Read the passage and examine the photos. Then, suggest two reasons that scientists think developing pollen grains made vascular plants the most successful plants that live on land. Passage: These mosses are nonvascular plants that grow closely packed together in moist places. The sperm they produce for sexual reproduction must swim to a nearby plant that has an egg that the sperm may fertilize. Seed plants, such as these conifers, are vascular plants that live in both moist and dry places. For sexual reproduction, conifers produce pollen grains that contain sperm that cannot swim. Conifers produce massive amounts of pollen grains that can be carried by wind.