IRRITABILITY. 



In a time varying from 30 seconds to several minutes a curvature is 

 begun. Note rapidity, extent, and duration. Place a small rod in 

 contact with the tendril. In a few hours it will have coiled around 

 it. Observe the formation of spirals in the free portion of the 

 tendril. (Fig. 60.) 



EXPERIMENT 80. 



RELATION OF HARDNESS OF OBJECTS TO CURVATURE PRODUCED IN TENDRILS. 



Test the effect of water, mercury, soft gelatine, glass, iron, and 

 wooden objects when brought in contact with tendrils. 



EXPERIMENT 81. 



ACTION OF LEAVES AND TENTACLES OF CARNIVOROUS PLANTS. 



Obtain several plants of Sundew (Drosera) from the swamps. 

 In digging them, care should be taken to leave a large mass of the 

 soil on the roots of each so that their growth may not be greatly 

 disturbed. Cover with a bell-jar and place in the sunlight. Touch 



FIG. 61. 



FIG. 62. 



Leaf of Dionaea expanded. 

 (Kerner.) 



Leaf of Drosera with right leaf half 

 contracted. (Darwin.) 



the tentacles with small pieces of a large variety of substances, 

 wood, sugar, starch, paste, alkali, meat, bits of stone, etc., and note 

 to what substances the tentacles react and the rapidity of move- 

 ment. Repeat with Dionaea. 



