FRANKINCENSE AND MYRRH 97 
of the chemical processes in each plant. Strangest 
of all are the indoloids in Aroids, Aristolochia, 
and Rafflesia, which attract carrion-loving flies 
and are said to arise from the breaking down of 
proteids. Besides the specificity of chemical com- 
position and scent there are other individual 
peculiarities, for some plants have fragrant leaves, 
while in others the incense is made only by the 
petals; some, like the grass of Parnassus, are sweet- 
scented only in the sunshine, while others, like t 
evening campion, wait for the night. The nauseat- 
ing smell of the corn-spurrey is particularly strong 
after a summer shower. 
The production of odoriferous substances is 
characteristic of flowering plants, but by no means 
confined to them; it is familiar, for instance, in the 
males of many butterflies and moths. Peculiarly 
transformed scales on the wings, or tufts of hairs 
on other parts of the body, exude an aromatic 
secretion, the secondary significance of which is 
that it appeals to the female insects. Some of 
the scents produced by male Lepidoptera are 
pleasant to the human olfactory sense, resembling 
musk, mint, vanilla, honey, and the like; others 
are suggestive of mice and bats. It is interest- 
ing to notice that in some cases, though glandular 
scales are abundantly present, we cannot smell 
anything, which probably means that the aromatic 
substances lie outside our range of olfactory stimu- 
lation, just as many rays of light lie beyond our 
range of vision. It may be recalled that the volatile 
