Polymorphism for interspecific cross-compatibility in phlox.
Extensive polymorphism for the cross-compatibility of Phlox pilosa with P. glaberrima occurs within Illinois populations. The polymorphism is genetically determined. Thus, there is an opportunity for selection to enhance existing cross-compatibility barriers in areas of species contact. There is no evidence that selection has favored the reinforcement of such barriers.
Levin
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Department of Botany, University of Texas at Austin, Austin, Tex. 78712.