Since the character is selected, not on account of its functional importance but on account of its combinative efficacity, there is no proof that in the internal hierarchy of any individual plant such and such a form of pistil or arrangement of stamens necessarily entails such and such a structure: if the germ of the Adoxa is placed between the calyx and the corolla, or if, in the arum, the stamens are arranged between the pistils, these are nothing more or less than 'singular structures'; their slight importance is a product of their rarity alone, whereas the equal division of calyx and corolla derives its value only from its frequency.