visible, and it may be remembered how in one of Andersen's
stories the elfin princess has the faculty of vanishing at will, by
putting a wand in her mouth.[18] But these were not the only plants
supposed to confer invisibility, for German folk-lore tells us how the
far-famed luck-flower was endowed with the same wonderful property; and
by the ancients the heliotrope was credited with a similar virtue, but
which Boccaccio, in his humorous tale of Calandrino in the "Decameron,"
applies to the so-called stone. "Heliotrope is a stone of such
extraordinary virtue that the bearer of it is effectually concealed from
the sight of all present."

Dante in his "Inferno," xxiv. 92, further alludes to it:

"Amid this dread exuberance of woe
Ran naked spirits winged with horrid fear,
Nor hope had they of crevice where to hide,
Or heliotrope to charm them out of view."

In the same way the agate was said to render a person invisible, and to
turn the swords of foes against themselves.[19] The Swiss peasants
affirm that the Ascension Day wreaths of the amaranth make the wearer
invisible, and in the Tyrol the mistletoe is credited with
this property.

But some plants, as we have already pointed out, were credited with the
magic property of revealing the presence of witches, and of exposing
them engaged in the pursuit of plying their nefarious calling. In this
respect the St. John's wort was in great request, and hence it was
extensively worn as an amulet, especially in Germany on St. John's Eve,
a time when not only witches by common report peopled the air, but evil
spirits wandered about on no friendly errand. Thus the Italian name of
"devil-chaser," from the circumstance of its scaring away the workers of
darkness, by bringing their hidden deeds to light. This, moreover,
accounts for the custom so prevalent in most European countries of
decorating doorways and windows with its blossoms on St. John's Eve. In
our own country Stowe[20] speaks of it as its having been placed over
the doors together with green birch, fennel, orpine, and white lilies,
whereas in France the peasantry still reverence it as dispersing every
kind of unseen evil influence. The elder was invested with similar
properties, which seem to have been more potent than even those
attributed to the St. John's wort. According to an old tradition, any
baptized person whose eyes were anointed with the green juice of its
inner bark could see witches in any part of