JVeaz'cr: effects of rusts ui'ON transpiration 



393 



ciiiia 7'itbiyo-z'cra sccalis, were weighed for the first time. The suc- 

 cessive transpiration losses are shown in figure 5. The dates on the 

 abscissae indicate the length of the intervals between weighings. 

 Throughout the period the sky was clouded much of the time and 

 conditions for maximum transpiration, as indicated by the evapora- 

 tion graph, were poor. Notwithstanding the fact that the rusted 

 area was small (only 0.8 per cent), still the appearance of the pus- 

 tules on January 13 and 14 was accompanied by a marked rise in the 

 transpiration of the rusted plants over the controls. 



From March 7 to March 14 relative transpiration data were ob- 

 tained from a battery of 9 rusted and 12 control rye plants. The 



Fig. 7. Graphs showing the relative 

 transpiration of healthy and 

 rust-infected oat plants. 



same rust was used as in the preceding case. The results are shown 

 in figure 6. The first rust pustules began to appear on March 9 and 

 10, and by the 14th a total pustular area of 3.8 per cent was deter- 

 mined. During the last two days of the experiment, the plants, be- 

 cause of high temperatures (85° to 92° F.) and low humidities (20 

 to 30 per cent), were kept in a semi-wilted condition. However, 

 no differences in the degree of wilting between rusted and control 

 plants could be determined. An analysis of the combined graphs 

 into their component parts shows that the plants with 6.5 per cent 

 of rusted area transpired during the last 4 days 8 grams more per 

 square decimeter than plants with only 0.9 per cent of infected area. 

 The graph for the plants with 4 per cent of rust showed transpira- 

 tion rates intermediate between these extremes. 



A third experiment with rye was conducted from November 15 



