386 



MODIFIED CIECUMN OTATION. 



Chap. VIL 



I/omcea cwrulea andpurpurea (Convolvulacese). — The Itiaves on 

 rery young plants, a foot or two in height, are depressed at night 



to between 68° and 80° 



Fig. 163. 



beneath the horizon ; 

 and some hang quite 

 vertically downwards. 

 On the following morn- 

 ing they again rise into 

 u, horizontal position. 

 The petioles become' 

 at night downwardly 

 curved, either through 

 their entire length or in 

 the upper part alone ; 

 and this apparently 

 causes the depression 

 of the blade. It seems 

 necessary that the 

 leaves should be well 

 illuminated during the 

 d^y in order to sleep, 

 for those which stood 

 on the back of a plant 

 before a north-east 

 window did not sleep. 



Nicotiana tahacum 

 (var. Virginian) and 

 glauca (Solaneae). — The 

 young leaves of both 

 these species sleep by 

 bendinh vertically up- 

 wards. Figures of two 

 shoots of N. glauca, 

 awake and asleep (Fig. 

 162), are given on p 

 385 : one of the shoots, 

 from which the photo- 

 graphs were taken, was 

 accidentally bent to one 

 side. 



At the base of the petiole of N. iabacum, on the outside, there 

 is a mass of cells, which are rather smaller than elsewhere, and 



SM'amJS 



.fh 



3'p.mJof'i 



i/im.iS" 



f^tcotiana tabacurn : circumnutation and nyc- 

 titropio movement of a leaf (Sj inches in 

 length), traced on a vertical glass, from 

 3 P.M. July 10th to 8.10 A.M. 13th. .4pex 

 of leaf 4 inches from glass. Temp. 17^°- 

 18^° C. Figure reduced to one-half 

 original scale. 



