The angiosperm fertilization is referred as double fertilization that is two gametic fusions occurs one by one.
It is gametic fusion between the male gamete and the egg resulting in the formation of zygote. The zygote which develops to the embryo. In this fertilization two nuclei are involved resulting in the formation of diploid zygote.
It is the gametic fusion of one male gamete with the diploid secondary nucleus resulting in the formation of the triploid nucleus. The triple fusion results in the formation of the triploid tissue known as the endosperm. The endosperm nurtures their by helping in the growth and development of the embryo.