40 Journal of Agricultural Research voi. x, no. i 



Livingston and Brown ^ investigated the water content of the leaves of 

 numerous plants growing in the vicinity of Tucson, Ariz., and found 

 that the time of the minimum water content of the leaves fell within an 

 • hour or two of the maximum evaporation rate. The minimum moisture 

 content of the leaves of most of these plants, estimated on both a dry 

 and a wet basis, occurred between i and 5 p. m. 



GENERAL CONCLUSIONS 



VARIATION OF THE WATER CONTENT 



The leaves of milo contained less water at all times than the leaves 

 of either com or kafir at the same stage of development. The average 

 water content per square meter of leaf for all the observations made was 

 I II. 4 gm. for milo, 123.2 gm. for com, and 126.3 g^i- for kafir. The 

 amount of water in the leaves of corn and kafir was practically the same 

 at like stages of growth. The small difference between the average 

 amount of water in the leaves of kafir as compared with those of com 

 is due to the fact that in one experiment in 19 14 and in two experiments 

 in 1 91 6 the leaves of the kafir were about 10 days younger than those 

 of the com and, as a consequence, contained a greater amount of water. 



Under the conditions of these experiments, the leaves of com in most 

 cases were wilted during the greater portion of the day. The first signs 

 of wilting were most generally observed between 9 a. m. and 10 a. m., 

 and in most cases no visible wilting could be observed after 4 p. m. The 

 kafir leaves wilted during the day, but not to the extent that the leaves 

 of the corn did, while the milo leaves showed little or no signs of wilting. 

 Under these conditions the average range between the maximum and 

 minimum amount of water per square meter of leaf during the 2-hour 

 periods from 7 a. m. to 7 p. m. was 13.8 gm. for com, 8.4 gm. for kafir, 

 and 7.8 gm. for milo. 



Table IV shows the average gain or loss of leaf water during each 

 2-hour period of the day from 7 a. m. to 5 p. m. for the experiments con- 

 ducted in 1914, 1915, and 1916. The average gain or loss for each period 

 is expressed in grams per square meter of leaf and in percentage based 

 on the water in the leaf at the beginning of the 2-hour period. 



The time of the day when the loss of leaf water ceases and an increase 

 in its amount begins depends upon the aerial conditions under which 

 the experiment is conducted. Under the conditions of these experi- 

 ments the leaves of the three plants, with but few exceptions, showed a 

 decrease in the water content between 7 and 1 1 a. m. In one-third of the 

 observations for com and milo and in one-fifth of the observations for 



' Livingston, B. E-, and Brown, W. H. relation of the daily march of transpiration to 



VARIATIONS IN THE WATER CONTENT OF FOLIAGE LEAVES. In Bot. GaZ., V. 53, no. 4, p. 309-330, pi. 



24-25. I9I2. 



