Pollination: Process by which pollen is transferred from the anther (male part) to the stigma (female part) of the plant. 

Mechanism which favour cross-pollination 

1. Bisexual flowers: When both male and female parts are present on the different flowers than it promote the cross pollination. For example, castor, papaya 

2. Dichogamy: Sometimes male or female mature slightly atdifferent times this nature is called dichogamy which favour the cross pollination and in this process if male part (Anther) of flower matures first then it is called protandry (eg. Maize) while, if female partmature (ovary) first then flower is to be called protogyny in nature. E.g., bajra 

3. Herkogamy: In this types of mechanism some structures prevent the self-pollination and promote cross pollination in bisexual flowers.eg. Alfa alfa 

4. Male sterility: Male sterility is defined as an absence or non-function of pollen grain in plant or incapability of plants to produce or release functional pollen grains and this mechanism promote the cross pollination. Eg. Cotton, Bajra etc. 

5. Self-Incompatibility: It refers to the failure of pollen to fertilize the same flower or other flower of the same plant, or it is the failure of pollen tube to penetrate the full length of style and effect fertilization. For example, mustard, cauliflower & cabbage etc.