Christmas tree cultivation species are grown as Christmas trees, although a handful of varieties stand out in popularity. In the United States, Douglas-fir, Scots pine and Fraser fir all sell well. Nordmann fir and Norway spruce sell well in the United Kingdom, the latter being popular throughout Europe. Like all conifers, Christmas trees are vulnerable to a range of pests. The final stage of cultivation, harvesting, is carried out in a number of ways; one of the more popular methods is the pick-your-own tree farm, where customers are allowed to roam the farm, select their tree, and cut it down themselves. Other farmers
Tree of virtues and tree of vices (c. 1310-1340). The nodes of the tree-diagrams are the Cardinal Virtues and the Cardinal Vices, respectively, each with a number of secondary virtues or secondary vices shown as leaves of the respective nodes. While on a tree of virtues, the leaves point upward toward heaven, on a tree of vices the leaves point downward toward hell. At the root of the trees, the virtues of "humilitas" "humility" and the vice of "superbia" "pride" is shown as the origin of all other virtues and vices, respectively. By this time, the concept of showing hierarchical concepts of medieval philosophy in diagrams also