POTATO IMPROVEMENT 223 



fendleri, which grows at a high altitude and endures extremes 

 of climate, with a domestic variety. The wild form produces 

 small tubers. In the F z generation forms appeared which were 

 identical with the wild parent together with many intermediate 

 types. 



Most of the observed variations in cultivated varieties have 

 occurred in the tubers, although the English ash-leaf varieties 

 are examples of a variation in leaf shape (East, 19076). 



Production of New Forms. For the purpose of differentiating 

 between two important phases of potato improvement, Stuart 

 (1915) has referred to "selection" as the "isolation and asexual 

 propagation of desirable strains or types" while "breeding" 

 is used only for sexual reproduction. With certain crops, such 

 as the potato, this terminology is distinctive. Such a restricted 

 usage of the word "selection" seems undesirable from the plant- 

 breeding standpoint. The same idea can be obtained by the use 

 of "clonal selection" to refer to the asexual propagation of de- 

 sirable strains or types. 



Systematic plant breeding with the idea of combining the 

 desirable characteristics of two parental varieties can be carried 

 out only after the breeder has familiarized himself with the 

 characters of particular varieties and of their wild relatives. 

 Thus, with the potato as with other crops the breeder should 

 first determine the ideal toward which he will work. Parental 

 varieties should than be selected because of some desirable 

 characters. By recombination of the favorable characters of 

 both parents, improvement may be obtained. Gilbert (1917) has 

 listed certain characters of the potato which are universally de- 

 sired. Some of these are: 



1. High yield. 



2. Good quality. 



3. Disease-resisting capabilities. 



4. Good keeping quality. 



5. Good color of flesh and skin. 



6. Skin of desirable texture. 



7. Tubers of good shape. 



8. Shallow eyes relatively few in number. 



9. Upright, vigorous plants. 



10. No tendency to make second growth. 



The desirability of most of these characters is self-evident. 

 The chief difficulties in the way of developing a standardized 

 method of attack arise from: 



