136 Bulletin 251. 



caused by cross-pollination. Mutations of self-fertilized plants thus 

 usually come true to type, while in cross-fertilized plants the mutation 

 must usually be cultivated in an isolated place and carefully selected 

 to weed out the effect of such crossing as has occurred. Many seedsmen 

 examine their trial grounds regularly for the sports or mutations and 

 many of our best varieties have resulted from the selection of such 

 sports. Livingston, of Ohio, who during his life was famous for the 

 number of new varieties of tomatoes which he produced, made it a prac- 

 tice to regularly search the fields of tomatoes which he grew for seed 

 purposes, for such sports and almost all of his numerous varieties were 

 produced by the discovery of such striking variations. 



From what has been said above it will be seen that fluctuating 

 variations are of value mainly in the production of improved strains of a 

 race which differ only in such characters as high yielding capacity, which 

 are soon lost when the selection is discontinued. Mutations or sports on 

 the contrary are of value in the production of distinctly new races and 

 varieties which maintain their new characters without continued selec- 

 tion. 



Aside from the above types of variations we have another type 

 usually known as physiological variation which is the direct reaction of 

 the plant to a certain environment. A simple illustration of such a varia- 

 tion is the difference in size due to growth on sterile and rich soil. Such 

 variations are not ordinarily inherited and are not known to be of any 

 value to the plant-breeder. 



Another kind of variation, probably of little value to the breeder of 

 annual plants and about which we as yet know very little, is the 

 so-called bud variations, sports or bud mutations. Chrysanthemum 

 and rose growers know that it is not a very uncommon thing for a plant 

 to produce a branch which will be entirely different from the remaining 

 portion of the plant. Valuable new varieties of roses, chrysanthemums, 

 carnations and some other flowers and fruits have been secured by the 

 selection and propagation of such bud variations. They seem in a large 

 measure to be comparable to mutations except that they originate in a 

 bud change instead of a change occurring in the sexual reproduction. It 

 is probable that they will ultimately be found to be due to similar 

 causes, being produced in the same way. 



Tlic forcing of variations. 



Little is known as yet as to how far we can go in forcing the varia- 

 tions of various types, other than through the hybridization of different 

 strains, varieties and species. The evidence now at command, indicates 

 that plants become more variable as they are highly fed and are manip- 

 ulated in various artificial ways, such as, budding, grafting and vegeta- 



