A seed is the embryonic stage of the plant life cycle. It is a reproductive structure that can grow into a new plant. Most seeds consist of three parts: embryo, endosperm, and seed coat. The embryo is a tiny plant that has a root, a stem, and one or more leaves. The endosperm is the nutritive tissue of the seed, often a combination of starch, oil, and protein. The seed coat is a protective covering that can help seeds remain viable for long periods of time.
Seeds are the product of the ripened ovule, after the embryo sac is fertilized by sperm from pollen, forming a zygote. The formation of the seed is the defining part of the process of reproduction in seed plants (spermatophytes) . Other plants such as ferns, mosses, and liverworts do not have seeds and use water-dependent means to propagate themselves.
Seeds are eminently suited to perform a wide variety of functions, including multiplication, perennation (surviving seasons of stress such as winter), dormancy (a state of arrested development), and dispersal. Seeds carry the food that helps the new plant begin to grow. This food store is in the endosperm, and/or in the cotyledons. Many kinds of seeds are good food for animals and people. The many kinds of grain that people grow, such as rice, wheat, and maize, are all seeds.
