We de-starch leaves so as to remove the starch produced in it during photosynthesis stored as food. Removing the starch would help us to infer our observations clearly as there is no change or substance that would effect the experiment we want to carry out. For example , the indicators we use might give blue-black or green colors just because of the presence or absence of starch.
The answer that best fits the description above is the hormone GLUCOCORTICOID. This was according to Hans Selye, an Austrian-Canadian endocrinologist. According to him, ill health induced by exposure of chronic stress is due to the secretion of the hormone glucocorticoid.