1. The most important development in Texas during the past year is the discovery that the essential differences between Zea and Euchlaena are not due to numerous genes scattered at random over all the chromosomes as we first thought, but are due to four chromosome segments which are transmitted in inheritance in almost the same manner as single genes. The fact that these segments all carry genes similar to those possessed by Tripsacum, and the simultaneous discovery that short segments of the chromatin are interchanged between Zea and Tripsacum in hybrids of these two genera, has led us to the conclusion that teosinte is nothing more than maize with several translocation segments from Tripsacum superimposed upon the maize germplasm; the product of a natural hybrid betwoen Zea and Tripsacum.
Two of these translocation segments have been located by linkage studies. They occur at opposite ends of chromosome 4 and both show linkage with Su and Tu. These translocation segments from Tripsacum are probably the cause of the unpaired terminal segments which Longley has observed in his cytological studies of the hybrid of maize and teosinte. We have verified his observations on the occurrence of these segments but we are not yet certain that they occur in every case on the chromosomes which he has designated.
The differences between the various kinds of teosinte which have been collected in Guatemala and Mexico may be attributed partly to the differences in the maize to which these translocations segments have been added, and partly to a loss of portions of one or more segments as the result of repeated hybridization with maize.
These new facts reopen the entire question of the origin of maize. With teosinte as a recent development out of the picture, it is reasonable to assume that maize originated from pod corn, which in the homozygous condition is frequently a perfect flowered plant similar to the Andropogonae, and which has the essential characteristics of a plant adapted to survival in the wild. The place of origin was probably in South America, either in Peru or Bolivia.
We suspect that the crossing of South American types of maize with Tripsacum to produce the new genus Euchlaena, has also resulted in some new types of maize previously not in existence, such as the pointed pop corns and the long slender flint and flour corns, neither of which are known in Peru or Bolivia. If this is the case most of our North American maize varieties, with the possible exception of the Southern Gourd-seed types, carry Tripsacum genes in their germplasm. It is possible that the knobs which many of our North American corn exhibit on the chromosomes have been received from Tripsacum via Euchlaena, in which case we are quite likely to find some South American varieties which are lacking in knobs.
These hypotheses suggest a number of genetic and cytological tests which will keep us well occupied for a number of years. We are having some difficulty in locating viable seed of Bolivian and Peruvian maize and if any of the readers of this letter have such seed available we should appreciate receiving some of it.
P. C. Mangelsdorf and R. G. Reeves