SENSITIVEN ESS. 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 
