Abstract: The nucleus vegetative in nature derived from unequal or equal division of the uninucleate pollen in rye anthers cultured in vitro develops into pollen embryoids or calli. The green haploid plantlets are differentiated successfully. The frequency of callus and embryoid formation may be efficiently increased when the spikes are pretreated at 1–3 ℃ for 7 days before inoculation. According to the condition in which the multinucleate (free nuclei) and multi-cellular pollen grains become abortive, it is suggested that the formation of new walls between the dividing cells and the opportune rupture of the pollen exine are the two critical factors, which determine whether the embryoids and calli will be able to develop once the microspores are initiated.