Abstract:Gas exchange in leaves of selected plants was measured by using LCA-4 portable photosynthesis and transpiration system (ADC, England). Analysis of the difference in net photosynthetic rate (Pn) between Mikania micrantha and its companion species was also made. Results were as follows : (1) Mikania micrantha, a herbaceous vine, had a strong capacity for CO2 fixation, the Pn being 21.56 μmol CO2 m-2S-1, which was higher than that in the accompanying somewhat woody twiner Pueraria lobata (16.97) and climbing herb