PROPERTIES OP THE LEAP OP DIOtLEA. 
9 
in water in which such leaves have been immersed even after a few minutes’ immersion. 
He further finds that if a freshly cut off leaf is immersed in water, the whole of the 
vein surface is wetted at once. The green surface of the lamina exhibits a beautiful 
silvery lustre indicating that air adheres to it, and that water comes very slowly and 
incompletely into contact with it. When the leaf is removed from the water, the 
veins remain permanently and completely wet, but the water runs off the rest of the 
surface, leaving it dry. Consequently he concludes that when moist electrodes are 
brought into contact with surfaces which thus differ, the diffusion processes which 
result from the contact must go on at different rates. 
By other experiments, physical rather than physiological, he has shown that in all 
bodies capable of imbibition with water, electrical changes are associated with the process 
of imbibition. His first experiments on the subject were made with the ordinary 
porous cells of batteries. Similar results were obtained by the investigation of non¬ 
living vegetable structures, as e.g., laminaria stems. By comparing these facts with 
those already stated as to the electrical phenomena observed in the investigation of 
leaves, he derived the conclusion that whatever differences present themselves between 
the different parts of leaves are due to “ Unterschied in der BenetzbarJceit” of the 
surfaces led off. What the direction of this effect is, Kunkel had determined by 
experiment. If a drop of water is placed on the green surface of a leaf between the 
veins and allowed to remain there some time and the leaf is now led off by another 
similar surface and by the drop, it is found that the surface first wetted is always 
positive to the other (p. 368). If after one electrode has been brought into contact 
with an ordinary surface, the other is applied to a vein, the direction of the difference 
is opposed to the normal. The vein is at first negative but the difference quickly 
diminishes and is soon reversed (p. 360). In other words, when a leaf or other similar 
structure is led off by two surfaces of which one is more <£ wettable ” than the other, 
the former is .positive to the latter, provided that both contacts have been made 
si multaneously. 
From these observations, of which the value and interest must be recognised as 
showing what sort of results may arise from imbibition processes taking place at sur¬ 
faces of contact, the author proceeds to draw inferences as to the nature of excitatory 
electromotive changes in the organs of plants, confining his attention to Mimosa. The 
excitatory effect in the swelling at the base of the leaf stalk of Mimosa , is described 
by Kunkel, on the basis of observations made with the capillary electrometer, the 
organ being led off by thread electrodes applied to its opposite ends as follows. It is 
said to consist of a “ Vorschlag,” in which the base becomes negative, followed by a 
larger excursion in the opposite direction. Kunkel thinks that this observation is in 
harmony with those of Munk. Three fragmentary experiments are given in confir¬ 
mation of this, on which the theory is founded, that inasmuch as in Mimosa the active 
motions of the leaf are caused by a sudden alteration in the distribution of water in 
the different parts of the swelling at the base of the leaf stalk, that these “ Wassem 
MDCCCLXXXII. C 
