nd spokes. Here not only strength, but
toughness and resilience are important. The results of a series
of tests on hickory by the U.S. Forest Service show that "the
work or shock-resisting ability is greatest in wide-ringed wood
that has from 5 to 14 rings per inch, is fairly constant from 14
to 38 rings, and decreases rapidly from 38 to 47 rings. The
strength at maximum load is not so great with the most
rapid-growing wood; it is maximum with from 14 to 20 rings per
inch, and again becomes less as the wood becomes more closely
ringed. The natural deduction is that wood of first-class
mechanical value shows from 5 to 20 rings per inch and that
slower growth yields poorer stock. Thus the inspector or buyer
of hickory should discriminate against timber that has more than
20 rings per inch. Exceptions exist, however, in the case of
normal growth upon dry situations, in which the slow-growing
material may be strong and tough."[20]

[Footnote 20: Bul. 80: The commercial hickories, pp. 48-50.]

The effect of rate of growth on the qualities of chestnut wood
is summarized by the same authority as follows: "When the rings
are wide, the transition from spring wood to summer wood is
gradual, while in the narrow rings the spring wood passes into
summer wood abruptly. The width of the spring wood changes but
little with the width of the annual ring, so that the narrowing
or broadening of the annual ring is always at the expense of the
summer wood. The narrow vessels of the summer wood make it
richer in wood substance than the spring wood composed of wide
vessels. Therefore, rapid-growing specimens with wide rings have
more wood substance than slow-growing trees with narrow rings.
Since the more the wood substance the greater the weight, and
the greater the weight the stronger the wood, chestnuts with
wide rings must have stronger wood than chestnuts with narrow
rings. This agrees with the accepted view that sprouts (which
always have wide rings) yield better and stronger wood than
seedling chestnuts, which grow more slowly in diameter."[21]

[Footnote 21: Bul. 53: Chestnut in southern Maryland, pp.
20-21.]

In diffuse-porous woods, as has been stated, the vessels or
pores are scattered throughout the ring instead of collected in
the early wood. The effect of rate of growth is, therefore, not
the same as in the ring-porous woods, approaching more nearly
the conditions in the conifers. In general it may be stated that
such woo