8 
PROFESSOR B. SANDERSON ON THE ELECTROMOTIVE 
The researches of Kunkel/“ like those of Munk, have been directed to two 
questions, viz. : to that of the differences of electric tension which present themselves 
in the uninjured leaf, and to the electromotive phenomena which follow excitation in 
the excitable organs of plants. As regards the first question, he has found that in 
leaves generally, when they are led off by non-polarizable electrodes in the usual way, 
differences of tension present themselves, these being always of such a nature that if 
one electrode is in contact with a vein, the other with the green surface between the 
veins, the former is positive to the latter (p. 359). But he considers this due, not 
to any real difference of tension between the surfaces, but exclusively to inhibition 
changes which begin at the moment that contact is made. As evidence that the 
relations of the two surfaces to water are different, he adduces the following 
observations. 
That diffusion actually takes place at the uninjured surfaces of leaves which are in 
contact with water, he proves by the observation that potassium salts may be detected 
observations are, happily, in accordance with mine, as may be seen by comparing his account of the 
phenomena with mine:— 
Sanderson, 1873. 
Wenn das Blatt so auf die Elektroden aufgelegt 
wird dass der normale Strom des Blattes durch 
eine Ablenkung der Nadel nack links angezeigt 
wird und die sensitiven Haare der oberen Flache 
beriihrt werden, so schwingt die Nadel nach rechts. 
. . . In jedem Falle kommt die Nadel nach der 
negativen Schwankung in einer Stellung zur Ruhe, 
die weiter nach links gelegen ist als zuvor, und 
nimmt dann allmaklig ihre friihere Stellung wieder 
ein. (Centralblatt, 1873, p. 835.) 
Munk, 1876. 
Reizen wir unser Blatt bei Ableitung von den 
beiden Enden der Mittelrippe, so beobachten wir 
FoJgendes: (Es sei z. B. eine Ablenkung von 
30 Sc. vorhanden.) Zuerst nach der Reizung 
nimmt die Ablenkung sehr rasch auf 25-30 Sc. ab, 
und darauf nimmt sie sogleich etwas langsamer, 
doch immer sehr rasch auf 40-60 Sc. zu. Nun 
verweilt der Spiegel nur momentan auf dem 
Maximum der Ablenkung und kebrt dann lang- 
sam, in etwa einer Minute, zu seiner Anfangsstel- 
lung zurlick (pp. 127, 128). 
Notwithstanding this close correspondence, Professor Munk speaks of my description as grossly defec¬ 
tive, “not merely in details, but in what is essential and important” (p. 124); and proceeds, that for 
aught I knew to the contrary, my “ negative Sclnvanlcung might be nothing more than a result of 
shifting of contacts. The serious defect, however, was not so much incompetence as an observer as 
inability to understand what I saw; for, referring to the very same observation further on, he says that 
“ Herr S. den Ei’folg der Reizung richtig beobachtet hat und nur seine Beobachtung durckaus missver- 
standen hat, indem er . . . eine negative Schwankung da zu sehen vermeinte, wo in der Wirklichkeit eine 
positive Schwankung mit negativem Vorschlage sich zeigte.” On another of my observations (see p. 152), 
which he had not time to repeat, but which he thinks may be relied on though it was made “ naturlicli 
ohne von seiner Bedeutung eine Ahnung zu haben,” he finds an additional prop for his own theories. In 
conclusion, Professor Munk congratulates himself on having substituted “ an die Stelle der Spurweisen 
und vielfacli unzutreffenden ersten Wahrnekmungen von Herrn Sanderson eine genauere Kenntniss des 
Dionasa-Blattes in elektriscber Beziehung.” 
* Kunkel. “ Electriscbe Untersuchungen an pflanzlichen und tkierischen Gebilden,"’ Pelugek’s 
Archiv, Bd. xxv. 
