The function of filiform apparatus is to:

The correct answer is Option (2) → Guide the entry of pollen tube into ovule

Option (1) Help in germination of pollen grains — Incorrect. Pollen grains germinate on the stigma, putting out a pollen tube through a germ pore. The filiform apparatus lies inside the ovule, in the synergids, and works later.

Option (2) Guide the entry of pollen tube into ovule — Correct. The filiform apparatus is a set of finger-like thickenings at the micropylar tip of the synergids. It guides the pollen tube into the synergid of the ovule.

Option (3) Help in the development of embryo — Incorrect. The embryo develops from the zygote after fertilisation. The filiform apparatus works before fertilisation, guiding the pollen tube into the synergid.

Option (4) Formation of male gametes — Incorrect. Male gametes are formed inside the pollen grain, when the generative cell divides. The filiform apparatus is part of the female gametophyte and plays no part in this.

NCERT Extract:
Pollination – “… Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one of the synergids through the filiform apparatus (Figure 1.12d, e). Many recent studies have shown that filiform apparatus present at the micropylar part of the synergids guides the entry of pollen tube.”