202 HAROLD H. PLOUGH 
LITERATURE CITED 
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1919 The genetics of purple ej'c color in Drosophila. Jour. Exp. Zool., 
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1919 Linear arrangement of genes and double crossing over. Proc. 
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Strong, L. C. 1920 Roughoid, a mutant located to the left of sepia. Biol. 
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Weinstein, a. 1918 Coincidence of crossing over in Drosophila. Genetics, 3, 
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