84 ILLINOIS STATE ACADEMY OF SCIENCE 



In every case transpiration readings were taken from 

 both the upper and lower surfaces of the leaves used and 

 the average of the two was taken as the result to be re- 

 corded. Also, whenever possible, readings were repeat- 

 ed one or more times and all readings taken were aver- 

 aged for each plant. The data given in the following 

 table, therefore, consist of averages rather than the re- 

 sults of single readings. 



RESULTS 



The results are given in tabular form below. The fig- 

 ures in columns A, B, C, D, E, and F give the number of 

 seconds required to change the color of the cobalt paper 

 by the transpiration of the plant named at the head of 

 the column. The columns headed A-B, A-C, etc. are dif- 

 ference columns and show the number of seconds more or 

 less that were required to change the color of the cobalt 

 paper on the foliar surfaces of the weeds than on thai! 

 of the corn. A plus sign in these columns indicates that 

 the number of seconds required for the color change was 

 more in the case of the corn than in that of the weed 

 while a minus sign indicates a greater number of seconds, 

 for the weed than for the corn. 



