Abstract
Summary: Although100years have passed since the discovery of double fertilization, details of the fertilization processes of flowering plants still remain unclear. This is mostly because thick layers of ovular sporophytic tissues hide the embryo sac(haploid female gametophyte)of most angiosperms. We established an in vitro fertilization system using Torenia fournieri, in which the embryo sac protrudes from the ovule. It was revealed that pollen tubes are directly guided to the embryo sac in vitro. Moreover, we succeeded in directly observing the discharge of the pollen tube contents into the embryo sac for the first time. Pollen tubes discharged their contents into the embryo sac explosively resulting in almost instantaneous breakdown of the synergid cell adjacent to the egg cell. The T. fournieri in vitro system revealed the covert sexual intercourse of flowering plants.
