76 BREEDING CROP PLANTS 



Classifications of some crops have recently been made and in the 

 next few years these will be improved further. The general 

 adoption of some standard variety classification is a necessity if 

 work of different investigators in crops is to be correlated. 



The central aim in crop improvement work is to find or produce 

 improved forms which when grown by farmers will excel in 

 quality, productivity, or ease of handling. It is a decided 

 advantage if the improved form can be distinguished from the 

 varieties commonly grown in the locality by some botanical or 

 morphological character difference. Kanred (Jardine, 1917) 

 wheat is an example of a new variety with such a character. 

 This variety, which was developed at the Kansas station, belongs 

 to the Crimean group of winter wheats. It gives larger yields 

 on the average than Turkey or Kharkov selections and excels in 

 resistance to black stem rust, Puecinia graminis tritici, and 

 leaf rust, Puecinia triticini. Its beak, i.e., the extension of the 

 outer glume in the form of an awn point, is longer than in the 

 common forms of Crimean winter wheat grown in Kansas. 

 Marquis wheat, which is so widely grown as a spring wheat in the 

 Northwest and Canada, differs in seed shape from other Fife 

 wheats commonly grown in these sections. Forms belonging; to 

 the same variety may frequently exhibit differences in productiv- 

 ity and this may be the sole distinguishing character difference. 

 Forms constantly differing from each other in one or more genetic 

 factor differences which may be expressed as yield, quality, or 

 disease resistance, or a minor botanical character and yet which 

 belong to the same variety group, may be called strains. This 

 is the lowest order of classification which can be adopted for seeded 

 crops. With a self-fertilized crop the strain may also be a pure- 

 line in the original sense as used by Johannsen. With cross- 

 fertilized crops the strain may be relatively pure for some particu- 

 lar character and may be heterozygous for other characters. 



Inheritance studies of many of our farm crops have been made. 

 As crossing is the only means of inducing variation that can be 

 carried out with success by the plant breeder, it becomes neces- 

 sary to know how individual characters are inherited. It is true 

 that yield is not a simple Mendelian character but is dependent 

 on many inherited factors and their manner of reaction to the 

 environment. At present, knowledge of inheritance may be 

 used only as a guide in working with these characters. As a rule, 

 the parental forms differ in botanical characters as well as in 



