we 
In the ‘‘ diffuse porous” woods (see figs. 4 and 5) like birch, poplar, 
gum, tulip, willow, etc., the rings are generally less conspicuous, being 
defined by a mere line, often scarcely perceptible in the fresh wood, 
and due to the fact that the outermost cells of the summer wood are 
always small, flattened in form, and usually have thick walls, while 
the adjoining innermost cells of the spring wood of the neighboring 
ring are much larger, not flattened, and always have thin walls, the 
effect being much increased by the regularity of the line along which 
these two forms of elements meet or touch each other. 
The annual rings in a tree grown in a park or under generally 
favorable conditions are widest near the base, and become narrower 
upward in the stem; and they are also widest near the pith, growing 
more and more 
narrow toward 
the bark. The 
same is true 
generally, but 
is often some- 
what reversed, 
especially in 
trees like the 
balsam, spruce, 
and oak, if the 
trees are shaded 
or otherwise 
hampered when 
young. 
In their width, 
the annual 
rings differ; oc- 
casionally they 
are half an inch 
and more wide; 
commonly they 
average from 
Fie. 2—Wood of spruce: 1, natural size; 2, small part of one ring mag- one-eighth inch 
nified 100 times (the vertical tubes are wood fibers, in this case all tO three-eighths 
_ “tracheids”’); m, medullary or pith rays; 7, transverse tracheids of inch in hard- 
pith rays; a, b, and c, bordered pits of the tracheids, enlarged. 
woods, and 
from one-twentieth inch to one-eighth inch in conifers, and cases 
are not rare where a whole century’s growth of a spruce or balsam 
amounts to but two to three inches on the radius of the stem. 
In all young, sound, and thrifty timber the rings are laid on with 
the utmost regularity and a cross section of a stem furnishes, there- 
fore, not only information as to the age of the given section, but is a 
