Page:Popular Science Monthly Volume 62.djvu/502

496 they are perfect, and retain, even after several generations, their original characters. They originate with a shock or jump and then are constant.

They are formed from the mother species as side issues, and not because the mother species undergoes a gradual change. On the contrary in nearly all mutations, the species continues unchanged, and to it belongs the great mass of individuals, until one day the struggle for life shall turn the scales.

Mutability is not one-sided, as many paleontological series would lead one to expect, but many-sided as must be deduced from the principles laid down by Darwin. And the new Oenotheras vary in different organs and in various directions; most frequently the new characters are injurious, sometimes indifferent, occasionally beneficial, probably at least. Next to strong new species there occur weak ones, next to these, those so weak as never to reach the flowering period; and finally sterile forms. From this array of forms nature, in the struggle for life, later on makes its choice; only those most fit continue to exist. Even here experiment confirms theory.

What is the duration of a mutation period? Geology answers: probably very long, for otherwise the chances of life of the new species would be too small. And it seems to me that in the case of Oenothera Lamarckiana I have seen neither the beginning nor the end. The fifteen years during which I studied the species comprises probably but a very small part of that period.