No. 532] GENETIC AL STUDIES OX (EX OTHER A 195 



Lamarckiana, for it is well known that a certain group 

 would follow witli persistence any clue that might give 

 evidence of its being or having been an American native 

 species. 



Critics of the evidence for Do Vries's mutation theory 

 have been aware of the point of weakness that lay in the 

 uncertain status of Oenothera Ltona rckiana and the sug- 

 gestions of Bateson and Saunders ('(VJ, p. 153), East 

 ('07, p. 34), Boulenger ('07, p. 363), Leclerc du Sablon 

 ('10, p. 266), Tower ('10, p. 32l>). and others have prob- 

 ably occurred to many, namely, that this plant is of hy- 

 brid origin and that the appearance of its ''mutations" 

 is due to the continued splitting off of variants after the 

 manner of hybrids. This view is held by a number of 

 American botanists with whom the writer is acquainted 

 and represents the attitude of those who are sceptical of 

 the importance of mutation as a factor of organic evolu- 

 tion in nature. If La ma rckiana is of hybrid origin it 

 should be possible to obtain evidence of its probable 

 parentage, and the present paper offers a hypothesis 

 with a considerable body of evidence in its favor. After 

 the evidence has been presented the hypothesis will be 

 discussed in the concluding section entitled "The Pos- 

 sible Origin of (Enothera LamarckUnia as a Hybrid of 

 0. biennis and 0. grandiflora." 



None of the hybrids of biennis and grandiflora de- 

 scribed in the following pages are identical with La- 

 marckiana. There are important differences, chiefly of 

 foliage and stem markings, which distinguish the hybrids 

 at a glance, but on the other hand these characters in 

 taxonomy would be considered of minor importance and 

 the hybrids, if their origin were unknown, could not be 

 placed elsewhere than next to Lamarckiana. Further- 

 more, these differences are of a sort that are likely to be 

 much less apparent when the results of crosses made 

 this summer (1910) between certain types recently dif- 

 ferentiated become known in succeeding cultures. In 

 an investigation of this character the results, as every 



