IN THE VEGETABLE KINGDOM 55 



ing on the banks of a river and explaining the principle 

 of gravity to an intelligent savage, illustrating the argu- 

 ment by the flow of the stream. He might reply : " You 

 say that water always flows towards the centre of gravity 

 by the line of least resistance, and that water, therefore, 

 does not flow uphill. But see that back-eddy. If the 

 stream is flowing downhill, the water which is flowing 

 back upstream must be flowing uphill. Clearly you must 

 be wrong." 



We have here a principle and a general rule deduced 

 from the principle. Our savage friend confounds the 

 two. For while there can be no real exceptions to a 

 principle properly so called throughout the class of facts 

 to which it applies, there may be many exceptions to 

 a general rule. In considering the facts, then, it should 

 be borne in mind that we have a principle and a number 

 of general rules deduced from the principle. While there 

 can be no real exceptions to the principle throughout 

 the class of facts to which it applies, there may be many 

 exceptions to the general rules. 



