No. 597] 



THE MUTATION THEORY 



r.23 



The speaker has recently observed, in several species of 

 Oenothera other than (E. Lamar ckiana, the origin of a 

 large number of different mutations. Several of these 

 have been found to belong to the type which we are at 

 present considering. That is to say, they give a progeny 

 which does not contain the parent species, and the muta- 

 tions themselves are produced by the parent species in 

 every generation. In the case of one mutation, described 

 a year ago as (E. pratincola mut. nummularia, the chro- 

 mosome number lias been determined as 14, the typical 

 number in the group. The remarkable fact about these 

 mutations of (E. pratincola, as far as work with them has 

 gone, is that their crosses with the parent species are 

 identical with the pistillate parent in the first hybrid gen- 

 eration. Mutation pollinated with parent species yields 

 the mutation. Species pollinated witli imitation yields 

 the species. 



This most interesting state of affairs is absolutely at 

 variance with the attempted Mendelian explanation. It 

 can be understood on the supposition that two types of 

 gametes are produced, which are by no means equivalent. 

 One type bears most of the characters which differentiate 

 the different species and forms from one another. The 

 other type seems to carry characters which are likely to 

 be common to a number of different species. In the par- 

 ticular species which gives rise to the mutations under dis- 

 cussion the gametes of the former class are female, those 

 of the latter, male. Thus it follows that a mutative modi- 

 fication of the germ plasm in one of these specie- might 

 affect only characters which were borne by one of the two 

 kinds of gametes. If so, we would have at once a simple 

 explanation of the behavior of the mutations which give 

 matroclinic crosses with their parent species. 



The same idea may readily be extended to cover the 

 oases of mutations which give progenies containing both 

 the mutational and the specific types. Perhaps the muta- 

 tive change is £ reversible one, and certain gametes in 

 each generation show reversion from the mutated to the 

 unmutated condition. Or perhaps in some species there 



