304 POPULAR GEOGRAPHY OP PLANTS. 



genus Agaricus, and having been first discovered by Dr. 

 Gardner, is named after him Agaricus Gardneri* 



But however beautiful vegetation may be in some parts 

 of Brazil, we cannot travel far into the interior without dis- 

 covering that perpetual verdure is. by no means the uni- 

 versal rule. In those regions where the atmosphere and 

 the soil are destitute of the proper degree of humidity, the 

 fall of the leaf takes place as in our colder zone. There is, 

 however, " a striking change in the relations of the different 

 seasons;" for the trees, instead of appearing leafless in win- 

 ter, there shed their leaves in summer : the same effect 

 which lack of heat produces upon the trees in our forests is 

 there occasioned by want of moisture. Nor is it only the 

 trees which lose their leaves, for even " the herbs vanish, 

 without leaving a trace of their existence." The light 

 forests of Brazil, called Catingas (Plate XVII. ), exhibit this 

 phenomenon; so beautiful a description of them is given 

 by Yon Martius, that a part at least of it must be here 

 borrowed from him.t " Everything around us," he says, 



* " There are other species of the same genus which exhibit a similar phe- 

 nomenon, namely, Agaricus olearius of De Candolle, and another very large- 

 one, occasionally found in Australia, which is described in Hooker's ' Journal 

 of Botany/ vol. i. p. 215." 



f As quoted by Meyen. 



