210 MUTATION AND PLANT BREEDING 



rions to micro-mutations. In Table 1 vital mutations are classified 

 in lour types according to degree of change of the phenotype. 



Table 1. — Phenotypic Classification of Vital-mutations. 



1. Macro-mutations Large mutations, drastic mutations (Grossmutationen) 



Detectable in a single plant 



a. Transspecific Systemic mutations, organization mutations 



b. Intraspecific 



2. Micro-mutations Small mutations (Kleinmutationen) 



Detectable in a group of plants 



a. Manifest 



b. Cryptic Detectable if the environment and/or genetic back- 



ground is changed 



Those deviations, which are easy to recognize in a single plant, 

 may be called macro-, or large, mutations. Macro-mutations usually 

 affect characters which are already known in the species, but some- 

 times the induced character is unknown in the species, in the genus, 

 or even in the family. (Particularly in cultivated plants the previous 

 separation into different species is sometimes not justified, e.g., 

 in wheat (61).) 



In contrast to these are micro-, or small, mutations (Klein- 

 mutationen) which cannot be detected with certainty in a single 

 plant but only in a group of at least, say, 30 or more individuals. 

 These micro-mutations may be classified into manifest and cryptic 

 micro-mutations, depending upon their degree of detection. Mani- 

 fest micro-mutations are detectable if, in the unchanged environ- 

 ment and genetic background, appropriate methods of screening 

 and observations are applied. Cryptic micro-mutations cannot be 

 recognized even in a large group of plants under "normal" grow- 

 ing conditions. A drastic change of the environment and /or the 

 genetic background may enable them to become manifest, where- 

 as under normal conditions they behave in a neutral manner. The 

 existence of cryptic mutations is more or less hypothetical and there 

 is scarcely any experimental evidence for them until now (see, how- 

 ever, 72). Nevertheless, they may have significance in evolution and 

 they could be of value for certain breeding purposes. The existence 

 of the other types of mutations has been shown repeatedly. Further 

 use of the term micro-mutation in this paper refers to manifest ones 

 only. 



