Ch. VI, 91 METHODS OF PLANT BREEDING 317 



perimental evidence, that some new kinds or species of or- 

 ganisms originate not slowly and gradually from other kinds, 

 but suddenly, — even so suddenly as in one step from parent 

 to offspring. Such new steps are supposed to be not frequent, 

 but occasional, long periods of stability alternating with 

 short periods of change. Upon forms thus originating 

 natural selection operates to preserve the best fitted kinds. 

 The species which thus originate, called often elementary 

 SPECIES, differ really, though only slightly, from those which 

 give rise to them ; and several mutational steps are needed 

 to make such markedly different species (Linn^an species), 

 as the older naturalists associated with that word. This 

 view is known as that of Mutation. Translated into terms 

 of the chromosome mechanism, it means that the determiners, 

 after long periods of transmission in stable form, suddenly 

 alter, apparently not by the interpolation of new ones so 

 much as by spontaneous sudden change in the old. But 

 the evidence on this matter is still in debate. 



9. The Methods used by Man in Breeding Better 



Plants 



Everybody knows that our most valued varieties of farm 

 and garden plants — our grains, fr-uits, vegetables, and 

 flowers — do not occur wild, but have been developed by 

 man from inferior wild kinds. Our principal grains. Wheat 

 and Corn, have been so far improved from their wild an- 

 cestors that we know only doubtfully what those were. 

 Our best known fruits, Apples, Pears, and Oranges, are 

 incomparably superior to the original kinds in size, flavoi-, 

 and other qualities we value. Among vegetables, the 

 Cabbage, Cauliflower, Brussels Sprouts, and others, most 

 diverse in aspect, are all known to have been derived in 

 gardens from a very simple little strand plant of western 

 Europe. In flowers, a great many of our garden favorites 

 have been improved from their wild states to a degree 

 which would render the relationship unsuspected were it 



