A seed enclose three generations one within the other:
(a) The ovule or megasporangium formed from the parent sporophyte is diploid (2n).
(b) An ovule consist of integument and nucellus. Both of them are diploid and belongs to sporophytic generation.
(c) The megaspores developing within the ovule is . formed by meiosis and is haploid (n). The megaspore develops into haploid female gametophyte which develops an egg (n).
(d) This represents haploid (n) gametophytic generation. The egg is then fertilized by a male gamete, to form a diploid (2n) zygote.
(e)The zygote then develops into an embryo or future sporophyte (2n).