1890 WEISMANN'S THEOEY 199 



lecture which I have just been giving in Edinburgh. 

 From this extract I think you will see that the one 

 point of difference does not redound to the credit of 

 Weismann's logic. After reading the extract in 

 conjunction with the papers in ' Nature,' perhaps you 

 will let me know whether you now understand my 

 view any better, or still beheve that the cessation of 

 selection alone can reduce the average of a useless 

 organ below fifty per cent, of its original size — so 

 long, that is, as the force of heredity continues unim- 

 paired. 



Gr. J. EOMANES. 



Some further letters to Mr. Thiselton Dyer and 

 to Mr. F. Darwin follow. 



To Professor Thiselton Dyer. 



December 20, 1888. 



Dear Dyer, — Would you mind sending me on a 

 postcard the name of the genus of plants the con- 

 stituent species of which you alluded to in the train 

 as being mutually fertile, and also separated from 

 one another topographically ? I want to get as many 

 of such cases as I possibly can, so, if any others occur 

 to you, please mention them Hkewise. 



By reading pages 401 and 404 of my paper, you 

 will see why such cases are of quite as much impor- 

 tance to me as the converse, viz. where closely allied 

 species inhabiting continuous areas are more or less 

 mutually sterile (see p. 392). 



If you have hitherto failed to apply these converse 

 tests to my theory, I cannot conceive by what other 



