Inconstancy of Improved Races 783 



of them has been counted and the figures com- 

 bined into curves, which at once show the whole 

 course of the pedigree-experiment. These 

 curves have in the main taken the same shape, 

 and have only gradually been moved in the 

 chosen direction. 



Three points are now to be considered in 

 connection with this experiment. The first is 

 the size of the cultures required for the result- 

 ing amelioration. In other words, would it have 

 been possible to attain an average of 20 rows 

 in a single experiment? This is a matter of cal- 

 culation, and the calculation must be based upon 

 the ^experience related above, that the progres- 

 sion in the case of maize is equal to two-fifths of 

 the parental deviation. A cob with 20 rows 

 means a deviation of 7 from the average of 13, 

 the incipient value of my race. To reach such 

 an average at once, an ear would be required 

 with 7x^/2=17% rows above the average, or 

 an ear with 30-32 rows. These never occur, 

 but the rule given in a previous lecture gives a 

 method of calculating the probability of their 

 occurrence, or in other words, the number of 

 ears required to give a chance of finding such 

 an ear. It would take too long to give this cal- 

 culation here, but I find that approximately 12,- 

 000 ears would be required to give one witli 28 

 rows, which was the highest number attained in 



