46 



THE COTTON PLANT IN EGYPT chap. 



given consistent results, four of which have been plotted 

 in Fig. 40. They show that transpiration is practically 

 in abeyance at night, slow in the early morning. By 

 9 a.m. in sunshine it has reached a maximum which is 

 maintained till past noon. The last result is perhaps 

 rather unexpected, seeing that the stomata are nearly 



0-150 



2 3 4 5 



Minutes (from moment of removal) 



Fig. 40. — Teanspieation in Field Chop. 



Bate of water-loss from detached leaves, plotted backwards to instant of 



removal. 



Initial weight of all four was about 0"85 gram ; areas, 30-40 sq. cm. 



closed, but it is easily explained when we remember the 

 increase in stringency of the environment which has 

 taken place during these four hours : Sun-temperature 

 has risen from about 50° C. to 75° C, shade-temperature 

 from about 25° C. to 35° C, and humidity has fallen 

 from about 60 per cent, to 20 ^er cent, of saturation. 

 During the afternoon the transpiration rate appears to fall 



