96 Plant Genetics 



As. stated before, most of the work on linkage and 

 crossing over has been done with the fruit fly. The 

 same technique, however, is now being applied among 

 plants. In a recent article White (3) discusses four 

 linkage groups in Pisum, and considerable data on 

 linkage and crossing over in corn are now being assembled 

 at Cornell under the able direction of Emerson. 



Perhaps a warning is needed as to the term correla- 

 tion in this connection. Coupling and linkage are 

 phenomena of inheritance, involving the reduction 

 division, the gametes, and the zygote. Correlation is 

 a physiological phenomenon that appears in the develop- 

 ing plant. A tall corn plant may produce large ears 

 merely because the plant is tall and regardless of the 

 determiners for ear size. This is correlation, and it 

 appeared, not in the gametes and zygote, but in the 

 physiology of the individual after it started to develop. 

 A correlation, therefore, may sometimes deceive as to 

 inheritance. 



1. Emerson, R. A., see Heredity and eugenics (Coulter, Castle, 

 Davenport, East, and Tower). Chicago. 191 2 (pp. loi- 

 104). 



2. Morgan, T. H., Heredity and sex. New York. 1914. 



3. White, Orland E., Inheritance studies in Pisum. IV. 

 Interrelation of the genetic factors in Pisum. Jour. Agric. 

 Research 11:167-190. 1917. 



