Abstract: The microstructure and ultrastructure of leaves in cucumber with CO₂ nrichment were investigated. It showed that the thickness of palisade tissue, epidermis and leaf increased simultaneously in CO₂ enriched leaves, and the ratio of palisade tissue to leaf thickness went up slightly. Longer and more tight ly arranged palisade cells were observed in leaves with CO₂ enrichment. Not only the number and size of chloroplast and starch grain, but also the number of grana and lamella increased as a result of CO₂ enrichment. No obvious chloroplast deterioration and thylakoid deformation were found in CO₂ enriched leaves. Enrichment at different CO₂ concentrations for three hours in morning was not very effective, but enrichment for six hours at 1 100+100 uL.L^-1 everyday produced most significant effects.

Key words: Cucumber, CO₂ enrichment, Leaf structrue