MUTANTS AND HYBRIDS OF THE OENOTHERAS. 51 



GENERAL SUMMARY. 



A brief rSsumS of the more salient features of the foregoing 

 paper will serve to emphasize the contributions made to the subject 

 during the course of the experimental work described. 



A continuance of the effort to trace the nativity of O. lamarckiana 

 has resulted in the discovery of records and specimens that appear 

 fairly conclusive that it is a true and independent species native to 

 America, although the matter is not decided with the finality afforded 

 by living specimens observed in the field. That this species has re- 

 mained unchanged during a period of a hundred and sixteen years is 

 established beyond doubt, and renders the matter of its nativity of com- 

 paratively little importance as to the standing of the mutants derived 

 from it. Perhaps no plant is known in which the purity of the strain 

 has been so critically examined as Lamarck's evening-primrose. Some 

 of the mutants are derivatives, most of which have become separated 

 from the parent-form by the acquisition of new characters, while others 

 are of a retrogressive character. Many of the new unit-characters dis- 

 played are not known in any of the other members of the natural group, 

 and thus may not be regarded as degressive acquisitions, or as due to 

 the retraction of a retrogressive step taken in the previous history of 

 the parent-species. 



The material used as O. biennis in the investigation described in 

 Die Mutationstheorie proves to be a large-flowered species, which 

 has probably been known to many workers as O. biennis grandiflora. 

 The uniformly unilateral character of the cross between this species and 

 O. lamarckiana (O. lamarckiana X O. biennis grandiflora) which was 

 an unitypic hybrid very similar to the poll en -parent, a result which led 

 De Vries to the conclusion that O. lamarckiana was a direct derivative 

 of the latter, probably by mutation. A re-examination of the evi- 

 dence, however, recalls that the cross with muricata was similarly 

 unilateral to the latter when used as a pollen-parent, and it is evident 

 that too much weight must not be given to the conclusion in question 

 until confirmatory evidence is obtained. 



A consideration of the groupings of characters leads to the con- 

 clusion that O. grandiflora Ait., 0. lamarckiana Ser., and O. argilli- 

 cola MacKenzie are much more closely related to one another by ana- 

 tomical characters and physiological traits than to biennis or any 

 other member of the genus. Furthermore, the ranges of the three 

 species mentioned appear to be more or less identical, or overlapping. 



O. grandiflora Ait. had been seen by but few botanists in a living 

 condition in America, and its place in the American flora had become 



