To solve this problem, we need to understand the function of the filiform apparatus in plant reproduction.$\newline \bullet$The filiform apparatus is a structure found in the synergid cells of the embryo sac in flowering plants.$\newline \bullet$Its primary function is to guide the pollen tube into the embryo sac for successful fertilization.$\newline \bullet$The pollen tube grows through the style and is directed by the filiform apparatus to ensure it reaches the egg cell.$\newline$Therefore, the correct function of the filiform apparatus is to guide the entry of the pollen tube.$\newline$This corresponds to Option 4.