The endosperm is the nutritive tissue in the seed, and it provides nourishment to the developing embryo.
In some seeds, the entire endosperm is utilised by the developing embryo. Due to the complete utilisation of endosperm, two cotyledons are formed in these seeds which stores the nutrients for the development of embryo. The cotyledons formed in these seeds are thick and fleshy. Such types of seeds are called non-endospermic seeds or non-albuminous seeds. These type of seeds are mostly found in dicotyledonous plants but castor being a dicot is an exception. Examples: Pea, Groundnut, etc. except Castor.
In some seeds, endosperm persists in seeds and is called endospermic seeds or albuminous seeds. These seeds do not completely utilise the endosperm while developing. Due to this, only one of the cotyledons is able to develop completely while the other is not. This is the reason, the cotyledons of endospermic seeds are mostly thin and papery. These types of seeds are mostly found in monocotyledonous plants. Examples: Maize and Wheat, coconut, Borassus etc, except orchids.