Chap. VII. SLEEP OF LEAVES. 327 



Oralis Valdioiana. — The leaves resemble those of the last 

 species, and the movements of two leaflets (the main petioles of 

 both having been secured) were 

 traced during two days; but the fig- 129. 



tracings are not given, as they 

 resembled that of 0. acetosella, with 

 the exception that the up and 

 down oscillations were not so fre- 

 quent during the day, and there Oxalis aceUsdla: circumnutM- 



was more lateral movement, so that ^'o" °/ ''*"^' "''j'" ,*^'"P '■■ 

 , ,,. -I ., 1 traced on Tertical elass 



broader ellipses were described. durini' 3 h. 40 m. 

 The leaves asvoke early in the morn- 

 ing, for by 6.45 a.m. on Juno 12th and 13th they had not only 

 risen to theif full height, but had already begun to fall, that is, 

 they were ciroumnutating. We have seen in the last chapter 

 that the cotyledons, instead of sinking, rise up vertically at 

 night. 



Oxalis Ortegesii. — The large leaves of this plant sleep like 

 those of the previous species. The main petioles are long, and 

 that of a young leaf rose 20° between noon and 10 p.m., whilst 

 the petiole of an older leaf rose only 13°. Owing to this rising 

 of the petioles, and the vertical sinking of the large leaflets, 

 the leaves become crowded together at night, and the whole 

 plant then exposes a much smaller surface to radiation than 

 during the day. 



Oxalis Plumierii. — In this species the three leaflets do not 

 surround the summit of the petiole, but the terminal leaflet 

 projects in the Kne of the petiole, with a lateral leaflet on each 

 side. They all sleep by bending vertically downwards, but 

 do not become at all folded. The petiole is rather Img, and, 

 one having been secured to a stick, the movement of the terminal 

 leaflet was traced during 45 h. on a vertical glass. It moved 

 in a very simple manner, sinking rapidly after 5 p.m., and 

 rising rapidly early next morning. During the middle of the day 

 it moved slowly and a little laterally. Consequently the ascend- 

 ing and descending lines did not coincide, and a single great 

 ellipse was formed each day. There was no other evidence of 

 circumnutation, and this fact is of interest, as we shall here- 

 after see. 



Oxalis sensitiva. — The leaflets, as in the last species, bend 

 vertically down at night, without becoming folded. The much 

 elongated main petiole rises considerably in the evening, but id 

 15 



