Transfer of pollengrains after sheding from the anther to the stigma of the carpel is called pollination. 

Pollination in flowering plants occurs by two methods- (1) Self Pollination and (2) Cross Pollination. 

(1) Self Pollination – Self pollination involves the transfer of pollengrains from the anther of the flower to the stigma of the same flower or another flower of the same plant. 

(2) Cross Pollination – Cross pollination involves the transfer of pollengrains from the flower of one plant to the stigma of the flower of another plant. 

Varied means of cross pollination in plants are– 

(a) Dicliny – Cross pollination always occurs when the plants are unisexual and dioecious. Ex-Papaya 

(b) Self Sterility – When the stigma of the gynoecium of a flower is not pollinated by pollengrains of the same flower. Ex-Pea, Potato etc.

(c) Dichogamy – When maturity of male and female parts of a bisexual flower occurs in different times. It is of two types. (i) Protogyny (wen gynoecious matures first. Ex-Banyan) and (ii) Protandry (When androecium matures first. Ex-Maize) 

(d) Herkogamy – In some flowers physical barrier present between anther and stigma which avoid self pollination. Ex- Calotropis 

(e) Heterostyly – The flowers of some plants have different lengths of stamens and styles so that self pollination is not possible. Ex-Primula, Oxalis etc.