READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



family, described above, namely, 0. lata, elliptica, nannella, rubri- 

 nervis, and also two new species, 0. spatulata and leptocarpa. 



In the lata family, only female flowers are produced, and, there- 

 fore, in order to obtain seeds they were fertilized with pollen from 

 other species. Here also appeared some of the new species already 

 mentioned, namely, albida, nannella, lata, oblonga, rubrinervis, and 

 also two new species, elliptica and subovata. 



De Vries also watched the field from which the original forms 

 were obtained, and found there many of the new species that appeared 

 under cultivation. These were found, however, only as weak young 

 plants that rarely flowered. Five of the new forms were seen either 

 in the Hilversum field, or else raised from seeds that had been collected 

 there. These facts show that the new species are not due to cultiva- 

 tion, and that they arise year after year from the seeds of the parent 

 form, 0. lamarckiana. 



Conclusions. From the evidence given in the preceding pages it 

 appears that the line between fluctuating variations and mutations 

 may be sharply drawn. If we assume that mutations have furnished 

 the material for the process of evolution, the whole problem appears 

 in a different light from that in which it was placed by Darwin when 

 he assumed that the fluctuating variations are the kind which give 

 the material for evolution. 



From the point of view of the mutation theory, species are no 

 longer looked upon as having been slowly built up through the selec- 

 tion of individual variations, but the elementary species, at least, 

 appear at a single advance, and fully formed. This need not neces- 

 sarily mean that great changes have suddenly taken place, and in 

 this respect the mutation theory is in accord with Darwin's view that 

 extreme forms that rarely appear, "sports," have not furnished the 

 material for the process of evolution. 



As De Vries has pointed out, each mutation may be different from 

 the parent form in only a slight degree for each point, although all 

 the points may be different. The most unique feature of these muta- 

 tions is the constancy with which the new form is inherited. It is 

 this fact, not previously fully appreciated, that De Vries's work has 

 brought prominently into the foreground. There is another point of 

 great interest in this connection. Many of the groups that Darwin 

 recognized as varieties correspond to the elementary species of De 

 Vries. These varieties, Darwin thought, are the first stages in the 

 formations of species, and, in fact, cannot be separated from species 

 in most cases. The main difference between the selection theory and 



