1. The leaves of the black mustard plant contained more volatile sulphur than the stems. The work on the roots was inconclusive. 2. The leaves contained more volatile sulphur when the plants were grown in sand with a complete nutrient solution than when grown in soil. 3. Sulphur and nitrogen are both components of allyl mustard oil. Growing the plants in a minus-sulphur nutrient solution caused an almost complete loss of pungency of the leaves. Minus-nitrogen leaves were somewhat more pungent than plus-nitrogen ones. 4. Young leaves contained more volatile sulphur than older ones. The upper leaves of the plant were more pungent than the lower and the leaves of plants grown a short time than those of plants grown a longer time. 5. Tissue of high water content contained less volatile sulphur than tissue of lower water content.