IMPROVEMENT OF POTATOES 443 



and cowpeas followed by rye; second year, Irish potatoes 

 followed by winter vetch or crimson clover. 



580. Crossing. Improvement in potatoes is commonly 

 accomplished in two ways, by selecting new varieties grown 

 from seed and by selecting the best tubers from the best hills 

 of some of the common varieties. If seed produced on potato 

 vines is planted, there will be great variation in the plants 

 which are obtained. This variation gives the breeder a wide 

 range from which to select. Crosses between two varieties 

 of known characters are sometimes made artificially with a 

 view to combining in one variety the good qualities of both. 

 The desired results are not always secured, as the poor quali- 

 ties of the two varieties crossed are as likely to predominate 

 in the progeny as the good ones. However, good results are 

 sometimes obtained from intelligent crossing and subsequent 

 selection, some of our leading varieties of potatoes having 

 been produced in this way. 



581. Selection. Breeding by selection is by far the most 

 common method of improving varieties of potatoes, and one 

 which may be practiced with profit by any careful grower. 

 It is based on the fact that the productivity of individual 

 tubers in a variety differs. By selecting those tubers which 

 appear to be best and then comparing their productivity by 

 planting them in a uniform field and harvesting the product 

 from each tuber separately, those which produce large yields 

 of good quality may be preserved and propagated. 



The method of selection most practical on the average 

 farm is to observe a large number of hills as they are dug and 

 save for seed the tubers from hills that produced the largest 

 number of desirable potatoes. Many experiments have 

 shown marked improvement from such methods of selection. 



