CIRCULAR NO. 16. 
United States Department of Agriculture, 
DIVISION OF FORESTRY. 
AGE OF TREES AND TIME OF BLAZING DETERMINED BY ANNUAL 
RINGS. 
THE ANNUAL RING. 
In all the timber trees of the temperate portion of our country the 
wood of the stem is laid on in sheets or layers which, on any cross 
section, appear as so many concentric rings. Generally these rings 
are sufficiently well defined to be readily counted, and since only one 
is formed each growing season they furnish a very convenient record 
of the age of the particular cross section and, if properly chosen, of 
the age of the tree. 
Viewing a cross section of the stem of a pine, fir, cedar, etc., these 
concentric yearly rings appear as alternate narrow bands or lines of 
lighter and darker color, the dark line, or ‘‘ summer wood,” occupying 
W SCHOLL.OEL 
Fig. 1.—‘* Nonporous” woods: A, fir; B, ‘‘hard” pine; C, soft pine; a. 7., annual ring; 0. e., 
outer edge of ring; i. e., inner edge of ring; s.w., summer wood; sp. w., spring wood; r. d., 
resin ducts. 
the outer portion of any one ring and being sharply contrasted 
against the lightest portion of the inner, lighter, or ‘‘spring wood,” 
part of the next ring. (See fig. 1, especially B, and also fig. 2.) 
In oak, ash, elm, hickory, locust, and other ‘‘ring-porous woods ” 
(see fig. 3), these rings are conspicuous through rows of pores, each 
row occupying the inner, or spring wood, part of a ring and being 
separated from the row of pores of the next ring by wood practically 
devoid of large pores. (See fig. 2.) 
