INTRODUCTORY ESSAY. 95 



Bengal, the west coast of the Madras peninsula, and of Cey- 

 lon, contrast strongly with the drier parts of the intertropical 

 zone, and still more so with the loosely-timbered districts of 

 Central India, and of the base of the western Himalaya. 

 The absolutely sterile deserts are confined to the extensive 

 plains, which are all cut off from the rains by being placed to 

 leeward of mountain-ranges, or by other causes. There are 

 hence in India no vast plains clothed with gigantic timber- 

 trees, such as cover immense areas of the American tropics ; 

 and even the valleys of the great Indian rivers, the Ganges, 

 Nerbada, etc., are nowhere heavily timbered, but are gene- 

 rally absolutely destitute of forest, and extremely populous 

 and highly cultivated*. 



The tropical forests of India may be divided into those 

 which inhabit perennially humid districts, and those which 

 are confined to regions presenting contrasted seasons, of sum- 

 mer rain and winter drought. 



The perennially humid forests are uniformly characterized 

 by the prevalence of Ferns, and, at elevations below 5000- 

 7000 feet, by the immense number of epiphytal Orchideoi, 

 Orontiacea, and Scitaminece : they contain a far greater 

 amount of species than the drier forests, and are further cha- 

 racterized by Zingiberacem, Xyriders, Palms, Pandanete, Dra- 

 cosna, Piper, Chloranthus, Urticacea {especially Artocarpea and 

 Fid), AraliacecB, Apocynem, shrubby Rubiacem, Aurantiaceae, 

 Garciniaceee, Anonacece, Nutmegs, and Dipterocarpem. 



The drier tropical forests of the regions with contrasted 

 seasons, are much modified in luxuriance arid extension by 

 the winter cold in those extratropical latitudes over which 

 they spread. In the chapter upon the meteorology of India, 

 it is shown that though the summer heat scarcely decreases 



* It is a mucli discussed question in India, whether the Gangetic plain was 

 ever covered with forest : the best authorities consider that it never was so ; but 

 there are others who hold the contrary opinion, and aver that the destruction 

 of the timber has produced a great change in the climate. The absence of vege- 

 table remains in the alluvium appears unfavourable to the latter opinion. 



