38 MAINE AGRICULTURAL EXPERIMENT STATION. I915. 



ent effect of a given selection is very much less noticeable or not 

 at all in the later years. It is probable that the effect in the first 

 year is due to physiological rather than genetic causes. 



6. Considering the effect of two and of three successive se- 

 lections in the plus direction lit is seen that there is an excess 

 deviation in the direction opposite to the selection. However, 

 with two and three selections in the minus direction there is an 

 excess in the directio'U of the selection (Table 7). These results 

 balance each other so that it appears safe to conclude that 

 neither were due to the effect of the selection. 



7. The methods of analysis described above leaves out of 

 account two factors, viz. the difference in the variability of 

 the dift'erent pure lines and second the size of the deviation of 

 the selected plant. The first of these factors can be partially 

 taken into account by expressing each deviation as a percent, of 

 its mean. The second factor can be accounted for by expressing 

 the deviation of each plant as an index. 



Dm — Dd 



I = 



Dm 

 where Din is the deviation of the mother plant from its mean 

 and Dd is the deviation of the daughter row from its mean. If 

 there is no eft'ect of the selection as Johannsen claims then this 

 index should on the average equal i. If regression takes place 

 within these pure lines as claimed by the Galton-Pearson theory 

 of ancestral 'heredity, the index would on the average approach 

 0.33. In general if the index is significantly less than i it 

 indicates some effect of the selection. 



8. For the yield of grain, these indices have been calculated 

 for the efi'ect of each selection upon the rows grown in each of 

 the following years. The average index for each class of 

 selection and for all the selections are given in Table 8. As 

 shown in their probable errors these mean indices are not sig- 

 nificantly different from i. This indicates that there is no effect 

 of the selections within these pure lines. 



