No. f>47] GEXET1CAL STUDIES OX (EX OTHER A 423 



8. Further Considerations on the Possible Origin of 

 Oenothera Lamarckiana as a Hybrid of 

 0. biennis and 0. grand if on, 



Among the most interesting of the results from the 

 cultures of the past summer (1911) have been those con- 

 cerned with the behavior of the hybrids of biennis and 

 grandiflora in the second generation. In the progeny of 

 the F, hybrid plants lO.SOLa and 10.30L& there was dear 

 evidence of an advance in the size of the flowers which 

 carried them in many plants beyond the size of the 

 grandiflora parent and as far as the larger-flowered 

 forms of Lamarckiana. The petals of these F, hybrid 

 plants measured about 2.2 cm. ; those of the largest of the 

 F 2 flowers measured 4.5 cm.; grandiflora B has petals 

 about 3.3 cm. long and those of the largest-flowered forms 

 of Lamarckiana measure about 4.5 cm. There was a 

 similar advance in the size of the leaf and the extent of 

 its crinkling, although the leaves did not reach the condi- 

 tions characteristic of Lamarckiana. This is clearly pro- 

 gressive evolution and doubtless can be maintained 

 through selection, though there may be in later genera- 

 tions constant retrogressive variation. 



This demonstration of a progressive advance in flower 

 measurements in the F 2 generation disarms those critics 

 (as Gates, '11) who in prematurely discussing my F, 

 hybrid plants W.'AQLa and 10.30L& apparently failed to 

 appreciate the basic principle that the characteristics of 

 an F, hybrid are shown by what it will do in the F, gen- 



menter in touch with present-dav genetics would hope to 

 get a perfect Lamarckiana type in the F, generation from 

 a cross between biennis and grandiflora, for the reason 

 that the characters of these species could neither blend 

 nor appear as dominant or recessive hi such a manner as 

 to give this type. But with a proper selection of parent 

 biotypes there is good reason to be hopeful that from the 

 F 2 generation of such a cross forms will appear with 



