"...Washington Irving, in Christmas Eve, relates the typical festivities surrounding the Twelve Days of Christmas, including kissing under the mistletoe (Washington Irving, The Sketch Book of Geoffrey Crayon, Gent). Irving continues his Christmas passage with a footnote:
"The mistletoe is still hung up in farm-houses and kitchens at Christmas, and the young men have the privilege of kissing the girls under it, plucking each time a berry from the bush. When the berries are all plucked the privilege ceases."
We moderns have conveniently forgotten the part about plucking the berries (which, incidentally, are poisonous), and then desisting from kissing under the mistletoe when the berries run out!"
Kissing under the mistletoe
According to Geek Trivia:
Which Common Christmas Decoration Is Actually A Parasite?
Among all the Christmas-related decorations millions will string, stand, and otherwise arrange this holiday season, only one of them is capable of wiping out entire swathes of forest. Mistletoe, an evergreen plant commonly hung in North American and European homes around Christmas, is a a hemi-parasitic plant that survives by driving its root structure right into the bark of a host tree and siphoning nutrients off of it–a large enough infestation can easily take down a healthy tree.