of the wood are small, very numerous, and rather evenly 

 scattered through the wood of the annual ring, so that the distinction 

 of the ring almost vanishes and the medullary or pith rays, in poplar, 

 can be seen, without being magnified, only on the radial section. 



DIFFERENT GRAIN OF WOOD. 



The terms "fine grained," "coarse grained," "straight grained" 

 and "cross grained" are frequently applied in woodworking. In com- 

 mon usage, wood is "coarse grained" if its annual rings are wide, 

 "fine grained" if they are narrow; in the finer wood industries a "fine- 

 grained" wood is capable of high polish while a "coarse-grained" wood 



