why is the process of fertilisation in a flowering plant referred to as double fertilisation

Hello Student
The fertilization occur in Flowering plant is Double because
1. The pollen tube forms in flowering plants by Pollen Grains releases two male gametes by entering in synergids. One male gamete is fuse with the nucleus of egg cell & produces Zygote and process is called Syngamy (Fertilisation Number 1)
2. Other male gamete moves towards the two polar nuclei of central cell and fuse with it forms Primary endosperm nucleus and process called TrIple Fusion