We may now proceed to examine the evidence from which De Vries has been led to the general conclusions given in the preceding pages. De Vries found at Hilversam, near Amsterdam, a locality where a number of plants of the evening primrose, _Œnothera lamarckiana_, grow in large numbers. This plant is an American form that has been imported into Europe. It often escapes from cultivation, as is the case at Hilversam, where for ten years it had been growing wild. Its rapid increase in numbers in the course of a few years may be one of the causes that has led to the appearance of a mutation period. The escaped plants showed fluctuating variations in nearly all of their organs. They also had produced a number of abnormal forms. Some of the plants came to maturity in one year, others in two, or in rare cases in three, years. A year after the first finding of these plants De Vries observed two well-characterized forms, which he at once recognized as new elementary species. One of these was _O. brevistylis_, which occurred only as female plants. The other new species was a smooth-leafed form with a more beautiful foliage than _O. lamarckiana_. This is _O. lævifola_. It was found that both of these new forms bred true from self-fertilized seeds. At first only a few specimens were found, each form in a particular part of the field, which looks as though each might have come from the seeds of a single plant. ŒNOTHERA LAMARCKIANA Elementary Species