2 BULLETIN 316, IT. S. DEPARTMENT OF AGRICULTURE. 
THE TREE AND ITS FORMS. 
The botanical name of the willow genus, Salix, comes from the 
Celtic sal, meaning near, and lis, water. The poplar is a genus of 
the same family. Both have more species and wider distribution 
in North America than on any other continent, the willows being 
more widely distributed than the poplars but less generally attaining 
tree size. 
The fruit of this group is the characteristic by which it is most 
easily distinguished. In both genera it is a catkin an inch or more 
long, made up of capsules borne on a stalk and containing a cottony 
mass to which are attached numerous minute seeds. The catkins 
of the willow are smaller than those of the poplar and are generally 
erect; those of the poplar are generally pendant. In both cases the 
seed has a tuft of silky hairs attached to the base. When the cap- 
sules open the tiny seeds are borne up by the cottony hairs and 
carried long distances by the wind. Willow seed consists of the bare 
embryo or new plant and is protected by a very thin covering. It 
germinates in a few hours in a moist place; but if it fails to secure 
this condition, it loses the power of germination in two or three days. 
The willows can be distinguished from the poplars by their leaves, 
the poplars having typically long-stalked wide leaves; the willows, 
short-stalked narrow ones. Willow leaves occur alternately on the 
branches. There are several scales on each winter bud of the poplar, 
but only one on each willow bad. 
The willows do not normally develop a strong taproot. However, 
those grown on dry upland situations and some of the drought- 
resistant species form semitaproot systems. Usually willows grow 
in moist situations and places where the water table is near the 
surface; so the root system is shallow, spreading, and fibrous. 
The bark of the different species of tree willows is very much the 
same, and does not furnish an obvious means of distinguishing them, 
except in the case of the sandbar willow, which has almost smooth 
bark even in trees of considerable size. 
The characteristics on which botanists separate the species are 
largely differences in the tiny flowers and the almost microscopical 
variations in the leaf parts. Several species are easily identified by 
the size, shape, or color of the leaves, but the majority have very 
similar gross characteristics. 
BLACK WILLOW. 
(Salix nigra Marsh.) 
The black willow is by far the most important of the native species. 
In the region of its best development trees have been found 4 feet in 
diameter at breastheight and 140 feet in height. The leaves are 
