432 



Prof. Burdon-Sanderson and Mr. F. J. M. Page [Dec. 14, 



lu the few cases in whicli we determined the moment at which the 

 variation commenced (by mechanical stimulation) on the internal and 

 external surface of the leaf respectively, we found that there was a dif- 

 ference in favour of the outside. Thus in one leaf (89) the delay at the 

 outer surface of the lobe was 0*18, at the inner 0*30, at the outer sur- 

 face of the midrib 0-34, and at the inner 0*38. 



"When, however, electrical stimulation is used, the diference becomes 

 very ob^dous. In one of the experiments already referred to, relating 

 to faradization with weak currents, we employed two movable electrodes, 

 one on the external, the other on the internal surface of a lobe of a leaf, 

 the fixed contact being on the petiole, and the needles being inserted into 

 the opposite lobe. When by this means the excursions were taken 

 alternately from the outer and inner surface, it became very obvious that 

 in every instance the outside excursion began first. At the commence- 

 ment of the experiment when the condition of the excited part remained 

 fairly normal, the delays in seconds were as follows : — 



Outside 0-48, 0-50, 0*52, 0-65, 0-49. 



Inside O'Tl, 0-61, 0-68, 0-75, 0-95. 



As exhaustion came on, the difference was more and more obvious. 

 The following observations were made at intervals of a minute : — 



Outside 0-69, 0-82, 0-93, 0-78, 0-98, 2-26. 



Inside 0-89, 0-99, 1-13, 1-08, 1-43, 3-57. 



After which no further results were produced until the distance of the 

 secondary coil was reduced from eight to seven centims. On then 

 exciting e\"ery half minute the results were : — 



Outside 0-56, 0-66, 1-32. 



Inside 0-71, 1-43, 1-89. 



After bringing the coil to six centims. we had : — 



Outside 0-60, 1-08. 



Inside 0-82, 2-07. 



When, instead of investigating contacts comprised within the central 

 parts of the leaf, a comparison is made between the time at which the 

 exciu'sion begins at the centre with that at which it becomes appreciable 

 towards the margin of the area of excitation, delays very much greater 

 than those we have been considering present themselves. Thus, when 

 mechanical stimulation is used, and the two movable electrodes are 

 placed severally on the under surface of the midrib, a httle beyond the 

 middle and on the bridge, the delays were : — 



On the midrib 0-27, 0-25, 0-22, 0-26, 0-32, 0*32, 



0-32, 0-25, 0-34, 0-18 ; 



On the bridge 0-66, 0-56, 0-55, 0-52, 0-51, 0-50, 



0-70, 0-74, 0-49, 0-56,— 



