The Ohio Vsl^aturalist, 



PUBLISHED BY 



The Biological Club of the Ohio State Uni'versity, 

 Volume IX. JANUARY, 1909. No. 3. 



TABLE OF CONTENTS. 



S.MITH— Recent Evajioration Invc stigations 417 



Detmers— Annual Report on the Plants New to the Ohio State List tor 1907-08 421 



Scott— The Ohio Species of the Genus Disoiiyclia 423 



Johnson— Variation in Syndesniou and Ilepatica 431 



RECENT EVAPORATION INVESTIGATIONS* 



J. Warren Smith. 



Evaporation depends in general upon the dryness of the air, 

 the velocity of the wind, and the temperature of the evaporating 

 water. It makes no appreciable difference whether the evap- 

 orating surface is in the sunshine or in the shade. 



The evaporation from a saturated soil covered with growing 

 plants is greater than from a water surface, but becomes less 

 when the level of complete saturation falls below the surface of 

 the ground. It has been calculated that when the water table is 

 six inches below the surface of the land the evaporation is 95% 

 of what it is from an open tank. 



Evaporation is greater from a forest of evergreen trees than 

 one of leafy trees; greater from leafy trees than from grass, and 

 greater from grass than a bare soil. 



Newell states that the runoff over any watershed is from 36% 

 to 47% of the rainfall, and the balance is evaporation, including 

 in that of course transpiration of plants. Over the Muskingum 

 watershed the average annual rainfall is 39.7 inches while the 

 runoff is 13.1 inches. 



Formulas for the annual evaporation over a watershed have 

 been worked out as follows: 



E = 15.50 + 0.16X annual rainfall. (1) 



or if thought best to consider the temperature, 



E = 15.50+ (0. 16 XR) X (0.05 XT— 1.48) (2) 



R.=mean annual rainfall; T=mean annual temperature. 



*Read at the meeting of the Ohio Academy of Science. 



417 



