The great virtues that lie hidden in nature would never have been revealed if alchemy had not uncovered them and made them visible. Take a tree, for example; a man sees it in the winter, but he does not know what it is, he does not know what it conceals within itself, until summer comes and discloses the buds, the flowers, the fruit [...] Similarly the virtues in things remain concealed to man, unless the alchemist disclose them, as the summer reveals the nature of the tree.

Paracelsus: Selected Writings, p. 218, Chapter 3