48 Snow .— The Conduction of Geotropic Excitation in Roots. 
Mica Slips inserted from one Side. 
m 
8. Twenty-two beans were taken, and a single transverse cut made just 
half-way through, at 2 mm. behind the vegetative apex. A slip of mica 
was slid into the cut. They were then pinned with the roots vertical. 
After twenty-four hdurs, eleven remained straight, one bent slightly away 
from the cut, nine bent slightly towards the cut, one bent strongly towards 
the cut. 
From this it is clear that the traumatic stimulus tends to produce 
a slight positive curvature. 
9. Six beans were taken, treated as in the last experiment, and then 
pinned with the root horizontal and the cut and mica slip on the upper 
side. All curved clearly down in the responding zone. 
10. Nine beans were taken at one time and treated in the same way, but 
pinned with the root horizontal and the cut and mica slip on the lower 
side. Two remained straight, one curved slightly down, six curved strongly 
down, making sharp curves of 6o° or 70° in the responding region. These 
curves were obviously altogether different from those in Experiment 8. 
11. Fourteen beans were taken, treated in the same way, and pinned so 
that the mica slips were inserted laterally in the horizontal root. Ten 
remained straight, two curved slightly down, two curved strongly down. 
From the results of Experiments 9 and 10 it is clear that after connexion 
between tip and responding zone has been broken to a depth of half-way 
through the root, either from above or from below, the geotropic excitation 
can be conducted back along the remaining intact half. This seems to 
happen more easily when the lower half is left intact, since with other less 
vigorous roots curvature often did not occur when it was the upper side 
that was intact, though it did when the lower side was intact. The case of 
the intact lateral half (Experiment 11) is more doubtful: possibly the 
excitation is transmitted successfully, but response becomes difficult if only 
a lateral half of the responding zone is affected. 
Mica Slips inserted from two Opposite Sides. 
12. Twenty-one beans were taken, and cuts made just half-way through 
the roots from opposite sides. One was at 2 mm. behind the vegetative 
apex, and one at 2*75 mm. behind. Mica slips were inserted. The beans 
were pinned with the roots horizontal, and the cuts one on the upper and 
one on the lower side. Only curvatures occurring above the second cut were 
considered. Sixteen remained straight, one bent well down, three bent 
slightly down, and one bent slightly up. 
