6 MR. J. BALL ON THE FLOHA 



April — corresponding to October in the nortlicrn homispliere 

 I found the mean temperature at Chicla about 52° Fahr., the 

 extremes observed being G5°*7 at noon on the 21st, and 42° soon 

 after sunrise on the 22nd, before the rays had reached the adjoin- 

 ing slopes. Eain, according to local information, occurs sparingly 

 at irregular, but not distant, intervals throughout the year. On 

 the night of the 21st rain fell in some abundance, and lay in the 

 form of snow on the higher parts of the range above the level of 

 about 15,000 feet, but had nearly disappeared two days later. It 

 would appear that as to the two main factors of climate — tem- 

 perature and moisture — there is a considerable difference between 

 the puna^ or plateau region between the two great ranges of the 

 Andes, and places of equal elevation on the western slope. 

 Poeppig, Tschudi, and other scientific travellers, agree in speaking 

 of the frequency of storms in the puna region, which, at heights 

 little exceeding 12,000 feet, are often accompanied by heavy snow, 

 and they record relatively sharp frosts at places not much higher 

 than Chicla- Speaking roughly, I am inclined to place the lower 

 limit of the Alpine zone on the puna at about 12,000 feet. It 

 may be taken for granted that with a moister climate the alpine 

 or proper Andine — flora is more fully developed there than on 

 the drier western slopes, while a few xerophilous species may be 

 confined to the latter region. 



Speaking of the Equatorial Andes, M. Andre is disposed to 

 divide the region above the temperate zone, admitting a subandine 

 as well as an andine zone, the latter corresponding to the alpine 

 zone of Gri^ebach and other writers. I was not satisfied that 

 the facts justified such a subdivision in the limited field of ob- 

 servation open to me. Some species are doubtless limited to 

 the lower part, and some others to the upper part of what I 

 have termed the temperate zone; but I perceived no indications 

 of a general change in the constituents, or in the aspect of the 

 flora, excepting those which I have already specified, and I should 

 divide the vegetation of the valley that extends from the water- 

 shed of tlie western Cordillera to the mouth of the Eimac near 

 Callao into three zones — a subtropical dry zone, ascending from 

 the coast nearly to the level of 8000 feet; a temperate zone, 

 reaching to a lieight of 12,500 or 13,000 feet ; and, finally, an 

 alpine zone, extending upward to tlie crest of the Cordillera. 

 The projecting eminences on the crest must certainly attain the 

 height of 17,000 feet above sea-level, and some of them may 



