The genetic manipulation of perennial woody tree species presents a range of additional challenges compared to that of annual weedy crop species. These include long generation times and reproductive cycle, the heterogeneity of plants under investigation and, when investigating xylogenesis, a number of physical and biochemical limitations to microscopic and molecular experimentation. Efforts have been made to understand molecular aspects of xylogenesis and have involved functional gene testing using transgenic approaches. These methods involve the production of plantlets from a variety of plant tissues using in vitro full plant regeneration techniques. Although these systems are effective, the time taken from transformation event, to plant establishment and growth, then finally to secondary wood production can take up to several years and requires high labor and technical inputs. (For complete abstract open document)