HETEROSIS IN A NEW POPULATION 



421 



ties is purely at random and not complete. Hybrid plants that appear in a 

 field of native corn in the succeeding generation, therefore, might be widely 

 scattered. But no matter how little seed these Fi plants may produce, if their 

 flowering periods coincide, then germplasm would be passed on to the native 

 variety through backcrosses. 



Thus by repeated backcrossing and the sifting action that always takes 

 place through natural and artificial selection, certain genes from an intro- 

 duced population may be readily transferred to a native population. These 

 might be additional favorable yield genes that express themselves in the na- 

 tive gene complex, or they might be other genes which permit the fuller ex- 

 pression of the yield genes which the native variety already contains, or both. 



r CON ICO 



CHALQUENO < 



PALOMCRO TOLUQUE/^0 



CACAHUACINTLE 



TUXPENO 



OLOTILLO 



r HARINOSO FLEXIBLE 



^TEOCINTLE 



■HARINOSO DE GUAT? 



L TEPECINTLE ^ 



L TEOCINTLE 



Fig. 27.1 — Prol)ahle origin of Chalqueno. 



p CONICO 



CONICO NORTE NO < 



PALOMERO TOLUauENO 



CACAHUACINTLt 



CELAYA 



Fig. 27.2 — Probable origin of Conico Norleno. 



