288 
RICHARD M. HOLMAN 
intensity of the stimulus may exercise upon the permanent curvature 
of the root an effect similar to that exerted by the different media, 
air and earth, it by no means follows that reduced sensibility of the 
roots in air is the cause of the difference in behavior with which we 
are concerned. Some other factor may, in the case of roots in air 
and earth, be responsible for the differences in curvature. This factor 
might be the presence or absence of some agency which without 
affecting the sensibility of the root can assist in the execution of the 
reaction. Such experiments as those of Elfving, which I have extended 
yield no conclusive answer to the question which I have sought to 
answer in this section of the present paper. Elfving's conclusion is 
however in no way contradicted by the evidence which I have secured. 
Do roots which have performed a geotropic curvature in air become 
plagiotropic? 
Fig. I. Primary roots growing in air and showing the tip curvature. A. and 
B. — Vicia faba var. equina; C. and D. — Lupinus alhus; E. — Vicia faba var. equina 
(this root had grown in moist air at 15° C. for 15 days); and F. — Vicia sativa. 
