54 FREAKS OF PLANT LIFE. 



the surface or confined by the pressure of the irritable 

 parts of the plant." The date attached to the plate 

 is 1790. 



Sir Joseph Hookeri has given a complete summary 

 of the history of all the observations which have 

 been made on the plant from the earliest times, 

 which may be consulted by any who desire a more 

 explicit narrative of the details than our space will 

 enable us to furnish. We direct ourselves at once 

 to the modus operandi by means of which the 

 plant achieves its object. This mechanism has 

 been compared by Dr. Burdon Sanderson to a 

 rat-trap. " When it (the leaf) is open, the lobes 

 are at right angles to each other. When an insect 

 comes into contact with either, at once they approach 

 each other, but this does not occur with the sudden- 

 ness and completeness that it occurs in a rat-trap. 

 The lobes begin to close sharply enough, but do not 

 come quite together, remaining for some time 

 entrotcvert. When the leaf is in this state of half- 

 closure, it is easy to see what is the significance of 

 the two sets of prongs. You see that they are set 

 on alternately, along the opposite edges of the lobes, 

 so that, just like the teeth of a rat-trap, they fit into 

 each other. It is not difficult to see why this is so, 

 i.e., why the spikes are arranged alternately. The 



' Address to the British Association at Belfast in 1874, 



