322 New combe. — Geo tropic Response at Various 
C. Summary. 
The present paper deals with two questions: (1) the angle of in- 
clination of primary roots and stems at which the strongest geotropic 
reaction is effected ; (2) the relative geotropic effect at equal angles of 
inclination above and below the horizontal plane. 
It has been shown that evidence on these questions has been heretofore 
too meagre, principally on account of the insufficiency of method employed. 
One of the methods employed by Sachs to settle the first question — that 
of the determination of the latent period — has been found by several 
experimenters to be difficult to use because the latent period seems to 
be almost the same for all angles of inclination, except for very small 
angles. The method of the comparison of angles attained in a given time, 
when roots and stems are placed at various angles of inclination, is not 
satisfactory, because the angle of inclination begins to change as soon 
as the curve begins. The method of measuring the angles attained after 
releasing plant members forced to retain fixed angles of inclination during 
prolonged stimulation is objectionable theoretically; and, in practice, roots 
so treated are found to behave very irregularly. 
In the present paper the method of alternate, intermittent stimulation 
has been most employed, and, in addition, the method of determining the 
perception period at 90° and 135 0 from the position of stable equilibrium, 
by stimulating for a time less than the latent period and then rotating the 
plant on the klinostat. 
The tests made by determining the perception period of the hypocotyls 
of Brassica alba and Rapha 7 ius sativus were not very decisive, since there 
is considerable irregularity of results ; but the weight of evidence indicated 
the position at 90° as having a shorter perception period than at 135 0 . 
The experiments by alternate stimulation on opposite sides of the 
same plant member for equal periods of time, but at different angles, leave 
no ambiguity. All of the five species of plants used showed their seedling 
stems responding to the position at 90° rather than to that at 135°} or any 
other angle from the position of stable equilibrium ; and all of the six 
species of plants used showed the same reaction with their primary roots. 
The experiments made to determine whether the geotropic effect 
is the same on plant members at equal distance above and below the 
horizontal were less uniform. By alternating plants every 15 minutes 
from a position above the horizontal plane on one side of the vertical plane 
to a position an equal distance below the horizontal on the other side of the 
vertical plane, the ensuing curvature after some hours would indicate which 
position was most influenced by the gravitation stimulus. It was found 
that for both roots and stems there were irregular curves, but that the large 
majority grew straight. 
