122 



PHYSICAL GEOGRAPHY. 



[Part I. 



ill the valley of the Ganges, found the fresh milky juice 

 of the Mudar (calotropis) to be but 72°, whilst the damp 

 sand in the bed of the river where it grew was from 

 90° to 104°. 



Even in temperate climates this phenomenon is calcu- 

 lated to excite admiration ; but it is still more striking 

 to find the Hke effect rather increased than diminished 

 in the tropics, where one would suppose that the juices, 

 especially of a small and delicate plant, before they could 

 be cooled by evaporation, would be hable to be heated 

 by the blazing sun. 



A difficulty would also seem to present itself in the 

 instance of fruit, whose juices, having to undergo a 

 chemical change, their circulation would be conjectured 

 to be slower ; and in the instance of those Avith hard skins, 

 such as the pomegranate, or with a tough leathery coat- 

 ing, hke the mango, the evaporation might be imagined 

 to be less than in those of a soft and spongy texture. 

 But all share alike in the general coolness of the plant, 

 so long as circulation supphes fluid for evaporation ; 

 and the moment this resource is cut off by the sepa- 

 ration of the fiaiit from the tree, the supply of moisture 

 faihng, the process of refrigeration is arrested, and the 

 charm of agreeable freshness gone. 



It only remains to notice the aquatic plants, which 

 are found in greater profusion in the northern and 

 eastern provinces than in any other districts of the 

 island, owing to the innumerable tanks and neglected 

 watercourses which cover the whole surface of this once 

 productive province, but which now only harbour the 

 alligator, or satisfy the thkst of the deer and the ele- 

 phant. 



The chief ornaments of these neglected sheets of water 



' See on tliis subject Lindlet's 

 Introduciion to Botany, vol. ii. book ii. 

 cli. viii. p. 215. 



CAlirENTEli, Animal Physiology, 



cli. ix. s. 407. Cartenxer's Vcye- 

 tahle Physiology, cb. xi. s. 407. Loncl. 



1848. 



