Seed-bearing vascular plants are more specialized to life on land than seedless vascular plants such as horsetails
and ferns. The male gametophytes are reduced to pollen grains, so free water is no longer
needed to allow the sperm to swim to the eggs. Wind and animal vectors are used instead to transfer the
sperms to the eggs. The eggs of these plants are enclosed in protective integument layers. The seeds
of angiosperms are further protected by their fruits, which are formed from the ovary walls.
Gymnosperms do not have fruit, so their seeds are "naked" ("gymno" means naked in Greek).