402 



MINNESOTA BOTANICAL STUDIES 



the corks and necks of the vials. The vials were then sealed with 

 the wax seal. Care was taken to assure a perfectly tight seal. The 

 vials and contents were wei,ched, placed under good transpiring con- 

 ditions for 48 hours and again weighed, the loss in weight being that 

 of the water transpired. The leaves were then cut at the surface of 

 the wax. Leaf prints were made in the usual manner and the lower 

 surface of the leaves (the upper was without pustules) photo- 

 graphed and enlarged, and the pustular area calculated as usual. 

 The results are shown in table IV\ 



TABLE IV 

 Experiment I 



Experiment II 



100 

 169 

 100 

 110 

 100 



69 

 100 

 157 

 100 



91 

 100 

 125 



The marked differences in the transpiration per unit area of the 

 control leaves may be due in a great measure to their differences in 

 age and relative cutinization. There seems to be little correlation 

 between the amount of the rusted area and the increase or decrease 

 of transpiration. In most cases, however, a marked increase in the 

 transpiration rate may be seen. Notwithstanding the results of the 



