The _bark_ on the trunk is frequently one inch thick, dark
grayish-brown, and broken by shallow fissures into flat ridges. The
inner bark is used to some extent for medical purposes, as it is
fragrant and when chewed, affords a slippery, mucilaginous substance,
whence the tree gets its name. The _winter buds_ are large and
conspicuously rusty-hairy.
The _leaves_ are simple, alternate on the stem, 4 to 6 inches in length,
sharp pointed, their bases unsymmetrical, doubly-toothed on the edges,
thick, dark green, and rough on both sides.
The _fruit_ consists of a seed surrounded by a thin, broad, greenish
wing, about one-half an inch in diameter; the _flowers_ appear in early
spring and the fruit ripens when the leaves are about half-grown.
The _wood_ is close-grained, tough, strong, heavy, hard, moderately
durable in contact with the soil. It is used for fence posts, crossties,
agricultural implements, ribs for small boats and for some other
purposes.
The water elm, _Planera aquatica_ Gmel., is a small tree with slender
branches forming a low broad head and is found in swamps in the valley
of the Wabash River in this State. It reaches its best development in
Arkansas and Louisiana. It has dull green leaves 2 inches long and 1
inch wide. The fruit is an oblong, dark brown drupe.
+HACKBERRY+ _Celtis occidentalis_ L.
THE rough-leaved hackberry is found sparsely throughout the State. It
occurs most abundantly and of greatest size in the rich alluvial lands
in the lower part of the State, but thrives, however, on various types
of soil, from the poorest to the richest. It is usually a medium-sized
tree from 30 to 50 feet high and 10 to 20 inches in diameter, but trees
3 feet in diameter are found in the Wabash bottoms in southern Illinois.
Its limbs are often crooked and angular and bear a head made of slender,
pendant branches or short, bristly, stubby twigs. In the open the crown
is generally very symmetrical. It makes an excellent shade tree.
[Illustration: HACKBERRY