Maize in Mexico. Maize in Mexico may ultimately be of practical importance to the U. S. corn belt because it constitutes such a reservoir of genic variability. We may also find that we must study Mexican varieties in order to understand our own, since ours ultimately came from the south. This will be rather difficult since the whole pattern of variation in Mexican maize is so different and so much more complex than that in the U.S. The over-all morphological diversity in the maize of a single Mexican town may be as great as in all of the U.S., yet in another Mexican region 300 miles away the varieties may be entirely different but quite as varied. These regional differences are due in part to the great differences in altitude, temperature, rainfall, and growing season which characterize Mexican agriculture.
During my six months in Mexico, I attempted to make a reasonably complete survey of the regions around Guadalajara (Jalisco, western Mexico) and Mexico City, with scattering collections through the intervening area. A random sample of 25 ears was taken from each field or corn crib and 15 measurements were made on each ear. A few collections have been examined cytologically for knob number and tested genetically for c, r, and pr. The following generalizations are already established.
1. Maize of western Mexico. In spite of much variation in color, row number, and kernel size, the maize of western Mexico is prevailingly long and slender-eared, tapering somewhat to the base and long and irregularly to the apex. Its husks are so tight that there are usually conspicuous striations running lengthwise of the ear. The row number is commonly 8 to 12, the kernels are frequently broad, seldom pointed, and the denting is slight or none. The plants are strong-rooted and stiff stalked. Chromosome knob numbers are high (10 or more) and the knobs are large. The recessive genes r, c, and pr are common.
2. Maize of the Mexico City Region. The maize of this region is prevailingly short-eared and sharply and regularly tapering to the apex. Row numbers are usually above 12, the kernels are more or less pointed and are frequently strongly dented. Chromosome knobs are 0 or a very few. The plants are shallow rooted, the tasselbranches few in number and the leaves broad.
In the intervening area between Mexico City and Jalisco an intermediate and variable type is commonly grown. This is particularly true of the Mexican corn belt (the "Bajio"), centered about the state of Guanajuato.
A few outstanding varieties have wide distribution and deserve special attention.
1. Maíz dulce, the sweet corn of western Mexico is in general unlike the corn of that region and shows striking similarities to similar sweet varieties in highland South America. Dr. Kelly and I have published a detailed report on it. (Ann. Mo. Bot. Gard. 1943).
2. Cachuazintle, a large kernelled white, flour corn grown in the region around Mexico City and southward. Its plant type is strikingly unlike the other maize of that region. It is "popped" by cooking in rapidly boiling water.
3. "Elote" corns with colored aleurone. Throughout all these regions varieties with colored aleurone (both Pr and pr are almost universally grown. They are said to be sweeter than the other varieties and are favored for green corn on the cob (elote) and parched cornmeal (pinole). Some of them have fine wrinkles and look as though they might carry su and an inhibitor.
4. Popcorns. There are at least 3 popcorns in Mexico if we include cachuazintle under that name. The other two are morphologically very different from each other in everything but popping ability. They are: Maíz reventador, the Jaliscan variety for which I have recently (Ann. Mo. Bot. Gard. 1944) published a detailed report and the rice pops of Toluca and other towns near Mexico City. The latter are similar to the semi-pointed dent corns of the same region in plant and tassel characters and are grown inter-mixed with them.