. British plants : their biology and ecology. Plants; Plant ecology. FRUITS AND SEEDS 195 berry-like fruits, whether true or false—, grapes, gooseberries, hips, etc.—are to be regarded as dehiscent, the fruit being broken open by birds. The biological classification of fruits and seeds depends upon the agents of their dispersal : l. Wind-Dispersed Fruits and Seeds—{a) Fruits.—These are invariably one-seeded—, achenes and mericarps. They are either light or small, or, if large, they are- smooth, so that they may easily be rolled along over the surface of the ground. Some are specially p
. British plants : their biology and ecology. Plants; Plant ecology. FRUITS AND SEEDS 195 berry-like fruits, whether true or false—, grapes, gooseberries, hips, etc.—are to be regarded as dehiscent, the fruit being broken open by birds. The biological classification of fruits and seeds depends upon the agents of their dispersal : l. Wind-Dispersed Fruits and Seeds—{a) Fruits.—These are invariably one-seeded—, achenes and mericarps. They are either light or small, or, if large, they are- smooth, so that they may easily be rolled along over the surface of the ground. Some are specially provided with hairs or wings. The achene of the dandelion (Fig. 82) has a hairy pappus, derived from the calyx, which acts as a kind of parachute. In the thistle the pappus is sessile (Fig. 103). The achene of clematis (Fig. 104) is provided with a long feathered awn, derived from the style ; while the mericarps of the stork's-bill (Erodium) and the pelargoniums have curved awns «. Fig. 103.—Achene (Cypsela) of Fig. 104.—Achene of Clematis Thistle. with Feathery Style. furnished with a fan of spreading hairs. Winged achenes are found in the samaras of the ash (Fig. 83) and the mericarps of the sycamore and maple (Fig. 94). (6) Seeds.—These are borne in capsules, which only dehisce when the weather is warm and dry, or when it is windy. The dehiscence is caused by the desiccation of the walls or parts of the walls. In most cases the seeds are very small and light. In the poppy the capsules are shaken by the wind, and the seeds jerked out through the valves. The dust-like seeds of the orchids are the smallest known. In pods the seeds are often large— , peas and beans—but they are smooth and round, and over an even surface they may be blown along by the wind some distance from the parent plant. In a few cases the seeds are provided with special mechanisms for wind-dispersal ; in the willowherb, willow, and poplar, they are feathered, like little thistle-frui
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