Correlations Among Stigma Depth, Style Length, and Pollen Grain Size: Do They Reflect Function or Phylogeny?

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Abstract
There is a positive correlation between stigma depth-our approximation of the distance a pollen tube has to grow to reach exogenous resources in the transmission tissue-and pollen grain size, but not between style length and pollen grain size among six species in Umbelliferae, eight species in Cruciferae, six species in Solanum, and 10 unrelated species whose pollen grains contain starch. The lack of a correlation between pollen volume and style length in comparisons of both related and unrelated species is inconsistent with the hypothesis that pollen grains must contain sufficient resources to sustain the growth of a pollen tube to an ovule. Positive correlations among style length, pollen grain size, and stigma depth in Polygonum suggest that correlations between style length and pollen grain volume among related species may reflect a phyletic rather than a functional relationship.
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