08-16-2017, 10:24 PM
Abstract
The flower-heads of the sunflower are well-suited for insect pollination as the crowding of the flowers ensures conspicuousness and the pollination of a maximum number of flowers by a single insect visit. The honey, secreted at the base of the style, is protected by the corolla tube from visits of short-tongued insects. When the flower open the receptive surfaces of the two stigmas are pressed together and occupy a position at the base of the tube formed by the united anthers; the latter split on the inside and the liberated pollen fills the cavity of the tube and exposes it to contat with visiting insects. Fianll, the style protrudes right throught the anther tube and the stigmas spread apart and expose their formerly hidden receptive surfaces. Thus, the life history of the flower falls into two stages, the first male and the second female. This favours cross-pollination as compared to self-pollination. The sun-flower is therefore practically self-sterile, though self-pollination may take place at a late stage, when cross-pollination has failed.
Pollination in legumes:
Pollination: As flowers are protandrous, usually cross pollination occurs. In Lathyrus and Pisum
pollination.
The mechanism of pollination in Fabaceae is 'piston mechanism'.
The type of pollination is entomophily.
The insects are attracted by the standard petal.
They alight on the wing petals and press them down in search of the nectar collected in the stamina
Due to this, the keel petals are also pressed down and open exposing the stigma and stamens.
The stigma which comes out first, brushes to the abdomen of the insect and collects the pollen.
When the anthers come in contact with the insect, the pollen is deposited on its body.
As the insect leaves the flower the essential organs return to their normal position.
Since the movement of essential organs is like that of a piston, it is called piston mechanism'.