THE MUTATED GENE 177 



Sturtevant (1927) produced mosaics of the Bar-eye mutant of 

 Drosophila with normal eye facets marked by color genes, by 

 introducing the Minute-n gene which has a mosaic-producing 

 effect, as mentioned above. He showed that mosaic spots of 

 Nonbar tissue situated in the periphery of the area of the would-be 

 normal eye are prevented from forming facets. Near the Bar 

 area, however, and in close contact with mosaic Nonbar tissue, 

 facets may be developed also in Bar tissue. The adjacent 

 normal tissue then exercises a facet-forming influence upon 

 tissue that would be unable to develop facets by the action of the 

 genes within its own cells. Sturtevant himself assumes that here 

 an influence beyond the cells containing the genes (an induction) 

 is seen, though he mentions also the alternative that a time rela- 

 tion might be involved, viz., a difference in regard to the time at 

 which the formation of facets is determined in different areas. 

 Huxley (1935c) has proposed a somewhat different explanation 

 in terms of growth rate, which however also requires a growth- 

 stimulating influence of normal on Bar tissue. (See also the work 

 of Huxley and Wolsky (1936) reported on page 33.) A similar 

 case is reported by Sturtevant (1932). He compared mosaic 

 patches of the mutant scute, which removes certain bristles in 

 Drosophila, with all-scute flies and finds that this scute effect 

 is smaller in little mosaic patches, indicating the possibility of 

 an influence of the normal surroundings on the mosaic spots. 

 Another similar case is found on a gray body with yellow mosaic 

 spots which are less yellow and less distinct than typical yellow. 

 Finally, a case ought to be mentioned that was described for 

 Habrobracon by Whiting, Greb, and Speicher (1934), and 

 A. R. Whiting, 1934. They produced eyes with mosaic spots 

 from binucleated eggs. Whenever any color from the orange 

 locus is associated in a mosaic with one of its alleles, no sharp line 

 of separation is found between the two, but continuous shading. 

 When, however, the white locus is involved, there is a clear-cut 

 mosaic. Adjacent cantaloupe and ivory tissue form a black 

 stripe in between, showing that from both spots reciprocal stuffs 

 diffuse which produce pigment when combined. 



Of significance in this connection also are the remarkable facts 

 found by Haberlandt (1935) in the chimeric Crataegomespili, 

 which have a skin of one and a core of the other species. The 

 palisade tissue, derived from Mespilus, is intermediate in char- 



