313 
Angles of Inclination . 
who employed it to determine the angle of inclination for maximum 
geotropic response of lateral roots. This method seems to me wholly free 
from objection. The plants are subjected for equal periods of time to 
gravitation stimulation, first on one side, then on the other, till by a summation 
of stimulations they curve. The direction of the curve, provided the great 
majority of plants behave alike, can be nothing less than an index of 
stronger geotropic stimulation or response. 
By this method, Miss Haynes, whose work is soon to be published, 
tested the stems, young and old, of ten to twelve species, and found all of 
them to curve in response to the horizontal position. It occurred to me 
that primary roots ought to be tested in the same way also, inasmuch as 
this method had not been used with them. The following pages contain 
a record of this and other tests with a discussion of the results. 
II. Experimentation and Discussion. 
i . Determination of the angle for maximum response by the method of 
perception-period. 
This method is not quite the same as that of the latent period discarded 
by Czapek \ because he found the curves in roots beginning in about the 
same time when the angle of inclination was anywhere between 20° and i6o° 
from the position of stable equilibrium. I have varied the method somewhat 
by exposing in each experiment two pots of seedlings of the same age for the 
same time, but less than the latent 'period, one at 90° and the other at 135 0 
from the position of stable equilibrium ; revolving them subsequently so as 
to neutralize gravitation, and observing the number of curvatures and the 
relative amplitude of the angles. In this series only the hypocotyls were used. 
The experiments were conducted in a dark room, at a temperature of 22° C. 
The first seedlings used were Brassica alba , L. Their latent period 
at 22° was found to be 20 min. for the earliest curve observed, while 
most of the stems showed no curves after 33 min. A pot with eight 
seedlings was turned horizontally, and another with fifteen seedlings was 
turned with the stems pointing 45 0 below the horizontal, both remaining 
in these positions for 33 min. The pot at 90° then showed three stems 
curved, while the one with stems 135 0 from the position of stable equilibrium 
showed but one curved. After 15 minutes’ revolution on the klinostat in 
the vertical plane of curvature, six of the eight stems stimulated at 90°, 
and ten of the fifteen stimulated at 135 0 showed geotropic curves. In each 
set three stems had attained an angle of 45 0 . 
In all the other experiments with the hypocotyls of Brassica alba the 
period of stimulation was less than the latent period, being in some cases 
ijl min. and in others 20 min. Records were made at several times 
during the revolution, but the period of 30 min. seemed to be the best one 
1 Untersnchungen iiber Geotropismns. Jahrb. f. wiss. Bot., xxvii, 1895, p. 283. 
