Evaporation and Plant Habitats in Jamaica. 271 



responding to the short period would be 6.7. The latter rate is 

 less than a single cubic centimeter per day. The average dailv 

 rate for the entire twenty-five days was 0.77 cc. in the ravine 

 and 8.2 in the open, the latter rate being 10.6 times the former. 

 While the rate in the open appears large by comparison with the 

 insignificant am.ount recorded in the ravine, a comparison of 

 this with the rates which are on record for other regions (r.ade 

 possible through the kindness of Prof. Livingston in furnishing 

 the. writer with unpubHshed data) shows that even the rate in 

 the open at Cinchona must be considered as relativelv low. 

 Fron^ a series of evaporation rates for various stations in the U. 

 S., carried on from the Desert Laboratory in 1907, in which 

 scries the instruments used were essentially the ordinary form 

 of atmom.eter as used in Jan^aica, the following selections have 

 been n:ade for comparison. The instruments in 1907 were oper- 

 ated in the open, at about the same height above the soil surface 

 as in the present series. Of course there is an imknown error 

 in the case of the data of 1907, due to the absorption of rain by 

 the cups. 



For the four weeks from May 19 to June 17, 1907, nearly the 

 same season of the year and length of period as that covered by 

 the Jam.aica observations, the daily rate at Cold Spring Harbor, 

 Long Island, varied from 15 cc. to 28 cc. and gave an average of 

 21 cc. Similar figures for West Raleigh, N. C, show a variation 

 from 13 cc. to 29 cc. and an average daily rate for the four weeks 

 of 22 cc. The rate at West Raleigh thus appears nearly thrice 

 as great, neglecting the rain error, as at Cinchona. The daily 

 rates at Tucson, Arizona, for the three weeks from May 26 to June 

 17, 1907, were 41, 50, and 40 cc, respectively, giving an average 

 of 44 cc, or a rate about 5.4 times as great as in the open at Cin- 

 chona. At Tucson the rain error was a vanishing quantity at 

 this season of the year, if, indeed, it was not actually nil. If 

 we consider the ravine habitat in Jamaica as a type of habitats 

 with very low evaporation rates, and the habitat in the open at 

 Tucson as a type of the other extreme, we may conclude, in 

 very general terms, that the range of evaporation rates for the 

 various unsubmerged plant habitats throughout the world may 

 be between the limits of the order of one and fiftv or sixty. 



