of the species around Amsterdam were in a non-mutable state. It is possible, as Weismann suggested in one of his first evolutionary essays (1872), that in the life of species, periods of constancy alternate with periods of changefulness. The human historian has often made a similar remark.
"In the course of his wanderings around Amsterdam, De Vries came across a deserted potato-field at Hilversum—a field of treasure for him. For there he found his long-looked-for mutable plant, an evening primrose (Œnothera lamarkiana). Like its nearest relatives, Œnothera biennis and Œnothera muricata, which it excels in size and beauty of flowers, it probably came from America, where it is a native. It had probably 'escaped' at Hilversum about 1875, and in the following ten years it had spread in hundreds over the field. It had been extremely prolific in its freedom; but that was not its chief interest.
"Its chief interest was its changefulness. It had, so to speak, frolicked in its freedom. Almost all its organisms were varying—as if swayed by a restless tide of life. It showed minute fluctuations from generation to generation; it showed extraordinary freaks like fasciation and pitcher-forming; it showed hesitancy as to how long it meant to live, for while the majority were biennial, many were annual, and
