Cytological Studies in Some Species of Panicum

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Abstract
Of 4 spp. of Panicum, 2 are diploids, P. antidotale and P. cymbiforme (2n = 18), and 2 are tetraploids, P. decompositum and P. repens (2n =36). An efficient technique for fixation and analysis for this material is described. The first 2 spp. are true diploids and show normal cytological behavior. The tetraploid, P. decompositum, turns out to be an allotetraploid. There is pronounced, clear and consistent secondary association of both at diakinesis and metaphase I. These bivalents tend to form 9 groups suggesting that 9 is the basic number for this spp. In P. repens the 36 chromosomes associate largely as bivalents. The frequency of quadrivalents is too low for it to be considered an autotetraploid. The presence of univalents at diakinesis and metaphase I, and chromatin bridges at anaphase and telophase, indicates structural hybridity. These irregularities at meiosis suggest P. repens is a segmental allotetraploid.