Figure 8.26 Sedge adaptation to water dispersal. A. A sedge plant. B. A sedge fruit. The seed is enclosed within an inflated covering that enables it to float on water.
fruits are beached before this occurs to ensure the survival of the species. The best known of ocean-dispersed plants is the coconut palm, whose large fruits apparently have been carried many hundreds of kilometers throughout the tropical seas of the world.
Fruits of some legumes, touch-me-nots, and members of other families mechanically eject seeds, sometimes with considerable force. For example, the splitting action of drying witch hazel capsules may fling the seeds over 12 meters (40 feet) away. Fruits of dwarf mistletoes may be violently released in response to the heat of a warm-blooded animal coming close to the plants. In fact, small welts have been raised by dwarf mistletoe fruits on the skin of humans who ventured close to the plants. In manroots and a few other members of the Pumpkin Family (Cucurbitaceae), the seed release resembles a geyser eruption as a frothy substance containing the seeds squirts out of one end of the melonlike fruits.
In filarees and other members of the Geranium Family (Geraniaceae), each carpel of the fruit splits away and curls back from a central axis. Each fruitlet consists of a single, pointed seed with a long, slender tail that is sensitive to changes in humidity (Fig. 8.27). At night when the humidity increases, the tail is relatively straight, but in the sun, it coils up like a corkscrew, literally drilling the pointed seed into the ground as it does so and effectively planting it in the process.
bank, carrying whole plants and their fruits to new locations. Large raindrops themselves may splash seeds out of their opened capsules.
Seeds and fruits of a few plants have thick, spongy pericarps that absorb water very slowly. Such fruits are adapted to dispersal by ocean currents, even though salt water eventually may penetrate enough to kill the delicate embryos. Enough
Figure 8.27 Filaree (Erodium) fruitlets. A. Under humid conditions. B. Under dry conditions. Alternate coiling and uncoiling causes the fruitlets to be "screwed" into the ground.
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