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RICHARD M. HOLMAN 
of rotation, were found to form a smaller angle with the radius of 
rotation than inverted control roots, also growing in air, formed with 
the perpendicular. Since those roots which in his experiments were 
subjected to the more intense stimulus had taken up, after twenty- 
four hours, a position more nearly parallel to the direction of the 
stimulating force than had the control roots, Elfving concluded that 
it was merely on account of weakened geotropism that roots in air 
under the stimulus of gravity often underwent no appreciable curva- 
ture when growing obliquely downward. When subjected to a 
centrifugal force of 50 times the intensity of gravity the roots in Elf- 
ving's experiments must have suffered considerably from water short- 
age and their growth rate must have been much below that of the 
control roots. This fact and the short duration of his experiments 
make it impossible for us to know whether or not the roots grown 
upon the centrifuge had completed the flattening of their curvatures 
at the time the observations were made. If Elfving's experiments had 
been continued for a longer period, and if observations of the growth 
of the roots had been made, it might have been clear that after the 
same increase in length the curvatures were approximately the same. 
Table II 
Two Series of Roots of Vicia faba var. equina from 4.5 to 6 cm. Long, of which One 
Series (r) was Subjected to a Stimulus of 4. X g to 8 X g on a Centrifuge and 
the Other Series (c) Remained Stationary 
The roots remained in moist air throughout the experiment. 
Root Number 
Original Angle of Root with 
Radius or Perpendicular 
Angle After 20% Hours 
Growth in 30^ Hours 
. 1 . 
c 
c 
I 
2 
3 
4 
68° 
78° 
70° 
76° 
66° 
76° 
88° 
14° 
13° 
9° 
16° 
25° 
70° 
72° 
3.0 cm. 
3.6 cm. 
3.6 cm. 
3.2 cm. 
2.4 cm. 
2.7 cm. 
3.0 cm. 
Mean ' 73° 
77° ' 13° 
55.6° 
3-35 cm. 
2.7 cm. 
On that account I performed a series of experiments to determine 
the actual effect of varying intensities of stimulus upon the curvature 
of roots in air. In some of the experiments the seedlings were rotated 
so that the stimulus was greater than that of gravity. In others the 
stimulus was less than that of gravity. Experiments were also per- 
formed in which roots in earth were subjected to a stimulus less than 
