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THE AMERICAN NATURALIST [Vol. XLIII 



and mentions the dry cured meat prepared by peasants 

 in some places in the Alps, which, it is stated, is due to 

 the greater drying power of the air. The reasoning is 

 all but conclusive. There can be no doubt though, that 

 the verdict of the soundest reasoning ought to be con- 

 firmed in the court of experimental evidence. 



In 1907, Livingstone measured evaporation in the Santo 

 Catalina mountains and found a decrease with altitude. 

 This, perhaps, was not surprising, seeing that the series 

 began in the desert below and extended to the cool moun- 

 tain regions above. 



During the past summer, I set up two series of instru- 

 ments in the Selkirks at altitudes ranging from 800 

 m. to 2,900 m. Mountain flanks having a fairly uniform 

 exposure were chosen, only short horizontal distances 

 were involved, two stations were chosen at each altitude 

 so that one might check the other. The season was favor- 

 able, being unusually warm and dry; one series was in 

 perfect operation for twelve weeks. The results on the 

 whole seem to exclude the idea that in the Selkirks 

 evaporation increases with altitude. The maximum in 

 each case was at the next lowest station, altitude of 1,1°° 

 meters. Above that there was a gradual and irregular 

 diminution. It may be that the lower temperatures of 

 higher altitudes more than offset the factors which make 

 for increased evaporation. Indeed, it appears certain 

 from the above data that for the Selkirks, such is the case. 



The data in question, however, present only weekly 

 totals. The possibility that excessive evaporation may 

 take place during certain portions of the day, still remains 

 to be studied. It must be ever kept in view, too, that it 

 is not the absolute amount of transpiration which is so 

 much of importance to the plant, as the balance between 

 water supply and water loss. If the lower soil tempera- 

 tures of higher altitudes make the obtaining of water 

 more difficult, then the same or even a diminished evapora- 

 tion rate might demand increased power of resistance on 

 the part of the plant. 



