30 BURTON EDWARD LIVINGSTON 



Andropogon halapense 



LEAP SURFACE 



TIME 



INDEX 





seconds 





Upper 



234 



0.043 



Lower 



33 



0.303 



Entire 





0.173 (average) 



Water test (saturated paper) 



10 





Here the index for the lower fohar surface is nearly eight times 

 as great as for the upper. 



Experiment VIII. In the open oak forest above Oracle (about 

 64 kilometers or 40 miles northeast of Tucson, altitude 1372 

 m., or 4500 feet) the foliar transpiring power of the two forms 

 Rhus aromatica var. mollis (Gray) Ashe and Ardostaphylos pun- 

 gens H. B. K. was determined during the twelfth hour, September 

 8, 1912; The two shrubs were growing within a few meters of 

 each other. The first named is characterized by gray bark, 

 hairy shoots, and rather large, thin, lobed leaves of a strikingly 

 mesophytic aspect; the other is one of the characteristic man- 

 zanitas with brownish red bark, smooth shoots and smaller, much 

 thicker, entire leaves of strikingly xerophytic aspect. The results 

 of the tests follow. 



Rhus aromatica var. mollis 



LEAF 8UBFACE 



TIME 



INDEX 





seconds 





Upper 





Not determined 



Lower 



85 



0.160 



Water test (saturated paper) 



14 





Ardostaphylos pungens 



Upper 



692 



0.020 



Lower 



139 



0.098 



Entire 





0.059 (average) 



Water test (saturated paper) 



14 





The hygrometric paper failed to lose all its blue color on the 

 upper surface of the leaves of the apparently mesophytic form, 

 and consequently an index of transpiring power cannot be obtained 

 for this surface by the present method. It is clear, however. 



