388 



MINNESOTA BOTANICAL STUDIES 



these conditions,'* a still closer anahsis of this particular case may be 

 given as it will help to explain similar conditions in the futvire. 



The first period of increased trans])iration was due to partly 

 sunny weather. This was followed by four days of cloudiness. 

 During this second period the hydro-thermograph registered a mean 



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l-"ig. 



An analysis of the combined graphs shown in figure 5. The light lines 

 indicate transpiration rates of control plants. 



of 70" F. with a range of about 10° F. while the relative humidity 

 fluctuated only a little above or below 50 per cent. Then came a 

 period of four days of sunshine when the day temperatures mounted 

 to 80° to 85° F. and the humidity at the same time decreased. Fi- 

 nally ensued a period of cloudiness when again both evaporation and 

 transpiration were lessened. 



