IRRITABILITY. 63 



from injury. By this " sensitiveness " of tendrils, climbing 

 plants are able to attach themselves to supports and lift their 

 leaves to sunlight. In certain carnivorous plants, such as Dro- 

 sera and Dionaea, the rapid movement of the tentacles and 

 leaves enables these plants to capture insects which are held 

 and whose substance is absorbed by the plant. 



EXPERIMENT 77. 



MOVEMENTS OF SENSITIVE-PLANTS. 



Grow Mimosa pudica (Sensitive-plant) from seed, in a pot. 

 Moisture and temperature of about 20 C. are necessary for the welfare 



FIG. 59- 



Mimosa pudica. The leaf on the left is in a normal position ; the one on the 

 right has been stimulated. (Detmer.) 



of the plant ; consequently it should be kept under a bell-jar slightly 

 raised at one side to allow for ventilation, and placed in the sun- 

 shine. Try the following experiments : a. Jar the entire plant by 

 striking the pot. In a few seconds the leaves take the position 

 shown in Fig. 59. b. Strike one of the terminal leaflets. The pairs 

 of leaflets fold up together in succession, and finally the whole leaf 

 sinks on its petiole, c. Touch the upper side of the pulvinus with 

 a pointed object. No movement follows, d. Touch the under side 

 in like manner. A movement results, e. With a sharp knife cut off 

 the petiole just above the pulvinus. A drop of water issues from the 

 lower surface, which in an uninjured leaf would pass into the leaf-stalk. 



