Growth and Development in the Young Tomato I. THE EFFECT OF TEMPERATURE AND LIGHT

SUMMARY Tomato seedlings were grown at constant temperatures of 25° and 15° C. in a 12-hour day at light intensities of 1,600, 800, and 400 f.c. The rate of increase in size of the shoot apex and the rates of formation and growth of leaf primordia during the vegetative phase were followed by dissecting samples from the time of cotyledon emergence onwards. The rate of enlargement of the shoot apex increased with light intensity, but apical enlargement was delayed at the higher temperature, the delay being longer the lower the light intensity. The rates of leaf formation and leaf growth in creased with both temperature and light intensity. Temperature had a larger effect on leaf growth than on leaf formation. More leaves were formed before flowering at 25o C. than at 15° C., the increase in leaf number being greater the lower the light intensity. It is suggested that the delay in the enlargement of the apex at high temperature can be explained in terms of competition for assimilate, the competitive potential of the expanding leaf primordia exceeding that of the apex at higher temperatures.