84 THE AMERICAN NATURALIST [Vol. LIII 



which 20 were carmine, and 23 were pink blossomed as 

 in the Mammoth. 



This same extracted white-flowered plant was also 

 crossed with Pink (Conn. Broadleaf) as follows: 



From the cross Pink (Conn. Broadleaf) ? X White 

 (extracted) J", 51 first generation plants were obtained, of 

 which 12 were carmine or approaching it, and 39 were 

 pink approximating the pink of the Broadleaf parent. 

 It is apparent that the extracted white used in these 

 crosses has somehow retained the factor of Carmine 

 which reappeared in the cross with Pink. 



From the results reported in this paper, the Mendelian 

 behavior of the cross Carmine X Pink is particularly 

 striking, and for those who wish to demonstrate before 

 students interested in questions of heredity simple Men- 

 delian behavior in a monohybrid, this particular tobacco 

 cross is especially suitable. Not only is the technique 

 of crossing easy, but a single fertile capsule from a cross 

 will produce several thousand seed. Furthermore, to- 

 bacco plants may be readily grown to the flowering stage, 

 in five or six inch pots under greenhouse conditions. 



Summary 



Among the varieties of tabacum, carmine and pink in 

 crosses behave as unit characters, carmine being domi- 

 nant. In the second generation perfect Mendelian segre- 

 gation follows, approximating very closely the theoret- 

 ical ratio of three carmines to one pink. The extracted 

 recessive pinks and the homozygous carmines breed 

 true. The heterozygous carmines again break up into 

 carmine and pink. If a heterozygous plant of the first 

 generation is crossed with a pure carmine, the progeny 

 will all produce carmine blossoms. If it is crossed with 

 a pink, carmines and pinks will appear in the progeny, 

 approximating the ratio 1 to 1. 



In crosses involving- eaiTiiiiK^ or pink witli white, white 

 behaves as a recessive, .-ipitcarino- in the second genera- 

 tion. 



