ORIENTATION OF PRIMARY TERRESTRIAL ROOTS 287 
roots, during a growth of 2-4 cm., bent until the end of each coincided 
with a radius of rotation. The curvatures were not appreciably 
different from those executed by roots under the normal stimulus of 
gravity. When subjected to a stimulus of (4 X g)/ 1,000 the roots, 
in a large proportion of cases, bent very gradually away from the 
axis of rotation. Then, after attaining an oblique position, they grew, 
in many cases, in an apparently straight line; in other cases in a curve 
of large radius. When similar roots were rotated at a rate only half 
as rapid, the stimulus being thus reduced from (4 X g)/i,ooo to 
(i X g)/i,ooo, they made no visible response. The behavior of roots 
planted in soil and subjected to stimuli of (35 X g)/i,ooo and 
(4 X ^)/i,ooo is shown in Table V. 
Table V 
Roots of Viciafaha var. equina Grown in Soil and Subjected to Stimuli of Less Intensity 
than Gravity 
All roots originally placed parallel to the centrifuge axis. 
Root Num- 
Original 
Angle After 
Angle After 
Angle After 
Angle After 
Stimulus 
ber 
N umber 
2 Cm. Growth 
4 Cm. Growth 
6 Cm. Growth 
8 Cm. Growth 
I 
7.0 
36 
10 
10 
10 
2 
9.1 
46 
46 
38 
3 
7-7 
45 
30 
32 
32 
4 
9.5 
90 
46 
36 
36 
5 
8.7 
60 
42 
21 
4/1000 X g 
6 
5-9 
53 
52 
7 
6.4 
70 
67 
8 
7.8 
40 
6 
9 
7-5 
27 
34 
I 
7.0 
0 
0 
2 
6.6 
0 
0 
3 
7-7 
23 
0 
4 
6.9 
33 
0 
0 
5 
7.6 
29 
7 
0 
35/1000 X g 
6 
10.3 
0 
7 
8.2 
16 
0 
0 
0 
8 
7.5 
0 
0 
0 
0 
9 
5-9 
19 
6 
4 
Note. — Dashes indicate that roots did not attain the length referred to. 
These results show that by reducing the stimulus below that of 
gravity roots in earth can be caused to execute curvatures like those 
of roots in air under the normal stimulus of gravity. 
Although all these centrifugal experiments, furnishing much more 
complete evidence than Elfving presented, show that changes in the 
