76 JOHN W. SHIVE AND WILLIAM H. MARTIN 



differ markedly in their transpiring power, as this is measured 

 by the method of standardized hygrometric paper. Prelimi- 

 naiy tests, however, made with leaves chosen as indicated 

 above, gave very uniform results. 



Nearly simultaneous tests with standardized hygrometric 

 paper were made throughout the day upon three sets or groups 

 of leaves: (1) upon sprayed leaves; (2) upon unsprayed leaves 

 on the same plant as the sprayed leaves, and (3) upon leaves 

 of the second unsprayed plant. For the sake of convenience in 

 presenting the data, the three groups of leaves will be desig- 

 nated as series A, series B, and series C, in the order given. 

 Three tests were made upon both the upper and lower foliar 

 surfaces, of different but apparently similar leaves of each of 

 the three groups. The observations, made at intervals of one 

 hour, were begun early in the morning (5.00 a.m.) and were con- 

 tinued until sunset. Owing to a heavy dew on the morning of 

 August 18, observations were not begun on this date until 9.00 

 a.m. Since the data for this day's tests are, therefore, not so 

 extensive as those for August 10 and for August 14, they are 

 given in full in table 1, where the hours are numbered consecu- 

 tively in the day. The tests were made, of course, within the 

 stated hour, usually within the first twenty or thirty minutes 

 of that hour, for the lower leaf surfaces. A somewhat longer 

 period of time was required for. the tests on the upper leaf sur- 

 faces where the stomata are less numerous than on the lower 

 surfaces; the number of stomata per square millimeter on the 

 upper and lower surfaces of the leaves of tomato plants being 

 estimated by Duggar'^ to be 12 and 130, respectively. The 

 temperatures given were read, at the beginning of the hour in- 

 dicated, from thermometers suspended among the leaves of 

 the plants. In table 1 are given, for each hour indicated, the 

 three individual time coefficients and the corresponding individual 

 indices of transpiring power, for upper and for lower leaf sur- 

 faces, for each series, as are also the averages of these. The 

 last line of each horizontal section of the table presents, in fuU- 



1^ Duggar, B. M., Plant Physiology. New York. 1915. 



