208 THE BOOK OF VEGETABLES 



drawn from federal and state experiments on a large 

 scale. 



Varieties |of Potatoes are, historically, almost innu- 

 merable; for practical use they are early, medium, and 

 late. New varieties are rarely maintained, and the ama- 

 teur or beginner will be wise to buy a variety locally 

 well known and successful, rather than buy at high 

 prices a novelty which may not have been sufficiently 

 tested. Experiments are now under way at many 

 stations, to produce or find disease-resistant varieties. 



Potato crops are usually early and late, though for 

 the garden a third crop is easily obtained, by starting 

 under glass. Earliness is partly a matter of variety, 

 but may be helped by sprouting the seed-piece, using 

 "quick" fertilizers, and by planting on early land pre- 

 pared in the previous fall. 



The worst insect enemy of the potato is the beetle 

 or potato-bug. The worst diseases are scab and the 

 early and late blights. 



Soil. Soil should first of all be free of scab; good 

 potatoes cannot be grown on infested land. If potatoes 

 or beets known to have scab have been grown on a given 

 plot, it must be given to other crops for several years 

 before Potatoes can safely be grown on it. 



Potatoes require a deep and moderately light or 

 sandy loam, well supplied with humus, and with an 

 open subsoil. If the soil is heavy, the tubers cannot so 

 easily enlarge ; if clayey, the ground will be too wet ; 



