SLEEP OF PLANTS. 



247 



roof over the edges of the closed side leaflets. By 

 this means a kind of cone is formed with the apex 

 towards the footstalk (fig. 39). The middle leaflet in 

 this movement passes through an angle of 90 to 140° 

 The falling of the middle leaflet in this " clover" was 

 observed on the morning of two days. On the first 

 day the leaflet fell between eight o'clock in the morn- 

 ing and three in the afternoon. On the second day 



it fell between seven 



Fig- 39-" 



-Leaflets of clover awake 

 and asleep. 



o'clock in the morn- 

 ing and one in the 

 afternoon. After this 

 fall the leaflet began 

 to rise again, but 

 slowly, until four 

 o'clock, when the 

 rapid rise for the 

 evening commenced. 1 It is interesting to compare 

 these two little plants with trifoliate leaves, and ob- 

 serve how the same end is attained, by two diverse 

 and opposite means, the one by rising, the other 

 by falling ; but both equally decided and remarkable. 

 The melilot is another plant with trifoliate leaves, 

 and this exhibits a different class of movements in 

 its nocturnal gyrations. Darwin has thus described 

 the process which he observed. " The three leaflets 



1 Darwin, " Movements of Plants," p. 352. 



