The Origin of Species 337 



hybrid nature was recognized, and some of them 

 have been repeatedly produced by artificial cross- 

 ing of the parent species. Narcissus poeticus 

 crossed with the daffodil (N. pseudo narcissus) 

 produces N. incomparabilis, a favorite garden 

 form which, however, has also been found repeat- 

 edly occurring wild where the two parent species 

 grow near each other. N. odorus has also been 

 shown to be a cross between N. poeticus and N. jon- 

 quilla. A species of Foxglove, Digitalis purpuras- 

 cens, is a cross between D. purpurea and D. lutea, 

 and the hybrid alpine rose, Rhododendron inter- 

 medium, of the Tyrol, grows with its parents, R. 

 ferrugineum and R. hirsutum, being sometimes 

 more abundant than either of the parent forms. 



One of the most remarkable of the hybrids is an 

 orchid, Nigritella suaveolens, which often occurs 

 in large numbers in the alpine meadows, and has 

 been shown to be a cross between N. angustifolia 

 and Gymnadenia conopsea, belonging to a different 

 genus. The orchids, however, are often more fer- 

 tile with pollen from other species or even other 

 genera, and many bi-generic hybrids are known to 

 the florist. It is even possible for plants belonging 

 to different families to cross. A hybrid has been 

 described (see Vernon, " Variations of Plants and 

 Animals," page 166) between Digitalis ambigua 

 (Scrophulariacea) and Sinningia speciosa (Ges~ 

 neracecu). 



In the United States a number of hybrids have 



