These results do suggest, however, that perhaps the experimental units should be operated with only Pothos leaves in them for some initial period of time, in order to establish a good range of CO2 concentrations before the peas are planted.  This latter feat could then be accomplished by (1) cutting small openings in the duct tape directly in front of each of the four bottles of sand at the appropriate time, (2) placing a pea seed on the end of the blade of a table knife that could be slid through these openings and then tilted to drop the seeds into the preformed (by pencil) holes in the sand of the bottles, and (3) covering the seeds by bending a coat hanger in such a manner that it could be inserted through the openings in the duct tape and used to push some of the sand that surrounds each hole into the hole, thereby covering the seed it contained.  If the seed released in the second of these steps failed to fall into the preformed hole, the coat hanger could also be used to roll the seed into it.