Jonathan apple trees were grown in culture solution with nitrogen supplied either as nitrate, as ammonium, or in both forms. In all cases ammonium led to earlier flowering and to a much higher proportion of flowers among the total buds; but when ammonium was supplied throughout the season alone or as ammonium nitrate, vegetative growth was less than with nitrate alone. When the trees were given only nitrate during the preceding season, except for an interval of 2 months (Dec.-Jan.) in which ammonium nitrate was supplied, the merits of both ions were combined; the growth was not reduced and the total number of flowers in the succeeding spring was 3 times as great as with nitrate alone.