RESPONSIVE CURVATURES— NEGATIVE GEOTROPISM 50I 



The first record was taken after the curvature movement, 

 due to gravitation at an angle of 45 °, had attained a constant 

 value. The tip of the flower was then found to be moving 

 at a rate of four divisions per minute. On changing the 

 angle to 135 , the rate of movement showed an imme- 

 diate increase, and attained in the course of five minutes 

 a permanent rate of 15*5 divisions per minute. It has been 

 said that the experimental adjustment of change of position 

 took only about a minute 

 to effect, yet on renewing 

 the record we find that the 

 effective increase thus esta- 

 blished in the gravitation- 

 stimulus was immediately 

 perceived and responded 

 to by the organ, in an 

 accelerated rate of curva- 

 ture. The permanent in- 

 creased rate at 135 is thus 

 found to be nearly four 

 times that at 45 °. The 

 organ was now returned 

 to its position at 45 , and 

 the rate once more fell till 

 it became nearly equal to 

 what it had originally been 

 at 45 , being only very 

 slightly greater. The organ 

 was once more placed at 13 5°, and the rate again rose, till it 

 reached slightly beyond its former value at that angle. The 

 ratio of the second rates determined at 45 and 13 5 was also 

 found to be almost as 1 is to 4 (fig. 208). 



With reference to the cause of this difference of gravita- 

 tional effect, Haberlandt suggested that it may lie in the 

 fact that the weight of the statoliths in 45 position is on the 

 basal half, while at 135 it is on the apical half (fig. 209) 

 The next point is, to account for the greater reaction of the 



Fig. 208. Response Records showing Dif- 

 ferences in Rate of Curvature according 

 as Specimen is held at Angles of 45 

 and 135° 



