Neo-Mendelism 85 



this basis may well result in a new race that breeds 

 true; and a race that breeds true is De Vries' definition 

 of a new species. To reestablish Darwin's theory of 

 natural selection is certainly an important consideration, 

 and the situation illustrates how genetics and evolution 

 are tied up together, so that neither one of them can 

 be appreciated fully without some knowledge of the 

 other. 



A few words may be said in reference to the reversion 

 of an old race to its original specific type. De~Vries 

 outlined the situation clearly, and his conclusions are 

 generally accepted. It is doubtful, however, whether 

 it has ever been understood, since no one has ever 

 devised a reasonable mechanism for such a reversion. 

 The conception of cumulative factors, however, supplies 

 this mechanism. A new race, developed by natural or 

 artificial selection among individual differences, means 

 the piUng up of cumulative factors in a given direction. 

 Stop the selection and the old plants with the small 

 number of factors are allowed to survive; reproduce, 

 cross with the new race, and eventually bring back the 

 old species to the original average condition. 



1. De Vries, H., Species and varieties, their origin by mutation. 

 Chicago. 1905. 



2. Emerson, R. A., and East, E. M., The inheritance of quantita- 

 tive characters in maize. Bull. Agric. Exper. Sta. Nebr. no. 2. 

 pp. 120. figs. 21. 1913. 



