ORIENTATION OF PRIMARY TERRESTRIAL ROOTS 297 
have so curved that the elongating region is horizontal and the tip 
directed obliquely downward to loose moist sawdust in a receptacle 
mounted upon a clinostat. If the ''upward" curvature appears also 
in the case of roots rotated upon the clinostat, we must assume that 
the curvature is of auto tropic nature rather than, as Nemec believed, 
the result of induced plagiotropism. I have performed a number of 
experiments with the object of thus determining the nature of the 
upward bending. In each of these experiments one series of roots 
was treated just as were those in Nemec's experiments, i. e., after 
inversion in air and curvature there such as has already been described, 
the roots were placed with the tips directed downward in loose moist 
sawdust, while a second series was similarly treated except that after 
being placed in the loose sawdust they were rotated upon the clinostat. 
In one of these experiments seedlings of Lupinus albus were used 
which, at the time they were inverted in air had lengths of from 2 to 
2.5 cm. They remained in air for 36 hours. The roots were then 
divided into two series, one of which was placed upon the clinostat 
while the other remained stationary with the root tips directed down- 
ward. Of fourteen roots on the clinostat, nine showed a distinct 
"upward" curvature while five merely flattened the curvature of 
the tip and then elongated in a straight line. The same number of 
the fourteen control roots as of the clinostat roots curved "upward." 
A similar experiment, in which roots of Pisum sativum were employed,, 
gave corresponding results. Of twelve of these roots rotated upon 
the clinostat, seven flattened the original curvature of the tip and 
bent "upward." Of eleven control roots, similarly treated, save that 
they remained at rest, four exhibited the upward curvature and all 
subsequently bent downward into the perpendicular. Other experi- 
ments with Pisum sativum and Viciafaba gave similar results. 
Since the curvatures which Nemec considered the result of induced 
plagiotropism also take place upon the clinostat, they must be con- 
sidered as autotropic. Not only is there no permanent taking on 
of plagiotropism by the root in air but the upward curvatures are not 
even the result of a transitory plagiotropism. 
Particularly significant in this connection is the behavior of roots 
planted horizontally or obliquely upward or inverted in loose moist 
sawdust behind the glass plate of a Sachs's box. These roots bend 
downward in a curve of very large radius as is shown by the accom- 
panying figure which is traced directly from photographs. 
