422 



E. J. WELLHAUSEN 



A classical example of such introgression is the introgression of genes from 

 teosinte into corn, a process which is still taking place in many areas of 

 Mexico. Teosinte grows as a weed in the corn fields of certain areas. Also the 

 Mexican farmers in some areas have been known to plant teosinte in their 

 corn fields based on a belief that such a practice would make their native 

 corns more drought resistant. The Fi hybrids between corn and teosinte are 

 very small-eared, and ears are difficult to collect because of their verj^ brittle 

 rachis. As such, the F/s have no value in artificial selection. However, the Fi's 

 shed pollen about the same time as the native corn variety, and a large num- 

 ber of backcrosses result with the corn parent as the female. Some of these are 

 unconsciously selected as seed for the following year since they cannot be 



(NAL - TCL 



BOL I TA - 



ZAMLore CHicc 



^T£PECINrL£ 



■ HARINOSO Oe GUAT ? 



■TEOCINTU 



REVENTADOR 



CHAPALOre 



I TEOCINTLE 



^TABLONCILLO 



^HARINOSO DC OCHO 



Fig. 27.3 — Probable origin of Bolita. 



[OLOTILLO 



r TUXPCNO 



VANDENO • 



^TEPECINTLE 



ZAPALOTE GRANDE . 



ZAPALOTE CHICO 



rHARINOSO FLEXIBLE 



\-TEOCWrLE 



tHARINOSO DE GUAT. ? 



TEOCINTLE 



,NAL -TEL 



■ TEPECINTLE 



HARINOSO DE GUAT. ? 



TEOCINTLE 



HARINOSO DE GUAT. 



Fig. 27.4 — Probable origin of Vandeiio. 



