WOODSORREL 



may fall in two to five seconds, but the recovery is very 

 slow. 



Vivisection is a cruel sort of proceeding, although it may 

 sometimes be necessary. The most curious vivisections have 

 been performed on Mimosa. When the leaflets are cut off^, it 

 is possible, on a stimulus being applied, to see water oozing 

 out of the cut surface of the stalk. This would go to show 

 that it is the water being discharged from the leaf-base that 

 produces the movement. 



There are, however, many points in the behaviour of the 

 Sensitive Plant which have not yet been explained. 



Possibly the curious Semaphore or Telegraph Plants, 

 whose leaflets suddenly and without any obvious reason move 

 with a jerk through an angle of several degrees, may also 

 be protected from animals by this uncanny and unusual 

 behaviour. 



But though the Sensitive Plant is certainly protected from 

 grazing animals by these movements, other advantages may 

 be derived. Heavy rain, for instance, such as occurs in the 

 tropics, will not injure its delicate leaves. Dust-storms will 

 not damage it, and at night there will be no loss of heat by 

 radiation. The " shrunk *" or folded condition of the leaflets 

 will decrease any chance of injury by raindrops, for the rain 

 will not fall on the broad surface of the leaflets. A nearly 

 vertical leaf also will not suffer the loss of heat which 

 a horizontal one would endure. 



Besides the plants mentioned above, there are several others 

 in which by a rather severe shaking the leaves can be made to 

 fold up. This is the case with the common Woodsorrel 

 {Oxalis acetosella), with the False Acacia {Rohinia\ and a 

 few others. 



The former has a peculiarly delicate leaf. In cold, wet 



196 



