July 2,1917 Variation of Water in Leaves of Corn arid Sorghums 35 



and night of 9.4, 12.7, and 8.5 gm. of water per square meter of leaf, 

 respectively, for com, kafir, and milo. 



For the 22 days the minimum amount of water in the corn leaves was 

 reached 4 times at 11 a. m.,^ 7 times at i p. m., 10 times at 3 p. m., and 

 once at 5 p. m., while in the same number of periods the milo leaves 

 reached their minimum amount of water twice at 11 a. m., 10 times at 

 I p. m., 9 times at 3 p. m., and once at 9 a. m. For 18 days the kafir 

 leaves showed the minimum amount of water twice at 11 a. m., 13 times 

 at I p. m., and 3 times at 3 p. m. The average difference between the 

 maximum and minimum amounts of water in the leaves during the day 

 was 13.8, 8.4, and 7.8 gm. per square meter of leaf surface, respectively, 

 for corn, kafir, and milo. The maximum evaporation as measured by 

 the Livingston porous-cup atmometers occurred 1 8 times between 2 and 3 

 p. m. and four times between 3 and 5 p. m. The evaporation as repre- 

 sented in figures i to 10 is plotted for 2-hour periods, so that the hour 

 of maximum evaporation may not be shown by the curves. The mini- 

 mum amount of water in the leaves during the day occurred 7 times for 

 com, twice for kafir, and 7 times for milo at the same time as the maxi- 

 mum evaporation. In 9 cases for corn, 12 for kafir, and 10 for milo the 

 minimum amount of water in the leaves was reached two hours before 

 maximum evaporation, while in 5 cases for corn, 4 for kafir, and 4 for 

 milo the lowest water content of the leaves occurred four hours before 

 the maximum evaporation. Thus, in two-thirds of the cases of com 

 and milo and in nine-tenths of the cases of kafir, the minim.um amount 

 of water in the leaves occurred under the condition of these experiments 

 from two to four hours earlier than did the maximum evaporation, as 

 shown by the Livingston porous-cup atraometer. 



During the night the maximum water content of the com leaves was 

 reached 3 times at 11 p. m., 3 times at i a. m., twice at 3 a. m., once at 

 9 p. m., and twice at 5 a. m. The leaves of kafir showed the greatest 

 amount of water once at 1 1 p. m., 5 times at i a. m., and 3 times at 5 a. m., 

 while the milo leaves reached their maximum water content once at 11 

 p. m., 4 times at i a. m., 3 times at 3 a. m., twice at 5 a. m., and once at 7 

 a. m. The lowest evaporation for the 1 1 night periods occurred 9 times 

 between 4 and 5 a. m. and twice between 2 and 3 a. m. The average 

 difference between the minimum and maximum water content of the 

 leaves per square meter of surface during the night was 10.3 gm. for com, 

 16 gm. for kafir, and 13.1 gm. for milo. The difference between the aver- 

 age minimum water content of the leaves during the day and the aver- 

 age maximum water content during the night was 23.8, 25.9, and 21.7 

 gm. per square meter of leaf for corn, kafir, and milo, respectively. It 

 is worthy of note that in all the night experiments abundant guttation 



I In the following discussion the tnaximutn or minimum amount of water or dry matter in the leaves is 

 considered as occurring at the close of a 2-hour period, but, as a matter of fact, it might liave occurred at 

 any time during the two preceding hours. 



