A seed is a fertilized, matured ovule of a flowering plant, containing an embryo. This tiny embryo enclosed within the seed devolves to form a new plant by the process of germination. Plant embryo in seeds have structures called cotyledons. The seed consists of three components: embryo, endosperm (sometimes perisperm), and seed-coat. Both endosperm and embryo are the products of double fertilization, whereas the seed-coat develops from the maternal, ovular tissues. The seed habit is a significant advancement in the evolution of higher plants. Seeds are the method of reproduction for flowering plants, including everything from trees to grasses to bushes. Each seed is capable of growing into a new plant, given the right conditions, and the vast majority of plants have seeds. There are two overarching categories of seeds: dicotyledonous and monocotyledonous.