The willow that children know and love the best is the pussy willow. It grows in damp or swampy places and before the leaves come out in the spring the “pussies” are seen on the branches. They are little, soft, silvery pussies, and it is not everybody who knows what they really are. [Illustration] Each “pussy” or catkin, as we must call it, is a group of small flowers, or rather flower-buds, for after the flowers are fully out the pussies lose their soft, silky appearance and no longer deserve to be called pussies. The older catkins are covered with stamens full of yellow pollen or else with seed pods. For willows bear two kinds of flowers, the stamen-bearing, or staminate flowers, and the seed-bearing, or pistillate flowers. [Illustration: Staminate catkin fully out.] The staminate flowers grow on one willow tree, and the pistillate ones on another. The pollen in the staminate flowers is very abundant and is carried by the wind or by insects to the pistillate flowers. If you shake a twig of ripe staminate catkins, your hands and clothes will be covered with pollen dust. [Illustration: Pistillate catkin.] Bees are fond of willow pollen and eagerly gather it in the early spring. The willow catkin has a tiny drop of nectar at the base of each little flower, and bees and flies are fond of this and visit the willows to get it. Of course, as the insects fly from one catkin to another, they carry pollen from one to another. After a time the staminate flowers wither and fall, but the pistillate ones are followed by seed pods, and the stem that bears them lengthens to make room for the growing pods, and at last when the seeds are ripe the pods split open and out come the _tiniest_ of little seeds, each with a tiny plume of down, and away they fly. There are a great many species of willow, and not all of them are as pretty as the pussy willow. One reason why the pussy willow is so pretty is that the catkins appear before the leaves. In some willows the catkins come with the leaves, and in some they come after the leaves are fully grown. Many willows have bright red or yellow or green stems that give color to the landscape even in midwinter. In all willows the pistillate catkins bear pods that open and let out fluffy seeds. [Illustration: Ripe willow catkin.] The cotton-wood trees are relatives of the willows. Their seeds are so very downy that when they are ripe the ground beneath the trees will often be white, as though a light snow had fallen. It is because the seeds are so abundantly supplied with soft cottony plumes that the tree is called cotton-wood. Poplars are also closely related to the willows and, like them, have fluffy seeds. In the early summer, if you look in the right place, you will see plenty of them.