THE COEFFICIENT OF MUTATION IN OENOTHERA BIENNIS L. 5 



whence Lamarck obtained the authentic specimen for his original 

 description. 1 ) 



Renner studied the empty seeds of 0. Lamar cki ana, which 

 constitute over one-half of the whole crop. He brings this phe- 

 nomenon in connection with the ability of this species to produce 

 twin hybrids, laeta and velutina, in certain crosses with older types, 

 and assumes that the sexual cells are one-half potential laeta, and 

 the other half potential velutina. In the normal fertilization of 

 0. Lamarckiana this would produce % laeta, % velutina, and y 2 of 

 the hybrid combination laeta x velutina. He further assumes that 

 in pure condition both the laeta and velutina qualities are incom- 

 patible with normal development, and that the germs which bear 

 them are doomed to die at an early stage, thereby leaving their 

 seeds empty. Only the combination laeta x velutina would be fit for 

 further growth, and if we assume that this shows the marks of 

 0. Lamarckiana, the constancy of this form would not be in con- 

 tradiction with the other hypotheses. If we accept these views, 

 all reasons for supposing a correlation between the splitting phe- 

 nomenon and the mutability would lose their value, and this 

 latter process would come much nearer to the corresponding 

 changes in 0. biennis and allied species. The hypothesis, although 

 resting on too large a number of suppositions, would in some sense 

 be a support for the theory of mutation, since it is evidently impos- 

 sible that these presumed qualities, which are incompatible with 

 life, could have evolved slowly on the ground of their utility in the 

 struggle for existence. Moreover, the hypothesis has no direct 

 bearing on the observed phenomena of mutation, and the fact that 

 in 0. biennis such empty seeds are wholly or almost wholly absent 

 proves beyond doubt that mutability may be independent of 

 them. Thus the hypothesis of Renner emphasizes the importance 

 of a study of the mutation phenomena in 0. biennis, in contra- 

 distinction to those in 0. Lamarckiana, at least for the present, 

 until facts are available to appreciate the correctness of his views. 



Obviously the hypothesis that 0. Lamarckiana might be a 

 hybrid, whilst 0. biennis is not, can in no way account for the 

 phenomena of mutation which are common to both of these species. 

 For this reason it seems important to describe the degree of muta- 



i) Blaringhem, L., Yl Oenothera Lamarckiana Ser. et les Oenotheres 

 de la foret de Fontainebleau. Travaux de biologie vegetale, dedi£s 

 a. Gaston Bonnier. Rev. Gen. Bot. 2^-.$$ — 50, 1914; see also my article 

 on p. 579, Opera VI. 



