DIVISIONS OF THE ANDEAN FLORA. 105 



through the temperate regions of the northern hemi- 

 sphere, and a smaller number of representative species 

 of groups belonging to the tropical American flora. 

 The climate of this region is marked by the absence 

 of all extremes of temperature. Cool nights, in which 

 frosts are infrequent and of short duration, alternate 

 with days wherein the shade temperature rarely sur- 

 passes 70°. The division between the temperate and 

 subtropical zones is marked rather by the more fre- 

 quent, though moderate, rainfall, which in the former 

 recurs at intervals throughout the year, than by any 

 marked change of temperature. Hence there may be 

 distinguished a rather broad intermediate zone in 

 which many of the characteristic forms of each meet 

 and are intermingled ; but this does not appear to be 

 defined by any genera, or even by more than a few 

 species peculiar to it, and does not deserve to be 

 treated apart in a general survey of the flora. 



The upper, or Alpine, zone of the Cordillera, ex- 

 tending from about thirteen thousand feet to the 

 utmost limit of vegetation, is well defined by the 

 circumstance that night frosts here recur throughout 

 the year, and snow lies at least occasionally on the 

 surface, while a somewhat greater amount of aqueous 

 precipitation, in the form of rain or snow, combined 

 with diminished evaporation, maintains a moderate 

 degree of moisture in the soil. The proportion borne 

 by some groups of the characteristic Andean flora as 

 compared with the entire vegetable population is here 

 larger than in the temperate zone, but other types 

 better adapted to the climate of the latter zone are 

 here nearly or altogether wanting. The forms com- 



