Practice question

Ancestral land plants required external thin film water for flagellated anterozoids to swim chemotactically to archegonia containing egg limiting reproduction to continuously moist microhabitats. Seed plants evolved siphonogamy where pollen grain upon hydration on stigma or micropylar droplet generates pollen tube via polarized tip growth through stylar transmitting tissue secreting chemoattractants LURE peptides delivering non-flagellated sperm nuclei directly to embryo sac. Tube growth entirely internal protected from desiccation environmental fluctuations. Even cycads ginkgo retaining large flagellated sperm maintain siphonogamy via tube delivering sperm to aqueous archegonial chamber, achieving reproductive independence from external environmental water availability for syngamy crucial step.