Swineherd under the Oak tree, from Bock's Kreuterbuch, Strassburg, 1546. At one time the value of a piece of woodland was estimated in terms of the number of pigs that could be fed on the acorns it produced (hence the saying, 'the best ham grows on Oaks'). In the autumn the herd of pigs was released into the the oak forest to gorge themselves on the nuts. The swine herd would accompany them and beat the trees to assist the release of the nuts. Acorns, used in this way, were also one of the earliest forms of taxation. This may be why Oak leaves were printed on coins apart from the fact, of course that the Oak is also a symbol of strength, stability and wealth.