Certain trees are considered to be under the protection of the 'fairies', and to destroy a fairy tree is a very dangerous act. WILLOW and ALDER are especially beloved of water spirits. Thorn trees are said to be sacred to the fairies, especially if three are found growing together. IVY is protective of milk. Ivy, woodbine and rowan are combined in wreaths and placed over the lintels of cow houses. Many plants are said to have magical properties, such as Saint John's Wort, pearlwort, vervain, yarrow, woodbine, foxglove and many others. Milk could be charmed from another's cows, but certain plants, such as pearlwort, could be used to counteract this.