June iQ, 1916 Correlated Characters in Maize Breeding 45 1 



distichous leaf blades all of which make an angle with the main axis — 

 but the extent of the cunning is much greater in some of the hybrid plants 

 than has ever been observed in pure Waxy Chinese plants. The angle 

 of the tassel axis had not been recorded for Waxy Chinese plants before 

 the season of 191 5, but thousands of individuals have been obser\^ed, and 

 it can be definitely stated that no plant showed a tassel inclined as much 

 as 90° from the perpendicular. 



In 148 hybrid plants of the second generation of the hybrid there were 

 12 plants with the axis of the tassel inclined from the perpendicular by 

 more than 100° and 5 plants having the angle of the tassel axis recorded 

 as more than 145°. The phenomenon is not due to any weakness of the 

 culm, as examples of more than 180° show (PI. LXII) ; in fact, the upper 

 part of the culm is particularly thick and rigid, a characteristic of the 

 Chinese parent. 



The positiveness of the character was well shown in some of the plants 

 where the curving of the culm caused it to break through the upper leaf 

 sheaths. In such plants the pendent tassels very strongly suggested the 

 "goose neck" of certain sorghum varieties. A plant of this type is 

 shown in Plate LXIII. 



CONCLUSIONS 



Two principal methods of breeding may be distinguished, depending 

 on the manner in which selection is applied : 



(i) Selection may be directed toward the isolation and propagation 

 of desirable types of individuals. The new type may occur as an aber- 

 rant individual or as a recognizably distinct strain within the variety, but 

 in either case it is differentiated from the stock by many characters. 



(2) Selection is directed to variations of the individual characters 

 regarding which improvement is desired. 



With most crop plants the method of selecting types has been by far 

 the most productive, but in the improvement of maize, this method has 

 figured very little. Selection has been by characters instead of by types. 



Why the isolation of types of plants has not been a factor in the im- 

 provement of maize has not been clear. Though diversities in plant 

 characters are obvious and striking, few breeders have been able to dis- 

 tinguish well-defined types of plants within commercial varieties. 



If recognizable types exist it must mean that groups of characters tend 

 to appear together; in other words, the characters are correlated. The 

 extent to which obvious characters are correlated is therefore proposed 

 as a measure of this tendency toward the persistence of types. In the 

 progeny of a hybrid between two very different maize varieties the results 

 here reported show that the characters studied, instead of forming cohe- 

 rent groups, are almost completely independent in inheritance. 

 37769°— 16 2 



