Pollen tubes elongate by tip growth toward the ovule to deliver the sperm cells during fertilization. Since pollen tubes from several species can be grown in vitro maintaining their polarity, pollen tube growth is a suitable model system to study cell polarity and tip growth. A. thaliana pollen tubes germinated in vitro for 6 h can reach up to 800 μm. By studying the phenotype of mutants of T-DNA insertion lines, genes involved in pollen tube growth can be identified. Moreover, components involved in the regulation of pollen tube growth such as calcium ions and reactive oxygen species (ROS) can be analyzed.