THE DAILY MOVEMENTS OF LEGUMINOUS LEAFLETS 



FRANK C. GATES 



Carthage College, Carthage, III. 



Photeolic, nyctotropic, or sleep movements of certain leaves, 

 particularly those of leguminous plants, are well known. The 

 normal day position of the leaflets is in a plane nearly at right 

 angles to the light. At night one of two distinct positions is 

 assumed. In certain species this consists of a folding upwards 

 and forwards, while in other species the leaflets droop or hang 

 straight down. Members of the Mimosatae and Caesalpiniatae 

 are examples of the first class and those of the Papilionatae of the 

 drooping position. The movement is brought about by differ- 

 ential turgor in the pulvini of the leaflets in response to the 

 stimulus of changing light and darkness in combination with 

 higher and lower temperature. Just how this brings about the 

 differential turgor is not at present understood. 



In addition to the photeolic movements just noted, another 

 movement takes place under certain conditions during the day- 

 time. This I have termed the xerofotic^ movement from the 

 fact that it is due to differential turgidit}^ in tlie pulvini caused 

 by a greater drying effect on the upper side under one-aided 

 illumination. 



In nature this movement takes place under the influence of 

 direct sunshine. In Gliricidia sepium it may be brought about 

 by the local application of chemical drying agents, as absolute 

 alcohol and xylol. The xerofotic movement in leguminous leaf- 

 lets consists of an upward bend of the whole leaflet to an angle 

 of between 45° and 70° above the horizontal. This position is 

 maintained until the difference in turgiditj^ is equalized. If of 

 large size, clouds passing over the sun are sufficient to permit 

 such equalization. Equalization always takes place as the sun 



1 Gates, F. C., Xerofotic Movements in Leaves. Bot. Gaz., 1916 (edition). 



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