54 
PROFESSOR B. SANDERSON ON THE ELEOTROMOTIYE 
Each of the two lobes of the leaf of Dionma is made up, for the most part, of 
cylindrical cells. The long axes of these cells (parenchyma cells) are all parallel to 
each other, and to the vascular bundles which run out from the midrib towards the 
margin. A transverse section of the leaf, made in such a way as to include a vascular 
bundle, shows that there are two or three layers of them, the most superficial of 
which are covered by the epidermis of the under and upper surfaces of the leaf. 
As they are alike in structure, it may be assumed that they have the same or similar 
functions. 
If it were possible, without injury, to investigate the electromotive properties of one 
of these cells individually, by leading off its opposite surfaces, we should probably find 
them to be isoelectrical both at rest and when excited ; for the electrical differences 
which exist in the cell are probably between the living inside and the non-living 
outside, and not between different parts of the surface. Consequently the electrical 
differences which show themselves between the opposite sides of the leaf blade which 
is made up of layers of such cells cannot be due to the summation of smaller 
differences between the two sides of the individual layer, for these are iso electrical. 
They must, therefore, be referred to the contact of different layers of cells with each 
other. But if electrical differences exist at the surfaces of contact of the cells, they 
must be associated with physical differences of other kinds. With respect to the 
nature of this difference it appears to be very probable that the most important 
element is migration of water. For on the one hand we know that in consequence of 
the surface evaporation, migration of water certainly exists, while on the other we have 
proof in the experiments of Dr. Kxjnkel, that such migration cannot occur without 
producing electrical differences. 
As has been so conclusively proved by the experiments of Pfeffer, those motions 
of the organs of plants which follow excitation are attended by diminution of the 
turgor or water-charge of the protoplasm of the excitable cells. The displacement of 
water occasioned by this discharge must unquestionably be attended by electrical 
change. In Dionaea the mechanical effect of an excitation can be seen from one to 
two minutes after the moment at which the excitation takes place. It is at the same 
moment that the second phase, or after effect, begins. In their origin, culmination, 
progress, and duration the two changes are closely associated. It therefore appears 
extremely probable that the two are causally related—that the positivity of the external 
surface is an expression of the electrical differences which exist between contiguous 
strata in different degrees of turgor—the less charged being negative to the more. 
The same theory affords us a complete and satisfactory explanation of the gradual 
change of potential which always results from repeated excitation, as well as for the 
fact so constantly observed, that the “ after effect ” which follows each of the first few 
excitations to which a leaf is subjected, is much greater in extent than those which 
occur after later ones, and that eventually the after effect fails entirely, reappearing 
after a period of repose. 
