Weaver: effects of rusts upon transpiration 



387 



This, as further data will show, is merely a variation of the indi- 

 viduals, and is not due to rust infection. On February 3, tiny 

 whitish areas began to appear and by the 5th numerous rust pustules 

 had broken through the epidermis. From this time there may be 



I'lg. 1. Graphs showing the relative transpiration of healthy and rust-infected wheat 

 plant. The broken line gives the evaporation in cc. during the same in- 

 tervals, as measured by porous cup atmometers. 



noted a decided increase in the water loss of the rusted over the 

 healthy plants. The final rusted area for the seven plants averaged 

 only 1.1 per cent of their transpiring surface. 



The close similarity in the general course of the graphs is no less 

 striking than their greater divergence when more severe environ- 

 mental conditions were brought to bear upon the plants. While 

 the graph of evaporation gives a rather satisfactory summation of 



