In angiosperms, one male gamete fuses with the egg cell and forms the zygote. This process is called syngamy. The other male gamete moves towards the centre and fuses with the secondary nucleus. This is called triple fusion. Triple fusion results in the formation of primary endosperm nucleus.
Thus syngamy produces zygote whereas triple fusion produces primary endosperm nucleus. The zygote gives rise to the embryo, while the primary endosperm nucleus develops into the endosperm.