No. 577] MUTATION THEORY OF BE VRIES 7 



up the continuity of the germ plasm, is hybridization. 

 Apposite in this connection is the wholesale hybridizing 

 practised by Burbank, for the purpose of bringing about 

 the necessary genetic plasticity in his cultures and thus 

 obtaining by resultant mutation or variation, new and 

 desirable varieties of useful plants. The morphological 

 peculiarities of hybrids have been clearly recognized for 

 nearly a hundred years. They are for example clearly 

 set down in Gaertner's rare and classic prize essay, en- 

 titled " Versuche und Beobacthungen ueber die Bastarder- 

 zeugung im Pflanzenreich " (Stuttgart, 1849). Curiously 

 enough these important criteria have been largely ignored 

 by the adherents of the mutation hypothesis of De Vries. 

 A very important and generally observed difference be- 

 tween hybrids and genetically pure species, is the very 

 easily detected one of pollen sterility, partial or complete. 

 Of course when the hybridizing forms show a considerable 

 degree of compatibility, this character may be inconspicu- 

 ous or even absent. Further even in cases where it is 

 originally present, it may be subsequently largely elimi- 

 nated by selection. De Vries himself has noted that about 

 one third of the pollen of 0. lamarckicma is abortive. The 

 English geneticist Bateson was struck with this peculiarity 

 of the species, so much discussed in recent years, in rela- 

 tion to its variable offspring in cultures and promptly and 

 first called attention to the obvious significance of this 

 feature, suggesting that 0. lamarckicma was a hybrid and 

 that its remarkable conduct was the result of hybridiza- 

 tion. This objection has in reality never been met. It is 

 the purpose of the present article to show on grounds 

 commonly accepted by geneticists and morphologists, that 

 not only is genus Oenothera in general characterized by 

 genetically impure or hybrid species, but that the condition 

 of genetical impurity is extremely common in the Ona- 

 graceae as a whole. 



It will be convenient to begin with the examination of 

 our common and very variable garden Fuchsias, which 

 belong to the family Onagracege. The common Fuchsia, 



