Filiform apparatus is characteristic feature of

The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergid.

The outer covering of endosperm separates the embryo by a proteinaceous layer called aleurone layer. The aleurone layer is made up of aleurone cells.

When the pollen grain is mature it contains two cells, the vegetative cell and generative cell. Generative cell divides mitotically to give rise to the two male gametes.

In Citrus and Mango varieties some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the embryos. Such embryos are called nucellar embryo.