Photosynthesis and starch production in Pelargonium leaf discs

A well watered Pelargonium plant shut in a warm dark cupboard for two days loses all the starch from its leaves. After two days the plant and the cells of the leaf are still alive and active. If discs are cut from the leaf with a cork borer, their ability to make starch under different conditions may be investigated. In a decolourised leaf the starch stains blue black with iodine solution.

In this investigation, we suggest that you use a variegated Pelargonium with white leaf patches; you will be varying the conditions of light available to the plant and feeding some of the plants in the dark with sugar.