THE MATERIAL BASIS OF MENDELIAN 

 PHENOMENA : 



DR. REGINALD R. GATES 

 Missouri Botanical C! ahdkx s, St. Louis, Mo. 



Since the rediscovery of Mendel's results at the begin- 

 ning of the century, a very extensive and important field 

 of hereditary phenomena has been actively developed, 

 and the conceptions and explanations of Mendel ian be- 

 havior have been changing with great rapidity. Many 

 explanations and views of the phenomena of dominance, 

 recessivity, latency and segregation have been proposed, 

 and the only conception of Mendel which has remained 

 essentially unmodified by Mendelians is that of the purity 

 or unity of the characters in the gametes. Even this 

 conception has been viewed by various workers in many 

 lights, with a more or less complete and sweeping denr 

 of an actual segregation of characters in the germ ce" 



In the time at my disposal I shall bring before y 

 the results of only one (Enothera cross, which shows M 

 delian behavior in certain characters, and in the discus- 

 sion of these results shall point out certain modifications 

 of our conceptions of Mendel ian segregation which they 

 necessitate. 



The cross in question is Oenothera nanella X 0. 

 biennis, 0. nanella being a mutant from 0. Lamarckiana 

 and the 0. biennis in the cross being from a wild race 

 growing around the New York Botanical Garden. The 

 seeds were first obtained from Dr. D. T. MacDougal. In 

 the F, of this cross two types were produced, evidently 

 corresponding to DeVries's twin hybrids. One of these 

 types breeds true in the second generation and is the 

 same as the type obtained in the F t of 0. Lamarckiana 

 X 0. biennis. The other is a new type, with unexpected 



