CHAP. VII. 



SLEEP OF LEAVES. 



375 



Fig. 157. 



A filament had been fixed on the previous evei jng, longi- 

 tudinally to the main petiole of a nearly full-grown, highly- 

 sensitive leaf (four inches in length), the stem having been 

 secured to a stick at its base ; and a tracing was made on a 

 vertical glass in the hot-house under a high temperature. In 

 the figure given (Fig. 157), the 

 first dot was made at 8.30 A.M. 

 August 2nd, and the last at 7 

 P.M. on the 3rd. During 12 h. on 

 the first day the petiole moved 

 thrice downwards and twice 

 upwards. "Within the same 

 length of time on the second 

 day, it moved five times down- 

 wards and four times upwards. 

 As the ascending and descend- 

 ing hues do not coincide, the 

 petiole manifestly circuninu- 

 tates ; the great evening fall 

 and nocturnal rise being an 

 exaggeration of one of the cir- 

 cumuutations. It should, how- 

 ever, be observed that the pe- 

 tiole fell much lower down in 

 the evenings than could be 

 seen on the vertical glass or is 

 represented in the diagram. 

 After 7 P.M. on the 3rd (when 

 the last dot in Fig. 157 was 

 made) the pot was earned into 

 a bed-room, and the petiole was 

 found at 12.50 A.M. (i.e. after 

 midnight) standing almost, up- 

 right, and much more highly 

 inclined than it was at 10.40 



P.M. When observed again at Mimosn ? udica : circram f nta . 



... , ,, , nvcmropic movement or main p- 



4 A.M. it had begun to fall, and tio i e) traccd during 34 h. ao m. 

 continued falling till 6.15 A.M., 



after which hour it zigzagged and again circumnutated. Similar 

 observations were made on another petiole, with nearly the 

 same result. 



On two other occasions the movement of the main petiole 



