LEAVES 



31 



into very numerous small leaflets, sometimes very small, 

 which stretch in pairs along the leaf branches. When a 

 drought begins, some pairs of leaflets fold 

 together, slightly reducing the surface ex- 

 posure. If the drought continues, more 



FIG. 27. Leaf of sensitive plant in two conditions: A, fully expanded, with the 

 four main branches and numerous leaflets well spread; B, after a shock of some 

 kind, the leaflets being thrown together forward and upward, the four branches 

 having been moved toward each other, and the main petiole having dropped 

 sharply downward. After DUCHARTRE. 



leaflets fold together, then still others, until finally all 

 the leaflets may be folded together, and the leaves them- 



A B 



FIG. 28. The day (A) and night (B) positions of the leaves of a clover-like plant. 

 After STRASBURGER. 



selves may bend against the stem. In this way the ex- 

 posed surface may be regulated according to the need. 



