228 THE ENTOMOLOGIST. 



Another question which here comes before us is the origin 

 and meaning of the odoriferous glands of leaves. Dr. Hooker 

 informed me that not only are the New Zealand plants 

 deficient in scented flowers, but equally so in scented leaves. 

 This led me to think that perhaps such leaves were in some 

 way an additional attraction to insects, though it is not easy 

 to understand how this could be, except by adding a general 

 attraction to the special attraction of the flowers, or by 

 supporting the larvae which, as perfect insects, aid in 

 fertilisation. Mr. Darwin, however, informs me that he 

 considers that leaf-glands bearing essential oils are a pro- 

 tection against the attacks of insects where these abound, 

 and would thus not be required in countries where insects 

 were very scarce. But it seems opposed to this view that 

 highly aromatic plants are characteristic of deserts all over 

 the world, and in such places insects are not abundant. 

 Mr, Stainton informs me that the aromatic Labiatae enjoy no 

 immunity from insect attacks. The bitter leaves of the 

 cherry-laurel are often eaten by the larvae of moths that 

 abound on our fruit-trees; while in the Tropics the leaves of 

 the orange tribe are favourites with a large number of Lepi- 

 dopterous larvae ; and our northern firs and pines, although 

 abounding in a highly aromatic resin, are very subject to the 

 attacks of beetles. My friend Dr. Richard Spruce — who, 

 while travelling in South America, allowed nothing connected 

 with plant-life to escape his observation — informs me that 

 trees whose leaves have aromatic and often resinous secretions 

 in immersed glands abound in the plains of tropical America, 

 and that such are in great part, if not wholly, free from the 

 attacks of leaf-eating ants, except where the secretion is 

 only slightly bitter, as in the orange tribe, orange-trees being 

 sometimes entirely denuded of their leaves in a single night. 

 Aromatic plants abound in the Andes up to about 13,000 

 feet, as well as in the plains, but hardly more so than in 

 Central and Southern Europe. They are, perhaps, most 

 plentiful in the dry mountainous parts of Southern Europe; 

 and, as neither here nor in the Andes do leaf-eating ants 

 exist. Dr. Spruce infers that, although in the hot American 

 forests where such ants swarm, the oil-bearing glands serve 

 as a protection, yet they were not originally acquired for that 

 purpose. Near the limits of perpetual snow on the Andes 



