It is certain, however, that a great many different phenomena have been described as will-o’-the-wisp. Some of these are: (1) The phosphorescence of decaying wood (“fox fire”) and other vegetable matter. This is due to luminous fungi. According to H. Molisch there are some forty-five species of fungi, including twenty species of bacteria, that have the property of luminosity. Sometimes the ground under a forest is illuminated on all sides with a soft, white light from decaying leaves. (2) Fireflies, including glowworms (the wingless females of the firefly and the larvæ). (3) Luminous birds and animals. Their luminosity is supposed to be due to parasitic fungi. Certain species of skunk have been described as giving off in the darkness a continuous flame, the head being fiery red, which blends into a bright blue at the tail. (4) Ball lightning. (5) St. Elmo’s fire. (6) Moving lanterns, distant lights of houses, and other lights due to human agency. (7) Burning gas ascending from marshes, stagnant pools, and the like. Marsh gas and other inflammable gases commonly rise from such places, and are often ignited by man, or by lightning, etc. Such fires are sometimes seen by day as well as by night. (8) Burning naphtha springs. Excluding the numerous reported cases of will-o’-the-wisp in which the phenomenon may be plausibly identified with one of those mentioned above, there remain several cases, some of them reported by very careful observers, which appear to belong to a different category. The reports in question differ somewhat in details, but yield the following composite description: Small luminous bodies, “about as large as your fist,” or “the size of a candle flame,” are seen hovering a few feet above the ground; not only over marshes and pools, but also over dry land. Sometimes they are stationary; at other times they appear to drift with the wind, or even to move independently. They appear and disappear, after the manner of fireflies. They do not set fire to objects with which they come in contact, and are believed to be without sensible heat. Their color is most often described as bluish, but may be yellow, purple, green, etc.; rarely pure white. They are without odor and without smoke. Traditionally they are associated with graveyards, but in very few of the cases heretofore recorded were they actually seen in such places. The popular idea that they flee from the traveler who tries to approach them and follow him when he seeks to avoid them is also unsupported by the evidence thus far adduced.