Mature seeds begin to germinate under suitable environmental conditions. After a series of growth processes, the radicle of the seed first breaks through the seed coat and grows downward to form a tap root. At the same time, the cells of the hypocotyl also grow and elongate accordingly, pushing the embryo or cotyledons out of the soil surface, and the embryo extends out of the soil surface to form stems and leaves. The cotyledons extend out of the soil along with the germ, and turn green after unfolding, such as cotton, rape, etc. After the young leaves of the embryo open and use photosynthesis, the cotyledons will wither and fall off. At this point, a young plant that can live independently has fully grown. This is a seedling.