His real predilection was pronounced enough in those early years. It was what the classical pedagogue would regard as child’s play and waste of time—zoology and botany. A large double window in his parents’ house was fitted up as a conservatory, and plants were gathered very zealously. His love of botany was so great that any one would have pronounced him a botanist in the making. But fate determined that he was to be a zoologist. In his eleventh year the boy, while paying a visit to his uncle Bleek (a professor of theology!) at Bonn, spent a whole day searching the remotest corners of the Siebengebirg for the _Erica cinerea_, which he had heard could not be found in any other part of Germany. At the Merseburg school he had two excellent teachers, Gandtner and Karl Gude, who fostered his inclination, and changed it from a mere collector’s eagerness into the finer enjoyment of the scientific mind. The young student wrote a contribution to Garcke’s _Flora Hallensis_. The professional decision gives many a troubled hour. It is significant to find that as the novice tended his herbarium it dawned on him that there was a weak point somewhere in the rigid classification given in the manuals of botany. The books said that there were so many fixed species, each invariably recognisable by certain characters. But when the youth tried to diagnose his plant-treasures in practice by these rules, there seemed to be always a few contraband species smuggled in, like the spectres in the Wahlpurgis night to which the sage vainly expostulates, “Begone: we have explained you away.” Often the individual specimens would not agree with the lore of the books. There were discrepancies; sometimes they cut across one type, sometimes another, and at times they shamelessly stretched across the gap between one rubric and another. What did it mean? Were there really no fixed species? Was “species” only an idea, and was the reality of the plant-world in a state of flux like the sea? Teachers and books insisted that the “species” is, in its absolute nature, the basis of all botanical science, the great and sacred foundation that the Moses of botany and zoology, Linné, had laid down for ever. How could it be so?