A poem written almost three thousand years ago speaks of the autumn color of summer plants. It is believed that this poem was written by Empress Koken of Japan on a plant of the genus Eupatorium. In fact, the leaves of the plants of this genus are yellowed in summer. Now, British researchers have identified the guilty of amarility. They find remnants of a virus that isolated DNA from yellowish plants and considered suspicious. After several tests, the muse of the three-thousand year poem has been revealed.