The promotive effect of Ca in semi-vitro culture of Oenothera biennis pollen was by and large identical to that of in vitro systems. This promotive effect became additive when boron was supplemented to the media and even more so if K was further supplemented. No such Ca action was observed then performed under the conditions of relatively low temperature. An uncoupling agent of ATP in respiration, DNP, inhibited the promotive action of B, but not that of Ca. The inhibitory effect of DNP was greater at low temperatures. IAA was rather inhibitory on pollen growth in semi-vitro culture, even much greater than it if DNP was supplemented to the IAA-containing media.