From my family's old The Christmas Carolers' Book in Story & Song by Torsten O. Kvamme, now out of print:

The Holly and the Ivy:

The beauties of Nature have always won the deep admiration of mankind and it was natural for pagan humanity to worship nature. Accordingly, we find many early carols about birds, flowers, and trees. In some of these we find the masculine (holly) and the feminine(ivy) elements symbolized. Originally some of these pagan carols were sung as a dance between the young men and the maidens-the men representing the holly and the maidens the ivy.

An amusing story concerning the rivalry of the sexes, as represented by the holly and ivy, is of an English knight who invited his tenants and their wives to dine with him at Christmas. When the food was on the table, the knight commanded that no man should eat until he who was master of his wife had sung a carol. After some hesitation, one of the men present arose and rather timidly sang a short carol. Then the command was given to the women's table that no woman should eat until she who was the master of her husband had sung a carol. "Whereupon," we are told, "they fell all to such a singing that there was never heard such a caterwauling piece of music, whereat the knight laughed heartily."

This carol, The Holly and the Ivy, has a curious blending of nature worship and Christianity. It is set to an old French carol-tune first published in England, in Sylvester's "Christmas Carols", 1861.