Transpiration Greatest During Sunshine 45 



until 6:15 P. M. the maize lost 7.5 pounds of water and the 

 evaporometer lost 67.5 c. c., or 4.12-cu. in. ; but during the night 

 again the loss from the maize was too small to be measured, 

 while the evaporometer showed a loss of 4.6 c. c., equal to .28 

 cu. in. 



On the next day, Aug. 9, all of the cylinders in the plant- 

 house were weighed during the forenoon, which was cloudy, but 

 in the afternoon it cleared and the sun shone brightly. During 

 the whole of the afternoon and until 9 P. M. we forced steam from 

 the boiler, under a pressure of 7 to 15 pounds, into the plant-house 

 through an inch pipe wide open, and kept the house closed 

 through the experiment. Steam filled the whole plant-house and 

 condensed upon the glass and walls, dripping in many places from 

 the roof. 



On the following morning, Aug. 10, a number of the cylinders 

 were again weighed, to see if there had been any loss of water 

 from the plants, and it was found that three of the small clover 

 cylinders had lost an average of 2 pounds each, while their mean 

 loss during the seven preceding days had been at the rate of 2f 

 pounds. Eight stalks of maize in a large cylinder lost 7 pounds, 

 while its mean loss per day had been 6f pounds. Six small cylin- 

 ders, each containing 4 stalks of maize, lost an average of 4| 

 pounds each, while the mean loss for the week had been 4g 

 pounds. 



It thus appears that during the night and cloudy weather 

 plants lose but little moisture, but that when the sun shines 

 brightly, even in an atmosphere nearly saturated with moisture, 

 there is a very marked loss of water from the growing plants, 

 and it would appear that the amount is nearly or quite as large 

 in a damp as in a dry air. These observations seem strange, 

 and need to be confirmed ; but they are in harmony with our 

 observations regarding the amount of water required for a pound 

 of dry matter. 



If we bring together all of the observations made in Wiscon- 

 sin on the amount of water used in the production of dry matter 

 by plants, they will stand as in the table which follows : 



