The protective outer covering of a seed, derived from the *integuments
of the ovule after fertilization. In primitive forms the outer integument may remain fleshy and the inner become lignified to form a sarcotesta and schlerotesta respectively. In more advanced forms both the integuments fuse and become hard and dry except for a small unthickened area at the *micropyle
, which facilitates radicle emergence at seed germination. In some species the outer surface of the testa becomes covered with mucilage, hairs, or fibres to aid seed dispersal. The fibrous nature of the cotton seed has long been exploited commercially.