gaul: induced mutants in seed-propagated species 211 



Naturally, the grouping as suggested in Table 1, is arbitrary 

 and has no meaning relative to the nature of changes of the genetic 

 material. Whether in individual cases the phenotypic change is 

 considered to be small or large will often depend on the methods 

 and personal view of the observer. Though it is not. possible to 

 construct sharply distinguished categories of mutations, the classi- 

 fications suggested may be of value for the communication of evolu- 

 tionary and plant breeding problems. 



Transspecific Macro-mutations 



The occurrence of transspecific mutations is very rare. Never- 

 theless, a number of more or less clear cases of both induced and 

 spontaneous mutations have been reported (see reviews in 44, 45, 79, 

 111, 117, 119). Recently, in barley, another induced macro-mutation 

 (57) has been described in more detail (91). The culms of that mutant 

 have no differentiated nodes. All the nodes are located in close 

 succession immediately above the root, and the culm is formed only 

 by one internode. Such a character is common in the Cyperaceae. 

 Another interesting example of a spontaneous macro-mutation was 

 recently described by Staudt (105) in Fragaria. 



Macro-mutations that are transspecific usually have a stronger 

 reduced vitality and/or fertility. They are of no immediate value 

 for plant breeding. However, if a definite character has to be trans- 

 ferred from a foreign species, it might be easier to use transspe- 

 cific mutants instead of interspecific hybridization. In agricultur- 

 al plants transspecific mutations which could serve for practical 

 breeding are scarcely known. Yet, it might be possible that they 

 will be found in the future, owing to the increased production of 

 mutations. Such mutations might also be of considerable interest in 

 ornamentals. 



Sometimes the manifestation of the mutant characters is not 

 constant but variable. This holds true, e.g. for some mutants of 

 Antirrhinum majus which were investigated by Stubbe, (111, 

 117). Thus, the mutant transcendens has a tendency to reduce the 

 number of stamens per flower from four to two. Flowers with two 

 stamens are characteristic in adjacent genera of the Scrophul- 

 ariaceae to which Antirrhinum belongs. However, in the mutant, 

 only 40 per cent of the flowers possess two stamens and the others 

 form three and four. Selection of stable types with two stamens 



