Corn seedlings started in the greenhouse and set outdoors were shorter at maturity than plants from the same seed started outdoors. To test the effect of temp. in the early stages of growth, seeds of a first-generation hybrid (WF9 X P8) were germinated in an incubator at 30 [degree]C until the shoots and roots were 1/4 to 1/2 inch long. Three lots were held at 40, 50, and 60[degree]C for 1 hr., and planted in pots and left in the greenhouse until growth was certain. They were then set in the field alongside plants from the same lot of seed sown in the open ground at the time the treated seedlings were incubated. All the treated seedlings were shorter in height, less vigorous in growth, and later in flowering than the untreated plants. All treated lots showed pollen sterility. This influence on growth is an antivernalization effect and may have wide usefulness in the production of hybrid seed.