VOLUME LX NUMBER 6 



THE 



Botanical Gazette 



DECEMBER 1915 



MASS mutation IN OENOTHERA PRATINCOLA' 



Harley Harris Bartleti 



(with fifteen figures) 



Introduction 



Of the several sjjiall-flowered wild evening primroses thus far 

 examined by the writer for mutability, no other has yielded as 

 valuable data as Oenothera pratincola. Certain mutations of this 

 species have been treated in a former article,'' of which this one is 

 in effect a continuation. To recapitulate very briefly, it may be 

 recalled that 0. pratincola, a species found wild at Lexington, 

 Kentucky, gives rise in successive generations to a small propor- 

 tion of mutations, belonging to several distinct types. Of these 

 the most conspicuous in the young condition is mut. nummularia, 

 which originates in every generation from seven of the eight inde- 

 pendent strains which have been studied. The eighth strain, 

 designated in the former article as Lexington E, shows the phenome- 

 non which the writer has elsewhere designated as mutation en 

 massed Mutant species in Oenothera, as typified by 0. Lamarck- 

 iana, give rise to few mutations. The frequency of mutations in 



• From the Bureau of Plant Industry, U.S. Department of Agriculture, Office of 

 Plant Physiological and Fermentation Investigations. PubUshed by permission of 

 the Secretary of Agriculture. 



2 Bartlett, H. H., Additional evidence of mutation in Oenothera. BoT. Gaz. 

 39:81-123. 1915. 



3 , Mutation en masse. Amer. Nat. 49:129-139. 1915. 



42s 



