580 THE PROBABLE ORIGIN OF OENOTHERA LAMARCKIANA SER. 



the liybrid might inherit this impurity and show phenomena which 

 might easily be mistaken for mutations. 



It so happens that 0. biennis is in a condition of mutabihty 

 analogous to that of 0. Lamarckiana, although not developed to 

 the same high degree. From time to time it produces dwarfs, 

 which are distinguished from it by exactly the same two characters 

 which differentiate the dwarfs of 0. Lamarckiana from their mother 

 species, namely, low stature and sensitiveness to the attacks of 

 some species of soil bacteria.^) Moreover, Stomps has shown that 

 0. biennis may, although very rarely, double the number of chromo- 

 somes in its sexual cells, which in 0. Lamarckiana produces the 

 two mutants 0. gigas and 0. semigigas.^) As is now generally 

 admitted, 0. gigas results from the pairing of two mutated sexual 

 cells, each of which had a double number of chromosomes. 0. 

 semigigas, on the other hand, is produced by the pairing of a sexual 

 cell mutated in the same way, with a normal gamete; therefore 

 it possesses only 21 chromosomes (14 + 7), while the number 

 in 0. gigas is 28. As yet, only semigigas mutants have been observed 

 coming from 0. biennis, and it is obvious that the double com- 

 bination must be much rarer. As a proof of this special kind of 

 mutability in 0. biennis, however, the observations of Stomps 

 are wholly sufficient. 



In quoting these facts, Davis says that if it can be shown "that 

 tested strains of this biennis are able to produce new forms of specific 

 rank or even marked varieties, the mutationists would have much 

 stronger evidence in support of the mutation theory than that 

 based on the behavior of 0. Lamarckiana."^) After conceding this 

 strong position to his adversaries, Davis subjects the results of 

 Stomps to a rather sharp criticism, which, unfortunately, is based 

 upon a confusion of two wholly distinct types, namely, 0. biennis 

 L. var. cruciata^) and 0. cruciata Nutt. He says: " It should be made 

 clear that the form (0. biennis cruciata) is recognized in the more 

 recent taxonomic treatments as a true species sharply distinguished 



1) Stomps, Th. J., Mutation bei Oenothera biennis L. Biol. Centralbl. 

 32:521 — 535, 19 12; also Zeylstra, H. H., Oenothera nanella De Vries, 

 eine krankhafte Pflanzenart. Biol. Centralbl. 31 : 129 — 138, 191 1. Vergl. 

 ferner: Gruppenweise Artbildung 1913 : 296 — 304. 



2) Stomps, Th. J., op. cit. p. 533. 



3) Davis, B. M. , Mutations in Oenothera biennis L. ? Amer. Nat. 

 47 : 116 — 121 (especially p. 116), 1913; see also op. cit. 47 : 540 — 596. 

 (especially p. 567), 19 13. 



4) Die Mutationstheorie 2:599, ^903- 



