sentences:  The transition to ovules continued with this megaspore being "boxed in" to its sporangium while it germinated.Then, the megagametophyte was contained within a waterproof integument, which enclosed the seed.The pollen grain, which contained a microgametophyte germinated from a microspore , was employed for dispersal of the male gamete, only releasing its desiccation-prone flagellate sperm when it reached a receptive megagametophyte.