VOLUME LX NUMBER 6 
THE 
BOTANICAL (CAAZELLE 
DECEMBER 1915 
MASS MUTATION IN OENOTHERA PRATINCOLA’ 
HARLEY HARRIS BARTLETT 
(WITH FIFTEEN FIGURES) 
Introduction 
Of the several small-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 O. 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, 
ted in the former article as Lexington E, shows the phenome- 
non “which the writer has elsewhere designated. as mutation en 
masses Mutant species in Oenothera, as typified by O. Lamarck- 
tana, give rise to few mutations. The frequency of mutations in 
m the Bureau of Plant Industry, U.S. Department of Agriculture, Office of 
Plant Physiological and Fermentation Investigations. Published by permission of 
the Secretary of Agriculture. 
2 Barttett, H. H., Additional evidence of mutation in Oenothera. Bot. Gaz. 
59: plac IQI5. 
, Mutation en masse. Amer. Nat. 49:129-139. 1915. 
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