5 6 4 SCIENCE PROGRESS 



Evaporation from a water surface is shown to be proportional 

 to (radius) 16 and the possible error in previous calibrations 

 is considered to be as high as 40 per cent. Ihe same -authors 

 have shown (Phil. Mag. 34, 308-21, 191 7) that the power 1-5 

 (above) is unaffected by changing external conditions, but 

 approaches 2 as the water level sinks below the rim of the 

 containing vessel. 



Briggs and Shantz (Journ. Agr. Res. 9, 277-92, 191 7) have 

 developed a point suggested by their earlier work (Journ. Agr. 

 Res. 5, 583, 1916) that the response of atmometers and plant 

 to climatic changes is not necessarily similar. Various types 

 of atmometer were used and differences were found between 

 these types as well as between atmometer and plant. Wind 

 velocity and solar radiation were the most disturbing factors. 

 Knight (Ann. of Bot. 31, 351, 191 7), also using various types of 

 atmometer, demonstrates the difference in response of plant 

 and atmometers to changes of wind velocity. Briggs and 

 Shantz find that a shallow tank corresponds most nearly to the 

 plant in its response to changing climatic conditions, and Knight 

 considers that the more convenient atmometers may be used 

 if wind velocity is controlled. These results have cast some 

 doubt upon the value of the results of many earlier transpira- 

 tion experiments in which atmometers were used without 

 controls of any kind, and close examination of the earlier papers 

 reveals figures and statements clearly demonstrating the un- 

 reliability of simple atmometer readings as corrections for 

 climatic changes. 



Briggs and Shantz (Journ. Agr. Res. 7, 155-212, 1916) 

 have continued their extensive large-scale open air trials on 

 transpiration and crop yield. Various crops have been dealt 

 with and the extent of correlation of the climatic factors 

 with transpiration rate has been calculated. As before, it was 

 found that some plants produce far more growth than others 

 per unit quantity of water transpired. 



The influence of stomatal change on transpiration, though 

 attracting less attention than formerly, has been the subject of 

 some work. Stalfelt (Sven. Bot. Tid. 10, 37-45, 191 6) finds 

 no simple relationship between stomatal aperture and trans- 

 piration, nor between the turgor of the guard cells and the 

 aperture. He prefers to allot shares in the control of stomatal 

 movement to a variety of factors, including water supply, 



