l^^F-" -' '' 



VOLUME LIX ^«J|BER 2 



THE 



Botanical Gazette 



FEBRUARY 1915 



ADDITIONAL EVIDENCE OF MUTATION IN 

 OENOTHERA^ 



Harley Harris Bartlett 

 (with seventeen EIGtTRES) 



Introduction 



Much of the advance which has been made in genetics and 

 practical breeding during the last decade has been a direct result 

 of the promulgation by De Vries of the theory of the origin of 

 species and varieties by mutation. That recessive Mendelian 

 variations originate singly by mutation has been shown by several 

 investigators, notably by Morgan, who has observed the origin of 

 more than 150 such variations in his cultures of Drosophila. Many 

 opponents of the mutation theory deny, however, that progressive 

 mutations ever occur in homozygous strains, or that true species, 

 differing from the parent in several independent characters, have 

 ever been observed to originate at a single step by mutation. 

 Davis,^ for example, is in accord with the mutationists in regarding 

 Oenothera gigas as a marked progressive mutation of specific rank, 

 but he denies that Oenothera Lamarckiana, the parent form of 0. 

 gigas, is homozygous. The facts (i) that 0. Lamarckiana is not 

 known as a native component of any flora, (2) that its known history 

 has been that of a cultivated plant or an escape from cultivation, 



' PubKshed by permission of the Secretary of Agriculture. 



' Davis, B. M., Cytological studies on Oenothera. III. A comparison of tlie 

 reduction divisions of Oenothera Lamarckiana and 0. gigas. Ann. Botany 2S : 941-974. 

 1911. "Oenothera gigas is a progressive mutant, its peculiarities being clearly asso- 

 ciated with the changes in its germ plasm incident upon the doubling of its chromosome 

 number'' {op. cit. p. 974). 



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