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Pollination (continued) nectar. Plants with flowers pollinated by birds other than hum- mingbirds (such as sunbirds in Africa) usually provide perches. Bat pollination Flowers pollinated by bats include those of the sausage tree, saguaro cactus, cup-and-saucer vine, and certain bananas. They are open in the evening, when they emit a rank or musty odor; their petal colors are either murky and nondescript or snow white; they are wide-mouthed and often bell-shaped; and they normally offer both nectar and pollen in abundance. Perhaps because pollinating bats have a poorly developed sonar sense, these flowers often hang down freely from ropelike twigs (flagelliflory) or grow on the main stem or limbs of the tree (cauliflory), which makes them easier to locate. However, it is also possible that these characteristics evolved to facilitate the dispersal of the fruits and seeds by bats, and that the pollina- tors may have been different animals. Hawkmoth pollination Flowers pollinated by hawkmoths have a great deal in common with those pollinated by hummingbirds, but they are white or light-colored and very fragrant, especially in the evening when they are open. Butterfly pollination Flowers pollinated by butterflies open in the daytime, are usually colorful and fragrant [butterfly bush (Buddleia) and lilacs], and either offer a flat landing space (Impatiens) or, when small, are combined in inflorescences that provide flattish surfaces to be walked on (red valerian and Buddleia). The nar- row flower tubes allow entry of the slender butterfly proboscis, but discriminate against other insects. Fly and beetle pollination Both flies and beetles are highly diversified groups, making it difficult to describe "typical" fly- or beetle-pollinated flowers. Trap flowers exploit types such as carrion and dung beetles (or flies), which are not at all adapted to flowers. However, many modern flowers cater to animals with highly specialized mouthparts, including certain longhorn beetles and the bee-fly Bombylius. Bee pollination The social bees, especially honeybees (Apis; Fig. 3) and bumblebees (Bombus), are the most important of all insect pollinators. Whereas honeybees are subtropical in origin, bumblebees are adapted to cold climates. The larvae of both Apis and Bombus live on pollen and honey (a modified nectar); the adults drink nectar. Among the physical and behavioral ad- aptations that the adults possess to obtain these foods are long tongues, hairy bodies, special pollen baskets on the hind legs, and a good color sense. To complement these attributes, the flowers pollinated by bees generally have bright colors, minty odors, and a landing platform, and their pollen grains are sticky, spiny, or highly sculptured for better adherence to the bees. In addition, honeybees have an excellent communication system: a worker bee can indicate both the direction and the distance of a rich food source by means of special dances, so that the resource can be exploited cooperatively. Wind pollination Wind pollination is prevalent in the primitive cycads and in conifers, but it also is found in such familiar flowering plants as grasses, rushes, sedges, cattails, plantains, nettles, hemp, sorrel, alder, birch, hazel, poplars, and temperate-region oaks. It offers advantages in regions where animal pollinators are scarce or where they cannot operate as a result of adverse environmental or seasonal conditions, such as strong winds. Wind-pollinated flowers are usually inconspicuous, being devoid of attractants and rewards for pollinators. They lack showy petals, fragrance, and nectar. To facilitate exposure to the wind, blooming often takes place in early spring before the leaves have emerged, or the flowers may be placed very high on the plant. In a number of species, the anthers burst open in an explosive fashion, scat- tering the pollen widely; the stigmas often are long and divided into arms or lobes, or they are feathery (like those of some wil- lows and cereals), thereby facilitating pollen catching. + ward ' s science Fig. 3: A honeybee (Apis), with pollen attached to its hind leg, pollinating a watermelon flower. (Credit: Stephen Ausmus/U.S. Department of Agriculture)