Starting with the right-hand leaf at the bottom of Plate II, we let our eye and mind be impressed by its characteristic form, seeking to take hold of the pattern after which it is shaped. Its edge bears numerous incisions of varying depths which, however, do not disturb the roundness of the leaf as a whole. If we re-create in our imagination the ‘becoming’ of such a leaf, that is, its gradual growth in all directions, we receive an impression of these incisions as ‘negative’ forms, because, at the points where they occur, the multiplication of the cells resulting from the general growth has been retarded. We observe that this holding back follows a certain order.