Double fertilization is different from single fertilization , because of the presence of 

Double fertilization is the characteristic of angiosperms. In this process, one male gamete fuses with the egg to form a zygote, which is known as syngamy. The other male gamete fuses with the two polar nuclei in the central cell to produce a triploid primary endosperm nucleus or PEN. This process is called as triple fusion occurs only in angiosperms .