ORIENTATION OF PRIMARY TERRESTRIAL ROOTS 295 
placed roots which were not "too young" in air with tips directed 
veitically upward. Then, after they had curved until the elongating 
region was approximately horizontal and the extreme tip acutely 
curved so that it pointed obliquely downward, he displaced the seed- 
lings so that the tips of the roots were directed straight downward. 
At this time the roots were surrounded by moist sawdust. He sub- 
sequently observed an upward curvature of these roots opposite to 
the curvature of the tip at the time the roots were placed in the saw- 
dust. 
Upon repetition of Nemec's experiments I found that a con- 
siderable number of the roots behaved as he reported.^ In my experi- 
ments roots of Vicia faba var. major and var. equina and of Lupinus 
alhus and Pisum sativum were employed. As in Nemec's experi- 
ments, the roots frequently behaved in the same manner when they 
were inverted in loose moist sawdust at the very beginning of the 
experiment instead of being permitted to undergo curvature from the 
inverted position in air. After thirty-six hours these roots had so 
curved that the elongating zone was nearly horizontal and the curved 
tips pointed obliquely downward. When the cultures were then 
placed so that the root tips pointed directly downward, there followed 
in a varying proportion of the individuals an upward curvature of the 
tip which was always opposite to the original tip curvature. This 
upward curvature, which was in some cases very acute, was never 
completely fixed but was always somewhat flattened as the root 
grew. The curved region was also pushed forward from behind by 
the elongation of the region of the root behind it. Thus thirty-six to 
forty-eight hours after the upward curvature took place the root 
exhibited a flat curvature some distance below the position which the 
tip of the root had occupied. In earth the upward curvature was 
almost entirely suppressed and when it did appear it was only as a 
slight and transitory upward inclination of the tip. In the experi- 
ments with roots in earth the inverted root was kept in moist air until 
the elongating region had reached the horizontal and the tip pointed 
obliquely downward. 
The roots in loose sawdust which bent upward did not, in my 
experiments, continue to grow in the oblique direction which they 
reached by reason of this upward curvature. Instead, in the course 
^ A full account of the conditions and course of Nemec's experiments, which 
mine followed exactly in method, will be found in his paper already cited. 
