THE 



AMERICAN NATURALIST 



Vol. XLIX March, 1915 No. 579 



MUTATION EN MASSE 

 HARLEY HARRIS BARTLETT 1 



During the writer's experiments with (Enothera two 

 different species have been discovered of which certain 

 strains give rise by mutation to large numbers of dwarfs. 

 In both cases the dwarfs occur in far greater numbers 

 than experience would lead one to expect, even in the most 

 actively mutant strain. Similar, although not exactly 

 parallel, phenomena have been observed by both de Vries 

 and Davis in certain hybrid Oenotheras, but not, as far as 

 the writer knows, in any unhybridized species. Since the 

 cultures have now been continued long enough so that 

 there can be no doubt as to the accuracy of the observa- 

 tions, the least complicated of the two cases is here placed 

 on record. It concerns (Enothera Reynoldsii sp. nov. (A 

 technical diagnosis of this species will be published else- 

 where.) The seeds from which the cultivated strain arose 

 were collected at Knoxville, Tennessee, in the fall of 1910, 

 by Dr. E. S. Reynolds, then connected with the botanical 

 department of the University of Tennessee. 



Fig. 1 is a diagram showing the size and relationship 

 of the cultures of (Enothera Reynoldsii which have thus 

 far been grown. No diversity was found in the small 

 F 1 and F 2 cultures, of only ten and five plants, respec- 

 tively, which were grown in 1911 and 1912. The F 8 

 generation of twenty-six plants, grown in 1913, exhibited 



1 Prom the Bureau of Plant Industry, U. S. Department of Agriculture, 

 Office of Plant Physiological and Fermentation Investigations. Published 

 by the permission of the Secretary of Agriculture. 



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