Chap. VII. SLEEP OF LEAVES 361 



raised to 120° F., and the sub-petiole straightened itself. Similar 

 experiments with leaves in water were twice repeated, with 

 nearly the same result. It should he added, that water raised 

 to even 122° F. does not soon kill a leaf. A plant was placed 

 in darkness at 8.37 a.m., and at 2 p.m. (i.e. after 5 h. 23 m.), though 

 the leaflets had sunk considerably, they had Dy no means ac- 

 quired their nocturnal vertically dependent position. Pfeffer, on 

 the other hand, says * that this occurred with him in from I h, 

 to 2 h. ; perhaps the difference in our results may be due to 

 the plant on which we experimented being a veiy yoimg and 

 vigorous seedling. 



The Movements of the Utile Lateral Leaflets. — These have been so 

 often described, that we will endeavour to be as brief as possible 

 in giving a few new facts and conclusions. The leaflets some- 

 times quickly change their position by as much as nearly 180° ; 

 and their sub-petioles can then be seen to become greatly curved. 

 They rotate on their own axes, so that their upper surfaces are 

 directed to all points of the compass. The figure described by 

 the apex is an irregular oval or ellipse. They sometimes re- 

 main stationary for a period. In these several respects there is 

 no difference, except in rapidity and extent, between their move- 

 ments and the lesser ones performed by the large terminal 

 leaflet whilst making its great oscillations. The movements of 

 the little leaflets are much influenced, as is well known, by 

 temperature. This was clearly shown by immersing leaves with 

 motionless leaflets in cold water, which was slowly raised to 

 103° P., and the leaflets then moved quickly, describing about a 

 dozen little irregular circles in 40 m. By this time the water 

 had become much cooler, and the movements became slower or 

 almost ceased ; it was then raised to 100° P., and the leaflets 

 again began to move quickly. On another occasion a tuft of 

 fine leaves was immersed in water at 58° F., and the leaflets 

 were of course motionless. The water was raised to 99°, and 

 the leaflets soon began to move; it was raised to 105°, and the 

 movements became much more rapid; each little circle or oval 

 being completed in from 1 m. 30 s. to 1 m. 45 s. There was, 

 however, no jerking, and this fact may perhaps be attributed to 

 the resistance of the water. 



Sachs states that the leaflets do not move until the surround- 

 ing air is as high as 71° — ^72° P., and this agrees with our 



* ' Die Period. Beweg.,' p. 39. 



