The existence of two supplementary functions, D and E, have also been proposed in addition to the A, B and C functions already discussed. Function D specifies the identity of the ovule, as a separate reproductive function from the development of the carpels, which occurs after their determination. Function E relates to a physiological requirement that is a characteristic of all floral verticils, although, it was initially described as necessary for the development of the three innermost verticils (Function E "sensu stricto"). However, its broader definition ("sensu lato") suggests that it is required in the four verticils. Therefore, when Function D is lost the structure of the ovules becomes similar to that of leaves and when Function E is lost "sensu stricto", the floral organs of the three outer most verticils are transformed into sepals, while on losing Function E "sensu lato", all the verticils are similar to leaves. The gene products of genes with D and E functions are also MADS-box genes.