Larger nucleus in a pollen grain is

Pollen grain is the mother cell of male gametophyte. Development of male gametophyte begins inside themicro sporangium. The microspore nucleus divide mitotically to form a smaller generative cell and a much larger, vegetative cell (tube cell). The generative cell produces two male gametes, whereas, the vegetative cell form pollen tube after pollination. Pollen grain contains two cells, i.e., tube cell and generative cell at the time of pollination.