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T'ai H. Roulston, James H. Cane, Stephen L. Buchmann, What Governs Protein Content of Pollen: Pollinator Preferences, Pollen-Pistil Interactions, or Phylogeny?, Ecological Monographs, Vol. 70, No. 4 (Nov., 2000), pp. 617-643
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Roulston et al. (2000) studied this question.
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