First, cut a white onion into 4 to 6 sections. Onion is an ideal model organism to study plasmolysys because its epidermis is easy to peel off and quite resistant. Pick the third leaf from the outside, as it usually shows the best compromise between tissue maturity and integrity. Cut 5mm-wide square sections with a scalpel. No need to goo al the way through the leaf. Just before treatment, peel off an epidermal section, either using tweezers, or your fingers. Make sure you do not peel off excess of fleshy material as you lift the layer. Place your sections in treatment solutions, usually distilled water and 1 molar sucrose, and incubate at room temperature for 10 minutes. Mount one section between a slide and a cover slip. To enhance the contrast, use iodine instead of water. It will stain starch and become darker as it gets concentated when the cells loose water. Place the cover slide and tap gently to remove excess air bubbles. Remove excess iodine with tissue paper. Immediately observe the sample under a light miscroscope. Use the coarse wheel to bring the stage up, and the fine wheel to focus. Move up in magnification power as needed. Count all cells in one field of view and note the number of cells that show plasmolysis. You may also take pictures and count later. This is a sample dipped into the sucrose solution, note how some cells show plasmolysis while others do not.