In castor seed, testa and tegmen are united together. The seed coat is tough and bright due to scleroproteins. Over narrower end, a brownish pad is found which is called the caruncle. The caruncle is carbohydrate in nature. This protects micropyle and develops as an integumental outgrowth after fertilization. Below the seed coat, a very thin membrane is found over the kernel and called perisperm (the persistent nucellus). Below perisperm, there is a large, white, swollen and oily mass called endosperm.