2. Pod corn. It was discovered this season that our homozygous stock of pod corn, as reported in a previous Letter, carries an allele intermediate between ordinary Tu and tu in its effects. We designate this tui. This raised the question of whether there are other weak alleles of Tu among living varieties. An examination of our collection of Latin American varieties indicates that many of the varieties of Mexico, Guatemala, Colombia, Ecuador, Peru and Bolivia may possess weak alleles of Tu. There is some genetic evidence for such a conclusion in F1 hybrids of United States and Latin American varieties with an inbred strain of intermediate tunicate. More than 100 such crosses (originally made to test for minus modifiers of Tu) were grown in 1947. The ears in different crosses varied from those in which the grains were completely covered with glumes to those in which the glumes were so reduced that the ears had the aspect of normal non‑tunicate ears. Plus and minus modifiers for tunicate are undoubtedly responsible for part of this variation, but the major part is probably due to weak alleles of Tu possessed by many of the Latin American varieties.
The reak tunicate condition, like intermediate and strong tunicate, is often associated with a flexible cob. In two different crosses, one involving the Guarany maize of Paraguay and the other a variety from Guatemala, flexibility of the cob was associated with the Su gene on the fourth chromosome. In one of these crosses, the percentage of crossing over between Su and flexibility was 31 per cent, which is approximately the same as previously reported between Su and Tu. Apparently the flexibility of the cob of some varieties is due to a weak allele of Tu.
An examiniation of prehistoric ears from Peru indicates that all, or practically all, are similar to the weak tunicate condition found in some modern Latin American varieties.
There are indications that Tu is a mutable locus. The gene tui apparently arose as a mutation in our Tu stock. More recently we have found a chimera in a Tutu stock in which part of the seeds were covered with glumes and part were naked. Covered seeds, when grown, gave rise to TuTu, Tutu, and tutu individuals; naked seeds produced only Tutu and tutu plants. Numbers are too small to prove the case but are suggestive.
The case for pod corn as the ancestral condition of cultivated maize is now perhaps as complete as it can be on the basis of circumstantial evidence. These are the salient facts:
1. Ears resembling pod corn are represonted on prehistoric pottery.
2. One prehistoric ear of pod corn is known.
3. The majority of prehistoric Peruvian ears appear to be a weak form of pod corn.
4. There are several historical references to pod corn in South America.
5. Many living varieties, especially those of South America, possess a weak allele of Tu.
6. The tu gene is mutable.
7. Pod corn possesses the principal characteristic which the comparative morphologist would expect to find in a wild maize ancestor.