196 The Origin of Species by Mutation. 



Apparent exceptions to this rule are so numerous that we 

 might be inchned to doubt its universal validity. But in 

 most cases it will be found that those who record such 

 exceptions have paid no regard to the possibility of cross- 

 fertilization by insects or by the wind. Crossing is cer- 

 tainly the simplest and most obvious explanation of them. 

 The whole subject of so-called atavism in plants demands 

 a careful re-investigation, for most of what passes as 

 atavism in the nursery and private gardens is nothing 

 more nor less than the result of accidental crossing. At 

 least so my researches into these phenomena lead me to 

 believe. 



I shall however return to this subject and deal with 

 it more thoroughly in a later section ; and shall confine 

 myself now to citing some of the more important in- 

 stances of constancy. 



The complete constancy of many varieties is well 

 known. As for example in the case of Matricaria Cham- 

 omilla discoidea and the corresponding varieties of Bi- 

 dens tripartita and Senecio Jacohaea. Also of Datura 

 tatula ineruiis/ of Ranuncidus arvensis iuermis,^ of the 

 peloric varieties of Antirrhinum majus,^ of Nigella sa- 

 tiva apetala,^ of Ilex Aqtd folium with yellow berries,'* 

 of weeping oaks and weeping birches,^ of red-leaved 

 Bcrheris,'^ of the peloric form of Corydalis solida,^ of 

 Hordeum trifurcatum, Rubus fruticosus laciniafus be- 

 sides countless garden plants and vegetables (sugar peas, 

 thornless spinach and so forth). 



^ Botan. Zeitung, 1873, p. 687. 



* Masters, Vegetable Teratology, p. 227. 



^Hoffmann, Botan. Zeitung, 1881, p. 410; a number of other 

 examples are recorded here. 



* Darwin, Variation in Animals and Plants, II, pp. 24, 26. 

 ^GoDRON, Mem. Acad. Stanislas, t868, p. 3. 



