Soon, as more species became available in the nineteenth century so did a better understanding of the characteristics necessary for the major divisions. Chief amongst these were Maximovicz's "Rhododendreae Asiae Orientali" and Planchon. Maximovicz used flower bud position and its relationship with leaf buds to create eight "Sections". Bentham and Hooker used a similar scheme, but called the divisions "Series". It was not until 1893 that Koehne appreciated the significance of scaling and hence the separation of lepidote and elepidote species. The large number of species that were available by the early twentieth century prompted a new approach when Balfour introduced the concept of grouping species into series. "The Species of Rhododendron" referred to this series concept as the Balfourian system. That system continued up to modern times in Davidian's four volume "The Rhododendron Species".