The chromatids of Tradescantia chromosomes are coiled together in a single coiled chromonema at early metaphase of the first meiotic division. At late metaphase the two coiled chromatids in each homologue separate, forming a bivalent with four separate coiled chromatids. The primary coils disappear during interphase, and at the second meiotic division only the secondary coils are found. 2. The primary coils of meiotic chromosomes are assumed to be caused by the contraction or compression of the two flexible chromatids within the chromosome pellicle without rotation of the chromatids. 3. The direction of the primary coils is apparently at random for the homologous chromosomes of each bivalent. Within each homologue the direction of coiling may change at the fiber constriction, but there is a tendency for the coiling to be in the same direction on both sides of the fiber. The direction of coiling may also change at an interstitial chiasma. 4. We have found no evidence that the meiotic chromatids are split in preparation for the division in the microspore.
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Sax et al. (1934) studied this question.