Explanation

The double fertilization was discovered by S G Nawaschin (1898) and Guignard in $Lilium\$and $Fritilari$a. Double fertilization 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 fertilization can be distinguished as : 1.Generative Fertilization: Fusion of one male gamete with the egg producing diploid zygote or oospore. 2.Vegetative Fertilization: Fusion of nucleus of second male gamete with the diploid secondary (fused) nucleus or the triple fusion, $i.e.,$ fusion of one male polar nuclei forming endosperm (3$n$).