386 



MODIFIED CIRCUMNUTATION. 



CHAP. VII. 



Ijomoea ccerulea and purpurea (Convolvulaceae). The leaves on 

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



to between 68 and 80 

 beneath 

 and 



Fig. 163. 



i\ 



ujr.*f>0u0? 



the horizon ; 

 some hang quite 

 vertically downwards. 

 On the following morn- 

 ing they again rise into 

 a 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 

 day in order to sleep, 

 for those which stood 

 on the back of a plant 

 before a north-east 

 window did not sleep. 



Nicotiana tabacum 

 (var. Virginian) and 

 glauca (Solanese). 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. tabacum, on the outside, there 

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



Nicotiana tabacum : circumnutation and nyc- 

 titropic movement of a leaf (5y- inches in 

 length), traced on a vertical glass, from 

 3 P.M. July 10th to 8.10 A.M. 13th. Apex 

 of leaf 4 inches from glass. Temp. 17 J- 

 18.j C. Figure reduced to one-half 

 original scale. 



