204 CLOVER, SLEEP. [CH. VIII 



outside of the rim so as to make sure tliat light is 

 excluded. After one or at most two hours the plants 

 may be examined, when the leaflets will be found in the 



Fia. 39. Exp. 254. 



nyctitropic position shown in fig. 39, where the left-hand 

 leaf is awake, the one on the right asleep: the lateral 

 leaflets are face to face and the terminal leaflet folded on 

 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. 



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 



