SENSITIVE PLANTS, 



become more tardy, as if debility ensued from over- 

 exertion. Too strong sunlight has a similar effect 

 in causing the leaflets to close. A strong puff of the 

 breath, or a shake of the pot, is enough to cause the 

 movement. It is by no means a slow and gradual 

 change, but an almost instantaneous one, sometimes 

 of the leaflets on both sides simultaneously, and 

 sometimes first of one side and then the other. The 

 return movement is much more deliberate, so that it 

 can scarcely be detected. 



Yet more remarkable movement takes place in 

 another celebrated plant, without a touch being 

 required to stimulate it. This is the " telegraph 

 plant" (or Desmodium gyrans), a native of Bengal. 

 The lateral leaflets keep constantly moving all day 

 long without any external impulse being given to 

 them. They move up and down and circularly, this 

 last motion being performed by the twisting of the 

 footstalks, and while one leaflet is rising its corre-' 

 sponding one opposite is generally being depressed. 

 The motion downwards is generally quicker, or more 

 irregular than the motion upwards, which is steady 

 and uniform. These motions are observable for 

 twenty-four hours in the leaves of a shoot which is 

 lopped off from the plant, if kept in water. If from 

 any obstacle the motion is retarded, upon its removal 

 it is renewed with greater velocity. The motion is 

 most evident when the sun's rays are upon the plant. 



