Why fruits are scattered.—A flowering plant is practically confined for life to the place where it first sprang up, so that it is unable to go about and select favourable situations for its offspring. On the other hand, if the seeds simply fell to the ground beneath the parent plant, the seedlings would generally be so crowded together that they would interfere very much with each other’s growth. In addition, they would often be under a great disadvantage, because the parent plant would keep so much light from them. Hence, very many plants have some special arrangement for scattering their seeds, so that some at least of the seeds will have a chance of falling in a place where they will obtain plenty of light, air, and good soil. [Pg 171] In this section we have studied examples of devices by which plants sow their own seeds. We shall see next that other plants call in the help of the wind and of animals. 36. SEEDS SOWN BY THE WIND. 1. The fruit of the dandelion.—Examine the manner in which the tiny flowers of the dandelion are grouped together to form the head (p. 113); and make out the various parts of the flower, especially the ovary—a little white knob at the bottom of the flower, and the calyx-tube—forming a tuft of fine hairs above the ovary. Trace the development of the fruits: the withering of the corollas and stamens, the elongation of the calyx-tube, and the expansion of the tuft of hairs to form a parachute. Blow a dandelion “clock” (the head of fruits), and notice how the parachutes float the fruits in the air. Examine “thistle down” and contrast it with the dandelion fruit. 2. The fruit of the willow.—Examine the ripened catkins of a female willow in June, and notice how each fruit has split into halves, which come apart and expose the silky seeds inside. Pull a tuft of seeds out and dry them in the sun. Notice that they wriggle and writhe about and gradually become entangled together into a woolly mass, which is easily blown away. 3. The elm fruit.—About the end of April look for elm fruits. Notice the flat green plate (wing) with the rounded swelling near the middle (Fig. 124, 5). Cut open the fruit and see that the swelling is caused by a single seed. How does the flat wing aid in the distribution of the seed? Compare the winged fruits of the ash and sycamore (Fig. 137). Do these winged fruits drop from the trees easily, or are they torn off by gales? Take a pair of sycamore fruits. Cut off the wing from one and let it and an uninjured fruit fall at the same instant from a height. Which reaches the ground first? Why? 4. Pine and fir cones.—Examine and compare pine and fir cones [Pg 172] of various ages. Break open a ripe cone and see the scales with the pairs of naked seeds, each seed bearing a thin, papery wing which has split off from the upper surface of the scale. Fig. 136.—“Clock” of Dandelion Fruits. (× ¼.)