POTATO IMPROVEMENT 



229 



from pink to white tubers, two permanent changes from long to 

 round tubers, and four instances of changes from shallow to deep 

 eyes were observed. On the basis of the modes of inheritance of 

 these characters, the hypothesis was made that the changes 

 resulted from the loss of dominant factors. Experiments in 

 selection for high nitrogen content gave negative results. The 

 statement was made, "it is true that all of the asexual variations 

 have been losses of characters, while in sexual reproduction the 

 formation of new characters occurs." This certainly substan- 

 tiates the belief that the production of improved varieties of 

 potatoes through bud mutation is not a promising method of 

 attack. East quotes A. W. Button, who states: 



"I have no hesitation in affirming that there is no potato in commerce 

 in England, and I might say in Europe, which owes its origin as a dis- 

 tinct potato to bud variation in any form whatever." 



If this statement is true, it seems fair to conclude that there has 

 been a somewhat loose usage of the term "bud mutation" in its 

 application to raising the standard of a variety by any of the 

 well-known methods such as tuber unit or hill selection (see 

 Chapter XVIII). Accumulated evidence certainly points to the 

 belief that the chief value of such work rests on the prob- 

 able elimination of degenerate strains. Evidence from Canada 

 presented by Macoun (1918) is particularly illuminating. Four 

 varieties, Early Rose, State of Maine, Empire State, and Dela- 

 ware, were grown in Canada at the Experimental Farm at Ottawa 

 from 1890 to 1909 inclusive. The better tubers were selected 

 from each year's crop and used to plant the following crop. 

 Results are presented in Table LVII. 



TABLE LVII. AVERAGE YIELD OF POTATOES OVER THE FIRST FOUR AND 



LAST FOUR YEARS OF A 16-YEAR PERIOD AND SUBSEQUENT 



YEARLY YIELDS OVER A FOUR-YEAR PERIOD 



