EXERCISE 65 

 RESPONSE TO TOUCH 



Materials. Small plants of the sort known as " sensitive plants " 

 (Mimosa pudica). These are often kept in homes and conservatories 

 as curiosities. They may be readily grown from seed. 



Directions for work. The plant will react most satisfactorily 

 when standing in good light. It should be placed in a window 

 some time before it is to be used, in order that it may have 

 time to recover from the disturbance occasioned by moving it, 

 and it is well to cover it with a glass bell jar to protect it 

 from accidental disturbance before time for the experiment. 



Tap one of the leaflets lightly with a pencil. What action 

 follows ? Repeat the tap, but somewhat more vigorously. Is 

 the reaction in any degree proportioned to the strength of the 

 stimulus ? 



Pinch a terminal leaflet on one of the leaves with the forceps 

 or the finger nails, using care not to shake the entire leaf. 

 Does the stimulus instantaneously affect the whole leaf, or is it 

 propagated from the place first affected to other parts of the 

 leaf ? What evidence do you have upon which you base your 

 conclusion? Describe in detail what happens in this experiment, 

 including the time intervals concerned, repeating the trial with 

 another leaf, if necessary, to secure data. 



Do the leaves recover their original condition after a period 

 of rest ? About how long does recovery require ? Are they 

 able to respond again after recovery ? Is the second response 

 apparently equal to and like the first response ? 



References 



BERGEN and CALDWELL. Practical Botany, pp. 388-389. 

 BERGEN and CALDWELL. Introduction to Botany, p. 22. 



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