ORIGIN OF ORGANIC FORMS 303 



of the same or a similar plant is sometimes less produc- 

 tive than that by means of pollen of another different 

 plant, and even that fertilisation with the pollen of 

 another species is sometimes more productive than that 

 with the pollen of the same species. Realising that it is 

 impossible to advance any positive criterion for differ- 

 entiating species from variations, the exponents of this 

 theory love to plead ' intuition ' as a guide to investigators 

 in the solution of this problem. The precarious nature, 

 however, of this famous adjunct intuition is well proved 

 by the following instances. It so happens that as long 

 as a genus contains but few species botanists agree as to 

 their number ; but as soon as a genus contains more 

 than, say, four species they begin to disagree. How 

 far this disagreement may carry them is shown by 

 the following example : according to some botanists 

 the genus Hieracium contains twenty species, according 

 to others three hundred. The same disagreement holds 

 with regard to the blackberry, willows, and many other 

 plants. Evidently some botanists take for a species 

 what for others is only a variety. In view of these 

 contradictions, systematists have coined the expression 

 good species to differentiate the evident and universally 

 acknowledged species from doubtful ones. These mani- 

 fold contradictions unmistakably bring us to the con- 

 clusion that it is impossible to draw a hard and fast line 

 between a species and a variety, that it is impossible 

 always and infallibly to apply to reality conceptions of 

 this kind. This inference necessarily raises the question 

 whether some logical fallacy has not slipped into the 

 argument, as was the case when we discussed the 

 difference between plants and animals. Perhaps neither 

 species nor variety exist in Nature as two qualitatively 

 different categories. Perhaps they are but typical 

 conceptions, creations of our own mind. Let us try 

 to make this clear by an example. We clearly realise 

 the difference between a child and a grown-up man. 



