KNOWLEDGE OF THE MUTATING OENOTHEEAS. 5 



the orisjin of such complex biological relationships. Darwin's principle of natural 

 selection, although unproven in such cases, still remains the only adequate theoretical 



explanation. 



To return to the question of crossing, and its effect upon O. Lamarckiana in relation 

 to the mutation phenomena : as I have stated elsewhere, it seems probable that this 

 behaviour is an expression of the germinal instability resulting from crossing of races 

 in the ancestry of the parent form. It is evidently not the re-appearance of forms 

 which entered into that ancestry, nor is it merely a case of hybrid splitting as that is 



h 



now understood. DeVries has classified mutations as progressive, retrogressive, and 

 dei?ressive, the last being the re-appearance of characters which had previously 



disappeared. From my study of the mutants of Oenothera they appear to me to i)e 

 (1) positive, due to plus variation in one or more characters, of which O. riihricalyx is 

 an example ; (2) negative, due to the minus variation or loss of one or more characters, 

 e.g., O. nanella; and (3) mutations involving a divergent change in various characters 

 to a new condition of equilibrium. Most of the mutants of Oenothera belong to the 

 last category, and even the positive and negative mutations involve changes in all the 

 other organs in most cases — e. g., O. gigas, O. lata, 0. nanella. Occasional positive or 

 negative mutants occur in Oenothera, in which only one character is afipected — e.g., 

 pigmentation in 0. rubricalyx. Mutations affecting single characters appear to be much 

 more common in other genera. But it is not certain that there is a real distinction here 

 between qualitative and quantitative mutations. In any case, DeVries is doubtless 

 correct that whether a single character or many are affected, the originating cause in. 

 each case is a single germinal change. Changes which affect every organ, including 

 foliage and flower characters, are probably more fundamental than those affecting only 

 colour characters, or the size of a particular organ. 



I have elsewhere pointed out (Gates, 1911 d, p. 599) that the appearance of the 

 mutants O. gigas and 0. 7^uhricalyx cannot be accounted for on the basis of hybrid 

 splitting, and also that the mutational changes may occur at different points in the life 

 cycle. "The evidence for tlie heterozygous character of the original 0. rulricabjx 

 mutant, and hence for the occurrence of this particular change during the reduction 

 divisions in one spore mother-cell, is particularly clear ; while the evidence from the 

 tetraploid number of chromosomes in 0. gigas (Gates, 1911 c) makes it probable that 

 the change here may have occurred in the fertilized e^^ or in an apogamously developed 

 megaspore *. The theory of DeVries regarding the origin of the mutants has been that 

 in every case the change occurred in the spore mother-cells, each mutant originating 

 from the union of the product of a mutated and a non-mutated spore. There 

 are, however, obvious difficulties with this view, as will be pointed out in a moment. 

 My cytological work (see Gates, 1908) with the Oenotheras showed the presence of 



^ 



♦ Since this was written, Stomps (1012) and Mias Lutz (1 912) have observed triploid mutants from LamarcJdana 

 having 21 chromosomes. This increases the probability that tetraploid mutants may originate from the union of 

 two unreduced germ-colls, but it by no means shows that they do not also originate in the manner I have 

 Bnggestod. I shall discuss this matter in detail elsewhere. 



