Explanation

Angiosperms. The double fertilisation was discovered by SG Nawaschin (1898) and Guignard in Lilium and Fritilaria. Double fertilisation is restricted only to angiosperms. When pollen tube enters ovule, it strikes one of the synergids and burst open to release the two male gametes, which fuse with two different structures in the same female gametophyte. Thus, double fertilisation can be distinguished as (i) Generative Fertilisation Fusion of one male gamete with the egg producing diploid zygote or oospore (ii) Vegetative Fertilisation Fusion of nucleus of second male gamete with the diploid secondary (fused) nucleus or the triple fusion, i.e., fusion of one male nucleus and two polar nuclei forming endosperm (3$n$)