It has been asserted that this phenomenon was due to optical illusion, but the experience of Goethe points to a different conclusion. He says, “On the 19th of June, 1799, late in the evening, when the twilight was passing into a clear night, as I was walking up and down with a friend in the garden, we remarked very plainly about the flowers of the Oriental poppy, which were distinguishable above every thing else by their brilliant red, something like flame. We placed ourselves before the plant, and looked steadfastly at it, but could not see the flash again, till we chanced in passing and repassing to look at it obliquely; and we could then repeat the phenomenon at pleasure. It appeared to be an optical illusion, and that the apparent flash of light was merely the spectral representation of the blossoms of a blue-green.” It is an interesting fact, that the light has been observed principally about yellow flowers, as the sunflower (_Helianthus annuus_), the _Rose d’Inde_ and _Oeillet d’Inde_, the garden marigolds (_Calendula_), yellow lily, and others. The Swedish naturalist, Professor Haggern, was fortunate in observing the light about the marigold. His first impression was, that it was an illusion; and to convince himself, he placed a man near at hand with orders to make a signal when he saw the light: the result was, that both observed it simultaneously. The light appeared as a flash, often in quick succession from the same flower, and again only after several moments. It was only observed at sunset on dry days. Professor Haggern’s observations were made upon the marigold, garden nasturtium (_Tropæolum majus_), the orange lily (_Lilium bulbiferum_), and the French and African marigolds (_Tagetes patula_ and _T. erecta_). He was at first disposed to consider the light due to some insect, but finally decided that it was electrical. In 1857 the press of Upsala, Sweden, contained accounts of remarkable lights that had been observed about a group of poppies in the Botanic Gardens. The observer, M. Th. Fries, a well-known botanist, in passing the flowers, noticed three or four emitting little flashes of light. Believing that he was the victim of an optical illusion, and wishing to satisfy himself, he took a friend to the place at the same hour on the following night, without, however, informing him what he had seen. The latter immediately noticed the light, and soon the garden was thronged with persons interested, who wished to see the flowers that “threw out flames.” Later, fourteen persons saw the exhibition at once, not only upon the _Papaver orientale_, but on the _Lilium bulbiferum_; and before the curious phenomenon ceased, over one hundred and fifty reliable observers were enabled to testify to the delight they had experienced in watching the gleams of light play about these flowers; the doubters and critics, of which there were many, being effectually silenced. [Illustration: PLATE XXI. LUMINOUS UMBELLULARIA.