THE PRINCIPLES OF NATURE STUDY 57 



of varying degrees up to contradiction, and that are con- 

 firmed upon reexamination. This is the useful situation 

 to develop, and it is the usual one if the work has been 

 well done. 



Confronted with the fact that many differences in evi- 

 dence are not due to mistakes but are real, the pupil has 

 reached an experience that is very important. He must 

 see for himself or be shown that while certain observed 

 features are different, others are similar. The result is 

 recognition of the facts that the characters in common are 

 the important ones, and that the characters which differ 

 are not so important, being only individual differences. 

 For example, a number of maples may have been under 

 observation, and the result will be sets of observations that 

 will show characters in common and characters that vary. 

 Those in common will be found to be the features that dis- 

 tinguish maples in general from other trees, while those that 

 vary will prove to be variations in individual maples, or 

 the variations which indicate the different species. Not 

 only will the difference between essentials and variations 

 be determined in this way, but the possible amount of 

 individual variation will often be quite impressive. It 

 will be realized, for example, how much maples may vary 

 and still be maples. Here, again, it is not a specific ex- 

 ercise which is recommended, but merely an illustration 

 given which applies to almost any material. 



A few experiences of the kind suggested certainly have a 

 tendency to develop caution. When differences in the 

 results of observation develop in connection with some 

 subsequent exercise, there is more toleration shown, the 

 tone of discussion or dispute is not so confident, and the 



