ORIENTATION OF PRIMARY TERRESTRIAL ROOTS 283 
of Lupinus albus so treated, all curved downward into the vertical 
when placed in earth. Roots were employed varying in length from 
3 to 12 cm. Three of the longer roots did not curve downward at once 
into the normal position when placed in soil. They executed a more 
gradual curvature than the others, although they also finally reached 
the perpendicular. (Very frequently long roots, even when they have 
not been kept in air or undergone previous curvature, approach the 
perpendicular position only very slowly when placed obliquely down- 
ward in earth.) In spite of repeated comparisons of the rate of down- 
ward curvature of roots placed horizontally in earth directly after 
removal from the germinating bed with that of roots similarly placed 
in earth after geotropic curvature and flattening of this curvature in 
air, I have been unable to detect any difference in the rapidity of the 
downward curvature. These facts indicate that any change in the 
geotonus of the root which may take place in air is lost when the root 
is brought into earth. If, as Nemec asserts, the root growing out of 
the perpendicular in air becomes plagiotropic, this plagiotropism is 
replaced by orthogeotropism when the root is placed in soil. Also, 
any considerable weakening or complete loss of geotropism which the 
roots in air experience disappears when the roots are placed in earth 
or other similar firm medium favorable to growth. Whatever change 
in the geotonus of roots may take place in air, there is no appreciable 
permanent change; for upon return to soil or sand or other firm and 
resistant medium such roots react just as do roots which have never 
grown in air. 
Are roots which have performed a geotropic curvature in air more 
weakly geotropic while they remain in that medium than are roots in 
earth? 
As I have already remarked, Sachs and Elfving assumed a weak- 
ening of the geotropism of roots in air which resulted in the roots 
discontinuing their curvature before the perpendicular was reached. 
Sachs's assumption was not based upon any specific experimental 
evidence. The only basis for Elfving's (1880, S. 32, ff.) conclusion 
was the results of experiments which he performed with seedlings of 
Pisum sativum rotated upon a centrifuge at such a rate that the roots 
were subjected to a stimulus 50 times that of gravity. The experi- 
ments were continued only for twenty-four hours and at the end of 
that period the roots upon the centrifuge, which at the beginning of 
the experiment had been placed with the tips directed toward the axis 
