Potato Breeding 59 



viduals within a pure line has httle, if any, effect in raising 

 the average of the Hne. Tliis has not been proved, by any 

 means, but the indications are that only a very slight ad- 

 vance is made by continued selection after a pure line has 

 been reached, unless an exceptionally good individual 

 should arise whose progeny would constitute a new and 

 better line. 



It will now be seen that the first work in improving 

 potatoes by selection is to determine the best tuber lines 

 and plant them for seed. This necessitates carrying out 

 a system of breeding whereby individual tubers must 

 be planted separately and properly labeled and their prog- 

 eny kept separate for a few years to determine whether 

 or not the desirable plants transmit their qualities to fu- 

 ture generations (see Plate VI). This is known as "pedi- 

 gree breeding." Myers gives the following table to show 

 variation in the yielding capacity of different tubers. 

 Each unit is the product of a different parental tuber : 



Table X 



Unit Yield in Bushels 



No. TO THE Acre 



1 110 



2 220 



3 220 



4 230 



5 280 



6 320 



7 240 



8 230 



9 230 



10 130 



11 210 



12 70 



13 190 



14 190 



15 25 



16 270 



