30 R. A. EMERSON 
pigment, commonly known as green (type Vic), the F, offspring are full 
purple. Whether or not a quantitative determination of purple pigment 
might reveal a difference, no dilution of the purple color is apparent to 
the eye in the F; plants. Four crosses of this sort with a total F; progeny 
of 111 purple plants are listed in table 1 (appendix, page 121). 
Seven F2 progenies of the F; plants recorded in table 1 are listed in 
group 1 of table 2. Fourteen other similar F. progenies are shown in 
group 2 of the same table. The F, plants from which these fourteen F»2 
progenies came are not recorded in table 1 because their purple parents 
were not homozygous. Some of the purple plants used as parents in 
these crosses were F*;’s of the original cross of purple with green. Others 
were from F,; or some later generation of other crosses having the purple 
type as one parent. In every case the other parent was a green plant 
of type VIc. Since the purple F, plants of these crosses were presumably 
the same genotypically as the F,’s shown in table 1, their F, progenies may 
well be included tentatively with those of group 1 of table 2. Each of the 
twenty-one F». lots exhibited six distinct classes of plants with respect to 
color. The 2117 plants were distributed among the six classes as follows: 
Parle Sun Dilute Dilute 
P red purple . sun red 
952 305 275 91 278 216 2 ee 
Obviously no simple 3:1 mendelian behavior is in evidence here. More- 
over, only four classes are expected in dihybrids where dominance is 
exhibited. With dominance trihybrids ordinarily give eight classes in F»2 
in the well-known numerical relation of 27:9:9:3:9:3:3:1, while only 
six classes were observed. Inspection of the distribution of the 2117 
individuals given above, however, suggests the possibility of a 27:9:9: 
3:9:7 relation, which should be realized in a trihybrid if the last three 
classes were indistinguishable. A comparison of observed numbers with 
those expected on this hypothesis follows: 
Sun Dilute Dilute 
Color types Purple red purple sun red 
Brown Green Total 
Brown Green Total 
Observed........ 952 305 275 91 278 ZIG a2 tla 
Calculated®...... 893 298 298 99 298 Day a AAMAS) 
Difference. ...... +59 +7 —23 —§ —20 —16 —1 
3 In this and most of the following comparisons, the theoretical distributions are calculated to the nearest 
whole number, 
