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MUTATION THEORY IN PRACTICAL BREEDING. 61 



experimental sources, while with similar frequency controversial 

 papers unsupported by experimental evidence, are being directed 

 against it. Under these conditions it is not difficult to foresee the 

 outcome. In science, truth will prevail, and the accumulation of ex- 

 perimental data can never be overthrown by volumes of speculative 

 character with whatever of warmth or asperity they may be written. 

 The fact that the mutation theory is a subject of controversy need not 

 concern us here, however, since even its most strenuous opponents 

 grant that it is supported by garden experience. As the practical 

 breeder is little concerned with what goes on outside of field and gar- 

 den cultures, there can be no controversy regarding the truth of the 

 jnutation theory in its applicability to economic breeding. 



The central doctrine of the mutation theory, is the origin of new 

 forms whether we call them species, elementary species, varieties, or 

 strains by the' sudden appearance of an aberrant specimen that 

 gives rise at once to the new strain by producing offspring like itself. 

 The alternative conception is that usually attributed to Darwin, in 

 which new hereditary lines are established by the gradual cumulative 

 action of the environment in selecting those slight variants which are 

 best qualified to meet the conditions under which they must live. 



Every breeder is familiar with the large number of unexpected 

 variations or sports that have been the starting points for new strains 

 both in plants and in animals; and the value of these sports to the 

 breeder is too well understood to need comment. It should be said, 

 however, that there is grave danger of ruining the reputation of the 

 words "mutant" and "mutation," and I earnestly ask your assist- 

 ance to prevent this. Certainly not every aberrant form we see is a 

 mutant, and when plants are capable of propagation by some vegeta- 

 tive means, as by bulbs, tubers, buds, cuttings, grafts, etc., many 

 striking individual variations may be preserved and extensively multi- 

 plied, which are not mutations at all. No combination of characters 

 resulting from the resolution and recombination of the parental quali- 

 ties in hybrids ought ever to be called a mutant, however striking or 

 unexpected it may be, because in these cases no really new r quality has 

 been produced, but only new combinations of qualities already in 

 existence. Mutations can only be recognized as such with certainty 

 when they arise in pure-bred strains. They are not to be distinguished 

 from fluctuations by being large and striking variations but by the 

 fact that they represent a fundamental change in the internal com- 

 position or structure of the vital substance, which renders the charac- 

 teristic qualities of the new form transmissible through sexually pro- 

 duced seeds. Variations that are thus transmitted are often very 

 insignificant, quantitatively, compared with others that are not so 

 transmitted. We must be careful, therefore, not to handle the word 

 " mutation " too lightly, since we can know that a plant is a mutant 

 only after a sufficient number of seed generations have been produced 

 to demonstrate the permanent character of the variation. 



Many economic varieties are the result of hybridizing natural 

 species, and this is especially true of perennials, which possess means 



