298 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 larve 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 Labiate enjoy no 
immunity from insect attacks. The bitter leaves of the 
cherry-laurel are often eaten by the larve 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 larve; 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 
