Felix qui potuit rerum cognoscere causas. Pub/ius Vergilius Mara Forests have long been one of mankind's most important natural re- sources and not the least because forests are, if properly managed, re- newable. They serve us in many different ways, but above all in pro- viding us with wood, one of the most remarkable and useful of all natural materials. Reaction wood, compression wood in gymnosperms and tension wood in the arboreal angiosperms, serves the function of making it possible for trees to perform movements. In the ancient Ginkgo and in the conifers, the ability to form compression...