46 



A MONTANE RAIN-FOREST. 



character of the daily humidity curve at Cinchona and in the ruinate 

 is not entirely due to their position on the leeward side of the mountains 

 but must be partly attributed to the fact that both of these localities 

 have been deforested. The traces mentioned were taken at New 

 Haven Gap, on the main ridge of the Blue Mountains, the first in a 

 small clearing, the second in the Windward Slope type of forest which 

 occupies the summit of the gap 200 yards distant. The former re- 

 sembled the traces taken at Cinchona and in the ruinate; the latter 

 showed a much more constant maintenance of high humidity, and 

 resembled the curves for Windward Slope Forest. 



The records secured at Sir John Peak were for the floor of an open 

 stand of Podocarpus on the extreme summit (see plate 18). The 

 curve from this location (plate 28, fig. A) is similar to that secured on 

 the Ridge at 5,000 feet (plate 24, fig. A), that is to say, it exhibits a 

 high and rather constant humidity on certain days those which are 

 rainy or entirely cloudy and on other days shows depressions which 

 are nearly as pronounced and long as those of the Leeward Slopes. 



EVAPORATION. 



The corrected readings of total weekly evaporation, which were 

 secured in the open air just outside the laboratory at Cinchona and in 

 two stations in the rain-forest, are exhibited in table 10. 1 There is, 

 roughly speaking, an inverse relation between the weekly rainfall and 

 the corresponding amount of evaporation. The highest weekly evapo- 

 ration rates were 125.1 c.c. for the week ending August 3, and 101 c.c. 

 for the week of November 22, in both of which weeks there was an 

 exceptionally light rainfall. The lowest weekly evaporation occurred 

 in the first two weeks of November, during a period of exceptionally 

 severe precipitation. The average daily evaporation during the 

 weeks of highest and lowest rate were respectively 17.9 and 1.8 c.c. 



The Ridge station was located in an open stand of Cyrilla, Tovomita, 

 Ilex, and Clethra, and the atmometer was placed on the ground in such 

 a position that it could be struck by the sun's rays during about half 

 of the day, owing to the openness of the forest canopy. The weekly 

 totals of evaporation for this station ranged from a maximum of 41.3 c.c 

 to a minimum of 5.8 c.c., the rate in the former case being slightly 



J The atmometers used were calibrated by comparison of their rate of loss with that of a standard 

 cup and with the loss from petri dishes. The standard used was Livingston's cup No. 405. The 

 petri dishes were of the standard size, 94 mm. in diameter, and were filled to within 3 mm. of the 

 rim. The readings in terms of No. 405 may be 

 converted into terms of standard No. 200 by 

 multiplying by 0.82. The following figures show the 

 coefficients of correction of the cups used, column A 

 being the original coefficients determined at Tuc- 

 Bon, B the coefficients determined at Cinchona in 

 July, C those determined at Cinchona in August, D 

 those at Cinchona in November, and E those found 

 in Tucson after use. 



