256 Retrograde Varieties 



In the first place it shows that a species- 

 hj^brid may derive all its distinguishing marks 

 from both parents. In this way it may become 

 intermediate between them, having some char- 

 acters in common with pollen-parent and others 

 with the pistil-parent. As far as these charac- 

 ters do not interfere with each other, they may 

 be fully developed side by side, and in the main 

 this is the wav in which hvbrid-characters are 

 evolved. But in most cases our existing knowl- 

 edge of the units is far too slender to give a 

 complete analysis, even of these distinguishing 

 marks alone. "We recognize the parental marks 

 more or less clearly, but are not prepared for 

 exact delimitations. Leaving these theoretical 

 considerations, we will pass to the description 

 of some illustrative examples. 



In the first place I will describe a hybrid be- 

 between two American species of Oenothera, 

 which I made some years ago. The parents were 

 the common evening-primrose or Oenothera 

 biennis and its small-flowered congener, Oeno- 

 thera muricata. These two forms were distin- 

 guished by Linnaeus as different species, but 

 have been considered by subsequent writers as 

 elementary species or so-called systematic va- 

 rieties of one species designated with the name 

 of the presumably older type, the 0. biennis. 

 Varietal differences in a physiologic sense they 



