8. YORKSHIRE. 55 



degree of moral certainty, a fort adapted to 

 ttyir own particular foils and Situations. 



But it has been already obferved, that 'va- 

 rieties degenerate : the old favourite forts of 

 this Diftrict were driven, until fome of the 

 individual plants barely produced their feed 

 again. 



Whoever has attended clofely to the work 

 of taking-up potatoes, mud have obferved 

 the great inequality in the produflivenefs of 

 individual plants. The difference in the pro- 

 duce of adjoining roots, where no difparity of 

 foil can influence, will fometimes be three or 

 four- fold. Hence it is evident^ that each 

 variety has its SUB-VARIETIES ; through 

 whofe means, it can hardly be doubted, the 

 parent variety may be improved, and its conti- 

 nuance be prolonged. 



Thus the farmer has another mea,n in his 

 power of improving the quality and produc- 

 tivenefs of his potatoe crop, by IMPROVING 

 VARIETIES, or, in other words, SELECTING 

 SUB-VARIETIES, fupcriorly adapted to bis foil 

 and fituation. 



Every attentive cultivator of this valuable 



root muft be acquainted with the wide diffe- 



E 4 rcnce 



