explain the process of double fertilisation in angiosperms.

list the changes each part of the fertilised ovule undergoes to develop into the seed.

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The fertilized ovule has following parts which undergo changes and develop into seeds:
Integument: Seed coat
Micropyle: The merging radical from the seed comes out from the micropyle
Nucellus: perisperm
Polar nuclei which undergo triple fusion: Endosperm
Zygote:  Embryo