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, Muller 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 chaff 
of wheat is independently produced by two factors, Z and S, but here 
also the factors are clearly not duplicates of each other, for S 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 7, each of which produces short 
awns in the absence of the other, but 7 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, 7. 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 
F,. two 15 : I ratios and two 3 : I ratios, in addition to one 4 : I and 
four 5:1 ratios. In the F; he records 4 families with a 2:1 ratio, 
one 3:1, two 4:1, four 15:1, and six pure rubricalyx (4. e€., 1 : 0), 
besides three families in which the pigmentation of all individuals 
was intermediate. Gates interprets the several 15:1 ratios as 
evidence that the R factor has become duplicated, but owing to the 
