In Datura ferox hyoscyamin is transformed into hyoscin. An alkaloid which may be 6–Oxyhyoscyamin is an intermediate in the biosynthesis of hyoscin from hyoscyamin. While hyoscyamin is synthesised in the roots its transformation into hyoscin takes place preferentially in the leaves. The same pattern of biosynthesis of hyoscin is found in other species of Datura and in Atropa belladonna. In contrast to Datura ferox, however, in most species biosynthesis of hyoscin is restricted to young plants. As the plants mature the enzymes involved in this transformation are inactivated and hyoscyamin begins to accumulate. The reverse reaction, transformation of hyoscyin into hyoscyamin, could not be demonstrated by feeding root cultures of Datura innoxia with 14C–marked hyoscin.