The structure and ultrastructure of the nectaries of the monoecious species Ecballium elaterium were studied. Large differences in size and structure of the nectaries were observed in the two genders of flowers, those of the staminate flowers being much larger and more developed than those of the pistillate flowers. The latter do not secrete measurable amounts of nectar. In the nectariferous cells, especially of the staminate flowers, numerous plasmodesmata are present. The pre-nectar originating in the phloem is stored in the plastids of the nectariferous cells primarily as starch grains. The nectar appears to be exuded from the nectary via modified stomata. Very small insects of the order Hemiptera were found to dwell inside the flowers of the two genders, but in different numbers; their number in the staminate flowers was more than twice that in the pistillate flowers. These insects may take part in the process of pollination.