286 
RICHARD M. HOLMAN 
was made of laminated wood and upon it were mounted the zinc lined, 
glass covered boxes in which the seedlings were fixed. Table III 
gives the results of one of a number of experiments with this apparatus 
in which the behavior of roots of seedlings upon the centrifuge was 
compared with that of roots at rest. The experiment to which 
Table III refers was performed with Pisum sativum but similar results 
were obtained with Vicia faha major. 
In addition to these experiments, which show clearly that increase 
in the intensity of the stimulus above that of gravity results in a 
more complete reaction of roots in air, other experiments were per- 
formed in which roots subjected to a stimulus of only a fraction of the 
intensity of gravity were compared with roots under the normal stimu- 
lus. The results of one such experiment are given in Table IV. 
The growth of the two series of roots was, in consequence of the care 
exercised to secure sufficient water supply, not appreciably different- 
Table IV 
Roots of Vicia faha var. equina of which One Series (r) was Subjected to a Stimulus of 
\ y. g and the Other Series {c) Remained at Rest 
Root Number 
Original Angle with Radius or 
Perpendicular 
Angle After 44 Hours 
c 
c 
I 
2 
3 
83° 
86° 
88° 
87° 
92° 
94° 
69° 
69° 
76° 
43° 
34° 
65° 
Mean 
86° 
91° 
71° 
47° 
As is seen in this table, decrease in the intensity of the stimulus 
below that of gravity results in a lesser curvature of the roots than 
takes place under the stimulus of gravity. As we have shown, roots 
under a stimulus of w X g in air tend to react as do roots in soil under 
a stimulus of I X It is also important to determine whether or not 
roots when grown in soil and subjected to a stimulus of gin tend to 
execute curvatures similar to those of roots in air under the normal 
stimulus. With this question in mind, I experimented with seedlings 
of Vicia faha var. equina, planted in soil in small Sachs's boxes which 
were mounted upon a motor driven clinostat in such a manner that 
the roots were parallel to the axis of rotation. When the rate of 
rotation was so rapid that the stimulus exceeded (3 X ^)/ 100 all the 
