Filiform apparatus is a characteristic feature of the synergid cells of the female gametophyte (embryo sac) in angiosperms. The filiform apparatus is a structure that extends from the micropylar end of the synergid and penetrates between the cells of the pollen tube.

Function:
The filiform apparatus plays a crucial role in guiding the pollen tube towards the embryo sac during fertilization. It secretes a glycoprotein-rich material that acts as a chemoattractant for the pollen tube. This material is released into the micropylar canal, which is the entry point for the pollen tube to enter the embryo sac.

Structure:
The filiform apparatus is a finger-like projection that extends from the synergid cell into the micropylar canal. It is composed of cytoplasmic strands and is covered by a plasma membrane. The cytoplasmic strands are highly organized and arranged in a parallel manner.

Significance:
The filiform apparatus is a crucial structure in the process of double fertilization in angiosperms. It plays a vital role in guiding the pollen tube towards the embryo sac and facilitates the fusion of the male and female gametes.

In conclusion, the filiform apparatus is a characteristic feature of the synergid cells of the female gametophyte in angiosperms. It secretes a glycoprotein-rich material that acts as a chemoattractant for the pollen tube and is crucial in guiding the pollen tube towards the embryo sac during fertilization.