Christmas tree cultivation tractors, and shaper sheers. Mechanized planters, at a cost of about US$4,000, are not essential but a work-saving luxury for farmers. Farmers can purchase seedlings, the lifeblood of a Christmas tree farm, from nurseries. One farmer in Oregon purchased seedlings for between US$200–300 per 1,000 plants. The farmer, a wholesaler, sold his final products for about $20 each; after the cost of the trees and other expenses, a profit of $2–3 per tree. The best-selling species in the North American market are Scots pine, Douglas-fir, noble fir, balsam fir, Fraser fir, Virginia pine, and eastern white pine, although other types
Noble polyhedron 'dual' covers both kinds. The dual of a noble polyhedron is also noble. Many are also self-dual: Noble polyhedron A noble polyhedron is one which is isohedral (all faces the same) and isogonal (all vertices the same). They were first studied in any depth by Hess and Bruckner in late 19th century, and later by Grünbaum. There are four main classes of noble polyhedra: If we allow some of Grünbaum's stranger constructions as polyhedra, then we have two more infinite series of toroids: We can distinguish between dual structural forms (topologies) on the one hand, and dual geometrical arrangements when