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PLANT PHYSIOLOGY 



half of the pulvinus is most concerned in the movements. The 

 rise to a higher position after cutting the top part, is due to the 

 fact that it is not restrained by the tension in the thicker-walled 

 cells of the upper half, which are no longer functional. 



Fig. 25. — The sensitive plant (Mimosa). A is the normal position of the 

 leaves and B is the position when touched, burned, etc.; p is the pulvinus. 

 (After Pfeffer.) 



The drooping of the leaf is due to the loss of water from the 

 cells of the pulvinus into the intercellular spaces. This causes a 

 loss in turgor with the resultant fall. Later the water is resorbed 

 from the intercellular spaces and the leaf assumes its normal posi- 



