12 



Hooker: Physiological observations 



5. Before the experiment it measured 2.7 mm. The reaction 

 is in all essential respects similar to the previous example, but 

 there are important differences. The tentacle was on a mature 

 leaf. It had not, however, been stimulated before the experiment. 

 Bending was produced by an elongation of the convex side and the 

 median section, accompanied by contraction of the concave side. 

 The increase in length on the abaxial side was twice as great as the 

 contraction of the adaxial side. The ultimate stage of bending 

 was reached 5 hours and 45 minutes after stimulation. Unbending 

 was caused by gradual growth on the concave side and in the 

 median section together with slight contraction of the convex side. 

 The original position was reached after 23 hours and 30 minutes. 

 The tentacle then measured 2.83 mm. It had grown 0.13 mm. 

 during the experiment. 



A third example is given in Table III. This tentacle was in 



Table III 



the third row from the outside, on a leaf in excellent condition. 

 It reacted with great rapidity. Movement was detected within 

 a minute after stimulation, and the bending was completed in 

 twenty minutes. The table shows clearly that elongation com- 

 menced in Segment 5, the most basal portion of the abaxial side; 

 after ten minutes Segment 4 likewise increased in length; and 

 after three minutes more Segment 3 began to grow. The drawings 

 in Fig. 6 show the bending, and illustrate the apical progress of 

 the reaction. As in the previous case, the bending was produced 



