1. Dunlap, J.M. and Stettler, R.F., Genetic Variation and Productivity of Populus trichocarpa and Its Hybrids. X. Trait Correlations in Young Black Cottonwood from Four River Valleys in Washington, Trees, 1998, vol. 13, pp. 28–39.
2. Ceulemans, R., Impens, I., and Steenackers, V., Variations in Photosynthetic, Anatomical, and Enzymatic Leaf Traits and Correlations with Growth in Recently Selected Populus Hybrids, Can. J. For. Res., 1987, vol. 17, pp. 273–283.
3. Larsson, S., Genetic Improvement of Willow for Short-Rotation Coppice, Biomass Bioenergy, 1998, vol. 15, pp. 23–26.
4. Zalenskii, O.V., Ekologo-fiziologicheskie aspekty izucheniya fotosinteza (Ecological and Physiological Aspects of Photosynthesis Studying, the 37th Timiryazev Lecture), Leningrad: Nauka, 1977.
5. Slemnev, N.N., Photosynthetic Characteristics of Mongolian Plants: Evolutionary, Ecological, and Phytocenological Aspects, Russ. J. Plant Physiol., 1996, vol. 43, pp. 366–382.