256 Retrograde Varieties 



In the first place it shows that a species- 

 hybrid may inherit the distinguishing marks 

 of both parents. In this way it may become in- 

 termediate between them, having some charac- 

 ters in common with the 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 way in which hybrid 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 

 between two species of Oenothera, which I 

 made some years ago. The parents were the 

 common evening-primrose or Oenothera bien- 

 nis and of 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 



