Weaver: effects of rusts upon transpiration 401 



creased transpiration rate over the normal. This became progres- 

 sively less and less, and during the last interval the rusted plant 

 transpired 27 per cent less water than the control. 



While the results are not conclusive, they are at least suggestive. 

 Sampson and Allen" have shown that "variation in transpiration per- 

 unit area for a given time is found to be but slight for plants of the 

 same species, when about the same age, grown and tested vmder sim- 

 ilar conditions, whether in their natural habitats or in the plant 

 house." Therefore an explanation of this phenomenon must be 

 sought elsewhere than in the individual variation in the transpira- 

 tion rates of the plants. 



Experiments with Carnations 



A non-glaucous variety of Dianthiis caryophylhis L. was used in 

 the following experiments. They were selected from stock material 

 on hand in the greenhouse. The plants were about 9 cm. high, of 

 approximately the same age and size. They were grown in 3-inch 

 pots. On October 24 several leaves on one of these plants were in- 

 oculated with spores of Uromyces caryophylliniis (Schrank) Wint. 

 After being two days in a saturated atmosphere under a bell jar the 

 plants were then sprinkled thoroughly morning and night. The 

 pustules began to appear in just 30 days. On November 28, when 15 

 patches of pustules had appeared, transpiration losses from the dis- 

 eased plant and also from a healthy one similarly treated, were re- 

 corded. The methods were the same as those described for sun- 

 flowers. The experiment was continued until December 23, during 

 which time six transpiration losses were determined. Throughout 

 the experiment the plants showed about the same amount of growth. 

 The final rusted area was approximated at 3 per cent of the total 

 transpiring surface. During the whole period of 25 days the rust- 

 infected plant lost slightly less water than the control. Unfortu- 

 nately, no time was found to repeat the experiment. However, two 

 experiments were performed with the excised leaves of carnation. 



In these experiments leaves from three carnation plants similar 

 to those previously used were employed. Rusted leaves were se- 

 lected which had healthy leaves opposite them. These pairs were 

 cut off under water as near the stem as possible and the ends placed 

 through slits in corks sunk in the necks of small vials which were 

 filled with water. The leaf surfaces were then dried as were also 



