Figure 1.

Plant materials used in this study. All in vitro materials were derived from the P. trichocarpa Nisqually-N1 genotype. A. Starting material. Internodes (shown with hash marks) were cut from thirty-eight day old Nisqually In vitro plants grown on Woody Plant Medium (WPM). B. Stem explants consisted of internodes 3–5 cm long; these were cultured on Callus Induction Medium (CIM-NB) in darkness for 4 weeks. C. Large calli formed on CIM-NB medium in the dark after 4 weeks of culture; whole calli (indicated by circle) were sampled. D. Remaining calli were transferred to Shoot Induction Medium (SIM-BN), where they were kept in light and were sub-cultured every two weeks. E. Shoots regenerated after 75 days of culture. Internodes (shown with hash marks) were excised from regenerated stems.