Control

Movement in this control tube helps reveal changes in gas volume caused by conditions such as temperature or air pressure rather than oxygen uptake by living seeds. Record both bead movements over the same interval. Treat movement towards a tube as positive and movement away as negative; subtract the signed control movement from the live-seed movement to obtain the corrected distance.

Set up the other in the same way but without removing its carbon dioxide; this is the control. Keep light intensity, temperature, exposure time, plant type and leaf size as similar as possible.