356 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
where a number of plants of the evening primrose, Oenothera lamarck- 
tana, 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 Hilversum, 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 elemen- 
tary 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. laevifolia. 
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. 
These two new forms, as well as the common O. lamarckiana, were 
collected, and from these plants there have arisen the three groups of 
families of elementary species that De Vries has studied. In his 
garden other new forms also arose from those that had been brought 
under cultivation. The largest group and the most important one 
is that from the original O. lamarckiana form. The accompanying 
table shows the mutations that arose between 1887 and 1899 from 
these plants. The seeds were selected in each case from self-fertilized 
plants of the Jamarckiana form, so that the new plants appearing 
in each horizontal line are the descendants in each generation of 
lamarckiana parents. It will be observed that the species, O. oblonga, 
appeared again and again in considerable numbers, and the same is 
true for several of the other forms also. Only the two species, O. gigas 
and O. scintillans, appeared very rarely (Fig. 59). 
Thus De Vries had, in his seven generations, about fifty thousand 
plants, and about eight hundred of these were mutations. When the 
flowers of the new forms were artificially fertilized with pollen from 
the flowers of the same plant, or of the same kind of plant, they gave 
rise to forms like themselves, thus showing that they are true elemen- 
tary species. It is also a point of some interest to observe that all 
these forms differed from each other in a large number of particulars. 
