4 INTRODUCTION. 



vital action is the less because the air is less 

 dense, therefore colder, and consequently has a 

 greater evaporative power : yet the mountainous 

 countries are better supplied with humidity than 

 plains; therefore, the dwarfed growth of plants, 

 in such situations, must be considered as resulting 

 much more from their diminished action than 

 from any excess of evaporation. 



Hence, if w^e ascend the slopes of mountains, 

 we find upon them plants rescmbhng those of 

 a succession of latitudes gradually getting colder, 

 than the mean temperature of that which an- 

 swers to the level of the sea in the same lati- 

 tude as the mountains ; so that, upon very lofty 

 mountains near the equator, the Andes, in upper 

 Peru, for example, we meet with something 

 resembling the succession of plants, in the 

 whole circuit of the globe ; but it is a resem- 

 blance only and not an identity, because, although 

 it be possible to find upon the side of the moun- 

 tain, places which have the same mean tem- 

 perature for the year, as is found in every 

 parallel of latitude, yet both the daily and sea- 

 sonable distribution of the sun's action are very 

 dilferent, and it necessarily follows that the habits 

 and even the characters of the plants are equally 

 so. 



