Lettuce growth and tipburn incidence as influenced by CO/sub 2/ concentration and light intensity

'Meikoningin', a butterhead lettuce cultivar was grown from seeding in fertilized peat soil at 70/sup 0/F, 80% relative humidity, with 16 hr of light and under CO/sub 2/ concentrations of 350 ppm and 2000 ppm. Within each CO/sub 2/ concentration were 2 light intensities: 1000 and 2000 ft-c. The higher CO/sub 2/ concentration increased the length and the width of the leaves while increased light intensity decreased length and width of the leaves. After 4 weeks of growth the number of leaves on the plants was about the same at the two CO/sub 2/ concentrations but was increased about 25% by increasing light intensity. Dry weight was increased almost 75% by raising CO/sub 2/ concentration and increased about 100% by raising light intensity. The incidence of tipburn was accelerated both by increasing CO/sub 2/ concentration and by increasing light intensity. Acceleration of tipburn appeared to be a consequence of an increased growth rate.