THE EFFECTS OF CERTAIN RUSTS UPON THE TRANS- 

 PIRATION OF THEIR HOSTS 



J. E. Weaver 



Transpiration has long been an interesting and important subject 

 for investigation. But, notwithstanding the vast amount of research 

 that has been done on the measurement of transpiration, at first in- 

 dependently of the relation to the ph3^sical environmental factors, 

 and more recently with exact measurements and correlations of 

 these, a survey of the published work discloses few studies upon the 

 transpiration of diseased plants. The present paper reports the re- 

 sults of experiments with rust-infected and healthy plants of eight 

 different species, of which the transpiration was measured for a 

 total of more than 200 individuals. The period of investigation ex- 

 tended from October, 1914, until April of the following spring. 



Review of Previous Investigations 



Although it is frequently assumed that the presence of disease 

 affects the rate of transpiration, there is very little published experi- 

 mental data to support this assumption. Blodgett^ has reported an 

 instance of relative transpiration in a healthy excised branch of 

 Ritbus sp. as compared with a similar branch infected with Gym- 

 noconia interstitialis. The branches were cut from adjacent plants 

 (on May 24) and immediately placed in water. "The leaf surface 

 was slightly greater in the healthy specimen, as the normal leaves 

 were larger than the rusted, but the number was nearly equal in the 

 two specimens. Large test-tubes were used, in which the branches 

 were left tightly corked over night. When examined on the morn- 

 ing of the 25th the healthy branch was not wilted, the rusted one 

 was considerably so. The rusted specimen evaporated 42 cc. while 



