31. THE WILLOW AND THE POPLAR.
1. The willow.—About the third week in March, examine willow trees, and notice the soft, round, silky bodies which spring alternately on the young twigs. On some trees these are broad and yellow; they are male catkins ([Fig. 120]). Pick off a flower and see the stamens (generally two stamens to each flower) inserted on a small silky bract ([Fig. 121], B). With a lens look for the honey cup at the bottom of the bract.
On other trees notice the long, narrow, silvery female catkins. Pick off a flower to see the single pistil with the forked style, also on a small, honeyed bract. Have you ever seen bees visiting the flowers? Are the catkins as conspicuous when the trees are in leaf? Is it an advantage to the trees to flower before the leaves come out? In June, examine the ripened female catkins. Pull out a tuft of the hairy seeds and dry it in the sun, noticing how they form a fluffy mass. Blow the mass of seeds. How do you think the seeds are dispersed?
2. The poplar.—Find male and female poplars and examine their flowers. Are the female flowers pollinated by insects or by the wind? Is self-fertilisation ever possible with willows and poplars? Why not? Which appear first, the flowers, or the leaves of poplars? Why?
Examine the leaves of the English poplar. Why do they turn over so easily, even with a very slight breeze? Are both sides of the leaf of the same colour?
Compare the Lombardy poplar with the English poplar.
The willow.—Many species of willow are known, but the sallow willow—called the saugh tree in Scotland—is common in coppices 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).