vi ELECTROMOTIVE ACTION IN VEGETABLE CELLS 9 



of much smaller, less conspicuous cells, rich in chlorophyll, and- 

 finally, the epidermis of the under surface of the leaf" (F. 

 Kurtz). 



The parenchyma of the leaf breaks through the epidermis of 

 the inner surface at the point where a sensory hair takes 

 origin. The par^nchymatous cells lying immediately below 

 the epidermis are smaller at this point, and form a cylinder 

 (circular in cross -section) consisting of 45 layers of polygonal 

 cells, which rise above the surface of the leaf, and constitute about 

 x=oth of the total length of the hair. From this cylinder the 

 true hair rises as a slender cone; it contains no vascular bundle, 

 and consists of long small cells (F. Kurtz, 8). 



If unpolarisable electrodes are applied to opposite ends of a 

 fresh uninjured leaf of Dioncea, a regular current (as first pointed 

 out by Burdon-Sanderson) is indicated on a galvanometer included 

 in the circuit, flowing in the leaf from the end proximal to the 

 stalk (according to Munk, the anterior end) to the distal (posterior) 

 end Sanderson's " normal leaf current." On leading off from 

 symmetrical points of the external (under) surface of the lamina, 

 Munk either found no current, or a weak, irregular effect. If 

 lines are conceived on the surface of a lobe, at right angles to 

 the mid-rib (Munk's " transverse-lines "), each point of the same 

 will be negative to the corresponding point of the mid-rib, the 

 more so within a certain range in proportion as the point upon the 

 transverse line is nearer the margin of the leaf. The line con- 

 necting the most negative points of all the cross-lines running 

 approximately parallel with the mid-rib is called by Munk the 

 " principal longitudinal line " of the lamina ; as the most positive 

 point of the leaf he opposes the anterior end of the posterior third 

 of the mid-rib. The distribution and magnitude of potential at the 

 upper (inner) surface of the leaf corresponds, according to Munk, 

 with that of the lower (outer) surface ; so that on leading off from 

 two corresponding points of both surfaces there should be no 

 current; this, as Burdon-Sanderson found later, is not the case. 

 The electromotive reactions of the leaf of Dioncea are associated 

 with its vitality, and at death decline to zero. The absolute 

 magnitude of E.M.F. is of considerable proportions. " The P.D. 

 between a point in the proximity of the principal longitudinal 

 line, and one in the posterior half (distal to the stalk) of the 

 mid-rib, is not infrequently 0'04-0'05 Dan." 



