VARIATION AND MUTATION 157 



tail and with greater emphasis such a theory of species-form- 

 ing by mutations; and finally in 1901 Hugo de Vries, the 

 famous botanist of Amsterdam, published in extenso the details 

 of many years of observation and experiment on the subject of 

 mutations, and reformulated definitively a theory of species- 

 forming by mutational or saltational variation, the now famil- 

 iar mutation theory. 



The following paragraphs from Morgan (" Evolution and 

 Adaptation/' pp. 294-297, 1903) give a concise statement of 

 the actual details of the mutations in the evening primrose ob- 

 served by de Vries : 



"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, (Enothera lamarck- 

 iana, 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 have 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 0. brevistylis, which occurred 

 only as female plants. The other new species was a smooth-leafed 

 form with a more beautiful foliage than 0. lamarckiana. This is 0. 

 Icevifolia. 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 0. lamarckiai/a, 

 were collected, and from these plants there have arisen the three 

 groups or 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 impor- 

 tant one, is that from the original 0. lamarckiana form. The accom- 

 panying table shows the mutations that arose between 1SS7 and 1899 



