120 PRACTICAL COURSE IN BOTANY 
usually consists of sapwood, which is soft and worthless as 
timber, while the dead interior forms the durable heart- 
wood so prized by lumbermen. The heartwood is useful to 
the plant principally in giving strength and firmness to the 
axis. It will now be seen why girdling a stem, — that is, chip- 
ping off a ring of the softer parts all round, will kill it, while 
vigorous and healthy trees are often seen with the center of 
the trunk entirely hollow. 
132. Different ways of cutting. — In studying the vertical 
arrangement of stems, two sections are necessary, a radial and 
a tangential one. The former passes along the axis, splitting 
the stem into halves (Fig. 135); the latter cuts between the 
axis and the perimeter, split- 
LSD ting off a segment from one 
side (Fig. 136). The appear- 
ance of the wood used in car- 
pentry and joiner’s work is due 
largely to the manner in which 
the planks are cut. 
a 133. The cross cut.— The 
1 Be section seen at the end of a log 
dime ot Gries 04, Som orton’. (Bigs, 132, 184) de walleg by 
ee bie Bice atic (from carpenters a cross cut. It 
passes at right angles to the 
grain of the wood, and severs what important structures? 
(116, 119, 122.) Examine a cross cut at the end of a rough 
plank, or the top of 
a stump or an old 
fence post, and tell 
why this kind of cut 
is seldom used in 
carpentry. 
134. The tangent 
cut is so called be- 
cause it is made at 
right angles to the ing ends of the medullary rays. 
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