Photosynthetic characteristics of Lactuca serriola L.

. Gas exchange responses of intact leaves of Lactuca serriola serriola and L. serriola integrifolia were examined. The light, temperature and intercellular CO 2 dependence of photosynthesis of these two forms of L. serriola were indistinguishable. Dependence of photosynthesis on leaf temperature differed only slightly between plants grown at approximately 10/3°C and those grown at 33/25°C with the thermal optimum shifting 4°C. Transpiration was shown to increase exponentially with leaf temperature. The gas exchange characteristics of L. serriola are discussed in relation to water relations, carbon gain and compass leaf orientation under field conditions.