What was done
The authors grew mint (Mentha sp. L.) and thyme (Thymus vulgaris L.) shoots in tissue culture tubes exposed to several atmospheric oxygen concentrations and atmospheric CO2 concentrations of 350 and 10,000 ppm to determine the influence of these two gasses on the growth of these herbaceous species.

What was learned
Regardless of atmospheric oxygen concentration, shoots of both mint and thyme exposed to elevated CO2 produced substantially more biomass than shoots grown at 350 ppm CO2.  At an ambient O2 concentration of 21%, for example, CO2-enriched shoots of mint and thyme attained fresh weights that were 3.1- and 5.8-fold greater, respectively, than those reached by shoots exposed to ambient O2 and CO2 concentrations.

What it means
As the atmospheric CO2 concentration increases, it is likely that young mint and thyme plants will exhibit increases in photosynthesis and biomass production.  Thus, the yields of these species in commercial herb farms should rise right along with future increases in the air's CO2 content.  The results of this study also indicate that the two plants respond favorably to atmospheric CO2 concentrations that are much higher than anything realistically anticipated to result from the burning of fossil fuels.