132 INBREEDING AND OUTBREEDING 



average row number and decrease in variability in the 

 eighth generation are probably due to the favorable grow- 

 ing conditions of that year — witness the high yields for 

 the inbred strains in that year as given in Table III. The 

 apparent rise in variability after the eighth generation 

 is in part due to the fact that the ears had become some- 



15 



d C o 

 > UK 



Ave . No . Rowa 

 of 1-7-1-1 



Ave. No. Hows 

 of 1-7-1-2 



Ave.c.V. 



— ) 1 1 1 



8 9 10 11 



Generations Intred 



Fia. 30. — Graphs showing reduction of variability and segregation of ear row number 

 in selfed strains of maize. 



what more irregular in row number, so that accurate de- 

 termination of number of rows has been more difficult in 

 the later generations. However, this rise is more appar- 

 ent than real as the values for the coefficients of variabil- 

 ity in the intermediate generations are probably lower 

 than they would have been if an adequate number of 

 plants had been grown. 



The effect of inbreeding upon variability is even more 



