1. Pod corn. The sterility of homozygous pod corn is largely due to an excessive vegetative proliferation which may take various forms. Ts5 is an important modifier to Tu; it brings Tu under "control" and prevents some of the unrestrained proliferation which characterizes Tu under some conditions.
Tu can also be brought under control by various unidentified genes in the modifier complex. It can be assumed that Tu is frequently a monstrous character because it is the product of the "wild" gene superimposed upon modern varieties which lack the modifiers which in wild maize must have kept the character under control. If this assumption is sound then modifiers of Tu should be particularly abundant in primitive varieties of maize. The nearest approach to "primitive" maize which we have so far discovered is the maize of the Guarany Indians of Paraguay. When this is crossed with Tu and the hybrid repeatedly backcrossed to Guarany, the glumes of the Tu tu plants are decidedly reduced. Other stocks are now being tested for their modifier complexes with regard to Tu.
We now have a homozygous true-breeding pod corn. Tu tu plants with both staminate and pistillate fertility were found some years ago but such plants are very difficult to self because of the long interval between silking and anthesis. Selfing, however, has finally been accomplished.
The hybrid of pod corn and Guarany mentioned above has unexpectedly furnished a most striking demonstration of the real nature of the ear of maize. Under certain conditions Guarany maize has a tendency to produce a partially indeterminate ear, which once protruding beyond the husks elongates considerably. Tu accentuates this tendency. During the past year we have obtained ears which are normal at the base but enormously elongated at the tip. This "stretching" shows that the ear of maize is fundamentally a simple spike with pairs of spikelets in whorls at the nodes of the rachis.