388 
Bayliss. — On the Galvanotropism of Roots . 
electrode. The currents used by him were so strong that the roots usually 
died. 
In 1883, Miiller-Hettlingen 1 published the results of his researches in 
the same subject. He used a horizontal glass plate, covered with a piece 
of flannel which dipped at opposite ends into water : on this flannel the 
seedlings were laid, and then covered with another glass plate which was 
prevented from touching the lower by glass supports : the current passed 
through the flannel, and so presumably through the roots. Here the 
curvature was towards the negative electrode, and these radicles seldom 
died 
Little reliance can, however, be placed on these experiments, for 
it is very uncertain how much, if any, current passed through the roots : 
also rheotropic, hydrotropic, and geotropic reactions were not rendered 
impossible. 
Miiller-Hettlingen’s work was closely followed by that of Brunchhorst, 2 
whose investigations seemed to reconcile these conflicting results. He 
drew the conclusion that the positive curvature observed by Elfving was 
due to the action of a strong current, while Muller-Hettlingen’s negative 
curvature was due to the latter using a much weaker current. The positive 
curvature he considered to be of a traumatropic nature, due to injury 
of the anodal side of the root, whereas the curvature to the negative 
electrode he supposed to be the result of a directive influence, and to 
be analogous to geotropic and heliotropic curves. 
In experiments with strong currents, Brunchhorst used a similar 
apparatus to Elfving, but when working with weak ones he used a glass 
cylinder rotating horizontally on a clinostat, thereby eliminating geotropic 
action. 
The strength of the currents used by these investigators is not very 
definitely stated ; Elfving used 2, 4, or 6 Leclanche cells, and Mtiller- 
Hettlingen 4 Grove’s cells ; but as these cells are liable to rapid and 
pronounced polarization when in constant use, the currents obtained could 
not have been of a very reliable or uniform nature. 
Brunchhorst estimates the strength of the currents he used by the 
amount of deposit of copper per hour ; but even this does not convey 
a very satisfactory idea of the current used. The current passed through 
water in which the roots were immersed, and since these and water have 
dissimilar resistances, the amount of current passing through them could 
not be determined from external measures of current strength. The current 
density in each root would depend as much upon the area of cross section 
of the surrounding water as upon the current strength in the external 
circuit. 
1 Miiller-Hettlingen, Pfl tiger’s Archiv, xxxi, 1883. 
2 Brunchhorst, Ber. d. Deutsch, Bot. Gesellsch., 1884. 
