278 TROPICAL NATCTRE, AND OTHER ESSAYS. 



trees ; while in the Tropics the leaves of the orange tribe 

 are favourites with a large number of lepidopterous 

 larvae ; and our northern firs and pines, although abound- 

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

 attacks of beetles. My friend Dr. Eichard Spruce — who 

 while travelling in South America allowed nothing con- 

 nected 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. Aro- 

 matic 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 more 

 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 such plants as occur are 

 not, so far as Dr. Spruce has observed, aromatic ; and 

 as plants in such situations can hardly depend on insect 

 visits for their fertilization, the fact is comparable with 

 that of the flora of New Zealand, and would seem, to 

 imply some relation between the two phenomena, though 

 what it exactly is cannot yet be determined. 



I trust I have now been able to show you that there 



