VOLUME XXIX NUMBER 1 
IpOTANTGAL + Gi AZ Eek 
JANUARY s900 
THE MECHANISM OF ROOT CURVATURE:! 
JAMES B. POLLOCK. 
(WITH ONE FIGURE) 
Introduction. 
THE question as to the mechanism by means of which grow- 
ing plant organs respond to external stimuli has engaged the 
_ attention of writers on the phenomena of plant life during the 
_ last hundred and fifty years. Some of the earlier writers supposed 
that plants turned toward the sunlight because the heat of the 
sun contracted the plant fibers on the side toward the light 
(1, 26). Du Hamel (15) assigned light as the cause of move- 
ment of leaves. He knew that stems grew upward in the dark 
and hence were not influenced in the direction of their growth 
by light alone, as had been supposed previously. 
In 1806 Knight (31) published his classical experiments with 
seeds germinated on rapidly revolving wheels, and he found that 
the roots grew outward, and the stems inward toward the center 
of revolution, Knight drew the conclusion that gravitation is 
the force that causes roots of seedlings to grow down and stems 
*The experiments reported in this paper were carried out at the coed of 
Michigan in connection with work for the degree of Doctor of Science, under th 
tion of Professor V. M. S alding. I wish to express my hearty thanks to ah te 
fessor Spalding and Professor F.C. Newcombe for many helpful suggestions and for 
the facilities of the botanical Sueur which were placed so unreservedly at my 
al. 
dispos 
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