EFFECT OF BORDEAUX MIXTURE ON TRANSPIRATION /O 



surface to give off-water vapor, in terms of the standard evaporat- 

 ing surface blanketed by one millimeter of air. 



The determination of the indices of transpiring power in 

 plants, by the method of standardized hygrometric paper, are 

 made upon the supposition that the temperature of the leaf 

 and that of the paper* slip at the time when the tests are made, 

 is the same as that of the surrounding air. A certain amount 

 of error may here be introduced, as Trelease and Livingston 

 have pointed out, since leaf temperature and air temperature at 

 any given moment are seldom exactly the same. It is scarcely 

 probable, however, that the difference in temperature between 

 the leaf and the surrounding air is ever sufficient to render the 

 results obtained from a series of tests very different from what 

 they would be if the supposition were entirely true. 



MEASUREMENTS AND RESULTS 



As has already been stated, the tomato plants used for these 

 tests were grown under agricultural conditions in the open field. 

 The plants were about 80 cm. tall, profusely branched, and in 

 full bloom when the tests were made. Two plants, growing 

 side by side, with an intervening space of about one meter, 

 were chosen for each days' experimentation. The leaves on 

 about one-half the branches of one plant were sprayed on their 

 upper and lower surfaces with Bordeaux mixture (4-4-50 for- 

 mula of agricultural practice), care being taken to secure a 

 complete covering with a fairly uniform fihn of the spray mate- 

 rial. The leaves were sprayed on the day preceding that dur- 

 ing which the tests were made. The leaves on the second plant 

 remained unsprayed. 



In selecting leaves to be tested, care was taken to choose only 

 those of approxunately the same age, on branches having about 

 the same relative position on the stem. It has been pointed 

 out by Bakke and by Bakke and Livingston'^ that leaves of dif- 

 ferent ages, and occupjdng different positions on the stem may 



^^ Bakke, A. L. and Livingston, B. E., Further studies on foliar transpiring 

 power in plants. Physiol. Res. 2: 51-71. 1916. 



