340 Curtis : The Work Performed in 



Here again it is evident that only in the remotest way is there 

 any conformity to the law of Poiseuille for capillary tubes, at least 

 the ratio of rate, length, radius and pressure can hardly be said to 

 show a variation in conformity to this law. Some stems offer a 

 resistance out of all proportion to their dimensions and the volume 

 of transpiration. Pelargonium is a striking example of this. It 

 is possible that this may be due in part to blocking by substances 

 escaping from the cut stems. In other instances equally striking 

 examples are sometimes met, the pressures ranging from .08 

 to .2 of an atmosphere per sq. cm. in the short lengths of stems 

 mentioned above. The irregularities shown in the 2d, 5th, 6th 

 and 7th columns of the first experiment with Viburnum are doubt- 

 less due to the fact that the negative pressure was not satisfied. 

 It was frequently noticed in such cases and particularly with stems 

 tested in the winter that they would show for hours an irregularity 

 and even an acceleration of rate. The rapid decline in the rate 

 in the short lengths is, of course, due to increased volume trans- 

 mitted. 



Electrical Currents and Conductivity 



In some work, conducted two years ago at the Physical Lab- 

 oratory, a slight difference of potential was shown to exist between 

 the top and bottom of trees. Haacke has also demonstrated the 

 presence of weak currents circulating in the plant cells. In view 

 of these facts and the marked effect of electrical currents upon 

 plants, lengths of stems under pressure and also transpiring stems 

 with potometer attached were submitted to currents from a double 

 18-inch plate, Winshurst static machine and also to the street 

 current, no volts. The current was applied to the stems by re- 

 moving two strips of the cortex 10 cm. apart and wrapping the 

 electrodes about the wood. 



III. 



C C RC RC 



Acalypha 39 39.5 42 39.5 52.5 54 54 56 



39.5 40.5 41.5 40.5 53 53 56.5 55 



39-5 40.5 42 40.5 54 53 57 54-5 

 39 41-5 

 39 41-5 



38.5 42 

 38 42 



39-5 



40.5 



54 



5i 



56 



54 



39 



41 



54-5 



5i 



57-5 



53 



39-5 



41-5 



55 



5i 



57-5 



54 



38 













