Double Fertilization
One male gamete fuses with the egg to form the diploid zygote. The process is called syngamy or generative fertilization. The diploid zygote finally develops into embryo. The other male gamete fuses with the two polar nuclei to form the triploid primary endosperm nucleus. The process is called the triple fusion or vegetative fertilization. The two acts of fertilization constitute the process of double Fertilization.
The process was demonstrated for the first time by Nawaschin (1898) in Lilium and Fritillaria.
Diagram showing the various stages of fertilization