SENSITIVENESS. 61 



or burnt or cut, it transmits an influence to the upper 

 adjoining part, causing it to bend away from the affected 

 side ; and, what is more surprising, the tip can distin- 

 guish between a slightly harder and softer object by 

 which it is simultaneously pressed on opposite sides. If, 

 however, the radicle is pressed by a similar object above 

 the tip, the pressed part does not transmit any influence 

 to the more distant parts, but bends abruptly towards the 

 object. If the tip perceives the air to be moister on one 

 side than on the other, it likewise transmits an influence 

 to the upper adjoining part, which bends towards the 

 source of moisture. When the tip is excited by light, 

 the adjoining part bends from the light ; but when 

 excited by gravitation, the same part tends towards the 

 centre of gravity. In almost every case we can clearly 

 perceive the final purpose or advantage of the several 

 movements. Two or perhaps more of the exciting causes 

 often act simultaneously on the tip, and one conquers 

 the other, no doubt, in accordance with its importance 

 for the life of the plant. The course pursued by the 

 radicle in penetrating the ground must be determined by 

 the tip ; hence it has acquired such diverse kinds of sen- 

 sitiveness. .It is hardly an exaggeration to say that the 

 tip of the radicle thus endowed, and having the power of 

 directing the movements of the adjoining parts, acts like 

 the brain of one of the lower animals, the brain being 

 seated within the anterior end of the body, receiving im- 

 pressions from the sense-organs, and directing the several 

 movements." 



Practical Inferences. It will be obvious, then, from 

 what has been before said, that for cultural purposes, 

 such as the various operations connected with tillage, the 

 nature, quantity, and time of application of manure, and 

 the like, the character of root-action in general must be 

 studied in connection with the nature and properties of 



