MULTIPLE FACTORS 223 
as one of two similar dominant factors producing a 
non-cumulative result. (Here, then, the 9AB re- 
semble the 3aB and 3Ab individuals and a 15:1 ratio 
results.) To those who reject the idea that domi- 
nance implies presence, recessiveness absence, there 
is no great distinction between this case and that of 
o'— cD Cd «D ed 
: \ ! \ | 
cp—| cpd.cp CD. ed 
15:4 
Ca— Cd. ed 
3:1 
«D— cD. Cd ©D.eD cDicd 
15st 1:0 air 
w= cd .Cd ed.cD dived 
5s ail gel or 
Fig. 54.—Diagram showing the kinds and composition of the F. capsules 
of Bursa bursa-pastoris. (After Shull.) 
the two whites with a 9:7 ratio. Shull found that 
when a plant of Bursa bursa-pastoris with round 
capsules is crossed to one with triangular capsules, 
the round is recessive to triangular in F;. In F, the 
round reappears only once in sixteen times (Fig. 54). 
Thus in this cross round may be treated as the result- 
ant of the two recessive factors, either of which by 
