Professor Carl von Naegeli of Munich University was famous as a stickler for precision and punctuality. And was proud of it. That may be why, as professor of botany, he had chosen hawkweeds (Hieracium) as the subject of his research, plants with crowns of yellow flowers resembling dandelions or sow-thistle. For work with them requires the utmost accuracy. The professor was exact in everything and always answered letters punctually. But one letter he had not answered for nearly two months, and that bothered him.