

THE WOOD. 38 
be the increase. Careful measurements on a simple plot of 336 
acres on a cut-over area on the Coconino National Forest showed 
that of trees 10 inches and over in diameter, there were at present on 
the area 2,644 blackjacks, averaging 15.9 inches in diameter, and 
814 yellow pine, averaging 21.7 inches. From Table 10 it is seen 
that a blackjack with a diameter of 15.9 inches will in 20 years grow 
to a diameter of 18.35; while a yellow pine, with a diameter of 21.7 
inches, will grow to a diameter of 23 inches in the same period. 
Using volume Tables 29 and 30, these mean trees have a volume of 510 
board feet, and will have in 20 years a volume of 808 board feet, 
showing a growth in volume for the 20 years of 63 per cent, or 3.15 
per cent per year. This calculation does-not allow for loss through 
lightning and decay, but since the total volume of blackjack and 
yellow pine at present classed as unhealthy amounts to 6,660 and 
24,490 board feet, respectively, it is apparent that the growth would 
equal at least 2 per cent per year. This figure, of course, is for very 
favorable situations, where the total volume of blackjack is prac- 
tically equal to the total volume of yellow pine left after cutting. 
THE WOOD. 
STRUCTURE.* 
A discussion of the characteristics of western yellow pine wood is 
presented here as an aid in the identification and for a better under- 
standing of its variable qualities. The characters helpful in recog- 
nizing the wood are treated under two heads: (1) The gross char- 
acters, and (2) the microscopic characters. Under the first head are 
considered such general characters as can readily be seen with the 
unaided eye or with a pocket lens magnifying from 4 to 6 diameters, 
while under the second is presented a full discussion of the minute 
‘structural characters of the wood. 
GROSS CHARACTERS. 
While generally the wood of western yellow pine is hard, com- 
pared with that of white pines, a good many trees yield wood closely 
resembling white pine in color, weight, and softness. However, in 
all grades of western yellow pine the late wood, the hardest part of 
the annual rings, is more pronounced, and therefore darker and 
harder than that of white pine, which has a more uniform structure. 
The heartwood of western yellow pine, very variable, but usually 
hard, is moderately heavy (30 pounds per cubic foot kiln dried), 
strong, and light reddish-brown in color. The sapwood is nearly 
white, usually varying from 3 to 6 inches in thickness (from 100 to 
900 annual rings of growth). 

1 Prepared by George B. Sudworth, dendrologist, and C. D. Mell, assistant dendrologist, 
Forest Service. 
5998°—Bull. 101—11—-—3 




