498 



THE AMERICAN NATURALIST [Vol. XL VIII 



In a recent review 1 of Stomps 's studies on (Enothera biennis 

 L. 2 from the sand dunes of Holland I protested against his desig- 

 nating as mutants a nanella type and a semi-gigas type which 

 were obtained in the second generation of crosses between (Eno- 

 thera "biennis Linnaeus and its variety O. biennis cruciata de 

 Vries. The criticism was presented on the general ground that 

 however close the possible relationships between the two parent 

 forms, they nevertheless constituted lines so far apart as to 

 render unsafe a conclusion that marked variants obtained from 

 their crossing are mutants in the sense of de Vries and Stomps. 

 Such variants, it seemed to me, might have been the result of 

 hybridism between two lines sufficiently divergent to upset the 

 similarity of germinal constitution shown in their vegetative 

 morphology, for the species biennis and its variety cruciata are 

 said to differ only in their flower structure. 



In that review I incorrectly associated 0. biennis cruciata de 

 Vries with 0. cruciata Nutt, an American species entirely dis- 

 tinct from the variety cruciata of de Vries, which has been found 

 only once (in the year 1900) on the sand dunes of Holland 

 among plants of 0. biennis. I greatly regret my confusion of 

 these two types, since I was led in my criticism to regard Stomps 's 

 crosses between biennis and biennis cruciata as though they were 

 crosses between two distinct although possibly closely related 

 species. In this I was clearly mistaken, since all of the evidence 

 short of experimental proof, which Stomps may yet obtain, indi- 

 cates that biennis cruciata de Vries is a variety of biennis L. and 

 arose as a mutation on the sand dunes of Holland. The crosses 

 of Stomps are, therefore, to be regarded as between a species and 

 its mutant variety. I trust that the mutation ists will accept this 

 acknowledgment of an error. 



There is, I believe, a body of naturalists for whom the value 

 of evidence for mutation rests fundamentally upon the unques- 

 tioned purity of the parent stock, and to them any cross, no matter 

 how close, is open to criticism. Stomps has justified his first con- 

 clusions by obtaining in later studies the same mutants biennis 

 nanella and biennis semi-gigas from lines of the pure species 0. 

 biennis Linnaeus. Had he waited for these later results before 



1 Davis, B. M., "Mutations in (Enothera biennis L.?" Ameeican Nat- 

 uralist, Vol. XLVIT, p. 116, 1913. 



2 Stomps, T. J., "Mutation bei (Enothera biennis L.," Biol. Centralb., Vol. 

 XXXII, p. 521, 1912. 



