The Reversal of Geotropic Response in the Stem 123 
EXPLANATION OF PLATE I 
Fig. 1. Seven sunflower seedlings, six of which show reversed geotropic curva¬ 
ture in 16 per cent, carbon dioxide (Exp. 12). 
Fig. 2. The same about 24 hours after the excess of carbon dioxide had been 
removed, showing recovered normal geotropic curvature. 
Fig. 3. A similar set of sunflower seedlings most of which show reversed geo¬ 
tropic curvature in 13-3 per cent, carbon dioxide (Exp. 15). One of the 
seedlings shows normal curvature, two show recovered normal response 
as well as a downward curvature. 
Fig. 4. The same about 12 hours after they had been removed and placed in 
fresh air and light, showing recovered normal geotropic curvature. 
