110 A MONTANE RAIN-FOREST. 



tropical montane rain-forest. Together with the structural diversities, 

 discoverable in the field or at the microscope, are diversities of physio- 

 logical behavior, discoverable by observation or experiment, and some- 

 times correlated with the structural features. There are quite as high 

 degrees of specialization to be found in the rain-forest as may be sought 

 in the desert. The prolonged occurrence of rain, fog, and high humidity 

 at relatively low temperatures places the vegetation of a montane 

 rain-forest under conditions which are so unfavorable as to be com- 

 parable with the conditions of many extremely arid regions. The 

 collective physiological activities of the rain-forest are continuous but 

 slow; those of arid regions are rapid, but confined to very brief periods. 

 In the regions of the earth which present intermediate conditions 

 between those of the desert and the reeking montane rain-forest may 

 be sought the optimum conditions for the operation of all essential 

 plant processes. It is, indeed, in such intermediate regions — tropical 

 lowlands and moist temperate regions — that the most luxuriant vege- 

 tation of the earth may be found, and it is also in such regions that the 

 maximum origination of new plant structures and new species has 

 taken place. 



