Seed develops from an ovule (consisting integument and nucellus) or megasporangium. Parts of ovule develop a haploid megaspore which grow into haploid female gametophyte. This female gametophyte develops an egg or oospore. The latter is fertilized by a male gamete and develop into a zygote (2n) . The zygote develops into an embryo or new sporophyte. The embryo (2n) is surrounded by female gemetophyte (n) , the latter by seed coat (2n) . In this way seed wontains three generations locked one within another. Of these, two generations occur within embryo.