346 BOTANICAL GAZETTE [may 



form which he assiimed to be O. grandiflora Aiton. It is evident 

 that the first condition of success in such work consists in the 

 purity and the immutability of the species which are to produce 

 the hybrid. If they are already in a mutable condition, it is to be 

 expected that their hybrids, or at least some of them, may com- 

 bine the different lines of mutability of their parents; and at all 

 events, the mutabiUty of such a hybrid would be no proof that this 

 phenomenon may be produced by means of crossing. On the other 

 hand, if the species to be crossed, or even only one of them, were 

 not pure, the hybrid might inherit this impurity and show phe- 

 nomena which might easily be mistaken for mutations. 



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

 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 O. Lamarckiana from their mother 

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

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

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

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

 two mutants O. gigas and O. semigigas.^ As is now generally 

 admitted, O. 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; there- 

 fore it possesses only 21 chromosomes (14-I-7), while the number 

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

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

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

 of mutabihty in O. 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 



= Stomps, Th. J., Mutation von Oenothera biennis L. Biol. Centralbl. 32:521- 

 535- 1912; alsoZEYLSTEAjH. H.,Oe«oi/(erano»eZ/oDeVries, einekrankhaftePflanzen- 

 art. Biol. Centralbl. 31:129-138. 1911. Vergl. femer: Gruppenweise Artbildung 

 1913:296-304. 



' Stomps, Th. J., op. cit. p. 533. 



