18 BULLETIN 933, U. S. DEPARTMENT OF AGRICULTURE. 
growth. The bark of a rapidly growing walnut tree is thin and reticu- 
lated in some places almost as much as the bark of ash ; but, as a rule, 
the ridges and furrows are much larger and less regular, and the retic- 
ulation is not apparent. The color of the bark from inside to outside is 
always dark, being almost black when it is wet after a rain. On slow- 
growing old trees the bark becomes several inches thick and is broken 
up into irregular blocks b}^ transverse cracks. This is especially true 
toward the southwestern limits of the walnut range' in Texas ; and 
there the color becomes lighter, being a reddish brown in. some locali- 
ties. The darker bark, as well as the greater straightness of bole and 
better general symmetry, are, however, usually sufficient when leaves 
and fruit are absent to distinguish walnut from butternut, or white 
walnut, as it is called in some sections. 
LEAVES, FLOWERS, AND NUTS. 
The leaves are pinnate, from 1 foot long on forest-grown trees 
to 2 feet on vigorous trees in the open, with from 15 to 23 leaflets, 
smooth and light shiny green above, paler and somewhat hairy 
below. The leaves closely resemble those of butternut and, to a 
less extent, those of ailanthus. In the midsummer the tree is very 
ornamental, but because the leaves are put out late the winter ap- 
pearance continues for a relatively long time. 
Flowers are borne at the same time the leaves begin to develop, 
the staminate or male flowers in catkins 3 to 5 inches long, and the 
pistillate or female flowers in inconspicuous clusters of two to five 
greenish flowers, on the ends of the branches. Only one or two of 
these pistillate flowers develop into nuts. The mature nuts are 
round to pear-shaped and 1J to 2 inches in diameter outside the 
greenish fleshy husk that incloses them. The nut proper is nearly 
spherical, with many ridges roughening the surface. The value of 
the nuts as articles of sale is variable. Although in general the 
nuts have meats moderate in size and difficult to remove from the 
shell, the nuts from certain trees are exceptional both as to size 
and cracking qualities. The trees that provide these exceptional 
nuts are of value in developing special horticultural varieties. 
SILVICAL CHARACTERISTICS. 
SOIL AND MOISTURE REQUIREMENTS. 
The requirement of black walnut for fertile, moist, but well- 
drained soils has already been discussed. This requirement should 
be kept in mind in selecting sites for the planting of walnut. In 
addition, because of the deep root system of walnut the subsoil 
underlying the planting site should be of a porous texture to a 
corresponding depth. A dry atmosphere does not seem greatly to 
