270 Cc. U. ARIENS KAPPERS 
stimulogenous outgrowth of the axis-cylinders from the acti- 
vated cell by and with the irradiating current from a primary or 
activating axis-cylinder in its neighborhood, gives us a key of 
exceptional importance to comprehend the phenomena of neuro- 
biotaxes in general, and the contrasting behavior in outgrowth 
direction between dendrites and axons and allows us to consider, 
perhaps to explain, how it is possible that a unit such as the neu- 
rone is may exhibit two opposite directions of growth. 
EXPERIMENTS CONCERNING PHENOMENA OF TROPISM AND TAXIS 
IN PLANTS AND ANIMALS. KATAPHORETIC PHENOMENA 
It is evident that, in any attempt to explain the neurobiotac- 
tic phenomena, these must be compared with other phenomena 
which are better adapted to experimental investigation. As 
such we may mention the galvano-tropic phenomena in the growth 
of plant-roots and the orientation of animals in the constant 
current, about which we have obtained many data during the 
last decennia. 
As is known, the phenomenon of galvanotropy in plant-roots 
was discovered in Hermann’s laboratory by Miiller-Hettlingen,” 
who found that, if the sprouting seed of the bean (Vicia faba) 
be exposed to a constant current, the tips of the root turn and 
grow towards the negative pole (kathode). 
An analogy" of this galvano-tropic phenomenon is found in 
the galvano-tactie phenomenon described by Bancroft,’ viz., 
that the tentacles and the manubrium cf a medusa, Polyorchis, 
during the transmission of a constant current turn towards the 
kathode. 
In the experiments with the latter this peculiar phenomenon was 
observed, viz., that with a long-continued current the side turned 
to the anode extended, becoming thinner and weaker; this last phenom- 
enon being a symptom of decay, according to this author (vide infra). 
16 Miiller-Hettlingen. Ueber galvanische Erscheinungen an Keimenden 
Samer. Pfliiger’s Archiv, Bd. 31, 1883, p. 192. 
16 Not a homology, probably. 
17 Jour. Exp. Zool., vol. 1, 1904, p. 289. 
