Circumnutation. 247 



these varieties of activity are simply modes in 

 which inherent and spontaneous activities manifest 

 themselves under these varying external influences. 



His preliminary investigations into the nature of 

 these innate powers of movement were directed to 

 that large class of plants known as twiners and 

 climbers, whose revolving motions were so thor- 

 oughly described in his work on " Climbing Plants." 

 It was here that he laid the foundation for those 

 later studies which eventually resulted in that great 

 work, almost his last, on the " Power of Movement 

 in Plants." In this work he demonstrates by an 

 enormous induction that the ample sweeps of the 

 twining plant are but the most obvious manifesta- 

 tions of a class of phenomena which are common to 

 the entire vegetable kingdom. 



Amid the varied forms of movement which plants 

 present, Darwin has succeeded in rinding one funda- 

 mental and generic one to which every other may 

 be referred. To this universal form of plant activity 

 he gives the name " circumnutation." Not only 

 twining stems and tendrils, but parts of flowers, tips 

 of growing shoots, caps of penetrating roots and 

 rootlets, radicles, epicotyls, cotyledons, and even 

 full-grown leaves, are incessantly describing circles, 

 ellipses, and other more or less regular geometrical 

 figures ; and he conclusively shows that it is out of 

 this primary form of activity that all the more 

 specialised forms already mentioned have been de- 

 veloped. All movements of the parts of plants are 

 thus to be interpreted as modified forms of this 

 innate periodic circumnutation which is common to 



