79. 



Harshberger (ll) who studied the curling of Rhododendron 

 maximum in v/hich it is the upper epidermis , instead of the 

 lower one fii' l-e comes exposed during curling, claims that 

 the rolling raovejnent of the leaf is due to the gradual 

 passage of the sap into the •'.rtercollular spaces or due 

 "to the movement of the liquid from cell to cell by- means of 

 protoplasmic bridges so that one part of the leaf becomes 

 highly turgescent and the other part more or less flaccid". 

 He also believes that low temperature is responsible for the 

 moving of the liquids toward the upper side of the petiole 

 and of the leaf ;while a higher tempeaature reverses the process 

 It is believed by Harshberger that turgidity is the main 

 factor in the mechanism ojf . theB6:-movements, 



It v.'as found from a study of cross sections of a curled 

 leaf that the cells showed considerable shrinkage and 

 deformation, According to Steinbrinck {2*f) the loss of water 

 from a plant tissue not only decreases the size of the 

 cells of the tissue and deforms them but also affects the 

 concentration of the cell sap v/hich during the giving off 

 of water pulls the cell membrane along v/ith it, As the 

 turgor becomes diminished the membrane weakens EUid the 

 cohesion of the concontrated cell sap draws the cell membrane 

 along v/ith it to the center producing thus a decrease in 

 volume of the tissue. This explanation seems applicable also 

 to the decrease in volume and to deformation of the cells 

 of the leaf in the curled state. 



