INHERITANCE— IMP RO VEMENT B V BREEDING 2 1 3 



Inbreeding, then, has no permanently injurious effect on CHAP, 

 the breed. 



167. Improvement in Yield by Use of First-generation 

 Crosses. — The facts mentioned in the last paragraph indicate 

 the possibility of utilizing the added vigour gained by crossing. 

 The suggestion of making practical use of this fact was made 

 by Prof. W. J. Beal, as long ago as 1876, but no advantage 

 appears to have been taken of the idea until quite recently, 

 when it was again brought forward by Shull (1), East (2), and 

 Collins (2). Increases of 5 1 per cent over the normal crop have 

 recently been obtained in this way in the United States. 



In the case of maize the beneficial effect is noticeable mainly 

 in the first season, and is said to disappear gradually. In the 

 case of wheat, Professor Biffen finds it applies only in the F l 

 generation. The principle, therefore, involves a new cross 

 each year ; this fact accounts for the loss of vigour and pro- 

 ductiveness which new breeds often show when grown on a 

 commercial scale. 



Difficulties in the use of first-generation crosses in farm 

 practice have been met with, but will doubtless be overcome in 

 time. 



168. Fundamental Points of Seed Selection. — The funda- 

 mental points in seed-maize selection are those which affect 

 yield and quality ; briefly they include : — 



1. Depth of grain ; 



2. Shape of grain ; 



3. Thickness of grain ; 



4. Narrowness of sulci ; 



5. Length of ear. 



The following points are of lesser importance, but should 

 not be neglected : — 



6. Shape of ear ; 



7. Straightness of row ; 



8. Regularity of grain in the row. 



9. Covering and regularity of the butt ; 



10. Covering and regularity of the tip ; 



1 1. Thickness of the cob. 



169. Correlation of Characters. — It is well known among 

 breeders both of plants and animals that certain characters in 

 an individual plant are more or less related to each other, and 



