VI 



ELECTROMOTIVE ACTION IN VEGETABLE CELLS 



21 



the leaf, and must with an ingoing direction be regarded in a 

 certain sense as its after-effect. 



Under these conditions it is clear that the manifestations of 

 excitation must be studied before the 

 state of rest. Jn leading off from the 

 upper and lower surface of a lobe, one 

 unpolarisable electrode being situated 

 between the three sensitive hairs, the 

 other directly opposite on the lower 

 (external) surface, and then exciting 

 the other lobe of the leaf mechanically 

 or electrically (as in Fig. 143), a diphasic variation appears 

 eacli time, as can easily be photographed with the capillary 

 electrometer (Fig. 144). 



In the case of a leaf " modified " by previous excitation, 

 where the lower surface is already positive to the upper, the 

 current is in the first place reversed shortly after stimulating, 

 the lower surface becoming rapidly negative. After about half 



FIG. 143. 



FIG. 144.^-Pliotographic record of the variations of an ingoing leaf-current, when one lobe is 

 electrically excited. The interruptions of the black line correspond with breaks in the 

 primary circuit of the induction-apparatus. Interval between the excitations about 5 sees. 

 Rapidity of plate about 1 cm. in 2 sees. (Burdon-Sanderson.) 



a second this phase will have reached its maximum, and a 

 second (somewhat slower) and opposite phase sets in, which is, 

 however, less marked, and reaches its maximum in about 

 lj sec. after excitation. This, as shown by the photogram, 

 decreases very gradually, and loses itself in the after-effect 

 described above, which is characterised by increased positivity 

 of the lower surface of the leaf ; it follows that the second phase 

 is distinct in the first excitation only, those immediately subsequent 

 producing merely a simple, monophasic variation. A long interval 



