1. Beckman, J S. 1977. Adaptive peroxidase allozyme differentiation between colonizing and established populations of Pinus ponderosa Laws, on the Shanahan Mesa, Boulder, Colorado. M.A. Thesis, University of Colorado.
2. Bradshaw, A D. 1972. Some evolutionary consequences of being a plant. Evol Biol, 5, 25–47.
3. Brown, A H D. 1979. Enzyme polymorphism in plant populations. Theor Pop Biol 15, 1–42.
4. Coles, J F, and Fowler, D P. 1976. Inbreeding in neighbouring trees in two white spruce populations. Silvae genetica, 25, 29–34.
5. Ehrlich, P R, White, R R, Singer, M C, McKechnie, S W, and Gilbert, L E. 1975. Checkerspot butterflies: a historical perspective. Science, 188, 221–228.