4 THE COEFFICIENT OF MUTATION IN OENOTHERA BIENNIS L. 



such small steps. They are doing this in their natural habitats 

 as well as in experimental cultures, and the variations produced 

 show no relation to the external conditions of their environment 

 or to the method of their culture. On this ground, the claim seems 

 justified that the mutations, directly observed in the primroses, 

 are similar to those which have produced in nature the specific 

 differences and the differentiating characters in this group. If 

 this is conceded, it follows that the analogous processes in other 

 genera, and even in the origin of the larger systematic groups, must 

 be viewed in the same way. This claim, however, has not escaped 

 serious objections. 



The main line of these attacks is based upon the vague and 

 double assumption that 0. Lamarckiana might be a hybrid, and 

 that its hybrid origin might account for its present mutability. 

 These two assumptions are evidently independent of one another 

 and would have to be proven separately. So far as I know, no 

 attempts have been made as yet to prove the second assumption, 

 and no hybrid races have been produced which, from this cause, give 

 rise to phenomena exactly duplicating the mutations of the prim- 

 roses. And it is evident that so long as such an analogy is only 

 an ardent wish of the critics, the question whether the mutating 

 primroses are of pure or of hybrid origin is not of paramount im- 

 portance for the appreciation of the fact of their mutability. 



The first attacks on the gametic purity of the mutating forms 

 have been directed only against 0. Lamarckiana, and at the present 

 time the most prominent adherents of this opinon are Davis and 

 Renner. They try to give proof of a separate hybrid nature for 

 this species on considerations which do not apply to 0. biennis 

 and the other mutating forms, and concede for these latter a pure 

 origin. 1 ) 



Davis based his arguments upon a historical research concerning 

 the origin of 0. Lamarckiana, and upon his attempts to duplicate 

 this form by crossing others which he assumed to be of pure line. 2 ) 

 A specimen collected by Michaux in the eastern part of the United 

 States, about a century ago, and studied by L. Blaringhem, proves 

 our plant to have been a component of the flora of this country, 



z 



i) Davis, B. M., Mutations in Oenothera biennis L. Amer. Nat. 47:116, 

 1913; and Parallel mutations in Oenothera biennis. Ibid. 48:499 — 501, 19 14. 



2) — , Some hybrids of Oenothera biennis and O. grandiflora that 

 resemble O. Lamarckiana. Amer. Nat 45:193 — 2$$, 191 1. 



