LEAF GROWTH IN MARQUIS WHEAT, AS REGULATED BY TEMPERATURE, LIGHT INTENSITY, AND DAYLENGTH

Abstract

The area of a fully-grown leaf lamina varied according to its position on the stem, and the temperature, light intensity, and photoperiod under which the plant was grown.In continuous illumination, raising the temperature by 5° intervals between 10 and 25 °C, resulted in progressively higher rates of leaf initiation, emergence, and expansion. The length of the lamina increased with each increase in temperature, but the breadth and thickness decreased. The greatest area of individual leaves was formed at 20 °C. Each increase in light intensity over the range 200, 500, 1000, 1750, and 2500 ft-c resulted in higher rates of leaf initiation, emergence, and expansion, and increases in breadth and thickness, but a decrease in length. The greatest area was formed at 1000–1750 ft-c.An increase in daylength from 8 to 24 hours increased leaf length, breadth, and area. This was a photoperiodic effect, unlike the increase in thickness with increased daylength, which was related to the total light energy received.Changes in leaf shape under different environmental conditions were not directly related to changes in leaf dry weight. A control of leaf growth by hormonal mechanisms sensitive to photoperiod seems more probable than does control by internal competition for assimilates among developing leaves.