Crossing and selfing tests, as well as studies on microsporogenesis and pollen behavior under natural and artifical conditions were carried out with the diploid species. Coffea congensis (2n=22). Microsporogenesis was found to be normal and eleven pairs of chromosomes could be counted at metaphase. Separation in anaphase was regular, two nuclei being formed with eleven chromosomes each; at the end of anaphase II the four microspores also had eleven chromosomes. Abnormal divisions, giving rise to 10- and 11-chromosome nuclei, appeared in only 6.1% of the p.m.c. Pollen grains (32.04 micra in diameter) were found to be larger than in Coffea Dewevrei and C. canephora, but smaller than in C. arabica. The representatives of Coffea congensis studied belonged to two groups: (1) the Bangelan group that produced viable male and female gametes. Plants of this group, however, were self-incompatible. (2) The Uganda group, composed of plants the pollen of which did not germinate under any conditions, thus making the plants of this group male sterile. This phenomenon was not yet known to occur in Coffea.