1890 OBJECTIONS TO THEOKY CONSIDEEED 211 



hear of any botanists visiting islands. Should you 

 ever hear of any you might let rne know. 



The second difficulty is one that lies against the 

 theory itself, and has always seemed to me most 

 formidable. But as nobody else has ever mentioned 

 it, I have not hitherto done so, as I want to work it 

 out quietly. I allude to your remark about the ex- 

 traordinary differences that obtain among different 

 genera with regard to the capability of intercrossing 

 exhibited by their constituent species. This, I 

 confess, has from the first appeared a tremendous 

 objection to my theory. On the other hand, I have 

 taken comfort from the consideration that besides 

 being a tremendous objection, it is also a tremendous 

 mystery. For, as it must admit of some explanation, 

 and as this explanation must almost certainly have 

 to do with the sexual system, it becomes not 

 improbable that when found the explanation may 

 square with p.s. That the difference in question is 

 functional and not structural (or physiological as 

 distinguished from morphological) seems to be proved 

 by the fact that in some cases it obtains as between 

 the most closely allied genera, being, e.g., most 

 strongly pronounced of all between Geranium and 

 Pelargonium. Even quite apart from my own theory, 

 it seems to me that this is a subject of the highest 

 importance to investigate. 



As regards sexual selection I allow, of course, that 

 the ' law of battle ' is a form of natural selection. 

 But where the matter is merely a pleasing of aesthetic 

 taste, and the resulting structures therefore only 

 ornamental, I can see nothing ' advantageous ' in the 



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