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of course possess nerves or a central nervous system ; 

 and we may infer that with animals such structures serve 

 only for the more perfect transmission of impressions, 

 and for the more complete intercommunication of the 

 several parts." 



Here we see how much light may be thrown on 

 animal structures and functions by vegetable physio- 

 logy. We learn to limit our ideas of the superiority 

 of animals by discovering how much of what we consider 

 peculiar to them is found in plants. We appreciate the 

 unity of biology, indivisible without injury to our know- 

 ledge of its parts. No structure in plants appears more 

 wonderful, as Darwin describes it, than the tip of the 

 rootlet of a seedling. It is impressed by and transmits 

 influences of pressure, injury, moisture, light, and gravity 

 to other parts, and determines the course pursued by the 

 rootlet in penetrating the ground. " It is hardly an ex- 

 aggeration 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;" and the brain of Charles Darwin, in working 

 out this acquisition of knowledge for mankind, has 

 added a new department to vegetable physiology and 

 to biology. 



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