iQU] DE VRIES— OENOTHERA LAMARCKIANA 349 



TRAM.' On no single field was the original form pure; it was always 

 mixed to such a degree with O. Tracyi and with their hybrids that 

 we found it impossible to collect undoubtedly pure grandiflora 

 seed from this locality. Moreover, the intermediate tj^es were 

 so numerous (over a dozen) that it was difl&cult to regard all of them 

 as normal hybrids between only two parents. To produce such 

 a diversity of forms, either one or both of the parents must have 

 been in a mutating condition, or more than two species must have 

 combined in the crosses. In both cases, the material can hardly 

 be considered as a fit starting-point for experiments bearing upon 

 the causal relations of crossing and mutability. 



Recently I have shown that besides 0. biennis some other 

 species of Oenothera are actually in a state of mutability, and espe- 

 cially has one of the most common American types thrown off 

 marked mutants in my experiment garden." The degrees of 

 development of this condition, however, are very different in 

 different species. In some of them mutations occur rarely, but 

 they serve to throw a doubt upon the stabiHty of those forms for 

 which no positive results have as yet been won. In other words, 

 we may say that almost all the nearest allies of O. Lamarckiana 

 are open to the suspicion of sharing at least some degree of the 

 mutability of this species. There is no use, therefore, in trying 

 to produce mutability by crosses of species of the same subgenus 

 (Onagra) in order to show that this phenomenon is only a result 

 of crossing, as is asserted by Davis. 



Moreover, I might point out that the question should be dealt 

 with from a general standpoint and not be limited to the evening 

 primroses. If it should be true that phenomena like those of 0. 

 Lamarckiana could be produced by crossing immutable species, it 

 would, of course, be of much higher scientific value to produce 

 them in other families or genera, or at least in the other subgenera of 

 the evening primroses. The chance of finding immutable parents 

 for a cross would be far greater and the proof could be given as 

 easily and in many cases with less amount of mechanical work 



» De Vries, Hugo, and Bartleix, H. H., The evening primroses of Dixie Land- 

 ing, Alabama. Science N.S. 3S:S99~6oi. 1912. 

 '° Gruppenweise Artbildung, pp. 296-312. 1913. 



