•Two evolutionary advances associated with this: 1.POLLEN GRAIN2.OVULEand SEED EVOLUTIONARY ADVANCE OF SEED PLANTS
POLLEN GRAINS: General characteristics •Male spores (MICRO-SPORES) with endosporic male gametophyte (MICROGAMETOPHYTE)
•Pollen grain germinates to produce POLLEN TUBEthat conveys the sperm to the eggPOLLEN GRAINS: General characteristics
•Pollen grain has resistant wall made of SPOROPOLLENIN POLLEN GRAINS: General characteristics
POLLEN GRAINS: Evolutionary advantages •In seedless vascular plants, the sperm (antherozoid) is motile, and has to swim to reach the egg in the archegonium; water is therefore required •In seed plants, the pollen grain is adapted for transporting the sperm: thick sporopollenin wall protects microgametophyte; pollen tube conveys sperm to the egg
OVULE: General characteristics The OVULEis a multi-layered structure: 1.