328 



1 cretin sterile. As the ngures given in Table I shew 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— 1) aB : ab 

 As the repulsion increases in intensity it is obvious that the 

 zygotes of the form AABB and aabb will become relatively 

 searcer, for there will be only one of each 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 2 f 1) AB : (n 2 — 1) Ab : (n 2 — 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 follows : 



r Blue Red 



Reference INo. Long Round Long Round 



No. 



61 



1910 



85 



33 



41 



1 





F 28 





60 



20 



23 





J7 



F 31 



}? 



9 



7 



5 





il 



F 32 





72 



35 



28 









Total 



226 



95 



97 



1 



