328 
1 cretin sterile. As the figures given in Table 1 sliew this 
expectation is closely realised by the facts of experiment, and we 
have little hesitation in regarding this explanation as the correct one. 
Moreover we are inclined to go further and to extend the 
principle to all cases of repulsion in plants. We consider then 
that where A and B are two factors between which repulsion 
occurs in the gametogenesis of the heterozygote formed by union 
of the gametes Ab and aB; the gametes produced by the hetero- 
zygote so derived form one or other term of the series 
AB : 3 Ab : 3 aB : ab 
AB : 7 Ab : 7 aB : ab 
AB : 15 Ab : 35 aB : ab, &c. 
and in we take 2n as the number of gametes in the series we 
obtain the general expressiön. 
AB : (n— 1) Ab : (n-^l) aB : ab 
As the repulsion increases in intensity it is obvious that the 
zygotes of the form AABB and aabb will become relatively 
scarcer, for there will be only one of eaeh of these two homo- 
zygous forms in the complete series of zygotes. At the same 
time the ratio of the three zygotic forms AB : Ab : aB approaches 
more and more nearly to the ratio 2:1:1 such as would occur 
if the repulsion were complete. This is brought out in the 
Upper part of Table II, where we have set out some of the 
gametic series in which partial repulsion is involved together with 
the series of resulting zygotes. The latter, as the Table shews, 
are covered by the general formula 
(2 n^ + 1) AB : (n^ — 1) Ab : (n^ — 1) aB : ab. 
Hitherto the only repulsion-series which we have been able to 
identify with certainty is the one with which we have just dealt, i. e. 
the 1 : 3 : 3 : 1 series for the factors N and F. It is however pro- 
bable that the case of blue, and long pollen is one in which the 
repulsion is of the 1 : 7 order. Up to the present time we have 
had four families of the mating Bl X bL, and the 419 plants 
recorded in F2 were distributed in the four zygotic classes as foUows : 
Reference No. ^^^^ 
No. 61 1910 
. F28 
. F31 
. F32 
Total 
Long 
Round 
Long 
Round 
85 
33 
41 
1 
60 
20 
23 
9 
7 
5 
72 
35 
28 
226 
95 
97 
1 
