GAUL: INDUCED MUTANTS IN SEED-PROPAGATED SPECIES 249 



128. Wohrmann, K. 1958. Untersuchungen iiber den Ahrchensitz bei 



Alopecurus pratensis L. Angexo. Bot., 32: 75-57. 



129. Zacharias, M. 1956. Mutationsversuche an Kulturpflanzen: VI. 



Rontgenbestrahlungen der Sojabohne. Zilchter, 11: 321-338. 



Comments 



Dermen: I am still unclear about the difference between macromutations 

 and micromutations. 



Gaul: The grouping has practical purposes onlv and may serve for 

 the communication of evolutionary and breeding problems. It con- 

 siders the phenotype only and has nothing to do with the change of the 

 genetic structure. The classification is simply based on the method 

 of detection, i.e., whether the mutation can be recognized with cer- 

 tainty in a single plant or in a large group of plants only. It is arbitrary 

 because there are all transitions from large alterations to small ones. How- 

 ever, in plant breeding, the selection procedure entirely depends on 

 whether one is dealing with macro- or micromutations. 



Strauss: It seems that the terms micromutation and macromutation 

 have been used by you in an operational or field sense only. Should not 

 these terms be defined more carefully in terms of actual gene changes? 



Gaul: This would be good if it is possible. A priori, I would not expect 

 that a "small change of the gene structure" would necessarily correspond 

 to a small change of the phenotype, and vice versa. 



MacKey: As to Doctor Gaul's definition of macromutations versus micro- 

 mutations, I must say that the plant breeder urgently needs a separation 

 of two such groups in his discussion, since they relate to the selection 

 methods applied. Personally, I do not hesitate to enlarge the earlier 

 concept of macromutation, since such shifts in meanings are common 

 in biological denomination rules. Doctor Gaul's "transpecific macro- 

 mutation" will be the old concept now in a strict sense. 



Frey: You have suggested improving the efficacy of mutation by (a) 

 better control of mutation induction, and (b) better control of selection. 

 I would like to see you add another category of great importance, name- 

 ly, analysis of the elements that constitute the characteristic to be modi- 

 fied and then an intelligent and logical selection of parent material 

 (the genotype) to be irradiated. 



