SHULL: DUPLICATION OF A LEAF-LOBE FACTOR 439 



Of cases in which two or more factors do not produce visibly 

 identical but only more or less similar results as in the black glume 

 color in oats (Nilsson-Ehle, 1908, 1909), there are many more in- 

 stances. These do not represent instances of duplication at all, of 

 course, though they may be expected to grade into cases which would 

 be indistinguishable from duplication. Several of the eye-color and 

 body-color factors of Drosophila appear to be of this nature, and some 

 real duplication may also be present in this group. Some of these 

 Drosophila characters should have been included in my former paper, 

 but they had not been to my knowledge cited as examples of "multiple" 

 factors. They have since been so treated, and with obvious propriety, 

 by Morgan, Sturtevant, MuUer and Bridges (1915). The characters 

 specifically mentioned by these authors are (a) pink eye-color which 

 is determined independently by factors associated respectively, one 

 with the sex (or X) chromosome, and the other with the "third" 

 chromosome; and (b) dark body-color, which is independently pro- 

 duced by two genes which have been designated "black" and "ebony," 

 one in the "second" and the other in the "third" chromosome. 

 Black and ebony are not identical but merely so similar that their 

 separation is not practicable when associated in the same family. 



Howard and Howard (1912, 1915) have shown that velvet chafif 

 of wheat is independently produced by two factors, L and S, but here 

 also the factors are clearly not duplicates of each other, for 5 produces 

 short hairs and L long silky hairs, while plants containing both factors 

 have a mixture of both types of hairs on the glumes. The same authors 

 have found the long awns of "bearded " wheat to result from the com- 

 bined action of two factors B and T, each of which produces short 

 awns in the absence of the other, but T produces shorter awns than 

 B and the T awns are most conspicuous in the distal part of the spike 

 while the B awns are more evenly distributed on the spike. In this 

 case the action of both B and T is cumulative, the fully awned 

 form appearing only when both B and T are homozygous, i. e., BBTT. 



An exceedingly interesting case of duplication, should it stand 

 the test of further analysis, is reported by Gates (1915) in a cross 

 between Oenothera rubricalyx and Oe. grandiflora; for, starting with a 

 heterozygous type supposedly monomeric with respect to the char- 

 acteristic red pigmentation of the rubricalyx bud, he secured in the 

 F2 two 15 : I ratios and two 3 : i ratios," in addition to one 4 : i and 

 four 5 : I ratios. In the F3 he records 4 families with a 2 : i ratio, 

 one 3:1, two 4:1, four 15 : i, and six pure rubricalyx (/. e., i : o), 

 besides three families in which the pigmentation of all individuals 

 was intermediate. Gates interprets the several 15 : i ratios as 

 evidence that the R factor has become duplicated, but owing to the 



