CHAP. VII. 



SLEEP OF LEAVES. 



369 



ciana Qilliesii (both belonging to Tribe 13), the leaves behave 

 in the same manner. 



Fig. 153. 



A. B. 



Ftematoxylon Campechianum : A, branch during daytime ; B, branch with 

 leaves asleep, reduced to two-thirds of natural scale. 



Cassia (Tribe 14). The nyctitropic movements of the leaves 

 in many species in this genus are closely alike, and are highly 

 complex. They were first briefly described by Linnaeus, and since 

 by Duchartre. Our observations were made chiefly on 0. flori- 

 bunda * and corymbosa, but several other species were casually 

 observed. The horizontally extended leaflets sink down verti- 

 cally at night ; but not simply, as in so many other genera, for 

 each leaflet rotates on its own axis, so that its lower surface 

 faces outwards. The upper surfaces of the opposite leaflets are 

 thus brought into contact with one another beneath the petiole, 

 and are well protected (Fig. 154). The rotation and other move- 

 ments are effected by means of a well-developed pulvinus at the 

 base of each leaflet, as could be plainly seen when a straight 

 narrow black line had been painted along it during the day. 

 The two terminal leaflets in the daytime include rather less than 

 a right angle : but their divergence increases greatly whilst they 



* I am informed by Mr. Dyer 

 that Mr. Bentham believes that 

 C. floribunda (a common green- 

 house bush) is a hybrid raised in 

 France, and that it comes very 



near to C. Icevigata. It is no doubt 

 the same as the form described by 

 Lindley (< Bot. Keg.,' Tab. 1422) 

 as C. Herbertiana. 



