SLEEP OF PLANTS. 



253 



remarkable. The leaf is 

 a very compound one (fig. 

 40) consisting of a petiole 

 with about seven pairs of 

 pinnae, or secondary peti- 

 oles, each of which is 

 feathered with little leaf- 

 lets. Towards night the 

 pinnae move forwards, 

 and sink downwards. 

 The leaflets become 

 directed towards the apex 

 of the pinna, and over- 

 lap each other, so that 

 the " pinnae then look 

 like bits of dangling 

 string" (fig. 41). Mere 

 verbal description can 



Fig. 40. — Leaf of Acacia Far- 

 nesiana awake. 



Fig. 41. — Leaf of Acacia Farnesiana in a sleeping condition, 

 give no idea of the contrast between the appear- 



