It is widely agreed that the tradition probably originates in a story from Norse mythology, in which the mother of Baldur, a Norse god, cast a spell to ensure that no plant growing on earth could be used to harm her son. But Loki, recognizing that mistletoe, as a parasitic plant, does not grow on earth, used the plant to make a spear to kill Baldur. By some tellings, after Baldur's death, his mother declared the mistletoe to be a symbol of love and promised to kiss anyone who passes under it. To avoid such kisses, then, was to encourage bad fortune. This interpretation is often disputed, however. The tradition of kissing beneath sprigs of mistletoe seems to have begun sometime between 1720 and 1784 in England, possibly due to a popular song of the era.