530 



The Philippine Journal of Science 



1914 



of rubber stopper and glass tube to a water bottle at a lower 

 level that the cup is kept constantly filled, the water evaporating 

 from the moist clay surface being replaced from the bottle. 

 Entrance of rain water around the stopper into the reservoir 

 is prevented by means of an apron of waterproof cloth. The 

 absorption of rain water by the clay cup and the flowing of this 

 water back into the reservoir is effectually prevented by the in- 

 sertion of a mercury valve between the reservoir and cup, 

 which allows free movement of water from the former to the 

 latter but not in the reverse direction. All readings from the 

 instruments were reduced to the standard used by Livingston. 

 The results are given in Table XLVI in the form of average 

 daily rates for periods of four weeks. The atmometer in the 

 undergrowth was placed 25 centimeters above the ground, the 

 one in the second story was protected by the canopy of both 

 the dominant and second story, while the one in the top of the 

 dominant story was fully exposed to both sun and wind. 



The rate of evaporation under the main canopy is low, par- 

 ticularly so near the ground. In the top of the dominant story 

 the rate of evaporation is much higher, being on the average 

 more than six times as great as near the ground. The effect 

 of seasonal changes on evaporation is marked. In the top of the 

 dominant story the daily rate of evaporation for periods of four 

 weeks varies from 8.4 cubic centimeters to 22.1 cubic centimeters. 



Table XLVI. — Daily rate of evaporation in forest of Mount Maquiling, 



Laguna Province, Luzon. 



Period. 



Jan. 3 to Jan. 31 .. 

 Jan. 31 to Feb. 28 . 

 Feb. 28 to Mar. 28. 

 Mar. 28 to Apr. 25 

 Apr. 25 to May 23, 

 May 23 to June 20. 

 June 20 to July 18. 

 July 18 to Aug. 15 

 Aug. 16 to Sept. 12 

 Sept. 12 to Oct. 10 

 Oct. 10 to Nov. 7-- 



Nov. 7 to Dec. 6 



Dec. e to Jan. 2... 



Average 



30 centi- 

 meters 

 above the 

 ground. 



In second 

 story 

 tree. 



cc. 

 1.4 

 2.5 

 4.2 

 5.3 

 3.6 

 4.9 

 1.6 

 1.7 

 1.2 

 2.1 

 1.6 

 1.2 

 0.7 



2.6 

 5.6 

 7.5 

 7.5 

 6.6 

 9.0 

 3.8 

 7.0 

 5.0 

 4.2 

 4.7 

 3.7 

 1.8 



2.5 



6.3 



Top of 



dominant 



tree. 



cc. 



8.4 

 15.4 

 20.0 

 19.7 

 18.4 

 22.1 

 13.7 

 20.9 

 16.9 

 15.4 

 13.0 

 11.4 



8.6 



16.7 



