SPECIES HYBRIDIZATION 



247 



when lamarckiana is crossed with rubrinervis, the rubrinervis pangen in 

 lamarckiana is in the labile condition, but in rubrinervis it is in the in- 

 active condition. Here, however, a difficulty is introduced by the fact 

 that the form corresponding to rubrinervis in FI is intermediate between 

 rubrinervis and lamarckiana, it is the form which de Vries calls sub- 

 robusta. Must we assume a fourth condition for the pangens in this 

 form? An additional difficulty is introduced when we consider crosses 

 of rubrinervis and nanella. Rubrinervis has arisen from lamarckiana 

 by mutation, by a change of the labile rubrinervis pangen in lamarckiana 

 into the inactive condition. But when rubrinervis is crossed with nanella, 

 FI consists entirely of lamarckiana and subrobusta plants. As we pointed 

 out, crosses of nanella with lamarckiana show that the nanella pangen 



NN 



rubrinervis 



NN Nn nn 



rubrinervis subrobusta nanella 



FIG. 105. Results of crossing two "mutants" of (Enothera lamarckiana. 



in lamarckiana is in the labile condition. How, then, should this 

 pangen have become inactive in rubrinervis which was supposedly de- 

 rived from lamarckiana by a change in the rubrinervis pangen? For 

 according to de Vries the behavior of the nanella pangen in such an 

 experiment is illustrated in Fig. 105 in which the active pangen 

 is designated by N, the labile pangen by N f , and the inactive pangen 

 by n. , 



Those who have attempted to apply a rigid Mendelian analysis to the 

 (Enothera phenomena have failed to do so without making assumptions 

 which thus far remain beyond the limits of experimental verification. 

 Nevertheless the work of such investigators as Heribert-Nilsson, Renner, 

 Davis, and others demonstrates that Mendelian analyses may be applied 

 to particular cases and that when the difficulties which occur in (Enothera 

 are considered, the facts thus far discovered do not preclude an ex- 

 planation on an essentially Mendelian basis. Davis in particular has 

 pointed out that thus far no species of (Enothera has been found which 

 will stand trial as of strict genetic purity. In all species apparently 

 50 per cent, or more of the pollen grains are abortive and similar 



