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 the 

 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 



