what is double fertilisation and triple fussion? how does fertilisation takes place in angiospermic plants?

Double fertilization is a characteristic feature of flowering plants. In the process of double fertilization out of the two sperm nucleus, one sperm nucleus fuses with the egg nucleus to form an embryo ( process is called syngamy) and another fuses with polar nuclei to form endosperm ( process is called triple fusion). Since two kinds of fusion—syngamy and triple fusion—take place, the process is known as double fertilisation.

Triple fusion:- During fertilization in flowering plants,out of the two sperm nucleus, one sperm nucleus fuses with the egg nucleus to form an embryo (process is called syngamy) and another fuses with 2 polar nuclei to form endosperm. So, this fusion of one of the male gamete with two polar nuclei to form endosperm is called triple fusion.