12 



A MONTANE RAIN-FOREST. 



In 1906 the night of January 12 was clear and still; that of February 

 28 was clear with a high wind; that of January 13 was clouded and still. 

 The readings were as follows : 



Table 3. 



These observations, taken on the open lawn at Cinchona, show that 

 the temperatures to which herbaceous vegetation in open situations 

 may be subjected are as much as 10.5° lower than the recorded air 

 temperatures on clear nights when active radiation is possible. The 

 fact that radiation takes place most actively during the early hours of 

 the night, while the minimum temperature is always reached just before 

 daybreak, makes it necessary to derive the lowest temperatures due to 

 radiation by subtracting 10° or thereabouts from a temperature higher 

 than the lowest minimum as shown by the records of monthly extremes. 

 This would still indicate the possibility of occasional frost at Blue 

 Mountain Peak, but probably no frost has ever taken place at altitudes 

 lower than 6,500 feet (1,980 meters). The open character of the vege- 

 tation on the higher peaks and ridges, to be presently described, would 

 make possible an amount of radiation sufficient to give a depression as 

 great as that observed at Cinchona. 



SOIL TEMPERATURE. 



Readings of the temperature of the soil at a depth of 6 feet were made 

 at Cinchona for five years, the apparatus being an ordinary driven 

 thermometer in metal casing. The instrument stood in ground covered 

 by a sod and was read twice daily, at 7 a. m. and 3 p. m. The mean 

 of these readings, when they were not the same, is taken as the daily 

 mean and in table 4 are exhibited the monthly means for the years 

 1892 to 1896, inclusive. 



Table 4. 



Annual mean 61.6° (16.4° C.) 



Annual mean range 2.9° (1.5° C.) 



