HYBRIDIZATION IN THE EVOLUTION OF MAIZE 



193 



until the following October and November. This derivative of a maize-teo- 

 sinte hybrid, therefore, carries at least two concealed characteristics of teo- 

 sinte: single spikelets and response to length of day. Genes for these two char- 

 acters do not express themselves in the derivative itself, but their presence 

 becomes immediately apparent when the derivative is crossed with teosinte. 

 The situation is comparable to the concealed genes for hair color and texture 



b^ 



i 





, c 



% 



^ 



Fig. 11.6 — A North .\merican stock is more potent in crosses with Nobogame teosinte (A) 

 and Durango teosinte (C) than the Guaranj' corn from Paraguay {B and D). This is at- 

 tributed to previous introgression of teosinte accompanied by the evolution of modifier 



complexes in North American varieties. 



in persons who are completely bald. The genes are there but have no oppor- 

 tunity to express themselves. 



Since varieties of maize which appear to be the product of previous teo- 

 sinte contamination, such as those of the Corn Belt, behave quite differently 

 in crosses from stocks known to be contaminated, there is at least an indica- 

 tion that such contamination has become modified through selection acting 

 upon the modifier complex. More data are obviously needed on this problem. 



A second question which arises in considering the effects of the natural 

 hybridization of com and teosinte is whether there is any mechanism which 



