Question

why development of pollen tube is the main function of vegetative cell and not providing nutrition to the male gametes.
"since vegetative cell also contains food reserve" ?

Answer 1

Vegetative cell forms the pollen tube and generative cell divides to form the 2 sperm cells. The pollen tube formed does not provide nutrition initially but after sometime it grows into nucellus and at this point it provides nutrition to the developing sperm cells (male gametes). So, we can say that vegetative cell provides nutrition to the male gametes after extending into nucellus.