GROWTH SUBSTANCES FOR GEOTROPISM 177 



ZONE 10 _ 



ZONE 9 _ 



ZONES 



ZONE? 



20NE6 



20 40 60 80 100 120 140 160 



Fig 54 —Course of curvature in different zones of the Avena coleoptile after 

 geotropic stimulation (30 minutes in a horizontal position). Ordinate: the size 

 of curvature (/..., the reciprocal values of the radii of curvature) ; abscissae time 

 in minutes. Zone 1 is at the tip, zone 10 at the base. (From Dolk, 1929b.) 



