TRANSPIRATION OF SILFHIUM 



311 



any marked degree, l)ut the guard cells were strongly cutinized 

 on the outside; the palisade cells were greatly elongated; and 

 water storage cells were abundant. 



In an effort to determine the condition of the stomata during 

 the long hot afternoons, pieces of leaves at different heights were 

 plunged into absolute alcohol between 2 and 3 p.m. to fix the 

 stomata for later examination. Subsequently, upon shaving off 

 pieces of the epidermis and examining them under the micro- 

 scope, it was found that all the stomata were more or less closed, 

 most of them completely so. This would suggest that during 



TABLE 1 



The number of stomata per square centimeter in leaves of Silphium from heights of 18, 



65 and 100 cm. 



the afternoon the stomata are practically closed, but the use of 

 rather large pieces of leaves renders the observation of somewhat 

 doubtful value. ^ 



EVAPORATION AT DIFFERENT HEIGHTS 



For the purpose of determining what effect height above the 

 ground has on evaporation, an experiment was performed at a 

 station set up on the laboratory grounds with Piche evapor- 

 imeters at different heights. The lowest evaporimeter was hung 

 so that the bottom was 10 cm. from the ground. In this position 

 it was somewhat protected by surrounding vegetation. The 



1 See Lloyd F. E. 

 p. 28. 1908. 



The Physiology of Stomata. Carn. Inst. Wash. Publ. 82, 



