Evolution of Seed

A journey of plants towards the evolution of seed is understandable.
Early primitive Vascular plants produce same size spores called homo-spores.
But with the passage of time some plants like lycophyta start to produce different types of spores like megaspores and microspores.
Microspores develop into male gametophyte while megaspore develops into female gametophyte.
After that Megaspores reduced into one and contained in sporangium. And then megasporangium gets integumented for seed development.
#SeedEvolution