To avoid confusion, have students cut a small notch in all strips at the green end. For each class, label petri dishes according to light treatment, add iodine solution, and have students leave their strips in the solution overnight. The iodine solution can be made by diluting a small bottle of iodine purchased at the drug store. After 24 hours, lab groups will remove a leaf strip from each treatment and examine it under the microscope. The strips should be drained briefly on a paper towel before being placed on a microscope slide.
Forceps are the best way to handle the small strips.
When students check the strips under the microscope they should check each pigment area. They should look for the characteristic dark starch granules and record their observations. The iodine will generally enter the leaf strips from the cut edges. Therefore, the students may have the most success in locating starch granules at the cut edge of the leaf strips. Using the microscope, look at the underside of the Setcreasea leaves.