290 
RICHARD M. HOLMAN 
Nemec has put forward the hypothesis that "not too young" 
seedHng roots of certain of the forms which I have used, when inverted 
in moist air become, after a time, plagiotropic. The evidence upon 
which he based this hypothesis was threefold : 
First, that in some cases roots grow for many hours straight ahead 
while in an oblique position or in the horizontal and that the tip, 
although generally forming a smaller angle with the vertical than does 
the elongating zone, frequently fails to reach the perpendicular. 
Second, that when the tips of the roots are brought into a per- 
pendicular position pointing downward they bend upward again into 
an oblique position. 
Third, that when the tips of such roots are displaced from the 
oblique position an accumulation of protoplasm takes place in the 
cells of the columella, this accumulation being in the same part of the 
perceptive cells at which a similar aggregation of protoplasm appears 
in corresponding cells of secondary roots which have been displaced 
from their normal position. 
The third reason which Nemec advanced in support of his belief 
that orthotropic roots may become plagiotropic cannot alone be con- 
sidered conclusive. It is really significant only if the other points are 
definitely established. 
My own numerous experiments with seedlings of Vicia faba var. 
major, V. f. var. equina, Vicia sativa, Lupinus alhus, Pisum sativum 
and Ervum lens whose roots were surrounded by moist air and were 
placed in various positions between 30° and 180° from the normal 
position have convinced me that such roots do tend to attain a quite 
definite oblique position, varying from 30° to 60° from the perpendicu- 
lar. Thereafter active curvature takes place very slowly if at all. 
The position of the terminal portion of the root may however change 
owing to passive bending of the region behind the zone of elongation 
by reason of the increasing length and weight of the younger part of 
the root. Roots of Vicia faba and Lupinus albus up to 2.5 or 3 cm. 
in length when placed horizontal in air generally bring the elongating 
region into this oblique position within 24 to 36 hours at a temperature 
of 18° to 20°. Older roots require a longer time. This oblique posi- 
tion in which the root frequently elongates without further active 
curvature is generally attained by an extensive geotropic curvature 
and subsequent autotropic flattening of the geotropic curvature. 
Often in the case of roots which are of considerable length before being 
