Sex Reversal and the Experimental Production of Neutral Tassels in Zea mays

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Abstract
The experiments here reported establish the fact that completely neutral, vestigial tassels can be developed at will in Zea mays by the simple control of environmental conditions, and that the natural photoperiodic gradient extending from Aug. to Nov. will sometimes produce 40% or more of neutral tassels in a population. With proper photo-periodicity, 7 general types of tassels can be developed: 3 of pure expression[long dash]staminate ([male]), carpellate ([female]), and vestigial (neuter) ; and 4 sex mosaics[long dash]staminate-neuter, carpellate-neuter, staminate-carpellate, and staminate-carpellate-neuter. With the decreasing photoperiodicity of autumn, femaleness is only expressed at the base of the tassel and the tip is always neuter, the staminate expression occurring in the middle region. With the increasing photoperiodicity of winter and early spring, femaleness may also be expressed at the tip of the tassel and its branches, or sometimes in such a way as to form a complex mosaic with carpellate spikelets scattered among the staminate ones. Experiments with highly inbred varieties show that pure lines react to changed photoperiodicity in the same way as commercial heterozygous varieties, giving rise to complete sex reversals, neutral vestigial tassels, and all the possible types of sex mosaics, as also extreme fluctuation series between members of a plot and fluctuation between successive plots developed in light periods of different lengths. [male] expression can be suppressed completely in the monoecious Zea mays when it is grown in a decreasing photo-periodic environment of suitable length. Entire plots of individuals can be developed without the appearance of a single stamen. The diversity of sexual expression obtained is absolutely due to the diversity of physiological conditions produced through the diversity of environments, and has nothing to do in general with any diversity of hereditary factors which might be present in the different individuals of a given plot, since pure lines show just as extreme fluctuation in sex reaction as heterozygous lines. The specific sex condition developed is not dependent on any balance of sex-determining or sex-producing genes. It is evident that genetic experiments involving sex conditions are of no value unless the reactions obtained are interpreted in the light of ecological conditions present.

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