In belladonna leaves, as well as in tobacco (AVERY 1933), there are cell differentiation gradients. One is along the major leaf-axis, and another from the midrib towards the leaf margin. Moreover, in both leaf laminae there are seven cell layers. In the least differentiated regions of the youngest leaves all cell layers show plastids with a membrane-bound body. As mesophyll differentiates, the frequency of such plastids decreases and, at the same time, their distribution in the different cell layers varies. According to our surveys, carried out into successively older leaves, we can assume that the plastid differentiation speed is not determined by light as much as by the cell's internal environment.