Microsporogenesis and pollen viability in New Zealand taxa ofPomaderrisLabill. (Rhamnaceae)

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Abstract
P. hamiltonii, P. phylicifolia var. ericifolia, (2n = 36). P. prunifolia var. edgerleyi, (2n = 37), and P. rugosa (20 = 48), showed varymg degrees of restitution at meiosis to give large, unreduced, pollen grains. Restitution was correlated with high univalent frequency per cell, and restituting cells showed little anaphase movement. Dyads replaced some tetrads at telophase II, some of these resulting from restitution at the first meiotic division and some from failure of the second division. Univalent frequencies were low in P. hamiltonii, variable between plants of P. phylicifolia var. ericifolia, and high in P. prunifolia var. edgerleyi, P. phylicifolia var. polifolia, (2n = 48), showed mostly bivalents at meiosis and restitution did. n~t occur. P. aspera (2n = 24), showed normal meiosis and high pollen viability. P. kumeraho, (2n = 24), showed some asyndesis, and fragments of unknown origin. Approximately 50% of the pollen, in all plants of P. kumeraho studied, was aborted.