1.   In fall, when darkness lasts longer, melatonin is secreted for longer periods.

2.   In spring, as days lengthen, melatonin is secreted for shorter periods.

3.   Melatonin is secreted only during darkness.

4.   The pineal gland of the brain began secreting melatonin at the onset of darkness and it continued pumping the hormone out at fairly high levels until morning.