366 MODIFIED CIEOUMNUTATION. Chap. VII, 



petiole), and the movement of the whole leaf was traced on a 

 vertical glass. This was a bad plan in some respects, because 

 the rotation of the leaflet, independently of its rising or falling, 

 raised and depressed the filament ; but it was the best plan for 

 our special purpose of observing whether the leaf moved much 

 after it had gone to sleep. The plant had twined closely round 

 a thin stick, so that the circumnutation of the stem was pre- 

 vented. The movement of the leaf was traced during 48 h., 

 from 9 A.M. July 10th to 9 a.m. July 12th. In the figure given 

 (Fig. 151) we see how complicated its course was on both days : 

 during the second day it changed its course greatly 13 times. 

 The leaflets began to go to sleep a little after 6 p.m., and by 

 7.15 P.M. hung vertically down and were completely asleep; 

 but on both nights they continued to move from 7.15 p.m. 

 to 10.40 and 10.50 p.m., quite as much as during the day ; and 

 this was the point which we wished to ascertain. "We see in 

 the figure that the great sinking movement late in the evening 

 does not differ essentially from the circumnutation during 

 the day. 



Qlycine fiispida (Tribe 8). — The three leaflets sink vertically 

 down at night. 



Erythrina (Tribe 8). — Five species were observed, and the 

 leaflets of all sank vertically down at night ; with E. caffra and 

 with a second unnamed species, the petioles at the same time 

 rose slightly. The movements of the terminal leaflet of &'. crista^ 

 gain (with the main petiole secured to a stick) were traced 

 from 6.40 a.m., June 8th, to 8 a.m. on the 10th. In order to 

 observe the nyctitropio movements of this plant, it is necessary 

 that it should have grown in a warm greenhouse, for out of 

 doors in our climate it does not sleep. We see in the tracing 

 (Fig. 152) that the leaflet oscillated twice up and down between 

 early morning and noon ; it then fell greatly, afterwards rising 

 till 3 P.M. At this latter hour the great nocturnal faU com- 

 menced. On the second day (of which the tracing is not given) 

 there was exactly the same double oscillation before noon, but 

 only a very small one in the afternoon. On the third morning 

 the leaflet moved laterally, which was due to its beginning to 

 assume an oblique position, as seems invariably to occur with 

 the leaflets of this species as they grow old. On both nights after 

 the leaflets were asleep and hung vertically down, they continued 

 to move a little both up and down, and from side to side. 



Erythrina caffra. — A filament was fixed transversely across 



