324 



L. A. GIDDINGS 



TRANSPIRATION FROM DIFFERENT SURFACES 



Another problem, not directly connected with the preceding, 

 was studied in the field experiments. For the purpose of making 

 a comparison between the amount of transpiration from the upper 

 and lower surfaces of Silphium leaves, vaseline was placed on 

 the upper surface of part of the leaves and on the lower surface 

 of the others. In the experiment given in detail the leaves were 



TABLE 9 



Transpiration {in grams per 100 sq. cm.) jrom upper and lower surfaces of leaves of 

 Silphium taken from different heights, ivith concurrent evaporation {in cubic 

 inches) from two Piche evaporimeters at different heights, relative humidity, and 

 wind velocity {in miles per hour). At the head of each transpiration columii 

 is stated the height from which the leaf tvas taken and the surface xvhich was trans- 

 piring. September 1, 1912 



taken from the same plant at different heights. No. 1 was taken 

 from a height of 20 cm., No. II from a height of 32 cm., No. Ill 

 from a height of 53 cm., and No. IV from a height of 72 cm. 

 No. I had vaseline on the upper surface; No. II on the lower 

 surface; No. Ill on the upper surface; and No. IV on the lower 

 surface. A number of experiments were performed with leaves 

 arranged as described, but the details for only one are given 

 in table 9. 



