Iodine is a starch test that is used to detect the presence of starch in a substance. However, when iodine is added to a leaf, it reacts with other substances in the leaf, such as chlorophyll, and not with the starch. Chlorophyll is a pigment present in leaves that gives them their green color, and it can interfere with the iodine test and make it difficult to determine if starch is present in the leaf. To test for starch in a leaf, it is necessary to first remove the chlorophyll by boiling the leaf in water or by using a solvent such as ethanol. After the chlorophyll is removed, the iodine test can be performed on the remaining material to detect the presence of starch.