GEOTROPISM 



435 



coutiuued for nearly 'JO minutes Tiie final equilibrium 

 was reached after a period of 8 hours (Fig. 161). 



Fig IGl.— The Conipleie Geotropic carve (Crininn). 



For studying the effect of an external agent on geotro- 

 pic action, the period of uniform movement is the most 

 suitable. Acceleration of the normal rate (with enhanced 

 steepness of curve) indicates that the external agent acts 

 with geotropism in a concordant manner ; depression of 

 the rate with resulting flattening of the curve shows, on 

 the other hand, the antagonistic effect of the outside 

 agent. 



DETERMINATION OF EFFECTIVE DIRECTION OF STIMULUS. 



The experiments which have been described show that 

 it is the upper side (on which the vertical lines of 



