Tin foil is used to block light. To see if the plant grows towards the light, whether it is caused by the tip of the coleoptile feeling the light. Agar sheets can absorb auxin and are used to see the coleoptile. Does the tip secrete any substance that makes the plant grow towards the light? You can do a comparative experiment using agar that has been in contact with the coleoptile tip and agar that has not been in contact with it. You can also draw the conclusion that the substance can make the plant grow and elongate. Mica sheets are transparent to light. , but it cannot transfer the substances that make plants grow like agar plates, and is used for comparison