Compared to Blue-white fluorescent light at 15°C, Blue light and low temperature (10°C) resulted in a restriction in the rate of leaf growth due primarily to a sharp fall in specific leaf area with mcreasmg plant size, which was much more pronounced in low temperature. There was scarcely any effect on the leaf weight/total dry weight distribution, hut the leaves had a much higher dry matter content than plants grown in Blue-white light. In Blue light the unit leaf rate was depressed on an energy basis, but not on a quantum basis. It was also depressed in low temperature. The depression of both unit leaf rate and leafiness resulted in a low relative growth rate in both treatments. The interrelationship of specific leaf area and unit leaf rate did not follow the same pattern as reported previously and this is discussed. The effects attributed to low temperature in field experiments were confirmed.