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THE AMERICAN NATURALIST [Vol. XLVIII 



tra," others resembled " Havana, " although of course the 

 majority were intermediate in various degrees. Several 

 plants combined the leaf size and habit of growth of the 

 " Havana" parent with the leaf number of the "Suma- 

 tra" parent. In other words, plants ivere produced in 

 the F 2 generation by the recombination of Mendelian fac- 

 tors that exactly repeated the type which Shamel had ob- 

 tained in the F z generation of the reciprocal cross made 

 in 1903 and which he thought was due to a mutation. 

 This fulfilled adequately the prediction made by us in 

 1908. 



Results of Selecting for High Number and Low Num- 

 ber of Leaves in the "Havana" X "Sumatra" 

 Cross 



In describing the reproduction of Shamel 's hybrid with 

 numerous large leaves by a reciprocal cross, there has 

 been a chronological inversion. This was done simply to 

 show that the original hybrid known commercially as 

 "The Halladay" was actually a recombination of Men- 

 delian factors in which the "Havana" and the "Suma- 

 tra" varieties differed. We will now describe the effects 

 of selection on the original "Halladay hybrid." 



It will be recalled that the selection experiment which 

 is the principal subject of this paper began with the self- 

 ing of 100 seed plants of ShamePs Halladay hybrid in 

 1908. These plants were the F 4 and F 5 generations of the 

 cross 1 1 Havana " X ' ' Sumatra. ' ' Plants numbered from 

 1 to 49 were the F 4 generation ; those numbered from 50 

 to 100 were the F 5 generation. They were apparently 

 breeding true for the short habit of growth and large- 

 sized leaf of the "Havana" parent and the goodly num- 

 ber of leaves of the "Sumatra" parent. The casual ob- 

 server either would have said with Shamel that here was 

 a mutation breeding as true as any tobacco variety, or 

 that a fixed hybrid, a hybrid homozygous in all of its 

 gametic factors, had been produced. Accurate data 

 taken on the progeny of those of the F 4 and F 5 seed plants 

 which it was possible for us to grow in our limited space, 



