250 



INDUSTRIAL PLANTS 



its separation into more (jr less delicate strantls when erushed. 

 Those who have had experience in chopping wood know that 

 the ax cleaves as a rule most easily when cutting to-ward 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, ('. 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 



»liiilll!!IM li I'lif" 



Fu;. 2129. — R;L(.li:il .sc-etioii of wiiitc pim- wood. Ma^^iiifiod about 50 diame- 

 ters. ie>ri>j;iiial-) 



each clo.sed and tapering at the emls; and besides these are 

 numerous flat bundles of much smaller tubes running at 

 right angles to the others and rai-liall>-. These bundles of 

 finer structure are called pitJi-niijK because they ar(^ .some- 

 what similar in texture to a cylinder of piUi in the center 

 of the log, anil .some of them al least, are extensions of it. 

 Their relative softn(>ss makes the wood most easily separated 

 along the ])lanes in which they lie. Even to the n:ik<'d e\'e 



tlieir ])i'ciiliar si n makes the ])ith-rays :ii)i)arent on a radial 



silffaee, and gi\'es an es|)eeiall\' at(racti\'e |)ri)minence to 

 them in what the dealers (•.•ill " (|uarter-sawed " timber. It is 

 plain als(j that thv Jtliril--<, by which name we shall understand 



