Pollen tube growth in Quercus

Fluorescence and brightfield microscopy were used to evaluate pollen tube growth in the Erythrobalanus and Lepidobalanus subgenera of the genus Quercus. All three species had the same pattern of pollen tube growth behavior, from the time pollen landed on the stigmas to the cessation of pollen tube elongation in mid-May. Pollen tubes grew from the apertures, penetrated the stigmatic epidermis, and produced a series of callose plugs as they advanced basipetally through the transmitting tissue of the styles. Pollen tubes grew through the solid transmitting tissue until they reached the level of the visible portion of the perianth, where the three styles join. In white oak, the arrested pollen tubes resumed growth in early June, and fertilization occurred during the week of June 11. In northern red oak and black oak, resumption of pollen tube growth occurred in the following growing season. Pollen tubes of northern red oak resumed growth in the May 22 collections and fertilization occurred during the week of June 12. In black oak, however, pollen tubes resumed growth in the June 5 collections and fertilization occurred in late June. The control over pollen tube elongation may be environmental or sporophytic