222 CLOVER, SLEEP. [CH. VIII 



to their edges. The experiment may also be made with 

 a sod of clover dug up and kept wet in a basin or even 

 with cut leaves in a bottle of water. 



Fig. 40. Exp. 254. 

 From The Power of Movement in Plants. 



By covering up one plant with a hollow bell-jar 

 containing potassium bichromate, and another with a bell 

 containing ammoniacal copper sulphate, it may be shown 

 that the orange light acts like darkness, while the blue 

 acts like daylight. 



Finally, a few plants should be kept dark for 5 or 6 

 days to observe the fact that the leaflets ultimately 

 assume a position resembling the day-position, except that 

 the leaflets droop somewhat. 



(255) Nyctitropic movements. 



To get a general idea of the varied character of 

 nyctitropic movements it is best to compare the diurnal 

 and nocturnal positions in a selection of plants. 



Trifolium has already been described ; as a contrast it 

 is well to examine the nocturnal positions of a trifoliate 

 Oxalis, such as 0. acetosella (in which the leaflets point 

 nearly vertically downwards at night), and of Marsilea 

 quadrifoliata (in which the four leaflets rise and arrange 

 themselves in a vertical packet). The nyctitropism of 



