This at all events was the opinion formed by the great body of naturalists at the end of the eighteenth and beginning of the nineteenth centuries, and to all intents and purposes in spite of the growth of evolutionary ideas, it remains the guiding principle of systematists to the present day. There are 'good species' and 'bad species' and the systematists of Europe and America spend most of their time in making and debating them. In some of its aspects the problem of course confronted earlier naturalists. Parkinson for instance (1640) in introducing his treatment of _Hieracium_ wrote, "To set forth the whole family of the Hawkeweedes in due forme and order is such a world of worke that I am in much doubt of mine own abilitie, it having lyen heavie on his shoudiers that hath already waded through them ... for such a multitude of varieties in forme pertaining to one herbe is not to be found againe in _rerum natura_ as I thinke," and the same idea, that the difficulty lay rather in man's imperfect powers of discrimination than in the nature of the materials to be discriminated, is reflected in many treatises early and late. It was however with the great ouburst of scientific activity which followed Linnaeus that the difficulty became acute. Simultaneously vast masses of new material were being collected from all parts of the world into the museums, and the products of the older countries were re-examined with a fresh zeal and on a scale of quantity previously unattempted. But the problem how to name the forms and where to draw lines, how much should be included under one name and where a new name was required, all this was felt, rather as a cataloguer's difficulty than as a physiological problem. And so we still hear on the one hand of the confusion caused by excessive "splitting" and subdivisions, and on the other of the uncritical "lumpers" who associate together under one name forms which another collector or observer would like to see distinguished.