Elevated CO₂Concentration Increases Stomate Numbers in Phaseolus vulgaris Leaves

Beans were grown under a constant CO2 concentration of either 400 or 1,200 μl liter-1. There was no significant difference in stomate density on the adaxial surface, but there was a significantly lower stomate density on the abaxial surface of leaves in the higher CO2 concentration. The leaf area was significantly greater at the higher CO2 concentration, and total number of stomates per leaf, calculated from the density and leaf area, was significantly greater for both surfaces of the leaf. We conclude that the observed CO2 effect on stomatal density is the result of the large change in leaf area.