The early development (ontogeny) of the carpels of 20 species belonging to 8 apocarpous families was investigated with the scanning electron microscope. The results indicate that on the floral apex a circular or a convex meristem develops into an obliquely ascidiate primordium by unequal growth of its periphery. By further unequal growth it develops into a young carpel. The terminal mouth of a cup becomes the lateral cleft of a carpel. The different forms of the young carpels in different species are defined by the varying degree of development of the adaxial region of the initial meristem and/or its margin on the side of the floral apex. This hypothesis is theoretically evaluated.