1907] CURRENT LITERATURE 219 
reverses with increasing concentration of solution when an electric current trav- 
erses it. Further, the reaction was found to be an additive effect, depending 
upon the sum of the specific actions of the cathions and the anions. From all 
the phenomena the author is led to a conclusion, neither novel nor very well 
founded, that with salts chemotropism and galvanotropism are identical, both 
being explicable by the migration of ions into the cell and the disturbance of 
electrical equilibrium they there produce. In chemotropism the agers is 
due to a concentration gradient, in galvanotropism to the electric current. 
non-electrolytes call forth chemotropic responses (as certainly they do) sake 
LENBERG would explain the action by a modification of the permeability of the 
eee to the internal salts, whose unequal outward diffusion disturbs the inner 
uilibrium. e experimental work of this paper lacks definiteness and 
seems to i devoid of sufficient precautions. 
GASSNER, working in Kny’s laboratory in Berlin, concludes that galvan- 
otropism is only a form of traumatropism.'’ His seedlings were placed in small 
boxes with perforated cork bottoms, through which the roots protruded into a 
vessel of tap water, frequently renewed, and through an equal cross-section of 
this passed the electric current from carbon electrodes of uniform size. He used 
the commercial current of 110 volts, up to 17 milliamperes. But as he found 
current density (strength of current divided by its cross-sections) to be a control- 
ling factor, caeteris paribus, he states this always in milliamperes per cm? 
this factor SCHELLENBERG seems to have paid no attention.) On that basis the 
currents used varied from 0.001 ma. to 5 ma., those most used lying below o. 1 ma. 
With weakest currents there was no curvature; with currents from a certain 
density and time of action up, a curvature toward the cathode; with stronger 
currents or longer time, first a curvature toward the anode in the part above the 
growing zone, then a paratonic growth-curvature toward the cathode in the 
growing zone, thus producing §-curvatures; with further increase in current, 
complete curvature toward the anode, the injury retarding or inhibiting growth 
on the cathode side even in the growing zone; with still stronger current, partial 
curvature toward the anode, growth being soon arrested by death; finally, no 
curvature with currents that cause death too promptly. Differences were ob- 
served in the response of different plants to like currents. The positive (toward 
anode) and negative curvatures are held to be of different nature. The former, 
earlier in time, is due to injury by reduction of turgor in full-grown cells on the 
anode side; the latter to retardation of growth on the cathode side of the growing 
region. (Since a current which will produce only positive curvature in a given 
time will with longer duration produce negative curvature, it would seem that 
such a distinction in “nature” could hardly be valid.) The negative curvature 
is analogous to curvatures due to geotropism, traumatropism, etc., in which the 
root tip is the percipient part. 
13 GASSNER, G., Der Galvanotropismus der Wurzeln. Bot. Zeit. 641:149-222. 
figs. 12. 1906 
