Page:Popular Science Monthly Volume 62.djvu/487

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APRIL, 1903.

By Professor HUGO de VRIES,


WHAT are species? To answer this question is as difficult now as it was in the days of Linnaeus. Formerly it was supposed that a certain number of forms had been created, and that these, obeying natural laws as yet undiscovered, had split up and so given rise to groups, which afterwards were called genera. Such genera were clover, rose and buttercup, plums, apples and pears. Among them, by the addition of a name, certain species were distinguished, such as red clover, white clover, etc.

Linnaeus, in his first publications, adopted the above view. 'Each genus is created as such,' is one of his best known theses. Later he changed this in so far as to declare species created, i. e., those species which he recognized as such, and which he had endowed with binomials. In this manner, the power to split up, to produce new forms, and thus to form groups, was transferred to the species, which offered the great advantage, that, since species greatly surpassed the genera in number, the necessary number of splittings was correspondingly reduced.

Next to the disciples of Linnaeus and a few others who still adhered to the old doctrine, there soon arose a group of botanists and zoologists who went much farther in applying the principle of Linnaeus than was intended by him. The former continued to consider

  1. Translated from 'Album der Natur,' by H. T. A. Hus, Assistant in Botany, University of Amsterdam, and revised by the author. Cf. 'Die Mutationstheorie, Versuche und Beobachtungen über die Entstehung von Arten im Pflanzenreich.' Bd. I., Entstehung der Arten durcb Mutation, Leipzig, Veit & Co., 1901.