Based on the experience we gained from Experiment #3, we put the tops back on the experimental units of that study immediately after harvesting the pea plants in order to keep the CO2 concentrations within them as close as possible to what they were at the end of that study, hoping that when we briefly removed them to plant the radishes, we would not have to start from scratch, so to speak, in developing a range of airspace CO2 concentrations within our three experimental units.  This strategy worked to a moderate degree.  Mean CO2 concentrations for the first week of the experiment were 531, 781 and 1365 ppm in the low-, medium- and high-CO2 experimental units.  As for the plants, all were up and doing well.