R. C. PUNNETT 87 



(a) Fanis. 38, 39, 40, 41. These four families are evidently of the 

 same nature as the parent family '12, 76. The three classes 

 normal sterile, cretin fertile, and cretin sterile are much in 

 the iDroportions that would be expected on a 3:1:1:3 re- 

 duplication system, but the number of normal fertiles is much 

 below expectation. These four families added to the parent 

 family ('12, 76) give the numbers : 



Normal Normal Cretin Cretin 



fertile sterile fertile sterile 



165 58 58 78 



Expect, on 3 : 1 : 1 : 3 basis ... 346 59 59 76 



The italicised figures shew that the three last classes are closely in 

 the ratio 7 : 7 : 9, as expected on the 3:1:1:3 system, but that the 

 normal fertiles are only about one half as numerous as would be ex- 

 pected. That there is something militating against the formation of 

 normal fertiles in such families is borne out by the following considera- 

 tion. Of the 11 Fi families grown from '12, 76, 10 contained all four 

 classes of plant, while one family had cretins but no steriles. Now 

 the normal fertiles from a family producing gametes on the system 

 3 NF : 1 Nf : 1 nF : 3 nf should be of five kinds, and in every 41 plants 

 these five kinds should be present in the following proportions: 



9 NNFF giving normal fertiles only. 



6 N N Ff ,, normal fertiles and steriles only. 



6 NnFF ,, normal and cretin fertiles only. 



18 NnFf ,, all four classes with coupling. 



2 NnFf „ „ „ „ repulsion. 



Hence out of 41 such plants only 20, or not quite one half, should give 

 the four classes. But of the 11 plants tested (Table X) no less than 

 10 gave all four classes. It would appear then that for some reason 

 or other the classes NNFF, NNFf, NnFF are not produced in the ex- 

 pected numbers, though why this should be so is at present quite 

 obscure. 



(h) Fams. 43, 45, 46. These three families are distinctly different 

 from those just considered and the combined figures 



Normal Normal Cretin Cretin 



fertile sterile fertile sterile 



75 23 21 5 



Expect 69-75 23-25 23-25 7-75 



