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 woods of medium growth afford stronger material than when very rapidly or very slowly grown.  In many uses of wood, strength is not the main consideration.  If ease of working is prized, wood should be chosen with regard to its uniformity of texture and straightness of grain, which will in most cases occur when there is little contrast between the late wood of one season’s growth and the early wood of the next.

HEARTWOOD AND SAPWOOD

Examination of the end of a log of many species reveals a darker-colored inner portion—­the heartwood, surrounded by a lighter-colored zone—­the sapwood.  In some instances this distinction in color is very marked; in others, the contrast is slight, so that it is not always easy to tell where one leaves off and the other begins.  The color of fresh sapwood is always light, sometimes pure white, but more often with a decided tinge of green or brown.