332 GBOEGE JOHN EOMANES 1893 



all over the world, for, wherever mountains are con- 

 cerned, stations are apt to be isolated by difference 

 of altitude, &c. 



Now if such be the case with the group in ques- 

 tion, the fact of its constituent species being freely 

 hybridisable when artificially brought together is 

 exactly what my theory requires. For the specific 

 differentiation has presumably been effected by 

 geographical (or topographical) isolation, without 

 physiological having had anything to do with it. 

 In fact, as stated over and over again in my original 

 paper, this correlation between geographical isolation 

 and cross-fertility is one of my lines of verification, 

 the other line being the correlation between identical 

 stations and cross-sterility. 



Now, as above stated, I have found both these 

 correlations to obtain in a surprisingly general 

 manner. 



I wish that, instead of perpetually misunderstand- 

 ing the theory, you English botanists would help me 

 by pointing out exceptions to these two rules, so that 

 I might specially investigate them. It seems to me 

 that the group you name goes to corroborate the 

 first of them, while all Jordan's work, for instance, 

 uniformly bears out the second. And whatever may 

 be thought about him in other respects, I am not 

 aware that anyone has ever refuted his observations 

 and experiments so far as I am concerned with them. 

 Yours ever sincerely, 



G-. J. ROMANES. 



