392 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



T. dadyloides, and among the least cornlike, has been hybridized with 

 corn, thus proving a definite relationship, though from the fact that 

 such hybrids are self-sterile it is concluded that the relationship is 

 remote. 



The grass known as teosinte has been found only in Mexico and 

 Guatemala. As yet, botanists recognize but two species of teosinte: 

 an annual form designated Euchlaena meiicana, and a perennial form 

 called E. perennis. This latter species has been found only in a very 

 restricted area in the State of Jalisco, Mexico, whereas the annual 

 species ranges from Southern Chihuahua, Mexico, to the Department 

 of Jutiapa in southern Guatemala (fig. 2). 



Both species of teosinte hybridize with corn, not only through 

 manual manipulation but also when growing naturally in the field 

 (pi. 16). 



Hybrids between corn and the perennial species of teosinte are only 

 partially fertile and are perennial in habit. Morphologically they re- 

 semble teosinte much more closely than corn. This failure of the two 

 parents to share equally in the characteristics of their mongrel off- 

 spring has been explained by a study of the hereditary mechanism of 

 the two grasses. 



The qualities of every individual, be it animal or plant, are deter- 

 mined primarily by the inheritance derived from the parents out of 

 whom it was fashioned. This inheritance, since the rediscovery of 

 Mendel's epochal work on hybrids, is known to be particulate in 

 nature, the parents passing on to their offspring definite particles now 

 named genes. These particles are carried in the cells in strings called 

 chromosomes, and for eveiy species there is a characteristic number of 

 such strings. In corn it has been found that the genes or hereditary 

 particles are carried in 20 strings or chromosomes, and such is the num- 

 ber found in all annual teosinte, but the perennial species of teosinte 

 possesses 40 chromosomes. This double number of chromosomes is 

 presumed to have come about by the failure of a sex cell to divide its 

 chromosomal content or by a doubling following fertilization — a proc- 

 ess that would give the resulting plants an extra set of genes. Thus 

 the hybrids between perennial teosinte and corn receive twice as many 

 hereditary particles or genes from the teosinte parent as they do from 

 the corn parent and this disparity accounts for the resemblance such 

 hybrids bear to the grass, teosinte. 



The annual form of teosinte hybridizes more freely with maize, and 

 the hybrid offspring are more nearly intermediate in morphological 

 structure between the two grasses. These hybrids are self-fertile, a 

 fact that establishes a very close relationship between the two parental 

 genera. 



Natural hybrids between teosinte and corn found in Mexico were 

 mistakenly interpreted once as wild maize, and in more recent times 



