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RICHARD M. HOLM AN 
zontal there is a slow downward curvature subsequent to the primary 
geotropic curvature and the flattening of that curvature. This 
secondary geotropic curvature, which may continue for as long as 
four to five days, appears to be due to a slight residue of the curvature 
of the extreme tip which is retained by the cells as they pass over into 
the phase of elongation. During this secondary geotropic curvature, 
2cn2 
Fig. 2. Diagrams showing the behavior of roots of Vicia faba var. equina 
about 2 cm. long when placed in air at the angles shown at i in the diagrams. 
the residue of the primary geotropic curvature of the root frequently 
undergoes further flattening. As a result of this decrease in the 
