42 



Plant Genetics 



investigators, however, claim that it cannot be applied 

 to all the situations that have been discovered. 



This hypothesis introduces some additional termi- 

 nology suggested by Bateson. In our illustration the 

 tall parent has two determiners for tallness and therefore 

 Bateson calls it duplex, having a double dose. For the 

 same reason the Fi individuals, having only one deter- 

 miner for tallness, he calls simplex. According to the 



WIS 



o o 



Tall Punt 



— > 



F, Hybrid 



Dwarf Puent 



Gametes 



Fig. 6. — Diagram showing how the original scheme must be modi- 

 fied to satisfy the presence and absence hypothesis. 



same terminology the dwarf parent is nulliplex with 

 respect to its character of tallness. 



Additional advantages of the presence and absence 

 hypothesis will appear in connection with a considera- 

 tion of blending inheritance and of cumulative factors 

 in inheritance. Attention, however, should be called 

 to the fact that those who accept the presence and ab- 

 sence hypothesis do not use the form of notation thus far 

 used in explaining Mendelian inheritance. Assume that 

 T is used to express the determiner for tallness, the same 

 letter (t) is used to express its absence. For example, 

 instead of using D for dwarfness, t is used for "lack 



