212 



MUTATION AND PLANT BREEDING 



proved impossible. When crossing this mutant with wild species 

 of the genus Antirrhinum, Stubbe (111, 117) had success in the 

 selection of forms which possess two stamens in every flower. From 

 Figure 1 it can be seen that already in the F 5 generation, 98 per 



100% 



90% 



70% 



50% 

 40% 



A majus gelblich 

 ssp.majus var ski alum 



George de Galomus ICorb/eee) 

 x 



A. ma jus S.50 mul leans cendens 2 



1349 1350 1351 1952 1953 1954 



'2 '3 'it. 15 I § 1 7 



1956 



1958 

 F, 



Figure 1. — Curve of selection of F 2 to F 9 for tioo stamens, after crosses 

 of the mutant trancendens 2 of Antirrhinum majus to A. majus gelblich 

 ssp. majus var. strictum. From Stubbe (117). 



cent of the flowers had two stamens. The introduction of numerous 

 other genes evidently increased the penetration of the mutated 

 character and led to its stabilization in the new "genetic environ- 

 ment". With other mutants forming variable numbers of stamens 

 up to eight, similar success in stabilizing was possible (111, 117). 

 These examples have been broached here because they offer 

 an interesting model for plant breeding. Macro-mutations may not 

 only be stabilized in a new genetic background, but it also seems to 

 be possible to modify their action and particularly to eliminate 

 undesired pleiotropic effects, as discussed later in this paper. 



