The presence of starch in green leaves can be tested by iodine test. In this test you have to pluck a leaf from a plant and put it in a test tube containing alcohol. Place this test tube in a beaker containing water and heat the water. As the alcohol begins to boil, the chlorophyll dissolves in it and after some time the leaf becomes pale.
You have to remove the leaf from alcohol and wash it in warm water. Lay the leaf in a dish and put a few drops of iodine on it. The color of the leaf changes into blue-black. This color shows the presence of starch in the leaf.