The willow.—Many species of willow are known, but the sallow willow—called the saugh tree in Scotland—is common in coppices [Pg 151] and hedges. It has purplish brown branches, and large, broad, downy leaves. In the willow the male and female flowers are produced on different trees, so that self-fertilisation is obviously impossible. The flowers of the male willow form broad yellow catkins which cling closely to the twig (Fig. 121). They are often called “golden palms.” Each flower consists of two stamens, borne on a silky scale which has a tiny honey cup at the base. The female flowers form long, narrow, and silvery catkins; each flower is merely a single pistil with a forked stigma, and, like a male flower, is supported on a small honeyed bract. The flowers appear in March, before the leaves, and the catkins are very conspicuous. They are visited by bees for the sake of the honey and pollen, pollination being thus effected. In June, the female catkins are ripe. Each ovary has now become a fruit, which opens and liberates the silky seeds. When the seeds dry, their fine hairs cling together so that a light fluffy mass is formed, which can be blown to great distances by the wind. Fig. 120.—Twig of male Willow, with catkins. (× ⅙) Fig. 121.—The Willow. A, flowering male-shoot (× ⅔); B, male flower with bract (magnified); C, female cone; D, E, female flowers (magnified); F, fruit (× ⅔); G, the same magnified; H, seed (magnified). The poplar.—The various poplars are also completely unisexual, that is, any one tree bears either male or female flowers, but not both. In this case also the flowers appear before the leaves; but the flowers are pollinated by the aid of the wind, not by insects, and nectaries are therefore not formed. The catkins are not very much like those of the willows in appearance, but the fruit and seeds are [Pg 152] very similar. Both willows and poplars are fond of the banks of streams. The English poplars are graceful trees which can be recognised at a distance by the manner in which the broad leaves turn on their long stalks, exposing the lighter-coloured under-surface at the slightest breath of wind. This is especially noticeable with the aspen or trembling poplar (Fig. 122). The Lombardy poplar is a tall, stiff tree. Fig. 122.—The Poplar. 1, male catkin (× ⅔); 2, female catkin (× ⅔); 3, male flower (× 2); 4, female flower (× 4); 5, the same in longitudinal section; 6, fruit; 7, the same after opening; 8, seeds (× 3); 9, diagram of male flower. 32. THE ELM, LIME, AND ASH. 1. The elm.—Notice the straight trunk, rough bark, and slender branches of the common elm. Examine the flowers in early spring and notice that each contains both stamens and pistil. When do the flowers open? When do the leaves expand? Draw a leaf and a fruit. What is the use of the broad plate of the fruit?