ORIENTATION OF PRIMARY TERRESTRIAL ROOTS 285 
that of gravity. This was done in order to determine whether roots 
thus treated would, Hke roots in air while under the stimulus of gravity, 
grow straight ahead in a position oblique to the stimulating force. 
The centrifuge first employed was one designed for the lecture table 
and intended for rotation at relatively low speeds. Being without 
provision for self-lubrication and having a very small disc this centri- 
fuge proved unsuitable for experiments which were to extend over a 
longer period than twenty-four to thirty hours at 20° C. Experi- 
ments with this apparatus which were continued for from twenty-four 
to thirty hours and in which a stimulus of from 4 to 10 g. was employed 
yielded, as is shown by Table II, results corresponding to those of 
Elfving's experiments. 
Table III 
Roots of Pisum sativum Subjected to a Stimulus of 1$ X g to 19 X g upon the Centri- 
fuge (r) and Kept at Rest {c) 
Each series consisted of 5 roots. 
Root 
Number 
Original 
Length, 
Cm. 
Original 
Angle with 
Radius or 
Perpen- 
dicular 
Angle after 
24 Hours 
Angle after 
45 Hours 
Angle after 
69 Hours 
Angle after 
93 Hours 
Length after 
95 Hours, 
Cm. 
c 
c 
c 
c 
c 
I 
2 
3 
4 
5 
4 
4-3 
3.1 
5.0 
4-5 
4- 3 
4.0 
2.8 
5- 0 
4.5 
158° 
143° 
130° 
130° 
130° 
134° 
130° 
123° 
127° 
155° 
65° 
80° 
77° 
95° 
76° 
115° 
95° 
94° 
112° 
104° 
30° 
50° 
62° 
65° 
35° 
95° 
80° 
90° 
88° 
91° 
20° 
40° 
25° 
30° 
24° 
67° 
65° 
69° 
60° 
75° 
26° 
16° 
13° 
20° 
12° 
51° 
61° 
56° 
48° 
63° 
II 
lO.I 
8.7 
137 
II. 0 
II. I 
II.7 
8.3 
II-3 
11.9 
Mean. . . 
4.2 
4.1 
138° 
134° 
79° 
104° 
48° 
89° 
28° 
67° 
17° 
56° 
10.9 
10.9 
Although in these experiments, owing to the relatively low rate of 
rotation and the care taken to provide sufficient water, the rate of 
growth of the centrifuged roots was not below that of the control roots, 
yet the experiments were not continued for a sufficient period. On 
that account I performed other experiments extending over a longer 
period. For this purpose a centrifuge was employed having a much 
larger disc than the one previously used and provided with self- 
oiling bearings. This apparatus, which was constructed by Mr. 
Arntzen, expert mechanician, civil engineering laboratory. University 
of California, was kept in motion by a 1/15 horse power induction 
motor with a speed of 1,800 revolutions per minute. Speed was re- 
duced by means of an adjustable friction drive. The revolving disk 
