XLVIL— JJIURNAL MOVEMENT DUE TO ALTERNATION 

 OF LIGHT AND DARKNESS 



SiK J. 0. J^OSK, 



Assisted Ini 

 Lalit Mohan Mukhbrji, b.sc. (Xawroji Scholar). 



The nyctitropic movements of the leaflet of Cassia 

 alata and of the terminal leaflet of Desmodium gi/Tans 

 furnish us with typical examples of the recurrent effects 

 of light and darkness. The petiole of Cassia contains a 

 number of paired leaflets each of which is about 5 cm. 

 long and 2'^> cm. broad. The leaflets are extremely 

 sensitive to light ; at night each pair of leaflets fold them- 

 selves in a forward direction (see Fig. laO). With the 

 appearance of light they open at first in a lateral direction ; 

 later on there is a twist of the pulvinus by which the 

 inner surface of the leaflets faces light coming from above 

 (p. 405). I shall show that the diurnal movements of the 

 leaflets are predominantly due to phototropic action. 



IJefore proceeding further it will be necessary to give 

 a general description of the experimental method employed, 

 and of the apparatus by which diurnal movements are 

 recorded. 



EXPERIMENTAL ARRANGEMENTS. 



The diurnal record is often taken continuously for 

 several days, and it is therefore necessary to take precau- 

 tions against the disturbing effect of watering the plant. 



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