A species of wood fungus found about the roots of old trees is designated “fairy-butter,” because after rain, and when in a certain degree of putrefaction, it is reduced to a consistency which, together with its colour, makes it not unlike butter.  The fairy-butter of the Welsh is a substance found at a great depth in cavities of limestone rocks.  Ritson, in his “Fairy Tales,” speaking of the fairies who frequented many parts of Durham, relates how “a woman who had been in their society challenged one of the guests whom she espied in the market selling fairy-butter,” an accusation, however, which was deeply resented.

Browne, in his “Britannia’s Pastorals,” makes the table on which they feast consist of: 

  “A little mushroom, that was now grown thinner
  By being one time shaven for the dinner.”

Fairies have always been jealous of their rights, and are said to resent any infringement of their privileges, one of these being the property of fruit out of season.  Any apples, too, remaining after the crop has been gathered in, they claim as their own; and hence, in the West of England, to ensure their goodwill and friendship, a few stray ones are purposely left on the trees.  This may partially perhaps explain the ill-luck of plucking flowers out of season[8].  A Netherlandish piece of folk-lore informs us that certain wicked elves prepare poison in some plants.  Hence experienced shepherds are careful not to let their flocks feed after sunset.  One of these plants, they say, is nightwort, “which belongs to the elves, and whoever touches it must die[9].”  The disease known in Poland as “elf-lock” is said to be the work of evil fairies or demons, and is cured by burying thistle-seed in the ground.  Similarly, in Iceland, says Mr. Conway, “the farmer guards the grass around his field lest the elves abiding in them invade his crops.”  Likewise the globe-flower has been designated the troll-flower, from the malignant trolls or elves, on account of its poisonous qualities.  On the other hand, the Bavarian peasant has a notion that the elves are very fond of strawberries; and in order that they may be good-humoured and bless his cows with abundance of milk, he is careful to tie a basket of this fruit between the cow’s horns.

Of the many legendary origins of the fairy tribe, there is a popular one abroad that mortals have frequently been transformed into these little beings through “eating of ambrosia or some peculiar kind of herb."[10]

According to a Cornish tradition, the fern is in some mysterious manner connected with the fairies; and a tale is told of a young woman who, when one day listlessly breaking off the fronds of fern as she sat resting by the wayside, was suddenly confronted by a “fairy widower,” who was in search of some one to attend to his little son.  She accepted his offer, which was ratified by kissing a fern leaf and repeating this formula: 

  “For a year and a day
  I promise to stay.”