BIOLOGY OF AGRICULTURAL PRODUCTION 97 



liens or cows in the ordinary barnyard may be " boarders.'' A 

 single specimen of plant or animal may produce a phenomenal 

 yield, but the progeny may revert to loafers and boarders. 

 Pure-bred strains have been carefully selected for generations, 

 until all bad heredity has been weeded out and the progeny 

 can be relied upon to be thoroughbreds, that is, to yield a 

 uniform, standard result. Collect records of various pure-bred 

 strains in the neighborhood and compare yields, as below : 



DIFFERENCES IN YIELD DUE TO VARIETY, EXPERIMENT STATION, 

 ROSTERN, CANADA 



Disease-resisting .strains. Variation applies to immunity 

 from disease as well as to any other character, and hence the 

 world is being searched for strains of animals and plants which 

 have developed resistance to prevailing diseases. Cattle from 

 India are being introduced into the south, because they are 

 immune to Texas fever. The ordinary Crimson Rambler rose 

 is much infested with mildew, while Van Fleet's seedling is 

 practically immune to it. Such immunity may extend even to 

 freedom from insects, as shown by many foreign introductions, 

 notably Rota rugosa and the flowering quince and snowball 

 from Japan. Thus in all sorts of epidemics it is of great im- 

 portance to note any immune individuals, and these should 

 be carefully preserved with a view to development of resistant 

 strains. Collect the data on any local work along this line. 



A good case in point occurred recently in the cabbage industry 

 of southeastern Wisconsin. A fungus suddenly appeared which took 



