SHULL: DUPLICATION OF A LEAF-LOBE FACTOR 443 



The morphological complexity of the character produced by the 

 B and B' factors is believed to indicate that duplication has come 

 about through a physical rearrangement in the genotype rather than 

 by a repeated mutation affecting in like manner chromosomes belong- 

 ing to distinct pairs. 



My acknowledgments and thanks are due to the following corre- 

 spondents, to whom I am indebted for seeds of the wild biotypes which 

 were used in the present study: D. T. MacDougal, F. Shreve, 

 J. M. Shull, C. A. Shull, A. H. Trow, Tine Tammes, G. Bitter, E. 

 Baur, L. Gross, G. Molon, and T. Z. Chang. 



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