Test for starch.

1.Heat a plant leaf in boiling water for 30 seconds 
2.Heat it in boiling alchohol for a few minutes
3.Wash with water and spread onto a white tile
4.Add iodine solution from a dropper
5.After a few minutes, the parts of the leaf that contain starch turn blue-black

Why is there a need to boil the leaf in alcohol?
Ans: It removes most of the leaves color so that it will have little chlorophyll left.
Why is the logic behind leaving the plant in the dark for a few days?
Ans: It will make sure that the plant will not produce any starch via photosynthesis during this period of time.