16 J. K. BREITENBECHER. 



of the necessity of sexual reproduction, but a mutation that took 

 place in a somatic cell could be discontinuous, although it would 

 not be transmitted sexually. This reasoning led the author to sug- 

 gest that these elytral mosaics in Bruchus should be called somatic 

 mutations. 



In plants mutations may occur in the germ cells or in any meri- 

 stematic tissue. According to Babcock and Clausen ('18), "Fac- 

 tor mutations in meristematic cells, or vegetative mutations, as dis- 

 tinguished from those originating in the germ cells, give rise to 

 simple bud sports or to chimeras according to the location of the 

 mutating cells. A bud sport is a shoot or branch which differs 

 genotypically in one or more characters from the remainder of the 

 plant. Here the factor mutation must occur in one of the undif- 

 ferentiated cells of the very young shoot. Just as in the case of 

 factor mutations in germ cells, so in vegetative mutations the 

 somatic effects range from single visible character differences to 

 manifold effects in which many structural details are different." 

 The fact that somatic factor mutations do occur in plants seems to 

 be well established, and, furthermore, these somatic factor muta- 

 tions display the same order of dominance, as manifested by factor 

 mutations, which occur in germ cells. Although somatic factor 

 mutations are extremely rare in animals as compared to this same 

 behavior in plants (because the latter can be propagated, while the 

 former can not be), this, in itself, is not sufficient argument to dis- 

 credit the idea that the same phenomena are involved. It appears, 

 therefore, in this relation that the mosaics in Bruchus are not 

 unlike somatic mutations in plants. Emerson ('21) has lately 

 noted similar phenomena in maize. 



The ordinary gynandromorph, as described by Morgan and 

 Bridges ('19), is an animal that shows some male characters on 

 one side of the body and female on the other, but the elytral 

 mosaics in Bruchus are not gynandromorphs in this sense because 

 the sexual organs are not modified, every mosaic being a normal 

 female. These authors ('19) further showed that sex-linked char- 

 acters are usually involved in the gynandromorphs of Drosophila. 

 There is evidence that nearly all gynandromorphs are potentially 

 females, but that a sex-mosaic results through the elimination of 

 one sex-chromosome immediately after fertilization ; this is due to 



