(d) In angiosperms one male gamete fuses with the egg to form diploid zygote. The process is called syngamy. The other male gamete fuses with the two polar nuclei to form triploid primary endosperm nucleus. The process is called triple fusion. These two acts together known as double fertilization. The process was Ist demonstrated by Nawaschin & Guignard in Fritillaria & Lilium.