A fruit is a fertilised ovary with seeds. However, certain fruits are formed without fertilisation and are seedless. Such fruits are called parthenocarpic fruits. Typically, a fruit is made of two parts – the pericarp and the seed. The pericarp is the fruit wall and can be thick and fleshy as in mango or dry as in hazelnut. In mango, the pericarp is differentiated into the outermost peel called epicarp, the thick pulpy middle layer called mesocarp, and the innermost layer that directly surrounds the seed called endocarp. Drupes are single-seeded, fleshy fruits that develop from monocarpellary, superior ovaries as seen in mango and peach.
Based on the number of cotyledons, the seeds of flowering plants are classified as dicotyledonous and monocotyledonous. In a dicotyledonous seed, the seed coat is made of the outer testa and the inner tegmen. The seed coat has a scar on its surface called the hilum, which helps attach the seed to the fruit. Above the hilum is the micropyle, a small pore in the outer coat of the seed. Inside the seed coat lies the embryo, which comprises an embryonal axis and two cotyledons. At the two ends of the embryonal axis lies the plumule and the radicle. The cotyledons store reserve food materials. In some seeds such as castor, the developing embryo is surrounded by a nutritive tissue called the endosperm, which helps the embryo to grow. Seeds with endosperm are called endospermic whereas the seeds without endosperm are called non-endospermic seeds.
Monocotyledonous seeds can be endospermic or non-endospermic. The endosperm of maize is bulky and stores food, while the embryo is tiny and placed in a grove at one end of the endosperm. The embryo is separated from the endosperm by an aleurone layer and is made of a single, large cotyledon called the scutellum. The embryo also has a short axis with a plumule and a radicle. The plumule is enclosed by a sheath called the coleoptile and the radicle by a sheath called the coleorhiza.