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THE POPULAR SCIENCE MONTHLY 



Fig. 8. First hybrid Generation of Cross between " Havana " and " Cuban " 

 Varieties of Tobacco shown in Iig. 7. Plant is taller than either parent showing 

 the increased vigor due to a cross. Size of leaf of " Havana " is dominant. Habit 

 of growth of " Cuban " is dominant. Number of leaves is intermediate, but ap- 

 proaches the " Cuban." 



But why should there not be complete segregation to the types of each 

 parent? In the first place, because it is likely that numerous sepa- 

 rately heritable characters are concerned, and when n pairs of characters 

 are concerned it takes four to the nth power seedlings to run an even 

 chance that there will be one plant like each of the parents. When we 

 consider that with ten pairs of characters, this means over 1,000,000 

 individuals, we can see with what enormous numbers one has to deal. 

 In the second place these hybrids are only partially fertile, and as I 

 have suggested in former papers, some consideration must be given 

 the fact that there may be selective fertilization that works against ex- 



