70 POPDLAE EEEOES. 



to be inherited, but that plants so treated are more 

 apt than others to fnrnish improved varieties. Such 

 treatment is therefore a legitimate method of 

 obtaining better varieties, but it alone does not 

 guarantee the permanence of varieties so produced, 

 though some varieties are more inclined to be per- 

 manent than others. 



Other causes of variation which may lead varie- 

 ties to run out or lose their valuable and distinctive 

 features are peculiarities of soil and climate. Dwarf 

 early varieties of corn and peas will lose these 

 characters and become larger and later if grown 

 for a few years on rich black soil. A cold climate 

 causes many plants to become dwarf in habit and 

 more fruitful. Oats rapidly degenerate in most 

 parts of the United States, but the remedy is not 

 so much the introduction of new varieties as the 

 frequent importation of fresh seed from regions 

 better adapted to this grain. 



Crossing is another cause of the degeneration of 

 varieties. Systematic improvers of plants are care- 

 ful to prevent crossing with inferior sorts. A few 

 years of careful selection, preventing the access of 

 pollen of inferior varieties, will generally produce 

 an excellent sort which can be depended on to 

 reproduce itself. When this variety, however, is 

 carried into general cultivation, and exposed to 



