THE TROPICAL ZONE. 183 



contributes ; melting as it does into the next the Equa- 

 torial and possessing many characters in common with it, 

 it nevertheless has its own peculiarities. Those maps on 

 which the "lines of equal heat" are marked, show at a 

 glance that in some parts of this belt of land the heat is 

 even equal to that of the Equatorial Zone ; but, in spite of 

 this heat, the vegetation in some of those parts is extremely 

 meagre, on account of the counteracting influence of drought 

 or barren soil ; and in certain localities which are more par- 

 ticularly exposed to the blighting effects of the monsoons, 

 vegetation during the summer is perfectly dried up. 



The points of resemblance between this zone and the 

 Equatorial are many more than the points of difference, so 

 that a description of one will be in great measure a descrip- 

 tion of both. The most distinctive marks of the Tropical 

 Zone are the prevalence of the Tree-ferns and the dense 

 underwood which chokes the forests; whilst in common 

 with the Equatorial Zone (as we shall see when we reach it), 

 they are entangled with a variety of climbing plants, called 

 by the general name of Lianas, amongst which are different 

 genera of the beautiful Convolvulus tribe : the blossoms of 

 some of these, called Ipomcea, are almost the same in general 

 appearance and tints of colour as the Convolvulus major of 



