CHAP. VII. SLEEP OF LEAVES. 355 



Bommet, les inferieures vers la base du petiole comrmm ; " but 

 the leaflets on a young plant observed by us in the green- 

 house merely sank vertically downwards at night. The leaflets 

 are raised in Sphcerophysa salsola, Colutea arborea, and Astra- 

 galus uliyinosus, but are depressed, according to Linnaeus, in 

 .Glycyrrhiza. The leaflets of Bobinia psrvdu-acacia likewise sink 

 vertically down at night, but the petioles rise a little, viz., in 

 one case 3, and in another 4. The circumnutating move- 

 ments of a terminal leaflet on a rather old leaf were traced 

 during two days, and were simple. The leaflet fell slowly, in a 

 slightly zigzag line, from 8 A.M. to 5 P.M., and then more 

 rapidly ; by 7 A.M. on the following morning it had risen to its 

 diurnal position. There was only one peculiarity in the move- 

 ment, namely, that on both days there was a distinct though 

 small oscillation up and down between 8.30 and 10 A.M., and 

 this -would probably have been more strongly pronounced if 

 the leaf had been younger. 



Coronilla rosea (Tribe 6). The leaves bear 9 or 10 pairs of 

 opposite leaflets, which during the day stand horizontally, with 



Fig. 146. 



Coronilla rosca : leaf asleep. 



their midribs at right angles to the petiole. At night they rise 

 up, so that the opposite leaflets come nearly into contact, and 

 those on the younger leaves into close contact. At the same 

 time they bend back towards the base of the petiole, until their 

 midribs form with it angles of from 40 to 50 in a vertical 

 plane, as here figured (Fig. 146). The leaflets, however, some- 

 times bend FO much back that their midribs become parallel to 

 and lie on the petiole. They thus occupy a reversed position 

 to what they do in several Lcguminossc, for instance, in Mimosa 



