No. 591] HYBRIDISM IN ANGIO SPERMS 



133 



Fortunately we are relieved from the uncertainties neces- 

 sarily connected with this kind of investigation, by the 

 discovery in more recent years that other and perhaps all 

 species of the genus possess the same features. The ac- 

 tivity of systematic botanists in recent years in making 

 new species of (Enothera is highly significant in the pres- 

 ent connection. The exceptional individuals which grow 

 up in cultures of species of (Enothera have been termed 

 by De Vries and his disciples ' 1 elementary species. ' ' The 

 biological world has been asked to believe that in the 

 appearance of these new forms in cultures of Oenothera, 

 we have the phenomenon of mutation or the origin of 

 species at a leap. This view of the matter is, however, 

 open to serious question. The species of (Enothera, as 

 well as their so-called mutants, are distinguished by a 

 degree of pollen sterility often extreme. This condition 

 has convinced so accomplished a geneticist as Professor 

 Bateson that the so-called elementary species of (Eno- 

 thera are segregates resulting from previous hybridiza- 

 tion. This view of the matter is supported by the fact 

 that the products of hybridization are often relatively 

 fixed forms, as indeed has been noted by Brainerd in his 

 extremely interesting observations on hybrid wild violets. 



Obviously the question of possible mutation in the 

 genus (Enothera entered into a new and biologically more 

 advantageous phase when other species than 0. lamarck- 

 iana came into the discussion. Clearly a still wider view 

 should even more clarify the situation. Two years ago 

 Miss Kuth Holden, who is at present living in Cambridge, 

 England, made the interesting discovery that the common 

 fireweed, Epilobium angustifolium, growing wild near 

 Cambridge and also cultivated in the Cambridge botanic 

 garden, was characterized by a large degree of sterility 

 of pollen. She at once generously communicated her dis- 

 covery to me and at the same time suggested a reason 

 for the condition of pollen found in the English specimens 

 of Epilobium angustifolium. I must here remind you 

 that under the genus Epilobium are included two distinct 



