250 INDUSTRIAL PLANTS 
its separation into more or less delicate strands when crushed. 
Those who have had experience in chopping wood know that 
the ax cleaves as a rule most easily when cutting toward the 
center of the log; less easily in any other lengthwise direc- 
tion, and least easily when directed slantingly or directly 
across the grain. This shows that the structural parts have 
a peculiarly definite arrangement. Something of this appears 
when we examine, for example, with a strong magnifier, the 
surface of a piece of pine wood, cut radially, 7. e., toward 
the center of the log. We see, as shown in Fig. 229, that the 
wood is made up mainly of very slender, thin-walled tubes 
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Fic. 229.—Radial section of white pine wood. Magnified about 50 diame- 
ters. (Original.) 
each closed and tapering at the ends; and besides these are 
numerous flat bundles of much smaller tubes running at 
right angles to the others and radially. These bundles of 
finer structure are called pith-rays because they are some- 
what similar in texture to a cylinder of pith in the center 
of the log, and some of them at least, are extensions of it. 
Their relative softness makes the wood most easily separated 
along the planes in which they lie. Even to the naked eye 
their peculiar sheen makes the pith-rays apparent on a radial 
surface, and gives an especially attractive prominence to 
them in what the dealers call “‘ quarter-sawed ”’ timber. It is 
plain also that the fibrils, by which name we shall understand 
