1 82 BOTANY OF CROP PLANTS 



in cultivation since prehistoric times, it is unknown in the 

 wild state. It is generally agreed, however, that it is dis- 

 tinctly of American origin. The nearest known wild relative 

 of maize is a Mexican grass, teosinte (Euchleena mexicana), 

 with which it is known to hybridize (Fig. 67). 



Harshberger is inclined to believe "that Indian com is the 

 result of a cross between teosinte and a race or variety of the 

 plant produced by successive cultivation of the wild plant 

 until its characters as a variety or a race have become fixed." 

 Collins produces evidence to show that maize originated as a 

 hybrid between teosinte and as unknown grass belonging to 

 the tribe Andropogoneae. He believes this grass to be much 

 like the earless varieties of pod corn {Zea tunicata). Mont- 

 gomery suggests that teosinte and corn had a common ances- 

 tor, which was a "large, much-branched grass, each branch 

 being terminated by a tassel-like structure, bearing herma- 

 phrodite flowers." His views coincide with those of East 

 and Hayes (see page 164). 



Environmental Relations.— Corn is a native of semi-trop- 

 ical America. Its range of distribution has been extended 

 widely through culture. A number of varieties will mature 

 grain as far north as southern Canada, and as a green fodder 

 it is raised in still colder regions, where the season is too short 

 to mature the grain. 



Flint varieties are now grown quite abundantly through- 

 out northern Wisconsin; they are better adapted to cool 

 climates than dent corn. In general, corn is not a big crop 

 north of the summer isotherm of 69°F. The principal corn 

 belt of the United States is a strip running from eastern 

 Nebraska to western Ohio, the northern limit being southern 

 Wisconsin and Minnesota. This is a region with warm sum- 

 mer days and nights. The chief limiting factor to corn grow- 

 ing in the northern tier of States is cool nights. 



