HEAT OF VEGKTABLES, 83 



dark Double Velvet Rose, a variety, as we presume of 

 Rosa centifolia. Another report of the same kind has 

 been raised concerning the Maltese Oranges, whose red 

 juice has been attributed to their being budded on a 

 Pomegranate stock, of which I have never been able to 

 obtain the smallest confirmation. 



Heat can scarcely be denominated a secretion, and yet 

 is undoubtedly a production, of the vegetable as well 

 as animal body, though in a much lower degree in the 

 former than the latter. The heat of plants is evinced 

 by the more speedy melting of snow when in contact 

 with their leaves or stems, compared with what is lodg- 

 ed upon dead substances, provided the preceding frost 

 has been sufficiently permanent to cool those substances 

 thoroughly. Mr. Hunter appears to have detected this 

 heat by a thermometer applied in frosty weather to the 

 internal parts of vegetables newly opened. It is evident 

 that a certain appropriate portion of heat is a necessary 

 stimulus to the constitution of every plant, without 

 which its Hving principle is destroyed. (IS) Most 

 tropical plants are as effectually killed by a freezing de- 

 gree of cold, as by a boiling heat, and have nearly the 



(13) [The tendency of plants is to preserve an uniform tem- 

 perature, and to resist both heat and cold. Fruits and leaves, 

 situated in the sun, preserve themselves cool, while surrounding 

 objects are heated. Sonnerat discovered in the island of Lucdu 

 a rivulet, the water of which was so hot, that a thermometer im- 

 mersed in it rose to i7^° Fahr. Swallows when fiying seven 

 feet high over it dropped down motionless. Notwithstanding- 

 the heat, he observed on its banks two species of Asfialathus, 

 and the Vitex agnus castua, which with their roots swept the 

 water. In the island of Tanna, Messrs. Forsters found the 



