The mature worker would look back on this dilemma of his youth with a smile of satisfaction thirty years afterwards. He would know then what sort of a nut it was that he was trying to crack in his early speculations. It was nothing less than the magnificent problem that presented itself to Darwin, the crucial question of the fixity or variability of species. “The problem of the constancy or transmutation of species,” he wrote, “arrested me with a lively interest when, twenty years ago, as a boy of twelve years, I made a resolute but fruitless effort to determine and distinguish the ‘good and bad species’ of blackberries, willows, roses, and thistles. I look back now with fond satisfaction on the concern and painful scepticism that stirred my youthful spirits as I wavered and hesitated (in the manner of most ‘good classifiers,’ as we called them) whether to admit only ‘good’ specimens into my herbarium and reject the ‘bad,’ or to embrace the latter and form a complete chain of transitional forms between the ‘good species’ that would make an end of all their ‘goodness.’ I got out of the difficulty at the time by a compromise that I can recommend to all classifiers. I made two collections. One, arranged on official lines, offered to the sympathetic observer all the species, in ‘typical’ specimens, as radically distinct forms, each decked with its pretty label; the other was a private collection, only shown to one trusted friend, and contained only the rejected kinds that Goethe so happily called ‘the characterless or disorderly races, which we hardly dare ascribe to a species, as they lose themselves in infinite varieties,’ such as rubus, salix, verbascum, hieracium, rosa, cirsium, &c. In this a large number of specimens, arranged in a long series, illustrated the direct transition from one good species to another. They were the officially forbidden fruit of knowledge in which I took a secret boyish delight in my leisure hours.”