Seed coat, testa

is wrapped in the skin structure outside the seed embryo and the endosperm. Beads derived from the embryo beads are formed by the outer beads for the outer skin, and the inner beads are developed to form the inner skin. Generally tough, with protective features. The outerm often has a corneal film, which is a thin-walled
or thick-walled tissue
composed of the epidermal layer, some of the epidermal layer can develop epidermal fur, such as cotton wool (cotton fibers) on the cotton seed skin. Inside the surface cortical layer is a woody layer of thick-walled cells, which also contain a thin-walled cell layer, but is often squashed. Some seeds are thick and hard, such as pine nuts, cottonseeds, and watermelon seeds. Some seeds are very thin skin, such as the red skin outside the peanut kernels, sunflower seeds outside the white film, its protective effect is not great. The seeding of cereal crops is often healed with the peel, which together plays the role of protecting the embryo and endosperm. When the seed matures, the cells that make up the skin generally die and the protopa disintegates, but still contains different pigments, making the seed appear different colors. Outside the mature skin, structures such as umbilical cords, ridges and ridges can usually be seen. The umbilical cord is the mark left on the seed skin when it is detached from the peel. Such as the black spots on the side of soybeans, that is, the umbilical cord, the seed ridge is derived from the seed seed skin of the inverted embryo beads on a bulging, the bread buried in a tube tissue, such as the castor seed side of the ridge, is the ridge;。