How does one lay the foundations of a science? In 322 BC, Theophrastus (372-286 BC) took over the school of his teacher Aristotle and thus also the first European institution of research, the Lyceum, which he managed for 35 years. One of the objectives of the Lyceum research team was that everything in nature was to be examined, and it was. In posterity, the botanical works of Theophrastus will still be examples of ground-breaking empirical research with long-lasting results. But from where did the project workers get the amount of botanical data, and according to which scientific principles did they process their results? This is the first Danish introduction to the botanical writings of Theophrastus -- one of the real classics of the history of science.