354 THE POPULAR SCIENCE MONTHLY 

Fic. 8. Frrst HYBRID GENERATION OF CROSS BETWEEN “ HAVANA ”’ AND “ CUBAN ” 
VARIETIBS oF TOBACCO SHOWN IN HIG. 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- 
