P. 136. Addition to the note on Tropæolum. In Sweden a very curious phenomenon has been observed on certain flowers, by M. Haggren, Lecturer in Natural History. One evening be perceived a faint flash of light repeatedly dart from a Marigold; surprized at such an uncommon appearance, he resolved to examine it with attention; and, to be assured that it was no deception of the eye, he placed a man near him, with orders to make a signal at the moment when he observed the light. They both saw it constantly at the same moment.
The light was most brilliant on Marigolds, of an orange or flame colour; but scarcely visible on pale ones.
The flash was frequently seen on the same flower two or three times in quick succession, but more commonly at intervals of several minutes; and when several flowers in the same place emitted their light together, it could be observed at a considerable distance.
This phaenomenon was remarked in the months of July and August, at sun-set, and for half an hour after, when the atmosphere was clear; but after a rainy day, or when the air was loaded with vapours, nothing of it was seen.
The following flowers emitted flashes, more or less vivid, in this order:
1. The Marigold, (Calendula Officinalis). 2. Garden Nasturtion, (Tropæolum majus). 3. Orange Lily, (Lilium bulbiferum). 4. The Indian Pink, (Tagetes patula et erecta).
Sometimes it was also observed on the Sun-flowers, (Helianthus annuus). But bright yellow, or flame colour, seemed in general necessary for the production of this light; for it was never seen on the flowers of any other colour.
To discover whether some little insects, or phosphoric worms, might not be the cause of it, the flowers were carefully examined even with a microscope, without any such being found.
From the rapidity of the flash, and other circumstances, it might be conjectured, that there is something of electricity in this phaenomenon. It is well known, that when the pistil of a flower is impregnated, the pollen bursts away by its elasticity, with which electricity may be combined. But M. Haggren, after having observed the slash from the Orange-lily, the anthers of which are a considerable space distant from the petals, found that the light proceeded from the petals only; whence he concludes, that this electric light is caused by the pollen, which in flying off is scattered upon the petals. Obser. Physìque par M. Rozier, Vol. XXXIII. p. iii.
P. 153. Addition to Avena. The following lines were by mistake omitted; they were designed to have been inserted after l. 102, p. 153.