Weaver: effects of rusts upon transpiration 



399 



Some stood at right angles to the normal position, some had turned 

 in such a manner as to expose the under surface directly upwards, 

 while all were more or less curled and twisted. 



The final leaf area was measured, and in determining the trans- 

 piration loss interpolations were made so as to give the leaf area 

 during the intervening periods. The increase in leaf area was 



Fig. 9. Graphs showing relative transpiration 

 rates between healthy and rusted 

 cockleburs. The heavy lines show 

 the transpiration of diseased plants. 



nearly twice as great in the healthy plants, owing in part to the 

 more vigorous growth of new leaves in the axils of both the cotyle- 

 dons and the first pair of leaves. The diseased and control plants 

 were found to have so nearly the same stem area, that it was not 

 included in the transpiring surface, since the epidermis is all but 

 destitute of stomata. 



In order to check the preceding experiment, another series of 

 healthy and infected plants was used. In this case the cotyledons 

 only were removed and the first three or four leaves infected. The 



