At the conclusion of this second week of our experiment, we again computed the weekly average carbon dioxide concentration of the air in each tank.  Then we computed the average, or mean, of our first two weekly averages to obtain the average CO2 concentration of the air in each tank since the start of the study.  On each succeeding week, we will follow this same procedure, so we will always know the mean airspace CO2 concentration of each of our poor man's biospheres over the entire expanse of the experiment to that point in time.

Over this second week of the study, root growth was evident in all six tanks; and by measuring the lengths of all roots on each of the plants sandwiched between the front glass panels of the aquariums and the pieces of black felt located right behind them, we were able to produce the graph of Figure 1.  In viewing this figure it can be seen that our partial closing of the holes in the polyethylene cover of Tank 3 did indeed bring its mean CO2 concentration down below that of Tank 4.  Also, the airspace CO2 concentrations of Tanks 1 and 2 dropped from above 400 ppm last week to just below 300 ppm this week.

In addition to new root growth, this week also saw the commencement of new vine growth in several of the tanks.  Figure 2 depicts this phenomenon in one of the plants of Tank 6, where the new vine is emerging from the junction of the original leaf stem with the original vine.  Since new-vine length can also be readily measured for the two front plants of each biosphere, we present the first graph of this parameter as a function of biospheric airspace CO2 concentration in Figure 3.