EFFECT OF BORDEAUX MIXTURE ON TRANSPIRATION 71 



ing of a cobalt chloride paper slip and slips of two permanent 

 color standards' 2 firmly joined together into a composite slip 

 which can be manipulated as a single piece. The permanent 

 color standards are both blue, one being a Httle less intense in 

 color than is thoroughly dry cobalt chloride paper, while the 

 other is just faintly but perceptibly blue. By means of the 

 composite slips, the two color standards and the cobalt chloride 

 paper are brought to the leaf surface simultaneously. When 

 the hygrometric paper is dry it has a slightly more intense blue 

 color than the dark blue standard, but the color becomes less 

 intense as moisture is absorbed. The test is begun when the 

 color of the hygrometric paper just matches that of the more 

 intensely colored standard. As the cobalt paper gradually 

 becomes less intense in color, due to the absorption of wacer, 

 a point is finally reached when its color just matches that of the 

 pale blue standard. WTien this point is reached the test is 

 considered ended. A test consists in determining the length 

 of time elapsing between the occurrence of a fixed dark blue 

 color and that of an equally fixed pale blue color. Since the 

 two color standards are permanent, they furnish these two fixed 

 points. In making a test, some error may, of course, occur from 

 a failure to judge the exact time when the colors are correctly 

 matched, either at the beginning or at the end of the test. 



In making the composite sUps, the cobalt chloride paper 

 and the two color standards were cut into 5 mm. squares. To 

 join these together firmly very thin, black, water-proofed, 

 gummed-cloth tape 2 cm. wide, was used. The tape was cut 

 into 2 cm. squares. Two of these squares were placed together 

 with the gimimed face of the one against the cloth surface of 

 the other, and the two were cemented together along one edge 

 to prevent them from shpping out of place. Three circular 

 holes, each 4 mm. in diameter were cut through this double 

 tape square by means of a cork borer. The holes were so cut 

 that each was about 1.5 mm. distant from the other two, thus 

 forming a triangular arrangement. One layer of the double 



^^ The permanent standard blue papers, as well as the cobalt chloride paper, 

 were secured from The Plant World, Tucson, Arizona. 



