According to this theory, the shoot apex is dome-shaped in outline and protected by a young leaf called primordial. It has two parts: an outer mantle like tunica and an inner mass of cells called corpus. Cells of tunica are smaller. They undergo anticlinal divisions and form the protoderm which later differentiates into the epidermis. Cells of the corpus are comparatively larger. They divide into all planes and form a ground meristem and procambium. Thus a theory is only applicable for differentiation of shoot apex.