A special feature of the meiotic divisions in the microsporocytes of this dihaploid was the configuration of bivalents at diakinesis. A salient characteristic of the bivalent was the intimate pairing of the homologues for each bivalent. In other words, the distance between any two chromosomes of a given pair was clearly shorter than that between any two homologues of the same division at diakinesis of an inbred maize. Even though this is just an estimate, lacking support by statistical data, the evidence was truly convincing. It is conceivable that this diploid plant was a homozygote originated by endomitosis during growth and differentiation. This plant was healthy and vigorous during the whole growth season. It was self-fertilized and the seed sets were close to 100 percent. However, its progeny plants were distinctly variable in height. The other characters such as time of flowering, leaf chlorophyll-content, earheight and number were impressively uniform. These are probably tangible evidence indicating the character of "mutable plant height" originated from mutation during culturing, since this character was not detected in the ancestral varieties. This strain of maize was subsequently named mph-1 (mutable plant height No. 1). Whether a transposable element is involved in this mutant is under investigation.

Y. C. Ting

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