How cross-pollination of plants takes place Everything inside a flower is arranged to make pollination possible. This operation involves the transfer of pollen from the anthers of the stamens to the pistil. It is very rare, however, that the pollen produced by one flower is used to fertilize the pistil in the same flower. Instead, flowers are designed to obtain pollen from other plants and their flowers. This enables better seed and fruits to be produced and is known as cross-pollination. Its usefulness was demonstrated by the great naturalist, Charles Darwin, in 1859. Cross-pollinating flowers occasionally have their pollen waiting on the stamens before the pistil is ready to take it; or the pistil may be ready but the stamens have produced no pollen. Some plants produce flowers with stamens only (male flowers) while others produce flowers with only pistils (female flowers). These plants are pollinated with the help of the wind which blows the pollen grains through the air. Such plants produce huge amounts of pollen because much of it is lost in the air and only a small quantity finally reaches its proper destination. How plants attract insects for pollination Some plants entrust their pollen to the winds. Others use water as a carrier and still others simply pollinate themselves. However in most cases the vital task of pollination is left up to insects. To attract insects plants produce flowers that have beautiful scents and colours. The shape of the flowers corolla, the part with the petals, is designed to let pollinating insects in but keep out other unwelcome creatures. Sometimes the pollinating mechanism inside a flower is amazingly complex. An example is the sage flower: when a bee is attracted by the scent or the nectar, it stands on the lowest petal to enter the flower. As it does so, the bee presses on a kind of lever which makes the flowers stamens come down and touch the hairy back of the bee, covering it with pollen. The bee then enters another flower and the whole operation is repeated. The sage is one of those plants that lets its stamens ripen before its pistils. So when the bee lands on a flower where the stamens and the anthers have withered away, there is a pistil waiting to pick up the pollen from the bees back to fertilize itself |
