way of illustration regarding the phosphorescence exhibited
by animals, terrestrial and marine; but it ought to be noticed that
there are also a few cases in which the same phenomenon is to be
witnessed in plants. These are not so numerous as was at one time
supposed, the property having been mistakenly ascribed to some plants
not really luminous.

[Illustration: A PHOSPHORESCENT SEA.]

In some instances the mistake appears to have been due to a subjective
effect produced by brilliantly colored (red or orange) flowers, such
as the great Indian cress, the orange lily, the sunflower, and the
marigold. The fact that such flowers do give out in the dusk sudden
flashes of light has often been stated on the authority of a daughter
of Linnaeus, subsequently backed by the assertions of various other
observers. But most careful observers seem to be agreed that the
supposed flashes of light are in reality nothing else than a certain
dazzling of the eyes.

In another case, in which a moss, _Schistostega osmundacea_, has been
stated to be phosphorescent, the effect is said to be really due to
the refraction and reflection of light by minute crystals scattered
over its highly cellular leaves, and not to be produced at all where
the darkness is complete.

Among plants, genuine phosphorescence is to be found chiefly in
certain fungi, the most remarkable of which is _Rhizomorpha
subterranea_, which is sometimes to be seen ramifying over the walls
of dark, damp mines, caverns, or decayed towers, and emitting at
numerous points a mild phosphorescent light, which is sometimes bright
enough to allow of surrounding objects being distinguished by it. The
name of "vegetable glow-worm" has sometimes been applied to this
curious growth.

Among other phosphorescent fungi are several species of Agaricus,
including the _A. olearius_ of Europe, _A. Gardneri_ of Brazil, and
_A. lampas_ of Australia, and besides the members of this genus,
_Thelaphora caerulea_, which is the cause of the phosphorescent light
sometimes to be seen on decaying wood--the "touchwood" which many boys
have kept in the hope of seeing this light displayed. The milky juice
of a South American Euphorbia (_E. phosphorea_) is stated by Martins
to be phosphorescent when gently heated. But phosphorescence is
evidently not so interesting and important a phenomenon in the
vegetable as it is in the animal kingdom.

The whole phenomenon is one that gives rise to a good many ques