In monocotyledons the seeds are generally endospermous. The internal structure of grain can be studied in a longitudinal section. It shows two distinct regions upper large region, the endosperm and lower smaller region, the embryo. The endosperm is surrounded by a special one cell thick layer, called aleurone layer. It is filled with aleurone grains which are proteinaceous in nature. Other components of this layer are phytin, carbohydrates and small amounts of phospholipids are also present.