In" this paper the authors discuss the nature of the calyx in the Ixorex (Rubiacex), calling special attention to this character in Coffea. The calyx of the goiaba variety of Coffea arabica L. differs from the normal type being well developed, foliaceous and persistent, the fruit being similar in appearance to the guava (Psidium guajava L.). It is supposed that the presence of a well developed calyx is a primitive character, the normal rudimentary calyx as found in the other representatives of the genus, having developed by rudimentation of the sepals through mutation. The results of the genetic analysis of this character indicate that one main pair of genetic factors is responsible for the development of a foliaceous calyx, the symbol sd sd (from "sépalas desenvolvidas") being proposed. F1 hybrids between "normal" (Sd Sd) and "goiaba" (sd sd) plants have intermediate sepals on their flowers and fruits, the heterozygote therefore showing incomplete dominance. The variability in size and shape of the sepals noted specially on the heterozygous plants is attributed to modifying factors which act upon the main pair of genes involved, particularly at the heterozygous condition ; physiological factors modify the expression of this character on fruits of the same individual plant and even on a single fruit.