As noted in § 780.804, it is ginning of seed cotton which converts the cotton to marketable form. Section 13(b)(15), however, provides an exemption only where the cotton is actually ginned “for market.” (Wirtz v. Southern Pickery, Inc. (W.D. Tenn.) 278 F. Supp. 729.) The ginning of cotton for some other purpose is not exempt work. Cotton is not ginned “for market” if it is not to be marketed in the form in which the ginning operation leaves it. Cotton is not ginned “for market” if it is being ginned preliminary to further processing operations to be performed on the cotton by the same employer before marketing the commodity in an altered form. (Compare Mitchell v. Park (D. Minn.), 14 WH Cases 43, 36 Labor Cases 65, 191; Bush v. Wilson & Co., 157 Kans. 82, 138 P. 2d 457; Gaskin v. Clell Coleman & Sons, 2 WH Cases 977.)