U. S. DEPARTMENT OF AGRICULTURE. 
LOCALITIES WHERE GROWN. 
Iii the second column of the tables are listed the States in which the 
test specimens originated. The locality of growth has in some cases 
an influence on the strength of timber. This influence is, however, 
usually overestimated; just as great differences exist ordinarily 
between stands of different character grown in the same section of 
the country as between stands grown in widely separated regions. 
For this reason it is considered better to average the various localities 
together. Douglas fir, however, has not been averaged in this man- 
ner. Silviculturists have recognized that there are two well-marked 
types 1 and various intergradations of Douglas fir. Strength tests 
confirm this fact and show that there is actually a difference in strength 
between the Rocky Mountain and Pacific Coast types of Douglas 
fir. For this reason averages are given for the Coast and for the 
Rocky Mountain regions rather than for the species as a whole. 
NUMBER OF TREES. 
The number of trees from which test specimens were taken is given 
in the third column of Table 1. As previously mentioned, five is the 
usual number from a single locality. 
NUMBER OF RINGS PER INCH. 
Rings per inch is an inverse measure of the rate of growth. It is 
taken along a radial fine on the end section of each specimen. One 
ring, consisting of a band of springwood and a band of summerwood, 
is formed by each year's growth; consequently, few rings per inch 
indicate fast growth, and vice versa. 
Rate of growth is extremely variable, and the values given are to 
be taken as averages of the material tested only. Rate of growth 
has no definite relation to strength in the sense of strength being in 
proportion, either directly or inversely, to the rate of growth. Tim- 
ber of any species which has grown with exceptional slowness is 
usually below the average of the species in strength values. In the 
coniferous species material of very rapid growth is also very likely 
to be below the average in strength. Among many of the hardwood 2 
species, however, timber of rapid growth is usually above the average 
in strength properties. 
1 See Forest Service Circular 150, "Douglas Fir: A Study of the Pacific Coast and Rocky Mountain 
Forms." 
2 A broad classification of timber species divides them into two groups: (1) Angiosperms, or trees with 
broad leaves, usually deciduous, the so-called "hardwoods"; (2) gymnosperms, or trees with needle or 
scalelike leaves, usually evergreen, most of them cone bearing, the so-called "softwoods." The two groups 
are popularly spoken of as "hardwoods" and "softwoods," or "hardwoods" and "conifers." The terms 
"hardwoods" and "softwoods" are therefore indicative of botanical classification and are not descriptive 
of the quality of the wood with respect to hardness. Such "hardwoods" as basswood and aspen are low 
in the scale of hardness; while the southern pines, tamarack, larch, and others, although called "softwoods," 
are quite hard. 
