Meetings of the Royal Botanical Society of The Netherlands

Cut-style pollination was carried out in lily to achieve interspecific crosses. Although there was abundant pollen tube growth, penetration of the ovules was rare. Using intraspecific compatible pollen and the cut-style pollination method, the percentage of ovules with a pollen tube in the micropyle was also low (about 8%, compared with about 85% when pollinated on the stigma). Placental pollination within the species Lilium longiflorum was used to study and influence this process. With this method not only the pollen grains or tubes could be manipulated, but also the pistil material, i.e. a placenta with ovules and a part of the ovary wall. After placental pollination, the pollen germinated. Part of the pollen tubes grew in between the ovules towards the inner integument which has formed the micropyle. Growth along the inner integuments and circling of pollen tubes was observed using scanning electron microscopy. Only a small percentage of the total number of ovules was penetrated by a pollen tube, comparable with that observed after cutstyle pollination. This percentage fluctuated strongly throughout the year and between experiments. The variation was much larger compared with the results of cut-style pollination. In attempts to find an explanation for this low percentage, variations were carried out, e.g. various ages of flowers, various tissue culture media, using a medium to promote pollen tube growth, various plant hormones, and pre-germinated pollen, but the percentage of penetration remained low. Sperm cell formation did take place in about one-third of the pollen tubes. Embryos (as a proof of fertilization) were hard to detect because they remained small, therefore the medium probably needs some modification.