54 
THE AMERICAN BOTANIST. 
with the brightness of a glow-worm when the surface had 
a wet cloth applied for a short time. The editor of the 
Gardeners Chronicle found that a small piece of this root 
retained its power of lighting up a good while, only the 
light got feebler. The Brahmins, it was said, knew its 
peculiarity, but all the plants did not possess this lumin- 
osity at their roots. They imagined the light of it drove 
away demons. 
What is singular also, the sap of some trees in exotic 
regions appear luminous, as it flows from a wound. One 
shrub, indeed, has been named Euphorbia phosphorea 
from this fact, and there are other instances. We have it 
on the authority of the late Professor Henslow that the 
European dittany {Dictamnas fraxinella) evolves some, 
inflammable gas in the evening, and, should the air be 
still, if a light is brought near, the plant will be enveloped 
in a transient flash, but receives no injury. Before hiS; 
time the daughter of Linnaeus had stated that a plant of 
D. albus, which she approached with a candle, became 
surrounded by a light blue flame. Dr. Hahn suggested 
the dittany might produce hydrogen or evolve an ethereal 
oil from the flowers; he made many experiments amongst 
species of Dictamnus unsuccessfully, but at last found a 
rather faded plant, from wdiich, when he held a match,- 
came a reddish crackling flame, having an incense-like 
smell. Then he ascertained this can only happen during 
the limited period of the flower's fading, and also that 
there are glands containing an aromatic oil. A Hima- 
layan species of the genus has the reputation of making a 
brilliant display after dark, even when not approached by 
a light. 
In 1843 Mr. Dowden described to the British Associa- 
tion aluminous appearance witnessed one August evening 
on the double variety of the common marigold. This w^as 
seen by four persons. During the twilight a golden flame 
appeared to play from petal to petal of some of the heads, 
making a sort of corona round the discs. This emanation 
grew less vivid as the light decreased, then vanished. 
