Pollen grain of Cycas are shed at stage

Pollen grain is

Pollen grain is

Pollen grain is

pollen grains

pollen grains

Pollen grains are shed at which stage?

60% of angiosperms, pollen grains shed at 2 celled stage, but in some species pollen grains are shed at 3 celled stage. Distinguish between 2 celled and 3 celled stage of pollen grains ?