NYCTITBOPJG MOVEMENTS. 



409 



lOGo. The ample revolving inovement is not conflned to stems, 

 iiiit is observed in some modified branches and leaves, for ex- 

 ample in certain ten- 

 drils, etc. A single 

 instance will serve to 

 show the remarkable 

 nature of the move- 

 ment in the case of 

 the tendrils of Echi- 

 nocystis lobata, as de- 

 scribed b}' Darwin:^ 

 ' ' These are usually 

 inclined at about 46° 

 above the horizon, but 

 they stiffen and straighten themselves so as to stand upright in 

 a part of their circular course ; namely, when the3' approach and 

 have to pass over the summit of the shoot from which they arise. 

 If they had not possessed and exercised this curious power, they 

 would infallibly have struck against the summit of the shoot and 

 been arrested in their course. As soon as one of these tendrils 



with its three branches be- 

 gins to stiffen itself and rise 

 up verticallj', the revolving 

 motion becomes more rajjid ; 

 and as soon as it has passed 

 over the point of difficulty, 

 its motion coinciding with 

 that from its own weight 

 causes it to fall into its previously inclined position so quickly 

 that the apex can be seen travelling like the hand of a gigantic 

 clock." 



1064. Jfyctitropic, or sleep, movements. The foliar organs of 

 manj- plants assume at nightfall, or just before, positions unlike 

 those which they have maintained during the day. In many 

 cases the drooping of the leaves at night is suggestive of rest, 

 and the name given by Linnaeus to this group of phenomena, 

 namely, "the sleep of plants," seems appropriate. But in numer- 

 ous cases the nocturnal position is one of obvious constraint, 

 and considerable force has to be expended in lifting the leaf to 



182 



1 Power of Movement in Plants, 1880, p. 266. 



Ftg. 181. Leaf of Coronilla rosea at night, f Darwin.) 



FiQ. 182. Leaf of White Clover. ^, day position ; B, night position. (Darwin.) 



