“…Alternatively, pollen tube growth rates in single‐donor pollinations, visualized with aniline blue, have been used to predict performance in mixed pollinations, again with mixed success (e.g., (Marshall and Diggle, 2001; Pasonen et al, 2002). Finally, pollen tube growth rates have been measured in some protandrous plants that have separate styles that lead to the same ovary, such as Dianthus chinensis , Hibiscus moscheutos , or species that have different channels in the style, such as Erythronium grandiflorum (Aizen et al, 1990; Cruzan, 1990a; Snow and Spira, 1991b, a). Generally, these methods are unable to account for pollen–pollen interactions, such as crowding or direct interference.…”