Foundations of the Mutation Concept. 11 



While the 15-chromosome mutants produce two types of 

 gametes, and hence are at least dimorphic in their offspring when 

 crossed back with the parent type, the tetraploid forms are also 

 peculiar in their inheritance, giving triploid intermediate hybrids 

 when crossed back with the parent (diploid) type. Such forms are 

 for the most part unstable, and although they occur in nature (e.g. 

 the well known natural hybrid between Drosera fotundifolia and 

 D. longifolia) yet their instability and partial sterility prevent their 

 giving rise to permanent intermediate links between the original 

 diploid species and its tetraploid derivative. Meiotic irregularities 

 in these hybrids may lead to the production of a series of plants 

 with new chromosome numbers, as is well known in the CEnotheras. 

 But seldom will a stable form arise having a balanced chromosome 

 equipment. With the exception of tetraploidy, therefore, none of 

 the types of visible chromosome change so far demonstrated in the 

 Oenotheras are likely to have played a very large role in any 

 phytogeny. They are chiefly valuable as a means of furnishing a 

 visible demonstration of the occurrence of germinal nuclear changes. 



All the evidence indicates that the great mass of mutations 

 originate as new Mendelian characters. Among such changes in the 

 CEnotheras are (E. rubricalyx, a dominant, and (E. gigas nnnella, 

 which in crosses with its parent form gigns behaves as a Mendelian 

 recessive. We may consider these two forms as types of Mendelian 

 mutants. On the basis of their inheritance as such, we must 

 assume that they originate through an alteration in a particular 

 locus of one chromosome, a view set forth elsewhere 1 and now 

 generally accepted. The history of (E. rubricalyx has been given 

 in the work cited, 2 but the salient points may be referred to here. 



One plant in a large culture of (E. rubrinervis 3 appeared with 

 an extreme increase in anthocyanin pigment, this red being 

 especially conspicuous on the sepals, flower stalk, stem, and the 

 under surface of the leaves, although histological examination shows 

 it to be present in increased quantity in all parts of the plant. The 

 original individual was heterozygous, originating therefore through 

 the union of a mutated with a non-mutated germ cell. The 

 premutation must then be considered to consist in a change, 



' The Mutation Factor, p. 300. 



The Mutation Factor, p. 102. 



1 It now appears (Lutz 1917b) that the form which other investigators, at 

 least MacDoujal, Miss Lutz and myself, regarded as rubrinervis, differs from 

 theAmsteidam rubrinervis, which is a less robust form. Further study by 

 de Vries has revealed several types closely related to rubrinervis, which will be 

 referred to later. 



