Page:Popular Science Monthly Volume 77.djvu/358

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 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 approaches 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 separately 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 extreme