Pollination

The transference of the pollen grains from the anther to the stigma is called pollination. It is of two types –
1. Self pollination 2. Cross pollination
Self pollination
Self pollination is the transference of pollen grains from the anther of a flower to the stigma of either the same or genetically similar flower. It is generally not dependent on any external agency for pollination. It is of two types:
a) Autogamy – It is the transfer of pollen grains from anther of a bisexual flower to its stigma. Both stamens and carpel mature at the same time. It occurs in several cereals (wheat, rice) some peas and flowers which do not open.
b) Geitonogamy – It is kind of self pollination where flowers could be bisexual or unisexual but are borne on the same plant. It may required an external agency like insects or wind.
Self pollination may occurs when the flowers are open (chasmogamy) or closed (elesistogamy). Chasmogamous self pollination occurs only when their anthers and stigma mature at the same time (homogamy).
The self pollinated flower are generally small, inconspicuous, colourless, odourless and nectaorless. Self pollination occurs by following methods:
1. Homogamy – In this case the anther and stigmas of a bisexual flower mature simultaneously. The pollen grains reach the mature stigma either by contact, wind, gravity, rain drop or even insects. Self pollination brought about by contact is called direct autogamy and remaining agencies perform indirect autogamy.
I. Direct autogamy – It is accomplished by the movement of floral parts on account of growth, bending or folding, in convolvulus lxoza, catharanthus and Gardenia the anthers are borne at the mouth of the corolla tube. With the growth of style the stigma comes in contact with ripe anthers and pollination occurs. Pollination takes place in Cotton when the stigma in being pushed out of the staminal tube due to the growth of the style.
In Mirabilis ( four o’clock plant) the filaments of ripe anthers bend and bring in contact with stigma. A similar curling of style takes place in Potato. The stigma of Sunflower has brushing hair which helps in pushing the pollen grains from the synantherous tube. The stigma curls back and receives the pollen grains present on the brushing hair. The closing of flowers at night performer self pollination in Argemone Mexicana.
II. Indirect autogamy – It occurs without coming contact of anthers and stigmas. The pollen grains reach the stigma by rain (e.g., Caltha) or gravity (e.g., Lilac). In Lilac the anther lie exactly above the stigmas. The pollen grains of the dehisced anther fall over the low lying stigmas under the influence of gravity.
In sanicula male and female flowers grow side by side. The long style of the female flowers bends over the male flowers to get pollinated.