Pollen tube entry site in ovule:
Ovule integuments envelop nucellus and embryo sac leaving narrow canal micropyle at micropylar pole oriented toward placenta. Micropyle serves as specific entry site for pollen tube guiding sperm toward egg apparatus; synergid-secreted LURE peptides diffuse through this opening creating chemotropic gradient directing final guidance and reception of tube. Chalazal pole connects via funiculus to maternal vasculature providing nutrients, hilum marks detachment scar, chalaza opposite micropyle hosts vascular termination. Thus micropyle as pollen tube entry portal ensures precise delivery and positioning of male gametes immediately adjacent to egg and central cell.
Ref: Dresselhaus & Franklin-Tong, Nature Plants 2013: pollen tube enters ovule via micropyle guided by synergid LURE peptides.