The stigma is the carpel's pollen-receiving region. Compatible pollen may form a pollen tube that grows toward an ovule; arrival alone does not establish fertilization.[ref]
32.2 Pollination and Fertilization. Biology 2e, §32.2 Incompatibility Genes in Flowers and Double Fertilization
A useful diagnostic question is what was actually observed: pollen on a stigma, a growing pollen tube, or a new plant embryo? Each observation tests a different stage. A pollen tube germination assay isolates the middle process for direct viewing.
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