Comparisons: The _Carolina poplar_, or Cottonwood (_Populus deltoides_) can be told from the Lombardy poplar by its wider crown and its more open branching, Fig. 41. It may be recognized by its big terminal twigs, which are light yellow in color and coarser than those of the Lombardy poplar, Fig. 42. Its bark is smooth, light and yellowish-green in young trees, and dark gray and fissured in older specimens. Its large, conical, glossy, chestnut-brown bud is also characteristic, Fig. 42. Its flowers, in the form of large catkins, a peculiarity of all poplars, appear in the early spring. The Carolina poplar is commonly planted in cities because it grows rapidly and is able to withstand the smoke and drouth conditions of the city. Where other trees, however, can be substituted with success, the poplar should be avoided. Its very fast growth is really a point against the tree, because it grows so fast that it becomes too tall for surrounding property, and its wood being extremely soft and brittle, the tree frequently breaks in windstorms. In many cases it is entirely uprooted, because it is not a deep-rooted tree. Its larger roots, which spread near the surface, upset the sidewalk or prevent the growth of other vegetation on the lawn, while its finer rootlets, in their eager search for moisture, penetrate and clog the joints of neighboring water and sewer pipes. The tree is commonly attacked by the _oyster-shell scale_, an insect which sucks the sap from its bark and which readily spreads to other more valuable trees like the elm. The female form of this tree is even more objectionable than the male, because in the early spring the former produces an abundance of cotton from its seeds which litters the ground and often makes walking dangerous. The only justification for planting the Carolina poplar is in places where the conditions for tree growth are so poor that nothing else will grow, and in those cases the tree should be cut back periodically in order to keep it from becoming too tall and scraggly. It is also desirable for screening in factory districts and similar situations. [Illustration: FIG. 42.--Bud of the Carolina Poplar.] The _silver_ or _white poplar_ (_Populus alba_) may be told from the other poplars by its characteristic smooth, _whitish-green bark_, often spotted with dark blotches, Fig. 43. The _leaves are silvery-white_ and downy on the under side. The twigs are dark green in color and densely covered with a white down. It grows to very large size and forms an irregular, wide-spreading, broad head, which is characteristically different from that of any of the other poplars. [Illustration: FIG. 43.--Bark of the Silver Poplar.]