356 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



the general growth of these plants during two separate periods; 

 one in early summer, the other in late summer. Even with the 

 usual application of artificial heat, the winter efficiency for plant 

 growth remained very low. 



The evaporation measurements as determined with the white atmom- 

 eters (Livingston, 1915) showed somewhat higher and more uni- 

 form values for the winter than for the summer. The most pro- 

 nounced seasonal fluctuation was shown by the indices of total 

 radiation. These measurements were obtained by determining the 

 difference in water evaporated from the black and white atmometers. 



