1894 ON PHYSIOLOGICAL SELECTION 339 



H&tel Costebelle, Hyeres : March 29. 



Dear Mr. Henslow, — I am still terribly ill and 

 cannot write much. We must have a talk. Could 

 you come to Oxford any day you like and be our 

 guest ? I think we might derive mutual benefit. I 

 shall be there from the middle of April till I do not 

 know when. Why not come on May 2, to hear 

 Weismann give his lecture in the afternoon ? 



I much wish you would save seed of any fixed 

 local varieties of plants you may find to be in seed, 

 while you are in Malta (or bulbs), in order to see 

 whether plants grown from them in England will or 

 will not prove fully fertile. This is in relation to my 

 own theory of physiological selection, according to 

 which isolation produces segregation of type ; in the 

 same way as it does that of a language — viz. by 

 prevention of intercourse with the parent type and 

 consequently with an independent history of varia- 

 tion. Where the isolation is due to physical barriers 

 (as at Malta) there is no need for any sexual differen- 

 tiation to originate a species. But on common areas, 

 sexual differentiation is the only means of securing 

 the isolation. Therefore (I say) we can see why 

 Jordan's French varieties all prove sterile with their 

 parent forms, and I should expect your Malta varie- 

 ties to prove fertile with theirs elsewhere. 



G. J. E. 



Costebelle : April 15, 1894. 



Dear Mr. Henslow, — Yes, please write when you 

 get back, suggesting any time you may find con- 

 venient for spending a day or two with us at 



z2 



