The Black Poplar (_Populus nigra_) appears to be so called not by reason of any blackness of leaf or bark, but because of the absence of any white or grey down on the underside of its leaves. Its bark is grey, like that of the species already mentioned, but readily distinguished from them by the great swellings and nodosities that mar the symmetry of its trunk. It is a tree of erect growth, fifty to sixty feet in height, with horizontal branches, and leaves that vary in shape from triangular and rhombic to almost circular, and in width from an inch to four inches. They have rounded teeth on the margins, which are at first also fringed, and in their young state the underside is silky. The flowers in the catkins of this and the next species are not so densely packed. Those of the male are two or three inches in length, and dark red in colour; their abundance before the tree has put out its leaves makes the male tree a conspicuous object. The female catkins are shorter and do not droop. When the roundish capsules burst in May or June to distribute their seeds, the white cotton with which the latter are invested gives prominence to the female tree. The wood is chiefly used by the turner; in Holland, where it is extensively cultivated, it provides the material for sabots. The Black Poplar is not a native of this country, but it is generally distributed throughout Europe and Northern Asia. The date of its introduction is not known, but it has been here for many centuries, and is quite naturalized, springing up on river banks and in other moist situations. Some botanists regard it as only a variety of the Lombardy Poplar, but apart from the very different habit of the tree--not by itself sufficient grounds for separation--there is the more important fact that the Black Poplar rarely produces suckers from its roots, whilst the Lombardy Poplar does so constantly. However, this is a point we can leave for the botanists to discuss; for the purposes of this book the two trees are sufficiently distinct to be treated separately.