Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
Used, in Amos 9:9, of a small stone or kernel; in Mt. 13:31, of an individual seed of mustard; in Jn. 12:24, 1 Cor. 15:37, of wheat. The Hebrews sowed only wheat, barley, and spelt; rye and oats are not mentioned in Scripture.